Performance Analysis of Scalable Optical Circuit Switch Employing Fast-Tunable AMZI Filters for Coherent Detection

High-port-count optical switches are expected to resolve the envisaged bandwidth and power crunch in intra-data center networks stemming from the slowdown of Moore's Law. This paper briefly reviews electrical switching technologies in current intra-data centers and discusses requirements for optical circuit switches in future data centers. We highlight an optical switch architecture that combines the two independent dimensions of space and wavelength to realize large port counts and fast switching. Wavelength routing is implementable with receiver-side channel selection using wavelength tunable filters (TFs). Coherent detection necessitates a fast-tunable local oscillator (LO) at the receiver. It can be cost-effectively realized using an LO bank that consists of fixed-wavelength laser sources and Silicon-photonic asymmetric Mach-Zehnder interferometer (AMZI) filters. Colorless detection that removes a TF at the front of the receiver is possible when the number of wavelength-division multiplexing (WDM) channels is small, however, as the number exceeds a certain limit the TF is needed to prevent power saturation of the receiver. We present an effective cooperative filtering scheme for transmission signals and LO channels sourced from an LO bank; it can detect C-band WDM coherent signals while easing the receiver's power limitation. The scheme is analyzed to clarify receiver performance and the switch port-count bounds under various operating conditions. We demonstrate that the cooperative filtering scheme effectively works from 60 (typical of coherent receivers) to > 116 wavelength channels, which is verified by experiments for 1,856 x 1,856 optical switching with the short switching time of 3.2 mu s.