Patent Application
20150293224
The present invention relates generally to the field of environment sensing, and more particularly to the use of Time of Flight (ToF) lidar sensors for real-time three-dimensional mapping and object detection, tracking identification and/or classification.
A lidar sensor is a light detection and ranging sensor. It is an optical remote sensing module that can measure the distance to a target or objects in a scene, by irradiating the target or scene with light, using pulses (or alternatively a modulated signal) from a laser, and measuring the time it takes photons to travel to said target or landscape and return after reflection to a receiver in the lidar module. The reflected pulses (or modulated signals) are detected, with the time of flight and the intensity of the pulses (or modulated signals) being measures of the distance and the reflectivity of the sensed object, respectively.
Conventional lidar sensors utilize mechanically moving parts for scanning laser beams. In some systems, including certain systems used in automotive applications, such as advanced driver assist systems (ADAS) and autonomous driving systems, it is preferred to use solid state sensors for a variety of potential advantages including but not limited to higher sensor reliability, longer sensor lifetime, smaller sensor size, lower sensor weight, and lower sensor cost.
Radio frequency (RF) delay lines used for the creation of radar phased arrays were used several decades ago for the solid state steering of radar signals. Photonic integrated circuit (PIC) based delay lines combined with detectors and RF antenna arrays were used two decades ago to improve the precision of delays in the solid state steering of radar signals. PICs with microscale and nanoscale devices can be used to produce optical phased arrays (OPAs), comprising tunable optical delay lines and optical antennas, for the solid state steering of laser beams. Phased Arrays in the optical domain that are produced to date are complex, costly and/or have a different purpose than beam forming and beam steering; some combine spatial filters, optical amplifiers and ring lasers (U.S. Pat. No. 7,339,727), some involve a plurality of optical input beams (U.S. Pat. No. 7,406,220), some involve volume diffraction gratings and a plurality of input directions (U.S. Pat. No. 7,428,100), some combine beams of a plurality of wavelengths (U.S. Pat. No. 7,436,588), some have optical phase reference sources and gain elements (U.S. Pat. No. 7,489,870), some have predetermined areas in the field of view and a plurality of beam forming elements (U.S. Pat. No. 7,532,311), and some have multiple frequencies and multiple optical phase reference sources (U.S. Pat. No. 7,555,217).
A lidar-based apparatus and method are used for the solid state steering of laser beams using Photonic Integrated Circuits (PICs). Integrated optic design and fabrication micro- and nanotechnologies are used for the production of chip-scale optical splitters that distribute an optical signal from a laser essentially uniformly to an array of pixels, said pixels comprising tunable optical delay lines and optical antennas. Said antennas achieve out-of-plane coupling of light.
As the delay lines of said antenna-containing pixels in said array are tuned, each antenna emits light of a specific phase to form a desired far-field radiation pattern through interference of these emissions. Said array serves the function of solid state optical phased array (OPA).
By incorporating a large number of antennas, high-resolution far-field patterns can be achieved by an OPA, supporting the radiation pattern beam forming and steering needed in solid state lidar, as well as the generation of arbitrary radiation patterns as needed in three-dimensional holography, optical memory, mode matching for optical space-division multiplexing, free space communications, and biomedical sciences. Whereas imaging from an array is conventionally transmitted through the intensity of the pixels, the OPA allows imaging through the control of the optical phase of pixels that receive coherent light waves from a single source.
The following drawings are illustrative of embodiments of the present invention and are not intended to limit the invention as encompassed by the claims forming part of the application.
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A lidar-based apparatus and method are used for the solid state steering of laser beams using Photonic Integrated Circuits (PICs). Integrated optic design and fabrication micro- and nanotechnologies are used for the production of chip-scale optical splitters that distribute an optical signal from a laser essentially uniformly to an array of pixels, said pixels comprising tunable optical delay lines and optical antennas. Said antennas achieve out-of-plane coupling of light.
As the delay lines of said antenna-containing pixels in said array are tuned, each antenna emits light of a specific phase to form a desired far-field radiation pattern through interference of these emissions. Said array serves the function of solid state optical phased array (OPA).
By incorporating a large number of antennas, high-resolution far-field patterns can be achieved by an OPA, supporting the radiation pattern beam forming and steering needed in solid state lidar, as well as the generation of arbitrary radiation patterns as needed in three-dimensional holography, optical memory, mode matching for optical space-division multiplexing, free space communications, and biomedical sciences. Whereas imaging from an array is conventionally transmitted through the intensity of the pixels, the OPA allows imaging through the control of the optical phase of pixels that receive coherent light waves from a single source.
Said optical splitters can be based on a variety of optical devices, including but not limited to:
Said optical splitters can be symmetric 1×N splitters (1 input, N outputs) or asymmetric splitters functioning as power taps.
Said optical splitters can be passive, or they can be tunable for splitting ratio adjustability.
Said delay lines can be based on true time delay, where a physical path length difference is used to generate the delay.
Said delay lines can be tuned based on a variety of methods, including but not limited to:
Wavelength alone can be used to raster a radiation pattern across the far field, resulting in a passive device where phase tuning elements are avoided, typically at the cost of a relatively wide beam in the far field and/or no means of arbitrarily shaping the radiation pattern. Given the typical result obtained with moderate fabrication accuracy, when wavelength tuning is used, it is preferably combined with phase tuning. However when the chip fabrication is done with high accuracy, resulting in a passive device with the desired radiation pattern shape in the far field, and when the application does not require varying the radiation pattern shape, as in lidar applications, steering can be done with wavelength tuning alone, significantly simplifying the device structure and controls.
When phase tuning is used, each pixel can have independent phase control for maximum flexibility and optimal control of the far field radiation pattern, or banding can be used to provide phase tuning to a plurality of pixels with one control signal for the simplification of the design, fabrication, testing, control and operation.
The actuation mechanisms used to tune said delay lines, and said optical splitters when they are tunable, can be any of a variety of mechanisms, including but not limited to:
The optical antennas can be any of a variety of nanostructures that can couple light out of the plane of the PIC, including but not limited to:
The out-of-plane coupling elements can also serve as collimators (e.g., HOE), or can be coupled to collimating optical elements.
The chip containing the OPA PIC is preferably compatible with a complementary metal-oxide-semiconductor (CMOS) process, and is preferably based on a silicon on insulator (SOI) structure.
The chip containing the OPA PIC is preferably held at an essentially constant temperature. Methods to hold the chip at an essentially constant temperature include but are not limited to the use of (a) heaters that hold the chip at a design temperature that exceeds the highest specified operating temperature or (b) thermoelectric coolers (TECs) that that hold the chip at any design temperature, even if lower than the highest specified operating temperature. In all chip temperature stabilization schemes, feedback signals from thermistors or resistance temperature detectors (RTDs) are preferably used to close the electrical control loop and maintain the desired temperature.
When an OPA PIC is based on a CMOS process, it can be integrated with control and/or processing electronics that use the same CMOS process.
The OPA PIC can create in the far field a radiation pattern that is spot which is small relative to the scene being mapped, and can scan it horizontally and vertically to produce two-dimensional scans which, combined with ToF distance measurements, produce three-dimensional maps; for this radiation pattern, on the receiving end of a lidar apparatus, a single receiver or a one-dimensional array of receivers or a two-dimensional array of receivers can be used to collect the ToF data that correspond to depth.
The OPA PIC can also create a radiation pattern whose envelope is elongated, to provide one-dimensional coverage, and can scan the pattern essentially perpendicularly to its long dimension to produce two-dimensional scans, and can be combined with ToF distance measurements to produce three-dimensional maps; for this radiation pattern, on the receiving end of a lidar apparatus, one-dimensional array of receivers or a two-dimensional array of receivers can be used to collect the ToF data that correspond to depth.
The OPA PIC can also create a radiation pattern whose envelope essentially covers the scene being mapped (e.g., a two-dimensional array of spots, a square, a rectangle, a disc, an ellipse, a racetrack shape), and can be combined with ToF distance measurements to produce three-dimensional maps; for this radiation pattern, on the receiving end of a lidar apparatus, a two-dimensional array of receivers can be used to collect the ToF data that correspond to depth.
For all OPA-PIC-containing lidar apparatus, multiple OPA chips can be used and/or OPA chips can be combined with mechanical motion to increase the field of view.
The present application claims the benefit of priority from U.S. Provisional Application Ser. No. 61/821,656, filed May 9, 2013. 7,339,727 B1March 2008Rothenberg7,406,220 B1July 2008Christensen7,428,100 B2September 2008Smith7,436,588 B2October 2008Rothenberg7,489,870 B2February 2009Hillis7,532,311 B2May 2009Henderson7,555,217 B2July 2009Hillis
