SMALL-SIGNAL ANALYSIS OF MODULATION CHARACTERISTICS IN A SEMICONDUCTOR-LASER SUBJECT TO STRONG OPTICAL-INJECTION

Injection locking of a semiconductor laser can induce major changes in the modulation characteristics of the laser, A small-signal analysis using the lumped element model shows that both the frequency and dampi ng of the characteristic resonances of the coupled complex field and f ree carriers (gain medium) are modified. The detuning between the inje cted field and the free-running oscillating field, the amplitude of th e injection held relative to the free-running held, the linewidth enha ncement factor, the cavity photon and spontaneous carrier decay rates, and the held enhancement of the decay rate are all key parameters in determining the changes to the modulation characteristics. For a broad range of parameters, there is simultaneous enhancement of the modulat ion bandwidth and stable, locked operation, The enhancement is a cavit y phenomena and does not occur in a traveling wave amplifier, It requi res that the frequency of the locking field be detuned from the inject ion-modified frequency of the cavity resonance, This causes a resonant enhancement of the modulation sideband associated with the preferred frequency of the optical cavity, Bandwidth enhancements beyond the fre e-running laser limit are possible over a range of injection levels an d injection frequency detunings.