Electroabsorption modulator for depth imaging and other applications

Patent metadata

Field	Value
Publication number	US-10254407-B2
Application number	US-201615057792-A
Country	US
Kind code	B2
Filing date	Mar 1, 2016
Priority date	Mar 2, 2015
Publication date	Apr 9, 2019
Grant date	Apr 9, 2019

Abstract

A TOF depth imaging system for providing a depth image of an object is provided comprising a light source configured to illuminate an object with amplitude modulated light characterized by a wavelength λ and a modulation frequency f, a surface-normal electroabsorption modulator configured to receive and to modulate reflected light from the object with the modulation frequency f, and an image sensor configured to receive and to detect modulated reflected light from the electroabsorption modulator. The electroabsorption modulator comprises a top doped layer of semiconductor, a bottom doped layer of semiconductor having opposite polarity to the top doped layer, and an active layer between the top and bottom doped layers, the active layer configured as a superlattice structure comprising multiple sublayers of semiconductor configured to provide alternating quantum wells and barriers, the active layer comprising quantum wells configured to exhibit delocalized electron-hole behavior.

First claim

What is claimed is:

1. A TOF depth imaging system for providing a depth image of an object, the system comprising:
a light source configured to illuminate an object with amplitude modulated light characterized by a wavelength λ and a modulation frequency f,
a surface-normal electroabsorption modulator configured to receive and to modulate reflected light from the object with the modulation frequency f, the electroabsorption modulator comprising
a top doped layer of semiconductor,
a bottom doped layer of semiconductor having opposite polarity to the top doped layer, and
an active layer between the top and bottom doped layers, the active layer configured as a superlattice structure comprising multiple sublayers of semiconductor configured to provide alternating quantum wells and barriers, the active layer comprising quantum wells configured to exhibit delocalized electron-hole behavior, wherein the electroabsorption modulator does not comprise an optical cavity; and
an image sensor configured to receive and to detect modulated reflected light from the electroabsorption modulator.

2. The TOF depth imaging system of claim 1 , further comprising a first driver in electrical communication with the light source, a second driver in electrical communication with the electroabsorption modulator, and a timing controller in electrical communication with the first and second drivers and the image sensor.

3. The TOF depth imaging system of claim 1 , wherein the active layer is configured to absorb light having a wavelength in the near-infrared region of the electromagnetic spectrum.

4. The TOF depth imaging system of claim 3 , wherein the multiple sublayers of semiconductor are composed of group III/V alloys.

5. The TOF depth imaging system of claim 1 , wherein the active layer is configured to absorb light having a wavelength in the short-wave infrared region of the electromagnetic spectrum.

6. The TOF depth imaging system of claim 5 , wherein the multiple sublayers of semiconductor comprise a multilayer structure of InGaAs/InGaAsP/InGaAsP/InGaAs or a multilayer structure of InAlAs/InGaAsP/InAlAs/InGaAs/InP.

7. The TOF depth imaging system of claim 1 , wherein the active layer is configured to absorb light having a wavelength in the mid-wave and long-wave infrared region of the electromagnetic spectrum and further wherein the multiple sublayers of semiconductor comprise a multilayer structure of InGaAsSb/InGaSb lattice matched to a GaSb substrate, or strain balanced to a GaSb substrate.

8. The TOF depth imaging system of claim 1 , wherein the active layer is configured to absorb light having a wavelength in the ultraviolet region of the electromagnetic spectrum and further wherein the multiple sublayers of semiconductor comprise a multilayer structure of InGaN/GaN/AlGaInN.

9. The TOF depth imaging system of claim 1 , wherein the active layer comprises stepped quantum wells composed of at least two quantum well sublayers of semiconductor, the at least two quantum well sublayers having different compositions.

10. The TOF depth imaging system of claim 9 , wherein the stepped quantum wells are two-step stepped quantum wells.

11. The TOF depth imaging system of claim 10 , wherein the two-step stepped quantum wells are composed of a first GaAs quantum well sublayer and a second Al x Ga 1-x As quantum well sublayer and the barriers are composed of Al x Ga 1-x As barriers.

12. The TOF depth imaging system of claim 1 , wherein the active layer comprises quantum wells having a type-II heterojunction.

13. The TOF depth imaging system of claim 1 , wherein the active layer comprises square quantum wells composed of a single layer of semiconductor and the TOF depth imaging system further comprises a voltage source configured to apply a delocalizing constant voltage to the electroabsorption modulator to achieve a delocalizing constant electric field.

14. The TOF depth imaging system of claim 1 , wherein the active layer has an overall thickness L and the overall thickness L is that which provides a minimum depth resolution coefficient K of the electroabsorption modulator.

15. The TOF depth imaging system of claim 14 , wherein the overall thickness L of the active layer is greater than a value at which value the depth resolution coefficient K would be minimized if the active layer did not comprise quantum wells configured to exhibit delocalized electron-hole behavior.

16. The TOF depth imaging system of claim 1 , wherein the active layer has an overall thickness L and the overall thickness L is in the range of from 1 μm to 20 μm.

17. The TOF depth imaging system of claim 1 , wherein the electroabsorption modulator is configured as a single-pass electroabsorption modulator.

18. The TOF depth imaging system of claim 1 , wherein the electroabsorption modulator is configured as a double-pass electroabsorption modulator.

19. The TOF depth imaging system of claim 1 , wherein the electroabsorption modulator is characterized by a first area and the image sensor is characterized by a second area, and further wherein the ratio of the first area to the second area is less than 1.

20. The TOF depth imaging system of claim 1 , further comprising a short-wave-infrared camera, wherein the image sensor is a component of the short-wave-infrared camera.

21. The TOF depth imaging system of claim 1 , wherein the modulation frequency f is at least 50 MHz.

22. A method of TOF depth imaging comprising:
illuminating an object with amplitude modulated light characterized by a wavelength λ and a modulation frequency f to generate reflected light from the object;
modulating the reflected light from the object using a surface-normal electroabsorption modulator to generate modulated reflected light, the electroabsorption modulator comprising
a top doped layer of semiconductor,
a bottom doped layer of semiconductor having opposite polarity to the top doped layer, and
an active layer between the top and bottom doped layers, the active layer configured as a superlattice structure comprising multiple sublayers of semiconductor configured to provide alternating quantum wells and barriers, the active layer comprising quantum wells configured to exhibit delocalized electron-hole behavior, wherein the electroabsorption modulator does not comprise an optical cavity; and
detecting the modulated reflected light from the electroabsorption modulator via an image sensor.

23. A TOF depth imaging system for providing a depth image of an object, the system comprising:
a light source configured to illuminate an object with amplitude modulated light characterized by a wavelength λ and a modulation frequency f,
a surface-normal electroabsorption modulator configured to receive and to modulate reflected light from the object with the modulation frequency f, the electroabsorption modulator comprising
a top doped layer of semiconductor,
a bottom doped layer of semiconductor having opposite polarity to the top doped layer, and
an active layer between the top and bottom doped layers, the active layer configured as a superlattice structure comprising multiple sublayers of semiconductor configured to provide alternating quantum wells and barriers, the active layer comprising quantum wells configured to exhibit delocalized electron-hole behavior, wherein the active layer has an overall thickness L and the overall thickness L is in the range of from 1 μm to 20 μm; and
an image sensor configured to receive and to detect modulated refl

Assignees

• Univ Northwestern

Inventors

• Mohseni Hooman

Classifications

• G01S7/4816 Primary

  of receivers alone · CPC title

• G01S17/894

  Three-dimensional [3D] imaging with simultaneous measurement of time-of-flight at a two-dimensional [2D] array of receiver pixels, e.g. time-of-flight cameras or flash lidar · CPC title

• G01S17/36

  with phase comparison between the received signal and the contemporaneously transmitted signal · CPC title

• G02F1/015

  based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction (G02F1/03 takes precedence) · CPC title

• G02F1/017

  Structures with periodic or quasi periodic potential variation, e.g. superlattices, quantum wells · CPC title