Micromachined tunable optical filter based on 1 d photonic band gap in silicon

Abstract

The proliferation of high speed internet, residential triple play and commercial carrier ethernet services has introduced an exponential growth of traffic in the metro access telecommunication networks demanding huge dynamic bandwidth provisioning. Passive optical network (PON) based on coarse wavelength division multiplexing (CWDM) has emerged as a promising method to cater to this requirement. As per access WDM enhancement standard G983.3; 1310nm, 1490nm and CWDM channels of C band is to be utilized for upstream, downstream and extended services/video respectively with the L band (1570nm-1625nm) left for future use. This thesis deals with the development of tunable optical filtering technology for CWDM networks with specific thrust on reducing the operational expenses. The TOF explored in this thesis is developed combining silicon photonic band gap (PBG) and micro electromechanical systems (MEMS). The PBG based Fabry- Perot filter designed as part of this work is numerically modeled using the general framework of transfer matrix method (TMM) incorporating influence of etch angle and thickness variation of PBG structures, dispersion of silicon and temperature dependence of silicon on its transfer characteristics. Electrostatically tunable optical filter was fabricated in silicon on insulator (SOI) wafer using deep reactive ion etching (DRIE). Fabrication induced geometrical asymmetry is found to lead to larger free spectral range and also larger intensity variation among the dropped channels. This TOF has integrated waveguides for input/output ports and hence the insertion loss is high due to coupling loss at the waveguide edges. The coupling arrangement with micro GRIN lensed fibers used in the case of fixed filters would provide lower insertion loss in place of waveguides used in the tunable DRIE based implementation albeit with increased steps in the process flow to create trench for inserting the fiber. newline