High-Q Microring Resonators with Bimodal SiN Waveguides: Microwave Photonic Applications

A high-Q microring resonator in all-pass configuration using a low-loss bimodal SiN waveguide design has been demonstrated and explored for microwave photonic applications. We have recorded a Q- as high as ~2X10^6 from such a device design by exciting fundamental mode into the bimodal bus and ring waveguides which was fabricated using in-house conventional silicon photonics process technology. Our experimental results show that an equivalent device design with a single-mode waveguide and fabricated with same fabrication process technology exhibit nearly 7 times lower Q-value (~ 2.5X10^5). The cavity loss is reduced because of the fact that the fundamental guided mode in a bimodal waveguide experiences lower scattering and bend-induced radiation losses (~0.1 dB/cm); scattering losses occurs mainly due to the waveguide sidewall roughness which in fact fabrication process dependent. Such a device has been used further to demonstrate a widely tunable narrow-bandpass microwave photonic filter. The experimental results exhibit a narrowband filter with a 3-dB bandwidth as low as 290 MHz with broad tunability from 5-45 GHz and the side-band rejection of ~30 dB has been recorded. Furthermore, the device was used to demonstrate widely tunable microwave oscillator with a signal-to-sidemode suppression ratio of up to 57-dB. Though both filter and oscillator can be tuned up to 60 GHz, we are limited to characterize it due to the phase modulator bandwidth (40 GHz) and the RF amplifier bandwidth (20 GHz).