0000000000190374
AUTHOR
S. Torres-peiró
Parallel laser micromachining based on diffractive optical elements with dispersion compensated femtosecond pulses
We experimentally demonstrate multi-beam high spatial resolution laser micromachining with femtosecond pulses. The effects of chromatic aberrations as well as pulse stretching on the material processed due to diffraction were significantly mitigated by using a suited dispersion compensated module (DCM). This permits to increase the area of processing in a factor 3 in comparison with a conventional setup. Specifically, 52 blind holes have been drilled simultaneously onto a stainless steel sample with a 30 fs laser pulse in a parallel processing configuration.
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.
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.
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.
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…
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.
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.
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…
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.
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 chirped fiber Bragg gratings by simple combination of stretching movements
Abstract A new stretching technique to fabricate chirped fiber Bragg gratings using a nonchirped phase mask is presented. It is based on continuous stretching and continuous UV beam scanning, which ensures phase matching between periods along the grating. Simple combinations of the fiber stretching movements of a pair of piezoelectric transducers are used to avoid unwanted period blurring and wavelength shifting. A third piezoelectric transducer can be easily added to the system to provide independent apodization through phase mask dithering. Successful fabrication of apodized and nonapodized chirped fiber gratings has been performed with this technique.
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…
Bistable phase locking in rocked lasers
Abstract We investigate analytically and numerically the dynamics of single mode lasers with periodic ac injection (rocked lasers). Such lasers show phase bistability as the phase of the light emitted by such lasers can lock to either of two values shifted by π. Locking regimes for different lasers are studied showing that the system response is strongly modified in class B lasers due to the influence of relaxation oscillations.