A quantum network system based on fiber-optic fabry-perot filters

Abstract

The application belongs to the technical field of quantum communication, and particularly relates to a quantum network system based on a fiber Fabry-Perot filter. In order to solve the problems of low performance of a point-to-multipoint quantum network system, difficulty in separating multiple user information operations, and instability of the system, a multi-ring multi-state discrete modulation scheme is used to replace a four-state discrete modulation scheme of an original system, so that the performance of the quantum network is significantly improved. A fiber Fabry-Perot filter with active locking replaces a fiber Bragg grating filter based on a fiber cavity, so that the separation of multiple user information can be easily realized, and the information intensity of the separated users is relatively stable. The operations of the two modified systems improve the performance of the system and reduce the complexity of the system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of quantum communication, and particularly relates to a quantum network system based on a fiber Fabry-Pérot (F-P) filter. ， F-P) filter. BACKGROUND

[0002] The latest progress of quantum computing highlights the security issues related to it. The current encryption algorithms 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), etc., whose security is guaranteed by the mathematical problems that are difficult to calculate. With the improvement of computing power, the security of such algorithms is facing an increasingly serious threat. Quantum key distribution (QKD) is an effective solution to communication security. It limits the means of attack by eavesdroppers to be limited by the principles of quantum mechanics. After more than twenty years of development, QKD has developed from the initial principle verification to how to promote its commercialization. However, due to the problems of distance expansion and network expansion, it limits its commercialization.

[0003] At present, the reported QKD networks can be divided into three categories. The first category is a trusted node network, which assumes that all nodes are trusted and are not threatened by eavesdroppers. In a real network, it is almost impossible to trust every connected node. This is equivalent to giving up the unconditional security of QKD. In addition, each node needs a complete transceiver device, which significantly increases the deployment cost of this type of network. The second category is a fully connected quantum network, which connects each user to all other users. This type of network has universality and robustness. However, the number of users n is limited by the channel arrangement combination of dense wavelength division multiplexing The third type is point-to-multipoint networks, in which a central point has the ability to send and receive information to multiple remote points simultaneously, especially suitable for quantum broadcast, quantum conference and other fields. Point-to-multipoint networks can share the encoding device of the sending end or the acquisition device of the receiving end, reducing resource overhead for network deployment and maintenance. This network structure can also more effectively utilize the bandwidth of the modulator or detector, because the signal stream is emitted from a single source point or converged into the same receiver. However, the current network structure separates or combines the information of users usually by using dense wavelength division multiplexer, passive beam splitter, active optical switch and other ways. The scheme using dense wavelength division multiplexer cannot share the encoding device of the sending end or the acquisition device of the receiving end. Although the schemes using passive beam splitter and active optical switch are feasible, the former sacrifices system performance to ensure the security of communication, 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 schemes decreases significantly.

[0004] Fortunately, a fiber Bragg grating based fiber cavities (FBG-FC) filtering network can separate the information of users without sacrificing system performance. This structure needs to use 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 slowly drifting with temperature changes, a temperature control instrument is needed to control the temperature change of the filtering network within the range of 0.01℃. However, the transmission peak of the FBG-FC will not drift in a short time, so the voltage loaded on the PZT needs to be constantly adjusted to adjust the position of the transmission peak of the FBG-FC. That is, the system does not have stability, and it is complex and difficult to operate the filtering structure. Under the premise of maintaining system performance, simplifying the process of separating the information of multiple users is a pending problem.

[0005] In addition, the system based on the FBG-FC filtering network uses a four-state discrete modulation scheme to encode user information. Because of the advantages of simplicity, ease of improving the repetition frequency of the system and other advantages, the four-state discrete modulation scheme is often used in continuous variable QKD, but the performance of this modulation scheme is low. Under the premise of maintaining the advantages of discrete modulation, improving the performance of the system is a problem to be solved. SUMMARY

[0006] The present application provides a quantum network system based on a fiber F-P filter 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 provides a novel and efficient quantum network system. The present application uses a locked fiber F-P filter to replace FBG-FC, which well solves the disadvantages of the original filter network difficult to operate and unstable transmission peak. In addition, the system uses multi-ring multi-state discrete modulation, and the key rate of the system is significantly improved. The operation of the two improved systems provides a feasible scheme for the practicalization of the quantum network.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0008] The present application provides a quantum network system based on a fiber F-P filter, comprising a quantum server, a first user module and a second user module.

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

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

[0011] The first user module and the second user module each comprise a polarization control module, a second laser, a fourth optical attenuator, a third beam splitter and a heterodyne detector; signal light output from the quantum channel is input into the third beam splitter through the polarization control module; the second laser outputs LLO, the LLO passes through the fourth optical attenuator and enters the third beam splitter; in the third beam splitter, the signal light and the LLO are coupled and interfered to obtain interference signals; the interference signals enter the heterodyne detector to extract frequency and phase information of a pilot signal, so as to recover quantum signals.

[0012] Further, the third user module, the fourth user module, the second optical filter assembly and the third optical filter assembly are arranged in the same way as the first user module and the first optical filter assembly, 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 second optical filter assembly, the signal light output from the optical attenuator in the second optical filter assembly is sent to the third user module through the 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 optical attenuator in the third optical filter assembly is sent to the fourth user module through the quantum channel, and the signal light output from the third port of the optical circulator in the third optical filter assembly is input into the second user module through the third optical attenuator and the quantum channel.

[0013] Further, the polarization control module comprises a polarization controller and a polarization beam splitter arranged in sequence, and is used for adjusting the polarization state of the signal light to the optimal interference state.

[0014] Further, the second laser in the first user module, the second user module, the third user module and the fourth user module has a frequency difference of 200MHz, 500MHz, 800MHz and 1.1GHz from the first laser respectively.

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

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

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

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

[0019] The quantum network system based on fiber optic FP filters designed in this invention still employs discrete modulation, but by changing it to a multi-ring, multi-state modulation format, the key rate of the system is significantly improved. A filtering network composed of an optical circulator and a fiber optic FP filter with a locked transmission peak separates user information, improving upon the original filtering network's operational difficulties and the instability of the transmission peak.

[0020] The quantum network system based on fiber optic FP filters designed in this invention has advantages such as high performance, robustness, simplicity, and low cost. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the quantum network system based on fiber optic FP filters in Example 1.

[0022] Figure 2 This is a schematic diagram of a quantum network system based on a fiber optic FP filter, as described in Example 2. Detailed Implementation

[0023] To further illustrate the technical solution of the present invention, the present invention will be further described below through embodiments.

[0024] Example 1

[0025] like Figure 1 As shown, this embodiment of a quantum network system based on a fiber optic FP filter includes a quantum server, a first user module, and a second user module. The quantum server acts as a transmitter, and the first and second user modules act as receivers.

[0026] The quantum server includes a first laser 1, which outputs continuous light. The continuous light passes sequentially through a first optical attenuator 2, an IQ modulator 3, and a first beam splitter 4. 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 to a first optical filter assembly. The first optical filter assembly includes 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 portion of the signal light is input to the first port of the optical circulator 6, and the signal light output from the second port of the optical circulator 6 is input to the fiber optic FP filter 7. The signal light separated by the fiber optic FP filter 7 is input to 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, and the other part of the signal light is input to the first user module through the second optical attenuator 10 and the quantum channel. The signal light output from the third port of the optical circulator 6 is input to the second user module through the third optical attenuator 11 and the quantum channel.

[0028] Both the first and second user modules 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 from the quantum channel is input to the third beam splitter 15 (50 / 50) via the polarization control module 12. The second laser 13 outputs an LLO (Light Loss Optical Array), which enters the third beam splitter 15 via the fourth optical attenuator 14. In the third beam splitter 15, the signal light and the LLO undergo coupling interference to produce an interference signal. This interference signal enters the heterodyne detector 16, where the orthogonal amplitude and phase components of the pilot signal and the quantum signal are extracted. The corresponding electrical signals are acquired using a high-speed oscilloscope, processed by a LabVIEW program, and the frequency difference between the quantum server and the lasers of the first and second user modules, as well as the relative phase change between the phase reference systems, are calculated to establish a reliable frequency estimate and phase reference for quantum signal extraction.

[0029] Example 2

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

[0031] The second optical filter assembly includes: a second optical circulator 17, a second 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 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 embodiments includes a polarization controller and a polarization beam splitter arranged in sequence, which are used to adjust the polarization state of the signal light to the 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 second laser 13 in the first user module, the second user module, the third user module and the fourth user module has a frequency difference of 200 MHz, 500 MHz, 800 MHz and 1.1 GHz from the first laser 1 respectively. The first optical attenuator 2 attenuates the optical power of the continuous light to 1 mW, and the attenuated continuous light is used as a continuous variable quantum key distribution light source and is modulated into an optical field with a repetition rate of 50 MHz by the 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 to introduce too much additional noise, the signals of the first, second, third and fourth user modules are shifted to the frequency spectrum positions of 300 MHz, 600 MHz, 900 MHz and 1.2 GHz respectively, to realize a four-sideband double-ring 8-state discrete modulation coherent state protocol. 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 suitable level (single photon level), the fourth optical attenuator 14 attenuates the optical power of the LLO to 4 mW, the fifth optical attenuator 21 attenuates the signal light intensity to a single photon level, and the sixth optical attenuator 26 attenuates the signal light intensity to a single photon level.

[0035] The first beam splitter 4 divides the continuous light into two parts of 10% and 90%. The 10% feedback light is received by the first detector 5 for bias point locking of the IQ modulator 3. The 90% continuous light is input into the first optical filter assembly of the filter network as signal light. The second beam splitter 8 divides the signal light into two parts of 50% and 50%. The 50% feedback light is received by the second detector 9. The 50% signal light is input into the first user module through 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 from the third port, which is reversely output by the fiber F-P filter 7. The fiber F-P filter 7 locks the position of the transmission peak according to the intensity of the first user module pilot signal monitored by the second detector 9, and maximizes the separation of the signal light of the first user module from the signal light containing information of all user modules. Subsequently, the second optical attenuator 10 adjusts the intensity of the signal light of the first user module to a suitable level according to the modulation variance of the feedback of the first user module, and sends it to the first user module through the insecure 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 fiber F-P filter 18 locks the position of the transmission peak according to the intensity of the pilot signal of the third user module monitored by the third detector 20, 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, the fifth optical attenuator 21 adjusts the intensity of the signal light of the third user module to a suitable level according to the modulation variance fed back by the receiving end third user module, and transmits the signal light to the third user module through 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 and output from the third port. After passing through the third optical circulator 22, the signal light enters the third fiber F-P filter 23. The third fiber F-P filter 23 locks the position of the transmission peak according to the intensity of the pilot signal of the fourth user module monitored by the fourth detector 25, 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 is sent to the fourth user module through a 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 is sent to the second user module through a quantum channel.

[0039] The main features and advantages of the present application are shown and described above, and it is obvious for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application.

[0040] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A quantum network system based on fiber Fabry-Perot filters, characterized in that, The quantum server, the first user module and the second user module are included. The quantum server includes a first laser (1) outputting continuous light, the continuous light sequentially passing through a first optical attenuator (2), an IQ modulator (3) and a first beam splitter (4), the continuous light being divided into two parts through the first beam splitter (4), one part of feedback light being received by a first detector (5), and the other part of signal light being input into a first optical filter assembly, the first optical filter assembly including an optical circulator (6), an optical fiber F-P filter (7), a second beam splitter (8), a second detector (9) and a second optical attenuator (10). In the first optical filter assembly, the other part of signal light is input into a first port of the optical circulator (6), signal light output from a second port of the optical circulator (6) is input into the optical fiber F-P filter (7), signal light separated by the optical fiber F-P filter (7) is input into the second beam splitter (8), the second beam splitter (8) divides the signal light into two parts, one part of feedback light is received by the second detector (9), and the other part of signal light is input into the first user module through the second optical attenuator (10) and a quantum channel, signal light output from a third port of the optical circulator (6) is input into the second user module through a third optical attenuator (11) and the quantum channel. 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), signal light output from the quantum channel is input into the third beam splitter (15) through the polarization control module (12), the second laser (13) outputs LLO, the LLO passes through the fourth optical attenuator (14) and enters the third beam splitter (15), in the third beam splitter (15), the signal light and the LLO are coupled and interfered to generate interference signals, the interference signals enter the heterodyne detector (16), the frequency and phase information of the pilot signal are extracted, and thus the quantum signal is recovered.

2. The quantum network system based on fiber Fabry-Perot filter according to claim 1, characterized in that, The third user module, the fourth user module, a second optical filter assembly and a third optical filter assembly are further included, the third user module and the fourth user module have the same structure as the first user module, the second optical filter assembly and the third optical filter assembly have the same structure as the first optical filter assembly, signal light output from the third port of the optical circulator (6) is input from a first port of an optical circulator in the second optical filter assembly, signal light output from an optical attenuator in the second optical filter assembly is sent to the third user module through a quantum channel, signal light output from the third port of the optical circulator in the second optical filter assembly is input from a first port of an optical circulator in the third optical filter assembly, signal light output from an optical attenuator in the third optical filter assembly is sent to the fourth user module through a quantum channel, and signal light output from the third port of the optical circulator in the third optical filter assembly is input into the second user module through the third optical attenuator (11) and the quantum channel.

3. The quantum network system based on 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 arranged in sequence, for adjusting the signal light polarization state to the optimal interference state.

4. The quantum network system based on fiber Fabry-Perot filter according to claim 2, wherein, The second laser (13) in the first user module, the second user module, the third user module and the fourth user module respectively has a frequency difference of 200MHz, 500MHz, 800MHz and 1.1GHz from the first laser (1).

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

6. The quantum network system based on fiber Fabry-Perot filter according to claim 2, wherein, The first optical attenuator (2) attenuates the optical power of the continuous light to 1mW, 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 the LLO to 4mW.

7. The quantum network system based on fiber Fabry-Perot filter according to claim 2, wherein, The first beam splitter (4) divides the continuous light into 10% and 90%, and the 10% feedback light is received by the first detector (5), and the 90% signal light is input into the first optical filter assembly, and the second beam splitter (8) divides the signal light into 50% and 50%, and the 50% feedback light is received by the second detector (9), and the 50% signal light is input into the first user module through the second optical attenuator (10) and the quantum channel.

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