About this Research Topic
Extensive mobile data communications produce burst of data traffic in information and communication networks. The data from the wireless terminals are transmitted through optical-fibre networks, and therefore, there are growing demands on performance enhancement in optical-fibre communication networks with respect to transmission speed and capacity. With the advent of high-speed photonic devices, data transmission beyond 100 Gbit/s has been achieved in the cutting-edge optical-fibre communication networks.
Photonic integrated circuits based on silicon photonics, which are fabricated on large-diameter silicon wafers by CMOS-based processes, are crucial for small-footprint optical components with low fabrication costs, and thus allow expansion of the high-speed optical-fibre networks over the globe. Integrated silicon Mach-Zehnder optical modulators are technology drivers for high-speed optical-fibre communications since they play significant roles in high-quality optical signal generation in diverse modulation formats without signal distortion such as frequency chirping.
Here, high-speed integrated silicon Mach-Zehnder optical modulators are reviewed in the light of science and technology for highly functional photonic integrated devices in the advanced optical-fibre communications. In particular, silicon Mach-Zehnder optical modulators operating on the physical principle of free-carrier plasma dispersion are the highlight of the review subjects in terms of high-speed operation with capabilities of small-footprint photonic integration and low power consumption. Optical modulation with bit rates of 100 Gbit/s and beyond has been realised using the silicon Mach-Zehnder optical modulators, which accommodate silicon-waveguide phase shifters having PN or PIN junctions. Device physics and performances of a variety of silicon-waveguide phase shifters are elaborated. Travelling-wave electrodes propagate microwave signals to the junctions in the phase shifters. Modelling and simulation based on physical profiles of carrier distribution in the junctions and lumped-element equivalent circuits for the travelling-wave electrodes are presented for performance analysis of the phase shifters and the travelling-wave electrodes. In the high-speed optical-fibre communications, polarisation-division multiplexing is exploited to data multiplexing. Monolithically integrated silicon Mach-Zehnder optical modulators for polarisation-division multiplexing are described in the aspects of device physics, fabrication and performance characterisation. Long-haul optical-fibre transmission and short-reach photonic networking using high-speed integrated silicon Mach-Zehnder modulators are presented for applications of the photonic integrated devices.
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