A polarization-encoded quantum key distribution system

Abstract

The present invention relates to a polarization-encoded quantum key distribution system, comprising a transmitting module and a receiving module; the transmitting module comprises a pulse laser, an intensity modulator, a polarization encoder and an electrically adjustable attenuator; the output end of the pulse laser is connected to the input end of the intensity modulator, the output end of the intensity modulator is connected to the input end of the polarization encoder, the output end of the polarization encoder is connected to the input end of the electrically adjustable attenuator, and the output end of the electrically adjustable attenuator is connected to the input end of the receiving module; the receiving module comprises a polarization controller, a polarization decoder, a third polarization beam splitter, a first single-photon detector and a second single-photon detector. The distribution system of the present invention has the advantages of simple system structure and low cost, and avoids attacks on non-ideal beam splitters during passive base selection.

Description

Technical Field

[0001] The invention belongs to the field of optical fiber quantum key distribution system, and specifically relates to a polarization coded quantum key distribution system. Background Art

[0002] With the development of science and technology, especially the threat of quantum computers, classical cryptography based on computational complexity will face unprecedented challenges. The quantum key distribution technology is guaranteed to be unconditionally secure by the basic principles of quantum mechanics, and combined with the one-time symmetric encryption system, it can meet people's growing demand for secure communications. At present, the BB84 protocol quantum key distribution system is becoming increasingly mature and has become practical.

[0003] The polarization-encoded QKD system is a typical system of the BB84 protocol quantum key distribution system. The system is mainly composed of a single-photon source, a polarization controller, a polarization beam splitter, a 3dB coupler, and a single-photon detector. At the transmitting end, each polarization state is generated by a laser and coupled to the same optical fiber through a polarization beam splitter and a 3dB coupler; the receiving end is divided into two paths by a beam splitter and two groups of basis vectors, and then polarization analysis is performed through a polarization beam splitter, and then detected on a single-photon detector. The transmitting end of this polarization-encoded QKD system requires 4 or 8 (to generate decoy states) single-photon sources, and the receiving end requires 4 single-photon detectors. Therefore, the system has the disadvantages of large size, high cost, and complex system. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a polarization-encoded quantum key distribution system, which has the advantages of simple system structure and low cost, and avoids attacks on non-ideal beam splitters during passive basis selection.

[0005] The present invention adopts the following technical solutions:

[0006] A polarization-encoded quantum key distribution system comprises a transmitting module and a receiving module; the transmitting module comprises a pulse laser, an intensity modulator, a polarization encoder and an electrically adjustable attenuator; the output end of the pulse laser is connected to the input end of the intensity modulator, the output end of the intensity modulator is connected to the input end of the polarization encoder, the output end of the polarization encoder is connected to the input end of the electrically adjustable attenuator, and the output end of the electrically adjustable attenuator is connected to the input end of the receiving module;

[0007] The receiving module includes a polarization controller, a polarization decoder, a third polarization beam splitter, a first single-photon detector and a second single-photon detector; the input end of the polarization controller is connected to the output end of the electrically adjustable attenuator, the output end of the polarization controller is connected to the input end of the polarization decoder, the output end of the polarization decoder is connected to the input end of the third polarization beam splitter, and the output end of the third polarization beam splitter is respectively connected to the input ends of the first single-photon detector and the second single-photon detector.

[0008] Preferably, the polarization encoder includes a first polarization beam splitter and a first phase modulator; the output end of the intensity modulator is connected to the first input end of the first polarization beam splitter, the first output end of the first polarization beam splitter is connected to the input end of the first phase modulator, the output end of the first phase modulator is connected to the second input end of the first polarization beam splitter, and the second output end of the first polarization beam splitter is connected to the input end of the electrically adjustable attenuator.

[0009] Further preferably, the polarization decoder includes a second polarization beam splitter and a second phase modulator; the output end of the polarization controller is connected to the first input end of the second polarization beam splitter, the first output end of the second polarization beam splitter is connected to the input end of the second phase modulator, the output end of the second phase modulator is connected to the second input end of the second polarization beam splitter, and the second output end of the second polarization beam splitter is connected to the input end of the third polarization beam splitter.

[0010] Further preferably, the connecting optical fibers between the intensity modulator and the first polarization beam splitter, and between the third polarization beam splitter and the second polarization beam splitter are both set to 45° fusion splicing; one of the connecting optical fibers between the first polarization beam splitter and the first phase modulator is set to 90° fusion splicing, and the other connecting optical fiber is provided with a delay line; one of the connecting optical fibers between the second polarization beam splitter and the second phase modulator is set to 90° fusion splicing, and the other connecting optical fiber is provided with a delay line.

[0011] Further preferably, the pulse emitted by the pulse laser is modulated by the intensity modulator and then transmitted to the first polarization beam splitter, the pulse emitted after being split by the first polarization beam splitter is transmitted to the first phase modulator for phase modulation, and the modulated pulse is attenuated into a light pulse through an electrically adjustable attenuator; the light pulse is polarization-state restored by a polarization controller and then transmitted to the second polarization beam splitter, the light pulse emitted after being split by the second polarization beam splitter is transmitted to the second phase modulator for phase modulation, and the modulated light pulse is split by a third polarization beam splitter and then transmitted to the first single-photon detector and the second single-photon detector respectively; finally, the two split light pulses are respectively measured for photon count by the first single-photon detector and the second single-photon detector.

[0012] The beneficial effects of the present invention are:

[0013] 1) Compared with the traditional polarization-coded QKD system, the present invention only needs one pulsed laser (a single-photon source) and one phase modulator (i.e., the first phase modulator) to generate the four polarization states required by the BB84 protocol. The receiving module only needs two single-photon detectors to replace the four detectors of the traditional polarization-coded QKD system to realize signal reception, which greatly simplifies the system structure and reduces the production cost.

[0014] 2) The present invention uses a Sagnac ring structure composed of a polarization beam splitter, and performs 90° fusion splicing of the optical fiber between the polarization beam splitter and the phase modulator in the ring, thereby avoiding the light pulse from returning from the incident end of the polarization beam splitter and emitting from another port, thereby eliminating the need for an optical circulator, which is beneficial to simplifying the system structure and reducing production costs.

[0015] 3) The transmitting module of the present invention only requires one pulsed laser, thus avoiding the side channel vulnerability caused by the inconsistent wavelengths of multiple lasers in the traditional polarization-coded QKD system; and the receiving module adopts phase modulator random modulation to perform active basis selection, thus avoiding the attack on the non-ideal beam splitter during passive basis selection. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural composition diagram of the distribution system of the present invention.

[0017] Figure numerals: 1-transmitting module, 2-receiving module, 11-pulsed laser, 12-intensity modulator, 13-polarization encoder, 14-electrically adjustable attenuator, 15-first polarization beam splitter, 16-first phase modulator, 21-polarization controller, 22-polarization decoder, 23-third polarization beam splitter, 24-first single-photon detector, 25-second single-photon detector, 26-second polarization beam splitter, 27-second phase modulator. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] like Figure 1As shown, a polarization-encoded quantum key distribution system includes a sending module 1 and a receiving module 2; the sending module 1 includes a pulse laser 11, an intensity modulator 12, a polarization encoder 13 and an electrically adjustable attenuator 14; the output end of the pulse laser 11 is connected to the input end of the intensity modulator 12, the output end of the intensity modulator 12 is connected to the input end of the polarization encoder 13, the output end of the polarization encoder 13 is connected to the input end of the electrically adjustable attenuator 14, and the output end of the electrically adjustable attenuator 14 is connected to the input end of the receiving module 2;

[0020] The receiving module 2 includes a polarization controller 21, a polarization decoder 22, a third polarization beam splitter 23, a first single-photon detector 24 and a second single-photon detector 25; the input end of the polarization controller 21 is connected to the output end of the electrically adjustable attenuator 14, the output end of the polarization controller 21 is connected to the input end of the polarization decoder 22, the output end of the polarization decoder 22 is connected to the input end of the third polarization beam splitter 23, and the output end of the third polarization beam splitter 23 is respectively connected to the input ends of the first single-photon detector 24 and the second single-photon detector 25.

[0021] The polarization encoder 13 includes a first polarization beam splitter 15 and a first phase modulator 16; the output end of the intensity modulator 12 is connected to the first input end of the first polarization beam splitter 15, the first output end of the first polarization beam splitter 15 is connected to the input end of the first phase modulator 16, the output end of the first phase modulator 16 is connected to the second input end of the first polarization beam splitter 15, and the second output end of the first polarization beam splitter 15 is connected to the input end of the electrically adjustable attenuator 14.

[0022] The polarization decoder 22 includes a second polarization beam splitter 26 and a second phase modulator 27; the output end of the polarization controller 21 is connected to the first input end of the second polarization beam splitter 26, the first output end of the second polarization beam splitter 26 is connected to the input end of the second phase modulator 27, the output end of the second phase modulator 27 is connected to the second input end of the second polarization beam splitter 26, and the second output end of the second polarization beam splitter 26 is connected to the input end of the third polarization beam splitter 23.

[0023] Specifically, the connecting optical fiber between the intensity modulator 12 and the first polarization beam splitter 15 is set to be fused at 45 degrees to generate polarized light. Entering the first polarization beam splitter 15;

[0024] One of the connecting optical fibers between the first polarization beam splitter 15 and the first phase modulator 16 is set to be 90° fused, and the other connecting optical fiber is provided with a delay line; one of the connecting optical fibers between the second polarization beam splitter 26 and the second phase modulator 27 is set to be 90° fused, and the other connecting optical fiber is provided with a delay line; the connecting optical fiber between the third polarization beam splitter 23 and the second polarization beam splitter 26 is set to be 45° fused;

[0025] Specifically, the connecting optical fibers between the first polarization beam splitter 15 and the first phase modulator 16 and between the second polarization beam splitter 26 and the second phase modulator 27 are both polarization-maintaining optical fibers.

[0026] When the distribution system of the present invention is working, the pulse emitted by the pulse laser 11 is modulated by the intensity modulator 12 and then transmitted to the first polarization beam splitter 15. The pulse components |H> and |V> emitted after being split by the first polarization beam splitter 15 are transmitted to the first phase modulator 16 for phase modulation. By controlling the voltage of the first phase modulator 16, a phase difference is generated between the pulse components |H> and |V> transmitted to the first phase modulator 16. The resulting polarization state is Four phase differences The corresponding four polarization states are shown in Table 1:

[0027] Table 1: Four phase differences The corresponding four polarization states

[0028]

[0029] The modulated pulse is attenuated into a single-photon-level optical pulse via the electrically adjustable attenuator 14; the optical pulse is polarized and restored via the polarization controller 21, that is, the polarization state of the received optical pulse is compensated to be consistent with the polarization state of the electrically adjustable attenuator 14 of the sending module, and then transmitted to the second polarization beam splitter 26. The optical pulse emitted after the beam splitting by the second polarization beam splitter 26 is transmitted to the second phase modulator 27 for random 2 phase modulation, which are 0 and π / 2 respectively; by adjusting the voltage of the second phase modulator 27, the phase difference between the two components of the optical pulse is The modulated light pulse is transmitted to the first single-photon detector 24 and the second single-photon detector 25 respectively after being split by the third polarization beam splitter 23; finally, the photon counts of the two split light pulses are measured by the first single-photon detector 24 and the second single-photon detector 25 respectively.

[0030] The transmitting module 1 modulates four phases, and the receiving module 2 modulates two phases. The corresponding response probability table of the first single photon detector 24 (SPD1) and the second single photon detector 25 (SPD2) is shown in Table 2:

[0031] Table 2: Response probability table of the first single photon detector 24 (SPD1) and the second single photon detector 25 (SPD2)

[0032]

[0033] The photon counts are measured by the first single photon detector 24 and the second single photon detector 25 for subsequent processing to generate a security key.

[0034] The distribution system of the present invention only needs one pulse laser and one phase modulator to generate the four polarization states required by the BB84 protocol. The receiving module only needs two single-photon detectors to replace the four detectors of the traditional polarization-encoded QKD system to realize signal reception. At the same time, the present invention uses a Sagnac ring structure formed by a polarization beam splitter, and the optical fiber between the polarization beam splitter and the phase modulator in the ring is 90° fused to avoid the light pulse from returning from the incident end of the polarization beam splitter and emitting from another port, thereby eliminating the need for an optical circulator. Therefore, the distribution system of the present invention greatly simplifies the system structure and reduces the production cost.

[0035] The transmitting module of the present invention only needs one pulsed laser, thus avoiding the side channel vulnerability caused by the inconsistent wavelengths of multiple lasers in the traditional polarization-coded QKD system; and the receiving module adopts phase modulator random modulation to perform active basis selection, thus avoiding the attack on the non-ideal beam splitter during passive basis selection.

[0036] In summary, the present invention provides a polarization-encoded quantum key distribution system, which has the advantages of simple system structure and low cost, and avoids attacks on non-ideal beam splitters during passive basis selection.

Claims

1. A polarization-encoded quantum key distribution system, characterized in that: The invention comprises a sending module (1) and a receiving module (2); the sending module (1) comprises a pulse laser (11), an intensity modulator (12), a polarization encoder (13) and an electrically adjustable attenuator (14); the output end of the pulse laser (11) is connected to the input end of the intensity modulator (12), the output end of the intensity modulator (12) is connected to the input end of the polarization encoder (13), the output end of the polarization encoder (13) is connected to the input end of the electrically adjustable attenuator (14), and the output end of the electrically adjustable attenuator (14) is connected to the input end of the receiving module (2); The receiving module (2) comprises a polarization controller (21), a polarization decoder (22), a third polarization beam splitter (23), a first single-photon detector (24) and a second single-photon detector (25); the input end of the polarization controller (21) is connected to the output end of the electrically adjustable attenuator (14), the output end of the polarization controller (21) is connected to the input end of the polarization decoder (22), the output end of the polarization decoder (22) is connected to the input end of the third polarization beam splitter (23), and the output end of the third polarization beam splitter (23) is respectively connected to the input ends of the first single-photon detector (24) and the second single-photon detector (25); The polarization encoder (13) comprises a first polarization beam splitter (15) and a first phase modulator (16); the output end of the intensity modulator (12) is connected to the first input end of the first polarization beam splitter (15), the first output end of the first polarization beam splitter (15) is connected to the input end of the first phase modulator (16), the output end of the first phase modulator (16) is connected to the second input end of the first polarization beam splitter (15), and the second output end of the first polarization beam splitter (15) is connected to the input end of the electrically adjustable attenuator (14); The polarization decoder (22) comprises a second polarization beam splitter (26) and a second phase modulator (27); the output end of the polarization controller (21) is connected to the first input end of the second polarization beam splitter (26), the first output end of the second polarization beam splitter (26) is connected to the input end of the second phase modulator (27), the output end of the second phase modulator (27) is connected to the second input end of the second polarization beam splitter (26), and the second output end of the second polarization beam splitter (26) is connected to the input end of the third polarization beam splitter (23); The connecting optical fibers between the intensity modulator (12) and the first polarization beam splitter (15), and between the third polarization beam splitter (23) and the second polarization beam splitter (26) are both set to be fused at 45°; one of the connecting optical fibers between the first polarization beam splitter (15) and the first phase modulator (16) is set to be fused at 90°, and a delay line is provided in the other connecting optical fiber; one of the connecting optical fibers between the second polarization beam splitter (26) and the second phase modulator (27) is set to be fused at 90°, and a delay line is provided in the other connecting optical fiber; The pulse emitted by the pulse laser (11) is modulated by the intensity modulator (12) and then transmitted to the first polarization beam splitter (15). The pulse emitted after being split by the first polarization beam splitter (15) is transmitted to the first phase modulator (16) for phase modulation. The modulated pulse is attenuated into a light pulse via an electrically adjustable attenuator (14). The light pulse is polarized by a polarization controller (21) and then transmitted to the second polarization beam splitter (26). The light pulse emitted after being split by the second polarization beam splitter (26) is transmitted to the second phase modulator (27) for phase modulation. The modulated light pulse is split by the third polarization beam splitter (23) and then transmitted to the first single photon detector (24) and the second single photon detector (25). Finally, the photon counts of the two split light pulses are measured by the first single photon detector (24) and the second single photon detector (25).

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