Vortex laser-based spaceborne wide-field-of-view lidar

Abstract

This invention provides a spaceborne wide-field-of-view lidar based on vortex lasers. This lidar, mounted on a satellite, enables precise positioning and imaging of targets on the ground or in the air. It employs a Gauss-Laguerre vortex laser as the carrier wave, featuring high weak echo signal detection capability, a wide field of view, large laser footprint size, high area coverage, and target type identification. First, based on prior information or infrared detection methods, the target is locked within a large area. Then, a column-by-column continuous scanning search strategy is used to perform a full-coverage scan within this area, combined with target type identification capabilities to achieve precise imaging and identification of the target.

Description

Technical Field

[0001] This invention relates to the technical field of spaceborne lidar, and more specifically, to a spaceborne wide-field-of-view lidar based on vortex lasers. Background Technology

[0002] Because lidar has its own illumination source, it can operate around the clock, unaffected by day or night, and boasts advantages such as narrow carrier linewidth, high resolution, and high sensitivity. The carrier wave of lidar contains information about amplitude, phase, frequency, and other aspects, playing an increasingly important role in numerous fields such as radar imaging, wind measurement, greenhouse gas detection, atmospheric environmental monitoring, underwater exploration, and deep space exploration.

[0003] Spaceborne lidar is a type of lidar mounted on spacecraft that operates outside the Earth's atmosphere. It has unique advantages such as all-weather operation, minimal atmospheric influence, and a wide field of view. However, due to the greater distance from the target, it also has disadvantages such as weaker echo signals and a smaller field of view.

[0004] Existing spaceborne lidar mainly employs the following two detection methods:

[0005] Direct detection system: Spaceborne lidar employing a direct detection system performs detection by modulating the intensity of the laser signal. (See appendix) Figure 1 The laser transmitter emits modulated laser pulse signals, and the receiver receives and processes the laser pulse echo signals. Because the satellite is far from the ground (typically on the order of hundreds of kilometers), the echo signal from the spaceborne lidar is extremely weak. The receiver receives a large amount of noise along with the laser echo signal. Since direct-detection lidar only utilizes the amplitude information of the laser carrier wave, its ability to suppress background noise is limited, resulting in low detection accuracy.

[0006] Coherent detection system: Spaceborne lidar employing a coherent detection system modulates not only the intensity of the laser signal but also its phase. The receiver utilizes the local oscillator laser to amplify the echo signal, thereby suppressing noise signals. (See appendix) Figure 2 Compared to direct detection systems, coherent detection systems can improve the received signal-to-noise ratio and enhance the ability to detect weak signals.

[0007] Both of the above-mentioned spaceborne lidar systems suffer from the following problems:

[0008] Laser lidar suffers from a small field of view and footprint diameter, resulting in poor coverage. While spaceborne lidar offers advantages in system performance such as operating range and ranging accuracy, it only becomes effective when the transmitting and receiving fields of view are relatively small due to factors like background light interference. With a fixed distance from the detection area, the small field of view inevitably limits the lidar's coverage performance, impacting its ability to search for and acquire targets.

[0009] The field of view and footprint size specifications of existing spaceborne lidar are shown in Table 1:

[0010] Table 1. Field of view and footprint size of existing spaceborne lidar

[0011]

[0012] As can be seen from the table, the existing spaceborne lidar has a small field of view and a small laser footprint size (on the order of hundreds of meters). When detecting larger target areas, it can only work by using a narrow field of view scanning method, and cannot perform wide field of view imaging with fast imaging speed, no distance correction processing and clear target.

[0013] Insufficient detection capability of weak echo signals: As spaceborne lidar is applied in a wider range of fields, in some situations it is necessary to detect targets at greater distances and with higher speeds, or targets with low reflectivity, which will further reduce the strength of the echo signal. Under strong background noise interference, existing lidar cannot achieve high-sensitivity active detection of weak echo signals in these situations. Even the most sensitive lidar currently available, which uses single-photon detection technology, has extremely demanding operating conditions and is highly susceptible to various noises, including solar background noise and man-made interference noise, making it unusable during the day or in complex environments.

[0014] In summary, there is an urgent need to invent a new type of spaceborne lidar that simultaneously possesses a wide field of view (wide laser footprint size and high coverage performance) and strong weak echo signal detection capability, with strong wide field of view imaging capability, and can detect a large area.

[0015] Therefore, a new technical solution is needed to improve the above-mentioned technical problems. Summary of the Invention

[0016] In view of the deficiencies in the prior art, the purpose of this invention is to provide a spaceborne wide-field-of-view lidar based on vortex lasers.

[0017] According to the present invention, a spaceborne wide-field-of-view lidar based on vortex laser includes a seed light source, a vortex modulator, a telescope, a vortex demodulator, a detector, and a data processing unit.

[0018] The seed light source is connected to a vortex modulator; the vortex modulator is connected to both a telescope and a vortex demodulator; the vortex demodulator is connected to a detector; and the detector is connected to a data processing unit.

[0019] Preferably, the seed light source generates a Gaussian laser, and the seed light source emits the Gaussian laser to a vortex modulator.

[0020] Preferably, the vortex modulator modulates the Gaussian laser into a vortex laser.

[0021] Preferably, the telescope emits a vortex laser and receives the echo light signal generated by the vortex laser reflected from the target.

[0022] Preferably, the vortex demodulator devortexes the echo optical signal.

[0023] Preferably, the detector images the echo light signal after devortexing.

[0024] Preferably, the data processing unit performs the final data processing.

[0025] Preferably, the lidar is mounted on a satellite.

[0026] Preferably, the seed light source generates Gaussian laser, which is then converted into vortex laser by a vortex modulator. After illuminating the target, the resulting echo is received by the telescope, demodulated by a vortex demodulator, and then enters the detector for imaging. Finally, the data is processed.

[0027] Preferably, the data processing unit performs imaging information and other information analysis to complete target acquisition and imaging.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The lidar of the present invention is mounted on a satellite to accurately locate and image targets on the ground or in the air. It uses Gauss-Laguerre vortex laser as the carrier and has the characteristics of high weak echo signal detection capability, large field of view, large laser footprint size, high area coverage, and target type identification.

[0030] 2. This invention utilizes vortex lasers for detection, exhibiting excellent weak echo signal detection capabilities, along with a large field of view, large laser footprint, and high area coverage. The lidar involved in this invention employs vortex lasers as carriers, and can be, but is not limited to, Gauss-Laguerre vortex lasers. The phase information contained in the vortex lasers enables the lidar to distinguish echo signals under low signal-to-noise ratio conditions, especially under background noise conditions such as Earth's blackbody radiation and sunlight reflected from the ground. The lidar involved in this invention uses vortex lasers to improve the detection signal-to-noise ratio, thus increasing the detection field of view and enlarging the laser footprint size while meeting the traditional lidar detection signal-to-noise ratio specifications. Attached Figure Description

[0031] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0032] Figure 1 This is a block diagram of the direct detection system spaceborne lidar of the present invention;

[0033] Figure 2 This is a block diagram of the coherent detection system spaceborne lidar receiver of the present invention;

[0034] Figure 3 This is a block diagram of the vortex lidar system of the present invention;

[0035] Figure 4 This is a cross-sectional phase distribution diagram of Gauss-Laguerre lasers with different radial quantum numbers and angular quantum numbers at the same transmission distance according to the present invention;

[0036] Figure 5 This is a phase information diagram of the vortex laser echo of the square target of the present invention;

[0037] Figure 6 Phase information diagram of vortex laser echo for a triangular target;

[0038] Figure 7 This is a phase information diagram of the vortex laser echo of the circular target of the present invention;

[0039] Figure 8 This is a schematic diagram of the single-scan light spot of the present invention;

[0040] Figure 9 This is a schematic diagram of the full coverage scanning of each column according to the present invention. Detailed Implementation

[0041] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0042] Example 1:

[0043] According to the present invention, a spaceborne wide-field-of-view lidar based on vortex laser includes a seed light source, a vortex modulator, a telescope, a vortex demodulator, a detector, and a data processing unit; the seed light source is connected to the vortex modulator; the vortex modulator is connected to both the telescope and the vortex demodulator; the vortex demodulator is connected to the detector; and the detector is connected to the data processing unit.

[0044] A seed light source generates a Gaussian laser, which is then emitted to a vortex modulator. The vortex modulator modulates the Gaussian laser into a vortex laser. A telescope emits the vortex laser and receives the echo signal generated by the vortex laser reflected from the target. A vortex demodulator devortexes the echo signal. The detector images the devortexed echo signal. The data processing unit performs final data processing. The photoradar is mounted on a satellite. After the seed light source generates a Gaussian laser, it is converted into a vortex laser by the vortex modulator. When it illuminates the target, it generates an echo, which is received by the telescope, demodulated by the vortex demodulator, and then enters the detector for imaging. Finally, data processing is performed. The data processing unit analyzes the imaging information and other information to complete target acquisition and imaging.

[0045] Example 2

[0046] Vortex lasers are a special type of laser with unique helical phase and orbital angular momentum characteristics. While ordinary Gaussian lasers exhibit a distribution of intensity that is stronger at the center and weaker at the outer edges within a cross-section over the same propagation distance, with the same phase, vortex lasers display an annular intensity distribution with varying phases within the cross-section. Two important parameters of vortex lasers are the radial quantum number and the angular quantum number. The radial quantum number affects the number of rings in the planar intensity annular distribution of the vortex laser, while the angular quantum number affects the number of cycles of planar phase change.

[0047] Due to their advantages, vortex lasers are already being used in fields such as particle manipulation, optical communication, microscopic imaging, quantum information, and measuring the rotational momentum of objects. However, there are currently no examples of vortex laser applications in satellite remote sensing.

[0048] A spaceborne wide-field-of-view lidar based on vortex lasers is mounted on a sun-synchronous orbit (polar orbit) satellite. The system includes a seed light source, a vortex modulator, a telescope, a vortex demodulator, a detector, and a data processing unit. A system block diagram is attached. Figure 3 As shown.

[0049] The vortex modulator and vortex demodulator will sculpt the output laser into a vortex laser and demodulate the echo signal into an image.

[0050] Utilizing the regular phase information contained in vortex lasers (as shown in the attached image) Figure 4 The characteristics shown can reduce the minimum resolvable signal-to-noise ratio by at least, but not limited to, two orders of magnitude. The spaceborne lidar based on vortex lasers of the present invention can effectively carry out echo signal detection under the interference of background light radiation such as spontaneous radiation of the earth, ground reflection of sunlight, and atmospheric scattering. That is, the spaceborne lidar based on vortex lasers of the present invention can work around the clock.

[0051] Due to the reduced signal-to-noise ratio requirement, the space-based vortex lidar designed in this invention can increase the field of view and laser footprint range while maintaining the echo signal resolution capability. The vortex laser itself carries regular phase information, and after modulation (reflection, diffraction) by targets of different shapes, the echo signal carries information about the target's shape characteristics. Therefore, the target's shape type can be identified by analyzing the phase information characteristics of the echo. Taking several special-shaped targets as examples, the echo phase information is shown in the attached figure. Figure 5 As shown; the spaceborne lidar involved in this invention utilizes this method to identify the shape type of a target; when capturing a target existing within its potential range, a vortex lidar generates a vortex laser, and a search strategy of sequential scanning, but not limited to, column-by-column, is employed to perform a full-coverage scan search within that range, such as... Figure 8 and Figure 9 As shown, the vortex laser illuminates the target and reflects the echo signal, which, combined with the target type recognition capability, enables accurate imaging and identification of the target. The single scan workflow is as follows: the ordinary Gaussian laser generated by the seed light source is converted into a vortex laser after passing through the vortex modulator. After illuminating the target, the echo is received by the telescope, demodulated by the vortex demodulator, and then enters the detector for imaging. Finally, the data is processed.

[0052] This embodiment provides a detailed implementation method and specific operation process based on the positioning process of an imaginary target of approximately 50m × 50m. However, the scope of protection of this invention is not limited to the following embodiment.

[0053] Reference Appendix Figure 3 As shown, the present invention provides a spaceborne wide-field-of-view lidar based on vortex laser, comprising a seed light source, a vortex modulator, a telescope, a vortex demodulator, a detector, and a data processing unit.

[0054] Prior information or infrared detection methods determine that the target exists within a 100km × 100km area, which is called the target potential region. The seed light source generates a conventional Gaussian laser. The conventional Gaussian laser is modulated into a vortex laser by the vortex modulator. The vortex laser is emitted from the telescope and illuminates the target potential region. A single scan is a vortex laser pulse signal with a circular field of view of 2.5km radius. A full-coverage scan is performed on the entire target potential region using a search strategy that is not limited to sequential scanning. The vortex laser illuminates the target and is reflected, and the echo signal is received by the telescope. The echo is devortexed after passing through the vortex demodulator. The devortexed echo signal is imaged by the detector. The data processing unit analyzes the imaging information and other information to complete target acquisition and imaging.

[0055] A spaceborne wide-field-of-view lidar technology solution based on vortex lasers is disclosed. This lidar, mounted on a satellite, comprises a seed light source, a vortex modulator, a telescope, a vortex demodulator, a detector, and a data processing unit. The seed light source generates Gaussian laser light and transmits it to the vortex modulator. The vortex modulator modulates the Gaussian laser light into a vortex laser. The telescope emits the vortex laser light and receives the echo light signal generated by the vortex laser light reflected from the target. The vortex demodulator devortexes the echo light signal. The detector images the devortexed echo light signal. The data processing unit performs final data processing.

[0056] Vortex laser-based spaceborne lidar systems utilize vortex lasers for detection, possessing excellent weak echo signal detection capabilities, and also feature a large field of view, large laser footprint, and high area coverage.

[0057] The lidar solution involved in this invention uses a vortex laser as the carrier, which can be, but is not limited to, a Gauss-Laguerre vortex laser. The phase information contained in the vortex laser enables the lidar to distinguish echo signals under low signal-to-noise ratio conditions, especially in the presence of background noise from Earth's blackbody radiation and sunlight reflected from the ground.

[0058] The lidar involved in this invention uses vortex lasers to improve the detection signal-to-noise ratio, thus increasing the detection field of view and enlarging the size of the laser footprint while meeting the traditional lidar detection signal-to-noise ratio specifications.

[0059] Vortex laser-based spaceborne lidar systems possess wide-field-of-view target imaging and localization capabilities. Due to the high resolution of weak signals, vortex lidar has a larger field of view and footprint size than traditional lidar, allowing a single scan to cover the entire target for overall localization and imaging.

[0060] Spaceborne lidar systems based on vortex lasers employ, but are not limited to, a vortex laser ring spot full-coverage scanning strategy. Scanning using this method can achieve full area coverage, as shown in the attached diagram. Figure 2 As shown, the intra-column scan spacing d r , column distance d c The equation below shows the inner and outer diameters of the light spot, respectively:

[0061]

[0062] The spaceborne lidar system based on vortex lasers has target type identification capabilities. The lidar system involved in this invention uses vortex lasers as carrier waves. The phase information of the echoes after reflection from targets of different shapes exhibits unique morphological characteristics. By analyzing the phase information in the echoes, the shape type of objects included in a single scan can be determined, thereby effectively eliminating interference from non-target objects of the same category.

[0063] Those skilled in the art can understand this embodiment as a more specific description of Embodiment 1.

[0064] Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various devices, modules, and units provided by the present invention in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; the devices, modules, and units for implementing various functions can also be considered as both software modules implementing the method and structures within the hardware component.

[0065] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A spaceborne wide-field-of-view lidar based on vortex lasers, characterized in that, It includes a seed light source, a vortex modulator, a telescope, a vortex demodulator, a detector, and a data processing unit; The seed light source is connected to a vortex modulator; the vortex modulator is connected to both a telescope and a vortex demodulator; the vortex demodulator is connected to a detector; and the detector is connected to a data processing unit. The spaceborne lidar system based on vortex lasers features a full-coverage scanning strategy using a vortex laser ring spot. Scanning according to this strategy achieves full area coverage, with an intra-column scanning spacing d. r , column distance d c The equation below shows the inner and outer diameters of the light spot, respectively: The lidar uses vortex lasers as carriers. The phase information of the echoes after reflection from targets of different shapes exhibits unique morphological characteristics. By analyzing the phase information in the echoes, the shape type of the object included in a single scan can be determined, thereby effectively eliminating interference from non-target objects of the same type.

2. The spaceborne wide-field-of-view lidar based on vortex laser according to claim 1, characterized in that, The seed light source generates a Gaussian laser, which is then emitted to a vortex modulator.

3. The spaceborne wide-field-of-view lidar based on vortex laser according to claim 1, characterized in that, The vortex modulator modulates the Gaussian laser into a vortex laser.

4. The spaceborne wide-field-of-view lidar based on vortex laser according to claim 1, characterized in that, The telescope emits vortex lasers and receives echo signals generated by the vortex lasers reflected from the target.

5. The spaceborne wide-field-of-view lidar based on vortex laser according to claim 1, characterized in that, The vortex demodulator devortexes the echo optical signal.

6. The spaceborne wide-field-of-view lidar based on vortex laser according to claim 1, characterized in that, The detector images the echo light signal after devortexing.

7. The spaceborne wide-field-of-view lidar based on vortex laser according to claim 1, characterized in that, The data processing unit performs the final data processing.

8. The spaceborne wide-field-of-view lidar based on vortex laser according to claim 1, characterized in that, The lidar is mounted on a satellite.

9. The spaceborne wide-field-of-view lidar based on vortex laser according to claim 1, characterized in that, The seed light source generates Gaussian laser, which is then converted into vortex laser by a vortex modulator. After illuminating the target, the resulting echo is received by the telescope, demodulated by a vortex demodulator, and then enters the detector for imaging. Finally, the data is processed.

10. The spaceborne wide-field-of-view lidar based on vortex laser according to claim 1, characterized in that, The data processing unit analyzes imaging information and other information to complete target acquisition and imaging.

Images