CN112929094B - High-speed safe optical communication system for key ciphertext simultaneous transmission - Google Patents
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Abstract
The invention discloses a high-speed secure optical communication system for simultaneously transmitting a key ciphertext and belongs to the technical field of secure communication. The invention hides the ASE noise with hidden key information in the ciphertext information light again, so that an eavesdropper is difficult to find effective information, and the safety of the system is improved. The thickness modulation of signals is realized in an optical domain by adjusting the optical power, the quantum noise stream encryption with higher covering level number is realized by using the thickness modulation, and the safety performance is improved. The key information is hidden in ASE noise through a white light interference structure, and the ciphertext information is modulated into a transmission ciphertext by utilizing the optical domain thickness. And then the channel for transmitting the key and the channel for transmitting the ciphertext are coupled to the same optical fiber through the optical multiplexing structure, so that the key ciphertext is transmitted simultaneously, namely, the key ciphertext is transmitted in the same optical fiber, the device has a simple structure, and the cost for sharing the key by the transmitting side and the receiving side is greatly saved.
Description
Technical Field
The invention belongs to the technical field of secure communication, and particularly relates to a high-speed secure optical communication system for key ciphertext simultaneous transmission.
Background
With the explosive growth of optical communication-related applications, security issues in optical communication have become very important. The traditional secret communication technology based on the data link layer is limited by an electronic processing bottleneck, meanwhile, the attack of a super computer and a quantum computer is difficult to resist, and the safety of the traditional secret communication technology is challenged. The secure optical fiber communication technology based on the physical layer has become a research hotspot due to the advantages of hardware encryption, no limitation of electronic processing bottleneck and the like. Quantum key distribution can provide absolute security in information theory due to the physical characteristics of quantum, but the device structure is more complex, and the rate of key distribution is lower, so that the key distribution is also more limited. Meanwhile, the current secure communication system structure generally adopts key ciphertext separation transmission, so that the cost of the sending end and the receiving end is greatly increased. Therefore, the key distribution rate is improved, the effective information is transmitted in a hiding mode, and the system without key distribution is realized, so that the key distribution method has important significance for improving the safety of a safety communication system and reducing the system cost.
In an encryption mode, a traditional stream cipher is formed by mapping a codebook generated by a seed key, a ciphertext and a plaintext have the same modulation format, and the security of the traditional stream cipher is gradually weakened along with the improvement of computing power and the development of a quantum computer. The quantum noise stream encryption mode utilizes the inevitable quantum noise in the system to cover signals, the difference between levels is reduced along with the increase of the number of levels, and the safety is correspondingly improved when the number of levels covered by the quantum noise is more. Because of the limitations of DAC bit number and signal transmission rate, the number of levels that can be covered by ordinary quantum noise stream encryption is limited, some research groups realize high-bit quantum noise stream encryption by coarse and fine modulation of low-bit DAC in the electrical domain at present, but there are problems of low modulation depth and signal-to-noise ratio, and the like, and realizing an enhanced quantum noise stream encryption in the optical domain is also a problem to be solved urgently.
Disclosure of Invention
Aiming at the defects and improvement requirements of the prior art, the invention provides a high-speed safe optical communication system for simultaneously transmitting a key ciphertext, which aims to realize enhanced quantum noise stream encryption on an optical domain by adjusting the optical power proportion of two parallel optical paths modulated by the thickness of a low-digit DAC; modulating information is concealed and transmitted at high speed through a white light interference structure; and the key ciphertext is transmitted in one optical fiber simultaneously through the optical multiplexing device.
To achieve the above object, according to one aspect of the present invention, there is provided a high-speed secure optical communication system for key ciphertext concurrent transmission, the system comprising: the device comprises a transmitting end, a signal transmission module and a receiving end;
the transmitting end includes: the device comprises a hidden signal transmitting module and a public signal transmitting module; the receiving end comprises a hidden signal receiving module, a public signal receiving module and a digital signal processing module;
the secret signal transmitting module is used for modulating the secret key information electric signal encrypted by the quantum noise flow to a wide-spectrum noise optical carrier, transmitting the modulated optical signal to the signal transmission module as a secret signal, and the spectral width of the wide-spectrum noise optical carrier is higher than 10 nm;
the public signal transmitting module is used for modulating the ciphertext information electric signal encrypted by the quantum noise flow to a narrow linewidth optical carrier, and transmitting the modulated optical signal to the signal transmitting module as a public signal, wherein the linewidth of the narrow linewidth optical carrier is lower than 100 MHz;
the signal transmission module is used for respectively transmitting the hidden signal and the public signal to the hidden signal receiving module and the public signal receiving module of the receiving end;
the secret signal receiving module is used for receiving the secret signal, carrying out photoelectric conversion and recovering key information used for quantum noise stream encryption;
the public signal receiving module is used for receiving public signals, carrying out photoelectric conversion and recovering ciphertext information;
and the digital signal processing module is used for carrying out digital signal processing on the recovered key information and the recovered ciphertext information and decrypting to obtain a plaintext.
Preferably, the common signal transmitting module includes:
the narrow linewidth light source is used for generating narrow linewidth laser, and transmitting the narrow linewidth laser to the first intensity modulation unit and the second intensity modulation unit respectively after shunting;
the first intensity modulation unit is used for carrying out intensity modulation on M bits before the PAM electrical signal on one path of optical carrier and transmitting the optical signal after coarse modulation to the power regulation unit;
the second intensity modulation unit is used for carrying out intensity modulation on N bits after the PAM electrical signal is carried out on the other path of optical carrier, and transmitting the finely modulated optical signal to the power regulation unit;
and the power adjusting unit is used for adjusting the power proportion of the two paths of optical signals and coupling the two optical paths, so that the adjusted coupled optical signal is a uniform M + N-bit PAM optical signal.
Preferably, the common signal transmitting module specifically includes the following devices:
a laser for emitting a light carrier to the third optical coupler;
the third optical coupler is used for branching the optical carrier, one path of the optical carrier is transmitted to the second polarization controller, and the other path of the optical carrier is transmitted to the third polarization controller;
the second polarization controller is used for adjusting the polarization state of the optical carrier to keep consistent with the polarization main shaft of the crystal in the second modulator and transmitting the adjusted optical carrier to the second modulator;
the third polarization controller is used for adjusting the polarization state of the optical carrier to keep consistent with the polarization main shaft of the crystal in the third modulator and transmitting the adjusted optical carrier to the third modulator;
the second intensity modulator is used for modulating the roughly modulated electrical signal data onto an optical carrier and transmitting the modulated optical signal to the 90-degree phase shifter;
the third intensity modulator is used for modulating the fine modulation electric signal data to an optical carrier and transmitting the modulated optical signal to the first variable optical attenuator;
a 90 ° phase shifter for performing a fixed pi/2 phase shift on the received coarse modulated optical signal and transmitting the optical signal to a fourth optical coupler;
the first variable optical attenuator is used for attenuating the fine modulation optical signal and transmitting the fine modulation optical signal to the fourth optical coupler;
and the fourth optical coupler is used for combining the optical signals and transmitting the optical signals to the multiplexer.
Preferably, the second intensity modulator and the third intensity modulator are mach-zehnder modulators for modulating the electrical signal to the amplitude of the optical signal, and the mach-zehnder modulators operate in a linear region of the modulation characteristic curve.
Preferably, the signal transmission module multiplexes the hidden signal and the common signal into the same optical fiber for transmission, and demultiplexes two paths of signals to the hidden signal receiving module and the common signal receiving module at a receiving end.
Preferably, the signal transmission module specifically includes the following devices:
the multiplexer is used for multiplexing the hidden signal and the public signal and transmitting the multiplexed optical signal to a standard single-mode optical fiber;
the standard single-mode optical fiber is used as a transmission channel of an optical signal and transmits the optical signal to the dispersion compensation optical fiber;
the dispersion compensation optical fiber is used for compensating dispersion generated by transmitting an optical signal in the optical fiber, and the compensated optical signal is transmitted to the optical amplifier;
the optical amplifier is used for compensating the optical power loss of the optical signal in the transmission process of the optical fiber, and the compensated optical signal is transmitted to the demultiplexing filter;
and the demultiplexing filter is used for demultiplexing the hidden optical signal and the public optical signal and transmitting the demultiplexed optical signals to the hidden signal receiving module and the public signal receiving module.
Preferably, the signal transmission module realizes multiplexing through a wavelength division multiplexing device or an optical coupler.
Preferably, the concealment signal transmitting module comprises:
the noise light source generating unit is used for generating a wide-spectrum noise light carrier wave in a linear polarization state and transmitting the wide-spectrum noise light carrier wave to the first Mach-Zehnder interferometer structural unit;
and the first Mach-Zehnder interferometer structural unit is used for modulating the secret key information encrypted by the quantum noise stream on the phase of the optical carrier.
Preferably, the concealment signal receiving module includes:
the second Mach-Zehnder interferometer structural unit is used for matching two paths of delay differences in the hidden signal transmitting module to be within the coherence length of the wide-spectrum noise light source and transmitting the delay differences to the first photoelectric conversion unit;
and the first photoelectric conversion unit is used for converting the optical signal into an electric signal, recovering key information used for encrypting the quantum noise flow which is transmitted in a hiding way, and transmitting the key information to the digital signal processing module.
Preferably, the common signal receiving module includes:
the optical filtering attenuation unit is used for filtering out-of-band noise of the demultiplexed public signal, and transmitting the optical power of the attenuator to the second photoelectric conversion unit after the optical power is received by the second photoelectric conversion unit;
and the second photoelectric conversion unit is used for receiving the filtered and attenuated public signal, demodulating a recovery ciphertext and transmitting the recovery ciphertext to the digital signal processing module.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) the invention hides ASE Noise (Amplifier spontaneous emission Noise) with hidden key information in the ciphertext information light again, so that an eavesdropper is difficult to find effective information, and the safety of the system is improved.
(2) Compared with the traditional quantum noise stream encryption, the invention provides improved coarse and fine modulation, the signal coarse and fine modulation is realized in an optical domain by adjusting the optical power (rather than the electric power), and an electric domain signal generated by a low-digit DAC (Digital-Analog converter) is synthesized into a high-digit encrypted signal, so that the masking level number is more, the quantum noise stream encryption with higher masking level number is realized by using the high-digit encrypted signal, and the safety performance is improved, namely the enhanced quantum noise stream cipher safety communication is realized; and because the power is adjusted in the optical domain instead of the electric domain to adjust the peak value of the electric signal, the modulation depth and the signal-to-noise ratio of the signal are improved, and the communication performance is improved.
(3) Compared with schemes such as quantum key distribution and the like, the method has the advantages that the key information is hidden and transmitted through a white light interference structure, namely the key information is hidden in ASE noise, ciphertext information is modulated into transmission ciphertext by utilizing the optical domain thickness, and the ciphertext has the level number with a very high order due to the adoption of an enhanced quantum noise stream encryption mode. And then the channel (secret channel) for transmitting the key and the channel (public channel) for transmitting the cipher text are coupled to the same optical fiber through the optical multiplexing structure, so that the cipher text of the key is transmitted simultaneously, namely the cipher text of the key is transmitted in the same optical fiber, the device has a simple structure, and the cost for sharing the key by the transmitting side and the receiving side is greatly saved.
Drawings
FIG. 1 is a schematic diagram of the system provided by the present invention;
FIG. 2 is a system block diagram of an embodiment of the present invention;
FIG. 3 is a schematic diagram of a quantum noise stream cipher provided by the present invention;
FIG. 4 is a schematic diagram of the principle of coarse and fine modulation in the electrical domain based on a single DD-MZM (Dual-Drive Mach-Zehnder Modulator) provided by the present invention;
FIG. 5 is a graph of levels before and after encryption and equalization of quantum noise stream at the receiving end according to the present invention;
FIG. 6 is a schematic diagram illustrating the principle of hidden transmission of white light interference provided by the present invention;
fig. 7 is a signal spectrum diagram of a signal transmission with concealment provided by the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, the high-speed secure optical communication system for key ciphertext concurrent transmission provided by the present invention includes: the device comprises a hidden signal transmitting module, a public signal transmitting module, a signal transmission module, a hidden signal receiving module, a public signal receiving module and a digital signal processing module.
The hiding signal transmitting module utilizes the noise light source generating unit to generate a wide-spectrum noise optical carrier in a linear polarization state, and utilizes the first Mach-Zehnder interferometer structure unit to modulate the secret key information encrypted by the quantum noise stream on the optical carrier phase, so that two optical links of the interferometer have certain delay difference, the interference phenomenon can not occur, and the hiding of effective information is realized. That is, the effective information is modulated in the optical phase and hidden in the wide-spectrum noise as a hidden signal.
The public signal transmitting module utilizes a narrow-linewidth light source to generate a narrow-linewidth laser carrier, utilizes a first modulation unit to modulate information needing coarse modulation on the intensity of the optical carrier, utilizes a second modulation unit to modulate information needing fine modulation on the intensity of the other optical carrier, utilizes a power adjusting and coupling unit to realize two-path optical power proportion adjustment, couples two optical paths and realizes optical coarse and fine modulation on an optical domain. Namely, the encrypted ciphertext information encrypted by the modulation enhanced quantum noise stream on the optical carrier is used as a public signal.
And the signal transmission module is used for carrying out signal multiplexing, transmission and signal quality compensation through the optical multiplexing unit and the signal transmission and compensation unit.
The hidden signal receiving module enables the received and secretly transmitted optical signals to enter the second Mach-Zehnder interferometer structural unit, the two paths of delay differences in the hidden signal transmitting module are matched in the structure and are within the coherence length of the broad-spectrum noise light source, then the two paths of delay differences are transmitted to the first photoelectric conversion unit, photoelectric conversion is carried out, and key information used for encrypting the secretly transmitted quantum noise flow is recovered.
And the public signal receiving module processes the optical signal by using the optical filtering attenuation unit, transmits the optical signal to the second photoelectric conversion unit and receives the public signal demodulation recovery ciphertext.
And the digital signal processing module is used for carrying out digital signal processing on the recovered key information and the recovered ciphertext information and decrypting to obtain a plaintext.
To further illustrate the system of the present invention, a high-speed secure optical communication system for key ciphertext simulcast will now be described in detail with reference to the embodiments.
Fig. 2 is a system block diagram of an embodiment of the present invention.
Further, the public signal transmitting module is discussed to realize the enhanced quantum noise stream encryption by combining formula derivation and a theoretical model.
The traditional stream cipher has a great hidden trouble that the encrypted ciphertext and the plaintext before encryption are usually signals in the same format, for example, for an on-off keying signal, a key sequence obtained by performing exclusive or operation on the on-off keying signal and a key is also an on-off keying signal. Therefore, the non-cooperative party can obtain the same ciphertext information as the cooperative party, and the secret key is cracked through various attack means such as quick correlation attack and the like, so that the plaintext information is obtained. Quantum noise stream ciphers differ from conventional stream ciphers in that they exploit the properties of quantum noise, including spontaneous emission noise of erbium-doped fiber amplifiers and shot noise of photodetectors, to achieve secure transmission of signals, which inevitably exist widely in various communication systems. As shown in fig. 3, which is a schematic diagram of a quantum noise stream cipher, the quantum noise stream cipher maps a plaintext signal into a super-dense modulated signal with the help of a key, so that an euclidean distance between each level of the signal is very short and much smaller than a scale of the quantum noise, and under the concealment of the quantum noise, a non-partner cannot make a correct decision to obtain information of a ciphertext, so that an existing attack means for a conventional stream cipher cannot be used for attacking the ciphertext.
The security performance of quantum noise stream encryption is mainly determined by the number of masking levels, namely the number of bits of a modulated optical signal, and Pulse Amplitude Modulation (PAM) is performed by using a single intensity modulator, so that the higher the pulse amplitude is, the higher the number of masking levels is, and the security is determined by the number of bits of a digital-to-analog converter (DAC). For example, 256 masking levels can be implemented using an 8-bit DAC. In order to overcome the shortage of DAC digit, the digit ' sum ' of DAC is mainly carried out by coarse and fine modulation, that is, the effect of high-digit DAC is realized by using the ' sum ' of multiple low-digit DACs, for example, 2 can be realized by using two 8-digit DACs to carry out ' sum16The number of levels is covered, and the safety is greatly improved.
Conventional coarse and fine modulation is mainly done in the electrical domain with a single double-drive mach-zehnder modulator (DD-MZM). As shown in FIG. 4, for a single DD-MZM, the upper arm inputs the electrical signal of M-bit, the lower arm inputs the electrical signal of N-bit, and the output optical field is assumed to be E0The output signal can be expressed as:
wherein S iscoarseAnd SfineFor the coarse and fine modulated signals, respectively, to make the synthesized PAM signal level intervals uniform, the coarse and fine modulated signals must satisfy the following peak-to-peak relationship:
wherein, M and N are binary digits of the coarse and fine modulation signals, respectively, so that the peak-to-peak difference of the electrical signals is very large in the conventional coarse and fine modulation scheme. This results in that, in the case where the peak-to-peak amplitude of one of the signals is constant, the peak-to-peak value of the other signal is very small, and the signal-to-noise ratio is very low, which results in deterioration of communication performance.
In an example of the present invention, an improved coarse and fine modulation architecture is shown in fig. 2 for a common signal transmission module, comprising: the laser device comprises a laser, a third optical coupler, a second polarization controller, a third polarization controller, a second modulator, a third modulator, a 90-degree phase shifter, a first variable optical attenuator and a fourth optical coupler. Narrow linewidth laser output by the laser is divided into two paths which respectively enter a second modulator and a third modulator to be subjected to coarse modulation and fine modulation, a coarse modulation light path realizes pi/2 phase shift through a 90-degree phase shifter, a fine modulation light path performs optical power attenuation through a first variable optical attenuator until the optical power of two parallel links meets a certain proportion requirement, and the two parallel links are combined and output through a fourth coupler. For the purpose of analysis, it is assumed that the second and third modulators are both MZM modulators biased at linear points, and each device is in an ideal state.
Improved coarse-fine modulation uses two MZMs in parallel to achieve coarse-fine modulation of the signal. The signals respectively output from the single MZM can be expressed as:
the total signal output is:
where α is the attenuation of the optical attenuation used to modulate the intensity of the optical signal to meet the peak-to-peak requirement of the signal, and j is the resulting fixed π/2 phase shift. The light intensity of the signal after passing through the light detector is as follows:
wherein,
wherein,
the additional phase shift caused by the slight time-varying optical path difference generated by the two optical paths under the influence of the environment such as stress and temperature can be ignored in the integrated device.
Further, in the present example, as shown in the common signal receiving module in fig. 2, the module includes: the optical filter, the second variable optical attenuator, the second photoelectric detector and the oscilloscope. The received optical signal is filtered, the optical power is attenuated, then the optical signal enters a photoelectric detector for photoelectric conversion, and then the optical signal is converted into a digital signal processing module by an oscilloscope for subsequent digital signal processing.
As shown in fig. 5, which is a level diagram before and after equalization at the receiving end after quantum noise stream encryption. The analysis shows that the system has better encryption effect, and the decoding of a legal receiver can also obtain lower error rate.
In general, the method for implementing the enhanced quantum noise stream encryption by adjusting the optical power of the parallel link to perform the optical coarse-fine modulation in this embodiment greatly improves the security performance and the communication performance compared with the conventional scheme.
Further, the realization of white light interference hidden transmission by the hidden signal transmitting module and the hidden signal receiving module is discussed by combining formula derivation and a theoretical model.
The principle of hiding transmission information by white light interference is shown in fig. 6, and four light paths are provided for a wide-spectrum light source from an emitting end to a receiving end: (a) 1-3; (b) 1-4; (c) 2-3; (d) 2-4. According to the theory of optical interference, only light within the coherence length can interfere, that is, only two optical paths (a) and (d) interfere when the delay difference between the two optical paths is within the coherence length of the light source by adjusting the delay lines t1 and t2, and data loaded on the optical phase on the link 2 is demodulated. At the photodetector end, two delay lines t1 and t2 are adjusted,
when the difference value of two paths of time delay is within the coherence length, I is 2| E | luminance2+2|E|2cos(u(t))；
When the two paths of delay difference values are beyond the coherence length, I is 4| E2。
As shown in fig. 2, the concealed signal transmitting module includes: the device comprises a wide-spectrum noise light source, a polarizer, a first optical coupler, a first polarization controller, a first modulator, a first optical delayer and a second optical coupler. The wide spectrum light with partial line is divided into two paths, one path of light is subjected to information up-regulation on the light phase through a phase modulator, the other path of light is subjected to certain delay difference through an optical delayer, and the two paths of light are combined through a coupler. The light source adopted in the module is an ASE noise light source, the spectrum width is 40nm, when the spectrum shape is approximate to a rectangle, the spectrum is converted into a spectrum with the coherence length of 60 mu m, namely the interference can be generated only when the difference of the lengths of the optical links of the two arms is within 60 mu m. And adjusting the optical delayer to ensure that the difference of the lengths of the two links exceeds the coherence length, namely ensuring that the interference does not occur in the hiding signal transmitting module.
In other words, in the hidden signal transmitting module, the key information used for quantum noise stream encryption is loaded on the phase of the wide-spectrum optical noise, the modulated spectrum information is simulated by the system as shown in fig. 7, the amplitude in the time domain is constant and hidden in the noise, the spectrum of the modulated information is hidden in the broadband noise spectrum in the spectrum domain, and it is difficult for an eavesdropper to know that the effective information exists in the spectrum, so that the hidden transmission is realized.
As shown in fig. 2, the concealed signal receiving module includes: a fifth optical coupler, a second optical delayer, a sixth coupler, a first photoelectric detector and an oscilloscope. The received optical signal is divided into two paths, wherein one path is delayed by matching with the optical delayer, so that the interference phenomenon can be generated only when the delay of the hidden signal transmitting module is kept within the coherence length of the wide-spectrum noise light source, and the key information used for encrypting the quantum noise flow modulated on the optical phase is demodulated.
Interference can be generated only when the optical delayer is adjusted to enable the optical path difference between the hidden signal transmitting module and the hidden signal receiving module to be within the coherence length of the wide-spectrum light source, data loaded on an optical phase on the link 1 are demodulated, the delay matching is better, and the demodulation performance is better.
Further, as shown in fig. 2, the signal transmission module includes: multiplexer, standard single mode fiber, dispersion compensation fiber, optical amplifier, and de-multiplexing filter. The optical signals of the hidden signal transmitting module and the public signal transmitting module are multiplexed into a standard single-mode optical fiber for transmission, the dispersion compensation optical fiber and the optical amplifier are used for respectively carrying out dispersion compensation and power compensation, and then the signals are demultiplexed to the hidden signal receiving module and the public signal receiving module through the demultiplexing filter. The secret key information encrypted by the quantum noise stream is loaded on the secret signal transmitting module, the cipher text information encrypted by the quantum noise stream is loaded on the public signal transmitting module, and the simultaneous transmission of the secret key and the cipher text is realized through multiplexing.
According to the content, the high-speed secure optical communication system for key ciphertext simultaneous transmission can be constructed, after 40Gb/s PAM4-QNSC signals modulated based on 8-bit and 6-bit DAC optical thickness are transmitted for 50 kilometers, the Error rate obtained after a receiving end is subjected to digital signal processing can be below an FEC (Forward Error Correction) decision line, and the demodulation performance of a legal receiving end is good.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A high-speed secure optical communication system for key ciphertext concurrent transmission, the system comprising: the device comprises a transmitting end, a signal transmission module and a receiving end;
the transmitting end includes: the device comprises a hidden signal transmitting module and a public signal transmitting module; the receiving end comprises a hidden signal receiving module, a public signal receiving module and a digital signal processing module;
the secret signal transmitting module is used for modulating the secret key information electric signal encrypted by the quantum noise flow to a wide-spectrum noise optical carrier, transmitting the modulated optical signal to the signal transmission module as a secret signal, and the spectral width of the wide-spectrum noise optical carrier is higher than 10 nm;
the public signal transmitting module is used for modulating the ciphertext information electric signal encrypted by the quantum noise flow to a narrow linewidth optical carrier, and transmitting the modulated optical signal to the signal transmitting module as a public signal, wherein the linewidth of the narrow linewidth optical carrier is lower than 100 MHz;
the signal transmission module is used for respectively transmitting the hidden signal and the public signal to the hidden signal receiving module and the public signal receiving module of the receiving end;
the secret signal receiving module is used for receiving the secret signal, carrying out photoelectric conversion and recovering key information used for quantum noise stream encryption;
the public signal receiving module is used for receiving public signals, carrying out photoelectric conversion and recovering ciphertext information;
and the digital signal processing module is used for carrying out digital signal processing on the recovered key information and the recovered ciphertext information and decrypting to obtain a plaintext.
2. The system of claim 1, wherein the common signal transmitting module comprises:
the narrow linewidth light source is used for generating narrow linewidth laser, and transmitting the narrow linewidth laser to the first intensity modulation unit and the second intensity modulation unit respectively after shunting;
the first intensity modulation unit is used for carrying out intensity modulation on M bits before the PAM electrical signal on one path of optical carrier and transmitting the optical signal after coarse modulation to the power regulation unit;
the second intensity modulation unit is used for carrying out intensity modulation on N bits after the PAM electrical signal is carried out on the other path of optical carrier, and transmitting the finely modulated optical signal to the power regulation unit;
and the power adjusting unit is used for adjusting the power proportion of the two paths of optical signals and coupling the two optical paths, so that the adjusted coupled optical signal is a uniform M + N-bit PAM optical signal.
3. The system of claim 1, wherein the common signal transmitting module comprises in particular the following components:
a laser for emitting a light carrier to the third optical coupler;
the third optical coupler is used for branching the optical carrier, one path of the optical carrier is transmitted to the second polarization controller, and the other path of the optical carrier is transmitted to the third polarization controller;
the second polarization controller is used for adjusting the polarization state of the optical carrier to keep consistent with the polarization main shaft of the crystal in the second modulator and transmitting the adjusted optical carrier to the second modulator;
the third polarization controller is used for adjusting the polarization state of the optical carrier to keep consistent with the polarization main shaft of the crystal in the third modulator and transmitting the adjusted optical carrier to the third modulator;
the second intensity modulator is used for modulating the roughly modulated electrical signal data onto an optical carrier and transmitting the modulated optical signal to the 90-degree phase shifter;
the third intensity modulator is used for modulating the fine modulation electric signal data to an optical carrier and transmitting the modulated optical signal to the first variable optical attenuator;
a 90 ° phase shifter for performing a fixed pi/2 phase shift on the received coarse modulated optical signal and transmitting the optical signal to a fourth optical coupler;
the first variable optical attenuator is used for attenuating the fine modulation optical signal and transmitting the fine modulation optical signal to the fourth optical coupler;
and the fourth optical coupler is used for combining the optical signals and transmitting the optical signals to the multiplexer.
4. The system of claim 3, wherein the second and third intensity modulators are Mach-Zehnder modulators for modulating an electrical signal onto an optical signal amplitude, and the Mach-Zehnder modulators operate in a linear region of a modulation profile.
5. The system as claimed in claim 1, wherein the signal transmission module multiplexes the hidden signal and the common signal into the same optical fiber for transmission, and demultiplexes two signals at a receiving end into the hidden signal receiving module and the common signal receiving module.
6. The system of claim 5, wherein the signal transmission module specifically comprises the following components:
the multiplexer is used for multiplexing the hidden signal and the public signal and transmitting the multiplexed optical signal to a standard single-mode optical fiber;
the standard single-mode optical fiber is used as a transmission channel of an optical signal and transmits the optical signal to the dispersion compensation optical fiber;
the dispersion compensation optical fiber is used for compensating dispersion generated by transmitting an optical signal in the optical fiber, and the compensated optical signal is transmitted to the optical amplifier;
the optical amplifier is used for compensating the optical power loss of the optical signal in the transmission process of the optical fiber, and the compensated optical signal is transmitted to the demultiplexing filter;
and the demultiplexing filter is used for demultiplexing the hidden optical signal and the public optical signal and transmitting the demultiplexed optical signals to the hidden signal receiving module and the public signal receiving module.
7. The system of claim 5, wherein the signal transmission module implements multiplexing through a wavelength division multiplexing device or an optical coupler.
8. The system of any of claims 1 to 7, wherein the suppressed signal transmission module comprises:
the noise light source generating unit is used for generating a wide-spectrum noise light carrier wave in a linear polarization state and transmitting the wide-spectrum noise light carrier wave to the first Mach-Zehnder interferometer structural unit;
and the first Mach-Zehnder interferometer structural unit is used for modulating the secret key information encrypted by the quantum noise stream on the phase of the optical carrier.
9. The system of any of claims 1 to 7, wherein the suppressed signal receiving module comprises:
the second Mach-Zehnder interferometer structural unit is used for matching two paths of delay differences in the hidden signal transmitting module to be within the coherence length of the wide-spectrum noise light source and transmitting the delay differences to the first photoelectric conversion unit;
and the first photoelectric conversion unit is used for converting the optical signal into an electric signal, recovering key information used for encrypting the quantum noise flow which is transmitted in a hiding way, and transmitting the key information to the digital signal processing module.
10. The system of any one of claims 1 to 7, wherein the common signal receiving module comprises:
the optical filtering attenuation unit is used for filtering out-of-band noise of the demultiplexed public signal, and transmitting the optical power of the attenuator to the second photoelectric conversion unit after the optical power is received by the second photoelectric conversion unit;
and the second photoelectric conversion unit is used for receiving the filtered and attenuated public signal, demodulating a recovery ciphertext and transmitting the recovery ciphertext to the digital signal processing module.
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