A frequency-modulated continuous-wave lidar chip based on a laser array

Abstract

The application discloses a frequency-modulated continuous wave laser radar chip based on a laser array, which comprises a substrate, a semiconductor laser array chip, an interference structure chip, a transmitting-receiving chip and a photonic lead waveguide structure; the semiconductor laser chip, the coherent detection chip and the transmitting-receiving chip are arranged on the substrate; the semiconductor laser array chip and the interference structure chip and the interference structure chip and the transmitting-receiving chip are coupled and connected through the photonic lead waveguide structure. The laser array chip emits light from both ends simultaneously, one end enters the transmitting-receiving chip as detection light and is emitted into free space, the returned light enters the interference structure chip after being received, the other end is coupled and interfered with the returned light in the interference structure chip as reference light, and the light is converted into an electric signal through a photoelectric detector. The chip significantly reduces the size, weight and power consumption of the frequency-modulated continuous wave laser radar system and improves the scanning speed and resolution of the frequency-modulated continuous wave laser radar system.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic technology, and in particular to a frequency-modulated continuous wave lidar chip based on a laser array. Background Technology

[0002] LiDAR, as a detection and ranging technology, is widely used in fields such as autonomous driving, robotics, and surveying. Traditional LiDAR uses time-of-flight ranging, which is limited by time resolution and is susceptible to interference from the environment and other light sources. Frequency-modulated continuous-wave (FM-WW) LiDAR uses coherent detection to convert distance information into frequency information, resulting in higher ranging resolution, a wider range, stronger anti-interference capabilities, and the ability to directly measure velocity, making it an important future development direction for LiDAR. However, compared to time-of-flight LiDAR, FM-WW LiDAR has a more complex system structure and is more difficult to integrate.

[0003] LiDAR needs to scan space during detection. To improve the scanning rate, multiple lasers are typically used for simultaneous multi-point scanning. However, frequency-modulated continuous wave (FM-CW) lidar requires the laser output signal to be split into probe and reference beams and then interfered. If multiple lasers are used simultaneously, the complexity of the system increases further, making integration difficult.

[0004] Frequency-modulated continuous-wave (FM-CHW) lidar based on laser arrays can simultaneously emit multiple wavelengths of light without interference. Combined with optical phased arrays, it enables simultaneous multi-point scanning, improving the scanning rate and resolution of FM-CHW lidar systems and possessing significant application value. Because this system requires interference between the probe and reference beams, the optical signals from different channels do not interfere with each other and are not affected by external light sources, giving it unique advantages compared to other lidar systems. However, existing FM-CHW lidar chips lack sufficient integration, making it difficult to integrate laser arrays and failing to fully meet the requirements of future lidar development. Summary of the Invention

[0005] The problem to be solved by this invention is to provide a frequency-modulated continuous wave lidar chip based on a laser array, which can realize the integration of a frequency-modulated continuous wave lidar system, significantly reduce the size, weight and power consumption of the system, improve the resolution of the lidar system, and solve the problem of waveguide structure intersection when using a laser array as a light source.

[0006] The present invention adopts the following technical solution: a frequency-modulated continuous wave lidar chip based on a laser array, comprising: a substrate, a semiconductor laser array chip, an interference structure chip, a transmitting and receiving chip, and a photonic lead waveguide structure;

[0007] The semiconductor laser chip, the interference structure chip, and the transmitter / receiver chip are all placed on the substrate;

[0008] The semiconductor laser array chip and the interference structure chip, as well as the interference structure chip and the transmitting and receiving chip, are all coupled and connected through a photonic lead waveguide structure.

[0009] One end of the semiconductor laser array chip is coupled to the input terminal of the emitter coupler of the interference structure chip, and the other end is coupled to the input terminal of the reference light of the interference structure chip.

[0010] The output terminal of the transmitter coupler of the interference structure chip is coupled to the transmitter structure of the transmitter-receiver chip, and the input terminal of the receiver coupler is coupled to the receiver structure of the transmitter-receiver chip.

[0011] Preferably, the substrate is a tungsten-copper substrate; the semiconductor laser array chip, the interference structure chip, and the transmitter-receiver chip are all mounted on the tungsten-copper substrate, and the height difference between different chips is compensated by the shape design of the tungsten-copper substrate; and the semiconductor laser array chip, the interference structure chip, and the transmitter-receiver chip are all mounted on their respective thin-film circuits to provide driving current and output electrical signals.

[0012] Preferably, both ends of the semiconductor laser array chip are coated with anti-reflection films to generate frequency-modulated continuous wave light signals, which are emitted simultaneously from both ends of the laser array.

[0013] One end, coupled to the input of the transmitter coupler of the interference structure chip, is used to generate the lidar detection light, which enters the transmitter-receiver chip and is emitted into free space. The return light is received and then enters the interference structure chip. The other end, coupled to the input of the reference light of the interference structure chip, is used as the reference light for the lidar. It couples and interferes with the return light in the interference structure chip and is converted into an electrical signal by a photodetector.

[0014] Preferably, the semiconductor laser array chip includes a grating layer fabricated based on reconstructed equivalent chirp technology. A sampling structure is fabricated in the grating unit through one holographic exposure and one sampling photolithography. A phase shift structure corresponding to the sampling structure is introduced in the +1 level grating unit. The +1 level grating unit is used as a resonant cavity. Each channel in the laser array achieves different lasing wavelengths by setting different sampling periods of the sampling structure.

[0015] Preferably, the optical frequency is linearly modulated by applying a specific periodic nonlinear triangular wave current to the semiconductor laser array chip through the laser, and the optical wave is amplified by a monolithically integrated semiconductor optical amplifier.

[0016] Preferably, the interference structure chip includes: a multimode interference coupler structure, a branch waveguide structure, and a photodetector structure;

[0017] The branched waveguide structure is divided into two ports, which are used to interfere the probe light with the reference light to form a coherent balanced detection structure; the electrodetector structure is used to convert the optical signal into an electrical signal output.

[0018] Preferably, the interference structure chip couples multiple probe optical signals into a single output through a multimode interference coupler structure, and evenly distributes the single-input return optical signal into multiple waveguides, thereby realizing multi-channel coupling of transmitted and returned light.

[0019] Preferably, the transmitting and receiving chip has an optical phased array structure for transmitting and scanning light; and a grating coupler structure or an optical phased array structure for receiving the returned light.

[0020] Preferably, in the transmitting and receiving chip, light of different wavelengths simultaneously enters the transmitting optical phased array structure to achieve multi-point simultaneous scanning.

[0021] Preferably, the transmit-receive chip expands the return light reception range by using a lens group.

[0022] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0023] 1. This invention uses photonic wire bonding technology to build a path between semiconductor laser array chips, interference structure chips and optical phased array chips, achieving more compact chip integration and significantly reducing the size, weight and power consumption of frequency modulated continuous wave lidar systems.

[0024] 2. This invention uses a laser array as a light source, with multiple different wavelengths of light emitted simultaneously without affecting each other. Combined with an optical phased array, it can achieve planar scanning, thereby improving the scanning rate and resolution of the frequency modulated continuous wave lidar system.

[0025] 3. This invention uses the emitted light from both ends of the laser array simultaneously, avoiding the waste of optical power while separating the reference optical path from the probe optical path, thus solving the problem of waveguide structure intersection when using a laser array as a light source. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the frequency-modulated continuous wave lidar chip in Embodiment 1 of the present invention;

[0027] Figure 2 This is a schematic diagram of the structure of the frequency-modulated continuous wave lidar chip in Embodiment 2 of the present invention;

[0028] Figure 3This is a schematic diagram illustrating the application of the frequency-modulated continuous wave lidar chip in a lidar system according to an embodiment of the present invention.

[0029] Explanation of markings in the diagram:

[0030] 1-Substrate; 2-Semiconductor laser array chip; 3-Interference structure chip; 4-Transmitter and receiver chip; 5-Photonic lead waveguide structure; 301-Multimode interference coupler; 302-Branch waveguide; 303-Photodetector; 401-Optical phased array; 402-Grate coupler. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the application will be further described in detail below with reference to the accompanying drawings. The described embodiments are only a part of the embodiments involved in this invention. All non-innovative embodiments based on this invention by other researchers in the art are within the protection scope of this invention.

[0032] Example 1

[0033] This embodiment provides a frequency-modulated continuous wave lidar chip based on a laser array, see appendix. Figure 1 It includes: substrate 1, semiconductor laser array chip 2, interference structure chip 3, transmit and receive chip 4, and photonic lead waveguide structure 5.

[0034] The semiconductor laser array chip 2, the interference structure chip 3, and the transmitter and receiver chip 4 are all placed on the substrate 1 and are connected to each other through the photonic lead waveguide structure 5.

[0035] The interference structure chip 3 includes: a multimode interference coupler 301, a branch waveguide 302, and a photodetector 303. The transmit and receive chip 4 includes: an optical phased array 401 and a grating coupler 402.

[0036] In this embodiment, the semiconductor laser array chip 2 has a grating layer, which is fabricated based on the reconstructed equivalent chirp technique. A sampling structure is created in the grating unit through a single holographic exposure and a single sampling photolithography step. A phase shift structure corresponding to the sampling structure is introduced in the +1 level grating unit. The +1 level grating unit is used as a resonant cavity. Different lasing wavelengths are achieved by adjusting the sampling period of the sampling structure, as shown in the following formula:

[0037]

[0038] Where, n eff λ represents the effective refractive index, λ represents the lasing wavelength, p represents the sampling period, and Λ0 represents the uniform grating period defined by holographic exposure.

[0039] In this embodiment, the multimode interference coupler 301 is an N×1 multimode interference coupler structure, and the branch waveguide 302 is a 2×2 branch waveguide structure.

[0040] The semiconductor laser array chip 2 is used to generate frequency-modulated continuous wave optical signals and emits them simultaneously from both ends of the laser array. One of them is used as a probe light and enters the N×1 multimode interference coupler structure, while the other is used as a reference light. The N×1 multimode interference coupler structure is used to couple the multiple probe light signals into a single output and distribute the single input return light signal evenly into the multiple waveguides.

[0041] The 2×2 branch waveguide structure is used to interfere the probe light with the reference light to form a coherent balanced detection structure; the photodetector 303 is used to convert the optical signal into an electrical signal output.

[0042] The optical phased array structure 401 is used for the emission and scanning of detection light. Light of different wavelengths is emitted at different angles, enabling simultaneous scanning of multiple points. The grating coupler 402 is used to receive the returned light signal.

[0043] Example 2

[0044] See appendix Figure 2 The transmitting and receiving chip has an optical phased array 401 for transmitting and scanning light; the receiving structure is also an optical phased array 401 for receiving the returned light.

[0045] Compared with Embodiment 1, this embodiment replaces the grating coupler 402 with an optical phased array 401 to receive the returned light.

[0046] It should be noted that using an optical phased array 401 can achieve directional reception of the returned light and suppress stray signals from other directions. However, since the transmission and reception angles need to be synchronized, the control complexity is greatly increased. It is suitable for scenarios with high precision requirements or a lot of external interference. Using a grating coupler 402 can maximize the reception of the returned light without additional control and is suitable for general scenarios.

[0047] Further, see Appendix Figure 3 The present invention applies the frequency-modulated continuous wave lidar chip based on laser array and the receiving lens system together in the lidar system. The transmitting and receiving chip 4 expands the receiving range of the returned light by using the lens group.

[0048] Specifically, in Embodiment 1, the optical axis of the receiving lens system should be aligned with the center of the grating coupler 402, and the focal plane of the receiving lens system should coincide with the grating coupler 402; in Embodiment 2, the optical axis of the receiving lens system should be aligned with the center of the grating coupling structure of the optical phased array receiving structure 401, and the focal plane of the receiving lens system should coincide with the grating coupling structure of the optical phased array receiving structure 401.

[0049] In use, taking Example 1 as an example, a linear frequency modulated continuous wave optical signal is generated by applying a specific periodic nonlinear triangular wave current to the semiconductor laser array chip 2. The signal is simultaneously output from both ends of the laser array chip. One end serves as the reference light entering a 2×2 branch waveguide, and the other end serves as the probe light entering an N×1 multimode interference coupler for wave combining and output. The signal is then emitted into free space through the optical phased array 401 and simultaneously scanned at multiple points. After being reflected by the target object, the signal reaches the receiving lens system and is then received by the grating coupler 402 and enters the lidar chip. After being split into multiple paths by the N×1 multimode interference coupler, the signal enters the 2×2 branch waveguide and undergoes interference mixing with the reference light to generate a beat frequency optical signal. Finally, the signal is converted into a beat frequency electrical signal by the photodetector 303, and the frequency of the signal is related to the distance to the target object.

[0050] When the object under test is stationary, the frequency of the beat frequency signal is proportional to the distance to the object. When the object moves, due to the Doppler effect, the beat frequency signal will have two frequencies. The frequency difference between the two frequencies is proportional to the radial velocity of the object, and the average value is proportional to the distance to the object. After data processing, the distance and radial velocity of the object can be obtained.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent substitutions, and improvements made by those skilled in the art to the above embodiments without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A frequency-modulated continuous wave lidar chip based on a laser array, characterized in that, include: Substrate (1), semiconductor laser array chip (2), interference structure chip (3), transmit and receive chip (4) and photonic lead waveguide structure (5); The semiconductor laser chip (2), the interference structure chip (3), and the transmitter-receiver chip (4) are all placed on the substrate (1); The semiconductor laser array chip (2) and the interference structure chip (3), as well as the interference structure chip (3) and the transmitting and receiving chip (4), are coupled and connected through a photonic lead waveguide structure (5). One end of the semiconductor laser array chip (2) is coupled to the input end of the emitter coupler of the interference structure chip (3), and the other end is coupled to the input end of the reference light of the interference structure chip (3). The output end of the transmitter coupler of the interference structure chip (3) is coupled to the transmitter structure of the transmitter-receiver chip (4), and the input end of the receiver coupler is coupled to the receiver structure of the transmitter-receiver chip (4). Both ends of the semiconductor laser array chip (2) are coated with anti-reflection films to generate frequency-modulated continuous wave light signals and emit them simultaneously from both ends of the laser array. One end of the laser radar detector is coupled to the input end of the transmitter coupler of the interference structure chip (3) and enters the transmitter receiver chip (4) to be emitted into free space. The return light is received and then enters the interference structure chip (3). The other end of the laser radar detector is coupled to the input end of the reference light of the interference structure chip (3) and is used as the reference light of the laser radar. It is coupled and interfered with the return light in the interference structure chip and converted into an electrical signal by the photodetector. The interference structure chip (3) couples multiple probe optical signals into a single output through a multimode interference coupler (301), and distributes the single-input return optical signal evenly into multiple waveguides, thereby realizing multi-channel coupling between the transmitted light and the returned light. In the transmitting and receiving chip (4), light of different wavelengths enters the transmitting optical phased array (401) simultaneously to achieve multi-point simultaneous scanning.

2. The frequency-modulated continuous wave lidar chip based on a laser array according to claim 1, characterized in that: The substrate (1) is a tungsten copper substrate; The semiconductor laser array chip (2), the interference structure chip (3) and the transmitting and receiving chip (4) are all mounted on a tungsten copper substrate, and the height difference between different chips is compensated by the shape design of the tungsten copper substrate; The semiconductor laser array chip (2), the interference structure chip (3), and the transmitter and receiver chip (4) are all mounted on their respective thin-film circuits to provide driving current and output electrical signals.

3. The frequency-modulated continuous wave lidar chip based on a laser array according to claim 1, characterized in that: The semiconductor laser array chip (2) includes a grating layer fabricated based on reconstructed equivalent chirp technology. A sampling structure is fabricated in the grating unit through one holographic exposure and one sampling photolithography. A phase shift structure corresponding to the sampling structure is introduced in the +1 level grating unit. The +1 level grating unit is used as a resonant cavity. Each channel in the laser array achieves different lasing wavelengths by setting different sampling periods of the sampling structure, as shown in the following formula: ； in, λ represents the effective refractive index, and λ represents the lasing wavelength. Indicates the sampling period. This represents the uniform grating period defined in holographic exposure.

4. The frequency-modulated continuous wave lidar chip based on a laser array according to claim 1, characterized in that: By applying a specific periodic nonlinear triangular wave current to the semiconductor laser array chip (2) through the laser, the optical frequency is linearly modulated, and the optical wave is amplified by a monolithic integrated semiconductor optical amplifier.

5. The frequency-modulated continuous wave lidar chip based on a laser array according to claim 1, characterized in that: The interference structure chip (3) includes: a multimode interference coupler (301), a branch waveguide (302), and a photodetector (303); The branch waveguide (302) is divided into two ports for interfering the probe light with the reference light to form a coherent balanced detection structure; the electrical detector (303) is used to convert the optical signal into an electrical signal output.

6. The frequency-modulated continuous wave lidar chip based on a laser array according to claim 1, characterized in that: The transmitting and receiving chip (4) has an optical phased array (401) as the transmitting structure, which is used to detect the emission and scanning of light; and a grating coupler (402) or optical phased array (401) as the receiving structure, which is used to receive the returned light.

7. The frequency-modulated continuous wave lidar chip based on a laser array according to claim 6, characterized in that: The transmit-receive chip (4) expands the return light reception range by using a lens group.

Images