Dynamic user phase coding quantum communication system

Abstract

The invention discloses a dynamic user phase coding quantum communication system, and the system is characterized in that a laser LD generates a pulse optical signal, the pulse optical signal enters a first SC device for initial phase modulation, and then enters a polarization modulation module for phase loading and polarization state adjustment; a pulse light signal is modulated into a signal state or decoy state pulse through an intensity modulator IM, the signal state or decoy state pulse is attenuated into a single photon level through an attenuator ATT, then the single photon level enters a selected user side Bob in each period, and the single photon level enters an original path after being modulated at the user side Bob; and after returning, interference is generated at the 50: 50 beam splitter BS, and finally the light is emitted to the detection unit for detection. The phase encoder and the N (N is greater than or equal to 2) polarization encoders are arranged, so that the strong anti-interference capability is improved; a plurality of polarization encoders are utilized to adjust the pulse optical signal into a polarization state to select a user, so that different users can perform independent communication on the same quantum channel, and the flexibility of user selection is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of quantum communication, and in particular to a dynamic user phase-coded quantum communication system. Background Art

[0002] Quantum communication technology uses the principles of quantum mechanics, especially quantum superposition and entanglement, to achieve secure transmission of information. Compared with traditional communication technology, quantum communication has extremely high security and cannot be eavesdropped or tampered with. Therefore, it has broad application prospects in the fields of military, finance and government confidential communications. The core technologies of quantum communication include (Quantum Key Distribition, QKD), quantum teleportation and quantum network.

[0003] At present, quantum communication mainly relies on two encoding methods: polarization encoding and phase encoding. Polarization encoding uses the polarization state of photons to transmit information, while phase encoding achieves information transmission by controlling the phase of photons. Although these methods guarantee the secure transmission of information to a certain extent, each has some limitations.

[0004] The quantum key distribution system can use polarization, phase and other optical degrees of freedom encoding. Polarization encoding: This method is simple and easy to implement, but it is easily affected by environmental noise and polarization mode dispersion in long-distance transmission, resulting in signal attenuation and increased bit error rate. Phase encoding: Phase encoding technology has high anti-interference ability to environmental noise, but in multi-user communication scenarios, how to effectively select and distinguish information from different users is still a challenge.

[0005] Therefore, further improvements are needed based on the existing polarization and phase coding to enhance the anti-interference capability of existing quantum communications and the flexibility of user selection, so as to achieve more efficient and secure quantum communications. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a quantum communication system with phase-coded polarization-selective users that has strong anti-interference capability and flexible user selection.

[0007] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a dynamic user phase-coded quantum communication system, including an LD laser LD, a first CIR circulator, a first SC device, a first polarization controller PC1, a polarization modulation module, a second CIR circulator, an intensity modulator IM, an attenuator ATT, a third CIR circulator, a detection unit, a 50:50 beam splitter BS, a second polarization controller PC2, a second four-port polarization beam splitter PBS2, a second delay line DL, a second SC device, a first receiving end Bob1, a third polarization controller PC3, a third four-port polarization beam splitter PBS3, a third delay line DL, and a third SC device, wherein:

[0008] The laser LD is used to generate a pulse light signal;

[0009] The first CIR circulator transmits the pulsed optical signal to the first SC device and the first polarization controller PC1;

[0010] The first SC device is used to modulate the initial phase φ∈{0,π / 2,π,3π / 2} of the initial pulsed optical signal;

[0011] The first polarization controller PC1 is used to modulate the initial pulse light signal into a 45° polarization state;

[0012] The polarization modulation module is used to perform phase loading and polarization state adjustment on the 45° polarization state pulse optical signal to change it into a horizontal polarization state;

[0013] The intensity modulator IM is used to modulate the pulsed light signal into a signal state or a decoy state pulse;

[0014] The attenuator ATT attenuates the pulse light signal to a single photon level;

[0015] The 50:50 beam splitter BS is used to split the pulse light signal into two pulse light signals, namely a first light beam and a second light beam;

[0016] The first light beam passes through the second four-port polarization beam splitter PBS2 to reach the selected user end Bob1, and returns along the original path after being modulated by the user end Bob1;

[0017] The second light beam passes through the third four-port polarization beam splitter PBS3 to reach the selected user end Bob2, and returns along the original path after being modulated by the user end Bob2;

[0018] When the returned first light beam and the second light beam arrive at the 50:50 beam splitter BS at the same time, they pass through the CIR circulator for the third time and are then emitted to the detection unit for detection.

[0019] Preferably, the polarization modulation module comprises a first polarization beam splitter PBS1, a first phase modulator PM1, a first Faraday rotator FR1 and a first delay line DL;

[0020] An input port of the first polarization beam splitter PBS1 is connected to the first CIR circulator via an optical signal; an output port of the first polarization beam splitter PBS1 is connected to the first Faraday rotator FR1 via a first delay line DL;

[0021] Another output port of the first polarization beam splitter PBS1 is connected to the first phase modulator PM1 through an optical signal;

[0022] The first phase modulator PM1 is connected to the first Faraday rotator FR1 via an optical signal.

[0023] Preferably, the detection unit includes a first single-photon detector D1 and a second single-photon detector D2.

[0024] Preferably, the first polarization controller PC1 adjusts the initial pulse light signal to a 45° polarized pulse light signal, and after sending it to the first polarization beam splitter PBS1, the 45° polarized pulse light signal is divided into two parts, horizontal polarization H and vertical polarization, with the same probability;

[0025] The horizontally polarized pulse is transmitted through the first polarization beam splitter PBS1;

[0026] The vertically polarized pulse first passes through the first phase modulator PM1 to be loaded with the phase △φ, then passes through the first Faraday rotator FR1 and the first delay line DL to become a horizontal polarization state, and then transmits through the first polarization beam splitter PBS1 to return to the first CIR circulator R.

[0027] The vertical polarization state |V> of the vertical polarization pulse V introduces an additional phase of π / 2 after being reflected by the first polarization beam splitter PBS1;

[0028] The horizontal polarization state |H> of the horizontally polarized pulse passes through the first Faraday rotator FR1, is input to the first polarization beam splitter PBS1, and is reflected back to the first CIR circulator.

[0029] Preferably, the pulse of the vertical polarization state |V> is first loaded with a phase △φ through the first phase modulator PM1, and then the vertical polarization state |V> is combined with the horizontal polarization state |H> at the first polarization beam splitter PBS1, and the combined pulse is emitted to the intensity modulator IM.

[0030] Preferably, the intensity modulator IM modulates the combined pulse light signal into a signal state or a decoy state pulse, and then transmits it to the attenuator ATT, and the attenuator ATT attenuates the signal state or the decoy state pulse to a single photon level to obtain a single photon pulse.

[0031] Preferably, the single-photon pulse passes through the third CIR circulator and reaches the 50:50 beam splitter BS113. The single-photon pulse at the 50:50 beam splitter BS113 is divided into two optical paths, a first optical path and a second optical path. The single-photon pulses in the first optical path and the second optical path respectively pass through the second four-port polarization beam splitter PBS2 and the third four-port polarization beam splitter PBS3 and reach the corresponding selected user ends Bob1 and Bob2.

[0032] Preferably, the horizontal polarization state |H> and the vertical polarization state |V> are represented by Jones matrices:

[0033]

[0034] Preferably, the vertical polarization state |V> introduces an additional phase of π / 2 after being reflected by the first polarization beam splitter PBS1, and the Jones matrix of the first Faraday rotator FR1 is expressed as:

[0035]

[0036] Preferably, the horizontal polarization state |H> after passing through the first Faraday rotator FR1 is expressed as:

[0037]

[0038] The beneficial technical effects of the present invention are as follows: the present invention is provided with a phase encoder and N (N≥2) polarization encoders are arranged step by step to modulate the pulse light signal, the phase encoder has a high anti-interference ability to environmental noise and interference, ensures the stability and reliability of the signal, and realizes a strong anti-interference ability;

[0039] Multiple polarization encoders are used to adjust the pulsed optical signal into a polarization state to select users, so that different users can communicate independently on the same quantum channel, greatly improving the flexibility of user selection and increasing flexibility and scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is an overall structural block diagram of a dynamic user phase-coded quantum communication system of the present invention;

[0041] Figure 2 This is a schematic structural diagram of an SC device of a dynamic user phase-coded quantum communication system of the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments, but the scope of protection claimed in the present invention is not limited to the following specific embodiments.

[0043] like Figure 1 As shown, a dynamic user phase-coded quantum communication system includes an LD laser 101, a first CIR circulator 102, a first SC (Sagnac ring) device 103, a first polarization controller PC1104, a polarization modulation module, a second CIR circulator 105, an intensity modulator IM 110, an attenuator ATT 111, a third CIR circulator 112, a detection unit, a 50:50 beam splitter BS113, a second polarization controller PC2114, a second four-port polarization beam splitter PBS2, a second delay line DL 116, a second SC device 117, a first receiving end Bob1118, a third polarization controller PC3119, a third four-port polarization beam splitter PBS3120, a third delay line DL 121, and a third SC device 122, wherein:

[0044] The laser LD 101 is used to generate a pulse light signal;

[0045] The first CIR circulator 102 transmits the pulsed optical signal to the first SC device 103 and the first polarization controller PC1104;

[0046] The first SC device 103 is used to modulate the initial phase φ of the initial pulse optical signal. A ∈{0,π / 2,π,3π / 2};

[0047] The first polarization controller PC1104 is used to modulate the initial pulse optical signal into a 45° polarization state;

[0048] The polarization modulation module is used to perform phase loading and polarization state adjustment on the 45° polarization state pulse optical signal to change it into a horizontal polarization state;

[0049] Specifically, the polarization modulation module includes a first polarization beam splitter PBS1106, a first phase modulator PM1107, a first Faraday rotator FR1108 and a first delay line DL109;

[0050] An input port of the first polarization beam splitter PBS1106 is connected to the first CIR circulator 102 via an optical signal; an output port of the first polarization beam splitter PBS1106 is connected to the first Faraday rotator FR1108 via a first delay line DL109;

[0051] Another output port of the first polarization beam splitter PBS1106 communicates with the first phase modulator PM1107 via an optical signal;

[0052] The first phase modulator PM1107 is connected to the first Faraday rotator FR1108 via an optical signal.

[0053] The intensity modulator IM 110 is used to modulate the pulsed light signal into a signal state or a decoy state pulse;

[0054] The attenuator ATT 111 attenuates the pulse light signal to a single photon level;

[0055] The 50:50 beam splitter BS113 is used to split the pulse light signal into two pulse light signals, namely a first light beam and a second light beam;

[0056] The first light beam passes through the second four-port polarization beam splitter PBS2115 to reach the selected user end Bob1118, and returns along the original path after being modulated by the user end Bob1118;

[0057] The second light beam passes through the third four-port polarization beam splitter PBS3120 to reach the selected user end Bob2123, and returns along the original path after being modulated by the user end Bob2123;

[0058] When the returned first light beam and the second light beam arrive at the 50:50 beam splitter BS113 at the same time, they pass through the CIR circulator 112 for the third time and are then emitted to the detection unit for detection.

[0059] The detection unit includes a first single-photon detector D1124 and a second single-photon detector D2125.

[0060] Specifically, the specific working process of this embodiment is as follows:

[0061] First, the laser LD 101 generates an initial pulse optical signal which enters the first CIR circulator 102. The first CIR circulator 102 transmits the pulse optical signal to the first SC device 103 and the first polarization controller PC1104. The first SC device 103 modulates the initial phase φ of the initial pulse optical signal. A ∈{0,π / 2,π,3π / 2}; after the first polarization controller PC1104 adjusts the initial pulse light signal to a 45° polarized pulse light signal, and sends it to the first polarization beam splitter PBS1106, the 45° polarized pulse light signal is divided into two parts, the horizontal polarization pulse H and the vertical polarization pulse V, with the same probability;

[0062] Among them, the horizontal polarization pulse H is transmitted through the first polarization beam splitter PBS1106; the vertical polarization pulse V is first loaded with phase △φ through the first phase modulator PM1107, and then changes to a horizontal polarization state after passing through the first Faraday rotator FR1108 and the first delay line DL 109, and then transmits through the first polarization beam splitter PBS1106 to return to the first CIR circulator 105. Therefore, the polarization direction of the combined pulse depends on the phase difference △φ between the two split pulses.

[0063] The specific transmission process of the horizontally polarized pulse H and the vertically polarized pulse V is as follows:

[0064] The vertical polarization state |V> of the vertically polarized pulse introduces an additional π / 2 phase after being reflected by the first polarization beam splitter PBS1; the horizontal polarization state |H> of the horizontally polarized pulse passes through the first Faraday rotator FR1, and then the horizontal polarization state |H> passes through the first phase modulator PM1107 without any modulation at the first phase modulator PM1107, and then is input into the first polarization beam splitter PBS1106 and reflected back to the first CIR circulator 105.

[0065] Similarly, the pulse of the vertical polarization state |V> first passes through the first phase modulator PM1107 to load the phase △φ, and then the vertical polarization state |V> is combined with the horizontal polarization state |H> at the first polarization beam splitter PBS1106. The combined pulse is transmitted to the intensity modulator IM 110.

[0066] The intensity modulator IM 110 modulates the combined pulse optical signal into a signal state or a decoy state pulse, and then transmits it to the attenuator ATT111. The attenuator ATT 111 attenuates the signal state or the decoy state pulse to a single photon level to obtain a single photon pulse.

[0067] Next, the single-photon pulse passes through the third CIR circulator 112 and reaches the 50:50 beam splitter BS113. At the 50:50 beam splitter BS113, the single-photon pulse is divided into two parts, namely, the first optical path and the second optical path. The single-photon pulses in the first optical path and the second optical path respectively pass through the second four-port polarization beam splitter PBS2 and the third four-port polarization beam splitter PBS3 and reach the corresponding selected user ends Bob1118 and Bob2123.

[0068] After the single-photon pulse is modulated by user Bob1118 or Bob2123, it returns to Alice's end. Since all pulsed optical signals pass through a round-trip path, the phase drift caused by the birefringence effect in the optical fiber can be automatically compensated. When the two separated pulsed optical signals arrive at the 50:50 beam splitter BS113 at the same time, they pass through the third CIR circulator 112 and enter the detection unit. The first single-photon detector D1124 and the second single-photon detector D2125 of the detection unit will respond to the interference results. The specific detection method and principle here adopt the existing detection method and principle and will not be described in detail.

[0069] If Alice wants to share a string of security keys with Bob1, Alice should first modulate the pulse light signal through the polarization modulation module composed of the first polarization beam splitter PBS1106, the first phase modulator FM1107, the first Faraday rotator FR1108 and the first delay line DL109 so that the polarization state of the pulse light signal becomes |D>. After passing through the second and third four-port polarization beam splitters PBS2115 and PBS3120, the pulse light signal becomes a superposition state of the path, which is expressed by the following formula:

[0070]

[0071] The single photon pulses of the first optical path first enter Bob 1, pass directly through Bob 1 without phase modulation, and then return. Then, these pulses pass through the second and third four-port polarization beam splitters PBS2115 and PBS3120 from path 1 and return to Alice. Next, the pulsed optical signal is loaded with a phase φ when passing through the third SC device 122. A (0 or π). Since the polarization state of the pulse has changed by 90°, the pulse light signal is reflected back to the 50:50 beam splitter BS 50:50 beam splitter 113 at the third four-port polarization beam splitter PBS3120. This process can be expressed by the following formula:

[0072]

[0073] Similarly, the single photon pulses of the second optical path pass through the opposite path. The single photon pulses of the second optical path do not modulate the phase when passing through the third SC device 122. Afterwards, the polarization direction changes by 90°. Similarly, these pulses pass through the first optical path to reach Bob 1. The pulsed optical signal is loaded with a phase φ at Bob 1. B (0 or π), and then return to the 50:50 beam splitter BS113. This process can be expressed by the following equation:

[0074]

[0075] Finally, the pulses from the first optical path and the second optical path interfere with each other at the 50:50 beam splitter BS113:

[0076]

[0077] If φ B1 and φ A When the phase difference is 0 or 2π, the first single-photon detector D1124 responds; if φ B1 and φ A When the phase difference is π, the second single-photon detector D2125 responds.

[0078] Similarly, if Alice wants to share a string of security keys with Bob2, she should first modulate the pulse light signal through the polarization modulation module so that the polarization state of the pulse light signal becomes |A>. Alice and Bob2 modulate the corresponding second SC device 117 to load the phase, and the process of sharing the key is similar to that of Alice and Bob 1, which can be expressed by the following formula:

[0079]

[0080] Similarly, if φ B2 and φ A When the phase difference is 0 or 2π, the first single-photon detector D1124 responds; if φ B2 and φ A When the phase difference is π, the second single-photon detector D2125 responds.

[0081] Specifically, in the aforementioned process, the expressions of the horizontally polarized H and vertically polarized V pulse optical signals at different stages are as follows:

[0082] The horizontal polarization state |H> and the vertical polarization state |V> of the two parts of the horizontal polarization H and the vertical polarization V are expressed by the Jones matrix as follows:

[0083]

[0084] The vertical polarization state |V> introduces an additional phase of π / 2 after being reflected by the first polarization beam splitter PBS1. The Jones matrix of the first Faraday rotator FR1108 is expressed as:

[0085]

[0086] The horizontal polarization state |H> after passing through the first Faraday rotator FR1 is expressed as:

[0087]

[0088] Then, the horizontal polarization state |H> passes through the first phase modulator PM1107 without any modulation at the first phase modulator PM1107, and is then input to the first polarization beam splitter PBS1106 and reflected back to the first CIR circulator 105, obtaining:

[0089]

[0090] Similarly, the pulse of vertical polarization state |V> first passes through the first phase modulator PM1107 to load the phase △φ, and becomes:

[0091]

[0092] Then, the vertical polarization state |V> after the pulse is combined at the first polarization beam splitter PBS1106 can be expressed as:

[0093]

[0094] Δφ=π

[0095] Δφ=0

[0096]

[0097] The present invention is provided with a phase encoder and multiple polarization encoders are arranged step by step to modulate the pulse light signal. The phase encoder has a high anti-interference ability to environmental noise and interference, ensures the stability and reliability of the signal, and realizes a strong anti-interference ability.

[0098] Multiple polarization encoders are used to adjust the pulsed optical signal into a polarization state to select users, so that different users can communicate independently on the same quantum channel, greatly improving the flexibility of user selection and increasing flexibility and scalability.

[0099] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs may also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the invention should also fall within the scope of protection of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the invention.

Claims

1. A dynamic user phase-coded quantum communication system, characterized in that: It includes an LD laser LD, a first CIR circulator, a first SC device, a first polarization controller PC1, a polarization modulation module, a second CIR circulator, an intensity modulator IM, an attenuator ATT, a third CIR circulator, a detection unit, a 50:50 beam splitter BS, a second polarization controller PC2, a second four-port polarization beam splitter PBS2, a second delay line DL, a second SC device, a first receiving end Bob1, a third polarization controller PC3, a third four-port polarization beam splitter PBS3, a third delay line DL, and a third SC device, wherein: The laser LD is used to generate an initial pulse light signal; The first CIR circulator transmits the initial pulsed optical signal to the first SC device and the first polarization controller PC1; The first SC device is used to modulate the initial phase φ of the initial pulse light signal A ∈{0,π / 2,π,3π / 2}; The first polarization controller PC1 is used to modulate the initial pulse light signal into a 45° polarization state; The polarization modulation module is used to perform phase loading and polarization state adjustment on the 45° polarization state pulse optical signal to change it into a horizontal polarization state; The intensity modulator IM is used to modulate the pulsed light signal into a signal state or a decoy state pulse; The attenuator ATT attenuates the pulse light signal to a single photon level; The 50:50 beam splitter BS is used to split the pulse light signal into two pulse light signals, namely a first light beam and a second light beam; The first light beam passes through the second four-port polarization beam splitter PBS2 to reach the selected user end Bob1, and returns along the original path after being modulated by the user end Bob1; The second light beam passes through the third four-port polarization beam splitter PBS3 to reach the selected user end Bob2, and returns along the original path after being modulated by the user end Bob2; When the returned first light beam and the second light beam arrive at the 50:50 beam splitter BS at the same time, they pass through the CIR circulator for the third time and are then emitted to the detection unit for detection.

2. A dynamic user phase coded quantum communication system as claimed in claim 1, characterized in that: The polarization modulation module includes a first polarization beam splitter PBS1, a first phase modulator PM1, a first Faraday rotator FR1 and a first delay line DL; An input port of the first polarization beam splitter PBS1 is connected to the first CIR circulator via an optical signal; an output port of the first polarization beam splitter PBS1 is connected to the first Faraday rotator FR1 via a first delay line DL; Another output port of the first polarization beam splitter PBS1 is connected to the first phase modulator PM1 through an optical signal; The first phase modulator PM1 is connected to the first Faraday rotator FR1 via an optical signal.

3. A dynamic user phase coded quantum communication system as claimed in claim 2, characterized in that: The detection unit includes a first single-photon detector D1 and a second single-photon detector D2.

4. A dynamic user phase coded quantum communication system as claimed in claim 3, characterized in that: The first polarization controller PC1 adjusts the initial pulse light signal to a 45° polarized pulse light signal, and then sends it to the first polarization beam splitter PBS1, where the 45° polarized pulse light signal is divided into two parts, a horizontal polarized pulse H and a vertical polarized pulse V, with the same probability; The horizontally polarized pulse is transmitted through the first polarization beam splitter PBS1; The vertically polarized pulse first passes through the first phase modulator PM1 to be loaded with the phase △φ, then passes through the first Faraday rotator FR1 and the first delay line DL to become a horizontal polarization state, and then transmits through the first polarization beam splitter PBS1 to return to the first CIR circulator R.

5. A dynamic user phase coded quantum communication system as claimed in claim 4, characterized in that: The vertical polarization state |V> of the vertical polarization pulse V introduces an additional phase of π / 2 after being reflected by the first polarization beam splitter PBS1; The horizontal polarization state |H> of the horizontally polarized pulse passes through the first Faraday rotator FR1, is input to the first polarization beam splitter PBS1, and is reflected back to the first CIR circulator.

6. A dynamic user phase coded quantum communication system as claimed in claim 5, characterized in that: The pulse of the vertical polarization state |V> is first loaded with a phase △φ by the first phase modulator PM1, and then the vertical polarization state |V> is combined with the horizontal polarization state |H> at the first polarization beam splitter PBS1, and the combined pulse is emitted to the intensity modulator IM.

7. A dynamic user phase coded quantum communication system as claimed in claim 6, characterized in that: The intensity modulator IM modulates the combined pulse light signal into a signal state or a decoy state pulse, and then transmits it to the attenuator ATT. The attenuator ATT attenuates the signal state or the decoy state pulse to a single photon level to obtain a single photon pulse.

8. A dynamic user phase coded quantum communication system as claimed in claim 7, characterized in that: The single-photon pulse passes through the third CIR circulator and reaches the 50:50 beam splitter BS113. At the 50:50 beam splitter BS113, the single-photon pulse is divided into two optical paths, the first optical path and the second optical path. The single-photon pulses in the first optical path and the second optical path respectively pass through the second four-port polarization beam splitter PBS2 and the third four-port polarization beam splitter PBS3 and reach the corresponding selected user ends Bob1 and Bob2.

9. A dynamic user phase coded quantum communication system as claimed in claim 8, characterized in that: The horizontal polarization state |H> and the vertical polarization state |V> are represented by Jones matrix:

10. A dynamic user phase coded quantum communication system as claimed in claim 9, characterized in that: The vertical polarization state |V> introduces an additional phase of π / 2 after being reflected by the first polarization beam splitter PBS1. The Jones matrix of the first Faraday rotator FR1 is expressed as: The horizontal polarization state |H> after passing through the first Faraday rotator FR1 is expressed as:

Images