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Digital level micro-fabrication for advanced optical structures

Hyperspectral instruments with physical sizes comparable to that of a bare sensing array are now possible. Compact Fabry-Perot (FP) etalon arrays allow for different spectral sensitivities to be assigned to the different pixels of a sensing array. Such arrays for hyperspectral imaging are commercially available but underutilized due to cost and performance tradeoffs. FP arrays were first made possible by binary or logarithmic fabrication, which reduces the number of lithography steps to log2(k) where k is the number of distinct levels of material required for the integrated optical element. However, significant yield loss results from the several lithography steps required in this process. We introduce a new binary etching technique that allows for the creation of an arbitrary number of distinct levels with a single greyscale lithography technique. Our technique has been used for the fabrication of distinct levels of 1 nm rms flatness with a controlled 10 nm resolution. This technique has been used to fabricate a staircase structure with greater than 100 distinct steps directly on a COTS optical imager. Details of the fabrication technique and characteristics of the optical element will be presented.