Method for assembling and adjusting superconducting nanowire single-photon detector in laser ranging telescope

Abstract

The invention relates to the technical field of optical adjustment, in particular to an adjustment method for a superconducting nanowire single-photon detector in a laser ranging telescope. In the coarse adjustment, an optical fiber is coupled and butted with a coupling lens in an onboard receiving terminal of a laser ranging telescope through an optical fiber port, and a collimation light source is fixed at the other end; the coupling lens and the optical fiber port are integrally fixed on a multi-dimensional adjusting mechanism; the collimation light source is turned on, after light is transmitted to the coupling lens through the optical fiber, light spots are continuously adjusted, so that the light spots can penetrate through the centers of all optical lenses in the onboard receiving terminal, and then the multi-dimensional adjusting mechanism is locked; the fine adjustment is to align the telescope with a target satellite, detect the photon count of the target satellite in real time, and then rotate the azimuth and pitch angle of the telescope to determine the position with the highest photon count; and changing a darker target satellite, and continuously adjusting until the photon counting is the highest and is not changed any more, thereby finishing fine adjustment. The method has the advantages that human eye observation and alignment are not depended; operation is simple and convenient, and precision is improved.

Description

Technical Field

[0001] The invention relates to the technical field of optical adjustment, and in particular to an adjustment method for a superconducting nanowire single-photon detector in a laser ranging telescope. Background Art

[0002] Laser ranging telescopes can achieve high-precision ranging of space targets and play an important role in the fields of space target and space environment monitoring. The increasing number of space debris seriously threatens the safety of spacecraft operation and needs to be orbited and removed in a timely manner. However, unlike cooperative satellites, the full-space reflection characteristics of space debris cause the number of echo photons to be at the single-photon level, which increases the difficulty of detection.

[0003] The commonly used avalanche single photon detector (SPAD) has the problems of high dark counts (103~106 counts / s) and low tolerance to photon energy. In a pulse cycle, it stops working after completing only one measurement. If it is unfortunately "closed" by noise, it will not be able to detect echo photons. This "closing" characteristic of SPAD reduces the probability of detecting effective echo photons.

[0004] The superconducting nanowire single photon detector (SNSPD) is a single photon detector with excellent performance. The biased nanowire produces a resistance state after absorbing photons, which affects the current distribution of the circuit. The light pulse response generated by the current change is read out through a low-noise amplifier. The SNSPD has the advantages of high sensitivity (less than the single photon level), low dark count rate (less than 100 counts / s), short recovery time (less than 20 ns), high working repetition frequency (greater than 100 MHz) and high photon energy saturation threshold. The SNSPD allows multiple photon detections within one pulse cycle. In addition, the superconducting nanowire single photon detector uses fiber coupling to introduce the echo signal into the detector, which is conducive to suppressing the influence of background noise on the single photon detector. At the same time, the superconducting nanowire single photon detector will automatically leave the superconducting state when encountering strong light, thereby greatly reducing the probability of the detector being damaged by strong light.

[0005] The Chinese invention patent publication number CN 116953953 B, publication date November 21, 2023, invention name "Method for adjusting single photon detector in large-aperture laser ranging optical system" proposes a method for adjusting an avalanche single photon detector (SPAD) in a laser ranging telescope. Currently, there are no reports on the application and adjustment method of SNSPD in laser ranging telescopes.

[0006] When using a superconducting nanowire single - photon detector for laser ranging, the echo signal needs to be introduced into the detector through fiber - optic coupling. Since the superconducting nanowire single - photon detector needs to work under cooling and has a relatively large size and cannot be integrated onto the telescope, the echo light signal received by the on - telescope optical system needs to be coupled into the optical fiber through a coupling lens, and then the echo light signal is transmitted through a long optical fiber to the superconducting nanowire single - photon detector below the telescope. The optical fiber needs to pass through and exit near the pitch axis and azimuth axis inside the telescope through a certain method, and an appropriate margin is reserved and then led to the lower end of the telescope, so as to avoid damaging the optical fiber when the telescope rotates. The distance that the optical fiber passes through usually reaches more than ten meters or even longer. Therefore, high alignment accuracy is required when coupling and transmitting the optical signal, otherwise the echo signal cannot be effectively transmitted.

[0007] In the traditional alignment method of superconducting nanowire single - photon detectors in laser - ranging telescopes, it is often necessary to aim at a star. Use the telescope to align with a bright star. If the starlight can be ideally and strictly aligned with the exact center of the coupling lens, use the starlight to pass through the axis of the coupling lens, and then fix the position of the coupling lens, then it is considered that the alignment is completed. However, in the actual process, the starlight is often very weak and may not be observable by the human eye, which leads to the inability to complete the above - mentioned alignment and axis - passing process. Even if it can be observed, the alignment by the human eye alone cannot meet the accuracy requirements. Therefore, the entire alignment process is seriously misaligned and the coupling and transmission of the echo light signal cannot be completed. Summary of the Invention

[0008] The present invention provides an alignment method for a superconducting nanowire single - photon detector in a laser - ranging telescope to solve the above problems.

[0009] The object of the present invention is to provide an alignment method for a superconducting nanowire single - photon detector in a laser - ranging telescope, which specifically includes the following steps: S1. Coarse alignment of the superconducting nanowire single - photon detector: Couple and dock the optical fiber through the fiber optic port with the coupling lens inside the on - telescope receiving terminal of the laser - ranging telescope, and fix the other end of the optical fiber to a collimated light source; Fix the coupling lens and the fiber optic port as a whole on a multi - dimensional adjustment mechanism; Turn on the collimated light source. After the light passes through the optical fiber and reaches the coupling lens, a light spot with a certain aperture is formed; Continuously adjust the light spot through the multi - dimensional adjustment mechanism so that the light spot can pass through the centers of all the optical lenses inside the on - telescope receiving terminal of the laser - ranging telescope. At this time, lock the multi - dimensional adjustment mechanism to complete the coarse alignment stage; S2. Fine alignment of the superconducting nanowire single - photon detector; The specific process of fine alignment is as follows: S201. Rotate the laser - ranging telescope to align with a target star, so that the target star is imaged at the center of the imaging unit of the laser - ranging telescope; S202. Disconnect the optical fiber from the collimated light source; connect one end of the superconducting nanowire single-photon detector to the oscilloscope and the other end to the optical fiber; use the oscilloscope to measure the photon count detected by the superconducting nanowire single-photon detector in real time; S203. Continuously rotate the azimuth angle of the laser ranging telescope in a small range to make the image of the target star move horizontally near the center of the imaging unit. Observe and record the photon count measured by the oscilloscope in real time, find the horizontal pixel position where the target star is imaged on the imaging unit when the photon count is the largest, and record the horizontal pixel position at this time; S204. Continuously rotate the pitch angle of the laser ranging telescope in a small range to make the image of the target star move vertically near the center of the imaging unit. Observe and record the photon count measured by the oscilloscope in real time, find the vertical pixel position where the target star is imaged on the imaging unit when the photon count is the largest, and record the vertical pixel position at this time; S205. Replace the target star with a star of a larger magnitude, rotate the laser ranging telescope, and image the star to the horizontal pixel position recorded in step S203 and the vertical pixel position recorded in step S204; repeat steps S203 and S204, and re-find and record the horizontal pixel position and the vertical pixel position where the target star is imaged on the imaging unit when the photon count is the largest respectively; S206. Gradually weaken the brightness of the target star aligned by the laser ranging telescope according to the magnitude, repeat step S205 until the position with the highest determined photon count no longer changes, and determine the optimal coupling position between the on-board receiving terminal of the laser ranging telescope and the superconducting nanowire single-photon detector to complete the fine adjustment.

[0010] Preferably, the adjustment directions of the multi-dimensional adjustment mechanism in step S1 include lifting, horizontal translation in the left and right directions, and rotation of the pitch angle and azimuth angle; the position, azimuth angle, and pitch angle of the light spot are continuously adjusted through the multi-dimensional adjustment mechanism.

[0011] Preferably, the laser ranging telescope includes a primary mirror, a secondary mirror, a tertiary mirror, and an on-board receiving terminal; the on-board receiving terminal includes an imaging unit, a collimating lens group, and a coupling lens; The primary mirror of the laser ranging telescope receives the parallel light from the target star at infinity, reflects and deflects it through the secondary mirror and the tertiary mirror to the on-board receiving terminal; after the light incident on the on-board receiving terminal is split by the beam splitting element, a part of the light forms an image of the target star through the imaging unit to correct the aberration; the other part of the light propagates forward to the collimating lens group to collimate the light and realize the conversion of parallel light; the coupling lens is used to converge and couple the previous parallel light to the optical fiber.

[0012] Preferably, the imaging unit includes a lens and a detector; the light forms an image of the target star through the imaging unit and finally forms an image on the detector of the imaging unit.

[0013] Preferably, in step S201, the target star is imaged at the center of the detector of the imaging unit of the laser ranging telescope; in step S203, the image of the target star is laterally moved near the center of the detector of the imaging unit; in step S204, the image of the target star is longitudinally moved near the center of the detector of the imaging unit.

[0014] Compared with the prior art, the present invention can achieve the following beneficial effects: The alignment method provided by the present invention is simple and convenient to operate; it takes into account the actual situation of the field, and no longer relies on the human eye to observe starlight for alignment; it rationalizes the alignment process by using the reverse transmission of the light emitted under the machine; the coupling lens and the optical fiber are installed on a multi-dimensional adjustment mechanism, which is convenient for adjustment; at the same time, an oscilloscope is introduced to detect the echo signal received by the superconducting nanowire single photon detector, greatly improving the accuracy. Description of the Drawings

[0015] Figure 1 It is a layout schematic diagram of an alignment component of a superconducting nanowire single photon detector in a laser ranging telescope according to an embodiment of the present invention.

[0016] Reference Signs: 1. Target star; 2. Primary mirror; 3. Secondary mirror; 4. Tertiary mirror; 5. Imaging unit; 6. Collimating lens group; 7. Coupling lens; 8. First optical fiber port; 9. Multi-dimensional adjustment mechanism; 10. Optical fiber; 11. Superconducting nanowire single photon detector; 12. Oscilloscope. Detailed Embodiments

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same modules are denoted by the same reference signs. In the case of the same reference signs, their names and functions are also the same. Therefore, their detailed descriptions will not be repeated.

[0018] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and do not constitute a limitation to the present invention.

[0019] The present invention provides an alignment method for a superconducting nanowire single photon detector in a laser ranging telescope; according toFigure 1 The assembly and adjustment components of the superconducting nanowire single-photon detector in the shown laser ranging telescope are built; The laser ranging telescope includes mirrors such as the primary mirror 2, secondary mirror 3, and tertiary mirror 4, as well as the on-aircraft receiving terminal; the primary mirror 2 on the main aperture of the laser ranging telescope receives the parallel light from the target star 1 at infinity, and is reflected by mirrors such as the secondary mirror 3 and tertiary mirror 4 and deflected to the on-aircraft receiving terminal of the laser ranging telescope; The on-aircraft receiving terminal of the laser ranging telescope includes a series of optical elements, including the imaging unit 5, collimating lens group 6, and coupling lens 7; the imaging unit 5 includes a lens and a detector; after the light incident on the on-aircraft receiving terminal is split by the beam splitting element, a part of the light forms an image of the target star 1 through the imaging unit 5 and finally forms an image on the detector to correct the aberration; another part of the light propagates forward to the collimating lens group 6, and for the 1064 nm band, collimates the light propagating through the previous optical path to change the light into parallel light with a certain aperture to achieve the conversion of parallel light; the coupling lens 7 is used to converge and couple the previous parallel light to the optical fiber 10; The coupling lens 7 and the optical fiber 10 are coupled and docked through the first optical fiber port 8, and the docking process can be achieved by means of a formed coupler product; then the coupling lens 7 and the first optical fiber port 8 are integrally fixed on the multi-dimensional adjustment mechanism 9, and precise adjustment is carried out by means of the multi-dimensional adjustment mechanism 9; the multi-dimensional adjustment mechanism 9 can achieve precise adjustment and locking functions, and the adjustment directions include lifting, translation in the left and right directions, and rotation of the pitch angle and azimuth angle.

[0020] Figure 1 The superconducting nanowire single-photon detector 11 is also shown, which is used to detect the photon signal transmitted by the on-aircraft receiving terminal of the laser ranging telescope; the oscilloscope 12 is used to measure the number of photon signals transmitted by the on-aircraft receiving terminal detected by the superconducting nanowire single-photon detector 11.

[0021] Specifically, it includes the following steps: S1. Coarse adjustment of the superconducting nanowire single-photon detector; the specific process of the coarse adjustment is as follows: S101. Build the assembly and adjustment components of the superconducting nanowire single-photon detector 11 in the laser ranging telescope; One end of the optical fiber 10 is coupled and docked with the coupling lens 7 in the on-aircraft receiving terminal of the laser ranging telescope through the first optical fiber port 8, and the other end of the optical fiber 10 is connected and fixed to a collimating light source through the second optical fiber port; The coupling lens 7 and the first optical fiber port 8 are integrally fixed on the multi-dimensional adjustment mechanism 9; S102. Turn on the collimating light source, and the light propagates through the optical fiber 10 to the first optical fiber port 8 and exits. After passing through the coupling lens 7, a light spot with a certain aperture is formed; S103. Visually observe the position of the light spot, and continuously adjust the position, azimuth, and pitch angle of the light spot through the multi-dimensional adjustment mechanism 9 so that the light spot can pass through the centers of all the optical lenses in the on-board receiving terminal of the laser rangefinder telescope. At this time, lock the multi-dimensional adjustment mechanism 9 to complete the rough adjustment stage.

[0022] S2. Fine adjustment of the superconducting nanowire single-photon detector; the specific process of the fine adjustment is as follows: S201. Determine the target star according to the stellar magnitude of 2-6; rotate the laser rangefinder telescope to aim at a target star so that the target star is imaged at the center of the detector of the imaging unit 5 of the laser rangefinder telescope; the optical path of the detector is also located in the on-board receiving terminal of the laser rangefinder telescope. Therefore: when rotating the azimuth angle of the laser rangefinder telescope, the position of the target star imaged on the detector of the imaging unit 5 will move horizontally; when rotating the pitch angle of the laser rangefinder telescope, the position of the target star imaged on the detector of the imaging unit 5 will move vertically; taking advantage of the high sensitivity of the superconducting nanowire single-photon detector 11, after the rough adjustment process is completed, the superconducting nanowire single-photon detector 11 can detect the optical signal of the starlight received by the laser rangefinder telescope. S202. Disconnect the optical fiber 10 from the collimated light source; connect one end of the superconducting nanowire single-photon detector 11 to the oscilloscope 12 and the other end to the optical fiber 10; use the oscilloscope 12 to measure the photon count detected by the superconducting nanowire single-photon detector 11 in real time. S203. Continuously rotate the azimuth angle of the laser rangefinder telescope in a small range to make the image of the target star move horizontally near the center of the detector of the imaging unit 5. At this time, the azimuth angle of the starlight signal reaching the coupling lens 7 and the optical fiber 10 changes; observe and record the photon count measured by the oscilloscope 12 in real time, find the horizontal pixel position when the target star is imaged on the detector of the imaging unit 5 when the photon count is the largest, and record the horizontal pixel position at this time. S204. Continuously rotate the pitch angle of the laser rangefinder telescope in a small range to make the image of the target star move vertically near the center of the detector of the imaging unit 5. At this time, the pitch angle of the starlight signal reaching the coupling lens 7 and the optical fiber 10 changes; observe and record the photon count measured by the oscilloscope 12 in real time, find the vertical pixel position when the target star is imaged on the detector of the imaging unit 5 when the photon count is the largest, and record the vertical pixel position at this time. S205. Replace the target star with a star of a larger magnitude, rotate the laser rangefinder telescope to image the star at the horizontal pixel position recorded in step S203 and the vertical pixel position recorded in step S204; repeat steps S203 and S204, and re-find the horizontal pixel position and the vertical pixel position when the target star is imaged on the detector of the imaging unit 5 when the photon count is the largest, and record the horizontal pixel position and the vertical pixel position at this time respectively. S206. Gradually weaken the brightness of the target star aimed at by the laser ranging telescope according to the magnitude, and repeat step S205 until the position with the highest determined photon count no longer changes. Determine the optimal coupling position between the on-board receiving terminal of the laser ranging telescope and the superconducting nanowire single-photon detector 11 at this time to complete the fine adjustment.

[0023] Principle description of the present invention: In the coarse adjustment stage, the principle of reversible light propagation is mainly utilized. Instead of being entangled in coupling and propagating the echo signal light on the telescope to below the machine, on the contrary, a collimated light source is installed at the port at one end of the fiber optic cable below the machine with a relatively long length. The light is conducted to the telescope on the machine through the fiber optic cable, and the spot emerging from the fiber optic port on the machine and passing through the coupling lens is continuously adjusted. Visually aim to make the spot pass through the centers of each optical lens on the machine. The adjustment process requires the assistance of a multi-dimensional adjustment mechanism.

[0024] In the fine adjustment process, the advantages of SNSPD are utilized, such as high sensitivity (less than the single-photon level), low dark count rate (less than 100 counts / s), short recovery time (less than 20 ns), high working repetition frequency (greater than 100 MHz), and high photon energy saturation threshold, allowing multiple photon detections within one pulse period. The telescope is aimed at multiple stars with different brightnesses. When aiming at a star, connect the oscilloscope to the SNSPD to detect the photon count of the target star in real time. Since the coarse adjustment of the superconducting nanowire single-photon detector has been completed at this time, only slightly change the azimuth and elevation angles of the telescope (in fact, slightly change the angle at which the echo light signal of the target star reaches the coupling lens and the fiber optic cable), and determine the position with the highest photon count. Then aim the telescope at the next star with a weaker brightness (the echo light signal of the weak star is also weak), which helps to improve the accuracy; repeat the above process and determine the position with the highest photon count again. Gradually weaken the brightness of the star aimed at by the telescope and repeat the above process until the position with the highest determined photon count no longer changes to complete the fine adjustment. The fine adjustment process must be carried out after the coarse adjustment is completed because both the coupling angle of the fiber optic cable and the detection angle of the superconducting nanowire single-photon detector have only a small range. If the deviation is slightly larger, the superconducting nanowire single-photon detector will not be able to detect the echo signal of the target star.

[0025] It should be understood that various forms of the flow shown above can be used, re-ordered, steps added or deleted. For example, the steps recorded in the disclosure of the present invention can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution disclosed in the present invention can be achieved. This is not limited herein.

[0026] The above specific embodiments do not constitute a limitation to the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for assembling and adjusting a superconducting nanowire single-photon detector in a laser ranging telescope, characterized in that: The specific steps include: S1. Coarse adjustment of the superconducting nanowire single-photon detector: couple the optical fiber through the optical fiber port and the coupling lens in the onboard receiving terminal of the laser ranging telescope, and connect the other end of the optical fiber to a collimated light source; fix the coupling lens and the optical fiber port as a whole on the multi-dimensional adjustment mechanism; turn on the collimated light source, and after the light passes through the optical fiber to the coupling lens, a light spot of a certain caliber is formed; the light spot is continuously adjusted through the multi-dimensional adjustment mechanism so that the light spot can pass through the center of all optical lenses in the onboard receiving terminal of the laser ranging telescope, and then the multi-dimensional adjustment mechanism is locked to complete the coarse adjustment stage; S2. Fine tuning of superconducting nanowire single photon detector; the specific process of fine tuning is as follows: S201. Rotate the laser ranging telescope to aim at a target star so that the target star is imaged at the center of the imaging unit of the laser ranging telescope; S202. Disconnect the optical fiber from the collimated light source; connect one end of the superconducting nanowire single-photon detector to an oscilloscope and the other end to the optical fiber; use the oscilloscope to measure the photon count detected by the superconducting nanowire single-photon detector in real time; S203. Continuously rotate the azimuth angle of the laser ranging telescope in a small range so that the image of the target star moves laterally near the center of the imaging unit, observe and record the photon counts measured by the oscilloscope in real time, find the lateral pixel position of the target star imaged on the imaging unit when the photon count is the largest, and record the lateral pixel position at this time; S204. Continuously rotate the elevation angle of the laser ranging telescope in a small range to make the image of the target star move longitudinally near the center of the imaging unit, observe and record the photon counts measured by the oscilloscope in real time, find the longitudinal pixel position of the target star imaged on the imaging unit when the photon count is the largest, and record the longitudinal pixel position at this time; S205. Replace a star with a larger magnitude as the target, rotate the laser ranging telescope, and image the star to the horizontal pixel position recorded in step S203 and the vertical pixel position recorded in step S204; repeat steps S203 and S204, find the horizontal pixel position and the vertical pixel position of the target star imaged on the imaging unit when the photon count is the largest, and record them respectively; S206. Continuously reduce the brightness of the target star at which the laser ranging telescope is aimed according to the magnitude, and repeat step S205 until the position with the highest photon count no longer changes. Determine the optimal coupling position between the onboard receiving terminal of the laser ranging telescope and the superconducting nanowire single-photon detector at this time, and complete fine-tuning.

2. The method for assembling and adjusting a superconducting nanowire single-photon detector in a laser ranging telescope according to claim 1, characterized in that: The adjustment direction of the multi-dimensional adjustment mechanism in step S1 includes lifting, translation in the left and right directions, and rotation of the pitch angle and azimuth angle; the position, azimuth angle and pitch angle of the light spot are continuously adjusted by the multi-dimensional adjustment mechanism.

3. The method for assembling and adjusting a superconducting nanowire single-photon detector in a laser ranging telescope according to claim 1, characterized in that: The laser ranging telescope comprises a primary mirror, a secondary mirror, a tertiary mirror, and an onboard receiving terminal; the onboard receiving terminal comprises an imaging unit, a collimating lens group, and a coupling lens; The primary mirror of the laser ranging telescope receives parallel light from a target star at infinity, reflects it through a secondary mirror and a tertiary mirror, and folds it to an onboard receiving terminal; after the light incident on the onboard receiving terminal is split by a beam splitter, a part of the light is imaged on the target star through an imaging unit to achieve aberration correction; the other part of the light is propagated forward to a collimating lens group to collimate the light, thereby achieving parallel light conversion; and a coupling lens is used to converge the preceding parallel light and couple it to an optical fiber.

4. The method for assembling and adjusting a superconducting nanowire single-photon detector in a laser ranging telescope according to claim 3, characterized in that: The imaging unit comprises a lens and a detector; light passes through the imaging unit to image the target star, and finally the image is formed on the detector of the imaging unit.

5. The method for assembling and adjusting a superconducting nanowire single-photon detector in a laser ranging telescope according to claim 4, characterized in that: In step S201, the target star is imaged at the center of the detector of the imaging unit of the laser ranging telescope; in step S203, the image of the target star is moved laterally near the center of the detector of the imaging unit; in step S204, the image of the target star is moved longitudinally near the center of the detector of the imaging unit.

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