System and method for enhancing spectrum demodulation rate of double optical frequency combs

Abstract

The invention provides a system and method for enhancing the spectrum demodulation rate of a dual-optical-frequency comb, and the system comprises a circulation light path which carries out the light splitting of excitation pulse light which is inputted to the circulation light path and corresponds to a first repetition frequency, thereby enabling one part of the excitation pulse light to be outputted towards a unit to be detected, and enabling the other part of the excitation pulse light to circulate along the circulation light path; the to-be-tested unit is used for modulating the excitation pulse light and outputting processing signal light carrying dynamic spectrum information generated based on an actual dynamic spectrum of the to-be-tested unit; the light combining unit is used for coupling the processing signal light and the sampling pulse light and outputting coupled signal light; the photoelectric detector performs light field cross-correlation-based detection on the coupled signal light and outputs a periodic electric signal; and the data acquisition and processing unit processes the periodic electric signal to obtain an actual dynamic spectrum corresponding to the unit to be detected. The detection efficiency is at least improved.

Description

Technical Field

[0001] This invention relates to the field of spectral detection technology, and in particular to a system and method for enhancing the spectral demodulation rate of dual optical frequency combs. Background Technology

[0002] In laboratory research and field applications such as chemical sensing, aerospace, and atmospheric monitoring, rapid and high-precision spectral measurements are crucial for materials analysis and mechanical measurements. With the continuous development of frequency comb technology, dual-comb spectroscopy has emerged as a revolutionary method in the field of optical spectroscopy. Dual-comb spectroscopy is similar to Fourier transform infrared spectroscopy (FTIR), but unlike traditional FTIR, it does not use any moving optical elements, enabling rapid and highly sensitive wide-range, high-resolution linear absorption spectral measurements. Furthermore, advancements in technologies such as miniature resonant optical frequency combs, single-cavity dual optical frequency combs, and electro-optic modulated optical frequency combs have made dual-comb spectroscopy systems more compact and easily deployed in field applications. Due to its unique advantages, dual-comb spectroscopy is not only suitable for basic scientific research but also widely used in various practical scenarios outside the laboratory.

[0003] In dual-comb spectroscopy, one frequency comb (signal comb) excites the spectral response of the sample under test, while the other frequency comb (reference comb) samples the signal comb in the time domain to obtain an interferogram. Because the repetition frequencies of these two frequency combs differ slightly, asynchronous sampling techniques can convert high-frequency optical signals that cannot be directly detected by electronic devices into processable radio frequency signals. In static measurements, dual-comb spectroscopy achieves high signal-to-noise ratio spectra by averaging single measurements in the time or spectral domains, revealing fine structures within the spectrum—one of its main advantages. However, many applications require real-time monitoring of dynamic spectral changes across different time scales, placing higher demands on dual-comb spectroscopy.

[0004] Therefore, there is an urgent need to provide a system and method for enhancing the spectral demodulation rate of dual optical frequency combs that can improve detection efficiency. Summary of the Invention

[0005] In view of the above problems, the present invention is proposed to provide a system and method for enhancing the spectral demodulation rate of dual optical frequency combs to overcome or at least partially solve the above problems.

[0006] According to one aspect of the present invention, an enhanced dual-frequency comb spectral demodulation rate system is provided, comprising:

[0007] The circular optical path is configured to split the excitation pulse light corresponding to the first repetition frequency input thereto, so that a portion of the excitation pulse light is output toward the unit under test and the other portion is circulated along the circular optical path.

[0008] The unit under test is configured to modulate the excitation pulse light input to it and output a processed signal light carrying dynamic spectral information based on the actual dynamic spectrum of the unit under test.

[0009] The beam combining unit is configured to couple the processing signal light input to it and the sampling pulse light corresponding to the second repetition frequency, and output the coupled signal light. The first spectrum of the corresponding laser pulse light and the second spectrum of the corresponding sampling pulse light have a spectral overlap range, and the spectral overlap range completely covers the spectral response range of the corresponding unit under test.

[0010] A photodetector is configured to detect coupled signal light input to it based on optical field cross-correlation and output a periodic electrical signal;

[0011] The data acquisition and processing unit is configured to process the periodic electrical signals input to it to obtain the actual dynamic spectrum of the corresponding unit under test.

[0012] Optionally, in the system according to the present invention, the sampling pulse light and the excitation pulse light are any one of ultraviolet pulse light, visible pulse light, infrared pulse light, X-ray pulse light, multi-wavelength tunable pulse light and terahertz pulse light.

[0013] Optionally, in the system according to the invention, the sampling pulse light and the excitation pulse light are directly output via at least one laser;

[0014] or,

[0015] The output is modulated via at least one laser, wherein the laser includes at least one of a solid-state laser, a fiber laser, a gas laser, a liquid laser, a microcavity laser, and a free-electron laser, and the modulation method includes at least one of intensity modulation, phase modulation, frequency modulation, and polarization modulation.

[0016] Optionally, in the system according to the invention, the light combining unit includes any one of an optical fiber coupler, a beam splitter prism, and a beam splitter.

[0017] Optionally, in the system according to the invention, the photodetector includes at least one of a PIN detector, an APD detector, a terahertz photoconductive antenna, a nonlinear optical crystal, and a superconducting detector.

[0018] According to another aspect of the present invention, a method for enhancing the spectral demodulation rate of dual optical frequency combs is provided, comprising the following steps:

[0019] The excitation pulse light corresponding to the first repetition frequency input to it is split based on the cyclic optical path, so that a part of the excitation pulse light is output towards the unit under test and the other part is cyclically circulated along the cyclic optical path.

[0020] Based on the unit under test, the excitation pulse light input to it is modulated, and the processed signal light carrying dynamic spectral information generated based on the actual dynamic spectrum of the unit under test is output.

[0021] The processing signal light input to the beam combining unit is coupled with the sampling pulse light corresponding to the second repetition frequency, and the coupled signal light is output. The first spectrum of the corresponding laser pulse light and the second spectrum of the corresponding sampling pulse light have a spectral overlap range, which completely covers the spectral response range of the corresponding unit under test.

[0022] The coupled signal light input to the photodetector is detected based on the cross-correlation of the optical field, and a periodic electrical signal is output.

[0023] The data acquisition and processing unit processes the periodic electrical signals input to it to obtain the actual dynamic spectrum of the corresponding unit under test.

[0024] Optionally, in the method according to the invention, the circulating optical path causes the excitation pulse light to make multiple round trips or folds back and forth, thereby increasing the number of excitation pulse light beams per unit time. The optical path length of the circulating optical path should be less than the cavity length of the laser corresponding to the emitted excitation pulse light, and the optical path length of the circulating optical path should be greater than the optical path length traversed by the duration of the excitation pulse light.

[0025] Optionally, in the method according to the present invention, the circulating optical path causes the excitation pulse light to make multiple round trips or folds back, and the number of round trips or folds back, N, is the ratio of the cavity length of the laser corresponding to the emitted excitation pulse light to the optical path length of the circulating optical path, taken downwards. The relationship between the number of signal pulses M and N increased per unit time is: M = N + 1.

[0026] Optionally, in the method according to the invention, modulating the excitation pulse light input to the unit under test based on the unit under test, and outputting a processed signal light carrying dynamic spectral information generated based on the actual dynamic spectrum of the unit under test, includes:

[0027] In response to the excitation pulse light input to the unit under test, the excitation pulse light is modulated by a linear optical process and / or a nonlinear optical process based on the unit under test, so as to determine the spectral change of the actual dynamic spectrum of the corresponding unit under test based on the excitation pulse light.

[0028] Dynamic spectral information is generated based on spectral changes, and processed signal light carrying dynamic spectral information is output.

[0029] Optionally, in the method according to the invention, the method further includes:

[0030] The overlapping range of the response spectrum does not completely cover the spectral response range of the corresponding unit under test. The spectrum of the sampled pulse light and / or the excitation pulse light is modulated based on power control, pulse waveform change, polarization control, beam splitting or nonlinear optical processes.

[0031] Optionally, in the method according to the present invention, processing the periodic electrical signal input to the data acquisition and processing unit to obtain the actual dynamic spectrum of the unit under test includes:

[0032] The data acquisition and processing unit performs denoising processing on the periodic electrical signal input to it to obtain a denoised signal. The denoising processing includes at least one of the following methods: wavelet transform, independent component analysis, empirical mode decomposition, principal component analysis, and phase matching.

[0033] The denoised signal is subjected to spectral acquisition processing to obtain the actual dynamic spectrum of the corresponding unit under test. The spectral acquisition processing includes at least one of the following: fast convolution, Fourier transform, inverse Fourier transform, short-time Fourier transform, wavelet transform, Hilbert transform, Hilbert-Huang transform, sine curve fitting, Ricker wavelet matching, S-transform, Cohen-type bilinear transform, adaptive filtering, and maximum likelihood estimation.

[0034] Optionally, in the method according to the invention, the excitation pulse light corresponding to the first repetition frequency input to it is split based on the cyclic optical path, such that a portion of the excitation pulse light is output toward the unit under test and another portion is cyclically circulated along the cyclic optical path, further comprising:

[0035] Obtain the detection cycle of the corresponding unit under test input from the management terminal, and determine the reference optical path length of the corresponding cyclic optical path based on the detection cycle;

[0036] A first fixed segment and a second fixed segment are determined to form a cyclic optical path, wherein the first end of the first fixed segment receives the excitation pulse light, the third end of the second fixed segment is connected to the second end of the first fixed segment, and the fourth end is connected to the first end;

[0037] In response to the optical path difference between the fixed lengths of the first fixed segment and the second fixed segment and the reference optical path length having a corresponding negative attribute, the mechanical end is controlled to disconnect the connection between the third end and the second end to form a customized accommodating area, and the beam splitting unit with a corresponding number of two splits is set to connect its included splitting input end to the second end.

[0038] Based on the optical path difference, a custom fiber segment is determined, and the robotic arm is controlled to connect the fifth end of the custom fiber segment to the first output end of the beam splitting unit and the sixth end to the third end, so as to place the custom fiber segment in the custom receiving area, wherein the second output end of the beam splitting unit faces the unit under test.

[0039] Optionally, in the method according to the invention, the method further includes:

[0040] In response to the optical path difference between the fixed lengths of the first fixed segment and the second fixed segment and the reference optical path length having corresponding positive values, the cyclic optical path is determined as the master optical path;

[0041] The control mechanism disconnects the connection between the third end and the second end to form a customized accommodating area, and sets the beam splitting unit with a corresponding number of three beam splitters to connect its beam splitting input end to the second end;

[0042] Based on the reference optical path length, a custom fiber segment is determined, and the robotic arm is controlled to connect the fifth end of the custom fiber segment to the first output end of the beam splitting unit and the sixth end to the third end, so as to place the custom fiber segment in the custom receiving area, wherein the second output end of the beam splitting unit faces the unit under test.

[0043] A third fixed segment and a fourth fixed segment of fixed length are determined to form a secondary optical path. The seventh end of the third fixed segment receives the excitation pulse light, and the ninth end of the fourth fixed segment is connected to the eighth end of the third fixed segment, and the tenth end is connected to the seventh end.

[0044] The control robot arm connects the eighth end to the beam splitting input end of the beam splitting unit and the ninth end to the third output end of the beam splitting unit.

[0045] According to the present invention, an optical fiber loop of physical length L is inserted into the signal path. Therefore, when the excitation pulse light passes through the optical fiber loop, a portion is emitted and coupled out to the detection system and photodetector. The remaining portion of the optical signal is circulated through the optical fiber loop, partially coupled out, and then reaches the detection system and optical fiber detector. The remaining portion continues to be coupled after passing through the optical fiber loop until the excitation pulse light attenuates to the point of being undetectable. By recirculating each incident pulse through the optical fiber loop and coupling out a portion at the loop's round-trip delay interval, the number of measurements to be performed on the detection system can be increased, thus increasing the operating frequency of the measurement system. By performing time-frequency transformation on the time-domain interferogram in the periodic signal, an undersampled dynamic spectrum of the same actual dynamic spectrum of the system under test is obtained. Further analysis and processing of the undersampled dynamic spectrum ultimately achieves the measurement of the actual dynamic spectrum of the system under test. Furthermore, this invention is applicable to existing dual-comb spectroscopy techniques, including, but not limited to, those based on micro-resonant dual-frequency combs, single-cavity dual-frequency combs, and electro-optic modulation dual-frequency combs. Attached Figure Description

[0046] Figure 1 A structural block diagram of an enhanced dual-frequency comb spectral demodulation rate system according to an embodiment of the present invention is shown;

[0047] Figure 2 A flowchart of a method for enhancing the spectral demodulation rate of dual optical frequency combs according to another embodiment of the present invention is shown;

[0048] Figure 3 A schematic diagram of the fiber optic ring-assisted dual-comb dynamic spectroscopy in this embodiment is shown.

[0049] Figure 4 A schematic diagram of a test system using a dual-wavelength passively mode-locked erbium fiber laser as a single-cavity dual-comb source is shown in this embodiment.

[0050] Figure 5 A typical interference pattern in the conventional dual-comb structure of this embodiment is shown;

[0051] Figure 6 The interference diagram of the dual optical comb interference after introducing the cyclic optical path in this embodiment is shown. Detailed Implementation

[0052] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0053] To address the problems existing in the prior art, the inventors proposed the solution of this invention. One embodiment of this invention provides a system for enhancing the spectral demodulation rate of a dual-frequency comb, wherein... Figure 1 The structural block diagram of the corresponding system is shown, such as Figure 1 As shown, the system includes: a circulating optical path, a unit under test, a light combining unit, a photodetector, and a data acquisition and processing unit.

[0054] For example, specifically in this embodiment, the circular optical path can be configured to split the excitation pulse light input to it at the corresponding first repetition frequency, so that a portion of the excitation pulse light is output toward the unit under test (DUT) and the other portion is circulated along the circular optical path; the DUT can be configured to modulate the excitation pulse light input to it and output a processing signal light carrying dynamic spectral information based on the actual dynamic spectrum of the DUT; the combining unit can be configured to couple the processing signal light input to it and the sampling pulse light at the corresponding second repetition frequency, and output a coupled signal light, wherein the first spectrum of the corresponding laser pulse light and the second spectrum of the corresponding sampling pulse light have a spectral overlap range, and the spectral overlap range completely covers the spectral response range of the corresponding DUT; the photodetector can be configured to detect the coupled signal light input to it based on optical field cross-correlation and output a periodic electrical signal; and the data acquisition and processing unit can be configured to process the periodic electrical signal input to it to obtain the actual dynamic spectrum of the corresponding DUT.

[0055] Furthermore, it can be noted that the sampling pulse light and the excitation pulse light in this embodiment can be any one of ultraviolet pulse light, visible pulse light, infrared pulse light, X-ray pulse light, multi-wavelength tunable pulse light, and terahertz pulse light.

[0056] Furthermore, the sampling pulse light and the excitation pulse light are directly output via at least one laser; or, they are modulated and output via at least one laser, wherein the laser includes at least one of a solid-state laser, a fiber laser, a gas laser, a liquid laser, a microcavity laser, and a free-electron laser, and the modulation method includes at least one of intensity modulation, phase modulation, frequency modulation, and polarization modulation.

[0057] That is, the sampling pulse light and the excitation pulse light can be generated directly by one or more lasers or modulated to generate two pulse lights with different repetition frequencies, or they can be composed of any two pulse lights with different repetition frequencies generated directly by one or more lasers or modulated to generate any two pulse lights with different repetition frequencies. The laser that generates two pulse lights with different repetition frequencies can be one or more of the following: solid-state laser, fiber laser, gas laser, liquid laser, microcavity laser, and free-electron laser. The modulation method that generates three pulse lights with different repetition frequencies can be one or more of the following: intensity modulation, phase modulation, frequency modulation, and polarization modulation.

[0058] Here, since there is a spectral overlap between the first spectrum of the corresponding sampling pulse light and the second spectrum of the corresponding excitation pulse light, and the spectral overlap completely covers the spectral response range of the corresponding unit under test, the shortest wavelength of the overlapping spectral region of the excitation pulse light and the sampling pulse light is smaller than the shortest wavelength of the spectral response characteristics of the unit under test, and the longest wavelength is larger than the longest wavelength of the spectral response characteristics of the unit system.

[0059] Furthermore, in this embodiment, the cyclic optical path mentioned in the system described in this embodiment can provide a corresponding cyclic path for pulsed light, which may specifically include a circulator or an optical fiber coupler, etc.

[0060] Furthermore, it can be noted that the light combining unit in this embodiment mainly couples the sampling pulse light and the signal light together. Therefore, the light combining device includes, but is not limited to, any one of the following: fiber optic coupler, beam splitter prism, and beam splitter.

[0061] Furthermore, in this embodiment, the photodetector can convert the coupled signal light into a periodic electrical signal. Therefore, the photodetector includes at least one of a PIN detector, an APD detector, a terahertz photoconductive antenna, a nonlinear optical crystal, and a superconducting detector.

[0062] Furthermore, in this embodiment, the data acquisition unit can acquire periodic electrical signals, process the periodic signals to obtain frequencies directly related to the frequency change of the spectral center frequency of the system under test, and use the frequencies of the sampling pulse light and the excitation pulse light to measure the frequency change of the spectral spectrum of the system under test; it can be a terminal with data processing functions, such as a computer.

[0063] It can be explained that, based on the aforementioned system, this embodiment inserts a cyclic optical path of physical length L into the signal path. When the excitation pulse light passes through the cyclic optical path, part of it is emitted and coupled out to the unit under test and the beam combining unit. The remaining part of the optical signal is circulated through the cyclic optical path and then coupled out to the unit under test and the beam combining unit. The remaining part continues to be coupled after passing through the cyclic optical path until the excitation pulse light decays to the point that it cannot be detected. That is, each incident pulse can be recirculated through the cyclic optical path, and part of it can be coupled out at the interval of the loop round-trip delay, which can improve the measurement efficiency of the unit under test. Furthermore, by performing time-frequency transformation on the time-domain interferogram in the periodic electrical signal, the undersampled dynamic spectrum of the same actual dynamic spectrum of the unit under test is obtained. The undersampled dynamic spectrum is further analyzed and processed accordingly to finally realize the measurement of the actual dynamic spectrum of the system under test.

[0064] Figure 2 A flowchart illustrating a method for enhancing the spectral demodulation rate of a dual-frequency comb, as proposed in another embodiment of this invention, is shown below. Figure 2 As shown, the method begins with step S1, which may include the following:

[0065] The excitation pulse light corresponding to the first repetition frequency input to the cyclic optical path is split so that a part of the excitation pulse light is output toward the unit under test and the other part is cyclically circulated along the cyclic optical path.

[0066] For example, in this embodiment, a portion of the excitation pulse light can reach the unit under test after passing through the circulating optical path, and a portion of the remaining light will then circulate to reach the unit under test. The remaining light will continue to circulate to reach the system under test. This process is repeated to form a signal light containing the actual dynamic spectral information of the system under test.

[0067] In one implementation, the cyclic optical path causes the excitation pulse to make multiple round trips or backtracks to increase the number of excitation pulses per unit time. The optical path length of the cyclic optical path should be less than the cavity length of the laser corresponding to the emitted excitation pulse, and the optical path length of the cyclic optical path should be greater than the optical path length traversed by the duration of the excitation pulse.

[0068] Alternatively, in another implementation, the circulating optical path causes the excitation pulse light to make multiple round trips or folds back. The number of round trips or folds back, N, is the ratio of the cavity length of the laser that emits the excitation pulse light to the optical path length of the circulating optical path, taken downwards. The relationship between the number of signal pulses M and N increased per unit time is: M = N + 1.

[0069] Additionally, it should be noted that since the detection cycle can be set by the user based on their needs when detecting the unit under test, in order to ensure that the excitation pulse light reaching the unit under test corresponds to the detection cycle during the circulation of the optical path, the optical path length of the circulation optical path needs to be adjusted before detection to improve the detection efficiency. The adjustment method may include the following steps:

[0070] Obtain the detection cycle of the corresponding unit under test input from the management terminal, and determine the reference optical path length of the corresponding cyclic optical path based on the detection cycle;

[0071] A first fixed segment and a second fixed segment are determined to form a cyclic optical path, wherein the first end of the first fixed segment receives the excitation pulse light, the third end of the second fixed segment is connected to the second end of the first fixed segment, and the fourth end is connected to the first end;

[0072] In response to the optical path difference between the fixed lengths of the first fixed segment and the second fixed segment and the reference optical path length having a corresponding negative attribute, the mechanical end is controlled to disconnect the connection between the third end and the second end to form a customized accommodating area, and the beam splitting unit with a corresponding number of two splits is set to connect its included splitting input end to the second end.

[0073] Based on the optical path difference, a custom fiber segment is determined, and the robotic arm is controlled to connect the fifth end of the custom fiber segment to the first output end of the beam splitting unit and the sixth end to the third end, so as to place the custom fiber segment in the custom receiving area, wherein the second output end of the beam splitting unit faces the unit under test.

[0074] For example, in this embodiment, the adjustment of the circulating optical path may specifically include the following method steps:

[0075] First, the management terminal can be understood as a control terminal used to input detection parameters. The detection cycle can be understood as the time required for a complete dynamic spectral detection of the unit under test (e.g., 10ms). It can be noted that this parameter can be input by the user based on the dynamic response characteristics of the unit under test (e.g., rapidly changing gas spectra, slowly changing liquid spectra). The reference optical path length is the standard optical path length that ensures the cycle frequency of the excitation pulse light matches the detection cycle (e.g., a detection cycle of 10ms corresponds to a reference optical path length of 3cm, that is, the time for the pulse light to cycle once along the optical path is equal to the detection cycle). It can be noted that the reference optical path length can be determined by the core logic calculation of "optical path length = speed of light × detection cycle" (the loss correction of light in the medium needs to be deducted). In this embodiment, the reference optical path length is directly derived from the detection cycle, which can provide a clear target value for subsequent optical path adjustment, avoid blind adjustment without basis, solve the problem of no standard for matching optical path length and detection cycle, and lay the foundation for rapid adjustment.

[0076] Next, it can be explained that in this embodiment, the circulating optical path is composed of two fixed-length optical paths, a first fixed segment and a second fixed segment. The first end of the first fixed segment is the entrance for the circulating optical path to receive external excitation pulse light. The second end of the first fixed segment is connected to the third end of the second fixed segment, and the fourth end of the second fixed segment is connected to the first end of the first fixed segment, thereby forming a complete closed loop (for example, the length of the first fixed segment is 1cm, the length of the second fixed segment is 1cm, and the initial total length of the circulating optical path is 2cm). Here, by clearly defining the composition and connection relationship of the two fixed segments of the circulating optical path, subsequent adjustments can be made only to the connection relationship of the fixed segments without disassembling the entire optical path, simplifying the adjustment process and solving the problem of complex adjustments caused by unclear optical path structure.

[0077] Finally, it should be noted that the negative optical path difference value in this embodiment refers to the total fixed length of the first fixed segment and the second fixed segment (e.g., 2cm) being less than the reference optical path length (e.g., 3cm), with a difference of -1cm (a negative value indicates insufficient optical path length). The mechanical end is an actuator used to automatically perform optical path connection / disconnection. By controlling it to disconnect the connection between the third end of the second fixed segment and the second end of the first fixed segment, a customized accommodating area for installing additional components (e.g., a gap for a customized optical fiber segment with a length adapted to the two fixed segments) can be formed between the two fixed segments. Here, the connection is automatically disconnected by the mechanical end, eliminating the need for manual operation, improving adjustment efficiency, and solving the problem of time-consuming manual disassembly of the optical path. Furthermore, the two-splitter unit is an optical splitter device with one splitter input and two outputs. Connecting its splitter input to the second end of the first fixed segment can... The system achieves the function of splitting the excitation pulse light (part of which is output to the unit under test, and the other part is used for looping). Here, a splitting unit with two splitters is selected, which can accurately match the requirements of splitting output and loop lengthening, eliminating the need for extra splitters, simplifying the optical path structure, and solving the problem of no basis for selecting the splitting unit. Furthermore, the customized fiber segment is a supplementary optical path whose length is determined according to the optical path difference (for example, a difference of -1cm means a customized fiber length of 1cm). Its length exactly makes up for the difference between the total length of the fixed segment and the length of the reference optical path. In this embodiment, by controlling the robotic arm, the fifth end of the customized fiber segment can be connected to the first output end of the splitting unit, and the sixth end can be connected to the third end of the second fixed segment. At the same time, the customized fiber segment is placed in the customized accommodating area (to avoid occupying extra space). The second output end of the splitting unit faces the unit under test and is used to output a part of the excitation pulse light to the unit under test.

[0078] It can be explained that the above technical solution enables automated installation of customized fiber optic segments using a robotic arm, ensuring accurate and rapid connection and avoiding errors and time consumption associated with manual connection. Simultaneously, the precise matching of the length difference of the customized fiber optic segments ensures complete consistency between the total length of the cyclic optical path (first fixed segment + splitting unit + customized fiber optic segment + second fixed segment) and the reference optical path length. This solves the problems of inaccurate lengthening and complex operation when the optical path length is insufficient. Furthermore, it achieves rapid and accurate matching between the cyclic optical path length and the detection cycle. The automated operation of the mechanical end and robotic arm avoids the time and errors associated with manual intervention. Standardized adjustment steps eliminate the need for repeated debugging, ensuring the optical path length is adjusted correctly the first time. The precisely matched optical path length also ensures that the cyclic frequency of the excitation pulse light matches the detection cycle, improving the spectral demodulation rate.

[0079] Furthermore, when the total length of the fixed segment of the cyclic optical path is greater than the length of the reference optical path (i.e., there is a positive attribute optical path difference), simply adjusting by cutting the optical path or leaving a portion of the optical path idle will lead to a waste of optical path resources and insufficient detection flexibility. Therefore, in order to solve this technical problem, this embodiment may further include the following steps:

[0080] In response to the optical path difference between the fixed lengths of the first fixed segment and the second fixed segment and the reference optical path length having corresponding positive values, the cyclic optical path is determined as the master optical path;

[0081] The control mechanism disconnects the connection between the third end and the second end to form a customized accommodating area, and sets the beam splitting unit with a corresponding number of three beam splitters to connect its beam splitting input end to the second end;

[0082] Based on the reference optical path length, a custom fiber segment is determined, and the robotic arm is controlled to connect the fifth end of the custom fiber segment to the first output end of the beam splitting unit and the sixth end to the third end, so as to place the custom fiber segment in the custom receiving area, wherein the second output end of the beam splitting unit faces the unit under test.

[0083] A third fixed segment and a fourth fixed segment of fixed length are determined to form a secondary optical path. The seventh end of the third fixed segment receives the excitation pulse light, and the ninth end of the fourth fixed segment is connected to the eighth end of the third fixed segment, and the tenth end is connected to the seventh end.

[0084] The control robot arm connects the eighth end to the beam splitting input end of the beam splitting unit and the ninth end to the third output end of the beam splitting unit.

[0085] For example, in this embodiment, when the total length of the fixed segment of the cyclic optical path is greater than the length of the reference optical path, the cyclic optical path can be modulated based on the following method steps:

[0086] First, in this embodiment, the positive optical path difference refers to the total fixed length of the first fixed segment and the second fixed segment (e.g., 4cm) being greater than the reference optical path length (e.g., 3cm), with a difference of +1cm (a positive value represents optical path length redundancy). The main optical path refers to the original loop optical path that still serves as the core loop path after adjustment, ensuring that the main loop function of the excitation pulse light is not affected. Here, by clearly defining the positive difference and the main optical path positioning, the failure of the main function caused by blind adjustment can be avoided, and at the same time, it provides a direction for subsequent utilization of redundant length, solving the problem of unclear adjustment target when optical path length is redundant.

[0087] Secondly, based on the foregoing, the third end is the end of the second fixed segment, and the second end is the end of the first fixed segment. After disconnecting the two using a robotic arm, a customized accommodating area for installing additional components can be formed between the two fixed segments (e.g., a gap to accommodate the beam splitter and the fiber optic customized segment). Furthermore, the beam splitter with three splitting paths is an optical splitter device with one beam splitting input and three outputs. By connecting the beam splitting input to the second end of the first fixed segment, the input excitation pulse light can be split into three beams, which are used for the main optical path circulation, the detection of the unit under test, and the secondary optical path expansion, respectively. This can meet the need to improve functionality by utilizing redundant length, avoid functional limitations caused by improper beam splitter selection, and solve the problem of poor beam splitter adaptability.

[0088] Next, a custom fiber segment can be determined based on the reference optical path length, and the robotic arm can be controlled to connect the fifth end of the custom fiber segment to the first output end of the beam splitting unit and the sixth end to the third end, so that the custom fiber segment is located in the custom accommodating area. The second output end of the beam splitting unit faces the unit under test. Here, the length of the custom fiber segment is determined by the reference optical path length and the required length of the main optical path (for example, the total fixed length is 4cm, the reference optical path length is 3cm, and a 1cm custom fiber segment needs to be customized to make up for the length difference after the adjustment of the main optical path). Furthermore, the robotic arm can automatically connect the fifth end of the custom fiber segment to the first output end of the beam splitting unit and the sixth end to the third end of the second fixed segment, so that the main optical path (first fixed segment, beam splitting unit, custom fiber segment, second fixed segment, first fixed segment) is closed. At the same time, the second output end of the beam splitting unit faces the unit under test and is used to output part of the excitation pulse light to the unit under test. The precise installation of the robotic arm ensures minimal optical path connection error, and the customized fiber segment length accurately matches the reference requirements, solving the problem of inaccurate length after adjustment of the main optical path. At the same time, the second output end of the beam splitter unit directly faces the unit under test, eliminating the need for additional optical path adapters and improving the detection response speed.

[0089] In this embodiment, the aforementioned secondary optical path is an additional cyclic optical path constructed using the redundant length of the primary optical path. It consists of two fixed-length optical paths, a third fixed segment and a fourth fixed segment. Initially, it is a closed loop (the seventh end of the third fixed segment receives the excitation pulse light, the eighth end connects to the ninth end of the fourth fixed segment, and the tenth end of the fourth fixed segment connects to the seventh end). It can serve as an additional pulse light cyclic path, improving the system's detection capability for multiple test units or increasing the pulse light repetition frequency. By using a robotic arm to connect the eighth end of the third fixed segment to the beam splitting input of the beam splitting unit and the ninth end of the fourth fixed segment to the third output of the beam splitting unit, the secondary optical path and the primary optical path can be connected through the beam splitting unit. The process involves the excitation pulse light entering the secondary optical path via the third output of the beam splitter, then returning to the beam splitter via the third fixed segment, forming a dual-loop path with primary and secondary components working together. This automated connection requires no manual adjustment, ensuring efficient and precise operation. The dual-loop path also improves the utilization rate of the excitation pulse light, adapting to simultaneous detection of multiple test units or increasing the detection sampling frequency of a single test unit, significantly improving detection efficiency. This solves the problem of wasted optical path redundancy resources and achieves efficient utilization and precise adaptation when optical path length is redundant: it ensures the primary optical path length matches the baseline requirements through customized fiber segments, and enhances the system's detection capability through secondary optical path expansion. Furthermore, the fully automated operation avoids the time and errors associated with manual intervention.

[0090] Step S2 includes the following:

[0091] The excitation pulse light input to the unit under test is modulated based on the unit under test, and the processed signal light carrying dynamic spectral information generated based on the actual dynamic spectrum of the unit under test is output.

[0092] For example, in this embodiment, when a portion of the light circulated through the loop optical path reaches the unit under test, it can be modulated by the unit under test to output a processing signal light carrying dynamic spectral information based on the actual dynamic spectrum of the unit under test, for subsequent signal processing.

[0093] Furthermore, in this embodiment, the aforementioned "modulation of the excitation pulse light input to the unit under test based on the unit under test, and output of the processed signal light carrying dynamic spectral information generated based on the actual dynamic spectrum of the unit under test" may further include the following steps:

[0094] In response to the excitation pulse light input to the unit under test, the excitation pulse light is modulated by a linear optical process and / or a nonlinear optical process based on the unit under test, so as to determine the spectral change of the actual dynamic spectrum of the corresponding unit under test based on the excitation pulse light.

[0095] Dynamic spectral information is generated based on spectral changes, and processed signal light carrying dynamic spectral information is output.

[0096] For example, in this embodiment, in the incident circular optical path of the excitation pulse light, part of it reaches the unit under test, and the rest of the light is circulated and then reaches the unit under test. This cycle is repeated to form a signal light containing the dynamic spectral information of the unit under test. The spectral changes generated in the signal light can be modulated by nonlinear optical processes (e.g., reflection, transmission, scattering) and nonlinear optical processes, or by a combination of different modulation methods. Furthermore, the dynamic spectral information of the unit under test is a periodic single-frequency signal or a frequency-converted signal.

[0097] In addition, it can be noted that the unit under test can be composed of a series of independent units under test that are not completely distributed in spatial position and that transmit, reflect, scatter, or a combination of all three to the pulse excitation pulse light.

[0098] Step S3 includes the following:

[0099] The processing signal light input to the beam combining unit is coupled with the sampling pulse light corresponding to the second repetition frequency, and the coupled signal light is output. The first spectrum of the corresponding laser pulse light and the second spectrum of the corresponding sampling pulse light have a spectral overlap range, which completely covers the spectral response range of the corresponding unit under test.

[0100] For example, in this embodiment, it can be explained that, based on the above, the optical combining unit couples the sampling pulse light and the signal light together, and the corresponding optical combining device includes, but is not limited to, an optical fiber coupler, a beam splitter prism, and a beam splitter. Furthermore, it is necessary to ensure that the first spectrum of the corresponding sampling pulse light and the second spectrum of the corresponding excitation pulse light have a spectral overlap range, and that the spectral overlap range completely covers the spectral response range of the corresponding unit under test. To meet this condition, this embodiment may further include the following steps:

[0101] The overlapping range of the response spectrum does not completely cover the spectral response range of the corresponding unit under test. The spectrum of the sampled pulse light and / or the excitation pulse light is modulated based on power control, pulse waveform change, polarization control, beam splitting or nonlinear optical processes.

[0102] For example, in this embodiment, when the spectral overlap range does not completely cover the spectral response range of the corresponding unit under test, the spectrum of the sampling pulse light and / or the excitation pulse light can be modulated based on the corresponding modulation process to meet the corresponding optical conditions.

[0103] Step S4 includes the following:

[0104] The photodetector detects the coupled signal light input to it based on optical field cross-correlation and outputs a periodic electrical signal.

[0105] For example, in this embodiment, after receiving the corresponding coupled signal light, the photodetector can further perform detection based on optical field cross-correlation and output a periodic electrical signal.

[0106] Step S5 includes the following:

[0107] The data acquisition and processing unit processes the periodic electrical signals input to it to obtain the actual dynamic spectrum of the corresponding unit under test.

[0108] For example, in this embodiment, the data acquisition and processing unit's acquisition and processing of periodic electrical signals includes denoising processing of the periodic electrical signals and spectral acquisition processing. That is, after denoising processing, the accuracy of acquiring periodic electrical signals can be improved, while spectral acquisition processing can acquire the actual dynamic spectrum of the corresponding unit under test.

[0109] Furthermore, in this embodiment, the aforementioned "processing the periodic electrical signal input to the data acquisition and processing unit to obtain the actual dynamic spectrum of the corresponding unit under test" may further include the following steps:

[0110] The data acquisition and processing unit performs denoising processing on the periodic electrical signal input to it to obtain a denoised signal. The denoising processing includes at least one of the following methods: wavelet transform, independent component analysis, empirical mode decomposition, principal component analysis, and phase matching.

[0111] The denoised signal is subjected to spectral acquisition processing to obtain the actual dynamic spectrum of the corresponding unit under test. The spectral acquisition processing includes at least one of the following: fast convolution, Fourier transform, inverse Fourier transform, short-time Fourier transform, wavelet transform, Hilbert transform, Hilbert-Huang transform, sine curve fitting, Ricker wavelet matching, S-transform, Cohen-type bilinear transform, adaptive filtering, and maximum likelihood estimation.

[0112] For example, in this embodiment, the denoising method includes, but is not limited to, signal denoising based on wavelet transform, signal denoising based on independent component analysis, signal denoising based on empirical mode decomposition, signal denoising based on principal component analysis, and signal denoising based on phase matching. The spectral response of the unit under test can be obtained using corresponding algorithms, including but not limited to one or more of the following: fast convolution, Fourier transform, inverse Fourier transform, short-time Fourier transform, wavelet transform, Hilbert transform, Hilbert-Huang transform, sine curve fitting, Ricker wavelet matching, S-transform, Cohen-type bilinear transform, and adaptive filtering. For broadband signal measurements, the algorithm also includes algorithms such as maximum likelihood estimation.

[0113] The following section provides a further description of the solution involved in this embodiment, taking into account practical application scenarios:

[0114] First, it can be noted that the first and second repetition frequencies of the laser pulse and the sampling pulse are f1 and f2, respectively, and the frequency difference between them is Δf = f1 - f2. The interference pattern between the two pulses repeats once every 1 / Δf seconds, which limits the effective sampling rate of dynamic spectral measurement. However, by introducing a cyclic optical path of physical length L into the signal path, such as... Figure 3 As shown, this cyclic optical route consists of fiber optic couplers, which recycle each incident pulse and couple a portion of it out at intervals equal to the loop round-trip delay. These intervals can be expressed as:

[0115] ;

[0116] Where, n g is the effective refractive index, and c is the speed of light.

[0117] Furthermore, the pulse signal output consists of a series of delayed copies of the original merging sequence, which can be represented as:

[0118]

[0119] Here, ck represents the complex amplitude of the k-th replica, which is determined by the coupling ratio, loop loss, and round-trip phase. Since the loss during each round trip attenuates the cyclic signal, this sequence forms a geometrically attenuated echo train. When the replicated laser pulse interferes with other pulses, the original interferogram is also replicated into multiple sub-interferograms, each time shifted. Assuming these sub-interferograms do not overlap and are resolvable, they can be resolved in a single refresh cycle. Multiple independent interferograms are obtained. The number of valid copies is determined by the following factors:

[0120]

[0121] Where Trep = 1 / f² is the repetition period of the laser pulse. Therefore, the effective demodulation rate is increased to:

[0122]

[0123] The repetition frequency difference can be increased without changing the comb source, thereby improving the sampling frequency of the system.

[0124] For example, when a laser generates two pulse trains with center wavelengths of 1543nm and 1570nm respectively, the average output power of OC1 is 0.87mW and 0.34mW respectively. Due to intracavity dispersion, the repetition frequencies of the two pulse trains are slightly different, resulting in a repetition frequency shift of Δfrep≈2059Hz.

[0125] Next, after passing through a coarse wavelength division multiplexer (CWDM), the 1570nm pulse is used as the laser pulse. This pulse is amplified to 43.1mW by fiber amplifier 1, undergoes nonlinear spectral broadening, and is injected into a passive fiber loop consisting of two 95:5 couplers (OC2 and OC3) with a loop length of 34.2cm. In each round trip, 5% of the energy is coupled out, producing a time-delayed replica with an average extracted power of 0.83mW. The delayed sequence interacts with a fiber Bragg grating (FBG) via the fiber loop. The FBG is mounted on a piezoelectric transducer driven by a signal generator, with a center wavelength of 1552.28nm and a corresponding reflected power of approximately 1.8μW. In the reference path, the 1543nm pulse is amplified to 65.6mW by fiber amplifier 2 and undergoes spectral broadening. A tunable optical filter selects the overlapping spectral region near 1552nm, resulting in a filtered output of 0.75mW.

[0126] Finally, the reflected signal and the reference comb are recombined at OC4 and detected by a balanced photodetector (200MHz bandwidth). The interferogram is recorded by a data acquisition card. The spectrum of a traditional dual-comb interferogram is shown below. Figure 5 As shown, the period of 500 μs is basically consistent with 1 / Δf. The introduction of the fiber loop resulted in multiple sub-interference patterns within the same refresh period, such as... Figure 6 As shown, these sub-interferograms are arranged according to the round-trip time of the fiber loop. With sequential delays of approximately 57 μs and maintaining good separation, it was confirmed that the fiber loop effectively replicated the interferogram and achieved multiple independent acquisitions within one cycle, thus improving the system sampling rate.

[0127] In the specification provided herein, the algorithms and displays are not inherently related to any particular computer, virtual system, or other device. Various general-purpose systems can also be used with the examples of this invention. The required structure for constructing such systems is apparent from the above description. Furthermore, this invention is not directed to any particular programming language. It should be understood that the contents of the invention described herein can be implemented using various programming languages, and the above description of specific languages ​​is for the purpose of disclosing preferred embodiments of the invention.

[0128] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0129] Similarly, it should be understood that, in order to streamline this disclosure and aid in understanding one or more of the various aspects of the invention, in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof.

[0130] Those skilled in the art will understand that modules, units, or components of the devices disclosed in the examples herein can be arranged in the devices described in this embodiment, or alternatively, can be located in one or more devices different from the devices in this example. The modules in the foregoing examples can be combined into a single module or, in addition, can be divided into multiple sub-modules.

[0131] Those skilled in the art will understand that the modules in the device of the embodiment can be adaptively changed and placed in one or more devices different from that embodiment. Modules, units, or components in the embodiment can be combined into a single module, unit, or component, and further, they can be divided into multiple sub-modules, sub-units, or sub-components.

[0132] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of the invention and form different embodiments.

[0133] Furthermore, some of the embodiments described herein are methods or combinations of method elements that can be implemented by a processor of a computer system or by other means of performing the functions. Therefore, a processor having the necessary instructions for implementing the methods or method elements forms means for implementing the methods or method elements. Furthermore, the elements described herein in the apparatus embodiments are examples of means for implementing the functions performed by elements for the purposes of carrying out the invention.

[0134] As used herein, unless otherwise specified, the use of ordinal numbers such as “first,” “second,” “third,” etc., to describe ordinary objects merely indicates different instances of similar objects and is not intended to imply that the objects being described must have a given order in time, space, ordering, or any other manner.

[0135] Although the invention has been described with respect to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and edibility purposes, and not for the purpose of explaining or limiting the subject matter of the invention.

Claims

1. A system for enhancing the spectral demodulation rate of dual optical frequency combs, characterized in that, include: The circular optical path is configured to split the excitation pulse light corresponding to the first repetition frequency input thereto, so that a portion of the excitation pulse light is output toward the unit under test and the other portion is circulated along the circular optical path. The unit under test is configured to modulate the excitation pulse light input to it and output a processed signal light carrying dynamic spectral information based on the actual dynamic spectrum of the unit under test. The beam combining unit is configured to couple the processing signal light input to it and the sampling pulse light corresponding to the second repetition frequency, and output the coupled signal light. The first spectrum of the corresponding laser pulse light and the second spectrum of the corresponding sampling pulse light have a spectral overlap range, and the spectral overlap range completely covers the spectral response range of the corresponding unit under test. A photodetector is configured to detect coupled signal light input to it based on optical field cross-correlation and output a periodic electrical signal; The data acquisition and processing unit is configured to process the periodic electrical signals input to it to obtain the actual dynamic spectrum of the corresponding unit under test.

2. The system according to claim 1, characterized in that, The light combining unit includes any one of an optical fiber coupler, a beam splitter prism, and a beam splitter.

3. The system according to claim 1, characterized in that, The photodetector includes at least one of a PIN detector, an APD detector, a terahertz photoconductive antenna, a nonlinear optical crystal, and a superconducting detector.

4. A method for enhancing the spectral demodulation rate of dual optical frequency combs, characterized in that, Includes the following steps: The excitation pulse light corresponding to the first repetition frequency input to it is split based on the cyclic optical path, so that a part of the excitation pulse light is output towards the unit under test and the other part is cyclically circulated along the cyclic optical path. Based on the unit under test, the excitation pulse light input to it is modulated, and the processed signal light carrying dynamic spectral information generated based on the actual dynamic spectrum of the unit under test is output. The processing signal light input to the beam combining unit is coupled with the sampling pulse light corresponding to the second repetition frequency, and the coupled signal light is output. The first spectrum of the corresponding laser pulse light and the second spectrum of the corresponding sampling pulse light have a spectral overlap range, which completely covers the spectral response range of the corresponding unit under test. The coupled signal light input to the photodetector is detected based on the cross-correlation of the optical field, and a periodic electrical signal is output. The data acquisition and processing unit processes the periodic electrical signals input to it to obtain the actual dynamic spectrum of the corresponding unit under test.

5. The demodulation method according to claim 4, characterized in that, The cyclic optical path causes the excitation pulse to travel back and forth multiple times, thereby increasing the number of excitation pulses per unit time. The optical path length of the cyclic optical path should be less than the cavity length of the laser corresponding to the emitted excitation pulse, and the optical path length of the cyclic optical path should be greater than the optical path length traversed by the duration of the excitation pulse.

6. The demodulation method according to claim 4, characterized in that, The circulating optical path causes the excitation pulse light to make multiple round trips or folds back. The number of round trips or folds back, N, is the ratio of the cavity length of the laser that emits the excitation pulse light to the optical path length of the circulating optical path, taken downwards. The relationship between the number of signal pulses M and N that are boosted per unit time is: M = N + 1.

7. The method according to claim 6, characterized in that, Based on the modulation of the excitation pulse light input to the unit under test, the processed signal light carrying dynamic spectral information generated based on the actual dynamic spectrum of the unit under test is output, including: In response to the excitation pulse light input to the unit under test, the excitation pulse light is modulated by a linear optical process and / or a nonlinear optical process based on the unit under test, so as to determine the spectral change of the actual dynamic spectrum of the corresponding unit under test based on the excitation pulse light. Dynamic spectral information is generated based on spectral changes, and processed signal light carrying dynamic spectral information is output.

8. The method according to claim 6, characterized in that, The data acquisition and processing unit processes the periodic electrical signal input to it to obtain the actual dynamic spectrum of the unit under test, including: The data acquisition and processing unit performs denoising processing on the periodic electrical signal input to it to obtain a denoised signal. The denoising processing includes at least one of the following methods: wavelet transform, independent component analysis, empirical mode decomposition, principal component analysis, and phase matching. The denoised signal is subjected to spectral acquisition processing to obtain the actual dynamic spectrum of the corresponding unit under test. The spectral acquisition processing includes at least one of the following: fast convolution, Fourier transform, inverse Fourier transform, short-time Fourier transform, wavelet transform, Hilbert transform, Hilbert-Huang transform, sine curve fitting, Ricker wavelet matching, S-transform, Cohen-type bilinear transform, adaptive filtering, and maximum likelihood estimation.

9. The method according to claim 6, characterized in that, The excitation pulse light corresponding to the first repetition frequency input to the circuit is split based on the cyclic optical path, so that a portion of the excitation pulse light is output towards the unit under test and the other portion circulates along the cyclic optical path. This also includes: Obtain the detection cycle of the corresponding unit under test input from the management terminal, and determine the reference optical path length of the corresponding cyclic optical path based on the detection cycle; A first fixed segment and a second fixed segment are determined to form a cyclic optical path, wherein the first end of the first fixed segment receives the excitation pulse light, the third end of the second fixed segment is connected to the second end of the first fixed segment, and the fourth end is connected to the first end; In response to the optical path difference between the fixed lengths of the first fixed segment and the second fixed segment and the reference optical path length having a corresponding negative attribute, the mechanical end is controlled to disconnect the connection between the third end and the second end to form a customized accommodating area, and the beam splitting unit with a corresponding number of two splits is set to connect its included splitting input end to the second end. Based on the optical path difference, a custom fiber segment is determined, and the robotic arm is controlled to connect the fifth end of the custom fiber segment to the first output end of the beam splitting unit and the sixth end to the third end, so as to place the custom fiber segment in the custom receiving area, wherein the second output end of the beam splitting unit faces the unit under test.

10. The method according to claim 9, characterized in that, The method further includes: In response to the optical path difference between the fixed lengths of the first fixed segment and the second fixed segment and the reference optical path length having corresponding positive values, the cyclic optical path is determined as the master optical path; The control mechanism disconnects the connection between the third end and the second end to form a customized accommodating area, and sets the beam splitting unit with a corresponding number of three beam splitters to connect its beam splitting input end to the second end; Based on the reference optical path length, a custom fiber segment is determined, and the robotic arm is controlled to connect the fifth end of the custom fiber segment to the first output end of the beam splitting unit and the sixth end to the third end, so as to place the custom fiber segment in the custom receiving area, wherein the second output end of the beam splitting unit faces the unit under test. A third fixed segment and a fourth fixed segment of fixed length are determined to form a secondary optical path. The seventh end of the third fixed segment receives the excitation pulse light, and the ninth end of the fourth fixed segment is connected to the eighth end of the third fixed segment, and the tenth end is connected to the seventh end. The control robot arm connects the eighth end to the beam splitting input end of the beam splitting unit and the ninth end to the third output end of the beam splitting unit.

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