Silicon photonics has emerged as one of the key technologies for data communications, especially in datacenters. Using standard CMOS fabrication steps, optical modulators, photodetectors, and passive optical components have been realized. The photonic circuits demonstrated so far are mostly static. We are interested in dynamically reconfigurable or tunable circuits in Si photonics, such as tunable filters or optical switches. In this project, we integrate MEMS with Si photonics on an silicon-on-insulator (SOI) platform. The optical waveguides and passive optical components are realized in the standard 220nm-thick SOI layer. We have added an additional Polysilicon layer on top of the SOI, separated by a low-temperature oxide (LTO) layer. The Polysilicon can be used to realize MEMS actuators, such as combdrive actuators or thermal actuators, as well as an additional high- refractive-index layer for controlling light. Our first demonstration vehicle is a tunable filter. The filter consists of a Fabry-Perot cavity formed between two waveguide reflectors. The reflector itself is made of Polysilicon grating on top of the SOI waveguide. We call this high-contrast-grating (HCG) reflector. The Polysilicon HCG reflectors released from the SOI waveguide, and are thus movable by MEMS actuators. We have integrated a combdrive actuator with the tunable filter. The transmission wavelength can be tuned by changing the cavity length. We have finished the development of the basic platform technology on 6-inch SOI wafers using deep-UV lithography, and have demonstrated optical grating couplers, waveguide splitters/combiners, and optical delay lines. We are in the process of optimizing our Polysilicon HCG reflector design, and hope to measure the performance of the device in a few months.
Project end date: 02/05/14