MEMS Micro-Mirror Array for Compact Image Polarimetry
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Solution Overview
Problem
Conventional image polarimeters require moving parts like motors to rotate polarizers and waveplates, making them bulky and incompatible with newer, higher-resolution focal plane arrays (FPAs) without replacing the polarization filters, which complicates compact packaging and image registration.
Innovation Solution
A Micro-Electro-Mechanical System (MEMS) Micro-Mirror Array (MMA) is segmented and equipped with polarizers, allowing mirrors to tip, tilt, and piston between frames to steer polarized light onto different parts of an optical detector, enabling the capture of multiple component polarized images without moving components during image acquisition, thus simplifying co-registration and accommodating various polarimetry techniques like Jones calculus and Stokes parameter computation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If motors are used to rotate polarizers and waveplates, then polarization components can be measured, but the device becomes bulky and incompatible with higher-resolution FPAs
Solution Approach 1:
The patent replaces motor-driven mechanical rotation of polarizers and waveplates with a MEMS micro-mirror array that uses electrostatic actuation to tip and tilt mirrors. This substitution eliminates bulky motors and mechanical rotation mechanisms while maintaining the ability to measure multiple polarization components through electronic control of mirror angles.
Solution Approach 2:
The MEMS micro-mirror array is divided into multiple segments, with each segment containing mirrors that can be independently controlled to specific angles. Each segment corresponds to a specific polarization component (0°, 45°, 90°, 135°), allowing simultaneous or sequential measurement of all polarization components without requiring full rotation of a single mechanical assembly.
2Measurement precision
If polarizers are fixed in front of the FPA, then polarization filtering is achieved, but replacing the FPA with higher resolution requires replacing the filter array
Solution Approach 1:
The system uses dynamically controllable MEMS mirrors instead of static polarizer filters. The mirrors can be electronically reconfigured to different angles without physical replacement, allowing the system to adapt to different FPA resolutions and configurations. The polarization measurement capability is maintained through electronic control rather than fixed optical filters.
3Measurement precision
If axially rotating polarizers are used to generate time-sequenced polarized images, then all polarization components can be captured, but image co-registration becomes complex due to time-varying changes
Solution Approach 1:
The MEMS mirrors are pre-configured to specific fixed angles corresponding to different polarization components (0°, 45°, 90°, 135°). This preliminary positioning eliminates the need for dynamic rotation during image capture, allowing all polarization components to be captured simultaneously or in a fixed sequence without time-varying changes that would complicate co-registration.
4Measurement precision
If a 2×2 filter array is placed in front of the FPA, then polarization filtering is achieved, but the system prevents compact packaging
Solution Approach 1:
The patent merges the polarization filtering function with the imaging detector by integrating the MEMS micro-mirror array directly with the FPA. The mirrors are positioned at or near the aperture stop, combining the polarization measurement function with the image capture function in a single integrated unit, eliminating the need for separate filter arrays and reducing overall system volume.
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
This approach allows for compact, efficient image polarimetry by stabilizing image acquisition and enabling the computation of polarization properties within a single frame, reducing aberrations and maintaining compatibility with higher-resolution FPAs without the need for filter replacements.
Implementation Method 1
The MEMS MMA responsive to command signals to tip and tilt the mirrors in the respective segments to reflect and steer polarized light having at least two different polarizations at respective steering angles to respective non-overlapping portions of a pixelated optical detector
Implementation Method 2
The MEMS MMA comprises a plurality of mirrors responsive to command signals to at least tip and tilt about first and second axes, respectively. The MEMS MMA is segmented into two or more segments with each segment including a plurality of mirrors; the mirrors in a given segment having polarizers that impart the same polarization with the polarizers in the two or more segments imparting different polarizations
Data Source
AI summary
An image polarimeter includes a MEMS MMA divided into two or more segments in which the mirrors in each segment are provided with a polarizer of a given polarization. The mirrors in each segment are tipped and tilted to steer polarized light onto different portions of an optical detector. In certain configurations the mirrors may also be pistoned to reduce aberrations. Each frame that is read out from the detector includes two or more distinct component polarized images having different polarizations P0, P2, . . . of the same scene to fully characterize the polarization properties of the scene. Since the mirrors only tip/tilt/piston in the dead period between frames, no components are moving during image acquisition and co-registration of the component polarized images is simple. The number of segments and the different polarizations may be selected to implement Jones calculus, Mueller calculus and Stokes parameters or other polarimetry techniques.