Network Node, Transmitter, and Receiver for Quantum Key Distribution in an Optical Fiber Network

Abstract

The present invention relates to a network node configured to operate in an optical fiber network. The network node comprises a QKD communication unit adapted to communicate with another QKD communication unit of at least one other network node of the optical fiber network according to a CV-QKD mode and / or a DV-QKD mode. The present invention also discloses a control unit 5 configured to control the QKD communication unit to operate in at least one of the CV-QKD mode and the DV-QKD mode. The control unit is configured to switch the operation of the QKD communication unit between the CV-QKD mode and the DV-QKD mode. [Representative diagram] Figure 3

Description

Technical Field

[0001] 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 Fund (ERDF) of the Programa operatiu FEDER de Catalunya 2014 - 2020, as managed by the Secretaria d’Universitats i Recerca of Departament d’Empresa i Coneixement of the Generalitat de Catalunya, for the benefit of the Emerging Technologies Cluster specialising in the exploitation and transfer of research results (QuantumCAT 001 - P - 001644).

[0002] The present invention relates to network nodes for quantum key distribution (QKD). In particular, the present invention relates to a network node configured to operate in an optical fiber network, an optical fiber network, a QKD transmitter configured to transmit information in the optical fiber network, and a QKD receiver configured to receive information in the optical fiber network. The present invention further relates to a combination of DV - QKD and CV - QKD techniques in such an optical fiber network.

Background Art

[0003] In a quantum communication network, information is shared between communicating parties by encoding information in the quantum state of light, which is generally composed of optical pulses containing photons. The quantum state / signal can carry one or more information bits by using properties of photons such as, for example, polarization, phase, energy / time, or angular momentum. Quantum key distribution (QKD) is a technique that enables two parties to share an encryption key by delivering a quantum signal through a communication channel.

[0004] The security of QKD depends on the laws of quantum physics, namely, Heisenberg's uncertainty principle and the no-cloning theorem, which enable the communicating parties to detect the presence of eavesdroppers in the channel. Furthermore, according to the laws of quantum mechanics, the measurement of a quantum state by an eavesdropper without prior knowledge of the encoding basis causes inevitable changes to the quantum state. Therefore, if an eavesdropper attempts to obtain information about the quantum signal, it will effectively introduce noise and / or errors that can be detected by the communicating parties.

[0005] In so-called prepare-and-measure QKD, the sender (Alice) prepares quantum signals containing encoded information according to a specific protocol and transmits these signals to the receiver (Bob) through an optical channel. Bob performs various measurements on the received quantum signals and obtains data that correlates with Alice's preparation choices. Then, using a classical communication channel, the correlated data is post-processed to extract the secret key. Two main examples of QKD implementations are discrete-variable QKD (DV-QKD) and continuous-variable QKD (CV-QKD).

[0006] In DV-QKD, the quantum signals are composed of single photons that contain information to generate keys encoded in degrees of freedom of photons, such as polarization, discrete-time modes, or phase, among others.

[0007] The protocol BB84, proposed in 1984 by Bennett and Brassard, is the first and most widely used DV-QKD protocol. A set of four quantum states that complete two conjugate bases, usually referred to as the Z basis and the X basis, is used. The states of each basis encode the bit values 0 and 1. The protocol starts when Alice prepares a single-photon sequence. For each photon, Alice randomly selects one of the four quantum states and assigns it to the photon by modulating the selected degree of freedom. Subsequently, the quantum signal is transmitted to Bob, who randomly configures his detection device to measure either the quantum state of the X basis or the Z basis.

[0008] Each time Bob selects the correct basis (i.e., the basis to which the received state belongs), he obtains a bit that perfectly correlates with Alice's choice. Conversely, when Bob selects the wrong basis, no correlation is seen between the bits. Subsequently, a screening procedure is performed, and the parties announce the selected basis and discard the data for which the basis does not match. Then, Alice and Bob share correlated data that may have noise added by an eavesdropper (Eve) on the channel. To identify a possible eavesdropper, the parties quantify the noise of the signal by making explicit a portion of the correlated data that will be excluded later. The remaining data is used to extract a secret key by error correction and privacy amplification algorithms.

[0009] As described above, in DV-QKD, single photons are used to encode and transmit information. Single photons are typically obtained by attenuating laser pulses, which poses a security problem since the number of photons per pulse follows a Poisson distribution. Therefore, Eve can obtain information from pulses with more than one photon (i.e., by using a photon number splitting attack). A countermeasure against this attack is the decoy state method, which is used in many conventional DV-QKD implementations and consists of estimating the number of received quantum states containing one photon by delivering additional decoy signals with the same Poisson distribution but different average photon numbers.

[0010] Implementations of DV-QKD over fiber links are generally performed by using the time-bin degree of freedom. A time-bin state is defined by a photon located in one of two possible time modes known as the "early" bin or the "late" bin. Then, the quantum state is encoded by placing photons in the early bin, the late bin, or the overlap of the early and late bins that includes a relative phase between them. The overlap states are referred to as the + and - states. Time-bin states are suitable for fiber links since they propagate over long distances with low decoherence. In addition to the BB84 protocol, there are other DV-QKD protocols that utilize time-bin quantum states, such as coherent one-way and differential phase shift.

[0011] In CV-QKD, generally, the coherent state of light (weak optical pulses) is used as the quantum signal, and information is encoded in the conjugate quadrature phase of the electromagnetic field. The quadrature phase is defined as corresponding to the amplitude and phase of the signal pulse, respectively. The most widely used CV-QKD protocol is GG02, proposed by Groosham and Grainger in 2002. In GG02, the quadrature phase of the optical signal follows a zero-centered Gaussian random distribution obtained by modulating the amplitude and phase of the pulse. In CV-QKD, this signal is measured by shot-noise-limited coherent detection. This is a major difference compared to the DV-QKD technique, where more advanced and thermally cooled single-photon detectors are used. In coherent detection, a high-intensity reference signal called the local oscillator (LO) is employed, which interferes with the received quantum signal to amplify it and obtain its quadrature phase value. For coherent detection, either the homodyne or heterodyne method can be used. In homodyne detection, Bob makes a random choice to measure either the X quadrature phase or the P quadrature phase by adding a 90° phase shift to the local oscillator, whereas in heterodyne detection, for example, by using a 90° optical hybrid to split the signal into two parts, Bob measures both quadrature phases simultaneously.

[0012] In the initial proof-of-concept experiments of CV-QKD, the local oscillator and the quantum signal were generated from the same laser, and both were sent to Bob by using time-division multiplexing. In this way, a stable phase relationship between the signal and the local oscillator was obtained. Nevertheless, the transmission of the local oscillator over the optical channel causes security problems and enables an eavesdropper to perform a calibration attack. Therefore, in many of the conventional CV-QKD implementation examples, the local oscillator is locally generated at Bob by an additional laser, and a reference pulse is sent from Alice to Bob to establish the phase relationship between the two lasers and to compensate for the phase drift in the optical fiber. In addition to GG02, proof-of-concept experiments of other CV-QKD protocols with discrete modulation have been conducted, which enables the simplification of implementation and data post-processing. In these protocols, instead of Gaussian modulation quadrature phase, a limited number of quadrature phase values are used to encode information, similar to QPSK used in classical communication.

[0013] Conventional QKD implementation examples mainly correspond to point-to-point links. However, QKD has also been integrated into optical networks, and DV-QKD and CV-QKD technologies have specific advantages that can be exploited when integrating QKD into optical networks. As an example, DV-QKD is more resistant to channel loss and is more suitable for long-distance links. On the other hand, since the local oscillator acts as a natural frequency filter, CV-QKD can coexist with high-intensity classical signals. Therefore, CV-QKD can be an option when the fiber link has several co-propagating classical data channels. As an example, the coexistence of CV-QKD and dense wavelength division multiplexing (DWDM) data channels has been demonstrated at a higher data rate compared to DV-QKD. Regarding the secret key rate, the comparison between CV-QKD and DV-QKD depends on the optical components adopted and the clock rate. Nevertheless, since more than one secret bit is extracted per symbol, CV-QKD is expected to provide a higher key rate at short distances, while DV-QKD will perform better than CV-QKD as the distance increases.

[0014] Some implementation examples of DV-QKD and CV-QKD technologies exist in various configurations. For example, as schematically illustrated in FIG. 1, a QKD transmitter and a receiver are integrated into a quantum communication network 1000, and nodes N1101-1108 of such a network may comprise QDV1-QDV7, which are DV-QKD systems, or QCV1-QCV5, which are CV-QKD systems. Such independent links of such a conventional QKD network shown in FIG. 1 by solid or dashed lines use either CV-QKD or DV-QKD technology. However, existing network and / or node configurations suffer from a lack of high-degree reconfigurability to optimize QKD performance according to the characteristics of this link.

[0015] Some existing QKD transmitters are available in DV-QKD schemes for implementing several DV-QKD protocols such as BB84, coherent one-way (COW), and differential phase shift (DPS). For example, a fiber-based QKD transmitter that asymmetrically uses a Mach-Zehnder interferometer and a dual-pulse generation stage can generate coherent pulses with various phases and relative intensities. Such a transmitter can operate with BB84 with time-bin encoding and can also be used for other DV-QKD protocols such as 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 was limited to DV-QKD protocols such as BB84, DPS, and COW.

[0016] Also, such a transmitter is optimized only for DV-QKD. Since the quantum state needs to be modulated from a continuous random distribution and a reference pulse with a higher intensity than the quantum state needs to be generated for phase recovery, the requirements for phase and amplitude modulation for implementing the CV-QKD protocol are more stringent. For this reason, it is necessary to have the ability to generate pulses with a high extinction ratio and a wide range of amplitude and phase levels (e.g., 1024 voltage levels for a 10-bit resolution distribution). In addition, CV-QKD including a true local oscillator may require two narrow linewidth (e.g., 20 kHz) lasers that are frequency locked. This constraint on the lasers can make it difficult to use methods such as injection synchronization and direct modulation for CV-QKD. Summary of the Invention Problems to be Solved by the Invention

[0017] In view of the above, an object of the present invention is to provide an improved network node and / or transmitter / receiver configuration that addresses one or more of the above-described problems, disadvantages, and / or issues. In other words, an improved and reconfigurable QKD network is needed to ensure interoperability between DV-QKD and CV-QKD systems and optimize QKD performance according to the characteristics of the line / network. Furthermore, there are also advantages in effectively combining CV-QKD and DV-QKD capabilities in the transmitter / receiver of an optical fiber network to achieve versatility and flexibility. Means for Solving the Problems

[0018] Certain embodiments of the invention disclosed herein generally relate to combining CV-QKD and DV-QKD techniques in an optical fiber network. The invention further relates to, for example, dynamic reconfigurability for optimizing performance according to characteristics of the optical fiber link / network (such as key rate, communication distance, number / presence of co-propagating classical channels, etc.) and switching between CV-QKD and DV-QKD modes. The invention also discloses a versatile transmitter and / or receiver that can use both CV-QKD and DV-QKD techniques to perform communication and optimize the QKD performance of the network.

[0019] In certain embodiments, the invention addresses the above objectives by providing a network node configured to operate in an 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, the control unit being configured to switch the operation of the QKD communication unit between the CV-QKD mode and the DV-QKD mode.

[0020] In this context, the term "network node" refers to a connected node that can receive, create, store, or transmit information over one or more network paths. For example, a network node can be an end node for transmitting information or a redistribution node. A network node can have software and / or hardware capabilities 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 location to another via optical / optical signals and / or electrical signals. The terms "CV-QKD mode" and "DV-QKD mode" can be understood as modes that use the "CV-QKD" technology / protocol and the "DV-QKD" technology / protocol, respectively.

[0021] According to this configuration, since the network node is provided with a QKD communication unit capable of communicating with another QKD communication unit of at least one other network 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 the operation of the QKD communication unit from DV-QKD to CV-QKD or vice versa. Due to such dynamic reconfigurability, for example, the QKD performance can be optimized according to the characteristics and / or requirements of the network, such as key rate, communication distance, classical co-propagating channels, etc. As an example, due to the dynamic switching, the network node can be configured to operate in the DV-QKD mode with its high secret key rate in a long-distance link / network, or can be switched to the CV-QKD mode for a short-distance link / network including some classical co-propagating data channels. Thus, in a situation where the performance and functionality are adapted according to the characteristics of the network configuration, a robust but simple method for reconfiguring the network by the network node according to the invention is obtained.

[0022] In certain embodiments 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 providing at least one QKD transmitter having the configuration of this QKD communication unit and capable of operating in both the CV-QKD and DV-QKD modes, the network node can achieve general interoperability and reconfigurability to optimize the QKD performance of the network.

[0023] In certain embodiments of the invention, the control unit may be configured to drive the QKD communication unit with a first predetermined electrical signal such that the QKD transmitter operates in either the CV-QKD mode or the DV-QKD mode. Thereby, a selection of using either the CV-QKD mode or the DV-QKD mode can be implemented via a simpler hardware or software configuration.

[0024] In certain embodiments of the invention, the QKD transmitter comprises a modulator unit configured to modulate the amplitude and / or phase of an optical signal emitted by at least one light source, and the electrical circuit may be configured to drive the modulator unit according to a first predetermined electrical signal. In this way, a simpler but general configuration is obtained for the transmitter to achieve switchability between the CV-QKD and DV-QKD modes.

[0025] It is advantageous if the QKD transmitter comprises an attenuator configured to attenuate the modulated optical signal to a predetermined level and / or set the average photon number required for the CV-QKD mode or the DV-QKD mode, and the electronic circuit is configured to control the attenuator. In one example, the attenuator is a variable optical attenuator by electrical control, and the electronic circuit may further be configured to control the attenuator according to a first predetermined electrical signal. The attenuator may be included before or after the modulator unit, but in both cases, it is included before the CV-QKD or DV-QKD signal is transmitted to the transmission channel.

[0026] In a particular embodiment 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 combinations thereof. In such multiplexing, a network node and / or network may be provided to perform DV-QKD and CV-QKD simultaneously, thereby enhancing versatility, adding degrees of freedom, and improving QKD performance. By way of example, the QKD transmitter may enable multiplexing of CV-QKD and DV-QKD signals by using a polarization switch or by using diverse wavelengths from at least one optical / laser source.

[0027] In a particular embodiment of the invention, the QKD transmitter may combine at least one CV-QKD transmitter and at least one DV-QKD transmitter, and the at least one CV-QKD transmitter and the at least one DV-QKD transmitter may share at least one optoelectronic component. Since the QKD transmitter shares at least one optoelectronic component between the CV-QKD transmitter and the DV-QKD transmitter, a single QKD transmitter may combine the DV-QKD and CV-QKD transmitters into a single element so as to be switchable to operate in either the CV-QKD mode or the DV-QKD mode, thereby achieving versatility and interoperability. This configuration also reduces the number of components.

[0028] The QKD communication unit may include 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 modes, the QKD communication unit and thus the network node can achieve general-purpose interoperability and reconfigurability to optimize the QKD performance of the network.

[0029] The control unit may be configured to drive the QKD communication unit with a second predetermined electrical signal so that the QKD receiver operates in either the CV-QKD mode or the DV-QKD mode. Thereby, a selection using either the CV-QKD mode or the DV-QKD mode can be implemented via a simpler hardware or software configuration.

[0030] In a specific embodiment of the invention, the QKD receiver may comprise a processing / detection unit configured to detect CV-QKD and DV-QKD signals in each of the CV-QKD mode and the DV-QKD mode, and an electronic circuit configured to drive the processing / detection unit according to a second predetermined electrical signal so that the QKD receiver operates in either the CV-QKD mode or the DV-QKD mode. Thereby, a simpler but more versatile configuration is provided for the receiver to achieve switchability between the CV-QKD and DV-QKD modes. As an example, the processing / detection unit of the QKD receiver may be a photodetector configured to detect CV-QKD and DV-QKD signals in each of the CV-QKD mode and the DV-QKD mode by using a polarization controller, an interferometer, a balance detector, and a polarization beam splitter or a wavelength division multiplexing device.

[0031] In a specific embodiment 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 combinations thereof. Such multiplexing provides a network node and / or network for performing DV-QKD and CV-QKD simultaneously, thereby enhancing versatility and adding degrees of freedom, and improving QKD performance. As an example, the QKD receiver may enable multiplexing of CV-QKD and DV-QKD signals by using a polarization beam splitter or a wavelength division multiplexing device configured to separate them for sending to corresponding detectors.

[0032] In certain embodiments of the invention, the QKD receiver may combine at least one CV-QKD receiver and at least one DV-QKD receiver, and the at least one CV-QKD receiver and the at least one DV-QKD receiver may share at least one optoelectronic component. Since the QKD receiver shares at least one optoelectronic component between the CV-QKD receiver and the DV-QKD receiver, a single QKD receiver can combine the DV-QKD and CV-QKD receivers into a single element so that it can be switched to operate in either the CV-QKD mode or the DV-QKD mode, thereby achieving versatility and interoperability. This configuration also reduces the number of components.

[0033] It is advantageous if 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 consist of the GG02 protocol and the discrete modulation CV-QKD protocol, and the at least one DV-QKD protocol may consist of the BB84 DV-QKD protocol, the coherent unidirectional DV-QKD protocol, the differential phase shift DV-QKD protocol, the three-state DV-QKD protocol, and the six-state DV-QKD protocol. Thus, the network nodes according to the invention can operate with various conventional CV-QKD and DV-QKD protocols, but can implement a flexible and reconfigurable network by being suitable for interoperability between CV-QKD and DV-QKD.

[0034] In a particular embodiment, the present invention addresses the above object by providing an optical fiber network, which 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.

[0035] Furthermore, each network node may comprise at least one CV-QKD transmitter and at least one DV-QKD transmitter. Similarly, the network node may also comprise at least one CV-QKD receiver and at least one DV-QKD receiver.

[0036] In a particular embodiment, the present invention addresses the above 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 the amplitude and / or phase of an optical signal emitted by at least one light source, and an electronic circuit configured to drive the modulator unit according to a predetermined electrical signal such that the QKD transmitter operates in either a CV-QKD mode or a DV-QKD mode. According to QKD, key data can be transmitted as quantum information from the QKD transmitter to, for example, a QKD receiver. By having at least one QKD transmitter capable of operating in at least one of the CV-QKD and DV-QKD modes in an optical fiber network, the network / node is thus versatile by being switchable / configurable between CV-QKD and DV-QKD, providing an efficient approach to optimizing the QKD performance of the network. Furthermore, by having an electronic circuit, the selection of using either the CV-QKD mode or the DV-QKD mode can be implemented via a simpler hardware or software configuration.

[0037] The QKD transmitter comprises an attenuator configured to attenuate the modulated optical signal to a predetermined level and / or set the average photon number required for the CV-QKD mode or the DV-QKD mode, and the electronic circuit may be configured to control the attenuator. In one example, the attenuator is a variable optical attenuator by electrical control, and the electronic circuit may further be configured to control the attenuator according to a predetermined electrical signal. The attenuator may be included before or after the modulator unit, but in both cases it is included before the CV-QKD or DV-QKD signal is transmitted to the transmission channel. The attenuator may be included to reduce the intensity and / or phase of the modulated light to a predetermined level or set the average photon number to a predetermined level, and such parameters can be monitored in real time in the network according to the claims, and / or the security of the network according to the claims can be guaranteed.

[0038] By using time, frequency, space, polarization multiplexing, or any one of these combinations, the QKD transmitter may be configured to operate simultaneously in the CV-QKD mode and the DV-QKD mode. Such multiplexing allows the QKD transmitter to perform DV-QKD and CV-QKD simultaneously, enhancing versatility, adding degrees of freedom, and improving QKD performance. As an example, the QKD transmitter enables multiplexing of CV-QKD and DV-QKD signals by using a polarization switch or using diverse wavelengths from at least one optical / laser source.

[0039] The QKD transmitter may combine at least one CV-QKD transmitter and at least one DV-QKD transmitter, and the at least one CV-QKD transmitter and the at least one DV-QKD transmitter may share at least one optoelectronic component. Since the QKD transmitter shares at least one optoelectronic component of the CV-QKD transmitter and the DV-QKD transmitter, a single QKD transmitter may combine the DV-QKD and CV-QKD transmitters into a single element so that it can be switched to operate in either the CV-QKD mode or the DV-QKD mode, thereby achieving versatility and interoperability.

[0040] In certain embodiments of the invention, the QKD transmitter of a network node may be adapted to communicate with a corresponding QKD receiver of at least one other network node of an 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 shifted to the receiver side.

[0041] It is advantageous if 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 consist of the GG02 protocol and the discrete modulation CV-QKD protocol, and the at least one DV-QKD protocol may consist of the BB84 DV-QKD protocol, the coherent one-way DV-QKD protocol, the differential phase shift DV-QKD protocol, the three-state DV-QKD protocol, the six-state DV-QKD protocol, and the decoy state DV-QKD protocol. Thus, the QKD transmitter of the invention can operate with various conventional CV-QKD and DV-QKD protocols, but is suitable for the interoperability between CV-QKD and DV-QKD, enabling the implementation of a flexible and reconfigurable network.

[0042] In certain embodiments, the present invention addresses the above object by providing a QKD receiver configured to receive information in an optical fiber network. The QKD receiver includes a processing / detection unit configured to receive and / or detect CV-QKD and DV-QKD signals in each of a CV-QKD mode and a DV-QKD mode, and an electronic circuit configured to drive the processing / detection unit according to a predetermined electrical signal such that the QKD receiver operates in either the CV-QKD mode or 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 modes in an optical fiber network, the network / network node becomes versatile due to the switchability / configurability between CV-QKD and DV-QKD, and an efficient method for optimizing the QKD performance of the network is obtained. Further, by having an electronic circuit, the selection of using either the CV-QKD mode or the DV-QKD mode can be performed via a simple hardware or software configuration. As an example, the processing / detection unit of the QKD receiver can be a polarization controller and / or one or more detectors configured to process and detect CV-QKD and / or DV-QKD signals in each of the CV-QKD mode and the DV-QKD mode, for example, by using a polarization beam splitter or a wavelength division multiplexing device.

[0043] The QKD receiver can 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 combinations thereof. Such multiplexing allows for enhancing versatility and adding degrees of freedom to improve QKD performance by providing a QKD receiver to perform DV-QKD and CV-QKD simultaneously. As an example, the QKD receiver can multiplex CV-QKD and DV-QKD signals by using a polarization beam splitter or a wavelength division multiplexing device configured to separate these signals for sending to corresponding detectors.

[0044] In certain embodiments of the invention, the QKD receiver may combine at least one CV-QKD receiver and at least one DV-QKD receiver, and the at least one CV-QKD receiver and the at least one DV-QKD receiver may share at least one optoelectronic component. Since the QKD receiver shares at least one optoelectronic component of the CV-QKD receiver and the DV-QKD receiver, a single QKD receiver may combine the DV-QKD and CV-QKD receivers into a single element so that it can be switched to operate in either the CV-QKD mode or the DV-QKD mode, thereby achieving versatility and interoperability.

[0045] In certain embodiments of the invention, the QKD receiver of the network node may be adapted to communicate with a 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 shifted to the transmitter side.

[0046] It is advantageous if 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 consist of the GG02 protocol and the discrete modulation CV-QKD protocol, and the at least one DV-QKD protocol may consist of the BB84 DV-QKD protocol, the coherent unidirectional DV-QKD protocol, the differential phase shift DV-QKD protocol, the three-state DV-QKD protocol, the six-state DV-QKD protocol, and the decoy state DV-QKD protocol. Accordingly, the QKD receiver according to the invention can operate with various conventional CV-QKD and DV-QKD protocols, but is suitable for interoperability between CV-QKD and DV-QKD, enabling the implementation of a flexible and reconfigurable network.

[0047] In certain embodiments, the present invention addresses the above object by providing a method for operating a network node of an optical fiber network, the network node comprising a quantum key distribution communication unit (QCD1) 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 a CV-QKD mode and a DV-QKD mode, the method including the step of switching the operation of the QKD communication unit (QCD1) between a CV-QKD mode and a DV-QKD mode. In this method, it is possible to dynamically switch the operation of the QKD communication unit from DV-QKD to CV-QKD or vice versa.

[0048] Advantageous embodiments of products and methods according to the invention are described below with reference to the figures.

Brief Description of the Drawings

[0049]

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Best Mode for Carrying Out the Invention

[0050] Hereinafter, with reference to the drawings, the features and advantageous embodiments of the present invention will be described in detail.

[0051] Network Node FIG. 2 schematically shows a block diagram of a network node N101 according to an embodiment of the present invention. In one particular embodiment, the network node N101 can be part of at least one optical fiber network for transmitting and / or receiving information such as quantum key information.

[0052] The network node N101 includes a quantum key distribution (QKD) communication unit QCD1 and a control unit (not shown). The QCD1 is configured to communicate with another QCD2 of at least one other network node N102 of the optical fiber network. In particular, the QCD1 is configured to communicate with another QCD2 according to at least one of a continuous variable (CV) QKD mode (dashed line in FIG. 1) and a discrete variable (DV) QKD mode (continuous line in FIG. 1). The control unit is configured to control the QCD1 to operate in at least one of the CV-QKD mode and the DV-QKD mode. In particular, the control unit is configured to switch the operation of the QCD1 between the CV-QKD mode and the DV-QKD mode.

[0053] The control unit of node N101 may include at least one or more of a microprocessor, a memory, monitoring means, electronic means, or a combination thereof. The microprocessor can calculate commands sent to the QKD communication unit QCD1 and / or its components. Other processor-based devices, such as application-specific processors or microcontrollers, can also be used in place of the microprocessor to perform similar functions. The memory may include a non-transitory computer-readable medium that can store executable instructions for controlling 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 include executable instructions that affect the operation of the microprocessor. The monitoring means may be configured to monitor the characteristics of the network and / or receive commands from the input interface of the network node N101 or from an external device. In one example, the monitoring means may include sensors that estimate the amount of noise / error or other specific performance characteristics unique to the optical fiber link / network. In another example, the input interface may include one or more input devices, buttons, or control devices that enable dynamic reconfiguration and switching between the CV-QKD mode and the DV-QKD mode.

[0054] The CV-QKD mode may refer to a mode in which each QKD communication unit is configured to implement a CV-QKD implementation. The DV-QKD mode may refer to a mode in which each QKD communication unit is configured to implement a DV-QKD implementation.

[0055] According to this configuration, since the network node N101 is provided with a QKD communication unit QCD1 that can communicate with another QKD communication unit QCD2 of at least one other network node N102 of the optical fiber network by at least one of the CV-QKD mode and the DV-QKD mode, the control unit can dynamically switch the operation of the QKD communication unit QCD1 from the DV-QKD to the CV-QKD mode, or vice versa. Such dynamic reconfigurability enables optimizing the QKD performance according to the characteristics of the network, such as, for example, the key rate, which can be the secret key rate in bits per second, the communication distance, the number / presence of co-propagating classical channels, and / or the requirements. As an example, DV-QKD can provide a higher secret key rate in long-distance links / networks. In such an example, the control unit can switch the QKD communication unit QCD1 to communicate in the DV-QKD mode. The control unit can perform a dynamic switch from the DV-QKD mode to CV-QKD to achieve a higher secret key rate in short-distance links / networks.

[0056] Another possible scenario is that while communicating in the DV-QKD mode, the QKD communication units QCD1 and QCD2 can detect an increment in noise, which may be due to a higher intensity of the classical data channel. In this case, the control unit switches from the DV-QKD mode to the CV-QKD mode, thus enabling coexistence with the co-propagating classical signal and a positive key rate. Therefore, the QKD communication unit QCD1 can communicate with the QKD communication unit QCD2 to request a mode switch to CV-QKD to optimize the secret key rate in a link / network containing noise.

[0057] The operation of the network node N101 illustrated in FIG. 2 is described below. In the above configuration, the QKD communication unit (QCD1) can be switched between the CV-QKD mode and the DV-QKD mode using the control unit. The switching operation can be implemented using hardware and / or software configurations.

[0058] Optical fiber network FIG. 3 schematically illustrates an optical fiber network 100 according to an embodiment of the present invention, having a plurality of network nodes N101 to N108. One or more of the plurality of network nodes N101, N102, N105, N106, N108 are according to an embodiment of the present invention. Specifically, one or more of the network nodes N101, N102, N105, N106, N108 may include QKD communication units QCD1-QCD5 capable of communicating by at least one of the CV-QKD mode and the DV-QKD mode. One or more of the nodes N103, N104, N107 may include QKD communication units QDV2, QDV3, QDV6 capable of communicating only by the DV-QKD mode. Similarly, one or more additional nodes (not shown) capable of communicating only by the CV-QKD mode may be provided.

[0059] As an example, network node N101 is configured to communicate with network node N102 in at least one of the CV-QKD mode (shown by a dashed line in FIG. 3) and the DV-QKD mode (shown by a solid line in FIG. 3). Network node N102 can communicate with other network nodes N101, N103, N104, N105. Depending on the configurability of the other network nodes N101, N103, N104, N105, the communication can be in at least one of the CV-QKD mode and the DV-QKD mode.

[0060] For example, network node N101 or N105 is configured to operate in either the CV-QKD mode or the DV-QKD mode. Accordingly, the communication between network node N102 and network node N101 or N105 can be switched between the CV-QKD mode and the DV-QKD mode to achieve optimized QKD performance. Network node N102 or N105 communicates with network nodes N103 or N104 respectively via the DV-QKD mode. Network nodes N103 and N104 communicate with each other via the DV-QKD mode.

[0061] Due to the combination of CV-QKD and DV-QKD technologies in the optical fiber network 100, the present invention enables dynamic reconfigurability and switching between CV-QKD and DV-QKD modes so as to optimize the QKD performance of the optical fiber network.

[0062] The present invention is not limited thereto. The optical fiber network may have any number of network nodes. All or some of the network nodes may be reconfigurable to switch between the CV-QKD mode and the DV-QKD mode. The network nodes can communicate with each other via one or more waveguides such as optical communication channels, optical fibers, and the like.

[0063] In an embodiment, each of the network nodes of the present invention may include at least one transmitter and / or at least one receiver as respective QKD communication units for communicating with other network nodes of the optical fiber network. The transmitter and the receiver may be configured to exchange CV-QKD signals and / or DV-QKD signals and thus are configured for QKD and are therefore referred to as a QKD transmitter and a QKD receiver, respectively.

[0064] 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. Hereinafter, the QKD transmitter and the QKD receiver are described using FIGS. 4A-7B.

[0065] QKD Transmitter Figure 4A shows a block diagram of a QKD transmitter 400A according to another embodiment of the invention. The QKD transmitter 400A is configured to operate in at least one of a CV-QKD mode and a DV-QKD mode. By having a QKD transmitter 400A capable of operating in both CV-QKD and DV-QKD modes, a network node can achieve general interoperability and reconfigurability to optimize the QKD performance of the previously disclosed network 100. The QKD transmitter is configured to transmit CV-QKD and / or DV-QKD signals to a receiver.

[0066] In an embodiment of the invention, in the QKD transmitter 400A, at least one CV-QKD transmitter and at least one DV-QKD transmitter can be combined into a single element. In a specific example, at least one CV-QKD transmitter and at least one DV-QKD transmitter can share at least one optoelectronic component. Since the QKD transmitter shares at least one optoelectronic component between the CV-QKD transmitter and the DV-QKD transmitter, a single QKD transmitter can combine the DV-QKD and CV-QKD transmitters into a single element so that it can be switched to operate in either the CV-QKD mode or the DV-QKD mode, thereby achieving versatility and interoperability. This configuration also reduces the number of components.

[0067] The QKD transmitter 400A includes 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 outside the QKD transmitter 400A.

[0068] At least one light source 401 is configured to emit an optical signal. For example, the light source can be a laser light source, particularly a continuous wave (CW) laser light source. Alternatively, the light source can be a pulsed laser light source. By being able to be an adjustable laser source, for example, the wavelength of the laser can be adjusted to enable quantum communication in a specific channel of the used band (e.g., the C band).

[0069] The modulator unit 403 can receive an optical signal emitted by at least one light source 401. The modulator unit 403 is configured to modulate the amplitude and / or phase of the received optical signal. The modulator unit 403 may include at least one amplitude modulator for modulating the amplitude of the optical signal and / or at least one phase modulator for modulating the phase of the optical signal, respectively. The amplitude and / or phase modulator may include one or more optical and / or electronic components. For example, the amplitude and / or phase modulator may include at least one material that exhibits an electro-optic effect such that the respective amplitude and / or phase modulation can be achieved by controlling the electric field of the material. The amplitude modulator preferably may have a predetermined extinction ratio (e.g., >20 dB) for reducing background noise. In the case of CV-QKD involving Gaussian modulation, the phase and / or amplitude modulator has a predetermined resolution and dynamic range such that a desired approximation can be obtained for the continuous modulation of the phase and amplitude. One or more optical and / or electronic components of the modulator may be one or more optoelectronic components shared by the corresponding CV-QKD transmitter and DV-QKD transmitter.

[0070] The electronic circuit 402 is configured to control the modulator unit 403. In particular, in such a manner that the QKD transmitter 400A operates in either the CV-QKD mode or the DV-QKD mode, the electronic circuit 402 is configured to drive the modulator 403 according to a first predetermined electrical signal. The electronic unit 402 enables the selection of the CV-QKD mode or the DV-QKD mode by setting the first predetermined electrical signal for driving the modulator unit 402. The electronic circuit 402 may be a hardware and / or software element. Thereby, the selection of using either the CV-QKD mode or the DV-QKD mode can be implemented via a simpler hardware and / or software configuration.

[0071] The first predetermined electrical signal of the electronic circuit 402 can be configured to drive the modulator unit 403. In particular, components of the modulator unit 403, such as one or more shared optoelectronic components of an amplitude and / or phase modulator, are configured to be driven by the first predetermined electrical signal to select one of the CV-QKD mode and the DV-QKD mode as the operating mode of the QKD transmitter 400A. In one example, the first predetermined electrical signal can determine whether the communication mode is the CV-QKD mode or the DV-QKD mode.

[0072] Examples of the electronic circuit 402 include, but are not limited to, electronic switches and field programmable gate arrays, and may be combined with one or more digital-to-analog converters. The electronic circuit 402 can be configured to control laser parameters of the light source 401, such as wavelength, frequency, output, and others. Additionally, the electronic circuit 402 may be configured to monitor the operation of optoelectronic components of the light source 401 and / or the modulator unit 403 using one or more analog-to-digital converters. In an embodiment, the electronic circuit 402 can be controlled by software.

[0073] According to another embodiment of the invention illustrated in FIG. 4A, the QKD transmitter 400A may further comprise an attenuator 405 configured to attenuate the modulated optical signal to a predetermined level and / or set the average photon number required for the CV-QKD mode or the DV-QKD mode. The electronic circuit 402 may be configured to control the attenuator 405. The attenuator 405 may be driven by a first predetermined electrical signal. For example, for a given communication mode, both the attenuation and the first predetermined electrical signal may be fixed. In one example, the attenuator 405 may be a fixed optical attenuator or a variable optical attenuator. The position of the attenuator 405 is not limited. For example, the attenuator 405 may be included before or after the modulator unit 403. To reduce the intensity and / or phase of the modulated light to a predetermined level or set the average photon number to a predetermined level, the attenuator 405 may be included, such parameters can be monitored in real time in the optical fiber network, and / or the security of the optical fiber network can be guaranteed. The attenuator 405 may comprise one or more optical and / or electronic components. One or more optical and / or electronic components of the attenuator 405 may be one or more optoelectronic components shared by the corresponding CV-QKD attenuator and DV-QKD attenuator. The electronic circuit 402 may be configured to enable the selection of the CV-QKD mode or the DV-QKD mode by setting a first predetermined electrical signal for driving the attenuator 405 and / or one or more shared optoelectronic components of the attenuator 405.

[0074] Figure 4B illustrates a QKD transmitter 400B, which is a specific implementation example of the embodiment / block diagram of the QKD transmitter 400A shown in Figure 4A. In this specific implementation example, the QKD transmitter 400B can perform DV-QKD and CV-QKD according to the DV-QKD BB84 time-bin protocol and the CV-QKD GG02 protocol, respectively. The modulator unit 403 may include two electro-optical amplitude modulators AM1 and AM2 for modulating the amplitude of the optical signal emitted by the light source 401, which is a continuous-wave laser in this specific implementation example, and an electro-optical phase modulator PM1 for modulating the phase of the emitted optical signal. Subsequently, in this specific implementation example, the attenuator 405, which is a variable optical attenuator controlled electrically, can attenuate the modulated optical signal to a predetermined level and / or set the average photon number required in the CV-QKD mode or the DV-QKD mode.

[0075] The specific implementation example may further include a beam splitter 407. The beam splitter 407 may be configured to split the modulated optical signal such that a part of the split modulated optical signal is sent for further processing such as average photon number measurement and the like, and the remaining part can be sent to the receiver (described later).

[0076] The electronic circuit 402 is configured to drive at least one of the laser light source 401, one or more modulators AM1, AM2, PM1, and the attenuator 405. In particular, one or more of these components can be driven according to a first predetermined electrical signal in such a way that the QKD transmitter 400B can operate in either the CV-QKD mode or the DV-QKD mode.

[0077] Figure 4C illustrates an example of a predetermined electrical signal for driving one or more electro-optic modulators of the QKD transmitter 400B shown in Figure 4B so as to implement the DV-QKD BB84 time-bin protocol and the CV-QKD GG02 protocol according to the DV-QKD mode and the CV-QKD mode, respectively. In other words, the predetermined electrical signal may include one or more electrical signals for driving one or more electro-optic modulators so that the QKD transmitter 400B operates in either the CV-QKD mode or the DV-QKD mode. In this example, the electrical signal corresponds to the time-bin BB74 DV-QKD protocol (left in Figure 4C) and the GG02 CV-QKD protocol with a true local oscillator (right in Figure 4C). When describing Figure 4C, the relevant portions of the background of the invention are not repeated and are incorporated herein by reference.

[0078] Regarding the time-bin BB84 protocol shown in Figure 4C (left), the first amplitude modulator 403, i.e., AM1, generates pulses with intensities according to four quantum states, namely, the early and late states from the Z basis and the two overlapping states + and - from the X basis corresponding to two pulses with equal intensities. Subsequently, the second amplitude modulator 403, i.e., AM2, performs the decoy state method. As an example, two decoys are implemented by adjusting the intensity levels of the states depicted in Figure 4C (left). The average photon number of the signal and the decoy states are adjusted by using the second amplitude modulator 403, i.e., AM2, and the attenuator 405, respectively. For example, signal pulses with an average photon number of 1 (i.e., on average 1 photon per pulse) and decoy states with average photon numbers of 0.1 and 0.01 may be used. Finally, the phase modulator 403, i.e., PM1, is used to set the phase differences of +π and -π for the states of the X basis and may also be used to add a uniformly distributed random phase between symbols as required by the security proof of the protocol.

[0079] Regarding the GG02 CV-QKD protocol, the electrical signals used to operate the QKD transmitter 400B are shown in Fig. 4C (right). In this example, the first amplitude modulator 403, AM1, generates pulses R and S with two different phases as reference and signal pulses, respectively. The reference pulses can be interleaved between the quantum signals composed of optical pulses with Gaussian-modulated quadrature phases X and P. By using the second amplitude modulator 403, AM2, to modulate the amplitude of the signal according to a Rayleigh random distribution, and the phase modulator 403, PM1, to modulate the phase according to a uniform random distribution, a quadrature phase by Gaussian modulation can be obtained. An attenuator 405 can be used to set the modulation variance of the signal to a value that can maximize the secret key rate (e.g., equal to twice the average photon number). In one embodiment, the amplitude of the reference pulses can usually be higher than that of the signal pulses so as to obtain accurate phase recovery.

[0080] Fig. 4D shows a block diagram of a QKD transmitter 400D according to another embodiment of the present invention. The QKD transmitter 400D includes all of the components, details, and functionality of the QKD transmitter 400A shown in Fig. 4A. The QKD transmitter 400D further includes a polarization switch 409. The polarization switch 409 facilitates the QKD transmitter 400D to operate simultaneously in the CV-QKD mode and the DV-QKD mode by using, for example, any one of time, frequency, space, polarization multiplexing, and combinations thereof. The QKD transmitter 400D can operate by sending the multiplexed CV-QKD and DV-QKD signals to a receiver (described later). The QKD transmitter 400E shown in Fig. 4E is a specific implementation example of the QKD transmitter 400D. In this implementation example, the polarization switch 409 can be configured to time-multiplex the CV-QKD and DV-QKD signals with orthogonal polarizations so that the QKD transmitter 400E can send time-multiplexed packets of the CV-QKD and DV-QKD signals to the receiver.

[0081] Figure 4F shows a block diagram of a QKD transmitter 400F according to another embodiment of the present invention. The QKD transmitter 400F includes all of the components, details, and functionality of the QKD transmitter 400A shown in Figure 4A. In the QKD transmitter 400F, the light source 401A is configured to operate at two different wavelengths / frequencies, one for the DV-QKD mode and the other for the CV-QKD mode, thereby achieving wavelength or frequency multiplexing. The light source 401A can be a single light source, such as an adjustable laser source configured to operate using two different wavelengths / frequencies, or two individual light sources each operating at a given wavelength / frequency that is the same or different from each other. The light source 401A can facilitate the simultaneous operation of the QKD transmitter 400F in the CV-QKD mode and the DV-QKD mode, for example, by using wavelength or frequency multiplexing and combinations thereof. The QKD transmitter 400G shown in Figure 4G is a specific implementation example of the QKD transmitter 400F. In this implementation example, the QKD transmitter 400G can wavelength or frequency multiplex the CV-QKD and DV-QKD signals and send the wavelength or frequency multiplexed packets of the CV-QKD and DV-QKD signals to the receiver.

[0082] The above-described time-bin BB84 protocol and GG02 CV-QKD protocol are merely examples of DV-QKD and CV-QKD protocols that can be performed by the QKD transmitters 400A-400G proposed in Figures 4A-4G, respectively. However, the present invention is not limited thereto. The predetermined electrical signal sent by the electrical circuit 402 can be modified to execute any protocol, such as a discrete modulation CV-QKD protocol, a coherent one-way DV-QKD protocol, a differential phase-shift DV-QKD protocol, a three-state DV-QKD protocol, a six-state DV-QKD protocol, a decoy-state DV-QKD protocol.

[0083] QKD Receiver The QKD receiver is configured to receive a QKD signal from the QKD transmitter. A conventional QKD receiver is configured to receive either a CV-QKD signal or a DV-QKD signal from their respective transmitters.

[0084] The conventional QKD receiver 500A shown in FIG. 5A generally includes a processing unit 501 for receiving CV or DV-QKD signals from respective CV or DV-QKD transmitters and / or for processing the received QKD signals, and a detection unit 502 for detecting the received QKD signals. The processing unit 501 may include one or more optoelectronic components. The one or more optoelectronic components of the processing unit 501 may include, but are not limited to, interferometers such as balanced / unbalanced Michelson interferometers or balanced / unbalanced Mach-Zehnder interferometers, one or more beam splitters, polarization components such as polarization-maintaining optical fibers (PMFs), polarization controllers, one or more modulators / demodulators, local oscillators, and other combinations. The detection unit 503 may include one or more optoelectronic components such as one or more single-photon detectors, heterodyne detectors, homodyne detectors, and others, but is not limited thereto.

[0085]

[0086] The upper diagram of FIG. 5B illustrates a conventional receiver 500B1 commonly used to perform the time-bin BB84 DV-QKD protocol. The receiver 500B1 includes an unbalanced interferometer with two arms, a beam splitter BS, and two Faraday mirrors FM disposed at the ends of each interferometer arm to make the interferometer polarization-independent. A fiber delay equal to the time separation between the "early" and "late" time modes of FIG. 4C may be added to one arm of the interferometer. The receiver 500B1 further includes at least two detectors D1, D2 and a circulator C for splitting the signal for detection by each detector D1, D2 such that the interferometer can use the same ports for input and output.

[0087] ​Alternatively, the lower diagram of FIG. 5B illustrates a receiver 500B2 commonly used to perform the time-bin BB84 DV-QKD protocol. Receiver 500B2 includes an unbalanced interferometer with two arms, a beam splitter BS, polarization maintaining members PMF added to both arms of the interferometer, and a polarization controller PC provided on the input side of the receiver to align the polarization of the received QKD signal with the axis of the polarization maintaining member PFM. A fiber delay equal to the time separation between the "early" and "late" time modes of FIG. 4C can be added to one arm of the interferometer. Receiver 500B1 further includes at least two detectors D1, D2 and a further beam splitter BS for splitting the signal for detection by each detector D1, D2.

[0088] FIG. 5C illustrates a conventional receiver 500C commonly used to perform the GG02 CV-QKD protocol. Receiver 500C is configured to interfere an input signal from a transmitter with a local oscillator so as to enable acquisition of the signal quadrature phase value. To maximize the interference, receiver 500C includes a polarization controller PC for aligning the polarization of the signal and the local oscillator LO. The receiver 500C shown in the upper diagram of FIG. 5C includes a heterodyne detector that can simultaneously detect the quadrature phases X and P by using a 90° optical hybrid OH and two detectors D1, D2. Alternatively, the receiver 500C shown in the lower diagram of FIG. 5C may include a homodyne detector that can detect the quadrature phases X and P one at a time by a single detector D by randomly varying the phase of the local oscillator between 0 and π using a phase modulator PM.

[0089] In embodiments of the present invention, conventional well-known DV-QKD and / or CV-QKD receivers such as those shown in FIGS. 5A-5C can be used in combination with the QKD transmitter of the invention illustrated in DV-QKD and / or CV-QKD communication in an optical fiber network in FIGS. 4A-4G.

[0090] The QKD receiver according to an embodiment of the invention will be described with reference to FIG. 6. The QKD receiver 600 is configured to receive CV and / or DV-QKD signals from, for example, a conventional CV and / or DV-QKD transmitter or a QKD transmitter according to the present invention, and / or to process the received QKD signals, and includes a processing unit 601 and a detection unit 603 configured to detect the received QKD signals. The processing unit 601 and the detection unit 603 may include the same components as the receiver 500A.

[0091] 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 according to, for example, a second predetermined electrical signal so that the QKD receiver 600 operates in either the CV-QKD mode or the DV-QKD mode. The electronic unit 605 enables the selection of the CV-QKD mode or the DV-QKD mode by setting a second predetermined electrical signal for driving the processing unit 601 and / or the detection unit 603. The electronic circuit 605 may be a hardware and / or software element. Examples of the electronic circuit 605 include, but are not limited to, an electronic switch, a polarization beam splitter (PBS), a wavelength division multiplexing device (WDM), a polarization controller, and others. In an embodiment, the electronic circuit 605 may be controlled by software.

[0092] The second predetermined electrical signal of the electronic circuit 605 may be configured to drive components of the processing unit 601 and / or the detection unit 603, particularly one or more optoelectronic 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 operating mode of the QKD receiver 600. The second predetermined electrical signal may be a signal in any form, but is a signal to the processing unit and / or the detection unit that switches the operation from CV-QKD to DV-QKD or vice versa.

[0093] In this way, since the QKD receiver 600 is configured to operate in at least one of the CV-QKD mode and the DV-QKD mode, general-purpose interoperability, reconfigurability, and switchability are achieved, and the QKD performance can be optimized.

[0094] In an embodiment, one or more optoelectronic components of the QKD receiver can be one or more optoelectronic components shared by a conventional CV-QKD receiver and a DV-QKD receiver. Similar to the QKD transmitter of the invention, the electronic circuit 605 of the QKD receiver is configured to appropriately detect DV and / or CV signals between the DV-QKD mode and the CV-QKD mode.

[0095] FIG. 7A illustrates a QKD receiver 700A according to a specific implementation example of an embodiment of the present invention. The QKD receiver 700A combines the components of the time-bin BB84 DV-QKD receiver 500B2 in FIG. 5B and the components of the GG02 CV-QKD receiver 500C in FIG. 5C (upper figure), and these are configured to be controlled by the electronic circuit 605 in this embodiment. The polarization controller PC is controlled by the electronic circuit 605 so that the QKD receiver 700A can operate in at least one of the DV-QKD mode and the CV-QKD mode. In this embodiment, the QKD receiver 700A includes a polarization beam splitter PBS configured to be controlled by the polarization controller PC. The electronic circuit 605 is configured to control the polarization controller PC, whereby the polarization controller PC is configured to send a signal to the polarization beam splitter PBS, and thus, the components of the DV-QKD receiver or the CV-QKD receiver operate to receive their respective QKD signals from, for example, the QKD transmitter of the present invention.

[0096] FIG. 7B illustrates an alternative QKD receiver 700B according to another specific implementation example of an embodiment of the present invention. The QKD receiver 700B is different from the QKD receiver 700A in that a polarization beam splitter PBS is replaced by a wavelength division multiplexing device WDM. The QKD receiver 700B can be used, for example, in an example where the light source 401A of the QKD transmitter 400F or 400G operates at two different wavelengths / frequencies, one for the DV-QKD mode and the other for the CV-QKD mode, as in the embodiment of FIG. 4E. In operation, the QKD transmitter 400C can multiplex the CV-QKD and DV-QKD signals by wavelength or frequency and send the wavelength or frequency multiplexed packets of the CV-QKD and DV-QKD signals to the QKD receiver 700B. According to the electronic circuit 605, the wavelength division multiplexing device WDM is configured to separate the DV and CV signals and send them to the corresponding detectors. In this multiplexed configuration, the QKD receiver 700B can perform the DV-QKD mode and the CV-QKD mode simultaneously.

[0097] The above-described time-bin BB84 protocol and GG02 CV-QKD protocol are merely examples of the DV-QKD and CV-QKD protocols that can be performed by the QKD receivers 600-700B proposed in FIGS. 6-7B. However, the present invention is not limited thereto. The predetermined electrical signal sent by the electronic circuit 605 can be modified to execute any protocol such as a discrete modulation CV-QKD protocol, a coherent one-way DV-QKD protocol, a differential phase shift DV-QKD protocol, a three-state DV-QKD protocol, a six-state DV-QKD protocol, a decoy state DV-QKD protocol, or the like.

[0098] Embodiments of the present invention provide a network node, an optical network, a QKD transmitter, a QKD receiver, and an operating method of the network node that enable the realization of a general-purpose and robust configuration and interoperability of an optical fiber network by dynamically switching the operation between the DV-QKD mode and the CV-QKD mode.

Description of Reference Numerals

[0099] 100 Optical Fiber Network 400A, 400B, 400C, 400D, 400E, 400F, 400G QKD (Quantum Key Distribution) Transmitter 401, 401A Light Source 402 Electronic Circuit 403 Modulator Unit 405 Attenuator 407 Beam Splitter 409 Polarization Switch 500A, 500B1, 500B2, 500C Conventional QKD (Quantum Key Distribution) Receiver 501 Processing Unit 503 Detection Unit 600 QKD (Quantum Key Distribution) Receiver 601 Processing Unit 603 Detection Unit 605 Electronic Circuit 700A, 700B QKD (Quantum Key Distribution) Receiver N101, N102, N103, N104, N105, N106, N107, N108 Network Node QCD1, QCD2, QCD3, QCD4, QCD5 QKD (Quantum Key Distribution) Communication Unit QDV2, QDV3, QDV6 Discrete Quantum Key System

Claims

1. A network node configured to operate in an optical fiber network, comprising: a quantum key distribution communication unit (QCD1) configured to communicate with another quantum key distribution 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; a control unit configured to control the quantum key distribution communication unit (QCD1) to operate in at least one of the CV-QKD mode and the DV-QKD mode; wherein: the control unit is configured to switch the operation of the quantum key distribution communication unit (QCD1) between the CV-QKD mode and the DV-QKD mode; the quantum key distribution communication unit (QCD1) comprises at least one QKD transmitter (400A-400G) configured to operate in at least one of the CV-QKD mode and the DV-QKD mode; the control unit is configured to drive the quantum key distribution communication unit (QCD1) with a first predetermined electrical signal such that the QKD transmitter (400A-400G) operates in either the CV-QKD mode or the DV-QKD mode; a network node.

2. The QKD transmitter (400A-400G) comprises: a modulator unit (403, AM1, AM2, PM1) configured to modulate the amplitude and / or phase of an optical signal emitted by at least one light source (401, 401A); an electronic circuit (402) configured to drive the modulator unit (403, AM1, AM2, PM1) according to the first predetermined electrical signal; The network node according to claim 1.

3. The QKD transmitter (400A-400G) comprises an attenuator (405) configured to attenuate the modulated optical signal to a predetermined level and / or set the average number of photons required for the CV-QKD mode or the DV-QKD mode, and the electronic circuit (402) is configured to control the attenuator (405). The network node according to claim 2.

4. The control unit is configured to operate the QKD transmitter (400A-400G) simultaneously in the CV-QKD mode and the DV-QKD mode by using any one of time, frequency, space, polarization multiplexing, and combinations thereof. The network node according to any one of claims 1 to 3.

5. The QKD transmitter (400A-400G) includes at least one CV-QKD transmitter and at least one DV-QKD transmitter, and the at least one CV-QKD transmitter and the at least one DV-QKD transmitter share at least one optoelectronic component. The network node according to any one of claims 1 to 4.

6. The quantum key distribution communication unit (QCD1) includes at least one QKD receiver (500A-700B) configured to operate in at least one of the CV-QKD mode and the DV-QKD mode. The network node according to any one of claims 1 to 5.

7. The control unit is configured to drive the quantum key distribution communication unit (QCD1) with a second predetermined electrical signal so that the QKD receiver (500A-700B) operates in either the CV-QKD mode or the DV-QKD mode. The network node according to claim 6.

8. The QKD receiver (500A-700B) a processing / detection unit (501, 601) configured to detect CV-QKD and DV-QKD signals in each of the CV-QKD mode and the DV-QKD mode; an electronic circuit (605) configured to drive the processing / detection unit (501, 601) according to the second predetermined electrical signal; The network node according to claim 7, comprising:

9. The control unit is configured to operate the QKD receiver (500A-700B) simultaneously in the CV-QKD mode and the DV-QKD mode by using any one of time, frequency, space, polarization multiplexing, and combinations thereof. The network node according to any one of claims 6 to 8.

10. The QKD receiver (500A-700B) combines at least one CV-QKD receiver and at least one DV-QKD receiver, and the at least one CV-QKD receiver and the at least one DV-QKD receiver share at least one optoelectronic component. The network node according to any one of claims 6 to 9.

11. The network node according to any one of claims 1 to 10, wherein the CV-QKD mode is based on at least one CV-QKD protocol, and the DV-QKD mode is based on at least one DV-QKD protocol.

12. The at least one CV-QKD protocol consists of a GG02 protocol and a discrete modulation CV-QKD protocol, and the at least one DV-QKD protocol consists of a BB84 DV-QKD protocol, a coherent one-way DV-QKD protocol, a differential phase shift DV-QKD protocol, a three-state DV-QKD protocol, a six-state DV-QKD protocol, and a decoy state DV-QKD protocol. The network node according to claim 11.

13. An optical fiber network comprising one or more network nodes according to any one of claims 1 to 12.

14. A QKD transmitter configured to transmit information in an optical fiber network, a modulator unit (403, AM1, AM2, PM1) configured to modulate the amplitude and / or phase of an optical signal emitted by at least one light source (401, 401A); an electronic circuit (402) configured to drive the modulator unit (403, AM1, AM2, PM1) according to a predetermined electrical signal so that the QKD transmitter operates in either a CV-QKD mode or a DV-QKD mode; A QKD transmitter comprising.

15. The QKD transmitter according to claim 14, further comprising an attenuator (405) configured to attenuate the modulated optical signal to a predetermined level and / or set the average number of photons required for the CV-QKD mode or the DV-QKD mode, and the electronic circuit (402) is configured to control the attenuator (405).

16. The QKD transmitter according to claim 14 or 15, wherein the QKD transmitter is 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 combinations thereof.

17. The QKD transmitter according to any one of claims 14 to 16, wherein the QKD transmitter combines at least one CV-QKD transmitter and at least one DV-QKD transmitter, and the at least one CV-QKD transmitter and the at least one DV-QKD transmitter share at least one optoelectronic component.

18. The QKD transmitter according to any one of claims 14 to 17, wherein the QKD transmitter of the network node is adapted to communicate with a corresponding QKD receiver (500A-700B) of at least one other network node of the optical fiber network according to the CV-QKD mode and / or the DV-QKD mode.

19. The QKD transmitter according to any one of claims 14 to 18, wherein the CV-QKD mode is based on at least one CV-QKD protocol, and the DV-QKD mode is based on at least one DV-QKD protocol.

20. The QKD transmitter according to claim 19, wherein the at least one CV-QKD protocol consists of the GG02 protocol and the discrete modulation CV-QKD protocol, and the at least one DV-QKD protocol consists of the BB84 DV-QKD protocol, the coherent one-way DV-QKD protocol, the differential phase shift DV-QKD protocol, the three-state DV-QKD protocol, the six-state DV-QKD protocol, and the decoy state DV-QKD protocol.

21. A QKD receiver configured to receive information in an optical fiber network, a processing / detection unit (501, 601) configured to receive and / or detect CV-QKD and DV-QKD signals in each of the CV-QKD mode and the DV-QKD mode; an electronic circuit (605) configured to drive the processing / detection unit (501, 601) according to a predetermined electrical signal so that the QKD receiver operates in either the CV-QKD mode or the DV-QKD mode; A QKD receiver comprising the above.

22. The QKD receiver according to claim 21, wherein the QKD receiver is 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 combinations thereof.

23. The QKD receiver according to claim 21 or 22, wherein the QKD receiver combines at least one CV-QKD receiver and at least one DV-QKD receiver, and the at least one CV-QKD receiver and the at least one DV-QKD receiver share at least one optoelectronic component.

24. The QKD receiver according to any one of claims 21 to 23, wherein the QKD receiver of the network node is adapted to communicate with a 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.

25. The QKD receiver according to any one of claims 21 to 24, wherein the CV-QKD mode is based on at least one CV-QKD protocol, and the DV-QKD mode is based on at least one DV-QKD protocol.

26. The QKD receiver according to claim 25, wherein the at least one CV-QKD protocol consists of a GG02 protocol and a discrete modulation CV-QKD protocol, and the at least one DV-QKD protocol consists of a BB84 DV-QKD protocol, a coherent one-way DV-QKD protocol, a differential phase shift DV-QKD protocol, a three-state DV-QKD protocol, a six-state DV-QKD protocol, and a decoy state DV-QKD protocol.

27. A method for operating a network node in an optical fiber network, the network node comprising: A quantum key distribution communication unit (QCD1) configured to communicate with another quantum key distribution 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; A control unit configured to control the quantum key distribution communication unit (QCD1) to operate in at least one of the CV-QKD mode and the DV-QKD mode; Comprising. Including the step of using the control unit to switch the operation of the quantum key distribution communication unit (QCD1) between the CV-QKD mode and the DV-QKD mode, The quantum key distribution communication unit (QCD1) includes at least one QKD transmitter (400A-400G) configured to operate in at least one of the CV-QKD mode and the DV-QKD mode, The control unit is configured to drive the quantum key distribution communication unit (QCD1) with a first predetermined electrical signal so that the QKD transmitter (400A-400G) operates in either the CV-QKD mode or the DV-QKD mode, Method.

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