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All-Optical Longitudinal Super Resolution

IP.com Disclosure Number: IPCOM000033073D
Publication Date: 2004-Nov-24
Document File: 3 page(s) / 1M

Publishing Venue

The IP.com Prior Art Database

Abstract

A new patented technology proposes an extended depth of focus (longitudinal super resolution) element configured as a phase-affecting, non-diffractive optical element defining a spatially low frequency phase transition that codes the lens aperture. Since this optical element contains low spatial frequencies, it is not sensitive to wavelengths and does not scatter energy towards the outer regions of the field of view. The optical element is a phase element and thus does not require apodization and its energetic efficiency is very high. Since the optical element does not require digital post processing it is adequate for ophthalmic applications. The optical element is a mask constructed out of transparent areas and pi-phase lines (e.g., grid) and/or one or more pi-phase circles that modulate the coherent transfer function of the lens. The positions of those pi-phase transitions are appropriately selected to generate invariance to quadratic phase distortions (that correspond to the effect of getting out of focus) under the operation of auto correlation.

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All-Optical Longitudinal Super Resolution

Zeev Zalevsky

Xceed Imaging Ltd.

1. Introduction

Extending the depth of focus of imaging systems is a very important core technology that may be used in allowing its incorporation into various camera aided and ophthalmic applications. Several previous approaches were suggested involving digital post processing [1-3], or aperture apodization [4-6], or diffraction optical phase elements such as multi focal lenses or spatially densed distributions that suffer from significant divergence of energy into region that are not the regions of interest [7].

A new patented technology that is briefly described in this paper proposes an extended depth of focus (EDOF) element configured as a phase-affecting, non-diffractive optical element defining a spatially low frequency phase transition that codes the lens aperture. Since this optical element contains low spatial frequencies, it is not sensitive to wavelengths and does not scatter energy towards the outer regions of the field of view. The optical element is a phase element and thus does not require apodization and its energetic efficiency is very high. Since the optical element does not require digital post processing it is adequate for ophthalmic applications. The optical element is a mask constructed out of transparent areas and pi-phase lines (e.g., grid) and/or one or more pi-phase circles that modulate the coherent transfer function (CTF) of the lens. The positions of those pi-phase transitions are appropriately selected to generate invariance to quadratic phase distortions (that correspond to the effect of getting out of focus) under the operation of auto correlation. Note that the operation of auto correlating the CTF is done to compute the optical transfer function (OTF) of the imaging system. The developed element is also not sensitive to its transversal, as well as longitudinal position, and is thus very suitable to be placed on eye glasses. For obtaining transversal insensitivity low spatial frequency, periodic replication of the mask contours (the contour or transition regions) is generated.

The position of the pi-phase transitions is computed using iterative algorithm in which M positions are examined and eventually those that provide maximal contrast of the OTF under a set of out of focus locations are chosen. The meaning of OTF’s contrast optimization is actually having the out of focused OTF bounded as much as possible away from zero.

Due to the fact that the aperture mask is constructed out of spatially low frequencies pi-phase transitions, it does not spread energies away from the zero order of diffraction and its energetic efficiency is close to 100%.

This patented technology was tested experimentally and proven to provide large depth of focus range overcoming distortions even of y=17.

2. Technical Description

The out of focus distortion is modeled by multiplying the aperture with the following expression:

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