Enhanced vision system implemented with optical shutter alternately transmitting visible radiation and near infrared radiation

• US 9,229,139 B2
• Filed: 07/17/2014
• Issued: 01/05/2016
• Est. Priority Date: 01/19/2012
• Status: Active Grant

• Current Assignee: LC-Tec Displays AB
• Original Assignee: LC-Tec Displays AB
• Inventors: Osterman, Jesper, Scheffer, Terry J.
• Primary Examiner(s): Qi, Mike
• Application Number:
  US14/334,517
• Publication Number:
  US 20140327837A1
• Time in Patent Office: 537 Days
• Field of Search: 349/2, 349/9, 349/96, 349/117
• US Class Current: 1/1
• CPC Class Codes: G02B 5/208 for use with infrared or ultraviolet radiation, e.g. for separating visible light from infrared and/or ultraviolet radiation
• CPC Class Codes: G02F 1/1396 the liquid crystal being selectively controlled between a twisted state and a non-twisted state, e.g. TN-LC cell G02F1/141 takes precedence
• CPC Class Codes: G02F 2203/11 involving infrared radiation
• CPC Class Codes: H04N 23/10 for generating image signals from different wavelengths
• CPC Class Codes: H04N 23/11 for generating image signals from visible and infrared light wavelengths
• CPC Class Codes: H04N 23/55 Optical parts specially adapted for electronic image sensors; Mounting thereof
• CPC Class Codes: H04N 23/63 by using electronic viewfinders
• CPC Class Codes: H04N 23/75 by influencing optical camera components

Abstract

An optical shutter employed in an enhanced vision system includes a wavelength selective polarizing filter in optical association with a liquid crystal polarization modulator to rapidly switch between optical states to alternately transmit visible (VIS) radiation and near infrared (NIR) radiation. The wavelength selective polarizing filter imparts a polarization state to incident radiation and transmits polarized radiation within at least the visible wavelength region. The liquid crystal polarization modulator receives incident radiation for internal propagation through the modulator and responds to first and second values of an applied control signal to switch the internally propagating radiation to, respectively, first and second polarization states. The switching between first and second polarization states produces, in cooperation with the wavelength selective polarizing filter, optical shutter output VIS and NIR radiation. A computer processes the output VIS and NIR radiation to produce for display a composite image formed of visible and infrared elements.

Claims

1. An enhanced vision system including an optical shutter that is rapidly switchable between optical states to alternately transmit visible radiation and near infrared radiation, comprising:

a wavelength selective polarizing filter constructed to impart a polarization state to incident radiation and transmit polarized radiation within at least the visible wavelength region of the electromagnetic spectrum;

a liquid crystal polarization modulator positioned to receive incident radiation for internal propagation through the liquid crystal polarization modulator, the liquid crystal polarization modulator optically associated with the wavelength selective polarizing filter and responsive to a first value and a second value of an applied control signal to switch the internally propagating radiation to, respectively, a first polarization state and a second polarization state to produce, in cooperation with the wavelength selective polarizing filter, optical shutter output radiation in different wavelength regions of the electromagnetic spectrum, the switching of the internally propagating radiation to the first polarization state causing transmission and blockage of the optical shutter output radiation within, respectively, the visible wavelength region and the near infrared region, and the switching of the internally propagating radiation to the second polarization state causing transmission and blockage of the optical shutter output radiation within, respectively, the near infrared wavelength region and the visible wavelength region;

a computer processing the transmitted optical shutter output radiation within the visible region to produce a first visible image and the transmitted optical shutter output radiation within the infrared region to produce a second visible image; and

an image display device receiving signals corresponding to the first and second visible images produced by the computer and combining the first and second visible images to produce a composite image formed of visible and infrared elements.

2. The enhanced vision system of claim 1, in which the first visible image is a full-color image.

3. The enhanced vision system of claim 1, in which the first visible image is a black-and-white image.

4. The enhanced vision system of claim 1, further comprising, in optical series arrangement, a wavelength selective polarizing filter pair including a wavelength selective polarizing filter transmitting polarized radiation within the visible wavelength region and a wavelength selective polarizing filter transmitting polarized radiation within the near infrared wavelength region;

in which the wavelength selective polarizing filter constructed to impart a polarization state to incident radiation constitutes a broadband wavelength selective polarizing filter that transmits polarized radiation in the visible wavelength region and the near infrared wavelength region; and

in which the liquid crystal polarization modulator is positioned between the broadband wavelength selective polarizing filter and the wavelength selective polarizing filter pair.

5. The enhanced vision system of claim 4, further comprising for viewing angle compensation an optical retarder positioned between the wavelength selective polarizing filters transmitting polarized radiation within the visible and near infrared wavelength regions.

6. The enhanced vision system of claim 5, in which the liquid crystal polarization modulator includes a twisted nematic liquid crystal device and the optical retarder includes a negative C retarder film.

7. The enhanced vision system of claim 5, in which the liquid crystal polarization modulator includes a liquid crystal device tuned to a design wavelength in the visible wavelength region, and in which the wavelength selective polarizing filter transmitting polarized radiation within the visible wavelength region is positioned between the liquid crystal device and the optical retarder.

8. The enhanced vision system of claim 5, in which the liquid crystal polarization modulator includes a liquid crystal device tuned to a design wavelength in the near infrared wavelength region, and in which the wavelength selective polarizing filter transmitting polarized radiation within the near infrared wavelength region is positioned between the liquid crystal device and the optical retarder.

9. The enhanced vision system of claim 4, in which the liquid crystal polarization modulator includes first and second liquid crystal devices positioned nearer to, respectively, the broadband wavelength selective polarizing filter and the wavelength selective polarizing filter pair, and further comprising first and second optical retarders for viewing angle compensation, the first optical retarder positioned between the broadband wavelength selective polarizing filter and the first liquid crystal device, and the second optical retarder positioned between the wavelength selective polarizing filters transmitting polarized radiation within the visible and near infrared wavelength regions.

10. The enhanced vision system of claim 9, in which the first optical retarder includes a negative C retarder film and the second optical retarder includes a positive C retarder film.

11. The enhanced vision system of claim 1, in which:

the wavelength selective polarizing filter constructed to impart a polarization state to incident radiation constitutes a broadband wavelength selective polarizing filter that transmits polarized radiation in the visible wavelength region and the near infrared wavelength region; and

the liquid crystal polarization modulator includes a guest-host liquid crystal mixture that includes a liquid crystal director and that, depending on an orientation of the liquid crystal director determined by one of the first and second polarization states to which the internally propagating radiation is switched, exhibits variable absorption of different radiation wavelength regions to produce the optical shutter output radiation in different wavelength regions of the electromagnetic spectrum.

12. The enhanced vision system of claim 1, in which the liquid crystal polarization modulator includes a guest-host liquid crystal mixture that includes a liquid crystal director contained between first and second electrodes and that exhibits variable absorption of different radiation wavelength regions, depending on the orientation of the liquid crystal director relative to the polarization state of the internally propagating radiation;

further comprising first and second wavelength selective polarizing filters imparting a polarization state to incident radiation within the visible wavelength region but not imparting a polarization state to incident radiation within the near infrared wavelength region, the first and second wavelength selective polarizing filters positioned adjacent different ones of the first and second electrodes of the liquid crystal polarization modulator; and

the liquid crystal polarization modulator and the first and second wavelength selective polarizing filters cooperating to selectively produce the optical shutter output radiation in the visible wavelength region and the near infrared wavelength region, as determined by one of the first and second polarization states to which the filter output radiation is switched.

13. The enhanced vision system of claim 12, in which the guest-host liquid crystal mixture that includes a liquid crystal director between the first and second electrodes comprises a twisted nematic liquid crystal structure of a twisted nematic liquid crystal cell.

14. The enhanced vision system of claim 13, in which the twisted nematic liquid crystal cell has a 270°

twisted nematic liquid crystal structure.