Diffractive Element Enlarges Exit Pupil in Optical Instruments
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Solution Overview
Problem
Conventional optical instruments have a fixed and small exit pupil size, requiring precise alignment of the observer's eye, and often include expensive field lens arrangements that complicate optical clarity and design.
Innovation Solution
The integration of a diffractive element at an intermediate image plane, featuring frusto-conical or frusto-cylindrical surfaces and tilted sections, creates an enlarged exit pupil, eliminating the need for a field lens arrangement and enhancing optical clarity by providing a single, continuous enlarged exit pupil with uniform energy distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional optical instrument uses a fixed exit pupil size determined by numerical aperture and magnification, then the optical design is simple, but the observer must accurately align the entrance pupil of the eye with the exit pupil to properly view the image
Solution Approach 1:
The patent segments the exit pupil into multiple discrete exit pupils by introducing a diffractive element with an array of diffractive units at the intermediate image plane. Each diffractive unit generates a separate exit pupil, and the collective arrangement of these multiple exit pupils creates an effectively enlarged exit pupil that is easier to align with the observer's eye while maintaining optical design simplicity.
2Reliability
If an optical instrument includes a field lens arrangement to relay the exit pupil, then the exit pupil can be viewed at the correct plane, but the field lens represents the most expensive component being a precision-ground and polished glass component
Solution Approach 1:
The patent replaces the mechanical field lens arrangement (precision-ground and polished glass components) with a diffractive element that uses diffraction of light to achieve the same function of creating and relaying multiple exit pupils. This substitution eliminates the need for expensive precision glass components while maintaining the reliability of exit pupil relay to the correct viewing plane.
3Adaptability or versatility
If the diffractive element uses areas with curved surfaces to produce diffractive interference, then the exit pupil array can be generated, but the manufacturing complexity increases
Solution Approach 1:
The patent employs areas with curved surfaces (frusto-conical or frusto-cylindrical shapes) in the diffractive units to generate the desired diffractive interference patterns and produce the array of exit pupils. The curved geometry provides the necessary optical path differences for effective diffraction while being manufacturable through techniques such as molding or lithography, balancing optical performance with fabrication feasibility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration allows for greater optical clarity and flexibility in viewing, enabling observers to view images from anywhere within the enlarged exit pupil without the need for precise alignment and reduces costs by omitting expensive field lens components.
Implementation Method 1
The diffractive units are effective to produce diffractive interference of light passing therethrough and generate an array of exit pupils
Data Source
Figure 1
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Figure 2(c)~2(d)
AI summary
An optical instrument for producing an optical image to be viewed by an observer, the optical instrument comprising : an optical system for producing an optical image of an object which is viewable by an observer at an exit pupil; and a diffractive element located at an image plane of the optical system for producing an array of exit pupils, which are perceivable as a single, enlarged exit pupil by the observer; wherein the diffractive element comprises a surface which has an array of diffractive units, each of which generates one of the exit pupils of the array of exit pupils, the diffractive units each comprising replications of a pattern of a plurality of separated areas which are effective to produce diffractive interference of light and generate a plurality of exit pupils which are displaced relative to one another in the form of an array of exit pupils, such as to be viewable as a single, continuous enlarged exit pupil, and the areas comprise irregular features of different sizes, both in horizontal and vertical section, which have curved surfaces at lateral faces thereof; wherein the diffractive units are disposed progressively radially outwardly from the optical axis of the diffractive element and configured progressively to provide for an increasing angular offset, such that, independent of location on the aperture of the diffractive element and without any relay lens arrangement, light from the received image is relayed to a common region on a viewing plane across the aperture of the diffractive element.