Tunable Optical Add/Drop Multiplexers Using Cascaded Mach Zehnder Coupler

Abstract

A tunable add/drop filter based on Cascaded Mach Zehnder (CMZ) coupler using SiO₂/silicon oxinitride (SiON) is presented with its mathematical model. The increase of filtered width (i.e., free spectral response) and lowering of crosstalk for this filter are optimized using its mathematical model with truncated binomial coupler distribution. The number of wavelength channels with 100 GHz (0.8 nm) channel spacing for 5-stage (M = 9, r = 2) truncated binomial CMZ filter with index contrast ～5% at ?20 dB crosstalk and the bending loss of 0.1 dB per MZ section are obtained as ～37 (free spectral range of 31 nm). It is seen that if during the fabrication process, waveguide core width w is increased or decreased by 0.1 μm (in percentage terms ～±6.6%), the crosstalk is slightly increased by ～7%. Thermal tuning for wavelength channels is achieved by thin film heater with low power thermooptic delay line structure which reduces the heating power by ～1.58 times in comparison to the conventional structure.