CN108737088B - Free space laser communication system based on quantum encryption - Google Patents
Free space laser communication system based on quantum encryption Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
- H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
- H04L9/0852—Quantum cryptography
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- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/70—Photonic quantum communication
Abstract
A free space laser communication system based on quantum encryption comprises a receiving module and a data decryption module, wherein the receiving module captures laser signals and communication request signals, amplifies and processes and quantizes the laser signals through broadband amplification and pulse code modulation, and converts the laser signals into digital signals after coding. After the computer module processes data, according to the communication request, the communication node information is recorded and freely organized into a communication network, the data are transmitted to the data encryption module, the quantum key is obtained by the quantum key terminal, the data are encrypted by the data encryption module, and the encrypted data are transmitted to a communication opposite side by the transmitting module. The communication node of the receiving party acquires the quantum key through the quantum key terminal, decrypts the received data through the data decryption module, and sends the decrypted data to the computer module for processing. The invention does not need to fix communication nodes or lay cables/optical cables, and can transmit in a long distance and bypass obstacles and adverse weather areas.
Description
Technical Field
The invention belongs to the field of laser communication and the field of data encryption, and particularly relates to a free space laser communication system based on quantum encryption.
Background
Although the modern society is an information society, various communication technical means are diversified, and mainly include optical fiber communication, digital microwave communication, satellite communication, mobile communication and the like. Optical fiber communication is a communication method that uses light waves as carrier waves and optical fibers as transmission media to transmit information from one place to another, and is called "wired" optical communication. The free space laser communication technology, i.e. the optical fiber-free optical communication technology, is a new technology appearing in recent years, and the principle of the technology is that carrier optical signals use the air as a transmission channel to complete point-to-point or point-to-multipoint information transmission. Satellite communication is communication between radio communication stations on earth (including in the ground and the lower atmosphere) using a satellite as a relay. The microwave communication is a communication directly using microwaves as a medium, does not require a solid medium, and can use microwave transmission when there is no obstacle in a straight distance between two points. Mobile communication is communication in which one or both of the communicating parties are in motion.
With the rapid development of internet technology, the requirements of people on communication technology and encryption technology are more and more demanding, and the disadvantages of the above schemes are very obvious: firstly, with the development of science and technology, the data of various resources such as pictures, videos and the like is larger and larger, the data exchange amount of people is also continuously improved, the requirement on the capacity of the communication technology is higher and higher, and the bandwidths of satellite communication, microwave communication and mobile communication are far lower than those of optical fiber communication and laser communication which take light as a medium. Secondly, for many places where cables or optical fibers are not easy to be laid, the distribution of communication base station equipment directly affects the quality of satellite communication and mobile communication, and most of the existing communication base stations are high in construction difficulty and high in consumption and also directly affect the construction and coverage rate of the communication base stations. Third, although the optical fiber communication has a large communication capacity, both communication nodes are often required to be fixed, and the flexibility and mobility of the optical fiber communication are far lower than those of mobile communication, satellite communication and laser communication, and the optical fiber communication cannot be applied to occasions where cables cannot be laid, such as ship-to-ship communication, satellite-to-satellite communication and air-to-ground communication. Finally, the most important is that the security and reliability of information transmission are increasingly challenged, and the new generation computing mode represented by quantum computing makes the traditional encryption/decryption modes such as RSA and DES face the collapse and is difficult to resist the attack of ultra-strong computing power.
With the rapid development of socioeconomic, information has become a strategic resource of socioeconomic development in China, and is also a basic element for promoting human progress. The free space laser communication equipment has the advantages of no electromagnetic interference, flexible networking, convenient installation and maintenance, high communication reliability, good confidentiality, excellent cost performance ratio and the like, can transmit data, voice and images with various rates, and has wide application prospect. The development of quantum computing technology provides a thought for improving the security of a communication system, but a communication technology with large communication traffic, high security and good mobility, in particular a free space laser communication system based on quantum encryption, is still lacked in the market at present.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a free space laser communication system based on quantum encryption, which provides more efficient and safe guarantee for the communication field by combining the existing laser communication technology and the quantum encryption technology.
The technical scheme adopted by the invention is as follows:
a free-space laser communication system based on quantum cryptography, comprising: the system comprises a receiving module, a data decryption module, a computer module, a quantum key terminal, a data encryption module, a transmitting module and an aiming mechanism; the system is used for two-way communication between two movable or fixed communication nodes, and can realize quantum encryption and quantum decryption of communication signals; a plurality of communication nodes can communicate with each other to freely form a communication network;
the receiving module is a laser sensing device and is used for capturing a laser signal and a communication request signal of a communication node of a transmitting party, screening the obtained laser signal carrying target information by a photoelectric detector, amplifying the signal by an amplifier, demodulating by a pulse code modem, and converting an analog signal into a digital signal;
the data decryption module is connected with the receiving module and the quantum key terminal, acquires a corresponding quantum key from the quantum key terminal, decrypts the encrypted digital signal transmitted by the receiving module, and restores the ciphertext into the original text;
the computer module is connected with the data decryption module and the data encryption module and used for responding to the laser communication request, finishing flexible networking and topology optimization of the communication node, processing decrypted data acquired from the data decryption module and finishing data encryption and communication preparation of transmitted data by using the data encryption module;
the quantum key terminal is connected with the data decryption module and the data encryption module, can perform quantum entanglement operation, and communicates with the communication node of the opposite side through a quantum channel to obtain a quantum key for encryption and decryption so as to finish decryption of received data or encryption of transmitted data;
the data encryption module is connected with the quantum key terminal and the computer module and used for encrypting data, when the data needs to be transmitted, the data needing to be transmitted is received from the computer module, the quantum key acquired by the quantum key terminal is adopted to carry out quantum encryption on the communication data acquired from the computer module, and a plaintext is converted into a ciphertext;
the transmitting module is connected with the data encryption module and used for transmitting data to be transmitted to a communication node of a receiving party in a laser mode, demodulating and amplifying necessary signals of the digital signals after quantum encryption through a pulse code demodulator, converting the digital signals into analog signals and transmitting the analog laser signals to the receiving party through a laser; the laser signal of a plurality of different wavelengths can be generated simultaneously so as to realize wavelength division multiplexing or dense wavelength division multiplexing;
the system also comprises a aiming mechanism which controls the azimuth angles of the transmitting module and the receiving module simultaneously and is used for aligning the laser receiving module and the transmitting module of both communication parties, the computer module responds to the communication request to determine the coordinates and the azimuth of the target of both communication parties, and the aiming mechanism accurately adjusts the laser transmitting angle of the transmitting module and the angle of the receiving module according to the coordinates and the azimuth information of both communication parties.
The computer module can respond to and record the communication node information and establish a routing table of the communication; calculating the topological connection and routing of the network during multi-node communication to form a self-organizing network, adding the freely added communication nodes into a routing table, and deleting the freely separated communication nodes from the routing table; calculating the optimal path through a routing algorithm of a computer, finding out the address of a sending node or a gateway at the next stage, and automatically updating routing information and communication node information; the network topology can be optimized in a complex terrain or obstacle environment or under complex meteorological conditions such as dense clouds, rain and snow, the curve transmission and the breakpoint continuous transmission of laser communication are realized, so that communication signals can bypass obstacles, complex areas or poor meteorological areas; when a communication node in the network is attacked or fails, other communication nodes can be selected through calculation to complete the continuous transmission of communication data. The receiving module is arranged on the surface of the communication node and used for converting the digital signal and the analog signal into each other; the receiving module comprises an optical receiving antenna, an optical filter and a light detector; the optical receiving antenna comprises a lens or a reflector, focuses the received optical signal and then sends the optical signal to the optical detector; the optical detector amplifies the laser signal to recover an electric signal, and the electric signal is sent to the electric receiver module to be demodulated into original information.
The aiming mechanism is used for aiming at a transmitting module and a receiving module of both communication parties, and consists of four parts, namely: the system comprises an optical antenna servo platform, an error detection processor, a beacon signal generator, a beacon light source and a control computer;
the optical antenna servo platform is used for enabling the output mechanical displacement or rotation angle to accurately track the input displacement or rotation angle;
the beacon signal generator and the beacon light source are used for generating beacon signals, outputting intermediate frequency signals through secondary frequency conversion and supplying the intermediate frequency signals to the optical antenna servo platform and the control computer for use;
the error detection processor can calculate the azimuth and beacon data of laser aiming to obtain an aiming error;
the control computer can calculate and generate a control logic signal to drive the motor to drive the transmitting module and the receiving module to rotate according to the aiming error calculated by the error detection processor, and the optical antenna servo platform determines the rotation direction of the antenna according to the driving voltage, so that the laser antenna is ensured to accurately point to the opposite communication party.
A free space laser communication method based on quantum encryption comprises the following steps: the system comprises a receiving module, a data decryption module, a computer module, a quantum key terminal, a data encryption module and a transmitting module; the communication parties aim at the transmitting module and the receiving module of the communication parties through an aiming mechanism, the receiving module captures laser signals, and the laser signals are amplified, processed, quantized and encoded to be converted into digital signals through broadband amplification and pulse code modulation; then, the data decryption module decrypts the signal by using the quantum key acquired by the quantum key terminal, and sends the decrypted data to the computer module; after the computer module processes the data, the data to be sent is transmitted to the data encryption module, the quantum key terminal obtains the quantum key, encrypts the data and sends the data to the receiving party through the laser channel.
A free space laser communication method based on quantum encryption comprises the following steps:
the first step is as follows: networking, namely forming a communication network through an aiming mechanism, determining communication requests of nodes of two parties by a computer module, forming the communication network with multiple communication nodes according to needs, and optimizing a network topology structure;
the second step is that: and (5) initializing a quantum key. Two communication parties apply for laser communication, and the two parties select 8 pairs of entangled photons from the entangled photon pairs, and the entangled photon pairs can be expressed as quantum states
The wavelengths are respectively: (b)1,g1),(b2,g2),...,(b8,g8)；
Further, the quantum key terminal distributes different entangled photon pairs according to each communication request;
at the moment, the quantum key terminal obtains the requests of both communication parties, and both parties analyze the communication request to make an entangled photon pair distribution scheme;
the third step: and negotiating the quantum key. The quantum key terminal publishes the distribution information of the entangled photon pairs to both communication parties through a classical channel, and then uses a quantum channel to send the information of the entangled photon pairs as a quantum key;
further, the two parties measure and evaluate the quantum sequence, and when the measurement error rate is smaller than a preset threshold value, the quantum communication is considered to be safe, and the business of the laser communication is received; if the error exceeds a preset threshold value, the quantum communication is considered to be invalid, and the quantum communication is invalidated;
and fourthly, encrypting and transmitting the information. After the quantum communication security is confirmed, the corresponding key is used for encrypting the data to be transmitted, and the encrypted ciphertext is used as the quantum communication service data.
Preferably, through the technologies of wavelength division multiplexing, dense wavelength division multiplexing and time division multiplexing decoding, each communication node completes QKD according to the entangled photon pair distribution information, performs multi-band information transmission of the same channel, and improves the communication transmission capacity.
The fifth step: and (6) decrypting the data. And the two communication parties arrange a laser communication decoding sequence according to the distribution information and then decode the encrypted ciphertext into plaintext according to a quantum decryption program.
The specific laser communication mode can be realized by combining a plurality of communication nodes to form a more complex quantum encryption laser communication mode, including a relay amplification mode, a ring network, a star network and the like, and further quantum encryption laser communication and a laser communication network with a flexible space structure are realized, and at the moment, the quantum key terminal can distribute entangled photon pairs according to different conditions. And after the distribution of the entangled photon pairs is finished, the computer module immediately publishes distribution information to a corresponding laser communication node of the network through a classical channel, and then the next node forwards encrypted information.
In a quantum communication network composed of a plurality of nodes, a specific networking plan is as follows:
the laser communication parties are shown as A, B, …, G and the like, the server is shown as S (if provided), each communication node can be fixed or mobile, each communication node can be in the network all the time during communication or can leave the communication network at any time, and the basic laser communication modes include the following modes:
mode 1: point-to-point laser communication modes, for example:
each communication node can freely join or leave the communication network at any time in the communication process;
mode 2: point-to-server laser communication modes, such as:
the communication node S serving as a server is generally always in the network during communication, and may be fixed or mobile;
mode 3: multipoint-to-point laser communication modes, for example:
the communication node a is generally always in the network during the communication process, and may be fixed or mobile;
in a quantum communication network composed of a plurality of nodes, in the second step: quantum key initialization, and the corresponding distribution of entangled photons is as follows:
mode 1: (g)1→A,b1→B),(g2→C,b2→D),(g3→E,b3→F),(g4→G,b4→H)；
Mode 2: (g)1→A,b1→S),(g2→B,b2→S),(g3→C,b3→S),(g4→D,b4→S)，
(g5→E,b5→S),(g6→F,b6→S),(g7→G,b7→S),(g8→H,b8→S)；
Mode 3: (g)1→A,b1→B),(b3→A,g3→C),(b4→A,g4→D),(b5→A,g5→E)，
(b6→A,g6→F),(b7→A,g7→G),(b8→A,g8→H),(g2→A,b2→S)。
The invention relates to a free space laser communication system based on quantum encryption, which has the following beneficial effects:
1. the communication capacity is large: the invention generates different laser carrying data with a plurality of wavelengths, and transmits multiband laser information in the same laser channel by wavelength division multiplexing, dense wavelength division multiplexing and time division multiplexing decoding technology, thereby improving the communication transmission capacity. The data code rate of l0Gb/s can be easily transmitted, and even higher, theoretically, the communication rate can be improved by 100 times to 1000 times compared with the existing communication modes (satellite communication, microwave communication, mobile communication and the like) based on radio waves.
2. The use is flexible: the device is suitable for being used in complex terrain environment, obstacle environment and complex meteorological condition. Different from large-capacity optical fiber communication, free space laser communication belongs to wireless communication, no line or optical fiber needs to be erected, and communication can be completed only by installing corresponding communication equipment for two nodes needing communication functions. And compared with a microwave antenna, the structure of the free space laser communication equipment is simpler. The diameter of the microwave antenna reaches dozens of meters, and the weight of the microwave antenna reaches dozens of tons or even hundreds of tons, while the transmitting antenna and the receiving antenna required by laser communication can be very small, the diameter is only dozens of centimeters, and the weight is only a few kilograms. The invention can self-organize the network, form the laser communication network with farther distance and flexible space structure, bypass complex terrains, obstacle environments or complex areas, and complex meteorological conditions such as dense clouds, rain and snow, and realize the curve transmission of laser communication, therefore, the invention can be directly used for realizing the large data volume communication among mobile communication nodes under the complex environment in which cables or optical fibers are difficult to lay, such as the communication among satellites, the communication among air spaces, the communication among ships and vessels, the communication in battlefield environment, and the like.
3. Strong anti-attack ability and anti-electromagnetic interference ability: the frequency of laser is extremely high, laser photons are not charged, and the laser photons cannot be damaged by a common electromagnetic interference method; meanwhile, the laser does not interfere with other electronic equipment. When a communication node in the network is attacked or fails, other communication nodes can be selected through calculation to complete the continuous transmission of communication data. Therefore, the communication device is far superior to satellite communication, microwave communication, and mobile communication, which are mainly electromagnetic signal communication, in interference performance and interference resistance performance.
4. The transmission confidentiality is relatively reliable: the laser transmission directivity is very good, the divergence angle is very small, and the divergence angle is milliradian magnitude, so the laser communication is point-to-point communication basically, and a communication counterpart can receive signals only when being aligned in a light spot range, so the signals are difficult to intercept and damage. The quantum entanglement channel has high concealment, the quantum state coding information on the single photon level is utilized, two communication parties can share different random keys each time, the single photon is inseparable and the quantum state is not clonable on the physical principle, the measurement can not be carried out on the premise of not influencing the quantum state, and the like, so that the quantum encryption has absolute security, the encryption mode of adopting the quantum one-time pad is theoretically proved to be unconditionally secure, even if the quantum communication is intercepted, the two communication parties can also find the quantum communication in time in the detection, and the security of the communication is improved. Laser photons are also particularly suitable for making entangled state photons.
5. Has long-term investment value: with the improvement of the technology, the continuous improvement of new devices and the continuous emergence of new devices, the free space laser communication technology has become a hot technology of the current information technology, the function and the position of the free space laser communication technology can be communicated with optical fibers, and the microwave communication is an indispensable technology for constructing future world-wide communication networks. The method is widely used in the military field and the civil field.
Drawings
FIG. 1 is a schematic diagram of the system of the present invention.
Fig. 2 is a flow chart of quantum cryptography communication according to the present invention.
Detailed Description
As shown in fig. 1, a free space laser communication system based on quantum cryptography includes a receiving module 101, a data decryption module 102, a computer module 103, a quantum key terminal 104, a data encryption module 105, a transmitting module 106, and an aiming mechanism 107.
The receiving module 101 is installed on a surface of the communication terminal, preferably, a broad surface for easily receiving a laser signal, and is used for converting a digital signal and an analog signal into each other. The receiving module mainly comprises an optical receiving antenna, an optical filter and a light detector. The optical receiving antenna mainly comprises a lens or a reflector, focuses the received optical signal and then sends the optical signal to the optical detector. The optical detector amplifies the laser signal to recover an electric signal, and the electric signal is sent to the electric receiver module to be demodulated into original information.
Preferably, a single photon detector is used, being a superconducting single photon detector, with a quantum efficiency of about 0.7% at counts less than 10 Hz. Under the transmission distance of 200 kilometers, the channel attenuation is 42dB, the bit error rate is 4.0%, and the safe code rate of 12bps is obtained under the universal independent attack. Preferably, the pulse signal is sampled using an FPGA and demodulated by 2 FSK. Preferably, a plurality of single photon detectors with different wavelengths are used, the multi-wavelength division multiplexing and dense wavelength division multiplexing technologies are realized to complete laser communication, and the communication capacity is improved.
Further, modulation and demodulation are used to realize conversion between signals, and available modulation methods mainly include: frequency modulation, phase modulation, amplitude modulation, etc., preferably using frequency modulation as the signal-to-signal conversion mechanism, the signal frequency is adjusted according to the signal magnitude. Further, 2FSK modulation is used, so that better noise resistance can be provided than other modes; preferably, the carrier signal is selected from square waves, the square wave efficiency is higher than that of other waves, and the square wave efficiency is easy to realize in an FPGA.
The receiving module 101 adopts a staggered tuning type broadband amplifying circuit, and several stages of amplifying circuits with tuning loops are connected in series, and the tuning center frequency of each stage is slightly staggered, so that the frequency band can be expanded. Preferably, a photo detector with a photomultiplier and a photo resistor as components is selected. The photomultiplier tube has good performance in terms of sensitivity. In the aspect of spectral response, the photomultiplier tube responds to the ultraviolet direction, and the photoresistor responds to the infrared direction, so that the combination performance of the photomultiplier tube and the photoresistor is better. Preferably, two or more receiving modules 101 and receiving antennas are used, so that multi-beam receiving and transmitting can be achieved, communication capacity is enlarged, hardware redundancy is formed, communication reliability is improved, even laser relay is enabled, and communication distance is prolonged.
The data decryption module 102 is connected to the receiving module 101 and the quantum key terminal 104, and is capable of obtaining a corresponding quantum key from the quantum key terminal 104, decrypting the encrypted digital signal transmitted by the receiving module 101, and restoring the ciphertext to the original text.
The computer module 103 is connected to the data decryption module 102, and is configured to respond to a laser communication request, process decrypted data obtained from the data decryption module 102, complete communication preparation of transmitting data, respond to and record communication node information, and establish a routing table of this communication; calculating the topological connection and routing of the network during multi-node communication to form a self-organizing network, adding the freely added communication nodes into a routing table, and deleting the freely separated communication nodes from the routing table; further, the topological connection and the routing of the network can be calculated during multi-node communication, and an ad hoc network is formed; furthermore, the optimal path can be calculated through a routing algorithm of the computer, the address of a sending node or a gateway at the next stage is found, and the transmission address of the data is automatically modified. Furthermore, the network topology can be optimized in a complex terrain or obstacle environment or under complex meteorological conditions such as dense clouds, rain and snow, and the like, and the curve transmission of laser communication is realized, so that the communication signal bypasses obstacles or bad meteorological areas.
Furthermore, time synchronization is used between computers of two communication parties, and the time synchronization module is used for sending synchronization information and communication early-stage preparation work, so that the states of a receiver and a sender are adjusted in time, and communication is ensured to be carried out in order.
The quantum key terminal 104 can prepare quantum keys for both communication parties, and preferably, establishes a quantum communication network by using an entangled photon pair, which is an entangled photon protocol based on multiple wavelengths.
Further, the quantum key terminal 104 implements high-speed quantum key distribution through a differential phase quantum key distribution protocol using a phase modulator. The phase modulator randomly modulates the phase information of each pulse, the laser is controlled to encode the information on the phases of two adjacent pulses, the receiver interferes with the two adjacent pulses when the receiver passes through the Mach-Zehnder delay interference ring, and the encoded phase information is obtained from the interference result. The length difference of two arms of the receiving Mach-Zehnder delay interference ring is equal to the optical path difference of the atmosphere channels of two adjacent pulses, if the phase difference of the two adjacent pulses is '0', the phase modulator sets bit information to '0', if the phase difference of the two adjacent pulses is pi, the phase modulator sets the bit information to '1', the bit '0' indicates that the phase is 0, and the bit '1' indicates that the phase difference is pi. The efficiency of the differential phase protocol is close to 1, and the safety of the differential phase quantum key distribution is proved to be safe to photon number separation attack, pervasive independent attack, sequence attack and zero bit error collective attack. The present system thus employs a differential phase protocol.
Further, the quantum key terminal 104, using a beam splitter, has one beam splitter for both the transmitting and receiving polarization interference rings, which aims to eliminate the side-band peak in the common unequal-arm Mach-Zehnder interference ring: when a common unequal-arm Mach-Zehnder interference ring is used for quantum key distribution, three pulse peaks are input to a single-photon detector in one clock period, the middle interference peak is a useful pulse carrying information, and only one pulse peak is in one clock period of the unequal-arm Mach-Zehnder interference ring, so that the unequal-arm Mach-Zehnder interference ring is suitable for quantum key distribution with high speed and low error code.
The encryption module 105 quantum-encrypts the communication data acquired from the computer module 103 by using the quantum key acquired by the quantum key terminal 104, and converts the plaintext into the ciphertext.
The communication information to be transmitted by the transmission module 106 and the computer module 103 is converted into corresponding electric signals by the transmission module, modulated onto optical carriers generated by the laser by the modulator, and then transmitted to the air space by the optical transmitting antenna. The emitted laser signals are transmitted through an atmospheric channel and reach a communication receiving end.
Further, the most core component of the transmitting module 106 is a laser for emitting light pulses to generate continuous light, preferably modulated by an intensity modulator into a pulse sequence with a half-width height of 15ps and a repetition frequency of 10 GHz. Further, lasers of different wavelengths have different attenuations in the atmosphere. Preferably, laser with the wavelength of 0.4-0.7 μm and the wavelengths of 0.9, 1.06, 2.3, 3.8 and 10.6 μm is used as an emission source, the attenuation is small, and the laser with the wavelength of 0.6 μm has strong penetrating capacity. Preferably, a plurality of laser emission sources with different wavelengths are used simultaneously, so that a plurality of laser signals with different wavelengths can be generated simultaneously, wavelength division multiplexing with multiple wavelengths and dense wavelength division multiplexing laser communication are realized, and the communication capacity is improved.
Further, a high-frequency power amplifier is used to convert the direct current signal into a high-frequency alternating current signal for output. Preferably, the amplifier can be divided into three operating states of A, B and C according to the difference of current conduction angles. The current flowing angle of the class-A amplifier is 360 degrees, and the amplifier is suitable for small-signal low-power amplification; the conduction angle of the class B amplifier current is about 180 °; the conduction angle of the class C amplifier current is less than 180 °. The electric signal is amplified by the amplifier and transmitted to the laser part, so that the signal ground conversion and transmission are facilitated, and the fuzzy distortion of the signal ground is avoided. Preferably, a digital laser is used. The modulator is like a reflective micro liquid crystal video, and the required laser mode can be obtained only by inputting a specific image to the display screen through a computer. Digital lasers can create almost any lasing mode. Different laser beams are selected under different communication environments to adapt to most communication environments.
The aiming mechanism 107, which is used for aiming at the transmitting module 106 and the receiving module 101 of both communication parties, mainly comprises four parts, namely an optical antenna servo platform, an error detection processor, a beacon signal generator, a beacon light source and a control computer. The optical antenna servo stage is used to make the mechanical displacement (or rotation angle) of the output accurately track the displacement (or rotation angle) of the input. The beacon signal generator and the beacon light source are used for generating beacon signals, outputting intermediate frequency signals through secondary frequency conversion and supplying the intermediate frequency signals to the optical antenna servo platform and the control computer for use. The error detection processor can calculate the direction of laser aiming and beacon data to obtain aiming error. The control computer can calculate and generate a control logic signal to drive the motor according to the aiming error calculated by the error detection processor, and the optical antenna servo platform determines the rotation direction of the antenna according to the driving voltage, so that the laser antenna is ensured to accurately point to the opposite communication party.
Fig. 2 is a quantum cryptography communication flow chart of a free-space laser communication system based on quantum cryptography according to an embodiment of the present invention.
The first step is as follows: and networking. The system forms a communication network through an aiming mechanism 107, a computer module 103 determines communication requests of nodes of two parties, further forms a communication network with multiple communication nodes according to needs, and optimizes a network topology structure;
the second step is that: and (5) initializing a quantum key. The two communication parties apply for laser communication,two sides select 8 pairs of entangled photons from the entangled photon pairs, and the entangled photon pairs can be expressed as quantum states
Having a wavelength of (b)1,g1),(b2,g2),...,(b8,g8)；
Further, the quantum key terminal distributes different entangled photon pairs according to each communication request;
at the moment, the quantum key terminal obtains the requests of both communication parties, and both parties analyze the communication request to make an entangled photon distribution scheme;
the third step: and negotiating the quantum key. The quantum key terminal publishes the distribution information of the entangled photon pairs to both communication parties through a classical channel, and then uses a quantum channel to send the information of the entangled photon pairs as a quantum key;
further, the two parties measure and evaluate the quantum sequence, when the measurement error rate is less than a preset threshold value, the quantum communication is considered to be safe, the business of the current laser communication is accepted, if the error exceeds the preset threshold value, the quantum communication is considered to be invalid, and the current quantum communication is abandoned;
and fourthly, encrypting and transmitting the information. After the quantum communication security is confirmed, the corresponding key is used for encrypting the data to be transmitted, and the encrypted ciphertext is used as the quantum communication service data.
Preferably, through wavelength division multiplexing, dense wavelength division multiplexing and time division multiplexing decoding technologies, each communication node completes QKD according to entangled photon distribution information, performs multi-band information transmission of the same channel, and improves communication transmission capacity.
The fifth step: and (6) decrypting the data. And the two communication parties arrange a laser communication decoding sequence according to the distribution information and then decode the encrypted ciphertext into plaintext according to a quantum decryption program.
Claims (7)
1. A free space laser communication system based on quantum cryptography, comprising: the system comprises a receiving module (101), a data decryption module (102), a computer module (103), a quantum key terminal (104), a data encryption module (105), a transmitting module (106) and an aiming mechanism (107); the system is used for two-way communication between two movable or fixed communication nodes, and can realize quantum encryption and quantum decryption of communication signals; a plurality of communication nodes can communicate with each other to freely form a communication network;
the receiving module (101) is a laser sensing device and is used for capturing a laser signal and a communication request signal of a communication node of a transmitting party, screening the obtained laser signal carrying target information by a photoelectric detector, amplifying the signal by an amplifier, demodulating by a pulse code modem, and converting an analog signal into a digital signal;
the data decryption module (102) is connected with the receiving module (101) and the quantum key terminal (104), the data decryption module (102) obtains a corresponding quantum key from the quantum key terminal (104), decrypts the encrypted digital signal transmitted by the receiving module (101), and restores the ciphertext into the original text;
the computer module (103) is connected with the data decryption module (102) and the data encryption module (105) and is used for responding to a laser communication request, completing flexible networking and topology optimization of a communication node, processing decrypted data acquired from the data decryption module (102) and completing data encryption and communication preparation of transmitted data by using the data encryption module (105);
the quantum key terminal (104) is connected with the data decryption module (102) and the data encryption module (105), can perform quantum entanglement operation, and communicates with the opposite communication node through a quantum channel to acquire a quantum key for encryption and decryption so as to complete decryption of received data or encryption of transmitted data;
the data encryption module (105) is connected with the quantum key terminal (104) and the computer module (103) and is used for encrypting data, when the data needs to be transmitted, the data needing to be transmitted is received from the computer module (103), the quantum key acquired by the quantum key terminal (104) is adopted to carry out quantum encryption on the communication data acquired from the computer module (103), and a plaintext is converted into a ciphertext;
the transmitting module (106) is connected with the data encryption module (105) and is used for transmitting data to be transmitted to a communication node of a receiving party in a laser mode, demodulating and amplifying necessary signals of the digital signals after quantum encryption through a pulse code demodulator, converting the signals into analog signals, and transmitting the analog laser signals to the receiving party by a laser; the laser signal of a plurality of different wavelengths can be generated simultaneously so as to realize wavelength division multiplexing or dense wavelength division multiplexing;
the system also comprises an aiming mechanism (107) which simultaneously controls the azimuth angles of the transmitting module (106) and the receiving module (101) and is used for aligning the laser receiving module (101) and the transmitting module (106) of both communication parties, the computer module (103) responds to a communication request to determine the coordinates and the azimuth of the target of both communication parties, and the aiming mechanism (107) accurately adjusts the laser transmitting angle of the transmitting module (106) and the angle of the receiving module (101) according to the coordinates and the azimuth information of both communication parties;
the aiming mechanism (107) is used for aligning the transmitting module (106) and the receiving module (101) of the two communication parties, and the aiming mechanism (107) is composed of four parts, namely: the system comprises an optical antenna servo platform, an error detection processor, a beacon signal generator, a beacon light source and a control computer;
the optical antenna servo platform is used for enabling the output mechanical displacement or corner to accurately track the input displacement or corner;
the beacon signal generator and the beacon light source are used for generating beacon signals, outputting intermediate frequency signals through secondary frequency conversion and supplying the intermediate frequency signals to the optical antenna servo platform and the control computer for use;
the error detection processor can calculate the azimuth aimed by the laser and beacon data to obtain an aiming error;
the control computer can calculate and generate a control logic signal according to the aiming error calculated by the error detection processor to drive the motor to drive the transmitting module (106) and the receiving module (101) to rotate, and the optical antenna servo platform determines the rotation direction of the antenna according to the driving voltage, so that the laser antenna can be ensured to accurately point to the opposite communication party.
2. The quantum cryptography-based free-space laser communication system according to claim 1, wherein: the computer module (103) can respond to and record the communication node information and establish a routing table of the communication; calculating the topological connection and routing of the network during multi-node communication to form a self-organizing network, adding the freely added communication nodes into a routing table, and deleting the freely separated communication nodes from the routing table; calculating the optimal path through a routing algorithm of a computer, finding out the address of a sending node or a gateway at the next stage, and automatically updating routing information and communication node information; the network topology can be optimized in a complex terrain or obstacle environment or under the meteorological conditions of dense clouds, rain and snow, the curve transmission and the breakpoint continuous transmission of laser communication are realized, and therefore communication signals can bypass obstacles, complex areas or bad meteorological areas; when a communication node in the network is attacked or fails, other communication nodes can be selected through calculation to complete the continuous transmission of communication data.
3. The quantum cryptography-based free-space laser communication system according to claim 1, wherein: the receiving module (101) is arranged on the surface of the communication node and is used for converting the digital signal and the analog signal into each other; the receiving module (101) comprises an optical receiving antenna, an optical filter and a light detector; the optical receiving antenna comprises a lens or a reflector, focuses the received optical signal and then sends the optical signal to the optical detector; the optical detector amplifies the laser signal to recover an electric signal, and the electric signal is sent to the electric receiver module to be demodulated into original information.
4. A free space laser communication method based on quantum encryption is characterized by comprising the following steps: the system comprises a receiving module (101), a data decryption module (102), a computer module (103), a quantum key terminal (104), a data encryption module (105) and a transmitting module (106);
the two communication parties aim at a transmitting module (106) and a receiving module (101) of the two parties through an aiming mechanism (107), the receiving module (101) captures laser signals, and the laser signals are amplified, processed, quantized and encoded to be converted into digital signals through broadband amplification and pulse code modulation; then, the data decryption module (102) decrypts the signal by using the quantum key acquired by the quantum key terminal (104), and sends the decrypted data to the computer module (103); after the computer module (103) processes data, the data to be sent is transmitted to the data encryption module (105), a quantum key terminal (104) acquires a quantum key, encrypts the data and sends the data to a receiving party through a laser channel;
the aiming mechanism (107) is used for aligning the transmitting module (106) and the receiving module (101) of the two communication parties, and the aiming mechanism (107) is composed of four parts, namely: the system comprises an optical antenna servo platform, an error detection processor, a beacon signal generator, a beacon light source and a control computer;
the optical antenna servo platform is used for enabling the output mechanical displacement or corner to accurately track the input displacement or corner;
the beacon signal generator and the beacon light source are used for generating beacon signals, outputting intermediate frequency signals through secondary frequency conversion and supplying the intermediate frequency signals to the optical antenna servo platform and the control computer for use;
the error detection processor can calculate the azimuth aimed by the laser and beacon data to obtain an aiming error;
the control computer can calculate and generate a control logic signal according to the aiming error calculated by the error detection processor to drive the motor to drive the transmitting module (106) and the receiving module (101) to rotate, and the optical antenna servo platform determines the rotation direction of the antenna according to the driving voltage, so that the laser antenna can be ensured to accurately point to the opposite communication party.
5. A free space laser communication method based on quantum encryption is characterized by comprising the following steps:
the first step is as follows: networking, namely forming a communication network through an aiming mechanism (107), determining communication requests of nodes of two parties by a computer module (103), forming the communication network of multiple communication nodes according to needs, and optimizing a network topology structure;
the second step is that: initializing a quantum key; two communication parties apply for laser communication and the two parties are subjected to entanglement photon pair8 pairs of entangled photons are selected, and the entangled photon pairs can be expressed in quantum state
The wavelengths are respectively:
(b1,g1),(b2,g2),...,(b8,g8)；
further, the quantum key terminal (104) allocates different entangled photons according to each communication request;
at the moment, the quantum key terminal (104) obtains the requests of both communication parties, and both communication parties analyze the communication requests to make an entangled photon distribution scheme;
the third step: negotiating a quantum key; the quantum key terminal (104) publishes the entangled photon distribution information to both communication parties through a classical channel, and then uses the quantum channel to send the entangled photon information as a quantum key;
further, the two parties measure and evaluate the quantum sequence, when the error is smaller than a preset threshold value, the quantum communication is considered to be safe, and the business of the laser communication is received and is to be carried out; if the error exceeds a preset threshold value, the quantum communication is considered to be invalid, and the quantum communication is invalidated;
fourthly, encrypting and transmitting information; after the quantum communication security is confirmed, encrypting the data to be transmitted by using a corresponding secret key, and using the encrypted ciphertext as the quantum communication service data;
through wavelength division multiplexing, dense wavelength division multiplexing and time division multiplexing decoding technologies, each communication node completes QKD according to entangled photon distribution information, multi-band information transmission of the same channel is carried out, and communication transmission capacity is improved;
the fifth step: data decryption; the two communication parties arrange a laser communication decoding sequence according to the distribution information and then decode the encrypted ciphertext into a plaintext according to a quantum decryption program;
the aiming mechanism (107) is used for aligning the transmitting module (106) and the receiving module (101) of the two communication parties, and the aiming mechanism (107) is composed of four parts, namely: the system comprises an optical antenna servo platform, an error detection processor, a beacon signal generator, a beacon light source and a control computer;
the optical antenna servo platform is used for enabling the output mechanical displacement or corner to accurately track the input displacement or corner;
the beacon signal generator and the beacon light source are used for generating beacon signals, outputting intermediate frequency signals through secondary frequency conversion and supplying the intermediate frequency signals to the optical antenna servo platform and the control computer for use;
the error detection processor can calculate the azimuth aimed by the laser and beacon data to obtain an aiming error;
the control computer can calculate and generate a control logic signal according to the aiming error calculated by the error detection processor to drive the motor to drive the transmitting module (106) and the receiving module (101) to rotate, and the optical antenna servo platform determines the rotation direction of the antenna according to the driving voltage, so that the laser antenna can be ensured to accurately point to the opposite communication party.
6. The free space laser communication method based on quantum cryptography according to claim 5, characterized in that: the specific laser communication mode uses a plurality of communication nodes for combination to form a more complex quantum encryption laser communication mode, including a relay amplification mode, a ring network or a star network, and realizes quantum encryption laser communication at a longer distance and a laser communication network with a flexible space structure, and at the moment, the quantum key terminal (104) distributes entangled photons according to different conditions; after the distribution of entangled photons is completed, the computer module (103) immediately publishes distribution information to a corresponding laser communication node of the network through a classical channel, and then the next node forwards encrypted information;
in a quantum communication network composed of a plurality of nodes, a specific networking plan is as follows:
several parties of laser communication are shown as A, B, …, G and the like, a server is shown as S, each communication node can be fixed or mobile, each communication node can be in a network all the time during communication or can leave the communication network at any time, and the basic laser communication modes include the following modes:
mode(s)1: point-to-point laser communication modes, for example:
each communication node can freely join or leave the communication network at any time in the communication process
Mode 2: point-to-server laser communication modes, such as:
the communication node S serving as a server is generally always in the network during communication, but may be fixed or mobile;
mode 3: a multi-point-to-point laser communication mode,
the communication node a is always in the network, fixed or mobile, during the communication.
7. The free space laser communication method based on quantum cryptography according to claim 5, characterized in that: in a quantum communication network composed of a plurality of nodes, in the second step: quantum key initialization, and the corresponding distribution of entangled photons is as follows:
mode 1: (g)1→A,b1→B),(g2→C,b2→D),(g3→E,b3→F),(g4→G,b4→H)；
Mode 2: (g)1→A,b1→S),(g2→B,b2→S),(g3→C,b3→S),(g4→D,b4→S)，(g5→E,b5→S),(g6→F,b6→S),(g7→G,b7→S),(g8→H,b8→S)；
Mode 3: (g)1→A,b1→B),(b3→A,g3→C),(b4→A,g4→D),(b5→A,g5→E)，(b6→A,g6→F),(b7→A,g7→G),(b8→A,g8→H),(g2→A,b2→S)。
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