Tunable diode laser control by a stepping Michelson interferometer

A tunable diode laser beam is sent through a Michelson interferometer and is locked to a fringe of the diode laser interference pattern by controlling the diode laser polarization current. The path difference change of the Michelson interferometer is controlled step by step by a stabilized He-Ne red laser. When the interferometer path difference increases or decreases, the polarization current of the diode is forced to change in order to preserve the interference order of the diode beam. At every step the diode frequency is accurately fixed and its phase noise significantly reduced.