Contents I. Introduction
Optical switches as well as other coplanar lightwave devices play an important role in optical communication networks[1],[2]. The thermo-optic (TO) ones are attractive for their small size, large scalability, and stability in longterm operation. Two material systems, namely, silica/silicon and polymer, are adopted in the design and fabrication of TO switches. Silica/silicon switch has a fast response speed of about 700 ns, which is owing to the large thermal conductivity of silicon and small device dimensions[3]. However, driving power of these switches is a little large. Shoji et al. reported a silicon nanowire waveguide TO switch with power consumption of 40 mW and response time of 30 µs[4]. Previous studies have investigated the suspended waveguide structure to reduce power consumption[5],[6]. However, what accompanied with the decreasing power consumption is the extremely complicated fabrication process. As a contrast, polymer switch has a lower power consumption and simpler fabrication technology. Polymeric multimode-interference (MMI) Mach-Zehnder interferometer (MZI) TO switches with power consumption of as low as 1.85 mW[7] and short response time of less than 0.2 ms[8] have been reported. Using direct ultraviolet photolithography, we have fabricated a polymer TO switch that exhibited power consumption of 7.5 mW and response time of 0.4 ms[9].
