A test device for a single-photon detector

Abstract

The present invention discloses a test device for a single-photon detector, comprising: a pulsed light source module for generating a single-photon light source that irradiates the single-photon detector; a mode switching module including a bias device, a mode switching switch, and a variable resistor; the variable resistor is disposed between a DC bias voltage source and an input terminal of the bias device; the mode switching switch is disposed between another input terminal of the bias device and a gate pulse bias source for switching between a gated mode and a free-running mode; an output terminal of the bias device is connected to an input terminal of the single-photon detector; a parameter extraction module including a discriminator and a logic judgment circuit; an input terminal of the discriminator is connected to an output terminal of the single-photon detector; the logic judgment circuit is respectively connected to an output terminal of the discriminator and a first pulse signal, and obtains photon counts through a first AND gate, and obtains dark counts through a NOT gate and a second AND gate. The present invention efficiently and flexibly realizes the switching between the gated mode and the free-running mode and the acquisition of performance parameters.

Description

Technical Field

[0001] The present invention relates to the technical field of single - photon detection and lidar technology, and particularly relates to a test device for a single - photon detector. Background Art

[0002] In 1905, Einstein proposed that light is composed of small energy units, that is, photons are the smallest constituent units of light. The energy of a single photon is approximately 10 - 19 joules in the visible or near - infrared band, and traditional photodetectors cannot effectively detect single photons. Single - photon detectors have many advantages such as high sensitivity, high signal - to - noise ratio, and low time jitter. Therefore, single - photon detectors came into being. Single - photon detection technology is widely used in weak - light detection fields such as quantum key distribution, laser ranging, bioluminescence detection, and DNA reactions.

[0003] Lidar is an important application of single - photon detectors in the field of laser ranging. Lidar is an optical remote - sensing technology based on optical detection and ranging. It uses a narrow - line - width short - pulse laser to emit photons in the atmosphere to generate backscattering. Receiving these weak backscattering signals requires highly sensitive optical detection equipment such as single - photon detectors.

[0004] The working modes of single - photon detectors are mainly divided into: gated mode and free - running mode. The gated mode is generally applied to the field of quantum communication. When performing performance tests in the research of single - photon detectors, the gated mode is also often used to adjust the test repetition frequency and dead time of single - photon detectors.

[0005] For lidar applications, the arrival time of the signal source is uncertain, so a single - photon detector needs to work in the free - running mode. For the performance characterization of single - photon detectors, the gated mode and the free - running mode are often required simultaneously. However, the differences between different voltage sources and different signal - processing methods lead to a lack of compatibility between the two test systems, greatly reducing the R & D test efficiency.

[0006] Generally, in order to characterize the performance of single - photon detectors such as SPAD (single - photon avalanche diode), some performance parameters applicable to single photons have been proposed in this field: photon counting, dark counting, detection efficiency, after - pulse probability, and dead time, etc. In the existing test schemes for single - photon SPADs, the characterization of these parameters is not direct and intuitive enough. Often, through complicated test processes and calculation processes, the corresponding performance parameters can be obtained, increasing the complexity of single - photon SPAD characterization.

[0007] In summary, in the prior art, there is a lack of a test device that can efficiently, standardize, and flexibly characterize the performance of single - photon detectors, and the test methods for photon counting, dark counting, etc. have a certain degree of complexity. Summary of the Invention

[0008] The object of the present invention is to overcome the deficiencies of the prior art and propose a test device for a single-photon detector, which solves the switching between detection modes through a mode switching module and improves the acquisition of performance parameters through a parameter extraction module.

[0009] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0010] On the one hand, a test device for a single-photon detector includes:

[0011] A pulse light source module for generating a single-photon light source for irradiating the single-photon detector;

[0012] A mode switching module includes a bias device, a mode switching switch, and an adjustable resistor; the adjustable resistor is arranged between a DC bias voltage source and an input end of the bias device; the mode switching switch is arranged between another input end of the bias device and a gate pulse bias source for switching between the gated mode and the free-running mode; an output end of the bias device is connected to an input end of the single-photon detector;

[0013] A parameter extraction module includes a discriminator and a logic judgment circuit; an input end of the discriminator is connected to an output end of the single-photon detector; the logic judgment circuit is respectively connected to an output end of the discriminator and a first pulse signal, and photon counts are obtained through a first AND gate, and dark counts are obtained through a NOT gate and a second AND gate.

[0014] Preferably, the test device for the single-photon detector further includes a refrigeration module, and the refrigeration module includes a closed cavity for providing a closed refrigeration environment for the single-photon detector; the single-photon detector is arranged in the refrigeration module.

[0015] Preferably, the pulse light source module includes a pulsed laser, a monitoring optical path, and an optical attenuator; the pulsed laser is connected to a signal generator for generating pulsed laser light; the monitoring optical path includes a 1 / 99 optical fiber splitter; the pulsed laser is divided into two paths by the 1 / 99 optical fiber splitter, and 1% of the split is connected to the optical attenuator to attenuate the pulsed laser light; an output end of the optical attenuator is connected to the photon detector through an optical fiber.

[0016] Preferably, the monitoring optical path further includes an optical power meter; the optical power meter is connected to the 99% split output by the 1 / 99 optical fiber splitter to monitor the pulsed light source.

[0017] Preferably, the mode switching module further includes a steady-state trigger and a digital delay unit; the steady-state trigger is disposed between the signal generator and the digital delay unit. The second pulse signal generated by the signal generator is modulated into a square wave level signal with the required pulse width and amplitude by the steady-state trigger, and is synchronized with the pulsed laser after passing through the digital delay unit to serve as a gate pulse bias source.

[0018] Preferably, the parameter extraction module further includes a low-pass filter; the low-pass filter is disposed between the single-photon detector and the discriminator.

[0019] Preferably, the parameter extraction module further includes an amplifier; the amplifier is disposed between the single-photon detector and the discriminator.

[0020] Preferably, the parameter extraction module further includes a counting unit; the counting unit is connected to the first AND gate for extracting photon counts; the counting unit is connected to the second AND gate for extracting dark counts.

[0021] Preferably, the counting unit includes an oscilloscope or a frequency counter.

[0022] Preferably, the single-photon detector includes a single-photon avalanche diode.

[0023] The present invention has the following beneficial effects:

[0024] (1) The present invention includes a mode switching module. The combination of the bias unit and the mode switching switch in it provides a simple and convenient implementation for the switching between the single-photon gating mode and the free-running mode. At the same time, the circuit in different modes is matched by adjustable resistors, meeting the requirements for the two modes in the performance verification of the single-photon detector.

[0025] (2) The present invention includes a parameter extraction module. The discriminator in it can convert the avalanche pulse signal output by the single-photon detector into a digital level signal; based on the digital level signal and the first pulse signal, photon counts are obtained through the first AND gate, and dark counts are obtained through the NOT gate and the second AND gate, thereby respectively realizing the separate statistics of optical counts and dark counts, simplifying the single-photon data processing process, and improving the efficiency of extracting performance parameters.

[0026] (3) The single-photon monitoring optical path of the present invention includes a 1 / 99 optical fiber splitter and an optical power meter; the pulsed laser is divided into two paths by the 1 / 99 optical fiber splitter. The 1% branch is connected to an optical attenuator to attenuate the pulsed laser to generate a single-photon light source, and the optical power meter is connected to the 99% branch to realize real-time monitoring of the pulsed light source, improving the efficiency of single-photon detection and the reliability of the output single-photon light source.

[0027] (4) The present invention includes a refrigeration module that provides a closed refrigeration environment for the single-photon detector, providing a stable and feasible environment for testing.

[0028] The following further describes the present invention in detail with reference to the accompanying drawings and embodiments, but the test device for a single-photon detector of the present invention is not limited to the embodiments. Description of the Drawings

[0029] Figure 1 It is a structural block diagram of the test device for the single-photon detector according to the embodiment of the present invention;

[0030] Figure 2 It is a structural block diagram of the pulse light source module according to the embodiment of the present invention;

[0031] Figure 3 It is a circuit schematic diagram of the mode switching module according to the embodiment of the present invention;

[0032] Figure 4 It is a structural block diagram of the parameter extraction module according to the embodiment of the present invention;

[0033] Figure 5 It is a structural block diagram of the logic judgment circuit according to the embodiment of the present invention;

[0034] Figure 6 It is a timing diagram of the test device for the single-photon detector according to the embodiment of the present invention; where (a) represents the second pulse signal output by the signal generator; (b) represents the first pulse signal; (c) represents the single-photon light source signal; (d) represents the pulse analog signal output by the SPAD; (e) represents the digital level signal output by the discriminator; (f) represents the photon counting level signal output by the first AND gate; (g) represents the output of the NOT gate; (h) represents the dark count level signal output by the second AND gate. Detailed Embodiment

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention; obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0036] In the description of the present invention, it should be noted that the terms "comprising", "including" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the presence of additional identical elements in the process, method, article or device including the said element.

[0037] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom end", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0038] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "provided with", "sheathed / connected", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection, can be a mechanical connection, can be an electrical connection, can be directly connected, or can be indirectly connected through an intermediate medium, and can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] See Figures 1 to 5 As shown, a test device for a single-photon detector of the present invention includes:

[0040] A pulse light source module 10 for generating a single-photon light source 101 that irradiates the single-photon detector 50;

[0041] A refrigeration module 20, including a closed cavity 201, for providing a closed refrigeration environment for the single-photon detector 50; the single-photon detector 50 is disposed within the refrigeration module 20;

[0042] The mode switching module 30 includes a bias unit 301, a mode switching switch 302, and a variable resistor 303; the variable resistor 303 is disposed between a DC bias voltage source 304 and an input terminal of the bias unit 301; the mode switching switch 302 is disposed between another input terminal of the bias unit 301 and a gate pulse bias source 305 for switching between a gated mode and a free-running mode; the output terminal of the bias unit 301 is connected in series with a single-photon detector 50 and then grounded. Further, a resistor Rs is also connected in series at the output terminal of the bias unit 301.

[0043] The parameter extraction module 40 includes a discriminator 401 and a logic judgment circuit 402; the input terminal of the discriminator 401 is connected to the output terminal of the single-photon detector 50; the logic judgment circuit 402 is respectively connected to the output terminal of the discriminator 401 and a first pulse signal 701, and a photon count 80 is obtained through a first AND gate 4021, and a dark count 90 is obtained through a NOT gate 4023 and a second AND gate 4022.

[0044] See Figure 1 As shown, the test device further includes a counting unit 60 in the parameter extraction module 40; the counting unit 60 is connected to the first AND gate 4021 for extracting the photon count 80; the counting unit 60 is connected to the second AND gate 4022 for extracting the dark count 90.

[0045] Specifically, the counting unit 60 includes an oscilloscope or a frequency counter.

[0046] Specifically, see Figure 2 As shown, the pulse light source module 10 mainly includes four parts: a pulse laser 101, a monitoring optical path, an optical attenuator 103, and an optical fiber 104. According to an embodiment of the present invention, the pulse laser 101 is used to generate pulsed laser light. A semiconductor laser can be used in cooperation with a modulation signal to achieve the excitation of pulsed laser light, or a pulsed laser can be directly used to achieve the excitation of pulsed laser light. Regardless of the method used to generate the pulsed laser source, the second pulse signal (which can be generated by a signal generator 70) used to excite the pulsed laser light will be regarded as a clock signal and serve as the source of the gate pulse bias source 305 of the single-photon detector SPAD.

[0047] In this embodiment, the first pulse signal 701 can be generated after the second pulse signal generated by the signal generator 70 is processed by a frequency reduction module (the frequency reduction ratio can be adjusted between 1 / 2 and 1 / 1000). Specifically, a frequency reduction module can be disposed after the pulse laser 101. One output of the frequency reduction module serves as the first pulse signal, and the other output is sent to the monitoring optical path. Of course, the first pulse signal 701 can also be separately generated as needed, and the specific generation method is not limited in this embodiment.

[0048] Specifically, the optical attenuator 103 can be an adjustable optical attenuator.

[0049] According to an embodiment of the present invention, the pulsed laser is connected to the monitoring optical path. The monitoring optical path includes a 1 / 99 optical fiber splitter 1021 and an optical power meter 1022. The pulsed laser is divided into two paths by the 1 / 99 optical fiber splitter 1021. Among them, 99% of the split is connected to the optical power meter 1022 to monitor the pulsed light source, and 1% of the split is connected to the optical attenuator 103 to attenuate the pulsed laser. The adjustable optical attenuator 103 is connected after the 1% optical fiber 104 split, and its output end is connected to the SPAD through the optical fiber 104. Finally, a single-photon light source 101 with 0.1 photon / pulse is obtained through attenuation. In one embodiment, the single-pulse energy of 1550 nm is about 1.282×10 -20 J. Taking the attenuator with an attenuation amplitude of 60 dB as an example, the pulsed energy before attenuation is 1.282×10 -14 J. Since a 1:99 optical fiber 104 splitter is used, the pulsed energy of the 99% optical fiber 104 split is 1.282×10 -12 J. The data measured by the optical power meter 1022 should be the average power of the optical pulse. Taking the optical pulse repetition frequency of 500 kHz as an example, the average power is 0.635 μW.

[0050] The pulsed laser in this embodiment is divided into two paths by the 1 / 99 optical fiber splitter 1021. 1% of the split is connected to the optical attenuator 103 to attenuate the pulsed laser to generate the single-photon light source 101. The optical power meter 1022 is connected to the 99% split to achieve real-time monitoring of the pulsed light source, improving the efficiency of single-photon detection and the reliability of the output single-photon light source 101.

[0051] Specifically, the refrigeration module 20 is used to provide a closed refrigeration environment for the SPAD and an optical coupling pigtail (the optical coupling pigtail connects the single-photon detector 50 SPAD to the input single-photon light source 101 and is responsible for coupling single photons to the photosensitive surface of the SPAD). According to an embodiment of the present invention, the refrigeration module 20 preferably can meet the refrigeration range from room temperature to -70°C. In order to provide a stable and feasible test environment, the closed cavity 201 needs to be vacuum-treated to eliminate the influence of water vapor condensation caused by refrigeration. According to an embodiment of the present invention, one end face of the vacuum cavity can be used to place the coupling optical window of the pulsed laser optical fiber 104 to improve the coupling efficiency of the single-photon light source 101 and simplify the optical fiber 104 coupling operation steps.

[0052] See Figure 3As shown, the mode switching module 30 includes: a DC bias voltage source 304, a gate pulse bias source 305, a bias unit 301, a mode switching switch 302, and a variable resistor 303. The DC bias voltage source 304 is used to provide a working voltage for the SPAD. In the gated mode, the DC bias voltage source 304 keeps the SPAD in the linear mode, that is, at a relatively high bias voltage before the breakdown voltage; in the free-running mode, the DC bias voltage source 304 keeps the SAPD at the working bias voltage in the Geiger mode. The gate pulse bias voltage source is a gate pulse signal, which is derived from the second pulse signal output by the signal generator 70. According to an embodiment of the present invention, the second pulse signal is modulated into a square wave level signal with the required pulse width and amplitude through a steady-state trigger, etc., then synchronized with the pulsed laser through a digital delay unit, and finally coupled with the DC bias voltage source 304 through the bias unit 301 (here, the coupling means electrical coupling, the coupling of the DC bias voltage source 304 and the pulse signal processed by the digital delay unit; after electrical coupling, it is connected to the two electrodes of the SPAD to supply power to the SPAD).

[0053] According to an embodiment of the present invention, a mode switching switch 302 is included between the digital delay unit and the bias unit 301 to switch between the gated mode and the free-running mode. At the same time, by adjusting the size of the variable resistor, the circuit is adapted to the free-running mode. Correspondingly, the size of the DC bias voltage source 304 should also be adjusted accordingly. As Figure 3 shown is the schematic diagram of the mode switching switch 302. According to an embodiment of the present invention, the mode switching switch 302 can realize the connection or disconnection of the bias unit 301 in the circuit to realize the connection or disconnection of the gate pulse signal. In addition, the variable resistor 303 is used to match the circuit in different modes. In the gated mode, the variable resistor 303 is used to debug the circuit to keep the gate pulse waveform, and generally needs to be adjusted between several hundred Ω and nearly one thousand Ω; in the free-running mode, the variable resistor 303 is used as the voltage-dividing resistor for avalanche self-quenching and usually needs to be adjusted to several hundred kΩ.

[0054] This embodiment provides a bias unit 301 with a circuit switching function, providing a simpler way to realize the single-photon detection mode switching. In the performance verification of the single-photon detector 50, both the gated mode and the free-running mode are necessary. Therefore, it is particularly important to switch between the modes conveniently.

[0055] See Figure 4As shown, the parameter extraction module 40 includes: a low-pass filter 403, an amplifier 404, a discriminator 401, and a logic judgment circuit 402. According to an embodiment of the present invention, in the gated operating mode, in the SPAD output signal, in addition to the single-photon avalanche pulse signal, there is also a differential noise signal caused by the gate pulse superimposed on it. It is necessary to extract the effective avalanche pulse signal from it through a signal extraction circuit. The SPAD output signal first passes through a low-pass filter to separate the avalanche pulse signal from the differential noise signal. The specific low-pass filter bandwidth can be adjusted accordingly according to the actual situation. After passing through the low-pass filter, the avalanche pulse signal generally has a large energy loss, and then it is necessary to amplify the signal through an amplifier. The amplified avalanche pulse signal then passes through the discriminator 401 to convert the avalanche pulse signal into a digital level signal for counting.

[0056] According to an embodiment of the present invention, in the free-running mode, the SPAD output signal is no longer superimposed with a differential noise signal. It can be processed by an amplifier and then input to the discriminator 401 to realize the conversion of the avalanche pulse signal into a digital level signal, so as to realize subsequent counting.

[0057] According to an embodiment of the present invention, the avalanche pulse signal is finally input into Figure 5 the logic judgment circuit 402 shown to extract different single-photon performance parameters. One of the input signals of the logic judgment circuit 402 is the first pulse signal 701 that has passed through a digital delay line. The other end is the level signal output by the discriminator 401, which is divided into multiple paths and is respectively processed with the first pulse signal 701 in different logic circuits to realize the separate extraction of the photon count 80 and the dark count 90. The effective extraction of single-photon performance parameters is realized.

[0058] Specifically, the logic judgment circuit 402 includes a first AND gate 4021, a second AND gate 4022, and a NOT gate 4023. The first pulse signal 701 and the level signal output by the discriminator 401 are respectively used as the two input signals of the first AND gate 4021, and the output signal of the first AND gate 4021 is the photon count 80 level signal. The first pulse signal 701 is used as the input signal of the NOT gate 4023, and the output signal of the NOT gate 4023 and the level signal output by the discriminator 401 are respectively used as the two input signals of the second AND gate 4022, and the output signal of the second AND gate 4022 is the dark count 90 level signal.

[0059] In this embodiment, through the logic judgment circuit 402, the extraction of parameters such as photon count 80 and dark count 90 is realized, and at the same time, the reliability of parameter extraction is improved. After the SPAD output signal is filtered and discriminated, it is divided into multiple paths of signals. Through different logic judgment circuits 402, the separate statistics of optical count and dark count 90 are realized respectively, which simplifies the single-photon data processing process and improves the efficiency of performance parameter extraction.

[0060] See Figure 6 As shown, it is the timing diagram of each signal of the test device of the single-photon detector according to the embodiment of the present invention, where (a) represents the second pulse signal output by the signal generator; (b) represents the first pulse signal; (c) represents the single-photon light source signal; (d) represents the pulse analog signal output by the SPAD; (e) represents the digital level signal output by the discriminator; (f) represents the photon count level signal output by the first AND gate; (g) represents the output of the NOT gate; (h) represents the dark count level signal output by the second AND gate.

[0061] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements can still be made, and these improvements should also be regarded as the protection scope of the present invention.

Claims

1. A test device for a single-photon detector, characterized in that Comprising: A pulsed light source module for generating a single-photon light source that irradiates a single-photon detector; A mode switching module including a bias device, a mode switching switch, and a variable resistor; The variable resistor is disposed between a DC bias voltage source and an input terminal of the bias device; the mode switching switch is disposed between another input terminal of the bias device and a gate pulse bias source for switching between a gated mode and a free-running mode; an output terminal of the bias device is connected to an input terminal of the single-photon detector; A parameter extraction module including a discriminator and a logic judgment circuit; an input terminal of the discriminator is connected to an output terminal of the single-photon detector; the logic judgment circuit is respectively connected to an output terminal of the discriminator and a first pulse signal, and photon counts are obtained through a first AND gate, and dark counts are obtained through a NOT gate and a second AND gate.

2. The test device for a single-photon detector according to claim 1, wherein It further includes a refrigeration module, and the refrigeration module includes an enclosed cavity for providing a closed refrigeration environment for the single-photon detector; the single-photon detector is disposed within the refrigeration module.

3. The test device for a single-photon detector according to claim 1, characterized in that The pulsed light source module includes a pulsed laser, a monitoring optical path, and an optical attenuator; the pulsed laser is connected to a signal generator for generating pulsed laser light; the monitoring optical path includes a 1 / 99 optical fiber splitter; the pulsed laser is divided into two paths by the 1 / 99 optical fiber splitter, and 1% of the split is connected to the optical attenuator to attenuate the pulsed laser; an output terminal of the optical attenuator is connected to the photon detector through an optical fiber.

4. The test device for the single-photon detector according to claim 3, characterized in that, The monitoring optical path further includes an optical power meter; the optical power meter is connected to the 99% split output by the 1 / 99 optical fiber splitter to monitor the pulsed light source.

5. The test device for the single-photon detector according to claim 1, characterized in that The mode switching module further includes a steady-state trigger and a digital delay unit; the steady-state trigger is disposed between the signal generator and the digital delay unit, and a second pulse signal generated by the signal generator is modulated into a square wave level signal with a required pulse width and amplitude through the steady-state trigger, and is synchronized with the pulsed laser after passing through the digital delay unit, serving as the gate pulse bias source.

6. The test device for a single-photon detector according to claim 1, characterized in that The parameter extraction module further includes a low-pass filter; the low-pass filter is disposed between the single-photon detector and the discriminator.

7. The test device for the single-photon detector according to claim 1, wherein The parameter extraction module further includes an amplifier; the amplifier is disposed between the single-photon detector and the discriminator.

8. The test device for the single-photon detector according to claim 1, characterized in that, The parameter extraction module further includes a counting unit; the counting unit is connected to the first AND gate for extracting photon counts; the counting unit is connected to the second AND gate for extracting dark counts.

9. The test device for the single-photon detector according to claim 8, characterized in that, The counting unit includes an oscilloscope or a frequency counter.

10. The test device for a single-photon detector according to claim 1, characterized in that, The single-photon detector includes a single-photon avalanche diode.

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