Optical bandpass filters for detector arrays’ modulation transfer function estimation by means of laser speckle

Abstract

Two apertures, a square slit (SS) and a diamond slit (DS), both zero’th-order magnitude transparencies with bandpass filters in their optical transfer functions (OTFs), are designed and optimized for the purpose of modulation transfer function (MTF) evaluation of detector arrays by means of laser speckle. The SS and DS apertures are compared to an existing design, the extended frequency aperture (EFA), and show, respectively, improvements of 464% and 58% in filter magnitude; improvements of 213.4% (a compromise) and 17% in bandwidth; and improvements of 627% and 423% in throughput, implying a greatly reduced laser power requirement. As a result, they should significantly enhance detector arrays’ MTF evaluations and at a greatly reduced cost. The DS aperture possesses identical OTFs in both the horizontal and vertical directions, enabling MTF evaluation using the bandpass filters in those directions from the same speckle data frame—previously not possible. The DS aperture can be further modified to yield filter magnitude and bandwidth improvements of 111% and 40%, respectively; although becoming easier to fabricate, this modification would be at a lower throughput improvement of 310% over the existing design.