Optical modelling of cone concentrators for positive and negative IR emitters

InSb optical cone concentrators are modelled to assess their optical perfor mance in positive and negative emission modes. The output distribution from the active layer is shown to be isotropic for thin active regions, tending towards Lambertian distribution as the layer thickness increases. Refracti on from the emitting surface is shown to make the distribution more Lambert ian. Optical efficiencies of straight-sided and Winston cone concentrators are modelled using a ray-tracing program, and those of straight-sided cones also determined using an analytical approximation, which allows use of the distribution derived earlier. The effect on the active layer thickness on the positive and negative emission is also determined. Normal light emittin g diode structures are found to be poor positive emitters and to draw large currents when used as negative emitters. A Winston cone of area gain equal to n(2) is found to be the best option for devices required to work in bot h positive and negative modes. Intermediate structures are also considered. The optimum active layer thickness is derived for three emitter configurat ions.