A High-Efficiency 50 GHz InGaAs Multimode Waveguide Photodetector

We propose a new type of side-illuminated pin photodetector with a multimode waveguide structure. Numerical and experimental results show that higher-order mode lights greatly enhance the coupling efficiency between the waveguide photodetector (WGPD) and a fiber, which leads to a high external quantum efficiency. Furthermore, the multimode WGPD has the major advantage that the external quantum efficiency and bandwidth can be derived independently of each other because the multimode waveguide structure can be designed without deteriorating electrical properties. The fabricated WGPD has an external quantum efficiency of 56% without AR coating and 68% with AR coating and an electrical 3 dB frequency greater than 50 GHz at a 1.55 μm wavelength.