We present simulations and characterization of gold coated diffractive optical elements (DOEs) that have been designed and fabricated in silicon for an industrial application of near-infrared spectroscopy. The DOE design is focusing and reflecting, and two-level and four-level binary designs were studied. Our application requires the spectral response of the DOE to be uniform over the DOE surface. Thus the variation in the spectral response over the surface was measured, and studied in simulations. Measurements as well as simulations show that the uniformity of the spectral response is much better for the four-level design than for the two-level design. Finally, simulations and measurements show that the four-level design meets the requirements of spectral uniformity from the industrial application, whereas the simulations show that the physical properties of diffraction gratings in general make the simpler tw level design unsuitable.

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We study optical spectral filter synthesis with arrays of piston-actuated micro-mirrors. We propose two algorithms for the calculation of the positions of the micro-mirrors, giving us control of both the amplitude and phase of the synthetic filter. Both algorithms for filter synthesis are explored in an analytic version and in numerical searches for the least deviations between the target and the synthesized filter. We measure the quality of the filter both in terms of the deviations and in filter transmissivity, and present results of numerical simulations for a wide selection of target filters. We find that numerical searches can sometimes yield considerable improvement in the filter synthesis compared to the analytic approximation.

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Diffractive optical elements (DOEs) represent small, lightweight and potentially low-cost alternatives to conventional optical components. We have evaluated photoresists and processes for fabrication of silicon micro-machined DOEs with a sub-micron pattern using an MA150 (Suss) proximity aligner. The resists HiPR 6512 (Fuji film), AZ ECI 3007 (AZ Electronics Materials), IX335 H (JSR Micro) and UVIII (Rohm and Haas) were all able to resolve the desired 0.8 µm pattern, but the wall angle obtained with IX335H was a superior 86°. Double development of the resists proved possible in a KOH-based developer but unfeasible in a TMAH-based developer. The final DOE device was successfully realized based on the optimized photolithography process.