A point-to-point optical fiber key distribution system based on scrambling

Abstract

The present invention discloses a point-to-point optical fiber key distribution system based on polarization scrambling, comprising a first light source, a first wavelength division device, a first polarization scrambling device, a first polarizer, a first photodetector, a second light source, a second wavelength division device, a second polarization scrambling device, a second polarizer, a second photodetector and an optical fiber link; the first light source, the first polarizer and the first polarization scrambling device are respectively connected to the first wavelength division device; the first photodetector is connected to the first polarizer; the second light source, the second polarizer and the second polarization scrambling device are respectively connected to the second wavelength division device; the second photodetector is connected to the second polarizer; the optical fiber link is connected between the first polarization scrambling device and the second polarization scrambling device. The present invention actively applies polarization state perturbation to the optical signals passing through the two parties of point-to-point communication in the forward and reverse directions, so that the intensity of the optical signal is highly correlated with the polarization state, the fluctuation rate and amplitude are greatly improved, and the high coding rate and low bit error rate of the key can be guaranteed.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of optical fiber key distribution, and in particular to a point-to-point optical fiber key distribution system based on scrambling. Background Art

[0002] As an important branch of confidential communication, the generation and transmission of communication keys is the key lifeline of the entire confidential communication system and the primary target of eavesdroppers. The generation of traditional keys relies on the complexity of the algorithm or the decomposition of large numbers based on number theory in order to prevent brute force cracking in a short period of time. However, the increasing maturity of quantum computers means that this type of encryption method will be eliminated in the near future.

[0003] Fiber-optic key distribution technology, as a low-cost, electromagnetic interference-resistant physical layer key generation solution, combines the functions of key generation and distribution. However, most of the fiber-optic key distribution solutions currently proposed are based on the perturbations passively imposed by the natural environment, and their key generation rate and system stability are not guaranteed. In addition, since standard communication optical fibers are usually wrapped in optical cables in practical applications, it is difficult to achieve the effect obtained in the laboratory.

[0004] In addition, bit errors caused by the delay of optical transmission are also common in key distribution systems based on optical channels. Assuming that the optical signal in direction A is randomly disturbed by the natural environment at a point P in the external optical fiber link, when the optical signal in direction B (the opposite direction in point-to-point transmission) reaches point P after a delay, the disturbance may be different from before, which means that the optical signals of the two communicating parties are disturbed differently, the reciprocity of the optical channel is broken, and bit errors occur.

[0005] Therefore, how to ensure high encoding rate and low bit error rate of keys in long-distance transmission is currently a difficulty and an urgent problem to be solved in improving the performance of fiber-optic key distribution systems. Summary of the invention

[0006] The present invention provides a point-to-point optical fiber key distribution system based on scrambling to solve the deficiencies of the prior art.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A point-to-point optical fiber key distribution system based on polarization scrambling comprises a first light source, a first wavelength division device, a first polarization scrambling device, a first polarizer, a first photodetector, a second light source, a second wavelength division device, a second polarization scrambling device, a second polarizer, a second photodetector and an optical fiber link; wherein:

[0009] The first light source, the first polarizer, and the first polarization scrambling device are respectively connected to the first wavelength division device; the first photodetector is connected to the first polarizer;

[0010] The second light source, the second polarizer, and the second polarization scrambling device are respectively connected to the second wavelength division device; the second photodetector is connected to the second polarizer;

[0011] The optical fiber link is connected between the first deflection scrambling device and the second deflection scrambling device;

[0012] The first light source and the second light source are both used to emit light signals;

[0013] The first wavelength division device is used to receive the optical signal from the first light source and transmit it to the first polarization scrambling device; and is used to receive the optical signal from the first polarization scrambling device and transmit it to the first polarizer;

[0014] The second wavelength division device is used to receive the optical signal from the second light source and transmit it to the second polarization scrambling device; and is used to receive the optical signal from the second polarization scrambling device and transmit it to the second polarizer;

[0015] The first polarization scrambling device and the second polarization scrambling device are both used to actively apply polarization state disturbance to the passing optical signal;

[0016] The optical fiber link is used to transmit optical signals;

[0017] The first polarizer and the second polarizer are both used to polarize the received optical signal;

[0018] The first photodetector and the second photodetector are both used to convert the polarized light signal into an electrical signal to obtain a corresponding key.

[0019] Furthermore, in the polarization scrambling-based point-to-point optical fiber key distribution system, the polarization angles of the first polarizer and the second polarizer are consistent.

[0020] Furthermore, in the scrambling-based point-to-point optical fiber key distribution system, the optical fiber link is a standard single-mode optical fiber.

[0021] Furthermore, in the scrambling-based point-to-point optical fiber key distribution system, both the first wavelength division device and the second wavelength division device are circulators.

[0022] Furthermore, in the scrambling-based point-to-point optical fiber key distribution system, the first light source and the second light source are both narrow-band light sources of 1548 nm.

[0023] Furthermore, in the scrambling-based point-to-point optical fiber key distribution system, the scrambling frequencies of the first scrambling device and the second scrambling device are both 1000 Hz.

[0024] Further, in the point-to-point optical fiber key distribution system based on polarization scrambling, the first polarization scrambling device is a polarization controller of model N7784B;

[0025] The second polarization scrambling device is a polarization scrambler with model number PSM002.

[0026] An embodiment of the present invention provides a point-to-point optical fiber key distribution system based on polarization scrambling. By actively applying polarization state perturbations to optical signals passing through the two parties of point-to-point communication in the forward and reverse directions, the intensity of the optical signal is highly correlated with the polarization state, and the fluctuation rate and amplitude are greatly improved. As a result, the optical signals received by the two communicating parties still have extremely high similarity after experiencing the same path and the same polarization scrambling, thereby ensuring a high coding rate and low bit error rate of the key and improving the performance of the optical fiber key distribution system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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 only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0028] Figure 1 It is a functional module diagram of a point-to-point optical fiber key distribution system based on scrambling provided by an embodiment of the present invention;

[0029] Figure 2 It is a schematic diagram of the comparison of original signals received by both communicating parties in a point-to-point optical fiber key distribution system based on scrambling provided by an embodiment of the present invention with an external optical fiber length of 20 kilometers;

[0030] Figure 3 It is a schematic diagram of the comparison of original signals received by both communicating parties within 2.3 milliseconds in a point-to-point optical fiber key distribution system based on scrambling provided by an embodiment of the present invention with an external optical fiber length of 40 kilometers;

[0031] Reference numerals:

[0032] A first light source 1, a first wavelength division device 2, a first polarization scrambling device 3, a first polarizer 4, a first photodetector 5, a second light source 6, a second wavelength division device 7, a second polarization scrambling device 8, a second polarizer 9, a second photodetector 10, and an optical fiber link 11. DETAILED DESCRIPTION

[0033] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions 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 embodiments described below 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.

[0034] In the description of the present invention, it is to be understood that when a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be a centrally disposed component. When a component is considered to be "disposed on" another component, it may be directly disposed on the other component or there may be a centrally disposed component.

[0035] In addition, terms such as "long", "short", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings and are only used to facilitate the description of the present invention. They do not indicate or imply that the device or component referred to must have this specific direction or operate with a specific direction structure, and should not be understood as a limitation of the present invention.

[0036] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0037] Embodiment 1

[0038] In view of the defects of the existing fiber optic key distribution technology, the applicant has actively conducted research and innovation based on many years of rich practical experience and professional knowledge in the research and design of such projects, and in conjunction with the application of academic theory, in the hope of creating a technology that can solve the defects in the existing technology and make the fiber optic key distribution technology more practical. After continuous research, design, repeated trials and improvements, the present invention with real practical value was finally created.

[0039] Please refer to Figure 1 The embodiment of the present invention provides a point-to-point optical fiber key distribution system based on polarization scrambling, comprising a first light source 1, a first wavelength division device 2, a first polarization scrambling device 3, a first polarizer 4, a first photodetector 5, a second light source 6, a second wavelength division device 7, a second polarization scrambling device 8, a second polarizer 9, a second photodetector 10 and an optical fiber link 11; wherein,

[0040] The first light source 1, the first polarizer 4, and the first polarization scrambling device 3 are respectively connected to the first wavelength division device 2; the first photodetector 5 is connected to the first polarizer 4;

[0041] The second light source 6, the second polarizer 9, and the second polarization scrambling device 8 are respectively connected to the second wavelength division device 7; the second photodetector 10 is connected to the second polarizer 9;

[0042] The optical fiber link 11 is connected between the first deflection scrambling device 3 and the second deflection scrambling device 8;

[0043] The first light source 1 and the second light source 6 are both used to emit light signals;

[0044] The first wavelength division device 2 is used to receive the optical signal from the first light source 1 and transmit it to the first polarization scrambling device 3; and is used to receive the optical signal from the first polarization scrambling device 3 and transmit it to the first polarizer 4;

[0045] The second wavelength division device 7 is used to receive the optical signal from the second light source 6 and transmit it to the second polarization scrambling device 8; and is used to receive the optical signal from the second polarization scrambling device 8 and transmit it to the second polarizer 9;

[0046] The first polarization scrambling device 3 and the second polarization scrambling device 8 are both used to actively apply polarization state disturbance to the passing optical signal;

[0047] The optical fiber link 11 is used to transmit optical signals;

[0048] The first polarizer 4 and the second polarizer 9 are both used to polarize the received optical signal;

[0049] The first photodetector 5 and the second photodetector 10 are both used to convert the polarized optical signal into an electrical signal to obtain a corresponding key.

[0050] Preferably, the polarization angles of the first polarizer 4 and the second polarizer 9 are consistent; the optical fiber link 11 is a standard single-mode optical fiber; the first wavelength division device 2 and the second wavelength division device 7 are both circulators, and of course they can also be other wavelength division devices that can separate incident light and outgoing light; the first light source 1 and the second light source 6 are both narrow-band light sources of 1548nm; the scrambling frequencies of the first polarization scrambling device 3 and the second polarization scrambling device 8 are both 1000Hz, specifically, the first polarization scrambling device 3 is a polarization controller with a model number of N7784B; the second polarization scrambling device 8 is a polarization scrambler with a model number of PSM002.

[0051] It should be noted that the optical path structure of the optical fiber key distribution system is a single-core bidirectional type, and at least one scrambling device is provided at each end of the optical path. When the optical signal emitted by both parties of the point-to-point communication passes through the scrambling device, its polarization state will be subject to random changes. The polarization state of the outgoing light obtained through this process will be closely related to the polarization state of the incident light and the effect of the scrambler, and then enters the photodetector to be received after the two communicating parties use the same polarizer. In this embodiment, the optical signal in the forward and reverse directions will be scrambled twice, which occurs before entering the external optical fiber link 11 and after exiting from the external optical fiber link 11. Due to the reciprocity of the optical channel, the signals received by the two communicating parties still have extremely high similarity after experiencing the same path and the same scrambling, and the two communicating parties can realize real-time symmetrical key exchange by digitizing the received analog signal.

[0052] The scrambling device outputs a stable polarization state within the scrambling cycle, and changes the output polarization state in the next cycle, and the output polarization state is related to the polarization state of the optical signal input to the scrambler. The scrambling device used can output a cryptographically secure random scrambling signal, and supports the input of a user-defined scrambling sequence to achieve user-controllable key sequence generation. The polarizer is used to polarize the optical signal to be received, and the polarization angles of the polarizers used by the communicating parties should be consistent to ensure that the received optical signals have the same polarization state. The received original signal is used to generate a symmetric key.

[0053] Since the fiber optic key distribution scheme proposed in the present invention has a stable and high-speed key generation rate, and since the signal strength is highly correlated with the polarization state, an eavesdropper cannot directly obtain the key through signal processing based on the signal stolen from the external optical fiber link 11 without the relevant information of the initial polarization state angle and the scrambling device. In addition, the key finally generated has been scrambled twice and polarized before being received. In the absence of relevant polarization information, the thief cannot perform polarization analysis on the stolen signal to restore the key.

[0054] Specifically, after two scramblings, the fluctuation speed and amplitude of the optical signal received by both ends of the communication are greatly improved. The specific quantification can be expressed by the decorrelation time of the signal:

[0055]

[0056] Among them, "*" is the autocorrelation function of the signal, "argmin" is the minimum value of the independent variable of the autocorrelation function, and the meaning of the decorrelation time can be briefly described as the shortest interval time between two adjacent sampling points in the received signal. In order to ensure the randomness of the key sequence, the signal needs to be resampled according to the decorrelation time of the signal before digitizing it, and the resampling rate is 1 / T d, that is, the shorter the decorrelation time, the higher the resampling rate. After the signal is resampled, the digital key sequence can be obtained using the dual threshold quantization protocol. The dual threshold quantization protocol uses two thresholds, high and low, to digitize the analog signal. If the resampled signal level is greater than the high threshold, the binary key bit is judged to be 1; if the resampled signal level is lower than the low threshold, the binary key bit is judged to be 0. If the signal level is between the two thresholds, the key bit will be abandoned. These two thresholds can be represented by q+ and q-:

[0057]

[0058] Among them, q+ and q- represent the upper threshold and the lower threshold respectively, and ε is a scalar that determines the final value of the threshold. Different ε values ​​can be used to obtain different key coding rates and bit error rates.

[0059] When the optical fiber length reaches a certain extent, the above optical transmission delay will become the main factor causing the bit error rate. The delay τ can be calculated by the following formula:

[0060]

[0061] Where L is the length of the external optical fiber link 11, n is the refractive index of the optical fiber core, c is the speed of light in a vacuum, and the delay is about 0.1 milliseconds at a fiber length of 20 kilometers. In this solution, the impact of the delay is manifested as a predictable signal mismatch that occurs at fixed intervals, such as Figure 3 As shown in the figure, T is the scrambling period of the scrambling device, which is the reciprocal of the scrambling frequency, and τ is the optical transmission delay related to the line length. The two signal mismatch times in the figure are consistent with the calculated optical transmission delay, indicating that optical transmission delay is the main source of bit errors over long distances. Since the polarization perturbation position is fixed in this scheme, the time interval of bit errors can be predicted by calculation, and filtering the mismatched signal through further algorithms can effectively suppress the increase in bit error rate.

[0062] The following is an example using a specific example.

[0063] go through Figure 2 This is the original signal received by both ends of the communication within 0.1 seconds. It can be seen that the two signals are highly similar, and the calculated cross-correlation peak of the two signals is about 0.9. According to the autocorrelation function, it can be calculated that the decorrelation time of the signal is about 0.6ms. The original signal is resampled according to the decorrelation time, and the resampling rate is 1666Sample / s. The key sequence obtained by converting the analog signal into digital bits through the dual threshold quantization scheme can achieve a coding rate of 1216bit / s under the condition of a bit error rate of 0.33%.

[0064] Although the terms such as light source, wavelength division device, polarization scrambling device, polarizer, photodetector, optical fiber link, etc. are used more frequently in this article, the possibility of using other terms is not excluded. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitation is contrary to the spirit of the present invention.

[0065] An embodiment of the present invention provides a point-to-point optical fiber key distribution system based on polarization scrambling. By actively applying polarization state perturbations to optical signals passing through the two parties of point-to-point communication in the forward and reverse directions, the intensity of the optical signal is highly correlated with the polarization state, and the fluctuation rate and amplitude are greatly improved. As a result, the optical signals received by the two communicating parties still have extremely high similarity after experiencing the same path and the same polarization scrambling, thereby ensuring a high coding rate and low bit error rate of the key and improving the performance of the optical fiber key distribution system.

[0066] Thus far, the description of the above-described embodiments is provided for the purpose of illustration and description. It is not intended to be exhaustive or to limit the present disclosure. The individual elements or features of a specific embodiment are generally not subject to the limitations of the specific embodiment, but when applicable, they can be interchanged and used for selected embodiments even if not specifically shown or described. In many respects, the same element or feature also can be changed. This variation is not considered to be a departure from the present disclosure, and all such modifications are intended to be included in the scope of the present disclosure.

[0067] Example embodiments are provided so that the present disclosure will be thorough and the scope will be fully conveyed to those skilled in the art. In order to thoroughly understand the embodiments of the present disclosure, numerous details are set forth, such as examples of specific parts, devices, and methods. Obviously, for those skilled in the art, it is not necessary to use specific details, the example embodiments can be implemented in many different forms, and neither should be construed as limiting the scope of the present disclosure. In certain example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0068] Here, specialized vocabulary is used only for the purpose of describing specific example embodiments, and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "a" and "the" used herein may be intended to include plural forms as well. The terms "including" and "having" are inclusive, and therefore specify the presence of the claimed features, wholes, steps, operations, elements and / or components, but do not exclude the presence or additional presence of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof. Unless the order of execution is clearly indicated, the method steps, processing and operations described herein are not interpreted as necessarily needing to be performed in the specific order discussed and shown. It should also be understood that additional or optional steps may be adopted.

[0069] When an element or layer is referred to as being "on ...", "engaged with ...", "connected to" or "coupled to" another element or layer, it may be directly on another element or layer, engaged with another element or layer, connected to or coupled to another element or layer, or there may be an intervening element or layer. In contrast, when an element or layer is referred to as being "directly on ...", "directly engaged with ...", "directly connected to" or "directly coupled to" another element or layer, there may be no intervening element or layer. Other words used to describe element relationships should be interpreted in a similar manner (e.g., "between ..." and "directly between ...", "adjacent" and "directly adjacent", etc.). The term "and / or" used herein includes any and all combinations of one or more of the associated listed items. Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts are not limited by these terms. These terms may only be used to distinguish one element, component, region or part from another element, component, region or part. Unless clearly indicated by the context, the use of terms such as "first", "second" and other numerical terms herein does not imply sequence or order. Therefore, the first element, component, region, layer or part discussed below can adopt the terminology of the second element, component, region, layer or part without departing from the teaching of the exemplary embodiment.

[0070] Spatially relative terms, such as "inside", "outside", "below", "below...", "lower", "above", "upper", etc., may be used herein for ease of description to describe the relationship between one element or feature and one or more other elements or features as shown in the figure. Spatially relative terms may be meant to include different orientations of the device in addition to the orientation depicted in the figure. For example, if the device in the figure is flipped, the elements described as "below other elements or features" or "below elements or features" will be oriented as "above other elements or features". Therefore, the example term "below..." may include both upward and downward orientations. The device can be oriented in other ways (rotated 90 degrees or other orientations) and interpreted with the spatially relative descriptions herein.

Claims

1. A point-to-point optical fiber key distribution system based on scrambling, characterized in that: It includes a first light source, a first wavelength division device, a first polarization scrambling device, a first polarizer, a first photodetector, a second light source, a second wavelength division device, a second polarization scrambling device, a second polarizer, a second photodetector and an optical fiber link; wherein, The first light source, the first polarizer, and the first polarization scrambling device are respectively connected to the first wavelength division device; the first photodetector is connected to the first polarizer; The second light source, the second polarizer, and the second polarization scrambling device are respectively connected to the second wavelength division device; the second photodetector is connected to the second polarizer; The optical fiber link is connected between the first deflection scrambling device and the second deflection scrambling device; The first light source and the second light source are both used to emit light signals; The first wavelength division device is used to receive the optical signal from the first light source and transmit it to the first polarization scrambling device; and is used to receive the optical signal from the first polarization scrambling device and transmit it to the first polarizer; The second wavelength division device is used to receive the optical signal from the second light source and transmit it to the second polarization scrambling device; and is used to receive the optical signal from the second polarization scrambling device and transmit it to the second polarizer; The first polarization scrambling device and the second polarization scrambling device are both used to actively apply polarization state disturbance to the passing optical signal; The optical fiber link is used to transmit optical signals; The first polarizer and the second polarizer are both used to polarize the received optical signal; The first photodetector and the second photodetector are both used to convert the polarized light signal into an electrical signal to obtain a corresponding key.

2. The point-to-point optical fiber key distribution system based on scrambling according to claim 1 is characterized in that: The polarization angles of the first polarizer and the second polarizer are consistent.

3. The point-to-point optical fiber key distribution system based on scrambling according to claim 1, characterized in that: The optical fiber link is a standard single-mode optical fiber.

4. The point-to-point optical fiber key distribution system based on scrambling according to claim 1, characterized in that: The first wavelength division device and the second wavelength division device are both circulators.

5. The point-to-point optical fiber key distribution system based on scrambling according to claim 1, characterized in that: The first light source and the second light source are both narrow-band light sources of 1548 nm.

6. The point-to-point optical fiber key distribution system based on scrambling according to claim 1, characterized in that: The scrambling frequencies of the first scrambling device and the second scrambling device are both 1000 Hz.

7. The point-to-point optical fiber key distribution system based on scrambling according to claim 6, characterized in that: The first polarization scrambling device is a polarization controller of model N7784B; The second polarization scrambling device is a polarization scrambler of model PSM002.

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