Silica-air double-clad optical fiber

A new design of the silica-air double-clad optical fiber is proposed. The fiber was prepared from an MCVD preform inserted into a supporting silica tube with a fluorine-doped connective element with a lower refractive index (Δn~-4×10^-3) and air as the second cladding. A numerical aperture as high as 0.3 was measured for the first cladding and for fiber lengths up to 50 cm. Although it is realized that the results are preliminary, the optimization of the fiber parameters promises a new all-glass design for double-clad optical fibers for high-power fiber laser applications     

Fiber laser polarization tuning using a Bragg grating in a Hi-Bifiber

Single- and dual-wavelength tunable lasing (around 1552 nm) has been obtained in an Er-doped low-Bi fiber laser with a Bragg grating mirror in a Hi-Bi fiber. Equal output powers for both laser lines and spectral spacing of up to 0.26 mm, larger than the original spacing between the resonance peaks of the grating (0.2 nm), can be easily achieved by employing a polarization controller inside of the laser cavity     

Enhancement in sensitivity for fiber-optic torsion sensors

We demonstrate a simple fiber-optic torsion sensor with enhanced sensitivity. The sensor is based on the combination of a Malus and a Fabry-Perot (MFP) interferometer and allows for the sensitive detection of changes in the polarization of the guided beam due to torsion applied to the fiber. The basic idea behind this optical arrangement is to enhance the sensitivity for the measurements of intracavity anisotropies due to multiple passes of the beam through the sensing area. Theoretical analysis based on Jones calculus for a fiber-optic MFP interferometer shows that small twists in the fiber can be monitored through variations on the transmission of the arrangement. Experimental results with a hybrid MFP arrangement of bulk optical components and optical fibers show that, compared to single-pass polarimeter measurements, an enhancement in sensitivity up to 116 can be effectively achieved.