Frequency modulated continuous wave lidar

Abstract

The application is suitable for the technical field of laser radar, and provides a frequency-modulated continuous wave laser radar, which comprises a frequency-modulated light source, a transceiver module and a silicon optical chip; the silicon optical chip is connected between the frequency-modulated light source and the transceiver module, and comprises a first waveguide layer and a second waveguide layer arranged in sequence; wherein the first waveguide layer can accommodate a light power greater than the light power that the second waveguide layer can accommodate, and two interlayer mode converters are formed between the first waveguide layer and the second waveguide layer; a first light splitting unit is integrated on the first waveguide layer, and the first light splitting unit is used for splitting the received laser beam into at least one probe light and at least one local oscillation light, and the light power of each local oscillation light is less than or equal to 50 mW; a coherent receiving module is integrated on the second waveguide layer. The frequency-modulated continuous wave laser radar provided by the application is small in size and high in integration.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser radar, and particularly relates to a frequency-modulated continuous wave laser radar. BACKGROUND

[0002] Laser radar is one of the core sensors widely used in automatic driving scenes and can be used to collect three-dimensional information of an external environment. According to a detection mechanism, laser radar can be mainly divided into two kinds of laser radars, namely, a time of flight (ToF) laser radar and a frequency-modulated continuous wave (FMCW) laser radar. The FMCW laser radar adopts a coherent receiving mode, and through balanced detection of signal light and local oscillator light at a receiving end, can effectively reduce the interference of external ambient light on the performance of the laser radar and improve the ranging performance of the laser radar. Meanwhile, the FMCW laser radar can additionally provide speed information in addition to spatial coordinate information, and is therefore considered as a mainstream laser radar technology of the next generation.

[0003] However, compared with the ToF laser radar, the FMCW laser radar uses a large number of optoelectronic devices, resulting in a relatively complex system structure. At present, most of the FMCW laser radars adopt a discrete device mode, have a very low integration level, a high cost and a large volume. The use of silicon-based optoelectronic technology can integrate multiple discrete devices on a chip, thereby effectively reducing the system volume and improving the integration level. However, the traditional silicon-based optoelectronic platform adopts a silicon waveguide mode to transmit optical signals, is affected by the two-photon absorption effect of silicon and cannot transmit optical signals with a large power. In the system architecture of the FMCW laser radar, the average output optical power of the frequency-modulated light source at the transmitting end can reach 100 milliwatts. If the frequency-modulated light source is directly coupled with the silicon optical chip, the two-photon absorption effect will be obviously excited, resulting in additional loss and even burning out the silicon waveguide, thereby causing the failure of the entire chip. Therefore, the frequency-modulated light source of the current FMCW laser radar is generally connected with an external fiber splitter and connected with the silicon optical chip after being split several times. Such a scheme has a large number of discrete fiber devices, resulting in a large system volume and a low integration level. SUMMARY

[0004] The application aims to provide a frequency-modulated continuous wave laser radar, and aims to solve the technical problem of a large volume and a low integration level of the frequency-modulated continuous wave laser radar in the prior art.

[0005] The application is implemented as follows. A frequency-modulated continuous wave laser radar comprises a frequency-modulated light source, a transceiver module and a silicon optical chip.

[0006] The frequency-modulated light source is configured to emit a laser beam.

[0007] The transceiver module is configured to receive the probe light output by the silicon optical chip, shape and collimate the probe light, and control the probe light to scan the target object, and is also configured to receive the echo signal reflected by the target object and transmit the echo signal to the silicon optical chip.

[0008] The silicon optical chip is connected between the frequency-modulated light source and the transceiver module, and includes a first waveguide layer and a second waveguide layer arranged in sequence. The first waveguide layer can accommodate a larger optical power than the second waveguide layer. Two interlayer mode converters are formed between the first waveguide layer and the second waveguide layer. A first light splitting unit is integrated on the first waveguide layer. The first light splitting unit is configured to split the received laser beam into at least one probe light and at least one local oscillator light. Each of the local oscillator lights has an optical power less than or equal to 50 mW. A coherent receiving module is integrated on the second waveguide layer. The coherent receiving module is in signal communication with the first light splitting unit through the interlayer mode converter, and is connected to an output end of the transceiver module for outputting the echo signal. The coherent receiving module is configured to combine the local oscillator light and the echo signal, perform coherent beat frequency, and transmit the processed signal to an external signal processing module.

[0009] In an optional embodiment, when the vertical distance between the second waveguide layer and the first waveguide layer is greater than 50 nm and less than 400 nm, the optical signals in the two waveguide layers can be converted between the layers through evanescent wave coupling in the interlayer mode converter.

[0010] In an optional embodiment, the first waveguide layer and the second waveguide layer are both tapered in the part located in the interlayer mode converter. The interlayer mode converter is a tapered waveguide mode converter.

[0011] In an optional embodiment, when the vertical distance between the second waveguide layer and the first waveguide layer is greater than 1 μm and less than 4 μm, the first waveguide layer and the second waveguide layer are both formed with a grating structure on the part located in the interlayer mode converter. The optical signals in the two waveguide layers can be converted between the layers through the grating structure.

[0012] In an optional embodiment, the first light splitting unit includes a first optical splitter. An input end of the first optical splitter is connected to an output end of the frequency-modulated light source. A first output end of the first optical splitter is connected to an input end of the transceiver module for outputting the probe light. A second output end of the first optical splitter is connected to a corresponding input end of the coherent receiving module through the interlayer mode converter for outputting the local oscillator light.

[0013] In an optional embodiment, the first light splitting unit comprises 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-modulated light source, a first output end of the first light splitter is connected with an input end of the transceiver module 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 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 interlayer mode converter for splitting the local light outputted by the first light splitter into multiple beams and outputting to the coherent receiving module.

[0014] In an optional embodiment, the second light splitting unit comprises a second light splitter, an input end of the second light splitter is connected with the 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 interlayer mode converter.

[0015] Alternatively, the second light splitting unit comprises a second light splitter and a third light splitter arranged in sequence along the transmission direction of the local light, an input end of the second light splitter is connected with the second output end of the first light splitter, a first output end of the second light splitter is connected with a corresponding input end of the coherent receiving module through the interlayer mode converter, a second output end of the second light splitter is connected with an input end of the third light splitter, and two output ends of the third light splitter are respectively connected with input ends of probe light paths in the coherent receiving module through the interlayer mode converter.

[0016] In an optional embodiment, the transceiver module comprises an optical amplification unit, a circulator and a scanning unit connected in sequence, the optical amplification unit is connected with the silicon optical chip for receiving and amplifying the probe light, and 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 echo signals reflected by the target object and transmit the echo signals to the coherent receiving module.

[0017] In an optional embodiment, the circulator and the scanning unit are respectively provided with multiple units and are connected in one-to-one correspondence.

[0018] In an optional embodiment, the coherent receiving module comprises a probe light path, the probe light path comprises a third light splitting unit, a mixing unit and a combining unit formed in sequence on the second waveguide layer.

[0019] The third light splitting unit is used for receiving echo signals of any polarization mode and / or local light, and decomposing the received light beams into multiple 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 light is a first sub-local light.

[0020] The mixing unit is configured to mix the sub-signal light and the first sub-local oscillator light to obtain a plurality of mixed lights;

[0021] The synthesizing unit is configured to photoelectrically convert the plurality of mixed lights to obtain a plurality of output coherent electrical signals.

[0022] In an optional embodiment, the coherent receiving module further comprises a nonlinear calibration optical path;

[0023] The nonlinear calibration optical path comprises, in sequence along a propagation direction of the local oscillator light, a fourth light splitting unit, a coupler and a first balanced detector formed on the second waveguide layer, the fourth light splitting unit is configured to receive the local oscillator light, split the local oscillator light into two beams of second sub-local oscillator light, and make the two beams of second sub-local oscillator light have different delays, the coupler is configured to mix the two beams of second sub-local oscillator light with different delays, and the first balanced detector is configured to receive mixed light output by the coupler and perform balanced detection.

[0024] In an optional embodiment, the first waveguide layer further integrates a first mode spot conversion unit, the first mode spot conversion unit is configured to match a mode field of light of the external device of the silicon optical chip with light of the first light splitting unit;

[0025] The coherent receiving module further comprises a second mode spot conversion unit formed on the second waveguide layer, the second mode spot conversion unit is configured to match a mode field of light of a corresponding device in the transceiver module with light of a corresponding device in the coherent receiving module.

[0026] The technical effects of the present application relative to the prior art are: the frequency-modulated continuous wave laser radar provided by the embodiments of the present application is provided with a silicon optical chip for connecting the frequency-modulated light source and the coherent receiving module, the silicon optical chip is formed with a first waveguide layer and a second waveguide layer, the tolerance of the first waveguide layer to optical power is higher than that of the second waveguide layer, therefore, a suitable first light splitting unit can be made on the first waveguide layer to realize the connection between the high-power frequency-modulated light source and the coherent receiving module in the silicon optical chip, and the benefits brought by this include but are not limited to: the external separate devices such as fiber optical splitters are no longer needed to complete the light splitting function, which can effectively improve the system integration and reliability, reduce the system size and cost; meanwhile, by using the interlayer mode converter, the optical signal of the first waveguide layer can be conveniently transferred to the second waveguide layer, and the second waveguide layer can adopt a silicon waveguide layer, therefore, the advantages of the original silicon layer device can be compatible; and since the silicon nitride layer and the silicon layer can be realized on the same silicon optical chip according to the current process, when the first waveguide layer adopts a silicon nitride waveguide layer and the second waveguide layer adopts a silicon waveguide layer, ultra-high density integration can be realized, and the process is CMOS (Complementary Metal Oxide Semiconductor, the abbreviation of Complementary Metal Oxide Semiconductor) compatible, which has extremely high mass production property. Since the optical power of the local oscillator light split by the first light splitting unit in the silicon optical chip is less than or equal to 50mW, the silicon layer two-photon absorption effect in the case of high-power output can be solved. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the description of the embodiments of the present application or the prior art. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0028] Figure 1 is a structural schematic diagram of the frequency-modulated continuous wave laser radar provided by the first embodiment of the present application;

[0029] Figure 2 is a sectional structure schematic diagram of the interlayer mode converter adopted by an embodiment of the present application;

[0030] Figure 3 is Figure 2 a top view structural schematic diagram of the interlayer mode converter shown in the figure;

[0031] Figure 4 is a sectional structure schematic diagram of the interlayer mode converter adopted by another embodiment of the present application;

[0032] Figure 5 is Figure 4A top view structural schematic diagram of the interlayer mode converter shown;

[0033] Figure 6 A structural schematic diagram of a frequency-modulated continuous wave laser radar provided by a second embodiment of the present application;

[0034] Figure 7 A structural schematic diagram of a frequency-modulated continuous wave laser radar provided by a third embodiment of the present application;

[0035] Figure 8 A structural schematic diagram of a frequency-modulated continuous wave laser radar provided by a fourth embodiment of the present application;

[0036] Figure 9 A structural schematic diagram of a frequency-modulated continuous wave laser radar provided by a fifth embodiment of the present application;

[0037] Figure 10 A structural schematic diagram of a frequency-modulated continuous wave laser radar provided by a sixth embodiment of the present application.

[0038] Legend of reference signs:

[0039] 100, frequency-modulated light source; 200, transceiver module; 210, optical amplification unit; 220, circulator; 230, scanning unit; 300, silicon optical chip; 301, first waveguide layer; 302, second waveguide layer; 303, interlayer mode converter; 304, substrate layer; 305, buried oxygen layer; 306, oxide layer; 307, upper cladding layer; 311, first optical splitter; 312, second optical splitter; 313, third optical splitter; 314, fourth optical splitter; 315, optical delay line; 321, first mode spot converter; 322, second mode spot converter; 323, third mode spot converter; 330, coherent receiving module; 331, coupler; 332, first balanced detector; 333, polarization beam splitting rotator; 334, mixing unit; 335, synthesis unit. DETAILED DESCRIPTION

[0040] Embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0041] In the description of the present application, it needs to be understood that the terms "length", "width", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0042] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features referred to. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly specified and limited.

[0043] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection", "fixing" and the like should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0044] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application will be further described in detail below in combination with the drawings and examples.

[0045] Please refer to Figure 1 In the embodiment of the present application, a frequency-modulated continuous wave laser radar is provided, which comprises a frequency-modulated light source 100, a transceiver module 200 and a silicon optical chip 300.

[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 transceiver module 200 is used to receive the detection light output by the silicon optical chip 300, and to shape and collimate the detection light and then control it to scan the target object. Meanwhile, the transceiver module 200 is also used to receive the echo signal reflected by the target object and to deliver the echo signal to the silicon optical chip 300.

[0048] Specifically, the transceiver module 200 can include a light adjustment module (such as one or more of a light amplification module, an angle reduction module, a beam expansion module, etc.) for shaping, a lens module for collimation, a circulator 220, and a scanning module, etc., can also include an optical module for shaping and collimation, a circulator 220, and a scanning module, and of course other forms can also be used as long as the above functions can be achieved, and specific selection can be made flexibly according to the use needs.

[0049] The silicon optical chip 300 is connected between the frequency-modulated light source 100 and the transceiver module 200. The silicon optical chip 300 includes a first waveguide layer 301 and a second waveguide layer 302 arranged in sequence. The first waveguide layer 301 can accommodate a larger optical power than the second waveguide layer 302, and two interlayer mode converters 303 are formed between the first waveguide layer 301 and the second waveguide layer 302. A first light splitting unit is integrated on the first waveguide layer 301. The first light splitting unit is used to split the received laser beam into at least one probe light and at least one local oscillator light, and the optical power of each local oscillator light is less than or equal to 50 mW. A coherent receiving module 330 is integrated on the second waveguide layer 302. The coherent receiving module 330 is in signal communication with the first light splitting unit through the interlayer mode converter 303, and is connected with an output end in the transceiver module 200 for outputting the echo signal, for combining the local oscillator light and the echo signal and performing coherent beat frequency, and for transmitting the processed signal to an external signal processing module.

[0050] Specifically, the first light splitting unit includes at least one light splitter, and the number and connection structure of the light splitter are determined according to the optical power of the finally output local oscillator light and / or the beam amount 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 silicon optical chip 300 passes through a light splitter is less than or equal to 50 mW, and then the first light splitting unit can only include one light 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 silicon optical chip 300 passes through a light splitter is greater than 50 mW, and then a light splitter can be added after the light splitter until the power of the local oscillator light output by the light splitter is less than or equal to 50 mW, and the addition of the light splitter is stopped.

[0051] The silicon optical chip 300 can be processed by a mature semiconductor processing technology. The first light splitting unit, the coherent receiving module 330, and the interlayer mode converter 303 can be made by CMOS technology after the corresponding waveguide layer is formed.

[0052] The frequency-modulated light source 100 and the transceiver module 200 are not arranged on the silicon optical chip 300, and are discrete devices or modules. Other devices can be placed on the silicon optical chip 300 in an integrated manner. The interlayer mode converter 303 is used to realize optical transmission between the first waveguide layer 301 and the second waveguide layer 302. When the optical signal is split several times, the optical power no longer excites the two-photon absorption effect of the silicon waveguide, and the optical signal can be converted from the first waveguide layer 301 to the second waveguide layer 302 through the interlayer mode converter 303. This is because the optical devices of the second waveguide layer 302 can realize smaller sizes, which is beneficial to the high integration of chips and systems.

[0053] The working principle of the frequency-modulated continuous wave laser radar provided by the embodiment of the application is as follows:

[0054] During detection, the output end of the frequency-modulated light source 100 is communicated with the input end of the first light splitting unit through the first waveguide layer 301, and then the frequency-modulated light source 100 sends a laser beam to the first light splitting unit, the laser beam enters the first light splitting unit in the silicon optical chip 300, is split into at least one probe light and at least one local light by the first light splitting unit, the optical power of each local light is less than or equal to 50 mW, and then the local light enters the coherent receiving module 330 through the interlayer mode converter 303; at the same time, the probe light output from the silicon optical chip 300 enters the transceiver module 200, and then is shaped and collimated by the transceiver module 200 to scan the target object.

[0055] Then, the echo signal reflected by the target object is transmitted to the coherent receiving module 330 through the transceiver module 200, and is mixed with the local light in the coherent receiving module 330, then is coherently frequency-mixed by the balanced detection unit in the coherent receiving module 330, and is output to the signal processing module outside the silicon optical chip 300 through the balanced detection unit, and the target distance and speed information are obtained by analyzing the signal processing module.

[0056] The frequency-modulated continuous wave laser radar provided by the embodiment of the present application is provided with a silicon optical chip 300 for connecting the frequency-modulated light source 100 and the coherent receiving module 330, and the silicon optical chip 300 is formed with a first waveguide layer 301 and a second waveguide layer 302, wherein the tolerance of the first waveguide layer 301 to the optical power is higher than that of the second waveguide layer 302, and therefore a suitable first light splitting unit can be made on the first waveguide layer 301 to realize the connection between the frequency-modulated light source 100 and the coherent receiving module 330 in the silicon optical chip 300. The benefits brought by this include but are not limited to: the external separate devices such as the fiber optical splitter are no longer needed to complete the light splitting function, and the system integration and reliability can be effectively improved, and the system size and cost can be reduced; meanwhile, the light signal of the first waveguide layer 301 can be conveniently transferred to the second waveguide layer 302 by using the interlayer mode converter 303, wherein the second waveguide layer 302 can adopt a silicon waveguide layer, and therefore the advantages of the original silicon layer device can be compatible; and since the silicon nitride layer and the silicon layer can be realized on the same silicon optical chip 300 according to the current process, when the first waveguide layer 301 adopts a silicon nitride waveguide layer and the second waveguide layer 302 adopts a silicon waveguide layer, the ultra-high density integration can be realized, and the process CMOS (Complementary Metal Oxide Semiconductor, the abbreviation of complementary metal oxide semiconductor) is compatible, and has extremely high mass productivity. Since the optical power of the local oscillator light split by the first light splitting unit in the silicon optical chip 300 is less than or equal to 50 mW, the silicon layer two-photon absorption effect in the case of high-power output can be solved.

[0057] In a specific embodiment, as shown in Figure 2 The silicon optical chip 300 includes a substrate layer 304, a buried oxygen layer 305, a second waveguide layer 302, an oxidation layer 306, a first waveguide layer 301 and an upper cladding layer 307 arranged in sequence. Specifically, the buried oxygen layer 305, the second waveguide layer 302, the oxidation layer 306, the first waveguide layer 301 and the upper cladding layer 307 are made layer by layer by epitaxial growth technology. It should be noted that the lengths of the first waveguide layer 301 and the second waveguide layer 302 are set according to the needs, and are generally less than the length of the substrate layer 304, and the oxidation layer 306 is connected with the buried oxygen layer 305 in the area beyond the coverage range of the second waveguide layer 302; and the upper cladding layer 307 is connected with the oxidation layer 306 in the area beyond the coverage range of the first waveguide layer 301. The first waveguide layer 301 is a silicon nitride waveguide layer, and the second waveguide layer 302 is a silicon waveguide layer.

[0058] The silicon waveguide layer is not suitable for transmitting a particularly large power optical signal, but has a high thermal-optical coefficient, which is conducive to reducing the power consumption of the device thereon; the silicon nitride waveguide can accommodate a larger optical power, but the chip made of the silicon nitride waveguide has a large power consumption. The frequency-modulated continuous wave laser radar provided in the embodiment is made of two waveguide layers of two different materials, and then the shortcomings of the waveguide layers are avoided, the excellent characteristics of the waveguide layers are fully utilized, and each device in the silicon optical chip 300 is prepared on a more suitable waveguide layer, so that the process requirement of device manufacturing is reduced. Since a good commercial SOI wafer can be obtained in the industry at present, the silicon nitride waveguide layer is generally above the silicon waveguide layer. At the same time, in order to reduce the volume of the interlayer mode converter 303, the output end of the first waveguide layer 301 and the input end of the second waveguide layer 302 are stacked. In this way, the volume of the interlayer mode converter 303 is minimized, the entire silicon optical chip 300 is compact in structure, and the manufacturing requirement is met.

[0059] Based on the existing chip preparation process, there are generally two cases for the vertical distance between the second waveguide layer 302 and the first waveguide layer 301: one case is that the two waveguide layers are close to each other, and the vertical distance between the two waveguide layers is in a range of greater than 50 nm and less than 400 nm; the other case is that the two waveguide layers are far away from each other, and the vertical distance between the two waveguide layers is in a range of greater than 1 μm and less than 4 μm. For the two cases, the structure of the interlayer mode converter 303 also changes accordingly.

[0060] Specifically, please refer to Figure 2 and Figure 3 When the vertical distance between the second waveguide layer 302 and the first waveguide layer 301 is greater than 50 nm and less than 400 nm, the distance between the first waveguide layer 301 and the second waveguide layer 302 is close, and generally there is a relatively thin oxide layer 306 between the two layers, so that the optical signals in the two waveguide layers can be converted between the layers through evanescent wave coupling in the interlayer mode converter 303, thereby realizing low-loss optical propagation between the two waveguide layers and facilitating design and processing. The interlayer mode converter 303 in the embodiment can adopt any interlayer mode converter 303 that can realize evanescent wave coupling, which is not uniquely limited here.

[0061] Please refer to Figure 3 In an optional embodiment, the portions of the first waveguide layer 301 and the second waveguide layer 302 located in the interlayer mode converter 303 are both tapered. The interlayer mode converter 303 is a tapered waveguide mode converter.

[0062] The mode effective refractive index of the light in the second waveguide layer 302 decreases with the decrease of the width, while the mode effective refractive index in the first waveguide layer 301 increases with the increase of the width, so as long as the widths on both sides of the two tapered waveguide mode converters are reasonably designed, the mode effective refractive index in the first waveguide layer 301 can be equal to the mode effective refractive index of the second waveguide layer 302 at a certain position, and then as long as the length of the tapered waveguide mode converter is long enough, the light can be slowly converted from the first waveguide layer 301 to the second waveguide layer 302. The whole conversion process is stable and mature in technology.

[0063] Please refer to Figure 4 and Figure 5 When the vertical distance between the second waveguide layer 302 and the first waveguide layer 301 is greater than 1 μm and less than 4 μm, the distance between the first waveguide layer 301 and the second waveguide layer 302 is relatively far, and generally there is a relatively thick oxide layer 306 between the two layers. In this way, in the interlayer mode converter 303, the light in the first waveguide layer 301 will not be coupled with the light in the second waveguide layer 302 by evanescent wave coupling, and two gratings are used here to achieve this. Specifically, the first waveguide layer 301 and the second waveguide layer 302 are both formed with grating structures on the part located in the interlayer mode converter 303. The light signals in the two waveguide layers can be converted between the layers by the grating structures.

[0064] Specifically, the above-mentioned grating structure can be prepared on the corresponding waveguide layer by etching process. The setting of the grating structure destroys the original waveguide structure, so that the light can be emitted or received in a certain direction. When preparing, the angle θ of the grating structure emitting upward or downward can be changed by changing the grating period and duty cycle of the grating structure. Similarly, the angle θ of the grating structure receiving from below or from above can be changed by changing the grating period and duty cycle of the grating structure. The above-mentioned angle θ can be calculated by simulation software before preparing the grating structure, so as to ensure that the prepared grating structure meets the requirements, and then the light signal can be converted between the two waveguide sections through the two relatively arranged grating structures. In this way, the local oscillator light output by the first light splitting unit can enter the second waveguide layer 302 through the grating structure on the first waveguide layer 301, and then enter the coherent receiving module 330, and then propagate in the coherent receiving module 330 through the second waveguide layer 302, and finally output to the external signal processing module for subsequent processing.

[0065] The above-mentioned grating structure is arranged in a fan shape to realize a larger range of signal reception and emission, so as to ensure that the light signal converted from the first waveguide layer 301 to the second waveguide layer 302 will not be lost or the signal loss will be reduced to a minimum state.

[0066] In the above optical signal transmission process, the light exit angle or light receiving angle of the grating structure is 0-90°. The specific angle can be determined according to the material and preparation process of the first waveguide layer 301, the second waveguide layer 302 and the corresponding interlayer mode converter 303, and is not limited herein.

[0067] In some embodiments, the light exit angle or light receiving angle of the grating structure is 0-60°. With this angle range, the range of optional materials is wider.

[0068] To avoid the occurrence of two-photon absorption effect of the silicon layer, the optical power of the local oscillator light split by the first light splitting unit in the silicon optical chip 300 needs to be less than or equal to 50mW, but the optical power of the laser beam emitted by the frequency-modulated light source 100 varies greatly, so the first light splitting unit also has multiple implementation modes.

[0069] The first implementation mode:

[0070] The optical power of the laser beam emitted by the frequency-modulated light source 100 is small, at this time only one optical splitter is arranged in the first light splitting unit, and the optical power of the local oscillator light split can meet the requirement and can be transmitted in the silicon layer. Specifically, please refer to Figure 1 , the first light splitting unit includes a first optical splitter 311, the input end of the first optical splitter 311 is connected with the output end of the frequency-modulated light source 100, the first output end of the first optical splitter 311 is connected with the input end of the transceiver module 200 for outputting the probe light, and the second output end of the first optical splitter 311 is connected with the corresponding input end of the coherent receiving module 330 through the interlayer mode converter 303 for outputting the local oscillator light. The first optical splitter 311 has one input end and two output ends in this embodiment, and the splitting ratio is generally between 10:90 and 50:50, which can be flexibly selected according to the use requirement, and is not limited herein. The first light splitting unit adopts this structure, which is simple in structure and convenient to assemble.

[0071] The second implementation mode:

[0072] The optical power of the laser beam emitted by the frequency-modulated light source 100 is large, and the optical power of the local oscillator light split by one optical splitter is greater than 50mW, at this time if the local oscillator light is directly input into the coherent receiving module 330, the two-photon absorption effect of the silicon layer may be excited. To avoid the above situation, in an optional embodiment, please refer to Figure 6 and Figure 7As shown, the first light splitting unit includes a first light splitter 311 and a second light splitting unit. An input end of the first light splitter 311 is connected with an output end of the frequency-modulated light source 100. A first output end of the first light splitter 311 is connected with an input end of the transceiver module 200 for outputting the probe light. A second output end of the first light splitter 311 is connected with an input end of the second light splitting unit for outputting the local oscillation light. Output ends of the second light splitting unit are connected with corresponding input ends of the coherent receiving module 330 through the interlayer mode converters 303.

[0073] In the embodiment, the first light splitter 311 has the same structure as the first light splitter 311 in the first form, and the light splitting ratio is also between 10:90 and 50:50, which can be flexibly selected according to the use requirement, and is not uniquely limited here. The second light splitting unit in the embodiment can include one or more light splitters, which can be determined according to whether the light power of the split local oscillation light meets the requirement. The specific performance is as follows:

[0074] The first case:

[0075] The local oscillation light split by the first light splitter 311 is further split by another light splitter, and any one of the output local oscillation lights can meet the preset requirement (the light power is less than or equal to 50 mW). Please refer to Figure 6 As shown, the second light splitting unit includes a second light splitter 312. An input end of the second light splitter 312 is connected with the second output end of the first light splitter 311. Two output ends of the second light splitter 312 are respectively connected with input ends of the coherent receiving module 330 through the interlayer mode converters 303 for splitting the local oscillation light output by the first light splitter 311 into multiple beams and outputting to the coherent receiving module 330. In the embodiment, the second light splitter 312 has two output ends, and the light splitting ratio is generally between 1:99 and 50:50, which can be flexibly selected according to the use requirement, and is not uniquely limited here. The second light splitting unit adopts this structure, which is simple in structure and convenient to assemble.

[0076] The second case:

[0077] Since the second optical splitter 312 is divided into two branches, one of which is used to transport the local oscillator light to the probe light path in the receiving module, and the other is used to transport the local oscillator light to the nonlinear calibration light path in the receiving module. The optical signal power required by the nonlinear calibration light path is very small, so in practice the second optical splitter 312 will divide most of the light into the probe light path in the receiving module as the local oscillator light signal for subsequent coherent detection. Therefore, when the optical power of the laser beam output by the frequency-modulated light source 100 is large, it is very likely that the output end of the second optical splitter 312 for transporting the local oscillator light to the probe light path in the coherent receiving module 330 will output local oscillator light with an optical power greater than 50 mW. At this time, in order to avoid the occurrence of two-photon absorption effect of the silicon layer, the second optical splitting unit can adopt the following form. Please refer to Figure 7 As shown in FIG. 12, the second optical splitting unit includes a second optical splitter 312 and a third optical splitter 313 arranged in sequence along the transmission direction of the local oscillator light. The input end of the second optical splitter 312 is connected with the second output end of the first optical splitter 311. The first output end of the second optical splitter 312 is connected with the input end of the probe light path in the coherent receiving module 330 through an interlayer mode converter 303. The second output end of the second optical splitter 312 is connected with the input end of the third optical splitter 313. The two output ends of the third optical splitter 313 are respectively connected with the corresponding input ends of the coherent receiving module 330 through interlayer mode converters 303. Specifically, the third optical splitter 313 in the embodiment can be a single optical splitter or a combination of multiple optical splitters, which can be determined according to the splitting effect, and is not limited to be unique.

[0078] In an optional embodiment, the third optical splitter 313 in each of the above embodiments has two output ends, and the splitting ratios of the two output ends are 50:50 respectively. This structure facilitates subsequent signal analysis.

[0079] In an optional embodiment, please refer to Figure 1 As shown in FIG. 12, the first waveguide layer 301 further integrates a first mode spot conversion unit. The first mode spot conversion unit is used to match the light of the external device of the silicon optical chip 300 with the light of the first optical splitting unit, so as to reduce the mode mismatch loss.

[0080] Specifically, the first mode spot conversion unit has a plurality of mode spot converters. The number of mode spot converters is consistent with the number of connection ports of the silicon optical chip 300 and the external device. The connection port here refers to a port for propagating light.

[0081] In a specific embodiment, please refer to Figure 1 As shown in FIG. 12, the first mode spot conversion unit includes a first mode spot converter 321 and a third mode spot converter 323.

[0082] The first mode spot converter 321 is connected between the frequency-modulated light source 100 and the first light splitting unit, and is used for mode field matching between the frequency-modulated light source 100 and the first light splitting unit. Specifically, the input end of the first mode spot converter 321 is connected with the output end of the frequency-modulated light source 100, and the output end is connected with the input end of the first light splitting unit. The first mode spot converter 321 is arranged, so as to reduce the mode mismatch loss in the process of transmitting the light emitted by the frequency-modulated light source 100 to the first light splitting unit, and to reduce the additional loss caused by the two-photon absorption of the silicon layer. Therefore, the first mode spot converter 321 can be implemented in the first waveguide layer 301. The first waveguide layer 301 can support higher optical power transmission, so that even if the output optical power of the external frequency-modulated light source 100 is as high as 100 milliwatts, the light can also enter the silicon optical chip 300 through the first mode spot converter 321.

[0083] The third mode spot converter 323 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 200, and is used for mode field matching between the first light splitting unit and the corresponding end of the transceiver module 200, so as to transmit the probe light output by the first light splitting unit to the transceiver module 200. Specifically, the input end of the third mode spot converter 323 is connected with the output end for outputting the probe light in the first light splitting unit, and the output end is connected with the input end of the transceiver module 200.

[0084] Specifically, the model of the first mode spot converter 321 and the third mode spot converter 323 can be flexibly selected according to the mode spot size of the devices at both ends of each mode spot converter, which is not uniquely limited here. At the same time, since the first mode spot converter 321 and the third mode spot converter 323 are both prepared on the first waveguide layer 301, and the first waveguide layer 301 can withstand higher optical power, compared with the mode spot converter prepared in the silicon layer, the first mode spot converter 321 and the third mode spot converter 323 provided in the embodiment have advantages in process tolerance and alignment tolerance. At the same time, the first mode spot converter unit adopts this structure, so that the devices inside and outside the silicon optical chip 300 can be flexibly selected, without being limited by the mode spot size of each other, which is convenient for design.

[0085] Please refer to Figure 1 As shown in FIG. 8, 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 with the silicon optical chip 300, and is used for receiving and amplifying the probe light, the circulator 220 and the scanning unit 230 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 330.

[0086] The optical amplification unit 210 in the embodiment can be any one or a combination of multiple of a rare earth doped fiber amplifier, a semiconductor optical amplifier, and a Raman amplifier, and is mainly used for amplifying the probe light and outputting an optical signal with higher optical power. The scanning unit 230 in the embodiment can include one or more optical beam scanning modules, each of which can be any one of a galvanometer, a rotating mirror, a MEMS micro-mirror, or a combination of the above, and is mainly used for shaping, collimating, and scanning the probe light.

[0087] The circulator 220 in the embodiment is used for the amplified laser beam to pass through, and is also used for deflecting the received echo beam and emitting it to the coherent receiving module 330. Specifically, in use, the probe light is input from the first port of the circulator 220, and then output from the second port of the circulator 220. After that, the light beam can be output from the free space by the scanning unit 230 and emitted to the target object. After that, the echo signal reflected by the target object can return to the scanning unit 230 in the original path, enter the second port of the circulator 220, and be output from the third port of the circulator 220 to the coherent receiving module 330. The transceiver module 200 adopts this structure, which is simple in structure, easy to assemble and maintain, and stable in working performance.

[0088] In the above embodiments, the scanning unit 230 can be provided with one or more. When the scanning unit 230 is provided with only one, the scanning angle range of the single scanning unit 230 is limited, and a large-angle scanning range cannot be achieved. Therefore, in order to improve the scanning angle range of the laser radar, multiple scanning units 230 can be used. At this time, the number of circulators 220 also needs to be changed. That is, the circulator 220 and the scanning unit 230 are respectively provided with multiple, and are connected one by one. The number of circulators 220 and scanning units 230 can be flexibly selected according to the use needs to meet the scanning needs of different ranges.

[0089] On the basis of the above embodiments, please refer to Figure 1 The coherent receiving module 330 includes a probe light path. The probe light path includes a third light splitting unit, a mixing unit 334, and a combining unit 335 formed on the second waveguide layer 302 in sequence.

[0090] 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 splitting rotators 333, which can be selected according to the application requirements. Specifically, when it is necessary to split the echo signal, a polarization beam splitting rotator 333 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 coherent receiving module 330, and the other is to complete beam splitting inside the coherent receiving module 330. If either the echo signal or the local oscillator light has already been split outside the coherent receiving module 330, then there is no need to set up a beam splitting structure for the corresponding beam inside the coherent receiving module 330. 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, it is acceptable.

[0091] The mixing unit 334 is used to mix the sub-signal light and the first sub-local oscillator light to obtain multiple mixed beams. Specifically, the mixing unit 334 includes at least two optical mixers, the number of which can be determined according to the number of sub-signal lights or the number of first sub-local oscillator lights.

[0092] The combining unit 335 is used to perform photoelectric conversion on multiple mixed beams to obtain multiple coherent electrical signals. Specifically, the combining unit 335 includes at least two balanced detectors, each of which is connected to the optical mixer in the mixing unit 334 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.

[0093] The coherent receiving module 330 adopts the structure provided in this embodiment, which is simple, stable, and easy to design.

[0094] In an optional embodiment, please refer to Figure 1 As shown, in addition to the aforementioned detection optical path, the coherent receiving module 330 also includes a nonlinear calibration optical path.

[0095] The nonlinear calibration light path comprises, in sequence along the local light propagation direction, a fourth light splitting unit, a coupler 331 and a first balanced detector 332 formed on the second waveguide layer 302, the fourth light splitting unit is configured to receive the local light, split the local light into two second local light beams, and make the two second local light beams have different delays, the coupler 331 is configured to mix the two second local light beams with different delays, and the first balanced detector 332 is configured to receive the mixed light output by the coupler 331 and perform balanced detection.

[0096] The coupler 331 in the embodiment is generally a 3dB coupler, and other couplers capable of achieving the above functions can also be used. In use, the output signal of the first balanced detector 332 can be further processed as the basis for calibration of the frequency-modulated light source 100. By using the frequency-modulated continuous wave laser radar provided in the embodiment, the frequency-modulated light source 100 can be calibrated in real time, so that the operator can timely find problems and adjust them, thereby ensuring the accuracy of the detection result.

[0097] In an alternative embodiment, as shown in Figure 1 The coherent receiving module 330 further comprises a second mode spot conversion unit formed on the second waveguide layer 302, and the second mode spot conversion unit is configured to perform mode field matching between the light of the corresponding device in the transceiver module 200 and the light of the corresponding device in the coherent receiving module 330, and reduce the mode mismatch loss.

[0098] Specifically, the second mode spot conversion unit comprises a second mode spot converter 322. The second mode spot converter 322 is connected in one-to-one correspondence with the output end of the echo signal in the transceiver module 200, so as to reduce the mode field mismatch loss of this part. Since this part of the light signal is generally weak and cannot easily excite the two-photon absorption effect of the silicon layer, it can be implemented on the second waveguide layer 302. If it is implemented on the first waveguide layer 301, an additional interlayer mode converter 303 is needed, which causes additional mode conversion loss and is not recommended.

[0099] By using the structure provided in the embodiment, the coherent receiving module 330 can realize stable transmission of the echo signal, and can make the devices in the silicon optical chip 300 except the mode spot converter be not affected by the mode spot size of other devices when designed, thereby facilitating the design.

[0100] The mode spot converter in each of the above embodiments can be any one of a tapered waveguide, a cantilever beam waveguide, a multilayer waveguide, etc., and can be flexibly selected according to the use needs.

[0101] To reduce the volume of the frequency-modulated continuous wave laser radar, we prefer to integrate the required light splitting structure of the echo signal and the local light in the silicon optical chip 300 and the silicon optical chip 300, so that the first light splitting unit and the third light splitting unit need to form a consistent number of sub-signal light and the first local light, and since the first light splitting unit has multiple implementation ways, the third light splitting unit in each of the above embodiments also has multiple implementation ways, and the implementation way of the third light splitting unit will change with the change of the implementation way of the first light splitting unit. For ease of understanding, the specific structure of the third light splitting unit will be described below with the example that the coherent receiving module 330 includes the above detection light path, the above nonlinear calibration light path, and the above second mode spot conversion unit.

[0102] Please refer to Figure 1 When the first light splitting unit adopts the first implementation way, that is, the first light splitting unit includes the above first light splitter 311, the third light splitting unit includes a polarization beam splitter rotator 333, and the above second light splitter 312, third light splitter 313 and fourth light splitter 314. Among them, the second light splitter 312 is connected with the output end of the first light splitter 311 for outputting local light through the third mode spot converter 323 and the second mode spot converter 322; the third light splitter 313 and the fourth light splitter 314 are respectively connected to the two output ends of the second light splitter 312, the third light splitter 313 decomposes the local light into a plurality of first sub-local light, one of the outputs of the fourth light splitter 314 is directly connected with the coupler 331, and the other output is connected with the coupler 331 through the optical delay line 315; the polarization beam splitter rotator 333 is connected with the circulator 220 through the fourth mode spot converter, and is used for dividing the echo signal into two sub-signal lights, and transmitting the two sub-signal lights into the corresponding optical mixers one by one. At this time, the fourth light splitter 314 is used for dividing the output light from the second light splitter 312 into two lights according to a certain light splitting ratio, one of the two lights enters the optical delay line 315, and the other light is directly connected with the coupler 331. The optical delay line 315 is used for generating a delay for the optical signal, and its output end is connected with the coupler 331.

[0103] Please refer to Figure 6 When the first light splitting unit adopts the first implementation way, that is, the first light splitting unit includes the above first light splitter 311, the third light splitting unit includes a polarization beam splitter rotator 333, and the above second light splitter 312, third light splitter 313 and fourth light splitter 314. Among them, the second light splitter 312 is connected with the output end of the first light splitter 311 for outputting local light through the third mode spot converter 323 and the second mode spot converter 322; the third light splitter 313 and the fourth light splitter 314 are respectively connected to the two output ends of the second light splitter 312, the third light splitter 313 decomposes the local light into a plurality of first sub-local light, one of the outputs of the fourth light splitter 314 is directly connected with the coupler 331, and the other output is connected with the coupler 331 through the optical delay line 315; the polarization beam splitter rotator 333 is connected with the circulator 220 through the fourth mode spot converter, and is used for dividing the echo signal into two sub-signal lights, and transmitting the two sub-signal lights into the corresponding optical mixers one by one. At this time, the fourth light splitter 314 is used for dividing the output light from the second light splitter 312 into two lights according to a certain light splitting ratio, one of the two lights enters the optical delay line 315, and the other light is directly connected with the coupler 331. The optical delay line 315 is used for generating a delay for the optical signal, and its output end is connected with the coupler 331.

[0104] Please refer to Figure 7As shown, when the first light splitting unit adopts the second case in the second implementation, the third light splitting unit includes a polarization beam splitter rotator 333 and the fourth light splitter 314 described above. At this time, the fourth light splitter 314 is used to split the output light from the second light splitter 312 into two beams of light according to a certain splitting ratio, one of which enters the optical delay line 315, and the other is directly connected to the coupler 331. The optical delay line 315 is used to produce a delay for the optical signal, and its output end is connected to the coupler 331.

[0105] In an optional embodiment, the fourth light splitter in each of the above embodiments has two output ends, and the splitting ratios of the two are 50:50 respectively. Using this structure facilitates subsequent signal analysis.

[0106] In each of the above embodiments, the polarization beam splitter rotator is connected to the circulator one by one through the fourth mode spot converter. Each polarization beam splitter rotator is used to split the echo signal of any polarization into two beams of polarization-determined sub-signal light, and its output is connected to the input end of the two optical mixers as signal light input. And the polarization state of the light output by each polarization beam splitter rotator is the same as that of the light output by the corresponding third light splitter.

[0107] Please refer to Figure 8 In a specific embodiment, the frequency-modulated continuous wave laser radar includes a frequency-modulated light source 100, an optical amplifier, a circulator 220, an interlayer mode converter 303, N scanning units 230, N circulators 220, 2N optical mixers, 2 first mode spot converters 321, 1 second mode spot converter 322, 1 third mode spot converter 323, N fourth mode spot converters, 2N+1 balanced detectors, N polarization beam splitter rotators 333, 1 first light splitter 311, 1 second light splitter 312, 1 third light splitter 313, and 1 fourth light splitter 314. The optical amplifier has N output ports, and the third light splitter 313 has 2N output ports. The third ports of the N circulators 220 are connected to the N polarization beam splitter rotators 333 through the fourth mode converters. The interlayer mode converter 303 is located between the first light splitter 311 and the second light splitter 312.

[0108] Please refer to Figure 9 As shown, if the number of channels is large, that is, the light entering the third light splitter 313 becomes more, resulting in that the optical power exceeds the requirement of the silicon waveguide, the interlayer mode converter 303 in the above frequency-modulated continuous wave laser radar can also be placed between the second light splitter 312 and the third light splitter 313, and between the second light splitter 312 and the fourth light splitter 314.

[0109] Please refer to Figure 10As shown, in order to realize the optical delay line 315 with longer length and smaller loss, the optical delay line 315 in each of the above embodiments can be made on the first waveguide layer 301. Then, an interlayer mode converter 303 can be added between the optical delay line 315 and the 3dB coupler, and an interlayer mode converter 303 can be added between the fourth optical splitter 314 and the 3dB coupler.

[0110] The above only describes the preferred embodiments of the present application, and only describes the technical principles of the present application. These descriptions are only for explaining the principles of the present application, and cannot be explained as the limitation of the protection scope of the present application in any way. Based on the explanations herein, any modification, equivalent replacement and improvement within the spirit and principle of the present application, and other specific embodiments of the present application which can be thought by those skilled in the art without creative labor, should be included in the protection scope of the present application.

Claims

1. A frequency-modulated continuous wave lidar, characterized in that, It includes a frequency-modulated light source, a transceiver module, and a silicon photonics chip; the frequency-modulated light source and the transceiver module are both located outside the silicon photonics chip; The frequency-modulated light source is used to emit a laser beam; The transceiver module is used to receive the probe light output by the silicon photonics chip, and to shape and collimate the probe 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 silicon photonics chip. The silicon photonic chip is connected between the frequency-modulated light source and the transceiver module. The silicon photonic chip includes a first waveguide layer and a second waveguide layer arranged sequentially. The first waveguide layer can accommodate a greater optical power than the second waveguide layer, and two inter-layer mode converters are formed between the first and second waveguide layers. A first beam splitting unit is integrated on the first waveguide layer. 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, and the optical power of each local oscillator beam is less than or equal to 50mW. A coherent receiving module is integrated on the second waveguide layer. The coherent receiving module is signal-connected to the first beam splitting unit through the inter-layer mode converter and is used to receive the local oscillator beam. The coherent receiving module is also connected to the output terminal of the transceiver module for outputting the echo signal, and is used to combine the local oscillator beam and the echo signal, perform coherent frequency beat, and transmit the processed signal to an external signal processing module. 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 silicon photonic chip and is used to receive and amplify the detection light. The circulator and the scanning unit 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.

2. The frequency-modulated continuous wave lidar as described in claim 1, characterized in that, When the vertical spacing between the second waveguide layer and the first waveguide layer is greater than 50 nm and less than 400 nm, the optical signals in the two waveguide layers can achieve inter-layer conversion through evanescent wave coupling in the inter-layer mode converter.

3. The frequency-modulated continuous wave lidar as described in claim 2, characterized in that, The portions of the first and second waveguide layers located within the interlayer mode converter are both tapered; the interlayer mode converter is a tapered waveguide mode converter.

4. The frequency-modulated continuous wave lidar as described in claim 1, characterized in that, When the vertical distance between the second waveguide layer and the first waveguide layer is greater than 1 μm and less than 4 μm, grating structures are formed on the portions of the first waveguide layer and the second waveguide layer located within the inter-layer mode converter; the optical signals within the two waveguide layers can achieve inter-layer conversion through the grating structures.

5. The frequency-modulated continuous wave lidar as described in claim 1, characterized in that, 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. The first output end of the first beam splitter is connected to the input end of the transceiver module and is used to output 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 interlayer mode converter and is used to output the local oscillator light.

6. The frequency-modulated continuous wave lidar as described in claim 1, characterized in that, 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. The first output end of the first beam splitter is connected to the input end of the transceiver module 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 interlayer mode converter for splitting the local oscillator light output by the first beam splitter into multiple beams and outputting them to the coherent receiving module.

7. The frequency-modulated continuous wave lidar as described in claim 6, characterized in that, The second beam splitting unit includes a second beam splitter, the input end of which 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 interlayer mode converter; 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 interlayer mode converter. 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 interlayer mode converter.

8. The frequency-modulated continuous wave lidar as described in any one of claims 1-7, characterized in that, The circulator and the scanning unit are provided in multiples, and are connected in a one-to-one correspondence.

9. The frequency-modulated continuous wave lidar as described in any one of claims 1-7, characterized in that, The coherent receiving module includes a detection optical path, which includes a third beam splitting unit, a mixing unit, and a combining unit sequentially formed on the second waveguide layer. 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; The mixing unit is used to mix the sub-signal light and the first sub-local oscillator light to obtain multiple mixed beams of light; The synthesis unit is used to perform photoelectric conversion on the multiple mixed beams to output multiple coherent electrical signals.

10. The frequency-modulated continuous wave lidar as described in claim 9, characterized in that, The coherent receiving module also includes a nonlinear calibration optical path; The nonlinear calibration optical path includes a fourth beam splitting unit, a coupler, and a first balanced detector, which are sequentially formed on the second waveguide layer 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 balanced detector is used to receive the mixed light output by the coupler and perform balanced detection.

11. The frequency-modulated continuous wave lidar as described in claim 9, characterized in that, The first waveguide layer also integrates a first mode conversion unit, which is used to perform mode field matching between the light from the external device of the silicon photonic chip and the light from the first beam splitter. The coherent receiving module further includes a second mode conversion unit formed on the second waveguide layer. The second mode conversion unit is used to perform mode field matching between the light of the corresponding device in the transceiver module and the light of the corresponding device in the coherent receiving module.

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