Compact microring resonator based on ultralow-loss multimode silicon nitride waveguide

Abstract

Silicon nitride (Si 3 N 4 ) waveguides with high confinement and low loss have been widely used in integrated nonlinear photonics. Indeed, state-of-the-art ultralow-loss Si 3 N 4 waveguides are all fabricated using complex fabrication processes, and all of those reported that high Q microring resonators (MRRs) are fabricated in laboratories. We propose and demonstrate an ultralow-loss Si 3 N 4 racetrack MRR by shaping the mode using a uniform multimode structure to reduce its overlap with the waveguide. The MRR is fabricated by the standard multi project wafer (MPW) foundry process. It consists of two multimode straight waveguides (MSWs) connected by two multimode waveguide bends (MWBs). In particular, the MWBs are based on modified Euler bends, and an MSW directional coupler is used to avoid higher-order mode excitation. In this way, although a multimode waveguide is used in the MRR, only the fundamental mode is excited and transmitted with ultralow loss. Meanwhile, thanks to the 180 deg Euler bend, a compact chip footprint of 2.226 mm perimeter with an effective radius as small as 195 μm and a waveguide width of 3 μm is achieved. Results show that based on the widely used MPW process, a propagation loss of only 3.3 dB∕m and a mean intrinsic Q of around 10.8 million are achieved for the first time.

Microwave Photonic Filters and Applications

“…In IMPF, the unit time delay can be significantly reduced to as small as 15.4 ps [109]. Therefore, the obtained IMPF is usually coherent MPF, which shows that quite large FSR and complex coefficients can be easily obtained.…”

“…The intuitive idea is to reduce the interaction between the optical field confined in the optical waveguide and the rough sidewall. To ensure single-mode propagation, the multimode waveguide can be connected with a single-mode waveguide with a linear adiabatic taper [109] or designed with adiabatic propagation [128]. Figure 17a,b shows the schematic diagram and the microscope image of the fabricated ultrahigh-Q MRR, respectively.…”

Compact multi-mode silicon-nitride micro-ring resonator with low loss

“…They optimized the waveguide width, adopted adiabatic multi-mode directional couplers, and employed modified Euler bends, consequently, the propagation loss is significantly reduced from 20 dB∕m down to 3.3 dB∕m. 4 Notably, all designs are realized in a multi-project wafer run and no additional process is required, distinguishing it from other complicated fabrication techniques.…”