Design a Phase Plate to Extend the Depth of Field for an Inexpensive Microscope System to Have the Muti-focus Ability

Abstract

We propose an optical technique, also called wave front coding, that can extend the depth of field optically by phase plate without the need of post digital image processing (PDIP). This technique can replace the present expensive mechanical scanning for achieving 3D information recording or to avoid keeping adjusting the structure of the objective. This phase plate can be fabricated by the emerging technology of laser direct-write photoresist patterning and subsequent reactive ion etching on a germanium substrate. The niche of our innovation is the exempt of PDIP. The dependence on PDIP causes the conventional researches in this field to develop a deteriorating phase plate to deteriorate the images in different depth to be the same worse. The deteriorated images can thus be fixed digitally by a same inverse optical transfer function method. In contrast, we replace the deteriorating plate with an improving plate. This plate can improve the defocus image in general. This freedom in limitation enables us to have a better imaging effect when designing the improvement plate. For example, in our design we do not need to worry about the null points existing in the inverse method since there is no inverse method for us at all.