Image-Sensor-Based Photoreceiver for Free-Space Optical Communications

An image-sensor-based photo receiver for free-space optical communications, especially, ones employing indoor optical wireless LANs, has been developed. The receiver enables a compact and intelligent optical communication system through its two functional modes: image-sensing and communication. We clarified that the diffusion of photo-generated electrons determines the minimum total transimpedance gain of the amplifier and the maximum intensity of optical communication signals. A 50×50-pixel photo receiver with four independent communication-output channels was designed and fabricated with standard 0.35 μ m CMOS technology. To amplify optical data in the communication mode, it has in-pixel trans-impedance amplifiers and column-parallel main amplifiers. Experiments conducted with it showed that data rates of 50Mbps and 30Mbps were possible for wavelengths of 650nm and 830nm, respectively. Transimpedance gain varied from 660k Ω to 4.9M Ω for the data rate of 10Mbps. We also successfully captured images at a frame rate of 50Hz.