Reflection-type orientation-switchable optical differentiator exemplified by the BK7-MoS₂ interface

Optical differential operation is an ultra-fast edge information extraction technology that enables identifying the image features, whereas current optical differentiators mainly operate along one or two differential orientations and is incompetent for switching the differential orientation. A reflection-type orientation-switchable optical differentiator is proposed and the BK7-MoS₂ interface is used as an example to analyze the edge detection performance. Theory suggests that there are dual modulation methods, one is tuning the incident polarization angle with a Brewster incident angle, and the other one is altering the incident angle with a nearly vertical incident polarization angle. The reason is that the term r_p/r_s tan α ≪ 1 is an ignored small quantity under these two situations and the spatial spectral transfer function is closely related to the scale coefficients C_x and C_y, whose magnitudes are both the incident polarization angle and incident angle dependent. Our optical differentiator can be combined with other tuning means since some two-dimensional materials are responsive to external stimuli, such as electrical or magnetic fields and defect engineering, these findings have potential applications in optical sensing, machine vision, and biomedical imaging.