Phase noise reduction by self-phase locking in semiconductor lasers using phase conjugate feedback

Abstract

Abstruct-A theoretical analysis of the behavior of the frequency/phase noise of semiconductor lasers with external phase conjugate feedback is presented. It is shown that the frequency noise is drastically reduced even for lasers with butt-coupled phase conjugate mirrors. In this laser system, the phase noise takes a finite-low value corresponding to a state of first-order self-phase locking of the laser. As a result, the spectral shape of the laser signal does not remain Lorentzian but collapses around the carrier to a delta function with a close to carrier noise level of less than -137 dBcMz. The total phase variance of this laser signal, in a 20 GHz noise bandwidth, is less than 0.002 rad'.

Stability properties of diode lasers with phase-conjugate feedback

“…The spectra for the solitary laser are shown for comparison. The spectra agree qualitatively with those obtained by Agrawal and Gray7 and Petersen et al 19 for an instantaneous PCM. There is one clear discrepancy, however: compared with the solitary laser, Agrawal sees a shift of the RO frequency in the laser with PCF, whereas Petersen and we do not see such a shift.…”

Stability and noise properties of diode lasers with phase-conjugate feedback

“…The spectra for the solitary laser are shown for comparison. The spectra agree qualitatively with those obtained by Agrawal and Gray [7] and Petersen et al [20] for an instantaneous PCM. There is one clear discrepancy, however.…”

“…Especially for ps, resonances are seen. Also, Petersen [20] and Bochove [14] found such oscillations in their spectra for an instantaneous mirror with . These resonances are not related to the RO, but correspond to the double-round-trip modes which were first described by AuYeung et al [21].…”

“…The variation of several other laser parameters does not reveal any substantial influence on the frequency . A feeling for the origin of the resonance at can be obtained by realizing that there is a frequency in the laser-with-PCF system that is proportional to the feedback strength: the laser resonance frequency at a given inversion with respect to the solitary laser frequency is given by (20) while for zero pump-detuning, the inversion depends linearly on [see (9)]. Combining (20) with (9) yields (21) This explains why does not depend on other parameters.…”

Self-pumped phase conjugate mirror using the divergent spherical wave

“…The PCM using semiconductor gain medium has a specific feature of fast response time on the order of subnanoseconds. If such a fast-response PCM cavity oscillates in self-pumped manner, we can expect to generate the light with drastically narrow spectral linewidth, as theoretically proposed by Petersen et al [2]. In this paper, we demonstrate phase conjugate wave generation using divergent spherical wave for the first time.…”