Effect of Injection Coherence on Noise and Bandwidth of Long-Cavity Colorless Laser Diode for Digital Modulation and Transmission

Abstract

The weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) injection-locked by three master sources with different degrees of coherence and directly modulated by two different digital modulation formats is demonstrated. The injection master coherence shows impact on noise, bandwidth, and modulation performances of the slave WRC-FPLD transmitter. Using the highly coherent master, the injectionlocked WRC-FPLD reduces its relative intensity noise peak at 5 GHz by 18 dB and increases its throughput frequency response by 5 dB. This enables the error-free ON-OFF keying (OOK) transmission at 10 Gb/s with a required receiving power sensitivity of −15 dBm at an error rate of 10 −9 . The eye diagrams simulated from the modified rate equations are also performed to show such improvements. With highly coherent injection-locking, the transmitted error of the WRC-FPLD carried orthogonal frequency division multiplexing (OFDM) data with a modulation bandwidth of 3.1 GHz can be minimized to 1.6 × 10 −13 . In comparison, the master-to-slave injectionlocked WPC-FPLD with partial coherence can also provide an 8-Gb/s OOK transmission with a receiving power sensitivity of −19 dBm at bit-error-rate (BER) of 10 9 . Such a cost-effective colorless source also supports a 16-quadrature-amplitude modulation OFDM transmission at 12.5 Gb/s with a BER of 5.6 × 10 −12 to serve multichannel application in next generation passive optical network.Index Terms-Modulation, injection-locked, coherence, semiconductor lasers, dense wavelength division multiplexed passive optical network (DWDM-PON).