Wavelength Tunable Filter with Poly-Si/SiO2 Multi-Layer by Thermo-optic Effect

초록

Wavelength tunable filter is the key component of Wavelength Division Multiplexing (WDM) systems. In this paper, we utilize thermo-optic effect of multi-layers whose refractive indexes are changed by temperature variation effect, to tune transmitted wavelength. Tunable filter is designed using Fabry-Perot interference effect. Distributed Bragg Reflector (DBR) mirror structure is composed of 4-pairs of high index poly-Si layer (n=3.48) and low index SiO2 layer (n=1.44). The filter has the structure of DBR layer/tunable cavity layer/DBR layer. The cavity material is poly-Si. Thickness of DBR mirror material is wave/4 and that of cavity layer is wave/2. Poly-Si has very high thermo-optic coefficient of dn/dT=2.25 x 10-4K-1. Thus it is efficient material for thermo-optic tunable filter. Poly-Si is deposited by LPCVD at 625C using SiH4, and SiO2 by PECVD at 300C using SiH4/N2O.