A single-photon spectrometer based on fiber dispersion

Abstract

The application discloses a single-photon spectrometer based on fiber dispersion, which comprises a frequency divider and a chopping device, a dispersion module, a single-photon detector and a time-to-digital converter connected in sequence, the frequency divider receives a driving pulse electric signal of a light source to be measured and reduces the frequency of the driving pulse electric signal while transmitting the driving pulse electric signal to the chopping device and the time-to-digital converter, the chopping device intercepts light pulses output by the light source to be measured based on the driving pulse electric signal after frequency reduction to form chopping pulses, because the frequency of the driving pulse electric signal of the light source to be measured is consistent with the frequency of the light pulses output by the light source to be measured, the period of the driving pulse electric signal after frequency reduction is an integer multiple of the period of the light pulses, the frequency reduction multiple of the frequency divider is adjusted so that the period of the driving pulse electric signal after frequency reduction is not less than the time-domain width of the chopping pulses after pulse broadening, that is, the period of the chopping pulses is not less than the time-domain width of the chopping pulses after pulse broadening, and thus the adjacent chopping pulses after pulse broadening are prevented from overlapping, and the accuracy and stability of the spectrum measurement are improved.

Description

Technical Field

[0001] This application belongs to the field of spectral measurement, and more specifically, relates to a single-photon spectrometer based on fiber dispersion. Background Technology

[0002] In the fields of quantum information and quantum optics, the preparation and manipulation of quantum states are strictly dependent on the spectral properties of photons. For example, the foundation of linear optical quantum computing—two-photon interference (also known as HOM interference)—requires that the spectra of the two interfering photons be strictly identical. In quantum optics experiments, the cross-correlation of the two-photon spectra of commonly used quantum light sources, such as those generated by spontaneous parametric down-conversion (SPDC) and four-wave mixing (FWM), is also an important parameter for evaluating the characteristics of these light sources.

[0003] Unlike classical optics, the light sources used in quantum optics experiments are on the single-photon scale, which cannot be detected by ordinary photodetectors. Avalanche photodiodes operating in Geiger mode are required for low-noise, high-sensitivity single-photon detection. Therefore, in terms of spectral measurements, quantum light source spectral measurements also require low-noise, low-attenuation single-photon spectrometers with sensitivity down to the single-photon level.

[0004] Traditional spectrometers based on spatial dispersion principles such as prisms and gratings can be divided into scanning and imaging types. Scanning spectrometers have moving parts and require only a single-point detector, but this scanning method suffers from significant attenuation for single-photon spectral detection. Imaging spectrometers collect and detect all dispersed light, avoiding the attenuation problem, but require expensive single-photon CCD detectors and liquid nitrogen cooling to reduce noise.

[0005] Currently, one widely used method for spectral measurement of quantum light sources, such as spontaneous parametric down-conversion and four-wave mixing, involves using dispersive optical fibers to separate single photons of different wavelengths in the time domain. Detection and time resolution are then achieved using a single-photon detector and a time-to-digital converter (TDC). Based on a pre-calibrated relationship between photon wavelength and arrival time, the spectral measurement result of the single photon is calculated, thus achieving single-photon spectral measurement. However, this method has two problems. First, when the light source under test is continuous light or has a high pulse frequency, photons from consecutive pulses overlap in the time domain after dispersion, making accurate spectral measurement impossible. Second, during the calibration process, the spectrometer must ensure that the input path of the calibrated photon is exactly the same as the input path of the photon under test. Otherwise, inconsistencies in path length will lead to different photon arrival times at the detector, affecting the spectral measurement results. Therefore, the spectrometer calibration process is difficult, and recalibration is required when the optical path of the photon under test changes, resulting in poor practicality. Summary of the Invention

[0006] To address the aforementioned issues, this application provides a single-photon spectrometer based on fiber dispersion. A chopper is used to intercept the light pulses output from the light source under test, forming a chopped pulse. This chopped pulse is then broadened by a dispersion module, and the period of the chopped pulse is not less than the time-domain width of the broadened pulse, thus avoiding overlap between adjacent chopped pulses. The specific solution is as follows:

[0007] This application discloses a single-photon spectrometer based on fiber dispersion, comprising a frequency divider and a chopper, a dispersion module, a single-photon detector, and a time-to-digital converter connected in sequence. The frequency divider is connected to both the chopper and the time-to-digital converter, and is used to receive the driving pulse electrical signal of the light source under test, down-frequency the driving pulse electrical signal, and simultaneously transmit the down-frequency driving pulse electrical signal to both the chopper and the time-to-digital converter. The chopper is used to intercept the light pulse output by the light source under test under the action of the down-frequency driving pulse electrical signal to form a chop pulse. The dispersion module is used to broaden the chop pulse so that photons of different wavelengths are separated in the time domain and transmitted to the single-photon detector. The period of the down-frequency driving pulse electrical signal is not less than the time domain width of the broadened chop pulse. The single-photon detector is used to convert photon signals of different wavelengths into corresponding electrical signals and acquire photon counts, while transmitting the converted electrical signals to the time-to-digital converter. The time-to-digital converter is used to record the time when the chopper forms the chop pulse and the time when the photon signals of different wavelengths are converted into corresponding electrical signals, and to calculate the time interval.

[0008] Furthermore, the single-photon spectrometer also includes an electrically adjustable optical delay unit. The output of the electrically adjustable optical delay unit is connected to the chopper, and one input of the electrically adjustable optical delay unit is connected to the single-photon detector. The electrically adjustable optical delay unit is used for delayed scanning of the light pulse output by the light source under test and obtains the optimal delay time of the light pulse output by the light source under test based on the photon count fed back by the single-photon detector.

[0009] Preferably, the single-photon detector is a single-photon avalanche diode.

[0010] Preferably, the dispersion module is an optical fiber or a fiber Bragg grating.

[0011] Preferably, the chopper is an MZI-type optical switch or a lithium niobate intensity modulator.

[0012] Preferably, the single-photon detector operates in free-running mode, continuously detecting input photons of different wavelengths.

[0013] Furthermore, the MZI type optical switch consists of a first beam splitter, an upper interference arm, a lower interference arm, a phase modulator, and a second beam splitter. The phase modulator is disposed on the upper interference arm or the lower interference arm and is used to adjust the phase of the optical pulse. The two ends of the upper interference arm are respectively connected to the upper output port of the first beam splitter and the upper input port of the second beam splitter. The two ends of the lower interference arm are respectively connected to the lower output port of the first beam splitter and the lower input port of the second beam splitter.

[0014] Furthermore, the lithium niobate intensity modulator comprises an input straight waveguide, a 3dB beam splitter, an upper transmission waveguide, a lower transmission waveguide, a 3dB beam combiner, an output straight waveguide, and modulation electrodes. The input straight waveguide is connected to the input end of the 3dB beam splitter. The two ends of the upper transmission waveguide are respectively connected to the upper output port of the 3dB beam splitter and the upper input port of the 3dB beam combiner. The two ends of the lower transmission waveguide are respectively connected to the lower output port of the 3dB beam splitter and the lower input port of the 3dB beam combiner. The output straight waveguide is connected to the output end of the 3dB beam combiner. There are a total of four modulation electrodes. Two modulation electrodes are symmetrically arranged on both sides of the upper transmission waveguide, and the other two modulation electrodes are symmetrically arranged on both sides of the lower transmission waveguide.

[0015] Overall, compared with the prior art, the above-described technical solutions conceived in this application can achieve the following beneficial effects:

[0016] This application provides a single-photon spectrometer based on fiber dispersion, including a frequency divider and a chopper, a dispersion module, a single-photon detector, and a time-to-digital converter connected in sequence. The frequency divider receives the driving pulse electrical signal of the light source under test and down-converts the driving pulse electrical signal while transmitting it to the chopper and the time-to-digital converter. The chopper intercepts the light pulse output by the light source under test based on the down-converted driving pulse electrical signal to form a chopped pulse. Since the frequency of the driving pulse electrical signal of the light source under test is the same as the frequency of the light pulse output by the light source under test, the period of the down-converted driving pulse electrical signal is an integer multiple of the period of the light pulse. By adjusting the down-conversion factor of the frequency divider, the period of the down-converted driving pulse electrical signal is not less than the time domain width of the chopped pulse after broadening, that is, the period of the chopped pulse is not less than the time domain width of the chopped pulse after broadening, avoiding the overlap of adjacent chopped pulses after broadening, and improving the accuracy and stability of spectral measurement. Furthermore, the time-to-digital converter uses the time when the chopper forms the chopping pulse as the starting time point for detection, and the period of the reduced-frequency drive pulse electrical signal is an integer multiple of the period of the optical pulse. Since the distance from the chopper to the single-photon detector and the time-to-digital converter is fixed at the factory, it does not need to be recalibrated when measuring different light sources, which improves measurement efficiency and makes it highly practical. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this embodiment or the prior art, the drawings used in the description of the embodiment or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of the structure of a single-photon spectrometer based on fiber dispersion provided in an embodiment of this application;

[0019] Figure 2 This is a timing diagram of the driving pulse electrical signal of the light source under test and the light pulse output by the light source under test in this application;

[0020] Figure 3 This is a schematic diagram illustrating pulse changes during detection according to an embodiment of this application;

[0021] Figure 4 This is a schematic diagram illustrating pulse changes during detection, according to another embodiment of this application.

[0022] Figure 5 A schematic diagram of the structure of a single-photon spectrometer based on fiber dispersion is provided for another embodiment of this application;

[0023] Figure 6 This is a schematic diagram of the structure of the MZI type optical switch in this application;

[0024] Figure 7 This is a schematic diagram of the lithium niobate intensity modulator in this application. Detailed Implementation

[0025] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the embodiments of this application will be further described in detail below with reference to the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0027] To facilitate understanding and explanation of the technical solutions provided in the embodiments of this application, the background technology of this application will be described first.

[0028] Currently, one widely used method for spectral measurement of quantum light sources, such as spontaneous parametric down-conversion and four-wave mixing, involves using dispersive optical fibers to separate single photons of different wavelengths in the time domain. Detection and time resolution are then achieved using a single-photon detector and a time-to-digital converter (TDC). Based on a pre-calibrated relationship between photon wavelength and arrival time, the spectral measurement result of the single photon is calculated, thus achieving single-photon spectral measurement. However, this method has two problems. First, when the light source under test is continuous light or has a high pulse frequency, photons from consecutive pulses overlap in the time domain after dispersion, making accurate spectral measurement impossible. Second, during the calibration process, the spectrometer must ensure that the input path of the calibrated photon is exactly the same as the input path of the photon under test. Otherwise, inconsistencies in path length will lead to different photon arrival times at the detector, affecting the spectral measurement results. Therefore, the spectrometer calibration process is difficult, and recalibration is required when the optical path of the photon under test changes, resulting in poor practicality.

[0029] Based on this, this application provides a single-photon spectrometer based on fiber dispersion, such as... Figure 1 As shown, the system includes a frequency divider and a chopper, a dispersion module, a single-photon detector, and a time-to-digital converter connected in sequence. The frequency divider is connected to both the chopper and the time-to-digital converter. It receives the driving pulse electrical signal from the light source under test, down-frequencyizes the driving pulse electrical signal, and transmits the down-frequency driving pulse electrical signal to both the chopper and the time-to-digital converter. The chopper is used to intercept the light pulse output by the light source under test and form a chop pulse under the action of the down-frequency driving pulse electrical signal. The dispersion module is used to broaden the chop pulse so that photons of different wavelengths are separated in the time domain and transmitted to the single-photon detector. The period of the down-frequency driving pulse electrical signal is not less than the time domain width of the broadened chop pulse. The single-photon detector is used to convert photon signals of different wavelengths into corresponding electrical signals and acquire photon counts. It also transmits the converted electrical signals to the time-to-digital converter. The time-to-digital converter records the time when the chopper forms the chop pulse and the time when the photon signals of different wavelengths are converted into corresponding electrical signals, and calculates the time interval.

[0030] It is important to note that the light source under test detected in this application outputs light pulses rather than continuous light. The light source under test outputs light pulses under the action of a driving pulse electrical signal, and this driving pulse electrical signal is simultaneously transmitted to a frequency divider. The frequency of the driving pulse electrical signal for the light source under test is consistent with the frequency of the light pulses output by the light source under test. Figure 2 As shown.

[0031] The frequency divider receives the drive pulse electrical signal and down-converts it so that the frequency of the output drive pulse electrical signal is an integer fraction of the frequency of the input drive pulse electrical signal. Since the frequency of the input drive pulse electrical signal is the same as the frequency of the light pulse output by the light source under test, the period of the down-converted drive pulse electrical signal is an integer multiple of the period of the light pulse.

[0032] In this application, the chopper is an MZI-type optical switch or a lithium niobate intensity modulator. The chopper intercepts the optical pulse output from the light source under test based on the down-frequency driven pulse electrical signal to form a chop pulse. Therefore, the period of the chop pulse is consistent with the period of the down-frequency driven pulse electrical signal and also with the period of the intercepted optical pulse, such as... Figure 3 and Figure 4 As shown. In one embodiment, see Figure 3 The pulse width of the driving pulse electrical signal is smaller than the width of the light pulse output by the light source under test. The chopper extracts a portion of the light pulse output by the light source under test based on the down-frequency driving pulse electrical signal to form a chop pulse. The width of each chop pulse is consistent with the pulse width of the down-frequency driving pulse electrical signal. In another embodiment, see... Figure 4 The pulse width of the driving pulse electrical signal is greater than the width of the light pulse output by the light source under test. The chopper intercepts the light pulse output by the light source under test based on the down-frequency driving pulse electrical signal to form a chopping pulse. In this state, the width of the intercepted single chopping pulse is the width of the light pulse output by the light source under test.

[0033] After the chopped pulse is transmitted to the dispersion module, its dispersion is broadened. The principle is that photons of different wavelengths propagate at different speeds on the dispersion module. Therefore, photons of different wavelengths are separated in the time domain after passing through the dispersion module, and their transmission times to the single-photon detector are different. By adjusting the down-frequency factor of the frequency divider, the period of the down-frequency driving pulse electrical signal is ensured to be no less than the time domain width of the broadened chopped pulse. In other words, the period of the chopped pulse is no less than the time domain width of the broadened chopped pulse. See [link to relevant documentation]. Figure 3 and Figure 4 This avoids overlap of adjacent chopper pulses after broadening, thus improving the accuracy and stability of spectral measurements.

[0034] A single-photon detector receives photon signals of different wavelengths, converts them into corresponding electrical signals, acquires photon counts, and transmits the converted electrical signals to a time-to-digital converter. In this application, a single-photon avalanche diode is preferred as the single-photon detector. A single-photon avalanche diode can detect individual particles of light, detect weak signals, and achieves picosecond-level detection accuracy. It has two operating modes: free-running mode and gated mode. In this application, the single-photon avalanche diode operates in free-running mode, continuously detecting photons of different wavelengths to reduce the attenuation of the chopper pulse in gated mode.

[0035] The chopper intercepts the light pulses output by the light source under test based on the down-frequency drive pulse electrical signal to form a chopped pulse. Simultaneously, the down-frequency drive pulse electrical signal is transmitted to a time-to-digital converter (TD-SCDMA). The TD-SCDMA records the timing of the down-frequency drive pulse electrical signal, i.e., the time it takes for the chopper to form each chopped pulse, serving as the start timing signal for the TD-SCDMA. The single-photon detector converts photon signals of different wavelengths into corresponding electrical signals, which are transmitted to the TD-SCDMA as the stop timing signal. Therefore, the TD-SCDMA can accurately measure the time interval between the start and stop timing signals of photons of different wavelengths within the same chopped pulse. Since photons of different wavelengths arrive at the single-photon detector at different times after passing through the dispersion module, the arrival time of photons of different wavelengths at the single-photon detector and the corresponding light intensity curve can be accurately measured. The light intensity is reflected by the photon count detected by the single-photon detector, thus obtaining the correlation curve between wavelength and light intensity, completing the spectral measurement function.

[0036] In this application, the time-to-digital converter uses the time when the chopper forms the chopping pulse as the starting time point of the detection, and the period of the driven pulse electrical signal after frequency reduction is an integer multiple of the period of the optical pulse. Since the distance from the chopper to the single-photon detector and the time-to-digital converter is fixed at the factory, it is not necessary to recalibrate when measuring different light sources under test, which improves the measurement efficiency and has strong practicality.

[0037] In another embodiment of this application, the fiber-optic dispersion-based single-photon spectrometer further includes an electrically tunable optical delay unit, such as... Figure 5 As shown, the output of the electrically adjustable optical delay unit is connected to a chopper, and one input of the electrically adjustable optical delay unit is connected to a single-photon detector. The electrically adjustable optical delay unit is used for delay scanning of the light pulse output by the light source under test and obtains the optimal delay time of the light pulse output by the light source under test based on the photon count fed back by the single-photon detector.

[0038] The electrically adjustable optical delay unit (EMU) allows for precise adjustment of optical delay, offering advantages such as low insertion loss and high integration. It enables delayed scanning of the light pulse output from the light source under test. The delay scan period (scan length) is the period of the chopped pulse. Within this period, the EMU continuously changes the delay value. A single-photon detector acquires the photon count at each delay value and feeds it back to the EMU. After completing the entire scan length, the EMU obtains the delay value corresponding to the maximum photon count. This delay value represents the optimal delay time for the light pulse output from the light source under test. The EMU then fixes the delay value corresponding to the maximum photon count and uses this value for spectral measurement of the light source under test.

[0039] In this application, the dispersion module is an optical fiber or a fiber Bragg grating to broaden the chopping pulse, so that photons of different wavelengths arrive at the single-photon detector at different times.

[0040] In one embodiment of this application, the chopper is an MZI-type optical switch. Specifically, the MZI-type optical switch consists of a first beam splitter, an upper interference arm, a lower interference arm, a phase modulator, and a second beam splitter, as shown below. Figure 6 As shown, a phase modulator is disposed on the upper or lower arm of the interference device. The phase modulator is used to adjust the phase of the optical pulse. The two ends of the upper arm are respectively connected to the upper output port of the first beam splitter and the upper input port of the second beam splitter. The two ends of the lower arm are respectively connected to the lower output port of the first beam splitter and the lower input port of the second beam splitter.

[0041] Assume that the upper output port of the second beam splitter is connected to the dispersion module for outputting chopping pulses, and the lower output port of the second beam splitter is an invalid output port.

[0042] When the pulse width of the driving pulse electrical signal is less than the width of the output light pulse of the light source under test, see [reference needed]. Figure 3 By adjusting the phase modulator, a portion of the optical pulses entering the MZI-type optical switch (such as optical pulse 1 and optical pulse 3) is output from the upper output port of the second beam splitter, while the remaining portions of optical pulses 1 and 3 are output from the lower output port of the second beam splitter. Similarly, optical pulses 2 and 4 are also output from the lower output port of the second beam splitter. By adjusting the phase modulator, a portion of the optical pulses entering the MZI-type optical switch (chopped pulses) is output from the upper output port of the second beam splitter to the dispersion module, while the remaining portions of the optical pulses that are not truncated, as well as optical pulses that do not correspond to the down-frequency driving electrical signal pulses (such as optical pulses 2 and 4), are output from the lower output port of the second beam splitter. These remaining portions are invalid outputs, thus achieving the purpose of obtaining chopped pulses. Specifically, the modulation time period of a single optical pulse by the phase modulator is consistent with the pulse time-domain width of the driving pulse electrical signal, and the modulation period of the phase modulator is consistent with the period of the truncated optical pulse.

[0043] When the pulse width of the driving pulse electrical signal is greater than the width of the output light pulse of the light source under test, see [reference needed]. Figure 4 By adjusting the phase modulator, optical pulses 1 and 3 are output from the upper output port of the second beam splitter, and optical pulses 2 and 4 are output from the lower output port of the second beam splitter, and so on, to achieve the purpose of obtaining chopping pulses.

[0044] In another embodiment of this application, the chopper is a lithium niobate intensity modulator. Specifically, the lithium niobate intensity modulator consists of an input straight waveguide, a 3dB beam splitter, an upper transmission waveguide, a lower transmission waveguide, a 3dB beam combiner, an output straight waveguide, and modulation electrodes, as shown below. Figure 7 As shown, the input straight waveguide is connected to the input end of the 3dB beam splitter. The two ends of the transmission upper waveguide are connected to the output upper port of the 3dB beam splitter and the input upper port of the 3dB beam combiner, respectively. The two ends of the transmission lower waveguide are connected to the output lower port of the 3dB beam splitter and the input lower port of the 3dB beam combiner, respectively. The output straight waveguide is connected to the output end of the 3dB beam combiner. There are a total of 4 modulation electrodes. Two modulation electrodes are symmetrically arranged on both sides of the transmission upper waveguide, and the other two modulation electrodes are symmetrically arranged on both sides of the transmission lower waveguide.

[0045] Symmetrical modulation electrodes are arranged on both sides of the upper and lower transmission waveguides. Under the influence of an applied electric field, these electrodes establish electric fields within the upper and lower transmission waveguides, respectively, causing changes in their refractive indices. By altering the modulation voltage of the applied electric field, phase changes in the optical pulses transmitted within the upper and lower transmission waveguides are achieved. Specifically, the optical pulse is transmitted through the input straight waveguide to a 3dB beamsplitter, where it is split into two beams of equal energy. These beams then travel through the upper and lower transmission waveguides, respectively. Based on symmetrically arranged modulation electrodes, the upper and lower waveguides, under the influence of an applied electric field, induce equal positive and negative phase changes in one beam in the upper waveguide and the other in the lower waveguide. These two phase-modulated beams are then combined by interference at a 3dB beam combiner and output through the output straight waveguide. Under the influence of an external electric field, the two beams of light after passing through the 3dB beam splitter develop a phase difference. By adjusting the voltage of the external electric field, which changes the phase difference between the two beams, interference synthesis at the 3dB beam combiner achieves either destructive or constructive interference of the optical pulses. In this application, the process of constructive interference is the process of forming a chopping pulse.

[0046] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes the aforementioned element.

[0047] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A single-photon spectrometer based on fiber dispersion, characterized in that, It includes a frequency divider and a chopper, a dispersion module, a single-photon detector, and a time-to-digital converter connected in sequence; the frequency divider is connected to the chopper and the time-to-digital converter respectively, and is used to receive the driving pulse electrical signal of the light source under test, reduce the frequency of the driving pulse electrical signal, and transmit the reduced driving pulse electrical signal to the chopper and the time-to-digital converter at the same time. The chopper is used to intercept the light pulse output by the light source under test and form a chop pulse under the action of the down-frequency driving pulse electrical signal; the dispersion module is used to broaden the chop pulse so that photons of different wavelengths are separated in the time domain and transmitted to the single-photon detector, and the period of the down-frequency driving pulse electrical signal is not less than the time domain width of the broadened chop pulse; the single-photon detector is used to convert photon signals of different wavelengths into corresponding electrical signals and acquire photon counts, and transmit the converted electrical signals to the time-to-digital converter, and the time-to-digital converter is used to record the time when the chopper forms the chop pulse and the time when the photon signals of different wavelengths are converted into corresponding electrical signals and calculate the time interval.

2. A single-photon spectrometer based on fiber dispersion according to claim 1, characterized in that, The single-photon spectrometer also includes an electrically adjustable optical delay unit. The output of the electrically adjustable optical delay unit is connected to the chopper, and one input of the electrically adjustable optical delay unit is connected to the single-photon detector. The electrically adjustable optical delay unit is used for delayed scanning of the light pulse output by the light source under test and obtains the optimal delay time of the light pulse output by the light source under test based on the photon count fed back by the single-photon detector.

3. A single-photon spectrometer based on fiber dispersion according to claim 1 or 2, characterized in that, The single-photon detector is a single-photon avalanche diode.

4. A single-photon spectrometer based on fiber dispersion according to claim 1 or 2, characterized in that, The dispersion module is an optical fiber or a fiber Bragg grating.

5. A single-photon spectrometer based on fiber dispersion according to claim 1 or 2, characterized in that, The chopper is an MZI type optical switch or a lithium niobate intensity modulator.

6. A single-photon spectrometer based on fiber dispersion according to claim 3, characterized in that, The single-photon detector operates in free-running mode, continuously detecting photons of different wavelengths.

7. A single-photon spectrometer based on fiber dispersion according to claim 5, characterized in that, The MZI type optical switch consists of a first beam splitter, an upper interference arm, a lower interference arm, a phase modulator, and a second beam splitter. The phase modulator is disposed on the upper interference arm or the lower interference arm and is used to adjust the phase of the optical pulse. The two ends of the upper interference arm are respectively connected to the upper output port of the first beam splitter and the upper input port of the second beam splitter. The two ends of the lower interference arm are respectively connected to the lower output port of the first beam splitter and the lower input port of the second beam splitter.

8. A single-photon spectrometer based on fiber dispersion according to claim 5, characterized in that, The lithium niobate intensity modulator comprises an input straight waveguide, a 3dB beamsplitter, an upper transmission waveguide, a lower transmission waveguide, a 3dB beam combiner, an output straight waveguide, and modulation electrodes. The input straight waveguide is connected to the input end of the 3dB beamsplitter. The two ends of the upper transmission waveguide are connected to the upper output port of the 3dB beamsplitter and the upper input port of the 3dB beam combiner, respectively. The two ends of the lower transmission waveguide are connected to the lower output port of the 3dB beamsplitter and the lower input port of the 3dB beam combiner, respectively. The output straight waveguide is connected to the output end of the 3dB beam combiner. There are four modulation electrodes in total. Two modulation electrodes are symmetrically arranged on both sides of the upper transmission waveguide, and the other two modulation electrodes are symmetrically arranged on both sides of the lower transmission waveguide.

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