Contrast designed an illuminator system based on an OSRAM high-power LED. The LED chosen for this project was an OSTAR projection LED. We designed a solid acrylic Compound Parabolic Concentrator (CPC), which is typically used to concentrate solar energy, to collimate the light from the LED. An array of hollow, hex cell tubes was placed in front of the CPC in order to achieve a sharp cutoff to the angular distribution of light. The hex cell array that we chose to use is an off-the-shelf product and features very thin walls, thereby minimizing its absorbing cross-section when viewed end-on. The CPC features extremely simple construction: no coating is required, since the CPC relies on highly-efficient Total Internal Reflection (TIR). The actual measured intensity data (5 million rays) for the OSTAR LED was used in this analysis.

The OSTAR LED and circuit board are shown in dark green in the figure above, the CPC is shown in teal blue, and the hex cell array is shown in gray. The light distribution is shown in two perpendicular planes, to give an idea of how the light is being distributed.

This design is intended to use as much light from the OSTAR LED as possible, while completely eliminating any light at divergence angles greater than 15 degrees. The plot below shows radiant intensity (on a log scale) as a function of angle (in degrees). The plot clearly shows that the intensity is relatively uniform and it drops off more than 9 orders of magnitude at divergence angles greater than 14 degrees.

This design uses two freeform mirrors to create an illuminator, using an OSRAM SFH 4230 high-power IR-LED (or IRED). The system was designed very quickly, using the 'Conjugate Surface' feature in ZEMAX. For this particular project, the infrared illumination was requried to pass through a 0.5in hole, and then was required to illuminate a volume measuring 23mm diameter by 1-inch long (located 2.1 inches away). The layout below shows the basic parameters that were used for this design.

Using Contrast (R) proprietary software, we easily converted the Conjugate Surfaces to Toroidal surfaces, and modeled the system using ZEMAX non-sequential analysis. The actual measured data (5 million rays) for the SFH 4230 IRED was used in this analysis.

The figure below shows the final freeform mirror illuminator layout. The OSRAM SFH 4230 IRED is shown in white, the two freeform mirrors are shown in gold, and the measured irradiance pattern is shown on the right side of the figure below.

SUMMARY

We have shown examples of two of the many illumination systems we have designed for our clients. Contact us to learn more about how Contrast Optical can solve your optical design problems.