Mixing optical beams for solar simulation-a new approach [to solar cell testing]

The authors describe the principle of a novel solar simulator based on mixing three optical beams of suitably selected spectral distribution to produce a single collimated beam that accurately reproduces a given spectral irradiance. The optical mixing is accomplished by means of a trifurcated randomized fiber-optic bundle. The output of the fiber is collimated to produce a beam which is highly uniform (typically better than ±1%) in the test plane. This design has applications as a one-sun as well as a concentrator simulator. It can also be used in a spectral response measurement system which can provide monochromatic and bias beams of identical uniformity. The overall optical throughput of the novel simulator system is very high, because the coupling efficiency at each end is very high, typically -75%. The output end of the fiber acts as an optical integrator with a very large number of optical elements (typically about 3000 compared to 16 to 35 used in standard simulators). The intensity of each beam can be independently controlled without changing the uniformity in the output beam. Use of the optical fiber makes the system compact and low-cost