Optical power couplers with arbitrary power splitting ratios are important components for many applications such as Mach-Zehnder interferometer-based structures, filters, switches, dispersion compensations, optical interconnects, and microring resonators. In this chapter, we present a new approach to achieve a very high compact coupler with arbitrary power splitting ratios on silicon on insulator (SOI) waveguides. The proposed device requires only one 4×4 multimode interference (MMI) coupler. We use a passive wide SOI waveguide to achieve the phase shifter. The footprint of the whole device is only about 6×150 μm2. A large fabrication tolerance of ±50 nm can be achieved. The modified effective index method, beam propagation method, finite difference method, and finite difference-time difference method are used to optimally design the whole device.
Part of the book: Emerging Waveguide Technology
We present a new approach for designing a compact microring resonator structure based on only one multimode waveguide, which can provide a very high free spectral range (FSR) and capability of controlling the critical coupling. The silicon on insulator (SOI) waveguide and graphene-silicon waveguide (GSW) are used for the proposed structure. By changing the applied voltage on the graphene sheet, we can achieve a full control of the critical coupling. Some important properties of the proposed microring resonator such as free spectral range and quality factor are analyzed. We show that our structure can provide all characteristics of a single microring resonator with universal applications such as optical switching, modulating, filtering and signal processing, etc.