COMPOUND PARABOLIC CONCENTRATORS FOR NARROW-BAND WIRELESS INFRARED RECEIVERS

We discuss the design of optical concentrators based on dielectric and hollow compound parabolic concentrators (CPCs), for use in free-space infrared communication receivers. In order to acheive a high signal-t o-noise ratio in a direct-detection receiver, it is desirable to use a n optical bandpass filter that passes the signal but attenuates ambien t radiation. Placement of a planar bandpass filter at the entrance ape rture of a CPC results in a receiver having a narrow passband and high gain, but a narrow acceptance angle. The addition of a second, angle- transforming CPC at the entrance aperture allows the receiver to achie ve simultaneously a narrow passband and an acceptance angle approachin g 90 deg. We have employed a Monte Carlo ray tracing method to calcula te the optical gains of several optical concentrator designs. We find that the optical gains of single and double CPCs are, respectively, ab out 94% and 93% those of ideal optical concentrators, while addition o f planar bandpass filters decreases these gains to about 88% and 86%, respectively. We compare the performance and size of CPC-based concent rators with those based on dielectric hemispheres fitted with hemisphe rical bandpass filters.