CN110518984B - Time synchronization method and system in quantum secret communication - Google Patents
Time synchronization method and system in quantum secret communication Download PDFInfo
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- CN110518984B CN110518984B CN201810488343.5A CN201810488343A CN110518984B CN 110518984 B CN110518984 B CN 110518984B CN 201810488343 A CN201810488343 A CN 201810488343A CN 110518984 B CN110518984 B CN 110518984B
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- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/70—Photonic quantum communication
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- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
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- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
- H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
- H04L9/0852—Quantum cryptography
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Abstract
The invention provides a time synchronization method and a system in quantum secret communication, comprising the following steps: s1, emitting signal light and synchronous light; s2, transmitting the signal light and the synchronous light through the same few-mode fiber channel after coupling the signal light and the synchronous light; s3, receiving the coupled signal light and the coupled synchronous light and splitting the signal light and the synchronous light; s4, detecting the signal light and the synchronous light, determining the link transmission delay between the signal light pulse and the synchronous light pulse, and synchronously correcting the signal light; s5, numbering the synchronous light frames, and marking each signal light pulse according to the synchronous light pulse time interval of each signal light pulse and the frame to which each signal light pulse belongs; s6, identifying the frame number of the synchronous light, and measuring the time interval of the synchronous light pulse of the signal light pulse from the frame to which the signal light pulse belongs; judging the mark number of the received signal light pulse according to the time interval; the labels of the received signal light pulses are in one-to-one correspondence with the labels of the transmitted signal light pulses.
Description
Technical Field
The invention relates to the technical field of quantum communication, in particular to a time synchronization method and a system in quantum secret communication.
Background
The quantum secret communication is based on the basic principle of quantum mechanics and has the characteristic of unconditional safety. The quantum secret communication takes single photon as a carrier, so that information between terminals is transmitted in a secret and safe manner. In recent decades, quantum secret communication technology has been rapidly developed, and core Quantum Key Distribution (QKD) has realized a series of engineering applications, so as to provide quantum security guarantee for information services in fields of national security, finance, electric power and the like.
The quantum key distribution is divided into a sending end Alice and a receiving end Bob, and single mode fibers are mostly adopted as transmission channels. The sending end Alice randomly selects a group of basis vectors ("+" basis vectors or "×" basis vectors) and encodes photons in a certain state under the basis vectors, so as to obtain four polarized photons, namely, a horizontal polarized state H (marked →), a vertical polarized state V (marked → x), a +45° polarized state P (marked ↗) and a-45 ° polarized state N (marked ↘). The photons are received by the receiving end Bob after being transmitted through the channel. Bob also randomly selects a set of basis vectors to measure after receiving the photons and records the measurement. Both Alice and Bob selection basis vectors are random and independent of each other.
And then, alice and Bob perform base vector comparison through a classical channel, namely, the base vector selected by Bob when publishing the measuring photon is compared with the base vector selected by Bob when transmitting the photon, the same data of the selected base vector is reserved, and the data of different base vectors are selected and discarded. And then obtaining a safe secret key through steps of error correction, privacy amplification and the like.
QKD devices need to self-calibrate before they operate in normal operation. The QKD device calibration operation mainly includes light intensity feedback, time-lapse scanning, polarization feedback, and synchronization correction.
The light intensity feedback function completes the intensity maintenance and stability, and compensates the fluctuation of the intensity modulator caused by the change of the external environment, so that the intensity modulator is kept in a preset state. The delay scanning function completes the optimization of the detection efficiency of the gated avalanche single photon detector. The gating signal of the gating single photon detector passes through a 4-path delay chip with adjustable delay, the delay value of the delay chip is adjusted to obtain a detection efficiency counting rate curve, and the maximum value is found, and the set value of the delay chip under the condition is an optimal value. The polarization feedback function is used for completing polarization state monitoring and feedback compensation of the QKD system signal light pulse based on polarization coding.
And finally, performing a synchronous correction step. The synchronization correction function performs a differential measurement of the time of the signal light pulses received by the detector relative to the arrival time of the synchronization light pulses because the fiber optic link and electronics can create different link delays for the signal light and the synchronization light. Therefore, the synchronous correction is started in the system initialization stage, and the time difference value is obtained through the synchronous correction function and can be used for judging the relative relation between the detection time position and the transmission sequence position subsequently.
The synchronous correction function ensures the time synchronization of both parties Alice and Bob of quantum secret communication in the communication process, ensures that both parties perform base vector comparison aiming at the base vector of the same photon state, and does not generate dislocation. Clock synchronization technology is a key technology of a quantum secret communication system and determines whether a secure quantum key can be generated.
Existing clock synchronization techniques mainly include two types. The first method is to transmit quantum signal light and a synchronous optical signal of clock synchronization through two optical fibers, respectively. The extra occupation of an optical fiber as a synchronous optical signal transmission channel greatly wastes optical fiber resources. In addition, the quantum signal light and the synchronous light are respectively transmitted in two optical fibers, the transmission environments of the quantum signal light and the synchronous light are different, and the defect of relative phase jitter exists in the transmission process. The second is a method based on wavelength division multiplexing, in which quantum signal light and synchronization light are transmitted through the same optical fiber. For example, the synchronization light wavelength is different from the quantum signal light wavelength, and the synchronization light frequency is much smaller than the quantum signal light frequency. The synchronous light and the quantum signal light are coupled into the same single mode fiber through the wavelength division multiplexer for transmission. The phase difference between the quantum signal light and the synchronous light is controlled through the time delay module, so that the synchronous light signal is ensured not to generate crosstalk on the quantum signal light.
For example, the quantum signal wavelength is 1550.12nm, the luminescence repetition frequency is 40MHz, the synchronization wavelength is 1570nm, and the luminescence repetition frequency is 100KHz. The synchronous light is used as a reference signal, and quantum signal light between two synchronous light signals forms a frame and is numbered. And Bob receives the synchronous optical signal and can determine the frame of the quantum signal light according to the synchronous optical number. And then measuring the time gap between a certain quantum signal light and the synchronous light to determine the number of the quantum signal light belonging to the frame, so that the time synchronization between Alice and Bob can be realized.
For the method of adopting two optical fibers to respectively transmit quantum signal light and synchronous light, the waste of optical fiber resources is serious. Moreover, since the quantum signal light and the synchronous light transmission channel are different, they are also affected differently by the external environment, causing a defect of relative phase jitter between them, and the defect is fatal to the high repetition frequency system. For a method that a single optical fiber transmits quantum signal light and synchronous light into the same optical fiber through a wavelength division multiplexing technology, although time synchronization between Alice and Bob can be well realized, because synchronous light needs to occupy a wavelength channel additionally, wavelength resources in an optical network are precious and limited, and occupying the wavelength channel is unfavorable for the construction of a large-scale quantum secret communication network.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, an object of the present invention is to provide a time synchronization method and system in quantum secret communication, which are used for solving the respective problems of the existing dual-fiber synchronization technology and Shan Qianbo minute synchronization technology. For the method of adopting two optical fibers to respectively transmit signal light and synchronous light, the waste of optical fiber resources is serious, and the signal light and synchronous light transmission channels are different and are affected by external environment, so that the relative phase jitter of the signal light and the synchronous light is easy to cause; the method of time synchronization of single optical fiber by wavelength division multiplexing technology occupies wavelength channel, which is unfavorable for the construction of large-scale quantum secret communication network.
The invention provides a time synchronization method in quantum secret communication, which comprises the following steps: s1, emitting signal light and synchronous light; s2, the signal light and the synchronous light are coupled and then transmitted through the same few-mode fiber channel; s3, receiving the coupled signal light and the coupled synchronous light and splitting the signal light and the synchronous light; s4, detecting the signal light and the synchronous light, determining the link transmission delay between the signal light pulse and the synchronous light pulse, and synchronously correcting the signal light; s5, numbering the synchronous light frames, and marking each signal light pulse according to the synchronous light pulse time interval of each signal light pulse and the frame to which the signal light pulse belongs; s6, identifying the frame number of the synchronous light, and measuring the time interval of the signal light pulse from the synchronous light pulse of the frame to which the signal light pulse belongs; judging the mark number of the received signal light pulse according to the time interval; and the received marks of the signal light pulses are in one-to-one correspondence with the transmitted marks of the signal light pulses.
In an embodiment of the invention, the step S1 further includes: and preparing and attenuating the signal light in a polarization state to prepare H, V, P, N four-path polarized light with single photon level.
In an embodiment of the invention, the step S1 further includes: attenuating the emergent synchronous light; and converting the mode of the attenuated synchronous light from a basic mode to a high-order mode.
In an embodiment of the invention, the step S1 further includes: determining a first time interval of the signal light pulse relative to the synchronization light pulse at the time of transmission; the step S4 further includes: determining a second time interval of the signal light pulses relative to the synchronization light pulses upon reception; and determining the link transmission delay between the signal light pulse and the synchronous light pulse according to the difference value between the first time interval and the second time interval.
The invention also provides a time synchronization system in quantum secret communication, which comprises: the synchronous light emitting device is used for emitting synchronous light and numbering frames of the synchronous light; the signal light emitting end is used for emitting signal light and marking each signal light pulse according to the time interval of the synchronous light pulse of the frame to which the signal light pulse belongs; the mode multiplexer is used for transmitting the signal light and the synchronous light through the same few-mode fiber channel after being coupled with each other; a mode demultiplexer for receiving the coupled signal light and the synchronization light and splitting the signal light and the synchronization light; a PIN detector for detecting the synchronization light, and identifying the frame number of the synchronization light; a single photon detector for detecting the signal light and measuring the time interval between the signal light pulse and the synchronous light pulse of the frame to which the signal light pulse belongs; judging the mark number of the received signal light pulse according to the time interval; the received marks of the signal light pulses are in one-to-one correspondence with the transmitted marks of the signal light pulses; and the correction module is used for determining the link transmission delay between the signal light pulse and the synchronous light pulse and synchronously correcting the signal light.
In an embodiment of the invention, the signal light emitting end further includes a polarization state preparation and attenuation module, which is configured to prepare and attenuate the polarization state of the signal light to prepare H, V, P, N four-path polarized light with a single photon level.
In an embodiment of the present invention, the synchronous light emitting device includes: a synchronous light emitter for emitting synchronous light; an optical attenuator for attenuating the emitted synchronization light; and a mode converter for converting the mode of the attenuated synchronous light from a fundamental mode to a higher-order mode.
In an embodiment of the invention, the signal light emitting end is further configured to determine a first time interval of the signal light pulse relative to the synchronization light pulse during transmission; the single photon detector is further configured to determine a second time interval of the signal light pulses relative to the synchronization light pulses upon reception; the correction module is further configured to determine a link transmission delay between the signal optical pulse and the synchronization optical pulse according to a difference between the first time interval and the second time interval.
As described above, the time synchronization method and system in quantum secret communication of the present invention have the following beneficial effects:
the quantum signal light and the synchronous light are coupled into the same optical fiber channel for transmission through the mode division multiplexer without adding additional optical fiber channels, so that optical fiber resources are greatly saved.
In addition, for the multi-channel QKD wavelength division multiplexing system, the synchronous light does not occupy wavelength channels, which is equivalent to reducing the wavelength division multiplexing insertion loss of each channel of quantum signal light, improving the performance of each channel of QKD service, including the code rate, the transmission distance and the like, and has objective economic benefit when a large-scale quantum secret communication network is built.
Drawings
Fig. 1 is a schematic flow diagram of a time synchronization method in quantum secret communication in the present invention.
Fig. 2 is a schematic diagram of a time synchronization system in quantum secret communication according to the present invention.
Fig. 3 is a schematic diagram of light pulses of a transmitting end synchronization light and a signal light during the quantum secret communication synchronization correction according to the present invention.
Fig. 4 is a schematic diagram of light pulses of synchronous light and signal light at a receiving end during synchronous correction of quantum secret communication in the invention.
Fig. 5 is a schematic diagram of optical pulses of transmitting-side synchronization light and signal light when quantum secret communication is time-synchronized in the present invention.
Fig. 6 is a schematic diagram of optical pulses of receiving-end synchronous light and signal light during time synchronization of quantum secret communication in the present invention.
Detailed Description
Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention. It should be noted that the following embodiments and features in the embodiments may be combined with each other without conflict.
It should be noted that the illustrations provided in the following embodiments merely illustrate the basic concept of the present invention by way of illustration, and only the components related to the present invention are shown in the illustrations, not according to the number, shape and size of the components in actual implementation, and the form, number and proportion of each component in actual implementation may be arbitrarily changed, and the layout of the components may be more complex.
Referring to fig. 1 to 6, it should be understood that the structures, proportions, sizes, etc. shown in the drawings attached to the present specification are shown only for the purpose of understanding and reading by those skilled in the art, and are not intended to limit the applicable limitations of the present invention, so that any structural modification, change in proportion, or adjustment of size does not have any technical significance, and all fall within the scope of the technical disclosure without affecting the efficacy and achievement of the present invention. Also, the terms such as "upper," "lower," "left," "right," "middle," and "a" and the like recited in the present specification are merely for descriptive purposes and are not intended to limit the scope of the invention, but are intended to provide relative positional changes or modifications without materially altering the technical context in which the invention may be practiced.
As shown in fig. 1 and fig. 3 to 6, fig. 1 is a schematic flow block diagram of a time synchronization method in quantum secret communication according to the present invention. Fig. 3 is a schematic diagram of light pulses of a transmitting end synchronization light and a signal light during the quantum secret communication synchronization correction according to the present invention. Fig. 4 is a schematic diagram of light pulses of synchronous light and signal light at a receiving end during synchronous correction of quantum secret communication in the invention. Fig. 5 is a schematic diagram of optical pulses of transmitting-side synchronization light and signal light when quantum secret communication is time-synchronized in the present invention. Fig. 6 is a schematic diagram of optical pulses of receiving-end synchronous light and signal light during time synchronization of quantum secret communication in the present invention. The invention provides a time synchronization method in quantum secret communication, which comprises the following steps:
s1, emitting signal light and synchronous light; when the signal light and the synchronization light are both in the fundamental mode during initial emission, after the emission, the synchronization light is converted into the higher-order mode, and in an embodiment of the present invention, step S1 further includes: after the signal light is subjected to polarization state preparation and attenuation, H, V, P, N four-path polarized light with single photon level is prepared. In another embodiment of the present invention, step S1 further includes: attenuating the emergent synchronous light; the mode of the attenuated synchronous light is converted from a fundamental mode to a higher order mode. In another embodiment of the present invention, step S1 further includes: determining a first time interval of the signal light pulse relative to the synchronous light pulse at the time of transmission;
s2, transmitting the signal light and the synchronous light through the same few-mode fiber channel after coupling the signal light and the synchronous light; the transmission channel is a few-mode optical fiber, multiplexing can be realized by increasing the mode of the light beam propagated in the single-core optical fiber, and the increase of the energy consumption requirement is not obvious on the premise of improving the transmission capacity. Compared with the traditional single-mode fiber, the mode field diameter of the few-mode fiber is larger, more transmission modes can be supported, and attenuation is not obviously increased. Compared with multimode fiber, the few-mode fiber has smaller transmission loss, longer transmission distance and easy control and reduced coupling between modes.
S3, receiving the coupled signal light and the coupled synchronous light and splitting the signal light and the synchronous light;
s4, detecting the signal light and the synchronous light, determining the link transmission delay between the signal light and the synchronous light, and carrying out synchronous correction on the signal light. At the start-up of the QKD device, a device calibration operation is performed, which includes a synchronization correction step. The synchronization correction step is to correct different delay values introduced by the synchronization light and the signal light after passing through the optical fiber link and the electronic circuit, and lay a foundation for accurately determining the time position of each signal light pulse.
S5, numbering the synchronous light frames, and marking each signal light pulse according to the synchronous light pulse time interval of each signal light pulse and the frame to which the signal light pulse belongs;
s6, identifying the frame number of the synchronous light, and measuring the time interval of the signal light pulse from the synchronous light pulse of the frame to which the signal light pulse belongs; judging the mark number of the received signal light pulse according to the time interval; and the received marks of the signal light pulses are in one-to-one correspondence with the transmitted marks of the signal light pulses. In an embodiment of the present invention, step S4 further includes: determining a second time interval of the signal light pulses relative to the synchronization light pulses upon reception; and determining the link transmission delay between the signal light pulse and the synchronous light pulse according to the difference value between the first time interval and the second time interval. After the synchronization correction is completed, the periodic synchronization light and the signal light are transmitted, and the synchronization light frequency is much smaller than the signal light frequency. Each synchronous light pulse is followed by a series of signal light pulses to form a frame of light pulse signal. Each synchronous light is numbered in sequence, and the time interval of a certain signal light pulse from the synchronous light pulse of the frame where the signal light pulse is located is measured, so that the number of the frame of the signal light pulse can be determined, and the time synchronization is completed.
In the following, an embodiment of the present invention is described, where the signal light with the emission mode of the transmitting end being the fundamental mode is processed by the signal light polarization state preparation and attenuation module to prepare H, V, P, N four-path polarized light with a single photon level. The synchronous light is identical to the signal light, and the emergent mode of the synchronous light is a fundamental mode. The synchronous light is attenuated by the light attenuator and then converted into LP11 mode or other higher order mode by the mode converter. The base modulus sub-signal light and the high-order mode synchronous light are coupled into the same few-mode fiber channel through a mode multiplexer for transmission. In general, a single mode optical fiber or a few-mode optical fiber may be used as a link between the signal light emitting end and the mode multiplexer, and a few-mode optical fiber may be used as a link between the mode converter and the mode multiplexer. At the receiving end, the signal light and the synchronous light are split by the mode demultiplexer, the signal light is received by a single photon detector at the receiving end, and the synchronous light is detected and received by a PIN detector. Typically, the link between the mode demultiplexer and the single photon detector may employ single mode optical fibers or few mode optical fibers, and the link between the mode demultiplexer and the PIN detector employs few mode optical fibers.
As shown in fig. 3-6, the QKD device is initially calibrated prior to normal operation. After light intensity feedback, delay scanning and polarization feedback are completed, a synchronous correction step is carried out one by one for H, V, P, N four paths of signal light. Taking the H-path signal light as an example, the synchronous light laser emits periodic pulse light with the repetition frequency of 100kHz, and the H-path signal light laser also emits periodic pulse signal light with the repetition frequency of 100kHz, and the wavelengths of the synchronous light and the signal light are the same. At the transmitting end, the signal light pulse is fixed with respect to the synchronization light pulse time interval, denoted as T1.
After passing through the optical fiber link and the electronic circuit, the detected synchronous optical pulse and the signal optical pulse have a difference value. The time interval T2 of the synchronous light pulse and the signal light pulse is determined after a plurality of detection statistics. Because the link delays are different, a time interval difference Δt is introduced at the receiving end compared to the time interval T1 of the synchronous optical pulse and the signal optical pulse at the transmitting end. Since the determination of the signal light pulse train number at the receiving end is done by means of measuring the time interval of its synchronizing light pulse with the belonging frame. For a certain optical pulse at the transmitting end, the time interval between the optical pulse and the synchronous optical pulse is T1, and at the receiving end, the detected signal light pulse and synchronization light pulse time interval becomes T2, and T1 and T2 differ by Δt. Therefore, when actually determining the position of the signal light pulse, it is necessary to subtract Δt. The aim of the synchronous correction is to recover the time interval between the signal light pulse of the receiving end and the synchronous light pulse to the time interval when the signal light pulse is transmitted to the transmitting end, thereby ensuring that the sequence number of the detected signal light pulse is consistent with the sequence number of the signal light pulse of the transmitting end.
After the synchronization correction is completed, the transmitting end performs serial numbering on each synchronization light pulse. Each signal light pulse is numbered according to the synchronous light pulse time interval of each signal light pulse and the frame to which the signal light pulse belongs. The transmitting end numbers the two synchronous optical pulses into a first frame and a second frame respectively. For the second signal light pulse a in the first frame, the time interval between the second signal light pulse a and the synchronizing light pulse a is Ta, and for the fourth signal light pulse b in the second frame, the time interval between the second signal light pulse a and the synchronizing light pulse b is Tb. At the receiving end, for the signal light pulse a, the first frame to which the signal light pulse a belongs is determined according to the synchronous light pulse a number of the frame where the signal light pulse a belongs, and the time interval Ta between the signal light pulse a and the synchronous light pulse a is measured to determine that the signal light pulse a is the second light pulse in the first frame. For the signal light pulse b, determining the second frame to which the signal light pulse b belongs according to the synchronous light pulse b number of the frame where the signal light pulse b belongs, and measuring the time interval Tb between the signal light pulse b and the synchronous light pulse b can determine the signal light pulse b as the fourth light pulse in the second frame. Therefore, the detected signal light pulses are guaranteed to be in one-to-one correspondence with the signal light pulses of the transmitting end, dislocation is avoided, and the purpose of time synchronization is achieved. The time synchronization can ensure that the sending end and the receiving end are aimed at the photon state of the same photon when performing base vector comparison, and ensure that the system can normally generate a safe quantum key.
Fig. 2 to 6 show a schematic diagram of a time synchronization system in quantum secret communication according to the present invention in fig. 2. Fig. 3 is a schematic diagram of light pulses of a transmitting end synchronization light and a signal light during the quantum secret communication synchronization correction according to the present invention. Fig. 4 is a schematic diagram of light pulses of synchronous light and signal light at a receiving end during synchronous correction of quantum secret communication in the invention. Fig. 5 is a schematic diagram of optical pulses of transmitting-side synchronization light and signal light when quantum secret communication is time-synchronized in the present invention. Fig. 6 is a schematic diagram of optical pulses of receiving-end synchronous light and signal light during time synchronization of quantum secret communication in the present invention. The invention also provides a time synchronization system in quantum secret communication, which comprises:
the synchronous light emitting device is used for emitting synchronous light and numbering frames of the synchronous light; the signal light emitting end is used for emitting signal light and marking each signal light pulse according to the time interval of the synchronous light pulse of the frame to which the signal light pulse belongs; when the signal light and the synchronous light are in the fundamental mode during initial emission, after the signal light and the synchronous light are emitted, the synchronous light is converted into the higher-order mode, and in an embodiment of the invention, the signal light emitting end further comprises a polarization state preparation and attenuation module for preparing and attenuating the polarization state of the signal light to prepare H, V, P, N four-path polarized light with single photon level. In another embodiment of the present invention, a synchronous light emitting device includes: a synchronous light emitter for emitting synchronous light; the optical attenuator is used for attenuating emergent synchronous light; and a mode converter for converting the mode of the attenuated synchronous light from the fundamental mode to the higher-order mode. In another embodiment of the present invention, the signal light emitting end is further configured to determine a first time interval of the signal light pulse relative to the synchronization light pulse when transmitting.
The mode multiplexer is used for transmitting the signal light and the synchronous light through the same few-mode fiber channel after coupling the signal light and the synchronous light; the transmission channel is a few-mode optical fiber, multiplexing can be realized by increasing the mode of the light beam propagated in the single-core optical fiber, and the increase of the energy consumption requirement is not obvious on the premise of improving the transmission capacity. Compared with the traditional single-mode fiber, the mode field diameter of the few-mode fiber is larger, more transmission modes can be supported, and attenuation is not obviously increased. Compared with multimode fiber, the few-mode fiber has smaller transmission loss, longer transmission distance and easy control and reduced coupling between modes.
And the mode demultiplexer is used for receiving the coupled signal light and the synchronous light and splitting the signal light and the synchronous light.
And the PIN detector is used for detecting the synchronous light and identifying the frame number of the synchronous light.
A single photon detector for detecting the signal light and measuring the time interval between the signal light pulse and the synchronous light pulse of the frame to which the signal light pulse belongs; judging the mark number of the received signal light pulse according to the time interval; and the received marks of the signal light pulses are in one-to-one correspondence with the transmitted marks of the signal light pulses.
And the correction module is used for determining the link transmission delay between the signal light pulse and the synchronous light pulse and synchronously correcting the signal light.
At the start-up of the QKD device, a device calibration operation is performed, which includes a synchronization correction step. The synchronization correction step is to correct different delay values introduced by the synchronization light and the signal light after passing through the optical fiber link and the electronic circuit, and lay a foundation for accurately determining the time position of each signal light pulse.
In an embodiment of the invention, the single photon detector is further configured to determine a second time interval of the signal light pulses relative to the synchronization light pulses upon reception; the correction module is further configured to determine a link transmission delay between the signal optical pulse and the synchronization optical pulse according to a difference between the first time interval and the second time interval. After the synchronization correction is completed, the periodic synchronization light and the signal light are transmitted, and the synchronization light frequency is much smaller than the signal light frequency. Each synchronous light pulse is followed by a series of signal light pulses to form a frame of light pulse signal. Each synchronous light is numbered in sequence, and the time interval of a certain signal light pulse from the synchronous light pulse of the frame where the signal light pulse is located is measured, so that the number of the frame of the signal light pulse can be determined, and the time synchronization is completed.
In the following, an embodiment of the present invention is described, where the signal light with the emission mode of the transmitting end being the fundamental mode is processed by the signal light polarization state preparation and attenuation module to prepare H, V, P, N four-path polarized light with a single photon level. The synchronous light is identical to the signal light, and the emergent mode of the synchronous light is a fundamental mode. The synchronous light is attenuated by the light attenuator and then converted into LP11 mode or other higher order mode by the mode converter. The base modulus sub-signal light and the high-order mode synchronous light are coupled into the same few-mode fiber channel through a mode multiplexer for transmission. In general, a single mode optical fiber or a few-mode optical fiber may be used as a link between the signal light emitting end and the mode multiplexer, and a few-mode optical fiber may be used as a link between the mode converter and the mode multiplexer. At the receiving end, the signal light and the synchronous light are split by the mode demultiplexer, the signal light is received by a single photon detector at the receiving end, and the synchronous light is detected and received by a PIN detector. Typically, the link between the mode demultiplexer and the single photon detector may employ single mode optical fibers or few mode optical fibers, and the link between the mode demultiplexer and the PIN detector employs few mode optical fibers.
As shown in fig. 3-6, the QKD device is initially calibrated prior to normal operation. After light intensity feedback, delay scanning and polarization feedback are completed, a synchronous correction step is carried out one by one for H, V, P, N four paths of signal light. Taking the H-path signal light as an example, the synchronous light laser emits periodic pulse light with the repetition frequency of 100kHz, and the H-path signal light laser also emits periodic pulse signal light with the repetition frequency of 100kHz, and the wavelengths of the synchronous light and the signal light are the same. At the transmitting end, the signal light pulse is fixed with respect to the synchronization light pulse time interval, denoted as T1.
After passing through the optical fiber link and the electronic circuit, the detected synchronous optical pulse and the signal optical pulse have a difference value. The time interval T2 of the synchronous light pulse and the signal light pulse is determined after a plurality of detection statistics. Because the link delays are different, a time interval difference Δt is introduced at the receiving end compared to the time interval T1 of the synchronous optical pulse and the signal optical pulse at the transmitting end. Since the determination of the signal light pulse train number at the receiving end is done by means of measuring the time interval of its synchronizing light pulse with the belonging frame. For a certain optical pulse at the transmitting end, the time interval between the optical pulse and the synchronous optical pulse is T1, and at the receiving end, the detected signal light pulse and synchronization light pulse time interval becomes T2, and T1 and T2 differ by Δt. Therefore, when actually determining the position of the signal light pulse, it is necessary to subtract Δt. The aim of the synchronous correction is to recover the time interval between the signal light pulse of the receiving end and the synchronous light pulse to the time interval when the signal light pulse is transmitted to the transmitting end, thereby ensuring that the sequence number of the detected signal light pulse is consistent with the sequence number of the signal light pulse of the transmitting end.
After the synchronization correction is completed, the transmitting end performs serial numbering on each synchronization light pulse. Each signal light pulse is numbered according to the synchronous light pulse time interval of each signal light pulse and the frame to which the signal light pulse belongs. The transmitting end numbers the two synchronous optical pulses into a first frame and a second frame respectively. For the second signal light pulse a in the first frame, the time interval between the second signal light pulse a and the synchronizing light pulse a is Ta, and for the fourth signal light pulse b in the second frame, the time interval between the second signal light pulse a and the synchronizing light pulse b is Tb. At the receiving end, for the signal light pulse a, the first frame to which the signal light pulse a belongs is determined according to the synchronous light pulse a number of the frame where the signal light pulse a belongs, and the time interval Ta between the signal light pulse a and the synchronous light pulse a is measured to determine that the signal light pulse a is the second light pulse in the first frame. For the signal light pulse b, determining the second frame to which the signal light pulse b belongs according to the synchronous light pulse b number of the frame where the signal light pulse b belongs, and measuring the time interval Tb between the signal light pulse b and the synchronous light pulse b can determine the signal light pulse b as the fourth light pulse in the second frame. Therefore, the detected signal light pulses are guaranteed to be in one-to-one correspondence with the signal light pulses of the transmitting end, dislocation is avoided, and the purpose of time synchronization is achieved. The time synchronization can ensure that the sending end and the receiving end are aimed at the photon state of the same photon when performing base vector comparison, and ensure that the system can normally generate a safe quantum key.
In summary, the time synchronization method and system in quantum secret communication of the present invention do not need to add additional optical fiber channels, and the quantum signal light and the synchronization light are coupled into the same optical fiber channel to be transmitted through the mode division multiplexer, which greatly saves optical fiber resources. In addition, for the multi-channel QKD wavelength division multiplexing system, the synchronous light does not occupy wavelength channels, which is equivalent to reducing the wavelength division multiplexing insertion loss of each channel of quantum signal light, improving the performance of each channel of QKD service, including the code rate, the transmission distance and the like, and has objective economic benefit when a large-scale quantum secret communication network is built. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The above embodiments are merely illustrative of the principles of the present invention and its effectiveness, and are not intended to limit the invention. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is intended that all equivalent modifications and variations of the invention be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.
Claims (8)
1. A method for time synchronization in quantum secret communication, comprising the steps of:
s1, emitting signal light and synchronous light;
s2, the signal light and the synchronous light are coupled and then transmitted through the same few-mode fiber channel;
s3, receiving the coupled signal light and the coupled synchronous light and splitting the signal light and the synchronous light;
s4, detecting the signal light and the synchronous light, determining the link transmission delay between the signal light pulse and the synchronous light pulse, and synchronously correcting the signal light;
s5, numbering the synchronous light frames, and marking each signal light pulse according to the synchronous light pulse time interval of each signal light pulse and the frame to which the signal light pulse belongs;
s6, identifying the frame number of the synchronous light, and measuring the time interval of the signal light pulse from the synchronous light pulse of the frame to which the signal light pulse belongs; judging the mark number of the received signal light pulse according to the time interval; and the received marks of the signal light pulses are in one-to-one correspondence with the transmitted marks of the signal light pulses.
2. The method for time synchronization in quantum secret communication according to claim 1, wherein the step S1 further comprises:
and preparing and attenuating the signal light in a polarization state to prepare H, V, P, N four-path polarized light with single photon level.
3. The method for time synchronization in quantum secret communication according to claim 1, wherein the step S1 further comprises:
attenuating the emergent synchronous light; and converting the mode of the attenuated synchronous light from a basic mode to a high-order mode.
4. A method of time synchronisation in quantum secret communications according to any one of claims 1 to 3, wherein step S1 further comprises: determining a first time interval of the signal light pulse relative to the synchronization light pulse at the time of transmission;
the step S4 further includes:
determining a second time interval of the signal light pulses relative to the synchronization light pulses upon reception;
and determining the link transmission delay between the signal light pulse and the synchronous light pulse according to the difference value between the first time interval and the second time interval.
5. A time synchronization system in quantum secret communication, comprising:
the synchronous light emitting device is used for emitting synchronous light and numbering frames of the synchronous light;
the signal light emitting end is used for emitting signal light and marking each signal light pulse according to the time interval of the synchronous light pulse of the frame to which the signal light pulse belongs;
the mode multiplexer is used for transmitting the signal light and the synchronous light through the same few-mode fiber channel after being coupled with each other;
a mode demultiplexer for receiving the coupled signal light and the synchronization light and splitting the signal light and the synchronization light;
a PIN detector for detecting the synchronization light, and identifying the frame number of the synchronization light;
a single photon detector for detecting the signal light and measuring the time interval between the signal light pulse and the synchronous light pulse of the frame to which the signal light pulse belongs; judging the mark number of the received signal light pulse according to the time interval; the received marks of the signal light pulses are in one-to-one correspondence with the transmitted marks of the signal light pulses;
and the correction module is used for determining the link transmission delay between the signal light pulse and the synchronous light pulse and synchronously correcting the signal light.
6. The system according to claim 5, wherein the signal light emitting end further comprises a polarization state preparation and attenuation module for preparing and attenuating the polarization state of the signal light to prepare H, V, P, N four-path polarized light with single photon level.
7. The time synchronization system in quantum secret communication according to claim 5, wherein the synchronization light emitting device comprises:
a synchronous light emitter for emitting synchronous light;
an optical attenuator for attenuating the emitted synchronization light;
and a mode converter for converting the mode of the attenuated synchronous light from a fundamental mode to a higher-order mode.
8. The time synchronization system in quantum secret communication according to any one of claims 5 to 7, wherein the signal light emitting end is further configured to determine a first time interval of the signal light pulse relative to the synchronization light pulse when transmitting;
the single photon detector is further configured to determine a second time interval of the signal light pulses relative to the synchronization light pulses upon reception;
the correction module is further configured to determine a link transmission delay between the signal optical pulse and the synchronization optical pulse according to a difference between the first time interval and the second time interval.
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| CN112019334A (en) * | 2020-09-25 | 2020-12-01 | 苏州同相智能信息技术有限公司 | Communication system for synchronously transmitting quantum encryption key and optical communication signal |
| CN114389715B (en) * | 2020-12-31 | 2024-04-16 | 广东国腾量子科技有限公司 | Synchronous optical detection and monitoring correction system of QKD |
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104065475A (en) * | 2014-06-27 | 2014-09-24 | 上海交通大学 | High-speed continuous variable quantum key distribution system and bit frame synchronization method thereof |
| CN105763259A (en) * | 2015-12-31 | 2016-07-13 | 北京邮电大学 | Mode frequency coding-based mode division multiplexing light transmission method and device |
| JP2016167655A (en) * | 2015-03-09 | 2016-09-15 | 三菱電機株式会社 | Optical transmission device and differential delay compensation method between adjacent channels applied to optical transmission device |
| CN208707646U (en) * | 2018-05-21 | 2019-04-05 | 科大国盾量子技术股份有限公司 | A kind of clock synchronization system in quantum secret communication |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104065475A (en) * | 2014-06-27 | 2014-09-24 | 上海交通大学 | High-speed continuous variable quantum key distribution system and bit frame synchronization method thereof |
| JP2016167655A (en) * | 2015-03-09 | 2016-09-15 | 三菱電機株式会社 | Optical transmission device and differential delay compensation method between adjacent channels applied to optical transmission device |
| CN105763259A (en) * | 2015-12-31 | 2016-07-13 | 北京邮电大学 | Mode frequency coding-based mode division multiplexing light transmission method and device |
| CN208707646U (en) * | 2018-05-21 | 2019-04-05 | 科大国盾量子技术股份有限公司 | A kind of clock synchronization system in quantum secret communication |
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