Integrated MOPA/modulator device produces watt-level output
Monolithic master oscillator/power amplifier (MOPA) structures capable of high-power, difffraction-limited output offer smaller, lower-cost replacements for many gas and solid-state lasers. Adding high-speed modulation capability makes MOPAs attractive for applications in satellite space communications and telecommunications, and researchers at SDL (San Jose, CA) recently demonstrated that approach by inserting an electro-absorption modulator between the master oscillator and power amplifier. The device emitted more than 1 W at 980 nm, and the modulator bandwidth was 5 GHz. Strained quantum wells of InGaAs formed the distributed Bragg reflector (DBR) master oscillator and amplifier region. The front and back mirrors of the DBR cavity were defined by second-order gratings. Light from the oscillator is injected through the front grating into the 500-µm long modulator, then passes to the 1.5-mm gain-guided power amplifier. In a self-homodyne setup, a linewidth of 750 kH¥was determined, and the researchers measured a small-signal modulation bandwidth of about 5 GHz, which they believe is the highest value reported for a monolithically integrated MOPA. This device could find use in free-space optical links for intersatellite optical communications.