Planar Optical Phased Array for Incoherent Star Direction Sensing
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Solution Overview
Problem
Conventional star trackers, both strapped-down and mechanically aimable, face challenges in precision aiming and are bulky, heavy, and energy-intensive, with difficulties in managing stray light from bright objects like the sun or moon, and are limited in the number of navigational stars they can use.
Innovation Solution
A zero-optical-path-length-difference optical phased array system with equal optical path lengths within a coherence length at a bandwidth greater than 0.1%, allowing for the use of incoherent light and enabling a smaller, lighter, and more efficient star tracker with dynamic beam steering capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a large lens is used in conventional star trackers, then the field of view and number of navigational stars increase, but the device becomes massive and occupies large volume
Solution Approach 1:
The patent divides the optical system into multiple discrete optical receivers arranged in an array, with each receiver having a small field of view. By segmenting the overall field of view across multiple receivers, the system achieves a large total field of view without requiring a single large lens, thereby reducing mass while maintaining versatility.
Solution Approach 2:
The patent transitions from a single-point optical reception approach to a two-dimensional array of optical receivers. This dimensional expansion allows the system to cover a large field of view through spatial distribution of multiple small receivers, eliminating the need for a large focal length and reducing overall device volume and mass.
2Adaptability or versatility
If mechanically aimable star trackers are used, then more navigational stars can be observed, but the device complexity and precision aiming requirements increase
Solution Approach 1:
The patent replaces the mechanical aiming mechanism with an electronic/phased array system. Instead of physically rotating or moving the entire optical system to track stars, the system uses an array of fixed receivers with electronic beam forming and signal processing to achieve the same functionality, thereby reducing mechanical complexity while maintaining the ability to observe multiple navigational stars.
Solution Approach 2:
The patent introduces dynamic electronic control of the optical receiver array, where the effective pointing direction can be changed electronically by adjusting the phase and amplitude of signals from individual receivers. This dynamic electronic steering replaces static mechanical aiming mechanisms, reducing complexity while maintaining versatility.
3Reliability
If conventional optical paths are used in phased arrays, then path difference compensation is needed, but this increases device complexity and reduces bandwidth
Solution Approach 1:
The patent designs the optical paths such that all receivers have equal optical path lengths to the focal plane, creating an equipotential optical system. This eliminates optical path difference and the need for complex compensation mechanisms, allowing the use of incoherent light sources and significantly increasing system bandwidth while maintaining reliable interference patterns.
Solution Approach 2:
The patent changes the optical path length parameter from variable to equal across all receivers. By setting all optical paths to be equal, the system eliminates the need for dynamic path compensation, enabling the use of incoherent light and broadening the operational bandwidth while simplifying the overall device structure.
4Device complexity
If strapped-down star trackers are used, then the device is mechanically simpler, but the fixed view angle limits the number of navigational stars
Solution Approach 1:
The patent segments the field of view across multiple optical receivers arranged in an array. Each receiver has a small fixed field of view, but the collective array covers a large total field of view. This segmentation allows the system to maintain simple fixed mechanical structures while achieving high adaptability through the distributed receiver configuration.
Solution Approach 2:
The patent expands from a single fixed viewing direction to a two-dimensional array of receivers, each with its own fixed viewing direction. This dimensional expansion allows the system to maintain simple fixed mechanical structures while achieving a large effective field of view through spatial distribution, thereby increasing the number of observable navigational stars.
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
Enables precise direction determination of incoherent optical sources like stars with improved sensitivity and reduced size and power consumption, overcoming the limitations of traditional star trackers by using a phased array system with equal optical path lengths and dynamic delay lines for beam steering.
Implementation Method 1
A first plurality of optical waveguides optically connects the first plurality of optical couplers to the first port via respective first optical paths
Implementation Method 2
Optical lengths of all the first optical paths are equal, within a criterion. The criterion is one coherence length at a bandwidth greater than about 0.1%
Data Source
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AI summary
A zero-optical-path-length-difference optical phased array built with essentially planar photonic devices determines a direction to an incoherent optical source, such as a star. The phased array can replace a 3-dimensional star tracker with a nearly 2-dimensional system that is smaller and lighter. The zero-optical-path-length-difference phased array can be optically connected to an interferometer. Driven by a light source, the zero-optical-path-length-difference phased array can be used as an optical projector.