Existing studies have paid much attention to stray light of lenses. However, the ghost reflection inside
FPA (Focal Plane Array) detector is almost ignored which is, in fact, also an unnegligible source of
stray light in digital imaging systems. Ghosting between window surfaces and CCD photosensitive area
is often a major source of stray light in FPA detectors, it may lead to image blur, color distortion, and
contrast reduction. Besides, diffraction pattern can be observed from front-illuminated CCD as the
incident beam can be diffracted by its polysilicon electrode gates at the surface. In this paper, we study
the generation mechanism and the reduction approaches to such stray light. Both front-illuminated and
back-illuminated CCDs (Charge Coupled Device) are investigated in our study. We build models to
identify stray light paths and predict window ghost image characteristics. Furthermore, three methods,
i.e., anti-reflective coating method, fluid-filled method and deconvolution method are presented to
decrease the stray light. The first anti-reflective coating method can be effectively used in back-thinned
CCDs to reduce the reflection and to maximize quantum efficiency. The second fluid-filled method
attempts to reduce the effects of unwanted light contamination by simulating some characteristics of the human eyes. The use of liquid can reduce the fresnel reflectance of interface. In addition, the acquired images contaminated by FPA's stray light are post-processed with the deconvolution method. Effectiveness of our proposed methods is verified with experiments. It is shown that stray light of FPA can be efficiently reduced.
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