Immersed Filter Stack for Compact SAL Seeker Throughput
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Solution Overview
Problem
Current laser-guided projectile systems have limitations in compactness and efficiency due to multiple 'air-to-glass' interfaces in their semi-active laser (SAL) seekers, which affect the throughput and field-of-view (FOV), leading to suboptimal performance in target detection and guidance.
Innovation Solution
A compact SAL seeker design featuring an integrated filter stack with a primary and secondary optical element, a spreader, and a detector sub-assembly with a field lens, where the spreader and filter are immersed within the optical media, reducing 'air-to-glass' interfaces and enhancing the effective FOV through spatial homogenization and aberration control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple air-to-glass interfaces are used in the SAL seeker optical system, then filtering and spatial homogenization functions are achieved, but throughput is reduced and field-of-view is limited
Solution Approach 1:
The patent combines the filter and spreader optical elements by immersing them directly in the optical media (gel or liquid crystal) without air-to-glass interfaces. This merging of optical functions into a single immersed assembly eliminates multiple refraction interfaces, reducing optical losses while maintaining filtering and spatial homogenization capabilities.
Solution Approach 2:
The patent introduces an optical gel or liquid crystal as an intermediary medium that optically couples the filter and spreader elements without requiring air-to-glass interfaces. This intermediary material has refractive index properties that match both the optical elements and the detector, enabling efficient light transmission while eliminating reflective losses at interface boundaries.
2Device complexity
If a compact SAL seeker design is implemented, then assembly complexity is reduced, but optical performance may be compromised
Solution Approach 1:
The patent merges the filter, spreader, and field lens into a single integrated optical assembly that is directly coupled to the detector. This consolidation reduces the number of separate components and alignment steps, simplifying assembly while maintaining precise optical performance through the immersive optical coupling that eliminates misalignment issues at multiple interfaces.
Solution Approach 2:
The patent implements a nested structure where the filter and spreader elements are positioned within the optical media of the field lens assembly, with the detector immersed at the focal plane. This nested arrangement allows multiple optical functions to be compactly integrated while maintaining their individual functional integrity and optical precision.
3Area of stationary object
If the detector is mounted on the backside of the field lens (immersed), then effective field-of-view is increased, but manufacturing complexity increases
Solution Approach 1:
The patent combines the detector mounting structure with the field lens assembly into a single integrated unit. The detector is permanently immersed and optically coupled to the field lens through the optical media, eliminating the need for separate mounting brackets, alignment mechanisms, and interface components, thereby simplifying manufacturing despite the immersed configuration.
Solution Approach 2:
The optical media itself serves as both the optical path and the mounting medium for the detector. The refractive index matching between the optical media, field lens, and detector creates self-aligning optical coupling that eliminates the need for complex alignment procedures and specialized manufacturing processes, making the immersed configuration as manufacturable as traditional designs.
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 improves the sensitivity and accuracy of target detection by increasing throughput and FOV, enabling more efficient guidance and reducing assembly and calibration complexities, resulting in a more reliable and effective projectile guidance system.
Implementation Method 1
a primary optical element including a forward-facing first lens element configured to focus the EMR
Implementation Method 2
a spreader configured to spatially homogenize EMR
Implementation Method 3
a filter configured to reject EMR outside the detection band
Implementation Method 4
a second (secondary) optical element including an aft-facing second lens element configured to control the aberration characteristics of the EMR transmitted through the optical sub-assembly
Implementation Method 5
a detector sub-assembly to generate at least one guidance signal in response to the position of the centroid of the focused EMR
Data Source
AI summary
A compact SAL seeker for a projectile guidance system comprises an optical sub- assembly to focus incident electro-magnetic radiation (EMR) such that target bearing in object space is mapped to a spatial irradiance in image space and a detector sub-assembly to generate at least one guidance signal in response to the position of the centroid of the focused EMR. The optical sub-assembly includes an integrated filter stack of a primary optical element, a spreader, a filter and secondary optical element in which at least one and typically both of the spreader and filter are immersed within the optical media of the stack. The detector sub-assembly may include a field lens in which the detector is immersed. Immersion reduces the number of "air-to-glass" interfaces, hence improves optical throughput. The detector sub-assembly may be integrally formed with a mounting bracket adapted to mate with mounting features on the optical sub-assembly to provide a self-aligned seeker.