One-to-many user QKD network system based on multi-core optical fiber and implementation method

Abstract

The invention relates to a one-to-many user QKD network system based on a multi-core optical fiber and an implementation method. The system comprises a signal sending end, a signal transmission unit and a user end, the signal transmitting end is used for chopping the continuous light into pulsed light with different frequencies, modulating the pulsed light with each frequency into decoy state pulses and signal state pulses with different intensities, and carrying out polarization state coding on each decoy state pulse and each signal state pulse to form quantum signals with different frequencies and carrying secret key information; the signal transmission unit firstly couples quantum signals with different frequencies to different fiber cores of the multi-core optical fiber for transmission, and then decouples the quantum signals from the multi-core optical fiber; a plurality of clients receive the quantum signals with different frequencies, randomly select basis vectors to perform single-photon polarization state measurement on the quantum signals, and respond to form codes. According to the invention, the problems of low communication efficiency, high system complexity and difficulty in meeting the urgent demand of future optical communication capacity expansion due to the fact that a QKD network is constructed based on a single-core optical fiber in the prior art can be solved.

Description

Technical Field

[0001] The present application relates to the field of quantum communication and optical communication technology, and in particular to a one-to-many user QKD network system based on multi-core optical fiber and an implementation method thereof. Background Art

[0002] Since the pioneering proposal of the BB84 protocol in 1984, quantum key distribution (QKD) technology has made continuous breakthroughs and successfully crossed the gap from laboratory exploration to practical application. With the increasing maturity of the technology, QKD has not only achieved a significant extension in transmission distance, but also achieved significant improvements in key distribution rate and system stability. Relying on the uncertainty principle and no-cloning theorem of quantum mechanics, QKD provides absolute protection for information security and has become a solid shield to protect information security in the communications field. To date, QKD networks have been widely deployed in many parts of the world, building a high-security information transmission line for key fields such as finance, government, and military.

[0003] However, most existing QKD networks are built on single-core optical fibers, which face challenges such as low communication efficiency and high system complexity. At the same time, with the continuous growth of optical communication capacity, traditional single-core optical fibers can no longer meet the urgent needs of future optical communication capacity expansion. Summary of the invention

[0004] The embodiments of the present application provide a one-to-many user QKD network system based on multi-core optical fiber and an implementation method to solve the problem that most QKD networks in the related art are built based on single-core optical fiber, facing challenges such as low communication efficiency and high system complexity, and it is difficult to meet the urgent needs of future optical communication capacity expansion.

[0005] In a first aspect, a one-to-multi-user QKD network system based on a multi-core optical fiber is provided, which includes a signal transmitting end, a signal transmission unit and a plurality of user ends connected in sequence;

[0006] The signal transmitting end is used to: in each cycle, according to the set timing, chop the continuous light into pulse lights of different frequencies, modulate the pulse lights of each frequency into decoy state pulses and signal state pulses of different intensities, and encode the polarization state of each decoy state pulse and signal state pulse to form quantum signals of different frequencies carrying secret key information;

[0007] The signal transmission unit is used to: first couple quantum signals of different frequencies to different cores of a multi-core optical fiber for transmission, and then decouple them from the multi-core optical fiber;

[0008] The multiple user terminals are used to respectively receive quantum signals of different frequencies, randomly select basis vectors to perform single-photon polarization state measurement on the quantum signals, and respond in coding.

[0009] In some embodiments, the signal transmitting end includes a first intensity modulator, a second intensity modulator, a polarization modulator, and an adjustable optical attenuator connected in sequence;

[0010] The first intensity modulator is used to: chop the continuous light into pulsed light of different frequencies according to a set timing in each cycle;

[0011] The second intensity modulator is used to: modulate the pulse light of each frequency into decoy state pulses and signal state pulses with different intensities;

[0012] The polarization modulator is used to: encode the polarization state of the decoy state pulse and the signal state pulse of each frequency pulse light to form a pulse light carrying secret key information;

[0013] The adjustable optical attenuator is used to attenuate the pulse light carrying the secret key information to the single photon level to obtain a quantum signal carrying the secret key information.

[0014] In some embodiments, the signal transmitting end further includes a laser, and the laser is connected to the first intensity modulator to emit continuous light to the first intensity modulator.

[0015] In some embodiments, the signal transmitting end includes a first intensity modulator, a polarization modulator, a second intensity modulator, and an adjustable optical attenuator connected in sequence;

[0016] The first intensity modulator is used to: chop the continuous light into pulsed light of different frequencies;

[0017] The polarization modulator is used to: encode the polarization state of pulses of pulsed light of each frequency;

[0018] The second intensity modulator is used to modulate the encoded pulses in the pulse light of each frequency into decoy state pulses and signal state pulses with different intensities to form pulse light carrying secret key information;

[0019] The adjustable optical attenuator is used to attenuate the pulse light carrying the secret key information to the single photon level to obtain a quantum signal carrying the secret key information.

[0020] In some embodiments, the signal transmitting end further includes a laser, and the laser is connected to the first intensity modulator to emit continuous light to the first intensity modulator.

[0021] In some embodiments, the signal transmission unit includes an optical switch, a multi-core fiber multiplexer, a multi-core fiber, and a multi-core fiber demultiplexer connected in sequence;

[0022] The optical switch is used to distribute quantum signals of different frequencies in response to the signal transmitting end;

[0023] The multi-core optical fiber multiplexer is used to: receive the distributed quantum signal and couple it into the corresponding core of the multi-core optical fiber;

[0024] The multi-core optical fiber demultiplexer is used to decouple quantum signals from the multi-core optical fiber.

[0025] In some embodiments, the user end includes a base vector beam splitter and two polarization beam splitters, each of the polarization beam splitters is connected to two single photon detectors;

[0026] The basis vector beam splitter is used to: perform basis vector selection on the quantum signal;

[0027] The polarization beam splitter is used to: measure the polarization state of a single photon in the quantum signal under a selected basis vector;

[0028] The single photon detector is used to measure the count information of the received polarization state and respond in coding.

[0029] In some embodiments, the number of frequencies of the continuous light chopped into pulsed light is the same as the number of the user ends.

[0030] In some embodiments, the polarization state includes two groups of non-orthogonal basis vectors Z basis and X basis, and the Z basis and the X basis each include two orthogonal polarization states.

[0031] In a second aspect, a method for implementing a one-to-multi-user QKD network based on a multi-core optical fiber is provided, which includes:

[0032] In each cycle, according to the set timing, the continuous light is chopped into pulsed light of different frequencies, and the pulsed light of each frequency is modulated into decoy state pulses and signal state pulses of different intensities, and the polarization state of each decoy state pulse and signal state pulse is encoded to form quantum signals of different frequencies carrying secret key information;

[0033] First, quantum signals of different frequencies are coupled to different cores of a multi-core optical fiber for transmission, and then decoupled from the multi-core optical fiber;

[0034] Quantum signals of different frequencies are received respectively, basis vectors are randomly selected to measure the single-photon polarization state of the quantum signal, and the response is coded.

[0035] The beneficial effects of the technical solution provided by this application include:

[0036] This application uses multi-core optical fiber for signal transmission. Multi-core optical fiber cleverly integrates multiple independent cores in a single optical fiber cladding. Each core can be used as a single-mode or multi-mode optical fiber, and can independently transmit multiple optical signals. This design allows each core to become an effective signal channel, which greatly improves the system capacity and communication efficiency. In addition, the multi-core structure of multi-core optical fiber is naturally adapted to multi-user access scenarios, so that one signal sending end of this application can correspond to multiple user ends, realizing quantum key distribution in a one-to-many user network environment. Multi-core optical fiber integrates multiple optical channels into one optical fiber, and has the advantages of low average optical channel cost, high integration, and large transmission capacity. This system not only improves the communication efficiency and practicality of the QKD system, but also provides strong support for solving the problem of future optical communication expansion. The implementation of this application will strongly promote the development of quantum communication technology and optical communication technology, and provide new solutions for the fields of information security and optical communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0038] Figure 1 A structural block diagram of a one-to-multi-user QKD network system based on multi-core optical fiber provided in an embodiment of the present application;

[0039] Figure 2 A structural block diagram of the transmitting end provided in an embodiment of the present application;

[0040] Figure 3 A structural block diagram of the user terminal provided in an embodiment of the present application.

[0041] In the figure: 10, transmitting end; 100, laser; 101, first intensity modulator; 102, second intensity modulator; 103, polarization modulator; 104, adjustable optical attenuator; 20, signal transmission unit; 200, multi-core optical fiber; 201, optical switch; 202, multi-core optical fiber multiplexer; 203, multi-core optical fiber demultiplexer; 30, user end; 300, basis vector beam splitter; 301, polarization beam splitter; 302, single photon detector. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0043] See also Figure 1 As shown, the embodiment of the present application provides a one-to-multi-user QKD network system based on a multi-core optical fiber, which includes a signal transmitting end 10, a signal transmission unit 20 and a plurality of user ends 30 connected in sequence; wherein:

[0044] The signal transmitting end 10 is used to: within each cycle, according to the set timing, chop the continuous light into pulse lights of different frequencies, modulate the pulse lights of each frequency into decoy state pulses and signal state pulses of different intensities, and encode the polarization state of each decoy state pulse and signal state pulse to form quantum signals of different frequencies carrying secret key information.

[0045] In each cycle, the continuous light is chopped into pulsed light of different frequencies according to the set timing, specifically including: the signal transmitting end 10 periodically modulates the pulsed light of different frequencies, for example, for better understanding, Figure 1 As shown, as an example, the cycle is time T. Within a cycle time T, the signal transmitting end 10 modulates pulsed light of four different frequencies, which are recorded as f1, f2, f3 and f4. In addition, the set timing within a cycle time includes the first time t1, the second time t2, the third time t3 and the fourth time t4 arranged in sequence. When pulsed light of different frequencies is formed according to the set timing, t1 corresponds to f2, t2 corresponds to f1, t3 corresponds to f3, and t4 corresponds to f4.

[0046] It is thus obtained that within the first cycle T, within the first time t1, the continuous light is chopped into pulse light of frequency f2; within the second time t2, the continuous light is chopped into pulse light of frequency f1; within the third time t3, the continuous light is chopped into pulse light of frequency f3; within the fourth time t4, the continuous light is chopped into pulse light of frequency f4.

[0047] In the second cycle T, in the first time t1, the continuous light is chopped into a pulse light of frequency f2; in the second time t2, the continuous light is chopped into a pulse light of frequency f1; in the third time t3, the continuous light is chopped into a pulse light of frequency f3; in the fourth time t4, the continuous light is chopped into a pulse light of frequency f4, and so on.

[0048] The signal transmission unit 20 is used to first couple quantum signals of different frequencies to different cores of the multi-core optical fiber 200 for transmission, and then decouple them from the multi-core optical fiber 200. The signal transmission unit 20 responds to the signal transmitting end 10 and couples quantum signals of different frequencies to different cores of the multi-core optical fiber 200 according to the set timing. For example, for better understanding, as an example, at the first time t1, the pulse light with a frequency of f2 is coupled to the first core, at the second time t2, the pulse light with a frequency of f1 is coupled to the second core, at the third time t3, the pulse light with a frequency of f3 is coupled to the third core, and at the fourth time t4, the pulse light with a frequency of f4 is coupled to the fourth core.

[0049] The plurality of user terminals 30 are used to respectively receive quantum signals of different frequencies, randomly select basis vectors to perform single-photon polarization state measurement on the quantum signals, and respond in coding.

[0050] This application uses multi-core optical fiber for signal transmission. Multi-core optical fiber cleverly integrates multiple independent cores in a single optical fiber cladding. Each core can be used as a single-mode or multi-mode optical fiber, and can independently transmit multiple optical signals. This design allows each core to become an effective signal channel, thereby greatly improving the system capacity and communication efficiency. In addition, the multi-core structure of the multi-core optical fiber is naturally adapted to multi-user access scenarios, so that one signal transmitting end 10 of this application can correspond to multiple user ends 30, realizing quantum key distribution in a one-to-many user network environment. Multi-core optical fiber integrates multiple optical channels into one optical fiber, and has the advantages of low average optical channel cost, high integration, and large transmission capacity. This system not only improves the communication efficiency and practicality of the QKD system, but also provides strong support for solving the problem of future optical communication expansion. The implementation of this application will strongly promote the development of quantum communication technology and optical communication technology, and provide new solutions for the fields of information security and optical communication.

[0051] To implement signal transmission, see Figure 2 As shown, in some preferred embodiments, the signal transmitting end 10 includes a first intensity modulator 101, a second intensity modulator 102, a polarization modulator 103 and an adjustable optical attenuator 104 connected in sequence. The first intensity modulator 101 is used to chop the continuous light into pulses of different frequencies according to a set timing in each cycle; the second intensity modulator 102 is used to modulate the pulses of each frequency into decoy state pulses and signal state pulses of different intensities; the polarization modulator 103 is used to encode the polarization state of the decoy state pulses and signal state pulses of the pulses of each frequency to form pulses carrying secret key information; the adjustable optical attenuator 104 is used to attenuate the pulses carrying the secret key information to the single photon level to obtain a quantum signal carrying the secret key information.

[0052] It should be noted that when modulating and encoding the pulse light, the QKD protocol is followed.

[0053] It should be noted that the above polarization state encoding refers to the use of the four polarization states of a single photon to encode to randomly form secret key information. The four polarization states are |H>, |V>, |A>, and |D>, where H>=|0> is a horizontal polarization state and |V>=|1> is a vertical polarization state. The two constitute a set of orthogonal complete basis vectors (Z basis); For a 45° polarization state, Polarization state, the two constitute another set of orthogonal complete basis vectors (X basis).

[0054] It can be seen that the polarization state includes two groups of non-orthogonal basis vectors Z basis and X basis, and both the Z basis and the X basis include two orthogonal polarization states.

[0055] In fact, in order to realize signal transmission, the signal transmitting end 10 has other implementation schemes. For example, as an example, the signal transmitting end 10 includes a first intensity modulator 101, a polarization modulator 103, a second intensity modulator 102 and an adjustable optical attenuator 104 connected in sequence; the first intensity modulator 101 is used to chop continuous light into pulsed light of different frequencies; the polarization modulator 103 is used to encode the polarization state of the pulses of each frequency pulsed light; the second intensity modulator 102 is used to modulate the encoded pulses in the pulsed light of each frequency into decoy state pulses and signal state pulses with different intensities to form a pulsed light carrying key information; the adjustable optical attenuator 104 is used to attenuate the pulsed light carrying key information to the single photon level to obtain a quantum signal carrying key information.

[0056] To generate continuous light, see Figure 2 As shown, the signal transmitting end 10 further includes a laser 100 , and the laser 100 is connected to the first intensity modulator 101 to emit continuous light to the first intensity modulator 101 .

[0057] To achieve signal transmission, see Figure 1 As shown, in some preferred embodiments, the signal transmission unit 20 includes an optical switch 201, a multi-core fiber multiplexer 202, a multi-core fiber 200 and a multi-core fiber demultiplexer 203 connected in sequence; the optical switch 201 is used to distribute quantum signals of different frequencies in response to the signal transmitting end 10, such as Figure 1 The pulse light has four frequencies, namely f1, f2, f3 and f4, and the optical switch 201 distributes the pulse lights of the four frequencies.

[0058] The multi-core optical fiber multiplexer 202 is used to receive the distributed quantum signal and couple it to the corresponding core of the multi-core optical fiber 200; Figure 1In the embodiment, the multi-core optical fiber multiplexer 202 couples the pulse lights of four frequencies, f1, f2, f3 and f4, respectively, into the four cores of the multi-core optical fiber 200 for transmission.

[0059] The multi-core fiber demultiplexer 203 is used to decouple the quantum signal from the multi-core fiber 200. Before entering the user end 30, the pulse light of each frequency is decoupled from the multi-core fiber 200 under the action of the multi-core fiber demultiplexer 203, so as to transmit the pulse light of different frequencies to different user ends 30.

[0060] When the signal transmission unit 20 performs signal transmission, the principle is as follows:

[0061] refer to Figure 1 As shown, first, on the classical channel, the users participating in the communication calibrate the core numbers of the multi-core optical fiber, and then the user end 30 submits a communication request to the signal transmitting end 10, and the signal transmitting end 10 counts and modulates the frequency of the pulse, and matches the frequency of the pulse light with the core of the multi-core optical fiber.

[0062] Taking a 4-core optical fiber as an example, if user QKD-RX1 (the second fiber core) applies for modulation to a pulse light of frequency f1; user QKD-RX2 (the third fiber core) applies for modulation to a pulse light of frequency f3; if user QKD-RX3 (the first fiber core) applies for modulation to a pulse light of frequency f2; user QKD-RX4 (the fourth fiber core) applies for modulation to a pulse light of frequency f4.

[0063] After the signal transmitting end 10 modulates the pulse light with frequencies of f1, f2, f3, and f4, it distributes it according to the fiber core channel of the user end 30. The signal transmitting end 10 controls the optical switch to connect with the corresponding fiber core channel: distributes the pulse light with a frequency of f1 to the second fiber core for transmission; distributes the pulse light with a frequency of f2 to the first fiber core for transmission; distributes the pulse light with a frequency of f3 to the third fiber core for transmission; and distributes the pulse light with a frequency of f4 to the fourth fiber core for transmission.

[0064] When the key information is transmitted to the user end 30, it is distributed to the corresponding user according to the previously negotiated fiber core channel.

[0065] See also Figure 3 As shown, in some preferred embodiments, the user end 30 includes a basis vector beam splitter 300 and two polarization beam splitters 301, each of the polarization beam splitters 301 is connected to two single-photon detectors 302; the basis vector beam splitter 300 is used to perform basis vector selection on the quantum signal; the polarization beam splitter 301 is used to measure the polarization state of the single photon in the quantum signal under the selected basis vector; the single-photon detector 302 is used to measure the counting information of the received polarization state and respond in coding.

[0066] For example, with Z as the basis vector, the basis vector beam splitter 300 first selects the basis of the pulse light, and the pulses of the two polarization states H> and |V> enter the two polarization beam splitters 301 respectively, and then the polarization beam splitter 301 performs polarization selection to make the polarization state |A > 、|D > The pulses enter two single photon detectors 302 respectively.

[0067] It can be understood that the number of frequencies at which the continuous light is chopped into pulsed light is the same as the number of the user ends 30 .

[0068] Of course, the number of the user terminals 30 may be greater than the number of pulse lights with different frequencies.

[0069] Based on the above system, the embodiment of the present application also provides a method for implementing a one-to-many user QKD network based on a multi-core optical fiber, which includes the following steps:

[0070] 101: In each cycle, according to the set timing, the continuous light is chopped into pulsed light of different frequencies, the pulsed light of each frequency is modulated into decoy state pulses and signal state pulses of different intensities, and the polarization state of each decoy state pulse and signal state pulse is encoded to form quantum signals of different frequencies carrying secret key information.

[0071] 102 : Firstly, quantum signals of different frequencies are coupled to different cores of the multi-core optical fiber 200 for transmission, and then decoupled from the multi-core optical fiber 200 .

[0072] 103: Respectively receive quantum signals of different frequencies, randomly select basis vectors to measure the single photon polarization state of the quantum signal, and respond in coding.

[0073] Using this method, quantum key distribution in a one-to-many user network environment is realized. Multi-core optical fiber integrates multiple optical channels into one optical fiber, which has the advantages of low average optical channel cost, high integration, and large transmission capacity. This method not only improves the communication efficiency and practicality of the QKD system, but also provides strong support for solving the problem of future optical communication capacity expansion. The implementation of this application will strongly promote the development of quantum communication technology and optical communication technology, and provide new solutions for the fields of information security and optical communication.

[0074] Taking the decoyed BB84-QKD protocol as an example, the modulation and demodulation principles of the BB84 protocol are followed.

[0075] The coding rate R of the decoyed BB84-QKD is:

[0076] R=q{Q1[1-H2(e1)]-fQμH2(Eμ)}

[0077] Among them, q = 0.5, because the signal transmitter and the user end have a 50% chance of selecting the same basis vector, Q μ is the total gain, E μ is the error rate, Q1 is the lower limit of single-photon gain, e1 is the upper limit of single-photon error rate, H2 is the binary Shannon entropy, and f is the error correction efficiency.

[0078] The signal transmitting end of the system uses the four polarization states of a single photon | H > , | V > , | A > , | D > To encode to randomly form key information.

[0079] The signal transmitter randomly encodes the chopped optical pulses and generates a string of key information to send to the user end. Different chopping frequencies correspond to different user ends. Each user end follows the following communication steps:

[0080] After the user receives the key information, since it does not know how the key sent by the signal sender is arranged, it randomly selects a basis vector (Z or X basis) to measure the polarization of the single photon and records the detection response result.

[0081] After completing the measurement, the user end publishes the basis vector selected during the measurement through the authenticated classical channel. Correspondingly, the signal transmitter also publishes its coding basis vector through this channel.

[0082] The signal transmitter and the user end filter out the mismatched information, retain the data for which the two select the same basis vector, and calculate the quantum bit error rate. If the quantum bit error rate is greater than a predetermined threshold, eavesdropping occurs and the communication is terminated. Otherwise, the communication is secure and the coding rates of the signal transmitter and the user end can be calculated.

[0083] In the description of the present application, it should be noted that the terms "upper", "lower", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0084] It should be noted that, in this application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0085] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A one-to-many user QKD network system based on multi-core optical fiber, characterized in that: It comprises a signal sending end (10), a signal transmission unit (20) and a plurality of user ends (30) which are connected in sequence; The signal transmitting end (10) is used to: in each cycle, according to a set timing, chop the continuous light into pulsed light of different frequencies, modulate the pulsed light of each frequency into decoy state pulses and signal state pulses of different intensities, and perform polarization state encoding on each decoy state pulse and signal state pulse to form quantum signals of different frequencies carrying secret key information; The signal transmission unit (20) is used to: firstly couple quantum signals of different frequencies to different cores of a multi-core optical fiber (200) for transmission, and then decouple them from the multi-core optical fiber (200); The plurality of user terminals (30) are used to respectively receive quantum signals of different frequencies, randomly select basis vectors to perform single photon polarization state measurement on the quantum signals, and respond in coding.

2. The one-to-many user QKD network system based on multi-core optical fiber as claimed in claim 1, characterized in that: The signal transmitting end (10) comprises a first intensity modulator (101), a second intensity modulator (102), a polarization modulator (103) and an adjustable optical attenuator (104) which are connected in sequence; The first intensity modulator (101) is used to: chop the continuous light into pulsed light of different frequencies according to a set timing in each cycle; The second intensity modulator (102) is used to modulate pulse light of each frequency into decoy state pulses and signal state pulses of different intensities; The polarization modulator (103) is used to: perform polarization state encoding on the decoy state pulses and signal state pulses of the pulse light of each frequency, so as to form pulse light carrying secret key information; The adjustable optical attenuator (104) is used to attenuate the pulse light carrying the secret key information to the single photon level to obtain a quantum signal carrying the secret key information.

3. The one-to-many user QKD network system based on multi-core optical fiber as claimed in claim 2, characterized in that: The signal transmitting end (10) further comprises a laser (100), wherein the laser (100) is connected to the first intensity modulator (101) so as to emit continuous light to the first intensity modulator (101).

4. The one-to-many user QKD network system based on multi-core optical fiber as claimed in claim 1, characterized in that: The signal transmitting end (10) comprises a first intensity modulator (101), a polarization modulator (103), a second intensity modulator (102) and an adjustable optical attenuator (104) which are connected in sequence; The first intensity modulator (101) is used to: chop continuous light into pulsed light of different frequencies; The polarization modulator (103) is used to: encode the polarization state of pulses of pulsed light of each frequency; The second intensity modulator (102) is used to modulate the encoded pulses in the pulse light of each frequency into decoy state pulses and signal state pulses with different intensities, so as to form pulse light carrying secret key information; The adjustable optical attenuator (104) is used to attenuate the pulse light carrying the secret key information to the single photon level to obtain a quantum signal carrying the secret key information.

5. The one-to-many user QKD network system based on multi-core optical fiber as claimed in claim 4, characterized in that: The signal transmitting end (10) further comprises a laser (100), wherein the laser (100) is connected to the first intensity modulator (101) so as to emit continuous light to the first intensity modulator (101).

6. The one-to-many user QKD network system based on multi-core optical fiber as claimed in claim 1, characterized in that: The signal transmission unit (20) comprises an optical switch (201), a multi-core optical fiber multiplexer (202), a multi-core optical fiber (200) and a multi-core optical fiber demultiplexer (203) which are connected in sequence; The optical switch (201) is used to distribute quantum signals of different frequencies in response to the signal transmitting end (10); The multi-core optical fiber multiplexer (202) is used to: receive the distributed quantum signal and couple it into the corresponding core of the multi-core optical fiber (200); The multi-core optical fiber demultiplexer (203) is used to decouple quantum signals from the multi-core optical fiber (200).

7. The one-to-many user QKD network system based on multi-core optical fiber as claimed in claim 1, characterized in that: The user end (30) comprises a base vector beam splitter (300) and two polarization beam splitters (301), and each of the polarization beam splitters (301) is connected to two single photon detectors (302); The basis vector beam splitter (300) is used to: perform basis vector selection on the quantum signal; The polarization beam splitter (301) is used to: measure the polarization state of a single photon in the quantum signal under a selected basis vector; The single photon detector (302) is used to measure the count information of the received polarization state and respond in coding.

8. The one-to-many user QKD network system based on multi-core optical fiber as claimed in claim 1, characterized in that: The number of frequencies of the continuous light chopped into pulsed light is the same as the number of the user ends (30).

9. The one-to-many user QKD network system based on multi-core optical fiber as claimed in claim 1, characterized in that: The polarization states include two groups of non-orthogonal basis vectors Z basis and X basis, and both the Z basis and the X basis include two orthogonal polarization states.

10. A method for implementing a one-to-many user QKD network based on multi-core optical fiber, characterized in that: It includes: In each cycle, according to the set timing, the continuous light is chopped into pulsed light of different frequencies, and the pulsed light of each frequency is modulated into decoy state pulses and signal state pulses of different intensities, and the polarization state of each decoy state pulse and signal state pulse is encoded to form quantum signals of different frequencies carrying secret key information; Firstly, quantum signals of different frequencies are coupled to different cores of a multi-core optical fiber (200) for transmission, and then decoupled from the multi-core optical fiber (200); Quantum signals of different frequencies are received respectively, basis vectors are randomly selected to measure the single-photon polarization state of the quantum signal, and the response is coded.

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