Compact On-Chip Optical Components Based on Multimode Interference Design Using High-Contrast Grating Hollow-Core Waveguides

Abstract

Low-loss high-contrast grating (HCG) hollow-core waveguide (HCW) is shown to be a promising candidate for building a variety of compact multimode interference (MMI) based optical components. First, we show that HCG-HCWs demonstrate self-imaging property essential for designing MMI components. Furthermore, strong confinement of light in the waveguide core and low-index guiding leads to compact optical components. Simulation results show extremely compact 2 × 2 coupler with a length of 26 μm (16 λ), footprint (length × width) of 85 μm2 (35 λ2) and a 3-dB splitter with a length of 3.6 μm (2.4 λ), and a footprint of 12 μm 2 (5 λ2). Simulation results agree well with the predictions of MMI theory and the design can be easily extended to realize 1 × N splitters and N × N couplers. As a proof of concept, a 1 × 4 splitter with equal power splitting ratio and low insertion loss is designed. In addition, an ultracompact 2 × 2 optical switch based on HCG-HCW is proposed and simulated. The two waveguide channels are isolated by a single layer of HCG. By a small change of the refractive index of this HCG, light can switch between the channels. By proper optimization of HCG parameters, only higher order modes are excited in the MMI region resulting in an ultracompact optical switch with a switching length of 60 μm, ∼25× smaller than conventional 2 × 2 MMI coupler.