Partially vertically elongated microring waveguide: simultaneously achieving a large FSR and high resonant peak intensity for an ultra-compact microring resonator

An ultra-compact microring resonator (MRR) with an ultra-large free spectral range (FSR) and low bending loss is proposed by introducing a partially vertically elongated (PVE) microring waveguide. Compared with the previously ultra-compact horizontally elongated microring resonator (HE-MRR), the ultra-compact MRR with a partially vertically elongated microring waveguide (PVE-MRR) exhibits a larger FSR of 117.2 nm. Though the proposed vertically elongated microring waveguide exhibits multimode resonances, the higher-order resonances can be suppressed by the low coupling ratio of the asymmetrical directional couplers (ADCs), the higher bending loss of the TE 1 mode, and the coverage effect of the main resonant peaks. Compared with traditional MRRs, the PVE microring waveguide nearly doubles the drop-port resonant peak intensity of MRRs.