US-12618974-B2 - Integrated bound-mode angular sensors

US12618974B2US 12618974 B2US12618974 B2US 12618974B2US-12618974-B2

Abstract

An angular sensitive time-of-flight position sensor device is provided and includes an array of pixels each comprising: a planar waveguide structure; a collection area with a grating pattern at a specific periodicity to couple incident light into the planar waveguide structure; at least one detector placed outside of the collection area and in a plane different from that of the planar waveguide structure; an output coupler to direct the light from planar waveguide to the at least one detector; a mask to shield the at least one detector from direct illumination; a narrow band light source that illuminates a field-of-view; a first electronics configured to detect the time-of-flight of light retroreflected, scattered, or both incident onto the position sensor and configured to provide distance ranging information; and a second electronics configured to interpret and retain time-of-flight information and configured to communicate with external electronics for system applications.

Inventors

Steven R.J. Brueck
Payman Zarkesh-Ha
Alexander Neumann

Assignees

UNM RAINFOREST INNOVATIONS

Dates

Publication Date: 20260505
Application Date: 20200314

Claims (12)

1 . An angular sensitive time-of-flight position sensor system device comprising: a light source that illuminates a field-of-view; an array of pixels fabricated atop a substrate, each pixel of the array of pixels comprising: a planar waveguide structure supporting a single transverse electric (TE) mode and a single transverse magnetic (TM) mode; a collection area with a grating structure pattern to couple light reflected and scattered from objects in the field-of-view that is illuminated into a mode of planar waveguide structure without any intervening imaging optical components; at least one detector, responsive to the light reflected and scattered from objects in the field-of-view that is illuminated, arranged peripherally to the collection area and vertically displaced from the center line of the planar waveguide structure; at least one output coupler to direct light propagating in the planar waveguide to the at least one detector; a cover to shield the at least one detector from direct illumination by the light reflected and scattered from objects in the field-of-view that is illuminated; a first electronics configured to measure time-of-flight of light reflected and scattered from the objects in the field-of-view that is illuminated; and a second electronics configured to interpret and retain time-of-flight information for each pixel and configured to communicate with external electronics for system applications.
2 . The system of claim 1 wherein the at least one output coupler is another grating structure and the at least one detector is incorporated in the plane of the substrate.
3 . The system of claim 1 wherein the at least one output coupler is configured by arranging the at least one detector in a region of evanescent fields of a waveguide mode in a cladding of the planar waveguide structure.
4 . The system of claim 1 wherein the grating structure pattern is a 2D grating pattern.
5 . The system of claim 4 wherein the 2D grating pattern has substantially the same periodicity in two orthogonal directions.
6 . The system of claim 4 wherein the 2D grating pattern has different periodicities in two orthogonal directions.
7 . The system of claim 1 wherein gratings in the collection area and gratings over at least one detector area have different coupling constants to allow use of a detector area smaller than the collection area.
8 . The system of claim 1 further comprising a silicon wafer as the substrate wherein the wafer provides mechanical support for the planar waveguide structure, incorporates the detectors and the electronics that provide the time-of-flight information.
9 . The system of claim 1 wherein the planar waveguide structure and the electronics are fabricated on two substrates and bonded together along with thru-silicon-vias for electrical connection.
10 . The sensor system of claim 1 , wherein a period and an area of each grating structure pattern is chosen to selectively couple light reflected and scattered from the objects in the field-of-view and incident on the collection area from a restricted set of angles.
11 . The sensor system of claim 10 , wherein the period and area of each collection area grating structure pattern across the array of pixels provide angularly resolved position information on the objects in the field-of-view.
12 . The sensor system of claim 1 , wherein the light source produces light in narrow spectral band, with a bandwidth less than an acceptance bandwidth of the collection area grating structure pattern.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a U.S. National Phase application of PCT/US2020/022855 filed Mar. 14, 2020, which claims priority to U.S. provisional application Ser. No. 62/818,965 filed Mar. 15, 2019, the entireties of which are incorporated herein by reference. GOVERNMENT SUPPORT STATEMENT This invention was made with government support under Grant No. EEC0812056 awarded by the National Science Foundation and under Grant DE-AR0000942 awarded by ARPA-E. The government has certain rights to the invention. FIELD OF THE INVENTION This invention is related to the field of angularly resolved optical detection, specifically to the use of multiplexed angularly sensitive bound-mode sensor arrays. BACKGROUND OF THE INVENTION Many emerging sensing applications require information on of the directionality of light incident from free space onto a detector. Examples include: lidar for autonomous platforms such as self-driving cars where obstacle detection and avoidance are a critical safety need; people counting in enclosed spaces for building HVAC control and energy conservation; activity sensing in indoor spaces without the use of cameras for privacy preservation, these spaces could include hospitals and nursing homes, schools, private homes, etc. These sensors could detect conditions, such as falls, and provide alerts for emergency response. The increasing senior citizen demographic is leading to increased need for such services. One approach to these needs is the use of time-of-flight (TOF) sensors, which rely on reflection and scattering of an optical signal and measurement of the time duration from the initiation of the pulse to the detection, to provide a distance measurement. Commercially available TOF sensors are single channel, including a source and a single detection element. Thus, these TOF sensors are not suitable for applications that require input from multiple directions or covering a large field of view. In particular, the lidar application requires sensing objects in multiple directions to avoid collisions, the people counting requires a high angular field of view to reduce the density of sensors that would be required for single direction sensors. The monitoring of spaces requires a low-resolution sensing, for example to see if someone has fallen, without the privacy concerns associated with imaging solutions such as cameras, but at the same time requires a wide field of view to assure coverage of, for example, a large meeting room. Some current solutions to the autonomous vehicle lidar problem include actively rotating frameworks which have issues with both size and reliability. An integrated solution would resolve many of the concerns. The cost and installation logistics of a large network of fixed angle sensors for indoor spaces would be prohibitive, a multi-angle sensor would be a much more efficient solution. An integrated solution requires a) a transmitter at a fixed wavelength (λ0) irradiating a wide angular cone with pulses with sufficient rise time to allow resolution commensurate with the application; b) retroreflections from objects within the irradiated space back to a detection array; c) coupling of the free space retroreflections (approximating plane waves at sufficient distances) to a semiconductor detector array retaining the incident angular information; and d) time-of-flight electronics. Grating coupling to a bound waveguide mode provides a mechanism that retains the angular information. The grating equation that describes the phase matching condition required for coupling from free space propagation to a bound waveguide mode for a geometry in which the incident angle is in the plane defined by the grating wavevector (normal to the grating lines) and the waveguide surface normal is given by: 2⁢⁢⁢sin⁢⁢θinλ0+j⁢2⁢di=±2⁢λ0⁢nm⁢o⁢d⁢eTE,TM⁡(λ0)(1) where θin is the angle of incidence (−1<sin θin<1), j is an integer (±1, ±2, . . . ), λ0 is the optical wavelength, di is the period of the i'th grating in the array; and nmodeTE,TM(λ0) is the modal wave vector (different for TE and TM polarization) typically given by a dispersion relation that takes into account the waveguide structure and the incident wavelength. The extension of this result to all angles of incidence (known as conical diffraction) will be discussed below. The bound mode can be either a surface plasma wave at a metal-dielectric interface, bound to the surface as a result of the negative dielectric constant of the metal, or a dielectric waveguide mode formed by a cladding-waveguide-cladding stack. In either case, the modal index nmodeTE,TM(λ0) is greater than the index of free space (nfree_space=1). A major advantage of a dielectric stack bound waveguide mode is that it is close to lossless (assuming low-loss dielectric materials such as SiO2 and Si3N4 or others). The only losses arise from fabrication imperfections (scattering sites/surface roughness) and from the re-radiation into free space as