Method for visualizing telescope focal length information, focal length adjustment method and aid

Abstract

The present application belongs to the field of optical instruments, and particularly relates to a telescope focal length information visualization method, a telescope focal length adjustment method based on the method, and a corresponding telescope focal length adjustment auxiliary tool. The scheme uses a laser to generate signal light, then divides the signal light into two parts, uses one part as a local oscillator light, and converts the other part into pulsed light through frequency shifting and pulse conversion. The pulsed light is then emitted through a telescope, and the echo signal received by the telescope is interfered with the local oscillator light. Finally, the interference signal is analyzed to obtain the signal-to-noise ratio curve of the telescope at different detection distances. The spatial distribution of the signal-to-noise ratio at different detection distances reflected by the signal-to-noise ratio curve is used to determine the current focal length information of the telescope. The present application also provides several typical hardware devices for implementing the scheme. The present application can solve the problems of large volume, fear of vibration, and the need for calibration in the existing collimator focusing method.

Description

Technical Field

[0001] This invention belongs to the field of optical instruments and meters, specifically relating to a method for visualizing telescope focal length information, a method for adjusting telescope focal length based on this method, and corresponding auxiliary tools for adjusting telescope focal length. Background Technology

[0002] In the field of laser telemetry, telescopes are typically used for optical transmission and reception. When using a telescope to measure distant targets, it is usually necessary to adjust the position of the fiber optic end face to maximize the telescope's focus distance and minimize the spread angle of the emitted beam, making it nearly parallel. When using a telescope to receive signals, the focal length needs to be adjusted to bring the parallel light entering the telescope tube as close as possible to the fiber optic or detector element. Therefore, depending on the application scenario, technicians typically need to precisely adjust the telescope's focal length according to the target.

[0003] Existing telescope focusing is usually accomplished through optical means, such as collimator focusing. The focusing principle of this method is: the telescope emits a laser beam that enters the collimator. Since the collimator has the characteristic of focusing a parallel beam to a single point, the focal length of the telescope can be adjusted to minimize the light spot on the CCD at the end of the collimator, which is the focal length that minimizes the spread angle of the emitted beam.

[0004] While collimator focusing is simple to operate, it also has several drawbacks. For example: (1) Large equipment size. The accuracy of optical focusing is proportional to the focal length. When adjusting a large telescope, the focal length of the collimator is around 10m, making the length of the collimator usually exceed 1m. (2) High precision requirements for instruments. For large telescopes with a diameter of 300mm or more, the collimator requires large-diameter lenses or mirrors, which require high processing precision. (3) Susceptible to vibration interference. The entire optical path has poor vibration resistance and requires a stable environment for placement. (4) Chromatic aberration exists. For lasers of different wavelengths, the final imaging lens may produce chromatic aberration, requiring the collimator to be pre-calibrated for specific wavelengths. Summary of the Invention

[0005] To address the problems of large size, susceptibility to vibration, and the need for calibration in existing telescope focusing methods, this invention provides a method for visualizing telescope focal length information, a focal length adjustment method, and auxiliary tools.

[0006] This invention is achieved using the following technical solution:

[0007] A method for visualizing telescope focal length information, comprising:

[0008] The signal light, matched to the operating wavelength of the telescope under test, is split into two paths. One path serves as the local oscillator, while the other path undergoes frequency shifting and pulse conversion to obtain pulsed light. The pulsed light is fed into the telescope under test and emitted into the atmosphere. The echo signal, after reflection from the atmosphere, is then received. Both the echo signal and the local oscillator are split separately. The resulting two beams are then focused and overlapped before being received by a balanced detector, which generates the corresponding interference signal.

[0009] After analog-to-digital conversion of the interference signal, each pulse cycle is divided into multiple signal segments according to a preset signal length. An FFT operation is performed on each signal segment to obtain spectral information. The corresponding segments from all pulse cycles are superimposed to obtain the power spectrum. The signal-to-noise ratio (SNR) of each signal segment is calculated based on the power spectrum. The discrete SNR values ​​are then fitted to generate an SNR curve. In the SNR curve, the x-axis represents the SNR value, and the y-axis represents the telescope's detection distance after conversion based on each signal segment.

[0010] The focus position during telescope detection is indicated by the peak value of the signal-to-noise ratio (SNR) in the SNR curve, the optimal detection distance corresponding to the peak value, and the rate of SNR decrease between the optimal detection distance and a further detection distance.

[0011] As a further improvement of the present invention, the frequency shift of the pulsed light relative to the original signal after frequency shifting is 50-100MHz.

[0012] and / or

[0013] The pulse width of the pulsed light is 100ns-1us, and the pulse repetition frequency is 1-10kHz.

[0014] As a further improvement of the present invention, the single-pulse energy of the pulsed light connected to the telescope is not less than 1 μJ.

[0015] As a further improvement of the present invention, the signal length of each segmented signal is 100ns-1us.

[0016] In this invention, the signal-to-noise ratio (SNR) of each signal segment is calculated using the following formula:

[0017]

[0018] In the above formula, Ps represents the power of the signal; Pn represents the power of the noise.

[0019] The present invention also includes a method for adjusting the focal length of a telescope, comprising the following steps:

[0020] S1: Implement the visualization method for telescope focal length information as described above.

[0021] S2: Observe the signal-to-noise ratio curve and make the following decisions based on the target adjustment according to different telescope focal lengths:

[0022] (1) When the outgoing light of the telescope needs to be as collimated as possible and the divergence angle as small as possible, the focal length-related equipment parameters of the telescope should be adjusted in a coordinated manner so that the signal-to-noise ratio curve decreases as gently as possible with distance. The test standard is that the difference between the signal-to-noise ratio at the optimal detection distance and at twice the optimal detection distance is close to but not less than 6dB.

[0023] (2) When it is necessary to use the telescope to observe a target at a specific distance, the telescope’s focal length-related equipment parameters are adjusted in a coordinated manner so that the vertical coordinate of the point in the signal-to-noise ratio curve that reaches the peak signal-to-noise ratio is located at a specific distance, and the peak signal-to-noise ratio at that point is maximized.

[0024] The present invention also includes an auxiliary tool for telescope focal length adjustment, which uses the aforementioned method for visualizing telescope focal length information to indicate the focal length of the telescope; the auxiliary tool includes: a laser, a first beam splitter, an acousto-optic frequency shifter, a pulse amplifier, a circulator, a second beam splitter, a balance detector, and a data processing module.

[0025] The laser is used to generate signal light that matches the operating wavelength of the telescope under test. The first beam splitter is a 1-to-2 beam splitter; it splits the signal light into two paths, one serving as the local oscillator and the other as pulsed light. An acousto-optic frequency shifter is used to shift the frequency of the signal input to the first beam splitter. A pulse amplifier is used to convert the frequency-shifted signal into pulsed light of a preset pulse width.

[0026] The circulator receives the pulsed light and directs it into the telescope; it also receives the echo signal collected by the telescope. The second beam splitter is a two-to-two beam splitter; it receives the echo signal and the local oscillator light, splits them separately, and then focuses and merges the two resulting beams before outputting them. The balanced detector receives the two signals output from the second beam splitter and generates the corresponding interference signal.

[0027] The data processing module is used to: (1) perform analog-to-digital conversion on the interference signal; (2) divide the signal of each pulse period into multiple signal segments according to the preset signal length; (3) perform FFT operation on each signal segment to obtain the spectrum information; (4) superimpose the corresponding segments of all pulse periods to obtain the power spectrum; (5) calculate the signal-to-noise ratio of each signal segment based on the power spectrum, fit the values ​​of each discrete signal-to-noise ratio, and generate a signal-to-noise ratio curve.

[0028] Furthermore, the telescope focal length adjustment auxiliary tool provided by the present invention also includes or is connected to a display module. The display module is used to visualize the signal-to-noise ratio curve, including graphical visualization and / or numerical visualization.

[0029] As a further improvement of the present invention, the pulse amplifier is also used to amplify the power of the input signal so that the single pulse energy of the output pulse light is not less than 1 μJ.

[0030] As a further improvement of the present invention, the first beam splitter includes one input port and two output ports, the second beam splitter includes two input ports and two output ports, and the circulator includes three ports. The laser, beam splitter, acousto-optic frequency shifter, pulse amplifier, circulator, telescope, beam splitter, and balanced detector are connected by optical fiber coupling to form the required optical path.

[0031] The technical solution provided by this invention has the following beneficial effects:

[0032] 1. The present invention omits the spatial optical path of several meters in the prior art and instead detects atmospheric echo signals of several kilometers in length. In this way, the device itself only needs some photoelectric detection and logic operation circuit boards, which can be integrated into a device smaller than a computer host, thus greatly reducing the size of the entire detection instrument.

[0033] 2. The testing instrument provided by this invention has an all-fiber structure and no high-precision optoelectronic devices, making it basically unaffected by environmental interference, resistant to transportation and impacts, and more stable.

[0034] 3. The hardware component of this invention only requires connecting to an optical fiber and reflecting the telescope into the atmosphere to indicate the focal length, without the need for optical calibration. After debugging using this device, it is ready to use simply by connecting the optical fiber coupled to the telescope to the system to be used; there is no need to move the telescope, making the operation process very convenient.

[0035] 4. The measurement method in this invention is basically consistent with the actual use scenario of the telescope, and the data has high reliability. During use, it does not require constructing a precise optical path to simulate the shape of light during long-distance transmission; instead, it directly collects far-field signals from the atmosphere. Therefore, no pre-calibration is required, avoiding systematic errors that may be caused by equipment inaccuracies.

[0036] 5. The signal-to-noise ratio curve obtained by the present invention contains more information than the spot information obtained by traditional methods. Existing technologies can only indicate the divergence angle through the spot, while this technology can measure the maximum signal distance and signal spatial attenuation information through the distribution of signal-to-noise ratio. Attached Figure Description

[0037] Figure 1This is a schematic diagram illustrating the principle of a method for visualizing telescope focal length information provided in Embodiment 1 of the present invention.

[0038] Figure 2 The working principle of a two-to-two beam splitter used in the interference process of local oscillator light and echo signal.

[0039] Figure 3 This is a typical power spectrum generated based on the interference signal.

[0040] Figure 4 This is a schematic diagram illustrating the principle of signal-to-noise ratio calculation.

[0041] Figure 5 This is an example image showing the signal-to-noise ratio curve generated using interference signals.

[0042] Figure 6 This is a system topology diagram of the telescope focal length adjustment auxiliary tool constructed in Embodiment 2 of the present invention.

[0043] Figure 7 A system topology diagram for an auxiliary tool designed using a pulsed laser capable of emitting local oscillator light and pulsed light.

[0044] Figure 8 System topology diagram of an auxiliary tool designed to replace a balanced detector with a single-photon detector. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0046] Example 1

[0047] This embodiment provides a method for visualizing telescope focal length information, based on a novel measurement principle. In short, the scheme splits the signal light into two parts: one part serves as the local oscillator, while the other is frequency-shifted and converted into pulsed light, which is then emitted through the telescope. The echo signal received by the telescope is then used to interfere with the local oscillator. Finally, spectral analysis is performed on the interference signal to obtain the signal-to-noise ratio (SNR) curves of the telescope at different detection distances. These SNR curves reflect the spatial distribution of the SNR of the detected signal at different detection distances, thereby determining the current focal length information of the telescope.

[0048] like Figure 1 As shown, the method for visualizing telescope focal length information in this embodiment includes two stages: the first is the light signal propagation stage, and the second is the signal processing and analysis stage. Specifically, it includes the following processes:

[0049] I. Optical Signal Propagation Stage

[0050] A laser with an emitted wavelength matched to the telescope's operating wavelength generates the original signal light. This signal light, matched to the telescope's operating wavelength, is split into two paths: one serves as the local oscillator, and the other undergoes frequency shifting and pulse conversion to obtain pulsed light. In this embodiment, both the original signal light and the split local oscillator are continuous optical signals, while the two pulsed lights are pulsed signals after frequency shifting and pulse conversion. The frequency shift of the pulsed light relative to the original signal is 50-100MHz. The pulse width of the converted pulsed light is 100ns-1us, and the pulse repetition frequency is 1-10kHz. It is important to note that this embodiment only requires the pulsed light and the local oscillator to originate from the same source and meet the aforementioned optical requirements; the order of the frequency shifting and pulse conversion operations performed on the split signal is not limited. Furthermore, this embodiment requires the single-pulse energy of the obtained pulsed light to be no less than 1μJ. To meet this requirement, the power of the original signal light emitted by the laser can be appropriately increased, or a signal power amplification step can be added during the signal conversion process from the split signal to the pulsed light. For example… A pulse amplifier is used to process the signal, achieving pulse conversion and power amplification.

[0051] The obtained pulsed light is fed into the telescope under test and emitted into the atmosphere. The echo signal, after reflection from the telescope, is then received. This echo signal is then interfered with the local oscillator light and detected by a balanced detector to form an electrical signal. Specifically, as... Figure 2 As shown, this embodiment can select a 2-to-2 beam splitter to achieve signal interference between the echo signal and the local oscillator light. The 2-to-2 beam splitter includes two signal input ports and two signal output ports; the echo signal and the local oscillator light are respectively connected to the two signal input ports via optical fibers. The 2-to-2 beam splitter performs beam splitting processing on the echo signal and the local oscillator light respectively, and the two resulting signals are focused and overlapped before being output through the two signal output ports; the output signals are received by the front element and the negative element of the balanced detector, respectively. The balanced detector generates the corresponding interference signal based on the received signals.

[0052] It is important to emphasize that the values ​​for parameters such as pulse width, pulse repetition frequency, and signal segment length introduced in this section are generally suitable. However, the range of these parameters can still be changed when facing different telescope detection distance requirements. For example, for telescopes with large apertures and long-distance detection needs, a larger pulse width and a lower repetition frequency can be used.

[0053] II. Signal Processing and Analysis Stage

[0054] (1) Signal Processing

[0055] In this embodiment, the interference signal output by the balanced detector is an electrical signal. This embodiment first performs analog-to-digital conversion on this electrical signal to obtain the corresponding digital signal. Then, the signal of each pulse cycle is divided into multiple signal segments according to a preset signal length, with each signal segment denoted as a bin. In this embodiment, the signal length of each bin after segmentation is 100 ns–1 μs. The signal length of each bin is on the same order of magnitude as the pulse width of the pulsed light; they can be the same or different. This embodiment performs a Fast Fourier Transform (FFT) operation on each signal segment to obtain spectral information. The corresponding segments from all pulse cycles are then superimposed to obtain the power spectrum. Figure 3 The image shows a typical power spectrum generated from an interference signal. In the power spectrum, the number of segments represents the signal distance, and the spectral intensity in a single segment characterizes the strength of the received signal at that distance.

[0056] Next, the signal-to-noise ratio (SNR) of each signal segment is calculated based on the power spectrum. For example... Figure 4 As shown, the calculation method involves calculating the signal shape through Gaussian fitting to obtain the signal area, and then dividing the signal area by the noise floor area. The specific formula for calculating the signal-to-noise ratio (SNR) is as follows:

[0057]

[0058] In the above formula, Ps represents the power of the signal; Pn represents the power of the noise.

[0059] After obtaining the signal-to-noise ratio (SNR) value for each bin, this embodiment converts the time-domain features of each bin into the corresponding detection distance, fits the discrete SNR values, and generates an SNR curve. Figure 5 This is a typical signal-to-noise ratio (SNR) curve. In the SNR curve, the x-axis represents the SNR value, and the y-axis represents the telescope's detection distance after conversion based on each signal segment. It should be noted that when fitting the SNR curve from discrete points in this implementation, the points can be directly connected sequentially, or new interpolation points can be generated using any function fitting algorithm based on existing points, resulting in a smoother curve. In practical applications, the former method is preferred.

[0060] (2) Image Analysis

[0061] The above steps yield the signal-to-noise ratio (SNR) curve, a function graph that reflects the SNR of the received echo signal at different detection distances. Since the telescope's receiving field of view typically gradually envelops the transmitted beam, the SNR generally reaches its maximum after traveling a certain distance. When the telescope's focal length (fiber position) is adjusted, the shape of this SNR curve changes, increasing or decreasing overall. Therefore, analyzing the changes in the SNR curve can determine the telescope's current focal length.

[0062] In this embodiment, as Figure 5 As shown, the peak signal-to-noise ratio (SNR) dB in the SNR curve is used. max Peak signal-to-noise ratio dB max The corresponding optimal detection distance D best And from the optimal detection distance D best To a greater detection range (e.g., twice the optimal detection range: 2D) bes The rate of decrease in signal-to-noise ratio between the two telescopes can indicate or even quantify the current focus position during telescope detection.

[0063] Example 2

[0064] Based on the solution in Embodiment 1, this embodiment further provides an auxiliary tool for adjusting the focal length of a telescope. This auxiliary tool is a hardware product designed using the principles of the solution in Embodiment 1. Specifically, the auxiliary tool in this embodiment uses the telescope focal length information visualization method as in Embodiment 1 to indicate the focal length of the telescope.

[0065] like Figure 6As shown, the auxiliary tools provided in this embodiment include: a laser, a first beam splitter, an acousto-optic frequency shifter, a pulse amplifier, a circulator, a second beam splitter, a balanced detector, and a data processing module. The laser, first beam splitter, acousto-optic frequency shifter, pulse amplifier, circulator, second beam splitter, and balanced detector constitute all the components that implement the "optical signal propagation stage" in Embodiment 1. The data processing module is used to perform all the components of the "signal processing stage." Specifically, the telescope focal length adjustment auxiliary tool provided in this embodiment also includes a display module for visualizing the signal-to-noise ratio (SNR) curve. Alternatively, a port is reserved in the auxiliary tool for connecting an external display module, which outputs a display signal for visualizing the SNR curve. The display module in this embodiment visualizes the SNR curve through graphical visualization and / or numerical visualization. The former refers to directly displaying the entire signal-to-noise ratio (SNR) curve, while the latter refers to displaying several key parameters of the function representing the SNR curve, such as the peak SNR value in the SNR curve, the optimal detection range corresponding to the peak SNR value, and the rate of SNR decrease between the optimal detection range and a more distant detection range.

[0066] Specifically, in this embodiment, the laser is used to generate signal light that matches the operating wavelength of the telescope under test. The first beam splitter is a 1-to-2 beam splitter; it splits the signal light into two paths, one serving as the local oscillator and the other as the source pulse. An acousto-optic frequency shifter is used to shift the frequency of the signal input to the first beam splitter. A pulse amplifier is used to convert the frequency-shifted signal into pulses of a preset pulse width. The pulse amplifier can also amplify the power of the input signal to ensure that the single-pulse energy of the output pulse is not less than 1 μJ.

[0067] The circulator receives the pulsed light and directs it into the telescope; it also receives the echo signal collected by the telescope. The second beam splitter is a two-to-two beam splitter; it receives the echo signal and the local oscillator light, splits them separately, and then focuses and merges the two resulting beams before outputting them. The balanced detector receives the two signals output from the second beam splitter and generates the corresponding interference signal.

[0068] The data processing module is used for: (1) performing analog-to-digital conversion on the interference signal; (2) dividing the signal of each pulse period into multiple signal segments according to the preset signal length; (3) performing FFT operation on each signal segment to obtain spectral information; (4) superimposing the corresponding segments of all pulse periods to obtain the power spectrum; and (5) calculating the signal-to-noise ratio of each signal segment based on the power spectrum, fitting the values ​​of each discrete signal-to-noise ratio, and generating a signal-to-noise ratio curve. In practical applications, the data processing module can be built using chips and modules such as acquisition cards, FPGAs (programmable circuits), and main control chips, and the corresponding computer programs can be burned into them.

[0069] Combination Figure 6 As can be seen, the first beam splitter in this embodiment includes one input port and two output ports, the second beam splitter includes two input ports and two output ports, and the circulator includes three ports. The laser output propagates to the input port of the first beam splitter. One output port of the first beam splitter is connected to the output port of the second beam splitter, and the other output port is connected to the input port of the acousto-optic frequency shifter. The output of the acousto-optic frequency shifter is connected to the input of the pulse amplifier. The amplified pulse light output by the pulse amplifier enters from port 1 of the circulator, exits from port 2, and enters the optical fiber coupling port of the telescope before exiting into the atmosphere. The laser is reflected in the atmosphere, re-received and coupled by the telescope, and then enters from port 2 of the circulator, exits from port 3, and enters the second beam splitter. The two output ports of the second beam splitter are connected to two surface elements of the balanced detector. Specifically, in the telescope focal length adjustment auxiliary tool of this embodiment, the laser, beam splitter, acousto-optic frequency shifter, pulse amplifier, circulator, telescope, beam splitter, and balanced detector are connected by optical fiber coupling to form the required optical path.

[0070] In the product design process of the telescope focal length adjustment auxiliary tool in this embodiment, a pulsed laser with built-in signal beam splitting, pulse conversion, and frequency division functions can also be selected for product design. This type of pulsed laser can output coherent original signal light and pulsed light, thereby providing the required local oscillator light and pulsed light. In this case, the product design schematic diagram of the auxiliary tool is as follows: Figure 7 As shown. Furthermore, the balanced detector mentioned in this embodiment can also be replaced with a single-photon detector, such as... Figure 8 As shown, correspondingly, after adopting a single-photon detector, there is no need to use an acousto-optic frequency shifter, nor is it necessary to separate a laser beam for interference. Instead, the circulator is connected to a filter and then to the single-photon detector. In the data processing module, FFT calculation is no longer performed. Instead, the single-photon signal is time-division accumulated.

[0071] Example 3

[0072] Based on Examples 1 and 2, this embodiment further provides a method for adjusting the focal length of a telescope, which includes the following steps:

[0073] S1: Implement the method for visualizing telescope focal length information as described in Example 1.

[0074] S2: Observe the signal-to-noise ratio curve and make the following decisions based on the target adjustment according to different telescope focal lengths:

[0075] (1) When it is necessary for the outgoing light of the telescope to be as collimated as possible and the divergence angle to be as small as possible, the focal length-related equipment parameters of the telescope are adjusted in a coordinated manner so that the signal-to-noise ratio curve decreases as gently as possible with distance.

[0076] In this embodiment, one of the criteria for determining whether the signal-to-noise ratio curve decreases as gently as possible with distance is: on the signal-to-noise ratio curve, the difference between the signal-to-noise ratio at the optimal detection distance and at twice the optimal detection distance is close to but not less than 6dB.

[0077] (2) When it is necessary to use the telescope to observe a target at a specific distance, the telescope’s focal length-related equipment parameters are adjusted in a coordinated manner so that the vertical coordinate of the point in the signal-to-noise ratio curve that reaches the peak signal-to-noise ratio is located at a specific distance, and the peak signal-to-noise ratio at that point is maximized.

[0078] Specifically, in Embodiment 3, the telescope focus adjustment auxiliary tool with a display, as described in Embodiment 2, is connected to the telescope to be focused via optical fiber. The signal-to-noise ratio (SNR) curve on the display is then observed in real time, and the telescope's focus is adjusted in real time based on the information provided in the SNR curve until the preset focusing target is met. Specifically, the focusing process in two typical scenarios is described in detail below:

[0079] Scenario 1: Use this device to focus the telescope so that the emitted light is as straight as possible and the divergence angle is as small as possible.

[0080] Implementation method:

[0081] (1) Connect the output fiber of the auxiliary tool to the telescope.

[0082] (2) Point the telescope at the atmosphere, with as few obstructions as possible in front of it. In the city, you can tilt it slightly upward to avoid surrounding buildings, but try not to raise the angle to more than 30°.

[0083] (3) Start the equipment and turn on the laser amplifier.

[0084] (4) Read the signal-to-noise ratio curve to determine whether the focal length meets expectations.

[0085] (5) Adjust the telescope focal length so that the signal-to-noise ratio curve decreases as slowly as possible with distance.

[0086] (6) After focusing the telescope, disconnect the telescope from the auxiliary tools.

[0087] Scenario 2: When observing a target at a specific distance using a telescope, such as a target 3km away, use auxiliary tools to adjust the telescope's maximum coupling efficiency to that distance.

[0088] Implementation method:

[0089] (1) Connect the output fiber of the auxiliary tool to the telescope.

[0090] (2) Point the telescope at the atmosphere, ensuring there are as few obstructions as possible in front of it. In urban areas, you can tilt it slightly upwards to avoid surrounding buildings, but try not to exceed 30° in elevation.

[0091] (3) Start the equipment and turn on the laser amplifier.

[0092] (4) Read the signal-to-noise ratio curve to determine whether the focal length meets expectations.

[0093] (5) Adjust the telescope focal length so that the signal-to-noise ratio peak is located at a distance of 3km and the signal-to-noise ratio peak is as high as possible.

[0094] (6) After completing the telescope adjustment, disconnect the telescope from the auxiliary tools.

[0095] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for visualizing telescope focal length information, characterized in that, It includes: The signal light, which is matched with the operating wavelength of the telescope under test, is split into two paths. One path is used as the local oscillator light, and the other path is converted into pulse light after frequency shifting and pulse conversion. The pulsed light is fed into the telescope under test and emitted into the atmosphere. Then the echo signal of the pulsed light emitted by the telescope after being reflected by the atmosphere is received. The echo signal and the local oscillator light are split into two beams respectively. The two beams obtained from each beam are focused and overlapped and then received by a balanced detector. The balanced detector generates a corresponding interference signal. After performing analog-to-digital conversion on the interference signal, the signal of each pulse period is divided into multiple signal segments according to a preset signal length; an FFT operation is performed on each signal segment to obtain the spectrum information; and the corresponding segments of all pulse periods are superimposed to obtain the power spectrum. The signal-to-noise ratio (SNR) of each signal segment is calculated based on the power spectrum. The discrete SNR values ​​are then fitted to generate an SNR curve. The horizontal axis of each point on the SNR curve represents the SNR value, and the vertical axis represents the telescope's detection distance after conversion based on each signal segment. The signal-to-noise ratio (SNR) peak value, the optimal detection distance corresponding to the SNR peak value, and the SNR decrease rate between the optimal detection distance and a further detection distance are used to indicate the current telescope's focusing position during detection.

2. The method for visualizing telescope focal length information as described in claim 1, characterized in that: The frequency shift of the pulsed light relative to the original signal after the frequency shift operation is 50-100MHz; and / or The pulse width of the pulsed light is 100ns-1us, and the pulse repetition frequency is 1-10kHz.

3. The method for visualizing telescope focal length information as described in claim 2, characterized in that: The single-pulse energy of the pulsed light connected to the telescope is not less than 1 μJ.

4. The method for visualizing telescope focal length information as described in claim 1, characterized in that: The signal length of each segment after segmentation is 100ns-1us.

5. The method for visualizing telescope focal length information as described in claim 4, characterized in that: The formula for calculating the signal-to-noise ratio (SNR) of each signal segment is as follows: In the above formula, Ps represents the power of the signal; Pn represents the power of the noise.

6. A method for adjusting the focal length of a telescope, characterized in that, It includes the following steps: S1: Implement the method for visualizing telescope focal length information as described in any one of claims 1-5; S2: Observe the signal-to-noise ratio curve and make the following decisions based on the target adjustment according to different telescope focal lengths: (1) When the outgoing light of the telescope needs to be as collimated as possible and the divergence angle as small as possible, the focal length-related equipment parameters of the telescope are adjusted in a coordinated manner to make the signal-to-noise ratio curve decrease as gently as possible with distance. The test standard is: the difference between the signal-to-noise ratio at the optimal detection distance and twice the optimal detection distance is close to but not less than 6dB. (2) When it is necessary to use the telescope to observe a target at a specific distance, the telescope’s focal length-related equipment parameters are adjusted in a coordinated manner so that the vertical coordinate of the point in the signal-to-noise ratio curve that reaches the peak signal-to-noise ratio is located at a specific distance, and the peak signal-to-noise ratio at that point is maximized.

7. An auxiliary tool for adjusting the focus of a telescope, characterized in that: It employs the telescope focal length information visualization method as described in any one of claims 1-5 to indicate the focal length of the telescope; the auxiliary tool includes: A laser, used to generate signal light that matches the operating wavelength of the telescope under test; The first beam splitter is a 1-to-2 beam splitter; the first beam splitter is used to split the signal light into two paths, one of which is used as the local oscillator light and the other is used to generate pulse light. An acousto-optic frequency shifter, used to perform frequency shifting on the input signal of the first beam splitter; A pulse amplifier is used to convert a frequency-shifted signal into a pulse of light with a preset pulse width. A circulator is used to receive the pulsed light and direct it into the telescope; the circulator is also used to receive the echo signal collected by the telescope. The second beam splitter is a two-to-two beam splitter; the second beam splitter receives the echo signal and the local oscillator light, and performs beam splitting processing on the two separately. Then, the two beams obtained from each beam are focused and superimposed before being output. A balanced detector is used to receive the two signals output by the second beam splitter and generate corresponding interference signals; The data processing module is used for: (1) performing analog-to-digital conversion on the interference signal; (2) dividing the signal of each pulse period into multiple signal segments according to the preset signal length; (3) performing FFT operation on each signal segment to obtain spectrum information; (4) superimposing the corresponding segments of all pulse periods to obtain the power spectrum; (5) calculating the signal-to-noise ratio of each signal segment according to the power spectrum, fitting the values ​​of each discrete signal-to-noise ratio and generating a signal-to-noise ratio curve.

8. The auxiliary tool for telescope focal length adjustment as described in claim 7, characterized in that: It also includes or is connected to a display module for visualizing the signal-to-noise ratio curve.

9. The auxiliary tool for telescope focal length adjustment as described in claim 7, characterized in that: The pulse amplifier is also used to amplify the power of the input signal so that the single-pulse energy of the output pulsed light is not less than 1 μJ.

10. The auxiliary tool for telescope focal length adjustment as described in claim 7, characterized in that: The first beam splitter includes one input port and two output ports, the second beam splitter includes two input ports and two output ports, the circulator includes three ports, and the laser, beam splitter, acousto-optic frequency shifter, pulse amplifier, circulator, telescope, beam splitter and balanced detector are connected by optical fiber coupling to form the required optical path.

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