Detection efficiency calibrating device and method for single-photon detector

Abstract

The invention relates to the field of detection efficiency detection of single-photon detectors, in particular to a detection efficiency calibrating device and method of a single-photon detector, and the device comprises a related photon source module, a standard single-photon detector, a to-be-detected single-photon detector, and a dual-channel counter / oscilloscope. The correlated photon source module generates two paths of single photons which are respectively connected with the standard single-photon detector and the to-be-detected single-photon detector, and output signals of the standard single-photon detector and the to-be-detected single-photon detector are connected with the dual-channel counter / oscilloscope. According to the method, errors caused by laser stability and operation time in the attenuation method measurement process can be eliminated, and the measurement accuracy is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of detection efficiency detection of single photon detector, and particularly relates to a detection efficiency detection device and detection method of single photon detector. BACKGROUND

[0002] With the development of quantum technology, single photon detectors play an important role in quantum secure communication, quantum detection, quantum radar, quantum imaging and other fields. The testing of related performance parameters of single photon detectors is the basis for their practical application, and the detection efficiency is a key parameter of single photon detectors. In order to further promote the application of single photon detectors in different fields, a standard, feasible and accurate testing system needs to be established.

[0003] Currently, the two main single photon detector detection efficiency testing methods include laser attenuation method and coincidence measurement method. The laser attenuation method uses an attenuator to attenuate single-wavelength laser to a single photon level, and then guides the attenuated photons into a single photon detector for detection. Specifically, the power of the laser is reduced as much as possible, the output power of the laser is measured, and then the attenuation ratio required to attenuate the power to a single photon level is calculated according to the power, wavelength, Planck constant and other related parameters. The attenuator is adjusted or different attenuation ratios of attenuators are combined to ensure that the output after the attenuator reaches the single photon level. The number of photons input into the single photon detector is calculated according to the output power of the laser, the attenuation ratio of the attenuator used, the photon energy and other parameters, and the counting value of the single photon detector obtained by using the counting module to calculate the detection efficiency of the single photon detector. The entire process can be traced back to the optical power reference and frequency reference.

[0004] The coincidence measurement method uses a laser and a nonlinear crystal to generate two entangled photons, and uses an optical system to filter and collimate the generated entangled photons and then guide them into two single photon detectors. The output signals of the two single photon detectors are connected to a time-to-digital converter or a time-correlated single photon counter, and a double-channel coincidence measurement is performed. According to the coincidence count and the count of the other channel, the detection efficiency of the single photon detector under test can be obtained. Subsequently, the single photon detector dead time, channel transmission rate, coincidence measurement module dead time, channel delay and other factors need to be corrected according to the mathematical model, and finally the corrected detection efficiency is obtained. Part of the correction in the entire process needs to be traced back to the optical power and frequency reference.

[0005] However, the above two methods have certain disadvantages, specifically as follows: (1) the laser attenuation method needs an attenuator with a high attenuation ratio, and at present, the attenuation ratio of the attenuator is calibrated under strong light, but in actual application, it is used under extremely weak light conditions, so there is a large error in the calibration of the attenuation ratio, which leads to the accumulation of errors in the test results, and finally the test result error is large. (2) The coincidence measurement method is more complex than the attenuation method, and at present, it is mainly based on laboratory devices, which cannot be applied to complex working scenes, and the results of coincidence measurement need to be corrected complexly to ensure the accuracy of the results, which increases the complexity of use and is not conducive to application and promotion. SUMMARY

[0006] In view of the problems in the prior art, the purpose of the present application is to provide a device and method that combines the respective advantages of two kinds of test methods for the detection efficiency of single photon detectors, uses two-way simultaneous measurement to solve the errors introduced by laser stability and operation time, uses a standard detector and a measured detector to measure simultaneously, and solves the problems of complex measurement, the need for professional knowledge, etc. through comparison and measurement, a detection efficiency detection device and method for single photon detectors.

[0007] To achieve the above purpose, the technical solution adopted by the present application is: a detection efficiency detection device for single photon detectors, comprising a correlated photon source module, a standard single photon detector, a measured single photon detector, and a dual-channel counter / oscilloscope, the correlated photon source module generates two single photons which are connected to the standard single photon detector and the measured single photon detector respectively, and the output signals of the standard single photon detector and the measured single photon detector are connected to the dual-channel counter / oscilloscope.

[0008] The detection efficiency detection device for single photon detectors described above, the correlated photon source module comprises a pump laser, a first filter, a waveguide, a temperature control module, a second filter, and a beam splitter, the laser generated by the pump laser is filtered by the first filter to remove stray light and then connected to the waveguide, the temperature control module controls the temperature of the waveguide, the output end of the waveguide is connected to the second filter to filter the remaining pump light, and then enters the beam splitter, and the beam splitter divides the filtered correlated photons into two single photons.

[0009] The detection efficiency detection device for single photon detectors described above, the output end of the waveguide is a single optical fiber, and the wavelength of the photons output by the waveguide is twice the wavelength of the light generated by the pump laser.

[0010] The detection efficiency detection device for single photon detectors described above, the photons output by the waveguide are filtered by the filter and then output as two channels of degenerate photons with the same wavelength through the beam splitter.

[0011] The detection efficiency testing device of the single photon detector, if the waveguide is designed as a type II phase matching mode, when the pump laser is e light, two generated degenerate photons are o light and e light respectively, and the beam splitter uses a polarization beam splitter for light splitting.

[0012] The detection efficiency testing device of the single photon detector, if the waveguide is designed as other phase matching modes, the two generated degenerate photons are not orthogonally polarized, the beam splitter uses 50:50 light splitting, the lengths of the split optical fibers are consistent, the wavelengths of the degenerate photons are consistent, the attenuations in the optical paths are the same, the incident photons received by the standard single photon detector and the to-be-tested single photon detector are the same, and are M.

[0013] The detection efficiency testing device of the single photon detector, by using a double-channel counter / oscilloscope to read the electric pulse signal counts output by the standard single photon detector and the to-be-tested single photon detector, the counts of the standard single photon detector and the to-be-tested single photon detector are obtained as N0 and N respectively, and then: , , The following can be obtained: , is the detection efficiency of the standard single photon detector, is the detection efficiency of the to-be-tested single photon detector.

[0014] The detection efficiency testing device of the single photon detector further includes a shell, a display, and an integrated circuit with a socket, the integrated circuit and the display are electrically connected and are installed in parallel in the shell, and the correlated photon source module, the standard single photon detector, the to-be-tested single photon detector, and the double-channel coincidence counter are plugged into the socket.

[0015] A detection method of a detection efficiency testing device of a single photon detector, including the following steps: Step 1: using the energy conservation in the spontaneous parametric down-conversion process of a nonlinear waveguide, a correlated photon source module outputs two degenerate photons with the same wavelength; Step 2: the two degenerate photons with the same wavelength enter a standard single photon detector and a to-be-tested single photon detector respectively, and by the energy conservation law, the incident photons are the same, and are M; Step 3: using a double-channel counter / oscilloscope to read the electric pulse signal counts of the standard single photon detector and the to-be-tested single photon detector, the counts of the standard single photon detector and the to-be-tested single photon detector are obtained as N0 and N respectively, and then: , , The following can be obtained: , wherein: This represents the detection efficiency of a standard single-photon detector. The value represents the detection efficiency of the single-photon detector under test.

[0016] The calibration method for the detection efficiency calibration device of the above-mentioned single-photon detector, wherein step 1 includes: Step a: After the pump laser generates laser light, it is connected to the first filter through the output fiber to filter out stray light other than the laser wavelength; Step b: The filtered laser is fed into a waveguide with designed parameters, and the wavelength of the output correlated photons is twice the wavelength of the pump laser; Step c: The output end of the waveguide is connected to a second filter using a single optical fiber to filter out residual pump light and output correlated photons. After the second filter, a polarization beam splitter or a 50:50 beam splitter is connected to split the photons.

[0017] The beneficial effects of the detection efficiency verification device and method for single-photon detectors of this invention are as follows: Utilizing a correlated photon source that directly generates single-photon level photons as the test source eliminates the error introduced by using the attenuation ratio calibrated under strong light in weak light, thus improving measurement accuracy; through simultaneous dual-channel measurement, it eliminates the errors introduced by laser stability and operation time during the alternating measurement process of the attenuation method, further improving measurement accuracy; by simultaneously measuring with a standard single-photon detector and the single-photon detector under test, it simplifies the alternating measurement process of the laser attenuation method and the subsequent correction process of the coincidence measurement method, thereby improving testing efficiency.

[0018] Conventional correlated photon sources result in different incident photons for the two single-photon detectors due to the different wavelengths of the two photons, thus requiring measurement of the attenuation of both paths. This device uses a correlated photon source that outputs degenerate photons as the test light source. The attenuation of the two photons before entering the single-photon detector is the same, thus they can cancel each other out, making it easier to obtain the detection efficiency of the single-photon detector under test.

[0019] After miniaturization, the modules can be integrated into small instruments, and the test results can be directly displayed on the monitor, realizing automated testing, improving testing efficiency, reducing errors introduced by human operation, and improving measurement accuracy; replacing the expensive coincidence measurement module in the coincidence measurement method with an oscilloscope / counter reduces costs. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the single-photon detector detection efficiency measurement device in an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the principle of single-photon detector detection efficiency testing in an embodiment of the present invention. Figure 3 This is a schematic diagram of the layout and testing of the single-photon detector tester in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the technical personnel in the art better understand the technical solutions of the present application, the technical solutions of the present application will be described below in conjunction with specific embodiments and drawings.

[0022] Embodiment 1 In the existing single photon detector detection efficiency test method, it is necessary to measure the transmittance or attenuation ratio under extremely weak light conditions. However, the current technical level cannot realize calibration at the single photon level, resulting in errors in the measurement results. The laser attenuation method is not simultaneous measurement, and it is necessary to first measure the optical power, connect the attenuation, and measure the single photon detector output count. This series of operations requires a certain time, and therefore the stability of the laser power and the operation time will affect the measurement results. In the measurement process of the coincidence measurement method, the transmittance of the channel, the dead time of the coincidence measurement module, the delay between the two channels and other parameters need to be measured. The correction parameters are obtained through a series of professional calculations. The process is relatively complex, and it is necessary to have relevant professional knowledge to complete the entire operation. Moreover, it is time-consuming and inefficient. The coincidence measurement method needs to be equipped with professional coincidence measurement modules such as time-to-digital converters or time-correlated single photon counters, which has a high cost.

[0023] The present embodiment provides a device and method that combines the advantages of the two test methods for single photon detector detection efficiency. The device of the present application mainly comprises a correlated photon source, a standard single photon detector, an oscilloscope / counter and the like.

[0024] The correlated photon source generates correlated photons through a waveguide pumped by a laser. The generation process relies on the parametric down-conversion effect of the waveguide. Specifically, a 405nm, 532nm, 775nm laser is used as a pump laser 1. The laser is usually a fiber laser, and the output fiber of the laser is connected to a first filter 2 for filtering other stray light except the wavelength of the laser.

[0025] The laser is connected to a waveguide 3 after the first filter. The main material of the waveguide is a nonlinear crystal such as PPLN or PPKTP. The waveguide needs to be temperature-controlled by a temperature control module 8. The output end of the waveguide is a single optical fiber, and the design parameters of the waveguide ensure that the wavelength of the output correlated photons is twice the wavelength of the pump laser.

[0026] The output end of the waveguide is connected to a second filter 4, which mainly filters the residual pump light and outputs the correlated photons. The second filter is connected to a polarization beam splitter or a 50:50 beam splitter.

[0027] The two optical fibers of the beam splitter 5 are connected to a standard single photon detector 6 and a single photon detector to be measured 9. The output signals of the two single photon detectors are connected to an oscilloscope or a counter.

[0028] Waveguide design mainly includes the design of parameters such as waveguide material, period of periodically polarized waveguide, waveguide length, and waveguide temperature control. Taking the commonly used PPLN waveguide as an example, the crystal polarization period and temperature control are designed using the following formula.

[0029] in: n j ( j = p, s, i) These represent the refractive indices of the pump light, signal light, and idle light within the crystal, respectively. ( j = p, s, i) These represent the wavelengths of the pump light, signal light, and idle light, respectively. In this example, the wavelength of the signal light is... and idle light wavelength They are equal, being the pump light wavelength. Twice as much; The polarization period of a nonlinear crystal; denoted as the crystal's temperature control temperature; n represents the refractive index of the pump light, signal light, and idle light in the crystal. , , , , , , , , , The parameters are constants, but the parameters corresponding to o-ray and e-ray are different, and the parameters corresponding to different types of PPLN crystals are also different.

[0030] The testing principle of this embodiment mainly utilizes the energy conservation during the correlation photon generation process. After special parameter design, the waveguide outputs two correlated photons with the same wavelength, which are degenerate photons. Parameters such as the waveguide period, temperature control, and phase matching angle are calculated according to some formulas, or "the period, temperature control, phase matching angle, and other parameters of the nonlinear medium inside the waveguide are designed for a specific pump wavelength to ensure that the wavelengths of the two output photons are twice the pump laser wavelength." If the waveguide is designed in type II phase-matching mode, and the pump laser is an e-beam, the two degenerate correlated photons generated are the o-beam and e-beam, respectively, which can be split using a polarization beam splitter. If the waveguide is designed in other phase-matching modes, the two degenerate correlated photons generated are not orthogonally polarized, and a 50:50 split can be used. Since the fiber lengths are consistent after splitting, the correlated photon wavelengths are consistent, and the attenuation in the optical path is also the same, the incident photons received by the standard single-photon detector and the single-photon detector under test are the same, both being M.

[0031] Using a dual-channel oscilloscope or counter to read the count of the electrical pulse signal output from the single-photon detector, the counts of the standard single-photon detector and the single-photon detector under test are N0 and N, respectively. Then: (1), (2), in: The detection efficiency of a standard single-photon detector; The value represents the detection efficiency of the single-photon detector under test.

[0032] Then we can obtain equations (1) and (2): (3).

[0033] like Figure 2 As shown, the system is divided into modules, including a correlated photon source, a standard single-photon detector, a single-photon detector under test (SPT), and an oscilloscope / counter. Using the correlated photon source as the test light source eliminates the cumbersome process of adjusting laser power during attenuation method testing, and ensures that the incident light received by the final SPT is a single photon. The standard SPT, the SPT, and a dual-channel oscilloscope are used as detection devices to resolve the complex result corrections in coincidence measurement method testing, directly obtaining the detection efficiency of the SPT. Through integrated and modular design, operational complexity is reduced, and testing of detectors at different wavelengths can be easily achieved by replacing the correlated photon source and the standard SPT.

[0034] like Figure 3 As shown, except for the single-photon detector under test, everything is integrated into one instrument, including a housing, a display, and a pre-programmed integrated circuit with ports. The relevant photon sources are connected via all-fiber optics and are in the form of standard PXIe or PXI boards. The single-photon detector and oscilloscope / counter are also in the form of PXIe or PXI boards. The three modules are inserted into the integrated unit. Through the pre-set program, the test results of the single-photon detector's detection efficiency are directly displayed on the screen. All components are connected via optical and electrical interfaces.

[0035] The waveguide is used as a nonlinear medium, the entire related photon source light path can be realized in a full-fiber form, integration is improved, and miniaturization and portability are realized.

[0036] Embodiment 2 A detection efficiency detection device of a single photon detector, comprising a related photon source module, a standard single photon detector 6, a single photon detector to be detected 9, and a double-channel counter / oscilloscope 7, the related photon source module generates two single photons which are connected to the standard single photon detector and the single photon detector to be detected, respectively, the output signals of the standard single photon detector and the single photon detector to be detected are connected to the double-channel counter / oscilloscope.

[0037] The related photon source module comprises a pump laser 1, a first filter 2, a waveguide 3, a temperature control module 8, a second filter 4, and a beam splitter 5, laser generated by the pump laser is connected to the waveguide after filtering stray light by the first filter, the temperature control module controls the temperature of the waveguide, the light output end of the waveguide is connected to the second filter to filter the residual pump light, and then enters the beam splitter, and the beam splitter divides the filtered laser into two single photons.

[0038] The output end of the waveguide is a single optical fiber, and the photon wavelength output by the waveguide is twice the photon wavelength generated by the pump laser.

[0039] The photons output by the waveguide are filtered by the filter and then output two wavelengths of degenerate photons by the beam splitter.

[0040] If the waveguide is designed in a type II phase matching mode, when the pump laser is e light, two degenerate photons generated are o light and e light, respectively, and the beam splitter uses a polarization beam splitter to split light.

[0041] If the waveguide is designed in other phase matching modes, the two degenerate photons generated are not orthogonally polarized, the beam splitter uses a 50:50 beam splitter, the lengths of the optical fibers after splitting are consistent, the wavelengths of the degenerate photons are consistent, the attenuations in the optical paths are the same, the incident photons received by the standard single photon detector and the single photon detector to be detected are the same, and are M.

[0042] The count of the electrical pulse signals output by the standard single photon detector and the single photon detector to be detected is read by the double-channel coincidence counter, and the counts of the standard single photon detector and the single photon detector to be detected are N0 and N, respectively. , , The following can be obtained: , wherein is the detection efficiency of the standard single photon detector, is the detection efficiency of the single photon detector to be detected.

[0043] Embodiment 3 A detection method of a detection device of a single photon detector, comprising the following steps: Step 1: two degenerate photons with the same wavelength are output by a correlated photon source module by using a nonlinear waveguide spontaneous parametric down-conversion process satisfying energy conservation.

[0044] Step 2: the two degenerate photons with the same wavelength enter a standard single photon detector and a single photon detector to be detected respectively, and the same incident photons are obtained, both being M.

[0045] Step 3: the electric pulse signal count of the standard single photon detector and the single photon detector to be detected is read by using a double-channel counter / oscilloscope, and the counts of the standard single photon detector and the single photon detector to be detected are N0 and N respectively, so that: , , , , is the detection efficiency of the standard single photon detector, is the detection efficiency of the single photon detector to be detected.

[0046] Specifically, step 1 comprises: Step a: after the pump laser generates laser, the laser is connected to a first filter through an output optical fiber, and other stray light except the wavelength of the laser is filtered.

[0047] Step b: the filtered laser is connected to a waveguide with special parameters, and the wavelength of the output correlated photon is twice the wavelength of the pump laser.

[0048] Step c: a single optical fiber is used at the light output end of the waveguide to connect a second filter, the residual pump light is filtered, the correlated photon is output, and a polarization beam splitter or a 50:50 beam splitter is connected after the second filter to split the photons.

[0049] The above embodiments are only used to illustrate the structural concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the essence of the present application should be covered within the protection scope of the present application.

Claims

1. A device for calibrating the detection efficiency of a single photon detector, characterized in that, The related photon source module, the standard single photon detector, the single photon detector to be measured, and the double-channel counter / oscilloscope are included.

2. The device for calibrating the detection efficiency of a single-photon detector according to claim 1, characterized in that The related photon source module includes a pump laser, a first filter, a waveguide, a temperature control module, a second filter, and a beam splitter.

3. The device for calibrating the detection efficiency of a single-photon detector according to claim 2, characterized in that The output end of the waveguide is a single optical fiber, and the wavelength of the photons output by the waveguide is twice the wavelength of the photons generated by the pump laser.

4. The device for calibrating the detection efficiency of a single-photon detector according to claim 3, characterized in that The energy conservation in the process of photon generation is utilized, and the two wavelengths of the degenerate photons output by the waveguide are the same.

5. The device for calibrating the detection efficiency of a single-photon detector according to claim 4, characterized in that If the waveguide is designed in a type II phase matching mode, when the pump laser is e light, the two wavelengths of the degenerate photons generated are o light and e light, respectively.

6. The device for calibrating the detection efficiency of a single-photon detector according to claim 4, characterized in that If the waveguide is designed in other phase matching modes, the two wavelengths of the degenerate photons generated are not orthogonal, the beam splitter uses 50:50 splitting, the lengths of the optical fibers after splitting are consistent, the wavelengths of the degenerate photons are consistent, the attenuations in the optical paths are the same, the incident photons received by the standard single photon detector and the single photon detector to be measured are the same, and are M.

7. The device for calibrating the detection efficiency of a single-photon detector according to claim 6, characterized in that The double-channel counter / oscilloscope is used to read the electric pulse signal counts output by the standard single photon detector and the single photon detector to be measured, and the counts of the standard single photon detector and the single photon detector to be measured are N0 and N, respectively. ， ， is obtainable: wherein is the detection efficiency of a standard single-photon detector, is the detection efficiency of the single-photon detector to be tested.

8. The device for calibrating the detection efficiency of a single-photon detector according to any one of claims 2 to 7, characterized in that, The related photon source module, the standard single photon detector, the single photon detector to be measured, and the double-channel counter / oscilloscope are included.

9. A method of calibrating a device for calibrating the detection efficiency of a single-photon detector, characterized in that The following steps are included: Step 1: The energy conservation in the process of spontaneous parametric down-conversion of a nonlinear waveguide is utilized, and the related photon source module outputs two wavelengths of degenerate photons. Step 2: The two wavelengths of the degenerate photons enter the standard single photon detector and the single photon detector to be measured, respectively. Step 3: The double-channel counter / oscilloscope is used to read the electric pulse signal counts output by the standard single photon detector and the single photon detector to be measured, and the counts of the standard single photon detector and the single photon detector to be measured are N0 and N, respectively. ， ， obtained wherein: is the detection efficiency of a standard single-photon detector, is the detection efficiency of the single-photon detector to be tested.

10. The method of claim 9, wherein the method further comprises: determining the detection efficiency of the single-photon detector based on the number of photons detected by the single-photon detector. Step 1 includes the following steps: Step a: After the pump laser generates laser light, the laser light is input into the first filter through an output optical fiber to filter out stray light other than the wavelength of the laser. Step b: The filtered laser light is input into the waveguide designed according to parameters, and the wavelength of the related photons output by the waveguide is twice the wavelength of the pump laser. Step c: the light output end of the waveguide is connected to a second filter using a single optical fiber, which filters the residual pump light and outputs the relevant photons. A polarization beam splitter or a 50:50 beam splitter is connected to the second filter to split the photons.

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