Tuning four-wave mixing through temperature in ethanol-filled photonic crystal fiber

In this paper, continuous tuning of four-wave mixing bands in an ethanol-filled photonic crystal fiber is investigated. A wide tuning range of the parametric bands, from 745 nm to 920 nm (signal) and from 1260 nm to 1710 nm (idler), is achieved through the thermo-optic effect. This corresponds to a frequency tuning range higher than 2000 cm−1; such wide range can be particularly useful in applications that require broadband wavelength conversion, e.g., CARS microscopy. Numerical calculations are in good agreement with experimental measurements.

Accurate mode characterization of two-mode optical fibers by in-fiber acousto-optics.

Acousto-optic interaction in optical fibers is exploited for the accurate and broadband characterization of two-mode optical fibers. Coupling between LP01 and LP1m modes is produced in a broadband wavelength range. Difference in effective indices, group indices, and chromatic dispersions between the guided modes, are obtained from experimental measurements. Additionally, we show that the technique is suitable to investigate the fine modes structure of LP modes, and some other intriguing features related with modes' cut-off.

Acousto-Optic Interaction for Accurate Two-Mode Optical Fibers Characterization

Accurate characterization of two-mode fibers by acousto-optic interaction is reported. Difference of modal index, group delay, and dispersion between the guided modes is obtained. Properties of the vector modes comprising the LP11 mode are investigated.

Control of the chromatic dispersion of photonic crystal fibers for supercontinuum and photon pairs generation

The interplay between chromatic dispersion and nonlinear effects is crucial for an efficient exploitation of non linear propagation in photonic crystal fibers (PCF). Once a PCF preform has been prepared, changing the parameters that control the fabrication process it is possible to adjust the dispersion properties of the fiber. In addition, it is particularly useful to develop postprocessing techniques that enable a fine adjustment of the dispersion along a section of PCF. The tapering of PCF, using a fusion and pulling technique, has been established as a rather useful technique to engineer the dispersion properties along tens of centimeters. Some of our recent experiments demonstrate that…

Actively mode-locked fibre ring laser based on in-fibre acousto-optic amplitude modulation

Recent advances in the development of all-fibre amplitude modulators have led to the implementation of a series of different actively mode-locked fibre lasers [1–4]. In-fibre acousto-optic modulation based on intermodal coupling induced my a standing flexural acoustic wave permits the implementation of broad bandwidth (1.5 nm), high modulation depth (0.72), low-insertion-loss (0.75 dB) all-fibre amplitude modulators that operate in the MHz frequency range. The experimental characterization of a laser with the configuration depicted in Fig. 1 (a) as a function of the radio frequency voltage that controls the modulator (see Fig. 1 (b)), the length of the Erbium doped fibre (EDF), and the opti…

Actively mode-locked all-fiber laser by 5 MHz transmittance modulation of an acousto-optic tunable bandpass filter

Active mode-locking of an all-fiber ring laser by transmittance modulation of an in-fiber acousto-optic tunable bandpass filter (AOTBF) is reported. Cavity loss modulation is achieved by full acousto-optic mode re-coupling cycle induced by standing flexural acoustic waves. The modulator permits the implementation of 28 dB of nonresonant light suppression, 1.4 nm of modulation bandwidth, 74% of modulation depth and 4.11 dB of optical loss in a 72.5 cm-long all-fiber configuration. The effects of the modulated AOTBF on the laser performance are investigated. Transform-limited optical pulses of 8.8 ps temporal width and 6.0 W peak power were obtained at 4.87 MHz repetition rate.

Characterization of fiber nonuniformities with ppm resolution using time-resolved in-fiber acousto-optics

Time-resolved acousto-optic interaction using flexural waves enables the characterization of fiber nonuniformities along sections of about 1-2 m. A resolution better than 10 ppm of fiber diameter and core refractive index is demonstrated.

Refractometric sensor based on whispering-gallery modes of thin capillarie.

Whispering-gallery modes resonances of submicron wall thickness capillaries exhibit very large wavelength shifts as a function of the refractive index of the medium that fills the inside. The sensitivity to refractive index changes is larger than in other optical microcavities as microspheres, microdisks and microrings. The outer surface where total internal reflection takes place remains always in air, enabling the measure of refractive index values higher than the refractive index of the capillary material. The fabrication of capillaries with submicron wall thickness has required the development of a specific technique. A refractometer with a response higher than 390 nm per refractive ind…

Interrogation of whispering-gallery modes resonances in cylindrical microcavities by backreflection detection

The excitation of whispering-gallery-mode resonances of cylindrical microcavities, using narrow fiber tapers, produces simultaneously the excitation of spiral modes. The power coupled to the spiral modes leads to a significant broadening of the dips observed in the spectrum of light transmitted through the taper. We demonstrate that whispering-gallery modes resonances of cylindrical microcavities can also be interrogated by measuring the reflection spectrum. Unlike the dips observed in transmission, the peaks in the reflection spectrum are symmetric and narrower than the corresponding transmission dips.

Passive compensation of the thermal drift of magnetostriction based Q-switched fiber lasers

Abstract The authors propose and demonstrate a method to compensate the thermal drift of magnetostriction based Q-switched fiber lasers, which is caused by the eddy currents induced in the Terfenol-D magnetostrictive actuators. The consequent wavelength detuning between the fiber gratings of the laser is passively compensated by the use of Monel 400 as thermal actuator of the non-modulated grating. A highly stable pulsed signal is achieved in the range of 1 Hz–5 kHz, with a wavelength detuning between gratings maintained below 10 pm. Furthermore, an optimization of the use of the pump power is proposed, utilizing part of it for simultaneously pumping a fiber optic based amplification stage.

Femtosecond parabolic pulse shaping in normally dispersive optical fibers

Formation of parabolic pulses at femtosecond time scale by means of passive nonlinear reshaping in normally dispersive optical fibers is analyzed. Two approaches are examined and compared: the parabolic waveform formation in transient propagation regime and parabolic waveform formation in the steady-state propagation regime. It is found that both approaches could produce parabolic pulses as short as few hundred femtoseconds applying commercially available fibers, specially designed all-normal dispersion photonic crystal fiber and modern femtosecond lasers for pumping. The ranges of parameters providing parabolic pulse formation at the femtosecond time scale are found depending on the initia…

Novel in-line fiber-optic filters and polarisers

Novel in-line devices, based on a tapered fiber whose uniform waist has been metal-coated, are reported. The resonant excitation of a surface plasma mode of the metal film allows for the design of wavelength filters and polarisers

Erbium-Doped-Silica Photonic Crystal Fiber Characterization Method: Description and Experimental Check

The present paper reports and discusses a characterization method for erbium-doped-silica photonic crystal fibers based on the measurement of pump power attenuation and gain together with the McCumber theory. The absorption and emission cross sections and the passive losses of the fiber were obtained from a fitting procedure of theoretical to experimental values. The method was checked by means of a home-made photonic crystal fiber to verify its reliability. Finally, it was found that the characteristic parameters obtained by this method can be used to accurately simulate the performance of the fiber and therefore to design devices based on it.

Study of upconversion in highly Er-doped photonic crystal fibers through laser-transient dynamics

The dynamic response after pump switch-on of a 980 nm pumped-ring laser based on an active photonic crystal fiber with an Er3+ ion concentration of ≈1020 ions cm−3 was registered. Then a numerical fitting procedure of a theoretical model was followed to the experimental values of the relaxation oscillation parameters as a function of the input pump power. Non-radiative energy-transfer mechanisms’ coefficients: homogeneous upconversion coefficient (Cup) and critical radii for upconversion (Ru) and migration (Rm) were determined. The calculated best-fit coefficients (Cup = 1.3  ×  10−24 m3 s−1, Ru = 9  ×  10−10 m, Rm = 13  ×  10−10 m) were compared to those obtained with other steady-state an…

Fibre Bragg gratings tuned and chirped using magnetic fields

The authors report on the use of magnetic fields in conjunction with magnetostrictive materials for tuning and chirping optical fibre Bragg gratings. The Bragg wavelength shifts as a consequence of the strain induced in the fibre by a magnetostrictive rod when a magnetic field is applied. A tuning range of 1.1 nm has been achieved by a magnetic field of 103 mT and the grating has been chirped by applying non-uniform magnetic fields.

Fiber Characterization Using Whispering Gallery Modes(Invited)

Fiber whispering gallery modes (WGMs) are surface waves that propagate azimuthally along the outer surface of the fiber cladding. Those waves that are in phase every turn give rise to narrow resonances defined by the resonant wavelength and a high Q factor. The actual values of the resonant wavelengths depend on the radius and the refractive index of the fiber cladding, enabling the development of several fiber characterization techniques. In addition, the typical high Q factor of these resonances (Q > 106) provides the characterization techniques with a low detection limit. Here, we report the development of a technique for measuring temperature profiles along the optical fiber, which enab…

Doubly active Q switching and mode locking of an all-fiber laser

Simultaneous and independent active Q switching and active mode locking of an erbium-doped fiber laser is demonstrated using all-fiber modulation techniques. A magnetostrictive rod attached to the output fiber Bragg grating modulates the Q factor of the Fabry-Perot cavity, whereas active mode locking is achieved by amplitude modulation with a Bragg-grating-based acousto-optic device. Fully modulated Q-switched mode-locked trains of optical pulses were obtained for a wide range of pump powers and repetition rates. For a Q-switched repetition rate of 500 Hz and a pump power of 100 mW, the laser generates trains of 12-14 mode-locked pulses of about 1 ns each, within an envelope of 550 ns, an o…

Measurement of Pockels’ coefficients and demonstration of the anisotropy of the elasto-optic effect in optical fibers under axial strain

The elasto-optic effect in optical fibers under axial strain can be characterized by means of the whispering gallery mode (WGM) resonances of the fiber itself. This technique enables a direct measurement of the anisotropy, the determination of the individual Pockels' coefficients, and the study of the wavelength dependence. The method is based on a rigorous theoretical study of WGM resonances in cylindrical microresonators. The shift of the WGM resonances as a function of strain was measured for the TE and TM modes, showing a strong modal anisotropy. In particular, the shift rate for TE modes was 1.84 times the one for TM modes. From these measurements, experimental values for the Pockels' …

Theoretical and Experimental Study of Polarization Modulation Instability in All-Normal Dispersion Photonic Crystal Fibers

Experimental observation of polarization modulation instability in all-normal dispersion photonic crystal fibers is reported. Stokes and anti-Stokes sidebands with spectral shift of 40 nm were observed when the fiber was pumped at 1064 nm. Experimental results are baked by a vectorial four-wave mixing model.

Single-mode Bragg gratings in tapered few-modes and multimode fibers

We propose the implementation of fiber Bragg gratings in tapered few-mode and multimode fibers to accomplish single-mode operation by reducing the core diameter, while preserving the core-cladding structure. The gratings present a single reflection band, and the device shows low insertion losses after the taper fabrication and the fiber Bragg gratings inscription. The excitation of high-order odd modes in the core of the fiber has been identified as the main loss mechanism; it can be prevented by means of symmetric illumination of the fibers. We also demonstrate the excitation of high-order cladding modes (cladding-air modes) along the taper transitions; these modes can be removed without a…

Temperature Sensor Based on Ge-Doped Microstructured Fibers

The fundamental mode cutoff properties of Ge-doped microstructured fibers, filled with a liquid, permit the implementation of wavelength- and amplitude-encoded temperature sensors with an ultra-high sensitivity. The cutoff wavelength changes with temperature, and the thermo-optic coefficient of the liquid determines the sensitivity of the sensor. Sensitivity as high as 25 nm/∘Cis reported. In addition, simple amplitude interrogation techniques can be implemented using the same sensor heads.

Polarization Modulation Instability in All-Normal Dispersion Microstructured Optical Fibers with Quasi-Continuous 1064 nm Pump

Polarization modulation instability (PMI) is a form of modulation instability that can exist in weakly birefringent optical fibers [1]. Sidebands can be generated by this effect when a polarization mode of the birefringent fiber is excited with an intense optical pump. The polarization state of the sidebands is orthogonal to the polarization of the pump signal. PMI has been observed in microstructured optical fibers (MOFs). PMI was reported in a large-air-filling fraction MOF that was pumped in the normal dispersion regime with visible light [2]. The coherent degradation of femtosecond supercontinuum light generated in all-normal dispersion (ANDi) MOFs due to PMI was recently investigated […

Fibres Are Looking Up: Optical Fibre Transition Structures In Astrophotonics

Recent developments in the astrophotonic applications of optical fibre taper transitions are discussed. For example, transitions between single multi-mode and multiple single-mode cores can help suppress the atmospheric OH emission that hampers ground-based IR astronomy.

Fiber laser with cladding-mode feedback based on intracavity long period grating

Cladding modes in fiber laser technology have considerable interest for dispersion compensation [1] and power scaling [2, 3]. A fiber laser with core-cladding conversion was made in convectional Erbium doped fiber by a combination of Bragg and external cavity mirrors and blocking the fundamental mode with a damaged core fiber [2]. Furthermore, the insertion of two long period gratings (LPG) in a fiber Bragg gratings (FBG) Fabry-Perot cavity has been proposed as a potential high-order-mode fiber laser [3]; however, no experimental demonstration has been reported yet because there are no ring-doped fibers available in the market. In this work, we present the first demonstration of an all-fibe…

Four Wave Mixing in Photonic Crystal Fibers:<br /> Tuning Techniques

We present an experimental and numerical study of four-wave mixing in photonic crystal fibers. Our objective is the development of tuning techniques based on tailoring de dispersion of the fibers. We demonstrate wide tuning ranges.

Instantaneous frequency measurement of dissipative soliton resonant light pulses

Fil: Cuadrado-Laborde, Christian. Universidad de Valencia. Departamento de Física Aplicada y Electromagnetismo. Instituto Universitario de Ciencia de los Materiales; España Fil: Cuadrado-Laborde, Christian. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Rosario; Argentina Fil: Cuadrado-Laborde, Christian. Pontificia Universidad Católica Argentina. Facultad de Química e Ingeniería del Rosario; Argentina Fil: Armas Rivera, I. Benemérita Universidad Autónoma de Puebla. Facultad de Ciencias Físico Matemáticas; Mexico Fil: Carrascosa, A. Universidad de Valencia. Departamento de Física Aplicada y Electromagnetismo. Instituto Universitario de Ciencia de los Materia…

Effects of refractive index changes on four-wave mixing bands in Er-doped photonic crystal fibers pumped at 976 nm.

An experimental study of the effects of an auxiliary 976 nm pump signal on the four-wave mixing parametric bands generated with a 1064 nm pump in a normal dispersion Er-doped photonic crystal fiber is presented. The four-wave mixing signal and idler bands shift to shorter and longer wavelengths, respectively, with increasing 976 nm pump power. It is shown that the wavelength-dependent resonant refractive index change in the erbium-doped core under 976 nm pumping is at the origin of the effect.

Photonic microwave tunable single-bandpass filter based on a Mach-Zehnder interferometer

The authors present the theoretical analysis and experimental demonstration of a novel single-bandpass tunable microwave filter. The filter is based on a broadband optical source and a fiber Mach-Zehnder interferometer and shows a high Q factor over a tuning range of 5-17 GHz. A generalized analysis considering that the optical signal propagates along optical delay lines with a dispersion slope different from zero is presented.

Highly sensitive optical hydrogen sensor using circular Pd-coated singlemode tapered fibre

A novel optical hydrogen sensor, based on the absorption change of the evanescent fields in a circular Pd-coated singlemode tapered fibre is presented. The proposed sensor is polarisation independent and its sensitivity is adjustable by means of the taper diameter, interaction length, and/or light wavelength. A simple light transmission measurement setup is used to test the sensor. The sensor is suitable for the detection of low hydrogen concentrations with high sensitivity and fast time response. Transmission changes as high as 60% are demonstrated.

Accurate modal characterization of optical fibers using acousto-optics

In-fiber acousto-optics enable accurate and broadband characterization of two mode optical fibers. Differential effective index, group index and dispersion are reported for two-mode optical fibers. Small phase differences between the quasi-degenerated vector modes comprising the LP 11 mode are also measured. In addition, a fine analysis of fiber axial non-uniformities can be performed using a time-resolved acousto-optic technique. In this case, sub-ppm changes of effective index are measured with few cm resolution along fiber sections of about 2 m.

Hybrid surface plasma modes in circular metal-coated tapered fibers

The theory of hybrid surface plasma modes in metal-coated dielectric cylinders has been developed in recent years. We demonstrate that tapered fibers with a uniform waist and a circular metal coating can be designed for an efficient excitation of the fundamental hybrid surface plasma mode. Our experimental results are in good agreement with the theory and give the basis for the development of a novel type of all-fiber polarization-independent refractive-index sensor and tunable broadband wavelength filter.

Fabrication of polarizing photonic crystal fibres and photonic crystal fibre tapers: Applications

We report the fabrication of an anisotropic photonic crystal fibre with polarization properties and photonic crystal fibre tapers for supercontinuum generation. The anisotropy of the fibre was created by enlarging four airholes next to the silica core. Different polarization regimes as a function of the geometric parameters, including polarizing behaviour at 1.55 mum, were obtained. In the second part of the paper, we report the fabrication of photonic crystal fibre tapers. We present experimental results on supercontinuum generation in photonic crystal fibre tapers using quasi-continuous pump pulses of 7 ns duration at 532 nm and at 1064 nm.

Polarization Modulation Instability in All-Normal Dispersion Microstructured Optical Fibers with sub-ns Pumping

The advent of microstructured optical fiber (MOF) technology gave a significant boost to research in nonlinear optics. MOFs have the advantage of high nonlinearity and designable dispersion, which makes this type of fiber an excellent platform for efficient generation of nonlinear effects. In the last years, MOFs exhibiting normal dispersion at any guiding wavelength (ANDi fibers) aroused the interest because of the possibility of using them for the generation of coherent and recompressible supercontinuum (SC) light. In this contribution, we present our recent results regarding the generation of the polarization modulation instability (PMI) effect in ANDi MOFs in the quasi-CW pump regime at…

Addressing substrate glutamine requirements for tissue transglutaminase using substance P analogues

AbstractWe have investigated the effect on the substrate requirements for guinea pig liver (tissue) transglutaminase of a set of 11 synthetic glutamine substitution analogues making up the full sequence of the naturally occurring tissue transglutaminase substrate substance P. While a number of peptide sequences derived from proteins that are well-recognized as tissue transglutaminase substrates have been studied, the enzyme activity using substitution analogues of full-length natural substrates has not been investigated as thoroughly. Thus, our set of substance P analogues only differs from one to other by one amino acid mutation while the length (of the peptide) is maintained as in the nat…

Measurement of the soliton number in guiding media through continuum generation.

No general approach is available yet to measure directly the ratio between chromatic dispersion and the nonlinear coefficient, and hence the soliton number for a given optical pulse, in an arbitrary guiding medium. Here we solve this problem using continuum generation. We experimentally demonstrate our method in polarization-maintaining and single-mode fibers with positive and negative chromatic dispersion. Our technique also offers new opportunities to determine the chromatic dispersion of guiding media over a broad spectral range while pumping at a fixed wavelength. (C) 2020 Optical Society of America

All polarization-maintaining passively mode-locked fiber-ring ytterbium-doped laser; from net-normal to net-anomalous dispersion

We investigated the behavior of a fiber-ring polarization-maintaining passively modelocked ytterbium-doped laser in a broad range of dispersion values; i.e., from highly net-normal to net-anomalous, with a special emphasis near the zero of chromatic dispersion. Different lengths of an ad hoc polarization-maintaining photonic crystal fiber were used as intracavity dispersion compensator to shift the operation of this laser from net-normal to the net-anomalous regime. The laser generated the shortest light pulses around the zero of dispersion: 6 ps / 7ps for −0.023 ps2 / 0.045 ps2 ; in both cases, pulses were not transform-limited, being theoretically possible an out-of-cavity recompression d…

Tapering photonic crystal fibres for supercontinuum generation with nanosecond pulses at 532nm

Experimental results on supercontinuum generation in photonic crystal fibre tapers using pump pulses of 7 ns duration at 532 nm are presented. Photonic crystal fibre tapers with the first wavelength of zero dispersion around 532 nm were fabricated. The generation of supercontinuum was investigated in normal and anomalous dispersion regimes. Supercontinuum spectra spanning more than 400 nm in the visible region are reported.

Tuning And Chirping Fiber Bragg Gratings By A Magnetic Field

Electrically tunable photonic true-time-delay line

We present a new application of the acousto-optic superlattice modulation of a fiber Bragg grating based on the dynamic phase and group delay properties of this fiber-optic component. We demonstrate a tunable photonic true-time-delay line based on the group delay change of the light reflected from the grating sidebands. The delay is electrically tuned by adjusting the voltage applied to a piezoelectric transducer that generates the acoustic wave propagating along the grating. In our experiments, a true-time delay of 400 ps is continuously adjusted (300 ps within the 3 dB amplitude range of the first sideband), using a 12 cm long uniform grating.

In-Fiber Acousto-Optics for the Broadband Measurement of the UV-Induced Refractive Index Change in Photosensitive Fibers

In fiber acousto-optics has been demonstrated to be a versatile, highly sensitive technique that allows characterizing different parameters of singlemode or few-mode fibers, such as dispersion curves, radius or core refractive index, in a broadband wavelength range. The working principle of the technique relies in the fact that a variation in a parameter of the fiber leads to a shift in the optical wavelength that fulfills the acousto-optic phase matching condition. Thus, by measuring this wavelength shift it is possible to evaluate the change in the parameter under study. The technique shows a low detection limit: for example, it is as low as 10-8 for the core refractive index, in singlemo…

Fiber-Optic Aqueous Dipping Sensor Based on Coaxial-Michelson Modal Interferometers

Fiber-optic modal interferometers with a coaxial-Michelson configuration can be used to monitor aqueous solutions by simple dipping of few centimeters of a fiber tip. The fabrication of these sensors to work around 850 nm enables the use of compact, robust, and low-cost optical spectrum analyzers. The use of this type of portable sensor system to monitor sewage treatment plants is shown.

Measurement of phase and group refractive indices and dispersion of thermo-optic and strain-optic coefficients of optical fibers using weak fiber Bragg gratings

In this work we report on the measurement, with record accuracy, of the absolute modal effective refraction index (phase index) of single-mode optical fibers by using Bragg gratings. We also demonstrate a new method to measure the group index of the fibers from the grating’s Bragg wavelength. We present as well the characterization of the thermo-optic and strain-optic coefficients as a function of the wavelength; the values we have obtained are the closest to those of pristine fiber measured with gratings technology so far. The phase index is measured with a set of gratings in the wavelength ranges from 1509 to 1563 nm, and the group index is obtained from the wavelength dependence of the p…

Modulation of coaxial modal interferometers based on long period gratings in double cladding fibers

This paper reports on the dynamic modulation of coaxial interferometers based on two cascaded long period gratings written in double cladding fibers. The interferometer is modulated by a piezoelectric ceramic which stretches one the gratings at tens of kHz, the output light is intensity modulated with an efficiency of 97 %. The device operates at 1530nm, has more than 50nm bandwidth, insertion loss of 0.4 dB and a temperature drift of 0.11 nm/ degrees C.

Design of double-tapered fibers for tailoring the acousto-optic spectral response

A model to shape the spectral response of acousto-optic devices based on tapered fibers is reported. A double-tapered structure was designed in order to obtain a flat attenuation response with 34 nm bandwidth.

Fundamental-mode cutoff in liquid-filled Y-shaped microstructured fibers with Ge-doped core

We report on the cutoff characteristics of a Ge-doped Y-shaped microstructured fiber in which the holes are filled with a liquid of refractive index higher than silica but lower than the Ge-doped core. It is found that the cutoff wavelength was very sensitive to temperature variations as a result of the refractive index changes of the liquid. The basic properties of such a fiber permit the fabrication of wideband tunable short-pass filters, as well as temperature sensors with high sensitivity. A temperature sensitivity of 25 nm/degrees C is reported.

Enhanced Q-switched distributed feedback fiber laser based on acoustic pulses

An acoustically Q-switched distributed feedback fiber laser with enhanced performance is presented. It is based on an FBG written in an erbium doped fiber, in which a dynamic defect is introduced by means of a short acoustic pulse. The performance of the laser depends on the reflectivity of the grating. In this work, we present two different Q-switched distributed feedback fiber lasers realized with active gratings of different reflectivities. Both lasers are characterized at different pump powers and repetition rates. It is shown that the performance of the laser based on the weaker grating was significantly improved with respect to the laser based on the stronger grating. In terms of peak…

Actively Q-switched and modelocked all-fiber lasers

Here we demonstrate active mode-locking (ML) and doubly-active Q-switching mode-locking (QML) of erbium-doped strictly all-fiber lasers. The active ML mechanism relies in the acoustooptic superlattice modulation (AOSLM) effect induced when longitudinal acoustic waves are launched along a fiber Bragg grating. In both regimes - ML as well as QML - we focus on the laser behavior when the AOSLM is driven by traveling acoustic waves, and next we compare these results with those obtained when the AOSLM is driven by standing acoustic waves. In the ML regime, optical pulses were obtained of 530 mW peak power, 700 ps temporal width, at a repetition rate of 4.1 MHz. On the other hand, in the QML regi…

Supercontinuum generation in Ge-doped Y-shaped microstructured tapered fiber

We have investigated the generation of supercontinuum in tapered Y-shaped fibers in the nanosecond pump regime. This fiber used to fabricate the tapers has, in addition, a Ge-doped core which enhances the nonlinearity of the material and the Raman gain. The fiber was pumped at 1064 nm in the ns pump regime (0.6 ns pulses and up to 3.2 kW peak power). The taper had a uniform waist of 0.9 μm diameter and 130 mm length, and the adiabatic transitions were 110 mm long. A flat spectrum spanning from 420 nm to 1870 nm was obtained using a single tapered fiber.

Photonic fractional Fourier transformer with a single dispersive device

In this work we used the temporal analog of spatial Fresnel diffraction to design a temporal fractional Fourier transformer with a single dispersive device, in this way avoiding the use of quadratic phase modulators. We demonstrate that a single dispersive passive device inherently provides the fractional Fourier transform of an incident optical pulse. The relationships linking the fractional Fourier transform order and scaling factor with the dispersion parameters are derived. We first provide some numerical results in order to prove the validity of our proposal, using a fiber Bragg grating as the dispersive device. Next, we experimentally demonstrate the feasibility of this proposal by us…

Waveguiding properties of a photonic crystal fiber with a solid core surrounded by four large air holes

The polarization-dependent guiding properties of a hexagonal-lattice photonic crystal fiber with a solid-core surrounded by four large air holes are investigated. The appearance of a polarization dependent cutoff frequency, together with several parameters as the birefringence, the modal effective area, the group velocity dispersion and the polarization dependent loss are analyzed. A collection of fibers with different structural parameters were fabricated and characterized. An effective anti-guide structure from at least 450 nm to 1750 nm, a polarizing fiber with a polarization dependent loss of 16 dB/m at 1550 nm, and an endlessly singlemode polarization-maintaining fiber with group biref…

All polarization-maintaining assively mode-locked yb-doped fiber laser : pulse compression using an anomalous polarization-maintaining photonic crystal fiber

We report the generation of short pulses at 1 μm using an all-polarization-maintaining (PM) fiber configuration. The pulses are provided by an all normal-dispersion Fabry-Perot Yb-doped cavity and are compressed with an anomalous polarization-maintaining photonic crystal fiber (PM PCF). Opposed to standard configurations; here the filtering action is solely performed by the finite bandwidth of the gain medium. The laser generates 8 ps width sech 2 profile pulses at 1046.8 nm with a −10 dB bandwidth of 5.9 nm. After compression using the PM PCF, pulses with an FWHM of 3 ps were obtained, limited by the actual value of the available anomalous dispersion. We also report the changes in the outp…

Electronic tuning of delay lines based on chirped fiber gratings for phased arrays powered by a single optical carrier

We propose a variable delay line for phased arrays antennas based on a chirped fiber grating. The line operates with an optical carrier at constant wavelength and the time delay of the radiofrequency modulating signal is modified stretching the grating with a piezoelectric translator, the grating response can be tuned at a speed of 0.68 nm/ms.

Fiber laser switched by a long period grating interferometer as an intra-cavity loss modulator

Abstract In this paper we present an actively switched fiber laser with an all-fiber long-period grating-based interferometer used as an intra-cavity loss modulator. The modulator consists of two equal long-period gratings written sequentially in the same piece of a double-clad optical fiber. One of the gratings is fixed onto a piezoceramic cylinder producing fast modulation of the interferometer transmission spectrum. The laser demonstrates a stable regime of pulsed emission at repetition rates in the range of tens of kHz.

Enhanced supercontinuum generation in the nanosecond pump regime using specialty microstructured fibers

Several alternatives have been investigated to achieve enhanced supercontinuum generation in the nanosecond pump regime using specialty silica-based microstructured optical fibers (MOFs). Among these alternatives we can point out the use of (a) MOF tapers, (b) highly Ge-doped core Y-shaped MOF and (c) Er-doped MOF. These specialty MOFs provide either an increased material nonlinear response or a rather small effective area, at the same time that the dispersion characteristics are adjusted to work at different excitation conditions. In our experiments, we have been using either a Q-switched Nd:YAG laser (10 Hz repetition rate) or an Yb-doped fiber laser (2 kHz repetition rate), both emitting…

Direct Bragg grating writing in a hybrid PDMS/silica photonic crystal fiber

Infiltration of materials into the air holes of the PCFs can potentially manipulate their optical properties creating a new category of fibers termed as hybrid PCFs [1] and many devices based on hybrid PCFs have been developed [2–5]. Recently, a hybrid PCF with poly-dimethylsiloxane (PDMS) elastomer inclusions has been demonstrated [6]. PDMS is widely used in the area of photonics and optofluidics. It is highly transparent with a refractive index ∼1.41, conserving the total internal reflection guiding mechanism of the hybrid PCF. When PDMS is irradiated with UV light its refractive index increases [7]. In this paper we present the first example of a Bragg grating directly written using UV l…

Instantaneous frequency measurement by in-fiber 0.5th order fractional differentiation

We experimentally demonstrate the possibility to retrieve the instantaneous frequency profile of a given temporal light pulse by in-fiber fractional order differentiation of 0.5th-order. The signal's temporal instantaneous frequency profile is obtained by simple dividing two temporal intensity profiles, namely the intensities of the input and output pulses of a spectrally-shifted fractional order differentiation. The results are supported by the experimental measurement of the instantaneous frequency profile of a mode-locked laser. Fil: Poveda-Wong, L.. Universidad de Valencia; España Fil: Carrascosa, A.. Universidad de Valencia; España Fil: Cuadrado Laborde, Christian Ariel. Consejo Nacion…

Modeling spectral correlations of photon-pairs generated in liquid-filled photonic crystal fiber

The generation of photon-pairs with controllable spectral correlations is crucial in quantum photonics. Here we present the design of a photonic crystal fiber to generate widely-spaced four-wave mixing bands with spectral correlations that can be tuned through the thermo-optic effect after being infiltrated with heavy water. We present a theoretical study of the purity of the signal (idler) photon generated as a function of temperature, pump spectral linewidth and the length of the fiber. 511-6/18-8876 CIIC155/2019 APN-624 TEC2016- 76664-C2-1-R PROMETEO/2019/048

In-fiber time-resolved acousto-optics

Time-resolved in-fiber acousto-optics permit the measurement of sub-ppm perturbations of the modal dispersion curves along sections of fiber exceeding 1 m long, with a spatial resolution in the order of few cm.

Acousto-optic interaction in biconical tapered fibers: shaping of the stopbands

The effect of a gradual reduction of the fiber diameter on the acousto-optic (AO) interaction is reported. The experimental and theoretical study of the intermodal coupling induced by a flexural acoustic wave in a biconical tapered fiber shows that it is possible to shape the transmission spectrum, for example, substantially broadening the bandwidth of the resonant couplings. The geometry of the taper transitions can be regarded as an extra degree of freedom to design the AO devices. Optical bandwidths above 45 nm are reported in a tapered fiber with a gradual reduction of the fiber down to 70 μm diameter. The effect of including long taper transition is also reported in a double-tapered st…

Dissipative soliton resonance in a full polarization-maintaining fiber ring laser at different values of dispersion

We investigated the dissipative solitons resonance in an ytterbium-doped fiber ring laser in which all the elements are polarization maintaining (PM). A semiconductor saturable absorber mirror was used as a mode-locker. The cavity included a normal dispersion single-mode fiber (SMF) and an anomalous dispersion photonic crystal fiber. The change of the length of the PM SMF allows the variation of the net-normal dispersion of the cavity in the range from 0.022 ps2 to 0.262 ps2. As the absolute value of the net-normal dispersion increases from 0.022 ps2 to 0.21 ps2, a square-shaped single pulse transformed to a single right-angle trapezoid-shaped pulse, and, at the dispersion of 0.262 ps2, to …

Improved time-resolved acousto-optic technique for optical fiber analysis of axial non-uniformities by using edge interrogation

The time-resolved acousto-optic technique demonstrated recently to be a very useful method for the analysis of fiber axial non-uniformities, able to detect variations of fiber diameter in the nanometric scale with a spatial resolution of few cm. An edge interrogation approach is proposed to improve further the performance of this technique. The detection of subnanometer fiber diameter changes or sub-ppm changes of the core refractive index is demonstrated.

In-Fiber Fractional Signal Processing: Recent Results and Applications

The implementation of mathematical operators using photonic signal processing –as for example, conventional differentiators and integrators– is particularly well suited to overcome the speed and bandwidth limitations of electronics. In the Laboratory of Fiber Optics of the University of Valencia we work on the development of in-fiber time-domain fractional operators and their applications. In the last years we have made some specific proposals to perform photonic fractional differentiation (PFD), photonic fractional integration (PFI), photonic fractional Hilbert transform (PFHT), and photonic fractional Fourier transform (PFFT), using fiber-based technologies. Recently, we have been able to…

Cylindrical optical microcavities: Basic properties and sensor applications

Abstract A detailed theoretical analysis of the basic properties of whispering-gallery modes (WGM) of thin capillaries is presented. The sensitivity of the resonances, as well as the Q factor is analyzed as a function of the structural parameters of the capillary and the refractive index inside the capillary. A practical application where thin capillaries are used for the measurement of glucose concentration in water is presented as a chemical sensor demonstrator. A best sensitivity of 1.24 nm/% of glucose concentration in water is reported, which corresponds to more than 850 nm/RIU. Additionally, different experimental approaches are discussed to improve the sensitivity and the detection l…

All-Normal-Dispersion Photonic Crystal Fibers Under Prism of Supercontinuum Generation and Pulse Compression

We discuss properties of all-normal-dispersion photonic crystal fibers in context of supercontinuum generation and compression of ultrashort pulses. The application of pump pulses typical for the state of the art Ti:Sapphire lasers allows obtaining quite flat and broad spectra extending more than one octave in this fiber. The influence of initial pump pulse parameters such as pulse energy, duration, and pump wavelength on the SC generation was investigated. It was shown that compression of pulses with such SC spectra allows obtaining a few cycle pulses up to 8.1 fs, if a simple quadratic compressor is used and single cycle pulses up to 2.5 fs, if full phase compensation is provided.

Tunable and reconfigurable microwave filter by use of a Bragg-grating-based acousto-optic superlattice modulator

We present an all-optical novel configuration for implementing multitap transversal filters by use of a broadband source sliced by fiber Bragg grating arrays generated by propagating an acoustic wave along a strong uniform fiber Bragg grating. The tunability and reconfigurability of the microwave filter are demonstrated.

Mode-locked Yb-doped all-fiber laser based on in-fiber acoustooptic modulation

We show what we believe is the first demonstration of an ytterbium-doped strictly all-fiber active mode-locking laser. The active control of the laser is based on in-fiber amplitude modulation at 11 MHz, which is achieved by using an all-fiber acoustooptic superlattice modulator driven by standing acoustic waves. In our experiments, the laser was operated at 1091.3 nm and had two stable regimes producing either a train of mode-locked single pulses or a train of pulse pairs. Best results for the mode-locked train of single pulses were 740 ps of time width and 26 mW of average power, at a pump power of 480 mW.

Supercontinuum Q-switched Yb fiber laser using an intracavity microstructured fiber

We report on an intracavity configuration for supercontinuum generation in a Q-switched Yb fiber laser. The supercontinuum laser includes a section of microstructured fiber within the Q-switched laser cavity. With 380 mW of pump power, the supercontinuum laser can emit broadband pulses of 6 microJ energy and 10 ns temporal width, at repetition rates from few hertz up to 2 kHz. The supercontinuum spectrum spans over a wavelength range in excess of 1.4 microm.

High-repetition rate acoustic-induced Q-switched all-fiber laser

We report a high repetition rate actively Q switched all fiber laser. The acousto optic interaction controls the cou pling between co propagating core and cladding modes and is used to modulate the optical losses of the cavity, which permits to perform active Q-switching. Using 1.4 m of 300 ppm Er-doped fiber and a maximum pump power of 120 mW, we have obtained up to 1 W peak power pulses, with a pulse repetition rate that can be continuously varied from 1 Hz to 120 kHz and a pulse width that changes from 70 ns to 2.2 μs.

Analysis of Fiber Inhomogeneity Using Time-Resolved Acousto-Optic Interaction

Workshop on Specialty Optical Fibers and their Applications 2013, Sigtuna Sweden, 28–30 August 2013

All-fiber noninterferometric narrow-transmission-bandpass filter

In-fiber mode engineering based on the combination of Bragg and long-period gratings (LPGs) permits the implementation of noninterferometric transmission filters with narrow passbands using standard single-mode fiber. The design of the bandpass filter is based on the coupling between propagating and counterpropagating cladding modes in two fiber Bragg gratings. A LPG located between the Bragg gratings transfers power from the input fundamental mode to a specific cladding mode and recouples the filtered signal to the output fundamental mode. The filter produces a series of narrow passbands of about 30 pm linewidth with a maximum transmittance above 60%, 20 dB isolation, and passband separati…

Analog Photonic Fractional Signal Processing

Fil: Cuadrado Laborde, Christian. Universidad de Valencia. Instituto Universitario de Ciencia de los Materiales; España Fil: Cuadrado Laborde, Christian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Cuadrado Laborde, Christian. Pontificia Universidad Católica Argentina. Facultad de Química e Ingeniería del Rosario; Argentina Fil: Poveda-Wong, Luis. Universidad de Valencia. Instituto Universitario de Ciencia de los Materiales; España Fil: Carrascosa, Antonio. Universidad de Valencia. Instituto Universitario de Ciencia de los Materiales ; España Fil: Diez, Antonio. Universidad de Valencia. Instituto Universitario de Ciencia de los Materiales; España Fil: Cruz, Jo…

Q-switched all-fibre laser using a fibre-optic resonant acousto-optic modulator

Abstract We report an actively Q-switched all-fibre laser using a fibre-optic resonant acousto-optic modulator as Q-switching element. The modulator consists of a short-length fibre Bragg grating modulated by a standing longitudinal elastic wave, being the grating length much shorter than the acoustic wavelength. Q-switch pulses were successfully obtained from an Er3+-doped fibre laser at repetition rates of 18 and 37 kHz.

Measurement of the Electrostriction-Induced Refractive Index Modulation Using Long Period Fiber Gratings

We report the measurement of the refractive index modulation in optical fibers generated by electrostrictively driven acoustic waves through the change in transmission in a long period fiber grating.

Transform-limited pulses generated by an actively Q-switched distributed fiber laser.

A single-mode, transform-limited, actively Q-switched distributed-feedback fiber laser is presented, based on a new in-line acoustic pulse generator. Our technique permits a continuous adjustment of the repetition rate that modulates the Q factor of the cavity. Optical pulses of 800 mW peak power, 32 ns temporal width, and up to 20 kHz repetition rates were obtained. The measured linewidth demonstrates that these pulses are transform limited: 6 MHz for a train of pulses of 10 kHz repetition rate, 80 ns temporal width, and 60 mW peak power. Efficient excitation of spontaneous Brillouin scattering is demonstrated.

Actively Q-switched DFB fiber laser for Brillouin sensor applications

Q-switching of distributed feedback (DFB) fiber lasers permits to achieve high peak powers, preserving an ultra narrow linewidth [1,2]. The development of a new in-line acousto-optic modulator based on a magnetostrictive actuator, instead of a piezoelectric-based device, permits an efficient excitation of elastic pulses propagating along the optical fiber and an easy access to both emission outputs of the laser. The repetition rate can be continuously adjusted, as well as the amplitude of the elastic pulses. The interaction of these elastic pulses with a fiber Bragg grating written in an erbium-doped fiber permits an actively Q-switched operation of the DFB fiber laser [3]. The birefringenc…

Generation of supercontinuum in erbium-doped microstructured optical fibers

We present experimental results on supercontinuum (SC) generation in Er-doped microstructured optical fibers (MOF) pumped with nanosecond pulses at 1064 nm. The Er doping increases the effective nonlinear refractive index [1]. As a result, nonlinear interactions are enhanced and broad supercontinuum spectra are generated with relatively low pump power. Supercontinuum spectra generated in two fibers with the zero dispersion wavelengths (ZDW) close to the pump wavelength are presented. The first MOF is an endlessly singlemode fiber with normal dispersion at the pump wavelength, while the second fiber is a large air-filling fraction MOF with anomalous dispersion at 1064 nm.

Fabrication of long period fiber gratings of subnanometric bandwidth.

This paper reports on the fabrication of long period fiber gratings having subnanometric bandwidth in the 1500 nm spectral region. Large gratings have been photo-inscribed in a high NA fiber, the grating pitch and the order of the HE cladding mode are optimized to produce gratings with a large number of periods and preventing the coupling to TE, TM or EH modes. Resonances with a FWHM of 0.83 nm and 0.68 nm have been achieved for gratings 15 and 20 cm long respectively, the free spectral range between transmission notches is 125 nm. The polarization effects and the sensitivity of the gratings to temperature and to strain variations are presented as well. © 2015 Optical Society of America Thi…

All-Optical Tuning of WGMs in Microspheres Made of Er/Yb Codoped Optical Fiber

All-optical, pump-assisted, thermal tuning of high-Q whispering-gallery mode (WGM) resonances of microspheres is demonstrated. The microspheres were made of an Er/Yb codoped single-mode silica optical fiber. The pump light absorbed by the active ions heats the microsphere, which leads to the shift of the resonances. A tuning range in excess of 2 nm in the C-band is achieved. The presence of active ions is restricted to the core of the microsphere. The WGM fields, which are confined in a region close to the surface of the microsphere, do not overlap with the dopant. Thus, high-Q resonances (>10 7 ) are achieved, as in pure silica microspheres, even at optical wavelengths within the absorptio…

Multicore optical fibres for astrophotonics

We report progress towards multimode (MM) fibre filters for suppressing the OH emission that hinders ground-based observation of the early Universe. Fibre Bragg gratings (FBGs) can filter these narrow spectral lines in single-mode (SM) fibres [1]. Implementing them in MM fibres well-matched to astronomical instruments requires transitions between the MM fibre and several SM fibres [2]. Such hand-crafted “photonic lanterns” require many identical FBGs to be made and spliced in place. Instead we are pursuing the idea in multicore (MC) fibres, Fig. 1(a). The FBG is written at once in all the SM cores. The fibre is jacketed with low-index glass and tapered to form the core and cladding of a MM …

Manufacturing of All-Fiber Q-Switch lasers for supercontinuum generation

This work exposes the fabrication process of an All-Fiber Q-Switch laser and its use as a pump source for the generation of supercontinuum (SCG) with tapered microstructured fiber devices (tapers).

Two-dimensional photonic-crystal microwave waveguide

This paper reports on the use of 2D photonic crystals to design microwave waveguides. The waveguide consists of a periodic arrangement of holes, with a square or rectangular cross section, that extends along the waveguide with a central defect defined by the absence of a hole. The theoretical analysis of such a structure is based on a biorthogonal-basis method and provides a full-vector description of the modes guided by the defect. Our results show that such a waveguide can be designed to support only one mode at any operating frequency. This mode is a polarization doublet whose dispersion is controlled by the geometrical parameters, thus permitting the design of a novel polarization-maint…

Coupling between counterpropagating cladding modes in fiber Bragg gratings

We present an experimental demonstration of energy transfer between counterpropagating cladding modes in a fiber Bragg grating (FBG). A strong FBG written in a standard photosensitive optical fiber is illuminated with a single cladding mode, and the power transferred between the forward propagating cladding mode and different backward propagating cladding modes is measured by using two auxiliary long period gratings. Resonances between cladding modes having 30 pm bandwidth and 8 dB rejection have been observed.

Microwave phase shifter based on fibre Bragg grating

A variable delay line is presented for phased array antennas based on a fibre Bragg grating which has a uniform period and operates at constant optical wavelength. The Bragg wavelength of a localised part of the fibre grating is modified by straining the fibre, the optical carrier is reflected by the strained part of the grating and the time delay of the microwave modulating signal is determined by the position where the strain has been applied. In this initial experiment time delay variations up to 330 ps in the frequency range 1 – 14 GHz have been achieved.

Measurement of the strain-optic coefficients of PMMA from 800 to 2000 nm

The strain-optic coefficients of PMMA are measured in a broad wavelength range from 800 to 2000 nm. The sensitivity of the azimuthal whispering gallery mode resonances to the strain is exploited to measure the strain-optic coefficients of PMMA micro-rods. The technique is based on measuring the wavelength shift of the resonances of both polarizations states, the TE and TM, when an axial strain is applied to the polymer rods. This method enables the determination of the strain-optic coefficients of the material in a broad wavelength range. In particular, in the near-infrared range, the PMMA exhibits negligible dispersion and anisotropy, and the strain-optic coefficients show constant values …

Polarization Modulation Instability in Dispersion-Engineered Photonic Crystal Fibers

Generation of widely spaced polarization modulation instability (PMI) sidebands in a wide collection of photonic crystal fibers (PCF), including liquid-filled PCFs, is reported. The contribution of chromatic dispersion and birefringence to the net linear phase mismatch of PMI is investigated in all-normal dispersion PCFs and in PCFs with one (or two) zero dispersion wavelengths. Large frequency shift sidebands are demonstrated experimentally. Suitable fabrication parameters for air-filled and liquid-filled PCFs are proposed as guidelines for the development of dual-wavelength light sources based on PMI.

General measurement technique of the ratio between chromatic dispersion and the nonlinear coefficient

Measuring the nonlinear coefficient γ of any guiding medium, regardless of the sign and magnitude of its group-velocity dispersion parameter β 2 , is challenging because of the lack of general solutions of the nonlinear Schrodinger equation (NLSE). Indeed, existing approaches typically need to disregard chromatic-dispersion effects to determine γ [1] . Here we propose an all-encompassing approach to measure the ratio β 2 /γ and prove our method in polarization-maintaining (PM) and single-mode (SM) fibers with positive and negative β 2 .

Wideband tuning of four-wave mixing in solid-core liquid-filled photonic crystal fibers

We present an experimental study of parametric four-wave mixing generation in photonic crystal fibers that have been infiltrated with ethanol. A silica photonic crystal fiber was designed to have the proper dispersion properties after ethanol infiltration for the generation of widely spaced four-wave mixing (FWM) bands under 1064 nm pumping. We demonstrate that the FWM bands can be tuned in a wide wavelength range through the thermo-optic effect. Band shifts of 175 and over 500 nm for the signal and idler bands, respectively, are reported. The reported results can be of interest in many applications, such as CARS microscopy.

Q-switching of an all-fiber laser by acousto-optic modulation of a fiber Bragg grating.

We report active Q-switching of an all-fiber laser using a Bragg grating based acousto-optic modulator. Q-switching is performed by modulating a fiber Bragg grating with an extensional acoustic wave. The acoustic wave modulates periodically the effective index profile of the FBG and changes its reflection features. This allows controlling the Q-factor of the cavity. Using 1 m of 300 ppm erbium-doped fiber and a maximum pump power of 180 mW, Q-switch pulses of 10 W of peak power and 82 ns wide were generated. The pulse repetition rate of the laser can be continuously varied from few Hz up to 62.5 kHz.

Anisotropic Elasto-optic Effect in Optical Fibers under Axial Strain: Experimental Observation by means of Whispering Gallery Modes Resonances

Experimental characterization of the refractive index anisotropy generated by the elasto optic effect in a conventional optical fiber under axial strain by using WGMs resonances and their tunability with strain.

Wavelength shift of four-wave mixing bands in photonic crystal fibers pumped in the normal dispersion regime

The generation of correlated photon pairs plays a central role in several quantum mechanics applications, such as quantum information, and cryptography [1]. Correlated photon pairs can be generated inside an optical fiber through the parametric process of degenerated four-wave mixing (FWM) [2]. In this paper we report the results of two different experiments where wavelength shift of FWM bands in normal dispersive PCFs is investigated.

Long-cavity all-fiber ring laser actively mode locked with an in-fiber bandpass acousto-optic modulator.

We demonstrate low-frequency active mode locking of an erbium-doped all-fiber ring laser. As the mode locker, we used a new in-fiber bandpass acousto-optic modulator showing 74% modulation depth, 3.7 dB power insertion losses, 4.5 nm of optical bandwidth, and 20 dB of nonresonant light suppression. The laser generates 330 ps mode-locked pulses over a 10 ns pedestal, at a 1.538 MHz frequency, with 130 mW of pump power. Fil: Cuadrado Laborde, Christian Ariel. Universidad de Valencia; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigaciones Opticas (i); Argentina. Provincia de Buenos Aires. Gobernación. Comisión de In…

Acousto-optic Modulators Based on Flexural Acoustic Waves and its Application to Mode-locked Fiber Lasers

Acousto-optic modulators based on flexural acoustic waves and its application to implement active mode-locking in fiber lasers is reported. Optical pulses as short as 25 ps temporal width were obtained at 2.46 MHz repetition rate.

Er-doped photonic crystal fibre characterization method based on McCumber theory

Characterization and modeling of Er-doped fibres [1] allowed in the past years fruitful developments of amplifiers and lasers. Since in a conventional fibre monomodal propagation of light is achieved in a very short length (once energy of other modes has been radiated) the cutback technique has been successfully used to determine absorption cross sections at the pump and gain band wavelengths. Emission cross sections have been usually determined instead from the measurement of gain or amplified spontaneous emission (ASE) spectrum together with the use of theoretical models. In a photonic crystal fibre (PCF) the limited size of the air-holes lattice originates energy radiation from the highe…

Actively Q-switched all-fiber lasers

Q-switching of fiber lasers using bulk elements has important drawbacks as reduced mechanical stability and high insertion losses. The development of efficient all-fiber modulation techniques is the key to obtain robust, compact and efficient Q-switched all-fiber lasers. Certainly, the development of fiber Bragg gratings (FBG) has been crucial to make progress on fiber lasers. FBGs permit a simple way to assemble all-fiber laser cavities and can be written in the active fiber itself. The Q-factor of this type of cavities is determined by the reflectivity of the FBGs and the losses of the fiber. Here, we focus on the use of magnetostrictive materials and the acousto-optic interaction to deve…

High accuracy measurement of Poisson's ratio of optical fibers and its temperature dependence using forward-stimulated Brillouin scattering

Transverse acoustic mode resonances enable a high accuracy determination of Poisson’s ratio and elastic properties of optical fibers. An all-optical pump and probe technique is used for efficient excitation and accurate characterization of both, radial and torsional-radial acoustic resonances of optical fibers. Simple and precise algebraic expressions for the frequencies of high order acoustic resonances are derived, enabling a rigorous analysis of the experimental data using standard least squares fitting. Following this approach, the determination of Poisson’s ratio does not require the measurement of any physical length, but only frequency measurements are required. An accuracy better th…

Back-scattering of whispering-gallery-modes resonances of cylindrical microcavities: Refractometric applications

Whispering-gallery modes (WGM) resonances of microcapillaries are directly compatible with microfluidic systems and have demonstrated its suitability for refractometric applications [1]. Microcapillaries with a submicrometric wall exhibit very large wavelength shifts as a function of the refractive index of the liquids that fill the inside of the capillary [2]. The spatial separation between the surface where the total internal reflection takes place (the outer surface) and the sensing surface (the inner surface) where the wave interacts with the analyte is a unique property that can be exploited to deal with analytes with a refractive index higher than that of the capillary [2].

Broadband Tuning of Polarization Modulation Instability in Microstructured Optical Fiber through Thermal Heating

Broadband tuning of polarization modulation instability in microstructured optical fibers is reported. Tunability is achieved by simultaneous birefringence-dispersion changes through thermal heating. 906 cm-1 frequency tunability range is attained.

In-line fiber-optic sensors based on the excitation of surface plasma modes in metal-coated tapered fibers

Abstract Metal-coated tapered fibers are reported as refractive index sensors based on the resonant excitation of surface plasma modes supported by the metal coating. The devices are easy to fabricate and constitute an alternative to metal-coated side-polished fibers and to other sensors made up of bulk components. We report the fabrication and power transmission properties of quasi-circular devices and asymmetric devices. Both sets of devices can be operated as wavelength output sensors, as well as amplitude output sensors. The transmittance of quasi-circular devices is polarization independent and it changes more than 30 dB as a function of external refractive index.

Measurement of UV-induced absorption and scattering losses in photosensitive fibers

UV-assisted fabrication of gratings using photosensitive fibers is a well-established technique, based on the UV-induced permanent modification of the refractive index of the fiber material. As a result, the absorption coefficient is also changed. Here, we exploit the thermal sensitivity of whispering gallery mode resonances of the fiber itself to measure the profile of the heating along an irradiated fiber versus the input power and for different UV radiation intensities. Our technique allows discriminating between the absorption and scattering contributions to the overall losses, by comparing the results obtained with our technique with direct transmission measurements. Different photosen…

All-Normal Dispersion Photonic-Crystal Fiber for Pulse-Preserving Supercontinuum Generation near 800 nm

All-normal dispersion photonic-crystal fiber is designed for pulse-preserving supercontinuum generation near 800 nm. Supercontinuum generation is analyzed numerically addressing the role of pump pulse energy and offset of the pump wavelength from the zero point of 3d-order dispersion.

Fiber Sensitivity Characterization near the Turning Point of the Acousto-Optic Interaction

In-fiber acoustic gratings exhibit a turning point in which the sensitivity of the coupling resonances to environment changes is extremely high. The frequency of the acoustic wave enables easy matching of the turning point.

Q-switched all-fiber laser based on magnetostriction modulation of a Bragg grating

We report an actively Q-switched all-fiber laser based on magnetostriction modulation of a Bragg grating. The laser employs a pair of Bragg gratings as reflective mirrors, one of which is bonded to a magnetostrictive element. Lengthening of the magnetostrictive element when a magnetic field is applied shifts the Bragg wavelength of the grating, allowing control of the Q-factor of the cavity and, thus, performing active Q-switching. The magnetostrictive modulator is small, compact and requires less than 300 mW electrical drive power. Using erbium-doped fiber and a maximum pump power of 120 mW, Q-switch pulses of more than 1 W peak power were obtained, with a pulse repetition rate that can be…

"Photonic lantern" spectral filters in multi-core fibre

Fiber Bragg gratings are written across all 120 single-mode cores of a multi-core optical Fiber. The Fiber is interfaced to multimode ports by tapering it within a depressed-index glass jacket. The result is a compact multimode "photonic lantern" filter with astrophotonic applications. The tapered structure is also an effective mode scrambler.

Time-resolved acousto-optic interaction in single-mode optical fibers: characterization of axial nonuniformities at the nanometer scale.

We report on a time-resolved acousto-optic interaction technique for the detection of axial nonuniformities in single-mode fibers. It is based on the propagation of short packets of flexural acoustic waves. Small axial nonuniformities (of the order of nanometers) are detected by measuring the transmittance of the fundamental mode as a function of time. It is shown that the technique allows the detection of axial nonuniformities along sections of single-mode fiber exceeding 1 m long with spatial resolution of the order of a few centimeters.

Experimental analysis of distributed pump absorption and refractive index changes in Yb-doped fibers using acousto-optic interaction.

In-fiber acousto-optic interaction is used to characterize the refractive index changes at the C band in a single-mode ytterbium-doped optical fiber under 980 nm pumping. The transmission notch created by the acoustic-induced coupling between the core mode and a cladding mode shifts to longer wavelengths when the pump is delivered to the fiber. The electronic contribution to the refractive index change is quantified from the wavelength shift. Using a time-resolved acousto-optic method, we investigate the distribution of pump absorption, and the resulting refractive index change profile, along sections of ytterbium-doped fiber exceeding 1 m long under different pump power levels.

An approach to the measurement of the nonlinear refractive index of very short lengths of optical fibers

A method for the measurement of the nonlinear-refractive index coefficient in single-mode optical fibers is presented. It takes advantage of the high sensitivity of the acousto-optic interaction effect in optical fibers to the fiber properties. Direct measurement of the nonlinear-refractive index change resulting from cross-phase modulation between a probe and a pump signal is obtained from the fiber's acousto-optic interaction performance. It is a non-interferometric method in which a very short length of fiber (<0.25 m) is required.

Fiber laser with combined feedback of core and cladding modes assisted by an intracavity long-period grating

We present a fiber laser made in a single piece of conventional doped-core fiber that operates by combined feedback of the fundamental core mode LP((0,1)) and the high-order cladding mode LP((0,10)). The laser is an all-fiber structure that uses two fiber Bragg gratings and a long-period grating to select the modes circulating in the cavity; the laser emits at the coupling wavelength between the core mode LP((0,1)) and the counterpropagating cladding mode LP((0,10)) in the Bragg gratings. This work demonstrates the feasibility of high-order mode fiber lasers assisted by long-period gratings.

All polarization-maintaining passively modelocked ytterbium-doped fiber lasers, behavior under two different cavity configurations

Fil: Cuadrado-Laborde, Christian. Universidad de Valencia. Departamento de Física Aplicada; España Fil: Cuadrado-Laborde, Christian. Consejo Nacional de Investigaciones Científicas. Instituto de Física Rosario; Argentina Fil: Cuadrado-Laborde, Christian. Pontificia Universidad Católica Argentina. Facultad de Química e Ingeniería del Rosario; Argentina Fil: Carrascosa, Antonio. Universidad de Valencia. Departamento de Física Aplicada; España Fil: Diez, Antonio. Universidad de Valencia. Departamento de Física Aplicada; España Fil: Cruz, J. L. Universidad de Valencia. Departamento de Física Aplicada; España Fil: Andrés, M. V. Universidad de Valencia. Departamento de Física Aplicada; España Abs…

Tunable chirp in Bragg gratings written in tapered core fibers

In this paper we present a technique to control the chirp of a fiber grating capable to produce positive or negative chirp in a single grating. The device is based on a uniform period grating written in a tapered core fiber, this grating has a positive chirp that can be reduced and removed by subjecting the fiber to mechanical stress, after some stress level the grating chirps to negative values. A chirp range of ±4 nm with respect to a central wavelength of 1546 nm has been experimentally achieved.

Mode locking of an all-fiber laser by acousto-optic superlattice modulation

Active mode locking of an erbium-doped all-fiber laser with a Bragg-grating-based acousto-optic modulator is demonstrated. The fiber Bragg grating was acoustically modulated by a standing longitudinal elastic wave, which periodically modulates the sidebands at twice the acoustic frequency. The laser has a Fabry-Perot configuration in which cavity loss modulation is achieved by tuning the output fiber Bragg grating to one of the acoustically induced sidebands. Optical pulses at 9 MHz repetition rate, 120 mW peak power, and 780 ps temporal width were obtained. The output results to be stable and has a timing jitter below 40 ps. The measured linewidth, 2.8 pm, demonstrates that these pulses ar…

Highly tunable optically switched time delay line for transversal filtering

A novel tunable dispersion device, based on two chirped fibre gratings subjected to non-uniform magnetic fields, is presented. A large degree of tunability is achieved from 250 to 750 ps/nm. This is used to demonstrate RF filtering in the 3-11 GHz range.

Study of the use of methanol-filled Er-doped suspended-core fibres in a temperature-sensing ring laser system

We report on an experimental/numerical investigation into the use of methanol-filled Er-doped suspended-core fibres (SCFs) in temperature-sensing ring laser systems. We have adopted a ring laser configuration that includes an Er-doped SCF as a temperature-dependent attenuator (TDA) with a step-index Er-doped fibre (EDF) as the laser active medium. The laser performance dependence on the temperature was measured both in continuous wave (CW) and transient regimes. CW laser output power and build-up time values are compared with those of similar laser systems based on other types of Er-doped PCFs or using other laser configurations. A notable variation of 0.73% °C−1 was achieved in CW operatio…

Efficient interrogation method of forward Brillouin scattering in optical fibers using a narrow bandwidth long-period grating

A new technique, to the best of our knowledge, for the characterization of the effective refractive index modulation in optical fibers due to transverse acoustic mode resonances excited by electrostriction is reported. The resonances excited by an optical pulse are probed by a narrow bandwidth long-period grating (LPG) inscribed in the fiber, which is interrogated by a continuous wave (CW) beam. The LPG used in this experiment has a narrow bandwidth and high sensitivity to small mode index perturbations, allowing the measurement of index variations from below 10 − 9 to 10 − 6 . Radial and torsional-radial acoustic modes were characterized up to 1.1 GHz. The linewidth of resonances was found…

Tunable narrowband fiber laser with feedback based on whispering gallery mode resonances of a cylindrical microresonator.

Narrowband filtering based on whispering gallery modes of a slightly tapered cylindrical optical microresonator was used to implement a tunable narrowband erbium-doped fiber laser. The laser can be set to emit a single longitudinal cavity mode (single frequency), although the laser cavity is a few meters long. In the single-frequency regime the laser can emit a maximum power of 0.380 mW with a linewidth <35 kHz and a signal-to-noise ratio exceeding 50 dB. Tunability is achieved by sliding the excitation point along the microcylinder. A tuning range of 1.16 nm is demonstrated.

Time-domain fiber laser hydrogen sensor.

We report a novel scheme for a fiber-optic hydrogen sensor based on an erbium-doped fiber laser with a palladium-coated tapered fiber within the laser cavity. The tapered fiber acts as a hydrogen-sensing element. When the sensing element is exposed to a hydrogen atmosphere, its attenuation decreases, changing the cavity losses and leading to a modification of the laser transient. The hydrogen concentration is obtained by simple measurement of the buildup time of the laser. This technique translates the measurement of hydrogen concentration into the time domain, and it can be extended to many intensity-based fiber sensors. Relative variations in the buildup time of up to 55% at an increase o…

Linearly polarized all-fiber laser using a short section of highly polarizing microstructured fiber

A linearly polarized all-fiber erbium laser is presented in this work. The polarization selective element consists on a piece of a single-mode, polarizing microstructured fiber, which is placed within the laser cavity. The microstructured fiber shows a regular lattice of air-holes, in which four holes next to the core were enlarged. This fiber shows a polarization dependent loss of 16 dB/m around 1550 nm. The laser cavity presents different losses for each polarization and, as a consequence, a highly polarized emission is obtained. The polarization ratio of the emitted power was in excess of 20 dB.

Q -switched and modelocked all-fiber lasers based on advanced acousto-optic devices

The interest in all-fiber lasers is stimulated by the inherent advantages they have over bulk lasers in aspects such as heat dissipation and robustness. The performance of Q-switched and modelocked fiber lasers can benefit enormously from the development of all-fiber configurations. A fiber laser with strictly all-fiber components can fulfil the requirements of mechanical stability, low maintenance, enhanced power efficiency, simplified assembly process, and low cost. In this framework, recent developments infiber acousto-optic devices are reviewed that have demonstrated new possibilities for actively Q-switched distributed feedback fiber lasers, modelocking lasers and doubly active Q-switc…

Broadband tuning of polarization modulation instability in microstructured optical fibers

The wideband tuning of strong bands generated through polarization modulation instability (PMI) in microstructured optical fibers (MOFs) is reported. Tunability is achieved by exploiting the dependence of the phase-matching condition on the fiber’s chromatic dispersion and birefringence, which is particularly sensitive when the fiber is pumped near the zero-dispersion wavelength. MOFs designed to accomplish PMI phase-matching when they are infiltrated with ethanol and pumped at 1064 nm were designed and fabricated. Taking advantage of the large thermo-optic coefficient of ethanol, both chromatic dispersion and birefringence were varied through temperature. Wavelength shifts from 937 nm to 8…

Supercontinuum generation with 532 nm quasi-continuum pulses in photonic crystal fibre tapers

We report experimental results on supercontinuum generation in PCF tapers using quasi-continuous pump pulses of 7 ns duration at 532 nm. SC generation in normal and anomalous dispersion regimes are presented. Introduction Supercontinuum generation (SC) in photonic crystal fibres (PCF), fibre tapers, and PCF tapers has been demonstrated in the past with pump pulses of fs, ps, and tenths of ns duration [1-2]. Here, we present experimental results on SC generation in PCF tapers using quasi-continuous pump pulses of 7 ns duration at 532 nm. Fabrication of the PCF tapers The PCF from which the tapers were made, was a large-air-hole PCF ("cobweb" PCF) with two rings of air holes around a solid si…

Broadband Tuning of Four-Wave Mixing Bands Using Photonic Crystal Fibers

We present an experimental study of the shift with temperature of widely-spaced FWM parametric bands generated in an ethanol-inflltrated photonic crystal fiber. We report broadband tuning of 175 nm and over 500 nm for the signal and idler bands, respectively, achieved through the thermo-optic effect. Numerical calculations were carried out and show good agreement with experimental data.

Analysis of whispering gallery modes resonators: wave propagation and energy balance models

Electromagnetic whispering gallery modes (WGM) are surface waves guided by the curvature of an interface. Microspheres, microdisks and microcylinders –as for example standard optical fibers– are high quality microresonators for the WGM. In fact, they can be regarded as compact and small ring resonators. Here, we present a comparison between wave propagation and energy balance models, stablishing the equivalence and discussing the basic characteristics of these two complementary approaches.

Alignment-free, all-spliced fiber laser source for CARS microscopy based on four-wave-mixing

An environmentally-stable low-repetition rate fiber oscillator is developed to produce narrow-bandwidth pulses with several tens of picoseconds duration. Based on this oscillator an alignment-free all-fiber laser for multi-photon microscopy is realized using in-fiber frequency conversion based on four-wave-mixing. Both pump and Stokes pulses for coherent anti-Stokes Raman scattering (CARS) microscopy are readily available from one fiber end, intrinsically overlapped in space and time, which drastically simplifies the experimental handling for the user. The complete laser setup is mounted on a home-built laser scanning microscope with small footprint. High-quality multimodal microscope image…

Excitation and interrogation of whispering-gallery modes in optical microresonators using a single fused-tapered fiber tip

We show that whispering-gallery modes (WGMs) in optical microresonators can be excited and detected using a fused-tapered fiber tip (FTFT). The fabrication of FTFTs is simple and inexpensive; they are robust and allow the excitation and interrogation of the resonances with a single fiber. Excitation of high-Q WGMs in silica microcylinders and microspheres is demonstrated.

Hydrogen sensor based on a palladium-coated fibre-taper with improved time-response

Abstract We report an experimental study of the response of a hydrogen sensor, based on a palladium-coated tapered optical fibre, at different temperatures in the range −30 to 80 °C. We have studied the transmission, the time-response and the initial response velocity, being able to correlate these measurements with the pressure–composition isotherms of the Pd–H system and its phase transitions. Heating of the palladium layer optically with an auxiliary laser diode permits to improve the sensor's time-response at low temperatures.

An optical pulse modulator based on an all-fiber mirror

Dynamic Characterization of Upconversion in Highly Er-Doped Silica Photonic Crystal Fibers

Measurements of time evolution of amplified spontaneous emission for square-wave modulated pump were made on a highly erbium-doped silica photonic crystal fiber and fitted to theoretical results calculated using different formalisms to describe the ${\rm Er}^{3+}$ -ion migration-assisted co-operative upconversion mechanism in the population densities rate equations. The determined characterization parameters are the constant homogeneous upconversion coefficient, 3.0 $\times 10^{-24}~{\rm m}^{3}/{\rm s}$ , the critical radii for upconversion and migration, 10.5 and 14A, respectively, and the rate of clustered ions, 14%. These parameters are analysed and compared to those obtained with contin…

Single-frequency active Q-switched Distributed Fiber Laser Using Acoustic Waves

This letter presents a single mode, actively Q-switched distributed feedback fiber laser. Acoustic pulses are launched into an erbium-doped fiber Bragg grating, resulting in the introduction of a traveling defect. Thus, a transmission peak appears in the reflection band while the pulse travels along the grating. This effect allows the laser to operate in a Q-switched regime, providing optical pulses which repetition rate was continuously tuned up to 10 kHz. Pulses of 168 mW of peak power and 73 ns of temporal width were obtained at low repetition rate.

All-fiber lasers actively modelocked by acousto-optic modulation

The development of all-fiber lasers is of high interest because of the intrinsic robustness, compactness and energy efficiency. In-fiber amplitude modulators based on acousto-optic modulation of fiber Bragg gratings (FBG) permit the implementation of novel all-fiber actively modelocked lasers. Using either traveling or standing longitudinal acoustic waves, optical pulses between 500 and 100 mW peak powers and ∼ 700 ps temporal width were obtained at 4.1 and 9 MHz repetition rates, respectively. Implementing a simultaneous active Q-switching, we have demonstrated a doubly active Q-switching and mode-locking of two different all-fiber laser configurations. In the case of the laser based on tr…

A frequency-output fiber optic voltage sensor with temperature compensation for power systems

Abstract We present a frequency-output fiber optic voltage sensor for power systems with temperature compensated response. The sensor employs PZT-type ceramic tubes, which are interrogated by a length of single-mode fiber coiled onto the tubes and a Mach–Zehnder interferometer. The combination of piezoelectric tubes with properties exhibiting opposite behavior to temperature changes is successfully exploited to passively compensate the temperature sensitivity of the sensor. The prototype reported here exhibits a resolution of 13 mV rms and the deviations of the sensor’s response due to temperature changes are within 1% over the temperature range between −30 and 70 °C. The device presented h…

Tunable Dispersion Compensator Based on a Fiber Bragg Grating Written in a Tapered Fiber

We report a novel dispersion tunable device for first-order dispersion compensation. It is based on a fiber Bragg grating written in a tapered fiber with a specific profile. The taper profile allows tuning the dispersion of the grating by stretching the fiber while the linearity of the group delay is preserved. A device with 0.8 nm of useful bandwidth and dispersion value tunable over more than 400 ps/nm is reported.

Chromatic Dispersion Control in Mode-Locked Yb-Doped Fiber Lasers Based on a Microstructured Optical Fiber

We present an experimental study on the use of solid core microstructured optical fibers (MOF) for managing the chromatic dispersion in an Yb-doped fiber laser passively mode-locked by a saturable absorber. The performance of the laser, in terms of pulse width and repetition rate, was investigated as a function of the net cavity dispersion.

Supercontinuum generation at 800 nm in all-normal dispersion photonic crystal fiber

We have numerically investigated the supercontinuum generation and pulse compression in a specially designed all-normal dispersion photonic crystal fiber with a flat-top dispersion curve, pumped by typical pulses from state of the art Ti:Sapphire lasers at 800 nm. The optimal combination of pump pulse parameters for a given fiber was found, which provides a wide octave-spanning spectrum with superb spectral flatness (a drop in spectral intensity of ~1.7 dB). With regard to the pulse compression for these spectra, multiple-cycle pulses (~8 fs) can be obtained with the use of a simple quadratic compressor and nearly single-cycle pulses (3.3 fs) can be obtained with the application of full pha…

Measurement of temperature profile induced by the optical signal in fiber Bragg gratings using whispering-gallery modes.

The temperature sensitivity of whispering-gallery mode resonances of an optical fiber is exploited to measure thermal effects induced by an optical signal of moderate power along a fiber Bragg gating (FBG). The UV inscription technique used for the fabrication of FBG introduces a permanent change in the absorption coefficient of the fiber; thus, thermal effects are expected. The resonance wavelength shift of whispering-gallery modes provides information about the temperature change in the fiber, point to point. We present the experimental characterization of the thermal effects in FBG as a function of the wavelength and the power of the launched optical signal through the grating.

Nonlinear coefficient measurement in highly dispersive fibers

We present a novel approach for measuring nonlinear coefficients in fibers with significant pulse broadening. We perform a proof-of-concept demonstration for 200-m-long polarization-maintaining and single-mode fibers pumped at 1060 nm with ps pulses.

Long-period grating assisted fractional differentiation of highly chirped light pulses

We experimentally demonstrate the possibility to perform a fractional differentiation of arbitrary order on a given light pulse by propagation through a single long-period grating. A simple analytical expression is obtained also, relating the fractional order of differentiation with the parameters of the long-period grating. A secant hyperbolic like pulse of 23 ps time width with a chirp parameter of -30 was successfully fractionally differentiated to the 0.5th order. The proposal was corroborated experimentally and numerically. The device may find applications in real time phase recovery. Fil: Poveda Wong, L.. Universidad de Valencia; España Fil: Carrascosa, A.. Universidad de Valencia; Es…

All-Fiber Laser With Intracavity Acousto-Optic Dynamic Mode Converter for Efficient Generation of Radially Polarized Cylindrical Vector Beams

We report an all-fiber laser that emits a radially polarized cylindrical vector beam (CVB) at 1&#x00A0;&#x03BC;m based on an intracavity acousto-optic mode converter. We efficiently generate the CVB, taking advantage of the acousto-optic coupling from the HE11 mode to the TM01 mode in a two-mode fiber. The laser can be switched from emitting a Gaussian-like beam to a radially polarized CVB. Radially polarized CVBs with modal and polarization purities &#x003E;98&#x0025; and a maximum power of 65&#x00A0;mW were generated.

Propagation length enhancement of surface plasmon polaritons in gold nano-/micro-waveguides by the interference with photonic modes in the surrounding active dielectrics

Abstract In this work, the unique optical properties of surface plasmon polaritons (SPPs), i.e. subwavelength confinement or strong electric field concentration, are exploited to demonstrate the propagation of light signal at 600 nm along distances in the range from 17 to 150 μm for Au nanostripes 500 nm down to 100 nm wide (30 nm of height), respectively, both theoretically and experimentally. A low power laser is coupled into an optical fiber tip that is used to locally excite the photoluminescence of colloidal quantum dots (QDs) dispersed in their surroundings. Emitted light from these QDs is generating the SPPs that propagate along the metal waveguides. Then, the above-referred propagat…

White light supercontinuum generation in a Y-shaped microstructured tapered fiber pumped at 1064 nm.

We report the generation of supercontinuum in a Ge-doped Y-shape tapered fiber pumped at 1064 nm in the ns pump regime. The taper was designed to have long taper transitions and a taper waist with a core diameter of 0.9 mum. The large air-filling fraction and diameter of the air-hole microstructure reduces the confinement loss at long wavelengths so, enabling the extension of the spectrum to longer wavelengths. Along the taper transition the zero-dispersion wavelength decreases as the diameter of the taper becomes smaller. The spectral components generated along the taper transition pump the taper waist, enhancing the generation of short wavelengths. A flat spectrum spanning from 420 nm to …

Effects of Temperature and Axial Strain on Four-Wave Mixing Parametric Frequencies in Microstructured Optical Fibers Pumped in the Normal Dispersion Regime

A study of the effect of temperature and axial strain on the parametric wavelengths produced by four-wave mixing in microstructured optical fibers is presented. Degenerate four-wave mixing was generated in the fibers by pumping at normal dispersion, near the zero-dispersion wavelength, causing the appearance of two widely-spaced four-wave mixing spectral bands. Temperature changes, and/or axial strain applied to the fiber, affects the dispersion characteristics of the fiber, which can result in the shift of the parametric wavelengths. We show that the increase of temperature causes the signal and idler wavelengths to shift linearly towards shorter and longer wavelengths, respectively. For t…

Widely Tunable Polarization Modulation Instability in D2O-Filled Microstructured Optical Fiber

Polarization modulation instability (PMI) is a nonlinear effect in which two pump photons with identical polarization propagating in a nonlinear medium give rise to two new photons of different frequency and orthogonal polarization with respect to the pump photons [1] . In this work, we report the experimental demonstration of broad spectral tuning of PMI generated in solid-core microstructured optical fibers (MOF) that were previously infiltrated with heavy water (D 2 O). MOFs were designed and fabricated with the appropriate dispersion characteristics to produce widely spaced PMI spectral bands when they were filled with D 2 O and pumped at 1064 nm. Heavy water was chosen due to suitable …

A Refractive Index Sensor Based on the Resonant Coupling to Cladding Modes in a Fiber Loop

We report an easy-to-build, compact, and low-cost optical fiber refractive index sensor. It consists of a single fiber loop whose transmission spectra exhibit a series of notches produced by the resonant coupling between the fundamental mode and the cladding modes in a uniformly bent fiber. The wavelength of the notches, distributed in a wavelength span from 1,400 to 1,700 nm, can be tuned by adjusting the diameter of the fiber loop and are sensitive to refractive index changes of the external medium. Sensitivities of 170 and 800 nm per refractive index unit for water solutions and for the refractive index interval 1.40-1.442, respectively, are demonstrated. We estimate a long range resolut…

Polarization Modulation Instability in All-Normal Dispersion Microstructured Optical Fibers With Quasi-Continuous Pump

We report the experimental observation of the polarization modulation instability (PMI) effect in all-normal dispersion (ANDi) microstructured optical fibers (MOFs) with quasi-continuous pumping. The small unintentional birefringence (~10-5), that any realistic non-polarization maintaining MOF exhibits, contributes to this nonlinear effect. PMI can produce two sidebands whose polarization state is orthogonal to the polarization of the pump. In this work, only one type of PMI process is observed, i.e., when the pump is polarized along the slow axis of the fiber and sidebands are generated in the fast axis mode. This PMI process was studied experimentally in two ANDi fibers with different dis…

Wavelength multiplexed hydrogen sensor based on palladium-coated fibre-taper and Bragg grating

A novel configuration of a wavelength multiplexed hydrogen sensor based on a palladium-coated tapered fibre and a fibre Bragg grating is presented. This scheme allows cascading several sensors along a single fibre, which increases the capability of implementing multipoint sensor networks for volumetric detection. Moreover, in this configuration the light interacts twice with the palladium layer, thus enhancing the sensitivity of the sensor.

Accurate measurement of Poisson ratio in optical fibers based on forward-stimulated Brillouin scattering

The interaction between light and sound in optical fibers is a phenomenon that researchers have been investigated for many decades. Among all the opto-acoustic effects that occurs in optical fibers, forward-stimulated Brillouin scattering (FSBS) has become of great interest as sensing mechanism due to the dependence of the excited acoustic resonances on both internal parameters [1] , [2] and surroundings [3] of the optical fiber. The vibrational modes behind FSBS are transverse acoustic resonances, in particular, the radial modes R 0m and the torsional-radial modes TR 2m . Most of the experiments reported based on FSBS exploit the properties of either the radial or the torsional-radial mode…

Phase recovery by using optical fiber dispersion

We propose a simple and fast procedure to retrieve the phase profile of arbitrary light pulses. It combines a first experimental stage, followed by a one-step numerical stage. To this end, it is necessary to perform a Fresnel transform, which is obtained just by propagating the light pulses through an optical fiber. We experimentally test this proposal recovering the phase profile in the light pulses provided by a passively mode-locked laser. The proposal is then compared with a temporal variation of the Gerchberg–Saxton recursive algorithm, which is specially modified for this purpose. Fil: Cuadrado Laborde, Christian Ariel. Universidad de Valencia; España. Consejo Nacional de Investigacio…

Anisotropic elasto-optic effect in optical fibers under axial strain: a perturbative approach

We present a perturbative approximation to calculate the relative shift of the WGM resonances in a conventional optical fibers when an axial strain is applied. We consider the anisotropic character of the elasto-optic effect.

Simultaneous temperature and ac-current measurements for high voltage lines using fiber Bragg gratings

We present an optical ac-current sensor, based on a fiber Bragg grating stretched by a magnetostrictive material, which enables a simultaneous measurement of high ac-currents and temperature. The proposed system is appropriated to monitor high voltages lines and can be installed without interrupting the current line, being characterized by an inherent electrical isolation.

Two-core transversally chirped microstructured optical fiber refractive index sensor

We present a sensing architecture consisting of a two-core chirped microstructured optical fiber (MOF) for refractive index sensing of fluids. We show that by introducing a chirp in the hole size, the MOF can be a structure with decoupled cores, forming a Mach-Zehnder interferometer in which the analyte directly modulates the device transmittance by its differential influence on the effective refractive index of each core mode. We show that by filling all fiber holes with analyte, the sensing structure achieves high sensitivity (transmittance changes of 300 per RIU at 1.42) and has the potential for use over a wide range of analyte refractive index.

&lt;title&gt;Tunable chirp in Bragg gratings written in tapered core fibers&lt;/title&gt;

In this paper we present a technique to control the chirp of a fiber grating capable to produce positive or negative chirp in a single grating. The device is based ona uniform period grating written in a tapered core fiber, this grating has a positive chirp that can be reduced and removed by subjecting the fiber to mechanical stress, after some stress level the grating chirps to negative values. A chirp range of +/- 4 nm with respect to a central wavelength of 1546 nm has been experimentally achieved.

Accurate and broadband characterization of few-mode optical fibers using acousto-optic coupling

Acousto-optic interaction in optical fibers is exploited for the accurate and broadband characterization of two-mode fibers. Differential modal index, group delay, and group-velocity dispersion is obtained. The technique is suitable for the characterization of few-mode fibers used in space-division multiplexing.

Tunable Four-wave Mixing Light Source Based on Photonic Crystal Fibers with Variable Chromatic Dispersion

We present a detailed experimental study of fourwave mixing tuning in photonic crystal fibers that were filled either with ethanol or with heavy water. It is demonstrated that wide tuning ranges can be achieved in both cases through the variable chromatic dispersion generated by thermo-optic effect. Tunability of the signal band from 745 nm to 919 nm, and of the idler band from 1260 nm to 1759 nm is demonstrated with a pump at 1064 nm. Numerical calculations were carried out and show good agreement with experimental measurements. We present a detailed experimental study of fourwave mixing tuning in photonic crystal fibers that were filled either with ethanol or with heavy water. It is demon…

Theory about the Embryo Cryo‐Treatment

Background To create hypothesis, which can give a logical explanation related to the benefits of freezing/thawing embryos. Cryopreservation is not only a technology used for storing embryos, but also a method of embryo treatment that can potentially improve the success rate in infertile couples. Methods From the analysis of multiple results in assisted reproductive technology, which have no satisfactory explanation to date, we found evidence to support a ‘therapeutic’ effect of the freezing/thawing of embryos on the process of recovery of the embryo and its subsequent implantation. Results Freezing/thawing is a way to activate the endogenous survival and repair responses in preimplantation …

Actively mode-locked fiber ring laser by intermodal acousto-optic modulation

We report an actively mode-locked fiber ring laser. A simple and low-insertion-loss acousto-optic modulator driven by standing flexural waves, which couples core-to-cladding modes in a standard single-mode optical fiber, is used as an active mechanism for mode locking. Among the remarkable features of the modulator, we mention its high modulation depth (72%), broad bandwidth (187 GHz), easy tunability in the optical wavelength, and low insertion losses (0.7 dB). The narrowest optical pulses obtained were of 95 ps time width, 21 mW peak power, repetition rate of 4.758 MHz, and 110 mW of pump power.