Spatial harmonic distortion: a test for focal plane nonlinearity

Glenn D. Boreman; Anthony B. Centore; Christopher R. Costanzo

doi:10.1117/12.55832

Abstract

A new measurement technique for focal plane linearity was investigated experimentally. The spatial harmonic distortion test consists of projecting spatial sine waves of irradiance onto a focal plane by means of a Young's fringe technique. If the detectors in the array have a linear responsivity, a sinusoidal input waveform is mapped to a sinusoidal output. However, if the detectors in the array have a nonlinear responsivity (i.e., saturation), then the output waveform will exhibit harmonic distortion. When the Fourier transform of the array data is taken, the content at the second and third harmonics of the original sine-wave spatial frequency indicates the amount of nonlinearity in the aggregate array response. Measurement results are included for two focal planes: a vidicon tube camera and a solid-state charge-injection device (CID) camera. The minimum harmonic distortion measured was 3%. The sensitivity of this test is limited ultimately by the amount of spatial nonuniformity. Numerical and analytical models are given that indicate the minimum detectable harmonic distortion is in the range of a few percent. This test also allows measurement of the spatial-frequency dependence of the nonlinearity, a quantity that is not accessible with the usual flat-field techniques for linearity assessment.

Citation Download Citation

Glenn D. Boreman, Anthony B. Centore, Christopher R. Costanzo, "Spatial harmonic distortion: a test for focal plane nonlinearity," Optical Engineering 30(5), (1 May 1991). https://doi.org/10.1117/12.55832

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