Injection Locking Properties of an Dual Laser Source for mm-Wave Communications

We for the first time, the optical injection locking (OIL) to a frequency comb of a hybrid
$\text{{InP-Si}}_{3}\text{{N}}_{4}$
dual laser source for high-purity mm-wave generation through optical heterodyning. Key performance parameters of the comb line demultiplexing functionality provided by this source under OIL – such as adjacent-comb-line side mode suppression ratio (SMSR) and locking range – are reported. It is also shown that the amount of free-running drift exhibited by the hybrid lasers (which should be as little as possible to keep them within the locking range) can be minimized by reducing the amount of bias level applied to the heater-based phase actuators present in such lasers. According to the measured drift, locking range and SMSR, these lasers have potential to achieve continuous locking with SMSR levels of more than 45 dB at comb line separations higher than 9 GHz. Successful carrier generation at 93 GHz is demonstrated by locking the two lasers to an optical frequency comb achieving an ultra-stable International Telecommunication Union (ITU)-compliant signal. Both real-time and DSP-aided data transmissions are demonstrated at this frequency achieving data rates of 12.5 and 28 Gbit/s, respectively.