Injection-locking technique for heterodyne optical phase locking of a diode laser

A novel technique is demonstrated for heterodyne optical phase locking of a diode laser to a single-frequency source by injection seeding. By modulation of the drive current of the diode laser at as much as several gigahertz, FM sidebands are imposed upon the output. We demonstrate that it is possible to phase lock either sideband to an injected beam. The carrier of the diode laser output is therefore locked in phase with the injected light but with a frequency difference given by the modulation of the drive current, The phase fluctuations between the lasers are analyzed, and the variance is found to be (4.4 degrees)(2), corresponding to 99.4% of the diode carrier light locked to the injected beam. (C) 1997 Optical Society of America.