Image polarimeter using a micro-electro-mechanical system (MEMS) micro-mirror array (MMA)

Patent metadata

Field	Value
Publication number	US-12259277-B2
Application number	US-202117479927-A
Country	US
Kind code	B2
Filing date	Sep 20, 2021
Priority date	Sep 20, 2021
Publication date	Mar 25, 2025
Grant date	Mar 25, 2025

Abstract

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.

First claim

We claim:

1. An image polarimeter, comprising:
an image forming system configured to collect light to form an image of a scene;
a pixelated optical detector;
a Micro-Electro-Mechanical System (MEMS) Micro-Mirror Array (MMA) positioned at or near an aperture stop of the image forming system, said MEMS MMA comprising a plurality of mirrors responsive to command signals to at least tip and tilt about first and second axes, respectively, said MEMS MMA 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, the polarizers in the two or more segments imparting different polarizations P0, P1, . . . , said 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 the pixelated optical detector;
a focusing element configured to focus the polarized light to form two or more component polarized images I0, I1, . . . of the same image of the scene on the respective portions of the optical detector; and
a MEMS MMA controller configured to generate the command signals to drive the MEMS MMA.

2. The image polarimeter of claim 1 , wherein the pixelated optical detector simultaneously reads out the two or more component polarized images I0, I1, . . . in a single frame at a frame rate, wherein each frame includes an imaging period in which the component polarized images I0, I1, . . . are detected and a dead period, wherein the mirrors are only tipped and tilted during the dead period and are fixed during the imaging period.

3. The image polarimeter of claim 1 , wherein at least one of the polarizers P0, P1, . . . includes a quarter-wave plate (QWP).

4. The image polarimeter of claim 1 , wherein the polarizer comprises a dielectric coating or a wire grid array configured to impart a linear polarization of a particular angular value.

5. The image polarimeter of claim 1 , wherein the focusing element is provided through actuation of the mirrors, which are responsive to command signals to tip and tilt to focus and steer the polarized light to form the component polarized images I0, I1, . . . on the respective non-overlapping portions of the optical detector.

6. The image polarimeter of claim 1 , wherein the mirrors piston in translation along a third axis, wherein the mirrors are responsive to command signals to piston to reduce aberrations in the component polarized images I0, I1, . . . .

7. The image polarimeter of claim 6 , further comprising a processor configures to (a) compute a nominal fixed piston for each said mirror in each segment to reduce aberrations for a fixed steering angle and a fixed focus to steer and focus the component polarized images onto the detector and (b) process the component polarized images to compute a dynamic piston for each said mirror in each segment to improve the quality of the component polarized images, wherein said processor provides the nominal fixed piston and dynamic piston for each said mirror to the MEMS MMA controller to generate command signals.

8. The image polarimeter of claim 1 , wherein the MEMS MMA is segmented into 4segments in which the mirrors have polarizers that impart different polarizations P0, P1, P2 and P3 in the different segments to produce four component polarized images I0, I1, I2 and I3, wherein polarizations P0, P1, P2 and P3 are configured to derive Stokes Parameters S0, S1, S2 and S3 from the four component polarized images I0, I1, I2 and I3.

9. The image polarimeter of claim 8 , where P0=0 degrees, P1=45 degrees, P2=90 degrees and P3=QWP45 degrees.

10. A polarized imaging system, comprising:
an image forming system configured to collect light to form an image of a scene;
a pixelated optical detector;
a Micro-Electro-Mechanical System (MEMS) Micro-Mirror Array (MMA) positioned at or near an aperture stop of the image forming system, said MEMS MMA comprising a plurality of mirrors responsive to command signals to at least tip and tilt about first and second axes, respectively, and to piston in translation along a third axis in three degrees-of-freedom (3DOF), said MEMS MMA 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, the polarizers in different segments imparting different polarizations P0, P1, . . . , said MEMS MMA responsive to command signals to tip and tilt the mirrors in the respective segments to reflect, focus and steer polarized light having at least two polarizations P0, P1, . . . , at respective steering angles to form component polarized images I0, I1, . . . of the same image of the scene on respective non-overlapping portions of the optical detector and responsive to command signals to independently piston the mirrors to reduce aberrations in the component polarized images I0, I1, . . . ; and
a MEMS MMA controller configured to generate the command signals to drive the MEMS MMA.

11. The image polarimeter of claim 10 , wherein the pixelated optical detector simultaneously reads out the two or more component polarized images I0, I1, . . . in a single frame at a frame rate, wherein each frame includes an imaging period in which the component polarized images I0, I1, . . . are detected and a dead period, wherein the mirrors are only tipped, tilted and pistoned during the dead period and are fixed during the imaging period.

12. The image polarimeter of claim 11 , wherein the MEMS MMA is segmented into 4 segments in which the mirrors have polarizers that impart different polarizations P0, P1, P2 and P3 in the different segments to produce four component polarized images I0, I1, I2 and I3, wherein polarizations P0, P1, P2 and P3 are configured to derive Stokes Parameters S0, S1, S2 and S3 from the four component polarized images I0, I1, I2 and I3.

13. The image polarimeter of claim 11 , further comprising a processor configures to (a) compute a nominal fixed piston for each said mirror in each segment to reduce aberrations for a fixed steering angle and a fixed focus to steer and focus the component polarized images onto the detector and (b) process the component polarized images to compute a dynamic piston for each said mirror in each segment to improve the quality of the component polarized images.

14. An image polarimeter, comprising:
an image forming system configured to collect light to form an image of a scene;
a pixelated optical detector;
a Micro-Electro-Mechanical System (MEMS) Micro-Mirror Array (MMA) positioned at or near an aperture stop of the image forming system, said MEMS MMA comprising a plurality of mirrors responsive to command signals to at least tip and tilt about first and second axes, respectively, said MEMS MMA segmented into four segments with each segment including a plurality of mirrors, the mirrors in a given segment having polarizers that impart the same polarization, the polarizers in the four segments imparting different polarizations P0, P1, P2 and P3, said MEMS MMA responsive to command signals to tip and tilt the mirrors in the respective segments to reflect, focus and steer polarized light having four polarizations P0, P1, P2 and P3 at respective steering angles to form component polarized images I0, I1, I2 and I3 of the same image of the scene on respective non-overlapping portions of the optical detector, wherein polarizations P0, P1, P2 and P3 are configured such that Stokes Parameters S0, S1, S2 and S3 are derivable from the four compo

Assignees

• Raytheon Co

Inventors

• Rogala Eric
• Uyeno Gerald P

Classifications

• G02B26/0833

  the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD (G02B26/0825 takes precedence; micromechanical devices in general B81B) · CPC title

• G02B27/286

  for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another (G02B5/3083 takes precedence; light guide coupling means utilising polarising elements G02B6/34) · CPC title

• G01J4/04 Primary

  Polarimeters using electric detection means (G01J4/02 takes precedence) · CPC title