Monolithic wavelength-selective switches and cross connects with integrated MEMS mirror array

Abstract

Wavelength-selective switches (WSSs) and wavelength-selective cross connects (WSXCs) enable flexible, intelligent wavelength-division-multiplexed (WDM) networks as well as reduce the operating cost. In a 1×N WSS, the wavelengths from the input port can be independently switched to any of the N output ports. WSXC allows switching of optical signals at wavelength level between N input ports and N output ports. Most of the WSS and WSXC reported to date are realized by free-space optical systems with either micro-electro-mechanical-systems (MEMS) or liquid crystal (LC) beamsteering array, or by silica-based planar lightwave circuits with cascaded 2×2 thermal optical switches. In this paper, we report on the approach to monolithically integrate the WSS and WSXC on a single silicon-on-insulator (SOI) chip. Optical waveguides, microgratings, parabolic reflectors, as well as MEMS active switching micromirrors are fabricated on the same substrate using a one-step etching process. We have successfully fabricated a 1×4 WSS with CWDM (20- nm) channel spacing on a 1×2-cm² chip, and achieved a fiber-to-fiber insertion loss of 11.7 dB, and a switching time of 0.5 msec. The monolithic 4x4 WSXC is realized by integrating four 4×1 WSSs and four 1×4 multi-mode interference (MMI) splitters on the same wafer. No fiber connections or external splitter are required. The fabricated 4×4 WSXC has a chip area of 3.2×4.6 cm² and an insertion loss of 24 dB, including a 6-dB splitting loss. The WSXC supports unicast, multicast, and broadcast functions. The devices can be further scaled to DWDM (100-GHz) channel spacing.