PHASE NOISE-REDUCTION BY SELF-PHASE LOCKING IN SEMICONDUCTOR-LASERS USING PHASE-CONJUGATE FEEDBACK

A theoretical analysis of the behavior of the frequency/phase noise of semiconductor lasers with external phase conjugate feedback is presen ted. It is shown that the frequency noise is drastically reduced even for lasers with butt-coupled phase conjugate mirrors. In this laser sy stem, the phase noise takes a finite-low value corresponding to a stat e of first-order self-phase locking of the laser. As a result, the spe ctral shape of the laser signal does not remain Lorentzian but collaps es around the carrier to a delta function with a close to carrier nois e level of less than -137 dBc/Hz. The total phase variance of this las er signal, in a 20 GHz noise bandwidth, is less than 0.002 rad2.