Multiple-Sagnac-Loop Mach-Zehnder Interferometer for Wavelength Interleaving, Thermo-Optical Switching and Matched Filteri

This theoretical modeling and simulation paper presents design and projected performance of an on-chip thermooptical multi Sagnac loop Mach-Zehnder interferometer (MZI), operating at C- band and 3300 nm for silicon-on-insulator and germanium-on-silicon technological platforms, respectively. The MZI arms are comprised of an N-cascaded connection of Sagnac loop reflectors, each pair separated by a waveguide whose length is designed according to the wavelength-channel spacing requirements. N is chosen according to the Butterworth filter technique to provide one spectral response having maximal flatness within the desired bandwidth. Switched, spatial routing of odd and even channels is achieved by shifting the Through and Drop MZI spectra along the wavelength axis by means of a low-power thermooptical heater stripe atop each loop-connector that changes its effective refractive index appropriately. We examined the SOI device performance for wavelength-division multiplexed wavelength (de)interleving. The analysis predicted good performance in terms of bandwidth, insertion loss, and channel isolation for 200, 50, and 25 GHz channel spacing. For the Ge-on-Si Sagnac MZI operating in the mid infrared, we showed that a comb filter is feasible whose lines exactly match the spectral signature of methane for trace-gas sensing applications.