CN111726229A - An adaptive multi-band underwater wireless quantum key distribution system and method - Google Patents

Abstract

The invention discloses an adaptive multi-band underwater wireless quantum key distribution system and method, comprising a transmitter and a receiver; on the basis of the BB84 communication protocol, the transmitter and receiver interact in real time with both ends, and According to the change of the quantum bit error rate (QBER) caused by the real-time change of the channel, the quantum optical signal and the classical optical signal of different wavelengths are generated through the adjustable optical module for underwater wireless quantum key distribution and underwater wireless classical optical communication; Based on the real-time changes of the water channels of different water bodies or the water channel of the same water body, the wavelength of the signal light is automatically adjusted to adapt to the changes of the water channel in real time, reduce the bit error rate, and finally realize the maximum key of the underwater wireless quantum key distribution system under the current channel. generation rate.

Description

An adaptive multi-band underwater wireless quantum key distribution system and method

technical field

The invention relates to an underwater wireless quantum communication method, belonging to the technical field of quantum key distribution, in particular to an adaptive multi-band underwater wireless quantum key distribution system and method.

Background technique

Driven by the communication needs of underwater sensor networks, submarines and various underwater vehicles, underwater wireless optical communication has developed rapidly in recent years, and underwater wireless quantum key distribution (Quantum Key Distribution-QKD) can be used for It provides absolutely secure means of confidentiality.

Common water bodies are mainly divided into freshwater and seawater. The main components of fresh water are pure water and dissolved substances such as carbonate, sulfate and calcium, while seawater is mainly composed of pure water and dissolved substances such as chloride.

According to the absorption coefficient of freshwater and seawater light, we can find that the optimal wavelengths of freshwater and seawater are both between 400-570nm. For light below 300nm and above 600nm, freshwater and seawater have strong absorption.

Because different concentrations of mixed organics are dissolved in the water body, these mixed organics absorb less red light, but as the wavelength decreases, their absorption becomes more and more obvious. When the concentration of mixed organic matter increases to a certain extent, it will cause the water body to appear yellowish brown, so these organic dissolved substances are also called yellow substances. Yellow substances mainly come from the decay of land or underwater plants, so the concentration of yellow substances in nearshore and submarine waters is the highest. In the middle of oceans, lakes and rivers, the content of yellow substances is greatly reduced, so the attenuation effect brought Also smaller. Generally speaking, yellow substances mainly absorb light in the blue band.

The composition of water bodies is not static. For example, precipitation and surface runoff will change the density, salinity and turbidity of seawater; during the period when algae, aquatic plants and other water plants are proliferating, underwater undercurrents and marine geological activities will bring sediment and aquatic plants on the seabed; temperature The changes cause the rapid growth and decay of plankton in the water body, which will change the composition of the water body and make the water channel change.

At present, there are two urgent problems in underwater wireless quantum key distribution and underwater wireless optical communication, that is, the attenuation caused by the absorption of light by the water body itself and the change of the channel attenuation coefficient caused by the real-time change of the water channel. Under the existing technology, we cannot change the inherent environment of the water channel, so we can only adjust the underwater communication device to adapt to different water channels to reduce the QBER (Quantum Bit Error Ratio) bit error rate. As mentioned above, in the actual communication process, the water channel changes dynamically. Therefore, a system that can automatically adjust in real time according to the dynamic changes of the water channel under water, select the optimal wavelength for key distribution and communication, and improve the transmission efficiency is particularly important.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an adaptive multi-band underwater wireless quantum key distribution system and method. The present invention can automatically adjust the real-time change and attenuation of the channel before and during distribution of the underwater wireless quantum key. The wavelength of quantum signal and classical signal light achieves the lowest quantum bit error rate (QBER) in the current channel environment, and solves the technical problem of low key transmission efficiency and communication efficiency in the prior art due to dynamic changes in water bodies.

In order to achieve the above purpose, the present invention provides an adaptive multi-band underwater wireless quantum key distribution system, the distribution system includes: a transmitter and a receiver; on the basis of the BB84 communication protocol, the transmitter and receiver Real-time interaction between terminals and two terminals, and according to the change of the quantum bit error rate (QBER) caused by the real-time change of the channel, the tunable optical module generates quantum optical signals and classical optical signals of different wavelengths for underwater wireless quantum key distribution and underwater wireless Classical Optical Communication.

Preferably, the transmitter includes a transmitter quantum communication module, a transmitter classic communication module, and a transmitter control processing module; the transmitter quantum communication module is connected to the transmitter control processing module, and the transmitter classical communication The module is connected with the transmitter control processing module.

Preferably, the receiver includes a receiver quantum communication module, a receiver classical communication module, and a receiver control processing module; the receiver quantum communication module is connected to the receiver control processing module, and the receiver classical communication The module is connected with the receiving end control processing module. That is to say, the classical communication modules of the transmitting end and the receiving end carry out two-way classical communication to complete the exchange of information.

Preferably, the calculation formula of the quantum bit error rate QBER is as follows:

In the formula, P represents the polarization ratio of the polarizing device, A is the receiving area of the detector (if there is a telescope, it is the receiving area of the telescope), Idc represents the dark count of the detector, L represents the ambient light irradiance spectral density, Δt' represents Door opening time of a single photon detector, Δt is the bit period, Ω is the solid angle of the field of view, h is Planck's constant, c is the speed of light, η is the detector efficiency, χ _c is the attenuation coefficient, r is the transmission distance, λ is the wavelength of the signal light, Δλ is the spectral width, and μ is the average number of pulsed photons emitted by the transmitter. Among the above parameters, when the system is working, except for the attenuation coefficient χ _c , which changes due to the change of the channel, the other parameters remain unchanged in the system.

When the change of the channel causes the quantum bit error rate (QBER) to change, monitor the change of the quantum bit error rate (QBER) in real time. When the quantum bit error rate (QBER) fluctuates beyond the preset threshold, re-test the quantum signal light of different wavelengths in the current water channel. The quantum bit error rate QBER, in which the wavelength corresponding to the minimum quantum bit error rate QBER, will be used as the working wavelength of the quantum signal light. The wavelength corresponding to the sub-small quantum bit error rate QBER will be used as the working wavelength of the classical signal light.

Before the system starts to work and enters the test phase, the wavelengths of quantum signals and classical signals used by the transmitter and receiver are all preset default wavelengths. During the test phase, the quantum communication module (1) of the transmitter sends 6-20 groups of Quantum signal test light of different wavelengths, through calculation, the quantum bit error rate QBER corresponding to the 6-20 groups of quantum signal test light of different wavelengths can be obtained respectively. Then, the wavelength corresponding to the minimum quantum bit error rate QBER is selected as the quantum signal light for underwater wireless quantum key distribution, and the wavelength corresponding to the sub-smallest quantum bit error rate QBER is selected as the classical signal light for underwater wireless classical communication.

The transmitting-end quantum communication module includes a laser module and an optical module, the laser module includes a first laser group, and the laser module includes four white-light lasers, and the four white-light lasers have the same model and the same parameters. The difference is that the outgoing laser light of the four lasers will pass through different optical lenses to generate four different linearly polarized lights. Then, through the first adjustable optical module, four kinds of linearly polarized quantum signal lights with required wavelengths are generated.

Preferably, the optical module includes a first fixed optical module and a first adjustable optical module, the transmitting-end classic communication module includes a second laser, an optical module and a first detector APD, the optical module The group includes a second fixed optical module and a second adjustable optical module, and the transmitter control processing module controls the first laser group, the second laser, the first adjustable optical module, and the second adjustable optical module. A set and a first detector APD, the first adjustable optical module outputs quantum signal light of a desired wavelength through rotation, and the second adjustable optical module outputs and receives classical signal light of a desired wavelength through rotation.

The first detector APD in the classic communication module of the transmitting end is used to detect the classical optical signal, that is, the classical signal light interacted between the receiving end and the transmitting end.

The second laser in the classic communication module at the transmitting end is used for classic communication, interaction and synchronization with the classic communication module at the receiving end. After the second laser emits laser light, it enters the second adjustable optical module through the second fixed optical module, and finally emits the classical signal light of the required wavelength.

Preferably, the receiver quantum communication module includes a detector group and an optical module, the detector group includes four photomultiplier tubes PMT, and the optical module includes a third fixed optical module and a third adjustable optical module Module, the classic communication module of the receiving end includes a third laser, an optical module and a second detector APD, the optical module includes a fourth fixed optical module and a fourth adjustable optical module, the receiving end The control processing module controls the detector group, the third laser, the third and fourth adjustable optical modules and the second detector APD. The receiving end control processing module controls the modulation of the third laser, and controls the third adjustable optical module to receive the quantum signal light of the required wavelength through rotation, and the fourth adjustable optical module to receive and transmit the required wavelength through rotation. Classic signal light. The receiving end control processing module is also responsible for data storage and signal processing at the receiving end, and controls the classic communication module at the receiving end to interact with the classic communication module at the transmitting end in real time.

The models and parameters of the first, second and third lasers are the same, and the wavelength ranges are all 200-1600 nm. The detector group consists of four photomultiplier tubes (PMTs) to detect quantum signal light on the order of single photons.

The function of the third laser in the classic communication module at the receiving end is to synchronize and interact with the classic communication module at the transmitting end. After the third laser emits laser light, it enters the fourth adjustable optical module through the fourth fixed optical module, and finally emits the classical signal light of the required wavelength.

The composition of the second adjustable optical module in the classic communication module at the transmitting end and the third adjustable optical module in the classic communication module at the receiving end are the same, and only narrow-band filters are installed in each optical opening, not including Attenuator. Because classical communication does not require attenuating laser light into single photons.

In the key distribution stage, the wavelength of the quantum signal light between the quantum communication module at the transmitting end and the quantum communication module at the receiving end is the wavelength corresponding to the minimum quantum bit error rate QBER, and the wavelength of the classical signal light between the classical communication module at the transmitting end and the classical communication module at the receiving end is the wavelength corresponding to the minimum quantum bit error rate QBER. is the wavelength corresponding to the sub-small quantum bit error rate QBER.

Preferably, the first adjustable optical module of the quantum communication module at the transmitting end and the second adjustable optical module of the classical communication module at the transmitting end have 6-20 optical openings, preferably 8-15, more It is preferably 8.

Narrowband filters with different wavelengths and attenuation sheets with different attenuation coefficients are installed in each opening of the first adjustable optical module, and only narrowband filters with different wavelengths are installed in each opening of the second adjustable optical module. Filter, narrow-band filter is used for wavelength selection, that is, white laser can get monochromatic laser of corresponding wavelength after passing through the narrow-band filter. The purpose of the attenuator is to attenuate the number of photons of the laser. Each quantum pulse needs to have a specified number of photons. The attenuation coefficient of the attenuator in each opening has been preset according to the light intensity of each wavelength of the laser. 0.1 photons per pulse after decay. The first adjustable optical module outputs quantum signal light of a desired wavelength through rotation, and the second adjustable optical module emits and receives classical signal light of a desired wavelength through rotation.

Preferably, the third adjustable optical module in the classical communication module at the receiving end and the fourth adjustable optical module in the quantum communication module at the receiving end have 6-20 optical openings, preferably 8-15 , more preferably 8, and each opening of the third adjustable optical module and the fourth adjustable optical module is only equipped with narrow-band filters of different wavelengths, and the third adjustable optical module passes through The rotation receives quantum signal light of a specific wavelength, and the fourth tunable optical module receives and emits classical signal light of a specific wavelength through rotation.

Only narrow-band filters are installed in each optical opening on the second, third, and fourth adjustable optical modules. The goal is to pass only the desired wavelengths, filtering out background light.

The first, second, third and fourth adjustable optical modules are a rotatable disc with a plurality of optical openings, the disc is fixed on the base and the disc is rotated by the servo motor according to the instructions of each control module . There are 6-20 optical openings on each disc, and the required optical lenses are installed in each opening.

The present invention also provides a method for distributing keys using the aforementioned adaptive multi-band underwater wireless quantum key distribution system, comprising the following steps:

SS1: The system is initialized, the transmitter and receiver are powered on, and all adjustable optical modules are rotated to the preset wavelength mode, that is, rotated to the position corresponding to the default wavelength;

SS2: In the handshake stage, the classic communication module on the transmitting end sends a handshake signal to inform the receiving end that it is ready to start receiving a test signal to test the quantum bit error rate QBER of quantum signals of different wavelengths. The handshake signal includes the system time and the tunable optical module’s rotation interval;

SS3: In the test stage, the transmitter control processing module controls the first adjustable optical module in the transmitter quantum communication module to rotate 6-20 times according to the set rotation interval, and respectively send 6-20 groups of test signals with different wavelengths. At the same time, the receiving end starts to rotate the fourth adjustable optical module in the quantum communication module of the receiving end 6-20 times synchronously according to the set rotation time interval, and receives 6-20 sets of test signals respectively;

SS4: In the wavelength selection stage, the quantum communication module at the receiving end interacts with the received 6-20 groups of test signals sent to the classical communication module at the transmitting end through the classical communication module at the receiving end, and controls the processing module through the control processing module at the transmitting end and the receiving end. Calculate, get the quantum bit error rate QBER of 6-20 groups of test signals with different wavelengths, sort these 6-20 groups of quantum bit error rate QBER from small to large, and select the smallest and second smallest groups of quantum bit error rates QBER. The corresponding wavelength is used as the working wavelength of the quantum signal light of underwater wireless quantum key distribution and the classical signal light of underwater wireless classical communication;

SS5: In the wavelength adjustment stage, the transmitter interacts with the receiver to determine the working wavelength of the quantum signal and the classical signal, and then the transmitter control processing module and the receiver control processing module synchronously rotate the transmitter quantum communication module and the transmitter classical communication respectively. The first, second, third and fourth adjustable optical modules in the module, the receiving end quantum communication module and the receiving end classical module, the first and third adjustable optical modules are rotated to the wavelength corresponding to the quantum signal light. The opening position, the second and fourth adjustable optical modules are rotated to the opening position corresponding to the wavelength of the classical signal light;

SS6: Key distribution and real-time monitoring stage, the conventional process of wireless quantum key distribution based on BB84 protocol: the transmitter and receiver interact in quantum channels and classical channels that have been trusted and authenticated to achieve key distribution, pairing Basic, error correction, error checking, and post-processing of privacy amplification. And during the key distribution process, the transmitter and receiver monitor the change of the quantum bit error rate (QBER) in real time. When the quantum bit error rate (QBER) fluctuation of the quantum signal light exceeds the preset threshold, the system re-enters the SS2 stage. The rate QBER fluctuation does not exceed the preset threshold until the key distribution is completed and the next step is entered.

SS7: The underwater wireless quantum key distribution process ends, the transmitter sends an end command, and the receiver enters the standby mode to wait for the next round of handshake signals.

Preferably, the output of the first laser group, the second laser and the third laser is a white laser with a wavelength range of 200-1600 nm, the first adjustable optical module, the second adjustable optical module, the third adjustable optical module The wavelengths of the narrow-band filters in the optical module and the fourth adjustable optical module are preferably 320.1nm, 336.1nm, 358.1nm, 382.0nm, 393.3nm, 396.8nm, 410.1nm, 430.7nm, 434.0nm, 438.3nm, 466.8nm, 486.1nm, 495.7nm, 516.7nm, 517.2nm, 518.3nm, 527.0nm, 587.5nm, 588.9nm, 589.5nm.

Compared with the prior art, the beneficial effects of the present invention are:

(1) According to the real-time change of the quantum bit error rate (QBER) caused by the real-time change of the water channel, the system selects the quantum optical signal and the classical optical signal of the optimal wavelength for underwater wireless quantum key distribution and underwater wireless optical communication. , reducing the quantum bit error rate (QBER) of the system and improving the final key generation rate and communication efficiency of the system under the current water channel;

(2) The optical structure of the system is simple, and there is no need to use precise optical devices such as nonlinear crystals, so the impact of environmental temperature changes on the system is small, the stability of the entire system is good, and the robustness of the system is improved;

(3) The wavelengths of the narrow-band filters in the adjustable optical module (AOM) are all selected from the wavelengths in the Fraunhofer spectrum, which can greatly reduce the influence of sunlight and background light on the system during work;

(4) This system is applicable to a wider range of working waters, such as estuaries, waters with unclear boundaries between seawater and freshwater; deep seas where water conditions have not yet been verified, and waters with more undercurrent and turbulent currents. The system can automatically switch the optimal working wavelength according to the change of the real-time water channel to adapt to the work in complex waters.

(5) Support long-term work, and will not suspend work due to complex changes in the water channel, and there is no need to artificially salvage the communication equipment and then re-modify and debug the wavelengths of quantum signal light and classical signal light according to changes in the water channel. Improve the work efficiency and endurance of underwater wireless quantum key distribution.

Description of drawings

FIG. 1 is a system frame diagram of the present invention.

FIG. 2 is a schematic diagram of the quantum communication module of the transmitter of the present invention.

FIG. 3 is a device diagram of a transmitter quantum communication module according to the present invention.

FIG. 4 is a schematic structural diagram of an optical filter and an attenuator in an adjustable optical module at the transmitting end of the present invention.

FIG. 5 is a schematic diagram of the adjustable optical module of the present invention.

FIG. 6 is a schematic diagram of a classic communication module of the transmitting end of the present invention.

FIG. 7 is a device diagram of a classic communication module at the transmitting end of the present invention.

FIG. 8 is a schematic diagram of a quantum communication module at the receiving end of the present invention.

FIG. 9 is a device diagram of a quantum communication module at the receiving end of the present invention.

FIG. 10 is a schematic diagram of a classic communication module at the receiving end of the present invention.

FIG. 11 is a device diagram of a classic communication module at the receiving end of the present invention.

FIG. 12 is a communication relationship diagram of the quantum communication module at the transmitting end and the quantum communication module at the receiving end according to the present invention.

In the figure: 1. The quantum communication module of the transmitter; 2. The classical communication module of the transmitter; 3. The control and processing module of the transmitter;

101, laser module; 102, optical module; 1021, filter; 1022, attenuator; 11, receiver quantum communication module; 22, receiver classic communication module; 33, receiver control processing module; 111, detection device group; 112. Optical module.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

As shown in Figure 1, an adaptive multi-band underwater wireless quantum key distribution system includes a transmitter and a receiver. Based on the BB84 communication protocol, the transmitting end and the receiving end interact in real time, and according to the change of the quantum bit error rate (QBER) caused by the real-time change of the channel, the tunable optical module generates quantum optical signals of different wavelengths and Underwater wireless quantum key distribution and underwater wireless classical optical communication using classical optical signals. The transmitter includes a transmitter quantum communication module 1, a transmitter classic communication module 2, and a transmitter control processing module 3. The transmitter quantum communication module 1 is connected to the transmitter control processing module 3, and the transmitter classical communication module 2 is connected to the transmitter control. The processing module 3 is connected.

1. Transmitter quantum communication module

Referring to FIGS. 2 and 3 , the quantum communication module 1 at the transmitting end includes a laser module 101 and an optical module 102 . The transmitting end quantum communication module 1 is connected with the transmitting end control processing module 3, and the transmitting end control processing module 3 is responsible for modulating the first laser group and controlling the rotation of the first adjustable optical module in the optical module, and outputs the quantum of the specified wavelength. signal light.

1) Laser module

The laser module includes a first laser group, and the first laser group adopts four white light lasers with the same parameters, the wavelength output range is 200nm-1600nm, and the power is stable.

2) Optical module

The optical module includes a first fixed optical module and a first adjustable optical module (AOM).

The first fixed optical module adopts BB84 protocol, including Glan prism polarizer (POL), attenuator (ATT), half wave plate (HWP), polarization dependent beam splitter (PBS) and polarization independent beam splitter (BS).

The first adjustable optical module (AOM) is controlled by the transmitter control processing module 3 and is a turntable that can rotate 360°. The turntable is fixed on the base, and there are 8 optical openings on the turntable. In this solution, 8 narrow-band filters 1021 with different wavelengths and 8 attenuators 1022 with different attenuation coefficients are installed on the first adjustable optical module (AOM) at the transmitting end, see Figure 4, Figure 5.

Because each quantum pulse needs to have a specified number of photons, the attenuation coefficient of the attenuator in each opening of the first tunable optical module in the quantum communication module at the transmitting end has been determined according to the light intensity of each wavelength of the first laser group and the The number of photons after the narrow-band filter is preset, and finally each pulse of the quantum signal light after passing through the first tunable optical module contains 0.1 photons.

The function of the first tunable optical module is to finally emit the quantum signal light of the desired wavelength.

2. The classic communication module of the transmitter

Referring to Figures 1, 6, and 7, the classic communication module 2 at the transmitting end is composed of a laser module, a detector module and an optical module. The transmitting-end classic communication module 2 is connected with the transmitting-end control processing module 3 and is responsible for the modulation of the second laser, and the transmitting-end control processing module 3 is also responsible for the rotation of the second adjustable optical module, the work of the first detector APD and the signal processing, and control the synchronization and interaction between the receiver and the transmitter.

1) Laser module

The laser module includes a second laser, which uses a white-light laser with the same parameters as the lasers in the first laser group in the quantum communication module at the transmitting end. Its wavelength output range is 200nm-1600nm, and the power is stable, and the processing module is controlled by the transmitting end. 3 Controls.

2) Detector module

The detector module is composed of a first detector APD, and the first detector APD is an avalanche diode detector, and its detection wavelength ranges from 300nm to 600nm. And the first detector APD is connected to the transmitter control processing module 3, converts the received optical signal into an electrical signal and then transmits it to the transmitter control processing module 3 for data processing and control.

3) Optical module

The optical module is composed of a fixed optical module and a second adjustable optical module. The fixed optical module is mainly composed of a polarization independent beam splitter (BS) and a mirror (MR), and its function is to convert the white laser emitted by the second laser. Directly injects into the second adjustable optical module (AOM), and then emits the classic signal light of the required wavelength through the second adjustable optical module, and receives the second adjustable optical module from the classic communication module at the receiving end. The incoming classical signal light is introduced into the first detector APD. There are 8 optical openings on the second adjustable optical module (AOM), and a narrow-band filter with the same wavelength as that in the first adjustable optical module (AOM) is installed in each optical opening. is the classical signal light of the desired wavelength for emission and reception.

3. Transmitter control processing module

The transmitter control processing module controls the operation and modulation of the first laser group and the second laser in the transmitter quantum communication module 1 and the transmitter classical communication module 2; controls the transmitter classical communication module 2 and the transmitter quantum communication module 1. The first and second tunable optical modules select the wavelengths of quantum signal light and classical signal light for underwater wireless quantum key distribution and underwater wireless classical optical communication according to the quantum bit error rate QBER. Control the work of the first detector APD in the classic communication module 2 of the transmitting end and process its signal.

The function of the transmitter control and processing module 3 is to control the cooperative work and data processing between the various modules of the transmitter, calculate the quantum bit error rate QBER of the quantum signal of each wavelength, select the optimal wavelength of the quantum signal light and the classical signal light, and Control the classic communication module 2 of the transmitting end and the classic communication module of the receiving end to synchronize and interact in real time.

The receiving end includes a receiving end quantum communication module 11, a receiving end classical communication module 22, and a receiving end control processing module 33. The receiving end quantum communication module 11 is connected with the receiving end control processing module 33, and the receiving end classical communication module 22 is controlled by the receiving end. The processing module 33 is connected.

4. Receiver quantum communication module

Referring to FIGS. 1 , 8 and 9 , the quantum communication module 11 at the receiving end includes a detector module 111 and an optical module 112 . The receiver quantum communication module 11 is connected with the receiver control processing module 33, and the receiver control processing module 33 is responsible for controlling the detector module 111 to work, process its data, and also control the rotation of the third adjustable optical module .

1) Optical module

The optical module includes a third fixed optical module and a third adjustable optical module (AOM).

The third fixed optical module adopts the BB84 protocol and consists of a half-wave plate (HWP), a polarization-dependent beam splitter (PBS) and a polarization-independent beam splitter (BS).

The third adjustable optical module (AOM) is controlled by the control processing module 33 at the receiving end, and is synchronized with the rotation of the first adjustable optical module (AOM) in the quantum communication module 1 at the transmitting end. Each of the eight openings of the third adjustable optical module (AOM) is installed with a narrow-band filter of the same wavelength as that in the first optical module, for receiving quantum signal light of a desired wavelength.

2) Detector module

The detector module consists of 4 photomultiplier tubes (PMT) with detection wavelengths ranging from 300nm to 600nm. The photomultiplier tube (PMT) receives the linearly polarized quantum signal light after beam splitting through the polarization independent beam splitter (BS) and the polarization dependent beam splitter (PBS), converts the optical signal into an electrical signal and transmits it to the receiving end control processing module 22, And by it for the corresponding data processing and control.

5. Receiver classic communication module

10 and 11, the classic communication module 22 at the receiving end includes a laser module, a detector module and an optical module. The third laser, detector, and optical module. The receiver classic communication module 22 is connected to the receiver control processing module 33 . The receiver control processing module 33 is responsible for the modulation of the third laser, the wavelength selection of the fourth tunable optical module, the work and signal processing of the detector APD, the underwater wireless post-processing process, and the classical communication and interaction with the receiver.

1) Laser module

The laser module includes a white-light laser with the same parameters as the lasers in the first laser group, the wavelength output range is 200nm-1600nm, and the power is stable. Controlled by the receiver control processing module 33;

2) Detector module

The detector module includes a second detector APD, the second detector APD is an avalanche diode detector (APD), and the detection wavelength ranges from 300nm to 600nm. And the detector is connected with the receiving end control processing module 33, converts the received optical signal into an electrical signal and then transmits it to the receiving end control processing module 33, and performs corresponding data processing and control by it;

3) Optical module

The optical module is composed of a fourth fixed optical module and a fourth adjustable optical module (AOM), wherein the fixed optical module is mainly composed of a polarization independent beam splitting prism (BS) and a reflector (MR). Its function is to directly inject the white laser light emitted by the third laser into the fourth adjustable optical module (AOM), emit the classical signal light of the required wavelength through the fourth adjustable optical module (AOM), and transmit the fourth adjustable optical module (AOM). The optical modulation module receives the classic signal light from the classic communication module at the transmitting end and introduces it into the second detector APD. The fourth adjustable optical module (AOM) has 8 optical openings, and each optical opening is installed with a narrow-band filter with the same wavelength corresponding to the second optical module. Receive the classical signal light of the desired wavelength.

Select to install narrow-band filters suitable for the following wavelengths in the eight optical openings in the first adjustable optical module, the second adjustable optical module, the third adjustable optical module and the fourth adjustable optical module Sheets: 438.3 nm, 466.8 nm, 486.1 nm, 495.7 nm, 517.2 nm, 518.3 nm, 527.0 nm, 546.0 nm. It should be noted that these 8 wavelengths are selected from the Fraunhofer dark line spectrum, which helps to reduce ambient noise caused by ambient light.

As shown in FIG. 12 , the communication relationship between the quantum communication module 1 at the transmitting end and the quantum communication module 11 at the receiving end is shown. The light of the four lasers Laser1, Laser2, Laser3 and Laser4 is first attenuated by an optical filter (ATT), and attenuated to an appropriate ratio. Generate horizontal, vertical, horizontal and vertical lines of polarized light respectively, and then the linearly polarized lights of Laser1 and Laser2 and Laser3 and Laser4 are combined once respectively, and each line of horizontal polarization and each line of vertical polarization enter a polarization beam splitter (PBS) each constituted a group. The linearly polarized light of Lsaser1 and Lsaser2 is rotated by a half-wave plate (HWP) into linearly polarized light of 45° and 135°, and then enters the polarization independent beam splitter (BS), and the other group directly enters the polarization independent beam splitter (BS), and finally passes through A tunable optical module (AOM-S) at the transmitter end equipped with a narrowband filter and an attenuator becomes a quantum signal light with a specific wavelength and each optical pulse containing 0.1 photons incident into the water channel.

The receiving end first passes through the adjustable optical module (AOM-R) at the receiving end. At this time, the wavelength of the narrow-band filter installed in the optical opening of the adjustable optical module (AOM-R) is the same as that of the adjustable optical module at the transmitting end. The wavelengths of the narrowband filters of the group (AOM-s) are consistent. The quantum signal light is firstly split into two equally through a polarization-independent beam splitter (BS). One line of light is rotated 45° by a half-wave plate (HWP) into a horizontal or vertical linearly polarized light, and then enters a polarization-related beam splitting prism (PBS), the horizontal linearly polarized light is reflected into PMT1, and the vertical linearly polarized light is projected into PMT2. One line of light directly passes through a polarization-dependent beam splitter prism (PBS), the horizontal linearly polarized light is reflected into PMT3, and the vertical linearly polarized light is projected into PMT4.

An adaptive multi-band underwater wireless quantum key distribution method of the present invention comprises the following steps:

SS1: The system is initialized, the transmitter and receiver are powered on, and all adjustable optical modules are rotated to the preset wavelength mode (that is, rotated to the position corresponding to the default wavelength);

SS2: In the handshake stage, the classic communication module of the transmitter sends a handshake signal to notify the receiver to start receiving the test signal to test the quantum bit error rate (QBER) of quantum signals of different wavelengths. The handshake signal includes the system time and the rotation interval of the adjustable optical module during the test phase;

SS3: In the test phase, the transmitter control processing module 3 controls the first adjustable optical module in the transmitter quantum communication module 1 to rotate 8 times according to the set rotation interval, and respectively send 8 groups of test signals with different wavelengths. At the same time, according to the set rotation time interval, the receiving end rotates the fourth adjustable optical module in the quantum communication module 11 of the receiving end and the adjustable optical module in the quantum communication module 1 of the transmitting end to rotate synchronously, rotate 8 times, and receive respectively 8 groups of test signals;

Choose narrow band filters for the following wavelengths: 438.3nm, 466.8nm, 486.1nm, 495.7nm, 517.2nm, 518.3nm, 527.0nm, 546.0nm;

SS4: In the wavelength selection stage, the receiving end quantum communication module 11 interacts with the received 8 groups of test signals sent to the transmitting end classical communication module 2 via the receiving end classical communication module 22, and controls the processing module 3 and the receiving end through the transmitting end control processing module 3 and the receiving end. The processing module 33 calculates to obtain the quantum bit error rates QBER of 8 groups of test signals with different wavelengths, sorts the eight groups of quantum bit error rates QBER from small to large, and selects the two groups corresponding to the smallest and next smallest quantum bit error rates QBER The wavelength is used as the working wavelength of the quantum signal light of underwater wireless quantum key distribution and the classical signal light of underwater wireless classical communication;

SS5: In the wavelength adjustment stage, the transmitter interacts with the receiver to determine the working wavelengths of quantum signals and classical signals. The first and second of the transmitter quantum communication module 1, the transmitter classical communication module 2, the receiver quantum communication module 11 and the receiver classical module 22 are rotated synchronously by the transmitter control processing module 3 and the receiver control processing module 33 respectively. , the third and fourth adjustable optical modules, the first and third adjustable optical modules are rotated to the opening position corresponding to the wavelength of the quantum signal light, and the second and fourth adjustable optical modules are rotated to the classical signal The aperture position corresponding to the light wavelength;

SS6: Key distribution and real-time monitoring stage, the conventional process of wireless quantum key distribution based on BB84 protocol: the transmitter and receiver interact in quantum channels and classical channels that have been trusted and authenticated to achieve key distribution, pairing Basic, error correction, error checking, and post-processing of privacy amplification. And during the key distribution process, the transmitter and receiver monitor the change of the quantum bit error rate (QBER) in real time. When the quantum bit error rate (QBER) fluctuation of the quantum signal light exceeds the preset threshold, the system re-enters the SS2 stage. If the quantum bit error rate (QBER) fluctuation does not exceed the preset threshold, go to the next step until the key distribution is completed;

The SS7 underwater wireless quantum key distribution process ends, the transmitter sends an end command, and the receiver enters the standby mode to wait for the next round of handshake signals.

Through the above steps, the underwater wireless quantum key distribution is finally completed. The wavelength of the signal light of the whole system is selected from the Fraunhofer dark-line spectrum, which can effectively reduce the interference of underwater ambient light to the system.

The present invention adapts to changes of underwater channels in real time through the above research, improves the efficiency of underwater wireless quantum key distribution, reduces the bit error rate, increases the transmission distance and the final key generation rate, and expands the water area of underwater wireless key distribution. , the optimal key generation rate and communication rate in any water area can be achieved.

The invention can automatically adjust the wavelength of the signal light used by the system based on the real-time change of the bit error rate of the water channels of different water bodies or the water channel of the same water body, so as to adapt to the change of the water channel in real time, reduce the bit error rate, and finally realize the underwater wireless quantum The maximum key generation rate of the key distribution system.

Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, and substitutions can be made in these embodiments without departing from the principle and spirit of the invention and modifications, the scope of the invention is defined by the appended claims and their equivalents.

Claims (10)

1. an adaptive multi-band underwater wireless quantum key distribution system, is characterized in that, described distribution system comprises: transmitting end, receiving end; On the basis based on BB84 communication protocol, described transmitting end and receiving end double Real-time interaction between terminals, and according to the change of the quantum bit error rate (QBER) caused by the real-time change of the channel, the tunable optical module generates quantum optical signals and classical optical signals of different wavelengths for underwater wireless quantum key distribution and underwater wireless classical optical signals. communication. 2. adaptive multi-band underwater wireless quantum key distribution system according to claim 1, is characterized in that: described transmitting end comprises transmitting end quantum communication module (1), transmitting end classical communication module (2), transmit A terminal control processing module (3); the transmitting terminal quantum communication module (1) is connected with the transmitting terminal control processing module (3), and the transmitting terminal classical communication module (2) is connected with the transmitting terminal control processing module (3) Connected. 3. The adaptive multi-band underwater wireless quantum key distribution system according to claim 1, wherein the receiving end comprises a receiving end quantum communication module (11), a receiving end classical communication module (22), a receiving end an end control processing module (33); the receiving end quantum communication module (11) is connected with the receiving end control processing module (33), and the receiving end classical communication module (22) is connected with the receiving end control processing module (33) connected. 4. adaptive multi-band underwater wireless quantum key distribution system according to claim 1, is characterized in that, the calculation formula of quantum bit error rate QBER is as follows:

In the formula, P represents the polarization ratio of the polarizing device, A is the receiving area of the detector (if there is a telescope, the receiving area of the telescope), ldc represents the dark count of the detector, L represents the ambient light irradiance spectral density, Δt' represents Door opening time of a single photon detector, Δt is the bit period, Ω is the solid angle of the field of view, h is Planck's constant, c is the speed of light, η is the detector efficiency, χ _c is the attenuation coefficient, r is the transmission distance, λ is the wavelength of the signal light, Δλ is the spectral width, and μ is the average number of pulsed photons emitted by the transmitter. 5. The adaptive multi-band underwater wireless quantum key distribution system according to claim 2, characterized in that: the transmitter quantum communication module (1) comprises a laser module (101) and an optical module (102) , the laser module (101) includes a first laser group, the laser module (101) includes four white-light lasers, and the optical module (102) includes a first fixed optical module and a first adjustable optical module The module, the classic communication module (2) of the transmitting end includes a second laser, an optical module and a first detector APD, and the optical module includes a second fixed optical module and a second adjustable optical module, so The transmitter control processing module (3) controls the first laser group, the second laser, the first adjustable optical module, the second adjustable optical module and the first detector APD. 6. The adaptive multi-band underwater wireless quantum key distribution system according to claim 3, wherein the receiver quantum communication module (11) comprises a detector group (111) and an optical module (112) , the detector group (111) includes four photomultiplier tubes PMT, the optical module (112) includes a third fixed optical module and a third adjustable optical module, the receiving end classic communication module (22 ) includes a third laser, a second detector APD and an optical module, the optical module includes a fourth fixed optical module and a fourth adjustable optical module, and the receiving end control processing module (33) controls the A detector group (111), a third laser, a third adjustable optical module and a fourth adjustable optical module, and a second detector APD. 7. The adaptive multi-band underwater wireless quantum key distribution system according to claim 5, characterized in that: the first adjustable optical module of the transmitting end quantum communication module (1) and the transmitting end classical communication module (2) There are 6-20 optical openings on the second adjustable optical module, preferably 8-15, more preferably 8, and each opening of the first adjustable optical module is provided with different optical openings Narrowband filters of different wavelengths and attenuators with different attenuation coefficients, only narrowband filters of different wavelengths are installed in each opening of the second tunable optical module, and the first tunable optical module is rotated to output The quantum signal light of the desired wavelength, the second tunable optical module emits and receives the classical signal light of the desired wavelength through rotation. 8. The adaptive multi-band underwater wireless quantum key distribution system according to claim 6, characterized in that: the third adjustable optical module and the receiving end quantum in the classical communication module (22) at the receiving end The fourth adjustable optical module in the communication module (11) has 6-20 optical openings, preferably 8-15, more preferably 8, the third adjustable optical module and the fourth adjustable optical module Only narrow-band filters of different wavelengths are installed in each opening of the group, the third adjustable optical module receives quantum signal light of a specific wavelength by rotation, and the fourth adjustable optical module is rotated to receive and emitting classical signal light of a specific wavelength. 9. A method of using the self-adaptive multi-band underwater wireless quantum key distribution system of claim 1-8 to distribute keys, characterized in that, comprising the following steps: SS1: The system is initialized, the transmitter and receiver are powered on, and all adjustable optical modules are turned to the preset wavelength mode; SS2: In the handshake phase, the classic communication module (2) of the transmitting end sends a handshake signal, notifying the receiving end that it is ready to start receiving the test signal to test the quantum bit error rate QBER of quantum signals of different wavelengths. The handshake signal includes the system time and the adjustable optical module. The rotation interval of the test phase; SS3: In the test stage, the transmitter control processing module (3) controls the first adjustable optical module in the transmitter quantum communication module (1) to rotate 6-20 times according to the set rotation interval, and send 6-20 groups respectively For test signals of different wavelengths, at the same time, the receiving end starts to rotate the fourth adjustable optical module in the quantum communication module (11) of the receiving end synchronously 6-20 times according to the set rotation time interval, and receives 6-20 sets of test signals respectively. ; SS4: In the wavelength selection stage, the quantum communication module (11) at the receiving end interacts with the received 6-20 sets of test signals via the classical communication module (22) at the receiving end and sends it to the classical communication module (2) at the transmitting end. The control processing module (3) and the receiver control processing module (33) calculate to obtain the quantum bit error rates QBER of 6-20 groups of test signals with different wavelengths, and sort the 6-20 groups of quantum bit error rates QBER from small to large , select the wavelengths corresponding to the smallest and second smallest quantum bit error rates QBER as the working wavelengths of the quantum signal light of underwater wireless quantum key distribution and the classical signal light of underwater wireless classical communication; SS5: In the wavelength adjustment stage, the transmitter interacts with the receiver to determine the working wavelengths of the quantum signal and the classical signal, and then the transmitter control processing module (3) and the receiver control processing module (33) synchronously rotate the transmitter quantum communication. The first, second, third and fourth adjustable optical modules in the module (1), the transmitting-end classical communication module (2), the receiving-end quantum communication module (11) and the receiving-end classical module (22), the The first and third adjustable optical modules are rotated to the aperture position corresponding to the wavelength of the quantum signal light, and the second and fourth adjustable optical modules are rotated to the aperture position corresponding to the wavelength of the classical signal light; SS6: In the key distribution and real-time monitoring stage, the conventional process of wireless quantum key distribution based on the BB84 protocol is carried out. The post-processing process of base, error correction, error checking, and private amplification, and in the key distribution process, the transmitter and receiver monitor the change of the quantum bit error rate QBER in real time. When the quantum bit error rate of the quantum signal light is If the QBER fluctuation exceeds the preset threshold, the system re-enters the SS2 stage. If the QBER fluctuation of the quantum bit error rate does not exceed the preset threshold, the next step will be entered until the key distribution is completed; SS7: The underwater wireless quantum key distribution process ends, the transmitter sends an end command, and the receiver enters the standby mode to wait for the next round of handshake signals. 10. The method for distributing keys according to claim 9, wherein the output of the first laser group, the second laser and the third laser is a white laser with a wavelength range of 200-1600 nm, the first adjustable The wavelengths of the narrowband filters in the optical module, the second adjustable optical module, the third adjustable optical module and the fourth adjustable optical module are selected from 320.1nm, 336.1nm, 358.1nm, 382.0nm, 393.3nm , 396.8nm, 410.1nm, 430.7nm, 434.0nm, 438.3nm, 466.8nm, 486.1nm, 495.7nm, 516.7nm, 517.2nm, 518.3nm, 527.0nm, 587.5nm, 588.9nm, 589.5nm.

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