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 letter, 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 $0.5~\mu \text{m}$ and $0.3~\mu \text{m}$ , 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.