Assessment of amplitude and phase modulation performance of high-frequency subcarrier optical communication systems based on heterodyning of sideband injection-locked semiconductor lasers

This paper present a theoretical assessment of the performance of subcarrier optical communication systems using sideband-injection locking and heterodyning. In this scheme, a master laser is strongly intensity modulated. The modulation sidebands of the master laser are injected into two slave lasers for the production of the subcarrier. One of the slave lasers is directly modulated to produce the amplitude and phase modulation on the subcarrier. First, using the Van der Pol equations for coupled oscillators, the small-signal response of the output power and phase of injection-locked semiconductor lasers was derived. Then the performances of the subcarrier optical communication systems based on amplitude modulation and phase modulation were assessed in terms of optimum power injection ratio and phase detuning between the master and slave lasers. For phase modulation, the performance was limited for two cases: lowest AM to PM conversion and highest PM modulation efficiency. The distortion and noise were calculated assuming coherent detection for phase modulation and envelope detection for amplitude modulation. Finally the signal to noise ratio is calculated and plotted.