10-Channel x 40Gb/s per channel DQPSK Monolithically Integrated InP-based Transmitter PIC

We report here the first demonstration of a large-scale monolithically integrated InP-based 10-channel x 40Gb/s per channel transmitter photonic integrated circuit (PIC) employing differential quadrature phase-shift key (DQPSK) modulation. Phase-based modulation formats can increase the spectral efficiency benefits in wavelength-division-multiplexed (WDM) optical transmission systems. The benefits of phase modulation and specifically DQPSK, however, come at the cost of increased complexity to both the transmitter and receiver architecture especially in terms of the large number of optical functions and the corresponding number of optical elements required to realize this modulation format. Large-scale photonic integration mitigates much of this complexity by monolithically integrating multiple optical functions and multiple WDM channels onto a single chip, thus reducing the number of individual optical packages requiring fiber-couplings by approximately 50-100x while simultaneously providing substantially higher reliability and reduced power consumption compared to solutions using discrete optical components. In this work, we demonstrate for the first time the capability of large-scale multi-channel PICs to employ phase modulators as well as differential quadrature phase-shift keying (DQPSK). Specifically, we demonstrate a 10-channel large-scale transmitter (Tx) PIC operating at 40Gb/s per channel using DQPSK modulation. This modulation format is advantageous as it offers high spectral efficiency, high tolerance to chromatic and polarization-mode dispersion, and very good optical signal-to-noise ratio (OSNR) tolerance (1). Given the spectral efficiency benefits of DQPSK modulation at 40Gb/s, combined with the reduced complexity and power enabled by photonic integration, monolithically integrated solutions are expected to play a critical role in next-generation optical transmission systems.