Patent Application
20240056294
This innovation has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 820466 and from the European Regional Development Funds (ERDF) allocated to the Programa operatiu FEDER de Catalunya 2014-2020, with the support of the Secretaria d'Universitats i Recerca of the Departament d'Empresa i Coneixement of the Generalitat de Catalunya for emerging technology clusters devoted to the valorization and transfer of research results (QuantumCAT 001-P-001644).
The present invention relates to a network node of a quantum key distribution (QKD). The present invention relates particularly to a network node configured to operate in an optical fiber network, an optical fiber network, a QKD transmitter configured to transmit information in an optical fiber network, and a QKD receiver configured to receive information in an optical fiber network. The present invention further relates to combination of DV-QKD and CV-QKD technologies in such optical fiber network.
In a quantum communication network, information is shared between communicating parties by encoding information in quantum states of light, which typically consists of light pulses containing photon(s). The quantum states/signals may carry one or more than one bit of information, for example, by using properties of the photon, such as its polarization, phase, energy/time, or angular momentum. Quantum key distribution (QKD) is a technology that allows two parties to share cryptographic keys by distributing quantum signals through a communication channel.
The security of QKD relies on the laws of quantum physics, namely the Heisenberg uncertainty principle and non-cloning theorem, which enables the communicating parties to detect the presence of an eavesdropper in the channel. Furthermore, according to the laws of quantum mechanics, measurement of the quantum states by an eavesdropper without prior knowledge of the encoding basis causes an unavoidable change to the quantum state. Therefore, any attempt of an eavesdropper to obtain information of the quantum signals will effectively introduce noise and/or errors that can be detected by the communicating parties.
In a so-called prepare-and-measure QKD, a transmitter (Alice) prepares quantum signals with encoded information according to a specific protocol, and transmits those signals to a receiver (Bob) through an optical channel. Bob performs different measurements on the received quantum signals obtaining data that is correlated to Alice's preparation choices. The correlated data is then post-processed, using a classical communication channel, to extract a secret key. The two main QKD implementations are Discrete-variable QKD (DV-QKD) and Continuous-variable QKD (CV-QKD).
In DV-QKD, the quantum signal consists of single photons with the information to generate a key encoded into a degree of freedom of the photons, such as the polarization, discrete temporal-mode, or phase and the likes
The protocol BB84, proposed in 1984 by Bennet and Brassard, is the first and most widely used DV-QKD protocol. It uses a set of four quantum states that complete two conjugated bases commonly referred to as the Z and X bases. The states of each basis encode the bit value 0 and 1. The protocol begins with Alice preparing a train of single-photons. For each photon, Alice randomly chooses one of the four quantum states and assigns it to the photon by modulating a chosen degree of freedom. Subsequently, the quantum signals are transmitted to Bob, who randomly configures his detection apparatus to measure quantum states of either the X or Z basis.
Every time that Bob chooses the correct basis (i.e. the basis where the received state belongs to), he obtains a bit that is perfectly correlated to Alice choice. Contrarily, when Bob choses the wrong basis, there is no correlation between the bits. Subsequently, a sifting procedure is carried out where the parties publicly announce the chosen bases and discard the data where the bases do not match. Then, Alice and Bob share correlated data that may have noise added by the presence of eavesdropper (Eve) in the channel. To identify a possible eavesdropper, the parties reveal part of the correlated data, which is later excluded, to quantify the noise of the signals. The remaining data is used to extract a secret key by means of error-correction and privacy amplification algorithms.
As mentioned above, DV-QKD uses single photons to encode and transmit information. Single photons are typically obtained by attenuating laser pulses, which has a security problem as the number of photons per pulse follows a Poissonian distribution. Hence, Eve could obtain information from the pulses that have more than one photon (i.e. make use of photon-number-splitting attacks). A countermeasure to this attack is the decoy-state method being used in most of the conventional implementation of DV-QKD, which consists on estimating the number of received quantum states with one photon by distributing additional decoy signals with the same Poissonian distribution but different mean photon number.
Implementations of DV-QKD in fiber links are typically done by using the time-bin degree of freedom. A time-bin state is defined by a photon located in one of two possible temporal modes, known as “early” bin or “late” bin. The quantum states are then encoded by placing a photon in an early bin, a late bin, or in a superposition of early and late bins with a relative phase between them. The superposition states are referred to as the + and −states. Time-bin states are suitable for fiber links because they could be propagated over long distances with low decoherence. In addition to the BB84 protocol, there are other DV-QKD protocols that make use of the time-bin quantum states, for example, coherent-one-way and differential phase shift.
CV-QKD typically uses coherent states of light (weak optical pulses) as quantum signals and the information is encoded in the conjugated quadratures of electromagnetic field. The quadratures are defined corresponding to the amplitude and phase of the signal pulses respectively. The most widely used CV-QKD protocol is the GG02 proposed by Groosham and Grainger in 2002. In GG02, the quadratures of optical signals follow zero-centered Gaussian random distribution, which are obtained by modulating the amplitude and phase of the pulses. In CV-QKD, the signals are measured by means of shot-noise limited coherent detection. This is a major difference compared to DV-QKD technology where more sophisticated and thermally cooled single photon detectors are used. Coherent detection employs a high-intensity reference signal called local oscillator (LO) which is interfered with the received quantum signals to amplify them and retrieve their quadratures values. The coherent detection could use homodyne or heterodyne scheme. In homodyne detection, Bob chooses randomly to measure either X or P quadrature by adding a 90° phase shift to the local oscillator, whereas in heterodyne detection, Bob measures both quadratures simultaneously by splitting the signal in two parts using for instance a 90° optical hybrid.
In early demonstrations of CV-QKD, the local oscillator and the quantum signals were generated from the same laser and both transmitted to Bob by using time multiplexing. This allows for a stable phase relation between the signal and local oscillator. Nevertheless, transmitting the local oscillator over the optical channel could open security problems allowing the eavesdropper to perform calibration attacks. Therefore, in most of the conventional implementations of CV-QKD, the local oscillator is generated locally at Bob with an additional laser, and reference pulses are sent from Alice to Bob to establish a phase relation between the two lasers and to compensate for phase drifts in the optical fiber. Besides GG02, other CV-QKD protocols with discrete modulation have been demonstrated, which allow for simplifying implementation and data post-processing. In these protocols, instead of Gaussian modulated quadratures, a restricted number of quadrature values are used to encode information, similarly to QPSK used in classical commutation.
The conventional QKD implementation mainly corresponds to point-to-point links. However, QKD could also be integrated into optical networks. DV-QKD and CV-QKD technology have specific advantages that can be exploited when integrating QKD into optical networks. For instance, DV-QKD can be more tolerant to channel losses and can be better suited for long distance links. On the other hand, CV-QKD can coexist with intense classical signals as the local oscillator acts as a natural frequency filter. Hence, CV-QKD could be a choice when the fiber link has several co-propagating classical data channels. For instance, coexistence of CV-QKD with a dense-wavelength-division multiplexing (DWDM) data channels has been demonstrated at a higher data rate as compared to DV-QKD. In term of secret key rate, the comparison of CV-QKD and DV-QKD can depend on the optical components and clock rates employed. Nevertheless, CV-QKD is expected to provide higher key rates at short distance as more than one secret bit could be extracted per symbol, whereas DV-QKD would outperform CV-QKD as the distance increases.
Several implementations of DV-QKD and CV-QKD technologies exist in different configurations. For example, as schematically illustrated in
Some existing QKD transmitters are available within a DV-QKD scheme for implementing several DV-QKD protocols, such as BB84, coherent-one-way (COW), and differential phase shift (DPS). For example, fiber based QKD transmitter that uses asymmetric a Mach-Zehnder interferometer and a double-pulse generation stage is capable of generating coherent pulses with different phases and relative intensities. Such transmitters can operate in BB84 with time-bin encoding, and also could be used for other DV-QKD protocols such as a six-state BB84. In another example, a modulator-free transmitter for QKD based on direct phase modulation of a semiconductor laser is implemented. However, its operability has been limited to DV-QKD protocols, such as BB84, DPS, and COW.
Moreover, such transmitters are optimized only for DV-QKD. The requirement in term of phase and amplitude modulation to implement CV-QKD protocols are more stringent, since the quantum states may need to be modulated from continuous random distributions, and reference pulses with high intensity compared to the quantum state need to be generated to perform phase recovery. For this reason, it may be required to have the capability of generating pulses with high extinction ratio, and a wide range of amplitude and phase levels (e.g. 1024 voltage levels, for distributions of resolution 10 bits). In addition, CV-QKD with true local oscillator may require two narrow-linewidth (e.g. 20 kHz) lasers that are frequency locked. This constraint on the lasers may cause difficulty in the use of schemes such as injection locking and direct modulation for CV-QKD.
In view of the above, it is an object of the present invention to provide an improved network node and/or transmitter/receiver configuration to address one or more of the above-mentioned challenges, disadvantages and/or problems. In other words, an improved and reconfigurable QKD network is needed to ensure interoperability between DV-QKD and CV-QKD systems, and to optimize QKD performance depending on characteristics of the link/network. Furthermore, there is also an advantage in combining CV-QKD and DV-QKD capabilities effectively in a transmitter/receiver of an optical fiber network to realize versatility and flexibility.
Specific embodiment(s) of the present invention disclosed herein relate generally to combining CV-QKD and DV-QKD technologies in an optical fiber network. The present invention further relates to dynamic reconfigurability and switching between CV-QKD and DV-QKD modes to optimize performance depending, for example, on characteristics of the optical fiber link/network (e.g. key rate, communication distance(s), number/presence of co-propagating classical channel, etc). The present invention also discloses a versatile transmitter and/or receiver that can perform communication using both CV-QKD and DV-QKD technologies to optimize the QKD performance of the network.
The present invention, in specific embodiment(s), addresses the above-mentioned object by providing a network node configured to operate in the optical fiber network. The network node comprises: a quantum key distribution (QKD) communication unit configured to communicate with another QKD communication unit of at least one other network node of the optical fiber network according to a continuous-variable (CV)-QKD mode and/or a discrete-variable (DV)-QKD mode; and a control unit configured to control the QKD communication unit to operate in at least one of the CV-QKD mode and the DV-QKD mode, wherein the control unit is configured to switch operation of the QKD communication unit between the CV-QKD mode and the DV-QKD mode.
In this context, the term “network node” refers to a connection node that can receive, create, store or send information along one or more network routes. For example, the network node can be an end node for transmitting information or a redistribution node. The network node can have a software and/or hardware capability to recognize, process and forward/receive information to/from other network nodes. The term “optical fiber network” can be understood as a network of one or more optical fibers for transmitting information from one place to another via optical/light and/or electrical signals. The terms “CV-QKD mode” and “DV-QKD mode” could be understood as modes using “CV-QKD” technology/protocol and “DV-QKD” technology/protocol, respectively.
According to this configuration, as the network node is equipped with the QKD communication unit which can communicate with another QKD communication unit of at least one other network node of the optical fiber network according to at least one of the CV-QKD mode and the DV-QKD mode, the control unit can dynamically switch operation of the QKD communication unit from DV-QKD to CV-QKD or vice versa. Such dynamic reconfigurability would allow to optimize QKD performance depending, for example, on characteristic(s) of the network and/or demand e.g. key rate, communication distance(s), number/presence of co-propagating classical channel, etc. For instance, because of the dynamic switching, the network node can be configured to operate in the DV-QKD mode, due to its higher secret key rate, over a longer-distance link/network, or can be switched to the CV-QKD mode for a short-distance link/network with several co-propagating classical data channels. Thus, in a situation in which depending on the characteristic of a network configuration the performance and functionalities are to be adapted, the inventive network node provides a robust yet simplified way to reconfigure the network.
In specific embodiment(s) of the invention, the QKD communication unit may comprise at least one QKD transmitter configured to operate in at least one of the CV-QKD mode and the DV-QKD mode. By having at least one QKD transmitter capable of operating in both the CV-QKD and the DV-QKD mode with this configuration of the QKD communication unit, the network node can achieve versatile interoperability and reconfigurability so as to optimize the QKD performance of the network.
In specific embodiment(s) of the invention, the control unit may be configured to drive the QKD communication unit with a first predetermined electric signal such that the QKD transmitter operates either in the CV-QKD mode or in the DV-QKD mode. With this, the selection of either using CV-QKD mode or the DV-QKD mode can be implemented via simpler hardware or software configuration.
In specific embodiment(s) of the invention, the QKD transmitter may comprise a modulator unit configured to modulate amplitude and/or phase of light signal emitted by at least one light source, and an electronic circuit may be configured to drive the modulator unit according to the first predetermined electric signal. This provides a simpler but versatile configuration for the transmitter to achieve switchability between the CV-QKD and the DV-QKD mode.
Advantageously, the QKD transmitter may comprise an attenuator configured to attenuate the modulated light signal to a predetermined level and/or set a mean photon number required for the CV-QKD mode or the DV-QKD mode, wherein the electronic circuit may be configured to control the attenuator. In one example, the attenuator can be an electrically-controlled variable optical attenuator, wherein the electronic circuit may further be configured to control the attenuator according to the first predetermined electric signal. The attenuator may be included before the modulator unit or after the modulator unit, but in both cases is included before the CV-QKD or DV-QKD signal(s) are transmitted to the transmission channel.
In specific embodiment(s) of the invention, the control unit may be configured to operate the QKD transmitter simultaneously in the CV-QKD mode and the DV-QKD mode by using any one of time, frequency, space, polarization multiplexing, and any combinations thereof. With such multiplexing, the network node and/or the network can be equipped to perform the DV-QKD and CV-QKD simultaneously, thereby increasing the versatility and provide additional degree of freedom to improve the QKD performance. For instance, the QKD transmitter may allow multiplexing of CV-QKD and DV-QKD signals by using a polarization switch or using different wavelengths from the at least one light/laser source.
In specific embodiment(s) of the invention, the QKD transmitter may combine at least one CV-QKD transmitter and at least one DV-QKD transmitter, the at least one CV-QKD transmitter and the at least one DV-QKD transmitter may share at least one opto-electronic component. As the QKD transmitter shares at least one opto-electronic component of the CV-QKD transmitter and the DV-QKD transmitter, the DV-QKD and CV-QKD transmitters could be combined into one single element such that the single QKD transmitter can be switched to operate either in the CV-QKD mode or in the DV-QKD mode, thereby achieving the versatility and interoperability. This configuration shall also reduce the number of components.
The QKD communication unit may comprise at least one QKD receiver configured to operate in at least one of the CV-QKD mode and the DV-QKD mode. By having at least one QKD receiver capable of operating in both the CV-QKD and DV-QKD mode, the QKD communication unit and thereby the network node can achieve versatile interoperability and reconfigurability so as to optimize the QKD performance of the network.
The control unit may be configured to drive the QKD communication unit with a second predetermined electric signal such that the QKD receiver operates either in the CV-QKD mode or in the DV-QKD mode. With this, the selection of either using CV-QKD mode or the DV-QKD mode can be implemented via simpler hardware or software configuration.
In specific embodiment(s) of the invention, the QKD receiver may comprise a processing/detection unit configured to perform detection of CV-QKD and DV-QKD signals in the CV-QKD mode and the DV-QKD mode respectively, and an electronic circuit configured to drive the processing/detection unit according to the second predetermined electric signal such that the QKD receiver operates either in the CV-QKD mode or in the DV-QKD mode. This provides a simpler but versatile configuration for the receiver to achieve switchability between the CV-QKD and the DV-QKD mode. For instance, the processing/detection unit of the QKD receiver can be a polarization controller, interferometer, balanced detectors, photon detectors configured to perform detection of CV-QKD and DV-QKD signals in the CV-QKD mode and the DV-QKD mode respectively by using a polarizing-beam splitter or a wavelength-division-multiplexer.
In specific embodiment(s) of the invention, the control unit may be configured to operate the QKD receiver simultaneously in the CV-QKD mode and the DV-QKD mode by using any one of time, frequency, space, polarization multiplexing, and any combinations thereof. With such multiplexing, the network node and/or the network can be equipped to perform the DV-QKD and CV-QKD simultaneously, thereby increasing the versatility and provide additional degree of freedom to improve the QKD performance. For instance, the QKD receiver may allow multiplexing of CV-QKD and DV-QKD signals by using the polarizing-beam splitter or the wavelength-division-multiplexer configured to separate CV-QKD and DV-QKD signals for sending them to corresponding detectors.
In specific embodiment(s) of the invention, the QKD receiver may combine at least one CV-QKD receiver and at least one DV-QKD receiver, the at least one CV-QKD receiver and the at least one DV-QKD receiver may share at least one opto-electronic component. As the QKD receiver shares at least one opto-electronic component of the CV-QKD receiver and the DV-QKD receiver, the DV-QKD and CV-QKD receivers could be combined into one single element such that the single QKD receiver can be switched to operate either in the CV-QKD mode or in the DV-QKD mode, thereby achieving the versatility and interoperability. This configuration shall also reduce the number of components.
Advantageously, the CV-QKD mode can be based on at least one CV-QKD protocol and the DV-QKD mode can be based on at least one DV-QKD protocol. For example, the at least one CV-QKD protocol may comprise of a GG02 protocol and a discrete-modulated CV-QKD protocol, wherein the at least one DV-QKD protocol may comprise of a BB84 DV-QKD protocol, a coherent one way DV-QKD protocol, a differential phase shift DV-QKD protocol, a three-states DV-QKD protocol, and a six-states DV-QKD protocol. Accordingly, the inventive network node can operate with different conventional CV-QKD and DV-QKD protocols but suitable for interoperability between CV-QKD and DV-QKD, thereby implementing a flexible and reconfigurable network.
The present invention, in specific embodiment(s), addresses the above-mentioned object by providing an optical fiber network, the optical fiber network comprises one or more network nodes each according to any of the above embodiments/examples. Thus, a dynamically reconfigurable and versatile network with optimized QKD performance can be realized.
Furthermore, each network node can be equipped with at least one CV-QKD transmitter and at least one DV-QKD transmitter. Similarly, network nodes can also be equipped with at least one CV-QKD receiver and at least one DV-QKD receiver.
The present invention, in specific embodiment(s), addresses the above-mentioned object by providing a QKD transmitter configured to transmit information in an optical fiber network. The QKD transmitter comprises a modulator unit configured to modulate amplitude and/or phase of light signal emitted by at least one light source, and an electronic circuit configured to drive the modulator unit according to a predetermined electric signal such that the QKD transmitter operates either in a CV-QKD mode or in a DV-QKD mode. According to QKD, key data can be transmitted from a QKD transmitter to, for example a QKD receiver as quantum information. By having at least one QKD transmitter capable of operating in at least one of the CV-QKD and the DV-QKD mode in the optical fiber network, the network/network node can therefore become versatile by being switchable/configurable between CV-QKD and DV-QKD, thereby providing an efficient way to optimize the QKD performance of the network. Further, by having the electronic circuit, the selection of either using CV-QKD mode or the DV-QKD mode can be implemented via simpler hardware or software configuration.
The QKD transmitter may comprise an attenuator configured to attenuate the modulated light signal to a predetermined level and/or set a mean photon number required for the CV-QKD mode or the DV-QKD mode, wherein the electronic circuit may be configured to control the attenuator. In one example, the attenuator can be an electrically-controlled variable optical attenuator, wherein the electronic circuit may further be configured to control the attenuator according to the predetermined electric signal. The attenuator may be included before the modulator unit or after the modulator unit, but in both cases is included before the CV-QKD or DV-QKD signal(s) are transmitted to the transmission channel. The attenuator can be included to reduce the intensity and/or phase of the modulated light to the predetermined level, or to set the mean photon number to the predetermined level to monitor such parameters in real time in the claimed network and/or to guarantee the security of the claimed network.
Advantageously, the QKD transmitter may be configured to operate simultaneously in the CV-QKD mode and the DV-QKD mode by using any one of time, frequency, space, polarization multiplexing, and any combinations thereof. With such multiplexing, the QKD transmitter can perform the DV-QKD and CV-QKD simultaneously, thereby increasing the versatility and provide additional degree of freedom to improve the QKD performance. For instance, the QKD transmitter may allow multiplexing of CV-QKD and DV-QKD signals by using a polarization switch or using different wavelengths from the at least one light/laser source.
The QKD transmitter may combine at least one CV-QKD transmitter and at least one DV-QKD transmitter, the at least one CV-QKD transmitter and the at least one DV-QKD transmitter may share at least one opto-electronic component. As the QKD transmitter shares at least one opto-electronic component of the CV-QKD transmitter and the DV-QKD transmitter, the DV-QKD and CV-QKD transmitters could be combined into one single element such that the single QKD transmitter can be switched to operate either in the CV-QKD mode or in the DV-QKD mode, thereby achieving the versatility and interoperability.
In specific embodiment(s) of the invention, the QKD transmitter of a network node may be adapted to communicate with corresponding QKD receiver of at least one other network node of the optical fiber network according to the CV-QKD mode and/or the DV-QKD mode. This configuration ensures that the versatility of the QKD transmitter can be translated to the receiver side.
Advantageously, the CV-QKD mode can be based on at least one CV-QKD protocol and the DV-QKD mode can be based on at least one DV-QKD protocol. For example, the at least one CV-QKD protocol may comprise of a GG02 protocol and a discrete-modulated CV-QKD protocol, wherein the at least one DV-QKD protocol may comprise of a BB84 DV-QKD protocol, a coherent one way DV-QKD protocol, a differential phase shift DV-QKD protocol, a three-states DV-QKD protocol, a six-states DV-QKD protocol and a decoy-state DV-QKD protocol. Accordingly, the inventive QKD transmitter can operate with different conventional CV-QKD and DV-QKD protocols but suitable for interoperability between CV-QKD and DV-QKD, thereby implementing a flexible and reconfigurable network.
The present invention, in specific embodiment(s), addresses the above-mentioned object by providing a QKD receiver configured to receive information in the optical fiber network. The QKD receiver comprises a processing/detection unit configured to perform reception and/or detection of CV-QKD and DV-QKD signals in a CV-QKD mode and a DV-QKD mode respectively, and an electronic circuit configured to drive the processing/detection unit according to a predetermined electric signal such that the QKD receiver operates either in the CV-QKD mode or in the DV-QKD mode. By having at least one QKD receiver capable of operating in at least one of the CV-QKD and DV-QKD mode in the optical fiber network, the network/network node can become versatile by being switchable/configurable between CV-QKD and DV-QKD, thereby providing an efficient way to optimize the QKD performance of the network. Further, by having the electronic circuit, the selection of either using CV-QKD mode or the DV-QKD mode can be implemented via simpler hardware or software configuration. For instance, the processing/detection unit of the QKD receiver can be a polarization controller and/or one or more detectors configured to perform processing of and detection of CV-QKD and/or DV-QKD signals in the CV-QKD mode and/or the DV-QKD mode respectively, for example, by using a polarizing-beam splitter or a wavelength-division-multiplexer.
The QKD receiver may be configured to operate simultaneously in the CV-QKD mode and the DV-QKD mode by using any one of time, frequency, space, polarization multiplexing and any combinations thereof. With such multiplexing, the QKD receiver can be equipped to perform the DV-QKD and CV-QKD simultaneously, thereby increasing the versatility and provide additional degree of freedom to improve the QKD performance. For instance, the QKD receiver may allow multiplexing of CV-QKD and DV-QKD signals by using the polarizing-beam splitter or the wavelength-division-multiplexer configured to separate CV-QKD and DV-QKD signals for sending them to corresponding detectors.
In specific embodiment(s) of the invention, the QKD receiver may combine at least one CV-QKD receiver and at least one DV-QKD receiver, the at least one CV-QKD receiver and the at least one DV-QKD receiver may share at least one opto-electronic component. As the QKD receiver shares at least one opto-electronic component of the CV-QKD receiver and the DV-QKD receiver, the DV-QKD and CV-QKD receivers could be combined into one single element such that the single QKD receiver can be switched to operate either in the CV-QKD mode or in the DV-QKD mode, thereby achieving the versatility and interoperability.
In specific embodiment(s) of the invention, the QKD receiver of a network node may be adapted to communicate with corresponding QKD transmitter of at least one other network node of the optical fiber network according to the CV-QKD mode and/or the DV-QKD mode. This configuration ensures that the versatility of the QKD receiver can be translated to the transmitter side.
Advantageously, the CV-QKD mode can be based on at least one CV-QKD protocol and the DV-QKD mode can be based on at least one DV-QKD protocol. For example, the at least one CV-QKD protocol may comprise of a GG02 protocol and a discrete-modulated CV-QKD protocol, wherein the at least one DV-QKD protocol may comprise of a BB84 DV-QKD protocol, a coherent one way DV-QKD protocol, a differential phase shift DV-QKD protocol, a three-states DV-QKD protocol, a six-states DV-QKD protocol and a decoy-state DV-QKD protocol. Accordingly, the inventive QKD receiver can operate with different conventional CV-QKD and DV-QKD protocols but suitable for interoperability between CV-QKD and DV-QKD, thereby implementing a flexible and reconfigurable network.
The present invention, in specific embodiment(s), addresses the above-mentioned object by providing a method of operation of a network node in an optical fiber network, the network node comprising a quantum key distribution (QCD1) communication unit configured to communicate with another QKD communication unit (QCD2-QCD5) of at least one other network node of the optical fiber network according to a continuous-variable (CV)-QKD mode and/or a discrete-variable (DV)-QKD mode, and a control unit configured to control the QKD communication unit (QCD1) to operate in at least one of the CV-QKD mode and the DV-QKD mode, the method comprising a step of switching operation of the QKD communication unit (QCD1) between the CV-QKD mode and the DV-QKD mode. With this method, it is possible to dynamically switch operation of the QKD communication unit from DV-QKD to CV-QKD or vice versa.
Advantageous embodiments of the inventive product(s) and method(s) will be described in the following by referring to the Figures.
In the following, features and advantageous embodiments of the present invention will be described in detail with reference to the Figures.
The network node N101 comprises a quantum key distribution (QKD) communication unit QCD1 and a control unit (not shown). The QKD communication unit QCD1 is configured to communicate with another QKD communication unit QCD2 of at least one other network node N102 of the optical fiber network. The QKD communication unit QCD1, in particular, is configured to communicate with the another QKD communication unit QCD2 according to at least one of a continuous-variable (CV)-QKD mode (dotted line in
The control unit of the node N101 may comprise at least one or more of a microprocessor, a memory, a monitoring means, an electronic means, or a combination thereof. The microprocessor can compute the command(s) to be sent to the QKD communication unit QCD1 and/or its components. Any other processor-based device such as an application specific processor or a microcontroller can also be used in place of microprocessor to perform a similar function. The memory may include a non-transitory computer-readable medium which can store executable instructions to control the QKD communication unit QCD1 to operate in at least one of the CV-QKD mode and the DV-QKD mode. The memory may also contain executable instructions that affect operation of the microprocessor. The monitoring means may be configured to monitor characteristic(s) of the network and/or to receive command from an input interface of the network node N101, or from an external device. In one example, the monitoring means may include sensor(s) to estimate the amount of noise/error or any other specific performance characteristic of the optical fiber link/network. In another example, the input interface may include one or more input devices, buttons or controls to allow dynamic reconfigurability and switching between the CV-QKD mode and the DV-QKD mode.
The CV-QKD mode may refer to the mode in which the respective QKD communication unit is configured to realize CV-QKD implementation. The DV-QKD mode may refer to the mode in which the respective QKD communication unit is configured to realize DV-QKD implementation.
According to this configuration, as the network node N101 is equipped with the QKD communication unit QCD1 which can communicate with the another QKD communication unit QCD2 of at least one other network node N102 of the optical fiber network according to at least one of the CV-QKD mode and the DV-QKD mode, the control unit can dynamically switch operation of the QKD communication unit QCD1 from DV-QKD to CV-QKD mode or vice versa. Such dynamic reconfigurability could allow to optimize QKD performance depending, for example, on characteristic(s) of the network and/or demand e.g. key rate, which can be a secret key rate, which is the number of secret bits per second, communication distance(s), number/presence of co-propagating classical channel, etc. For instance, DV-QKD can provide a higher secret key rate over a longer-distance link/network. In such instances, the control unit can switch the QKD communication unit QCD1 to communicate in the DV-QKD mode. The control unit can switch dynamically from the DV-QKD mode to the CV-QKD for achieving higher secret key rate over a short-distance link/network.
Another possible scenario is that while communicating in the DV-QKD mode, the QKD communication units QCD1 and QCD2 could detect an increment in the noise, which may be due to a higher intensity of classical data channel. In this case, the control unit can switch from the DV-QKD mode to the CV-QKD mode, which can thus co-exist with co-propagating classical signals and allow for a positive key rate. Hence, the QKD communication unit QCD1 can communicate with the QKD communication unit QCD2 demanding a mode switching to the CV-QKD to optimize the secret key rate over a noisy link/network.
An operation of the network mode N101, illustrated in
For instance, the network node N101 is configured to communicate with the network node N102 in at least one of the CV-QKD mode (shown as dotted line in
For example, the network node N101 or N105 is configured to operate either in the CV-QKD mode or in the DV-QKD mode. Accordingly, the communication between the network node N102 and the network node N101 or N105 can be switched between the CV-QKD mode and the DV-QKD mode for achieving the optimized QKD performance. The network node N102 or N105 communicates with the network node N103 or N104, respectively, via DV-QKD mode. The network nodes N103 and N104 communicate with each other via DV-QKD mode.
Due to the combination of CV-QKD and DV-QKD technologies in the optical fiber network 100, the present invention allows dynamic reconfigurability and switching between CV-QKD and DV-QKD mode to optimize QKD performance of the optical fiber network.
The present invention is not limited thereto. The optical fiber network can have any number of network nodes. All or some of the network nodes can be reconfigurable to switch between CV-QKD mode and DV-QKD mode. The network nodes can communicate with each other via one or more waveguides such as optical communication channel, optical fibers and the likes.
In an embodiment, each of the network nodes of the present invention can include at least one transmitter and/or at least one receiver, as part of the respective QKD communication unit, for communicating with other network nodes of the optical fiber network. The transmitter and receiver can be configured to exchange CV-QKD signal and/or DV-QKD signal, and thus are configured for QKD, and hence have been termed as QKD transmitter and QKD receiver, respectively.
The QKD communication unit may comprise at least one QKD transmitter and/or at least one QKD receiver configured to operate in at least one of the CV-QKD mode and the DV-QKD mode. In the following, QKD transmitter and QKD receiver will be described using
In an embodiment of the invention, the QKD transmitter 400A may combine at least one CV-QKD transmitter and at least one DV-QKD transmitter into a single element. In a specific example, the at least one CV-QKD transmitter and the at least one DV-QKD transmitter may share at least one opto-electronic component. As the QKD transmitter shares at least one opto-electronic component of the CV-QKD transmitter and the DV-QKD transmitter, the DV-QKD and CV-QKD transmitters could be combined into one single element such that the single QKD transmitter can be switched to operate either in the CV-QKD mode or in the DV-QKD mode, thereby achieving the versatility and interoperability. This configuration shall also reduce the number of components.
The QKD transmitter 400A comprises an electronic circuit 402 and a modulator unit 403. At least one light source 401 can be provided to be part of the QKD transmitter 400A or external to the QKD transmitter 400A.
The at least one light source 401 is configured to emit light signal. For example, the light source can be a laser light source, in particular, a continuous wave (CW) laser light source. Alternatively, the light source can be a pulsed laser light source. The light source can be a tunable laser source, whereby the wavelength of the lasers could be tuned to allow, for example, for quantum communication in a specific channel of the band being used (e.g. C-band).
The modulator unit 403 may receive the light signal emitted by the at least one light source 401. The modulator unit 403 is configured to modulate amplitude and/or phase of the received light signal. The modulator unit 403 may comprise one or more amplitude modulators for modulating the amplitude of the light signal and/or at least one phase modulator for modulating the phase of the light signal, respectively. The amplitude and/or phase modulator may comprise one or more optical and/or electronic component(s). For example, the amplitude and/or phase modulator may comprise at least one material which exhibits electro-optic effect such that the respective amplitude and/or phase modulation can be achieved by controlling electric field in the material. The amplitude modulator can preferably have a predetermined extinction ratio (e.g. >20 dB) to reduce the background noise. In case of CV-QKD with Gaussian modulation, the phase and/or amplitude modulators could have a predetermined resolution and dynamic range to obtain a desired approximation of continuous modulation of phase and amplitude. The one or more optical and/or electronic component(s) of the modulators can be the shared one or more opto-electronic components of the corresponding CV-QKD transmitter and the DV-QKD transmitter.
The electronic circuit 402 is configured to control the modulator unit 403. In particular, the electronic circuit 402 is configured to drive the modulator unit 403 according to a first predetermined electric signal in such a way that the QKD transmitter 400A operates either in the CV-QKD mode or in the DV-QKD. The electronic unit 402 can allow selecting the CV-QKD mode or the DV-QKD mode by setting the first predetermined electric signal that drive the modulator unit 402. The electronic circuit 402 can be a hardware and/or a software element. With this, the selection of either using the CV-QKD mode or the DV-QKD mode can be implemented via simpler hardware and/or software configuration.
The first predetermined electric signal of the electronic circuit 402 can be configured to drive the modulator unit 403. In particular, the components of the modulator unit 403, such as one or more shared optical-electrical component(s) of the amplitude and/or phase modulator is(are) configured to be driven by the first predetermined electric signal so as to select one of the CV-QKD mode and the DV-QKD mode as the mode of operation of the QKD transmitter 400A. In an example, the first predetermined electric signal can determine whether the communication mode is the CV-QKD mode or the DV-QKD mode.
Examples of the electronic circuit 402 include, but not limited to, an electronic switch, a field-programmable-gate-array and may also be combined with one or more digital-to-analog converters. The electronic circuit 402 may be configured to control the laser parameters of the light source 401, such as wavelength, frequency, power and the likes. Additionally, the electronic circuit 402 may be configured to monitor, using one or more analog-to-digital converters, the operation of the light source 401 and/or optical-electrical components of the modulator unit 403. In an embodiment, the electronic circuit 402 can be controlled by a software.
According to another embodiment of the invention as illustrated in
The specific implementation can further include a beam-splitter 407. The beam splitter 407 can be configured to split the modulated light signals, so that one part of the split modulated light signals can be sent for further processing such as measurement of mean photon number and the likes, and the remaining part can be sent to the receiver (described later).
The electronic circuit 402 is configured to drive at least of the laser light source 401, the one or more modulators AM1, AM2, PM1, and the attenuator 405. In particular, one or more of these components can be driven according to the first predetermined electric signal in such a way that the QKD transmitter 400B can operate either in the CV-QKD mode or in the DV-QKD mode.
For the time-bin BB84 protocol as shown in
The electrical signals used to operate the QKD transmitter 400B for the GG02 CV-QKD protocol are shown in
The time-bin BB84 protocol and GG02 CV-QKD protocol mentioned above are just one example of a DV-QKD and a CV-QKD protocol, respectively, that can be performed with the QKD transmitter 400A-400G proposed in
The QKD receiver is configured to receive QKD signals from the QKD transmitter. Conventional QKD receiver is configured to receive either the CV-QKD signal or the DV-QKD signal from the respective transmitter.
The conventional QKD receiver 500A, illustrated in
Alternatively,
In an embodiment of the present invention, any conventionally known DV-QKD and/or CV-QKD receivers, such as the ones illustrated in
A QKD receiver 600 according to an embodiment of the invention is described with reference to
The QKD receiver 600 further includes an electronic circuit 605 configured to control the processing unit 601 and/or the detection unit 603. In particular, the electronic circuit 605 is configured to drive the processing unit 601 and/or the detection unit 603, for example according to a second predetermined electric signal, in such a way that the QKD receiver 600 operates either in the CV-QKD mode or in the DV-QKD. The electronic unit 605 can allow selecting the CV-QKD mode or the DV-QKD mode by setting the second predetermined electric signal that drive the processing unit 601 and/or the detection unit 603. The electronic circuit 605 can be a hardware and/or a software element. Examples of the electronic circuit 605 include, but not limited to, an electronic switch, a polarizing-beam splitter (PBS), a wavelength-division-multiplexer (WDM), a polarization controller and the likes. In an embodiment, the electronic circuit 605 can be controlled by a software.
The second predetermined electric signal of the electronic circuit 605 can be configured to drive the components of the processing unit 601 and/or the detection unit 603, in particular the one or more opto-electronic components of the processing unit 601 and/or the detection unit 603 so as to select one of the CV-QKD mode and the DV-QKD mode as the mode of operation of the QKD receiver 600. The second predetermined electric signal can be any form of signal but is a signal to the processing unit and/or the detecting unit to switch the operation from CV-QKD to DV-QKD and vice versa.
The QKD receiver 600 is thus configured to operate in at least one of the CV-QKD mode and the DV-QKD mode, thereby versatile interoperability, reconfigurability and switchability can be achieved, and the the QKD performance can be optimized.
In an embodiment, the one or more opto-electronic component(s) of the QKD receiver can be the one or more opto-electronic components shared by the conventional CV-QKD receiver and the DV-QKD receiver. Similarly to the QKD transmitter of the invention, the electronic circuit 605 of the QKD receiver is configured to perform detection of DV and/or CV signals by suitably between the DV-QKD mode and the CV-QKD mode.
The time-bin BB84 protocol and GG02 CV-QKD protocol mentioned above are just one example of a DV-QKD and a CV-QKD protocol, respectively, that can be performed with the QKD receiver 600-700B proposed in
The embodiments of present invention provide a network node, an optical network, a QKD transmitter, a QKD receiver, and a method of operation of the network node according to which operation between the DV-QKD and CV-QKD mode can be dynamically switched, thereby it is possible to realize a versatile, and robust reconfiguration of an optical fiber network and interoperability.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20383141.7 | Dec 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/051021 | 1/19/2021 | WO |
