| The use of phase-only apodization elements to improve the performance of conventional and confocal imaging systems is investigated theoretically and experimentally. The primary objective of the work is optical superresolution which aims to reduce the width of the point spread function with respect to the diffraction limit.; Numerical optimization methods are employed to find new multi-level phase-only filters suitable for optical data storage and confocal microscopy. The solutions satisfy specific beam shape requirements and are designed with a certain amount of defocus. The defocus maximizes the Strehl ratio in order to maintain a certain level of transverse resolution. Imaging performance is evaluated in terms of the images of simple objects—a point, a plane, two closely-spaced points or planes, and an edge.; Phase-only elements are shown to be beneficial for improving aspects of imaging performance. They can be used to decrease the size of the image of a single point or plane or to improve the discrimination of two closely-spaced points or planes. The tradeoffs associated with these resolution improvements are documented in terms of various criteria, including image contrast and mensuration error. An important result is that while phase—only elements can improve the two-point resolution limit, the apparent position of the two closely-spaced points is more uncertain.; Using diffractive optics technology, several two- and three-zone phase-only elements are fabricated as surface-relief optical elements. Experiments for phase-apodized and unapodized systems are conducted to verify the theoretical model. The experimental results correlate well with the theoretical predictions for those cases which are tested. Key experimental results include the first measurement of the three-dimensional point spread function of a multi-level phase-only element, the first demonstration of two-point superresolution with a phase-only element, and the first demonstration of the effect of phase-only filters on the confocal images of an edge and a plane. |
