Photonic Imaging Array for Star Tracking
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Solution Overview
Problem
Conventional star trackers are large, heavy, energy-intensive, and face challenges in preventing stray light, particularly when navigational stars are close to bright objects like the sun or moon, limiting their precision and efficiency in 3D scanning and requiring complex mechanical aiming.
Innovation Solution
A photonic imaging system using a wafer with optical couplers and detectors in planar arrays, combined with Butler matrices and multi-modal interferometers, forming an analog 2-dimensional optical Fourier transformer to process optical signals efficiently and reduce complexity, enabling smaller, lighter, and more precise star tracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large lens is used in conventional star trackers, then measurement precision is improved, but weight and volume increase significantly
Solution Approach 1:
The patent divides the optical system into multiple small aperture elements arranged in an array, replacing the single large lens. Each aperture element processes a portion of the field of view, and the overall system achieves high precision through the collective action of multiple segmented elements combined with electronic beamforming via Butler matrices.
Solution Approach 2:
The patent replaces the mechanical optical system (large physical lens and focal plane) with a photonic integrated circuit system using waveguides, optical couplers, and Butler matrices. This substitution eliminates the need for large mechanical components while maintaining or improving measurement precision through optical field processing.
2Measurement precision
If a long focal length is used in conventional star trackers, then measurement precision is improved, but volume occupied increases
Solution Approach 1:
The patent transitions from a traditional 3D optical path (requiring long focal length distance) to a planar 2D integration architecture using waveguides and photonic circuits. The optical processing occurs in the lateral dimensions of the chip plane rather than requiring extended axial distance, dramatically reducing volume while maintaining precision.
Solution Approach 2:
The patent replaces the mechanical focal length requirement with optical field manipulation through Butler matrices and waveguide phase control. The precision is achieved through optical path difference control in the photonic circuit rather than through physical focal length, eliminating the volume penalty of long focal lengths.
3Adaptability or versatility
If mechanical aiming is used to track stars, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent implements dynamic beam steering through electronic control of the Butler matrix phase shifters, allowing the optical beam to be electronically directed to different fields of view without mechanical movement. This provides adaptability for tracking multiple stars while eliminating mechanical complexity.
Solution Approach 2:
The patent replaces the mechanical aiming system with an optical-electronic beamforming system using Butler matrices. The adaptability to track different stars is achieved through electronic phase control rather than mechanical rotation, significantly reducing device complexity while maintaining versatility.
4Ease of manufacture
If conventional optical systems are used, then ease of manufacture is improved, but energy consumption increases
Solution Approach 1:
The patent replaces conventional bulk optical components with photonic integrated circuits that can be manufactured using standard semiconductor fabrication processes. This substitution reduces energy consumption through miniaturization and integration while maintaining manufacturing ease through established CMOS-compatible fabrication techniques.
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 system achieves efficient 2D scanning with improved precision and reduced size and energy consumption, capable of processing incoherent radiation and handling multiple navigational stars, while maintaining high sensitivity and pixel density.
Implementation Method 1
Each optical coupler has an output. Each optical coupler is configured to couple an optical signal from free space to its respective output
Implementation Method 2
The first and second optical phasing networks cooperate to form an analog 2-dimensional optical Fourier transformer
Implementation Method 3
A Butler matrix (first described by Jesse Butler and Ralph Lowe in 'Beam-Forming Matrix Simplifies Design of Electronically Scanned Antennas'
Implementation Method 4
A star tracker typically includes a lens that projects an image of a star onto a photocell, or that projects an image of one or more stars onto a light-sensitive sensor array (digital camera)
Data Source
AI summary
A multi-beam optical phased array on a single planar waveguide layer or a small number of planar waveguide layers enables building an optical sensor that performs much like a significantly larger telescope. Imaging systems use planar waveguides created using micro-lithographic techniques. These imagers are variants of “phased arrays,” common and familiar from microwave radar applications. However, there are significant differences when these same concepts are applied to visible and infrared light.