KR102168674B1 - Polarization robust plug-and-play CV QKD system - Google Patents

Abstract

The present invention relates to a plug-and-play continuous variable quantum cryptographic key distribution system independent of polarization shake, and the continuous variable quantum cryptographic key distribution system of the present invention is robust and independent of polarization shake caused by a channel attack by an attacker (Eve). It provides plug-and-play continuous variable quantum encryption key distribution.

Description

Plug-and-play continuous variable quantum cryptographic key distribution system independent of polarization shake {Polarization robust plug-and-play CV QKD system}

The present invention relates to a continuous variable quantum encryption key distribution (CV QKD, Continuous Variable Quantum Key Distribution) system, in particular, to a plug and play continuous variable quantum encryption key distribution system independent of polarization shake.

1 is a diagram for describing a general continuous variable quantum encryption key distribution system. Referring to FIG. 1, first, a pulse wave is generated through an amplitude modulator (AM) for continuous light (CW) in a transmitter (Alice), and then a signal is transmitted to a polarization beam splitter (PBS). Separate into (signal) pulse and LO (local oscillator) pulse. Next, the signal pulse is modulated to a desired data value through an amplitude modulator (AM) and a phase modulator (PM). Thereafter, the modulated signal pulses having polarizations perpendicular to each other and the LO pulses are combined through a polarization beam splitter (PBS) and output to an optical fiber channel.

In the receiver Bob, first, the signal received through the channel is corrected for polarization shake flowing through the channel through a dynamic polarization controller (DPC). The corrected signal is divided into signal pulses and LO pulses again through a polarization beam splitter (PBS), and the reference phase of the LO pulse to determine the quadrature of the homodyne detector through a phase modulator (PM). Reference phase) (0 degrees or 90 degrees) is arbitrarily modulated, and signal pulses and LO pulses are combined through a beam splitter (BS) to perform state detection according to the homodyne method.

However, in the conventional continuous variable quantum cryptographic key distribution (CV QKD), there is a risk that a quantum level signal pulse and a strong signal LO pulse can greatly reduce secrecy due to a channel attack by an attacker (Eve). There is a problem.

Accordingly, the present invention was conceived to solve the above problems, and an object of the present invention is to provide a robust plug-and-play continuous variable quantum cryptographic key distribution system regardless of polarization shake caused by a channel attack by an attacker (Eve). I have to.

First, summarizing the features of the present invention, a continuous variable quantum cryptographic key distribution system according to an aspect of the present invention for achieving the above object comprises: an amplitude modulator for generating a pulse wave for continuous light; A polarization controller for polarization correction for the pulsed wave; Phase modulator; Faraday Mirror; The output of the polarization controller is received through a first port and separated into an LO pulse to a second port and a signal pulse to a third port, and the separated LO pulse is reflected through the phase modulator and the Faraday mirror to be 90 degrees. A transmission target that receives the LO pulse whose polarization is rotated as a reference LO pulse through the second port and outputs it to the fourth port, and the separated signal pulse is transmitted to the transmitter through a quantum channel and then returned as a response from the transmitter. A polarization beam splitter for receiving the signal pulse encoded for the encryption key through the third port and outputting the received signal pulse to the fourth port; A polarization rotator for rotating polarized light with respect to the output of the fourth port, which is output by combining the reference LO pulse and the encoded signal pulse that are orthogonal to each other; And a state detector that performs state detection for detecting a digital bit corresponding to the transmission target encryption key from the output of the polarization rotator.

The transmitter performs encryption key distribution in a plug-and-play format that provides the encoded signal pulses using the signal pulses from the receiver without using an optical source for encoding.

The polarization rotator rotates and outputs polarized light by 45 degrees with respect to the output of the fourth port. The polarization rotator allows (the encoded signal pulse + the reference LO pulse) and (the encoded signal pulse-the reference LO pulse) to be combined and output.

The state detector may perform the state detection in either a homodyne or heterodyne method.

The transmitter includes a first port for receiving the received signal pulse and outputting the encoded signal pulse, a second port for outputting a first polarization component for the received signal pulse, and the received signal pulse. A polarization beam splitter including a third port outputting a second polarization component; A phase modulator sequentially coupled on an optical path between the second port and the third port; Amplitude modulator; Polarization rotator; And a random number generator for providing a random number to the phase modulator and the amplitude modulator. The polarization rotator rotates the incident pulse by 90 degrees and outputs it.

In addition, a method of distributing a continuous variable quantum encryption key according to another aspect of the present invention uses a polarization beam splitter to provide an LO pulse to a second port and a signal pulse to a third port for a pulse wave input to the first port. The separated LO pulse is reflected through a phase modulator and a Faraday mirror, and the LO pulse whose polarization is rotated by 90 degrees is input to the second port as a reference LO pulse, and is output to the fourth port, and the separated signal Receiving a signal pulse encoded for a transmission target encryption key returned as a response from the transmitter to the third port after the pulse is transmitted to the transmitter through the quantum channel and outputting the signal to the fourth port; Rotating polarized light with respect to the output of the fourth port, which is output by combining the reference LO pulse and the encoded signal pulse that are orthogonal to each other using a polarization rotator; And performing a state detection for detecting a digital bit corresponding to the transmission target encryption key from the output of the polarization rotator using a state detector.

According to the continuous variable quantum encryption key distribution system according to the present invention, since it is possible to distribute the continuous variable quantum encryption key in a plug-and-play form regardless of polarization shaking caused by a channel attack by an attacker (Eve), it is possible to effectively guarantee confidentiality. System can be provided.

That is, according to the continuous variable quantum encryption key distribution system according to the present invention, since the strong signal LO pulse is not transmitted through the channel, it is robust against the attack from the attacker (Eve), and the signal pulse is transmitted to the transmitter (Alice) through the channel. Since the polarization shaking during transmission is automatically corrected, there is an advantage in that transmission through a channel is possible without a separate dynamic polarization controller. In the existing method, since signal pulses and LO pulses are sent to the same channel, it is necessary to clarify the distinction between signal pulses and LO pulses by using methods such as TDM and PDM, but in the present invention, since only signal pulses are transmitted through channels, separate signals The advantage is that there is no extinction problem.

The accompanying drawings, which are included as part of the detailed description to aid understanding of the present invention, provide embodiments of the present invention and describe the technical spirit of the present invention together with the detailed description.
1 is a diagram for describing a general continuous variable quantum encryption key distribution system.
2 is a view for explaining the continuous variable quantum encryption key distribution system of the present invention.
3 is a waveform diagram illustrating the generation of the LO pulse and the signal pulse of the amplitude modulator of FIG. 2.
FIG. 4 is a diagram illustrating reflection of an LO pulse polarized at 90 degrees in the Faraday mirror of FIG. 2.
FIG. 5 is a diagram for explaining the operation of the receiver Bob of FIG. 2.
6 is a view for explaining the operation of the polarization rotator of FIG. 2.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. In this case, the same components in each drawing are indicated by the same reference numerals as possible. In addition, detailed descriptions of functions and/or configurations already known are omitted. In the following, a part necessary for understanding an operation according to various embodiments will be mainly described, and descriptions of elements that may obscure the subject matter of the description will be omitted. In addition, some elements of the drawings may be exaggerated, omitted, or schematically illustrated. The size of each component does not fully reflect the actual size, and therefore, the contents described herein are not limited by the relative size or spacing of the components drawn in each drawing.

In describing the embodiments of the present invention, when it is determined that a detailed description of a known technology related to the present invention may unnecessarily obscure the subject matter of the present invention, a detailed description thereof will be omitted. In addition, terms to be described later are terms defined in consideration of functions in the present invention and may vary according to the intention or custom of users or operators. Therefore, the definition should be made based on the contents throughout this specification. The terms used in the detailed description are only for describing the embodiments of the present invention, and should not be limiting. Unless explicitly used otherwise, expressions in the singular form include the meaning of the plural form. In this description, expressions such as "comprising" or "feature" are intended to refer to certain features, numbers, steps, actions, elements, some or combination thereof, and one or more other than those described. It should not be construed to exclude the presence or possibility of other features, numbers, steps, actions, elements, any part or combination thereof.

In addition, terms such as first and second may be used to describe various components, but the components are not limited by the terms, and the terms are used to distinguish one component from other components. Is only used.

2 is a view for explaining the continuous variable quantum encryption key distribution system 100 of the present invention.

Referring to FIG. 2, a system 100 for a continuous variable quantum encryption key distribution (CVQKD) according to an embodiment of the present invention includes a transmitter (Alice) and a receiver (Alice) communicating over a quantum channel 190, which is an optical fiber transmission path. Bob).

In the present invention, the transmitter (Alice) does not use an optical source such as a laser for encoding itself, and uses an optical signal pulse received from the receiver (Bob) to provide an encoded signal pulse for the transmission target encryption key. Encryption key distribution is performed in the form of plug-and-play.

The transmitter (Alice) and the receiver (Bob) may be included in a variety of optical communication equipment on a network, that is, a network that provides a public channel such as a wired/wireless Internet or a mobile communication network. For example, Ethernet equipment, L2/L3 equipment, servers on the network, etc. are transmitters (Alice) for providing or receiving quantum encryption keys according to the continuous variable quantum encryption key distribution protocol in order to transmit and receive data necessary for each other through optical communication. And a receiver (Bob).

As shown in FIG. 2, the receiver Bob includes an amplitude modulator 111, a polarization controller 112, a polarization beam splitter 113, and a phase modulator 114. ), a Faraday mirror 115, a polarization rotator 181, and a state detector 182. The transmitter Alice includes a polarization beam splitter 121, a polarization rotator 122, an amplitude modulator 123, a phase modulator 124, and a random number generator 125.

In order for the transmission target encryption key to be distributed between the transmitter (Alice) and the receiver (Bob), first, the amplitude modulator 111 modulates the continuous light (CW), and the signal pulse and the LO ( local oscillator) generates a pulse wave containing a pulse. A signal pulse and a local oscillator (LO) pulse may be quantum state data whose phases are orthogonal. For example, each is in-phase X quadrature, quadrature- phase) may be quantum state data in the form of a P quadrature.

The polarization controller 112 performs polarization correction on the pulse wave generated by the amplitude modulator 111, and operates so that a power ratio between a signal pulse and a local oscillator (LO) pulse becomes a predetermined ratio.

The polarization beam splitter 113 receives the output of the polarization controller 112 through a first port (left port in the drawing) and reflects an LO pulse (eg, a horizontal polarization component H-pol) to a second port (upper port in the drawing). ) And a signal pulse (eg, vertical polarization component V-pol) passing through the third port (the right port in the drawing). In addition, the polarization beam splitter 113 is a reference LO pulse returned through the phase modulator 114 and the Faraday mirror 115 at the second port (the upper port in the drawing), and the transmitter at the third port (the right port in the drawing). The signal pulses encoded for the transmission target encryption key returned through (Alice) are summed and output through the fourth port (lower port in the drawing). The reference LO pulse returning from the second port (the upper port in the drawing) and the signal pulse encoded for the transmission target encryption key returning from the third port (the right port in the drawing) are orthogonal to each other.

The phase modulator 114 performs phase modulation on the separated LO pulse from the polarization beam splitter 113 received through an optical fiber channel (quantum channel) to obtain an oscillation signal having a predetermined phase.

The Faraday mirror 115 rotates the polarized light by 45 degrees using the magnet 117 for the incident light, that is, the LO pulse that has passed through the phase modulator 114 as shown in FIG. 4, and reflects it in phase using the mirror 118. , The reflected LO pulse rotates the polarization further 45 degrees in the same direction through the magnet 117.

The LO pulse returned from the Faraday mirror 115 is phase modulated once more by the phase modulator 114, and the LO pulse returned to the second port (the upper port in the drawing) of the polarization beam splitter 113 is input as a reference LO pulse. And output through the fourth port (lower port in the drawing) of the polarization beam splitter 113. That is, the separated LO pulse is reflected through the phase modulator 114 and the Faraday mirror 115, and the LO pulse polarized at 90 degrees returning to the same path is the second port of the polarization beam splitter 113 (top port in the drawing). It is input as a reference LO pulse and is output through the fourth port (lower port in the drawing) of the polarization beam splitter 113.

On the other hand, the signal pulse (eg, vertical polarization component V-pol) separated by the polarization beam splitter 113 is output from the third port (the right port in the figure), and the transmitter (Alice) through the quantum channel 190 Is sent to.

A signal pulse (eg, vertical polarization component V-pol) transmitted through the quantum channel 190 may be distorted into arbitrary polarization while passing through the channel. Polarization shake may occur due to channel attack by an attacker (Eve). Even if such polarization shake occurs, the transmitter (Alice) encodes the transmission target encryption key using the received signal pulse (e.g., vertical polarization component V-pol) and maintains the original power response pulse. Is transmitted to the receiver Bob through the quantum channel 190.

In the transmitter (Alice), first, the polarization beam splitter 121 transmits a signal pulse (eg, vertical polarization component V-pol) received through the first port (the port on the left side of the drawing) to the second port It is reflected through the upper port) and passed through the third port (the right port in the drawing) to separate the first polarized component (eg, horizontally polarized component) and the second polarized component (eg, vertically polarized component).

A phase modulator 124, an amplitude modulator 123, and a polarization rotator 122 are sequentially coupled between the second port (the upper port in the drawing) and the third port (the right port in the drawing), and the random number generator 125 is A random number is provided to the phase modulator 124 and the amplitude modulator 123 to support encoding (modulation) of the encryption key to be transmitted. The polarization rotator 122 rotates the input pulse (or input light) by 90 degrees and outputs it.

That is, as shown in FIG. 5, the first polarization component (eg, horizontal polarization component) of the path (a) reflected by the second port (the upper port of the drawing) of the polarization beam splitter 121 is the phase modulator 124, the amplitude The first port (the left port in the figure) is output through the modulator 123 and the polarization rotator 122, and the (b) path passed through the third port (the right port in the figure) of the polarization beam splitter 121 The two polarized components (eg, vertically polarized components) are output through the polarization rotator 122, the amplitude modulator 123, and the phase modulator 124 to the first port (left port in the drawing).

Accordingly, the signal pulse (eg, vertical polarization component V-pol) received from the polarization beam splitter 121 is converted to the first polarized component (eg, horizontally polarized component) and the second The polarization component (e.g., vertically polarized light component) is separated, but since the pulses of the (a) path and (b) path are summed and returned to the first port (left port in the drawing) of the polarization beam splitter 121, the transmitter ) May transmit a signal pulse encoded for the transmission target encryption key to the quantum channel 190 so that the original power is maintained without distortion even with polarization shake in the quantum channel 190.

Thereafter, the polarization beam splitter 113 of the receiver (Bob) encodes the transmission target encryption key returned in response to the signal pulse (eg, vertical polarization component V-pol) transmitted to the transmitter (Alice). The resulting signal pulse is input through the third port (right port in the drawing) and reflected, and output through the fourth port (lower port in the drawing).

In this way, the separated LO pulse reflected by the polarization beam splitter 113 is reflected through the phase modulator 114 and the Faraday mirror 115 and returns to the same path and passes through the phase modulator 114 again, while 90 degree polarization is The rotated LO pulse is input as a reference LO pulse to the second port (upper port in the drawing) of the polarization beam splitter 113 and is output through the fourth port (lower port in the drawing) of the polarization beam splitter 113. In addition, when a signal pulse (e.g., vertical polarization component V-pol) is transmitted to the transmitter (Alice) through the polarization beam splitter 113, the transmitter (Alice) responds to the transmission target encryption key. The encoded signal pulse is input through the third port (right port in the drawing), reflected, and output through the fourth port (lower port in the drawing).

When the orthogonal reference LO pulse and the encoded signal pulse for the transmission target encryption key are combined and output through the fourth port (lower port in the drawing) of the polarization beam splitter 113, the polarization rotator 181 is shown in FIG. Likewise, the polarization is rotated (eg, rotated by 45 degrees) with respect to the output of the fourth port (the lower port in the drawing). Through this, the polarization rotator 181 is formed in each of the orthogonal polarization directions (eg, X-axis, Y-axis) as shown in FIG. 6, (the encoded signal pulse + the reference LO pulse) and (the encoded signal pulse- The reference LO pulse) may be combined and output.

The state detector 182 performs state detection for detecting a digital bit corresponding to the transmission target encryption key from the output of the polarization rotator 181. The state detector 182 may perform state detection in a homodyne or heterodyne method. In the case of the homodyne method, as shown in FIG. 2, the state detector 182 uses a polarization beam splitter (PBS) to form a component of each orthogonal polarization direction (e.g., X-axis, Y-axis), (the encoded signal pulse + the above). Reference LO pulse) and (the encoded signal pulse-the reference LO pulse) are separated, the phase of the local oscillator (OSC) is adjusted using the difference in photoelectric conversion, etc., and the corresponding encoded signal through digital processing A corresponding electrical signal, that is, digital bit information, may be generated by performing state detection on the quantum state data of the pulse. Although not shown, the heterodyne method can be applied when the frequency of the signal pulse on the quantum channel and the local oscillator are different, and the phase of the local oscillator (OSC) is adjusted using a signal for the sum and difference of the two frequencies, A corresponding electrical signal, that is, digital bit information, may be generated by performing state detection on quantum state data of a corresponding encoded signal pulse through digital processing.

As described above, according to the continuous variable quantum encryption key distribution system 100 according to the present invention, it is possible to distribute the continuous variable quantum encryption key in a plug-and-play form regardless of polarization shaking caused by a channel attack by an attacker (Eve). Therefore, it is possible to provide a robust system that effectively guarantees confidentiality. In other words, since the strong signal LO pulse is not transmitted through the channel, it is resistant to attacks from the attacker (Eve), and since the polarization shaking while the signal pulse is transmitted to the transmitter (Alice) through the channel is automatically corrected, separate dynamic polarization There is an advantage of being able to transmit through a channel without a dynamic polarization controller. In the conventional method, since signal pulses and LO pulses are sent to the same channel, it is necessary to clarify the distinction between signal pulses and LO pulses by using methods such as TDM (Time Division Multiplex) and PDM (Pulse Duration Modulation). Since only signal pulses are transmitted, there is an advantage that a separate signal extinction problem does not occur.

As described above, in the present invention, specific matters such as specific components, etc., and limited embodiments and drawings have been described, but this is provided only to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments. , Anyone with ordinary knowledge in the field to which the present invention belongs will be able to make various modifications and variations without departing from the essential characteristics of the present invention. Therefore, the spirit of the present invention is limited to the described embodiments and should not be defined, and all technical ideas that have equivalent or equivalent modifications to the claims as well as the claims to be described later are included in the scope of the present invention. Should be interpreted as.

Receiver (Bob)
Amplitude modulator (111)
Polarization controller (112)
Polarization beam splitter(113)
Phase modulator (114)
Faraday Mirror(115)
Polarizing Rotator (181)
Status detector (182)
Transmitter (Alice)
Polarization beam splitter (121)
Polarizing Rotator(122)
Amplitude Modulator(123)
Phase modulator (124)
Random number generator(125)

Claims (8)

An amplitude modulator that generates a pulse wave for continuous light; A polarization controller for polarization correction for the pulsed wave; Phase modulator; Faraday Mirror;
The output of the polarization controller is received through a first port and separated into an LO pulse to a second port and a signal pulse to a third port, and the separated LO pulse is reflected through the phase modulator and the Faraday mirror to be 90 degrees. A transmission target that receives the LO pulse whose polarization is rotated as a reference LO pulse through the second port and outputs it to the fourth port, and the separated signal pulse is transmitted to the transmitter through a quantum channel and then returned as a response from the transmitter. A polarization beam splitter for receiving the signal pulse encoded for the encryption key through the third port and outputting the received signal pulse to the fourth port;
A polarization rotator for rotating polarized light with respect to the output of the fourth port, which is output by combining the reference LO pulse and the encoded signal pulse that are orthogonal to each other; And
A state detector for detecting a digital bit corresponding to the transmission target encryption key from the output of the polarization rotator
Continuous variable quantum cryptographic key distribution system comprising a. The method of claim 1,
The transmitter is a continuous variable quantum encryption key distribution system, characterized in that the encryption key distribution in a plug-and-play format that provides the encoded signal pulses using the signal pulses from a receiver without using an optical source for encoding. The method of claim 1,
The polarization rotator is a continuous variable quantum encryption key distribution system, characterized in that the output by rotating the polarization 45 degrees with respect to the output of the fourth port. The method of claim 3,
The polarization rotator includes a sum signal of the encoded signal pulse and the reference LO pulse, and the encoded signal pulse and the reference LO pulse in each direction orthogonal to each other by a polarization beam splitter included in the state detector. A continuous variable quantum cryptographic key distribution system, characterized in that rotating the polarization so as to be separated into a difference signal between. The method of claim 1,
The state detector, a continuous variable quantum cryptographic key distribution system, characterized in that for performing the state detection in any one of a homodyne or heterodyne method. The method of claim 1,
The transmitter,
A first port for receiving the received signal pulse and outputting the encoded signal pulse, a second port for outputting a first polarization component for the received signal pulse, and a second polarization component for the received signal pulse A polarization beam splitter including a third port for outputting a signal;
A phase modulator sequentially coupled on an optical path between the second port and the third port; Amplitude modulator; Polarization rotator; And
Random number generator for providing a random number to the phase modulator and the amplitude modulator
Continuous variable quantum cryptographic key distribution system comprising a. The method of claim 6,
The polarization rotator is a continuous variable quantum cryptographic key distribution system, characterized in that the incident pulse is rotated 90 degrees polarized light. Using a polarization beam splitter, the pulse wave received through the first port is separated into an LO pulse to the second port and a signal pulse to the third port, and the separated LO pulse is reflected through a phase modulator and a Faraday mirror. The LO pulse, whose polarization is rotated by 90 degrees, is input to the second port as a reference LO pulse and outputs to the fourth port, and the separated signal pulse is transmitted to the transmitter through the quantum channel, and then the transmitter returns to the corresponding response. Receiving a signal pulse encoded for an incoming transmission target encryption key through the third port and outputting it through the fourth port;
Rotating polarized light with respect to the output of the fourth port, which is output by combining the reference LO pulse and the encoded signal pulse, which are orthogonal to each other, using a polarization rotator; And
Performing state detection for detecting a digital bit corresponding to the transmission target encryption key from the output of the polarization rotator using a state detector
Continuous variable quantum encryption key distribution method comprising a.

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