Configurable Imaging Spectropolarimeter with Movable Mirror
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Solution Overview
Problem
Conventional spectropolarimeters suffer from low efficiency, spatial registration issues, and sensitivity problems due to sequential measurement of different polarizations or separate focal plane arrays, leading to inefficient photon collection and potential errors from scene changes during polarization switching.
Innovation Solution
A configurable imaging transform spectrometer that dynamically enables or disables polarimetry by frequency shifting one polarization to a unique frequency band, allowing simultaneous, perfectly registered measurements of both polarizations on a single focal plane array, using a movable mirror to introduce a variable optical path length and control mirror velocities for orthogonal polarizations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sequential measurement of different polarizations is used, then polarimetry can be performed, but measurement time increases and sensitivity decreases due to inefficient photon collection
Solution Approach 1:
The patent applies periodic action by modulating the movable mirror at different velocities for different polarizations. The mirror oscillates back and forth, creating periodic modulation of the optical path length. By controlling the mirror velocity to be different for orthogonal polarizations, the system encodes polarization information in the frequency domain, enabling simultaneous measurement of both polarizations without sequential switching, thus reducing measurement time while maintaining measurement precision.
Solution Approach 2:
The patent implements dynamics by making the mirror velocity variable and controllable. Instead of a fixed mirror position or constant velocity, the system dynamically adjusts the mirror velocity based on the polarization state. This dynamic control allows the system to optimize the measurement process for different polarizations simultaneously, improving both measurement precision and reducing time loss compared to static sequential measurement approaches.
2Measurement precision
If separate focal plane arrays are used for different polarizations, then polarimetry can be performed, but device complexity increases and spatial registration issues occur
Solution Approach 1:
The patent merges the measurement of different polarizations into a single focal plane array. By encoding polarization information in the frequency domain through differential mirror velocity modulation, both polarization states are detected simultaneously by the same detector array. This eliminates the need for separate focal plane arrays for different polarizations, reducing device complexity while avoiding spatial registration issues that would arise from combining data from multiple detectors.
Solution Approach 2:
The patent transitions from spatial separation of polarization measurements to frequency domain separation. Instead of using separate detectors in space for different polarizations, the system encodes polarization information in the frequency dimension through differential mirror velocity modulation. This dimensional transformation allows a single focal plane array to capture both polarization states without spatial registration problems, simplifying the device while maintaining measurement precision.
3Adaptability or versatility
If polarizer is placed at the input to the system, then polarimetry function can be enabled, but additional signal loss occurs at the system input
Solution Approach 1:
The patent replaces the conventional optical approach of using input polarizers with a mechanical modulation approach. Instead of filtering polarizations at the input using polarizing optics (which causes signal loss), the system uses a single movable mirror whose velocity is modulated according to the polarization state. This mechanical substitution eliminates the need for input polarizers and their associated signal losses while enabling the polarimetry function through frequency-encoded detection.
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 efficient, simultaneous measurement of dual polarizations with perfect registration, improving sensitivity and reducing errors by allowing on-demand polarimetry without additional signal loss, and transitioning between spectral imaging and polarimetry modes.
Implementation Method 1
By scanning the movable mirror over some distance, an interference pattern or interferogram is produced that encodes the spectrum of the source
Implementation Method 2
Electromagnetic radiation 120 incident on the beamsplitter 115 from a radiation source (not shown) is divided into two parts, each of which propagates down one of the two arms
Implementation Method 3
Mirror 105 is a fixed mirror and mirror 110 is a movable mirror. Radiation 120a in a first optical path is reflected by the beamsplitter 115 and reflected by the fixed mirror 105
Implementation Method 4
The FTS uses the Discrete Fourier Transform (DFT) or its faster algorithm, the Fast Fourier Transform (FFT), to convert the auto-correlation (each spectral amplitude encoded as the amplitude of a cosine signal) to physical spectra
Implementation Method 5
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
Data Source
Figure 1A~1B
Figure 2
Figure 3~4
AI summary
A multimode configurable imaging spectropolarimeter in which the polarimetry function can be activated and deactivated on demand.