Frequency Modulated Continuous Wave LiDAR

Abstract

This invention relates to the field of lidar technology and provides a frequency-modulated continuous wave lidar, including a frequency-modulated light source, a transceiver module, a PLC chip, and a coherent receiving module. The frequency-modulated light source emits a laser beam. The PLC chip is connected between the frequency-modulated light source and the transceiver module. The PLC chip integrates a first beam splitting unit and a first mode conversion unit. The first beam splitting unit splits the received laser beam into at least one probe beam and at least one local oscillator beam, each with an optical power of less than or equal to 50mW. The coherent receiving module is connected to both the PLC chip and the transceiver module. The coherent receiving module receives the local oscillator beam output from the PLC chip and the echo signal output from the transceiver module, combines the local oscillator beam and the echo signal, performs coherent frequency beats, and finally transmits the signal to an external signal processing module. The frequency-modulated continuous wave lidar provided by this invention is small in size and highly integrated.

Description

Technical Field

[0001] This invention belongs to the field of lidar technology, and particularly relates to a frequency-modulated continuous wave lidar. Background Technology

[0002] LiDAR is one of the core sensors widely used in autonomous driving scenarios, capable of collecting three-dimensional information about the external environment. Based on their detection mechanism, LiDAR can be mainly divided into two types: Time-of-Flight (ToF) and Frequency Modulated Continuous Wave (FMCW) LiDAR. FMCW LiDAR employs coherent reception, using a balanced detection method at the receiver that combines signal light and local oscillator light. This effectively reduces interference from ambient light, improving ranging performance. Furthermore, in addition to providing spatial coordinate information, FMCW LiDAR can also provide velocity information, thus being considered the next-generation mainstream LiDAR technology.

[0003] However, compared to ToF lidar, FMCW lidar uses a large number of optoelectronic devices, resulting in a more complex system structure. Currently, most FMCW lidar systems use discrete components, leading to low integration, high cost, and large size. Silicon-based optoelectronics technology can integrate multiple discrete components onto a single chip, effectively reducing system size and increasing integration. However, traditional silicon-based optoelectronic platforms use silicon waveguides to transmit optical signals, which are limited by silicon's two-photon absorption effect, preventing the transmission of high-power optical signals. In the FMCW lidar system architecture, the average output power of the frequency-modulated light source at the transmitting end can reach 100 milliwatts. Directly coupling the frequency-modulated light source to the silicon photonic chip would excite a significant two-photon absorption effect, causing additional losses and potentially burning out the silicon waveguide, leading to chip failure. Therefore, current FMCW lidar frequency-modulated light sources are generally connected to an external fiber optic splitter and undergo several beam splits before connecting to the silicon photonic chip. This approach involves numerous discrete fiber optic components, resulting in a large system size and low integration. Summary of the Invention

[0004] The purpose of this invention is to provide a frequency modulated continuous wave lidar, which aims to solve the technical problems of large size and low integration of existing frequency modulated continuous wave lidars.

[0005] The present invention is implemented as follows: a frequency-modulated continuous wave lidar includes a frequency-modulated light source, a transceiver module, a PLC chip, and a coherent receiving module.

[0006] The frequency-modulated light source is used to emit a laser beam;

[0007] The PLC chip is connected between the frequency-modulated light source and the transceiver module. The PLC chip integrates a first beam splitting unit and a first mode-spot conversion unit. The first beam splitting unit is used to split the received laser beam into at least one probe beam and at least one local oscillator beam. The optical power of each local oscillator beam is less than or equal to 50mW. The first mode-spot conversion unit is used to perform mode field matching between the light from the external devices of the PLC chip and the light from the internal devices of the PLC chip.

[0008] The transceiver module is used to receive the detection light output by the PLC chip, and to shape and collimate the detection light to control it to scan the target object. It is also used to receive the echo signal reflected by the target object and to transmit the echo signal to the coherent receiving module.

[0009] The coherent receiving module is connected to the PLC chip and the transceiver module respectively. The coherent receiving module is used to receive the local oscillator light output by the PLC chip and the echo signal output by the transceiver module, combine the local oscillator light and the echo signal and perform coherent beat frequency, and finally transmit the signal to the external signal processing module.

[0010] In an optional embodiment, the first beam splitting unit includes a first beam splitter. The input end of the first beam splitter is connected to the output end of the frequency-modulated light source through the first mode conversion unit. The first output end of the first beam splitter is connected to the input end of the transceiver module through the first mode conversion unit for outputting the probe light. The second output end of the first beam splitter is connected to the corresponding input end of the coherent receiving module through the first mode conversion unit for outputting the local oscillator light.

[0011] In an optional embodiment, the first beam splitting unit includes a first beam splitter and a second beam splitting unit. The input end of the first beam splitter is connected to the output end of the frequency-modulated light source through the first mode conversion unit. The first output end of the first beam splitter is connected to the input end of the transceiver module through the first mode conversion unit for outputting the probe light. The second output end of the first beam splitter is connected to the input end of the second beam splitting unit for outputting local oscillator light. The output end of the second beam splitting unit is connected to the corresponding input end of the coherent receiving module through the first mode conversion unit for splitting the local oscillator light output by the first beam splitter into multiple beams and outputting them to the coherent receiving module.

[0012] In an optional embodiment, the second beam splitting unit includes a second beam splitter, the input end of the second beam splitter is connected to the second output end of the first beam splitter, and the two output ends of the second beam splitter are respectively connected to the corresponding input ends of the coherent receiving module through the first mode conversion unit;

[0013] Alternatively, the second beam splitting unit includes a second beam splitter and a third beam splitter arranged sequentially along the local oscillator light transmission direction. The input end of the second beam splitter is connected to the second output end of the first beam splitter. The first output end of the second beam splitter is connected to the corresponding input end of the coherent receiving module through the first mode conversion unit. The second output end of the second beam splitter is connected to the input end of the third beam splitter. The two output ends of the third beam splitter are respectively connected to the input end of the probe optical path in the coherent receiving module through the first mode conversion unit.

[0014] Alternatively, the second beam splitting unit includes a second beam splitter and a fourth beam splitter arranged sequentially along the local oscillator light transmission direction. The input end of the second beam splitter is connected to the second output end of the first beam splitter. The first output end of the second beam splitter is connected to the corresponding input end of the coherent receiving module through the first mode conversion unit. The second output end of the second beam splitter is connected to the input end of the fourth beam splitter. The first output end of the fourth beam splitter is connected to the corresponding input end of the coherent receiving module through the first mode conversion unit. The second output end is connected to the input end of the nonlinear calibration optical path in the coherent receiving module through a sequentially connected optical delay line and the first mode conversion unit.

[0015] Alternatively, the second beam splitting unit includes a second beam splitter, a third beam splitter, and a fourth beam splitter. The input end of the second beam splitter is connected to the second output end of the first beam splitter. The first output end of the second beam splitter is connected to the input end of the third beam splitter, and the second output end is connected to the input end of the fourth beam splitter. The two output ends of the third beam splitter are respectively connected to the input end of the probe optical path in the coherent receiving module through the first mode conversion unit. The first output end of the fourth beam splitter is connected to the corresponding input end of the coherent receiving module through the first mode conversion unit. The second output end is connected to the input end of the nonlinear calibration optical path in the coherent receiving module through a sequentially connected optical delay line and the first mode conversion unit.

[0016] In an optional embodiment, the first speckle conversion unit includes a first speckle converter, a second speckle converter, and a fifth speckle converter;

[0017] The first mode field converter is connected between the frequency-modulated light source and the first beam splitting unit, and is used to perform mode field matching between the frequency-modulated light source and the first beam splitting unit;

[0018] The second mode field converter is connected one-to-one between the output end of the first beam splitting unit for outputting the local oscillator light and the input end of the coherent receiving module for receiving the local oscillator light, for performing mode field matching between the corresponding ends of the first beam splitting unit and the coherent receiving module;

[0019] The fifth mode field converter is connected between the output end of the first beam splitter unit for outputting the probe light and the input end of the transceiver module, and is used to perform mode field matching between the corresponding ends of the first beam splitter unit and the transceiver module.

[0020] In an optional embodiment, the transceiver module includes an optical amplification unit, a circulator, and a scanning unit connected in sequence. The optical amplification unit is connected to the PLC chip and is used to receive and amplify the detection light. The circulator and the scanning unit are used to cooperate with each other to control the amplified detection light to scan the target object, and are also used to cooperate with each other to receive the echo signal reflected back from the target object and transmit the echo signal to the coherent receiving module.

[0021] In an optional embodiment, multiple circulators and scanning units are provided, and they are connected in a one-to-one correspondence.

[0022] In an optional embodiment, the coherent receiving module includes a silicon photonic chip and a detection optical path formed within the silicon photonic chip, the detection optical path including a third beam splitting unit, a mixing unit and a combining unit connected in sequence;

[0023] The third beam splitting unit is used to receive echo signals and / or local oscillator light of arbitrary polarization mode, and decompose the received beam into multiple sub-beams with defined polarization; wherein, the sub-beam corresponding to the echo signal is a sub-signal light, and the sub-beam corresponding to the local oscillator light is a first sub-local oscillator light;

[0024] The mixing unit is used to mix the sub-signal light and the first sub-local oscillator light to obtain multiple mixed light beams;

[0025] The synthesis unit is used to perform photoelectric conversion on the multiple mixed beams to output multiple coherent electrical signals.

[0026] In an optional embodiment, the coherent receiving module further includes a nonlinear calibration optical path formed within the silicon photonics chip;

[0027] When the first beam splitting unit does not include the fourth beam splitter, the nonlinear calibration optical path includes the fourth beam splitting unit, the coupler, and the first balance detector connected in sequence along the propagation direction of the local oscillator light. The fourth beam splitting unit is used to receive the local oscillator light, split the local oscillator light into two second sub-local oscillator light beams, and make the two second sub-local oscillator light beams have different delays. The coupler is used to mix the two second sub-local oscillator light beams with different delays. The first balance detector is used to receive the mixed light output by the coupler and perform balance detection.

[0028] When the first beam splitting unit includes a fourth beam splitter, the nonlinear calibration optical path includes a coupler and a first balanced detector connected sequentially along the propagation direction of the local oscillator light. The coupler is used to mix two local oscillator lights with different delays, and the first balanced detector is used to receive the mixed light output by the coupler and perform balanced detection.

[0029] In an optional embodiment, the coherent receiving module further includes a second mode conversion unit formed within the silicon photonic chip, the second mode conversion unit being used to perform mode field matching between the light from external devices of the silicon photonic chip and the light from internal devices of the silicon photonic chip.

[0030] The technical advantages of this invention compared to existing technologies are as follows: The frequency-modulated continuous wave lidar provided in this embodiment adds a PLC chip between the frequency-modulated light source and the coherent receiving module to connect the two. The PLC chip can use a large-section silicon dioxide waveguide, which has higher tolerance for optical power. Therefore, a suitable beam splitter structure and mode converter structure can be fabricated on the PLC chip as a connection chip between the high-power frequency-modulated laser and the silicon photonics chip. The benefits include, but are not limited to: eliminating the need for external discrete components such as fiber optic beam splitters to complete the beam splitting function, effectively improving system integration and reliability, and reducing system size and cost; in addition, compared with fabricating mode converters on silicon chips, the PLC chip provided in this embodiment has advantages in terms of process tolerance and alignment tolerance; the PLC chip can integrate various passive devices such as beam splitters, mode converters, and optical delay lines, and the use of PLC waveguides can achieve longer optical delay lines, reducing losses. Furthermore, since the optical power of the local oscillator light split by the first beam splitting unit in the PLC chip is less than or equal to 50mW, the silicon layer two-photon absorption effect under high-power output conditions can be solved. In addition, the PLC chip in this embodiment can support higher optical power transmission. Therefore, even if the output optical power of the external frequency-modulated light source is as high as milliwatts, it can still enter the PLC chip through the first mode conversion unit, making the frequency-modulated continuous wave lidar provided in this embodiment more widely applicable. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the structure of the frequency-modulated continuous wave lidar provided in the first embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of the structure of the frequency-modulated continuous wave lidar provided in the second embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of the structure of the frequency-modulated continuous wave lidar provided in the third embodiment of the present invention;

[0035] Figure 4 This is a schematic diagram of the structure of the frequency-modulated continuous wave lidar provided in the fourth embodiment of the present invention;

[0036] Figure 5 This is a schematic diagram of the structure of the frequency-modulated continuous wave lidar provided in the fifth embodiment of the present invention;

[0037] Figure 6 This is a schematic diagram of the structure of the frequency-modulated continuous wave lidar provided in the sixth embodiment of the present invention.

[0038] Explanation of reference numerals in the attached figures:

[0039] 100. Frequency-modulated light source; 200. Transceiver module; 210. Optical amplification unit; 220. Circulator; 230. Scanning unit; 300. PLC chip; 311. First beam splitter; 312. Second beam splitter; 313. Third beam splitter; 314. Fourth beam splitter; 315. Optical delay line; 321. First mode converter; 322. Second mode converter; 323. Fifth mode converter; 400. Coherent receiving module; 410. Silicon photonics chip; 421. Coupler; 422. First balanced detector; 423. Polarization beam rotator; 430. Mixer unit; 440. Synthesizer unit; 450. Third mode converter; 460. Fourth mode converter. Detailed Implementation

[0040] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0041] In the description of this invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0042] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0043] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0045] Please refer to Figures 1 to 6 As shown, in this embodiment of the invention, a frequency-modulated continuous wave lidar is provided, including a frequency-modulated light source 100, a transceiver module 200, a PLC chip 300, and a coherent receiving module 400.

[0046] The frequency-modulated light source 100 is used to emit a laser beam. Specifically, the laser beam is a frequency-modulated continuous wave signal.

[0047] The PLC chip 300 is connected between the frequency-modulated light source 100 and the transceiver module 200. The PLC chip 300 integrates a first beam splitting unit and a first mode-spot conversion unit. The first beam splitting unit splits the received laser beam into a probe beam and at least one local oscillator beam. The optical power of each local oscillator beam is less than or equal to 50mW. The first mode-spot conversion unit performs mode field matching between the light from external devices and the light from internal devices of the PLC chip 300.

[0048] Specifically, the first beam splitting unit includes at least one beam splitter. The number and connection structure of the beam splitters are determined according to the final output local oscillator light power and / or the beam size of the probe light. For example, when the optical power of the laser beam output by the frequency-modulated light source 100 is low, the optical power of the local oscillator light after the laser beam entering the PLC chip 300 passes through a beam splitter is less than or equal to 50mW. In this case, the first beam splitting unit may include only one beam splitter. When the optical power of the laser beam output by the frequency-modulated light source 100 is high, the optical power of the local oscillator light after the laser beam entering the PLC chip 300 passes through a beam splitter is greater than 50mW. In this case, beam splitters may be added after the beam splitter until the power of the local oscillator light output by the beam splitter is less than or equal to 50mW, at which point the addition of beam splitters is stopped.

[0049] The first mode conversion unit has multiple mode converters, and the number of mode converters is consistent with the number of connection ports between the PLC chip 300 and external devices. Here, the connection ports refer to those used for light propagation.

[0050] The transceiver module 200 is used to receive the probe light output by the PLC chip 300, and after shaping and collimating the probe light, it controls the light to scan the target object. It is also used to receive the echo signal reflected by the target object and transmit the echo signal to the coherent receiving module 400.

[0051] Specifically, the transceiver module 200 may include one or more optical adjustment modules for shaping (such as an optical amplification module, an angle reduction module, a beam expander module, etc.), a lens module for collimation, a circulator, and a scanning module, etc. It may also include an optical module for shaping and collimation, a circulator, and a scanning module. Of course, other forms may also be adopted, as long as the above functions can be achieved. The specific choice can be made flexibly according to the usage requirements.

[0052] The coherent receiving module 400 is connected to the PLC chip 300 and the transceiver module 200 respectively. The coherent receiving module 400 is used to receive the local oscillator light output by the PLC chip 300 and the echo signal output by the transceiver module 200, combine the local oscillator light and the echo signal and perform coherent beat frequency, and finally transmit the signal to the external signal processing module.

[0053] The aforementioned frequency-modulated light source 100 and transceiver module 200 are not mounted on a chip, but are discrete devices or modules. The output terminal of the frequency-modulated light source 100 is connected to the input terminal of the first mode conversion unit in the PLC chip 300.

[0054] The working principle of the frequency-modulated continuous wave lidar provided in this embodiment of the invention is as follows:

[0055] During detection, the frequency-modulated light source 100 emits a laser beam, which enters the first beam splitting unit after passing through at least one mode converter in the first mode conversion unit. The first beam splitting unit splits the beam into at least one probe beam and at least one local oscillator beam, and the optical power of each local oscillator beam is less than or equal to 50mW. Then, the local oscillator beam is output through the corresponding mode converter in the first mode conversion unit and enters the coherent receiving module 400. At the same time, the probe beam is output through the corresponding mode converter in the first mode conversion unit and enters the transceiver module 200. The transceiver module 200 then shapes and collimates the beam to scan the target object.

[0056] The echo signal reflected by the target object is then transmitted to the coherent receiving module 400 via the transceiver module 200. It is mixed with the local oscillator light in the coherent receiving module 400. After that, it is coherently beat-frequency through the balanced detection unit in the coherent receiving module 400. Then, it is output to the signal processing module located outside the silicon photonics chip 410 via the balanced detection unit. The signal processing module analyzes the signal to obtain information such as the target distance and speed.

[0057] The frequency-modulated continuous wave lidar provided in this embodiment of the invention adds a PLC chip 300 between the frequency-modulated light source 100 and the coherent receiving module 400 to connect the two. The PLC chip 300 can use a large-section silicon dioxide waveguide, which has higher tolerance to optical power. Therefore, a suitable beam splitter structure and mode converter structure can be fabricated on the PLC chip 300 as a connection chip between the high-power frequency-modulated laser and the silicon photonic chip 410. The benefits of this include, but are not limited to: eliminating the need for external discrete devices such as fiber optic beam splitters to complete the beam splitting function, which can effectively improve the system integration and reliability, and reduce the system size and cost; in addition, compared with fabricating the mode converter on the silicon chip, the PLC chip 300 provided in this embodiment of the invention has advantages in terms of process tolerance and alignment tolerance; the PLC chip 300 can integrate a variety of passive devices such as beam splitters, mode converters, and optical delay lines 315, and the use of PLC waveguides can realize a longer optical delay line 315, reducing losses. Furthermore, since the optical power of the local oscillator light split by the first beam splitting unit in the PLC chip 300 is less than or equal to 50mW, the silicon layer two-photon absorption effect under high-power output conditions can be resolved. In addition, the PLC chip 300 in this embodiment can support higher optical power transmission. Therefore, even if the output optical power of the external frequency-modulated light source 100 is as high as 100 milliwatts, it can still enter the PLC chip 300 through the first mode conversion unit, making the frequency-modulated continuous wave lidar provided in this embodiment more widely applicable.

[0058] To avoid the two-photon absorption effect in the silicon layer, the optical power of the local oscillator light split by the first beam splitting unit in the PLC chip 300 needs to be less than or equal to 50mW. However, the optical power of the laser beam emitted by different frequency-modulated light sources 100 varies, so there are multiple ways to implement the first beam splitting unit.

[0059] First implementation method:

[0060] The laser beam emitted by the frequency-modulated light source 100 has relatively low optical power. Therefore, only one beam splitter is needed in the first beam-splitting unit, and the resulting local oscillator light has sufficient power to meet the requirements and can be transmitted through the silicon layer. For specific details, please refer to... Figure 1 As shown, the first beam splitting unit includes a first beam splitter 311. The input end of the first beam splitter 311 is connected to the output end of the frequency-modulated light source 100 through a first mode conversion unit. The first output end of the first beam splitter 311 is connected to the input end of the transceiver module 200 through the first mode conversion unit and is used to output probe light. The second output end of the first beam splitter 311 is connected to the corresponding input end of the coherent receiving module 400 through the first mode conversion unit and is used to output local oscillator light. In this embodiment, the first beam splitter 311 has one input end and two output ends. The beam splitting ratio is generally between 10:90 and 50:50, and can be flexibly selected according to the application needs. No single limitation is made here. The first beam splitting unit adopts this structure, which is simple and easy to assemble.

[0061] The second implementation method:

[0062] The laser beam emitted by the frequency-modulated light source 100 has a relatively high optical power. After being split by a beam splitter, the optical power of the split local oscillator light is greater than 50mW. If this local oscillator light is directly input into the coherent receiver module 400, it may excite the two-photon absorption effect in the silicon layer. To avoid this situation, in an optional embodiment, please refer to... Figures 2 to 5 As shown, the first beam splitting unit includes a first beam splitter 311 and a second beam splitting unit. The input end of the first beam splitter 311 is connected to the output end of the frequency-modulated light source 100 through a first mode conversion unit. The first output end of the first beam splitter 311 is connected to the input end of the transceiver module 200 through the first mode conversion unit and is used to output probe light. The second output end of the first beam splitter 311 is connected to the input end of the second beam splitting unit and is used to output local oscillator light. The output end of the second beam splitting unit is connected to the corresponding input end of the coherent receiving module 400 through the first mode conversion unit.

[0063] In this embodiment, the structure of the first beam splitter 311 is the same as that in the first form, and the beam splitting ratio is also between 10:90 and 50:50. The specific ratio can be flexibly selected according to usage needs, and is not limited to a single ratio. The second beam splitting unit in this embodiment may include one or more beam splitters, depending on whether the optical power of the split local oscillator light meets the requirements. Specifically, it manifests in the following ways:

[0064] First scenario:

[0065] The local oscillator light split by the first beam splitter 311 is then split by another beam splitter, and any output beam of local oscillator light can meet the preset requirements (optical power less than or equal to 50mW). Please refer to [reference needed]. Figure 2 As shown, the second beam splitting unit includes a second beam splitter 312. The input of the second beam splitter 312 is connected to the second output of the first beam splitter 311. The two outputs of the second beam splitter 312 are respectively connected to the input of the coherent receiving module 400 through corresponding mode converters in the first mode conversion unit. This is used to split the local oscillator light output from the first beam splitter 311 into multiple beams and output them to the coherent receiving module. In this embodiment, the second beam splitter 312 has two outputs, and the splitting ratio is generally between 1:99 and 50:50. The specific ratio can be flexibly selected according to the application requirements, and no single limitation is made here. This structure of the second beam splitting unit is simple and easy to assemble.

[0066] The second scenario:

[0067] Because the second beam splitter 312 splits into two branches, one branch is used to send local oscillator light to the probe optical path in the receiving module 400, and the other branch is used to send local oscillator light to the nonlinear calibration optical path in the receiving module 400. Since the nonlinear calibration optical path requires very little optical signal power, in practice, the second beam splitter will split most of the light into the probe optical path in the receiving module 400 as the local oscillator light signal for subsequent coherent detection. Therefore, when the optical power of the laser beam output from the frequency-modulated light source 100 is high, it is very likely that the output end of the second beam splitter 312 used to send local oscillator light to the probe optical path in the coherent receiving module 400 will have an output local oscillator light power greater than 50mW. In this case, to avoid the two-photon absorption effect of the silicon layer, the second beam splitter unit can adopt the following form. Please refer to... Figure 3As shown, the second beam splitting unit includes a second beam splitter 312 and a third beam splitter 313 arranged sequentially along the local oscillator light transmission direction. The input end of the second beam splitter 312 is connected to the second output end of the first beam splitter 311. The first output end of the second beam splitter 312 is connected to the input end of the probe optical path in the coherent receiving module 400 through a first mode conversion unit. The second output end of the second beam splitter 312 is connected to the input end of the third beam splitter 313. The two output ends of the third beam splitter 313 are respectively connected to the corresponding input ends of the coherent receiving module 400 through the first mode conversion unit. Specifically, in this embodiment, the third beam splitter 313 can be a single beam splitter or a combination of multiple beam splitters, depending on the beam splitting effect, and is not uniquely limited here.

[0068] The third scenario:

[0069] The output terminal of the second beam splitter 312, used to transmit local oscillator light to the nonlinear calibration optical path in the coherent receiving module 400, has an output local oscillator light power greater than 50mW. Please refer to [reference needed]. Figure 4 As shown, the second beam splitting unit includes a second beam splitter 312 and a fourth beam splitter 314 arranged sequentially along the local oscillator light transmission direction. The input terminal of the second beam splitter 312 is connected to the second output terminal of the first beam splitter 311. The first output terminal of the second beam splitter 312 is connected to the corresponding input terminal of the coherent receiving module 400 through a first mode conversion unit. The second output terminal of the second beam splitter 312 is connected to the input terminal of the fourth beam splitter 314. The first output terminal of the fourth beam splitter 314 is connected to the corresponding input terminal of the coherent receiving module 400 through the first mode conversion unit. The second output terminal is connected to the input terminal of the nonlinear calibration optical path in the coherent receiving module 400 through a sequentially connected optical delay line 315 and the first mode conversion unit. Specifically, the fourth beam splitter 314 can be a single beam splitter or a combination of multiple beam splitters, depending on the beam splitting effect; no single limitation is made here.

[0070] The fourth scenario:

[0071] The optical power of the local oscillator light output from both output terminals of the second beam splitter 312 is greater than 50mW. Please refer to [reference needed]. Figure 5As shown, the second beam splitting unit may include a second beam splitter 312, a third beam splitter 313, and a fourth beam splitter 314. The input end of the second beam splitter 312 is connected to the second output end of the first beam splitter 311. The first output end of the second beam splitter 312 is connected to the input end of the third beam splitter 313. The second output end is connected to the input end of the fourth beam splitter 314. The two output ends of the third beam splitter 313 are respectively connected to the input end of the probe optical path in the coherent receiving module 400 through the first mode conversion unit. The first output end of the fourth beam splitter 314 is connected to the corresponding input end of the coherent receiving module 400 through the first mode conversion unit. The second output end is connected to the input end of the nonlinear calibration optical path in the coherent receiving module 400 through the optical delay line 315 and the first mode conversion unit connected in sequence.

[0072] Specifically, the third beam splitter 313 and the fourth beam splitter 314 mentioned above can be a single beam splitter or a combination of multiple beam splitters, depending on the beam splitting effect, and are not limited to one specific type here.

[0073] In an optional embodiment, the third beam splitter 313 and the fourth beam splitter 314 in the above embodiments each have two output terminals, and their splitting ratios are 50:50. This structure facilitates subsequent signal analysis.

[0074] In the above embodiments, please refer to Figures 1 to 6 As shown, the first mode conversion unit includes a first mode converter 321, a second mode converter 322 and a fifth mode converter 323.

[0075] The first mode-field converter 321 is connected between the frequency-modulated light source 100 and the first beam-splitting unit to perform mode field matching between the frequency-modulated light source 100 and the first beam-splitting unit, thereby reducing mode mismatch loss during the transmission of light emitted from the frequency-modulated light source 100 to the first beam-splitting unit. Specifically, the input terminal of the first mode-field converter 321 is connected to the output terminal of the frequency-modulated light source 100, and the output terminal is connected to the input terminal of the first beam-splitting unit.

[0076] The second mode-spot converter 322 is connected one-to-one between the output terminal of the first beam splitter unit used to output local oscillator light and the corresponding input terminal of the coherent receiving module 400. It is used to perform mode field matching between the corresponding ends of the first beam splitter unit and the coherent receiving module 400, thereby reducing mode mismatch loss during the transmission of local oscillator light output from the first beam splitter unit to the coherent receiving module 400. Specifically, the second mode-spot converter 322, the output terminal of the first beam splitter unit used to output local oscillator light, and the input terminal of the coherent receiving module 400 used to receive local oscillator light are configured in a one-to-one correspondence. The input terminal of each second mode-spot converter 322 is connected to one of the output terminals of the first beam splitter unit used to output local oscillator light, and the output terminal is connected to one of the input terminals of the coherent receiving module 400.

[0077] The fifth mode-spot converter 323 is connected between the output terminal of the first beam splitter unit used to output the probe light and the input terminal of the transceiver module 200. It performs mode field matching between the corresponding ends of the first beam splitter unit and the transceiver module 200 to reduce mode mismatch loss during the transmission of the probe light output from the first beam splitter unit to the transceiver module 200. Specifically, the input terminal of the fifth mode-spot converter 323 is connected to the output terminal of the first beam splitter unit used to output the probe light, and the output terminal is connected to the input terminal of the transceiver module 200.

[0078] Specifically, the models of the first pattern converter 321, the second pattern converter 322, and the fifth pattern converter 323 can be flexibly selected according to the pattern size of the devices at both ends of each pattern converter, and there is no single limitation here. The first pattern conversion unit adopts this structure, which allows for flexible selection of devices inside and outside the PLC chip 300 without being limited by the pattern size of each other, which facilitates the design.

[0079] Please refer to Figures 1 to 6 As shown, in an optional embodiment, the transceiver module 200 includes an optical amplification unit 210, a circulator 220, and a scanning unit 230 connected in sequence. The optical amplification unit 210 is connected to the PLC chip 300 and is used to receive and amplify the detection light. The circulator 220 and the scanning unit 230 are used to cooperate to control the amplified detection light to scan the target object, and are also used to cooperate to receive the echo signal reflected back from the target object and transmit the echo signal to the coherent receiving module 400.

[0080] In this embodiment, the optical amplification unit 210 can be any one or a combination of rare-earth-doped fiber amplifiers, semiconductor optical amplifiers, and Raman amplifiers. It is mainly used to increase the gain of the probe light and output a higher optical signal. In this embodiment, the scanning unit 230 can include one or more beam scanning modules. Each beam scanning module can be any one of a galvanometer, a rotating mirror, a MEMS micro-mirror, etc., or a combination of the above methods. It is mainly used to achieve the shaping, collimation, and scanning of the probe light.

[0081] In this embodiment, the circulator 220 is used to allow the amplified laser beam to pass through, and also to deflect the received echo beam and direct it towards the coherent receiving module 400. Specifically, in use, the probe light is input through the first port of the circulator 220, then output through the second port of the circulator 220. This beam can then be output from free space through the scanning unit 230 and emitted onto the target object. The echo signal reflected back from the target object can then return through the scanning unit 230, enter through the second port of the circulator 220, and be output to the coherent receiving module 400 through the third port of the circulator 220. The transceiver module 200 adopts this structure, which is simple, easy to assemble and maintain, and has stable operating performance.

[0082] In the above embodiments, one or more scanning units 230 can be provided. When only one scanning unit 230 is provided, since the scanning angle range of a single scanning unit 230 is limited, it is impossible to achieve a large-angle scanning range. Therefore, in order to improve the scanning angle range of the lidar, multiple scanning units 230 can be used. At this time, the number of circulators 220 also needs to be changed accordingly. That is, multiple circulators 220 and multiple scanning units 230 are provided, and they are connected in a one-to-one correspondence. The number of circulators 220 and multiple scanning units 230 can be flexibly selected according to the usage needs to meet the scanning needs of different ranges.

[0083] Based on the above embodiments, please refer to Figures 1 to 6 As shown, the coherent receiving module 400 includes a silicon photonic chip 410 and a detection optical path formed within the silicon photonic chip 410. The detection optical path includes a third beam splitting unit, a mixing unit 430, and a combining unit 440 connected in sequence.

[0084] The third beam splitting unit is used to receive echo signals and / or local oscillator light of arbitrary polarization modes, and decomposes the received beam into multiple sub-beams with defined polarization. For ease of description, the sub-beam corresponding to the echo signal is referred to as the sub-signal light, and the sub-beam corresponding to the local oscillator light is referred to as the first sub-local oscillator light. Specifically, the third beam splitting unit may include one or more beam splitters, and may also include one or more polarization beam splitter rotators 423, which can be selected according to the application requirements. Specifically, when it is necessary to split the echo signal, a polarization beam splitter rotator 423 is generally used to split the echo signal into multiple sub-signal lights; when it is necessary to split the local oscillator light, a common beam splitter is generally sufficient to split the local oscillator light into multiple first sub-local oscillator lights. In this embodiment, both the echo signal and the local oscillator light have two configuration methods: one is to complete beam splitting outside the silicon photonics chip 410, and the other is to complete beam splitting inside the silicon photonics chip 410. If either the echo signal or the local oscillator light has already been split outside the silicon photonics chip 410, then there is no need to set up a beam splitting structure for the corresponding beam inside the silicon photonics chip 410. Regardless of the configuration, as long as the final number of sub-signal lights and the number of first sub-local oscillator lights are consistent, a one-to-one correspondence can be achieved, satisfying the requirements of subsequent signal analysis.

[0085] The mixing unit 430 is used to mix the sub-signal light and the first sub-local oscillator light to obtain multiple mixed beams. Specifically, the mixing unit 430 includes at least two optical mixers, and the number of optical mixers can be determined according to the number of sub-signal lights or the number of first sub-local oscillator lights.

[0086] The combining unit 440 is used to perform photoelectric conversion on multiple mixed beams to obtain multiple coherent electrical signals. Specifically, the combining unit 440 includes at least two balanced detectors, each of which is connected to the optical mixer in the mixing unit 430 to receive and process the mixed light to form corresponding coherent electrical signals. These coherent electrical signals can then be output to an external signal processing device for further processing.

[0087] The coherent receiving module 400 adopts the structure provided in this embodiment, which is simple, stable, and easy to design.

[0088] In an optional embodiment, please refer to Figures 1 to 6 As shown, in addition to the aforementioned detection optical path, the coherent receiving module 400 also includes a nonlinear calibration optical path formed within the silicon photonic chip 410.

[0089] When the first beam splitting unit does not include the fourth beam splitter 314, the nonlinear calibration optical path includes the fourth beam splitting unit, the coupler 421, and the first balance detector 422 connected in sequence along the propagation direction of the local oscillator light. The fourth beam splitting unit is used to receive the local oscillator light, split the local oscillator light into two second sub-local oscillator lights, and make the two second sub-local oscillator lights have different delays. The coupler 421 is used to mix the two second sub-local oscillator lights with different delays. The first balance detector 422 is used to receive the mixed light output by the coupler 421 and perform balance detection.

[0090] When the first beam splitting unit includes a fourth beam splitter 314, the nonlinear calibration optical path includes a coupler 421 and a first balance detector 422 connected sequentially along the propagation direction of the local oscillator light. The coupler 421 is used to mix two local oscillator lights with different delays, and the first balance detector 422 is used to receive the mixed light output by the coupler 421 and perform balance detection.

[0091] In this embodiment, the coupler 421 is generally a 3dB coupler, but other couplers capable of achieving the above functions can also be used. In use, the output signal of the first balanced detector 422 can be further processed to serve as the basis for calibrating the frequency-modulated light source 100. Using the frequency-modulated continuous wave lidar provided in this embodiment, the frequency-modulated light source 100 can be calibrated in real time, allowing operators to promptly identify and adjust any problems, thereby ensuring the accuracy of the detection results.

[0092] In an optional embodiment, please refer to Figures 1 to 6 As shown, the coherent receiving module 400 further includes a second mode conversion unit formed within the silicon photonic chip 410. The second mode conversion unit is used to perform mode field matching between the light from external devices of the silicon photonic chip 410 and the light from internal devices of the silicon photonic chip 410.

[0093] Specifically, the second mode-spot conversion unit includes a third mode-spot converter 450 and a fourth mode-spot converter 460. The third mode-spot converter 450 is connected one-to-one with the second mode-spot converter 322, and is used to perform mode field matching between the light from the internal devices of the silicon photonic chip 410 and the light from outside the silicon photonic chip 410. The light from outside the silicon photonic chip 410 refers to the light output by the second mode-spot converter 322 in the PLC chip 300. To ensure that the local oscillator light can be stably transmitted from outside the silicon photonic chip 410 to inside the silicon photonic chip 410, the mode fields of the second mode-spot converter 322 and the third mode-spot converter 450 can be designed to be close. The fourth mode-spot converter 460 is connected one-to-one with the echo signal output terminal in the transceiver module 200 to reduce the mode field mismatch loss in this part.

[0094] The coherent receiving module 400 adopts the structure provided in this embodiment, which can realize stable transmission of light inside and outside the silicon photonic chip 410, and can make the devices inside and outside the silicon photonic chip 410, except for the mode converter, not affected by the mode size of other devices during the design, thus facilitating the design.

[0095] The mode converters in the above embodiments can be any of the following structures: tapered waveguide, cantilever beam waveguide, multilayer waveguide, etc., and can be flexibly selected according to the application requirements.

[0096] To reduce the size of the frequency-modulated continuous wave lidar, we preferably integrate the beam splitting structure required for the echo signal and local oscillator light into the PLC chip 300 and the silicon photonics chip 410. Thus, after passing through the first and third beam splitting units, an equal number of sub-signal lights and a first sub-local oscillator light need to be formed. Since the first beam splitting unit has multiple implementations, the third beam splitting unit in the above embodiments also has multiple implementations, and the implementation of the third beam splitting unit changes depending on the implementation of the first beam splitting unit. For ease of understanding, we will now describe the specific structure of the third beam splitting unit using the coherent receiving module 400, which includes the aforementioned detection optical path, nonlinear calibration optical path, and second mode conversion unit, as an example.

[0097] Please refer to Figure 1 As shown, when the first beam splitting unit adopts the first implementation method, that is, when the first beam splitting unit includes the first beam splitter 311 mentioned above, the third beam splitting unit includes the polarization beam splitter rotator 423, as well as the second beam splitter 312, the third beam splitter 313 and the fourth beam splitter 314 mentioned above. The second beam splitter 312 is connected to the output end of the first beam splitter 311 for outputting local oscillator light via the third mode converter 450 and the second mode converter 322. The third beam splitter 313 and the fourth beam splitter 314 are respectively connected to the two output ends of the second beam splitter 312. The third beam splitter 313 decomposes the local oscillator light into multiple first sub-local oscillator lights. One output end of the fourth beam splitter 314 is directly connected to the coupler 421, and the other output end is connected to the coupler 421 via the optical delay line 315. The polarization beam rotator 423 is connected to the circulator 220 via the fourth mode converter 460 and is used to split the echo signal into two sub-signal lights, and transmit the two sub-signal lights one-to-one to the corresponding optical mixers. At this time, the fourth beam splitter 314 is used to split the output light from the second beam splitter 312 into two beams at a certain splitting ratio. One beam enters the optical delay line 315, and the other beam is directly connected to the coupler 421. The optical delay line 315 is used to delay the optical signal, and its output is connected to the coupler 421.

[0098] Please refer to Figure 2As shown, when the first beam splitting unit adopts the first case in the second implementation method, that is, the first beam splitting unit includes the first beam splitter 311 and the second beam splitter 312, the third beam splitting unit includes the polarization beam splitter rotator 423, as well as the aforementioned third beam splitter 313 and fourth beam splitter 314.

[0099] Please refer to Figure 3 As shown, when the first beam splitting unit adopts the second implementation method in the second case, the third beam splitting unit includes the polarization beam rotator 423 and the aforementioned fourth beam splitter 314. In this case, the fourth beam splitter 314 splits the output light from the second beam splitter 312 into two beams at a certain splitting ratio. One beam enters the optical delay line 315, and the other beam is directly connected to the coupler 421. The optical delay line 315 is used to generate a delay in the optical signal, and its output is connected to the coupler 421.

[0100] Please refer to Figure 4 As shown, when the first beam splitting unit adopts the third case in the second implementation method, the third beam splitting unit includes the polarization beam splitter rotator 423 and the aforementioned third beam splitter 313.

[0101] Please refer to Figure 5 As shown, when the first beam splitting unit adopts the fourth case in the second implementation method, the third beam splitting unit includes a polarization beam splitter rotator 423.

[0102] In the above embodiments, the polarization beam splitter 423 is connected to the circulator 220 in a one-to-one correspondence through the fourth mode converter 460. Each polarization beam splitter 423 is used to split an echo signal with arbitrary polarization into two sub-signal lights with defined polarization. Its output is connected to the input of two optical mixers as the signal light input. Moreover, the polarization state of the light output by each polarization beam splitter 423 is the same as the polarization state of the light output by the corresponding third beam splitter 313.

[0103] Please refer to Figure 6 As shown, in a specific embodiment, the frequency-modulated continuous wave lidar includes a frequency-modulated light source 100, an optical amplifier, a circulator 220, N scanning units 230, N circulators 220, 2N optical mixers, two first mode converters 321, one second mode converter 322, one third mode converter 450, N fourth mode converters 460, 2N+1 balanced detectors, N polarization beam splitters 423, one first beam splitter 311, one second beam splitter 312, one third beam splitter 313, and one fourth beam splitter 314. The optical amplifier has N output ports, and the third beam splitter 313 has 2N output ports. The third ports of the N circulators 220 are all connected to the N polarization beam splitters 423 via the fourth mode converters.

[0104] The above description is merely a preferred embodiment of the present invention and only specifically describes the technical principles of the present invention. These descriptions are only for explaining the principles of the present invention and should not be construed as limiting the scope of protection of the present invention in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention, as well as other specific embodiments of the present invention that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of the present invention.

Claims

1. A frequency modulated continuous wave lidar, characterized in that, The frequency modulation light source, the transceiver module, the PLC chip and the coherent receiving module are included. The frequency modulation light source is used for emitting a laser beam. The PLC chip is connected between the frequency modulation light source and the transceiver module, and the PLC chip is internally integrated with a first light splitting unit and a first mode spot conversion unit. The transceiver module is used for receiving the probe light output by the PLC chip, shaping and collimating the probe light, and controlling the probe light to scan a target object, and is also used for receiving a reflected echo signal from the target object and transmitting the echo signal to the coherent receiving module. The coherent receiving module is connected with the PLC chip and the transceiver module respectively, and includes a silicon optical chip and a probe light path formed in the silicon optical chip. The first light splitting unit includes a first light splitter, an input end of the first light splitter is connected with an output end of the frequency modulation light source through the first mode spot conversion unit, a first output end of the first light splitter is connected with an input end of the transceiver module through the first mode spot conversion unit and is used for outputting the probe light, and a second output end of the first light splitter is connected with a corresponding input end of the coherent receiving module through the first mode spot conversion unit and is used for outputting the local light.

2. The frequency modulated continuous wave lidar of claim 1, wherein, The first light splitting unit includes a first light splitter and a second light splitting unit, an input end of the first light splitter is connected with an output end of the frequency modulation light source through the first mode spot conversion unit, a first output end of the first light splitter is connected with an input end of the transceiver module through the first mode spot conversion unit and is used for outputting the probe light, a second output end of the first light splitter is connected with an input end of the second light splitting unit and is used for outputting the local light, and an output end of the second light splitting unit is connected with a corresponding input end of the coherent receiving module through the first mode spot conversion unit and is used for splitting the local light output by the first light splitter into multiple beams and outputting the multiple beams to the coherent receiving module.

3. The frequency modulated continuous wave lidar of claim 1, wherein, The second light splitting unit includes a second light splitter, an input end of the second light splitter is connected with a second output end of the first light splitter, and two output ends of the second light splitter are respectively connected with corresponding input ends of the coherent receiving module through the first mode spot conversion unit.

4. The frequency modulated continuous wave lidar of claim 3, wherein, ​ Or, the second light splitting unit comprises a second light splitter and a third light splitter arranged in sequence along the local light transmission direction, the input end of the second light splitter is connected with the second output end of the first light splitter, the first output end of the second light splitter is connected with the corresponding input end of the coherent receiving module through the first mode spot conversion unit, the second output end of the second light splitter is connected with the input end of the third light splitter, and the two output ends of the third light splitter are respectively connected with the input ends of the probe light path in the coherent receiving module through the first mode spot conversion unit. Or, the second light splitting unit comprises a second light splitter and a fourth light splitter arranged in sequence along the local light transmission direction, the input end of the second light splitter is connected with the second output end of the first light splitter, the first output end of the second light splitter is connected with the corresponding input end of the coherent receiving module through the first mode spot conversion unit, the second output end of the second light splitter is connected with the input end of the fourth light splitter, the first output end of the fourth light splitter is connected with the corresponding input end of the coherent receiving module through the first mode spot conversion unit, and the second output end is connected with the input end of the nonlinear calibration light path in the coherent receiving module through the optical delay line and the first mode spot conversion unit connected in sequence. Or, the second light splitting unit comprises a second light splitter, a third light splitter and a fourth light splitter, the input end of the second light splitter is connected with the second output end of the first light splitter, the first output end of the second light splitter is connected with the input end of the third light splitter, and the second output end is connected with the input end of the fourth light splitter, the two output ends of the third light splitter are respectively connected with the input ends of the probe light path in the coherent receiving module through the first mode spot conversion unit, the first output end of the fourth light splitter is connected with the corresponding input end of the coherent receiving module through the first mode spot conversion unit, and the second output end is connected with the input end of the nonlinear calibration light path in the coherent receiving module through the optical delay line and the first mode spot conversion unit connected in sequence.

5. The frequency modulated continuous wave lidar of any one of claims 1-4, wherein, The first mode spot conversion unit comprises a first mode spot converter, a second mode spot converter and a fifth mode spot converter. The first mode spot converter is connected between the frequency-modulated light source and the first light splitting unit, for field matching between the frequency-modulated light source and the first light splitting unit. The second mode spot converter is connected between the output end for outputting the local light in the first light splitting unit and the input end for receiving the local light in the coherent receiving module in one-to-one correspondence, for field matching between the first light splitting unit and the corresponding end of the coherent receiving module. The fifth mode spot converter is connected between the output end for outputting the probe light in the first light splitting unit and the input end of the transceiver module, for field matching between the first light splitting unit and the corresponding end of the transceiver module.

6. The frequency modulated continuous wave lidar of any one of claims 1-4, wherein, The transceiving module comprises an optical amplification unit, a circulator and a scanning unit connected in sequence, the optical amplification unit is connected with the PLC chip, and is used for receiving and amplifying the probe light, the circulator and the scanning unit are used for cooperating with each other to control the amplified probe light to scan the target object, and are also used for cooperating with each other to receive the echo signal reflected by the target object and transmit the echo signal to the coherent receiving module.

7. The frequency modulated continuous wave lidar of claim 6, wherein, The circulator and the scanning unit are respectively provided with a plurality of units and are connected in one-to-one correspondence.

8. The frequency modulated continuous wave lidar of any of claims 1-4, wherein, The probe light path comprises a third light splitting unit, a mixing unit and a synthesis unit connected in sequence; The third light splitting unit is used for receiving echo signals of any polarization mode and / or local oscillator light, and decomposing the received light beams into a plurality of polarization-determined sub-beams; wherein the sub-beam corresponding to the echo signal is a sub-signal light, and the sub-beam corresponding to the local oscillator light is a first sub-local oscillator light; The mixing unit is used for mixing the sub-signal light and the first sub-local oscillator light to obtain a plurality of mixed light beams; The synthesis unit is used for photoelectric conversion of the plurality of mixed light beams to obtain a plurality of coherent electrical signals.

9. The frequency modulated continuous wave lidar of claim 8, wherein, The coherent receiving module further comprises a nonlinear calibration optical path formed in the silicon optical chip; When the first light splitting unit does not comprise a fourth light splitter, the nonlinear calibration optical path comprises a fourth light splitting unit, a coupler and a first balanced detector connected in sequence along the propagation direction of the local oscillator light, the fourth light splitting unit is used for receiving the local oscillator light, dividing the local oscillator light into two beams of second sub-local oscillator light, and making the delay of the two beams of second sub-local oscillator light different, the coupler is used for mixing the two beams of second sub-local oscillator light with different delays, and the first balanced detector is used for receiving the mixed light output by the coupler and performing balanced detection; When the first light splitting unit comprises a fourth light splitter, the nonlinear calibration optical path comprises a coupler and a first balanced detector connected in sequence along the propagation direction of the local oscillator light, the coupler is used for mixing the two beams of local oscillator light with different delays, and the first balanced detector is used for receiving the mixed light output by the coupler and performing balanced detection.

10. The frequency modulated continuous wave lidar of claim 8, wherein, The coherent receiving module further comprises a second mode spot conversion unit formed in the silicon optical chip, and the second mode spot conversion unit is used for matching the light of the device outside the silicon optical chip with the light of the device inside the silicon optical chip.

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