Integrated transceivers for optical wireless communications

Line-of-sight free-space optical links can provide extremely high bandwidth communications, but this usually requires that transmitter and receiver are precisely aligned. In order to allow terminals to be mobile, links must be able to track users within their field of view so that the link is maintained. There are various means to do this, but all require complex subsystems with a number of different optical, optoelectronic, and electrical components. In this paper, a solid-state tracking architecture is introduced and a seven-channel tracking system demonstration described. The system is designed to operate at 155 Mb/s and is, to the best of our knowledge, the first that uses an integrated approach. Arrays of novel resonant cavity LED (RCLED) emitters that operate at 980 nm are used as sources. These are flip-chip bonded to arrays of CMOS driver circuits and integrated with the necessary transmitter optics. The receiver uses a back-illuminated detector array flip-chip bonded to arrays of custom CMOS receivers. All these components are custom and have performance substantially better than nonoptimized commercially available components. In the paper, the design and fabrication of the optics, optoelectronics, and electronics required for this is described. Successful operation of all the subsystems is detailed, together with results from an initial link demonstration.