Simulating the effects of refractive index difference on the coupling efficiency of periodically segmented waveguide mode converter

Efficient coupling of micro/nano-optical waveguides with single-mode fibers is the premise for the efficient operation of the integrated photonic chip, which directly determines its optical performance. In this paper, the design principles of periodically segmented waveguide (PSW) structure used for high-efficiency fiber-chip coupling are proposed, and the effects of refractive index difference Δ on coupling efficiency and structural parameters are studied by simulation. It is found that as the Δ of the PSW increases, the period of the PSW tends to be smaller, and the coupling efficiency decreases continuously, reduced by around 0.673 dB in the range of Δ = 3% to Δ = 7%. Through the analysis of PSW optical mechanisms, it demonstrates that the main reason for the decrease of coupling efficiency is that the transmission loss of the tapered section increases sharply with the increase of Δ. High-Δ PSW is difficult to apply to highly integrated silica optical chips due to the unignorably insertion loss.