Theory of a semiconductor laser with phase-conjugate optical feedback

The effects of phase-conjugate feedback on semiconductor laser mode structure and dynamics are studied, beginning with a derivation of the system's coherent optical rate equation. For fast-responding phase-conjugating mirror (PCM) a multimode external cavity longitudinal mode spectrum arises that is in many ways similar to that of conventional external feedback lasers, except that the spacing of the external resonator modes equals half that of a conventional external cavity of equal length. A linearized stability analysis based on rate equations for longitudinal modes shows that the external cavity modes alternate in stability as function of increasing frequency shift from the pump. These modes also appear as spikes in the random intensity noise and phase noise spectra. It is shown that the locked phase of the field must be controlled to achieve stable operation, and may be used to maximize the fraction of energy in the central ''spike'' of the laser spectrum. Finally, the effects of pump noise on laser linewidth, and the finite PCM response time, are described.