Active narrow-band interferometric circuit, method and quantum communication system

Abstract

The application provides an active narrow-band interference circuit, a method and a quantum communication system, and relates to the technical field of single-photon detection. The active narrow-band interference circuit comprises: a first power division combiner, which is used for dividing an input signal into a first signal and a second signal, and the power ratio of the first output end and the second output end is N:1; a first signal channel, which is used for transmitting the first signal; a second signal channel, which is used for transmitting the second signal; and a second power division combiner, which has a power ratio of N:1 between the first input end and the second input end, and is used for synthesizing the signals transmitted by the first signal channel and the second signal channel, so that the interference of the fundamental frequency signal and the high-order harmonic signal of the gate signal capacitance response is cancelled out, and an avalanche pulse signal is output. The application can solve the contradiction between the power balance requirement of interference cancellation and the weak signal amplitude reservation: by optimizing the power ratio of the power division combiner and combining the power loss compensation of the amplification component, the output signal power is greatly improved.

Description

Technical Field

[0001] This application relates to the field of single-photon detection technology, and more specifically, to an active ultra-narrowband interference circuit, method, and quantum communication system. Background Technology

[0002] Single-photon detectors are core devices in quantum communication, quantum computing, and optical quantum sensing. Among them, single-photon detectors based on semiconductor avalanche diodes (APDs) are widely used due to their fast response speed and high detection efficiency. To suppress after-pulse noise and improve the photon count rate of APD single-photon detectors, existing technologies typically employ gate-driven methods to control the operation of the APD, thereby reducing avalanche charge and post-avalanche recovery time.

[0003] However, parasitic capacitance exists in the APD device itself and its peripheral circuitry. This parasitic capacitance causes the gating circuit to generate a capacitive response. The fundamental frequency and higher harmonic frequencies of this capacitive response signal can mask the avalanche narrow pulse signal caused by photons, severely affecting the accuracy of single-photon detection. To solve this problem, existing technologies employ passive ultra-narrowband interferometry (UNIC) circuits to eliminate the aforementioned capacitive response interference.

[0004] The core structure of existing passive ultra-narrowband interference circuits includes a power-division synthesizer, a broadband path (main path), and a narrowband path. The broadband path transmits a composite signal of the avalanche narrow pulse signal and the fundamental and higher harmonics of the gated signal's capacitive response. The narrowband path extracts a single frequency component of the gated signal's capacitive response through an ultra-narrowband bandpass filter, and then uses the power-division synthesizer to perform interference cancellation with the broadband path signal to eliminate interference.

[0005] However, existing passive ultra-narrowband interferometric circuits have significant drawbacks: to achieve destructive interference, the input signal power ratio of the power-dividing synthesizer is set to 1:N, and the output is set to N:1, resulting in the final output signal power being only N / (N+1)² of the input signal. For example, when N=9, the output signal power is only 9% of the input signal, resulting in extremely high signal power loss. This makes it impossible to guarantee the effective detection of weak avalanche pulse signals, severely limiting the application of single-photon detectors in low-light-intensity scenarios.

[0006] Therefore, how to retain the amplitude of weak signals while meeting the power balance requirements of interference cancellation has become a technical problem that urgently needs to be solved in the existing technology. Summary of the Invention

[0007] To address the shortcomings of existing passive ultra-narrowband interference circuits, such as high signal power loss and difficulty in detecting weak signals, this application provides an active ultra-narrowband interference circuit, method, and quantum communication system. This effectively resolves the contradiction between the "power balance requirement of interference cancellation" and the "preservation of weak signal amplitude." While eliminating interference from the gate circuit's capacitor response, it maximizes the preservation of the avalanche pulse signal's power, thereby improving the efficiency and reliability of single-photon detection.

[0008] According to a first aspect of this application, at least one embodiment of this application provides an active ultra-narrowband interference circuit, comprising: a first power-division combiner for dividing an input signal into a first signal and a second signal, the first power-division combiner including a first output terminal and a second output terminal, the first output terminal being used to output the first signal, the second output terminal being used to output the second signal, the power ratio of the first output terminal and the second output terminal being N:1, wherein N is greater than 1; and a first signal path, the input terminal of which is connected to the first output terminal for transmitting the first signal, the first signal including an avalanche pulse signal, a fundamental frequency signal of a gated signal capacitor response, and higher harmonics. A signal; a second signal path, the input of which is connected to the second output, for transmitting the second signal, the second signal including the fundamental frequency signal and higher harmonic signals of the gated signal capacitor response; a second power distribution synthesizer, including a first input and a second input, the first input being connected to the output of the first signal path, the second input being connected to the output of the second signal path, the power ratio of the first input and the second input being N:1, for synthesizing the signals transmitted by the first signal path and the second signal path, thereby canceling the interference of the fundamental frequency signal and the higher harmonic signals of the gated signal capacitor response, and outputting an avalanche pulse signal.

[0009] For example, in some embodiments of this application, the second signal path includes a bandpass filter for filtering the second signal to extract the fundamental frequency signal and higher harmonic signals of the gated signal capacitor response.

[0010] For example, in some embodiments of this application, the second signal path includes a phase offset component for offsetting the phase of the second signal by 180°.

[0011] For example, in some embodiments of this application, the second signal path includes an amplification component for amplifying the second signal so that the power difference between the second signal and the first signal is less than a set threshold, thereby satisfying the interference power requirement.

[0012] According to a second aspect of this application, at least one embodiment of this application provides an active ultra-narrowband interferometry method, the active ultra-narrowband interferometry method being executed by an active ultra-narrowband interferometry circuit as described in any one of the first aspects, the active ultra-narrowband interferometry method comprising: splitting an input signal into a first signal and a second signal, the power ratio of the first signal and the second signal being N:1, wherein N is greater than 1, the first signal comprising an avalanche pulse signal, a fundamental frequency signal responding to a gated signal capacitor, and a higher harmonic signal, the second signal comprising a fundamental frequency signal responding to a gated signal capacitor, and a higher harmonic signal; transmitting the first signal and the second signal in separate paths; performing filtering, phase shifting, and amplification processing on the second signal; receiving the transmitted first signal and the processed second signal; combining the first signal and the second signal, thereby causing the interference of the fundamental frequency signal responding to a gated signal capacitor and the higher harmonic signal to cancel each other out, and outputting an avalanche pulse signal, wherein the power ratio at the input terminals of the first signal and the second signal is N:1.

[0013] For example, in some embodiments of this application, the filtering, phase shifting and amplification of the second signal includes: performing phase adjustment on the filtered second signal to shift the phase of the second signal by 180°.

[0014] For example, in some embodiments of this application, the filtering, phase shifting and amplification of the second signal includes: amplifying the phase-shifted second signal so that the power difference between the second signal and the first signal is less than a set threshold, thereby meeting the interference power requirement.

[0015] According to a third aspect of this application, at least one embodiment of this application provides a quantum communication system, comprising: a single-photon detector for detecting photon signals during quantum communication, operating in a gate-driven manner, and outputting a raw signal, wherein the raw signal includes a photon-induced avalanche pulse signal, a fundamental frequency signal of the gate circuit capacitor response, and higher harmonic signals; and an active ultra-narrowband interference circuit as described in any one of the first aspects, connected to the single-photon detector, for receiving the raw signal, eliminating the fundamental frequency signal of the gate circuit capacitor response and higher harmonic signals in the raw signal through interference cancellation, retaining the avalanche pulse signal and outputting it.

[0016] Through the above exemplary embodiments, the active ultra-narrowband interference circuit, method, and quantum communication system provided in this application have at least one of the following beneficial effects:

[0017] To resolve the contradiction between the "power balance requirement for interference cancellation" and the "preservation of weak signal amplitude": by optimizing the power ratio of the first power distribution synthesizer and the second power distribution synthesizer (both N:1), and by compensating for power loss with the amplification components of the second signal path, the output signal power is significantly improved.

[0018] Stable interference signal cancellation effect: Using an ultra-narrow bandpass filter with a stopband bandwidth of no more than 1MHz and a transition band of less than 5MHz, the interference signal component of the gate circuit capacitor response is accurately extracted, and the circuit operation is not affected by the working state of the APD device itself, and can stably provide a wide and continuous frequency domain passband to process avalanche narrow pulse signals.

[0019] Optimized single-photon detection performance: It has minimal impact on the signal-to-noise ratio, pulse waveform, and jitter of avalanche narrow pulse signals, significantly improves the detection efficiency of single-photon detectors, enhances the afterpulse suppression effect, and improves the time resolution, thus ensuring the efficient and stable operation of quantum communication systems.

[0020] Simple structure and easy to implement: Based on the existing passive ultra-narrow band interference circuit, only the amplification component is added and the power ratio setting of the power distribution synthesizer is optimized. No complex structural modifications are required, which is convenient for industrial production and practical application.

[0021] It should be understood that the above general description and the following detailed description are merely exemplary and do not limit this application. Attached Figure Description

[0022] The above and other objects, features, and advantages of this application will become more apparent from the detailed description of exemplary embodiments with reference to the accompanying drawings. The drawings described below are merely some embodiments of this application and are not intended to limit the scope of this application.

[0023] Figure 1 This is a schematic diagram of the active ultra-narrow band interference circuit in an embodiment of this application;

[0024] Figure 2 A schematic diagram illustrating an exemplary active ultra-narrowband interferometry method is shown. Detailed Implementation

[0025] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this application will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0026] The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of these specific details, or other methods, components, materials, devices, etc. In these cases, well-known structures, methods, devices, implementations, materials, or operations will not be shown or described in detail.

[0027] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0028] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0029] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of exemplary embodiments, and the modules or processes in the drawings are not necessarily essential for implementing this application, and therefore cannot be used to limit the scope of protection of this application.

[0030] Figure 1 This is a schematic diagram of the active ultra-narrow band interference circuit in an embodiment of this application.

[0031] like Figure 1 As shown, the active ultra-narrow band interference circuit includes: a first power distribution combiner 1, a first signal path 2, a second signal path 3, and a second power distribution combiner 4.

[0032] The first power distribution synthesizer 1 includes a first output terminal and a second output terminal, used to divide the input signal into a first signal and a second signal. The first output terminal is used to output the first signal, and the second output terminal is used to output the second signal. The signal power ratio between the first output terminal and the second output terminal is N:1 (N is greater than 1). Through this power distribution ratio, most of the signal energy enters the first signal path, laying the foundation for the preservation of weak signals.

[0033] The input terminal of the first signal path 2 is connected to the first output terminal of the first power distribution synthesizer 1, forming a broadband path for the complete transmission of the first signal. The first signal is a composite signal, including a photon-induced avalanche pulse signal, the fundamental frequency signal of the gated circuit capacitor response, and higher harmonic signals. This path does not change the frequency components and phase of the signal, but only achieves distortion-free transmission of the signal.

[0034] The input terminal of the second signal path 3 is connected to the second output terminal of the first power distribution synthesizer 1. It is a narrowband path used to transmit and process the second signal. The second signal includes the fundamental frequency signal and higher harmonic signals of the gate circuit capacitor response.

[0035] According to an example embodiment, the second signal path 3 includes a bandpass filter 31, a phase shift component 32, and an amplification component 33.

[0036] The bandpass filter 31 is used to perform narrowband filtering on the second signal to extract the frequency components of the fundamental frequency signal and the higher harmonic signals of the gate circuit capacitor response.

[0037] According to some embodiments, the stopband bandwidth of the bandpass filter 31 is no more than 1MHz and the transition band is less than 5MHz, ensuring that only the target interference signal is filtered out.

[0038] The phase shift component 32 is used to adjust the phase of the second signal, shifting the phase of the second signal by 180°, so as to provide phase conditions for the interference cancellation with the first signal.

[0039] The amplification component 33 is used to compensate for the power loss caused by the bandpass filter 31 and the phase offset component 32 during the filtering process.

[0040] According to some embodiments, the amplification factor of the amplification component 33 is determined based on the actual power loss of the bandpass filter 31 and the phase shift component 32, so that the power difference between the filtered second signal and the first signal is less than a set threshold, thereby meeting the interference power requirements.

[0041] The second power distribution combiner 4 includes a first input terminal and a second input terminal. The first input terminal is connected to the output terminal of the first signal path 2, and the second input terminal is connected to the output terminal of the second signal path 3. The signal power ratio between the first input terminal and the second input terminal is N:1. The second power distribution combiner 4 is used to receive the composite signal transmitted from the first signal path 2 and the interference signal processed by the second signal path 3. By superimposing the two signals, interference cancellation is achieved, ultimately eliminating the fundamental frequency signal and higher harmonic signals of the gate circuit capacitor response, and outputting only the avalanche pulse signal.

[0042] With the structure described above in this application, the output signal power is N²:(N+1) times the input signal power. 2It balances the requirements of "power balance for interference cancellation" and "preservation of weak signal amplitude". For example, when N=9, the output signal power can reach 81% of the input signal, which is much higher than the 9% of existing passive ultra-narrowband interference circuits, ensuring the effective detection of weak avalanche pulse signals.

[0043] This application also provides an active extremely narrowband interference method.

[0044] like Figure 2 As shown, the active ultra-narrow band interferometry method is performed by the active ultra-narrow band interferometry circuit as described above. The active ultra-narrow band interferometry method includes:

[0045] S1. Signal Allocation Step: The input raw signal (output signal from the single-photon detector) is divided into a first signal and a second signal by a first power allocation synthesizer. The power ratio of the first signal and the second signal is N:1 (N is greater than 1). The first signal includes an avalanche pulse signal, the fundamental frequency signal of the gate circuit capacitor response, and higher harmonic signals. The second signal includes the fundamental frequency signal of the gate circuit capacitor response and higher harmonic signals.

[0046] S2. Split Transmission Steps: Transmit the first signal through the first signal path, maintaining the frequency components, phase, and power characteristics of the first signal unchanged. Transmit the second signal through the second signal path, preparing for subsequent signal processing.

[0047] S3, Second signal processing steps: The second signal is sequentially processed by filtering, phase shifting, and amplification:

[0048] Filtering: The fundamental frequency signal and higher harmonic signals of the gate circuit capacitor response in the second signal are extracted by a bandpass filter, and other irrelevant signals are filtered out.

[0049] Phase shift processing: The phase of the filtered second signal is shifted by 180° using a phase shift component to ensure that it is out of phase with the interference signal in the first signal.

[0050] Amplification process: The second signal after phase shift is amplified by an amplification component to compensate for power loss during the filtering process, so that the power difference between the second signal and the first signal is less than a set threshold, thus meeting the interference power requirements.

[0051] S4. Signal Synthesis Interference Step: The first signal transmitted through the first signal path and the second signal processed by the second signal path are received through the second power distribution synthesizer. The power ratio of the first signal and the second signal at the input of the second power distribution synthesizer is N:1. After the two signals are superimposed, interference cancellation occurs. The fundamental frequency signal and higher harmonic signals of the gate circuit capacitor in the first signal are canceled by the second signal, and finally an avalanche pulse signal is output.

[0052] The working principle of the active ultra-narrowband interference circuit of this application is explained below with reference to specific scenarios:

[0053] 1. The raw signal output by the single-photon detector (including avalanche pulse signal, fundamental wave signal and higher harmonic signal) is input into the first power distribution synthesizer 1.

[0054] 2. The first power distribution combiner 1 receives the raw signal output from the single-photon detector and divides it into a first signal and a second signal with a power ratio of 9:1. The first signal includes an avalanche pulse signal, a fundamental wave signal, and higher harmonic signals, while the second signal includes the fundamental wave signal and higher harmonic signals.

[0055] 3. The first signal is transmitted through the first signal path 2, and the frequency, phase and power of the signal remain unchanged during the transmission process; the second signal is transmitted through the second signal path 3 and enters the subsequent processing stage.

[0056] 4. Filtering: Bandpass filter 31 filters the second signal, allowing only the fundamental signal and higher harmonic signals to pass through, while filtering out other noise.

[0057] Phase shift processing: Phase shift component 32 shifts the phase of the filtered fundamental signal and higher harmonic signals by 180°;

[0058] Amplification process: Amplification component 33 amplifies the phase-shifted fundamental signal and higher harmonic signals by 20dB to compensate for the power loss of bandpass filter 31.

[0059] 5. The first input terminal 41 of the second power distribution synthesizer 4 receives the first signal, and the second input terminal 42 receives the processed second signal. The two signals are superimposed at a power ratio of 9:1. Since the fundamental and higher harmonic signals in the second signal are close in power and opposite in phase to the fundamental and higher harmonic signals in the first signal, they interfere and cancel each other out. The final output is a pure signal that only includes the avalanche pulse signal, and the output power is 81% of the original input signal power.

[0060] This application also provides a quantum communication system.

[0061] The quantum communication system includes a single-photon detector and the active narrowband interference circuit described above.

[0062] The single-photon detector uses a semiconductor avalanche diode (APD) as its core, operating in a gate-driven manner to reduce avalanche charge and recovery time. It is used to detect photon signals during quantum communication and outputs the original signal. The original signal is a composite signal, including the avalanche pulse signal induced by the photon, the fundamental frequency signal from the capacitive response of the gate circuit, and higher harmonic signals.

[0063] The input of the active ultra-narrowband interference circuit is connected to the output of the single-photon detector to receive the original signal output by the detector. Through the principle of interference cancellation, the fundamental frequency signal and higher harmonic signals of the gated circuit capacitance response in the original signal are eliminated, while the avalanche pulse signal is retained and output, providing an accurate signal source for signal identification and data transmission in quantum communication systems.

[0064] Through the above exemplary embodiments, the active ultra-narrowband interference circuit, method, and quantum communication system provided in this application have the following beneficial effects: They effectively resolve the contradiction between the "power balance requirement for interference cancellation" and the "preservation of weak signal amplitude." By optimizing the power ratio (both N:1) of the first and second power distribution synthesizers, and combining this with the amplification components of the second signal path to compensate for power loss, the output signal power is significantly improved, ensuring effective detection of weak avalanche pulse signals. Simultaneously, by employing an ultra-narrowband bandpass filter with a stopband bandwidth of no more than 1MHz and a transition band of less than 5MHz, the interference signal components of the gate circuit's capacitor response can be accurately extracted. Furthermore, the circuit operation is unaffected by the operating state of the APD device itself, and can stably provide a wide and continuous frequency domain passband for processing avalanche narrow pulse signals, with stable interference signal cancellation effect. In addition, this application has minimal impact on the signal-to-noise ratio, pulse waveform, and jitter of avalanche narrow pulse signals, significantly improving the detection efficiency of single-photon detectors, enhancing the after-pulse suppression effect, and improving time resolution, thus ensuring the efficient and stable operation of quantum communication systems. Moreover, based on existing passive ultra-narrowband interference circuits, it only adds an amplification component and optimizes the power ratio setting of the power distribution synthesizer, without requiring complex structural modifications. The structure is simple, easy to implement, and convenient for industrial production and practical applications.

[0065] It should be clearly understood that this application describes how specific examples are formed and used, but this application is not limited to any details of these examples. Rather, based on the teachings of the disclosure of this application, these principles can be applied to many other embodiments.

[0066] Furthermore, it should be noted that the above figures are merely illustrative representations of the processes included in the method according to exemplary embodiments of this application, and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0067] Exemplary embodiments of this application have been specifically shown and described above. It should be understood that this application is not limited to the detailed structures, arrangements, or implementation methods described herein; rather, this application is intended to cover various modifications and equivalent arrangements that fall within the objectives and scope of the appended claims.

Claims

1. An active ultra-narrow band interference circuit, characterized in that, include: A first power division combiner is used to divide an input signal into a first signal and a second signal. The first power division combiner includes a first output terminal and a second output terminal. The first output terminal is used to output the first signal, and the second output terminal is used to output the second signal. The power ratio between the first output terminal and the second output terminal is N:1, where N is greater than 1. The first signal path has its input end connected to the first output end and is used to transmit the first signal, which includes an avalanche pulse signal, a fundamental frequency signal of the gating signal capacitor response, and a higher harmonic signal. A second signal path, whose input terminal is connected to the second output terminal, is used to transmit the second signal, which includes a fundamental frequency signal and higher harmonic signals in response to a gated signal capacitor. The second signal path includes: An amplification component is used to amplify the second signal so that the power difference between the second signal and the first signal is less than a set threshold, thereby meeting the interference power requirement. The second power distribution synthesizer includes a first input terminal and a second input terminal. The first input terminal is connected to the output terminal of the first signal path, and the second input terminal is connected to the output terminal of the second signal path. The power ratio of the first input terminal and the second input terminal is N:

1. It is used to synthesize the signals transmitted by the first signal path and the second signal path, so that the interference of the fundamental frequency signal and the higher harmonic signal of the gated signal capacitor response cancels out, and an avalanche pulse signal is output.

2. The active ultra-narrow band interference circuit as described in claim 1, characterized in that, The second signal path includes: A bandpass filter is used to filter the second signal to extract the fundamental frequency signal and higher harmonic signals of the gated signal capacitor response.

3. The active ultra-narrow band interference circuit as described in claim 1, characterized in that, The second signal path includes: A phase offset component is used to offset the phase of the second signal by 180°.

4. An active ultra-narrowband interferometry method, characterized in that, The active ultra-narrowband interferometry method is performed by the active ultra-narrowband interferometry circuit as described in any one of claims 1-3, and the active ultra-narrowband interferometry method includes: The input signal is divided into a first signal and a second signal, with a power ratio of N:1, where N is greater than 1. The first signal includes an avalanche pulse signal, a fundamental frequency signal of the gated signal capacitor response, and a higher harmonic signal. The second signal includes a fundamental frequency signal of the gated signal capacitor response and a higher harmonic signal. The first signal and the second signal are transmitted separately. The second signal is then filtered, phase-shifted, and amplified. The system receives the first transmitted signal and the processed second signal, combines the first signal and the second signal to cancel the interference of the fundamental frequency signal and the higher harmonic signal of the gated signal capacitor response, and outputs an avalanche pulse signal, wherein the power ratio of the input terminals of the first signal and the second signal is N:

1.

5. The active ultra-narrowband interferometry method as described in claim 4, characterized in that, The filtering, phase shifting, and amplification processing of the second signal includes: The filtered second signal is phase-adjusted so that its phase is shifted by 180°.

6. The active ultra-narrowband interferometry method as described in claim 5, characterized in that, The filtering, phase shifting, and amplification processing of the second signal includes: The second signal after phase shift is amplified so that the power difference between the second signal and the first signal is less than a set threshold, thereby meeting the interference power requirements.

7. A quantum communication system, characterized in that, include: A single-photon detector is used to detect photon signals in quantum communication. It operates based on a gate-driven method and outputs a raw signal, which includes a photon-induced avalanche pulse signal, a fundamental frequency signal of the gate circuit capacitor response, and higher harmonic signals. The active ultra-narrowband interference circuit as described in any one of claims 1-3 is connected to the single-photon detector and is used to receive the original signal. Through interference cancellation, it eliminates the fundamental frequency signal and higher harmonic signals of the gate circuit capacitor response in the original signal, retains the avalanche pulse signal, and outputs it.

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