Enhanced optical coupling performance in an InGaAs photodiode integrated with wet-etched microlens

In this letter, we report over 50% enhancement in optical coupling tolerance between a single-mode fiber and a photodiode. The enhancement is made possible by integrating a microlens on the polished backside of an InGaAs photodiode device. The microlenses are fabricated by one step wet chemical etching in the mixed solution of bromic acid and hydrogen peroxide. Surface profiles of the microlenses are simulated using the finite-difference-method to solve a simplified diffusion model. The optical coupling tolerance is also theoretically calculated based on ray optics, of which results show an excellent agreement with the experimental data.