III–V-on-lithium-niobate balanced photodetector enabled by direct wafer bonding for optical computing

Abstract

Balanced photodetectors (BPDs) reject common-mode laser intensity noise while preserving the differential signal, making them an essential receiver building block for coherent optical links and for emerging coherent optical-computing architectures that require signed (bipolar) photocurrent accumulation. Integrating such detectors on the thin-film lithium-niobate-on-insulator (LNOI) platform—which already offers low-loss routing and high-speed electro-optic modulation—is a key step toward complete on-chip photonic systems. Here we demonstrate III–V-on- LNOI BPDs enabled by direct wafer bonding. The devices reach an external responsivity of ∼0.2A/W around 1550 nm, corresponding to 67% quantum efficiency, with closely matched responsivities of the two photodiodes over the 1500–1630nm range and a static common-mode rejection ratio (CMRR) of 47.7 dB at 1550 nm. The radio-frequency response shows a ∼16 GHz bandwidth, and a fixed-path-mismatch frequency-sweep measurement yields more than 40 dB CMRR at selected frequencies. These results establish a compact, well-matched balanced-detection building block on LNOI.