We propose a 30 GHz radio over free-space optical (FSO) communication system for indoor wireless communication applications using a newly developed high-speed photodetector array (PDA) device. The new device performs the role of a photodetector with high optical alignment robustness and also acts as a 30 GHz optical-to-radio converter. Small high-speed photodetectors of 30 m size are arranged in a 6 × 6 square-shaped alignment to achieve -4.4 dBm RF output at 30 GHz with an external amplifier. A 3-5 dB in-plane RF power distribution in the 4 × 4 PDA region was evaluated. To confirm the proposed concept, a 1 m long radio transmission over a 1.5 m long FSO transmission setup was demonstrated by switching the optical paths. We successfully confirmed a high data rate of up to 21.1 Gbps using several modulation formats under a static optical path switching condition. Additionally, stable and reproducible error vector magnitudes with a range of approximately 9% were recognized during the 10 switching cycles under a dynamic optical path switching condition.
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