L. Petersen et al., PHASE NOISE-REDUCTION BY SELF-PHASE LOCKING IN SEMICONDUCTOR-LASERS USING PHASE-CONJUGATE FEEDBACK, IEEE journal of quantum electronics, 30(11), 1994, pp. 2526-2533
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.