Time-multiplexed broadband and multi-filtered electro-optic sensor

• US 9,488,444 B2
• Filed: 04/29/2013
• Issued: 11/08/2016
• Est. Priority Date: 04/29/2013
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Streuber, Casey T., Easton, Michael P., Pflibsen, Kent P.
• Primary Examiner(s): Ratcliffe, Luke
• Assistant Examiner(s): Abraham, Samantha K
• Application Number:
  US13/872,617
• Publication Number:
  US 20140320843A1
• Time in Patent Office: 1,289 Days
• US Class Current: 1/1
• CPC Class Codes: F41G 7/008 Combinations of different guidance systems
• CPC Class Codes: F41G 7/2253 Passive homing systems, i.e. comprising a receiver and do not requiring an active illumination of the target
• CPC Class Codes: F41G 7/2293 using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 3/784 using a mosaic of detectors
• CPC Class Codes: G02B 26/0875 by means of one or more refracting elements
• CPC Class Codes: G02B 26/10 Scanning systems
• CPC Class Codes: G02B 27/1013 for colour or multispectral image sensors, e.g. splitting an image into monochromatic image components on respective sensors spectral imaging systems G01J

Abstract

An EO sensor is configured to time multiplex a primary optical channel that provides high detection sensitivity to maintain high SNR and a multi-filtered optical channel that provides detection in different measurement bands (e.g. spectral, polarization, amplitude or phase). The channels may, for example, be time multiplexed based on range to target or within each integration period of the EO sensor. The multi-filtered optical channel uses a field directing array to sample the FOV to form different optical sub-channels that are filtered by different optical filters. These sub-channels may be spatially multiplexed onto different sub-regions of the detector or may be time multiplexed onto the entire detector. The light modulator used to time multiplex the primary and multi-filtered optical channels may be used to time de-multiplex spatially overlapping regions of the FOV onto a pixel of the detector in order to detect high spatial resolution images with low resolution detectors.

Claims

1. An electro-optic (EO) sensor, comprising

an objective optical system that forms an image within a field of view (FOV) from incident optical radiation;

a light modulator configured to alternately direct the incident optical radiation in the FOV to a primary optical channel and to a multi-filtered optical channel to time multiplex the FOV;

said primary optical channel comprising a relay optic configured to relay the image of the FOV onto a detector configured to convert optical radiation into a first electrical signal;

said multi-filtered optical channel comprising,

a focusing optic configured to collimate the incident optical radiation in the FOV;

a field directing having a plurality of tilt cells configured to spatially sample the optical radiation over the FOV, each tilt cell comprising first and second optical tilt elements that tilt the sampled optical radiation by different first and second tilt angles, respectively, to map the sampled FOV to first and second spatially separated optical sub-channels;

first and second optical filters positioned in said first and second spatially separated optical sub-channels, respectively, to filter the optical radiation, said first and second optical filters having different measurement bands; and

one or more detectors that convert the filtered incident optical radiation in the different measurement bands into a second electrical signal.

2. The EO sensor of claim 1, further comprising:

a processor configured to control the light modulator to direct the incident optical radiation in the FOV to the primary optical channel when a range to target is greater than a threshold and to the multi-filtered optical channel when the range to target is less than the threshold.

3. The EO sensor of claim 1, wherein the sensor has a sensor update rate corresponding to an integration period, further comprising:

a processor configured to control the light modulator to direct the incident optical radiation the FOV to the primary optical channel for a fixed portion of the integration period such that the detector outputs the first electrical signal at the sensor update rate at the end of each integration period and to the multi-filtered optical channel for the unused portion of the integration period such that the detector outputs the second electrical signal at the sensor update rate with a fixed delay from the end of each integration period.

4. The EO sensor of claim 1, wherein the sensor has a sensor update rate corresponding to an integration period, further comprising:

a processor configured to control the light modulator to direct the incident optical radiation to the FOV to the primary optical channel for a first portion of the integration period and to the multi-filtered optical channel for a second portion of the integration period.

5. The EO sensor of claim 4, wherein the processor varies the first portion of the integration period to maintain a minimum signal to noise ratio (SNR) in the primary optical channel.

6. The EO sensor of claim 1, wherein the primary optical channel includes either no filter or a single band filter.

7. The EO sensor of claim 1, further comprising folding mirrors that fold the primary optical channel and the multi-filtered optical channel onto the same detector.

8. The EO sensor of claim 1, wherein the multi-filtered optical channel directs the filtered optical radiation in the first and second optical sub-channels onto different first and second sub-regions of the detector.

9. The EO sensor of claim 1, wherein the multi-filtered optical channel overlaps the filtered optical radiation in the first and second spatially separated optical sub-channels onto the detector, wherein said light modulator comprises an array of addressable elements to independently and selectively direct optical radiation with different portions of the FOV to the first and second optical tilt elements in said tilt cells, said light modulator responsive to a control signal to time multiplex the filtered optical radiation in the first and second spatially separated optical sub-channels.

10. The EO sensor of claim 9, wherein said primary optical channel and said multi-filtered optical channel form a shared optical channel, wherein said light modulator is responsive to a control signal to simultaneously overlap the optical radiation in the first and second optical sub-channels to output the first electrical signal.

11. The EO sensor of claim 1, wherein the first and second optical filters comprise one of different spectral bands, different polarizations, different amplitudes or different phases.

12. The EO sensor of claim 1, wherein the focusing optic comprises an optical focusing array comprising an optical focusing element for each of said first and second optical tilt elements in each of said tilt cells in the field directing array, wherein said first and second tilt angles are substantially uniform across the field directing array.

13. The EO sensor of claim 1, wherein said first and second optical tilt elements are fixed.

14. The EO sensor of claim 1, wherein said field directing array is reconfigurable to provide different first and second tilt angles.

15. The EO sensor of claim 1, wherein in said multi-filtered optical channel different portions of the FOV that map to different tilt cells overlap at the detector, wherein said light modulator comprises an array of addressable elements to independently and selectively direct optical radiation within different portions of the FOV to the first and second optical tilt elements in said tilt cells, further comprising:

a processor configured to generate control signals for the addressable elements corresponding to at least one of the first and second optical sub-channels to pass optical radiation for a different one of said tilt cells in a time sequence to time de-multiplex the spatially overlapping portions of the FOV at the detector, each said detector pixel detecting only the optical radiation from the one selected portion of the FOV at a given time.

16. An electro-optic (EO) sensor, comprising

an objective optical system that forms an image within a field of view (FOV) from incident optical radiation;

a spatial light modulator comprising an array of addressable elements to independently and selectively direct optical radiation within different portions of the FOV, said spatial light modulator responsive to control signals to alternately direct the incident optical radiation in the FOV to a primary optical channel and to a multi-filtered optical channel to time multiplex the FOV;

said primary optical channel comprising a relay optic configured to relay the image of the FOV onto a detector configured to convert optical radiation into a first electrical signal;

said multi-filtered optical channel comprising,

a focusing optic configured to collimate the incident optical radiation in the FOV;

a field directing array having a plurality of tilt cells configured to spatially sample the optical radiation over the FOV, each tilt cell comprising first and second optical tilt elements that tilt the sampled optical radiation by different first and second tilt angles, respectively, to map the sampled FOV to first and second spatially separated optical sub-channels, wherein said first and second optical tilt elements in each said tilt cell map to a different addressable element in said spatial light modulator;

first and second optical filters positioned in said first and second optical sub-channels, respectively, to filter the optical radiation, said first and second optical filters having different measurement bands;

wherein different portions of the FOV that map to different tilt cells spatially overlap at a common image plane;

a pixelated detector positioned at or near the common image plane, said detector configured to convert the filtered incident optical radiation in the different measurement bands into a second electrical signal; and

a processor configured to generate control signals for the addressable elements corresponding to at least one of the first and second optical sub-channels to pass optical radiation for a different one of said tilt cells in a time sequence to time de-multiplex the spatially overlapping portions of the FOV at the detector, each said detector pixel detecting only the optical radiation from the one selected portion of the FOV at a given time.

17. An electro-optic (EO) sensor, comprising

an objective optical system that forms an image within a field of view (FOV) from incident optical radiation;

a focusing optic configured to collimate the incident optical radiation in the FOV;

a field directing array having a plurality of tilt cells configured to spatially sample the optical radiation over the FOV, each tilt cell comprising first and second optical tilt elements that tilt the sampled optical radiation by different first and second tilt angles, respectively, to map the sampled FOV to first and second spatially separated optical sub-channels;

first and second optical filters positioned in said first and second optical sub-channels, respectively, to filter the optical radiation, said first and second optical filters having different measurement bands; and

one or more detectors that convert the filtered incident optical radiation in the different measurement bands into an electrical signal.

18. The EO sensor of claim 17, wherein different portions of the FOV that map to different tilt cells overlap at the detector, wherein said light modulator comprises an array of addressable elements to independently and selectively direct optical radiation within different portions of the FOV to the first and second optical tilt elements in said tilt cells, further comprising:

a processor configured to generate control signals for the addressable elements corresponding to at least one of the first and second optical sub-channels to pass optical radiation for a different one of said tilt cells in a time sequence to time de-multiplex the spatially overlapping portions of the FOV at the detector, each said detector pixel detecting only the optical radiation from the one selected portion of the FOV at a given time.

19. The EO sensor of claim 17, wherein the filtered optical radiation in the first and second optical sub-channels is directed onto different first and second sub-regions of the detector.

20. The EO sensor of claim 17, wherein the filtered optical radiation in the first and second spatially separated optical sub-channels is spatially overlapped onto the detector, wherein said light modulator comprises an array of addressable elements to independently and selectively direct optical radiation with different portions of the FOV to the first and second optical tilt elements in said tilt cells, said light modulator responsive to a control signal to time multiplex the filtered optical radiation in the first and second spatially separated optical sub-channels.