CN114338020B - Quantum key distribution coding device - Google Patents
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Abstract
A quantum key distribution coding device comprises a laser LD, a path selection module, a first phase modulator PM1, a second phase modulator PM2, a first Faraday mirror FM1, a second Faraday mirror FM2, an optical switch OS, a first beam splitter BS1 and a first polarization beam splitter PBS1, wherein the path selection module is used for enabling an optical pulse incident from a first port to reach a second port to be output only through a horizontal polarization component, enabling the optical pulse incident from the second port to be output from a third port after polarization and 45-degree rotation, and enabling the optical pulse incident from the third port to reach a fourth port to be output. Compared with the prior art, the method can switch the coding mode to realize time phase coding and phase coding, and has stronger flexibility and scene adaptability. And moreover, the preparation of the trap state and the time mode is not required to be carried out by using an intensity modulator, so that the preparation stability of the signal state and the trap state and the stability of the coding state are improved.
Description
Technical Field
The invention relates to the technical field of quantum phase encoding, in particular to a quantum key distribution encoding device.
Background
The quantum key distribution has information theory security, the security of the quantum key distribution is guaranteed by the basic principle of quantum mechanics, the threat from a quantum computer can be resisted, and the quantum key distribution has an important role in secret communication. Common encoding methods for quantum key distribution systems include polarization encoding, phase encoding, and time-phase encoding. Because the polarization state is extremely unstable in the optical fiber channel, an active polarization compensation module needs to be added at the receiving end for polarization encoding, and the complexity and instability of the system are increased. The phase coding has high stability, channel disturbance does not need to be compensated, but phase drift caused by the change of the environment of the equipment is compensated. The time phase coding adopts a group of time basis vectors and a group of phase basis vectors for coding, so that the stability is higher, but a detection time mode needs a higher-speed single-photon detector. Therefore, different encoding schemes can only be applied to specific application scenarios.
The conventional quantum key distribution system needs to design a corresponding optical path to realize a specific coding mode, and most of the conventional quantum key distribution systems cannot be compatible with other coding modes, so that the coding device lacks universality, and cannot realize the switching of the coding modes according to the requirements of practical application so as to meet the optimization of system performance. Conventional time phase coding schemes generally use an unequal-arm interferometer, an intensity modulator and a phase modulator for coding, wherein the unequal-arm interferometer is used for generating double pulses with time difference, the intensity modulator prepares time bits by controlling the pulse amplitude of different time windows, the phase modulator is used for modulating the phase difference between the two pulses to perform phase coding, the modulation rate requirements of the intensity modulator and the phase modulator are high, and the coding accuracy depends on the extinction ratio of the intensity modulator. And the intensity modulator is sensitive to the ambient temperature and needs to be calibrated in real time, which increases the complexity of the system. While the general phase encoding scheme is based on a double unequal arm mach-zehnder interferometer or a faraday-michelson interferometer, the phase modulator is arranged on the long arm or the short arm of the interferometer, and the loss of the two arms of the interferometer is inconsistent. In addition, the existing encoding apparatus generally uses a separate intensity modulator to perform the modulation of the signal state and the decoy state, and also needs to perform real-time calibration.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a quantum key distribution coding device which is used for solving the technical defects in the prior art that the coding mode of a quantum key distribution system cannot be switched, the loss of two time modes is inconsistent due to the insertion loss of a phase modulator, the requirements on the speed of the phase modulator and the intensity modulator are high, the cost and the complexity are high, and the like.
The invention provides a quantum key distribution encoding device as follows:
the technical scheme of the invention is realized as follows:
a quantum key distribution coding device comprises a laser LD, a path selection module, a first phase modulator PM1, a second phase modulator PM2, a first Faraday mirror FM1, a second Faraday mirror FM2, an optical switch OS, a first beam splitter BS1 and a first polarization beam splitter PBS1, wherein the path selection module is used for enabling an optical pulse incident from a first port to reach a second port to be output only through a horizontal polarization component, enabling the optical pulse incident from the second port to be output from a third port after polarization and 45-degree rotation, and enabling the optical pulse incident from the third port to reach a fourth port to be output; the laser LD is connected to a first port of a path selection module, a second port of the path selection module is sequentially connected to a first phase modulator PM1 and a first faraday mirror FM1, a second port of the path selection module is welded to a polarization maintaining optical fiber between the first phase modulator PM1 at 45 °, a third port of the path selection module is sequentially connected to a second phase modulator PM2 and a second faraday mirror FM2, a fourth port of the path selection module is connected to a first port of an optical switch OS, the second port of the optical switch OS is welded to a first port of a first beam splitter BS1 at 45 °, a third port of the optical switch OS is connected to a second port of a first beam splitter BS1, a third port of the first beam splitter BS1 is connected to a first port of a first polarization beam splitter PBS1, and a second port of the first polarization beam splitter 1 and a fourth port of the polarization maintaining optical fiber PBS are directly connected to a polarization maintaining optical fiber PBS1, the third port of the first polarizing beam splitter PBS1 outputs the encoded state.
Preferably, the path selection module includes a second polarization beam splitter PBS2 and a first circulator CIR1, the third port of the second polarization beam splitter PBS2 is connected to the first port of the first circulator CIR1 after being fused by 45 ° through a polarization maintaining fiber, the first port and the second port of the second polarization beam splitter PBS2 are respectively used as the first port and the second port of the path selection module, and the second port and the third port of the first circulator CIR1 are respectively used as the third port and the fourth port of the path selection module.
Preferably, the path selection module includes a second splitter BS2, a first polarizer POL1 and a second circulator CIR2, a second port of the second splitter BS2 is connected to an input port of the first polarizer POL1, input and output polarization directions of the first polarizer POL1 are aligned with a slow axis of the polarization-maintaining fiber, a third port of the second splitter BS2 is connected to a first port of the second circulator CIR2 after being fused at 45 ° by the polarization-maintaining fiber, the first port of the second splitter BS2 is used as a first port of the path selection module, an output port of the first splitter BS1 is used as a second port of the path selection module, and the second port of the second circulator CIR2 are respectively used as a third port and a fourth port of the path selection module.
Preferably, the path selection module includes a third beam splitter BS3, a second polarizer POL2 and a third circulator CIR3, an input port and an output port of the second polarizer POL2 are respectively connected to a third port of the third beam splitter BS3 and a first port of a third circulator CIR3, an input polarization direction of the second polarizer POL2 is aligned with a slow axis of the polarization maintaining fiber, an output direction is at a 45 ° included angle with the slow axis of the polarization maintaining fiber, the first port and the second port of the third beam splitter BS3 are respectively used as a first port and a second port of the path selection module, and the second port and the third port of the third circulator CIR3 are respectively used as a third port and a fourth port of the path selection module.
Preferably, the path selection module includes a fourth circulator CIR4 and a third polarizer POL3, the second port of the fourth circulator CIR4 is connected to the input port of the third polarizer POL3, the input polarization direction of the third polarizer POL3 and the slow axis of the polarization maintaining fiber form an included angle of 45 °, the output direction is aligned with the slow axis of the polarization maintaining fiber, the first port, the third port and the fourth port of the fourth circulator CIR4 are respectively used as the first port, the third port and the fourth port of the path selection module, and the output port of the third polarizer POL3 is used as the second port of the path selection module.
Preferably, the optical fibers inside the coding device are all polarization maintaining optical fibers.
Preferably, the polarization maintaining optical fiber is welded at 45 degrees, and can be replaced by a half-wave plate, and the slow axis of the half-wave plate and the slow axis of the polarization maintaining optical fiber form an included angle of 22.5 degrees.
Preferably, the optical switch OS and first beam splitter BS1 positions may be switched.
Compared with the prior art, the invention has the following beneficial effects:
the quantum key distribution coding device can switch coding modes to realize time phase coding and phase coding, and has strong flexibility and scene adaptability. And the intensity modulator is not needed to be used for preparing the decoy state and the time mode, but the intensity modulation and the coding are realized through the stable modulation of the polarization state twice, so that the requirement on the speed of the phase modulator is reduced, and the stability of the preparation of the signal state and the decoy state and the stability of the coding state are improved. In addition, two time modes generated by the coding device have consistent loss and are mutually vertical in polarization, so that the non-interference component can be eliminated to improve the energy utilization rate, and the safe code rate of the system can be further improved.
Drawings
FIG. 1 is a schematic block diagram of a quantum key distribution phase encoding apparatus according to the present invention;
FIG. 2 is a schematic block diagram of a first embodiment;
FIG. 3 is a functional block diagram of a second embodiment;
FIG. 4 is a functional block diagram of a third embodiment;
fig. 5 is a schematic block diagram of a fourth embodiment.
Detailed Description
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown.
As shown in fig. 1, a quantum key distribution encoding device includes a laser LD, a path selection module, a first phase modulator PM1, a second phase modulator PM2, a first faraday mirror FM1, a second faraday mirror FM2, an optical switch OS, a first beam splitter BS1, and a first polarization beam splitter PBS1, wherein the path selection module is configured to cause an optical pulse incident from a first port thereof to reach a second port and output the optical pulse only through a horizontal polarization component, cause the optical pulse incident from the second port to pass through polarization and 45 ° rotation and output the optical pulse from the third port and cause the optical pulse incident from the third port to reach a fourth port and output the optical pulse; the laser LD is connected to a first port of a path selection module, a second port of the path selection module is sequentially connected to a first phase modulator PM1 and a first faraday mirror FM1, a second port of the path selection module is welded to a polarization maintaining optical fiber between the first phase modulator PM1 at 45 °, a third port of the path selection module is sequentially connected to a second phase modulator PM2 and a second faraday mirror FM2, a fourth port of the path selection module is connected to a first port of an optical switch OS, the second port of the optical switch OS is welded to a first port of a first beam splitter BS1 at 45 °, a third port of the optical switch OS is connected to a second port of a first beam splitter BS1, a third port of the first beam splitter BS1 is connected to a first port of a first polarization beam splitter PBS1, and a second port of the first polarization beam splitter 1 and a fourth port of the polarization maintaining optical fiber PBS are directly connected to a polarization maintaining optical fiber PBS1, the third port of the first polarizing beam splitter PBS1 outputs the encoded state.
The specific encoding process is as follows:
the laser LD generates a horizontally polarized optical pulse P0, enters from the first port of the path selection module and exits from the second port, and after 45 ° polarization rotation, the optical pulse becomes 45 ° linear polarization, where the horizontal polarization component propagates along the slow axis of the first polarization maintaining fiber PMF1, and the vertical polarization component propagates along the fast axis of the first polarization maintaining fiber PMF 1. Then enters a first phase modulator PM1, and generates a phase difference between the horizontal polarization component and the vertical polarization component by modulating the voltage V1 loaded on the first phase modulator PM1
The two components are reflected by a first Faraday mirror FM1 after passing through a second section of polarization-maintaining optical fiber PMF2, the polarization is rotated by 90 degrees, voltage V2 is loaded when the two components reach a first phase modulator PM1 after passing through a second section of polarization-maintaining optical fiber PMF2 again, and the phase difference corresponding to the horizontal polarization component and the vertical polarization component is
Then passes through the first section of polarization-maintaining optical fiber PMF1 again, and the polarization state of the light pulse before returning to the 45-degree fusion point is obtained again according to the Jones matrix
Wherein the content of the first and second substances,
for the phase difference between the fast and slow axes of the first section (second section) polarization-maintaining optical fiber, the polarization state of the light pulse when the light pulse exits from the second port of the path selection module is
The polarization maintaining fiber, the phase modulator, the Faraday reflector and the 45-degree polarization rotating Jones matrix are respectively
Ignoring the global phase factor, one can obtain that the polarization state of an optical pulse can be written as
The phase difference between the horizontal polarization component H and the vertical polarization component V is
。
The light pulse enters a second port of the path selection module after passing through the 45-degree welding point again, and the polarized state is polarized
Corresponding light intensity of
。
By adjusting the voltages V1 and V2 when the light pulse passes twice through the first phase modulator PM1, the phase difference can be controlled
Thereby modulating the intensity of the optical pulses to prepare the signal state and the decoy state.
The signal state or decoy state pulse after the light intensity modulation is emitted from the third port of the path selection module after the polarization rotation of 45 degrees again, the signal state or decoy state pulse after the light intensity modulation is reflected by the second phase modulator PM2 and the second Faraday mirror FM2 in sequence and then returns to the third port of the path selection module again, the signal state or decoy state pulse after the polarization rotation of 45 degrees is emitted from the fourth port of the path selection module, the signal state or decoy state pulse after the polarization rotation of 45 degrees reaches the first port of the optical switch OS after the signal state or decoy state pulse exits from the fourth port of the path selection module, and the signal state or decoy state pulse reaches the first port of the optical switch OS after the polarization rotation of the first port of the optical switch OS
The phase difference between the horizontal polarization component H and the vertical polarization component V is
，
And
which are the phase differences of the horizontally and vertically polarized components of the optical pulse when they pass the second phase modulator PM2 back and forth twice. By adjusting the voltages V1 and V2 when the light pulse passes twice through the first phase modulator PM1, this can be achieved
。
When the control optical switch is switched to the state 0, the optical pulse is emitted from the second port of the control optical switch, and the encoding device can realize time phase encoding. The optical pulse reaches the first port of the first beam splitter BS1 after undergoing a polarization rotation of 45 °, exits from the third port thereof, and changes its polarization state
When is coming into contact with
The time corresponding to 4 polarization states are respectively
, 
, 
,
. When the light pulse reaches the first port of the first polarization beam splitter PBS1, the horizontal polarization component of the light pulse is directly transmitted, and after exiting from the third port, the light pulse propagates along the slow axis of the polarization maintaining fiber, the vertical polarization component is reflected to the second port, and after entering the fourth port along the polarization maintaining fiber with the length L, the light pulse is reflected to the third port, and propagates along the fast axis of the polarization maintaining fiber, the time lag t = L/(n × c), n is the slow axis refractive index of the polarization maintaining fiber, and c is the speed of light in vacuum. Thus, the state of polarization
The coded state output after entering the first polarization beam splitter PBS1 is a time mode
The polarization state is still vertical polarization; polarization state
The coded state output after entering the first polarization beam splitter PBS1 is a time mode
The polarization state is still horizontal polarization; polarization state
The coded state output after entering the first polarization beam splitter PBS1 is
(ii) a Polarization state
The coded state of the output after entering the first polarization beam splitter PBS1 is
。
When the control light switch is switched to state 1, the light pulse is emitted from the third port thereof, and the encoding device can realize phase encoding. The optical pulse passes through the second port of the first beam splitter BS1 and exits the third port thereof, and the polarization state changes to
When it comes to
The time corresponding to the 4 polarization states are respectively
, 
, 
,
. Thus, the state of polarization
The coded state of the output after entering the first polarization beam splitter PBS1 is
(ii) a Polarization state
The coded state of the output after entering the first polarization beam splitter PBS1 is
(ii) a Polarization state
The coded state of the output after entering the first polarization beam splitter PBS1 is
(ii) a Polarization state
The coded state of the output after entering the first polarization beam splitter PBS1 is
。
As shown in fig. 2, a first embodiment of the quantum key distribution encoding apparatus of the present invention:
the structure of the coding device is as follows: the path selection module comprises a second polarization beam splitter PBS2 and a first circulator CIR1, a third port of the second polarization beam splitter PBS2 is connected with a first port of a first circulator CIR1 after being fused for 45 degrees through a polarization maintaining optical fiber, a first port and a second port of the second polarization beam splitter PBS2 are respectively used as a first port and a second port of the path selection module, and a second port and a third port of the first circulator CIR1 are respectively used as a third port and a fourth port of the path selection module.
An encoding process of the embodiment is as follows:
the laser LD generates a horizontally polarized light pulse P0, which enters from the first port of the second polarization beam splitter PBS2, is transmitted from the second port, sequentially passes through 45 ° polarization rotation, the first phase modulator PM1, the first faraday mirror FM1, is reflected, passes through the first phase modulator PM1 again, and 45 ° polarization rotation, and enters the second port of the second polarization beam splitter PBS2Then the vertical polarization component is reflected to a third port and propagates along the slow axis of the polarization maintaining fiber, and the polarization state of the light pulse is changed
Light intensity of
. By adjusting the voltages V1 and V2 when the light pulse passes twice through the first phase modulator PM1, the phase difference can be controlled
Thereby modulating the intensity of the optical pulses to prepare the signal state and the decoy state.
The signal state or decoy state pulse after the light intensity modulation enters the first port of the first circulator CIR1 after polarization rotation of 45 degrees and is emitted from the second port, the signal state or decoy state pulse sequentially passes through the second phase modulator PM2 and the second Faraday mirror FM2 to be reflected and then returns to the second port of the first circulator CIR1 again, the signal state or decoy state pulse after the light intensity modulation reaches the first port of the optical switch OS after being emitted from the third port, and the polarization state of the light pulse is
The phase difference between the horizontal polarization component H and the vertical polarization component V is
，
And
which are the phase differences of the horizontally and vertically polarized components, respectively, of the optical pulses as they traverse the second phase modulator PM2 twice. By adjusting the voltages V1 and V2 at which the light pulse passes twice through the first phase modulator PM1, this can be achieved
。
When the control optical switch is switched to the state 0, the optical pulse is emitted from the second port, and the encoding device can realize time phase encoding. When the control light switch is switched to state 1, the light pulse is emitted from the third port thereof, and the encoding device can realize phase encoding.
As shown in fig. 3, a second embodiment of the quantum key distribution encoding apparatus of the present invention:
the structure of the coding device is as follows: the path selection module comprises a second beam splitter BS2, a first polarizer POL1 and a second circulator CIR2, wherein a second port of the second beam splitter BS2 is connected with an input port of a first polarizer POL1, input and output polarization directions of the first polarizer POL1 are aligned with a slow axis of a polarization-maintaining optical fiber, a third port of the second beam splitter BS2 is connected with a first port of a second circulator CIR2 after being fused for 45 degrees through the polarization-maintaining optical fiber, the first port of the second beam splitter BS2 serves as a first port of the path selection module, an output port of the first polarizer POL1 serves as a second port of the path selection module, and the second port and the third port of the second circulator CIR2 serve as a third port and a fourth port of the path selection module respectively.
The second encoding process is as follows:
the laser LD generates a horizontally polarized light pulse P0, which enters from the first port of the second beam splitter BS2, is transmitted from the second port, passes through the first polarizer POL1, 45-degree polarization rotation, the first phase modulator PM1, the first Faraday mirror FM1 in sequence, then is reflected to pass through the first phase modulator PM1, 45-degree polarization rotation, the first polarizer POL1 again, enters the second port of the second beam splitter BS2, then half of the component is reflected to the third port, and propagates along the slow axis of the polarization-maintaining fiber, and the polarization state of the light pulse changes to be
Light intensity of
. By adjusting the voltages V1 and V2 when the optical pulse passes twice through the first phase modulator PM1, it is possible to adjust the voltage of the optical pulseControlling phase difference
Thereby modulating the intensity of the optical pulses to prepare the signal state and the decoy state.
The signal state or decoy state pulse after the light intensity modulation enters the first port of the second circulator CIR2 after polarization rotation of 45 degrees and is emitted from the second port, the signal state or decoy state pulse sequentially passes through the second phase modulator PM2 and the second Faraday mirror FM2 to be reflected and then returns to the second port of the second circulator CIR2 again, the signal state or decoy state pulse after the light intensity modulation reaches the first port of the optical switch OS after being emitted from the third port, and the polarization state of the light pulse is
The phase difference between the horizontal polarization component H and the vertical polarization component V is
，
And
which are the phase differences of the horizontally and vertically polarized components, respectively, of the optical pulses as they traverse the second phase modulator PM2 twice. By adjusting the voltages V1 and V2 at which the light pulse passes twice through the first phase modulator PM1, this can be achieved
。
When the control optical switch is switched to the state 0, the optical pulse is emitted from the second port of the control optical switch, and the encoding device can realize time phase encoding. When the control light switch is switched to state 1, the light pulse is emitted from the third port thereof, and the encoding device can realize phase encoding.
As shown in fig. 4, a third embodiment of the quantum key distribution encoding apparatus of the present invention:
the structure of the coding device is as follows: the path selection module comprises a third beam splitter BS3, a second polarizer POL2 and a third circulator CIR3, an input port and an output port of the second polarizer POL2 are respectively connected with a third port of the third beam splitter BS3 and a first port of a third circulator CIR3, the input polarization direction of the second polarizer POL2 is aligned with the slow axis of the polarization-maintaining optical fiber, the included angle between the output direction and the slow axis of the polarization-maintaining optical fiber is 45 degrees, a first port and a second port of the third beam splitter BS3 are respectively used as a first port and a second port of the path selection module, and a second port and a third port of the third circulator CIR3 are respectively used as a third port and a fourth port of the path selection module.
The third encoding process of the embodiment is as follows:
the laser LD generates a horizontally polarized light pulse P0, the light pulse P0 enters from the first port of the second beam splitter BS2, is transmitted from the second port, sequentially passes through 45-degree polarization rotation, the first phase modulator PM1, the first Faraday mirror FM1, is reflected, passes through the first phase modulator PM1 again and the 45-degree polarization rotation, enters the second port of the second beam splitter BS2, half of the component is reflected to the third port, the horizontally polarized component passes through the second polarizer POL2, and the polarization state is
Light intensity of
. By adjusting the voltages V1 and V2 when the light pulse passes twice through the first phase modulator PM1, the phase difference can be controlled
Thereby modulating the intensity of the optical pulses to prepare the signal state and the decoy state.
When the signal state or decoy state pulse after the light intensity is modulated exits from the output port of the second polarizer POL2, because the included angle between the polarization direction and the polarization maintaining fiber is 45 degrees, the polarization state rotates 45 degrees, then the signal state or decoy state pulse enters the first port of the third circulator CIR3 to exit from the second port, sequentially passes through the second phase modulator PM2 and the second Faraday reflector FM2 to be reflected, and then returns to the third circulator againThe second port of CIR3, which emerges from the third port and reaches the first port of optical switch OS, is such that the polarization state of the optical pulse is
The phase difference between the horizontal polarization component H and the vertical polarization component V is
，
And
which are the phase differences of the horizontally and vertically polarized components, respectively, of the optical pulses as they traverse the second phase modulator PM2 twice. By adjusting the voltages V1 and V2 at which the light pulse passes twice through the first phase modulator PM1, this can be achieved
。
When the control optical switch is switched to the state 0, the optical pulse is emitted from the second port, and the encoding device can realize time phase encoding. When the control light switch is switched to state 1, the light pulse is emitted from the third port thereof, and the encoding device can realize phase encoding.
As shown in fig. 5, a quantum key distribution encoding apparatus according to a fourth embodiment of the present invention:
the structure of the coding device is as follows: the path selection module comprises a fourth circulator CIR4 and a third polarizer POL3, a second port of the fourth circulator CIR4 is connected with an input port of a third polarizer POL3, an included angle between an input polarization direction of the third polarizer POL3 and a slow axis of the polarization-maintaining optical fiber is 45 degrees, an output direction of the third polarizer POL3 is aligned with the slow axis of the polarization-maintaining optical fiber, a first port, a third port and a fourth port of the fourth circulator CIR4 are respectively used as a first port, a third port and a fourth port of the path selection module, and an output port of the third polarizer POL3 is used as a second port of the path selection module.
The fourth encoding process of the embodiment is as follows:
the laser LD generates a horizontally polarized light pulse P0, enters from the first port of the fourth circulator CIR4 and exits from the second port, and because the included angle between the slow axis of the polarization-maintaining optical fiber at the second port of the fourth circulator CIR4 and the polarization direction of the third polarizer POL3 is 45 degrees, only half of the light intensity passes through the third polarizer POL 3. The light pulse is emitted from the third polarizer POL3 and then propagates along the slow axis of the polarization-maintaining fiber, sequentially passes through 45-degree polarization rotation, the first phase modulator PM1 and the first Faraday mirror FM1, is reflected, passes through the first phase modulator PM1 again and the 45-degree polarization rotation again, returns to the third polarizer POL3, only the horizontal polarization component passes through, and the polarization state is
Light intensity of
. By adjusting the voltages V1 and V2 when the light pulse passes twice through the first phase modulator PM1, the phase difference can be controlled
Thereby modulating the intensity of the optical pulses to prepare the signal state and the decoy state.
When the signal state or decoy state pulse after the light intensity modulation exits from the output port of the third polarizer POL3, because the included angle between the polarization direction and the polarization maintaining fiber is 45 degrees, the polarization state rotates 45 degrees, then the pulse enters the second port of the fourth circulator CIR4 to exit from the third port, the pulse returns to the third port of the fourth circulator CIR4 after being reflected by the second phase modulator PM2 and the second Faraday reflector FM2 in sequence, the pulse exits from the fourth port to reach the first port of the optical switch OS, and the polarization state of the optical pulse is at this moment
The phase difference between the horizontal polarization component H and the vertical polarization component V is
，
And
which are the phase differences of the horizontally and vertically polarized components of the optical pulse when they pass the second phase modulator PM2 back and forth twice. By adjusting the voltages V1 and V2 at which the light pulse passes twice through the first phase modulator PM1, this can be achieved
。
When the control optical switch is switched to the state 0, the optical pulse is emitted from the second port of the control optical switch, and the encoding device can realize time phase encoding. When the control light switch is switched to state 1, the light pulse is emitted from the third port thereof, and the encoding device can realize phase encoding.
The present invention also provides a quantum key distribution system, which may include any one of the above-described encoding apparatuses.
According to the embodiments of the present invention, the invention provides a quantum key distribution encoding device, which can switch encoding modes to implement time phase encoding and phase encoding, and has strong flexibility and scene adaptability. And the intensity modulator is not needed to be used for preparing the decoy state and the time mode, but the intensity modulation and the coding are realized through the stable modulation of the polarization state twice, so that the requirement on the speed of the phase modulator is reduced, and the stability of the preparation of the signal state and the decoy state and the stability of the coding state are improved. In addition, two time modes generated by the coding device have consistent loss and mutually vertical polarization, so that a non-interference component can be eliminated to improve the energy utilization rate, and the safe code rate of the system can be further improved.
Claims (6)
1. A quantum key distribution coding device is characterized by comprising a laser LD, a path selection module, a first phase modulator PM1, a second phase modulator PM2, a first Faraday mirror FM1, a second Faraday mirror FM2, an optical switch OS, a first beam splitter BS1 and a first polarization beam splitter PBS1, wherein the path selection module is used for enabling an optical pulse incident from a first port to reach a second port to be output only through a horizontal polarization component, enabling the optical pulse incident from the second port to be output from a third port after polarization and 45-degree rotation, and enabling the optical pulse incident from the third port to reach a fourth port to be output; the laser LD is connected to a first port of a path selection module, a second port of the path selection module is sequentially connected to a first phase modulator PM1 and a first faraday mirror FM1, a second port of the path selection module is welded to a polarization maintaining optical fiber between the first phase modulator PM1 at 45 °, a third port of the path selection module is sequentially connected to a second phase modulator PM2 and a second faraday mirror FM2, a fourth port of the path selection module is connected to a first port of an optical switch OS, the second port of the optical switch OS is welded to a first port of a first beam splitter BS1 at 45 °, a third port of the optical switch OS is connected to a second port of a first beam splitter BS1, a third port of the first beam splitter BS1 is connected to a first port of a first polarization beam splitter PBS1, and a second port of the first polarization beam splitter 1 and a fourth port of the polarization maintaining optical fiber PBS are directly connected to a polarization maintaining optical fiber PBS1, the third port of the first polarizing beam splitter PBS1 outputs the encoded state.
2. The quantum key distribution encoding apparatus according to claim 1, wherein the path selection module includes a second polarization beam splitter PBS2 and a first circulator CIR1, a third port of the second polarization beam splitter PBS2 is connected to a first port of a first circulator CIR1 after being fused by 45 ° via a polarization maintaining fiber, a first port and a second port of the second polarization beam splitter PBS2 are respectively used as a first port and a second port of the path selection module, and a second port and a third port of the first circulator CIR1 are respectively used as a third port and a fourth port of the path selection module.
3. The quantum key distribution encoding apparatus of claim 1, wherein the path selection module comprises a second splitter BS2, a first polarizer POL1 and a second circulator CIR2, wherein a second port of the second splitter BS2 is connected to an input port of the first polarizer POL1, input and output polarization directions of the first polarizer POL1 are aligned with a slow axis of the polarization-maintaining fiber, a third port of the second splitter BS2 is connected to a first port of the second circulator CIR2 after being fused by 45 ° through the polarization-maintaining fiber, the first port of the second splitter BS2 serves as a first port of the path selection module, an output port of the first polarizer POL1 serves as a second port of the path selection module, and the second and third ports of the second circulator CIR2 serve as third and fourth ports of the path selection module, respectively.
4. The quantum key distribution encoding apparatus of claim 1, wherein the path selection module comprises a third beam splitter BS3, a second polarizer POL2 and a third circulator CIR3, wherein the input port and the output port of the second polarizer POL2 are respectively connected with the third port of the third beam splitter BS3 and the first port of the third circulator CIR3, the input polarization direction of the second polarizer POL2 is aligned with the slow axis of the polarization-maintaining fiber, the output direction is at a 45 ° included angle with the slow axis of the polarization-maintaining fiber, the first port and the second port of the third beam splitter BS3 are respectively used as the first port and the second port of the path selection module, and the second port and the third port of the third circulator CIR3 are respectively used as the third port and the fourth port of the path selection module.
5. The quantum key distribution encoding apparatus of claim 1, wherein the path selection module comprises a fourth circulator CIR4 and a third polarizer POL3, the second port of the fourth circulator CIR4 is connected to the input port of the third polarizer POL3, the input polarization direction of the third polarizer POL3 is at an angle of 45 ° with the slow axis of the polarization-maintaining fiber, the output direction is aligned with the slow axis of the polarization-maintaining fiber, the first port, the third port and the fourth port of the fourth circulator CIR4 are respectively used as the first port, the third port and the fourth port of the path selection module, and the output port of the third polarizer POL3 is used as the second port of the path selection module.
6. The quantum key distribution encoding device of any one of claims 1-5, wherein the optical fibers inside the encoding device are all polarization maintaining optical fibers.
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