Tilted Image Plane Imaging with Fourier Filtering

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Solution Overview

Problem

Conventional imaging systems are easily detectable by optical augmentation techniques due to retro-reflection, which limits their use in applications where stealth is required, and tilting the image plane alone is insufficient to eliminate retro-reflection while maintaining image focus.

Innovation Solution

The implementation of a non-retro-reflective imaging system using a tilted image plane in combination with Fourier optical filtering, along with segmented or 'sliced source' imaging, to eliminate residual retro-reflection and ensure in-focus image formation, thereby preventing retro-reflection and enhancing system capability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the image plane is oriented perpendicular to the optical axis, then the image remains in focus across the entire active area of the sensor array, but the system becomes retro-reflective and easily detectable by optical augmentation techniques

Engineering Contradiction:

Improveimage focusVSAvoidretro-reflection detectability

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The image plane is segmented into multiple discrete sensor elements arranged in a non-planar configuration. Each sensor element is positioned at a different angle relative to the optical axis, allowing the system to maintain focus for multiple incident angles simultaneously while eliminating retro-reflection in any single direction.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The sensor array is transitioned from a two-dimensional planar arrangement to a three-dimensional non-planar configuration. By tilting and positioning sensor elements at different depths and angles, the system achieves focus for oblique incident rays without creating retro-reflective pathways back to the source.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Object-affected harmful factors

If the image plane is tilted relative to the optical axis to reduce retro-reflection, then retro-reflection is reduced, but the image becomes out of focus across the sensor array

Engineering Contradiction:

Improveretro-reflectionVSAvoidimage focus

Core Design Contradiction:

Object-affected harmful factorsVSManufacturing precision

Solution Approach 1:

The tilted image plane is segmented into multiple sensor elements, each independently positioned and oriented to receive light at the appropriate angle. This segmentation allows each element to maintain proper focus for its specific angular range while the overall array reduces retro-reflection through the tilted configuration.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the sensor array are given different local orientations and positions relative to the optical axis. Each sensor element is locally optimized to receive focused light from its specific angular sector, while the collective arrangement provides overall retro-reflection reduction.

Inventive Principle:

Principle #3Local quality

3Object-affected harmful factors

If a filter is added to block retro-reflective rays, then retro-reflection is eliminated, but the system complexity increases

Engineering Contradiction:

Improveretro-reflectionVSAvoidsystem complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The retro-reflective rays are extracted and blocked at the Fourier plane, which is the frequency domain representation of the optical field. By placing the filter at this specific location in the optical path, the system eliminates retro-reflection with minimal additional complexity, as the filter only needs to be positioned at a single critical plane rather than throughout the entire optical system.

Inventive Principle:

Principle #2Taking out (Extraction)

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

The solution effectively eliminates retro-reflection, allowing for covert imaging while maintaining excellent image formation and reducing the system's size, weight, and complexity, making it undetectable by optical augmentation devices.

Implementation Method 1

at least one optical element configured to receive electromagnetic radiation and to focus the electromagnetic radiation onto a tilted image plane

Methodology Applied

Scientific EffectOptical focusing: Focusing

Implementation Method 2

a filter configured to block rays of the electromagnetic radiation that would be normally incident on the imaging sensor from reaching the image sensor

Methodology Applied

Scientific EffectOptical filtering: Filter (optical)

Data Source

PatentUS9165963B2Non-retro-reflective imaging using tilted image planes

Publication Date: 2015.10.20 RAYTHEON CO

AI summary

A non-retro-reflective imaging system and methods in which tilted image plane imaging is combined with selective Fourier filtering to substantially eliminate retro-reflection from the system. In certain examples, tilted image plane imaging is achieved using sliced source imaging. Through rotation of the image plane, the majority of incident light is reflected off-axis, rather than being retro-reflected. The Fourier filter is used to block incoming light from a particular angle that would otherwise be normally incident on the rotated image plane and retro-reflected. One example of a non-retro-reflective imaging system includes an optical element that focuses electromagnetic radiation onto a tilted image plane, an imaging sensor co-aligned with the tilted image plane, and a Fourier filter positioned in a Fourier plane of the optical element, a position of the Fourier filter in the Fourier plane determined by the tilt angle of the tilted image plane.