Assessment of direct modulation in wireless fiber links based on heterodyning of sideband injection-locked semiconductor lasers

This paper presents an assessment of wireless fiber links based on heterodyning of sideband-injection locked semiconductor lasers under direct current modulation. Using the Van der Pol equations for coupled oscillators, the small-signal response of the output power and phase of injection-locked semiconductor lasers are derived. The resultant intensity and phase modulation of the injection locked laser are assessed in terms of optimum power injection ratio and phase detuning between the master and slave lasers. Intensity and phase modulation have opposite preferable locking conditions. Optimizing the locking conditions increases the efficiency of phase modulation and ensures negligible amplitude modulation of the generated microwave signal. The performance of the PM system remains superior to the AM system for all locking conditions