Numerical Modeling of the Optical Multiplexer on SOI Constructed by Multiple Coupled Waveguides

A new tunable optical multiplexer which utilized multiple coupled silicon wire waveguides on SOI structures is proposed and numerically studied. For the study, a modified effective index method, which utilizes the combined index profile with two spatial parameters, has been used. It correctly describes, in the 2-D case (with the 1% error), both the phase and the group indexes in a 3-D silicon wire waveguide and makes it possible to simulate complicated SOI structures by 2-D FDTD. The proposed multiplexer contains multiple silicon wire crossings. In order to provide a negligible scattering, the crossings are realized by means of a vertical up and down coupling through the silica buffer of tapered Si wires with the upper thick polymer waveguide. FDTD modeling proves a general conception of the multiplexer on SOI and demonstrates that a short 0.26 mm structure with 32 couplers has spectral resolutions 1.4 nm, internal loss -0.7 dB and sidelobes -20 dB. It provides the wavelength tuning (without Vernier principle) within FSR 35 nm at optical wavelength 1550 nm by the four sets of thermo-optical phase shifters with ΔT <;140 °C. A device of 0.7 cm in size will provide a 0.05 nm filter linewidth. It is CMOS compatible.