Receiving and transmitting coaxial device based on frequency conversion laser ranging system

Abstract

The invention discloses a receiving and transmitting coaxial device based on a frequency conversion laser ranging system. The receiving and transmitting coaxial device comprises a wavelength spectroscope, a frequency converter, a telescope system, a 4f system, a pinhole diaphragm, an acousto-optic modulator and a detector. When the pulse laser is emitted, the pulse laser enters the frequency converter through the wavelength spectroscope to generate laser with one, two or more wavelengths required by distance measurement, and the laser is emitted to a detection target through the telescope system. A laser echo is reflected by a detection target, and the laser echo penetrates through the telescope system, is reflected by the wavelength spectroscope, penetrates through the 4f system, the acoustic optical modulator and the small-hole diaphragm and enters the detector to be detected. The frequency of the pulse laser is converted through the frequency converter, and the wavelength spectroscope transmits (reflects) the pulse laser and reflects (transmits) the converted laser, so that the pulse laser emission and the laser echo output by the telescope are realized, the receiving and transmitting of the laser ranging system are coaxial, and an effective ranging way is provided for remote laser ranging.

Description

Technical Field

[0001] The invention belongs to the field of laser ranging, and more particularly relates to a device for coaxial transmission and reception of a frequency conversion-based laser ranging system. Background Art

[0002] Artificial satellites are widely used in communications, meteorology, military, and other fields. The Global Positioning System (GPS) and my country's BeiDou positioning system, in particular, have revolutionized our lifestyles and promoted the harmonious development of humanity. At the same time, with the increase in space activity, the amount of space debris is also increasing, posing an increasingly serious threat to spacecraft and missions already in orbit or to be launched in the future, and increasing the potential hazard to manned spaceflight. Consequently, countries around the world are investing significant resources in research to monitor and detect space debris, conduct precise orbit determination of space debris, and improve spacecraft's ability to avoid it. Laser ranging, with its long-range and high-accuracy measurements, is widely used in the detection of space targets, meeting the needs of measuring satellites and space debris, and enabling ranging from low-Earth orbit satellites to the moon.

[0003] To reduce the laser's launch angle and manufacturing costs, satellite laser ranging telescope systems increasingly use the same large-aperture telescope for both laser emission and echo detection. In these coaxial laser ranging systems, the transmitter-receiver switching device is a core component. In 2008, TW Murphy, JR E.G. Delberger, JB R. Battat, et al. published an article titled "The Apache Point Observatory Lunar Laser-ranging Operation: Instrument Description and First Detections" in the journal Publications of the Astronomical Society of the Pacific. The article proposed a transmitter-receiver switching method that uses a rotating plane mirror (with different coatings at different positions) to switch between laser emission and echo detection. However, the use of a rotating mirror carries inherent risks; improper rotation could damage the detector or laser. In 2016, Dongsheng Zhai of Yunnan Astronomical Observatory, Chinese Academy of Sciences proposed a transceiver switching method in his doctoral dissertation. Although this device ensures transmission efficiency and fixes the transceiver switching device, reducing some risks that may be introduced by rotating the transceiver switching device, the size of the frame and the lens itself causes the reception efficiency to be blocked. In 2016, JJ Eckl and KUS Schreiber gave a report entitled "Recent Achievements in mono-static, high-repetition rate ranging at the WLRS" at the 20th International Conference on Laser Ranging. The paper proposed a device that uses polarization method to achieve transceiver switching. This device also effectively avoids some risks that may be introduced by the rotating switching device. However, due to the large changes in the polarization state of the echo reflected from the satellite or space target, the echo efficiency is greatly attenuated. Summary of the Invention

[0004] The purpose of the present invention is to provide a coaxial transmitting and receiving device based on a frequency conversion laser ranging system, which can better compress the emission angle of the emitted laser, reduce the manufacturing cost, and reduce other risks brought by the transmitting and receiving switching device.

[0005] The present invention adopts the following technical solutions: A coaxial transmitter-receiver device based on a frequency conversion laser ranging system includes a wavelength spectrometer, a frequency converter, a telescope system, a 4f system, a pinhole aperture, an acousto-optic modulator, and a detector. After being reflected by the spectrometer and entering an optical frequency conversion crystal, pulsed laser light generates laser light of one or more ranging wavelengths, which is then transmitted to the detection target via the telescope system. The detection target reflects the laser light, and the laser echo passes through the telescope system, is reflected by the wavelength spectrometer, and then passes through the 4f system, the acousto-optic modulator, and the pinhole aperture to be incident on the detector. The frequency of the pulsed laser light is converted by the frequency converter, and the wavelength spectrometer transmits (or reflects) the pulsed laser light while reflecting (or transmitting) the converted laser light, thereby achieving coaxial transmitter-receiver communication with the telescope.

[0006] Preferably, the wavelength spectrometer is coated with a 45° beam splitting anti-reflection and high-reflection film, so that a certain wavelength of laser light is transmitted and another wavelength of laser light is reflected, and the thickness is 1 to 5 mm.

[0007] Preferably, the frequency conversion crystal is a nonlinear optical parametric crystal such as LBO, BBO, or KDP. Alternatively, it can be a Raman scattering medium such as KGW or H2, or a frequency conversion medium such as Brillouin scattering. It should have a clear aperture of 10-20 cm, a thickness of 2-30 mm, a high damage threshold, and be coated with an antireflection coating for pulsed and transmitted lasers.

[0008] Preferably, the telescope system is an achromatic transmission or reflection telescope system, which can meet the requirements of achromatic transmission of multiple wavelengths.

[0009] Preferably, the 4f system is composed of two convex lenses, the distance between the two convex lenses is the sum of the focal lengths of the connected convex lenses, and the two convex lenses are coated with an anti-reflection film consistent with the laser echo.

[0010] Preferably, the acousto-optic modulator is composed of an acousto-optic crystal and a driver, has a light aperture of 4 to 15 mm, and a thickness of 2 to 30 mm, and can achieve a deflection of the light beam of 16 to 30 mrad under the driver.

[0011] Preferably, the pinhole diaphragm can be electrically driven and controlled, and the aperture range of the pinhole diaphragm is 0.1 to 4 mm.

[0012] Preferably, the detector is a single photon detector or other photoelectric detector.

[0013] The beneficial effects brought about by the technical solution provided by the present invention are: (1) A frequency converter and an achromatic telescope system are used to convert the frequency of the pulsed laser to a suitable measurement laser wavelength, and the emitted laser and the laser echo are sent and received coaxially with the telescope laser.

[0014] (2) A wavelength beam splitter is used to realize the transmission (reflection) of the pulsed laser and the reflection (transmission) of the laser echo, ensuring that the pulsed laser and the laser echo can be transmitted separately through the wavelength beam splitter.

[0015] (3) The use of an acousto-optic modulator and a small aperture prevents the forward reflected light of the frequency converter from returning to the detector and causing damage to the detector. BRIEF DESCRIPTION OF THE DRAWINGS In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 Schematic diagram of laser emission in a coaxial transmitting and receiving device based on a frequency conversion laser ranging system according to the present invention; Figure 2 Schematic diagram of laser echo reception in a coaxial transceiver device based on a frequency conversion laser ranging system according to the present invention; Figure 3 This is a timing diagram of a coaxial transceiver device based on a frequency conversion laser ranging system.

[0017] In the picture: Wavelength spectrometer 1, frequency converter 2, telescope system 3, 4f system 4, 4f system first convex lens 41, 4f system second convex lens 42, pinhole aperture 5, acousto-optic modulator 6, detector 7. DETAILED DESCRIPTION

[0018] The preferred embodiments of the present invention are given below in conjunction with the accompanying drawings and described in detail to enable a better understanding of the functions and features of the present invention.

[0019] like Figure 1 The device is shown as a coaxial transmitter-receiver device based on a frequency conversion laser ranging system according to a preferred embodiment of one embodiment of the present invention. The device includes a wavelength spectrometer 1, a frequency converter 2, a telescope system 3, a 4f system 4, a pinhole diaphragm 5, an acousto-optic modulator 6, and a detector 7. After the pulsed laser passes through the spectrometer 1 and enters the frequency converter 2, it generates one or more laser beams of ranging wavelengths. The beams are then expanded and emitted by the telescope system 3 to the detection target. The acousto-optic modulator 6 begins operating when the pulsed laser is output. The forward scattered light of the one or more laser beams of ranging wavelengths generated by the frequency converter 2 is reflected by the wavelength spectrometer 1 and passes through the first convex lens 41. Under the action of the acousto-optic modulator 6, the light path is deflected and blocked by the pinhole diaphragm 5, preventing the forward scattered light from entering the detector 7 and preventing damage to the detector.

[0020] See also Figure 2 , which is a schematic diagram of a laser echo in a coaxial transmitter-receiver device based on a frequency conversion laser ranging system according to a preferred embodiment. At this time, the acousto-optic modulator 6 is not operating. The laser echo reflected from the detection target passes through the telescope system 3, is reflected by the wavelength spectrometer 1, and then passes through the 4f system 4, the acousto-optic modulator 6, and the pinhole diaphragm 5 to be incident on the detector 7, thus achieving detection of the laser echo.

[0021] Thus, the frequency of the pulsed laser is converted by the frequency converter 2, and the wavelength spectroscope 1 transmits (or reflects) the pulsed laser and reflects (or transmits) the converted laser, thereby achieving the output of the pulsed laser and the laser echo at the same telescope, achieving the coaxial transmission and reception of the laser ranging system. Figure 1 In this embodiment, the wavelength spectrometer is coated with a 45° beam splitting anti-reflection and high-reflection film with a thickness of 1 to 5 mm, so that a certain wavelength of laser light is transmitted and another wavelength of laser light is reflected.

[0022] The frequency conversion crystal 2 can be a current nonlinear optical parametric crystal such as LBO, BBO, or KDP, or can also be a Raman scattering medium such as KGW or H2, or a frequency conversion medium such as Brillouin scattering. It has an aperture of 10-20 cm, a thickness of 2-30 mm, a high damage threshold, and is coated with an antireflection coating for both pulsed and emitted lasers. This allows for frequency conversion of pulsed laser light, generating pulsed outputs of other laser wavelengths.

[0023] The telescope system 3 is an achromatic transmission or reflection telescope system, which can meet the requirements of achromatic transmission of multiple wavelengths.

[0024] The 4f system 4 consists of a first convex lens 41 and a second convex lens 42 . The distance between the two convex lenses is the sum of the focal lengths of the first convex lens 41 and the second convex lens 42 . The two lenses are coated with an anti-reflection film consistent with the laser echo.

[0025] The acousto-optic modulator 5 is composed of an acousto-optic crystal and a driver, has an aperture of 4 to 15 mm, and a thickness of 2 to 30 mm, and can achieve a deflection of the light beam of 16 to 30 mrad under the driver.

[0026] The pinhole diaphragm 6 can be electrically driven and controlled, and the aperture range of the pinhole diaphragm is 0.1 to 4 mm.

[0027] The detector 7 is a single photon detector or other photoelectric detector.

[0028] See also Figure 3, is a timing diagram of a coaxial transmission and reception method based on a frequency conversion laser ranging system. Pulsed laser light passes through wavelength beam splitter 1 and frequency converter 3 to generate laser light of other wavelengths. This is then emitted through telescope system 3. AOM 5 is in operation. Frequency converter 3 and the atmosphere will produce backscattered light on the converted wavelength laser light. The backscattered light is reflected by wavelength beam splitter 1 and passes through the first convex lens 41 of the 4f system and the AOM 5. During operation, the AOM deflects the backscattered light emission path onto the pinhole aperture 6, preventing the backscattered light from entering the detector. When receiving the laser echo, the AOM is not in operation. The laser echo passes through wavelength beam splitter 1, 4f system 4, AOM 5, and pinhole aperture 6 to the detector, where it is detected.

[0029] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Various modifications are possible. In other words, any simple, equivalent changes and modifications made in accordance with the claims and description of the present invention are within the scope of protection of the patent claims. Anything not fully described in this invention constitutes conventional technology.

Claims

1. A coaxial transceiver device based on a frequency conversion laser ranging system, characterized in that: The device comprises a wavelength spectroscope (1), a frequency converter (2), a telescope system (3), a 4f system (4), a pinhole diaphragm (5), an acousto-optic modulator (6), and a detector (7).

2. The wavelength spectrometer (1) according to claim 1 is coated with a 45° beam splitting anti-reflection and high-reflection film, has a thickness of 1 to 5 mm, and a light aperture of 5 to 20 cm.

3. According to claim 1, the frequency conversion crystal (2) is a nonlinear crystal such as the current nonlinear optical parameter LBO, BBO, KDP, etc., and can also be a Raman scattering medium such as KGW, H2 or a frequency conversion medium such as Brillouin scattering, with a light aperture of 10 to 20 cm, a thickness of 2 to 30 mm, a high damage threshold, and is coated with an anti-reflection film for pulsed laser and emitted laser.

4. The telescope system (4) is an achromatic transmission or reflection telescope system, which can meet the requirements of achromatic transmission of multiple wavelengths.

5. The 4f system (4) is composed of a first convex lens (41) of the 4f system and a second convex lens (42) of the 4f system. The distance between the two convex lenses is the sum of the focal lengths of the first convex lens (41) and the second convex lens (42) of the 4f system, and is coated with an anti-reflection film consistent with the laser echo.

6. The acousto-optic modulator (5) is composed of an acousto-optic crystal and a driver, has a light aperture of 4 to 15 mm, a thickness of 2 to 30 mm, and is coated with an anti-reflection film consistent with the laser echo, and can achieve a deflection of the light beam of 16 to 30 mrad.

7. The pinhole diaphragm (6) can be controlled by electric drive, and the aperture range of the pinhole diaphragm is: 0.1~4mm.

Images