Stability properties of diode lasers with phase-conjugate feedback

For a diode laser subjected to feedback from a phase-conjugating mirror we present (a) the first exact stability analysis and (b) various spectra. The stability properties are intermediate between those of the injection laser and the laser with conventional optical feedback. The role of a finite response-time is to drastically enhance the steady-state stability. For moderate feedback the frequency noise is suppressed by several orders of magnitude, and the main relaxation frequency of the laser shows a crossover from the usual relaxation oscillation frequency to a new frequency determined by the amount of feedback. This may be of technological importance since it improves the modulation bandwidth.