Tlinable optical add/drop multiplexers using Cascaded Mach Zehnder coupler

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 similar to 5% at -20 dB crosstalk and the bending loss of 0.1 dB per MZ section are obtained as similar to 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 mu m (in percentage terms similar to +/- 66%), the crosstalk is slightly increased by similar to 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 similar to 1.58 times in comparison to the conventional structure.