A method and system for measuring spectral response of a superconducting nanowire single-photon detector

Abstract

The application discloses a spectrum response measurement method and system suitable for a superconducting nanowire single-photon detector. The method calibrates the system efficiency of the superconducting nanowire single-photon detector under different wavelengths and polarization conditions by adjusting the wavelength and polarization state of incident laser, so as to obtain the relationship between the efficiency and the wavelength under TE mode and TM mode, and provide a basis for adjusting the structure of the detector.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of superconducting nanowire single-photon detector, and particularly relates to a spectral response measurement method suitable for a superconducting nanowire single-photon detector. BACKGROUND

[0002] A superconducting nanowire single-photon detector (SNSPD) is a high-sensitivity light detector for efficiently, quickly and accurately detecting single photons. A photosensitive part of the detector is made of a nanowire meander structure of a superconducting thin film material, such as niobium nitride, molybdenum silicon or the like. The detector is biased at a state slightly lower than a superconducting critical current when working, and the nanowire is in a superconducting state. When the nanowire absorbs a photon, a superconducting Cooper pair is scattered into quasi-particles, and a high-resistance hot spot is generated in a local area of the nanowire. The current density on both sides of the hot spot increases, and the hot spot area increases to a certain range with the assistance of the current Joule heat. When the current density on both sides of the hot spot exceeds the critical current density of the material, the superconducting state of the absorption area is destroyed, the current on the nanowire decreases, the Joule heat effect weakens, and the hot spot area disappears through the cooling of the nanowire itself and the substrate, and the nanowire returns to the superconducting state. The process of absorbing a photon by the detector is manifested as a rapid rise and then an exponential decay of an electrical pulse on the circuit. By amplifying this pulse signal, an obvious pulse signal can be detected on the external circuit to realize single-photon detection.

[0003] The SNSPD can realize single-photon detection from the visible light band to the infrared band. The coupling efficiency of the detector of the same device design is different for different wave bands. In addition, the SNSPD has polarization sensitivity due to the meander structure of the nanowire. The absorption rate of incident light (TE wave) with the electric field polarization direction parallel to the nanowire is higher than that of incident light (TM wave) with the electric field polarization direction perpendicular to the nanowire. When this polarization sensitivity needs to be utilized (such as polarization measurement of remote sensing imaging and polarization imaging in a scattering medium), it is necessary to increase the ratio of the absorption rate of the TE wave to the absorption rate of the TM wave. When the intensity of light is detected, the polarization sensitivity should be weakened as much as possible. Therefore, in order to meet the actual application requirements of the superconducting nanowire single-photon detector, it is very important to measure the system efficiency of the detector in different wave bands and the system efficiency of the detector in the TE mode and the TM mode. SUMMARY

[0004] The present application aims to improve the system efficiency of the detector in different wave bands and the system efficiency of the detector in the TE mode and the TM mode. The present application provides a spectral response measurement method suitable for a superconducting nanowire single-photon detector and a system thereof.

[0005] Technical solution: A spectral response measurement method suitable for superconducting nanowire single-photon detector, used to calculate the influence of current detector system efficiency on laser wavelength; comprising the following steps:

[0006] The step of constructing an optical circuit capable of adjusting the wavelength and polarization state of incident laser;

[0007] The step of building a readout circuit for reading out the number of response pulses of the detector under different wavelength and polarization conditions;

[0008] By adjusting the optical circuit, the wavelength of the current laser is controlled to be a specified initial wavelength, and the wavelength of the laser coupled to the detector is sequentially increased according to the set step and time interval, and by adjusting the optical circuit, the incident light is adjusted to be a horizontal polarization state, a vertical polarization state, a 45° linear polarization state, and a circular polarization state under each wavelength, while the number of response pulses under the corresponding state is measured;

[0009] The number of response pulses of the detector under different wavelength and polarization conditions is obtained by the readout circuit;

[0010] The number of response pulses is converted into system efficiency to obtain the system efficiency of the detector under horizontal polarization light, vertical polarization light, 45° linear polarization light, and circular polarization light incident conditions;

[0011] Based on the system efficiency of the detector under horizontal polarization light, vertical polarization light, 45° linear polarization light, and circular polarization light incident conditions, the system efficiency of the detector under TE mode and TM mode is obtained.

[0012] The optical circuit includes a tunable laser, a fixed attenuator, a polarization synthesizer, a beam splitter, an optical power meter, an adjustable attenuator, and a counter; the emitted laser of the tunable laser passes through the fixed optical attenuator and the polarization synthesizer, and is divided into two beams by the beam splitter, one of which is connected to the optical power meter, and the other is attenuated by the adjustable attenuator and used as the input laser of the detector.

[0013] The readout circuit includes a T-type biasing device and a radio frequency amplifier; the output end of the detector is connected to the radio frequency and direct current port of the T-type biasing device, the direct current biasing port of the T-type biasing device is connected to a biasing circuit for providing a constant current bias to the detector, and the radio frequency port of the T-type biasing device is connected to the radio frequency amplifier; the output end of the radio frequency amplifier is connected to the counter;

[0014] The measurement steps of the spectral response measurement include:

[0015] Control the biasing circuit to place the detector in a state below its critical current;

[0016] Based on the parameters of the optical power meter and the adjustable attenuator, the optical power of the tunable laser is controlled so that the laser coupled to the detector is at the single-photon level. The current laser wavelength is controlled to be the specified initial wavelength, and the wavelength of the laser coupled to the detector is sequentially increased according to the set step size and time interval.

[0017] The polarization synthesizer is controlled to modulate the input laser into horizontally polarized light, vertically polarized light, 45° linearly polarized light, and circularly polarized light at each wavelength.

[0018] In each time interval, the number of response pulses from the RF amplifier is read from the counter;

[0019] Convert the number of response pulses into system efficiency;

[0020] Repeat the above steps until the wavelength reaches the final wavelength;

[0021] The system efficiency of the detector was obtained under incident conditions of horizontally polarized light, vertically polarized light, 45° linearly polarized light, and circularly polarized light.

[0022] Based on the system efficiency of the detector under incident conditions of horizontally polarized light, vertically polarized light, 45° linearly polarized light, and circularly polarized light, the system efficiency of the detector in TE mode and TM mode is obtained.

[0023] This invention automatically modulates the polarization state according to instructions at each wavelength, and the system efficiency under four conditions can be obtained in a single measurement.

[0024] Furthermore, the bias circuit is formed by connecting a bias resistor and an adjustable voltage source in series. By controlling the adjustable voltage source, the detector is placed in a state below its critical current.

[0025] Furthermore, according to formula (1), the number of response pulses is converted into system efficiency:

[0026] SDE=N P / (P in / hv) (1)

[0027] In the formula, P in P is the incident light power. in / hv is the number of photons, N P SDE represents the system efficiency, which is the number of response pulses.

[0028] Furthermore, the measurement steps for the spectral response measurement also include: obtaining the system efficiency of the detector in TE mode and TM mode; specifically including:

[0029] Let Q be the system efficiency of the detector under the incident conditions of horizontally polarized light, vertically polarized light, 45° linearly polarized light, and circularly polarized light. 0° Q90° , Q 45° , Q c , the system efficiency of the detector under the TE mode and TM mode is Q TE , Q TM , then:

[0030] Q TE +Q TM =Q 0° +Q 90° (2)

[0031]

[0032] The system efficiency of the detector under the TE mode and TM mode can be obtained.

[0033] The application further discloses a spectral response measurement system suitable for a superconducting nanowire single-photon detector, which is used for calculating the influence of a current detector system efficiency on a laser wavelength; and comprises:

[0034] An optical circuit is used for receiving control instructions from a control computer, controlling the wavelength of laser coupled to the detector, and receiving control instructions from the control computer to sequentially modulate the input laser coupled to the detector into horizontal polarized light, vertical polarized light, 45° linear polarized light and circular polarized light.

[0035] A readout circuit is used for reading the pulse signal of the detector.

[0036] A counter is used for reading the number of pulse signals from the readout circuit.

[0037] The control computer is connected with the optical circuit, the readout circuit and the counter, and is used for controlling the optical circuit, controlling the readout circuit, obtaining the number of pulse signals from the counter, and converting the number of response pulses into the system efficiency of the detector under the horizontal polarized light / vertical polarized light / 45° linear polarized light / circular polarized light incident condition, and obtaining the system efficiency of the detector under the TE mode and TM mode based on the system efficiency of the detector under the horizontal polarized light, vertical polarized light, 45° linear polarized light and circular polarized light incident condition.

[0038] Further, the optical circuit is composed of the following optical instruments:

[0039] The optical instruments comprise a tunable laser, a fixed attenuator, a polarization synthesizer, a beam splitter, an optical power meter, an adjustable attenuator and a counter; the emitted laser of the tunable laser is divided into two beams by the beam splitter after passing through the fixed optical attenuator and the polarization synthesizer, one of the two beams is connected to the optical power meter, and the other beam is attenuated by the adjustable attenuator and used as the input laser of the detector.

[0040] Further, the readout circuit comprises a T-type biasing device and a radio frequency amplifier; the output of the detector is connected to the radio frequency and direct current ports of the T-type biasing device, the direct current biasing port of the T-type biasing device is connected to a biasing loop for providing constant current biasing to the detector, and the radio frequency port of the T-type biasing device is connected to the radio frequency amplifier; the output of the radio frequency amplifier is connected to the counter.

[0041] Further, the biasing loop is obtained by connecting a biasing resistor and an adjustable voltage source in series.

[0042] Further, the control computer comprises a polarization control module, a spectral scanning module, a response counting module and a system efficiency calculation module.

[0043] The polarization synthesizer in the optical loop is connected to the polarization control module, and is used to modulate the input laser into horizontal polarization light / vertical polarization light / 45° linear polarization light / circular polarization light according to the control command of the polarization control module.

[0044] The tunable laser in the optical loop is connected to the spectral scanning module, and is used to control the optical power of the tunable laser according to the control command of the spectral scanning module, so that the laser coupled to the detector is single-photon level, the current laser wavelength is a specified initial wavelength, and the wavelength of the laser coupled to the detector is sequentially increased according to the set step and time interval.

[0045] The counter is connected to the response counting module, and is used to record the number of response pulses in each time interval according to the control command of the response counting module.

[0046] The system efficiency calculation module is used to convert the number of response pulses into the system efficiency of the detector under the incident conditions of horizontal polarization light / vertical polarization light / 45° linear polarization light / circular polarization light according to formula (1):

[0047] SDE = N P / (P in / hv) (1)

[0048] In the formula, P in is the incident optical power, P in / hv is the number of photons, N P is the number of response pulses, and SDE is the system efficiency.

[0049] Further, the system efficiency calculation module further comprises calculation for obtaining the system efficiency of the detector under TE mode and TM mode according to the system efficiency of the detector under the incident conditions of horizontal polarization light / vertical polarization light / 45° linear polarization light / circular polarization light.

[0050] Let the system efficiency of the detector under the incident conditions of horizontal polarization light, vertical polarization light, 45° linear polarization light and circular polarization light be Q0° , Q 90° , Q 45° , Q c , the system efficiency of the detector under the TE mode and TM mode is Q TE , Q TM , then:

[0051] Q TE +Q TM =Q 0° +Q 90° (2)

[0052]

[0053] The system efficiency of the detector under the TE mode and TM mode can be obtained.

[0054] Compared with the prior art, the present application has the following advantages:

[0055] The conventional polarization controller mainly changes the polarization state through rotation and extrusion, and the adjustment speed is slow, and with the change of the transmission distance of light in the optical fiber and the change of the wavelength, the polarization state of the output light also changes, and the polarization stability is poor, which will seriously affect the accuracy of the measurement experiment, the present application can obtain the system efficiency of the detector under the TE mode and TM mode through the system efficiency of the input laser under the horizontal polarization state, the vertical polarization state, the 45° linear polarization state and the circular polarization state, avoid the influence of the wavelength change on the polarization state, and improve the measurement accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 is the conceptual model diagram of the present application;

[0057] Figure 2 is the system scanning result, the horizontal coordinate is the wavelength, the unit is nm, and the vertical coordinate is the system efficiency SDE, the square curve in the figure is the single photon efficiency curve of the SNSPD device of the present application under the TE mode scanning in the 1490-1640nm wavelength band, and the circular curve is the single photon efficiency curve of the SNSPD device of the present application under the TE mode scanning in the 1490-1640nm wavelength band;

[0058] Figure 3 is the SNSPD spectral scanning measurement program front panel suitable for the example, and the selected area is the wavelength scanning setting area. DETAILED DESCRIPTION

[0059] The technical scheme of the present application will be further described in combination with the drawings.

[0060] As Figure 1As shown, a spectral response measurement method suitable for a superconducting nanowire single-photon detector of the present application mainly comprises: a control computer controlled based on a SNSPD spectral scanning measurement program, an optical instrument part and a circuit part.

[0061] The optical instrument part comprises a tunable laser, a fixed attenuator, a polarization synthesizer, a beam splitter, an optical power meter and an adjustable attenuator; the circuit part comprises a readout circuit and a counter; the tunable laser emits laser light, which is split into two beams by the beam splitter after passing through the fixed optical attenuator and the polarization synthesizer, one of the two beams is connected to the optical power meter, and the other beam is attenuated by the adjustable attenuator and then transmitted to the detector in the low-temperature device by an optical fiber, i.e., the input signal of the detector is transmitted to the low-temperature environment by the optical fiber, and the output signal of the detector is transmitted out by a coaxial cable and then read out by the superconducting nanowire single-photon detector readout circuit and transmitted to the counter.

[0062] The components involved in the present application will be further described. The tunable laser is a continuous laser, and the tunable laser is connected to the control computer by a LAN Interface and is controlled by the SNSPD spectral scanning measurement program to output, and the output laser is transmitted to the fixed attenuator by a polarization maintaining optical fiber for first-stage attenuation.

[0063] The polarization synthesizer comprises a lithium niobate high-speed polarization controller, a polarization analyzer and a microcontroller driving circuit. The polarization synthesizer receives the laser light from the fixed attenuator by a polarization maintaining optical fiber, modulates the polarization, and provides a stable state of polarization (SOP). The polarization synthesizer is connected to the control computer by a USB Interface, and the polarization modulation state is controlled by the SNSPD spectral scanning measurement program.

[0064] The beam splitter receives the modulated laser light, divides the input laser light into two beams, one of which is connected to the optical power meter by an optical fiber, and the other of which is connected to the adjustable attenuator. The adjustable attenuator attenuates the received laser light according to the power measured by the optical power meter, and couples the attenuated laser light to the detector through the optical fiber interface of the low-temperature device.

[0065] The detector receives the optical signal from the optical circuit through the optical fiber interface of the cryogenic device, and is connected to the superconducting nanowire single-photon detector readout circuit through the coaxial cable interface of the cryogenic device; wherein the superconducting nanowire single-photon detector readout circuit is composed of a direct current bias circuit and a radio frequency amplification circuit. The direct current bias circuit includes a T-type bias device, a bias resistor and an adjustable voltage source; the radio frequency amplification circuit includes a radio frequency amplifier; the coaxial cable interface of the cryogenic device is connected to the radio frequency and direct current port (RF+DC) of the T-type bias device, the direct current bias port (DC) is connected to the 100KΩ bias resistor and the adjustable voltage source, which provides a constant current bias for the detector, the radio frequency port (RF) is connected to the radio frequency amplifier, and the output end of the radio frequency amplifier is connected to the counter through the coaxial line. The adjustable voltage source is connected to the control computer through the GPIB interface and is controlled by the SNSPD spectrum scanning measurement program, and the voltage output is adjusted according to the critical current of the detector.

[0066] The counter is connected to the control computer through the GPIB interface and is controlled by the SNSPD spectrum scanning measurement program, and the number of response pulses from the radio frequency amplifier is read out.

[0067] The above-mentioned SNSPD spectrum scanning measurement program comprises:

[0068] Firstly, the adjustable voltage source is controlled to provide a constant bias current, and the detector is placed in a state slightly lower than its critical current;

[0069] The polarization synthesizer is controlled to modulate the input laser into horizontal polarized light, vertical polarized light, 45° linear polarized light and circular polarized light in turn, the tunable laser power is controlled according to the optical power meter and the attenuator parameters, so that the laser coupled to the detector is single-photon level, and the incident light wavelength is gradually changed.

[0070] At the same time, the number of response pulses from the detector is read from the counter, and the influence of the current detector system efficiency on the laser wavelength is calculated.

[0071] Embodiment:

[0072] Take the superconducting nanowire single-photon detector installed in the G-M refrigerator as an example, introduce the process of circuit building and spectral response measurement. First, use the polarization maintaining optical fiber to connect the output end of the tunable laser to the input end of the fixed attenuator, and the output end of the fixed attenuator is connected to the input end of the polarization synthesizer through the polarization maintaining optical fiber. The tunable laser can be selected from Keysight N7778C. The polarization synthesizer can be selected from Keysight N7786B. Connect the merging port of the beam splitter to the output end of the polarization synthesizer, connect the first beam port of the beam splitter to the optical power meter, and connect the second beam port to the input end of the adjustable attenuator. The output end of the adjustable attenuator is connected to the fiber interface of the refrigeration device through a single-mode optical fiber, and the other end of the optical fiber has been coupled to the SNSPD chip. The adjustable attenuator can be selected from EXFO FVA-600 variable attenuator.

[0073] After the optical instrument is installed, the readout circuit part is installed. First, connect the radio frequency and direct current common port of the T-type biasing device to the coaxial interface of the refrigeration device, and the other end of the coaxial interface has been connected to the SNSPD chip. The radio frequency output port of the T-type biasing device is connected to the radio frequency amplifier, which can be selected from Miteq AM-1309. The output end of the radio frequency amplifier is connected to the counter for counting the response signal, or connected to the oscilloscope to record the response waveform. An external voltage stabilizing power supply is used to provide power bias for the radio frequency amplifier. The direct current bias port of the T-type biasing device is connected to the biasing circuit, which is composed of a 100KΩ resistor and a voltage source in series. The voltage source can be selected from Keithley SourceMeter 2400.

[0074] The tunable laser, polarization synthesizer, voltage source and counter are connected to the control computer through their respective interfaces, and the output is controlled by the SNSPD spectral scanning measurement program.

[0075] The control program is divided into polarization control module, spectral scanning module and response counting module.

[0076] First, the initial wavelength, step and cutoff wavelength of this scan can be set, such as Figure 3, the spectral scanning module controls the current output laser wavelength to be the specified initial wavelength, and sequentially increases according to the set step and time interval, at the current wavelength, the polarization control module modulates the polarization state, and sequentially modulates the input laser into horizontal polarized light, vertical polarized light, 45° linear polarized light and circular polarized light, at the same time, the response counting module records the number of response pulses under four polarization states in each time interval, and converts it into system efficiency according to formula (1), and obtains the system efficiency of the SNSPD chip under TE mode and TM mode at the current wavelength according to formula (2), and displays the current data point on the front panel X-Y graph, repeats the above steps until the wavelength is the termination wavelength, at this time, the X-Y graph displays the system efficiency of the SNSPD chip under TE mode and TM mode, such as Figure 2 , and automatically saves the current scanning results, and saves the image and data as BMP image and txt text respectively.

[0077] Wherein, the X-Y graph horizontal coordinate is wavelength λ, unit is nm, and the vertical coordinate is system efficiency (SDE, system detection efficiency).

[0078] Let the incident light power be P in , the corresponding photon number is P in / hv, and the number of generated electric pulses is N P , then:

[0079] SDE=N P / (P in / hv) (1)

[0080] Let the system efficiency of the SNSPD chip under the conditions of horizontal polarized light, vertical polarized light, 45° linear polarized light and circular polarized light be Q 0° , Q 90° , Q 45° , Q c , and the system efficiency of the SNSPD chip under TE mode and TM mode be Q TE , Q TM , then:

[0081] Q TE +Q TM =Q 0° +Q 90° (2)

[0082]

[0083] After the above measurement is completed, the system efficiency-wavelength curve of the SNSPD chip under TE mode and TM mode can be obtained.

Claims

1. A method of spectral response measurement suitable for superconducting nanowire single-photon detectors for calculating the effect of the wavelength of the laser light on the current detector system efficiency; characterized in that: The method comprises the following steps: a step of constructing an optical circuit capable of adjusting the wavelength and polarization state of incident laser; a step of building a readout circuit for reading out the number of response pulses of the detector under different wavelength and polarization conditions; by adjusting the optical circuit, the wavelength of the current laser is controlled to be a specified initial wavelength, and the wavelength of the laser coupled to the detector is sequentially increased in a set step and time interval, and by adjusting the optical circuit, the incident light is sequentially adjusted to be a horizontal polarization state, a vertical polarization state, a 45° linear polarization state, and a circular polarization state under each wavelength, and the number of response pulses under the corresponding state is measured; by the readout circuit, the number of response pulses of the detector under different wavelength and polarization conditions is obtained; the number of response pulses is converted into system efficiency to obtain the system efficiency of the detector under the incident conditions of horizontal polarized light, vertical polarized light, 45° linear polarized light, and circular polarized light; based on the system efficiency of the detector under the incident conditions of horizontal polarized light, vertical polarized light, 45° linear polarized light, and circular polarized light, the system efficiency of the detector under TE mode and TM mode is obtained; the optical circuit comprises a tunable laser, a fixed attenuator, a polarization synthesizer, a beam splitter, an optical power meter, and an adjustable attenuator, and is connected as follows: the emitted laser of the tunable laser passes through the fixed optical attenuator and the polarization synthesizer, is split into two beams by the beam splitter, one beam is connected to the optical power meter, and the other beam is attenuated by the adjustable attenuator and used as the input laser of the detector; by adjusting the optical circuit, the wavelength of the current laser is controlled to be a specified initial wavelength, and the wavelength of the laser coupled to the detector is sequentially increased in a set step and time interval, and by adjusting the optical circuit, the incident light is sequentially adjusted to be a horizontal polarization state, a vertical polarization state, a 45° linear polarization state, and a circular polarization state under each wavelength, and the number of response pulses under the corresponding state is measured; specifically comprising: according to the parameters of the optical power meter and the adjustable attenuator, the optical power of the tunable laser is controlled so that the laser coupled to the detector is single-photon level, the wavelength of the current laser is controlled to be a specified initial wavelength, and the wavelength of the laser coupled to the detector is sequentially increased in a set step and time interval; the polarization synthesizer is controlled to modulate the input laser to be horizontal polarized light, vertical polarized light, 45° linear polarized light, and circular polarized light under each wavelength; according to formula (1), the number of response pulses is converted into system efficiency: SDE = N P / (P in / hv) (1) where P is the incident optical power, in P is the incident optical power, in N is the number of photons, P SDE is the system efficiency; the system efficiency of the detector under TE mode and TM mode is obtained based on the system efficiency of the detector under the incident conditions of horizontal polarized light, vertical polarized light, 45° linear polarized light, and circular polarized light; specifically comprising: The system efficiency of the detector under the incident conditions of horizontal polarized light, vertical polarized light, 45° linear polarized light and circular polarized light is Q 0° , Q 90° , Q 45° , Q c , and the system efficiency of the detector under the TE mode and TM mode is Q TE , Q TM , and the following equation is established: Q TE +Q TM =Q 0° +Q 90° (2) the system efficiency of the detector under TE mode and TM mode is obtained.

2. The method of claim 1, wherein the method is applied to a superconducting nanowire single-photon detector. The readout circuit comprises a T-type biasing device and a radio frequency amplifier; the output end of the detector is connected with the radio frequency and direct current port of the T-type biasing device, the direct current biasing port of the T-type biasing device is connected with a biasing loop for providing constant current biasing for the detector, and the radio frequency port of the T-type biasing device is connected with the radio frequency amplifier; the output end of the radio frequency amplifier is connected with a counter, and the counter is used for reading the number of response pulses of the detector under different wavelength and polarization conditions.

3. The method of claim 2, wherein the method is applied to a superconducting nanowire single-photon detector. The biasing loop is obtained by connecting the biasing resistor and the adjustable voltage source in series, and the detector is placed in a state below the critical current by controlling the adjustable voltage source.

4. A spectral response measurement system suitable for superconducting nanowire single-photon detectors for calculating the effect of the wavelength of the laser light on the current detector system efficiency; characterized in that: It comprises: an optical loop for receiving control instructions from a control computer, controlling the wavelength of the laser coupled to the detector, and receiving control instructions from the control computer to sequentially modulate the input laser coupled to the detector into horizontal polarization light, vertical polarization light, 45° linear polarization light and circular polarization light; a readout circuit for reading the pulse signal of the detector; a counter for reading the number of pulse signals from the readout circuit; a control computer connected with the optical loop, the readout circuit and the counter, for controlling the optical loop, controlling the readout circuit, obtaining the number of pulse signals from the counter, and converting the number of response pulses into the system efficiency of the detector under the conditions of horizontal polarization light, vertical polarization light, 45° linear polarization light and circular polarization light, and obtaining the system efficiency of the detector under the TE mode and TM mode based on the system efficiency of the detector under the conditions of horizontal polarization light, vertical polarization light, 45° linear polarization light and circular polarization light; The control computer comprises a polarization control module, a spectral scanning module, a response counting module and a system efficiency calculation module; The polarization synthesizer in the optical loop is connected with the polarization control module, and is used for modulating the input laser into horizontal polarization light / vertical polarization light / 45° linear polarization light / circular polarization light according to the control command of the polarization control module; The tunable laser in the optical loop is connected with the spectral scanning module, and is used for controlling the optical power of the tunable laser according to the control command of the spectral scanning module, so that the laser coupled to the detector is single-photon level, the current wavelength of the laser is set as a specified initial wavelength, and the wavelength of the laser coupled to the detector is sequentially increased according to the set step and time interval; The counter is connected with the response counting module, and is used for recording the number of response pulses in each time interval according to the control command of the response counting module; The system efficiency calculation module is used for converting the number of response pulses into the system efficiency of the detector under the conditions of horizontal polarization light / vertical polarization light / 45° linear polarization light / circular polarization light according to formula (1): SDE = N P / (P in / hv) (1) where P is the incident optical power, in P is the incident optical power, in N is the number of photons, P SDE is the system efficiency; The system efficiency calculation module further comprises a calculation for obtaining the system efficiency of the detector under the TE mode and TM mode based on the system efficiency of the detector under the conditions of horizontal polarization light, vertical polarization light, 45° linear polarization light and circular polarization light: Let Q be the system efficiency of the detector under the incident conditions of horizontally polarized light, vertically polarized light, 45° linearly polarized light, and circularly polarized light. 0° Q 90° Q 45° Q c The system efficiencies of the detector in TE mode and TM mode are Q, respectively. TE Q TM Then we have: Q TE +Q TM =Q 0° +Q 90° (2) The system efficiency of the detector under the TE mode and TM mode can be obtained.

5. The spectral response measurement system for superconducting nanowire single-photon detectors according to claim 4, characterized in that: The optical loop is composed of the following optical instruments connected together: The optical instrument comprises a tunable laser, a fixed attenuator, a polarization synthesizer, a beam splitter, an optical power meter, an adjustable attenuator and a counter; the tunable laser emits laser light, which passes through the fixed optical attenuator and the polarization synthesizer, is split into two beams by the beam splitter, one of the two beams is connected to the optical power meter, and the other beam is attenuated by the adjustable attenuator and used as input laser light of the detector. The readout circuit comprises a T-type biasing device and a radio frequency amplifier; an output end of the detector is connected to radio frequency and direct current ports of the T-type biasing device, a direct current biasing port of the T-type biasing device is connected to a biasing loop for providing a constant current bias for the detector, and a radio frequency port of the T-type biasing device is connected to the radio frequency amplifier; and an output end of the radio frequency amplifier is connected to the counter.

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