Spectral measurement system and method based on double optical combs and single photon counting

Abstract

The invention discloses a spectral measurement system and method based on double optical combs and single photon counting, and belongs to the field of optical precision measurement. The spectral measurement system comprises a first optical frequency comb, a second optical frequency comb, a first beam splitter, a second beam splitter, a first beam combiner, a second beam combiner, a coaxial transceiving system, a single-photon detector, a single-photon counter, a photoelectric detector and a data acquisition and processing module, wherein the first optical frequency comb and the second optical frequency comb have tiny repetition frequency difference. Two paths of time domain amplification interference signals of measuring light and reference light are obtained through optical asynchronous sampling by utilizing a double-optical-comb technology, the measuring light is used for gas spectrum detection, and the reference light is simultaneously used as a reference spectrum and a timing starting signal of a single-photon counter; long-distance non-cooperative target gas spectral measurement is realized through a single-photon detector and a single-photon counter, a time domain interference signal after a measurement light path is amplified is obtained, and the absorption spectrum information of the measured gas is extracted by utilizing Fourier transform, so that long-distance non-cooperative target high-precision spectral measurement is realized.

Description

Technical Field

[0001] The invention belongs to the field of optical precision measurement, and relates to a spectrum measurement system and method based on dual optical combs and single photon counting. Background Art

[0002] Long-distance and high-precision spectral measurement is of great significance for gas leak detection in large oil and gas pipelines and wide-scale hazardous gas detection. An optical frequency comb usually refers to a mode-locked pulse laser with precise control in the time and frequency domains. An optical frequency comb has a time domain pulse sequence with equal time intervals in the time domain, and a series of frequency comb teeth with completely equal frequency intervals in the frequency domain. An optical frequency comb can simultaneously generate millions of optical frequency comb teeth with a certain optical frequency, so it has more advantages in spectral measurement. However, the application of a single optical frequency comb in spectral measurement and analysis still needs to rely on traditional spectral analysis methods. This is because optical frequency signals up to THz cannot be directly obtained through photodetectors, which greatly limits the application expansion of optical frequency combs. The introduction of dual-comb spectral measurement technology solves this problem. Dual-comb spectral measurement technology is a new type of optical detection technology developed on the basis of optical frequency comb technology. The overlapping optical frequency components of the two optical frequency combs are down-converted through the beat frequency to form a radio frequency comb with a repetition frequency of Δfrep, so that it can be directly measured quickly through a photodetector, which has an incomparable advantage in measurement speed. Compared with the traditional Fourier transform infrared spectrometer, the dual-comb spectral measurement technology is no longer limited to the displacement scanning detection structure, and the accuracy of its measurement results is only determined by the properties of the dual-comb light source itself, so it has a faster measurement speed and higher measurement efficiency. However, the existing dual-comb spectral measurement is to place the measured gas in the measurement optical path. The measurement optical path needs to cooperate with cooperative targets such as cones or reflectors to ensure the echo energy. The frequency down-conversion is achieved through the asynchronous sampling of the local oscillator light, and then it is detected and collected by the detector. The spectral absorption change on the measurement optical path is compared with the reference light, and then the measured gas information is solved. This method requires the cooperative target to maintain the measurement light echo energy. In addition, under non-cooperative targets, in order to maintain energy matching, the local oscillator light and the measurement light can be combined into a beam before the spectral measurement, but the received light energy loss is large and the measurement distance is short. Therefore, in some scenarios where it is impossible to install cooperative targets at long distances to ensure the echo energy for spectral measurement, such as gas leak detection in large oil and gas pipelines and large-scale hazardous gas detection, the existing dual-comb spectroscopy technology is not applicable.

[0003] Single-photon detectors have high sensitivity and are capable of detecting weak signals at the photon level. However, unlike ordinary photodetectors, they can only output a voltage signal to record whether a photon is collected. They cannot directly generate the entire pulse shape information and therefore cannot be used directly for spectral measurement. Combining a single-photon detector with a single-photon counter can restore the pulse shape through histogram accumulation of multiple pulse cycles. Combined with dual-light comb spectroscopy technology, high-precision spectral measurement of long-distance non-cooperative targets can be achieved. Summary of the invention

[0004] In order to achieve high-precision spectral measurement of long-distance non-cooperative targets, the purpose of the present invention is to provide a spectral measurement system and method based on dual-comb and single-photon counting, which utilizes dual-comb technology to obtain two-way time-domain amplified interference signals of measurement light and reference light through optical asynchronous sampling, wherein the measurement light is used for gas spectrum detection, and the reference light is used as a reference spectrum and a timing start signal for a single-photon counter at the same time. The gas spectrum measurement of long-distance non-cooperative targets is achieved through single-photon detectors and single-photon counters, and the time-domain interference signal after the measurement light path is amplified is obtained, and the absorption spectrum information of the measured gas is extracted using Fourier transform.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] The present invention discloses a spectrum measurement system based on dual optical combs and single photon counting, comprising a first optical frequency comb and a second optical frequency comb with a small repetition frequency difference, a first beam splitter, a second beam splitter, a first beam combiner, a second beam combiner, a coaxial transceiver system, a single photon detector, a single photon counter, a photoelectric detector and a data acquisition and processing module.

[0007] The first optical frequency comb emits a pulse laser which passes through the first beam splitter and is divided into laser one and laser two. The second optical frequency comb emits a pulse laser which has a small repetition frequency difference with the first optical frequency comb and passes through the second beam splitter and is divided into laser three and laser four. Laser one and laser four generate optical asynchronous sampling after passing through the second beam combiner, and interference amplification is performed in the time domain to generate measurement path laser. Laser two and laser three also undergo optical asynchronous sampling after passing through the first beam combiner, and amplification is performed in the time domain to generate reference path laser. The reference path laser passes through the photoelectric detector and outputs the reference path pulse electrical signal one and the reference path pulse electrical signal two after time domain amplification. The pulse electrical signal one is given to the single photon counter to record the starting time of the histogram accumulation. The reference path pulse electrical signal two is given to the data acquisition and processing module, and the reference spectrum information is obtained after Fourier transform. The measurement path laser passes through the coaxial light receiving and emitting The optical system transmits to the measured gas and non-cooperative target, wherein part of the wavelength band of the measuring laser reacts with the measured gas and is absorbed. The non-cooperative target returns the measuring laser to the original path and re-enters the coaxial transceiver optical system and transmits it to the single-photon detector. The single-photon detector converts the received weak measuring laser into an electrical signal as the stop time, and gives it to the single-photon counter to record the stop time. Since the light intensity of the measuring laser is very weak after being reflected by the non-cooperative target, the single-photon counter performs multi-pulse histogram accumulation to restore the time-domain amplified measuring laser pulse electrical signal. The measuring pulse electrical signal is input into the data acquisition and processing module, and the measuring spectrum information is obtained through Fourier transform. The data acquisition and processing module solves the absorption spectrum information of the measured gas after comparison, and then measures the gas composition.

[0008] A spectrum measurement system based on dual optical combs and single photon counting also includes a pulse shaping module. The pulse shaping module is divided into two shaping modes: pulse shaping module one or pulse shaping module two, both of which can achieve the purpose of pulse shaping. The reference path laser is a pulse interference signal after optical asynchronous sampling. Each pulse interference signal has multiple sub-pulse peaks, which will trigger the single photon counter multiple times, causing timing confusion and unable to recover the measurement path pulse electrical signal after time domain interference amplification, resulting in inability to perform spectrum measurement. The pulse shaping module is used to shape the reference path electrical signal into a stable pulse electrical signal for stably triggering the single photon counter.

[0009] The pulse shaping module adopts pulse shaping module 1 for pulse shaping. Pulse shaping module 1 includes a frequency doubling crystal and a dichroic mirror, which is located between the first beam splitter and the photodetector. After the reference laser pulse passes through the frequency doubling crystal, the interference pulse signal with multiple sub-pulse peaks is converted into a pulse laser with a single peak value. The dichroic mirror separates the reference laser before frequency doubling, transmits the reference laser pulse after frequency doubling, and then outputs a stable electrical pulse signal with a single peak value through the photodetector for stable timing of the subsequent single photon counter.

[0010] The pulse shaping module adopts pulse shaping module 1 for pulse shaping. Pulse shaping module 2 includes a pulse delayer, which is located between the photodetector and the single photon counter. Its function is to set the pulse width to add a dead time after the pulse delayer is triggered once. During the dead time, the pulse delayer will not respond to other sub-pulse peaks of the interference pulse signal again. By setting the length of the dead time, the situation where the single photon counter triggers multiple peaks in the interference envelope is solved, ensuring that for the same pulse interference signal, the single photon counter is only triggered once, which is used for the subsequent stable timing of the single photon counter.

[0011] The method of optical asynchronous sampling is as follows: the first optical frequency comb and the second optical frequency comb have a small repetition frequency difference. After the optical pulses of the first optical frequency comb and the second optical frequency comb are combined, due to the existence of the small repetition frequency difference, each cycle of the second optical frequency comb has an asynchronous misalignment with the first optical frequency comb. After multiple cycles of asynchronous optical sampling of the second optical frequency comb, the first optical frequency comb is asynchronously sampled and amplified in the time domain.

[0012] The method for recovering the interference signal of the measuring optical path through multi-cycle accumulation is as follows: before the pulse laser occurs, a reference laser is separated out and converted into an electrical signal by a photoelectric detector, which is given to a single-photon counter as the starting time; the measuring laser separated out by the pulse laser has a very weak light intensity of only photon level after irradiating a non-cooperative target, and a single photon is detected by a single-photon detector and an electrical signal is output, which is given to a single-photon counter to record the stop time. In each pulse laser cycle, a time value of a returned photon is counted, but there is no information on the complete pulse shape. After multiple pulse cycles, the histogram is accumulated in the time domain. Since the probability of photon counting is highest at the position with the target, after the histogram is accumulated, the shape of the pulse laser is restored according to the histogram accumulation result, and the interference signal of the measuring optical path is recovered through multi-cycle accumulation.

[0013] The optical frequency comb is one of a fiber optical frequency comb, an electro-optic comb, or a microcavity optical comb that is fully locked or has undergone dual optical comb noise compensation.

[0014] The coaxial transceiver system is one of a perforated reflector, an optical fiber circulator, and a polarization splitter system.

[0015] A spectrum measurement method based on dual light comb and single photon counting is implemented based on the spectrum measurement system based on dual light comb and single photon counting. A spectrum measurement method based on dual light comb and single photon counting comprises the following steps:

[0016] In the first step, the first optical frequency comb and the second optical frequency comb are subjected to optical asynchronous sampling to generate time-domain amplified optical pulses of the measurement path laser and the reference path laser; in the second step, the time-domain amplified optical pulses of the reference path laser are converted into electrical signals through a photoelectric detector, and then divided into reference path pulse electrical signal 1 and reference path pulse electrical signal 2, the reference path pulse electrical signal 1 is used as the start time of the single-photon counter timing, the measurement path laser interacts with the measured gas through the coaxial transceiver system, and is received by the single-photon detection system as the single-photon counter timing stop signal, and the time-domain amplified interference signal carrying the gas absorption spectrum information is restored through the accumulation of multiple pulse cycle histograms; in the third step, the reference path and measurement path interference signals are transformed into the frequency domain through Fourier transform and the gas absorption spectrum information is extracted through data processing.

[0017] In the third step, the amplitude spectrum signals corresponding to the reference optical path and the measurement optical path in the frequency domain are I1(f) and I2(f), where f corresponds to the RF frequency after time domain amplification. According to the absorptivity definition shown in the following formula, the absorptivity R(f) of the laser emitted by the optical frequency comb after passing through the gas to be measured is:

[0018]

[0019] Beneficial effects:

[0020] 1. The present invention discloses a spectral measurement system and method based on dual optical combs and single photon counting, which utilizes dual optical comb technology to obtain two-way time-domain amplified interference signals of measuring light and reference light through optical asynchronous sampling, wherein the measuring light is used for gas spectrum detection, and the reference light is simultaneously used as a reference spectrum and a timing start signal of a single photon counter. The gas spectrum measurement of a long-distance non-cooperative target is realized through a single photon detector and a single photon counter, and the time-domain interference signal after the measurement light path is amplified is obtained. The absorption spectrum information of the measured gas is extracted using Fourier transform, which can realize high-precision spectral measurement of a long-distance non-cooperative target.

[0021] 2. The present invention discloses a spectrum measurement system and method based on dual optical comb and single photon counting. Before the pulse laser occurs, a reference path laser is separated and converted into an electrical signal by a photoelectric detector, which is given to a single photon counter as the start time. The measurement path laser separated by the pulse laser has a very weak light intensity after irradiating a non-cooperative target, and the light intensity returned is only at the photon level. The single photon detector detects a single photon and outputs an electrical signal, which is given to the single photon counter to record the stop time. After multiple pulse cycles, the histogram accumulation is performed in the time domain. Since the probability of photon counting is the highest at the position with the target, after the histogram accumulation, the shape of the pulse laser is restored according to the histogram accumulation result, and a multi-cycle accumulation and restoration measurement optical path interference signal is obtained, which is used to extract the absorption spectrum information of the measured gas. Traditional dual optical comb spectrum measurement requires a cooperative target, such as a corner reflector, to ensure the echo energy. The present invention can combine the time-correlated single photon counting technology to realize the measurement of the absorption gas component on the non-cooperative target path. At the same time, the wide spectrum characteristics of the optical frequency comb can be used to simultaneously perform long-distance measurement of multiple gas components. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of a spectral measurement system based on dual optical combs and single photon counting;

[0023] Figure 2 This is the principle diagram of the histogram accumulation of the interference signal after dual frequency comb amplification via a single photon counter;

[0024] Among them, 1 is the first optical frequency comb, 2 is the second optical frequency comb, 3 is the first beam splitter, 4 is the second beam splitter, 5 is the first beam combiner, 6 is the first beam combiner, 7 is the photoelectric detector, 8 is the coaxial transceiver optical system, 9 is the single photon detector, 10 is the single photon counter, and 11 is the data acquisition and processing module. DETAILED DESCRIPTION

[0025] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0026] Embodiment 1:

[0027] like Figure 1 As shown, the present embodiment discloses a spectral measurement system based on dual optical combs and single photon counting, comprising a first optical frequency comb 1 and a second optical frequency comb 2 with a small repetition frequency difference, a first beam splitter 3, a second beam splitter 4, a first beam combiner 5, a second beam combiner 6, a coaxial transceiver system 8, a single photon detector 9, a single photon counter 10, a photodetector 7 and a data acquisition and processing module 11.

[0028] The first optical frequency comb 1 emits a pulsed laser with a central wavelength of 1560nm, a spectral width of 1450nm to 1680nm, and a repetition rate of 200MHz. After passing through the first beam splitter 3, it is divided into laser 1 and laser 2. The second optical frequency comb 2 emits a pulsed laser with a slight repetition rate difference of 1kHz from the first optical frequency comb 1, with a repetition rate of 200.1MHz, a central wavelength of 1560nm, and a spectral width of 1450nm to 1680nm. After passing through the second beam splitter 4, it is divided into laser 3 and laser 4. Laser 1 and laser 4 generate optical asynchronous sampling after passing through the second beam combiner, such as Figure 2 As shown in a and 2b, the measurement path laser is generated by interference amplification in the time domain. Laser 2 and laser 3 are also optically asynchronously sampled after passing through the first beam combiner 5. Figure 2 As shown in a and 2b, the reference laser is amplified in the time domain to generate a reference laser; the reference laser passes through the photodetector 7, and outputs the reference pulse electrical signal 1 and the reference pulse electrical signal 2 after time domain amplification. The pulse electrical signal 1 is given to the single photon counter 10 to record the starting time of the histogram accumulation, and the reference pulse electrical signal 2 is given to the data acquisition and processing module 11, and the reference spectrum information is obtained through Fourier transformation; the measuring laser is emitted to the measured gas and the non-cooperative target through the coaxial transceiver optical system 8, wherein part of the wavelength band of the measuring laser reacts with the measured gas and is absorbed, and the first optical frequency comb 1 and the second optical frequency comb 1 are used to generate the reference spectrum information; The frequency comb 2 covers the spectral band of 1450nm to 1680nm, and the corresponding gas absorption peaks are 1653nm for methane, 1572nm for carbon dioxide, and 1542nm for acetylene. The non-cooperative target returns the measurement path laser to the original path and enters the coaxial transceiver optical system 8 again, and transmits it to the single-photon detector 9. The single-photon detector 9 converts the received weak measurement path laser into an electrical signal as the stop time, and gives it to the single-photon counter 10 to record the stop time. Since the light intensity of the measurement path laser is very weak after being reflected by the non-cooperative target, the multi-pulse histogram accumulation is performed by the single-photon counter 10, as shown in FIG. Figure 2 As shown in c, the time-domain amplified pulse electrical signal of the measuring path laser is restored, and the pulse electrical signal of the measuring path is input into the data acquisition and processing module 11. After Fourier transformation, the absorption spectrum information of methane, carbon dioxide and acetylene corresponding to the measuring path is obtained. After comparison, the data acquisition and processing module 11 solves the absorption spectrum information of the measured gas, and then measures the gas components, including methane, carbon dioxide and acetylene.

[0029] A spectrum measurement system based on dual optical combs and single photon counting also includes a pulse shaping module. The pulse shaping module is divided into two shaping modes: pulse shaping module one or pulse shaping module two, both of which can achieve the purpose of pulse shaping. The reference path laser is a pulse interference signal after optical asynchronous sampling. Each pulse interference signal has multiple sub-pulse peaks, which will trigger the single photon counter 10 multiple times, causing timing confusion and unable to recover the measurement path pulse electrical signal after time domain interference amplification, resulting in inability to perform spectrum measurement. The pulse shaping module is used to shape the reference path electrical signal into a stable pulse electrical signal for stably triggering the single photon counter 10.

[0030] The pulse shaping module adopts pulse shaping module 1 for pulse shaping. Pulse shaping module 1 includes frequency doubling crystal, frequency doubling crystal and dichroic mirror, wherein the frequency doubling crystal is periodically polarized potassium titanyl phosphate crystal, referred to as PPKTP crystal, which can double the first optical frequency comb and the second optical frequency comb pulse laser with a central wavelength of 1560nm to a pulse laser with a central wavelength of 780nm. The frequency doubling crystal and the dichroic mirror are located between the first beam splitter 3 and the photodetector 7. After the reference laser pulse passes through the frequency doubling crystal, the interference pulse signal with multiple sub-pulse peaks is converted into a pulse laser with a single peak value. The dichroic mirror separates the reference laser before frequency doubling, transmits the reference laser pulse after frequency doubling, and then outputs a stable electrical pulse signal with a single peak value through the photodetector 7, which is used for the subsequent stable timing of the single photon counter 10.

[0031] The pulse shaping module adopts pulse shaping module 1 for pulse shaping. Pulse shaping module 2 includes a pulse delayer, model DG645, located between the photodetector 7 and the single photon counter 10, and its function is to set the pulse width to add a dead time after the pulse delayer is triggered once, and the dead time is 50ns. During the 50ns dead time, the pulse delayer will not respond to other sub-pulse peaks of the interference pulse signal again. By setting the length of the dead time, the situation of multiple peak triggering of the single photon counter 10 in the interference envelope is solved, ensuring that for the same pulse interference signal, the single photon counter 10 is only triggered once, which is used for the subsequent stable timing of the single photon counter 10.

[0032] like Figure 2 As shown in a and 2b, the method of optical asynchronous sampling is: the first optical frequency comb 1 and the second optical frequency comb have a small repetition frequency difference of 1kHz. After the optical pulses of the first optical frequency comb 1 and the second optical frequency comb are combined, due to the existence of the small repetition frequency difference of 1kHz, each cycle of the second optical frequency comb has an asynchronous misalignment with the first optical frequency comb 1. After multiple cycles of asynchronous optical sampling of the second optical frequency comb, the first optical frequency comb 1 is asynchronously sampled and amplified in the time domain. The time domain pulse period after amplification is 1 / 1kHz=1ms, and the pulse frequency after amplification is 1kHz.

[0033] like Figure 2 As shown in c, the method for recovering the interference signal of the measuring optical path through multi-cycle accumulation is as follows: a reference laser is separated before the pulse laser occurs and converted into an electrical signal by the photoelectric detector 7, which is given to the single-photon counter 10 as the starting time; the measuring laser separated by the pulse laser has a very weak light intensity of only photon level after irradiating the non-cooperative target, and the single-photon detector 9 detects a single photon and outputs an electrical signal, which is given to the single-photon counter 10 to record the stop time. Within each pulse laser cycle, that is, within 1ms, a time value of a returned photon will be counted, but there is no information about the complete pulse shape. After multiple pulse cycles, the histogram accumulation is performed in the time domain, for example, 1000 cycles, corresponding to 1s. Since the probability of photon counting is highest at the position with the target, after the histogram is accumulated within 1s, the interference shape of the amplified pulse laser is restored according to the histogram accumulation result, and the multi-cycle accumulation and recovery of the interference signal of the measuring optical path is obtained.

[0034] The optical frequency comb is one of a fiber optical frequency comb, an electro-optic comb, or a microcavity optical comb that is fully locked or has undergone dual optical comb noise compensation.

[0035] The coaxial transceiver system is one of a perforated reflector, an optical fiber circulator, and a polarization splitter system.

[0036] A spectrum measurement method based on dual light comb and single photon counting is implemented based on the spectrum measurement system based on dual light comb and single photon counting. A spectrum measurement method based on dual light comb and single photon counting comprises the following steps:

[0037] In the first step, the first optical frequency comb 1 and the second optical frequency comb 2 are subjected to optical asynchronous sampling to generate time-domain amplified optical pulses of the measurement laser and the reference laser. The amplified time-domain pulse period is 1 / 1kHz=1ms, and the amplified pulse frequency is 1kHz; in the second step, the reference laser time-domain amplified optical pulse is converted into an electrical signal by the photodetector 7, and then divided into reference pulse electrical signal 1 and reference pulse electrical signal 2. The reference pulse electrical signal 1 is used as the timing start time of the single photon counter 10. The measurement laser reacts with the measured gas methane, carbon dioxide, and acetylene through the coaxial transceiver system, and is received by the single photon detection system as the timing stop signal of the single photon counter 10. After multiple pulse period histogram accumulation, the time-domain amplified interference signal carrying the gas absorption spectrum information is restored; in the third step, the reference and measurement interference signals are Fourier transformed into the frequency domain and the gas absorption spectrum information is extracted after data processing, including methane, carbon dioxide, and acetylene. .

[0038] In the third step, the amplitude spectrum signals corresponding to the reference optical path and the measurement optical path in the frequency domain are I1(f) and I2(f), as shown in the following formula:

[0039]

[0040] Where f corresponds to the RF frequency after time domain amplification, and its value should be less than half of the repetition rate of the first optical frequency comb 1, corresponding to n△f, that is, an integer multiple of the repetition rate difference, δ is the impulse function, E, f and φ correspond to the electric field intensity, frequency and initial phase of the optical frequency comb, p and q correspond to the pth longitudinal mode of optical comb 1 and the qth longitudinal mode of optical comb 2, respectively, P and Q are the sets of all longitudinal modes p and q that meet the optical downsampling conditions of the dual optical comb, α(f p ) and α(f q ) is the spectral absorption rate corresponding to the pth and qth longitudinal modes. The measured gas absorption rate R(f p -f q ), can be calculated by the following formula

[0041]

[0042] What is obtained at this time is the RF spectrum absorbance. Since the RF spectrum has a one-to-one correspondence with the optical spectrum, the actual absorption spectrum information can be solved by conventional methods such as comparison with the standard spectrum database and connection with the ultra-stable continuous laser beat frequency.

[0043] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A spectral measurement system based on dual optical combs and single photon counting, characterized in that: It includes two first optical frequency combs and second optical frequency combs with a small repetition frequency difference, a first beam splitter, a second beam splitter, a first beam combiner, a second beam combiner, a coaxial transceiver system, a single photon detector, a single photon counter, a photoelectric detector and a data acquisition and processing module; The first optical frequency comb emits a pulse laser which passes through the first beam splitter and is divided into laser one and laser two. The second optical frequency comb emits a pulse laser which has a small repetition frequency difference with the first optical frequency comb and passes through the second beam splitter and is divided into laser three and laser four. Laser one and laser four generate optical asynchronous sampling after passing through the second beam combiner, and interference amplification is performed in the time domain to generate measurement path laser. Laser two and laser three also undergo optical asynchronous sampling after passing through the first beam combiner, and amplification is performed in the time domain to generate reference path laser. The reference path laser passes through the photoelectric detector and outputs the reference path pulse electrical signal one and the reference path pulse electrical signal two after time domain amplification. The pulse electrical signal one is given to the single photon counter to record the starting time of the histogram accumulation. The reference path pulse electrical signal two is given to the data acquisition and processing module, and the reference spectrum information is obtained after Fourier transform. The measurement path laser passes through the coaxial light receiving and emitting The optical system transmits to the measured gas and non-cooperative target, wherein part of the wavelength band of the measuring laser reacts with the measured gas and is absorbed. The non-cooperative target returns the measuring laser to the original path and re-enters the coaxial transceiver optical system and transmits it to the single-photon detector. The single-photon detector converts the received weak measuring laser into an electrical signal as the stop time, and gives it to the single-photon counter to record the stop time. Since the light intensity of the measuring laser is very weak after being reflected by the non-cooperative target, the single-photon counter performs multi-pulse histogram accumulation to restore the time-domain amplified measuring laser pulse electrical signal. The measuring pulse electrical signal is input into the data acquisition and processing module, and the measuring spectrum information is obtained through Fourier transform. The data acquisition and processing module solves the absorption spectrum information of the measured gas after comparison, and then measures the gas composition.

2. A spectral measurement system based on dual optical combs and single photon counting as claimed in claim 1, characterized in that: It also includes a pulse shaping module, which is used to shape the reference circuit electrical signal into a stable pulse electrical signal for stably triggering the single photon counter.

3. A spectral measurement system based on dual optical combs and single photon counting as claimed in claim 2, characterized in that: The pulse shaping module adopts pulse shaping module one for pulse shaping; pulse shaping module one includes a frequency doubling crystal and a dichroic mirror, and is located between the first beam splitter and the photodetector. After the reference path laser pulse passes through the frequency doubling crystal, the interference pulse signal with multiple sub-pulse peaks is converted into a pulse laser with a single peak value. The dichroic mirror separates the reference path laser before frequency doubling, transmits the reference path pulse laser after frequency doubling, and then passes through the photodetector to output a stable electrical pulse signal with a single peak value, which is used for the subsequent stable timing of the single photon counter.

4. A spectral measurement system based on dual optical combs and single photon counting as claimed in claim 2, characterized in that: The pulse shaping module adopts pulse shaping module one for pulse shaping; pulse shaping module two includes a pulse delayer, which is located between the photodetector and the single-photon counter. Its function is to add a dead time after the pulse delayer is triggered once by setting the pulse width. During the dead time, the pulse delayer will not respond to other sub-pulse peaks of the interference pulse signal again. By setting the length of the dead time, the situation where the single-photon counter is triggered by multiple peaks in the interference envelope is solved, ensuring that for the same pulse interference signal, the single-photon counter is only triggered once, which is used for subsequent stable timing of the single-photon counter.

5. A spectral measurement system based on dual optical combs and single photon counting as claimed in claim 1, characterized in that: The method of optical asynchronous sampling is as follows: the first optical frequency comb and the second optical frequency comb have a small repetition frequency difference. After the optical pulses of the first optical frequency comb and the second optical frequency comb are combined, due to the existence of the small repetition frequency difference, each cycle of the second optical frequency comb has an asynchronous misalignment with the first optical frequency comb. After multiple cycles of asynchronous optical sampling of the second optical frequency comb, the first optical frequency comb is asynchronously sampled and amplified in the time domain.

6. A spectrum measurement system based on dual optical combs and single photon counting as claimed in claim 1, characterized in that: The method for recovering the interference signal of the measuring optical path through multi-cycle accumulation is as follows: before the pulse laser occurs, a reference laser is separated out and converted into an electrical signal by a photoelectric detector, which is given to a single-photon counter as the starting time; the measuring laser separated out by the pulse laser has a very weak light intensity of only photon level after irradiating a non-cooperative target, and a single photon is detected by a single-photon detector and an electrical signal is output, which is given to a single-photon counter to record the stop time, and a histogram accumulation is performed in the time domain after multiple pulse cycles. Since the probability of photon counting is highest at the position where there is a target, after the histogram accumulation, the shape of the pulse laser is restored according to the histogram accumulation result, and the interference signal of the measuring optical path is recovered through multi-cycle accumulation.

7. A spectrum measurement system based on dual optical combs and single photon counting as claimed in claim 1, characterized in that: The optical frequency comb is one of a fiber optical frequency comb, an electro-optic comb, or a microcavity optical comb that is fully locked or has undergone dual optical comb noise compensation.

8. A spectrum measurement system based on dual optical combs and single photon counting as claimed in claim 1, characterized in that: The coaxial transceiver system is one of a perforated reflector, an optical fiber circulator, and a polarization splitter system.

9. A spectrum measurement method based on dual light comb and single photon counting, implemented based on a spectrum measurement system based on dual light comb and single photon counting according to claim 1, 2, 3, 4, 5, 6, 7 or 8, characterized in that: The following steps are included: In the first step, the first optical frequency comb and the second optical frequency comb are subjected to optical asynchronous sampling to generate time-domain amplified optical pulses of the measurement path laser and the reference path laser; In the second step, the reference path laser time-domain amplified light pulse is converted into an electrical signal through a photoelectric detector, and then divided into reference path pulse electrical signal 1 and reference path pulse electrical signal 2. The reference path pulse electrical signal 1 is used as the start time of the single-photon counter timing. The measuring path laser interacts with the measured gas through the coaxial transceiver system and is received by the single-photon detection system as the single-photon counter timing stop signal. The time-domain amplified interference signal carrying the gas absorption spectrum information is restored through the accumulation of multiple pulse cycle histograms. In the third step, the interference signals of the reference path and the measurement path are transformed into the frequency domain through Fourier transform and the gas absorption spectrum information is extracted through data processing.

10. A spectrum measurement method based on dual optical combs and single photon counting as claimed in claim 9, characterized in that: In the third step, the amplitude spectrum signals corresponding to the reference optical path and the measurement optical path in the frequency domain are I1(f) and I2(f), where f corresponds to the RF frequency after time domain amplification. According to the absorptivity definition shown in the following formula, the absorptivity R(f) of the laser emitted by the optical frequency comb after passing through the gas to be measured is:

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