We have developed compact InP-based Mach-Zehnder modulators (MZMs) for small-form-factor pluggable coherent transceivers. In this paper, we introduce InP-based photonic integration circuit (PIC) technologies for high-performance MZMs. As the first topic, we show our design concept for a multi-quantum well (MQW) with a large refractive-index change and a low excess loss for a low-loss MZM with a low driving voltage. We fabricated dual polarization (DP) inphase and quadrature modulators (IQMs) in the form of a PIC in which we monolithically integrated a quad MZM based on the designed MQW. It operated at a half-wavelength voltage of 1.9 V with an excess loss of less than 1 dB as designed. We achieved 32-Gbaud DP-QPSK operation with a 0.2-dB penalty compared with a lithium niobate modulator. We also show another newly developed high-speed IQM for future higher-speed systems. We reduced the RF signal loss of an MZM by reducing the series resistance of the overcladding and optimizing the RF electrode structure. The fabricated high-speed IQM operated at higher than 64 Gbaud with QPSK/16QM modulations. Furthermore, we present an InP-MZM integrated with a new type of spot-size converter (SSC) fabricated with a three-dimensional semiconductor process. The SSC integrated MZM exhibited an insertion loss improvement of ~3 dB compared with our conventional InP-MZM for an optical system with a 4.5-μm mode field diameter. The low loss characteristics are beneficial in that they allow us to reduce the MZM-module cost thanks to an improved loss budget for optical assembly.
Y. Ueda, Y. Ogiso, and N. Kikuchi, "InP PIC technologies for high-performance Mach-Zehnder modulator," Proc. SPIE 10129, Optical Metro Networks and Short-Haul Systems IX, 1012905 (Presented at SPIE OPTO: February 01, 2017; Published: 28 January 2017); https://doi.org/10.1117/12.2253492.
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