CN112769554B - Noise processing system and noise processing method for quantum classical fusion transmission - Google Patents
Noise processing system and noise processing method for quantum classical fusion transmission Download PDFInfo
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Abstract
The invention discloses a noise processing system for quantum classical fusion transmission, which comprises a sending party, a receiving party, a first DWDM and a second DWDM; the sender, the first DWDM, the second DWDM and the receiver are connected in sequence through optical fibers and are used for signal transmission; the sender is configured as n senders, and the receiver is configured as n receivers; wavelength is distributed at equal intervals by DWDM channels used by a sender and a receiver, a data signal is distributed in a higher waveband, a quantum signal is distributed in a lower waveband, and a synchronous signal is distributed between the data signal and the quantum signal. The distribution formula can reduce the noise interference of strong classical signals to quantum signals. And the quantum signals are distributed in a lower waveband, so that the Raman noise suffered by the quantum signals is reduced. Meanwhile, a filter is arranged between the second DWDM and the receiving party, and the crosstalk of adjacent channels is further reduced. The system can support more users to the maximum under the condition of a certain key rate.
Description
Technical Field
The invention relates to the technical field of quantum information and optical communication, in particular to a quantum and classical fusion transmission system and a noise processing method.
Background
Quantum key distribution is to guarantee communication security by using quantum mechanical characteristics. It enables both parties to generate and share a random and secure key. One of the most important and unique properties of quantum key distribution is: both parties to the communication will perceive it if a third party attempts to eavesdrop. This property is based on the fundamental principle of quantum mechanics: any measurement of a quantum system will cause interference to the system. A third party attempting to eavesdrop on the password must somehow measure it, and these measurements can cause a noticeable anomaly. The information is transmitted through the quantum superposition state or the quantum entanglement state, a communication system can detect whether interception exists, and when the interception probability is lower than a threshold value, a key which is unconditionally safe in theory can be generated.
In order to avoid the interference of the classical strong light signal to the quantum signal of the single photon level, the quantum signal and the classical signal are often transmitted in different optical fibers. Although this approach effectively avoids the interference of classical light with quantum light, the cost required to lay the fiber link is greatly increased. Therefore, in optical fiber communication, dense Wavelength Division Multiplexing (DWDM): i.e., the ability to transmit multiple optical signals over the same optical fiber, is one of the attractive technologies for simultaneously transmitting quantum signals and classical data signals.
However, in a system based on DWDM quantum and classical fusion transmission, due to the interaction between light and a medium or the like and the interaction between lights of different frequencies, certain background noise such as raman scattering, four-wave mixing, rayleigh scattering, brillouin scattering, and the like may be generated in a channel. Because the classical signal light is strong, the generation of large noise does not have great influence on the classical signal, and therefore the interference on the classical signal can be ignored. However, the quantum signal is weak, and the generated background noise can seriously affect the quality of the quantum signal. Especially four-wave mixing and raman scattering. Effective reduction or even elimination of raman scattering and four-wave mixing is a problem that needs to be addressed at present.
Four-wave mixing is a nonlinear effect that when light waves with different frequencies in an optical fiber are intersected in a nonlinear material, new frequency light waves are possibly generated. Suppose that the frequencies of three optical waves in the channel are respectively f i 、f j 、f k (k ≠ i, j), then the new frequency generated by the four-wave mixing is f ijk ＝f i +f j -f k (1)；
As can be seen from equation (1), for DWDM systems with equal frequency channel spacing, the new frequency components generated by four-wave mixing will overlap with the signal frequency, and especially for quantum signals, will introduce large interference. Severely impacting QKD performance.
Chinese patent publication No. CN 11124514A discloses a quantum-classical signal common-fiber transmission type QKD system transmitting apparatus, which refers to a scheme for eliminating the influence of four-wave mixing noise on a QKD system during common-fiber transmission, and the scheme is based on a four-wave mixing effect, and when the polarization directions of two beams of pump light are the same and are perpendicular to the polarization of signal light, the intensity of idler frequency light newly generated by the four-wave mixing effect is minimum zero. The synchronous signal transmitting end and the data signal transmitting end are respectively connected with a polarization regulator, so that the polarization directions of synchronous signals and data signal light rotate by 90 degrees when the synchronous signals and the data signal light are emitted. In an actual system, however, the synchronization signal light, the classical signal light, and the quantum signal light come from different lasers, and their polarization directions are not necessarily the same. After the synchronous signal light and the classical signal light rotate by 90 degrees through the circulator, the included angle between the synchronous signal light and the quantum signal light is not necessarily 90 degrees, and therefore the practicability is reduced.
Disclosure of Invention
The invention aims to provide a noise processing system for quantum classical fusion transmission, which has a simple structure, can accurately inhibit four-wave mixing noise caused by classical signals, and can reduce Raman scattering and crosstalk of adjacent channels. The scheme is easy to realize and has the advantage of strong practicability.
In order to achieve the purpose, the invention provides a noise processing system for quantum classical fusion transmission, which has the following specific technical scheme:
a noise processing system for quantum classical fusion transmission comprises a sending party, a receiving party, a first DWDM and a second DWDM; the sender, the first DWDM, the second DWDM and the receiver are connected in sequence through optical fibers and used for signal transmission;
the sender is configured as n sending terminals ALICE, and the receiver is configured as n receiving terminals BOB; the n sending terminals are respectively a first sending terminal ALICE1, a second sending terminal ALICE2, an ALICE 8230, an ALICEn 8230, and an n sending terminal ALICEn; the n receiving terminals are respectively a first receiving terminal BOB1, a second receiving terminal BOB2, \8230;, and an nth receiving terminal BOBn;
the system comprises a first sending end, a second sending end, a third sending end, \ 8230 \ 8230;, an nth sending end (namely ALICE1 to ALICEn), a first receiving end, a second receiving end, a third receiving end, \ 8230; \ 8230;, and an nth receiving end (BOB 1 to BOBn) are respectively connected with a first DWDM and a second DWDM after being subjected to DWDM by a wavelength division multiplexer, namely the first sending end, the second sending end, \\ 8230;, the nth sending end is connected with the first DWDM, and the first receiving end, the second receiving end, \\ 8230;, and the nth receiving end is connected with the second DWDM;
the first transmitting end comprises a quantum signal transmitting end, a data signal transmitting end, a synchronous signal transmitting end, a variable attenuator, a first polarization modulation unit, a second polarization modulation unit and a wavelength division multiplexer (DWDM); the quantum signal sending end is connected with a first DWDM through a wavelength division multiplexer DWDM; the data signal transmitting end is connected with the first DWDM through the variable attenuator, the first polarization modulation unit and the wavelength division multiplexer DWDM; the synchronous signal sending end is connected with the first DWDM through a second polarization modulation unit and a wavelength division multiplexer DWDM;
the first receiving end comprises a quantum signal receiving end, a synchronous signal receiving end, a data signal receiving end and a filter; the quantum signal receiving end is connected with a second DWDM through a filter and a wavelength division multiplexer DWDM; the data signal receiving end and the synchronous signal receiving end are connected with a second DWDM through a wavelength division multiplexer DWDM;
the structure and connection of the second sending terminal, the third sending terminal, the fourth sending terminal, the fifth sending terminal and the sixth sending terminal are consistent with those of the first sending terminal; the structure and the connection of the second receiving terminal, the third receiving terminal, \8230 \ 8230 `, and the nth receiving terminal are consistent with the first receiving terminal.
In the first sending end, a quantum signal sent by a quantum signal sending end, a data signal sent by a data signal sending end and a synchronous signal sent by a synchronous signal sending end are multiplexed by a wavelength division multiplexer DWDM and then sent to a first DWDM;
in the first receiving end, the multiplexed quantum signals, data signals and synchronous signals are sent to a wavelength division multiplexer DWDM after passing through a second DWDM; after the DWDM is de-multiplexed, the quantum signals, the data signals and the synchronous signals are respectively sent to a quantum signal receiving end, a data signal receiving end and a synchronous signal receiving end.
In the signal transmission process of a sender and a receiver, the quantum signal sending end is configured to send a quantum signal, the quantum signal is sent to the second DWDM through the wavelength division multiplexer DWDM and the first DWDM, and is sent to a quantum signal receiving end after being filtered by the wavelength division multiplexer DWDM and the filter; wherein the filter is configured to reduce crosstalk of adjacent channels;
the data signal transmitting end is connected with the first DWDM through a variable attenuator, a first polarization modulation unit and a wavelength division multiplexer DWDM, and the data signal receiving end is connected with the second DWDM through the wavelength division multiplexer DWDM; wherein the first polarization modulation unit comprises a phase modulator, a polarization beam splitter and a circulator; the data signal transmitting end is configured to transmit a data signal, the data signal is subjected to transmission power reduction through the variable attenuator, the phase of the data signal is adjusted through the polarization modulation unit, the adjusted data signal is transmitted to the second DWDM through the first DWDM after being multiplexed with the quantum signal and the synchronous signal through the wavelength division multiplexer DWDM, and the data signal is received by the correspondingly connected data signal receiving end after being demultiplexed through the wavelength division multiplexer DWDM.
In the above, the circulator of the first polarization modulation unit has three ports, which are a first port, a second port and a third port; the first port is connected with the variable attenuator, the second port is connected with the polarization beam splitter, and the third port is connected with the wavelength division multiplexer DWDM; the polarization beam splitter is connected with the phase modulator;
the synchronous signal sending end is connected with the first DWDM through a second polarization modulation unit and a wavelength division multiplexer DWDM, and the synchronous signal receiving end is connected with the second DWDM through the wavelength division multiplexer DWDM; wherein the second polarization modulation unit comprises a phase modulator, a polarization beam splitter and a circulator; after the synchronous signal sending end is configured to send the synchronous signal to the first DWDM, the first DWDM sends the received synchronous signal to the second DWDM, and the synchronous signal receiving end which is correspondingly connected receives the received synchronous signal.
In the second polarization modulation unit, the connection structure of the circulator, the polarization beam splitter, and the phase modulator is the same as that of the first polarization modulation unit.
In the above, the circulator of the first polarization modulation unit has the same structure as the circulator of the second polarization modulation unit.
In the above, the circulator in the second polarization modulation unit has three ports, and a first port of the circulator is connected to the synchronization signal transmitting terminal.
Preferably, the quantum signal transmitting end adopts an unequal arm interferometer MZI structure.
More preferably, the quantum signal transmitting end comprises a pulse laser, an intensity modulator and two beam splitters which are connected in sequence, wherein a phase modulator PM is further arranged between the two beam splitters A 。
Preferably, the channel spacing of the first DWDM and the second DWDM is 100G or 200G.
In another preferred embodiment, the quantum signal receiving end adopts an unequal arm interferometer MZI structure.
Preferably, the quantum signal receiving end comprises two beam splitters and a phase modulator PM B And two detectors; the two detectors are respectively connected with the same beam splitter, and the phase modulator is arranged between the two beam splitters.
Preferably, the positions of the quantum signal, the data signal and the synchronization signal in the channel are a lower band, a higher band and a high band in sequence.
Specifically, the lower band refers to a band range of 1530nm to 1540nm, the higher band refers to a band range of 1543nm to 1553nm, and the higher band refers to a band range of 1555nm to 1565nm.
As described above, the data signal and the synchronization signal are received by the data signal receiving terminal and the synchronization signal receiving terminal, respectively, after passing through the second DWDM.
The invention also provides a noise processing method applied to the noise processing system of the quantum classical fusion transmission, which comprises the following steps:
the method comprises the following steps: the quantum signal is subjected to phase modulation through the phase modulator, the synchronous signal and the data signal enter the circulator from a first port of the circulator and enter the polarization beam splitter through a second port of the circulator, the polarization beam splitter divides incident light into horizontal polarized light and vertical polarized light, wherein the phase of the horizontal polarized light is not adjusted after the vertical polarized light is transmitted clockwise and modulated through the phase modulator and the horizontal polarized light is transmitted anticlockwise and modulated through the phase modulator; the horizontal polarized light and the vertical polarized light return to the polarization beam splitter again and are output through a third port of the circulator after being combined; modulating the phase in real time through a phase modulator to ensure that the polarization of the synchronous signal is the same as that of the data signal and is vertical to that of the quantum signal; according to the four-wave mixing effect, when the polarization directions of the two beams of pump light are the same and are perpendicular to the polarization of the signal light, the intensity of the idler frequency light newly generated by the four-wave mixing effect is at least zero. Here, the sync signal light and the data signal represent two pump lights, and the quantum signal light represents a signal light. By using this effect, the influence of four-wave mixing can be eliminated.
Step two: in the channel distributed at equal intervals, the quantum signal is distributed at a lower waveband, the synchronous signal is distributed at a middle waveband, and the data signal is distributed at a higher waveband. Meanwhile, the quantum signal distribution can reduce the Raman noise received by the quantum signal distribution in a lower waveband.
Step three: the quantum signals demultiplexed by the second DWDM are filtered by a filter to remove the interference of adjacent channels, the phase of the quantum signals is adjusted by the unequal-arm interferometer again to avoid phase fluctuation, and finally the quantum signals are detected by a detector D0 or D1 of a receiver to improve the key rate of the quantum signals.
Step four: the data signal and the synchronization signal demultiplexed by the second DWDM are received by a data signal receiving end and a synchronization signal receiving end, respectively.
In the above step one, before the data signal is transmitted into the first DWDM, the transmission power of the strong data signal is reduced through the variable attenuator, so as to avoid power leakage and crosstalk between adjacent channels due to excessive power, and reduce spontaneous raman noise caused by the strong data signal.
Compared with the prior art, the invention has the beneficial effects that:
(1) According to the four-wave mixing effect, when the polarization directions of the two beams of pump light are the same and are perpendicular to the polarization of the signal light, the intensity of the idler frequency light newly generated by the four-wave mixing effect is at least zero. In the technical scheme, the synchronous signal light and the classical signal light (namely, data signals) correspond to pump light, and the quantum signal light corresponds to signal light and is modulated in real time through the phase modulator respectively. The polarization of the synchronous light and the polarization of the classical data light are the same, and the synchronous light and the classical data light are vertical to the polarization of the quantum light; based on this, when the three beams of light are multiplexed into one optical fiber through the first DWDM, the four-wave mixing effect can be automatically suppressed, the intensity of the generated idler frequency light is zero at the minimum, and the interference of the four-wave mixing to the quantum signal can be eliminated.
(2) When the data signal, the synchronous signal and the quantum signal are transmitted in the channels distributed at equal intervals, the data signal, the synchronous signal and the quantum signal are respectively arranged in a lower waveband, a middle waveband and a higher waveband. The crosstalk of adjacent channels can be reduced, and the influence of Raman scattering noise on quantum signals is reduced.
(3) The system employs a dual MZI architecture. And phase fluctuation in the quantum signal transmission process is automatically compensated.
(4) The data signal transmitting end is connected with the variable attenuator, so that the transmitting power of the data signal can be reduced, and the interference of the data signal to the quantum signal and the crosstalk of adjacent channels are reduced.
Drawings
FIG. 1 is a block diagram of the overall structure of a noise processing system for quantum classical fusion transmission provided by the present invention;
fig. 2 is a schematic diagram of a quantum signal transmitting end of the noise processing system for sub-classical fusion transmission provided by the present invention;
fig. 3 is a schematic view of a quantum signal receiving end structure of a noise processing system for quantum classical fusion transmission provided by the present invention;
FIG. 4 is a schematic structural diagram of ALICE1 and BOB1 of a noise processing system for quantum classical fusion transmission provided by the present invention;
fig. 5 is an allocation diagram of quantum channels, synchronization channels, and data channels in the channel equal interval allocation method of the noise processing system for classical quantum fusion transmission provided by the present invention;
fig. 6 is a polarization modulation unit diagram of a noise processing system of quantum classical fusion transmission provided by the invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art based on the embodiments of the present invention without inventive step, are within the scope of the present invention.
This example describes a specific implementation of the present invention by taking a decoy state based on phase encoding and a BB84 protocol as an example; fig. 4 is a specific process of information transfer in this embodiment.
As shown in fig. 1 to 5, the present embodiment provides a noise processing system for quantum classical fusion transmission, including a transmitting side, a receiving side, a first DWDM and a second DWDM; the sender, the first DWDM, the second DWDM and the receiver are connected in sequence through optical fibers and are used for signal transmission;
the sender is configured as n sending terminals ALICE, and the receiver is configured as n receiving terminals BOB; the n sending terminals are respectively a first sending terminal ALICE1, a second sending terminal ALICE2, an ALICE 8230, an ALICEn 8230, and an n sending terminal ALICEn; the n receiving terminals are respectively a first receiving terminal BOB1, a second receiving terminal BOB2, \8230;, and an nth receiving terminal BOBn; in the present embodiment, as shown in fig. 1, n =3 is exemplified.
After passing through a wavelength division multiplexer DWDM, the first sending end ALICE1, the second sending end ALICE2, the third sending end ALICE3, the first receiving end BOB1, the second receiving end BOB2 and the third receiving end BOB3 are respectively connected with the first DWDM and the second DWDM, namely the first sending end ALICE1, the second sending end ALICE2 and the third sending end ALICE3 are connected with the first DWDM, and the first receiving end, the second receiving end BOB2 and the third receiving end BOB3 are connected with the second DWDM;
the first sending terminal ALICE1 comprises a quantum signal sending terminal, a data signal sending terminal, a synchronous signal sending terminal, a variable attenuator, a first polarization modulation unit, a second polarization modulation unit and a wavelength division multiplexer DWDM; the quantum signal transmitting end is directly connected with a first DWDM through a wavelength division multiplexer DWDM; the data signal transmitting end is connected with the first DWDM through the variable attenuator, the first polarization modulation unit and the wavelength division multiplexer DWDM; the synchronous signal sending end is connected with the first DWDM through a second polarization modulation unit and a wavelength division multiplexer DWDM;
the first receiving terminal BOB1 comprises a quantum signal receiving terminal, a synchronous signal receiving terminal, a data signal receiving terminal, a filter and a wavelength division multiplexer DWDM; the quantum signal receiving end is connected with a second DWDM through a filter and a wavelength division multiplexer DWDM; the data signal receiving end and the synchronous signal receiving end are both directly connected with a second DWDM through a wavelength division multiplexer DWDM;
the second sending terminal, the third sending terminal, \8230;, the nth sending terminal and the first sending terminal have the same devices and connections, and are briefly indicated by blocks.
The second receiving end, the third receiving end, \8230 \ n receiving end and the first receiving end have the same devices and connections, and are indicated by blocks in brief.
In the present embodiment, the first polarization modulation unit includes a phase modulator PM1, a polarization beam splitter PBS, and a circulator CIR; the second polarization modulation unit comprises a phase modulator PM2, a polarization beam splitter PBS and a circulator CIR; wherein, the circulator is used for: the light can only be transmitted in the direction indicated by the arrow in the figure, and the polarizing beam splitter functions to split the input photons into horizontal and vertical portions.
Take data signal modulation as an example: the data signal enters the first polarization modulation unit through the first port 1 of the circulator.
Before modulation: in > = α | H > + β | V > (2)
Equation (2) represents an arbitrary light beam entering the first polarization modulation unit. | H>And | V>Representing the horizontal and vertical components, respectively. Alpha and beta represent the proportionality coefficients of the horizontal and vertical components, respectively, and | alpha- 2 +|β| 2 =1. When this polarization state enters the polarization modulation unit, the horizontal polarization component is reflected and propagates counterclockwise. Passes through the phase modulator PM1 without being loaded with phase, and is then transmitted out by the PBS. While the vertical polarization component is transmitted by the PBS and propagates clockwise, and the phase modulator is phase-modulated by PM1
And then reflected off the PBS to combine with the previously transmitted light.
After being modulated by the polarization modulation unit, the modulated signal light is output from the third port 3 of the circulator and enters the first DWDM.
After modulation:
in the formula (3)
The phase of the phase modulator PM1 is indicated.
And
the phases introduced in the first polarization modulation element for the clockwise and counter-clockwise propagating polarization components, respectively. Since both components respectively complete the first polarization modulation unit in a very short time,
and
the difference is negligibly small. By using
The global phase in the first polarization modulation unit is represented, and the output of the polarization state is not influenced. The modulated output is therefore:
before the synchronous signal modulation: in > = α | H > + β | V > (5)
After modulation:
where θ 2 denotes the phase of the phase modulator PM2, θ path The global phase in the second polarization modulation unit is represented, and the output of the polarization state is not influenced.
Wherein
Theta 2 can be adjusted at will; by adjusting in real time
The value of theta 2 can realize the modulation of any polarization state. Therefore, in the four-wave mixing effect, the polarization of the synchronous signal light and the polarization of the data signal light are always the same and are vertical to the polarization of the quantum signal light, and the purpose of enabling the intensity of idler frequency light newly generated by the four-wave mixing effect to be zero at the minimum is achieved.
In the signal transmission process of a sender and a receiver, the quantum signal sending end is configured to send a quantum signal, the quantum signal is sent to a second DWDM through a first DWDM, and is sent to a quantum signal receiving end after being filtered by the filter; wherein the filter is used for reducing crosstalk of adjacent channels;
the data signal transmitting end is connected with the first DWDM through a variable attenuator, a first polarization modulation unit and a wavelength division multiplexer DWDM, and the data signal receiving end is connected with the second DWDM through the wavelength division multiplexer DWDM; wherein the first polarization modulation unit comprises a phase modulator, a polarization beam splitter and a circulator; the data signal transmitting end is configured to transmit a data signal, the data signal is subjected to the phase adjustment of the data signal by the polarization modulation unit after the transmission power of the data signal is reduced by the variable attenuator, and then the adjusted data signal is transmitted to the second DWDM by the first DWDM and received by the correspondingly connected data signal receiving end.
The variable attenuator is used for reducing the sending power of a data signal sending end, and further reducing power leakage and crosstalk of adjacent channels caused by overhigh data signal power.
The synchronous signal sending end is connected with the first DWDM through a second polarization modulation unit and a wavelength division multiplexer DWDM, and the synchronous signal receiving end is connected with the second DWDM through the wavelength division multiplexer DWDM; wherein the second polarization modulation unit comprises a phase modulator, a polarization beam splitter and a circulator; the synchronous signal sending end is configured to send a synchronous signal to the first DWDM after multiplexing with the quantum signal and the data signal by the wavelength division multiplexer DWDM, send the received synchronous signal to the second DWDM by the first DWDM, and receive the synchronous signal by the correspondingly connected synchronous signal receiving end after demultiplexing by the wavelength division multiplexer DWDM.
According to the four-wave mixing effect, when the polarizations of the two pump lights are the same and are perpendicular to the polarization of the signal light, the intensity of the idler frequency light newly generated by the four-wave mixing effect is at least zero. The polarization modulation unit consisting of the phase modulator, the circulator and the polarization beam splitter at the sending end of the synchronous signal and the data signal can adjust the polarization of the synchronous signal and the data signal, so that the polarization of the synchronous signal and the polarization of the data signal are consistent and are vertical to the polarization of the quantum signal. Here, the synchronization signal light and the data signal light correspond to two pumping lights, and the quantum signal light corresponds to the signal light, and based on this effect, when the three beams of light are multiplexed into one optical fiber through the first DWDM, the four-wave mixing effect is automatically suppressed, and the intensity of the idler frequency light generated thereby is at least zero. The interference of four-wave mixing on the quantum signal can be eliminated.
In this embodiment, the channel spacing of the first and second DWDMs is allocated at equal intervals. As can be seen from the Raman spectrogram, the Raman scattering noise of the quantum signal light at a lower waveband is smaller. The transmission power of the data signal is higher than that of the synchronous signal, and in order to reduce the interference of the data signal to the quantum signal, the synchronous signal and the data signal are respectively placed in a lower band, a middle band and a higher band, as shown in fig. 5. The quantum signals are distributed in a lower waveband, and Raman noise suffered by the quantum signals is reduced. The synchronous signal is arranged between the quantum signal and the data signal, so that the quantum signal is far away from the data signal with larger transmission power. And reducing the interference of the data signal to the quantum signal. Under the condition that the total channel number in the channel is far larger than the available channel number, the quantum signal can be further far away from the synchronous signal, and the interference noise suffered by the quantum signal and the crosstalk of an adjacent channel are further reduced.
In this embodiment, the quantum signal transmitting end adopts an unequal arm interferometer MZI structure; specifically, the quantum signal transmitting end comprises a pulse laser, an intensity modulator and two beam splitters, which are respectively BS1 and BS2, which are connected in sequence; wherein a phase modulator PM is further arranged between the two beam splitters BS1 and BS2 A 。
The intensity modulator is used in a decoy state protocol based on phase coding, and by sending signal states and decoy states with different intensities to a detection party, an eavesdropper cannot distinguish the signal states from the decoy states, so that the safety of the system is improved. The beam splitter BS uses a splitting ratio of 1.
In the present embodiment, the channel spacing of the first DWDM and the second DWDM is 100G or 200G, which channel spacing is used, as the case may be.
In this embodiment, the quantum signal transmitting end adopts an unequal arm interferometer MZI structure. Specifically, the quantum signal receiving end comprises two beam splitters BS1 and BS2 and a phase modulator PM B And two detectors D0, D1; wherein, the two detectors are respectively connected with the same beam splitter BS2, and the phase modulator PM B Is arranged between the two beam splitters.
In the present embodiment, in fig. 1, the synchronization signal receiving end and the data signal receiving end may receive the synchronization signal and the received data signal, respectively.
As shown in fig. 4, the figure is used for illustrating the connection relationship between the first sending terminal ALICE1 and the first receiving terminal BOB1 and the first DWDM and the second DWDM in the noise processing system, so as to explain the specific processing procedure of the information; the embodiment also provides a noise processing method applied to the noise processing system for quantum classical fusion transmission, which comprises the following steps:
the method comprises the following steps: after being modulated by the intensity modulator 2, the quantum signals enter the phase modulator 3 for phase modulation, the synchronous signals and the data signals enter the circulator from the first port 1 of the circulator 7 or 12, enter the phase modulator 9 or 14 through the second port 2 for modulation, and are output from the third port 3 of the circulator; it is ensured that the synchronization signal and the data signal are polarized the same and perpendicular to the polarization of the quantum signal. According to the four-wave mixing effect, when the polarization directions of the two beams of pump light are the same and are perpendicular to the polarization direction of the signal light, the intensity of idler frequency light newly generated by the four-wave mixing effect is minimum zero. Here, the sync signal light and the data signal represent two pump lights, and the quantum signal light represents a signal light. By using this effect, the influence of four-wave mixing can be eliminated.
In step one, before the data signal is transmitted into the first DWDM16, the transmission power of the strong data signal is reduced through the variable attenuator 11, so as to avoid power leakage and crosstalk between adjacent channels due to excessive power, and reduce spontaneous raman noise caused by the strong data signal.
In step one, the data signal, the sync signal, and the quantum signal are multiplexed by the wavelength division multiplexer DWDM15 and then transmitted to the first DWDM.
Step two: in the channel DWDM15 distributed at equal intervals, the quantum signal is distributed at a lower wave band, the synchronous signal is distributed at a middle wave band, and the data signal is distributed at a higher wave band, so that the distribution formula can reduce the interference of the strong data signal to the quantum signal. Meanwhile, the quantum signal is distributed in a lower waveband, so that the influence of Raman noise can be reduced.
Step three: the quantum signal after multiplexing by wavelength division multiplexer DWDM15 sends the quantum signal after wavelength division multiplexer DWDM18 de-multiplexing via second DWDM17, at first filters through wave filter 19, filters the interference of adjacent channel, adjusts the phase place of quantum signal through the not equal arm interferometer again, avoids the phase fluctuation, is surveyed by detector D023 or D124 at last, improves quantum signal's key rate.
Step four: the data signal and the synchronization signal, which are demultiplexed by the wavelength division multiplexer 18 via the second DWDM17, are received 25 by the data signal receiving end 26 and the synchronization signal receiving end, respectively.
Specifically, a filter 19 is further provided between the second DWDM17 and the quantum signal receiving terminal. The filter 19 can further reduce the crosstalk between adjacent channels and reduce the error rate of the system. In the system, three-stage filters are adopted, and the connection mode among the filters is cascade connection. Compared with a first-stage filter, the three-stage filtering can greatly improve the filtering efficiency and the signal-to-noise ratio of quantum signal light.
The above examples are only intended to illustrate the technical solution of the present invention, and not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (8)
1. A noise processing system for quantum classical fusion transmission is characterized by comprising a sending party, a receiving party, a first DWDM and a second DWDM; the sender, the first DWDM, the second DWDM and the receiver are connected in sequence through optical fibers and used for signal transmission;
the sender is configured as n senders, and the receiver is configured as n receivers; the n sending terminals are respectively a first sending terminal, a second sending terminal, \8230 \ 8230;, and an nth sending terminal; the n receiving terminals are respectively a first receiving terminal, a second receiving terminal, \8230;, and an nth receiving terminal;
the first sending end, the second sending end, the third sending end, \8230 \ 8230 `, the nth sending end is connected with the first DWDM, and the first receiving end, the second receiving end, the third receiving end, \8230 `, the nth receiving end is connected with the second DWDM;
the first transmitting end comprises a quantum signal transmitting end, a data signal transmitting end, a synchronous signal transmitting end, a variable attenuator, a first polarization modulation unit, a second polarization modulation unit and a wavelength division multiplexer (DWDM); the quantum signal transmitting end is connected with a first DWDM through a wavelength division multiplexer DWDM; the data signal transmitting end is connected with the first DWDM through the variable attenuator, the first polarization modulation unit and the wavelength division multiplexer DWDM; the synchronous signal sending end is connected with the first DWDM through a second polarization modulation unit and a wavelength division multiplexer DWDM;
in the first sending end, a quantum signal sent by a quantum signal sending end, a data signal sent by a data signal sending end and a synchronous signal sent by a synchronous signal sending end are multiplexed by a wavelength division multiplexer DWDM and then sent to a first DWDM;
the first receiving end comprises a quantum signal receiving end, a synchronous signal receiving end, a data signal receiving end, a filter and a wavelength division multiplexer (DWDM); the quantum signal receiving end is connected with a second DWDM through a filter and a wavelength division multiplexer DWDM; the data signal receiving end and the synchronous signal receiving end are connected with a second DWDM through a wavelength division multiplexer DWDM;
in the first receiving end, the multiplexed quantum signals, data signals and synchronous signals are sent to a wavelength division multiplexer (DWDM) after passing through a second DWDM; after the DWDM is de-multiplexed, the quantum signals, the data signals and the synchronous signals are respectively sent to a quantum signal receiving end, a data signal receiving end and a synchronous signal receiving end;
the structure and the connection of the second sending end, the third sending end, \8230 \ 8230;, and the nth sending end are consistent with the first sending end; the structure and the connection of the second receiving end, the third receiving end, \8230 \ 8230;, the nth receiving end are consistent with the first receiving end;
the first polarization modulation unit comprises a circulator, a polarization beam splitter and a phase modulator PM1;
the circulator of the first polarization modulation unit is provided with three ports, namely a first port, a second port and a third port; wherein the first port is connected to the variable attenuator, the second port is connected to the polarization splitter, and the third port is connected to the wavelength division multiplexer DWDM; the polarization beam splitter is connected with the phase modulator PM1;
in the first polarization modulation unit, the data signal passing through the variable attenuator enters from the first port of the circulator, and the polarization state of the data signal is divided into a horizontal polarization component and a vertical polarization component by the polarization beam splitter; the horizontal polarization component is reflected and propagates anticlockwise, does not load a phase when passing through the phase modulator PM1, and is transmitted out by the polarization beam splitter; the vertical polarization component is transmitted by the polarization beam splitter, propagates clockwise, modulates the phase when passing through the phase modulator PM1, and is reflected by the polarization beam splitter to combine with the previous transmitted beam; the data signal light modulated by the first polarization modulation unit is output from a third port of the circulator and enters a wavelength division multiplexer (DWDM) at the sending end;
the second polarization modulation unit comprises a circulator, a polarization beam splitter and a phase modulator PM2;
the circulator of the first polarization modulation unit has the same structure as the circulator of the second polarization modulation unit; the circulator in the second polarization modulation unit is provided with three ports, and a first port of the circulator is connected with the synchronous signal transmitting end;
in the second polarization modulation unit, the synchronization signal enters from the first port of the circulator, and the polarization state of the synchronization signal is divided into a horizontal polarization component and a vertical polarization component by the polarization beam splitter; as in the modulation process in the first polarization modulation unit, the vertical polarized light is transmitted clockwise through the phase modulator PM2 for phase modulation, and after the horizontal polarized light is transmitted counterclockwise through the phase modulator PM2, the phase of the horizontal polarized light is not adjusted; the synchronous signal light modulated by the second polarization modulation unit is output from a third port of the circulator and enters a wavelength division multiplexer (DWDM) at the sending end;
in the first DWDM and the second DWDM, channel intervals adopt equal interval distribution; and the quantum signal, the synchronization signal and the data signal are respectively placed in a lower waveband, a middle waveband and a higher waveband; the quantum signals are distributed to the lower wave band, and Raman noise suffered by the quantum signals is reduced.
2. The noise processing system according to claim 1, wherein the quantum signal transmitting end is configured to transmit a quantum signal, and the quantum signal is transmitted to the second DWDM through the wavelength division multiplexer DWDM and the first DWDM, and is transmitted to the quantum signal receiving end after being filtered by the wavelength division multiplexer DWDM and the filter; wherein the filter is used to reduce crosstalk of adjacent channels.
3. The noise processing system of claim 2, wherein the data signal transmitting end is connected to a first DWDM via a variable attenuator, a first polarization modulation unit, and a wavelength division multiplexer DWDM, and the data signal receiving end is connected to a second DWDM via a wavelength division multiplexer DWDM; the data signal transmitting end is configured to transmit a data signal, the data signal is subjected to transmission power reduction through the variable attenuator, the phase of the data signal is adjusted through the first polarization modulation unit, the adjusted data signal is transmitted to the second DWDM through the first DWDM after multiplexing with the quantum signal and the synchronous signal through the wavelength division multiplexer DWDM, and the data signal is received by the correspondingly connected data signal receiving end after demultiplexing through the wavelength division multiplexer DWDM.
4. The noise processing system of claim 2, wherein the synchronization signal transmitting end is connected to the first DWDM through a second polarization modulation unit and a wavelength division multiplexer DWDM, and the synchronization signal receiving end is connected to the second DWDM through a wavelength division multiplexer DWDM; after the synchronous signal sending end is configured to send the synchronous signal to the first DWDM, the first DWDM sends the received synchronous signal to the second DWDM, and the synchronous signal receiving end correspondingly connected receives the synchronous signal.
5. The noise processing system according to claim 2, wherein the quantum signal transmitting end adopts an unequal arm interferometer MZI structure, and comprises a pulse laser, an intensity modulator and two beam splitters which are connected in sequence, and a phase modulator is further disposed between the two beam splitters.
6. The noise processing system of claim 2, wherein the quantum signal receiving end adopts an unequal arm interferometer MZI structure; wherein, the quantum signal receiving end comprises two beam splitters and a phase modulator PM B And two detectors; wherein, the two detectors are divided intoAre respectively connected with the same beam splitter, and the phase modulator is arranged between the two beam splitters.
7. The noise processing system of claim 1, wherein the channel spacing of the first and second DWDMs is 100G or 200G.
8. A noise processing method of quantum classical fusion transmission, applied to the noise processing system according to any one of claims 1 to 7, the noise processing method comprising the steps of:
the method comprises the following steps: the quantum signal is subjected to phase modulation through the phase modulator, the synchronous signal and the data signal enter the circulator from a first port of the circulator and enter the polarization beam splitter through a second port of the circulator, the polarization beam splitter divides incident light into horizontal polarized light and vertical polarized light, wherein the vertical polarized light is transmitted clockwise and modulated through the phase modulator, the horizontal polarized light is transmitted anticlockwise and modulated through the phase modulator, and the phase of the horizontal polarized light is not adjusted; the horizontal polarized light and the vertical polarized light return to the polarization beam splitter again and are output through a third port of the circulator after being combined; modulating the phase in real time through a phase modulator to ensure that the polarization of the synchronous signal is the same as that of the data signal and is vertical to that of the quantum signal; according to the four-wave mixing effect, when the polarization directions of the two beams of pump light are the same and are vertical to the polarization of the signal light, the intensity of idler frequency light newly generated by the four-wave mixing effect is minimum zero;
step two: in the channels distributed at equal intervals, quantum signals are distributed at a lower waveband, synchronous signals are distributed at a middle waveband, and data signals are distributed at a higher waveband, so that the interference of strong data signals on the quantum signals is reduced, and the Raman noise suffered by the quantum signals distributed at the lower waveband is reduced;
step three: the quantum signals demultiplexed by the second DWDM are filtered by a filter to remove the interference of adjacent channels, the phase of the quantum signals is adjusted by the unequal-arm interferometer again to avoid phase fluctuation, and finally the quantum signals are detected by a detector of a receiver to improve the key rate of the quantum signals;
step four: the data signal and the synchronous signal which are demultiplexed by the second DWDM are respectively received by a data signal receiving end and a synchronous signal receiving end;
in the first step, before the data signal is transmitted into the first DWDM, the transmission power of the strong data signal is reduced through the variable attenuator, so as to avoid power leakage and crosstalk between adjacent channels caused by excessive power, and reduce spontaneous raman noise caused by the strong data signal.
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