CN103929251B - Low noise QKD and WDM classic communication network compatible method and device - Google Patents

Abstract

The invention discloses a method and device compatible with low-noise QKD (quantum key distribution) and WDM (wavelength division multiplexing) classical communication network, which is to time-division multiplex quantum signals and classical signals of the same wavelength into the same optical fiber; The filter filters out the spontaneous Raman scattering noise generated by the classical signal. After the spontaneous Raman scattering noise is filtered by the filter, there is still a small amount of noise that will cover the quantum signal, and the noise generated by the classical signal that still exists after passing through the filter is discarded. The quantum signal covered by the noise makes the output quantum signal not affected by the noise, so that the low-noise QKD is compatible with the WDM classical communication network. In the present invention, the classical data signal of the same wavelength does not produce four-wave mixing, and discarding a small part of the quantum signal covered by the noise can approximately completely eliminate the influence of spontaneous Raman scattering noise on the quantum signal, and realize that the quantum signal is approximately invariant Affected by noise from classical signals.

Description

A method and device for compatibility between low-noise QKD and WDM classic communication network

technical field

The present invention relates to the field of quantum communication, and more specifically, relates to a method and device compatible with low-noise QKD (quantum key distribution) and WDM (wavelength division multiplexing) classical communication network.

Background technique

In recent years, QKD (Quantum Key Distribution) has greatly improved its transmission distance and security key rate, but the experimental realization needs to be completed in dark fiber or new fiber. In order to utilize the existing optical fiber infrastructure and save optical fiber bandwidth resources, a method of co-existing the quantum key distribution system and the classical data communication system in the same optical fiber came into being. When the quantum signal is transmitted together with a few WDM (Wavelength Division Multiplexing) classical signals, it will be affected by spontaneous Raman scattering and four-wave mixing, which increases the bit error rate of quantum key distribution; and when the quantum signal When co-transmitted with a large number of WDM classical signals, it will be affected by stimulated Raman scattering, stimulated Brillouin scattering and four-wave mixing, and may even make quantum key distribution impossible to operate at all. People have carried out theoretical and experimental studies on the wavelength division multiplexing transmission of quantum signals and several WDM classical signals in the same optical fiber. It has been confirmed through experiments that quantum signals will be affected by four-wave mixing and spontaneous Raman scattering noise, and proposed The noise reduction scheme has continuously increased the transmission distance of quantum signals and continuously reduced the bit error rate. But so far, the bit error rate is still high and the transmission distance is relatively short in the quantum signal and a dozen or more WDM classical signal wavelength division multiplexing long-distance transmission schemes.

Contents of the invention

In order to overcome at least one defect (deficiency) described in the above-mentioned prior art, the present invention provides a method compatible with low-noise QKD and WDM classic communication network, which effectively reduces the impact of QKD and WDM classic communication network on the same optical fiber transmission. Noise effect.

Another object of the present invention is to propose a low-noise QKD device compatible with WDM classic communication network.

In order to solve the problems of the technologies described above, the technical solution of the present invention is as follows:

A low-noise QKD method compatible with WDM classical communication networks, time-division multiplexing quantum signals and classical signals of the same wavelength into the same optical fiber, and the spontaneous Raman scattering noise generated by the classical signal is distributed around the classical signal; using a filter Filter out the spontaneous Raman scattering noise generated by the classical signal, and there will still be a small amount of noise after the spontaneous Raman scattering noise is filtered by the filter, and a small amount of spontaneous Raman scattering noise will cover the quantum signal, and will still exist after passing through the filter The quantum signal covered by the noise generated by the classical signal is discarded, so that the output quantum signal is not affected by the noise, so that the low-noise QKD is compatible with the WDM classical communication network.

Among them, when the classical signal is transmitted in the optical fiber, it will generate spontaneous Stokes Raman scattering noise and spontaneous anti-Stokes Raman scattering noise with different wavelengths from the classical signal. When the wavelength of the quantum signal and the classical signal are the same, the quantum signal The wavelength of is different from the wavelength of spontaneous Raman scattering noise, and it is easier to filter out the noise with a filter at this time. The quantum signal and the classical signal are time-division multiplexed in the same optical fiber, so that the quantum signal and the classical signal with the same wavelength can be separated, and the noise generated by the classical signal only covers a small part of the quantum signal before passing through the filter, so that more different signals can be obtained. Quantum signals covered by noise. Due to the bandwidth of the filter, a small part of the quantum signal after passing through the filter is still covered by spontaneous Raman scattering noise with a wavelength similar to the quantum signal, and this part of the quantum signal covered by the noise is discarded to achieve low-noise QKD Compatible with WDM classic communication network.

In a preferred solution, the number of quantum signals that need to be discarded is obtained in the following manner:

According to the group velocity dispersion effect, the quantum signal pulse broadening after passing through the optical fiber with length L is obtained as:

Δt _cla =Δt _quan =t ₀ [1+(L|β ₂ |)/t ₀ ² ] ^1/2

Where Δt _cla is the classical signal broadening, Δt _quan is the quantum signal broadening, t ₀ is the initial pulse width of the quantum signal and the classical signal, L is the fiber length, and β ₂ is the group velocity dispersion coefficient;

According to the quantum signal stretching, the pulse repetition frequency of the quantum signal is 1/Δt _quan , and the pulse cycle time of the quantum signal is obtained at the same time;

The distribution time τ1 of the spontaneous Raman scattering noise generated by the classical signal is:

τ1＝|L/v _Raman -L/v _cla |

where the spontaneous Raman scattering light velocity v _Raman and the classical signal velocity v _cla are respectively:

v _Raman = c/n _Raman

v _cla =c/n _cla

where n _Raman is the refractive index of spontaneous Raman scattered light in the fiber, n _cla is the refractive index of the classical signal in the fiber, and c is the speed of light in vacuum;

Therefore, the distribution time of the spontaneous Raman scattered light generated by the classical signal after passing through the filter is:

τ=L*|Δn|/c

Where Δn=n _Raman -n _cla is the refractive index difference between the spontaneous Raman scattered light with the longest wavelength and the classical signal after passing through the filter or the spontaneous Raman scattered light with the shortest wavelength and the classical signal after passing through the filter The refractive index difference in the fiber, where the wavelength of the spontaneous Raman scattered light with the longest wavelength after passing through the filter is the upper limit of the bandwidth of the filter, and the wavelength of the spontaneous Raman scattered light with the shortest wavelength after passing through the filter is the filter The lower limit of the bandwidth;

Abandon the quantum signals within the time interval Δt _U and the time interval Δt _L , where the time interval Δt _U is the distribution time of the Stokes spontaneous Raman scattering noise after passing through the filter, and the time interval Δt _L is the antispatial noise after passing the filter Distribution time of Stokes spontaneous Raman scattering noise;

According to the distribution time τ after the spontaneous Raman scattering generated by the classical signal passes through the filter and the pulse cycle time of the quantum signal, the number of quantum signals covered by noise is calculated, that is

Wherein, the pulse broadening of the quantum signal after passing through the optical fiber is Δt _quan , and the repetition frequency of the quantum signal and the pulse cycle time of the quantum signal can be obtained according to the pulse broadening of the quantum signal. Then according to the formula of the noise distribution time generated by the classic signal and the bandwidth of the filter, the bandwidth Δλ of the filter is: λ _U -λ _L = Δλ, where λ _U is the upper limit of the bandwidth of the filter, and λ _L is the lower limit of the bandwidth of the filter ; Calculate the distribution time of the noise generated by the classical signal after passing through the filter. Finally, the number of quantum signals covered by noise is calculated according to the distribution time of the noise passing through the filter and the pulse period time of the quantum signal.

In a preferred solution, the wavelength of the quantum signal and the classical signal of the same wavelength is set to 1550nm.

Among them, the quantum signal and the classical signal have the same wavelength, and the wavelength of the spontaneous Raman scattering noise generated by the classical signal is different from the wavelength of the classical signal, so the wavelength of the quantum signal is different from the wavelength of the spontaneous Raman scattering noise. In this case, Quantum signals are easier to extract from noise. The wavelength of the signal is set to 1550nm mainly to consider the minimum loss window of optical fiber communication. However, for classical communication systems with different operating wavelengths, the wavelength of the quantum signal can be set to the wavelength required by the classical communication system at the same time. At this time, the respective keys can be increased. Rate.

In a preferred solution, the quantum signal and the classical signal are time-division multiplexed to the same optical fiber through a TDM (Time Division Multiplexing) switch node, and the TDM switch node is implemented by a MEMS (Micro Electro Mechanical System) optical switch, which can be It is used for signal time division multiplexing and can also be used for signal demultiplexing.

Among them, the quantum signal and the classical signal have the same wavelength, and the time division multiplexing of the quantum signal and the classical signal makes it easier to separate the quantum signal from the classical signal. The TDM switch node uses MEMS optical switches, which are small in size, light in weight, low in energy consumption, small in inertia, and short in response time, which can improve the key rate of quantum signals and classical signals.

A device for applying the described method of low-noise QKD compatible with WDM classic communication network, comprising sequentially connected transmitting end and receiving end,

The transmitting end includes a quantum signal transmitting end and a data signal transmitting end, wherein the signal transmitted by the quantum signal transmitting end and the signal transmitted by the data signal transmitting end are multiplexed into the same optical fiber through a TDM switch node;

The quantum signal transmitting end includes a clock signal generator, a laser in the Alice end, an attenuator, a synchronous laser, a frequency divider FD and a first TDM switch node; wherein a part of the clock signal sent by the clock signal generator triggers the clock signal in the Alice end The laser outputs a quantum signal, and the other part is divided by the frequency divider FD to trigger the synchronous laser to output a synchronous signal. The output quantum signal is strongly attenuated by the attenuator to prepare a seductive state and encoded by the encoding unit and the synchronous signal is complexed through the first TDM switch node. used in the same fiber;

The data signal transmitting end includes n data signals of different wavelengths, a WDM-TDM switch node and an erbium-doped fiber amplifier; the n data signals of different wavelengths are converted into a column of TDM data with the same wavelength by the WDM-TDM switch node Signal, the TDM data signal of the same wavelength is amplified by the erbium-doped fiber amplifier, and the amplified TDM data signal, as well as the quantum signal and synchronization signal multiplexed into the same fiber are multiplexed into the same fiber through the TDM switch node;

The receiving end includes a third TDM switch node, a fourth TDM switch node, a TDM-WDM switch node, a filter, a photoelectric converter, and a frequency multiplier; the third TDM switch node is used to demultiplex the multiplexed signal into a TDM The data channel and the channel containing the synchronous signal and the quantum signal, wherein the TDM data signal in the TDM data channel is converted into n data signals of different wavelengths through the TDM-WDM switch node, and the data signals of different wavelengths are respectively output to the respective receiving ends; including The channel of the synchronous signal and the quantum signal is demultiplexed into a synchronous channel and a quantum channel through the fourth TDM switch node, wherein the quantum signal in the quantum channel is filtered by a filter and then input to the Bob end, decoded at the Bob end, and the synchronous channel in the The synchronous signal is converted into a clock signal by a photoelectric converter, and then the clock signal is multiplied to the previous frequency by a frequency multiplier, which is used to trigger the SPD (Single Photon Detector) in the Bob end to detect the quantum signal.

Quantum signal transmission process: at the quantum signal transmitting end, part of the clock signal sent by the clock signal generator triggers the laser in the Alice end to output a quantum signal, and then the quantum signal is strongly attenuated by the attenuator to prepare a seductive state and encoded by the encoding unit. A part is divided by the frequency divider FD to trigger the synchronous laser to output a synchronous signal, and use the first TDM switch node to time-division multiplex the synchronous signal and the quantum signal.

Data signal transmission process: At the data signal transmitting end, data signals of different wavelengths are converted into TDM data signals of the same wavelength through a WDM-TDM conversion node, and the TDM data signals pass through EDFA to amplify the signal for further transmission. Quantum signals are time-division multiplexed together using TDM switch nodes, and then enter the same long-haul optical fiber for transmission.

The quantum signal, the synchronous signal and the data signal are demultiplexed into a TDM data channel and a channel including the synchronous signal and the quantum signal when using the third TDM switch node. At the receiving end of the quantum signal, the quantum signal and the synchronous signal are demultiplexed using the fourth TDM optical switch. The quantum signal passes through a filter to filter out the spontaneous Raman scattering noise and is decoded at the Bob end and then input to the SPD at the Bob end. The synchronous signal passes through the photoelectric The converter converts it into a clock signal, and then the clock signal is multiplied by a frequency multiplier to trigger the SPD to detect the quantum signal.

In a preferred solution, the quantum signal transmitting end further includes a first filter, the first filter is connected to the laser in the Alice end and is located behind the laser;

The data signal transmitting end further includes a second filter, and the erbium-doped fiber amplifier is connected to the TDM switch node through the second filter.

Wherein the first filter is used to filter out the noise from the laser in the Alice terminal, and the second filter is used to filter out the noise from the EDFA.

In a preferred solution, the WDM-TDM switch node is composed of a nonlinear fiber loop mirror and a high repetition rate monolithic integrated mode-locked semiconductor laser; the TDM-WDM switch node uses a nonlinear fiber loop mirror .

Among them, the WDM-TDM switch node composed of a nonlinear fiber loop mirror and a high repetition rate monolithic integrated mode-locked semiconductor laser can realize the conversion of multiple data signals with different wavelengths into time-division multiplexed data signals, and its isolation is relatively high. high. The TDM-WDM switch node composed of nonlinear optical fiber loop mirror can realize the conversion of time-division multiplexed data signals into multiple data signals of different wavelengths.

Compared with the prior art, the beneficial effects of the technical solution of the present invention are: 1. All classical signals have the same wavelength, so four-wave mixing does not occur, so quantum signals are not affected by four-wave mixing. 2. The quantum signal and the classical signal have the same wavelength, but the spontaneous Raman scattering has a different wavelength from the classical signal, so it is easier to filter out the noise around the quantum signal. 3. Approximately complete removal of spontaneous Raman scattering noise by discarding a fraction of the quantum signal.

Description of drawings

Figure 1 is a structural diagram of a noise reduction device for communicating quantum signals and classical signals in the same optical fiber.

Fig. 2 is a schematic diagram of the structure of the quantum signal transmitting end.

Fig. 3 is a schematic diagram of the time distribution of Stokes spontaneous Raman scattering and anti-Stokes spontaneous Raman scattering noise.

detailed description

The accompanying drawings are for illustrative purposes only and cannot be construed as limiting the patent;

In order to better illustrate this embodiment, some parts in the drawings will be omitted, enlarged or reduced, and do not represent the size of the actual product;

For those skilled in the art, it is understandable that some well-known structures and descriptions thereof may be omitted in the drawings.

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Figures 1 and 2, a low-noise QKD and WDM classical communication network compatible method and device to reduce the impact of the coexistence of quantum channels and classical channels, including sequentially connected senders and receivers,

The transmitting end includes a quantum signal transmitting end and a data signal transmitting end, wherein the signal transmitted by the quantum signal transmitting end and the signal transmitted by the data signal transmitting end are time-division multiplexed into the same optical fiber through a TDM switch node;

The quantum signal transmitting end includes a clock signal generator, a laser in the Alice end, a synchronous laser, a frequency divider FD, an attenuator, and a first TDM switch node; wherein a part of the clock signal sent by the clock signal generator triggers the output of the laser in the Alice end Quantum signal, and then the quantum signal is strongly attenuated by the attenuator to prepare the temptation state and encoded by the encoding unit, and the other part is divided by the frequency divider FD to trigger the synchronous laser to output the synchronous signal, and the output quantum signal and synchronous signal pass through the first TDM switch node Multiplexing into the same fiber;

The data transmitting end includes n data signals of different wavelengths, a WDM-TDM switch node and an erbium-doped fiber amplifier EDFA; n data signals of different wavelengths are converted into a column of TDM data signals with the same wavelength through the WDM-TDM switch node, and the same wavelength The TDM data signal is amplified by the erbium-doped fiber amplifier, and the amplified TDM data signal, as well as the quantum signal and synchronization signal multiplexed into the same fiber are multiplexed into the same fiber through the TDM switch node;

The receiving end includes a third TDM switch node, a fourth TDM switch node, a TDM-WDM switch node, a filter F3, a photoelectric converter and a frequency multiplier; the third TDM switch node is used to demultiplex the multiplexed signal into TDM data Channels and channels containing synchronous signals and quantum signals, in which the TDM data signals in the TDM data channel are converted into n data signals of different wavelengths through the TDM-WDM switch node, and the data signals of different wavelengths are respectively output to their respective receiving ends; including synchronization The channel of the signal and the quantum signal is demultiplexed into a synchronous channel and a quantum channel through the fourth TDM switch node, wherein the quantum signal in the quantum channel is filtered by a filter and then input to the Bob end, and decoded at the Bob end, and the synchronization in the synchronous channel The signal is converted into a clock signal through a photoelectric converter, and then the clock signal is multiplied to the previous frequency by a frequency multiplier, which is used to trigger the detector in the Bob end to detect the quantum signal.

In this scheme, the classic signal has two roles: the synchronization signal and the data signal, assuming that the wavelengths of the two signals are the same. In order to distinguish their functions, they are collectively referred to as synchronization signals in quantum systems and data signals in classical systems.

At the sending end of the quantum signaling system, Alice and the synchronization signal are triggered by the same clock generator. In order to reduce the noise from the laser, the first filter F1 is connected after the Alice-side laser at the transmitting end to filter out the noise, and then the signal is strongly attenuated by the attenuator to prepare the temptation state, and encoded by the encoding unit. In order to reduce the noise from the classical signal, the trigger signal sent to the synchronous laser is frequency-divided by a frequency divider to reduce the pulse repetition frequency (the spontaneous Raman scattering noise from the synchronous signal is distributed between the two synchronous signals in the time domain, when When we increase the pulse repetition frequency of the synchronization signal, the noise from the synchronization signal will cover the quantum signal, thereby increasing the bit error rate). Then, the quantum signal and the clock signal are multiplexed into the same optical fiber by the first TDM switch node, the first TDM switch node is realized by a MEMS optical switch, and finally the multiplexing of the classical signal and the quantum signal in the scheme diagram can be obtained burst.

At the data signal transmitting end, n data signals with different wavelengths are converted into a series of TDM signals with the same wavelength by a WDM-TDM switch node, where the WDM-TDM switch node uses a nonlinear optical fiber loop mirror and a high repetition rate single On-chip integrated mode-locked semiconductor lasers. Then the TDM data signal is amplified by an EDFA to realize long-distance transmission, and a second filter F2 is added after the EDFA to filter out noise from the EDFA. Afterwards, the quantum signal, synchronization signal and data signal are time-division multiplexed into the same optical fiber through the TDM switch node, and the quantum signal and the classical signal have the same wavelength at this time. In order to increase the bit rate, in this embodiment, the wavelength of the quantum signal and the classical signal is set to 1550nm.

At the receiving end, the third TDM switch node demultiplexes the multiplexed signal into a data signal and a quantum signal.

At the receiving end of the quantum signal, the fourth TDM switch node is used to demultiplex the synchronous signal and the quantum signal. A photoelectric converter is used to convert the synchronous signal into a clock signal, a frequency multiplier multiplies the frequency of the clock signal to the previous frequency, and then the synchronous signal is used to trigger the detector to detect the quantum signal. Filter F3 before Bob is used to filter out spontaneous Raman scattering noise.

At the data signal receiving end, the TDM-WDM switch node is used to convert the data TDM signal into data signals of different wavelengths. The TDM-WDM switch node uses a nonlinear fiber loop mirror to realize its function, and then the classical signals of different wavelengths are sent to their respective receivers.

The principle of realizing QKD noise reduction of the present invention is:

When the wavelength of the classical signal is different from that of the quantum signal, the spontaneous Raman scattering noise from the classical signal is distributed between the two classical signals in the time domain. Raman scattering noise will cover the quantum signal and increase the bit error rate of the qubit. In order to solve this problem, the wavelength of the quantum signal and the classical signal are set to the same wavelength in this embodiment, because the wavelength of the spontaneous Raman scattering noise is different from the wavelength of the classical signal, so the wavelength of the spontaneous Raman scattering noise is different from the wavelength of the quantum signal , so we can easily filter out the spontaneous Raman scattering noise. However, even if the bandwidth of the filter F3 is very small, there will still be some noise with a wavelength within the bandwidth of the filter F3 that can pass through the filter and cause an increase in the bit error rate. In order to eliminate these noises, discard the quantum signal covered by the noise, this part The quantum signal is negligible compared to the total quantum signal.

In order to obtain quantum signals with high pulse repetition frequency, quantum signal broadening needs to be calculated. According to the group velocity dispersion effect, the quantum signal pulse broadening after passing through the optical fiber with length L is obtained as:

Δt _cla =Δt _quan =t ₀ [1+(L|β ₂ |)/t ₀ ² ] ^1/2

Where Δt _cla is the classical signal broadening, Δt _quan is the quantum signal broadening, t ₀ is the initial pulse width of the quantum signal and the classical signal, L is the fiber length, and β ₂ is the group velocity dispersion coefficient.

According to the quantum signal stretching, it can be obtained that the pulse repetition frequency of the quantum signal is approximately 1/Δt _quan .

Since the classical signal will produce Stokes spontaneous Raman scattering and anti-Stokes spontaneous Raman scattering, two kinds of noise should be removed. The time interval Δt _U in Figure 3 is the Stokes spontaneous Raman after passing through the filter F3 The distribution time of Raman scattering noise, the time interval Δt _L is the distribution time of anti-Stokes spontaneous Raman scattering noise after passing through the filter F3. In order to ensure that the quantum signal is not affected by noise, the quantum signal in these two times needs to be discarded.

Assuming that the power of the classical signal light is not enough to generate stimulated Raman scattering and stimulated Brillouin scattering, the distribution time of spontaneous Raman scattering noise is:

τ＝|L/v _Raman- L/v _cla |

where the spontaneous Raman scattered light velocity and the classical signal velocity are respectively

v _Raman = c/n _Raman and v _cla = c/n _cla

Where n _Raman is the refractive index of spontaneous Raman scattered light in the fiber, n _cla is the refractive index of the classical signal in the fiber, and c is the speed of light in vacuum.

Therefore, the distribution time of the spontaneous Raman scattering noise generated by the classical signal after passing through the filter F3 is:

τ=L*|Δn|/c

Where Δn=n _Raman -n _cla is the refractive index difference between the longest-wavelength spontaneous Raman scattered light and the shortest-wavelength classical signal in the fiber after passing through the filter, and the longest-wavelength spontaneous Raman scattering after passing through the filter The wavelength of light is the upper limit of the bandwidth of the filter, and the wavelength of the spontaneous Raman scattered light with the shortest wavelength after passing through the filter is the lower limit of the bandwidth of the filter;

The bandwidth Δλ of the filter F3 before Bob is:

λ _U -λ _L = Δλ

Among them, λ _U is the upper limit of the bandwidth of the filter F3, and λ _L is the lower limit of the bandwidth of the filter F3.

According to the distribution time τ of the spontaneous Raman scattering noise generated by the classical signal passing through the filter F3 and the pulse cycle time of the quantum signal, the number of quantum signals covered by the noise is calculated, namely

Assuming that the wavelength of the classical signal and the quantum signal are both 1550nm and the initial pulse width is 50fs, then the group velocity dispersion coefficient of the signal with a wavelength of 1550nm in the optical fiber is β ₂ =22.8ps ² /km, and after the transmission length is 90km in the optical fiber, The pulse stretching of the quantum signal is 45.3ps. When the ratio of the time interval between pulses to the pulse width of the quantum signal is 3:1, the repetition frequency of the quantum signal is about 5GHz, and the pulse cycle time is 0.2ns at this time; suppose The central wavelength of the filter is 1550nm, and the bandwidth is 0.2nm. According to the distribution of the refractive index of signals of different wavelengths when they are transmitted in the optical fiber, the difference in refractive index between the noise with the longest wavelength and the classical signal after passing through the filter is approximately 1× 10 ^-6 , and the refractive index difference between the noise with the shortest wavelength and the classical signal after passing through the filter is approximately 1×10 ^-6 , so the distribution time of the spontaneous Raman scattering noise after passing through the filter F3 is 6ps; The cycle time and the noise distribution time after passing through the filter can be used to calculate the number of noises to be approximately 1, that is, at this time, only one quantum signal adjacent to the classical signal can be discarded to achieve low-noise QKD compatibility with WDM classical communication networks.

The same or similar reference numerals correspond to the same or similar components;

The purpose of describing the positional relationship in the drawings is only for illustrative purposes and cannot be understood as a limitation to this patent;

Apparently, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, rather than limiting the implementation of the present invention. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. All modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (6)

1. a kind of method that low-noise QKD is compatible with WDM classical communication network, it is characterized in that, The quantum signal and the classical signal of the same wavelength are time-division multiplexed into the same fiber, and the spontaneous Raman scattering noise generated by the classical signal is distributed around the classical signal; the filter is used to filter the spontaneous Raman scattering noise generated by the classical signal, and the spontaneous Raman After the Mann scattering noise is filtered by the filter, there is still a small amount of noise, and a small amount of spontaneous Raman scattering noise will cover the quantum signal, and the quantum signal covered by the noise generated by the classical signal that still exists after passing through the filter is discarded, so that The output quantum signal is approximately not affected by noise, so that low-noise QKD is compatible with WDM classical communication network; The number of quantum signals that need to be discarded is obtained according to the following method: According to the group velocity dispersion effect, the pulse broadening of the quantum signal after passing through the optical fiber with length L is obtained as: Δt _cla =Δt _quan =t ₀ [1+(L|β ₂ |)/t ₀ ² ] ^1/2 Where Δt _cla is the classical signal broadening, Δt _quan is the quantum signal broadening, t ₀ is the initial pulse width of the quantum signal and the classical signal, L is the fiber length, and β ₂ is the group velocity dispersion coefficient; According to the quantum signal stretching, the pulse repetition frequency of the quantum signal is 1/Δt _quan , and the pulse cycle time of the quantum signal is obtained at the same time; The distribution time τ1 of the spontaneous Raman scattering noise generated by the classical signal is: τ1＝|L/v _Raman -L/v _cla | where the spontaneous Raman scattering light velocity v _Raman and the classical signal velocity v _cla are respectively: v _Raman = c/n _Raman v _cla =c/n _cla where n _Raman is the refractive index of spontaneous Raman scattered light in the fiber, n _cla is the refractive index of the classical signal in the fiber, and c is the speed of light in vacuum; Therefore, the distribution time of the spontaneous Raman scattering noise generated by the classical signal after passing through the filter is: τ=L*|Δn|/c Where Δn=n _Raman -n _cla is the refractive index difference between the spontaneous Raman scattered light with the longest wavelength and the classical signal after passing through the filter or the spontaneous Raman scattered light with the shortest wavelength and the classical signal after passing through the filter The refractive index difference in the fiber, where the wavelength of the spontaneous Raman scattered light with the longest wavelength after passing through the filter is the upper limit of the bandwidth of the filter, and the wavelength of the spontaneous Raman scattered light with the shortest wavelength after passing through the filter is the filter The lower limit of the bandwidth; Abandon the quantum signals within the time interval Δt _U and the time interval Δt _L , where the time interval Δt _U is the distribution time of the Stokes spontaneous Raman scattering noise after passing through the filter, and the time interval Δt _L is the antispatial noise after passing the filter Distribution time of Stokes spontaneous Raman scattering noise; According to the distribution time τ after the spontaneous Raman scattering noise generated by the classical signal passes through the filter and the pulse cycle time of the quantum signal, the number of quantum signals covered by the noise is calculated, namely 2. the method that low-noise QKD according to claim 1 is compatible with WDM classical communication network, it is characterized in that, the quantum signal of described same wavelength and the wavelength of classical signal are set to 1550nm. 3. The method for low-noise QKD compatible with WDM classical communication network according to claim 2, characterized in that, said quantum signal and classical signal are time-division multiplexed to the same optical fiber through a TDM switch node. 4. A device for applying the method for the low-noise QKD described in any one of claims 1 to 3 to be compatible with the WDM classical communication network, characterized in that it comprises a sending end and a receiving end connected in sequence, The transmitting end includes a quantum signal transmitting end and a data signal transmitting end, wherein the signal transmitted by the quantum signal transmitting end and the signal transmitted by the data signal transmitting end are multiplexed into the same optical fiber through a TDM switch node; The quantum signal transmitting end includes a clock signal generator, a laser in the Alice end, an attenuator, a synchronous laser, a frequency divider FD and a first TDM switch node; wherein a part of the clock signal sent by the clock signal generator triggers the clock signal in the Alice end The laser outputs a quantum signal, and the other part is divided by the frequency divider FD to trigger the synchronous laser to output a synchronous signal. The output quantum signal is strongly attenuated by the attenuator to prepare a seductive state and is encoded and multiplexed with the synchronous signal through the first TDM switch node. in the same fiber; The data signal transmitting end includes n data signals of different wavelengths, a WDM-TDM switch node and an erbium-doped fiber amplifier; the n data signals of different wavelengths are converted into a column of TDM data with the same wavelength by the WDM-TDM switch node Signal, the TDM data signal of the same wavelength is amplified by the erbium-doped fiber amplifier, the amplified TDM data signal, and the quantum signal and synchronization signal multiplexed into the same fiber are multiplexed into the same fiber through the TDM switch node; The receiving end includes a third TDM switch node, a fourth TDM switch node, a TDM-WDM switch node, a filter, a photoelectric converter, and a frequency multiplier; the third TDM switch node is used to demultiplex the multiplexed signal into a TDM The data channel and the channel containing the synchronous signal and the quantum signal, wherein the TDM data signal in the TDM data channel is converted into n data signals of different wavelengths through the TDM-WDM switch node, and the data signals of different wavelengths are respectively output to the respective receiving ends; including The channel of the synchronous signal and the quantum signal is demultiplexed into a synchronous channel and a quantum channel through the fourth TDM switch node, wherein the quantum signal in the quantum channel is filtered by a filter and then input to the Bob end, decoded at the Bob end, and the synchronous channel in the The synchronous signal is converted into a clock signal by a photoelectric converter, and then the clock signal is multiplied to the previous frequency by a frequency multiplier, which is used to trigger the single photon detector SPD in the Bob end to detect the quantum signal. 5. The device according to claim 4, wherein the quantum signal transmitting end further comprises a first filter, and the first filter is connected to the laser in the Alice end and is located behind the laser; The data signal transmitting end further includes a second filter, and the erbium-doped fiber amplifier is connected to the TDM switch node through the second filter. 6. The device according to claim 5, wherein the WDM-TDM switch node is composed of a nonlinear optical fiber loop mirror and a high repetition rate monolithic integrated mode-locked semiconductor laser; the TDM-WDM switch The nodes employ nonlinear fiber optic loop mirrors.