Adiabatic Coupler with Design-Intended Splitting Ratio

We demonstrate adiabatic couplers (ADCs) with design-intended splitting ratios (SRs) for the silicon-on-insulator (SOI) platform. The operational principle, numerical simulations, and experimental results on the designed ADC are presented. In the operational principle, we derive the analytical relationship between the SR and the effective index-difference, based on which we calculate the corresponding SRs under various output waveguide width-differences at a central wavelength of 1310 nm. For the simulation process, a segmented optimization method is employed to analyze the adiabatic transition process through the ADC. From the experiment results, broadband ADCs with design-intended power SRs, from 7%/93% to 50%/50%, are fabricated and then tested over a bandwidth of 100 nm, i.e., from 1260 to 1360 nm for the fundamental transverse electric (TE) mode. Furthermore, the thermal stability of the ADC is investigated. When increasing the stage temperature from 20  $^\circ$ C to 50  $^\circ$ C, the variances of the SRs for different wavelengths across O band are within 1.3%, which makes the design a potential candidate for performance robustness against temperature variations.