Numerical and experimental investigation of InP/InGaAsP asymmetric twin-waveguide

Asymmetric twin-waveguide (ATG) has been emerged as a highly effective platform for the seamless integration of diverse functional devices with photonic integrated circuits (PICs). In this paper, we present a comprehensive exploration of the design and analysis of the ATG structure, specifically tailored for waveguide photodiodes. Employing the transfer matrix method and effective refractive index approach, we meticulously engineer a diluted waveguide that achieves high edge coupling efficiency of 94%--serving as a component for efficiently coupling to commercial single-mode fibers. Additionally, using the super mode theory, we design the rib waveguide for single-mode transmission, effectively maximizing energy transmission with a proportion of 100%. Finally, we fabricate the entire ATG structure and construct a test platform to evaluate alignment tolerance and transmission loss. The experimentally tested 1dB tolerance in the horizontal and vertical directions are 0.5 μm and 0.3 μm, respectively. The transmission loss is near to 1.6 dB /mm. Our design strategy provides a universal approach for engineering multilayer waveguides in any materials.