In this work we present the broadband characterization of in-fiber acousto-optic interaction in fiber SM2000 (Thorlabs), with a special focus on the sensitivity of the technique as a measurement tool of the parameters of the fiber. The acoustooptic interaction technique provides good sensitivity when measuring parameters of singlemode or few-mode fibers: dispersion curves, radius, or core refractive indices (both linear and nonlinear) can be determined by means of this tool with accuracy. The basics of the technique rely on its resonant character: as a parameter of the fiber changes, the optical wavelength that fulfills the acousto-optic phase-matching condition shifts. The measurement of the acousto-optic phase matching curve provides information about the sensitivity of the technique as a function of variations of different parameters of the fiber. Such measurements can be performed in a broadband spectral range, using a single section of fiber of some tens of cm. In this paper, we report the measurement in detail of the acousto-optic dispersion curves for the couplings LP01-LP1,1-4, in the optical range 1.0-2.0 μm. From these data, we characterize the sensitivity of the technique for the measurement of the core radius, external radius and numerical aperture of the fiber, especially around the turning point of the phase-matching curve for the acousto-optic coupling.
Whispering gallery mode resonators (WGMR) have attracted a great interest in the last decade. WGMR have been fabricated in different geometries, solid and hollow, spherical, toroidal, and bottled shaped. Hollow spherical WGMR or microbubble resonators (MBR) are the last arrived in the family of resonators. The approach used for their fabrication is based on surface tension driven plastic deformation on a pressurized capillary, similar to glassblowing. Using such technique we are able to fabricate large surface area and thin spherical shells with high quality factor (Q).
MBR are efficient phoxonic cavities that can sustain both optical photons and acoustic phonons. It has been demonstrated that MBR can be used to study Turing comb patterns (Kerr modulation) and Stimulated Brillouin Scattering (SBS). Radiation pressure is another mechanism that also leads to excitation of acoustic phonons with lower frequencies, in the range of hundreds of kHz to tens of MHz in the case of silica MBR. The frequency of such oscillations occurs very close to the mechanical eigenfrequencies of the cavity.
We have studied the temporal behavior of the cavity, the coexistence and the suppression of the oscillation while generating Turing comb patterns. The observed phenomenology can be explained by the geometrical characteristics of a MBR. MBRs are spheroidal WGM resonators with quite dense spectral characteristics. The total dispersion of MBR is anomalous and large, as expected for very large MBR. Thus, Kerr comb formation is allowed for all MBR used in this work.
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.