Heterodyne starring array active imager

• US 10,587,347 B1
• Filed: 08/22/2019
• Issued: 03/10/2020
• Est. Priority Date: 08/22/2018
• Status: Active Grant

• Current Assignee: Richard H. Vollmerhausen
• Original Assignee: Richard H. Vollmerhausen
• Inventors: Vollmerhausen, Richard H.
• Primary Examiner(s): Dobson, Daniel G
• Application Number:
  US16/548,757
• Publication Number:
  US 20200067603A1
• Time in Patent Office: 201 Days
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/481 Constructional features, e.g. arrangements of optical elements
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/4917 superposing optical signals in a photodetector, e.g. optical heterodyne detection
• CPC Class Codes: H01S 3/0635 provided with a periodic structure, e.g. using distributed feed-back, grating couplers controlling, e.g. modulating distributed feed-back lasers H01S3/102
• CPC Class Codes: H01S 3/08086 Multiple-wavelength emission
• CPC Class Codes: H04B 10/40 Transceivers
• CPC Class Codes: H04B 10/50 Transmitters
• CPC Class Codes: H04B 10/60 Receivers
• CPC Class Codes: H04B 10/64 Heterodyne , i.e. coherent receivers where, after the opto-electronic conversion, an electrical signal at an intermediate frequency [IF] is obtained

Abstract

A heterodyne starring array active imager for producing an image. The imager comprises a light source intermittently illuminating a scene and an array of light collecting sites imaging the scene, each one comprising: a coupling component optically coupling scene light into a first waveguide and a local oscillator light coupled into a second waveguide. The first and second waveguides coupled to a third waveguide such that the scene light and local oscillator light propagate into the third waveguide. A square law photo detector associated with each light collecting site receives the merged light for heterodyning the scene light and the local oscillator light. Components receive and process the heterodyned light from the photo detectors to produce a frame signal for each light collecting site. A read-out device produces an array signal responsive to the frame signal from each light collecting site.

Claims

1. A heterodyne starring array active imager for producing an image, the heterodyne starring array imager comprising:

a light source for intermittently illuminating a scene;

an array of light collecting sites imaging the scene, each one of the light collecting sites comprising;

a coupling component for optically coupling scene light into a first waveguide;

a local oscillator light coupled into a second waveguide;

the first and second waveguides coupled to a third waveguide, the scene light and the local oscillator light merging and propagating into the third waveguide;

a square law photo detector for receiving light propagating in the third waveguide, wherein heterodyning of the scene light and the local oscillator light occurs at the photo detector to produce a photo detector output signal;

components for processing and integrating a plurality of the photo detector output signals to produce a frame signal; and

a read-out device producing an array signal responsive to the frame signal from each light collecting site.

2. The heterodyne starring array imager of claim 1 wherein while the light source illuminates the scene, a wavelength of the local oscillator light is changed such that a difference frequency of the local oscillator light and the scene light is outside a temporal bandwidth of the square law photo detector.

3. The heterodyne starring array imager of claim 1 wherein the coupling component comprises a horn coupler or a Bragg grating coupler.

4. The heterodyne starring array imager of claim 3 wherein the horn coupler or the Bragg grating coupler is fabricated in silicon.

5. The heterodyne starring array imager of claim 1 further comprising a polarization diversifier for converting the scene light to a single mode, the polarization diversifier disposed between the coupling component and the first waveguide.

6. The heterodyne starring array imager of claim 1 wherein the light source comprises a continuous laser source with a gate to provide gated control of illumination to intermittently illuminate the scene, and wherein the gated control is adjustable to provide different range gate settings.

7. The heterodyne starring array imager of claim 1 wherein the components for processing and integrating comprise components for AC coupling, rectifying, and low pass filtering or integrating the photo detector output signal to produce the frame signal.

8. The heterodyne starring array imager of claim 1 wherein the array of light collecting sites comprises an N×

M array of light collecting sites where N and M are integer values.

9. The heterodyne starring array imager of claim 1 wherein the light source comprises a pulsed light source.

10. The heterodyne starring array imager of claim 1 wherein the scene light and the local oscillator light are of the same mode.

11. The heterodyne starring array imager of claim 1 wherein intermittently illuminating the light source comprises pulsing the light source on and off, and wherein integrating by the components does not begin until a period of time after an on pulse illuminating the light source has ended.

12. The heterodyne starring array imager of claim 1 wherein intermittently illuminating the light source comprises pulsing the light source on and off, and wherein for a first frame a duty cycle of the on and off pulses is 0.5, and wherein during subsequent frames the duty cycle is reduced to 0.

13. The heterodyne starring array imager of claim 1 further comprising a component for preventing the scene light from entering the first waveguide when the light source is illuminating the scene.

14. The heterodyne starring array image of claim 13 wherein the component comprises a Mach Zehnder interferometer disposed between the coupling component and the first waveguide, the Mach Zehnder interferometer operating as an optical switch.

15. The heterodyne starring array imager of claim 1 wherein a wavelength of the local oscillator light is shifted when the light source is illuminating the scene such that the photo detector output signal is outside a bandwidth of the square law photo detector when the light source is illuminating the scene.

16. The heterodyne starring array imager of claim 1 wherein each photodetector output signal is generated responsive to light reflected from the scene as collected by one of the light collecting sites from the array of light collecting sites.

17. The heterodyne starring array imager of claim 1 wherein the intermittently illuminated light is illuminates the scene for a time t_laser with a duty cycle of 0.5, and wherein a wavelength of the local oscillator light is selected such that heterodyning of the scene light and the local oscillator light generates a photo detector output signal within a bandwidth of the square law photodetector during t_laser, and wherein for a period at least equal to t_laser a wavelength of the local oscillator light is shifted such the heterodyning of the scene light and the local oscillator light generates a photo detector output signal outside a bandwidth of the square law photodetector.

18. The heterodyne starring array imager of claim 17 wherein the period is at least equal to t_laser or is greater than t_laser.

19. The heterodyne starring array imager of claim 1 wherein a spectral bandwidth of the local oscillator light is smaller than a spectral bandwidth of the scene light.

20. A heterodyne starring array active imager for producing an image, the heterodyne starring array imager comprising:

a continuous laser light source for intermittently illuminating a scene by operation of an adjustable range gate, wherein intermittently illuminating the light source comprises pulsing the light source on and off, and wherein for a first frame a duty cycle of the on and off pulses is 0.5, and wherein during subsequent frames the duty cycle is reduced to 0;

an N×

M array of light collecting sites imaging the scene, wherein N and M are integers and each one of the light collecting sites comprising;

a coupling component further comprising a horn coupler or a Bragg grating coupler for optically coupling scene light into a first waveguide;

a Mach Zehnder interferometer disposed between the coupling component and a first waveguide, the Mach Zehnder interferometer operating as an optical switch;

a polarization diversifier for converting the scene light to a single mode, the polarization diversifier disposed between the Mach Zehnder and the first waveguide;

a local oscillator light coupled into a second waveguide, wherein a spectral bandwidth of the local oscillator light is smaller than a spectral bandwidth of the scene light;

the first and second waveguides coupled to a third waveguide, the scene light and the local oscillator light merging and propagating into the third waveguide;

a square law photo detector for receiving light propagating in the third waveguide, wherein heterodyning of the scene light and the local oscillator light occurs at the photo detector to produce a photo detector output signal;

wherein while the light source illuminates the scene, a wavelength of the local oscillator light is changed such that a difference frequency of the local oscillator light and the scene light is outside temporal bandwidth of the square law photo detector;

components for AC coupling rectifying, and low pass filtering or integrating a plurality of the photo detector output signals to produce a frame signal; and

a read-out device producing an array signal responsive to the frame signal from each light collecting site.