A lidar ranging and imaging system and method

Abstract

The application discloses a laser radar ranging and imaging system and method, the system comprising a dual-wavelength laser emission module, a common-path optical transceiver module and a non-splitting detection module; the common-path optical transceiver module is used for combining the violet laser pulse and the near-infrared laser pulse into a coaxial laser beam and directing the coaxial laser beam to a target, receiving echo light signals returned from the target and containing the violet laser pulse and the near-infrared laser pulse and guiding the echo light signals out as a whole; the non-splitting detection module comprises a gallium nitride photodetector, a silicon photomultiplier detector and a signal processor. The application utilizes the dual-function characteristics of the gallium nitride photodetector, i.e. the absorption of violet light and the transmission of infrared light, to directly separate the water-bottom echo and the water-surface echo at a physical layer. The design fundamentally eliminates the depth measurement error caused by signal aliasing in a traditional single-wavelength system, and significantly improves the measurement accuracy.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser ranging and imaging technology, in particular to a laser radar ranging and imaging system and method. BACKGROUND

[0002] Laser radar technology and semiconductor optoelectronic devices have developed rapidly in recent years and have shown important value in multiple industries. Laser radar has a wide range of applications in high-precision measurement, environmental perception, and other fields, especially in water depth measurement, which provides an effective means for obtaining water surface and water bottom distance information. With the continuous progress of related technologies, people have higher requirements for the precision, efficiency, and cost of laser radar in water depth measurement, expecting it to better adapt to complex measurement environments and provide more accurate data support for related fields of research and application.

[0003] In the laser radar technology for water depth measurement, traditional methods have their own characteristics to solve measurement problems. Single-wavelength lasers such as green light are commonly used to obtain water bottom echo signals by utilizing the penetration ability of laser in water. Meanwhile, to address the shortcomings of single-wavelength systems, the industry has proposed a dual-wavelength detection scheme. In addition, traditional silicon-based detectors are often used for signal detection.

[0004] However, the existing technology has obvious defects. Single-wavelength technology cannot effectively distinguish between reflection signals from the water surface and reflection signals from the water bottom, and when the water body is turbid or there is wave disturbance on the water surface, the two signals are easily mixed and overlapped, leading to measurement errors. Traditional silicon-based detectors have low quantum efficiency in the blue-green light band and are easily disturbed by ambient light, resulting in insufficient sensitivity for weak echo signals after penetrating the water body. The receiving end of the existing dual-wavelength detection scheme usually needs to use optical elements such as beam splitters to separate signals of different wavelengths, making the optical path complex and causing significant loss of optical energy, reducing the overall detection efficiency of the system. SUMMARY

[0005] To solve the technical problems in the existing technology, the present application provides a laser radar ranging and imaging system and method.

[0006] The laser radar ranging and imaging system and method provided by the present application adopt the following technical solutions:

[0007] A laser radar ranging and imaging system, comprising:

[0008] a dual-wavelength laser emission module for emitting purple light laser pulses in a first wavelength range and near-infrared laser pulses in a second wavelength range;

[0009] A common-path optical transceiver module for combining the violet laser pulses and the near-infrared laser pulses into a coaxial laser beam and directing the coaxial laser beam to a target, and receiving a return optical signal containing the violet laser pulses and the near-infrared laser pulses from the target and guiding the return optical signal as a whole out of the common-path optical transceiver module;

[0010] A non-splitting detection module including a gallium nitride photodetector, a silicon photomultiplier detector, and a signal processor, the gallium nitride photodetector is disposed on a path of the return optical signal for absorbing and detecting the violet part of the return optical signal, the silicon photomultiplier detector is disposed on a side of the gallium nitride photodetector opposite to the return optical signal for receiving and detecting the near-infrared part of the return optical signal penetrating the gallium nitride photodetector, and the signal processor is in communication connection with the gallium nitride photodetector and the silicon photomultiplier detector for calculating distance or three-dimensional shape information according to the received signals.

[0011] In some embodiments, the dual-wavelength laser emission module includes a violet laser, a near-infrared laser, a first collimating mirror, and a second collimating mirror, the violet laser is configured to generate violet laser pulses, the near-infrared laser is configured to generate near-infrared laser pulses, the first collimating mirror is disposed on a first emission path of the violet laser, the second collimating mirror is disposed on a second emission path of the near-infrared laser, and the first emission path and the second emission path are coaxial, and an emission end of the violet laser and an emission end of the near-infrared laser are oppositely disposed.

[0012] The common-path optical transceiver module includes a beam combining mirror having a first reflecting surface and a second reflecting surface perpendicular to each other, the first reflecting surface is disposed on the first emission path and forms a 45° angle with the first emission path, the second reflecting surface is disposed on the second emission path and forms a 45° angle with the second emission path, the violet laser pulses and the near-infrared laser pulses generated by the violet laser and the near-infrared laser, respectively, are first collimated by the first collimating mirror and the second collimating mirror, respectively, and then reflected by the first reflecting surface and the second reflecting surface, respectively, and combined into the coaxial laser beam.

[0013] In some embodiments, the common-path optical transceiver module further comprises an aperture mirror and a scanning galvanometer assembly, the aperture mirror has a central aperture in the center thereof, the central aperture is located on the path of the coaxial laser beam, the scanning galvanometer assembly is disposed on the side of the aperture mirror away from the beam combiner, the coaxial laser beam passes through the central aperture and is guided to the target by the scanning galvanometer assembly, and the return light signal from the target is guided to the mirror surface of the aperture mirror by the scanning galvanometer assembly and is reflected to the receiving end of the gallium nitride photodetector.

[0014] In some embodiments, the scanning galvanometer assembly comprises a first rotatable galvanometer, a second rotatable galvanometer, and a first galvanometer driver and a second galvanometer driver for driving the rotation of the first rotatable galvanometer and the second rotatable galvanometer respectively, wherein, in the emission path, the first rotatable galvanometer performs the first deflection on the coaxial laser beam, and the second rotatable galvanometer performs the second deflection on the light beam reflected by the first rotatable galvanometer to guide the light beam to the target; in the receiving path, the return light signal is collected and guided by the second rotatable galvanometer and the first rotatable galvanometer in reverse order.

[0015] In some embodiments, the non-splitting detection module further comprises a filter, the filter is disposed on the optical path between the gallium nitride photodetector and the silicon photomultiplier detector, and is used for filtering out stray light and allowing only near-infrared light in a preset wavelength range to pass through.

[0016] In some embodiments, the gallium nitride photodetector comprises a sapphire substrate, an n-type gallium nitride semiconductor layer formed on the sapphire substrate, a p-type gallium nitride semiconductor layer formed on the n-type gallium nitride semiconductor layer and constituting a p-n junction with the n-type gallium nitride semiconductor layer, and a p-type electrode and an n-type electrode electrically connected to the p-type gallium nitride semiconductor layer and the n-type gallium nitride semiconductor layer respectively.

[0017] The selective response of the gallium nitride photodetector to violet light and near-infrared light is based on the band gap energy of the gallium nitride material constituting the n-type gallium nitride semiconductor layer and the p-type gallium nitride semiconductor layer: the energy of the violet light photons is higher than the band gap energy, so the violet light photons are absorbed by the p-n junction to generate a photocurrent; the energy of the near-infrared light photons is lower than the band gap energy, so the near-infrared light photons are transmitted through the gallium nitride photodetector.

[0018] In some embodiments, the distance between the gallium nitride photodetector and the silicon photomultiplier detector along the light signal incident path is less than 1 millimeter, and the gallium nitride photodetector and the silicon photomultiplier detector constitute a confocal plane integrated package.

[0019] In some embodiments, the first wavelength ranges from 380 nanometers to 420 nanometers, and the second wavelength ranges from 895 nanometers to 915 nanometers.

[0020] The application also provides a laser radar ranging and imaging method, which is suitable for the laser radar ranging and imaging system and comprises the following steps:

[0021] The dual-wavelength laser emission module and the common-path optical transceiver module synchronously and coaxially emit the violet laser pulses and the near-infrared laser pulses to the water body;

[0022] The common-path optical transceiver module combines the violet laser pulses and the near-infrared laser pulses into a coaxial laser beam and directs the coaxial laser beam to the water body, receives the echo optical signals containing the violet laser pulses and the near-infrared laser pulses returned from the water body, and leads the echo optical signals out as a whole, wherein the violet laser pulses penetrate the water body and are reflected by the water bottom, carrying the water bottom distance information, and the near-infrared laser pulses are reflected by the water surface, carrying the water surface distance information;

[0023] The gallium nitride photodetector absorbs and detects the violet laser pulse part in the echo optical signals to generate a first electric signal, and the silicon photomultiplier detector receives and detects the near-infrared laser pulse part in the echo optical signals penetrating the gallium nitride photodetector to generate a second electric signal;

[0024] The signal processor calculates the time difference between the first electric signal and the second electric signal, and calculates the water depth of the water body according to the time difference.

[0025] In some embodiments, the water depth of the water body is calculated by the following formula:

[0026]

[0027] wherein, Depth is the water depth of the water body, Δt is the time difference between the first electric signal and the second electric signal, c is the speed of light in vacuum, n is the refractive index of the water body.

[0028] In summary, the application has at least one of the following beneficial technical effects:

[0029] 1. The dual-functionality of the gallium nitride (GaN) detector, which absorbs violet light and transmits infrared light, directly separates the underwater echo (violet light) from the water surface echo (infrared light) at the physical level. This design fundamentally eliminates the depth measurement error caused by signal aliasing in traditional single-wavelength systems, significantly improves measurement accuracy, and the innovative GaN+SiPM confocal plane integrated detection module eliminates the need for dichroic mirrors and other optical elements required by traditional dual-wavelength systems, greatly simplifying the optical system structure. This non-splitting design avoids severe light energy loss, and the light energy utilization rate of the echo signal is revolutionarily improved from about 45% in the traditional scheme to more than 95%.

[0030] 2. Based on the physical properties of gallium nitride material, the detector has natural cutoff and suppression capability for most visible light (>450nm) in sunlight, which can effectively suppress more than 90% of environmental light interference, reduce the requirement for subsequent optical filtering system, and enhance the robustness of the system under various lighting conditions. The silicon photomultiplier detector has a built-in narrowband filter to resist solar background noise; it has the potential for all-weather operation.

[0031] 3. By using an open-hole mirror, the emission path and the receiving path are ingeniously integrated on the same optical axis, realizing an efficient common-path design. This design takes advantage of the diameter difference between the emitted light beam and the returned light beam. Most of the returned signal photons are effectively collected and reflected by the mirror to the detector, with little effect on the receiving efficiency, ensuring extremely high echo signal receiving efficiency. Only a small part of the echo energy coincides with the emission path and is lost through the central hole, which is negligible for the entire echo signal. This ensures that the detector can receive as much effective signal energy as possible, minimizing signal loss.

[0032] 4. Due to the elimination of expensive and precisely calibrated optical elements, and the use of highly integrated non-splitting detection modules, the overall manufacturing cost, size, and debugging difficulty of the system are significantly reduced, laying the foundation for providing a commercially viable, mobile platform-mounted high-precision hydrographic surveying and mapping innovation solution. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a structural schematic diagram of a laser radar ranging and imaging system provided by an embodiment of the present application;

[0034] Figure 2 is a structural schematic diagram of a gallium nitride photodetector in Figure 1

[0035] Figure 3 is a pulse timing diagram of a laser radar ranging and imaging system;

[0036] ​Explanation of reference signs: 1, dual-wavelength laser emission module; 11, violet laser; 12, near-infrared laser; 13, first collimating mirror; 14, second collimating mirror; 2, common-path optical transceiver module; 21, beam combiner; 22, aperture mirror; 23, scanning galvanometer assembly; 231, first rotatable galvanometer; 232, second rotatable galvanometer; 24, aperture stop; 3, non-splitting detection module; 31, gallium nitride photodetector; 311, sapphire substrate; 312, n-type gallium nitride semiconductor layer; 313, p-type gallium nitride semiconductor layer; 314, p-type electrode; 315, n-type electrode; 32, silicon photomultiplier detector; 33, optical filter; 34, signal processor; 35, third collimating mirror; 4, target. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be further described in detail below with reference to the drawings. The described embodiments are only possible technical implementations of the present application, but are not limited thereto, and other embodiments obtained by those skilled in the art without creative effort based on the embodiments of the present application are also within the protection scope of the present application.

[0038] Embodiment 1: Laser radar ranging and imaging system;

[0039] Please refer to Figure 1 The laser radar ranging and imaging system provided by the embodiments of the present application includes a dual-wavelength laser emission module 1, a common-path optical transceiver module 2, and a non-splitting detection module 3. The dual-wavelength laser emission module 1 is used to emit violet laser pulses in a first wavelength range and near-infrared laser pulses in a second wavelength range. The common-path optical transceiver module 2 is used to combine the violet laser pulses and the near-infrared laser pulses into a coaxial laser beam and direct the coaxial laser beam to a target 4, and receive a return light signal containing the violet laser pulses and the near-infrared laser pulses returned from the target 4 and guide the return light signal as a whole out. The non-splitting detection module 3 includes a gallium nitride photodetector 31, a silicon photomultiplier detector 32, and a signal processor 34. The gallium nitride photodetector 31 is arranged on the path of the return light signal and is used to absorb and detect the violet part in the return light signal. The silicon photomultiplier detector 32 is arranged on the side of the gallium nitride photodetector 31 facing away from the return light signal and is used to receive and detect the near-infrared part in the return light signal that has penetrated the gallium nitride photodetector 31. The signal processor 34 is in communication connection with the gallium nitride photodetector 31 and the silicon photomultiplier detector 32 and is used to calculate the distance or three-dimensional shape information according to the received signals. The system achieves the effect of high-precision and high-efficiency dual-wavelength laser radar ranging and imaging, because the system detects by dual-wavelength and physically separates different wavelength signals, avoids signal aliasing, improves light energy utilization, and enhances the detection capability of weak signals.

[0040] The specific description of each module is as follows:

[0041] Please refer to Figure 1 The dual-wavelength laser emission module 1 is responsible for generating and preliminarily processing laser pulses of two wavelengths. In a preferred scheme, it includes a violet laser 11, a near-infrared laser 12, a first collimating mirror 13, and a second collimating mirror 14. The violet laser 11 can be a violet LED or the like, which is used to generate violet laser pulses. The near-infrared laser 12 can be an infrared laser diode or the like, which is used to generate near-infrared laser pulses. The first collimating mirror 13 is arranged on a first emission light path of the violet laser 11, which can collimate the light emitted by the violet laser 11 to form a parallel light beam, or can be replaced by a lens group or the like. The second collimating mirror 14 is arranged on a second emission light path of the near-infrared laser 12, which also serves to collimate the near-infrared light, and can be replaced by other collimating structures. The first emission light path and the second emission light path are coaxial, and the emission end of the violet laser 11 is arranged opposite to the emission end of the near-infrared laser 12.

[0042] In this embodiment, the violet laser 11 can be a violet LED with a center wavelength of 405 nm, and the near-infrared laser 12 can be an infrared laser diode with a center wavelength of 905 nm. The emission ends of the two are arranged opposite to each other, and their light paths (the first emission light path and the second emission light path) are on the same straight line.

[0043] The common-path optical transceiver module 2 is the hub of the system's light path, responsible for beam combining, scanning, emission, and reception. It includes a combining mirror 21, a hole mirror 22, a scanning galvanometer assembly 23, and an aperture stop 24, wherein:

[0044] The combining mirror 21 has a first reflecting surface and a second reflecting surface perpendicular to each other. The first reflecting surface is arranged on the first emission light path and forms a 45° angle with the first emission light path, and the second reflecting surface is arranged on the second emission light path and forms a 45° angle with the second emission light path. In this way, the violet laser pulses and the near-infrared laser pulses generated by the violet laser 11 and the near-infrared laser 12, respectively, are first collimated by the first collimating mirror 13 and the second collimating mirror 14, respectively, and then reflected by the first reflecting surface and the second reflecting surface, respectively, and combined into a coaxial laser beam. The combining mirror 21 here can also be replaced by other optical structures with combining function.

[0045] The hole mirror 22 has a central hole in the center, which is located on the path of the coaxial laser beam, for allowing the emitted coaxial laser beam to pass unobstructed.

[0046] The aperture stop 24 is arranged on the light path after the hole mirror 22, for shaping the coaxial laser beam and controlling the quality of the coaxial laser beam.

[0047] The scanning galvanometer assembly 23 is arranged on the side of the aperture mirror 22 away from the beam combiner 21. The coaxial laser beam passes through the central aperture and is guided by the scanning galvanometer assembly 23 to the target 4. The echo signal returned from the target 4 is guided by the scanning galvanometer assembly 23 to the mirror surface of the aperture mirror 22 and is reflected to the receiving end of the gallium nitride photodetector 31. The scanning galvanometer assembly 23 can precisely control the direction of the laser beam and realize scanning of the target 4 region.

[0048] Specifically, please refer to Figure 1 The scanning galvanometer assembly 23 includes a first rotatable galvanometer 231, a second rotatable galvanometer 232, and a first galvanometer driver and a second galvanometer driver for driving the two rotatable galvanometers, respectively. In the transmission path, the first rotatable galvanometer 231 performs the first deflection on the coaxial laser beam, and the second rotatable galvanometer 232 performs the second deflection on the light beam reflected by the first rotatable galvanometer 231 to guide it to the target 4. In the receiving path, the echo signal is collected and guided by the second rotatable galvanometer 232 and the first rotatable galvanometer 231 in reverse order. The first rotatable galvanometer 231 and the second rotatable galvanometer 232 can be a mirror structure driven by a galvanometer motor, and the first galvanometer driver and the second galvanometer driver can be a step motor driver, of course, other driving modes that can realize the rotation control of the galvanometer can also be used.

[0049] The non-splitting detection module 3 is responsible for separating and detecting the echo signals of the two wavelengths without splitting. It includes a gallium nitride photodetector 31, a silicon photomultiplier detector 32, a filter 33, and a signal processor 34.

[0050] Please refer to Figure 1 and Figure 2 The gallium nitride photodetector 31, as the first level detector, has a specific multi-layer structure, including a sapphire substrate 311, an n-type gallium nitride semiconductor layer 312 formed on the sapphire substrate 311, a p-type gallium nitride semiconductor layer 313 formed on the n-type gallium nitride semiconductor layer 312 and constituting a p-n junction with the n-type gallium nitride semiconductor layer 312, and a p-type electrode 314 and an n-type electrode 315 electrically connected to the p-type gallium nitride semiconductor layer 313 and the n-type gallium nitride semiconductor layer 312, respectively. The selective response of the gallium nitride photodetector 31 to violet light and near-infrared light is based on the band gap energy of the gallium nitride material constituting the n-type gallium nitride semiconductor layer 312 and the p-type gallium nitride semiconductor layer 313: the energy of the violet light photon is higher than the band gap energy, so it is absorbed by the p-n junction to generate photocurrent; the energy of the near-infrared light photon is lower than the band gap energy, so it transmits through the gallium nitride photodetector 31. The sapphire substrate 311 here can also be replaced by other substrate materials with similar support and optical properties.

[0051] The core principle of this technical solution lies in the ingenious utilization of the bandgap energy characteristics of gallium nitride (GaN) semiconductor materials. Semiconductor materials can only absorb photons with energy higher than their bandgap energy, while remaining transparent to photons with energy lower than their bandgap energy. This solution precisely selects two laser wavelengths so that their photon energies are located precisely on both sides of the bandgap energy of the GaN material:

[0052] Violet light (approximately 405nm): Its photon energy is higher than the band gap energy of gallium nitride semiconductor materials, so it can be efficiently absorbed by gallium nitride detectors to produce the photoelectric effect.

[0053] Near-infrared light (approximately 905nm): Its photon energy is lower than the band gap energy of gallium nitride semiconductor materials, so it cannot be effectively absorbed and can penetrate gallium nitride detectors at a high rate.

[0054] Leveraging this physical characteristic, this scheme uses only a gallium nitride detector to act as a "color separator" in a traditional optical path, directly achieving the separation of two wavelength signals at the physical level, thus constructing a "non-splitting" detection module.

[0055] The silicon photomultiplier tube detector 32 (SiPM), as the second-stage detector, is positioned immediately behind the gallium nitride photodetector 31. The distance between the two is less than 1 mm, forming a confocal planar integrated package to maximize light energy utilization and reduce system size.

[0056] The filter 33 is disposed in the optical path between the gallium nitride detector and the silicon photomultiplier tube detector 32. It is usually a narrow-band filter 33 that only allows near-infrared light in a specific wavelength range (such as 905nm±10nm) to pass through, and is used to filter out ambient stray light and improve the signal-to-noise ratio.

[0057] The signal processor 34 is communicatively connected to the gallium nitride detector and the silicon photomultiplier tube detector 32, and is responsible for receiving electrical signals and performing subsequent calculations.

[0058] Preferably, the reflected echo light signal is focused by a third collimating lens 35 before illuminating the gallium nitride photodetector 31, so as to ensure that the size of the echo spot matches the effective area of ​​the gallium nitride photodetector 31, thereby optimizing the receiving efficiency.

[0059] The system works as follows:

[0060] Signal transmission: The system sends a trigger signal, and the violet laser 11 and near-infrared laser 12 in the dual-wavelength laser emission module 1 synchronously emit violet laser pulses with center wavelengths of 405nm and 905nm, respectively. After being collimated by the first collimating lens 13 and the second collimating lens 14, the two beams are precisely combined into a single coaxial dual-wavelength laser beam by the beam combiner 21.

[0061] Scanning and emission: The coaxial laser beam passes through the central hole of the aperture reflector 22 and reaches the scanning galvanometer assembly 23. The first rotatable galvanometer 231 and the second rotatable galvanometer 232 are precisely deflected under the control of the driver to modulate the path of the laser beam in two dimensions, so that it is directed towards the water body (target 4) in a scanning manner.

[0062] Signal reception: After the light beam reaches the water body, the two wavelengths undergo different physical interactions: the near-infrared light with an energy of 905nm has a high reflectivity at the water-air interface, and most of its energy is directly reflected by the water surface; while the violet light with an energy of 405nm penetrates the water body and is reflected by the target 4 at the bottom of the water due to its excellent penetrability in water. Therefore, two echo light signals carrying information about the water surface and the bottom of the water are generated respectively. These two echo light signals return along approximately the original path and are collected in reverse order by the first rotatable galvanometer 231 and the second rotatable galvanometer 232 of the scanning galvanometer assembly 23, and guided to the reflective surface of the aperture reflector 22.

[0063] Detection and Separation: The apertured reflector 22 reflects the echo beam carrying information about the water surface and bottom to the non-splittered detection module 3. The beam reflected by the apertured reflector 22 first illuminates the gallium nitride photodetector 31. Its internal pn junction absorbs the 405nm violet echo (bottom signal) and generates a photocurrent, completing the signal detection of distant targets 4 such as the bottom. The 905nm near-infrared echo (water surface signal) directly penetrates the gallium nitride photodetector 31 with an infrared transmittance of about 60%. After further purification by the filter 33, it is received by the silicon photomultiplier tube detector 32 behind it, completing the signal detection of near targets 4 such as the water surface.

[0064] Calculation and Imaging: The electrical signals generated by the two detectors are sent to the signal processor 34. The module calculates the water depth by measuring the time difference between the surface signal detected by the silicon photomultiplier tube detector 32 and the seabed signal detected by the gallium nitride detector, ultimately generating the water depth information or a three-dimensional seabed image of target 4. The entire process achieves high-precision water depth measurement with high light energy utilization, and is suitable for fields such as hydrological mapping, environmental monitoring, and underwater security.

[0065] It should be noted that the central aperture does not significantly affect the reflection of the echo signal. The principle is as follows: the system emits a collimated laser beam with a very narrow diameter. Its spot diameter is precisely controlled to be smaller than the size of the central aperture, allowing it to pass through unobstructed. When the laser illuminates a distant target 4 (such as the water surface or bottom), diffuse reflection occurs. The returned echo signal is no longer a narrow beam, but a diverging light cone with a much larger diameter. When this wide light cone returns to the aperture reflector 22, its coverage area is much larger than the area of ​​the central aperture. Therefore, the vast majority of the echo photons illuminate the reflector surfaces around the central aperture and are effectively collected and reflected to the detector. Only a very small portion of the energy at the center (coinciding with the emission path) is lost through the aperture; this loss is negligible for the overall echo signal. This design cleverly utilizes the characteristic that the beam diverges after long-distance propagation and diffuse reflection, achieving coaxial integration of the emission and reception optical paths with almost no impact on the echo signal reception efficiency.

[0066] The lidar ranging and imaging system of this embodiment emits laser pulses of different wavelengths through a dual-wavelength laser emitting module 1, combines them using a common-path optical transceiver module 2, and guides them to the target 4, then receives the echo signal. A non-splitting detection module 3 uses a gallium nitride photodetector 31 and a silicon photomultiplier tube detector 32 to physically separate and detect signals of different wavelengths, avoiding the signal aliasing and light energy loss problems of traditional technologies. The signal processing module calculates distance or three-dimensional morphological information based on the detected signals, achieving high-precision and high-efficiency dual-wavelength lidar ranging and imaging. Compared with existing technologies, it has higher accuracy, lower cost, and stronger anti-interference capabilities.

[0067] Example 2: LiDAR ranging and imaging method;

[0068] The lidar ranging and imaging method provided in this application includes the following steps:

[0069] The dual-wavelength laser emitting module 1 and the common-path optical transceiver module 2 synchronously and coaxially emit violet laser pulses and near-infrared laser pulses into the water body.

[0070] The common-path optical transceiver module 2 combines the violet laser pulse and the near-infrared laser pulse into a coaxial laser beam and guides it to the target water body 4. It also receives the echo light signal returned from the water body, which contains the violet laser pulse and the near-infrared laser pulse, and exports the echo light signal as a whole. The violet laser pulse penetrates the water body and is reflected by the bottom of the water, carrying the distance information of the bottom of the water body, while the near-infrared laser pulse is reflected by the surface of the water body, carrying the distance information of the surface of the water body.

[0071] The gallium nitride photodetector 31 absorbs and detects the violet laser pulse portion of the echo light signal to generate a first electrical signal, and the silicon photomultiplier tube detector 32 receives and detects the near-infrared laser pulse portion of the echo light signal that has penetrated the gallium nitride photodetector 31 to generate a second electrical signal.

[0072] The signal processor 34 calculates the time difference between the first electrical signal and the second electrical signal, and calculates the water depth of the water body based on the time difference.

[0073] Specifically, the water depth is calculated using the following formula:

[0074]

[0075] in, Depth The water depth of the water body. Δt The time difference between the first electrical signal and the second electrical signal. c The speed of light in a vacuum. n is the refractive index of the water body.

[0076] Figure 3 This is a pulse timing diagram that explains the Time-of-Flight (ToF) principle of distance measurement in this system.

[0077] t0 (trigger): Represents the trigger moment of laser emission, which is the starting point of timing.

[0078] tNIR1, tNIR2: Represent the first near-infrared (NIR) signal to return. Because NIR is reflected by the nearest surface (such as water), it arrives at the detector first.

[0079] tv(n), tv(n+1)...: Represents the violet signal that returns slightly later. Because the violet light penetrates the first surface and is reflected by more distant targets (such as the seabed), it requires a longer flight time. n represents the nth measurement point in the scanning process.

[0080] `tof(tv(n))` represents the total flight time of the violet light signal, calculated as `tof = tv(n) - t0`. The system calculates the precise distance to distant targets by accurately measuring this `tof` value, multiplying it by the speed of light, and dividing by 2. Simultaneously, by calculating the time difference between `tv(n)` and `tNIR`, the thickness or distance between two surfaces (e.g., water depth) can be obtained.

[0081] The implementation principle of this embodiment is as follows: Based on the dual-function characteristics of gallium nitride photodetector 31 (violet light absorption / infrared transmission), physical separation of violet light (bottom water) and infrared (surface water) signals is achieved, eliminating the depth measurement error caused by signal aliasing in traditional single-wavelength systems. The confocal plane integrated module (GaN+SiPM) eliminates optical components such as dichroic mirrors and filters 33, increasing the light energy utilization rate from 45% in traditional dual-wavelength systems to over 95%. The natural ultraviolet cutoff characteristics of gallium nitride material suppress 90% of visible light interference. The silicon photomultiplier tube detector 32 has a built-in narrowband filter 33 (905nm±10nm) to resist solar background noise, enabling all-weather detection and providing a high-precision, low-cost, and robust innovative solution for hydrological mapping.

[0082] The installation and preparation method of this system is as follows:

[0083] Step 1: Obtain or fabricate a gallium nitride detector. Specifically, a gallium nitride detector can be obtained through any of the following methods: photolithography, ICP (Inductively Coupled Plasma) dry etching, or electron beam evaporation.

[0084] Step 2: Match a suitable SiPM detector according to the size of the gallium nitride detector. The distance between the gallium nitride detector and the SiPM detector is 0.5mm. They are fixed with transparent epoxy resin and covered with a cutoff filter 33 on top.

[0085] Step 3: Install the receiving optical receiving system on the integrated detector system.

[0086] The beneficial effects of the technical solution provided in this application include:

[0087] 1. Utilizing the dual-functionality of gallium nitride (GaN) detectors—absorbing violet light and transmitting infrared light—the underwater echo (violet light) and surface echo (infrared) are directly separated at the physical level. This design fundamentally eliminates the depth measurement error caused by signal aliasing in traditional single-wavelength systems, significantly improving measurement accuracy. The innovative GaN+SiPM confocal plane integrated detection module eliminates the need for dichroic mirrors and other beam-splitting elements required in traditional dual-wavelength systems, greatly simplifying the optical system structure. This beam-splitting-free design avoids severe light energy loss, revolutionarily increasing the light energy utilization rate of the echo signal from approximately 45% in traditional schemes to over 95%.

[0088] 2. Based on the physical properties of gallium nitride materials, the detector has a natural ability to cut off and suppress most visible light (>450nm) in sunlight, which can effectively suppress more than 90% of ambient light interference, reduce the requirements for subsequent filtering systems, and enhance the robustness of the system under various lighting conditions. The silicon photomultiplier tube detector 32 has a built-in narrowband filter 33 to resist solar background noise; it has the potential to work in all weather conditions.

[0089] 3. By employing an apertured reflector 22, the transmitting and receiving optical paths are cleverly integrated onto the same optical axis, achieving a highly efficient common-path design. This design utilizes the diameter difference between the transmitted and returned beams. The vast majority of the returned signal photons are effectively collected by the mirror and reflected back to the detector, with almost no impact on the receiving efficiency, ensuring extremely high echo signal reception efficiency. Only a very small portion of the echo energy coinciding with the transmitting path passes through the central aperture and is lost; this loss is negligible for the overall echo signal. This ensures that the detector can receive as much effective signal energy as possible, minimizing signal loss.

[0090] 4. By eliminating the expensive and precisely calibrated spectroscopic elements and adopting a highly integrated non-spectrally oriented detection module 3, the overall manufacturing cost, size, and debugging difficulty of the system are significantly reduced, laying the foundation for providing a commercially feasible, mobile-platform-compatible, high-precision hydrological mapping innovation solution.

[0091] The specific embodiments described above do not constitute a limitation on the scope of protection of this application. Any other corresponding changes and modifications made based on the technical concept of this application should be included within the scope of protection of this application.

Claims

1. A lidar ranging and imaging system, characterized in that, include: A dual-wavelength laser emitting module (1) is used to emit violet laser pulses in the first wavelength range and near-infrared laser pulses in the second wavelength range; The common-path optical transceiver module (2) is used to combine the violet laser pulse and the near-infrared laser pulse into a coaxial laser beam and guide it to the target (4), and to receive the echo light signal returned from the target (4) containing the violet laser pulse and the near-infrared laser pulse and export the echo light signal as a whole. The non-splitter detection module (3) includes a gallium nitride photodetector (31), a silicon photomultiplier tube detector (32), and a signal processor (34). The gallium nitride photodetector (31) is located on the output path of the echo light signal and is used to absorb and detect the violet light portion of the echo light signal. The silicon photomultiplier tube detector (32) is located on the side of the gallium nitride photodetector (31) away from the output of the echo light signal and is used to receive and detect the near-infrared portion of the echo light signal that has penetrated the gallium nitride photodetector (31). The signal processor (34) is communicatively connected to both the gallium nitride photodetector (31) and the silicon photomultiplier tube detector (32) and is used to calculate the distance or three-dimensional shape information based on the received signals from the silicon photomultiplier tube detector (32) and the gallium nitride photodetector (31).

2. The lidar ranging and imaging system according to claim 1, characterized in that, The dual-wavelength laser emission module (1) includes a violet laser (11), a near-infrared laser (12), a first collimating lens (13), and a second collimating lens (14). The violet laser (11) is used to generate violet laser pulses, and the near-infrared laser (12) is used to generate near-infrared laser pulses. The first collimating lens (13) is disposed on the first emission optical path of the violet laser (11), and the second collimating lens (14) is disposed on the second emission optical path of the near-infrared laser (12). The first emission optical path and the second emission optical path are coaxial, and the emitting end of the violet laser (11) is disposed opposite to the emitting end of the near-infrared laser (12). The common-path optical transceiver module (2) includes a beam combiner (21). The beam combiner (21) has a first reflective surface and a second reflective surface that are perpendicular to each other. The first reflective surface is disposed on the first emitting optical path and forms a 45° angle with the first emitting optical path. The second reflective surface is disposed on the second emitting optical path and forms a 45° angle with the second emitting optical path. The violet laser pulse and the near-infrared laser pulse generated by the violet laser (11) and the near-infrared laser (12) are first collimated by the first collimating lens (13) and the second collimating lens (14), respectively, and then reflected by the first reflective surface and the second reflective surface, respectively, and then combined into the coaxial laser beam.

3. The lidar ranging and imaging system according to claim 2, characterized in that, The common-path optical transceiver module (2) further includes an aperture mirror (22) and a scanning galvanometer assembly (23). The aperture mirror (22) has a central hole located on the path of the coaxial laser beam. The scanning galvanometer assembly (23) is located on the side of the aperture mirror (22) away from the beam combiner (21). After the coaxial laser beam passes through the central hole, it is guided to the target (4) by the scanning galvanometer assembly (23). The echo light signal returned from the target (4) is guided to the mirror surface of the aperture mirror (22) via the scanning galvanometer assembly (23) and reflected to the receiving end of the gallium nitride photodetector (31).

4. The lidar ranging and imaging system according to claim 3, characterized in that, The scanning galvanometer assembly (23) includes a first rotatable galvanometer (231), a second rotatable galvanometer (232), and a first galvanometer driver and a second galvanometer driver that drive the two to rotate respectively. In the transmission path, the first rotatable galvanometer (231) deflects the coaxial laser beam for the first time, and the second rotatable galvanometer (232) deflects the beam reflected from the first rotatable galvanometer (231) for the second time to guide it to the target (4). In the receiving path, the echo light signal is collected and guided by the second rotatable galvanometer (232) and the first rotatable galvanometer (231) in reverse order.

5. The lidar ranging and imaging system according to claim 1, characterized in that, The non-spectral detection module (3) also includes a filter (33), which is disposed in the optical path between the gallium nitride photodetector (31) and the silicon photomultiplier tube detector (32) to filter out stray light and allow only near-infrared light within a preset wavelength range to pass through.

6. The lidar ranging and imaging system according to claim 1, characterized in that, The gallium nitride photodetector (31) includes a sapphire substrate (311), an n-type gallium nitride semiconductor layer (312) formed on the sapphire substrate (311), a p-type gallium nitride semiconductor layer (313) formed on the n-type gallium nitride semiconductor layer (312) and forming a pn junction therewith, and a p-type electrode (314) and an n-type electrode (315) electrically connected to the p-type gallium nitride semiconductor layer (313) and the n-type gallium nitride semiconductor layer (312), respectively. The selective response of the gallium nitride photodetector (31) to violet and near-infrared light is based on the band gap energy of the gallium nitride material constituting the n-type gallium nitride semiconductor layer (312) and the p-type gallium nitride semiconductor layer (313): the energy of violet photons is higher than the band gap energy, so they are absorbed by the pn junction to generate photocurrent; the energy of near-infrared photons is lower than the band gap energy, so they are transmitted through the gallium nitride photodetector (31).

7. The lidar ranging and imaging system according to claim 1, characterized in that, The distance between the gallium nitride photodetector (31) and the silicon photomultiplier tube detector (32) along the optical signal incident path is less than 1 mm, and they form a confocal planar integrated package.

8. The lidar ranging and imaging system according to claim 1, characterized in that, The first wavelength ranges from 380 nanometers to 420 nanometers, and the second wavelength ranges from 895 nanometers to 915 nanometers.

9. A lidar ranging and imaging method, applicable to the lidar ranging and imaging system as described in any one of claims 1-8, and comprising the following steps: Through the dual-wavelength laser emission module (1) and the common-path optical transceiver module (2), violet laser pulses and near-infrared laser pulses are synchronously and coaxially emitted into the water body; The common-path optical transceiver module (2) combines the violet laser pulse and the near-infrared laser pulse into a coaxial laser beam and guides it to the water body. It also receives the echo light signal returned from the water body, which contains the violet laser pulse and the near-infrared laser pulse, and exports the echo light signal as a whole. The violet laser pulse penetrates the water body and is reflected by the bottom of the water, carrying the bottom distance information, while the near-infrared laser pulse is reflected by the surface of the water body, carrying the surface distance information. The gallium nitride photodetector (31) absorbs and detects the violet laser pulse portion in the echo light signal to generate a first electrical signal, and the silicon photomultiplier tube detector (32) receives and detects the near-infrared laser pulse portion in the echo light signal that has penetrated the gallium nitride photodetector (31) to generate a second electrical signal. The signal processor (34) calculates the time difference between the first electrical signal and the second electrical signal, and calculates the water depth of the water body based on the time difference.

10. The lidar ranging and imaging method according to claim 9, characterized in that, The water depth of a body of water can be calculated using the following formula: Where Depth is the water depth, Δt is the time difference between the first and second electrical signals, c is the speed of light in a vacuum, and n is the refractive index of the water.

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