Enhancement of imaging performance of a variable focus Fresnel zone plate based on a single, binary, phase-only SLM

摘要

It is shown that the imaging performance of a variable focus optical system based on a single, binary, phase-only spatial light modulator (SLM) can be improved in important respects by combining it with a fixed phase mask with either two or four phase levels separated by π/2. With the SLM encoded as a modified Fresnel zone plate, the images associated with one member of each of the pair of foci, ±f, ±f/3; ±f/5, etc. are deflected and blocked by a stop enabling a single image plane to dominate the performance. Analytical expressions are derived for the peak amplitudes of the point spread functions of a simple imaging system. The simulated performance of a variable focus system is reported in which the intensity in a single selected image plane, scanned in the z-direction, is about an order of magnitude greater than other image planes and in which the scan range is approximately doubled by switching between +f and -f foci.