Narrow linewidth 1.5 μm semiconductor laser with a resonant optical reflector

A compact narrow linewidth semiconductor laser is described. An emission linewidth of 135 kHz at 5 mW of output power is obtained from a 1.5-μm semiconductor laser butt coupled to an external resonant optical reflector (ROR). The ROR, made with dielectric waveguides on silicon substrate, has transmission and reflection bandwidths as narrow as 0.35 Å.