CN111010270A - MDI-QKD system synchronization device and method of optical-electric-optical mode - Google Patents
MDI-QKD system synchronization device and method of optical-electric-optical mode Download PDFInfo
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- H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
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- H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
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Abstract
The invention provides a synchronization device and a synchronization method for an MDI-QKD system in an optical-electrical-optical mode. The method comprises the following steps: the synchronous light pulse and the signal light pulse are transmitted to an Alice end and a Bob end and are converted into synchronous electric pulses, the signal light pulse is encoded, the time delay of the synchronous electric pulses is adjusted, the synchronous electric pulses are converted into the synchronous light pulse and are transmitted to a detection module to be converted into the synchronous electric pulses, and a single photon detector and a collection card are triggered to work. Compared with other modes for generating synchronous electric pulses in the QKD system, the invention reduces the problem of high coding complexity, overcomes the defect of unstable interference in the prior art, and has the advantages of reliable transmission and high detection efficiency in the QKD system.
Description
Technical Field
The invention belongs to the technical field of electronics, and further relates to a device and a method for synchronizing a measurement-independent quantum key distribution (MDI-QKD) system independent of a measurement device of an optical-electrical-optical mode in the technical field of quantum communication.
Background
A key technology of the QKD system is synchronization of information of both the transmitting and receiving parties, and subsequent key extraction can be performed only if the signal light and the synchronization light are synchronized. Meanwhile, in order to reduce the error rate, it is required to remove the dark count as much as possible. In order to ensure the accuracy of single photon counting, the synchronous signal of the transmitting end needs to be accurately transmitted to the receiving end without error, and the synchronous signal is kept synchronous with the detection signal of the single photon detector. If the synchronization precision is higher, the single-photon counter is more accurate, the dark count capable of being removed is more, and the performance of the QKD system is better, so that the key of the QKD system is the design of the synchronization method.
Quantum communication technology, Inc., Anhui, discloses a quantum key distribution QKD system synchronization apparatus in the patent document "a QKD system synchronization apparatus" (application number: 201310434795.2 application publication number: CN 104468092A) applied by Quantum communication technology, Inc. The device comprises a sending device for sending synchronous light and signal light, a photoelectric conversion device, an adjustable time delay module, a single photon detector and a data acquisition module. The synchronization device realizes an end-to-end quantum key distribution system. The low-jitter frequency doubling device in the synchronization device can realize the frequency consistency of the synchronization light and the signal light, and reduces the influence of the synchronization light on the signal light. However, the synchronizing device has the following disadvantages: the synchronization device and the synchronization method are two-end QKD systems based on BB84 protocol, the coding method and the synchronization device are too simple, and for the MDI-QKD system, the synchronization device and the synchronization method can not ensure the interference of the signal light pulse at the Alice end and the signal light pulse at the Bob end at the detection end.
Tombalin discloses a synchronization method for synchronizing light and signal light by using different optical fibers in the published paper "experimental study on safety of practical quantum key distribution system" (2015 paper of doctor academic degree of university of Chinese science and technology). The synchronization method is based on an MDI-QKD system, and comprises the steps of sending synchronization light pulses to an Alice end and a Bob end from a detection end, detecting synchronization light signals by the Alice and the Bob through linear photodiodes, converting the synchronization light signals into synchronization electric pulses to serve as trigger signals for encoding work of the Alice end and the Bob end, and even though the synchronization method cannot cause extra dark counting of the signal light pulses. But the synchronization method still has the following defects: after the synchronous electric pulse finishes the coding work, the synchronous electric pulse is not transmitted to the detection end to trigger the single photon detector and the acquisition card to work, the stable interference of the synchronous electric pulse at the Alice end and the synchronous electric pulse at the Bob end at the detection end can not be ensured, and the accurate synchronization can not be realized.
Disclosure of Invention
The present invention aims to provide a synchronization device and method for MDI-QKD system in optical-electrical-optical mode, which can realize stable interference between the synchronous optical pulse at Alice end and the synchronous optical pulse at Bob end at the detection end by adjusting the time delay of the synchronous electrical pulse after encoding and converting the synchronous electrical pulse into the synchronous optical pulse to be transmitted to the detection end.
In order to achieve the purpose, the specific idea of the invention is that synchronous light pulse is generated outside, the synchronous light pulse and the signal light pulse are transmitted to a coding end, the synchronous light pulse is converted into synchronous electric pulse at the coding end, a Field Programmable Gate Array (FPGA) at the coding end is triggered to realize the coding of the signal light pulse, after the coding is completed, if the signal light pulse at an Alice end and the signal light pulse at a Bob end have time delay difference, the time delay of the synchronous electric pulse is adjusted, then the synchronous electric pulse is converted into synchronous light pulse and transmitted to a detection end, and the synchronous light pulse is converted into synchronous electric pulse single photon triggering detector and acquisition card at the detection end to work.
In order to achieve the purpose, the device comprises a first photoelectric conversion module, a coding module, a time delay adjusting module, an optical fiber channel module, a second photoelectric conversion module, a detection module and an electro-optical conversion module. The input end of the first photoelectric conversion module is connected with an externally input synchronous optical pulse; the output end of the first photoelectric conversion module is connected with the input end of the coding module; the output end of the first photoelectric conversion module is connected with the input end of the time delay adjusting module; the output end of the time delay adjusting module is connected with the input end of the electro-optical conversion module; the output end of the electro-optical conversion module is connected with the input end of the optical fiber channel module, and the output end of the optical fiber channel module is connected with the input end of the second photoelectric conversion module; the output end of the second photoelectric conversion module is connected with the input end of the detection module; wherein the content of the first and second substances,
the first photoelectric conversion module is used for converting the synchronous light pulses transmitted to the Alice end and the Bob end into synchronous electric pulses;
the encoding module comprises a field programmable gate array FPGA, an intensity modulator IM and a phase modulator PM, wherein the field programmable gate array FPGA is used for generating an electric pulse driving signal, the intensity modulator IM is used for modulating the amplitude of a first pulse of a signal light pulse, and the phase modulator PM is used for modulating the phase of a second pulse of the signal light pulse;
the time delay adjusting module is used for adjusting the time delay of the synchronous electric pulse to enable the signal light pulse at the Alice end and the signal light pulse at the Bob end to realize interference at the detection end;
the electro-optical conversion module comprises a synchronous laser and an intensity modulator IM, wherein the synchronous laser is used for generating synchronous light with continuous sinusoidal waveform, the intensity modulator IM is used for modulating the synchronous light with continuous sinusoidal waveform into synchronous light pulse, and the synchronous electric pulse is required to be used as a driving signal;
the optical fiber channel module is used for transmitting the synchronous optical pulse and the signal optical pulse to a detection end by using one optical fiber through a Wavelength Division Multiplexer (WDM);
the second photoelectric conversion module is used for converting the synchronous light pulse into a synchronous electric pulse again and triggering the single-photon detector and the acquisition card of the detection module to work;
the detection module is used for triggering the single-photon detector to detect the signal light pulse by taking the synchronous electric pulse as a synchronous trigger signal of the single-photon detector and the acquisition card and triggering the acquisition card to acquire the output of the single-photon detector.
The method comprises the following specific steps:
(1) transmitting the synchronous light pulse to an Alice end and a Bob end:
generating a synchronous optical pulse with a wavelength different from that of the signal optical pulse, and transmitting the synchronous optical pulse and the signal optical pulse to an Alice end and a Bob end by a Wavelength Division Multiplexer (WDM);
(2) converting the synchronization light pulse into a synchronization electric pulse:
when the synchronous light pulse reaches the Alice end and the Bob end, the photoelectric converter of the first photoelectric conversion module converts the synchronous light pulse into the synchronous electric pulse and divides the synchronous electric pulse into two paths, one path is sent to the delay adjusting module, and the other path is sent to the field programmable gate array FPGA of the coding module;
(3) encoding the signal light pulse:
(3a) when the synchronous electric pulse reaches the field programmable gate array FPGA of the coding module, the field programmable gate array FPGA generates an electric pulse signal, the frequency of the electric pulse signal is consistent with that of the signal light pulse, the pulse width of the electric pulse signal is equal to that of the signal light pulse, and the amplitude of the electric pulse signal is larger than or equal to that of the signal light pulse;
(3b) the FPGA transmits an electric pulse signal to an intensity modulator IM, the intensity modulator IM modulates a first pulse of an input signal light pulse to enable the amplitude of the first pulse to be equal to the amplitude of the input electric pulse signal, and the amplitude of a second pulse of the signal light pulse is kept unchanged to finish time coding;
(3c) field programmableThe gate array FPGA generates three electric pulse signals, the frequency of each electric pulse signal is consistent with that of a signal light pulse, the pulse width is equal to or larger than that of the signal light pulse, and the amplitudes are V respectively0、2V0、3V0In which V is0Is the half-wave voltage of the phase modulator PM;
(3d) the FPGA transmits an electric pulse signal to the phase modulator PM at each time, the phase modulator PM modulates the phase of the second pulse of the signal light pulse according to the amplitude of the input electric pulse signal, the phase of the first pulse of the signal light pulse is kept unchanged, and phase encoding is completed;
(4) adjusting the time delay of the synchronous electric pulse:
(4a) when the synchronous light pulses of the Alice end and the Bob end have time delay difference at the detection end, the interference is unstable, and the time delay adjusting module needs to adjust the time delay of the input synchronous electric pulses;
(4b) external resistor R for adjusting delay chip in delay moduleSAnd an external capacitor CEAnd a threshold voltage V of the digital-to-analog converterbTo delay the synchronous electrical pulse;
(5) converting the synchronization electrical pulse into a synchronization optical pulse:
(5a) the time delay adjusting module sends the delayed synchronous electric pulse to the intensity modulator IM;
(5b) the intensity modulator IM takes the transmitted synchronous electric pulse as a driving pulse and converts the continuous sine wave-shaped synchronous light generated by the synchronous laser into a synchronous light pulse;
(5c) the wavelength division multiplexer WDM transmits the synchronous light pulse and the coded signal light pulse to the detection end through the optical fiber channel module;
(6) converting the synchronization light pulse into a synchronization electric pulse:
when the synchronous light pulse reaches the detection end through the optical fiber channel module, the photoelectric converter of the second photoelectric conversion module converts the synchronous light pulse into synchronous electric pulse and sends the synchronous electric pulse to the single-photon detector and the acquisition card in the detection module;
(7) and synchronously operating the electric pulse trigger single-photon detector and the acquisition card:
(7a) when the synchronous electric pulse reaches the single photon detector, triggering the single photon detector to start detecting signal light pulse by a detection gate, and when the single photon detector detects each signal light pulse, adding 1 to a counter in the single photon detector;
(7b) and when the synchronous electric pulse reaches the acquisition card in the detection module, triggering the acquisition card to acquire the output signal of the single photon detector.
Compared with the prior art, the invention has the following advantages:
firstly, because the coding module in the device of the invention adopts the FPGA to code the signal light pulse, and uses the synchronous electric pulse as a trigger signal to generate an electric pulse signal which is sent to the intensity modulator IM and the phase modulator PM to modulate the amplitude and the phase of the signal light pulse, the invention overcomes the problem that the real-time synchronization can not be realized because the electric pulse signal has delay difference in the transmission process of each device in the prior art, thereby having the advantage of high real-time property.
Secondly, because the method adopts the synchronous method of the photo-electric-optical mode, the synchronous light pulse is converted into the synchronous electric pulse in the coding module, the field programmable gate array FPGA of the coding module is triggered to code the signal light pulse, the time delay of the synchronous electric pulse is adjusted, the synchronous electric pulse is converted into the synchronous light pulse and is transmitted to the detection module, the synchronous light pulse is converted into the synchronous electric pulse, and the single photon detector and the acquisition card are triggered to work.
Drawings
FIG. 1 is a block diagram of the apparatus of the present invention;
FIG. 2 is a flow chart of the method of the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
The apparatus of the present invention will be further described with reference to the apparatus block diagram of figure 1.
The device comprises a first photoelectric conversion module, a coding module, a time delay adjusting module, an electro-optical conversion module, an optical fiber channel module, a second photoelectric conversion module and a detection module. The input end of the first photoelectric conversion module is connected with an externally input synchronous optical pulse; the output end of the first photoelectric conversion module is connected with the input end of the coding module; the output end of the first photoelectric conversion module is connected with the input end of the time delay adjusting module; the output end of the time delay adjusting module is connected with the input end of the electro-optical conversion module; the output end of the electro-optical conversion module is connected with the input end of the optical fiber channel module, and the output end of the optical fiber channel module is connected with the input end of the second photoelectric conversion module; the output end of the second photoelectric conversion module is connected with the input end of the detection module; wherein the content of the first and second substances,
the first photoelectric conversion module is used for converting synchronous light pulses transmitted to the Alice end and the Bob end into synchronous electric pulses, driving a Field Programmable Gate Array (FPGA) of the coding module to code the signal light pulses, and if the voltage of the electric pulses is small, the voltage of the electric pulses needs to be amplified through an amplifier.
The encoding module comprises a field programmable gate array FPGA, an intensity modulator IM and a phase modulator PM, wherein the field programmable gate array FPGA is used for generating an electric pulse driving signal and transmitting the electric pulse driving signal to the intensity modulator IM and the phase modulator PM, the intensity modulator IM is used for modulating the amplitude of a first pulse of a signal light pulse, and the phase modulator PM is used for modulating the phase of a second pulse of the signal light pulse.
The time delay adjusting module is used for enabling the signal light pulse at the Alice end and the signal light pulse at the Bob end to realize interference at the detection end by adjusting the time delay of the synchronous electric pulse, the time delay adjusting module comprises an AD9501 time delay chip, an external resistor and an external capacitor, the time delay chip internally comprises a ramp voltage generator, an 8-bits digital-to-analog converter and a voltage comparator, the external resistor is connected between the 7 th pin of the time delay chip and the ground in parallel, and the external capacitor is connected between the 6 th pin of the time delay chip and the 7V power supply in parallel.
The electro-optical conversion module comprises a synchronous laser and an intensity modulator IM, wherein the synchronous laser is used for generating synchronous light with continuous sine waveform, the intensity modulator IM is used for modulating the synchronous light with the continuous sine waveform into synchronous light pulse, and the synchronous electric pulse is used as a driving signal of the intensity modulator IM.
And the optical fiber channel module is used for transmitting the synchronous optical pulse and the signal optical pulse to the detection end by using one optical fiber through a Wavelength Division Multiplexer (WDM).
And the second photoelectric conversion module is used for converting the synchronous light pulse into a synchronous electric pulse again and triggering the single-photon detector and the acquisition card of the detection module to work.
The detection module is used for triggering the single-photon detector to detect the signal light pulse by taking the synchronous electric pulse as a synchronous trigger signal of the single-photon detector and the acquisition card and triggering the acquisition card to acquire the output of the single-photon detector.
The specific steps of the method of the present invention are further described below with reference to fig. 2.
And step 1, transmitting the synchronous light pulse to an Alice end and a Bob end.
The method is characterized in that a synchronous optical pulse is externally generated, the wavelength of the synchronous optical pulse is different from that of a signal optical pulse, the signal optical pulse is generally 1550nm, the synchronous optical wavelength can be 1570nm or 1530nm, the pulse width of the synchronous optical pulse is larger than that of the signal optical pulse, because the MDI-QKD system adopting time phase coding is adopted, the signal optical pulse has two narrow pulses in one period, the interval is constant, the pulse widths of the two narrow pulses are consistent, the synchronous optical pulse and the signal optical pulse are transmitted to an Alice end and a Bob end in one optical fiber through a wavelength division multiplexer, and Alice and Bob are both communication parties in the QKD system.
And 2, converting the synchronous light pulse into a synchronous electric pulse.
When the synchronous light pulse reaches the Alice end and the Bob end, the photoelectric converter of the first photoelectric conversion module converts the synchronous light pulse into a synchronous electric pulse, then the synchronous electric pulse is divided into two paths, one path enters the delay adjusting module and is used for adjusting the delay of the synchronous electric pulse, and the other path enters the field programmable gate array FPGA of the encoding module and triggers the FPGA to encode the signal light pulse of the Alice end and the Bob end.
And 3, encoding the signal light pulse.
When the synchronous electric pulse reaches the Alice end and the Bob end, the field programmable gate array FPGA of the coding module generates an electric pulse signal, the frequency of the electric pulse signal is consistent with that of the signal light pulse, the pulse width is larger than or equal to that of the first pulse of the signal light pulse, and the amplitude of the electric pulse signal is larger than that of the first pulse of the signal light pulse.
The optical signal input end of the intensity modulator IM is connected with a signal optical pulse, the field programmable gate array FPGA transmits a generated electric pulse signal to the electric signal input end of the first intensity modulator IM, the amplitude of the first pulse of the modulated signal optical pulse is equal to the amplitude of the input electric pulse signal, and the amplitude of the second pulse of the modulated signal optical pulse is kept unchanged, so that the time coding of the signal optical pulse is completed.
Because the time interval between two pulses of the signal light pulse is determined, after the FPGA completes time coding on the first signal light pulse, three electric pulse signals are simultaneously generated, the pulse width of each electric pulse signal is equal to or larger than that of the signal light pulse, and the amplitude of each electric pulse signal is respectively V0、2V0、3V0In which V is0Is the half-wave voltage of the phase modulator.
The FPGA transmits an electric pulse signal to the electric signal input end of the phase modulator PM at each time, the optical signal input end of the phase modulator PM is connected with the output of the first intensity modulator IM, the phase modulator PM modulates the phase of the second pulse of the signal optical pulse according to the amplitude of the input electric pulse signal, the phase of the first pulse of the signal optical pulse is kept unchanged, and the phase coding of the signal optical pulse is completed. The synchronous electric pulse is used as a synchronous trigger signal of the field programmable gate array FPGA, and the time phase coding of the signal light pulse is completed.
And 4, adjusting the time delay of the synchronous electric pulse.
When the synchronous light pulses of the Alice end and the Bob end have time delay difference at the detection end, namely the signal light pulses of the Alice end and the Bob end do not interfere, the time delay of the synchronous electric pulse needs to be adjusted, and when the synchronous electric pulse reaches the time delay adjusting module, the rising edge of the synchronous electric pulse triggers a ramp wave voltage generator of a time delay chip AD9501 of the time delay module to generate ramp wave voltage VaAt this time, VaIs larger than the threshold voltage V of the digital-to-analog converter of the time delay chipbThe delay chip starts to delay the synchronous electric pulse, and the adjustable delay time of the delay chip is t ═ Rs×(Ce+8.5PF)×3.84×(Vb/256)。
External resistor R for changing time delay chipSAnd an external capacitor CEAnd a threshold voltage V of the digital-to-analog converterbTo adjust the time delay of the synchronous electrical pulses, the threshold voltage V of the D/A converterbThe time delay difference is set by an 8-bits digital programming device, when the time delay difference needing to be adjusted is smaller than 326ns, an external capacitor needs to be opened, the time delay difference is the time difference between the Alice end signal light pulse and the Bob end signal light pulse reaching a single photon detector, and when V is less than the time delay difference of the Alice end signal light pulse and the Bob end signal light pulse reaching the single photon detector, the time delay difference isaLess than VbAnd when the time is up, the voltage comparator of the time delay chip sets the output high, the time delay chip finishes time delay, and the time-delayed electric pulse signal is output.
And 5, converting the synchronous electric pulse into a synchronous optical pulse.
The time delay adjusting module transmits the delayed electric pulse signal to the electric signal input end of the second intensity modulator IM, if the synchronous electric pulse voltage is less than the required input voltage V of the intensity modulatorcThe amplitude of the synchronous electrical pulse needs to be amplified by an amplifier and then transmitted to the electrical signal input of the intensity modulator IM.
The optical signal input end of the intensity modulator IM is connected with the output end of the synchronous laser, and the electric pulse signal drives the intensity modulator to convert the synchronous light of continuous sine waveform generated by the synchronous laser into the synchronous light of pulse form. This synchronization light pulse coincides with the synchronization light pulse generated in step 1.
The wavelength division multiplexer WDM transmits the synchronous light pulse and the coded signal light pulse to the detection end through an optical fiber channel module, wherein the optical fiber channel module is a laboratory optical fiber with the length of [20,100], and the unit is kilometer.
And 6, converting the synchronous light pulse into a synchronous electric pulse.
When the synchronous light pulse reaches the detection end through the optical fiber channel module, the photoelectric converter of the second photoelectric conversion module converts the synchronous light pulse into the synchronous electric pulse and divides the synchronous electric pulse into two paths, one path is sent to the electric signal input end of the single-photon detector to trigger the single-photon detector to detect the signal light pulse, and the other path is sent to the acquisition card to trigger the acquisition card to acquire the output of the single-photon detector.
And 7, synchronously operating the electric pulse triggered single photon detector and the acquisition card.
When the synchronous electric pulse reaches the single-photon detector of the detection module, the single-photon detector is triggered to open the detection gate to start detecting the signal light pulse, and when the single-photon detector detects each signal light pulse, a counter in the single-photon detector is added with 1.
When the synchronous electric pulse reaches the acquisition card in the detection module, the acquisition card is triggered to acquire the output signal of the single photon detector, and the output signal is used as a data source for subsequent error correction and amplification.
Claims (3)
1. A MDI-QKD system synchronization device of an optical-electric-optical mode comprises a coding module, an optical fiber channel module, a second photoelectric conversion module and a detection module, and is characterized by also comprising a first photoelectric conversion module, a time delay adjusting module and an electro-optical conversion module; the input end of the first photoelectric conversion module is connected with an externally input synchronous optical pulse; the output end of the first photoelectric conversion module is connected with the input end of the coding module; the output end of the first photoelectric conversion module is connected with the input end of the time delay adjusting module; the output end of the time delay adjusting module is connected with the input end of the electro-optical conversion module; the output end of the electro-optical conversion module is connected with the input end of the optical fiber channel module, and the output end of the optical fiber channel module is connected with the input end of the second photoelectric conversion module; the output end of the second photoelectric conversion module is connected with the input end of the detection module; wherein the content of the first and second substances,
the first photoelectric conversion module is used for converting the synchronous light pulses transmitted to the Alice end and the Bob end into synchronous electric pulses;
the encoding module comprises a field programmable gate array FPGA, an intensity modulator IM and a phase modulator PM, wherein the field programmable gate array FPGA is used for generating an electric pulse driving signal, the intensity modulator IM is used for modulating the amplitude of a first pulse of a signal light pulse, and the phase modulator PM is used for modulating the phase of a second pulse of the signal light pulse;
the time delay adjusting module is used for adjusting the time delay of the synchronous electric pulse to enable the signal light pulse at the Alice end and the signal light pulse at the Bob end to realize interference at the detection end;
the electro-optical conversion module comprises a synchronous laser and an intensity modulator IM, wherein the synchronous laser is used for generating synchronous light with continuous sinusoidal waveform, the intensity modulator IM is used for modulating the synchronous light with continuous sinusoidal waveform into synchronous light pulse, and the synchronous electric pulse is required to be used as a driving signal;
the optical fiber channel module is used for transmitting the synchronous optical pulse and the signal optical pulse to a detection end by using one optical fiber through a Wavelength Division Multiplexer (WDM);
the second photoelectric conversion module is used for converting the synchronous light pulse into a synchronous electric pulse again and triggering the single-photon detector and the acquisition card of the detection module to work;
the detection module is used for triggering the single-photon detector to detect the signal light pulse by taking the synchronous electric pulse as a synchronous trigger signal of the single-photon detector and the acquisition card and triggering the acquisition card to acquire the output of the single-photon detector.
2. The MDI-QKD system synchronization apparatus as claimed in claim 1, wherein said delay adjusting module comprises an AD9501 delay chip, an external resistor and an external capacitor, the delay chip comprises a ramp voltage generator, an 8-bits dac, and a voltage comparator, the external resistor is connected in parallel between the 7 th pin of the delay chip and ground, and the external capacitor is connected in parallel between the 6 th pin of the delay chip and a 7V power supply;
3. the MDI-QKD system synchronization method of an optical-electrical-optical mode of the synchronization apparatus as set forth in claim 1, wherein: when the signal light pulse of the Alice end and the signal light pulse of the Bob end have time delay difference at the detection end, the time delay of the coded synchronous electric pulse is adjusted, and the synchronous electric pulse is converted into the synchronous light pulse to be transmitted to the detection end, wherein the method specifically comprises the following steps:
(1) transmitting the synchronous light pulse to an Alice end and a Bob end:
generating a synchronous optical pulse with a wavelength different from that of the signal optical pulse, and transmitting the synchronous optical pulse and the signal optical pulse to an Alice end and a Bob end by a Wavelength Division Multiplexer (WDM);
(2) converting the synchronization light pulse into a synchronization electric pulse:
when the synchronous light pulse reaches the Alice end and the Bob end, the photoelectric converter of the first photoelectric conversion module converts the synchronous light pulse into the synchronous electric pulse and divides the synchronous electric pulse into two paths, one path is sent to the delay adjusting module, and the other path is sent to the field programmable gate array FPGA of the coding module;
(3) encoding the signal light pulse:
(3a) when the synchronous electric pulse reaches the field programmable gate array FPGA of the coding module, the field programmable gate array FPGA generates an electric pulse signal, the frequency of the electric pulse signal is consistent with that of the signal light pulse, the pulse width of the electric pulse signal is equal to that of the signal light pulse, and the amplitude of the electric pulse signal is larger than or equal to that of the signal light pulse;
(3b) the FPGA transmits an electric pulse signal to an intensity modulator IM, the intensity modulator IM modulates a first pulse of an input signal light pulse to enable the amplitude of the first pulse to be equal to the amplitude of the input electric pulse signal, and the amplitude of a second pulse of the signal light pulse is kept unchanged to finish time coding;
(3c) the FPGA generates three electric pulse signals, the frequency of each electric pulse signal is consistent with that of the signal light pulse, the pulse width is equal to or larger than that of the signal light pulse, and the amplitudeAre each V0、2V0、3V0In which V is0Is the half-wave voltage of the phase modulator PM;
(3d) the FPGA transmits an electric pulse signal to the phase modulator PM at each time, the phase modulator PM modulates the phase of the second pulse of the signal light pulse according to the amplitude of the input electric pulse signal, the phase of the first pulse of the signal light pulse is kept unchanged, and phase encoding is completed;
(4) adjusting the time delay of the synchronous electric pulse:
(4a) when the synchronous light pulses of the Alice end and the Bob end have time delay difference at the detection end, the interference is unstable, and the time delay adjusting module needs to adjust the time delay of the input synchronous electric pulses;
(4b) external resistor R for adjusting delay chip in delay moduleSAnd an external capacitor CEAnd a threshold voltage V of the digital-to-analog converterbTo delay the synchronous electrical pulse;
(5) converting the synchronization electrical pulse into a synchronization optical pulse:
(5a) the time delay adjusting module sends the delayed synchronous electric pulse to the intensity modulator IM;
(5b) the intensity modulator IM takes the transmitted synchronous electric pulse as a driving pulse and converts the continuous sine wave-shaped synchronous light generated by the synchronous laser into a synchronous light pulse;
(5c) the wavelength division multiplexer WDM transmits the synchronous light pulse and the coded signal light pulse to the detection end through the optical fiber channel module;
(6) converting the synchronization light pulse into a synchronization electric pulse:
when the synchronous light pulse reaches the detection end through the optical fiber channel module, the photoelectric converter of the second photoelectric conversion module converts the synchronous light pulse into synchronous electric pulse and sends the synchronous electric pulse to the single-photon detector and the acquisition card in the detection module;
(7) and synchronously operating the electric pulse trigger single-photon detector and the acquisition card:
(7a) when the synchronous electric pulse reaches the single photon detector, triggering the single photon detector to start detecting signal light pulse by a detection gate, and when the single photon detector detects each signal light pulse, adding 1 to a counter in the single photon detector;
(7b) and when the synchronous electric pulse reaches the acquisition card in the detection module, triggering the acquisition card to acquire the output signal of the single photon detector.
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| CN113438077A (en) * | 2021-07-14 | 2021-09-24 | 中国科学技术大学 | Quantum key distribution networking system and quantum key distribution method |
| CN114268421A (en) * | 2021-12-17 | 2022-04-01 | 安徽问天量子科技股份有限公司 | Method for transmitting single-fiber QKD system synchronization signal |
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