CPC Optic

Lately I have been doing some simulation of a neat little optic device called a CPC. Short for Compound Parabolic Concentrator. This is a class of optic device known as a non-imaging optic. As the name implies it is used to concentrate a beam into a small area. It does so much more efficiently than imaging optics. Here is a picture of a CPC:



My Matlab program treats the CPC as a solid of revolution made of a material with index n2 and surrounding air index n1. The program performs ray tracing to find which rays reach the detector at the CPC exit aperture.

The figure below shows a Matlab result of several ray traces. Note the rays enter the entrance aperture and may bounce around several times, or not at all, before hitting the sensor at the exit aperture on the left.





CPC's can be made of molded plastic (Polystyrene for example) and therefore can be made very inexpensive in large volumes.



Because the incident angle can exceed the critical TIR angle, asin(n1/n2), the outer surface is metalized to preserve 100% TIR. Otherwise drop outs would occur at the sensor. This is shown in the angle scan of the next figure. In this figure a point light source is placed at 10mm in front of the entrance aperture on the CPC centerline and the angle is rotated through the full sweep to characterize the CPC.



Another item of note is that if the surface is not metalized then touching the surface will create evanescent coupling that will degrade the optical coupling

This has been my fun with CPC optics. I hope you found this interesting and maybe even useful.