Diode-pumped solid-state lasers for coherent communications

Abstract

Semiconductor laser diodes with output near 0.8 μm can pump Nd:YAG and other solid-state laser materials. The efficiency of conversion from laser diode radiation to solid-state laser output is between 25 and 50 %. A properly designed diode-pumped solid-state laser will oscillate in a fundamental spatial mode even if the pump is highly multimode. It is possible to take advantage of the Watt level output of available laser diodes to achieve hundreds of milliwatts in a TEM00 mode. The goal of narrow-linewidth single-frequency output is met if the solid-state laser resonator is a monolithic nonplanar ring.1 The monolithic construction of the resonator leads to the narrow (1-kHz) linewidth; the ring resonator permits oscillation at high power (>70 mW) in a single frequency. Diode-pumped rings can be tuned in frequency over 100 MHz in a few microseconds using an applied stress; tuning over tens of gigahertz is possible in a few seconds using temperature. We have demonstrated phase locking of two diode-pumped rings with phase error of 1.7° rms. Direct modulation of these lasers is not possible. A given laser cannot be tuned more than 100 GHz. However, there are over a dozen solid-state laser hosts, each of which lases at slightly differing wavelengths near 1.06 and 1.32 μm. The typical separation between available wavelengths is 100 GHz. Thus wavelength-division multiplexing is possible.