Wireless infrared data links: ray-trace simulations of diffuse channels and demonstration of diffractive element for multibeam transmitters

Abstract

Free-space IR transmission provides high bandwidth and good security with small-sized and low-cost links, for instance, for high- bit-rate wireless LANs. Some robustness against shadowing is achieved using diffuse channels, but disadvantages are high path loss and multipath propagation. We use ray-trace simulation software to analyze IR channels in realistic office rooms. Simulations are performed to test the methods and to specify the bandwidth and power budget requirements of diffuse links. Both diffuse and specular reflections as well as shadowing effects due to furniture are considered. Based on the study, novel Monte Carlo ray-tracing software, such as ASAP (Advanced System Analyses Program), are suitable for analyzing the multipath dispersion and the optical power budget of infrared links in realistic indoor environments. The simulations also reveal the benefits of quasidiffuse link configurations, which are composed of multibeam transmitters with restricted beam divergences as well as of detectors with narrow fields of view. For implementation of multibeam transmitters we design an array- type diffractive element that modifies the beams of a 2-D vertical-cavity surface-emitting laser (VCSEL) array. A single element providing the largest 50-deg illumination angle is fabricated for demonstration. The measured diffraction efficiency is in fair agreement with the calculated one after considering the properties of the real VCSEL beam.