Investigation of modulated speckle using double-aperture pupil
Speckle phenomenon is ubiquitous in any coherent imaging systems and quantitative interpretations are often anchored on the knowledge of statistical speckle properties. Modulation of speckle results from coherent superposition of fields coming off or through multi-aperture pupils. This work investigates the effects of spacing between two circular pupils on speckle modulation using spectral analysis and 3D visualizations. Numerical simulations involve a random field passing through a double-aperture pupil. Speckle power spectral densities are then calculated and analyzed. Axial propagation of modulated speckle is also investigated. Results show that as the spacing of the aperture pupils decreases, fringe modulated speckle decrease in spatial frequency. Along the direction of beam propagation, the mean modulated speckle size slowly varies. Highly-sensitive, noise-robust and controllable, speckle modulation can be used in developing strategies for optical metrology.