Large Submillimeter High-Speed Photodetector for Large Aperture FSO Receiver

We report a large submillimeter high-speed arrayed photodetector (PD) with a single-output design for high optical-alignment robustness free-space optical (FSO) communications. To realize a large photodetective area with a single-output design of over 10 Gbps, 8 × 8 multi-pixel PDs were designed and fabricated in a series–and-parallel network. To avoid sacrificing the frequency response, we successfully developed a large photodetective area PD, as large as 0.4 mm × 0.4 mm, with the same frequency response (8.5 GHz) as that in a small single PD (40-μm diameter worth). With the photodetector design and its characteristics, a high data-rate FSO demonstration of up to 25 Gbps for 10-m FSO communications was presented.