Optical injection locking to optical frequency combs for superchannel coherent detection.

Optical injection locking characteristics of a distributed feedback laser are experimentally investigated for multiple-wavelength injection. Using a three-wavelength source generated by intensity modulation as the injected signal, it was found that the presence of adjacent lines could cause disturbance to the locking if a minimum guard band between the respective locking limits of two adjacent lines was not observed. With a 21-line comb with 20 GHz line spacing as the injected signal, the injection locking range was observed to become asymmetrical in relation to the laser free-running frequency under high-power injection conditions and was found to be dependent on whether the laser was locked to lines located at centre and or edges of the comb. Finally, the use of the injection locked laser as a seed laser for generating a local oscillator (LO) comb for superchannel coherent detection was investigated and the phase error between the input and LO combs analysed.