Compact All-InP Laser-Vector-Modulator for Generation and Transmission of 100-Gb/s PDM-QPSK and 200-Gb/s PDM-16-QAM

A compact indium phosphide (InP)-based integrated transmitter assembly consisting of a tunable laser and a double-nested Mach-Zehnder modulator (vector modulator) was successfully used for the generation of Nyquist-prefiltered quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (16-QAM) signals at 32 Gbaud. With external polarization division multiplexing (PDM) emulation and digital coherent detection, we realized data rates of 128 Gb/s with PDM-QPSK and 256 Gb/s with PDM-16-QAM from a commercially available small-form factor device originally designed for 40-Gb/s direct-detection differential QPSK applications. We transmitted these two signals over 8000 and 960 km of standard single mode fiber, respectively. We also compared the performance of the integrated transmitter with a LiNbO₃ based vector modulator, using a high-performance 100-kHz external-cavity laser and a low-cost 200-kHz to 400-kHz integrated laser assembly as optical local oscillators. The all-InP integrated laser-vector-modulator transmitter was found to be a viable solution for long-haul 100 and 200-Gb/s coherent optical transmission systems.