3D design and analysis of an electro-optically tunable athermal and polarization-insensitive ring resonator-based add-drop filter for DWDM systems

Dense Wavelength Division Multiplexing system-based optical networks are currently the most appropriate solutions for all-optical networks that efficiently utilize the large bandwidth offered by optical fiber networks. Tunable ring resonator-based filters are highly attractive owing to their bandwidth and channel tunability, high spectral selectivity, low losses, low power consumption, and compactness; thus they are very good candidates for optical integrated circuits at a very large scale. We used titanium oxide and silicon oxide as the upper-cladding and under-cladding materials, respectively, around a silicon-rich nitride core to design an electro-optically tunable, polarization-insensitive, and thermally resilient sixth-order add-drop optical filter in the L-band (1565 nm-1625 nm). A thin film of lithium niobate added on the top of silicon oxide was used to enhance the tunability of the filter. A 3D multiphysics approach considering thermo-optic, and stress-optical effects while minimizing the polarization rotation has been adopted to solve the electromagnetic problem in a filter that can accommodate arbitrary Transverse Electric and Transverse Magnetic polarized optical signals. The device has a bandwidth of 50 GHz (linewidth of 0.4 nm) at a resonant wavelength of 1575.4 nm, an extended FSR of 2.512 THz, and losses of 0.82 dB in the bandpass. The filter is ultra-compact with a footprint of 15 mu m x 160 mu m. We achieved a high quality factor of 3250, a tunability efficiency of 8.95 pm/V, and a finesse of 31. To the best of our knowledge, it is the first time a complementary metal-oxide-semiconductor-compatible, electro-optically tunable, athermal, polarization-insensitive high order add-drop filter in the L-band with a top-flat response in the passband, and with an extended FSR has been designed for Dense Wavelength Division Multiplexing systems.