CN110868293A - Time division multiplexing high-speed QKD system and method - Google Patents
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Abstract
The invention discloses a time division multiplexing high-speed QKD system and a time division multiplexing high-speed QKD method. The QKD system comprises a sending end, a receiving end and a time division multiplexing demultiplexing device, wherein the sending end comprises a first laser which sends classical light and synchronous light, carries out time division multiplexing and sends out time division multiplexing light; the quantum key coding unit receives the optical signal to carry out quantum key coding and sends out the optical signal in a quantum light form; the first wavelength division multiplexing unit receives the time division multiplexing light and the quantum light, performs wavelength division multiplexing, and emits wavelength division multiplexing light. The invention can effectively reduce the influence of classical optical Raman scattering on quantum light, realize high-speed quantum key distribution, improve the system code rate, and has simple system structure and low realization cost.
Description
Technical Field
The invention relates to the technical field of quantum secure communication, in particular to a time division multiplexing high-speed QKD system and a time division multiplexing high-speed QKD method.
Background
As a new technology developed on the basis of quantum mechanics, modern communication, modern cryptography and the like, the quantum secret communication technology encrypts information by using a one-time pad mode based on the basic principle of quantum mechanics, has the characteristic of indecipherability and has incomparable security advantages. The Quantum Key Distribution (QKD) technology is a Key technology for Quantum secret communication, and the currently adopted basic protocol is BB84 protocol and decoy BB84 protocol developed on the basis of BB84 protocol. One of the issues of intensive research on quantum key distribution technology at present is how to implement quantum key distribution by using the existing optical fiber communication network.
In the prior art, a quantum key distribution technology using a time division multiplexing technology is used to implement quantum key distribution using an existing optical fiber communication network, fig. 1A shows a schematic structural diagram of a transmitting end in the prior art, fig. 1B shows a schematic structural diagram of signal time slot modulation in the prior art, and fig. 2 shows a schematic structural diagram of a receiving end in the prior art. In the prior art scheme shown in fig. 1A, light with a wavelength λ emitted by a laser is input into three different modulators respectively after passing through a beam splitter, where the light is modulated and emitted by the modulator 1 to be synchronous light, modulated and emitted by the modulator 2 to be quantum light, modulated and emitted by the modulator 3 to be classical light, wavelengths of the synchronous light, the quantum light and the classical light are all λ, and the modulator 1, the modulator 2 and the modulator 3 modulate the synchronous light, the quantum light and the classical light according to a time slot shown in fig. 1B. Since the classical light is strong light and produces strong raman scattering effect, the wavelengths of raman scattering noise are various wavelengths including λ, and the attenuation of the noise also requires a certain time. Therefore, in the prior art, after the emission of the classical light, there is a "clean-up period" before the emission of the quantum light, which reduces the effective coding time of the system. As shown in fig. 2, after receiving an optical signal from a transmitting end, a receiving end in the prior art first demultiplexes the optical signal and then splits the optical signal to transmit the optical signal to different optical detectors, which produces a large attenuation effect on the light intensity, so that the transmitting end needs to emit strong light, and the raman scattering noise is in a positive correlation with the light intensity. Therefore, in the prior art, the following problems occur, firstly, the implementation scheme in the prior art is complex and the cost is high due to the fact that a multi-channel modulator is required to adjust optical signals, secondly, a strong raman scattering effect is generated due to the fact that a sending end needs to send strong classical light, and a long clearing period is needed for reducing the influence of raman scattering noise on quantum light, so that high-speed emission cannot be achieved due to the fact that the key emission frequency is low.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides a time division multiplexing method of a time division multiplexing high-speed QKD system, which comprises the following steps: at a first laser, performing time division multiplexing on classical light and synchronous light to form time division multiplexed light, wherein the wavelength of the synchronous light is the same as that of the classical light; receiving time division multiplexed light from a first laser; receiving quantum light from a quantum key encoding unit, wherein the quantum light is different in wavelength from the time division multiplexed light; and wavelength division multiplexing the time division multiplexing light and the quantum light at a wavelength division multiplexer to form wavelength division multiplexing light and emit the wavelength division multiplexing light.
The method as above, wherein the classical light is a narrow pulse with a duty cycle of 30% or less, alternatively 20%, alternatively 10%.
The method as described above, wherein the synchronization light is a narrow pulse with a duty cycle of 1% or less, or 1 ‰.
The method as described above, wherein the period of the synchronization light is T1, 5us ≦ T1 ≦ 30 us.
The method as described above, wherein the period of the quantum light is t, 5ns ≦ t ≦ 60 ns.
The method as described above, wherein the period of the classical light is T2, T ≦ T2 ≦ T1.
The method as described above, wherein the time-division multiplexed light satisfies the following equation: t is less than or equal to delta T is less than or equal to T1/2; wherein t is the period of quantum light; Δ T is the time difference between the synchronization light and the adjacent classical light; t1 is the period of the synchronization light.
In another aspect of the present invention, a transmitting end of a time-division multiplexing high-speed QKD system is provided, including: a quantum key encoding unit configured to receive an optical signal for quantum key encoding to form quantum light, a period t of the quantum light being greater than or equal to 5ns and less than or equal to 60 ns; a first laser configured to emit classical light and synchronous light having the same wavelength, and to time-division multiplex the classical light and the synchronous light to emit time-division multiplexed light, the time-division multiplexed light being different in wavelength from the quantum light, the synchronous light having a period T1 of 5us or more and 30us or less, the classical light period T2 being a quantum light period T or more and 30us or less, and a synchronous light period T1 or more; a first wavelength division multiplexing unit configured to receive the time division multiplexed light and the quantum light, perform wavelength division multiplexing, and emit wavelength division multiplexed light.
In the transmitting end, the classical light is a narrow pulse with a duty cycle of 30% or less, or 20%, or 10%.
In the above transmitting end, the synchronous light is a narrow pulse with a duty ratio of 1% or less, or 1 ‰.
In the above transmitting end, the first wavelength division multiplexing unit is further a wavelength division multiplexer having an isolation degree of 60dB or more.
In another aspect of the present invention, a receiving end of a time-division multiplexing high-speed QKD system is provided, which includes: the second wavelength division multiplexing unit, a time division demultiplexing device and a quantum key decoding unit; the second wavelength division multiplexing unit is configured to receive and demultiplex wavelength division multiplexing light emitted by a transmitting end, transmit the obtained time division multiplexing light to the time division demultiplexing device, and transmit the obtained quantum light to the quantum key decoding unit; and the time division multiplexing de-multiplexing device is configured to receive and detect the time division multiplexing light, convert the time division multiplexing light into a time division multiplexing electrical signal, and further process the time division multiplexing electrical signal to obtain a synchronous electrical signal, a classical electrical signal; the quantum key decoding unit is configured to receive the quantum light and decode the quantum light to obtain a quantum key.
The receiving end as described above, further may include: a second laser, and a third optical transmission unit; the second laser configured to emit classical light for establishing classical communication between the receiving end and the transmitting end; and a third optical transmission unit comprising three optical interfaces, wherein the optical signal input by the first interface is output from the second interface, the optical signal input by the second interface is output from the third interface, the first interface is configured to receive the classical light emitted by the second laser and transmit the classical light to the second wavelength division multiplexing unit, and the second interface receives the time division multiplexing light and transmits the time division multiplexing light to the time division demultiplexing device.
The receiving end as described above, wherein the time division multiplexing apparatus further includes: a second optical detection unit configured to receive and detect the time-division multiplexed light and convert the time-division multiplexed light into a time-division multiplexed electrical signal; the clock distribution unit comprises a signal input port and two or more signal output ports, and is configured to receive the time division multiplexing electric signals, distribute the time division multiplexing electric signals to form a first time division multiplexing signal and a second time division multiplexing signal, and output the first time division multiplexing signal and the second time division multiplexing signal; a programmable unit configured to emit a first control signal for detecting a synchronous electrical signal, a second control signal for detecting a classical electrical signal; a first logic unit including two or more signal input ports, one signal output port having a logic operation function, configured to receive the first time division multiplexing signal, the first control signal, and to process the first control signal to send out the synchronous electrical signal; and the second logic unit comprises two or more signal input ports and one signal output port, has a logic operation function, is configured to receive the second time division multiplexing signal and the second control signal, and sends out the classical electric signal after processing.
At the receiving end, the signal characteristics of the first time-division multiplexed electrical signal and the second time-division multiplexed electrical signal are consistent with the signal characteristics of the time-division multiplexed electrical signal.
In another aspect of the present invention, a method for demultiplexing a time-division multiplexed high-speed QKD system is provided, including: the second optical detection unit receives and detects the time division multiplexing light, and converts the time division multiplexing light into a time division multiplexing electric signal; receiving the time division multiplexing electric signals by the clock distribution unit and distributing to form a first time division multiplexing electric signal and a second time division multiplexing electric signal; sending out a first control signal for detecting a synchronous electrical signal and a second control signal for detecting a classical electrical signal by the programmable unit; the first time division multiplexing electric signal and the first control signal are input into the first logic unit, and after being processed, a synchronous electric signal is output; and the second time division multiplexing electric signal and the second control signal are input into the second logic unit, and after being processed, a classical electric signal is output.
In another aspect of the present invention, a quantum key distribution method for a time-division multiplexing high-speed QKD system is provided, including: the first laser emits classical light and synchronous light, performs time division multiplexing and emits time division multiplexing light; the quantum key coding unit is used for carrying out quantum key coding and emitting quantum light; receiving the time division multiplexing light and the quantum light by a first wavelength division multiplexing unit, carrying out wavelength division multiplexing, emitting wavelength division multiplexing light, and transmitting the wavelength division multiplexing light through a channel; receiving the wavelength division multiplexing light by a second wavelength division multiplexer and demultiplexing to obtain time division multiplexing light and quantum light; receiving and decoding the quantum light by a quantum key decoding unit to obtain a quantum key; and a time division multiplexing de-multiplexing device receives the time division multiplexing light for detection and converts the time division multiplexing light into a time division multiplexing electrical signal, and the time division multiplexing electrical signal is further processed to obtain a synchronous electrical signal, namely a classical electrical signal.
In another aspect of the present invention, a unidirectional system of a time-division-multiplexed high-speed QKD system is proposed, which includes any one of the above-described time-division-multiplexing methods, or any one of the above-described transmitting ends, or any one of the above-described receiving ends, or any one of the above-described de-time-division-multiplexing methods, or any one of the above-described quantum key distribution methods.
In another aspect of the present invention, a two-way system of a time-division-multiplexed high-speed QKD system is proposed, which includes any one of the above-described time-division-multiplexing methods, or any one of the above-described transmitting ends, or any one of the above-described receiving ends, or any one of the above-described de-time-division-multiplexing methods, or any one of the above-described quantum key distribution methods.
The time division multiplexing high-speed QKD system and the time division multiplexing high-speed QKD method can effectively reduce the influence of classical optical Raman scattering on quantum light, realize high-speed quantum key distribution, improve the system code rate, and have simple system structure and low realization cost.
Drawings
Fig. 1A shows a schematic structure diagram of a transmitting end of a time division multiplexing quantum key distribution system in the prior art;
FIG. 1B shows a signal slot modulation diagram of a prior art time division multiplexed quantum key distribution system;
fig. 2 shows a schematic structure diagram of a receiving end of a time division multiplexing quantum key distribution system in the prior art;
fig. 3 shows a schematic structural diagram of an exemplary embodiment of a transmitting end according to the present invention;
fig. 4 shows a signal slot modulation diagram of a transmitting end according to the present invention;
fig. 5 shows a schematic structural diagram of an exemplary embodiment of a transmitting end according to the present invention;
fig. 6 shows a schematic structural diagram of an exemplary embodiment of a receiving end according to the present invention;
fig. 7 shows a schematic structural diagram of an exemplary embodiment of a de-time division multiplexing apparatus according to the present invention;
fig. 8 shows a schematic diagram of the initialization phase of the de-time division multiplexing device according to the invention;
fig. 9 shows a signal diagram of an initialization phase of the de-time division multiplexing device according to the invention;
fig. 10 shows a schematic diagram of the working phases of a de-time division multiplex apparatus according to the invention;
fig. 11 shows a signal diagram of the operating phase of a de-time division multiplex device according to the invention;
FIG. 12 shows a flow chart of a method of de-time division multiplexing according to the invention;
FIG. 13 is a schematic diagram illustrating one exemplary embodiment of a one-way QKD system in accordance with the present invention;
FIG. 14 is a schematic diagram illustrating one exemplary embodiment of a two-way QKD system in accordance with the present invention;
fig. 15 shows a flow diagram of a quantum key distribution method according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, 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 some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the following detailed description, reference is made to the accompanying drawings that form a part hereof and in which is shown by way of illustration specific embodiments of the application. In the drawings, like numerals describe substantially similar components throughout the different views. Various specific embodiments of the present application are described in sufficient detail below to enable those skilled in the art to practice the teachings of the present application.
Fig. 3 illustrates an exemplary embodiment of a transmitting end according to the present invention. The basic structure of the transmitting end of the present invention can be exemplarily illustrated by the embodiment of fig. 3. As shown in fig. 3, the transmitting end of the present invention may include a quantum key encoding unit 101, a first laser 103, a first wavelength division multiplexing unit 201, a first optical transmission unit 203, and a first optical detection unit 301.
In some embodiments, the quantum key encoding unit 101 may receive the optical signal, perform quantum key encoding, and transmit the encoded quantum signal in the form of quantum light, and the quantum key encoding unit 101 may be a polarization encoding device, a time encoding device, a phase encoding device, or a time phase encoding device, preferably a time phase encoding device. The probability of quantum key encoding by the quantum key encoding unit 101 is random, and after quantum key encoding is completed, the wavelength λ is t1The period t is within the range of 5ns to 60 ns. The quantum key encoding unit 101 may include an encoding preparation device that receives the optical signal to perform quantum key encoding; can comprise a decoy state preparation device for carrying out decoy statesPreparing; can comprise a single-photon preparation device for preparing single photons.
In some embodiments, the first lasers 103 may emit light having the same wavelength λ2Wherein the synchronization light is operable to transmit the encoded synchronization signal and the classical light is operable to transmit the encoded classical signal. The first laser 103 may send a sync light during the initialization phase of the present invention and send a sync light or a classical light during the operation phase of the present invention. The synchronous light emitted by the first laser 103 can transmit synchronous frames meeting the requirements of synchronous digital transmission, the digital synchronous transmission can adopt an optical fiber channel to realize the functions of multi-node synchronous information transmission, multiplexing, add-drop multiplexing, cross connection and the like, the synchronous light emitted by the first laser 103 can be narrow pulses with the duty ratio less than or equal to 1 percent, and further narrow pulses with the duty ratio less than or equal to 1 per thousand, the period of the synchronous light emitted by the first laser 103 is T1, and the numerical range of the period T1 is 5 us-T1-30 us; the classical light emitted by the first laser 103 can be a classical light pulse with a pulse width capable of being modulated, and the classical light is a narrow pulse with a duty cycle less than or equal to 30%; preferably, the pulse is a narrow pulse with a duty ratio of 20% or less; further preferably a narrow pulse having a duty ratio of 10% or less; the period of the classical light emitted by the first laser 103 is T2, and the value range of the period T2 is T < T2 < T1.
The first laser 103 adopts time division multiplexing technology in the process of emitting the classical light and the synchronous light, the channel transmission time is divided into different time slots, and the system allocates the different time slots after division to the synchronous light and the classical light, thereby realizing the time division multiplexing of the synchronous light and the classical light. The first laser 103 modulates the synchronous light and the classical light emitted by it according to the time slot modulation diagram shown in fig. 4. The first laser 103 modulates the synchronization light according to the time slot diagram shown in the first row of fig. 4, where the synchronization light wavelength is λ as shown in the first row of fig. 42The period is T1, T1 is more than or equal to 5us and less than or equal to 30 us; the first laser 103 modulates the classical light according to the time slot diagram shown in the second row of fig. 4, the classical light wavelength being λ as shown in the second row of fig. 42The period is T2, T is more than or equal to T2 and more than or equal to T1; first laser 103And time division multiplexing the synchronous light and the classical light according to a time slot diagram shown in the third row of fig. 4, realizing the time division multiplexing of the classical light and the synchronous light, and emitting the time division multiplexed light, wherein the time difference between the synchronous light and the adjacent classical light is delta T, and the value range of the time difference is T less than or equal to delta T less than or equal to T1/2.
In some embodiments, the first wavelength division multiplexing unit 201 includes a first port C, a second port R, and a third port T. The first wavelength division multiplexing unit 201 is a bidirectional optical element, and can be set in the following mode: when light in the first frequency range is incident from the second port R and/or light in the second frequency range is incident at the third port T, the incident light of the second port R and the incident light of the third port T are combined into one path of output at the first port C; when light is incident on the first port C, the second port R outputs light in the first frequency range, and the third port T outputs light in the second frequency range. Wherein the first frequency range may be different from the second frequency range.
The first wavelength division multiplexing unit 201 may be a sparse wavelength division multiplexer, a dense wavelength division multiplexer, a band pass wavelength division multiplexer, or a fiber bragg grating, but is not limited thereto. Since the sparse wavelength division multiplexer, the dense wavelength division multiplexer, and the band pass wavelength division multiplexer have a common port, a reflection port, and a transmission port, and the isolation of the transmission port is greater than that of the reflection port, it is preferable to use these three wavelength division multiplexers, and set the common port to the first port C, the reflection port to the second port R, and the transmission port to the third port T. Preferably, the first wavelength division multiplexing unit 201 may be a wavelength division multiplexer having an isolation degree of 60dB or more.
The quantum light emitted by the quantum key encoding unit 101 and the time division multiplexing light emitted by the first laser 103 may be input through the second port R of the first wavelength division multiplexing unit 201 or may be input through the third port T of the first wavelength division multiplexing unit 201, and further the quantum light emitted by the quantum key encoding unit 101 may be input through the third port T of the first wavelength division multiplexing unit 201, which may facilitate the transmission port with the maximum isolation degree to eliminate the influence of local fluorescence on the quantum light. The classical light emitted by the receiving end of the present invention is transmitted to the first wavelength division multiplexing unit 201 via the channel, and is transmitted to the first single photon detection unit 301 via the first wavelength division multiplexing unit 201.
In some embodiments, the first optical transmission unit 203 may include three optical interfaces: a first interface, a second interface and a third interface; wherein the optical signal input from the first interface is output from the second interface, and the optical signal input from the second interface is output from the third interface. Preferably, the first optical transmission unit 203 may be a circulator. A first interface of the first optical transmission unit 203 is connected to the first laser 103 to receive the time division multiplexed light emitted by the first laser 103; the second interface of the first optical transmission unit 203 is connected to the first wavelength division multiplexer 201, so as to transmit the time division multiplexing light emitted by the first laser 103 to the first wavelength division multiplexer 201, and receive the classical light emitted by the receiving end of the present invention transmitted by the first wavelength division multiplexing unit 201; the third interface of the first optical transmission unit 203 is connected to the first optical detection unit 301, so as to receive the classical light emitted from the system receiving end transmitted from the first wavelength division multiplexing unit 201, and transmit the classical light to the first optical detection unit 301.
In some embodiments, the first light detection unit 301 may include a PN junction type photodetector, or may include a PIN type photodetector, or may include an Avalanche Photodiode (APD) detector, or may include a pull-through avalanche photodiode (RAPD) detector, and may be configured to receive and detect the classical light emitted by the receiving end of the present invention, so that the classical communication link is established between the transmitting end of the present invention and the receiving end of the present invention.
In the present invention, the first laser 103 may emit light having a wavelength λ2Synchronous light with period T1 and wavelength of λ2The classical light with the period of T2 is modulated according to the time slot diagram shown in the first row of fig. 4, the classical light is modulated according to the time slot diagram shown in the second row of fig. 4, and the classical light and the synchronous light are time-division multiplexed according to the time slot diagram shown in the third row of fig. 4, so that the time-division multiplexing of the classical light and the synchronous light is realized, and the light with the wavelength of λ is emitted2In the emitted time-division multiplexed light, the synchronization light and the phaseThe numerical range of the time difference delta T between the adjacent classical lights is more than or equal to the period T of the quantum light and less than or equal to T1/2; the quantum key encoding unit 101 may perform quantum key encoding and emit light with a wavelength λ1Quantum light of period t; wavelength lambda of the time division multiplexed light2With wavelength lambda of quantum light1Are not equal; the first wavelength division multiplexing unit 201 may receive the wavelength λ emitted by the first laser 1032The wavelength emitted by the time division multiplexing optical and quantum key encoding unit 101 is lambda1And wavelength division multiplexing the time division multiplexing light and the quantum light, and then sending out the wavelength division multiplexing light and transmitting the wavelength division multiplexing light through a channel.
In the invention, the quantum light and the time division multiplexing light, namely the quantum light and the classical light or the synchronous light have different wavelengths, and the wavelength division multiplexing can be carried out, which means that the quantum light is not subjected to time division multiplexing, so that the problem that a relatively long 'clearing period' is required before the quantum light is emitted in the prior art can not be generated, the sending frequency of the quantum light is not influenced by the time division multiplexing, and the high-speed sending of the quantum key can be realized. In addition, the transmitting end of the invention does not need to use a plurality of modulators to modulate the classical light and the synchronous light during time division multiplexing, thereby simplifying the system structure and reducing the cost.
Fig. 5 shows a schematic structural diagram of an exemplary embodiment of a transmitting end according to the present invention. The embodiment shown in fig. 5 has similar functions with similar devices and structures as the embodiment shown in fig. 3. As shown in fig. 5, the transmitting end of the present invention may include a first attenuator 401, a second optical transmission unit 205, and a first filtering unit 403.
In some embodiments, the first attenuator 401 may be an electrically adjustable attenuator, and may receive the classical light or the synchronous light or the time-division multiplexed light emitted from the first laser 103, and adjust the light intensity of the classical light or the synchronous light or the time-division multiplexed light to output to the first wavelength division multiplexing unit 201. In the invention, the system can obtain the light intensity value required by the system according to the sensitivity of the optical detector at the receiving end, the attenuation condition of classical light or synchronous light or time division multiplexing light after time division multiplexing in the transmission process of a system link. The first attenuator 401 can precisely adjust the intensity of the classical light or the synchronous light emitted from the first laser 103 or the time-division multiplexed light after time-division multiplexing according to the light intensity requirement of the system to meet the requirement of the system.
In some embodiments, the second optical transmission unit 205 may include three optical interfaces: a first interface, a second interface and a third interface; wherein the optical signal input from the first interface is output from the second interface, and the optical signal input from the second interface is output from the third interface. Preferably, the second optical transmission unit 205 may be a circulator. A first interface of the second optical transmission unit 205 is connected to the quantum key encoding unit 101 and receives quantum light emitted by the quantum key encoding unit 101; a second interface of the second optical transmission unit 205 is connected with the first filtering unit 403 to transmit the quantum light received by the second optical transmission unit 205 to the first filtering unit 403; a third interface of the second optical transmission unit 205 is connected to the first wavelength division multiplexing unit 201 to transmit the quantum light filtered by the first filtering unit 403 to the first wavelength division multiplexing unit 201.
In some embodiments, the first filtering unit 403 may receive the quantum light emitted by the quantum key encoding unit 101 transmitted through the second optical transmission unit 205, filter spontaneous emission noise generated by a laser in the quantum light, and in the case that the quantum key encoding unit 101 employs time coding or phase coding or time phase coding, may increase an extinction ratio of the coding so as to reduce a system error, and output the quantum light with noise filtered out to the second interface of the second optical transmission unit 205. Preferably, the first filtering unit 403 may be a filter, and further may be a grating filter.
Fig. 6 shows a schematic structural diagram of an exemplary embodiment of a receiving end according to the present invention. As shown in fig. 6, the receiving end of the present invention may include a second laser 105, a second wavelength division multiplexing unit 207, a third optical transmission unit 209, a time division demultiplexing device 305, and a quantum key decoding unit 303.
In some embodiments, the second laser 105 may emit classical light, which may be transmitted to the transmitting end of the present invention through a channel and detected by the first single-photon detection unit 301 of the transmitting end to establish a classical communication link between the receiving end of the present invention and the transmitting end of the present invention.
In some embodiments, the second wavelength division multiplexing unit 207 includes a first port C, a second port R, and a third port T. The second wavelength division multiplexing unit 207 is a bidirectional optical element, and can be set to the following mode: when light in the first frequency range is incident from the second port R and/or light in the second frequency range is incident at the third port T, the incident light of the second port R and the incident light of the third port T are combined into one path of output at the first port C; when light is incident on the first port C, the second port R outputs light in the first frequency range, and the third port T outputs light in the second frequency range. Wherein the first frequency range may be different from the second frequency range.
The second wavelength division multiplexing unit 207 may be a sparse wavelength division multiplexer, a dense wavelength division multiplexer, a band pass wavelength division multiplexer, or a fiber bragg grating, but is not limited thereto. Since the sparse wavelength division multiplexer, the dense wavelength division multiplexer, and the band pass wavelength division multiplexer have a common port, a reflection port, and a transmission port, and the isolation of the transmission port is greater than that of the reflection port, it is preferable to use these three wavelength division multiplexers, and set the common port to the first port C, the reflection port to the second port R, and the transmission port to the third port T. Preferably, the second wavelength division multiplexing unit 207 may be a wavelength division multiplexer having an isolation degree of 60dB or more.
The second wavelength division multiplexing unit 207 receives the wavelength division multiplexing light transmitted by the transmitting end of the present invention, and performs wavelength division demultiplexing on the received wavelength division multiplexing light, wherein the quantum light obtained by wavelength division demultiplexing is transmitted to the quantum key decoding unit 303, and the time division multiplexing light obtained by wavelength division demultiplexing is transmitted to the time division demultiplexing device 305.
In some embodiments, the third optical transmission unit 209 may include three optical interfaces: a first interface, a second interface and a third interface; wherein the optical signal input from the first interface is output from the second interface, and the optical signal input from the second interface is output from the third interface. Preferably, the third optical transmission unit 209 may be a circulator. The third optical transmission unit 209 is connected to the second laser 105 at the first interface, and receives the classical light emitted by the second laser 105; the second interface of the third optical transmission unit 209 is connected to the second wavelength division multiplexing unit 207, so as to output the classical light emitted by the second laser 105 to the second wavelength division multiplexing unit 207 and receive the time division multiplexed light transmitted by the second wavelength division multiplexing unit 207; the third interface of the third optical transmission unit 209 is connected to the demultiplexing device 305 to transmit the time-division multiplexed light received by the third optical transmission unit 209 to the demultiplexing device 305.
In some embodiments, the de-time multiplexing apparatus 305 may receive the time-division multiplexed light transmitted through the third optical transmission unit 209, detect the received time-division multiplexed light, convert the time-division multiplexed light into a time-division multiplexed electrical signal, and further process the time-division multiplexed electrical signal to obtain a synchronous electrical signal and a classical electrical signal.
In some embodiments, the quantum key decoding unit 303 may receive the quantum light transmitted by the second wavelength division multiplexing unit 207, and detect the quantum light to decode the quantum key to obtain the encoded information therein. The quantum key decoding unit 303 may detect and decode various forms of quantum key encoding such as polarization encoding, time encoding, phase encoding, time phase encoding, and the like, and preferably may detect and decode time encoding, phase encoding, or time phase encoding.
In some embodiments, the quantum key decoding unit 303 may include a first single-photon detector 3031, a second single-photon detector 3033, a third single-photon detector 3035, and a fourth single-photon detector 3037, which may be a PN junction type photodetector, a PIN type photodetector, an Avalanche Photodiode (APD) detector, or a pull-through avalanche photodiode (RAPD) detector. When detecting the time phase code, the first single-photon detector 3031 and the second single-photon detector 3033 can be time code detectors, and can detect 0 code or 1 code in the Z-basis vector time code; the third single-photon detector 3035 and the fourth single-photon detector 3037 can be phase coding detectors and can detect 0 codes or 1 codes of X basis vectors or Y basis vectors; when detecting the polarization codes, the first single-photon detector 3031, the second single-photon detector 3033, the third single-photon detector 3035 and the fourth single-photon detector 3037 can respectively detect the H/V/P/N codes of the polarization codes; when detecting the phase code, the first single-photon detector 3031, the second single-photon detector 3033, the third single-photon detector 3035 and the fourth single-photon detector 3037 can respectively detect 0, pi/2, pi and 3 pi/2.
Fig. 7 shows a schematic structural diagram of an exemplary embodiment of a de-time division multiplexing apparatus according to the present invention. As shown in fig. 7, the time division multiplexing apparatus of the present invention may include a second optical detection unit 307, a clock distribution unit 501, a programmable unit 601, a first logic unit 603, and a second logic unit 605, where the programmable unit 601 may include a control chip 6011, a signal generation device 6013, and a delay device 6015.
In some embodiments, the second optical detection unit 307 may receive and detect the optical signal and obtain a corresponding electrical signal, and the second optical detection unit 307 may be a PN junction type photodetector, a PIN type photodetector, an Avalanche Photodiode (APD) detector, or a pull-through type avalanche photodiode (RAPD) detector. The clock distribution unit 501 may include one signal input port, may include two or more signal output ports, and may output the input electrical signals through different output ports after being distributed according to system requirements. Preferably, the clock distribution unit 501 may be a clock distributor.
In some embodiments, the programmable unit 601 may issue different signals according to different working phases of the present invention, may issue a scan signal during the initialization phase, and may issue a control signal during the working phase. The programmable unit 601 may include a control chip 6011, and may issue an operation instruction to the signal generation device 6013 or the delay device 6015; the signal generating device 6013 may receive an operation instruction of the control chip 6011, generate different electrical signals in different working stages of the present invention, send a scanning signal in an initialization stage, and send a control signal in a working stage; the delay device 6015 may receive an operation instruction of the control chip 6011 and the electrical signal generated by the signal generation device 6013, and perform a delay operation on the received electrical signal according to the received operation instruction.
In some embodiments, the first logic unit 603 is a circuit capable of performing a logic operation, and may be an and gate circuit, an or gate circuit, or an nor gate circuit, an xor gate circuit, or an xnor gate circuit. The first logic unit 603 may include two or more signal input ports and may include one signal output port. Preferably, the first logic unit 603 may be a logic chip. The second logic unit 605 has a similar structure and function to the first logic unit 603. Preferably, the first logic unit 603 and the second logic unit 605 may be and circuits.
The inventive de-time division multiplexing device can have different operation modes in the inventive initialization phase or working phase.
Fig. 8 shows a schematic diagram of an initialization phase of the time division multiplexing apparatus according to the present invention, and fig. 9 shows a signal diagram of an initialization phase of the time division multiplexing apparatus according to the present invention. During the initialization phase of the present invention, the first laser 103 emits a synchronization light, which is transmitted to the time division multiplexing apparatus of the present invention through a channel. The second light detecting unit 307 receives and detects the synchronization light, and converts the synchronization light into a synchronization electrical signal shown in the first row of fig. 9, where the synchronization electrical signal and the synchronization light have the same signal characteristics of period, wavelength, pulse width, duty ratio, frequency, and the like. The clock distribution unit 501 receives the synchronization electrical signal and distributes it to the first logic unit 603. In the initialization stage, the sending end of the invention can send the information such as the period, the pulse width and the like of the synchronous light to the time division multiplexing device at the receiving end through a classical channel. After receiving the information of the period, pulse width, etc. of the synchronizing light, the programmable unit 601 sends a signal generating instruction to the signal generating device 6013 from the control chip 6011, randomly generates a scanning signal as shown in the second row of fig. 9, which has the same period as the synchronizing electrical signal and has a pulse width 1.5 to 3 times as long as the pulse width of the synchronizing electrical signal, and sends the scanning signal to the first logic unit 603 through the delay device 6015. After receiving the synchronization signal and the scan signal, the first logic unit 603 performs an and gate logic operation. If the first logic unit 603 does not output high level after the and gate operation, that is, the scanning signal does not scan the synchronous electrical signal, the control chip 6011 instructs the delay device 6015 to perform a delay operation for a certain time on the scanning signal generated by the signal generation device 6013 to obtain the scanning signal shown in the third row of fig. 9, and sends the scanning signal to the first logic unit 603, and then the first logic unit 603 performs the and gate operation on the received synchronous electrical signal and the scanning signal until there is a high level output, at this time, the programmable unit 601 may generate a first control signal 705 as shown in the fourth row of fig. 9, which has the same period and the same frequency as the synchronous electrical signal and has a pulse width 1.5 to 3 times as the pulse width of the synchronous electrical signal, so as to detect the synchronous electrical signal, perform the negation operation on the first control signal 705 and generate a second control signal 707 as shown in the fifth row of fig. 9, for detecting classical electrical signals.
Fig. 10 shows a schematic diagram of the operating phases of the de-time division multiplex device according to the invention. Fig. 11 shows a signal diagram of the operating phases of a time division multiplex de-multiplexer device according to the invention. As shown in fig. 11, the first row is a time-division multiplexed electrical signal, the second row is a first time-division multiplexed electrical signal 701, the third row is a second time-division multiplexed electrical signal 703, the fourth row is a first control signal 705, the fifth row is a second control signal 707, the sixth row is a synchronous electrical signal, and the seventh row is a classical electrical signal.
In the working phase of the present invention, the second optical detection unit 307 receives the time division multiplexing light emitted by the transmitting end of the present invention, detects the received time division multiplexing light, converts the time division multiplexing light into a time division multiplexing electrical signal, and obtains the time division multiplexing electrical signal as shown in the first row of fig. 11, where the obtained time division multiplexing electrical signal and the time division multiplexing light have the same signal characteristics such as period, frequency, wavelength, duty cycle, pulse width, and the like. The clock distribution unit 501 may receive the time-division multiplexed electrical signal shown in the first row of fig. 11, distribute the received time-division multiplexed electrical signal, and output a first time-division multiplexed electrical signal 701 shown in the second row of fig. 11 and a second time-division multiplexed electrical signal 703 shown in the third row of fig. 11, where signal characteristics and values of the first time-division multiplexed electrical signal 701 and the second time-division multiplexed electrical signal 703 are consistent with the time-division multiplexed electrical signal. The first logic unit 603 receives a first time division multiplexed electrical signal 701 as shown in the second row of fig. 11 and a first control signal 705 sent by the programmable unit 601 as shown in the fourth row of fig. 11. The first logic unit 603 may receive the first time division multiplexing electrical signal 701 and the first control signal 705, perform an and gate logic operation, and output a synchronous electrical signal as shown in the sixth row of fig. 11, where the obtained synchronous electrical signal has the same signal characteristics as the synchronous light, such as period, frequency, wavelength, duty cycle, and pulse width. The second logic unit 605 receives the second time-division-multiplexed electrical signal 703 shown in the third row of fig. 11 and the second control signal 707 sent by the programmable unit 601 shown in the fifth row of fig. 11. The second logic unit 605 may receive the second time-division multiplexing electrical signal 703 and the second control signal 707, perform an and gate logic operation, and output a classical electrical signal as shown in the seventh row of fig. 11, where the obtained classical electrical signal has the same signal characteristics as the classical light, such as period, frequency, wavelength, duty cycle, and pulse width.
Fig. 12 shows a flow chart of a method of demultiplexing according to the invention. As shown in fig. 12, the time division multiplexing method of the present invention may include the steps of:
s1201: the second optical detection unit 307 receives and detects the time division multiplexing light, and converts the time division multiplexing light into a time division multiplexing electrical signal;
s1202: the clock distribution unit 501 receives the time division multiplexed electrical signal and distributes the time division multiplexed electrical signal to form a first time division multiplexed electrical signal 701 and a second time division multiplexed electrical signal 703;
s1203: the programmable unit 601 generates a first control signal 705 for detecting a synchronous electrical signal, a second control signal 707 for detecting a classical electrical signal;
s1204: the first time division multiplexing electrical signal 701 and the first control signal 705 are input to the first logic unit 603, and after performing and gate logic operation, a synchronous electrical signal is output; the second time-division multiplexed electrical signal 703 and the second control signal 707 are input to the second logic unit 605, and subjected to and gate logic operation, and then output as a classical electrical signal.
Fig. 13 is a schematic diagram illustrating an exemplary embodiment of a one-way QKD system according to the present invention. The embodiment shown in fig. 13 is similar to the previous embodiments in terms of similar devices and structures with similar functions. The one-way QKD system of the present invention, as shown in fig. 13, may include a transmitting end, a channel, and a receiving end. The transmitting end may include a quantum key encoding unit 101, a first laser 103, a first wavelength division multiplexing unit 201, a first optical transmission unit 203, and a first optical detection unit 301. The quantum key encoding unit 101 may perform quantum key encoding and emit quantum light; the first laser 103 may emit classical light or synchronous light, and perform time division multiplexing on the classical light and the synchronous light to emit time division multiplexed light; the first wavelength division multiplexer 201 receives the time division multiplexed light and the quantum light, performs wavelength division multiplexing, emits the wavelength division multiplexed light, and transmits the wavelength division multiplexed light to a receiving end through a quantum channel. The receiving end may include a second laser 105, a second wavelength division multiplexer 207, a third optical transmission unit 209, a quantum key decoding unit 303, a de-time multiplexing device 305. The receiving end receives the wavelength division multiplexed light transmitted through the channel. The second wavelength division multiplexer 207 demultiplexes the wavelength division multiplexing light received by the receiving end, and the demultiplexed time division multiplexing light is transmitted to the time division demultiplexing device 305, and the demultiplexed quantum light is transmitted to the quantum key decoding unit 303. The time division multiplexing demultiplexing device 305 may receive and detect the time division multiplexing light, convert the time division multiplexing light into a time division multiplexing electrical signal, and process the time division multiplexing electrical signal to obtain a synchronous electrical signal and a classical electrical signal; the quantum key decoding unit 303 may receive, detect and decode the quantum light to obtain the quantum key.
Fig. 14 shows a schematic diagram of an exemplary embodiment of a two-way QKD system according to the present invention. The embodiment shown in fig. 14 is similar to the previous embodiments in terms of similar devices and structures with similar functions. The two-way QKD system of the present invention as shown in fig. 14 may include a first transmitting-receiving end, a channel, and a second transmitting-receiving end. The first transmitting and receiving end may include a first quantum key encoding unit 101, a first laser 103, a first wavelength division multiplexing unit 201, a first optical transmission unit 203, a third wavelength division multiplexing unit 211, a first optical detection unit 301, and a second quantum key decoding unit 309. The second transceiver may include a second laser 105, a second quantum key encoding unit 107, a second wavelength division multiplexing unit 207, a third optical transmission unit 209, a fourth wavelength division multiplexing unit 213, a first quantum key decoding unit 303, and a time division demultiplexing device 305. The present embodiment can implement bidirectional quantum key distribution.
Fig. 15 shows a flow diagram of a quantum key distribution method according to the present invention. As shown in fig. 15, the quantum key distribution method of the present invention includes the following steps:
s1501: the quantum key encoding unit 101 performs quantum key encoding and emits quantum light;
s1502: the first laser 103 emits classical light, synchronous light, and performs time division multiplexing to emit time division multiplexed light;
s1503: the first wavelength division multiplexer 201 receives the time division multiplexing light and the quantum light, performs wavelength division multiplexing, emits wavelength division multiplexing light, and transmits the wavelength division multiplexing light through a channel;
s1504: the second wavelength division multiplexer 207 receives and demultiplexes the wavelength division multiplexing light to obtain time division multiplexing light and quantum light;
s1505: the quantum key decoding unit 303 receives and decodes the quantum light to obtain a quantum key;
s1506: the demultiplexing device 305 receives the tdm light, detects the tdm light, converts the tdm light into a tdm electrical signal, and further processes the tdm electrical signal to obtain a synchronous electrical signal and a classical electrical signal.
The above embodiments are provided only for illustrating the present invention and not for limiting the present invention, and those skilled in the art can make various changes and modifications without departing from the scope of the present invention, and therefore, all equivalent technical solutions should fall within the scope of the present invention.
Claims (19)
1. A method of time-division multiplexing a time-division multiplexed high-speed QKD system, comprising:
at a first laser, performing time division multiplexing on classical light and synchronous light to form time division multiplexed light, wherein the wavelength of the synchronous light is the same as that of the classical light;
receiving time division multiplexed light from a first laser;
receiving quantum light from a quantum key encoding unit, wherein the quantum light is different in wavelength from the time division multiplexed light; and
and wavelength division multiplexing the time division multiplexing light and the quantum light at a wavelength division multiplexer to form wavelength division multiplexing light and emit the wavelength division multiplexing light.
2. The method of claim 1, wherein the classical light is a narrow pulse with a duty cycle of 30% or less, or 20%, or 10%.
3. The method of claim 1, wherein the synchronization light is a narrow pulse with a duty cycle of 1% or less, or 1% o.
4. The method of claim 1, wherein the period of the synchronization light is T1, 5us ≦ T1 ≦ 30 us.
5. The method of claim 1, wherein the quantum light has a period of t, 5ns ≦ t ≦ 60 ns.
6. The method of claim 1, wherein the period of the classical light is T2, T ≦ T2 ≦ T1.
7. The method of claim 1, wherein the time-division multiplexed light satisfies the following equation:
t≤ΔT≤T1/2；
wherein t is the period of quantum light; Δ T is the time difference between the synchronization light and the adjacent classical light; t1 is the period of the synchronization light.
8. A transmitting end of a time-division-multiplexed high-speed QKD system, comprising:
a quantum key encoding unit configured to receive an optical signal for quantum key encoding to form quantum light, a period t of the quantum light being greater than or equal to 5ns and less than or equal to 60 ns;
a first laser configured to emit classical light and synchronous light having the same wavelength, and to time-division multiplex the classical light and the synchronous light to emit time-division multiplexed light, the time-division multiplexed light being different in wavelength from the quantum light, the synchronous light having a period T1 of 5us or more and 30us or less, the classical light period T2 being a quantum light period T or more and 30us or less, and a synchronous light period T1 or more;
a first wavelength division multiplexing unit configured to receive the time division multiplexed light and the quantum light, perform wavelength division multiplexing, and emit wavelength division multiplexed light.
9. The transmission end of claim 8, the classical light is a narrow pulse with a duty cycle of 30% or less, or 20%, or 10%.
10. The transmitting end of claim 8, wherein the synchronization light is a narrow pulse with a duty cycle of 1% or less, or 1 ‰.
11. The transmitting end of claim 8, the first wavelength division multiplexing unit further being a wavelength division multiplexer having an isolation degree of 60dB or more.
12. A receiving end of a time-multiplexed high-speed QKD system, comprising: the second wavelength division multiplexing unit, a time division demultiplexing device and a quantum key decoding unit;
the second wavelength division multiplexing unit is configured to receive the wavelength division multiplexing light and demultiplex the wavelength division multiplexing light, transmit the obtained time division multiplexing light to the de-time division multiplexing device, and transmit the obtained quantum light to the quantum key decoding unit; and
the time division multiplexing de-multiplexing device is configured to receive and detect the time division multiplexing light, convert the time division multiplexing light into a time division multiplexing electrical signal, and further process the time division multiplexing electrical signal to obtain a synchronous electrical signal, a classical electrical signal;
the quantum key decoding unit is configured to receive the quantum light and decode the quantum light to obtain a quantum key.
13. The receiving end according to claim 12, further comprising: a second laser, and a third optical transmission unit;
the second laser configured to emit classical light for establishing classical communication between the receiving end and the transmitting end;
and a third optical transmission unit comprising three optical interfaces, wherein the optical signal input by the first interface is output from the second interface, the optical signal input by the second interface is output from the third interface, the first interface is configured to receive the classical light emitted by the second laser and transmit the classical light to the second wavelength division multiplexing unit, and the second interface receives the time division multiplexing light and transmits the time division multiplexing light to the time division demultiplexing device.
14. The receiving end according to claim 12, wherein the time division multiplexing apparatus further comprises:
a second optical detection unit configured to receive and detect the time-division multiplexed light and convert the time-division multiplexed light into a time-division multiplexed electrical signal;
the clock distribution unit comprises a signal input port and two or more signal output ports, and is configured to receive the time division multiplexing electric signals, distribute the time division multiplexing electric signals to form a first time division multiplexing signal and a second time division multiplexing signal, and output the first time division multiplexing signal and the second time division multiplexing signal;
a programmable unit configured to emit a first control signal for detecting a synchronous electrical signal, a second control signal for detecting a classical electrical signal;
a first logic unit including two or more signal input ports, one signal output port having a logic operation function, configured to receive the first time division multiplexing signal, the first control signal, and to process the first control signal to send out the synchronous electrical signal;
and the second logic unit comprises two or more signal input ports and one signal output port, has a logic operation function, is configured to receive the second time division multiplexing signal and the second control signal, and sends out the classical electric signal after processing.
15. The receiving end of claim 14, wherein the signal characteristics of the first time-division multiplexed electrical signal and the second time-division multiplexed electrical signal are consistent with the signal characteristics of the time-division multiplexed electrical signal.
16. A method of time-division multiplexing (TDM) demultiplexing for a time-division multiplexed (TDM) high-speed QKD system, comprising:
the second optical detection unit receives and detects the time division multiplexing light, and converts the time division multiplexing light into a time division multiplexing electric signal;
receiving the time division multiplexing electric signals by the clock distribution unit and distributing to form a first time division multiplexing electric signal and a second time division multiplexing electric signal;
sending out a first control signal for detecting a synchronous electrical signal and a second control signal for detecting a classical electrical signal by the programmable unit;
the first time division multiplexing electric signal and the first control signal are input into the first logic unit, and after being processed, a synchronous electric signal is output;
and the second time division multiplexing electric signal and the second control signal are input into the second logic unit, and after being processed, a classical electric signal is output.
17. A method of quantum key distribution for a time-division-multiplexed high-speed QKD system, comprising:
the first laser emits classical light and synchronous light, performs time division multiplexing and emits time division multiplexing light;
the quantum key coding unit is used for carrying out quantum key coding and emitting quantum light;
receiving the time division multiplexing light and the quantum light by a first wavelength division multiplexing unit, carrying out wavelength division multiplexing, emitting wavelength division multiplexing light, and transmitting the wavelength division multiplexing light through a channel;
receiving the wavelength division multiplexing light by a second wavelength division multiplexer and demultiplexing to obtain time division multiplexing light and quantum light;
receiving and decoding the quantum light by a quantum key decoding unit to obtain a quantum key;
and a time division multiplexing de-multiplexing device receives the time division multiplexing light for detection and converts the time division multiplexing light into a time division multiplexing electrical signal, and the time division multiplexing electrical signal is further processed to obtain a synchronous electrical signal, namely a classical electrical signal.
18. A one-way system of a time-multiplexed high-speed QKD system, comprising the time-multiplexing method of any one of claims 1-7 or the transmitting end of any one of claims 8-11 or the receiving end of any one of claims 12-15 or the de-time-multiplexing method of claim 16 or the quantum key distribution method of claim 17.
19. A bi-directional system of a time-multiplexed high-speed QKD system, comprising the time-multiplexing method of any one of claims 1-7 or the transmitting end of any one of claims 8-11 or the receiving end of any one of claims 12-15 or the de-time-multiplexing method of claim 16 or the quantum key distribution method of claim 17.
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