A decoding device for a polarization-encoded quantum key distribution system

Abstract

A decoding device for a polarization-coded quantum key distribution system, the decoding device comprising a polarization-maintaining beam splitter, a polarization controller, an optical fiber delay line, a decoding network, a first single-photon detector, and a second single-photon detector. The first output end of the polarization-maintaining beam splitter is connected to the polarization controller, the second output end of the polarization-maintaining beam splitter is connected to the optical fiber delay line, the output ends of the polarization controller and the optical fiber delay line are both connected to the input end of the decoding network, and the output end of the decoding network is respectively connected to the first single-photon detector and the second single-photon detector. Compared with the prior art, the decoding device for a polarization-coded quantum key distribution system of the present invention can reduce the required single-photon detectors to 2 by adopting a polarization beam splitter network and an optical fiber delay line, reducing the complexity and production cost of the system, but without additional loss, and correspondingly without reducing the secure coding rate of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum polarization encoding, and particularly to a decoding device for a polarization-encoded quantum key distribution system. Background Art

[0002] Quantum key distribution can provide unconditional secure key distribution for two communication parties over long distances, and its information-theoretic security is guaranteed by the basic principles of quantum mechanics. Currently, the QKD technology based on the BB84 protocol has been relatively mature. The conventional polarization-encoded QKD system needs to use multiple lasers and single-photon detectors to prepare and measure 4 polarization states. A typical polarization-encoding scheme is as Figure 1 shown. This scheme includes a sender Alice and a receiver Bob, and consists of a laser, a polarization beam splitter PBS, a polarization controller PC, a beam splitter BS, and a single-photon detector SPD. At the sender, each polarization state is generated by a laser and coupled into the same optical fiber through a polarization beam splitter and a beam splitter, etc. At the receiver, it is split into two paths by a beam splitter, divided into two groups of basis vectors, then undergoes polarization analysis through a polarization beam splitter, and then is detected by a single-photon detector.

[0003] This polarization-encoded QKD scheme requires 4 single-photon detectors at the receiver, so it has the disadvantages of large volume, high cost, and complex system. Summary of the Invention

[0004] Aiming at the above defects existing in the prior art, the present invention provides a decoding device for a polarization-encoded quantum key distribution system as follows:

[0005] The technical solution of the present invention is realized as follows:

[0006] A decoding device for a polarization-encoded quantum key distribution system, the decoding device includes a polarization-maintaining beam splitter, a polarization controller, an optical fiber delay line, a decoding network, a first single-photon detector, and a second single-photon detector. The first output end of the polarization-maintaining beam splitter is connected to the polarization controller, the second output end of the polarization-maintaining beam splitter is connected to the optical fiber delay line, the output ends of the polarization controller and the optical fiber delay line are both connected to the input end of the decoding network, and the output end of the decoding network is respectively connected to the first single-photon detector and the second single-photon detector.

[0007] Preferably, the decoding network includes a first polarization beam splitter, a second polarization beam splitter, a third polarization beam splitter, and a fourth polarization beam splitter, all of which are three-port devices. The input end of the first polarization beam splitter is connected to the output end of the polarization controller. The first output end of the first polarization beam splitter is connected to the first input end of the second polarization beam splitter. The second output end of the first polarization beam splitter is connected to the first input end of the fourth polarization beam splitter. The input end of the third polarization beam splitter is connected to the output end of the fiber optic delay line. The first output end of the third polarization beam splitter is connected to the second input end of the second polarization beam splitter. The second output end of the third polarization beam splitter is connected to the second input end of the fourth polarization beam splitter. The output end of the second polarization beam splitter is connected to a first single photon detector, and the output end of the fourth polarization beam splitter is connected to a second single photon detector.

[0008] Preferably, the decoding network includes a fifth polarization beam splitter and a sixth polarization beam splitter, both of which are four-port devices. The first input end of the fifth polarization beam splitter is connected to the output end of the polarization controller. The second input end of the fifth polarization beam splitter is connected to the first output end of the sixth polarization beam splitter. The first output end of the fifth polarization beam splitter is connected to a first single photon detector. The second output end of the fifth polarization beam splitter is connected to the first input end of the sixth polarization beam splitter. The second input end of the sixth polarization beam splitter is connected to the output end of the fiber optic delay line. The second output end of the sixth polarization beam splitter is connected to a second single photon detector.

[0009] Preferably, the decoding network includes a seventh polarization beam splitter, which is a four-port device. The first input end of the seventh polarization beam splitter is connected to the output end of the polarization controller. The second input end of the seventh polarization beam splitter is connected to the output end of the fiber optic delay line. The first output end of the seventh polarization beam splitter is connected to a first single photon detector. The second output end of the seventh polarization beam splitter is connected to a second single photon detector.

[0010] Compared with the prior art, the present invention has the following beneficial effects:

[0011] The decoding device of the polarization-coded quantum key distribution system of the present invention can reduce the required single photon detectors to 2 by using a polarization beam splitter network and a fiber optic delay line, reducing the complexity and production cost of the system, but without additional loss, and correspondingly without reducing the secure coding rate of the system. Description of the Drawings

[0012] Figure 1 is a schematic diagram of the principle of a typical quantum key distribution system in the prior art;

[0013] Figure 2 is a schematic diagram of the principle of Embodiment 1 of the present invention;

[0014] Figure 3 is a schematic diagram of the principle of Embodiment 2 of the present invention;

[0015] Figure 4 This is the principle block diagram of Embodiment 3 of the present invention.

[0016] In the figure: polarization-maintaining beam splitter 100, polarization controller 200, optical fiber delay line 300, decoding network 400, first polarization beam splitter 410, second polarization beam splitter 420, third polarization beam splitter 430, fourth polarization beam splitter 440, fifth polarization beam splitter 450, sixth polarization beam splitter 460, seventh polarization beam splitter 470, first single-photon detector 500, second single-photon detector 600. Specific implementation mode

[0017] Next, the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention.

[0018] As Figures 2 to 4 shown, a decoding device of a polarization coding quantum key distribution system of the present invention, the decoding device includes a polarization-maintaining beam splitter 100, a polarization controller 200, an optical fiber delay line 300, a decoding network 400, a first single-photon detector 500 and a second single-photon detector 600. The first output end of the polarization-maintaining beam splitter 100 is connected to the polarization controller 200, the second output end of the polarization-maintaining beam splitter 100 is connected to the optical fiber delay line 300, the output ends of the polarization controller 200 and the optical fiber delay line 300 are both connected to the input end of the decoding network 400, and the output end of the decoding network 400 is respectively connected to the first single-photon detector 500 and the second single-photon detector 600.

[0019] Embodiment 1, as Figure 2 shown, the decoding network 400 includes a first polarization beam splitter 410, a second polarization beam splitter 420, a third polarization beam splitter 430 and a fourth polarization beam splitter 440, all of which are three-port devices. The input end of the first polarization beam splitter 410 is connected to the output end of the polarization controller 200. The first output end of the first polarization beam splitter 410 is connected to the first input end of the second polarization beam splitter 420. The second output end of the first polarization beam splitter 410 is connected to the first input end of the fourth polarization beam splitter 440. The input end of the third polarization beam splitter 430 is connected to the output end of the optical fiber delay line 300. The first output end of the third polarization beam splitter 430 is connected to the second input end of the second polarization beam splitter 420. The second output end of the third polarization beam splitter 430 is connected to the second input end of the fourth polarization beam splitter 440. The output end of the second polarization beam splitter 420 is connected to the first single-photon detector 500, and the output end of the fourth polarization beam splitter 440 is connected to the second single-photon detector 600.

[0020] The input end of the polarization-maintaining beam splitter 100 is the quantum state receiving port of the receiving end and is connected to the optical fiber channel. The first output end of the polarization-maintaining beam splitter 100 is connected to the polarization controller 200 to rotate the polarization state of the incoming photons by 45°, serving as the measurement basis vectors of ±45° polarization. The second output end of the polarization-maintaining beam splitter 100 is connected to the optical fiber delay line 300, serving as the measurement basis vectors of horizontal and vertical polarization. The output end of the polarization controller 200 is connected to the input end of the first polarization beam splitter 410, and the output end of the optical fiber delay line 300 is connected to the input end of the third polarization beam splitter 430. The first output end of the first polarization beam splitter 410 is connected to the first input end of the second polarization beam splitter 420 through the optical fiber 1, and the second output end of the first polarization beam splitter 410 is connected to the first input end of the fourth polarization beam splitter 440 through the optical fiber 3. The first output end of the third polarization beam splitter 430 is connected to the second input end of the second polarization beam splitter 420 through the optical fiber 2, and the second output end of the third polarization beam splitter 430 is connected to the second input end of the fourth polarization beam splitter 440 through the optical fiber 4. The output end of the second polarization beam splitter 420 is connected to the input end of the first single-photon detector 500, and the output end of the fourth polarization beam splitter 440 is connected to the input end of the second single-photon detector 600. The optical fibers 1, 2, 3, and 4 are all polarization-maintaining optical fibers and have the same length.

[0021] The optical signal received by the receiving end enters from the input end of the polarization-maintaining beam splitter 100 and is divided into two pulse components. The first pulse component enters the polarization controller 200 and is then divided into two optical pulses with perpendicular polarizations by the first polarization beam splitter 410. Among them, the horizontally polarized optical pulse enters the second polarization beam splitter 420 through the optical fiber 1 and finally enters the first single-photon detector 500; the vertically polarized optical pulse enters the fourth polarization beam splitter 440 through the optical fiber 3 and finally enters the second single-photon detector 600. The two single-photon detectors detect the received optical pulses to complete the quantum state measurement under the ±45° basis vectors. After the second pulse component enters the optical fiber delay line 300 and is delayed for a period of time, it is decomposed into two optical pulses with perpendicular polarizations by the third polarization beam splitter 430. Among them, the horizontally polarized optical pulse enters the fourth polarization beam splitter 440 through the optical fiber 4 and finally enters the second single-photon detector 600; the vertically polarized optical pulse enters the second polarization beam splitter 420 through the optical fiber 2 and finally enters the second single-photon detector 600. The two single-photon detectors detect the received optical pulses to complete the quantum state measurement under the horizontal and vertical basis vectors. The optical fiber delay line 300 causes a time difference in the measurement of the two sets of basis vectors by the single-photon detector, and this time difference is equal to half of the quantum state preparation period of the quantum key distribution system.

[0022] Embodiment 2, as Figure 3As shown, the decoding network 400 includes a fifth polarization beam splitter 450 and a sixth polarization beam splitter 460, both of which are four-port devices. The first input end of the fifth polarization beam splitter 450 is connected to the output end of the polarization controller 200. The second input end of the fifth polarization beam splitter 450 is connected to the first output end of the sixth polarization beam splitter 460. The first output end of the fifth polarization beam splitter 450 is connected to the first single-photon detector 500. The second output end of the fifth polarization beam splitter 450 is connected to the first input end of the sixth polarization beam splitter 460. The second input end of the sixth polarization beam splitter 460 is connected to the output end of the fiber optic delay line 300. The second output end of the sixth polarization beam splitter 460 is connected to the second single-photon detector 600.

[0023] The input end of the polarization-maintaining beam splitter 100 is the quantum state receiving port of the receiving end and is connected to the fiber optic channel. The first output end of the polarization-maintaining beam splitter 100 is connected to the polarization controller 200, which rotates the polarization state of the incoming photons by 45° to serve as the measurement basis vectors of ±45° polarization. The second output end of the polarization-maintaining beam splitter 100 is connected to the fiber optic delay line 300 to serve as the measurement basis vectors of horizontal and vertical polarization. The output end of the polarization controller 200 is connected to the first input end of the fifth polarization beam splitter 450. The output end of the fiber optic delay line 300 is connected to the first input end of the sixth polarization beam splitter 160. The first output end of the fifth polarization beam splitter 450 is connected to the input end of the first single-photon detector 500. The second output end of the fifth polarization beam splitter 450 is connected to the second input end of the sixth polarization beam splitter 460 through fiber 1. The first output end of the sixth polarization beam splitter 460 is connected to the input end of the second single-photon detector 600. The second output end of the sixth polarization beam splitter 460 is connected to the second input end of the fifth polarization beam splitter 450 through fiber 2. Both fiber 1 and fiber 2 are polarization-maintaining fibers and have the same length.

[0024] The optical signal received by the receiving end enters from the input end of the polarization-maintaining beam splitter 100 and is divided into two pulse components. The first pulse component enters the polarization controller 200, and then is divided into two optical pulses with perpendicular polarizations by the fifth polarization beam splitter 450. Among them, the horizontally polarized optical pulse enters the first single-photon detector 500; the vertically polarized optical pulse enters the sixth polarization beam splitter 460 through the optical fiber 2 and finally enters the second single-photon detector 600. The two single-photon detectors detect the received optical pulses to complete the quantum state measurement under the ±45° basis vectors. After the second pulse component enters the optical fiber delay line 300 and is delayed for a period of time, it is decomposed into two optical pulses with perpendicular polarizations by the sixth polarization beam splitter 460. Among them, the horizontally polarized optical pulse enters the second single-photon detector 600; the vertically polarized optical pulse enters the fifth polarization beam splitter 450 through the optical fiber 2 and finally enters the second single-photon detector 600. The two single-photon detectors detect the received optical pulses to complete the quantum state measurement under the horizontal and vertical basis vectors. The optical fiber delay line 300 causes a time difference in the measurement of the two sets of basis vectors by the single-photon detectors, and this time difference is equal to half of the quantum state preparation period of the quantum key distribution system.

[0025] Embodiment 3, as Figure 4 shown, the decoding network 400 includes a seventh polarization beam splitter 470 with four ports. The first input end of the seventh polarization beam splitter 470 is connected to the output end of the polarization controller 200, the second input end of the seventh polarization beam splitter 470 is connected to the output end of the optical fiber delay line 300, the first output end of the seventh polarization beam splitter 470 is connected to the first single-photon detector 500, and the second output end of the seventh polarization beam splitter 470 is connected to the second single-photon detector 600.

[0026] The input end of the polarization-maintaining beam splitter 100 is the quantum state receiving port of the receiving end and is connected to the optical fiber channel. The first output end of the polarization-maintaining beam splitter 100 is connected to the polarization controller 200, which rotates the polarization state of the incoming photons by 45° as the measurement basis vector of ±45° polarization. The second output end of the polarization-maintaining beam splitter 100 is connected to the optical fiber delay line 300 as the measurement basis vector of horizontal and vertical polarizations. The output end of the polarization controller 200 is connected to the first input end of the seventh polarization beam splitter 470, and the output end of the optical fiber delay line 300 is connected to the second input end of the seventh polarization beam splitter 470. The first output end of the seventh polarization beam splitter 470 is connected to the input end of the first single-photon detector 500, and the second output end of the seventh polarization beam splitter 470 is connected to the input end of the second single-photon detector 600.

[0027] The optical signal received by the receiving end enters from the input end of the polarization-maintaining beam splitter 100 and is divided into two pulse components. The first pulse component enters the polarization controller 200 and is then divided into two optical pulses with perpendicular polarizations by the seventh polarization beam splitter 470. Among them, the horizontally polarized optical pulse enters the first single-photon detector 500; the vertically polarized optical pulse enters the second single-photon detector 500. The two single-photon detectors detect the received optical pulses to complete the quantum state measurement under the ±45° basis vectors. The second pulse component enters the optical fiber delay line 300 and is delayed for a period of time, and then is decomposed into two optical pulses with perpendicular polarizations by the seventh polarization beam splitter 470. Among them, the horizontally polarized optical pulse enters the second single-photon detector 600; the vertically polarized optical pulse enters the second single-photon detector 600. The two single-photon detectors detect the received optical pulses to complete the quantum state measurement under the horizontal and vertical basis vectors. The optical fiber delay line 300 causes a time difference in the measurement of the two sets of basis vectors by the detectors, and this time difference is equal to half of the quantum state preparation period of the quantum key distribution system.

[0028] Based on the structure and principle of the present invention, it can be seen that the decoding device of a polarization-encoded quantum key distribution system of the present invention can reduce the required single-photon detectors to 2 by using a polarization beam splitter network and an optical fiber delay line, reducing the complexity and production cost of the system, but without additional loss, and correspondingly without reducing the secure coding rate of the system.

Claims

1. A decoding device for a polarization-coded quantum key distribution system, characterized in that, The decoding device includes a polarization-maintaining beam splitter, a polarization controller, an optical fiber delay line, a decoding network, a first single-photon detector, and a second single-photon detector. The first output end of the polarization-maintaining beam splitter is connected to the polarization controller, and the second output end of the polarization-maintaining beam splitter is connected to the optical fiber delay line. The output ends of the polarization controller and the optical fiber delay line are both connected to the input end of the decoding network. The output end of the decoding network is respectively connected to the first single-photon detector and the second single-photon detector. The decoding network includes a fifth polarization beam splitter and a sixth polarization beam splitter, both of which are four-port devices. The first input end of the fifth polarization beam splitter is connected to the output end of the polarization controller. The second input end of the fifth polarization beam splitter is connected to the first output end of the sixth polarization beam splitter. The first output end of the fifth polarization beam splitter is connected to the first single-photon detector. The second output end of the fifth polarization beam splitter is connected to the first input end of the sixth polarization beam splitter. The second input end of the sixth polarization beam splitter is connected to the output end of the optical fiber delay line. The second output end of the sixth polarization beam splitter is connected to the second single-photon detector.

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