1 × 4 Integrated Microlenses High-Rate Photodetector Array for Optical Communication Transmission

Toward the application of 400 G optical receiver chips in optical communication systems, this paper presents a
$1\times 4$
photodetector (PD) array with a monolithic integrated InP microlenses structure. The absorption layer of the PD array in question includes the non-depleted, partially depleted, and depleted regions. This third-order composite absorber layer accelerates the diffusion of electrons in the absorber layer and balances the transport times of holes and electrons. Therefore, the high-speed and high responsivity characteristics of the device can be realized. The integration of InP microlenses on the backside of the PD allows the effective photosensitive surface area to be increased and the incident light alignment deviation to be compensated. Tests yielded a 3-dB bandwidth of the PD array at 1310 nm greater than 40 GHz, with a peak responsivity of 0.64 A/W. The responsivity of two types of PDs was measured when incident at a distance of
$10~\mu \text{m}$
away from the main optical axis. The responsivity of the integrated microlenses decreased to 67.05% of the maximum value. Compared to the device without integrated microlenses, the responsivity increased by 66.76%.