A Semiconductor Laser as a Stable Phase Conjugate Mirror for Linewidth Reduction of Another Semiconductor Laser

An AlGaAs laser was used as a phase conjugate mirror. Reflectivities as high as 103 and bandwidth as wide as 1.9 GHz were observed. The linewidth of a second AlGaAs laser was reduced to 1/5 times that of its free-running value by optical feedback of the phase conjugate wave generated by the first laser. The reduced linewidth was independent of the separation between the two lasers, and was maintained in a stable manner for over two hours.