US20200371215A1

US20200371215A1 - Solid state lidar with silicon photonics and metasurface

Info

Publication number: US20200371215A1
Application number: US16/654,817
Authority: US
Inventors: Aditya Jain; Zoran Jandric; Krishnan Subramanian
Original assignee: Seagate Technology LLC
Current assignee: Luminar Technologies Inc
Priority date: 2019-05-24
Filing date: 2019-10-16
Publication date: 2020-11-26
Also published as: US11460545B2; US20200371208A1

Abstract

A device includes a substrate an array of disk-shaped structures arranged above the substrate. Each disk-shaped structure includes an aperture filled with an optoelectrical material. A method includes passing a light beam through a metasurface. The method also includes varying voltage applied to the metasurface to change a phase of the light beam to steer the light beam in a two-dimensional pattern.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No. 62/852,858, filed May 24, 2019, which is herein incorporated by reference in its entirety.

SUMMARY

In certain embodiments, a device includes a substrate an array of disk-shaped structures arranged above the substrate. Each disk-shaped structure includes an aperture filled with an optoelectrical material.
In certain embodiments, system includes a substrate that is at least semi-transparent. The system also includes a tunable metasurface that is optically coupled to the substrate and arranged to steer a light beam in two dimensions.
In certain embodiments, a method includes passing a light beam through a metasurface. The method also includes varying voltage applied to the metasurface to change a phase of the light beam to steer the light beam in a two-dimensional pattern.
While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a LIDAR device, in accordance with certain embodiments of the present disclosure.

FIG. 2A shows a top view of a disk-shaped structure of the LIDAR device of FIG. 1, and FIG. 2B shows a perspective view of the disk-shaped structure, in accordance with certain embodiments of the present disclosure.

FIGS. 3A and 3B show schematics of electrical components of the LIDAR device of FIG. 1, in accordance with certain embodiments of the present disclosure.

FIG. 4 shows an exemplary schematic of a scanning path generated by the LIDAR device of FIG. 1, in accordance with certain embodiments of the present disclosure.

FIG. 5 shows a block diagram of a method of using the LIDAR device of FIG. 1, in accordance with certain embodiments of the present disclosure.

FIG. 6 shows a block diagram of a making the LIDAR device of FIG. 1, in accordance with certain embodiments of the present disclosure.

While the disclosure is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the disclosure to the particular embodiments described but instead is intended to cover all modifications, equivalents, and alternatives falling within the scope of the appended claims.

DETAILED DESCRIPTION

Certain embodiments of the present disclosure relate to measurement devices and techniques for light detection and ranging, which is commonly referred to as LIDAR, LADAR, etc. Current commercially-available LIDAR devices are mechanical and typically use a series of spinning mirrors that steer many narrow light beams. These devices are expensive, consume a large amount of power, and have moving pieces that can break or become misaligned during use, which negatively affects performance.
An alternative to mechanical LIDAR devices are solid state LIDAR devices. Solid state LIDAR devices consume less power, are cheaper to manufacture, and can be designed to have a smaller footprint than mechanical LIDAR devices. Certain embodiments of the present disclosure are accordingly directed to solid state LIDAR systems, methods, and devices that can be used to steer light to generate scanning patterns of light (e.g., paths along which light is scanned) with a two-dimensional field of view.
FIG. 1 shows a schematic of a device 100 such as a LIDAR/LADAR device that can emit and steer light. The device 100 includes a substrate 102 and a metasurface above the substrate 102. The metasurface shown in FIG. 1 includes an array of resonators (e.g., Mie resonators) in the form of an array of disk-shaped structures 104 (hereinafter referred to as the disks 104) arranged above and coupled to the substrate 102. The resonators of the metasurface can be considered to be non-radiating, subwavelength resonators. Non-radiating metasurfaces include metasurfaces that cannot radiate light without the aid of a light scattering mechanism (e.g., scattering structures discussed herein) whereas radiating metasurfaces imply metasurfaces that can radiate light without the aid of a light scattering mechanism.
As discussed in more detail below, the resonators can comprise dielectric metamaterials with optoelectrical properties that can be controlled (e.g., by altering voltages applied to respective resonators) to alter polarization of light passing through the resonators. The resonators use carrier accumulation in an optoelectrical material to alter (e.g., tune) the phase of the light passing through the resonators. Altering polarization of the light can alter the angle at which light emits from the resonators. As such, the metasurface can be described as a tunable metasurface that is used for free space illumination and that is capable of steering light in two dimensions.
For simplicity, the device 100 in FIG. 1 is shown with only twelve disks 104, but it is contemplated that the device 100 can include thousands of disks 104 (e.g., 1,000-100,000 disks 104). For example, the array of disks 104 can include a 200×200 disk array such that the device 100 includes 40,000 disks 104. The number of disks 104 in the array may depend on a number of factors, including but not limited to the desired overall size of the device 100, the desired size of the light beam emitted by the device 100, and the permissible amount of interference within the emitted light beams. The larger the array the less likely the device 100 will be susceptible to side-lobe-based interference.
In certain embodiments, the centers of adjacent disks 104 within the array of disks are separated from each other by substantially the same distance. In certain embodiments, to avoid interference within the light emitted from the disks 104, the spacing distance is around or at least one half of the wavelength of light that is passed through the disks 104. For example, for a light beam at a wavelength of 1550 nm, the spacing between the centers of the disks 104 can be 750 nm. Such spacing helps prevent side-lobe-based interference. In certain embodiments, the disks 104 are intended to be substantially uniform such that each disk 104 has substantially the same dimensions and orientation. In certain embodiments, the disks 104 have diameters in the range of 600-800 nm (e.g., 650 nm, 700 nm, 750 nm) and heights in the range of 75-125 nm (e.g., 80 nm, 90 nm, 100 nm, 110 nm). Given the small dimensions, once the disks 104 are manufactured, the dimensions of the disks 104 may vary from disk to disk. For example, if the intended diameter of the disks 104 is 700 nm, some disks 104 may have diameters of 705 nm while others have diameters of 690 nm. As another example, the disks 104 may not form perfectly uniform disks.
The substrate 102 can comprise one or more transparent or semi-transparent materials such as silicon dioxide (SiO₂) or polymers (e.g., polycarbonate, high-index plastics). The device 100 can include a cover 106, which can comprise one or more transparent or semi-transparent materials such as SiO₂or polymers and which can encapsulate the disks 104.
In certain embodiments, the disks 104 comprise one or more transparent or semi-transparent materials such as silicon (e.g., polysilicon). In certain embodiments, the silicon is doped with a conductive material such that the disks 104 are electrically conductive. In other embodiments, the disks 104 comprise silicon and one or more layers comprising an optoelectrical material such as indium tin oxide. In such embodiments, the optoelectrical material can be deposited as a layer on top of the disks 104.
In certain embodiments, each disk 104 includes a scattering structure such as an aperture that extends through the disk 104, a protrusion that extends from the disk 104, or a combination of an aperture and a protrusion. As will be described in more detail below, the disks 104 shown in FIGS. 1, 2A, and 2B feature apertures 108. In certain embodiments, the scattering structure is shaped and positioned such that the disks 104 are asymmetrical (e.g., one half of the disk 104 is nota mirror replica of the other half of the disk 104). Without a scattering structure, light directed to the disks 104 would rotate within the disks 104 and no resonance of the light would be excited. The scattering structure, therefore, helps to excite a resonance (e.g., a fundamental dark mode Mie resonance) of the light passing through the disks 104.
As noted above, the disks 104 in FIGS. 1, 2A, and 2B include apertures 108, which are shown as being rectangular-shaped (e.g., slot-shaped) although other shapes can be used. In certain embodiments, the apertures 108 are filled with an optoelectrical material such as indium tin oxide or liquid crystal materials. In embodiments with protrusions as the scattering structure, the protrusion can comprise an optoelectrical material such as indium tin oxide. In embodiments with layered silicon and an optoelectrical material, the aperture 108 can be filled with air (e.g., an empty aperture) instead of being filled with an optoelectrical material. In certain embodiments, the optoelectrical material is positioned in areas of the disks 104 with the most electrical field which increases the effectiveness of the optoelectrical material and its ability to assist with steering light passing through the disks 104.
Each disk 104 is shown as being mechanically and electrically coupled to an electrode 110, which comprises one or more conductive materials such as gold. The electrode 110 may be deposited in a hole in the disk 104. In certain embodiments, the electrodes 110 are positioned in areas of the disk 104 that generate an electric field that is lower than other areas of the disk 104. Such positioning minimizes how the electrodes 110 affect the optical properties of the disks 104. For the disks 104 shown in FIGS. 1, 2A, and 2B, the area with the lowest electric field is near the center of the disks 104 so the electrodes 110 are positioned at a center area of each disk 104. As will be described in more detail below, the electrodes 110 direct voltage through the disks 104. As the applied voltage is varied, light passed through the disks 104 can be steered along a desired path.
As shown in FIG. 1, the substrate 102 is optically coupled to a light source 112. In certain embodiments, the light source 112 is manufactured separately from the other components of the device 100 and later attached to the substrate 102 or to a waveguide (not shown) positioned between the light source 112 and the substrate 102. The light source 112 emits a light beam and is arranged such that the emitted light beam is directed towards the substrate 102 or to a separate waveguide. As will be described in more detail below, the emitted light passes through the substrate 102 towards a bottom side of the disks 104, then through the disks 104 (which individually steer—over time—portions of the emitted light passing through the respective disks 104), and then through the cover 106 such that a light beam is emitted from the device 100.
The light source 112 can be a laser (e.g., a laser such as a VCSEL and the like) or a light-emitting diode. In certain embodiments, the light emitted is coherent light. In certain embodiments, the light source 112 emits light within the infrared spectrum (e.g., 905 nm or 1550 nm frequencies) while in other embodiments the light source 110 emits light within the visible spectrum (e.g., a 485 nm frequency). In certain embodiments, the light source 112 is configured to emit light in pulses. Non-limiting examples of pulse rates for the light source 112 include 100-1000 kHz, 200-800 kHz, and 300-600 kHz. Although the measurement devices described herein reference are typically described in the context of pulsed, time-of-flight LIDAR approaches, the device 100 can be used for continuous-wave LIDAR, frequency-modulated LIDAR, amplitude-modulated LIDAR, etc., as well.
As mentioned above, when the light emitted from the light source 112 passes through the disks 104, the voltage applied to the disks 104 via the electrodes 110 can be varied such that the light can be steered. FIG. 3A shows a schematic of the electrodes 110 electrically coupled to a power source 114 (e.g., an amplifier) via respective conductive traces 116. For clarity, in FIG. 3A, only a few of the electrodes 110 are shown for the array of disks 104 (and therefore only a few of the conductive traces 116) and the disks 104 themselves are not shown. The power source 114 provides the voltage to the conductive traces 116, which pass the voltage to the electrodes 110, which pass the voltage through the disks 104 to a ground connection 120 (shown in FIG. 3B). FIG. 3B shows a schematic of disks 104 that are coupled to conductive bridges 118 (e.g., doped silicon bridges) that are interconnected between the disks 104 and that ultimately lead to the ground connection 120. The power source 114 is coupled to a controller 122 (shown in FIG. 3A), which is configured to control how the applied voltage is applied across the various traces 116 (and therefore electrodes 110 and disks 104). The controller 122 may be physically located on the device 100 (e.g., the same circuit package of the power source 114) or may be off-device.
As mentioned above, the light emitted from the light source 112 passes through the disks 104. When the voltage applied to the electrodes 110 (and therefore applied to the disks 104) is altered, the angle at which the emitted light is directed from the disks 104 is altered. Changes in voltage applied to the disks 104 changes the carrier density within the disks 104 which changes the effective index of the mode which changes the phase of the light passing through the disks 104. As the phase changes, the angle at which the emitted light is directed from the disks 104 changes. The equations below explain how phase changes in the X-direction (see FIG. 1) and phase changes in the Y-direction (see FIG. 1) affect the angle at which emitted light is directed from the disks 104:
$\begin{matrix} \sin (ϕ_{t}) = \frac{1}{k} \frac{d ϕ}{dx} & EQ . 1 \\ \cos (θ_{t}) \sin (ϕ_{t}) = \frac{1}{k} \frac{d ϕ}{dy} & EQ . 2 \end{matrix}$
where k represents a wave vector constant of the emitted light (which is dependent on the wavelength of the emitted light), where φ represents an angle with respect to a given disk 104 shown in FIG. 2B, and where θ represents another angle with respect to a given disk 104 shown in FIG. 2B.
In certain embodiments, the voltage applied to each electrode 110 (and therefore each disk 104) is different. For example, the voltage applied to each electrode 110 can be different but the difference between the applied voltages from electrode 110 to electrode 110 can be the same (e.g., when the voltage applied to the first electrode 110 in a row of the array is 50 mV, the voltage applied to the next electrode 110 in the row is 60 mV and the voltage applied to the next electrode 110 in the row is 70 mV, and so on).
The voltages applied to each electrode 110 can be modified over time to create a light pattern. FIG. 4 shows an example light pattern 124 created over time when the emitted light 126 (represented by dotted lines in FIG. 4) from the device 100 is steered. In certain embodiments, the light pattern 124 is a raster-scan-like pattern. The emitted light 126 is transmitted out of the device 100 (e.g., through the cover 106) towards objects. In certain embodiments, the emitted light 126 is a coherent light beam that diverges as it propagates through air.
A portion of the emitted light 126 reflects off the objects and returns through the cover 106. This reflected light, referred to as backscattered light, is represented in FIG. 4 by a phantom line and reference number 128. The backscattered light 128 can be detected by a detector 130, which includes one or more photodetectors/sensors. In response to receiving the focused backscattered light 128, the detector 130 generates one or more sensing signals, which are ultimately used to detect the distance and/or shapes of objects that reflect the emitted light 126 back to the detector 130. In certain embodiments, the detector 130 includes one or more focusing devices such as lenses that focus the backscattered light 128 towards the one or more sensors.
FIG. 5 outlines steps of a method 200 for using the device 100. The method 200 includes passing a light beam through a metasurface (block 202 in FIG. 5). The method 200 also includes varying a voltage applied to the metasurface to change a phase of the light beam to steer the light beam in a two-dimensional pattern (block 204 in FIG. 5).
FIG. 6 outlines steps of a method 300 for making the device 100. First, a layer (e.g., silicon dioxide) for the substrate 102 is deposited (e.g., sputter deposition or vacuum deposition) (block 302 in FIG. 6). Next, a layer (e.g., silicon) for the disks 104 is deposited on the substrate 102 (block 304 in FIG. 6). In certain embodiments, the layer for the disks 104 is doped to make the disks 104 conductive. The shape of the disks 104 and the apertures 108 are defined using photolithography (e.g., masks, reactive ion etching) (block 306 in FIG. 6). The optoelectrical material can be deposited to fill the apertures 108 (e.g., via masks and deposition) (block 308 in FIG. 6) and/or to create protrusions on the disks 104. The electrodes 110 can be created by making a hole that at least partially extends within the disks 104 and depositing a conductive material to fill the hole (block 310 in FIG. 6). Other steps can be carried out to make the device 100. For example, the disks 104 and electrodes 110 can be encapsulated by depositing silicon dioxide on top of the disks 104 and the electrodes 110 (e.g., for the cover 106). As another example, the light source 112 can be optically coupled directly or indirectly to the substrate 102.
Various modifications and additions can be made to the embodiments disclosed without departing from the scope of this disclosure. For example, while the embodiments described above refer to particular features, the scope of this disclosure also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present disclosure is intended to include all such alternatives, modifications, and variations as falling within the scope of the claims, together with all equivalents thereof.

Claims

We claim:

1. A device comprising:

a substrate; and

an array of disk-shaped structures arranged above the substrate, each disk-shaped structure includes an aperture filled with an optoelectrical material.

2. The device of claim 1, wherein the optoelectrical material comprises indium tin oxide or a liquid-crystal material.

3. The device of claim 1, wherein the array of disk-shaped structures includes 10,000-50,000 disk-shaped structures.

4. The device of claim 1, further comprising:

electrodes coupled to each of the disk-shaped structures.

5. The device of claim 4, wherein the electrodes are positioned at a center of each of the disk-shaped structures.

6. The device of claim 4, wherein the electrodes comprise gold. The device of claim 1, further comprising:

a power source coupled to the electrodes and a controller, wherein the controller is configured to vary voltage applied to the electrodes.

8. The device of claim 7, wherein the voltage is varied to steer a beam emitted from the array of disk-shaped structures.

9. The device of claim 1, wherein the disk-shaped structures comprise silicon.

10. The device of claim 1, further comprising:

a light source arranged to direct a light beam towards the substrate towards a bottom side of the disk-shaped structures.

11. The device of claim 10, wherein separate portions of the light beam pass through each disk-shaped structure, wherein the disk-shaped structures are configured to steer the portions of the light beam in two dimensions.

12. The device of claim 11, further comprising:

a cover in which the disk-shaped structures are embedded, wherein a single beam is emitted from the cover.

13. The device of claim 1, wherein the disk-shaped structures are separated by at least one half of a wavelength of light passed through the disk-shaped structures.

14. The device of claim 1, wherein the aperture is slot-shaped.

15. The device of claim 1, wherein the aperture makes the disk-shaped structures nonsymmetrical.

16. A system comprising:

a substrate that is at least semi-transparent; and

a tunable metasurface optically coupled to the substrate and arranged to steer a light beam in two dimensions.

17. The system of claim 16, further comprising:

a light source optically coupled to the substrate and to the tunable metasurface and arranged to direct the light beam towards the substrate and the metasurface.

18. The system of claim 16, further comprising:

a light sensor arranged to detect light backscattered from the light beam.

19. A method comprising:

passing a light beam through a metasurface; and

varying voltage applied to the metasurface to change a phase of the light beam to steer the light beam in a two-dimensional pattern.

20. The method of claim 19, wherein the metasurface includes an array of disk-shaped structures, wherein passing the light beam through the metasurface includes passing separate portions of the light beam through individual disk-shaped structures in the array.