High-Stability 1.5micron External-Cavity Semiconductor Lasers for Phaselock Applications
01 January 1989
Applications using phaselocked semiconductor lasers, such as homodyne detection, require lasers with narrow linewidth and high frequency stability. We describe the design and operating characteristics of two 1.5micron external-cavity semiconductor lasers built for such applications. Measured beat linewidth is 4 kHz, and the spectral density of relative frequency noise deviates significantly from the intrinsic white spectrum only at frequencies below 4 kHz. We estimate that this frequency jitter will induce approximately 1.1degrees rms phase error in a second-order homodyne optical phaselock loop that is optimized for the present beat linewidth. These lasers have been phaselocked with 8degrees rms phase error.