Potentials and Limitations of Multipath Lenses for Optical Wireless Transceivers

The superior modulation bandwidth of laser diodes (LDs) makes them an ideal candidate for transmitters in optical wireless communication (OWC). One of the most important limitations in human-accessible environments is laser safety which limits the transmission power and thereby coverage and range. The average LD power can be increased by means of optical components to reduce the power density or to increase the maximum permissible exposure (MPE). The power density is reduced by increasing the beam diameter and the emission angle e to reduce the impinging optical power onto the human eye. The MPE is the limit value for the laser class defined by IEC 60825-1. Within certain limits, the MPE is influenced by the wavelength λand the size of the apparent source. A large apparent source avoids sharp focus points on the retina. Traditionally, the apparent source and thereby the MPE is increased by using conventional lenses, different kinds of diffusers, LD arrays, or multiple distributed fibers. Recently, a new approach with multipath lenses (MPLs) was demonstrated in a Gbit/s OWC Link.