Integration of polymeric optical waveguides with SOI MEMS structures

Abstract

Optical switches based on deflection of a waveguide element offer low crosstalk, low polarization dependency, low power consumption, and high degree of integration. Such switches made by post processing of polymeric waveguides onto MEMS structures of silicon-on-insulator (SOI) efficiently combine low loss waveguides with the exceptional mechanical properties of single crystalline silicon. An important aspect of this concept is that it allows independent optimization of the mechanical and optical structures by efficiently separating the two. Well established, high yield methods exist for structuring silicon based on deep reactive ion etching (DRIE), which allows the formation of mechanical structures with high aspect ratio. The mechanical structure can then be planarized for further processing by utilizing spin coating properties of certain polymers. This allows post processing of high-resolution passive polymeric waveguide networks that can fulfil a variety of functions depending on the application, including spot-size transformers for low loss coupling to optical fibers. These waveguides can also potentially be integrated with CMOS or active optoelectronic elements into forming highly functional hybrid photonic integrated circuits, partly facilitated by the low temperatures required for processing of polymers. This paper highlights key process technologies and specifically discusses issues related to an optical switch that was developed for proof of concept. This switch was made of 5μm thick SOI with 3μm wide, high optical confinement polymeric waveguides. Switching times were down to 30μs, switching voltages 20 to 50V, and crosstalk was -32dB. The paper further outlines possible applications of the switch to state-of-the-art problems in photonics.