Abstract
This work demonstrates a waveguide photodiode based on a vertical three-layer multi-segment taper coupling structure. The upper taper waveguide controls local effective index, phase matching, and absorber overlap, enabling gradual mode transfer from the lower waveguide to the top absorption layer. Compared with rectangular and linear taper devices, the multi-segment taper improves absorber overlap and longitudinal absorption uniformity, leading to an internal responsivity of 0.88 A/W at -3.5 V. The device also maintains higher RF output power at large photocurrent and a comparable 3 dB bandwidth of about 43 GHz. Experimental tolerance measurements show that stable responsivity is maintained for input mode offsets within ±0.6 μm and interlayer lateral misalignment within ±0.4 μm.