Imaging Spectropolarimeter Spatial Polarization Multiplexing
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Solution Overview
Problem
Conventional spectropolarimeters suffer from low efficiency and inability to measure orthogonal polarizations simultaneously, leading to signal loss and spatial registration issues when attempting to combine spectral imaging and polarimetry.
Innovation Solution
A dual-beam interferometric transform spectrometer with spatially registered focal plane arrays and integrated polarizers that transmit specific pairs of polarizations, allowing for simultaneous measurement and interpolation of all four polarizations, reducing signal loss and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single focal plane array is used to measure polarizations sequentially with a switchable polarizer, then the device complexity is reduced, but the signal loss increases and measurement precision deteriorates
Solution Approach 1:
The focal plane array is segmented into multiple pixel groups, where each group is associated with a specific polarization state. This allows simultaneous measurement of different polarizations across different pixel groups without sequential switching, eliminating the signal loss associated with time-division multiplexing while maintaining manageable device complexity through structured pixel organization.
Solution Approach 2:
The patent transitions from temporal multiplexing (sequential measurement) to spatial multiplexing (simultaneous measurement across different pixels). By distributing polarization measurements across the spatial domain of the focal plane array, the system achieves simultaneous polarization measurement without the signal loss inherent in sequential approaches.
2Adaptability or versatility
If a linear polarizer is inserted into the optical path to enable polarimetry, then the polarimetry function is added, but the photon collection efficiency decreases and the device complexity increases
Solution Approach 1:
Instead of using a single linear polarizer that blocks half the light, the patent assigns different polarization measurement capabilities to different local regions (pixel groups) of the focal plane array. Each region is optimized for measuring a specific polarization state, allowing the system to capture all polarization information without the 50% photon loss inherent in conventional linear polarizers.
Solution Approach 2:
The focal plane array is designed to perform multiple functions simultaneously: spectral imaging and polarimetry. By integrating polarization sensitivity directly into the detector array rather than using external polarizing optics, the system achieves universal functionality without the photon collection efficiency penalties of conventional approaches.
3Measurement precision
If two separate instruments (polarimeter and imaging spectrometer) are used to obtain both polarimetric and spectral information, then the measurement precision for each function is improved, but the device complexity and loss of time increase
Solution Approach 1:
The patent merges the polarimeter and imaging spectrometer into a single integrated instrument. The focal plane array is designed to simultaneously perform spectral imaging and polarimetry by assigning different pixel groups to measure different polarization states, enabling both functions to operate concurrently rather than sequentially.
Solution Approach 2:
The system maintains continuous measurement of both spectral and polarimetric information without the interruptions required by sequential instrument operation. By simultaneously measuring all polarization states across the focal plane array, the system eliminates the time loss associated with switching between separate instruments while maintaining the measurement precision of each function.
4Measurement precision
If orthogonal polarization pairs are measured simultaneously using separate focal plane arrays, then the signal-to-noise ratio improves, but the device complexity and loss of time increase
Solution Approach 1:
The patent combines multiple focal plane arrays into a single integrated array with spatially distributed polarization measurement capabilities. By organizing pixels into polarization-specific groups within one array, the system achieves the signal-to-noise ratio benefits of multiple arrays while reducing the complexity and time overhead associated with coordinating and registering multiple separate detectors.
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 enables high extinction and accurate simultaneous collection of all four polarizations, enhancing the signal-to-noise ratio and reducing errors in polarimetric imaging, while maintaining the efficiency of spectral imaging.
Implementation Method 1
Radiation 120a in a first optical path is reflected by the beamsplitter 115
Implementation Method 2
Radiation 120b in a second optical path is transmitted through the beamsplitter 115
Implementation Method 3
When the position of the movable mirror 110 is varied along the axis of the corresponding arm (indicated by arrow 130), an interference pattern, or interferogram, is swept out at the focal plane array 125 as the two phase-shifted beams interfere with each other
Implementation Method 4
a first polarizer coupled to the first focal plane array and configured to transmit only a first pair of polarizations to the first focal plane array
Data Source
AI summary
An imaging interferometric transform spectropolarimeter configured to simultaneously collect four polarizations. In one example, an spectropolarimeter includes a dual-beam interferometric transform spectrometer configured to receive electromagnetic radiation from a viewed scene, and including first and second focal plane arrays that are spatially registered with one another, a first polarizer coupled to the first focal plane array and configured to transmit only a first pair of polarizations to the first focal plane array, and a second polarizer coupled to the second focal plane array and configured to transmit only a second pair of polarizations to the second focal plane array, the second pair of polarizations being different than the first pair of polarizations.