Integrated optical comb generation for coherent communications using injection locked semiconductor lasers

Slotted Fabry-Perot (SFP) semiconductor laser diodes provide single mode operation, which is useful in various telecommunications applications. Under optical injection locking these lasers can be used in the production of single mode coherent combs. These combs have potential application in coherent wavelength division multiplexing (CoWDM) . With this experiment two separate SFP lasers were injection locked from the same master laser. A high speed LiNbO₃ Mach-Zender (MZ) modulator was used to provide amplitude modulation to create sidebands which were spaced from the carrier by the modulation frequency. An erbium doped fibre amplifier is used to boost the signal due to losses incurred through the modulator. The modulator was biased about the null to allow for carrier suppression. The lasers used for this particular experiment were multimode lasers. Locking was optimised by examining the optical spectrum of the output of the lasers on an optical spectrum analyser (OSA). The wavelength of the TLS was altered in order to maximise the side mode suppression ratio (SMSR).