Converging TIR lens for nonimaging concentration of light from compact incoherent sources

The total internal reflection lens is a multi-faceted non-imaging device that was introduced in a paper we presented at the SPIE Non-Imaging Optics conference two years ago, with emphasis on solar-energy concentration. This paper will discuss the concentration on a target of the light emitted omnidirectionally from a compact source, such as an incandescent filament, a light- emitting diode, or an arc lamp. The converging type of TIR lens can efficiently concentrate this light into the relatively restricted range of acceptance angles typical of optical fibers and image illumination subsystems. It can replace the conventional ellipsoidal reflector and is superior to it in two ways: (1) its interception efficiency is considerably higher, when used with a back mirror; (2) its aberrations are lower in magnitude, because of the additional degrees of design freedom possible in the three-faced facets of the TIR lens. However, it is more sensitive to lens optical quality, so that theoretically possible results are best achieved with diamond-turning of lenses or molds. Also, TIR lenses are sensitive to errors in source position.