Abstract

With the availability of compact high brightness laser diodes as pumps and low loss glasses as the hosts for rare earths, a significant new category of lasers has emerged. The small diameters for single mode fibers gives high thermal gradients that readily dissipate any heating so as to allow CW operating for outputs as high as several watts. The greatest attenuation has been given to erbium in silica operating at 1.53-1.55 μm as an optical amplifier for communications. It gives gains approaching 40 dB, gain coefficients greater titan 5 dB/mW for pumping at 0.98 or 1.47 nm, and saturation outputs of 18 dBm in fibers that are readily compatible with commercial fibers. In a double clad silica fiber, Nd at 1.06 μm can give an efficiency greater than 50% when pumped with a high output multiple stripe laser diode. In silica, laser emission has also been obtained from Pr, Sm, Ho, Tm and Yb. The lower energy phonon spectra of heavy metal fluorides has allowed for significant population in energy levels that are quenched in silicates, thereby giving additional laser transitions. Particularly striking in this regard are Ho and Tm which lase at shorter wave lengths than the pump by up-conversion through stepwise absorption of successive pump photons. Tm can lase at 455 and 480 nm when pumped with 640-690 nm radiation. Energy transfer between ions has been used for fluorescence sensitization, terminal state depletion and up-conversion. The configurations for laser oscillators, amplifiers, and super-luminescent sources will be discussed.

© 1991 Optical Society of America