Coherent Injection-Locking of Long-Cavity Colorless Laser Diodes With Low Front-Facet Reflectance for DWDM-PON Transmission

Long-cavity colorless laser diodes with different front-facet antireflection (AR) coatings are employed to perform the wavelength injection-locked ON–OFF-keying (OOK) data transmission. By changing front-facet reflectance of laser diode from 0.2% to 1.2%, the received OOK data enhance its Q factor by 6.3% and reduces its bit error rate (BER) by more than two orders of magnitude, which benefits from the improved signal-to-noise ratio and extinction ratio by up to 8.0%. Enlarging the injection-locking power from –6 to –3 dBm essentially helps the long-cavity colorless laser diode to promote its receiving power sensitivity from –27.9 to –29.2 dBm at BER of 10
$^{-9}$
. However, the similar device with lower AR reflectance shows an opposite trend. The injection-locking-induced enhancement is limited within a frequency region controlled by the injection power, which results from a large disparity between continuous-wave injection and stimulated emission inside the long-cavity colorless laser diode. At same biased current and front-facet reflectance, a higher injection level provides a larger modulation throughput at a cost of decreasing bandwidth. The overinjection causes a limitation on frequency bandwidth of the long-cavity colorless laser diodes with lower front-facet reflectance. The numerical simulations with modified rate equations for the injection-locked long-cavity colorless laser diode with lower front-facet reflectance also elucidate that the transmission degrades distinctly at larger injection powers.