Quantum communication equipment based on phase coding and QKD system

Abstract

The utility model discloses quantum communication equipment based on phase coding and a QKD system, and relates to the technical field of quantum communication, the quantum communication equipment based on phase coding comprises a laser, a decoy state modulation module and an optical fiber interferometer, and the output end of the laser is optically connected with the input end of the decoy state modulation module; the output end of the decoy state modulation module is optically connected with the input end of the optical fiber interferometer; the optical fiber interferometer comprises an unequal-arm optical fiber interferometer, the unequal-arm optical fiber interferometer comprises a polarization-maintaining beam splitter, a first polarization-maintaining polarization beam splitter, a phase modulator and a second polarization-maintaining polarization beam splitter, and the phase modulator is in bidirectional optical connection with the first polarization-maintaining polarization beam splitter and the second polarization-maintaining polarization beam splitter. The first polarization-maintaining polarization beam splitter and the second polarization-maintaining polarization beam splitter are in bidirectional optical connection, so that deviation caused by a birefringence effect when pulse light in different polarization states is subjected to phase modulation can be eliminated, and the bit error rate of a QKD system is reduced.

Description

Technical Field

[0001] The present invention relates to the field of quantum communication technology, and in particular to a quantum communication device and a QKD system based on phase coding. Background Art

[0002] The current quantum key distribution (QKD) system is mainly based on polarization coding and phase coding. During the phase coding process, a pulse of light will produce three pulses of light: front, middle, and back after interference. Among these three pulses of light, only the middle pulse of light is generated by interference, and the front and back pulses of light do not interfere. The front and back pulses of light are discarded during detection, causing the QKD system to lose at least half of the number of photons, resulting in low photon utilization and low coding rate. In addition, the current QKD system transmits pulses of H and V polarization states simultaneously in the fiber interferometer. When the pulse light is modulated by a phase modulator, there is a deviation in the phase of the two polarization states due to the birefringence effect of the optical fiber. There are errors in both phase encoding and phase decoding, resulting in a high bit error rate.

[0003] In order to improve the code rate of the QKD system, the main method currently used is to increase the frequency of the QKD system. Although this method can achieve the effect of improving the code rate, while increasing the repetition frequency, it increases the difficulty of designing the phase-modulation drive signal and the detector drive signal, and has more stringent requirements on components and higher costs. At the same time, the jitter, rising edge time, and falling edge time of the phase-modulation drive signal and the detector drive signal will increase the bit error rate of the QKD system. Summary of the invention

[0004] The embodiments of the present invention provide a quantum communication device and a QKD system based on phase coding to at least partially solve the defects of the prior art.

[0005] In order to achieve the above objectives, the phase-coded quantum communication device and QKD system provided in the embodiments of the present invention adopt the following technical solutions:

[0006] In a first aspect, a phase-encoded quantum communication device provided by an embodiment of the present invention includes:

[0007] The output end of the laser is optically connected to the input end of the decoy state modulation module.

[0008] The output end of the decoy state modulation module is optically connected to the input end of the fiber interferometer.

[0009] The fiber interferometer comprises an unequal-arm fiber interferometer, which comprises a polarization-maintaining beam splitter, a first polarization-maintaining polarization beam splitter, a phase modulator and a second polarization-maintaining polarization beam splitter, wherein the input end of the polarization-maintaining beam splitter is optically connected to the output end of the entrapped state modulation module, the phase modulator is optically connected to the first polarization-maintaining polarization beam splitter and the second polarization-maintaining polarization beam splitter in a bidirectional manner, respectively, and the first polarization-maintaining polarization beam splitter and the second polarization-maintaining polarization beam splitter are optically connected in a bidirectional manner.

[0010] In some examples, the sum of the fiber length L2 from the polarization-maintaining beam splitter to the first polarization-maintaining polarization beam splitter and the fiber length L3 from the first polarization-maintaining polarization beam splitter to the phase modulator is equal to the sum of the fiber length L1 from the polarization-maintaining beam splitter to the second polarization-maintaining polarization beam splitter and the fiber length L4 from the second polarization-maintaining polarization beam splitter to the phase modulator.

[0011] In some examples, the fiber optic interferometer is a Sagnac interferometer.

[0012] In some examples, the phase-encoded quantum communication device disclosed in the embodiments of the present invention further includes:

[0013] An optical attenuator is optically connected to the polarization-maintaining beam splitter.

[0014] In some examples, the unequal-arm fiber interferometer is an MZ interferometer.

[0015] In a second aspect, a phase-coding-based QKD system provided by an embodiment of the present invention includes the phase-coding-based quantum communication device disclosed in the first aspect.

[0016] Compared with the prior art, the phase-coded quantum communication device and QKD system provided by the embodiments of the present invention have the following beneficial effects:

[0017] Quantum communication equipment only needs to modulate pulse light of one polarization state through a phase modulator, eliminating the deviation caused by the birefringence effect when phase modulating pulse light of different polarization states, and reducing the bit error rate of the QKD system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A schematic diagram of the structure of a phase-encoded quantum communication device provided in an embodiment of the present invention.

[0020] Figure 2 A phase-coding-based QKD system is provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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.

[0022] Example 1 Figure 1 As shown, the phase-encoded quantum communication device provided by the embodiment of the present invention includes a laser, a entrapped state modulation module and a fiber interferometer. Among them:

[0023] The output end of the laser is optically connected to the input end of the decoy state modulation module.

[0024] In particular, a laser is used to prepare and output a first pulse light.

[0025] Specifically, the laser is a gain-switched semiconductor laser, which can generate pulsed light with a set frequency based on an external driving signal.

[0026] The output end of the decoy state modulation module is optically connected to the input end of the fiber interferometer.

[0027] The fiber interferometer includes an unequal-arm fiber interferometer, which includes a polarization-maintaining beam splitter, a first polarization-maintaining polarization beam splitter, a phase modulator and a second polarization-maintaining polarization beam splitter, wherein the input end of the polarization-maintaining beam splitter is optically connected to the output end of the entrapped state modulation module, the phase modulator is optically connected to the first polarization-maintaining polarization beam splitter and the second polarization-maintaining polarization beam splitter in a bidirectional manner, respectively, and the first polarization-maintaining polarization beam splitter and the second polarization-maintaining polarization beam splitter are optically connected in a bidirectional manner.

[0028] The decoy state modulation module is used to generate and output a second pulse light having a set ratio of a signal state and a decoy state based on the first pulse light.

[0029] Specifically, the decoy state modulation module generates a second pulse light with a set ratio of signal state and decoy state by controlling the light intensity of the first pulse light. The decoy state pulse light in the second pulse light is used for decoy state encoding to avoid the situation where the QKD system generates a photon number splitting attack.

[0030] The optical fiber interferometer is used to generate and output a third pulse light of an orthogonal polarization state with a fixed phase difference and a fixed delay difference based on the second pulse light.

[0031] Specifically, the third pulse light includes pulse light in a horizontal polarization state (H polarization state) and pulse light in a vertical polarization state (V polarization state).

[0032] In some examples, the fiber optic interferometer is a Sagnac interferometer.

[0033] Specifically, the phase modulator is on the long arm of the unequal-arm fiber interferometer, and the polarization-maintaining polarization beam splitter is used to split the linearly polarized pulse light into pulse light of H polarization state and pulse light of V polarization state, and maintain the polarization state of the linearly polarized pulse light after splitting unchanged; the polarization-maintaining beam splitter is used to split the pulse light into two beams according to energy.

[0034] The polarization-maintaining beam splitter is used to split the second pulse light into a fourth pulse light and a fifth pulse light according to energy, wherein the fourth pulse light is input into the first polarization-maintaining polarization beam splitter, and the fifth pulse light is input into the second polarization-maintaining polarization beam splitter.

[0035] The first polarization-maintaining polarization beam splitter is used to split the fourth pulse light into a pulse light in a first H polarization state and a pulse light in a first V polarization state, input the pulse light in the first H polarization state into the phase modulator, and input the pulse light in the first V polarization state into the second polarization-maintaining polarization beam splitter.

[0036] The second polarization-maintaining polarization beam splitter is used to split the fifth pulse light into a pulse light in a second H polarization state and a pulse light in a second V polarization state, input the pulse light in the second H polarization state into the phase modulator, and input the pulse light in the second V polarization state into the first polarization-maintaining polarization beam splitter, wherein the pulse light in the first H polarization state and the pulse light in the second H polarization state pass through the long arm of the unequal-arm fiber interferometer, and the pulse light in the first V polarization state and the pulse light in the second V polarization state pass through the short arm of the unequal-arm fiber interferometer.

[0037] The phase modulator is used to simultaneously modulate the phases of the first H-polarization state pulse light and the second H-polarization state pulse light, and respectively generate and output a sixth pulse light with the fixed phase difference and a seventh pulse light with the fixed phase difference, wherein the sixth pulse light is input into the second polarization-maintaining polarization beam splitter, and the seventh pulse light is input into the first polarization-maintaining polarization beam splitter, and both the sixth pulse light and the seventh pulse light are pulse lights in the H-polarization state.

[0038] Specifically, since the pulse light of the first H polarization state and the pulse light of the second H polarization state reach the phase modulator at the same time, the pulse light of the first H polarization state and the pulse light of the second H polarization state are phase modulated at the same time. That is, the split second pulse light only needs to pass through the phase modulator to modulate the pulse light of one polarization state, eliminating the deviation caused by the birefringence effect when phase modulating the pulse light of different polarization states, and reducing the bit error rate of the QKD system.

[0039] Specifically, the fixed phase difference is 0 or π / 2 or π or 3π / 2. When the fixed phase difference is 0 or π, the phase encodings of two consecutive pulses of the corresponding pulse light are Z0 or Z1 respectively; when the fixed phase difference is π / 2 or 3π / 2, the phase encodings of two consecutive pulses of the corresponding pulse light are X0 or X1.

[0040] The first polarization-maintaining polarization beam splitter is also used to combine the second V polarization state pulse light with the seventh pulse light to generate and output an eighth pulse light, wherein the eighth pulse light is two pulse lights of V and H polarization states with a fixed delay difference and a fixed phase difference.

[0041] The second polarization-maintaining polarization beam splitter is further used to combine the pulse light of the first V polarization state with the sixth pulse light to generate and output a ninth pulse light. The eighth pulse light and the ninth pulse light have a fixed delay difference, the size of which depends on the difference between the long arm and the short arm of the unequal-arm fiber interferometer, and the eighth pulse light is two pulse lights of V and H polarization states with a fixed delay difference and a fixed phase difference.

[0042] The polarization-maintaining beam splitter is further used to combine the eighth pulse light with the ninth pulse light to generate and output the third pulse light.

[0043] In particular, in order to ensure the accuracy of phase encoding, the sum of the fiber length L2 from the polarization-maintaining beam splitter to the first polarization-maintaining polarization beam splitter and the fiber length L3 from the first polarization-maintaining polarization beam splitter to the phase modulator is equal to the sum of the fiber length L1 from the polarization-maintaining beam splitter to the second polarization-maintaining polarization beam splitter and the fiber length L4 from the second polarization-maintaining polarization beam splitter to the phase modulator, ensuring that the first H polarization state and the second H polarization state are phase modulated at the same time, that is, L2+L3=L1+L4.

[0044] In some examples, the unequal-arm fiber interferometer is an MZ interferometer.

[0045] Specifically, since the unequal-arm fiber interferometer is an MZ interferometer, the pulse light is transmitted unidirectionally in the unequal-arm fiber interferometer, which doubles the bandwidth of the QKD system compared to the round-trip FM interferometer. In addition, the phase modulator in the unequal-arm fiber interferometer only modulates one polarization of light, eliminating the modulation deviation caused by the birefringence effect of different polarizations, and reducing the bit error rate.

[0046] In some examples, the optical attenuator is optically connected to the polarization-maintaining beam splitter to attenuate the energy of the third pulse light to a single-photon level, generate and output a tenth pulse light, wherein the tenth pulse light is input into a receiving end of a phase-encoded QKD system through a quantum channel.

[0047] Specifically, the optical attenuator is an adjustable optical attenuator, which is used to attenuate the energy of the third pulse light to a single photon level and transmit the tenth pulse light to the receiving end through the channel to facilitate detection by the receiving end.

[0048] Example 2 Figure 2 As shown, the phase-coding-based QKD system provided by an embodiment of the present invention includes the phase-coding-based quantum communication device disclosed in the first aspect.

[0049] The basic principles disclosed in the present invention are described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, effects, etc. mentioned in the present invention are only examples and not limitations, and it cannot be considered that these advantages, strengths, effects, etc. are required by each embodiment disclosed in the present invention. In addition, the specific details disclosed above are only for the purpose of illustration and ease of understanding, and are not limiting. The above details do not limit the present invention to being implemented by adopting the above specific details.

[0050] Each embodiment in this specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system embodiment, since it basically corresponds to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0051] The block diagrams of the devices, apparatuses, equipment, and systems involved in the disclosure of the present invention are only illustrative examples and are not intended to require or imply that they must be connected, arranged, and configured in the manner shown in the block diagrams. As will be appreciated by those skilled in the art, these devices, apparatuses, equipment, and systems can be connected, arranged, and configured in any manner. Words such as "including", "comprising", "having", etc. are open words, referring to "including but not limited to", and can be used interchangeably with them. The words "or" and "and" used here refer to the words "and / or" and can be used interchangeably with them, unless the context clearly indicates otherwise. The word "such as" used here refers to the phrase "such as but not limited to", and can be used interchangeably with it.

[0052] The method and apparatus disclosed in the present invention may be implemented in many ways. For example, the method and apparatus disclosed in the present invention may be implemented by software, hardware, firmware, or any combination of software, hardware, and firmware. The above sequence of steps for the method is for illustration only, and the steps of the method disclosed in the present invention are not limited to the sequence specifically described above, unless otherwise specifically stated. In addition, in some embodiments, the present invention may also be implemented as a program recorded in a recording medium, which includes machine-readable instructions for implementing the method disclosed in the present invention. Therefore, the present invention also covers a recording medium storing a program for executing the method disclosed in the present invention.

[0053] It should also be noted that in the apparatus, equipment and method disclosed in the present invention, each component or each step can be decomposed and / or recombined. These decompositions and / or recombinations should be regarded as equivalent schemes disclosed in the present invention. The above description of the disclosed aspects is provided to enable any technician in the field to make or use the present invention. Various modifications to these aspects are very obvious to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of the present invention. Therefore, the present invention is not intended to be limited to the aspects shown here, but to the widest range consistent with the principles and novel features disclosed herein.

[0054] The above description has been given for the purpose of illustration and description. In addition, this description is not intended to limit the embodiments disclosed in the present invention to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, changes, additions and sub-combinations thereof.

[0055] It is understandable that the related features in the above methods and devices can be referenced to each other. In addition, the "first", "second" and the like in the above embodiments are used to distinguish the embodiments, but do not represent the advantages and disadvantages of the embodiments.

[0056] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included within the scope of the claims of the present application.

[0057] It should be noted that the above embodiments do not limit the present invention in any form, and any technical solutions obtained by equivalent replacement or equivalent transformation shall fall within the protection scope of the present invention.

Claims

1. A quantum communication device based on phase encoding, It is characterized in that include: A laser, an output end of which is optically connected to an input end of a decoy state modulation module; The output end of the decoy state modulation module is optically connected to the input end of the fiber interferometer; The fiber interferometer comprises an unequal-arm fiber interferometer, which comprises a polarization-maintaining beam splitter, a first polarization-maintaining polarization beam splitter, a phase modulator and a second polarization-maintaining polarization beam splitter, wherein the input end of the polarization-maintaining beam splitter is optically connected to the output end of the entrapped state modulation module, the phase modulator is optically connected to the first polarization-maintaining polarization beam splitter and the second polarization-maintaining polarization beam splitter in a bidirectional manner, respectively, and the first polarization-maintaining polarization beam splitter and the second polarization-maintaining polarization beam splitter are optically connected in a bidirectional manner.

2. The phase-coded quantum communication device according to claim 1, Features: The sum of the fiber length L2 from the polarization-maintaining beam splitter to the first polarization-maintaining polarization beam splitter and the fiber length L3 from the first polarization-maintaining polarization beam splitter to the phase modulator is equal to the sum of the fiber length L1 from the polarization-maintaining beam splitter to the second polarization-maintaining polarization beam splitter and the fiber length L4 from the second polarization-maintaining polarization beam splitter to the phase modulator.

3. The phase-coded quantum communication device according to claim 1, Features: The optical fiber interferometer is a Sagnac interferometer.

4. The phase-encoded quantum communication device according to claim 1, It is characterized in that Also includes: An optical attenuator is optically connected to the polarization-maintaining beam splitter.

5. The phase-encoded quantum communication device according to claim 1, It is characterized in that The unequal-arm optical fiber interferometer is an MZ interferometer.

6. A phase-encoded QKD system, It is characterized in that A phase-coding-based quantum communication device comprising any one of claims 1-5.

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