DE102018116957B4 - HETEROGENEOUS INTEGRATION OF CURVED MIRROR STRUCTURE FOR PASSIVE ALIGNMENT IN CHIP-SCALE LIDAR - Google Patents

Abstract

A coherent chip-scale lidar system (110) comprising:a photonic chip (230) comprising a light source (240), a transmit beam coupler (250) configured to provide an output signal (246), and a receive beam coupler (260) configured to receive a received signal (262) based on a reflection of the output signal (246) by a target;a transmit beam controller configured to transmit the output signal (246) out of the system;a receive beam controller configured to receive the received signal (262) into the system;a curved transmit beam mirror (210b) configured to reflect the output signal (246) from the transmit beam coupler (250) to the transmit beam controller, anda curved receive beam mirror (210a) configured to reflect the received signal (262) from the receive beam steering device to the receive beam coupler (260), wherein the curved transmit beam mirror (210b) and the curved receive beam mirror (210a) are formed in a substrate (320) that is heterogeneously integrated with the photonic chip (230);wherein the photonic chip (230) is formed on a packaging substrate (330), the transmit beam steering device and the receive beam steering device are also formed on the packaging substrate (330), and the transmit beam steering device and the receive beam steering device are not formed parallel to the photonic chip (230) on the packaging substrate (330).

Description

INTRODUCTION

The present disclosure relates to the heterogeneous integration of a curved mirror structure for passive alignment in a chip-scale lidar.

Vehicles (e.g., automobiles, trucks, construction equipment, agricultural equipment, automated factory equipment) are increasingly equipped with sensors that provide information to augment or automate vehicle operations. Example sensors include radio detection and ranging systems (radar systems), cameras, microphones, and light detection systems (LIDAR systems). An example lidar system is a coherent lidar system that transmits a frequency modulated continuous wave (FMCW) signal and relies on optical coherence between the transmitted signal and a return signal resulting from reflected scattering of the transmitted signal by a target to perform detection of the target. In an application, such as the automotive application, where reducing the size of various sensors and systems may be desirable, chip-scale lidar may be used. In a chip-scale lidar system, components such as the light source and photodetectors may be fabricated on an integrated circuit called a photonic chip. For effective operation of the lidar system, mirrors, which collimate light and act as intermediaries between the light-emitting and receiving elements on the photonic chip, and sensing elements (i.e., beam steering devices), which ultimately transmit light and receive reflections, must be properly aligned with both the elements on the photonic chip and the sensing elements.

US 2017 / 0 184 450 A1 describes an optical circuit using solid-state photonics. The optical circuit includes a phased array of solid-state waveguides that perform beam steering of an optical signal. The optical circuit includes a modulator for modulating a bit sequence to the carrier frequency of the optical signal, and the beam-steered signal includes the modulated bit sequence. The optical circuit includes a photodetector for detecting a reflection of the beam-steered optical signal. The optical circuit automatically correlates the reflection signal with the bit sequence to produce a processed signal.

US 2017 / 0 153 319 A1 describes a lidar system having a light source configured to emit light pulses. The lidar system further includes a plurality of optical links and a plurality of sensor heads. Each optical link couples the light source to a corresponding sensor head, and each optical link is configured to transmit at least a portion of the emitted light pulses from the light source to the corresponding sensor head. Each sensor head includes a scanner configured to scan light pulses across a field of view of the sensor head, wherein the scanned light pulses include the portion of the emitted light pulses transmitted from the light source to the sensor head through the corresponding optical link. Each sensor head also includes a receiver configured to detect at least a portion of the scanned light pulses scattered or reflected from a target located below the sensor head.

It is desirable to provide a heterogeneous integration of a curved mirror structure for passive alignment in a chip-scale lidar.

BRIEF DESCRIPTION

According to the invention, a coherent chip-scale lidar system includes a photonic chip including a light source, a transmit beam coupler for providing an output signal, and a receive beam coupler for receiving a received signal based on a reflection of the output signal by a target. The system also includes a transmit beam controller for transmitting the output signal out of the system and a receive beam controller for receiving the received signal into the system. A curved transmit beam mirror reflects the output signal from the transmit beam coupler to the transmit beam controller, and a curved receive beam mirror reflects the received signal from the receive beam controller to the receive beam coupler. The curved transmit beam mirror and the curved receive beam mirror are formed in a substrate that is heterogeneously integrated with the photonic chip.

In addition to one or more of the features described herein, the photonic chip includes alignment marks to facilitate passive alignment of the photonic chip with the substrate comprising the curved transmit beam mirror and the curved receive beam mirror.

In addition to one or more of the features described herein, the light source outputs a frequency modulated continuous wave as the output signal.

According to the invention, the photonic chip is formed on a packaging substrate.

According to the invention, the transmit beam control device and the receive beam control device are also formed on the packaging substrate.

According to the invention, the transmit beam control device and the receive beam control device are not formed parallel to the photonic chip on the packaging substrate.

In addition to one or more of the features described herein, a center distance between the curved transmit beam mirror and the curved receive beam mirror is the same as a distance between the transmit beam coupler and the receive beam coupler on the photonic chip.

In addition to one or more of the features described herein, the curved transmit beam mirror is formed using lithographic techniques with a curvature configured to collimate the output signal from the transmit beam coupler, and the curved receive beam mirror is formed using lithographic techniques with a curvature configured to focus the received signal from the receive beam steering device onto the photonic chip coupler.

In addition to one or more of the features described herein, a second curved transmit beam mirror is embossed based on a shape formed from the curved transmit beam mirror, and a second curved receive beam mirror is embossed based on a shape formed from the curved receive beam mirror.

In addition to one or more of the features described herein, the lidar system is located within or on a vehicle and detects a position and a velocity of an object relative to the vehicle.

According to the invention, a method of assembling a coherent lidar system includes forming a curved transmit mirror and a curved receive mirror side by side in a substrate as a curved mirror structure. The method also includes forming a photonic chip on a packaging substrate, the photonic chip including a light source, a transmit beam coupler configured to provide an output signal, and a receive beam coupler for receiving a received signal based on a reflection of the output signal by a target. The curved mirror structure is heterogeneously integrated with the photonic chip.

According to the invention, the method also includes arranging a transmit beam control device and a receive beam control device next to each other on the packaging substrate.

In addition to one or more of the features described herein, arranging the transmit beam control device and the receive beam control device includes separating the transmit beam control device and the receive beam control device by a distance equal to a center distance between the curved transmit mirror and the curved receive mirror.

In addition to one or more of the features described herein, the arrangement of the transmit beam steerer and the receive beam steerer is on a non-parallel plane with the photonic chip.

In addition to one or more of the features described herein, heterogeneously integrating the curved mirror structure with the photonic chip includes using alignment marks on the photonic chip to passively align the curved mirror structure with the photonic chip.

In addition to one or more of the features described herein, forming the curved transmit mirror and the curved receive mirror includes using photolithography and etching.

In addition to one or more of the features described herein, the method also includes forming a second curved transmit mirror and a second curved receive mirror, embossing the second curved transmit mirror and the second curved receive mirror using molds formed from the curved transmit mirror and the curved receive mirror, respectively.

In yet another exemplary embodiment, a vehicle includes a coherent chip-scale lidar system including a photonic chip including a light source, a transmit beam coupler for providing an output signal, and a receive beam coupler for receiving a received signal based on a reflection of the output signal by a target and focusing it on a receive beam coupler on the photonic chip. The system also includes a transmit beam steering device. device to transmit the output signal out of the system and a receive beam steering device to receive the received signal into the system. A curved transmit beam mirror reflects the output signal from the transmit beam coupler to the transmit beam steering device and a curved receive beam mirror reflects the received signal from the receive beam steering device to the receive beam coupler.

The curved transmit beam mirror and the curved receive beam mirror are formed in a substrate that is heterogeneously integrated with the photonic chip. The vehicle also includes a vehicle controller to use information from the lidar system to augment or automate vehicle systems.

In addition to one or more of the features described herein, the transmit beam steering device and the receive beam steering device are not formed parallel to the photonic chip on the packaging substrate.

In addition to one or more of the features described herein, a center distance between the curved transmit beam mirror and the curved receive beam mirror is the same as a distance between the transmit beam coupler and the receive beam coupler on the photonic chip.

The above features and advantages as well as other features and functions of the present disclosure will be readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

• 1 ist ein Blockdiagramm eines Szenarios, das ein kohärentes Chip-Scale-Lidar-System gemäß einer oder mehreren Ausführungsformen beinhaltet;
• 2 ist ein Blockdiagramm des Lidar-Systems mit heterogen integrierten gekrümmten Spiegeln gemäß einer oder mehreren Ausführungsformen;
• 3 zeigt eine Seitenansicht des Lidar-Systems, das eine exemplarische Anordnung des heterogen integrierten gekrümmten Spiegels gemäß einer oder mehreren Ausführungsformen zeigt; und
• 4 ist ein Prozessablauf eines Verfahrens zum Zusammenbauen eines Lidar-Systems mit heterogen integrierten gekrümmten Spiegeln gemäß einer oder mehreren Ausführungsformen.

Other features, advantages and details appear only by way of example in the following detailed description of the embodiments, which detailed description refers to the drawings, wherein:

• 1 is a block diagram of a scenario involving a coherent chip-scale lidar system, in accordance with one or more embodiments;
• 2 is a block diagram of the lidar system with heterogeneously integrated curved mirrors according to one or more embodiments;
• 3 shows a side view of the lidar system showing an exemplary arrangement of the heterogeneously integrated curved mirror according to one or more embodiments; and
• 4 is a process flow of a method for assembling a lidar system with heterogeneously integrated curved mirrors according to one or more embodiments.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present invention in its scope or uses. It should be understood that throughout the drawings, corresponding reference characters designate like or corresponding parts and features.

As previously mentioned, a mirror that collimates and directs light from the light emitting element on a photonic chip to a beam scanning device that emits the light from the lidar and a mirror that directs light from a beam scanning device and focuses it onto the light receiving element on a photonic chip must be properly aligned with the respective beam scanning device and element on the photonic chip. Embodiments of the methods and systems described herein relate to heterogeneous integration of a curved mirror structure for passive alignment in a chip-scale lidar. Heterogeneous integration refers to the assembly of separately manufactured components on a single chip. According to one or more embodiments, curved mirrors are lithographically formed in a substrate to enable nanometer-level precision in the formation. According to embodiments described in detail herein, the curved mirror structure including the substrate and the curved mirrors is aligned and heterogeneously integrated with a photonic chip.

In particular, alignment marks are used to precisely align and heterogeneously integrate the curved mirror structure with the photonic chip. Using the alignment marks, the curved mirrors and the photonic chip are passively aligned, so that a closed-loop controller is not required to bring the mirrors into alignment according to an active alignment procedure. The curved mirrors are also aligned with the beam steering devices, which are mirrors or other reflectors that can be actuated by a two-dimensional (2D) microelectromechanical system (MEMS).

According to an exemplary embodiment, 1 a block diagram of a scenario rios, which includes a coherent chip-scale lidar system 110. The lidar system 110 includes a heterogeneous integration of a curved mirror 210 ( 2 ) with a photonic chip 230 ( 2 ) for passive alignment, as described with reference to 3 and 4 described in detail. The 1 The vehicle 100 shown is a motor vehicle 101. A coherent lidar system 110, which is described with reference to 2 described in more detail, is shown on the roof of the motor vehicle 101. According to alternative or additional embodiments, one or more lidar systems 110 may be located elsewhere in or on the vehicle 100. Another sensor 115 (e.g., camera, sonar, radar system) is also shown. Information obtained from the lidar system 110 and one or more other sensors 115 may be provided to a controller 120 (e.g., an electronic control unit (ECU)) for image or data processing, target detection, and subsequent vehicle control.

The controller 120 may use the information to control one or more vehicle systems 130. In an exemplary embodiment, the vehicle 100 may be an autonomous vehicle, and the controller 120 may perform known vehicle operation control using information from the lidar system 110 and other sources. In alternative embodiments, the controller 120 may augment vehicle operation using information from the lidar system 110 and other sources as part of a known system (e.g., collision avoidance system, adaptive cruise control system). The lidar system 110 and one or more other sensors 115 may be used to detect objects 140, such as the pedestrian 145 walking in 1 The controller 120 may include processing circuitry, which may include an application specific integrated circuit (ASIC), an electronic circuit, a hardware computer processor (shared or dedicated or group), and memory executing one or more software or firmware programs, combinational logic circuitry, and/or other suitable components that provide the described functionality.

2 is a block diagram of the lidar system 110 with heterogeneously integrated curved mirrors 210a, 210b (generally referred to as 210) according to one or more embodiments. The center distance c between the curved mirrors 210a, 210b is shown in 2 indicated and with reference to 3 The alignment marks 201 are also further discussed with reference to 3 The exemplary lidar system 110 is a bistatic system that includes a separate path for transmitting light and for receiving reflected light from the target 140. That is, two separate beam steering devices, which in the exemplary embodiment of 2 shown 2D MEMS mirrors 220a, 220b (generally referred to as 220).

The photonic chip 230 includes a light source 240. The light source 240 may include components that are not located on the photonic chip 230. For example, the light source 240 may be a laser diode that includes, for example, an oscillator on the photonic chip 230 and an off-chip power source. The modulation of the power source results in a frequency modulated continuous wave (FMCW) signal 242 output from the light source 240. The signal 242 is split by a splitter 245 into the output signal 246, which is provided to the transmit beam coupler 250 (e.g., grating or edge coupler) for transmission. The FMCW signal 242 is also split into the local oscillator (LO) signal 247. The output signal 246 is reflected from the curved mirror 210b to the 2D MEMS mirror 220b. As 2 , the transmission from the 2D MEMS mirror 220b is scattered by the target 140. A portion of this scattered reflection is received by the 2D MEMS mirror 220a and reflected by the curved mirror 210a to the receive beam coupler 260 (e.g., grating or edge coupler). The distance g between the transmit beam coupler 250 and the receive beam coupler 260 is in 2 indicated and further with reference to 3 discussed.

The received signal 262 is combined with the LO signal 247 at the combiner 265 and then split into combined signals 267a and 267b (generally referred to as 267). Each combined signal 267 is provided to a photodetector 270a, 270b (generally referred to as 270). The received signal 262 and the LO signal 247 in each combined signal 267 interfere with each other in each photodetector 270. The photodetectors 270 convert the result of the interference into electrical currents 275a, 275b (generally referred to as 275), also referred to as clock signals. The two photodetectors 270 are used in accordance with a known symmetric detector technique to cancel the intensity noise in the LO signal 247 (which is caused by the light source 240 and thus is the same in the output signal 246 and the LO signal 247) that is common to both photodetectors 270. The electrical currents 275 from each of the photodetectors 270 are combined and processed to provide three-dimensional information such as the range to the target 140 and the relative speed of the target 140 to the lidar. System 110 as a function of two-dimensional spatial coordinates. The processing may be performed, for example, within the lidar system 110 by a processor 280 or outside the lidar system 110 by the controller 120. The processor 280 may include processing circuitry similar to that discussed for the controller 120.

3 shows a side view of the lidar system 110 showing an exemplary arrangement of the heterogeneously integrated curved mirror 210 according to one or more embodiments. 3 shows a curved mirror 210 and a 2D MEMS mirror 220 because a side view is shown. A second curved mirror 210 and a corresponding second 2D MEMS mirror 220 are respectively shown behind the visible curved mirror 210 and the visible 2D MEMS mirror 220 from the 3 In this case, the center distance c between the curved mirrors 210, which is shown in 2 is indicated, correspond to the distance g between the transmit beam grating coupler 250 and the receive beam grating coupler 260, which are arranged on the photonic chip 230 in 2 shown. How 3 , the curved mirror 210 is formed in a substrate 320. The substrate 320 may include material that is thermally matched to the photonic chip 230. The substrate 320 is connected to the photonic chip 230 by metal interconnects 310 or other interconnect material, such as epoxy, that are aligned with the alignment marks 201 on the photonic chip 230. Alignment is ensured by the alignment marks 325 on the substrate 320 in which the curved mirror 210 is formed.

The curved mirrors 210 are formed by lithographic techniques to allow for precise dimensions and curvatures. The precise curvature of the curved mirror 210b ensures collimation of the output signal 246 from the photonic chip 230 directed to the 2D MEMS mirror 220, and the precise curvature of the curved mirror 210a ensures focusing of the received signal 262 from the 2D MEMS mirror 220 directed to the photonic chip 230. The curved mirrors 210 may be coated to improve reflection. How 3 shows, the photonic chip 230 and the 2D MEMS mirror 220 are formed in a packaging substrate 330.

According to an exemplary embodiment, a curved primary mirror 210 may be formed using lithographic techniques such that subsequent curved mirrors 210 in subsequent lidar systems 110 may be formed using embossing based on the primary mirror. Alignment marks 201 on the photonic chip 230 facilitate precise alignment of the curved mirror 210 with the photonic chip 230. That is, the substrate 320 in which the curved mirrors 210 are formed is bonded to the photonic chip 230 using the alignment marks 201. When curved primary mirrors 210 are formed, subsequent embossed curved mirrors 210 may still be precisely aligned with the photonic chip 230 based on the alignment marks 201. Using the alignment marks 201, the curved mirrors 210 and the photonic chip 230 are passively aligned without the need for a closed-loop active alignment control process that involves moving the curved mirrors 210 until alignment is achieved.

How 3 shows, the curved mirrors 210 are also passively aligned with the corresponding 2D MEMS mirrors 220. Proper alignment results in the center of the light beam aligned by the curved transmit mirror 210b being aligned with the center of the 2D transmit MEMS mirror 220b, and the center of the light beam aligned by the 2D MEMS receive mirror 220a being aligned with the center of the curved receive mirror 210a. An exemplary, non-limiting width d of the beam transmitted between the curved mirrors 210 and the 2D MEMS mirrors 220 is 2.3 millimeters (mm). Collimated light from the curved mirror 210b to the 2D MEMS mirror 220b is scattered out of the lidar system 110. Similarly, scattered reflected light directed from the 2D MEMS mirror 220a to the curved mirror 210a is collimated by the curved mirror 210a and provided to the photonic chip 230. As 3 , the 2D MEMS mirrors 220 are not parallel to the photonic chip 230. An exemplary angle A may be 12 degrees and an exemplary height h3 may be 5.2 mm. An exemplary height h1 may be 1 mm and h2 may be 4 mm. The dimensions provided are intended to be exemplary and in no way limiting.

4 is a process flow of a method 400 for assembling a lidar system 110 with heterogeneously integrated curved mirrors 210 according to one or more embodiments. At block 410, designing two curved mirrors 210 involves taking several factors into account. As previously mentioned, the center distance distance c of the curved mirrors 210 is designed to be identical to the distance g between the transmit beam coupler 250 and the receive beam coupler 260 on the photonic chip 230. Additionally, the three-dimensional curvature of the curved mirror 210 used in the transmit path is designed for appropriate beam diameter and divergence of the output signal 246, and the three-dimensional curvature of the curved mirror 210 used in the receive path is designed for appropriate focusing of the received signal 262 onto the receive beam grating coupler 260. Fabricating the curved mirrors 210 using three-dimensional lithography and etching at block 420 ensures nanometer-level precision for the dimensions and curvature.

According to an exemplary embodiment, the lithographic techniques are used only for the curved primary mirrors 210. According to this embodiment, in block 430, embossing of curved mirrors 210 from the primary mirror for each subsequent lidar system 110 is performed. At block 440, performing heterogeneous integration of the curved mirrors 210 with the photonic chip 230 includes using aligned thermocompression (i.e., metal bonding) or adhesive bonding. The alignment marks 201 on the photonic chip 230 and the alignment marks 325 on the substrate 320 are used to ensure proper passive alignment without the need for active closed-loop control.

While the above disclosure has been described with reference to exemplary embodiments, those skilled in the art will understand that various changes may be made and corresponding other parts may be substituted for the individual parts without departing from the scope of the disclosure. Moreover, many modifications may be made to adapt a particular material situation to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiments disclosed, but will include all embodiments falling within the scope thereof.

Claims (8)

A coherent chip-scale lidar system (110) comprising: a photonic chip (230) comprising a light source (240), a transmit beam coupler (250) configured to provide an output signal (246), and a receive beam coupler (260) configured to receive a received signal (262) based on a reflection of the output signal (246) by a target; a transmit beam controller configured to transmit the output signal (246) out of the system; a receive beam controller configured to receive the received signal (262) into the system; a curved transmit beam mirror (210b) configured to reflect the output signal (246) from the transmit beam coupler (250) to the transmit beam controller, and a curved receive beam mirror (210a) configured to reflect the received signal (262) from the receive beam controller to the receive beam coupler (260), wherein the curved transmit beam mirror (210b) and the curved receive beam mirror (210a) are formed in a substrate (320) heterogeneously integrated with the photonic chip (230); wherein the photonic chip (230) is formed on a packaging substrate (330), wherein the transmit beam control device and the receive beam control device are also formed on the packaging substrate (330), and the transmit beam control device and the receive beam control device are not formed parallel to the photonic chip (230) on the packaging substrate (330). Lidar system (110) to Claim 1 wherein the photonic chip (230) includes alignment marks to facilitate passive alignment of the photonic chip (230) with the substrate (320) comprising the curved transmit beam mirror (210b) and the curved receive beam mirror (210a). Lidar system (110) to Claim 1 , wherein a center distance between the curved transmit beam mirror (210b) and the curved receive beam mirror (210a) is the same as a distance between the transmit beam coupler (250) and the receive beam coupler (260) on the photonic chip (230), the curved transmit beam mirror (210b) is formed using lithographic techniques with a curvature configured to collimate the output signal (246) from the transmit beam coupler (250), the curved receive beam mirror (210a) is formed using lithographic techniques with a curvature configured to focus the received signal (262) from the receive beam steering device onto the photonic chip coupler, a second curved transmit beam mirror is embossed based on a shape formed from the curved transmit beam mirror (210b), and a second curved Receiving beam mirror is embossed based on a shape formed from the curved receiving beam mirror (210a). Lidar system (110) to Claim 1 wherein the lidar system (110) is located within or on a vehicle and is configured to detect a position and a velocity of an object relative to the vehicle. A method of assembling a coherent lidar system (110), comprising: forming a curved transmit mirror (210b) and a curved receive mirror (210a) side by side in a substrate (320) as a curved mirror structure; forming a photonic chip (230) on a packaging substrate (330), the photonic chip (230) including a light source (240), a transmit beam coupler (250) configured to provide an output signal (246), and a receive beam coupler (260) for receiving a received signal (262) based on a reflection of the output signal (246) by a target; heterogeneously integrating the curved mirror structure with the photonic chip (230); and arranging a transmit beam control device and a receive beam control device side by side on the packaging substrate (330). Procedure according to Claim 5 wherein arranging the transmit beam control device and the receive beam control device includes separating the transmit beam control device and the receive beam control device by an equal distance as a center distance between the curved transmit mirror (210b) and the curved receive mirror (210a), and arranging the transmit beam control device and receive beam control device on a non-parallel plane with the photonic chip (230). Procedure according to Claim 5 wherein heterogeneously integrating the curved mirror structure with the photonic chip (230) includes using alignment marks on the photonic chip (230) to passively align the curved mirror structure with the photonic chip (230). Procedure according to Claim 5 wherein forming the curved transmit mirror (210b) and the curved receive mirror (210a) includes using photolithography and etching, and the method also includes forming a second curved transmit mirror and a second curved receive mirror, embossing the second curved transmit mirror and the second curved receive mirror using molds formed from the curved transmit mirror (210b) and the curved receive mirror (210a), respectively.

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