Quantum network system based on optical fiber Fabry-Perot filter

Abstract

The invention belongs to the technical field of quantum communication, and particularly relates to a quantum network system based on an optical fiber Fabry-Perot filter. In order to solve the problems that a point-to-multipoint quantum network system is low in performance, operation of separating multiple pieces of user information is difficult, and the system is unstable, a multi-ring multi-state discrete modulation scheme is adopted to replace a four-state discrete modulation scheme of an original system, and the performance of the quantum network is remarkably improved. The active locking optical fiber Fabry-Perot filter replaces an optical fiber Bragg grating filter based on an optical fiber cavity, separation of multi-user information can be easily achieved, and the strength of user information separation is stable. Through the two operations of modifying the system, the performance of the system is improved, and the complexity of the system is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of quantum communication, and specifically relates to a method based on optical fiber Fabry-Perot ( F a b ry– Pé ro t ， Quantum network system of FP) filter. Background Art

[0002] The latest progress in quantum computing has highlighted the security issues associated with it. The encryption algorithms currently used are based on classical symmetric encryption algorithms and asymmetric encryption algorithms, such as Advanced Encryption Standard (AES), Rivest-Shamir-Adleman (RSA), elliptic curve Diffie-Hellman (ECDSE) and other algorithms, whose security is guaranteed by difficult-to-calculate mathematical problems. With the improvement of computing power, the security of this algorithm faces increasingly serious threats. Quantum key distribution (QKD) is an effective solution to communication security. It limits the means by which eavesdroppers can carry out attacks to the limitations of quantum mechanics. After more than 20 years of development, QKD has evolved from the initial principle verification to how to promote its commercialization. However, its commercialization is limited by problems such as distance expansion and network expansion.

[0003] At present, the reported QKD networks can be divided into three categories. The first category is the trusted node network, which assumes that all nodes are trustworthy and not threatened by eavesdroppers. In real networks, it is almost impossible to trust every connected node. This is equivalent to giving up the unconditional security of QKD. In addition, each node requires a complete transceiver device, which significantly increases the deployment cost of such networks. The second category is a fully connected quantum network, which fully connects each user to all other users. This type of network is universal and robust. However, the number of users n is limited by the channel arrangement and combination of dense wavelength division multiplexing. The third type is a point-to-multipoint network, in which the central point has the ability to send and receive information to multiple remote points at the same time, which is particularly suitable for quantum broadcasting, quantum conferences and other fields. Point-to-multipoint networks can share the encoding device at the transmitter or the acquisition device at the receiver, reducing resource overhead for network deployment and maintenance. This network structure can also make more efficient use of the bandwidth of the modulator or detector because the signal stream is emitted from a single source point or converged to the same receiver. However, at present, this network structure usually uses dense wavelength division multiplexing, passive beam splitters, active optical switches and other methods to separate or combine user information. The solution using dense wavelength division multiplexing cannot share the encoding device at the transmitter or the acquisition device at the receiver. Although the solution using passive beam splitters and active optical switches is feasible, the former ensures the security of communication at the expense of system performance, and the latter divides time into multiple time periods, each time period communicates with different users. As the number of users increases, the performance of these two solutions is significantly reduced.

[0004] Fortunately, without sacrificing system performance, a fiber Bragg grating based fiber cavities (FBG-FC) filter network can achieve the separation of user information. This structure requires the use of a data acquisition card, a piezoelectric transducer (PZT) and a high-voltage amplifier to jointly control the position of the transmission peak. In order to prevent the transmission peak of the FBG-FC from drifting slowly with temperature changes, a temperature control instrument is required to control the temperature change of the filter network within 0.01°C. Nevertheless, the transmission peak of the FBG-FC will not drift for a short time, so it is necessary to continuously adjust the voltage loaded on the PZT to adjust the position of the FBG-FC transmission peak. In other words, the system is not stable, and it is complex and difficult to manipulate the filter structure. Simplifying the process of separating multiple user information while maintaining system performance is an unresolved problem.

[0005] In addition, the system based on the FBG-FC filter network uses a four-state discrete modulation scheme to encode user information. Due to the advantages of the four-state discrete modulation scheme, such as simplicity and ease of improving the repetition frequency of the system, it is often used by continuous variable QKD, but the performance of this modulation scheme is relatively low. Under the premise of maintaining the advantages of discrete modulation, improving the performance of the system is a problem that needs to be solved at present. Summary of the invention

[0006] In view of the above problems, the present invention provides a quantum network system based on optical fiber FP filter, so as to make up for the defects of high complexity, unstable transmission peak and low key rate of the filter network based on FBG-FC, and provide a novel and efficient quantum network system. The present invention adopts a locked optical fiber FP filter to replace FBG-FC, which well solves the disadvantages of the original filter network being difficult to operate and the unstable transmission peak. In addition, the system significantly improves the key rate of the system by adopting multi-ring multi-state discrete modulation. The operation of these two improved systems provides a practical solution for the practical application of quantum networks.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention provides a quantum network system based on an optical fiber FP filter, comprising a quantum server, a first user module and a second user module;

[0009] The quantum server comprises a first laser, the first laser outputs continuous light, the continuous light passes through a first optical attenuator, an in-phase and quadrature (IQ) modulator and a first beam splitter in sequence, and the continuous light is divided into two parts by the first beam splitter, a part of the feedback light is received by a first detector, and the other part of the signal light is input into a first optical filter component, the first optical filter component comprises an optical circulator, an optical fiber FP filter, a second beam splitter, a second detector and a second optical attenuator;

[0010] In the first optical filter assembly, another part of the signal light is input into the first port of the optical circulator, the signal light output from the second port of the optical circulator is input into the optical fiber FP filter, the signal light separated by the optical fiber FP filter is input into the second beam splitter, the second beam splitter divides the signal light into two parts, one part of the feedback light is received by the second detector, and the other part of the signal light is input into the first user module via the second optical attenuator and the quantum channel, and the signal light output from the third port of the optical circulator is input into the second user module via the third optical attenuator and the quantum channel;

[0011] The first user module and the second user module both include a polarization control module, a second laser, a fourth optical attenuator, a third beam splitter, and a heterodyne detector. The signal light output by the quantum channel is input into the third beam splitter via the polarization control module. The second laser outputs LLO. The LLO enters the third beam splitter via the fourth optical attenuator. In the third beam splitter, the signal light and the LLO are coupled and interfered to obtain an interference signal. The interference signal enters the heterodyne detector to extract the frequency and phase information of the pilot signal, thereby restoring the quantum signal.

[0012] Furthermore, it also includes a third user module, a fourth user module, a second optical filter assembly and a third optical filter assembly. The structures of the third user module and the fourth user module are the same as those of the first user module. The structures of the second optical filter assembly and the third optical filter assembly are the same as those of the first optical filter assembly. The signal light output by the third port of the optical circulator is input from the first port of the optical circulator in the second optical filter assembly. The signal light output by the optical attenuator in the second optical filter assembly is sent to the third user module via a quantum channel. The signal light output by the third port of the optical circulator in the second optical filter assembly is input from the first port of the optical circulator in the third optical filter assembly. The signal light output by the optical attenuator in the third optical filter assembly is sent to the fourth user module via a quantum channel. The signal light output by the third port of the optical circulator in the third optical filter assembly is input into the second user module via the third optical attenuator and the quantum channel.

[0013] Furthermore, the polarization control module includes a polarization controller and a polarization beam splitter which are arranged in sequence and are used to adjust the polarization state of the signal light to an optimal interference state.

[0014] Furthermore, the frequency differences between the second laser in the first user module, the second user module, the third user module and the fourth user module and the first laser are 200 MHz, 500 MHz, 800 MHz and 1.1 GHz respectively.

[0015] Furthermore, the first laser is a high-performance continuous single-frequency laser with a line width of 100 Hz and a wavelength of 1550.12 nm.

[0016] Further, the first optical attenuator attenuates the optical power of the continuous light to 1 mW, the second optical attenuator attenuates the signal light intensity to a single photon level, the third optical attenuator attenuates the signal light intensity to a single photon level, and the fourth optical attenuator attenuates the optical power of the LLO to 4 mW.

[0017] Furthermore, the first beam splitter divides the continuous light into two parts, 10% and 90%, 10% of the feedback light is received by the first detector, and 90% of the signal light is input into the first optical filter assembly; the second beam splitter divides the signal light into two parts, 50% and 50%, 50% of the feedback light is received by the second detector, and 50% of the signal light is input into the first user module via the second optical attenuator and the quantum channel.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] The quantum network system based on the optical fiber FP filter designed by the present invention still adopts discrete modulation, and by changing to a multi-ring multi-state modulation format, the key rate of the system is significantly improved. The filter network composed of an optical circulator and an optical fiber FP filter with a locked transmission peak is used to separate user information, which improves the problem of the original filter network being difficult to operate and the unstable transmission peak.

[0020] The optical fiber FP filter-based quantum network system designed by the present invention has the advantages of high performance, robustness, simplicity, low cost, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of a quantum network system based on optical fiber FP filter of Example 1.

[0022] Figure 2 This is a schematic diagram of a quantum network system based on optical fiber FP filter according to Example 2. DETAILED DESCRIPTION

[0023] In order to further illustrate the technical solution of the present invention, the present invention is further described below through embodiments.

[0024] Example 1

[0025] like Figure 1 As shown, a quantum network system based on an optical fiber FP filter of this embodiment includes a quantum server, a first user module and a second user module, the quantum server serves as a transmitting end, and the first user module and the second user module serve as receiving ends;

[0026] The quantum server comprises a first laser 1, which outputs continuous light. The continuous light passes through a first optical attenuator 2, an IQ modulator 3 and a first beam splitter 4 in sequence. The first beam splitter 4 divides the continuous light into two parts, one part of the feedback light is received by a first detector 5, and the other part of the signal light is input into a first optical filter assembly. The first optical filter assembly comprises an optical circulator 6, an optical fiber FP filter 7, a second beam splitter 8, a second detector 9 and a second optical attenuator 10.

[0027] In the first optical filter assembly, another part of the signal light is input to the first port of the optical circulator 6, the signal light output from the second port of the optical circulator 6 is input to the optical fiber FP filter 7, the signal light separated by the optical fiber FP filter 7 is input to the second beam splitter 8, the second beam splitter 8 divides the signal light into two parts, a part of the feedback light is received by the second detector 9, and the other part of the signal light is input to the first user module via the second optical attenuator 10 and the quantum channel, and the signal light output from the third port of the optical circulator 6 is input to the second user module via the third optical attenuator 11 and the quantum channel;

[0028] The first user module and the second user module both include a polarization control module 12, a second laser 13, a fourth optical attenuator 14, a third beam splitter 15, and a heterodyne detector 16. The signal light output by the quantum channel is input into the third beam splitter 15 (50 / 50) via the polarization control module 12. The second laser 13 outputs LLO, and the LLO enters the third beam splitter 15 via the fourth optical attenuator 14. In the third beam splitter 15, the signal light and the LLO are coupled and interfered to obtain an interference signal. The interference signal enters the heterodyne detector 16 to extract the orthogonal amplitude component and the orthogonal phase component of the pilot signal and the orthogonal amplitude component and the orthogonal phase component of the quantum signal. The corresponding electrical signal is collected by a high-speed oscilloscope, processed by the Labview program, and the frequency difference between the quantum server and the first user module laser (the second user module laser) and the relative phase change between the phase reference system are calculated to establish a reliable frequency estimation and phase reference for the extraction of quantum signals.

[0029] Example 2

[0030] like Figure 2 As shown, on the basis of Example 1, this embodiment adds a third user module, a fourth user module, a second optical filter assembly and a third optical filter assembly. The structures of the third user module and the fourth user module are the same as those of the first user module. The structures of the second optical filter assembly and the third optical filter assembly are the same as those of the first optical filter assembly. The signal light output from the third port of the optical circulator 6 is input from the first port of the optical circulator in the second optical filter assembly. The signal light output from the attenuator in the second optical filter assembly is sent to the third user module via a quantum channel. The signal light output from the third port of the optical circulator in the second optical filter assembly is input from the first port of the optical circulator in the third optical filter assembly. The signal light output from the attenuator in the third optical filter assembly is sent to the fourth user module via a quantum channel. The signal light output from the third port of the optical circulator in the third optical filter assembly is input via a third attenuator 11 and a quantum channel.

[0031] The second optical filter assembly includes: a second optical circulator 17 , a second optical fiber FP filter 18 , a fourth beam splitter 19 , a third detector 20 and a fifth optical attenuator 21 .

[0032] The third optical filter assembly includes: a third optical circulator 22 , a third optical fiber FP filter 23 , a fifth beam splitter 24 , a fourth detector 25 and a sixth optical attenuator 26 .

[0033] The polarization control module 12 in the above embodiment includes a polarization controller and a polarization beam splitter which are arranged in sequence, and is used to adjust the polarization state of the signal light to an optimal interference state.

[0034] The first laser 1 is a high-performance continuous single-frequency laser with a line width of 100 Hz and a wavelength of 1550.12 nm. The frequency difference between the second laser 13 in the first user module, the second user module, the third user module and the fourth user module and the first laser 1 is 200 MHz, 500 MHz, 800 MHz and 1.1 GHz respectively. The first optical attenuator 2 attenuates the optical power of the continuous light to 1 mW. The attenuated continuous light is used as a continuous variable quantum key distribution light source and modulated into a light field with a repetition rate of 50 MHz by an IQ modulator 3. The quantum signals and pilot signals of the four user modules are encoded in a time-division multiplexing manner. In order to prevent the modulation depth of the pilot signal from being too large and introducing too much additional noise, the signals of the first, second, third and fourth user modules are shifted to 300 MHz, 600 MHz, 900 MHz and 1.2 GHz spectrum positions respectively, realizing a four-sideband dual-loop 8-state discrete modulation coherent state protocol. The second optical attenuator 10 attenuates the signal light intensity to the single photon level, the third optical attenuator 11 attenuates the signal light intensity to an appropriate level (single photon level), the fourth optical attenuator 14 attenuates the optical power of LLO to 4 mW, the fifth optical attenuator 21 attenuates the signal light intensity to the single photon level, and the sixth optical attenuator 26 attenuates the signal light intensity to the single photon level.

[0035] The first beam splitter 4 divides the continuous light into two parts, 10% and 90%, 10% of the feedback light is received by the first detector 5 and used for bias point locking of the IQ modulator 3, 90% of the continuous light is input as signal light into the first optical filter component of the filtering network, the second beam splitter 8 divides the signal light into two parts, 50% and 50%, 50% of the feedback light is received by the second detector 9, and 50% of the signal light is input into the first user module via the second optical attenuator 10 and the quantum channel.

[0036] The purpose of the optical circulator in the optical filter assembly is to output the signal light of the second user module, the third user module, and the fourth user module reversely output by the optical fiber FP filter 7 from the third port. The optical fiber FP filter 7 monitors the intensity of the pilot signal of the first user module according to the second detector 9, locks the position of the transmission peak, and maximizes the separation of the signal light of the first user module from the signal light containing the information of all user modules. Subsequently, according to the modulation variance fed back by the first user module, the second optical attenuator 10 adjusts the intensity of the signal light of the first user module to an appropriate level and sends it to the first user module through the unsafe quantum channel.

[0037] The signal light of the second user module, the third user module, and the fourth user module enters the first port of the second optical circulator 17 and is output from the second port. In order to separate the signal light of the third user module from the signal light containing the information of the second user module, the third user module, and the fourth user module, the second optical fiber FP filter 18 monitors the intensity of the pilot signal of the third user module according to the third detector 20, locks the position of the transmission peak, and maximizes the separation of the signal light of the third user module from the signal light containing the information of the second user module, the third user module, and the fourth user module. Subsequently, under the simplest optical path, according to the modulation variance fed back by the third user module at the receiving end, the fifth optical attenuator 21 adjusts the intensity of the signal light of the third user module to an appropriate level, and transmits it to the third user module via a long-distance single-mode optical fiber.

[0038] The signal light of the remaining fourth user module and the second user module is input from the second port of the second optical circulator 17, output from the third port, and enters the third optical fiber FP filter 23 after passing through the third optical circulator 22. The third optical fiber FP filter 23 monitors the intensity of the pilot signal of the fourth user module according to the fourth detector 25, locks the position of the transmission peak, and maximizes the separation of the signal light of the fourth user module from the signal light containing the information of the fourth user module and the second user module. According to the modulation intensity fed back by the fourth user module, the signal light of the fourth user module is attenuated to a suitable level by the sixth optical attenuator 26 and sent to the fourth user module through the quantum channel. Finally, according to the modulation intensity fed back by the second user module, the signal light of the second user module is attenuated to a suitable level by the third optical attenuator 11 and sent to the second user module through the quantum channel.

[0039] The above shows and describes the main features and advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and scope of the equivalent elements of the claims are included in the present invention.

[0040] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A quantum network system based on an optical fiber Fabry-Perot filter, characterized in that: comprising a quantum server, a first user module and a second user module; The quantum server comprises a first laser (1), the first laser (1) outputs continuous light, the continuous light passes through a first optical attenuator (2), an IQ modulator (3) and a first beam splitter (4) in sequence, and the first beam splitter (4) splits the continuous light into two parts, one part of the feedback light is received by a first detector (5), and the other part of the signal light is input into a first optical filter component, the first optical filter component comprises an optical circulator (6), an optical fiber FP filter (7), a second beam splitter (8), a second detector (9) and a second optical attenuator (10); In the first optical filter component, another part of the signal light is input into the first port of the optical circulator (6), the signal light output from the second port of the optical circulator (6) is input into the optical fiber FP filter (7), the signal light separated by the optical fiber FP filter (7) is input into the second beam splitter (8), the second beam splitter (8) splits the signal light into two parts, one part of the feedback light is received by the second detector (9), the other part of the signal light is input into the first user module via the second optical attenuator (10) and the quantum channel, and the signal light output from the third port of the optical circulator (6) is input into the second user module via the third optical attenuator (11) and the quantum channel; The first user module and the second user module both comprise a polarization control module (12), a second laser (13), a fourth optical attenuator (14), a third beam splitter (15), and a heterodyne detector (16); the signal light output by the quantum channel is input into the third beam splitter (15) via the polarization control module (12); the second laser (13) outputs an LLO; the LLO enters the third beam splitter (15) via the fourth optical attenuator (14); in the third beam splitter (15), the signal light and the LLO are coupled and interfered to generate an interference signal; the interference signal enters the heterodyne detector (16); the frequency and phase information of the pilot signal are extracted, thereby restoring the quantum signal.

2. A quantum network system based on optical fiber Fabry-Perot filter according to claim 1, characterized in that: The device also comprises a third user module, a fourth user module, a second optical filter assembly and a third optical filter assembly. The structures of the third user module and the fourth user module are the same as those of the first user module. The structures of the second optical filter assembly and the third optical filter assembly are the same as those of the first optical filter assembly. The signal light outputted from the third port of the optical circulator (6) is inputted from the first port of the optical circulator in the second optical filter assembly. The signal light outputted from the optical attenuator in the second optical filter assembly is sent to the third user module via a quantum channel. The signal light outputted from the third port of the optical circulator in the second optical filter assembly is inputted from the first port of the optical circulator in the third optical filter assembly. The signal light outputted from the optical attenuator in the third optical filter assembly is sent to the fourth user module via a quantum channel. The signal light outputted from the third port of the optical circulator in the third optical filter assembly is inputted from the third optical attenuator (11) and the quantum channel.

3. A quantum network system based on optical fiber Fabry-Perot filter according to claim 2, characterized in that: The polarization control module (12) comprises a polarization controller and a polarization beam splitter which are arranged in sequence and are used to adjust the polarization state of the signal light to an optimal interference state.

4. A quantum network system based on optical fiber Fabry-Perot filter according to claim 2, characterized in that: The frequency differences between the second laser (13) in the first user module, the second user module, the third user module and the fourth user module and the first laser (1) are 200 MHz, 500 MHz, 800 MHz and 1.1 GHz respectively.

5. A quantum network system based on optical fiber Fabry-Perot filter according to claim 2, characterized in that: The first laser (1) is a high-performance continuous single-frequency laser with a line width of 100 Hz and a wavelength of 1550.12 nm.

6. A quantum network system based on optical fiber Fabry-Perot filter according to claim 2, characterized in that: The first optical attenuator (2) attenuates the optical power of continuous light to 1 mW, the second optical attenuator (10) attenuates the signal light intensity to a single photon level, the third optical attenuator (11) attenuates the signal light intensity to a single photon level, and the fourth optical attenuator (14) attenuates the optical power of LLO to 4 mW.

7. A quantum network system based on optical fiber Fabry-Perot filter according to claim 2, characterized in that: The first beam splitter (4) divides the continuous light into two parts, 10% and 90%, 10% of the feedback light is received by the first detector (5), and 90% of the signal light is input into the first optical filter component; the second beam splitter (8) divides the signal light into two parts, 50% and 50%, 50% of the feedback light is received by the second detector (9), and 50% of the signal light is input into the first user module via the second optical attenuator (10) and the quantum channel.

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