Camera comprising an infrared illuminator and a liquid crystal optical filter switchable between a reflection state and a transmission state for infrared imaging and spectral imaging, and method thereof

Patent metadata

Field	Value
Publication number	US-10972643-B2
Application number	US-201816002862-A
Country	US
Kind code	B2
Filing date	Jun 7, 2018
Priority date	Mar 29, 2018
Publication date	Apr 6, 2021
Grant date	Apr 6, 2021

Abstract

An optical filter for a camera is switchable between a reflection state and a transmission state. The optical filter includes a first plurality of liquid crystals configured to dynamically form cholesteric phase structures in the reflection state that block right-handed circularly polarized light in a spectral light sub-band and transmit light outside of the spectral light sub-band. The first plurality of liquid crystals dynamically forms a nematic phase arrangement in the transmission state that transmits light in the spectral light sub-band. The optical filter further includes a second plurality of liquid crystals configured to dynamically form cholesteric phase structures in the reflection state that block left-handed circularly polarized light in the spectral light sub-band and transmit light outside of the spectral light sub-band. The second plurality of liquid crystals dynamically form a nematic phase arrangement in the transmission state that transmits light in the spectral light sub-band.

First claim

The invention claimed is:

1. A camera comprising:
an infrared (IR) illuminator configured to emit active IR light in an IR light sub-band;
a sensor array including a plurality of sensors;
an optical filter for the sensor array switchable between a reflection state and a transmission state, the optical filter including:
a first plurality of liquid crystals configured to
dynamically form cholesteric phase structures that in the reflection state block right-handed circularly polarized light in a spectral light sub-band and transmit light outside of the spectral light sub-band, and
dynamically form a nematic phase arrangement in the transmission state that transmits light in the spectral light sub-band, and

a second plurality of liquid crystals configured to
dynamically form cholesteric phase structures in the reflection state that block left-handed circularly polarized light in the spectral light sub-band and transmit light outside of the spectral light sub-band, and
dynamically form a nematic phase arrangement in the transmission state that transmits light in the spectral light sub-band, wherein the optical filter is configured to transmit IR light in an IR light sub-band in both the transmission state and the reflection state; and

a controller machine configured to:
switch the optical filter to the reflection state to block spectral light in the spectral light sub-band,
activate the IR illuminator to illuminate a subject with the active IR light while the optical filter is in the reflection state,
address the sensors of the sensor array while the optical filter is in the reflection state,
determine, for each of the plurality of sensors of the sensor array, a depth value indicative of a depth of the subject based on a measured aspect of the active IR light emitted from the IR illuminator and reflected from the subject back to each of the plurality of sensors,
switch the optical filter to the transmission state to allow transmission of spectral light in the spectral light sub-band,
deactivate the IR illuminator such that the IR illuminator does not emit active IR light while the optical filter is in the transmission state, and
address the sensors of the sensor array while the optical filter is in the transmission state.

2. The camera of claim 1 , wherein the optical filter is configured to block substantially all visible light in all visible light sub-bands when the optical filter is in the reflection state.

3. The camera of claim 1 , where the optical filter includes a plurality of liquid crystal layers, where different liquid crystal layers of the plurality of liquid crystal layers are configured to block spectral light in different spectral light sub-bands and transmit spectral light outside of the spectral light sub-bands in the reflection state, and to transmit spectral light in the spectral light sub-band in the transmission state.

4. The camera of claim 3 , wherein the controller machine is configured to adjust one or more of a center wavelength of the selected spectral light sub-band and a bandwidth of the selected spectral light sub-band by switching one or more liquid crystal layers from the transmission state to the reflection state.

5. The camera of claim 1 , where the plurality of sensors of the sensor array are differential sensors, and where the controller machine is configured to activate the IR illuminator in synchrony with addressing the differential sensors of the sensor array to differentially measure the measured aspect of the active IR light emitted from the IR illuminator and reflected from the subject back to each of the plurality of sensors.

6. A method comprising:
switching an optical filter of a camera to a reflection state to block spectral light in a spectral light sub-band, the optical filter including a first plurality of liquid crystals configured to dynamically form cholesteric phase structures that in the reflection state block right-handed circularly polarized light in a spectral light sub-band and transmit light outside of the spectral light sub-band, and a second plurality of liquid crystals configured to dynamically form cholesteric phase structures in the reflection state that block left-handed circularly polarized light in the spectral light sub-band and transmit light outside of the spectral light sub-band, wherein the optical filter is configured to transmit IR light in an IR light sub-band different than the spectral light sub-band in the reflection state;
activating an IR illuminator of the camera to illuminate a subject with the active IR light while the optical filter is in the reflection state;
addressing each of a plurality of sensors of a sensor array of the camera while the optical filter is in the reflection state;
determining, for each of the plurality of sensors of the sensor array, a depth value indicative of a depth of the subject based on a measured aspect of the active IR light emitted from the IR illuminator and reflected from the subject back to each of the plurality of sensors;
switching the optical filter to a transmission state to allow transmission of spectral light in the spectral light sub-band, wherein the first plurality of liquid crystals is configured to dynamically form a nematic phase arrangement in the transmission state that transmits light in the spectral light sub-band, and the second plurality of liquid crystals is configured to dynamically form a nematic phase arrangement in the transmission state that transmits light in the spectral light sub-band;
deactivating the IR illuminator such that the IR illuminator does not emit active IR light while the optical filter is in the transmission state;
addressing the sensors of the sensor array while the optical filter is in the transmission state; and
determining, for each of the plurality of sensors of the sensor array, one or more spectral light values based on one or more measurements of the sensor.

7. The method of claim 6 , wherein the optical filter is configured to block substantially all visible light in all visible light sub-bands when the optical filter is in the reflection state.

8. The method of claim 6 , where the optical filter includes a plurality of liquid crystal layers, where different liquid crystal layers of the plurality of liquid crystal layers are configured to block spectral light in different spectral light sub-bands and transmit spectral light outside of the spectral light sub-bands in the reflection state, and to transmit spectral light in the spectral light sub-band in the transmission state.

9. The method of claim 8 , further comprising:
adjusting one or more of a center wavelength of a selected spectral light sub-band and a bandwidth of the selected spectral light sub-band by switching one or more liquid crystal layers from the transmission state to the reflection state.

10. The method of claim 6 , where the plurality of sensors of the sensor array are differential sensors, and where the method further comprises activating the IR illuminator in synchrony with addressing the differential sensors of the sensor array to differentially measure the measured aspect of the active IR light emitted from the IR illuminator and reflected from the subject back to each of the plurality of sensors.

11. A camera comprising:
an infrared (IR) illuminator configured to emit active IR light in an IR light sub-band;
a sensor array including a plurality of sensors;
an optical filter for the sensor array switchable between a reflection state and a transmission state, the optical filter including:
a first layer of liquid crystals configured to
dynamically form cholesteric phase structures in the reflection state that block circularly polarized l

Assignees

• Microsoft Technology Licensing Llc

Inventors

• Akkaya Onur Can
• Bamji Cyrus Soli

Classifications

• H04N23/55 Primary

  Optical parts specially adapted for electronic image sensors; Mounting thereof · CPC title

• G03B11/00

  Filters or other obturators specially adapted for photographic purposes · CPC title

• G02F2203/01

  transmissive · CPC title

• G02F2203/02

  reflective · CPC title

• G02F1/133509

  Filters, e.g. light shielding masks · CPC title