Design And Simulation Of Ultra-compact Optical Waveguide Device With Trench Based Rectangular Ring Resonator

As integrated photonics technology has developed rapidly, conventional optical devices used in optical communications have the trend of possessing these features of high density integration, low power consumption and miniaturization. As a typical structure used integrated optical devices, the further reduced size of microring resonator is limited by radius of curvature due to the waveguide bending loss. It is challenging to scale down the chip area of microring based devices and improve its integration density. Here we propose to utilize an rectangular ring resonator consisting of trench couplers and 90 ° waveguide bends, which can alleviate the size limitations of traditional microring resonators. Our study shows that a shallow etched and weak confinement waveguide is beneficial to the cavity design such as small cavity length, meanwhile we achieve a larger free spectrum range of the device and an improved space efficiency on chip.Current microring resonator based optical filters usually have some drawbacks such as narrow bandwidth and larger radius of curvature for reducing bending loss. An ultra-compact optical filter consisting of rectangular ring resonator incorporated with two Mach-Zehnder interferometers has been proposed and optimized. The performances such as transfer function, quality factor, and transmission characteristic are analyzed by using state-space representation and finite difference time domain(FDTD) methods, respectively. The dependence of filtering features on both different coupling coefficients and loss coefficients is calculated with state-space representation method. The FDTD simulation results show the device exhibits an asymmetric wavelength interleaver filtering effect with the different ratio of pass-band and stopband bandwidth when the coupler reflection coefficient is close to the coupler transmission coefficient. The quality factor of ~3120 and the free spectral range of ~50.6 nm are observed in such small 25 μm × 8 μm chip area when the coupler reflection coefficient is far larger than the coupler transmission coefficient. The compact configuration of device layout is beneficial to the extension at twodimensional directions for highly dense photonic integrated circuits.Modulation bandwidth of a conventional high Q ring modulator is limited by its long photon lifetime due to intracavity index modulation mechanism used in the device. Towards solving this issue, we demonstrate an ultra-compact coupling modulation based electro-optic modulator that can break this limitation. A time domain dynamic model is used to evaluate the device performance, and the results show a modulation phase change of < 0.2 π, the state modulation depth of >0.96(normalized maximum of 1.0), and the modulation bandwidth of > 100 GHz. This high speed modulator exhibits a small chip area of 10 μm × 15 μm and a lower power consumption.In summary, trench couplers based devices such as optical filters and modulators have been comprehensively analyzed and studied for their static and dynamic characteristics by using a state space representation method, a discrete time-domain model, and a finite difference time domain(FDTD) simulation methods. The investigation of this work provides a new idea and a new method for two-dimensional dense planar integration of photonic integrated circuits, and the formed devices can be potentially used in optical interconnect on-chip.