Passively Modelocked All-PM Thulium-Doped Fiber Laser at 2.07μm

Here we present a self-started passively mode-locked thulium-doped fiber laser with in-band pumping at 1561 nm that fully retains polarization and emits beyond 2 μm. We obtained a sequence of light pulses at 13.084 MHz, where the pulse and spectral widths were 94 ps and 70 pm, respectively, at 2069.5 nm. The measured instantaneous angular frequency shows that these light pulses are chirp-free.

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.

Development and analysis of a model based on chirped fiber Bragg gratings employed for cracks characterization in materials

In this work a model was developed that allows to understand the behavior of a chirped fiber Bragg grating for the detection and characterization of cracks in materials. In addition to the amplitude response, we show that the group delay of the grating provides useful information for the characterization of the crack. The position of the crack can be determined thanks to the linear chirp of the grating that fixes a correlation between the spatial position and both, the wavelength and the group delay. However, our analysis shows that this simple approach has a source of error, which can be overcome if a controllable external strain can be applied to the embedded grating, additional to the st…

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…

Analysis of a microwave time delay line based on a perturbed uniform fiber Bragg grating operating at constant wavelength

This paper presents the modeling of a new microwave time delay line based on a uniform fiber Bragg grating (FBG) with a section which period has been perturbed. The time delay can be modified by changing the position of the perturbation along the grating. Theoretical results are presented for a 5-cm long uniform grating and optical signal is modulated up to 18 GHz. Experimental setup used magnetic fields to change the period locally along the grating and a 330 ps maximum time delay is shown. Comparison between calculations and measurements show a perfect agreement. Such a delay line offers many advantages for beamforming applications in phased array antennas where the operation at a fixed w…

Strain and temperature measurement discrimination with forward Brillouin scattering in optical fibers

A novel method that enables simultaneous and discriminative measurement of strain and temperature using one single optical fiber is presented. The method is based on the properties of transverse acoustic mode resonances (TAMRs) of the optical fiber. In particular, it is based on the different sensitivity to temperature and strain that exhibit the radial modes R0,m and a family of torsional-radial modes denoted as T R 2 , m ( 1 ) . We show that the resonance frequencies of both types of resonances shift linearly with temperature and strain, but at different rates. By the combined use of the different sensitivities of the two families of TAMRs, we experimentally demonstrate discriminative mea…

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.

Highly Efficient Holmium-Doped All-Fiber ∼2.07-μm Laser Pumped by Ytterbium-Doped Fiber Laser at ∼1.13 μm

We report a 2.07-μm Holmium-doped all-fiber laser (HDFL) pumped by a 1.13-μm Ytterbium-doped fiber laser (YDFL). Home-made alumino–germano–silicate holmium-doped fiber (HDF) served here as an active medium, optimized in terms of chemical composition and co-dopants’ concentrations. Laser action at 2.07 μm was assessed in simple Fabry–Perot cavity, formed by a couple of home-made fiber Bragg gratings (FBGs), inscribed directly in the HDF; this allowed notable diminishing of intracavity loss of the 2.07-μm laser. HDF was in-core pumped by the 1.13-μm double-clad YDFL with a power of ∼12.5 W, in turn pumped in-clad by a laser diode (LD) operated at 0.97 μm with ∼24.5-W output. Using optimal len…

Effective length of short Fabry-Perot cavity formed by uniform fiber Bragg gratings

In this paper, we describe the properties of Fabry-Perot fiber cavity formed by two fiber Bragg gratings in terms of the grating effective length. We show that the grating effective length is determined by the group delay of the grating, which depends on its diffraction efficiency and physical length. We present a simple analytical formula for calculation of the effective length of the uniform fiber Bragg grating and the frequency separation between consecutive resonances of a Fabry-Perot cavity. Experimental results on the cavity transmission spectra for different values of the gratings' reflectivity support the presented theory.

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.

Simple high-resolution wavelength monitor based on a fiber Bragg grating

A compact and low-cost device for monitoring the peak wavelength of single-peak spectral distributions is presented. The system is based on the transmission properties of a fiber Bragg grating when its period is modulated. Different types of optical signal, such as the emission of distributed-feedback lasers and the reflection of a broadband optical source produced by fiber gratings used in sensor systems, can be measured with this device. We demonstrate that a high wavelength resolution of micro 1 pm can be achieved and that our proposal can be used for real-time monitoring.

ASE narrow‐band noise pulsing in erbium‐doped fiber amplifier and its effect on self‐phase modulation

In this paper, we report a study of the features of polarized and unpolarized narrow-band amplified spontaneous emission (ASE) in a low-doped erbium fiber at 976-nm pumping. We demonstrate that ASE noise can be treated as a train of Gaussian-like pulses with random magnitudes, widths, and inter-pulse intervals. ASE noise can also provide a statistical analysis of these three parameters. We also present the data that reveal ASE noise’s role in optical spectrum broadening through self-phase modulation of light propagating in a communication fiber. In particular, the data show that the ASE noise derivative defines the broadening’s spectral shape.

Threshold of a Symmetrically Pumped Distributed Feedback Fiber Laser With a Variable Phase Shift

In this paper, we study, both theoretically and experimentally, the threshold characteristics of a distributed feedback fiber laser that depend on the value of a phase shift introduced into the fiber Bragg grating structure. We show that as the phase shift possesses a noticeable birefringence, the laser oscillates at any phase shift value. We also reveal that the laser threshold is different for the cavity eigen polarizations and depends on the phase shift value. We derive a simple analytical formula to calculate the laser threshold in the case of pi phase shift; this formula can be utilized to estimate a minimal threshold value for the laser with certain active fiber and Bragg grating para…

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…

High frequency microwave signal generation using dual-wavelength emission of cascaded DFB fiber lasers with wavelength spacing tunability

[EN] A dual wavelength fiber laser source based on two cascaded phase-shifted fiber Bragg gratings is presented The gratings are written in an erbium-doped fiber each configuring the cavity of a distributed feedback fiber laser The spacing between lasing modes is controlled dynamically by the use of piezoelectric actuators A continuous tuning range of 5-724 pm of the wavelength difference which is equivalent to a photodetected 072-92 GHz range is obtained Efficient generation from the L to the W microwave and millimeter bands has been achieved by heterodyne photodetection of the dual-wavelength optical signal (C) 2010 Elsevier BV All rights reserved

Sensitivity optimization with cladding-etched long period fiber gratings at the dispersion turning point

This work presents a refractive index sensor based on a long period fiber grating (LPFG) made in a reduced cladding fiber whose low order cladding modes have the turning point at large wavelengths. The combination of these parameters results in an improved sensitivity of 8734 nm/refractive index unit (RIU) for the LP0,3 mode in the 1400-1650 wavelength range. This value is similar to that obtained with thin-film coated LPFGs, which permits to avoid the coating deposition step. The numerical simulations are in agreement with the experimental results. This work was supported in part by the Spanish Ministry of Education and Science-FEDER TEC2013-43679-R. J.L. Cruz also acknowledges financial s…

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.

Influence of Cavity Loss Upon Performance of Q-Switched Erbium-Doped Fiber Laser

Performance of an actively Q-switched erbium-doped fiber laser in function of intracavity loss is discussed. We show experimentally and theoretically (employing a distributed model that takes into account two contra-propagating laser waves) that the laser performance strongly depends on the intracavity loss of different kinds. We reveal in particular that the dominant source of smaller than expected pulse energy is the loss via excited-state absorption, inherent in erbium-doped fibers. We also discuss the other important processes involved in active Q-switching, such as passive losses and residual active fiber charge, the impact of which is clarified by a straightforward comparison of the m…

Comparison of asymmetric and symmetric cavity configurations of erbium-doped fiber laser in active Q-switched regime

We present a comparative analysis of the dynamics of an actively Q-switched erbium-doped fiber laser assembled in two configurations of Fabry–Perot cavity, asymmetric and symmetric, specified by the location of an acousto-optic Q-switch modulator relative to the output couplers. In both configurations, the length of an active (Er3+-doped) fiber is chosen such that the laser does not spuriously emit at the moments when the modulator is blocked, which is important for the pulse-on-demand operation. We show experimentally that the symmetric cavity configuration permits enlarging of the active fiber length twice as compared to the asymmetric one, thereby increasing the energy and decreasing the…

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…

Group Delay and Spectral Phase Retrieval of Light Pulses by Spectral Intensity Measurements

We discuss a method to determine both the group delay and the phase of a given pulse in the Fourier optics domain. The proposal is based on the measurement of two intensity spectra, before and after a known quadratic phase modulation. A simple analytical equation is then used to determine the group delay in one step. If necessary, the spectral phase can be determined by simple spectral integration of the determined group delay. The proposal is supported by various numerical results and an experimental measurement to prove the concept.

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…

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.

Tunable dispersion device based on a tapered fiber Bragg grating and nonuniform magnetic fields

We present a new variable dispersion device based on tuning the chirp of a tapered fiber Bragg grating by means of a magnetic transducer. By using a nonuniform magnetic field, we demonstrate a 188-472-ps/nm dispersion tuning range, suitable for tunable radio-frequency filters and dispersion compensation, among others.

Real-time and low-cost sensing technique based on photonic bandgap structures

[EN] A technique for the development of low-cost and high-sensitivity photonic biosensing devices is proposed and experimentally demonstrated. In this technique, a photonic bandgap structure is used as transducer, but its readout is performed by simply using a broadband source, an optical filter, and a power meter, without the need of obtaining the transmission spectrum of the structure; thus, a really low-cost system and real-time results are achieved. Experimental results show that it is possible to detect very low refractive index variations, achieving a detection limit below 2 x 10(-6) refractive index units using this low-cost measuring technique. (C) 2011 Optical Society of America[

Tunable Dual-Wavelength Thulium-Doped Fiber Laser Based on FBGs and a Hi-Bi FOLM

A tunable dual-wavelength thulium doped fiber laser is demonstrated experimentally. For the first time for the 2- $\mu \text{m}$ wavelength band we propose the independent tuning of the generated laser lines based on fiber Bragg gratings and the use of a Hi-Bi fiber optic loop mirror for the fine adjustment of the cavity losses to obtain stable dual-wavelength operation. Dual-wavelength laser generation with the laser lines separation in the range from 0.3 to 6.5 nm is obtained. The laser emission exhibits an optical signal-to-noise ratio better than 56 dB. Improved stability with output power fluctuations less than 1 dB is observed in dual-wavelength generation with equal power of lines.

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.

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…

Recent Advances in Forward Brillouin Scattering: Sensor Applications

In-fiber opto-mechanics based on forward Brillouin scattering has received increasing attention because it enables sensing the surrounding of the optical fiber. Optical fiber transverse acoustic resonances are sensitive to both the inner properties of the optical fiber and the external medium. A particularly efficient pump and probe technique—assisted by a fiber grating—can be exploited for the development of point sensors of only a few centimeters in length. When measuring the acoustic resonances, this technique provides the narrowest reported linewidths and a signal-to-noise ratio better than 40 dB. The longitudinal and transverse acoustic velocities—normalized with the fiber radius—can b…

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…

Dispersion induced effects of high-order optical sidebands in the performance of millimeter-wave fiber-optic links

In this paper, chirped fiber Bragg gratings (CFBGs) are proposed as signal-phase controllers for microwave-photonic wireless downstream fiber links. The effect of high-order modulation optical sidebands that disturbs the output mm-wave signal due to the chromatic dispersion induced by the gratings is studied theoretically and experimentally. The 1st and 2nd mm-wave harmonics of the output signal have been measured for conventional intensity modulation and for intensity modulation with optical carrier suppression. In the last case, data transmission at 2.5 Gb/s is demonstrated through a chirped grating of 280 ps/nm dispersion in a 40-GHz modulated link.

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.

Denaturing for Nanoarchitectonics: Local and Periodic UV-Laser Photodeactivation of Protein Biolayers to Create Functional Patterns for Biosensing

[EN] The nanostructuration of biolayers has become a paradigm for exploiting nanoscopic light-matter phenomena for biosensing, among other biomedical purposes. In this work, we present a photopatterning method to create periodic structures of biomacromolecules based on a local and periodic mild denaturation of protein biolayers mediated by UV-laser irradiation. These nanostructures are constituted by a periodic modulation of the protein activity, so they are free of topographic and compositional changes along the pattern. Herein, we introduce the approach, explore the patterning parameters, characterize the resulting structures, and assess their overall homogeneity. This UV-based patterning…

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…

Passive interferometric interrogation of a magnetic field sensor using an erbium doped fiber optic laser with magnetostrictive transducer

Abstract An erbium doped (Er3+) fiber optic laser is proposed for magnetic field measurement. A pair of FBGs glued onto a magnetostrictive material (Terfenol-D rod) modulates the laser wavelength operation when subject to a static or a time dependent magnetic field. A passive interferometer is employed to measure the laser wavelength changes due to the applied magnetic field. A data acquisition hardware and a LabVIEW software measure three phase-shifted signals at the output coupler of the interferometer and process them using two distinct demodulation algorithms. Results show that sensitivity to varying magnetic fields can be tuned by introducing a biasing magnetic field. A maximum error o…

Polarization switchable Erbium-doped all-fiber laser

We report an experimental study of an erbium-doped all-fiber laser with electrically switchable output polarization. Fiber Bragg grating written in a polarization maintaining optical fiber and attached to a piezo-ceramic actuator is used to commute the polarization state of the laser emission. The laser oscillates at one of two orthogonal polarizations depending on voltage applied to the actuator.

Long- and short-term stability of all polarization-maintaining thulium doped passively mode-locked fiber lasers with emission wavelengths at 1.95 µm and 2.07 µm

In this work, we compare the operation of a passively modelocked polarization-maintaining emission in two thulium-doped fiber lasers pumped at 1561 nm, with emission at wavelengths of 1.951 μm in one case and 2.07 μm in the other. We obtained a sequence of light pulses at 15.6 MHz, whose temporal width was 81 ps at 1.95 μm, and a sequence of light pulses at 13.1 MHz, whose temporal width was 94 ps at 2.07 μm. Finally, we also measured the long-term stability of this setup during a 24-h operation, as well as the short-term stability in a simulated harsh environment. The results confirm the superior performance of fiber laser systems with a fully polarization-maintaining design.

Power-dependent effective reflection of fiber Bragg grating as output coupler of Ytterbium-doped fiber laser

In this paper, we discuss the effective reflection of a fiber Bragg grating and its dependence on laser power when it is used as an output coupler of an ytterbium-doped fiber laser (here the effective reflection is considered to be a part of intracavity laser power reflected by the grating back to the laser cavity). We propose and discuss an experimental technique based on spectral and power analysis and derive simple formulae that permits one to obtain the intra-cavity power and the grating effective reflection. We show that, due to spectral broadening, the effective reflection dramatically decreases with increasing laser power, the effect precisely fitted using the derived formulae descri…

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.

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.

Corrections to “Light Modulation Based on Fiber Cladding Mode Coupling Between Concatenated Long-Period Gratings” [Feb 1 152-154]

In the above paper (ibid., vol. 23, no. 3, pp. 152-154, Feb. 1, 2011), there is an error in the eighth line of the abstract. The correct sentence is presented here.

Excited-state absorption in erbium-doped silica fiber with simultaneous excitation at 977 and 1531 nm

We report a study of the excited-state absorption (ESA) in erbium-doped silica fiber (EDF) pumped at 977 nm, when the fiber is simultaneously excited by signal radiation at 1531 nm. We show, both experimentally and theoretically, that ESA efficiency at 977 nm gets strongly enhanced only in the presence of signal power. Experimentally, this conclusion is supported through the detection of upconversion emission, a “fingerprint” of the ESA process, and through the measurements of the EDF nonlinear transmission coefficient for the pump wavelength, which is sensitive to the ESA value. It is shown that the experimental data are precisely modeled with an advanced five-level Er3+ model developed fo…

White light sources filtered with fiber Bragg gratings for RF-photonics applications

Abstract In this paper we demonstrate that broadband light emitters filtered with fiber Bragg gratings are a suitable light source for RF-photonics applications. A 0.075 nm bandwidth fiber grating illuminated by a light emitter of 40 nm bandwidth has been used as light source to feed a microwave phase shifter based on a chirped fiber Bragg grating. The device operates successfully in the tested frequency range (0.5–6) GHz and has been optically tuned in a range of 4 nm.

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…

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.

Induced attenuation in Ce3+ and Nd3+ doped fibers irradiated with electron beams under low dose regime

Abstract In this paper, we study the feasibility of rare earth doped optical fibers as dosimeters based on the attenuation induced by electron beams under standard conditions in radiotherapy. Neodymium and cerium doped fibers have been irradiated with 10 MeV electrons, the radiation-induced loss and the dynamic response have been measured in the wavelength range 1200–1600 nm. The sensitivity of the fibers is of the order of 0.1 (dB/m)/Gy and has a linear dependence on the dose.

An optical pulse modulator based on an all-fiber mirror

Dynamic path length changes in all-fiber mirrors: Transmission modulation

Abstract In this paper, we present a technique to modulate the transmission of an all-fiber mirror. This technique is based on the phase modulation of the light in the fiber loop, combined with the time delay between the clockwise and anticlockwise propagating beams. Using Jones calculus, a theoretical analysis has been carried out to describe the effects of static polarization changes and a dynamic phase modulation. An experimental all-fiber optical mirror has been constructed, and using a 1–MHz piezoelectric disc as the phase modulator, we demonstrate that it is possible to achieve either a 1–MHz or 2–MHz transmission modulation by adjusting the polarization state.

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.

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 dual-wavelength operation of an all- fiber thulium-doped fiber laser based on tunable fiber Bragg gratings

Tunable dual-wavelength emission of a Tm-doped fiber laser based on two fiber Bragg gratings (FBGs) is experimentally demonstrated. By using two FBGs with central wavelengths at 2069.30 and 2069.44 nm, stable dual-wavelength laser generation in the 2 ?m wavelength region is achieved by adjusting the differential loss of the two wavelengths in the laser cavity. Strain applied on the FBG allows independent tuning of the simultaneously generated wavelengths with separation between the laser lines in a range from 0.54 to 9 nm. The laser has output power fluctuations less than 0.093% for an output power of 77.3 mW.

Oligonucleotide-Hybridization Fiber-Optic Biosensor using a Narrow Bandwidth Long Period Grating

Nanometric narrowband Long Period Gratings (LPG) are investigated for the implementation of improved fiber optic biosensors. The reduction of more than one order of magnitude in the linewidth of the LPG with respect standard LPG at 1500 nm, leads to the improvement of the resolution of the sensor. By selecting the proper fabrication parameters (high numerical aperture, relatively high order mode and large length), LPGs with a 3-dB bandwidth of 1.5 nm were fabricated. The sensitivity of the LPG as a refractometer was calculated, and experimentally characterized in detail. In particular, the LP0,17 and LP0,18 resonances were investigated, in order to select the most suitable one for the bioex…

Fabrication of Optical Fiber Devices

In this paper we present the main research activities of the Laboratorio de Fibras Opticas del Instituto de Ciencia de los Materiales de la Universidad de Valencia. We show some of the main results obtained for devices based on tapered fibers, fiber Bragg gratings, acousto-optic effects and photonic crystal fibers.

Intensity-Modulated Optical Fiber Sensor for AC Magnetic Field Detection

An erbium-doped (Er3+) fiber optic laser is proposed for sensing alternated magnetic fields by measuring the laser intensity modulation. The sensor is fabricated using two partially overlapped narrow-band fiber Bragg gratings (FBGs) and a section of doped fiber in a Fabry–Perot configuration. Laser power stability and bandwidth are studied while changing the overlap. A bulk rod of TbDyFe, a magnetostrictive material, is glued to both the FBGs and the laser wavelength and power are modulated according to the magnetic field. Acquisition and processing are done using virtual instrumentation. Results have shown the possibility of detecting 11.18 $\mu \text{T}_{\mathrm {{rms}}}/\surd $ Hz for an…

Tunable chirped fibre Bragg grating device controlled by variable magnetic fields

A novel dynamic chirping fibre Bragg grating device based on a magnetic field applied to a magnetostrictive transducer capable of tuning its dispersion is presented. Chirping ranges up to 300 ps/nm have been demonstrated, which are suitable for several applications such as tunable transversal filtering and dynamic dispersion compensation.

Dual-kind Q-switching of erbium fiber laser

Two different regimes of Q-switching in the same implementation of an actively Q-switched erbium-doped fiber laser are demonstrated. Depending on the active fiber length and repetition rate of an intracavity Q-cell (acousto-optic modulator), the laser operates either in the regime of common, rather long and low-power, pulses composed of several sub-pulses or in the one of very short and powerful stimulated Brillouin scattering-induced pulses. The basic physical reason of the laser system to oscillate in one of these two regimes is the existence or absence of CW narrow-line “bad-cavity” lasing in the intervals when the Q-cell is blocked.

In-fiber Fabry-Perot refractometer assisted by a long-period grating

We present an optical fiber refractometer based on a Fabry-Perot interferometer defined by two fiber Bragg gratings and an intracavity long-period grating that makes the light confined in the resonator interact with the surrounding medium. The external refractive index is monitored by the resonant frequencies of the Fabry-Perot interferometer, which can be measured either in transmission or in reflection. In this first experiment, wavelength shifts measured with a resolution of 0.1 pm have allowed one to establish a refractive index detection limit of 2.1x10(-5).

A distributed model for continuous-wave erbium-doped fiber laser

Abstract A distributed model of a continuous-wave erbium-doped fiber laser is discussed. The model is based on two contra-propagated traveling laser waves, and includes inhomogeneous pumping, excited state absorption at the pump and the laser wavelengths, amplified spontaneous emission and radial distribution of populations of erbium levels. It is shown that excited state absorption is a main limiting factor to the laser's efficiency. Moreover, consideration of radial distributions of erbium levels' populations in the model reduces laser efficiency and decreases optimal reflection of the laser output coupler. The modeling results are in excellent agreement with the experimental study on the…

Erbium doped optical fiber lasers for magnetic field sensing

In this work two erbium doped optical fiber laser configurations for magnetic field measurement are implemented and compared. The first laser is set-up in a loop configuration and requires only a single FBG (Fiber Bragg Grating), acting as mirror. A second laser employs a simpler linear cavity configuration but requires two FBGs with spectral overlap to form the laser cavity. A bulk magnetostrictive material made of Terfenol-D is attached to the laser FBGs enabling modulation of its operation wavelength by the magnetic field. Moreover, a passive interferometer was developed to demodulate the AC magnetic field information where the corresponding demodulation algorithms were software based. B…

Temperature independence of birefringence and group velocity dispersion in photonic crystal fibres

Experimental results are presented for the dependence of the dispersion and the birefringence of a highly birefringent photonic crystal fibre with temperature. It is shown that, unlike conventional optical fibres, where temperature induces stress regions between the different materials present in their structure, photonic crystal fibres exhibit no dependence with temperature of these optical properties owing to the single material nature of their structures.

Smart Q-switching for single-pulse generation in an erbium-doped fiber laser

In this paper, we report an active Q-switching of an erbium-doped fiber laser with special modulation functions and novel laser geometry. We experimentally demonstrate that using such a smart Q-switch approach, Q-switch ripple-free pulses with Gaussian-like shape and 17.3 ns width can be easily obtained. The idea behind the smart Q-switch is to suppress one of two laser waves contra-propagating along the fiber cavity, which arises after Q-cell opening, and to eliminate the minor sub-pulses.

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.

<title>Tunable chirp in Bragg gratings written in tapered core fibers</title>

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.

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.