Abstract

Experimental studies of potentially compact, high-gain, polarization-insensitive, low-noise crystalline fiber amplifiers for the important telecommunications wavelength of 1.3 µm will be reported for the first time. Crystalline hosts are attractive because they should provide higher gains per unit pump power than amorphous hosts,¹ owing to their approximately 5-20 times narrower fluorescence spectra. Attaining high pump intensity along the length of the active medium is an even greater concern for practical amplifiers than for laser end pumped oscillators because much higher gains per unit pump power are required. The technology for fabricating suitable low-loss crystalline fiber waveguides is still in its infancy. Small diameter fibers of Nd:YAG were fabricated by means of laser- heated pedestal growth.² Gains of 3.4 dB were obtained from a 16 /im diameter, 1 cm long, unclad Nd:YAG fiber pumped by 0.809 radiation from a 140 mW Ti:sapphire laser. Studies of the dependence of amplifier gain on fiber diameter confirmed a strong dependence of gain G on diameter D (G α D^−1.7). Extrapolation of the results indicates that gains in excess of 30 dB could be achieved by reducing the fiber diameter to 4µm. We shall describe our investigations of techniques for reducing the effective diameter of these crystalline fibers.

© 1990 Optical Society of America