We present the measurement of the temperature variation along a fiber Bragg grating (FBG) written in a photosensitive fiber, using azimuthal whispering gallery modes (WGM) resonances of the fiber itself. The FBG is regarded as a cylindrical microresonator, in which the azimuthal WGM resonances are excited with an auxiliary 2 μm taper. The wavelengths of the WGM resonances shift as the temperature of the grating increases at a given point. The temperature profile along the FBG is obtained by monitoring the WGM resonances at different points, as a function of the power and wavelength of the optical signal. Our experiments give useful information to study the small absorption changes produces by the standard UV photo-inscription technique and the thermally induced chirping effects generated when FBGs are used with moderate power levels.
We present the fabrication and characterization of a microstructured fiber with ultrahigh birefringence. The fiber, consisting on a small elliptical core suspended from thin silica bridges, has been fabricated adapting the stack and draw method for microstructured fibers to the well known fabrication procedure for conventional elliptical core optical fibers. The ellipticity of the core and the air-hole array has been achieved by controlling the lateral tension between the preform and the jacketing tube. The group index birefringence has been measured using a frequency-domain modulated carrier method and a modal interferometer method. Both methods proved appropriate and showed consistent results. A group index birefringence higher than 7 x 10-3 is demonstrated, being this value higher than those reported to date.
We report a high efficiency and high repetition rate acoustic-induced Q-switched Er-doped-fiber laser. Two fiber Bragg gratings were used as cavity mirrors, whilst the active Q-Switching was performed by temporally controlling the Q-cavity factor by coupling light from the core mode to cladding modes using flexural acoustic waves. The acousto-optic attenuator was implemented by applying a RF signal to a piezoelectric disc and using an aluminum horn to focus the acoustic wave in a tapered fiber. The RF signal that drives the piezoelectric disc was amplitude modulated with a rectangular wave of variable frequency and duty cycle. Q-switched laser pulses of ~ 1 W peak power, 0.1 - 2 μs pulse width and continuously variable frequency up to 100 kHz, were obtained. The laser efficiency of energy conversion was as high as 20%.
A wavelength-switchable fiber ring laser that includes a Bragg grating-based acousto-optic modulator is reported. When a longitudinal acoustic wave propagates along a fiber grating, it modulates periodically the effective period, which causes that additional bands of reflection appear on both sides of the Bragg wavelength. Wavelength switching of the laser emission is achieved by dynamic adjust of the peak reflectivity of the different bands.
We present a nonlinear highly birefringent microstructured fiber. The fiber has been fabricated adapting the fabrication method for microstructured fibers to the conventional one for elliptical-core fibers. Birefringence higher than 7 x 10-3 is demonstrated.