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.
Ytterbium absorbs at 915 and 976nm. It also emits at 976nm and from 1060nm to even 1150nm, showing a quantum
efficiency of up to 86%. In this experimental work, our novel inner cavity structures were firstly characterized and
studied as free-running lasers from the 4% Fresnel reflection from the flat-cleaved fiber facets. The available pump
source, a commercially available laser diode, had a maximum power of 0.5W at 915nm from which a coupled power
(into the inner cladding) of 1W was reached; fiber laser efficiency reached, in our best case, 55% with respect to
launched pump power. For the second part of the work, polarization controlled Yb-doped fiber laser cavities were
studied by way of inserting a polarized beam splitter and a &lgr;/4 wave-plate into de cavity. From this, 177mW of single
polarization output were obtained by rotating the wave-plate until the maximum points were identified on a wave-plate
angle vs. output power plot. The maximum output power was 200mW from 60° to 90° aprox. Now, based on the data
obtained, one can claim that at least 40% of the maximum output power available from the laser was linearly polarized.
Finally, a 600 lines/mm bulk grating was employed in order to obtain laser tuning results on a traditional way. i.e. by
reflecting lasing into the cavity and selecting output from the close end. The tuning range was measured to be from
1088nm up to 1097nm. All these results and possible applications will be discussed in detail.