Solid-state tracking integrated optical wireless transceivers for line-of-sight optical links

Most free-space line-of sight systems require tracking in order to keep links aligned, and in order to achieve this a number of disparate optical, optoelectronic and electronic components are required. A key factor in determining the performance of these systems is the ability to integrate these in a scalable compact fashion, and to optimise components for the somewhat distinct requirements of free-space links. A number of UK universities have been involved in a consortium that has fabricated integrated transceivers that use fully custom components optimised for an indoor free-space link application. The transmitters use arrays of Resonant Cavity LED (RCLED) devices integrated with custom CMOS driver circuitry and the necessary beamshaping optics, so that operating a particular LED in the array transmits light at a particular angle. A similar approach is taken at the receiver; light from a particular angle illuminates one element of a PIN photodiode array. This is integrated with an array of custom CMOS receivers and the necessary optics, creating a compact receiver subsystem. In this paper the components and subsystems are detailed and their application to long-distance links discussed.