Analysis and design of thermo-optical variable optical attenuator using three-waveguide directional couplers based on SOI

A thermo-optical variable optical attenuator (VOA), consisting of three cascaded three-waveguide directional couplers, was designed on Silicon-On-Insulator (SOI) wafer. Thermo-optical dynamic, static analysis and optical propagation characteristic simulation at the wavelength of 1550 nm were presented. The dynamic attenuation range from 0.14 dB to 50 dB was achieved by a refractive index (RI) variation: 0 to 5.55 x 10(-3), (the corresponding temperature variation: 0 to 30 degrees C). The response time was about 5 micros, which was attributed to Si/Al(2)O(3)/Si structure. The device could be easily used to fabricate multi-channel VOA as the basic unit and integrated in silicon optoelectronic circuits.