CN113310574B - Superconducting single photon detector detection efficiency testing device and method - Google Patents
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Abstract
The invention provides a detection efficiency measuring device and method of a superconducting single photon detector, wherein the device consists of a wide spectrum relative detection efficiency measuring system and an absolute detection efficiency measuring system under a special wavelength point. The measurement method comprises the steps of firstly, completing the broadband relative detection efficiency measurement of the superconducting single-photon detector under a specific polarization condition, and obtaining a relative detection efficiency curve; and then, measuring the absolute detection efficiency of a plurality of special wavelength points under the same polarization condition, and correcting a relative detection efficiency curve by using the absolute detection efficiency of the wavelength points, thereby realizing the accurate measurement of the broadband absolute detection efficiency under the specific polarization condition. The method is simple and quick, and is used for realizing absolute measurement of the detection efficiency of the superconducting single-photon detector in a wide spectral range; meanwhile, the detection efficiency of the superconducting single-photon detector is measured under different incident light polarization states.
Description
Technical Field
The invention belongs to the technical field of single photon detection, and particularly relates to a device and a method for testing the detection efficiency of a superconducting single photon detector.
Background
The development of quantum information technology represented by quantum communication, quantum computation and quantum precision measurement does not leave the effective support of various extreme sensitivity detectors. The single photon detection technology as an ultimate sensitivity optical signal measurement technology has become one of the indispensable key core technologies for the development of the technical field of quantum information. The single photon detectors widely applied in ultraviolet-visible light wave band at present mainly comprise photomultiplier tubes and avalanche photodiodes based on silicon materials. The near-infrared band single photon detector is mainly an avalanche photodiode made of InGaAs material, but indexes such as detection efficiency, time jitter and the like are far from those of a visible band single photon detector, so that various superconducting single photon detectors working in an infrared band are rapidly developed and applied under the background, wherein the superconducting nanowire single photon detector, the superconducting conversion edge single photon detector and the like are representative. Compared with a superconducting conversion edge single-photon detector, the superconducting nanowire single-photon detector has the advantages of higher counting rate, low requirement on the lowest working temperature, relatively compact system device and wide application in engineering application fields such as quantum radar and quantum secret communication.
The detection efficiency is taken as the most core technical index of the superconducting single photon detector, and how to accurately calibrate the detection efficiency is a research hotspot in the world at present, and particularly, the detection efficiency measurement under a wide band is a research difficulty. At present, the detection efficiency of a single photon detector is measured by a standard detector method and a related photon method internationally, the detector method traces the detection efficiency to the current optical power reference low-temperature radiometer, the related photon method is an absolute calibration method and does not need to trace the source of a measurement value, but the two methods have certain defects in the aspect of measuring the broadband detection efficiency. In addition, the chip structure of the superconducting nanowire single photon detector determines that the detection efficiency of the superconducting nanowire single photon detector has strong correlation with the polarization state of incident light, and the application of the superconducting nanowire single photon detector in various specific fields is limited by taking the polarization sensitivity as the intrinsic characteristic, so that the detection efficiency of the superconducting nanowire single photon detector in different polarization states needs to be accurately calibrated, and the application development of the type of single photon detector and the quantum information technology is promoted.
The existing method for testing and calibrating the detection efficiency of the superconducting single-photon detector has the following defects: (1) the detection efficiency measuring device under the broadband is complex and has low precision. The single-photon detector detection efficiency testing method based on the standard detector can realize detection efficiency measurement under a broadband condition, but due to the long tracing link, the difference between the working dynamic range of the standard detector and the working dynamic range of the single-photon detector is large, and the absolute light attenuation cannot be accurately measured, so that the final detection efficiency measurement precision is low; the single photon detector detection efficiency test method based on the standard detector can realize accurate measurement of detection efficiency under specific wavelength, but due to the limitation of a parametric down-conversion mechanism and the optical characteristics of the nonlinear crystal, the detection efficiency measurement under the broadband condition is difficult to realize. (2) The influence of the polarization state on the detection efficiency is not considered, and the detection result cannot accurately reflect the polarization sensitivity of the superconducting single-photon detector.
Disclosure of Invention
Aiming at the defects of the existing single-photon detector detection efficiency testing method and device, the invention mainly solves the technical problems of rapid and accurate testing of superconducting single-photon detector detection efficiency under the condition of a wide waveband, polarization sensitivity characteristic testing of the superconducting single-photon detector detection efficiency and the like. Aiming at the defects of the prior art, the invention provides a device and a method for testing the detection efficiency of a superconducting single-photon detector, and the method is simple, convenient and quick and is used for realizing absolute measurement of the detection efficiency of the superconducting single-photon detector in a wide spectral range; meanwhile, the detection efficiency of the superconducting single photon detector under different incident light polarization states is measured.
The technical scheme of the invention is as follows: a detection efficiency testing device of a superconducting single photon detector comprises a wide spectrum relative detection efficiency measuring system and an absolute detection efficiency measuring system under a special wavelength point; the broad spectrum relative detection efficiency measurement system comprises: the device comprises a wide-spectrum laser light source, a monochromatic system, a light beam collimation system, an optical gate, a polarization modulation system, a semi-transparent and semi-reflective mirror, a monitoring detector, a standard detector, a diaphragm, a filter wheel, a linear gradient filter, a lens, a superconducting single-photon detector, a counter, a computer and a polarization maintaining optical fiber; the wide-spectrum laser emitted by the wide-spectrum laser light source is subjected to monochromatic splitting by a monochromatic system and then outputs monochromatic laser with a certain divergence angle, and the monochromatic laser is shaped by a light beam collimation system and then is converted into a collimated light beam; under the condition that the optical shutter is opened, the monochromatic laser sequentially passes through the optical shutter and the diaphragm and then enters a polarization modulation system, and the monochromatic laser with a specific polarization direction is output after polarization modulation; the laser after polarization modulation is divided into two paths according to a specific proportion by a semi-transparent semi-reflecting mirror, one path enters a monitoring detector and is used for monitoring laser power fluctuation, the other path passes through a light filter arranged on a light filter wheel, a linear gradient light filter and a plurality of diaphragms, then the laser power is attenuated to a single photon magnitude, the attenuated laser is converged and coupled into a polarization maintaining optical fiber through a lens and is transmitted to a superconducting single photon detector through the optical fiber, and a pulse signal of the superconducting single photon detector is screened and extracted by a counter and then is transmitted to a computer for data processing; the absolute detection efficiency measuring system includes: the device comprises a polarization modulation system, a lens, a superconducting single-photon detector, a counter, a computer, a pumping light source, a polarizer, a wave plate, a reflector, a nonlinear crystal, a dichroic mirror, a filter wheel, a long-wavelength-pass filter, a dichroic beam splitter, a single-photon detector, a coincidence measurement system and a polarization maintaining optical fiber; pumping laser emitted by a pumping light source firstly enters a polarizer and a wave plate for polarization modulation, the polarized and modulated pumping light is converted by a reflector and then is coupled into a nonlinear crystal through a lens for parametric down-conversion to generate two paths of collinear related photons, and the related photons are further shaped into collimated light through the lens; after passing through a dichroic mirror, a long-wave pass filter and a dichroic mirror, the collimated related photons filter residual pump photons in the related photons; the filtered related photons are divided into two paths according to the wavelength by a dichroic beam splitter, one path of the photons enters a single photon detector after being converged by a lens, filtered by a long-wave pass filter and a filter in a filter wheel, and the other path of the photons enters a superconducting single photon detector after being subjected to polarization modulation by a polarization modulation system and filtered by the lens-converged long-wave pass filter and the filter in the filter wheel; counting signals of the single-photon detector and the superconducting single-photon detector are accessed to a coincidence measurement system for coincidence test, and the coincidence test signals are accessed to a computer for absolute detection efficiency analysis of the superconducting single-photon detector.
In the device, the wavelength range of the wide-spectrum laser light source in the wide-spectrum relative detection efficiency measurement system covers the working wavelength range of the superconducting single-photon detector, and the pulse light source or the continuous output light source is selected according to the working mode of the superconducting single-photon detector.
In the device, the wide-spectrum laser light source in the wide-spectrum relative detection efficiency measurement system is an LDLS type wide-spectrum light source; the monitoring detector and the calibration detector in the broad spectrum relative detection efficiency measuring system both select the trap detector with corresponding working wavelength and are calibrated through relative spectrum response.
In the device, the filter wheel and the two groups of linear gradient filters in the wide-spectrum relative detection efficiency measurement system form a strong light attenuation system, and the same standard detector is required to measure the transmittance of the strong light attenuation system under the specific wavelength and polarization state in each detection efficiency test process.
In the device, the wavelength and the working mode of a pump light source in the absolute detection efficiency measuring system need to be matched with a calibration wavelength and the working mode of a superconducting single-photon detector; the nonlinear crystal in the absolute detection efficiency measurement system needs to perform special selection on the parameters of period and phase matching angle according to the calibration wavelength, is used for realizing collinear output of related photons and performs crystal switching according to the calibration wavelength; the working mode of the single-photon detector in the absolute detection efficiency measuring system needs to be matched with a superconducting single-photon detector, and the single-photon detector is a superconducting type single-photon detector or an APD type non-superconducting single-photon detector.
A method for testing the detection efficiency of a superconducting single photon detector comprises the following steps:
step A: firstly, measuring the broadband relative detection efficiency of the superconducting single-photon detector under a specific polarization condition to obtain a relative detection efficiency curve;
and B: and then, measuring the absolute detection efficiency under a plurality of special wavelength points under the same polarization condition, and correcting a relative detection efficiency curve by using the absolute detection efficiency under the wavelength points, thereby realizing the accurate measurement of the broadband absolute detection efficiency under the specific polarization condition.
In the above method, in the step a, the method for obtaining the relative detection efficiency curve includes the following steps:
step 1, completing the construction of a relative detection efficiency measurement system, and setting the wavelength lambda of a monochromatic systemiOpening the optical gate and setting the polarization direction theta of the calibration light pathi；
step 4, testing and recording the optical power before the light attenuation by using a standard detector
Testing and recording optical power before optical attenuation using a monitor probe
Step 5, opening the superconducting single-photon detector, and simultaneously reading and recording the reading of the superconducting single-photon detector
Monitoring detector readings
Step 6, calculating the wavelength lambdaiDirection of polarization θiRelative detection efficiency of superconducting single photon detector under conditions
Equation (1) is as follows:
in the above-mentioned formula, the compound has the following structure,
at a wavelength of λiThe energy of the single photon of (2),
h is the Planck constant, c is the speed of light;
step 7, adjusting the polarization direction theta of the incident lightjObtaining a relative detection efficiency curve of the superconducting single-photon detector under all polarization states of the wavelength;
step 9, obtaining the optimal polarization direction theta of the superconducting single photon detectormaxRelative detection efficiency versus wavelength curve of (b).
In the method, in the step B, the method for measuring absolute detection efficiency includes the following steps:
step 21, completing the construction of an absolute detection efficiency measuring system, and selecting and switching different nonlinear crystals according to different calibration wavelength points;
step 23, obtaining the optimal polarization direction theta according to the test in the relative detection efficiency test process of the superconducting single photon detectormaxSetting the polarization direction of the related photon coupled into the superconducting single photon detector as thetamax；
in the above formula, McoincTo match the count value, M2The count value of the other path of single photon detector;
and 25, taking the absolute detection efficiency at the wavelength point as a reference, and performing up-and-down translation on the relative detection efficiency curve of the superconducting single-photon detector to obtain an absolute detection efficiency curve of the superconducting single-photon detector.
In the above method, after step 24, the method further sets up the correction of the coincidence measurement result, and deducts the influence of the light path transmittance and the factors in coincidence measurement process, such as coincidence gate width, dead time, back pulse, coincidence missing, and accidental coincidence setting, on the test result.
In the method, before step 21, that is, before absolute detection efficiency calibration is performed, the transmittance measurement of two paths of related photons in an optical system needs to be completed; and the polarization direction of the relevant photons needs to be set to be consistent with the polarization direction of incident light in the process of calibrating relative detection efficiency.
Compared with the prior art, the invention has the beneficial effects that: (1) compared with the traditional superconducting single-photon detector detection efficiency test method, the method based on the combination of the relative detection efficiency of the broad spectrum and the absolute detection efficiency of the special wavelength point is an absolute test method, the test wavelength range is wider, the precision is higher, and the device and the operation are simpler. (2) The absolute testing device and the testing method for the detection efficiency of the superconducting single-photon detector under different polarization states are innovatively provided, and the change condition of the detection efficiency along with the change of the polarization states can be better reflected.
Drawings
Fig. 1 is a schematic diagram of a relative detection efficiency measurement system according to the present invention.
Fig. 2 is a schematic diagram of an absolute detection efficiency measurement system according to the present invention.
FIG. 3 is a graph of detection efficiency versus polarization angle of incident light in accordance with the present invention.
FIG. 4 is a graph of detection efficiency as a function of wavelength for the present invention.
Detailed Description
In order to facilitate an understanding of the invention, reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The invention provides a device and a method for testing the detection efficiency and the polarization sensitivity characteristic of a broadband superconducting single photon detector, aiming at the problems of narrow test wavelength range, low precision, lack of polarization sensitivity characteristic test capability and the like of the conventional superconducting single photon detector detection efficiency measurement method.
Example one
In order to solve the technical problems, the invention provides a detection efficiency measuring device of a superconducting single photon detector, which consists of a wide-spectrum relative detection efficiency measuring system and an absolute detection efficiency measuring system under a special wavelength point.
(1) Relative detection efficiency measuring system
A schematic diagram of a relative detection efficiency measurement system, as shown in fig. 1, includes: the device comprises a wide-spectrum laser light source 1, a monochromatic system 2, a light beam collimation system 3, an optical gate 4, a polarization modulation system 5, a half-transmitting and half-reflecting mirror 6, a monitoring detector 7, a standard detector 8, a diaphragm 9, a filter wheel 10, a linear gradient filter 11, a lens 12, a superconducting single-photon detector 13, a counter 14, a computer 15 and a polarization-maintaining optical fiber 26.
The wide-spectrum laser emitted by the wide-spectrum laser light source 1 is subjected to monochromatic splitting by the monochromatic system 2 and then outputs monochromatic laser with a certain divergence angle, and the monochromatic laser is shaped by the light beam collimation system 3 and then is converted into a collimated light beam; under the condition that the optical shutter 4 is opened, the monochromatic laser sequentially passes through the optical shutter 4 and the diaphragm 9 and then enters the polarization modulation system 5, and the monochromatic laser with a specific polarization direction is output after polarization modulation; the laser after polarization modulation is divided into two paths according to a specific proportion by a half-transmitting and half-reflecting mirror 6, one path enters a monitoring detector 7 for monitoring laser power fluctuation, and the other path passes through a light filter arranged on a light filter wheel 10, a linear gradient light filter 11 and a plurality of diaphragms 9, and then the laser power is attenuated to a single photon magnitude (10E6 photons/s magnitude); the attenuated laser is converged and coupled into a polarization maintaining optical fiber 26 through a lens 12, and is transmitted to a superconducting single-photon detector 13 through the optical fiber, and a pulse signal of the superconducting single-photon detector 13 is screened and extracted by a counter 14 and then is transmitted to a computer 15 for data processing. In the above, the measurement of the relative detection efficiency of the superconducting single-photon detector under different wavelengths and different polarization states can be realized by adjusting the output wavelength of the monochromatic system and the polarization modulation system.
In the above, the wavelength range of the wide-spectrum laser light source needs to cover the working wavelength range of the superconducting single-photon detector, and the pulse light source or the continuous output light source is selected according to the working mode of the superconducting single-photon detector;
in the above, the wide-spectrum laser light source may also be LDLS or other types of wide-spectrum light sources;
in the above, the monitoring detector and the calibration detector both select a trap detector with corresponding operating wavelength, and are calibrated through relative spectral response;
in the above, the filter wheel and the two groups of linear gradient filters form a strong light attenuation system, and the same standard detector is required to measure the transmittance of the strong light attenuation system under the specific wavelength and polarization state in each detection efficiency test process;
in the above, the adjustment of the attenuation ratio of the strong light attenuation system can be realized by rotating the filter wheel 10 and moving the linear gradient filter 11;
in the above, in order to reduce the polarization loss in the transmission process of incident light, the incident optical fiber of the superconducting single-photon detector selects a polarization maintaining optical fiber;
in the above, the test system is also suitable for measuring the relative detection efficiency of other non-superconducting single-photon detectors such as APD.
(2) Absolute detection efficiency measuring system
The schematic diagram of the absolute detection efficiency measuring system, as shown in fig. 2, includes: the device comprises a polarization modulation system 5, a lens 12, a superconducting single photon detector 13, a counter 14, a computer 15, a pumping light source 16, a polarizer 17, a wave plate 18, a reflecting mirror 19, a nonlinear crystal 20, a dichroic mirror 21, a filter wheel 10, a long-wave pass filter 22, a dichroic beam splitter 23, a single photon detector 24, a coincidence measurement system 25 and a polarization-maintaining optical fiber 26.
The pump laser emitted by the pump light source 16 firstly enters the polarizer 17 and the wave plate 18 for polarization modulation, the pump light after polarization modulation is converted by the reflector 19 and then coupled into the nonlinear crystal 20 through the lens 12 for parametric down-conversion to generate two paths of collinear related photons, and the related photons are further shaped into collimated light by the lens 12; the collimated related photons pass through a dichroic mirror 21, a long-wave pass filter 22 and the dichroic mirror 21, and then pump photons remaining in the related photons are filtered; the filtered related photons are divided into two paths according to the wavelength by a dichroic beam splitter 23, one path of the photons is converged by a lens 12, filtered by a long-wave pass filter 22 and a filter in a filter wheel 10 and then enters a single photon detector 24, and the other path of the photons is firstly subjected to polarization modulation by a polarization modulation system 5 and then enters a superconducting single photon detector 13 after being converged by the lens 12, filtered by the long-wave pass filter 22 and the filter in the filter wheel 10; counting signals of the single-photon detector 24 and the superconducting single-photon detector 13 are accessed to the coincidence measurement system 25 for coincidence test, and the coincidence test signals are accessed to the computer 15 for absolute detection efficiency analysis of the superconducting single-photon detector 13.
In the above, a large number of pump light photons are still parametric in two paths of related photons generated by the nonlinear crystal;
in the above, the wavelength and the working mode of the pump light source need to be matched with the calibration wavelength and the working mode of the superconducting single photon detector;
in the above, the nonlinear crystal needs to perform special selection and design of parameters such as period, phase matching angle, etc. according to the calibration wavelength, to realize collinear output of related photons, and perform crystal switching according to the calibration wavelength;
the working mode of the single-photon detector is matched with that of the superconducting single-photon detector, and the single-photon detector can be a superconducting single-photon detector or an APD non-superconducting single-photon detector;
in the above, before calibrating the absolute detection efficiency, the transmittance of two paths of related photons in the optical system needs to be measured;
in the above, the polarization direction of the relevant photon needs to be consistent with the polarization direction of the incident light in the calibration process of the relative detection efficiency.
Example two
On the basis of the embodiment, the invention further provides a method for testing the detection efficiency of the superconducting single-photon detector, which comprises the following steps:
step A: firstly, measuring the broadband relative detection efficiency of the superconducting single-photon detector under a specific polarization condition to obtain a relative detection efficiency curve;
and B: and then, measuring the absolute detection efficiency under a plurality of special wavelength points under the same polarization condition, and correcting a relative detection efficiency curve by using the absolute detection efficiency under the wavelength points, thereby realizing the accurate measurement of the broadband absolute detection efficiency under the specific polarization condition.
Further, the following steps:
in the step a, the method for obtaining the relative detection efficiency curve includes the following steps:
step 1, completing the construction of a relative detection efficiency measuring system according to the graph 1, and setting the wavelength lambda of a monochromatic systemiOpening the optical gate and setting the polarization direction theta of the calibration light pathi；
step 4, testing and recording the optical power before the light attenuation by using a standard detector
Testing and recording optical power before optical attenuation using a monitor probe
Step 5, opening the superconducting single-photon detector, and simultaneously reading and recording the reading of the superconducting single-photon detector
Monitoring detector readings
Step 6, calculating the wavelength lambdaiDirection of polarization θiRelative detection efficiency of superconducting single photon detector under conditions
Equation (1) is as follows:
in the above formula, the first and second carbon atoms are,
at a wavelength of λiThe energy of the single photon of (a),
h is the Planck constant, c is the speed of light;
step 7, adjusting the polarization direction theta of the incident lightjAnd obtaining a relative detection efficiency curve of the superconducting single photon detector under all polarization states of the wavelength, as shown in fig. 3.
step 9, obtaining the optimal polarization direction theta of the superconducting single photon detectormaxThe relative detection efficiency versus wavelength curve for the following is shown in fig. 4.
Further, the following steps:
in step B, the method for measuring absolute probe efficiency includes the following steps:
step 21, completing the construction of an absolute detection efficiency measuring system according to the graph shown in fig. 2, and switching different nonlinear crystals according to different selection of calibration wavelength points;
step 23, obtaining the optimal polarization direction theta according to the test in the relative detection efficiency test process of the superconducting single photon detectormaxSetting the polarization direction of the related photon coupled into the superconducting single photon detector as thetamax；
in the above formula, McoincTo match the count value, M2The count value of the other path of single photon detector;
further, in order to improve the measurement accuracy of the absolute detection efficiency of the superconducting single-photon detector, the coincidence measurement result is corrected, the light path transmittance is deducted, and the influence of the coincidence measurement process on the test result, such as coincidence with the gate width, dead time, rear pulse, coincidence loss, accidental coincidence setting and the like, is deducted.
And 25, taking the absolute detection efficiency at the wavelength point as a reference, and translating the relative detection efficiency curve of the superconducting single-photon detector up and down to obtain the absolute detection efficiency curve, as shown in fig. 4.
Compared with the prior art, the invention has the beneficial effects that: (1) compared with the traditional superconducting single-photon detector detection efficiency test method, the method based on the combination of the relative detection efficiency of the broad spectrum and the absolute detection efficiency of the special wavelength point is an absolute test method, the test wavelength range is wider, the precision is higher, and the device and the operation are simpler. (2) The absolute testing device and the testing method for the detection efficiency of the superconducting single-photon detector under different polarization states are innovatively provided, and the change condition of the detection efficiency along with the change of the polarization states can be better reflected.
The technical features mentioned above are combined with each other to form various embodiments which are not listed above, and all of them are regarded as the scope of the present invention described in the specification; further, modifications and variations may be suggested to those skilled in the art in light of the above teachings, and it is intended to cover all such modifications and variations as fall within the scope of the appended claims.
Claims (9)
1. A superconducting single photon detector detection efficiency testing device is characterized by comprising a wide spectrum relative detection efficiency measuring system and an absolute detection efficiency measuring system under a special wavelength point; the broad spectrum relative detection efficiency measurement system comprises: the device comprises a wide-spectrum laser light source, a monochromatic system, a light beam collimation system, an optical gate, a polarization modulation system, a semi-transparent and semi-reflective mirror, a monitoring detector, a standard detector, a diaphragm, a filter wheel, a linear gradient filter, a lens, a superconducting single-photon detector, a counter, a computer and a polarization maintaining optical fiber; the wide-spectrum laser emitted by the wide-spectrum laser light source is subjected to monochromatic splitting by a monochromatic system and then outputs monochromatic laser with a certain divergence angle, and the monochromatic laser is shaped by a light beam collimation system and then is converted into a collimated light beam; under the condition that the optical shutter is opened, the monochromatic laser sequentially passes through the optical shutter and the diaphragm and then enters a polarization modulation system, and the monochromatic laser with a specific polarization direction is output after polarization modulation; the laser after polarization modulation is divided into two paths according to a specific proportion by a semi-transparent semi-reflecting mirror, one path enters a monitoring detector and is used for monitoring laser power fluctuation, the other path passes through a light filter arranged on a light filter wheel, a linear gradient light filter and a plurality of diaphragms, then the laser power is attenuated to a single photon magnitude, the attenuated laser is converged and coupled into a polarization maintaining optical fiber through a lens and is transmitted to a superconducting single photon detector through the optical fiber, and a pulse signal of the superconducting single photon detector is screened and extracted by a counter and then is transmitted to a computer for data processing; the absolute detection efficiency measurement system includes: the device comprises a polarization modulation system, a lens, a superconducting single photon detector, a computer, a pumping light source, a polarizer, a wave plate, a reflector, a nonlinear crystal, a dichroic mirror, a filter wheel, a long-wavelength-pass filter, a dichroic beam splitter, a single photon detector, a coincidence measurement system and polarization-maintaining optical fibers; pumping laser emitted by a pumping light source firstly enters a polarizer and a wave plate for polarization modulation, the polarized and modulated pumping light is converted by a reflector and then is coupled into a nonlinear crystal through a lens for parametric down-conversion to generate two paths of collinear related photons, and the related photons are further shaped into collimated light through the lens; the collimated related photons pass through a dichroic mirror, a long-wave pass filter and the dichroic mirror, and then pump photons remained in the related photons are filtered; the filtered related photons are divided into two paths according to the wavelength by a dichroic beam splitter, one path of the photons enters a single photon detector after being converged by a lens, filtered by a long-wave pass filter and a filter in a filter wheel, and the other path of the photons enters a superconducting single photon detector after being subjected to polarization modulation by a polarization modulation system and filtered by the lens, the long-wave pass filter and the filter in the filter wheel; counting signals of the single-photon detector and the superconducting single-photon detector are accessed to a coincidence measurement system for coincidence test, and the coincidence test signals are accessed to a computer for absolute detection efficiency analysis of the superconducting single-photon detector.
2. The test apparatus of claim 1 wherein the wide spectrum laser light source in the wide spectrum relative detection efficiency measurement system has a wavelength range that covers the operating wavelength range of the superconducting single photon detector and selects either the pulsed light source or the continuous output light source depending on the operating mode of the superconducting single photon detector.
3. The test apparatus as claimed in claim 1, wherein the broad spectrum laser light source in the broad spectrum relative detection efficiency measurement system is an LDLS type broad spectrum light source; the monitoring detector and the calibration detector in the broad spectrum relative detection efficiency measuring system both select the trap detector with corresponding working wavelength and are calibrated through relative spectrum response.
4. The test apparatus as claimed in claim 1, wherein the filter wheel and the two sets of linear graduated filters in the broad spectrum relative detection efficiency measurement system form a strong light attenuation system, and the transmittance of the strong light attenuation system is measured by using the same standard detector during each detection efficiency test.
5. The test apparatus of claim 1, wherein the wavelength and the operation mode of the pump light source in the absolute detection efficiency measurement system need to match the user-selected calibration wavelength and the operation mode of the superconducting single photon detector; the nonlinear crystal in the absolute detection efficiency measuring system needs to perform special selection on parameters of period and phase matching angles according to calibration wavelength, is used for realizing collinear output of related photons, and performs crystal switching according to the calibration wavelength; the working mode of the single-photon detector in the absolute detection efficiency measuring system needs to be matched with that of a superconducting single-photon detector, and the single-photon detector is a superconducting type single-photon detector or an APD type non-superconducting single-photon detector.
6. A superconducting single photon detector detection efficiency test method using the superconducting single photon detector detection efficiency test apparatus as claimed in claim 1, comprising the steps of:
step A: firstly, measuring the broadband relative detection efficiency of the superconducting single-photon detector under a specific polarization condition to obtain a relative detection efficiency curve;
and B: and then, measuring the absolute detection efficiency under a plurality of special wavelength points under the same polarization condition, and correcting a relative detection efficiency curve by using the absolute detection efficiency under the wavelength points, thereby realizing the accurate measurement of the broadband absolute detection efficiency under the specific polarization condition.
7. The method of claim 6, wherein in step a, the method of obtaining a relative detection efficiency curve comprises the steps of:
step 1, completing the construction of a relative detection efficiency measurement system, and setting the wavelength lambda of a monochromatic systemiOpening the shutter to set the polarization direction θi；
Step 2, setting the optical power of the wide-spectrum laser light source to a high gear, and testing and recording the transmittance of the strong light attenuation system under the wavelength by using the same standard detector
The strong light attenuation system is formed by a filter wheel and two groups of linear gradient filters in the wide spectrum relative detection efficiency measurement system;
step 3, setting the light power of the wide-spectrum laser light source to a low gear, adjusting and locking a filter wheel and two groups of linear gradient filters, and attenuating the light intensity to a single photon magnitude;
step 4, testing and recording the optical power before light attenuation by using a standard detector
Testing and recording optical power before optical attenuation using a monitor probe
Step 5,Opening the superconducting single-photon detector, and simultaneously reading and recording the reading of the superconducting single-photon detector
Monitoring detector readings
Step 6, calculating the wavelength lambdaiDirection of polarization θiRelative detection efficiency of superconducting single photon detector under conditions
Equation (1) is as follows:
in the above-mentioned formula, the compound has the following structure,
at a wavelength of λiThe energy of the single photon of (a),
h is the Planck constant, c is the speed of light;
step 7, adjusting the polarization direction theta of the incident lightjObtaining a relative detection efficiency curve of the superconducting single-photon detector under all polarization states of the wavelength;
step 8, obtaining the optimal polarization direction theta of the superconducting single photon detector according to the test result of the step 7maxIn which polarization direction the wavelength lambda of the monochromatic system is adjusted according to the method described abovejObtaining the optimal relative detection efficiency of the superconducting single-photon detector in the whole working spectral range;
step 9, obtaining the optimal polarization direction theta of the superconducting single photon detectormaxRelative detection efficiency versus wavelength curve of (b).
8. The method of claim 7, wherein in step B, the method of absolute probe efficiency measurement comprises the steps of:
step 21, completing the construction of an absolute detection efficiency measurement system, and selecting and switching different nonlinear crystals according to different calibration wavelength points;
step 22, according to different calibration wavelengths, rotating the filter wheel to switch the optical filter to a corresponding wavelength, finely adjusting the position of the coupling lens, and coupling related photons into the single photon detector;
step 23, obtaining the optimal polarization direction theta according to the test in the relative detection efficiency test process of the superconducting single photon detectormaxSetting the polarization direction of the related photon coupled into the superconducting single photon detector as thetamax；
Step 24, calculating by using coincidence measurement method to obtain wavelength lambdajDirection of polarization θmaxThe absolute detection efficiency of the superconducting single photon detector under the condition is shown in the formula (2) as follows:
in the above formula, McoincTo match the count value, M2The count value of the other path of single photon detector;
step 25, with wavelength λjAnd (4) taking the lower absolute detection efficiency as a reference, and carrying out up-and-down translation on the relative detection efficiency curve of the superconducting single-photon detector to obtain the absolute detection efficiency curve.
9. The method of claim 8, wherein after step 24, correcting the coincidence measurement result, and subtracting the optical path transmittance and the influence of the coincidence measurement process, such as coincidence of gate width, dead time, post pulse, coincidence loss, and accidental coincidence, on the test result are set.
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