CN210007715U

CN210007715U - Quantum key distribution phase codec, corresponding codec device and system

Info

Publication number: CN210007715U
Application number: CN201920296077.6U
Authority: CN
Inventors: 许华醒
Original assignee: China Electronics Technology Group Corp CETC
Current assignee: China Electronics Technology Group Corp CETC; Electronic Science Research Institute of CTEC
Priority date: 2019-03-08
Filing date: 2019-03-08
Publication date: 2020-01-31
Anticipated expiration: 2029-03-08

Abstract

The utility model provides a quantum key distribution phase codec and corresponding coding and decoding device and system, this phase codec includes the beam splitter, respectively through two arm and beam splitter optical coupling's two polarization orthogonal rotation reflection device, among two reflection device or every reflection device is including the polarization beam splitter that has input port and two output ports, and through this input port coupling to corresponding arm, two output ports of every polarization beam splitter are through transmission light path coupling, reflection device including polarization beam splitter is provided with phase modulator and half-wave plate on transmission light path, the polarization direction of the light pulse of input half-wave plate is 45 degrees with the contained angle of the fast axle of half-wave plate or slow axle, the utility model discloses make can encode and decode the interference to the input light pulse of arbitrary polarization state steadily, solved phase coding and time bit-phase coding quantum key distribution and use in polarization induction decline cause the unable steady operation's of system problem, the loss of interferometer department reduces simultaneously.

Description

Quantum key distribution phase codec, corresponding codec device and system

Technical Field

The utility model relates to a secret communication technology field of optical transmission especially relates to kinds of quantum key distribution phase codec based on polarization quadrature rotation reflection, including this phase codec's corresponding coding and decoding device and quantum key distribution system.

Background

The quantum secret communication technology is the leading-edge hotspot field combining quantum physics with information science, the quantum secret communication can realize the safe transmission of information on a public channel based on the quantum key distribution technology and times of secret code principles, the quantum key distribution is based on the physical principles of quantum mechanics Heisebang uncertain relation, quantum unclonable theorem and the like, the secret key can be safely shared among users, potential eavesdropping behaviors can be detected, and the quantum secret communication technology can be applied to the fields of high-safety information transmission requirements of national defense, government affairs, finance, electric power and the like.

The ground quantum key distribution is mainly based on optical fiber channel transmission, and because phase encoding adopts the phase difference of front and back optical pulses to encode information and can be stably maintained in the long-distance optical fiber channel transmission process, the phase encoding and the time bit-phase encoding based on the unequal arm interferometer are the main encoding schemes for quantum key distribution application. However, the manufacturing of the optical fiber has non-ideal conditions such as non-circular symmetry of the cross section, nonuniform distribution of the refractive index of the fiber core along the radial direction, and the like, and the optical fiber is influenced by temperature, strain, bending, and the like in the actual environment, and can generate random birefringence effect. Therefore, after the optical pulse is transmitted by the long-distance optical fiber and transmitted by the two-arm optical fiber of the unequal-arm interferometer, the problem of polarization-induced fading exists when the unequal-arm interferometer is used for phase decoding interference, so that the decoding interference is unstable, and the error rate is increased. If use the equipment of rectifying, can increase system complexity and cost, and to strong interference condition such as aerial fiber cable, road bridge optical cable difficult to realize stable application.

The unequal arm faraday-michelson interferometers have been proposed in the prior art to maintain a stable output of the interference results when the optical pulse is affected by the random birefringence of the fiber channel and the change in polarization state resulting therefrom, however, such interferometers have large losses, wherein the insertion loss of the phase modulator is which is the major factor causing large losses, in particular, when the phase modulator is placed in arm of the interferometer, the optical pulse will pass through the phase modulator twice due to the back-and-forth transmission, resulting in large losses of the interferometer and low system efficiency.

For quantum key distribution phase encoding and time bit-phase encoding schemes, how to stably and efficiently perform interferometric decoding is a hotspot and difficult problem for quantum secret communication application based on the existing optical cable infrastructure.

SUMMERY OF THE UTILITY MODEL

The utility model discloses a main aim at provides kinds of quantum key distribution phase place codecs based on polarization quadrature rotation reflection, including this phase place codec's corresponding codec and quantum key distribution system to solve the unstable difficult problem of phase place decoding interference that polarization induction fading arouses in phase place coding and time bit-phase place coding quantum key distribution is used, reduce the loss of interferometer department simultaneously.

The utility model provides an at least following technical scheme:

Quantum Key distribution phase codec comprising a beam splitter, two reflecting devices optically coupled with the beam splitter via two arms respectively, wherein each of the reflecting devices is a polarization orthogonal rotation reflecting device, or each of the two reflecting devices comprises a polarization beam splitter having an input port and two output ports and is coupled to a corresponding arm of the two arms via the input port of the polarization beam splitter, wherein the two output ports of each polarization beam splitter are optically coupled with each other via a transmission optical path, at least of the reflecting devices comprising a polarization beam splitter are provided on their transmission optical paths with half-wave plates, the polarization direction of an optical pulse input to the half-wave plates is at an angle of 45 degrees to the fast or slow axis of the half-wave plates, and at least of the reflecting devices comprising a polarization beam splitter are provided on their transmission optical paths with a phase modulator.

2. The phase codec of claim 1, wherein the two reflective devices are identically constructed polarization orthogonal rotating reflective devices or differently constructed polarization orthogonal rotating reflective devices.

3. The phase codec of claim 1, wherein the transmission optical path is a polarization maintaining optical path.

4. The phase codec of claim 1, wherein the beam splitter is a polarization maintaining beam splitter.

5. The phase codec of claim 1, wherein the two arms are each polarization-maintaining optical paths, and the optical devices on the two arms are polarization-maintaining optical devices and/or non-birefringent optical devices.

6, dc modulation quantum key distribution phase codec, comprising a pre-splitter and two phase codecs according to any in schemes 1-5, the two phase codecs are optically coupled to the pre-splitter via two sub-optical paths, respectively, wherein of the splitter of each phase codec, which is not coupled to the ports of the two arms of the phase codec, is optically coupled to a corresponding sub-optical path of the two sub-optical paths, each sub-optical path is provided with optical circulators, and the phase modulators are dc phase modulators.

7, quantum key distribution time bit-phase codec, comprising a front splitter and phase codecs according to of schemes 1-5, the phase codecs being optically coupled to the front splitter via sub-optical paths, wherein of the ports of the splitter of the phase codecs not coupled to the two arms are optically coupled to sub-optical paths.

8, d.c. modulation quantum key distribution time bit-phase codec, comprising a front splitter and phase codecs according to in schemes 1-5, the phase codecs are optically coupled to the front splitter via sub-optical paths, wherein of the ports of the splitter of the phase codecs, which are not coupled to the two arms, are optically coupled to sub-optical paths, wherein optical circulators are arranged on the sub-optical paths, and the phase modulators are d.c. phase modulators.

9. The codec device according to claim 7 or 8, further comprising a splitter coupled to the front splitter via another sub-optical paths.

10, a quantum key distribution system, comprising:

the phase codec according to of any of claims 1 to 5 or the codec device according to of claims 6 to 9, which is disposed at a receiving end of the quantum key distribution system for decoding, and/or

The phase codec according to of any one of schemes 1 to 5 or the codec device according to of schemes 6 to 9, which is provided at a transmitting end of the quantum key distribution system for encoding.

The utility model discloses an unexpected beneficial effect has been realized from this to the creative structure for can be to the input light pulse of arbitrary polarization state to encode and decode interference steadily, utilize the utility model discloses a scheme, can realize the stable interference output in phase decoding interferometer department to the input light pulse of arbitrary polarization state, solved phase coding and time bit-phase coding quantum key distribution and used polarization induction decline and cause the unable problem of stable work of system.

Drawings

Fig. 1 is a schematic structural diagram of a quantum key distribution phase codec based on polarization orthogonal rotation reflection according to a preferred embodiment of the present invention ;

fig. 2 is a schematic structural diagram of another preferred embodiment of the present invention illustrating a structure of a quantum key distribution phase codec based on polarization orthogonal rotation reflection;

FIG. 3 is a schematic diagram of the structure of polarization orthogonal rotation reflectors that can be used in the phase encoder/decoder of the present invention;

FIG. 4 is a schematic diagram of another polarization orthogonal rotation reflectors that can be used in the phase encoder/decoder of the present invention;

FIG. 5 is a schematic diagram of another polarization orthogonal rotation reflectors that can be used in the phase encoder/decoder of the present invention;

fig. 6 is a schematic structural diagram of a dc modulation quantum key distribution phase encoding and decoding device based on polarization orthogonal rotation reflection according to a preferred embodiment of the present invention ;

fig. 7 is a schematic structural diagram of a quantum key distribution time bit-phase encoding and decoding device based on polarization orthogonal rotation reflection according to a preferred embodiment of the present invention ;

fig. 8 is a schematic structural diagram of a dc modulation quantum key distribution time bit-phase encoding and decoding device based on polarization orthogonal rotation reflection according to a preferred embodiment of the present invention .

Detailed Description

The following detailed description of the preferred embodiments of the invention, which is incorporated in and constitutes part of this application , and together with embodiment of the invention serves to explain the principles of the invention, a detailed description of known functions and structures of devices described herein will be omitted for clarity and simplicity.

The quantum key distribution phase codec based on polarization orthogonal rotation reflection of the preferred embodiment of the present invention is shown in fig. 1, and comprises a beam splitter 101, and two

reflection devices

102 and 103.

Two reflecting

devices

102 and 103 are optically coupled to the beam splitter 101 via two arms (upper and lower arms in fig. 1), respectively.

According to the present invention, both reflecting

means

102 and 103 are polarization orthogonal rotating reflecting means, and at least of these two reflecting means comprise a phase modulator.

For example, assuming that the two orthogonal polarization states are x-polarization state and y-polarization state respectively, the x-polarization state transmitted to polarization orthogonal rotating reflection devices along the optical path is converted into the y-polarization state orthogonal thereto after being reflected by the polarization orthogonal rotating reflection at the reflection device, and the y-polarization state transmitted to the reflection device along the optical path is converted into the x-polarization state orthogonal thereto after being reflected by the polarization orthogonal rotating reflection at the reflection device.

Here, the polarization orthogonal rotation reflection device including the phase modulator may be referred to as a "polarization orthogonal rotation reflection device having a phase modulation function".

The beam splitter 101 is used to split the incoming input optical pulses of any polarization state into two optical pulses for transmission along the two arms, respectively.

The two arms are used for respectively transmitting the two paths of light pulses.

For example, in possible applications, the phase modulator may randomly modulate either a 0 degree phase or a 90 degree phase, where each of the two

reflective devices

102 and 103 includes a phase modulator, the difference between the phases modulated by the two phase modulators is determined by the quantum key distribution protocol, depending on the particular application.

For example, the birefringent phase modulator may be a lithium niobate phase modulator that may be controlled and adjusted by controlling the voltage applied to the lithium niobate crystal to which the phase modulation experienced by each of the two orthogonal polarization states by the lithium niobate phase modulator may be controlled and adjusted.

The

reflection devices

102 and 103 are respectively used for reflecting the two light pulses transmitted by the two arms from the beam splitter 101 back to the beam splitter 101 to be combined and output by the beam splitter 101.

Because the two

reflection devices

102 and 103 are polarization orthogonal rotation reflection devices, for each paths of optical pulses in the two paths of optical pulses, when the path of optical pulse is reflected by the corresponding reflection device in the two reflection devices, the two orthogonal polarization states of the path of optical pulse are subjected to polarization orthogonal rotation reflection, so that after the reflection of the corresponding reflection device, each orthogonal polarization state of the path of optical pulse is converted into a polarization state orthogonal to the orthogonal polarization state.

The present invention proposes three inventive configurations of polarization orthogonal rotating reflective devices, namely configuration 1, configuration 2 and configuration 3 described below.

According to configuration 1, the polarization orthogonal rotation reflection apparatus includes a polarization beam splitter having an input port and two output ports, the two output ports of the polarization beam splitter being optically coupled to each other via transmission optical paths, a half-wave plate being disposed on the transmission optical paths, and a polarization direction of an optical pulse inputted to the half-wave plate being at an angle of 45 degrees with respect to a fast axis or a slow axis of the half-wave plate, the polarization orthogonal rotation reflection apparatus having configuration 1, when used in a phase codec of the present invention, can be coupled to the arm by coupling the input port of the polarization beam splitter thereof to arm of the phase codec.

According to configuration 2, the polarization quadrature rotation reflection device comprises a polarization beam splitter having an input port and two output ports, the two output ports of the polarization beam splitter being optically coupled to each other via transmission optical paths, said transmission optical paths being formed by a polarization maintaining fiber, the slow axis and the fast axis of said polarization maintaining fiber respectively maintaining stable transmission of the two orthogonal polarization states of the optical pulses input into the polarization maintaining fiber, i.e. the polarization states are unchanged, and the two output ports of the polarization beam splitter and the polarization maintaining fiber being configured such that the optical pulses output by the two output ports of the polarization beam splitter are both coupled to the slow axis of the polarization maintaining fiber for transmission or are both coupled to the fast axis of the polarization maintaining fiber for transmission by the polarization maintaining fiber twisting 90 degrees or twisting (90+ n 180 degrees), where n is an integer, the optical pulses output by the two output ports of the polarization beam splitter are both coupled to the slow axis of the polarization maintaining fiber for transmission or are both coupled to the fast axis of the polarization maintaining fiber for transmission by the polarization maintaining fiber twisting (90+ n 180 degrees), the polarization maintaining fiber is configured to always transmit the optical pulses along the polarization maintaining fiber, the polarization beam splitter, and the polarization decoder is configured to always transmit the fast axis of the polarization maintaining fiber for transmission along the polarization encoding device ().

According to configuration 3, the polarization quadrature rotating reflective device comprises a polarization beam splitter having an input port and two output ports, the two output ports of the polarization beam splitter being optically coupled to each other via transmission light paths, the transmission light path being formed by a polarization maintaining fiber comprising an odd number of 90 degree fusion splices, each 90 degree fusion splice being formed by fusion splicing a slow axis of the polarization maintaining fiber in alignment with a fast axis of the polarization maintaining fiber, the polarization quadrature rotating reflective device having configuration 3 when used in a phase codec may be coupled to the phase codec by coupling the input port of its polarization beam splitter to the arm of the phase codec.

With the polarization orthogonal rotation reflection device of any configurations of configurations 1, 2, and 3 described above, phase modulators may be inserted on the transmission optical path between the two output ports of the polarization beam splitter in the polarization orthogonal rotation reflection device.

Returning to the phase codec of fig. 1, at least of the

reflective devices

102 and 103 may be polarization quadrature rotation reflective devices employing in configurations 1, 2 and 3 above, when 0 reflective devices in the

reflective devices

102 and 103 are polarization quadrature rotation reflective devices employing in configurations 1, 2 and 3 above, another reflective devices may be polarization quadrature rotation reflective devices employing in configurations 1, 2 and 3 above, or other configurations of polarization quadrature rotation reflective devices, such as a quarter-wave 4 wave plate mirror, "a quarter-wave wave plate mirror" including a mirror and a quarter-wave , the mirror being formed in bulk with the quarter-wave at the back end of the quarter-wave wave plate, wherein the polarization direction of the input quarter-wave differs from the fast or slow axis of the quarter-wave plate, and the slow transmission of the optical pulse passing through a quarter-wave plate 8990 may be achieved by a slow mirror 8945 plated on the side of the quarter-wave plate 8536.

When only of the reflecting

devices

102 and 103 are polarization quadrature rotating reflecting devices employing of the above-described configurations 1, 2, and 3, the reflecting devices include phase modulators, and when two of the reflecting

devices

102 and 103 each employ the polarization quadrature rotating reflecting device of any of the above-described configurations 1, 2, and 3, or two of the two reflecting devices may include phase modulators.

For the phase codec of fig. 1, the relative delay of the two optical pulses may be achieved by adjusting the lengths of the two arms and/or adjusting the transmission optical paths in or two reflecting devices of the two

reflecting devices

102 and 103, which adopt configurations selected from configurations 1, 2, and 3.

Thus, for each light pulses in the split two light pulses, the two orthogonal polarization states of the light pulse may be maintained constant during the time the beam splitter splits to the respective reflecting device for reflection and during the time the respective reflecting device reflects to the beam splitter for combining the beams.

Further, the beam splitter 101 of the phase codec may be a polarization maintaining beam splitter.

Another preferred embodiment of the phase codecs of of the present invention is shown in fig. 2, and comprises a polarization maintaining beam splitter 203, a polarization orthogonal rotation reflection device 204, and a polarization orthogonal rotation reflection device 205 (hereinafter also referred to as reflection device 204 and reflection device 205, respectively).

of the two ports 201 and 202 on the side of polarization maintaining beam splitter 203 serves as the input port of the phase codec, polarization maintaining beam splitter 203 and reflecting devices 204 and 205 constitute an unequal arm michelson interferometer, with the two arms in between being the polarization maintaining fiber optical path, at least of reflecting device 204 and reflecting device 205 contains a phase modulator, and either port 201 or 202 of polarization maintaining beam splitter 203 can serve as the output port of the phase codec.

During operation, an optical pulse enters the polarization maintaining beam splitter 203 through the port 201 or 202 of the polarization maintaining beam splitter 203 and is divided into two optical pulses by the polarization maintaining beam splitter 203, optical pulses in the two optical pulses are transmitted to the reflecting device 204 through the polarization maintaining optical fiber and are reflected back by the reflecting device 204, optical pulses are transmitted to the reflecting device 205 through the polarization maintaining optical fiber and are reflected back by the reflecting device 205, phase modulation is performed on the phase modulator in the reflecting device 204 and/or 205 according to a quantum key distribution protocol, and the two reflected optical pulses which are relatively delayed are combined by the polarization maintaining beam splitter 203 and then output through the port 201 or 202.

Where the at the input and output ports of the polarization maintaining beam splitter 203 are the same ports, the phase codec may also include an optical circulator, which may be located in front of the polarization maintaining beam splitter 203. an incoming loop input optical pulse of any polarization state may be input from the port of the optical circulator and output from the second port of the optical circulator to the polarization maintaining beam splitter 203, and the combined beam output from the polarization maintaining beam splitter 203 is input to the second port of the optical circulator and output from the third port of the optical circulator.

Fig. 3 is a schematic diagram showing the structure of polarization quadrature rotation reflection devices with phase modulation function, which can be used in the phase codec of the present invention.

The polarization orthogonal rotation reflection device with phase modulation function shown in fig. 3 includes the following components: a polarization beam splitter 302, a polarization maintaining fiber 303, and a phase modulator 304.

Polarization beam splitter 302 includes three ports, port A, port B, and port C, which may be referred to as an input port, an th output port, and a second output port, ports 301 of polarization beam splitter 302, i.e., port A, serve as the input port and the output port of the device, port B and port C of polarization beam splitter 302 are connected by polarization maintaining fiber 303, optical pulses output by ports B and C of polarization beam splitter 302 are coupled to the slow axis transmission of polarization maintaining fiber 303 or are coupled to the fast axis transmission of the polarization maintaining fiber 303, and phase modulator 304 is inserted into the optical path of polarization maintaining fiber 303 connecting ports B and C of polarization beam splitter 302.

When the polarization optical pulse input polarization splitter 302 is operated, an input optical pulse is input into the polarization beam splitter 302 through a port A of the port 301, namely the polarization beam splitter 302, the input optical pulse can be regarded as being composed of two orthogonal polarization states which can be respectively marked as an x polarization state and a y polarization state, the polarization beam splitter 302 splits the polarization of the input optical pulse into a second optical pulse in the x polarization state and a second optical pulse in the y polarization state, the second optical pulse is output through a port B and a port C of the polarization beam splitter 302, the second optical pulse in the x polarization state output by the port B of the polarization beam splitter 302 is coupled to a slow axis of the polarization-preserving fiber 303 for transmission, and is input into the phase modulator 304 through a port D of the polarization beam splitter 304, the second optical pulse after the phase modulation is output through a port E of the phase modulator 304 and transmitted to a port C of the polarization beam splitter 302 along a slow axis of the polarization-preserving fiber 303, the polarization beam splitter 304 is converted into a polarization state input optical pulse in the polarization beam splitter 302, the polarization beam splitter 304, the polarization beam splitter 12 is reflected by the polarization beam splitter, and is converted into a polarization state, the polarization beam splitter 12 is input into a polarization state, the polarization beam splitter 12 is reflected by the polarization beam splitter 12, the polarization beam splitter 12 is reflected by the polarization beam splitter, the polarization beam splitter 12 is reflected by the polarization beam splitter 12, the polarization beam splitter 12 is reflected by the polarization beam splitter, the polarization beam splitter 12 is input into the polarization beam splitter, the polarization beam splitter 12, the polarization beam splitter 12 is reflected by the polarization beam splitter, the polarization beam splitter 12 is changed into the polarization state of the polarization state, the polarization state of the polarization beam splitter 12 is changed.

The phase modulator 304 may be a birefringent phase modulator or a single polarization phase modulator.

Port B and port C of polarization splitter 302 may both be coupled to the fast axis of polarization maintaining fiber 303, with the results unaffected.

Fig. 4 is a schematic diagram showing another polarization orthogonal rotation reflection devices with phase modulation function, which can be used in the phase codec of the present invention.

The polarization orthogonal rotation reflection device with phase modulation function shown in fig. 4 includes the following components: a polarization beam splitter 402, a polarization maintaining fiber 403, a phase modulator 404, and a 90 degree splice point 405.

The polarization beam splitter 402 includes three ports, port A, port B, port C may be referred to as an input port, an th output port, and a second output port, ports 401 of the polarization beam splitter 402, i.e., port A, as the input port and the output port of the device, port B and port C of the polarization beam splitter 402 are connected by polarization maintaining fiber 403. optical pulses output by port B of the polarization beam splitter 402 are coupled to the slow axis of the polarization maintaining fiber 403 and optical pulses output by port C of the polarization beam splitter 402 are coupled to the fast axis of the polarization maintaining fiber 403, or optical pulses output by port B of the polarization beam splitter 402 are coupled to the fast axis of the polarization maintaining fiber 403 and optical pulses output by port C of the polarization beam splitter 402 are coupled to the slow axis of the polarization maintaining fiber 403. the polarization maintaining fiber 403 contains a 90 degree splice point 405, and the 90 degree splice point 405 is fused by aligning the slow axis of the polarization maintaining fiber with the fast axis of the polarization maintaining fiber 403 connecting ports B and C of the polarization beam splitter 402.

When the polarization beam splitter 402 is in the polarization state, the polarization beam splitter 402 splits the polarization of the input optical pulse into a second path of optical pulse in the x-polarization state and a second path of optical pulse in the y-polarization state, which are output by the port B and the port C of the polarization beam splitter 402, respectively, the second path of optical pulse in the x-polarization state output by the port B of the polarization beam splitter 402 is coupled to the slow axis of the polarization maintaining optical fiber 403 for phase modulation by the port D of the phase modulator 404, the second path of optical pulse after phase modulation is output by the port E of the phase modulator 404 and is transmitted to the 90-degree fusion point 405 along the slow axis of the polarization maintaining optical fiber 403, the second path of optical pulse after phase modulation is output by the port E of the phase splitter 404 and is transmitted to the port C of the polarization beam splitter 403 along the fast axis of the polarization beam splitter 403, the second path of optical pulse after phase modulation is transmitted to the port C of the polarization beam splitter 403, the polarization beam splitter 402 is converted into a polarization beam splitter 404, the polarization beam splitter 404 is transmitted to the port C of the polarization beam splitter 403, the polarization beam splitter 402 is transmitted to the polarization beam splitter 403, the polarization beam splitter 402 is transmitted to the polarization beam splitter 404, the polarization beam splitter 404 is transmitted to the polarization beam splitter 403, the polarization beam splitter 404 is transmitted to the polarization beam splitter 403, the polarization beam splitter 404 is transmitted to the polarization beam splitter 403, the polarization beam splitter 404 is transmitted to the polarization beam splitter 403, the polarization beam splitter 404 is transmitted to the polarization beam.

The th optical pulse input to the phase modulator 404 through the port D and the second optical pulse input to the phase modulator 404 through the port E are input to the phase modulator 404 in the same polarization state and subjected to the same phase modulation, so as to realize polarization-independent phase modulation.

Although only degree fusion splices 405 are shown in FIG. 4, this is exemplary only, and the polarization maintaining fiber 403 may contain any odd number of 90 degree fusion splices, each 90 degree fusion splice being made by fusion splicing the polarization maintaining fiber slow axis in alignment with the polarization maintaining fiber fast axis, where the polarization maintaining fiber 403 contains more than 1 odd number of 90 degree fusion splices, the results are unaffected, except that the second optical pulses and the second optical pulses output by ports B and C of the polarization beam splitter 402 each alternate between traveling along the polarization maintaining fiber slow axis and traveling along the polarization maintaining fiber fast axis more times as they travel along the polarization maintaining fiber 403, the number of transitions being equal to the number of 90 degree fusion splices.

Polarization orthogonal rotation is performed on two orthogonal polarization states by using the polarization maintaining fiber 403 containing an odd number of 90-degree fusion points, so that the phase between the x-polarization state and the y-polarization state of the input light pulse and the phase between the y-polarization state and the x-polarization state of the output light pulse are kept the same.

The phase modulator 404 may be a birefringent phase modulator or a single polarization phase modulator.

When port B of the polarization beam splitter 402 is coupled to the fast axis of the polarization maintaining fiber 403 and port C of the polarization beam splitter 402 is coupled to the slow axis of the polarization maintaining fiber 403, the above result is not affected.

The position and connection order of the phase modulator 404 and the 90 degree weld 405 are changed, and the above result is not affected.

Fig. 5 is a schematic diagram showing another polarization orthogonal rotation reflection devices with phase modulation function, which can be used in the phase codec of the present invention.

The polarization orthogonal rotation reflection apparatus having the phase modulation function shown in fig. 5 includes the following components: a polarization beam splitter 502, a phase modulator 503, a half wave plate 504.

The polarization beam splitter 502 includes three ports, port A, port B, port C may be referred to as an input port, an th output port, and a second output port, respectively ports 501 of the polarization beam splitter 502, i.e., port A, serve as an input port and an output port of the apparatus, port B and port C of the polarization beam splitter 502 are connected by a transmission optical path, more specifically, port B of the polarization beam splitter 502 is connected by a transmission optical path to port D of the phase modulator 503, port E of the phase modulator 503 is connected by a transmission optical path to the half-wave plate 504, the half-wave plate 504 is connected by a transmission optical path to port C of the polarization beam splitter 502, the transmission optical paths between port B of the polarization beam splitter 502 and port D of the phase modulator 503, the transmission optical path between port E of the phase modulator 503 and the half-wave plate 504, the transmission optical paths between the half-wave plate 504 and port C of the polarization beam splitter 502 are all polarization maintaining optical paths, e.g., polarization maintaining optical fiber optical paths, polarization direction of polarization state of the half-wave plate 504 and slow axis or fast axis of the optical pulse 45 degrees are input.

When the polarization beam splitter device works, an input optical pulse is input into the polarization beam splitter 502 through the port 501, namely the port A of the polarization beam splitter 502, the input optical pulse can be regarded as being composed of two orthogonal polarization states which can be respectively marked as an x polarization state and a y polarization state, the polarization beam splitter 502 transmits a second path of optical pulse in the x polarization state and a second path of optical pulse in the y polarization state to be output through the port B and the port C of the polarization beam splitter 502, the second path of optical pulse in the x polarization state output by the port B of the polarization beam splitter 502 is input into the phase modulator 503 and subjected to phase modulation, the second path of optical pulse after phase modulation is output from the port E of the phase modulator 503 to the half-wave plate 504, the second path of optical pulse after polarization orthogonal rotation through the half-wave plate 504, the polarization state of the second path of optical pulse is converted into the y polarization state from the x polarization state to be output from the polarization beam splitter 502, the polarization beam splitter 502 converts the polarization state into the polarization state of the polarization beam splitter into the polarization beam splitter component in the polarization state A, the polarization beam splitter, and the polarization beam splitter output polarization beam splitter 502.

The th optical pulse input to the phase modulator 503 through the port D and the second optical pulse input to the phase modulator 503 through the port E are input to the phase modulator 503 in the same polarization state and undergo the same phase modulation, so as to realize polarization-independent phase modulation.

The phase modulator 503 may be a birefringent phase modulator or a single polarization phase modulator.

The position and connection order of the phase modulator 503 and the half-wave plate 504 are changed, and the above result is not affected.

The utility model discloses a phase place codec can be used as direct current modulation quantum key distribution phase place codec's component, can be used as quantum key distribution time bit-phase place codec's component, also can be used as direct current modulation quantum key distribution time bit-phase place codec's component.

kinds of direct current modulation quantum key distribution phase encoding and decoding devices based on polarization orthogonal rotation reflection of the phase encoder and decoder of the present invention are shown in FIG. 6, which comprises a pre-beam splitter 603,

optical circulators

604 and 610, polarization maintaining

beam splitters

605 and 611, and polarization orthogonal

rotation reflection devices

606, 607, 612 and 613 (hereinafter also referred to as

reflection devices

606, 607, 612 and 613, respectively).

Polarization maintaining beam splitter 605, two reflecting

devices

606 and 607, and two arms between polarization maintaining beam splitter 605 and the two reflecting devices constitute polarization maintaining unequal arm michelson interferometer, i.e. phase codec according to the present invention, two arms of phase codec are polarization maintaining fiber optical path, at least of reflecting

devices

606 and 607 comprises a dc phase modulator.

Similarly, polarization maintaining beam splitter 611, two reflecting devices 612 and 613 and two arms between polarization maintaining beam splitter 611 and the two reflecting devices form a second polarization maintaining unequal arm Michelson interferometer, i.e., a second phase codec according to the present invention.

The following describes an example of the codec device of fig. 6 for decoding.

The th port A and the second port B of the optical circulator 604 are respectively connected with the output ports of the pre-splitter 603 and the th input ports of the polarization-maintaining splitter 605, the optical pulses input into the rd phase codec are decoded and then output by the 4 output ports 608 of the polarization-maintaining splitter 605, or are transmitted to the second port B of the optical circulator 604 through the other output ports (i.e. the input ports of the polarization-maintaining splitter 605) of the polarization-maintaining splitter 605 and output from the third port C of the optical circulator 604, the th port A and the second port B of the polarization-maintaining splitter 610 are respectively connected with the other output ports of the pre-splitter 603 and the input ports of the polarization-maintaining splitter 611, the optical pulses input into the second phase codec are decoded and then output by the 3 output ports of the polarization-maintaining splitter 614, or are transmitted to the third port B of the optical circulator 610 through the output ports of the polarization-maintaining splitter, i.e. the 73742 output ports of the polarization-maintaining splitter 611 and the output ports of the optical circulator 610.

In operation, an optical pulse enters the beam splitter 603 through a port 601 or 602 of the beam splitter 603, and is split into a second optical pulse and a second optical pulse by the beam splitter 603, a second optical pulse is input through a second port a of the optical circulator 604, and is output to the polarization maintaining beam splitter 605 through a second port B of the optical circulator 604, the polarization maintaining beam splitter 605 splits the input second optical pulse into two second optical sub-pulses, a 5393 optical sub-pulse of the second optical pulse is transmitted to the reflecting device 606 through the polarization maintaining optical fiber and is reflected back by the reflecting device 606, another optical sub-pulse of the second optical sub-pulse is transmitted to the reflecting device 607 through the polarization maintaining optical fiber and is reflected back by the reflecting device 607, a direct current phase modulator in the reflecting device 606 and/or 607 according to a quantum key distribution protocol, a second reflected back two second optical sub-pulses reflected back through the polarization maintaining beam splitter 608, or reflected back to the second optical pulse splitter 613 according to a quantum key distribution protocol, and is output to the second direct current phase modulator 613 through a second polarization maintaining optical pulse splitter B port B613, and is reflected back through a second optical pulse splitter 42, and is output through a polarization maintaining optical fiber branch splitter 42, and is output through a direct current phase modulator B42, and is reflected back through a polarization maintaining optical pulse phase modulator 42, and is output through a polarization maintaining optical fiber branch fiber 612, and is output as direct current optical fiber branch fiber.

Next, the encoding and decoding apparatus of fig. 6 will be described by way of example for encoding.

The optical pulses input from the third port C of the optical circulator 604 are input to the second port B of the optical circulator 604 via the second port B of the optical circulator 604, the phase codec, the 4 ports 608 of the polarization beam splitter 605, the 825 phase codec, the optical pulses output from the polarization beam splitter 605 to the second port B of the optical circulator 604 after being encoded by the phase codec , and the 856 ports a of the optical circulator 604 to the second port B of the optical circulator 604, and the encoded 366 ports of the front polarization beam splitter 603, the encoded 3648 optical pulses input from the third port B of the polarization beam splitter 603, the encoded 36610 optical pulses input to the polarization beam splitter 611 via the polarization beam splitter 610, the encoded 3648 optical pulses input from the polarization beam splitter 603 to the polarization beam splitter 610 via the polarization beam splitter 610, and the encoded 3648 optical pulse encoded 36610 after being input to the polarization beam splitter 603, the encoded 3648 optical circulator 603, the encoded 36610 from the polarization beam splitter 603, the encoded B of the polarization beam splitter 610 to the encoded third port B of the polarization beam splitter 611, and the encoded 366 optical circulator 603, the encoded 3648 optical circulator 603, the encoded 36610 after being output from the polarization beam splitter 610 to the encoded B of the polarization beam splitter 603, the encoded 366 port B, the encoded 3648 port B, the encoded 36610, the encoded by the encoded 3 port of the polarization beam splitter 603, the polarization beam splitter 610, the encoded 3 phase encoder 603, and the encoded 3 phase encoder 603, the encoded 366 port B, the encoded 3 phase encoder 603, and the encoded 3 phase encoder 603, and the encoded 3, the encoded 3 port B, the encoded 3 phase encoder 603, and the encoded 3, the encoded 3 port B, the encoded by the input to the encoded 3, the input to the third port B, the input to the third port of the polarization beam splitter 610 of the front polarization beam splitter 611, the polarization beam splitter 610, the polarization beam splitter.

The quantum key distribution time bit-phase codec device based on polarization orthogonal rotation reflection using the phase codec of the present invention is shown in fig. 7, and includes

beam splitters

703 and 704, polarization maintaining beam splitter 707, and polarization orthogonal rotation reflection devices 708 and 709 (hereinafter also referred to as reflection device 708 and reflection device 709, respectively).

Polarization maintaining beam splitter 707, two reflecting

means

708 and 709, and two arms between polarization maintaining beam splitter 707 and the two reflecting means constitute a polarization maintaining unequal arm michelson interferometer, i.e. a phase codec according to the present invention.

The following describes an example of the codec device of fig. 7 for decoding.

The splitter 703 is a pre-splitter, and two ports 701 and of 702 on the side are input ports of the device, the splitter 704 splits optical pulses from the splitter 703 and outputs the optical pulses from the

ports

705 and 706, and the optical pulses input to the polarization maintaining unequal arm michelson interferometer are decoded and output from the port 710.

During operation, an input optical pulse enters the beam splitter 703 through a

port

701 or 702 of the beam splitter 703, and is split into two optical pulses by the beam splitter 703 for transmission, optical pulses from the beam splitter 703 are input to the beam splitter 704, and are output through a

port

705 or 706 after being split by the beam splitter 704 to implement time bit decoding, another optical pulses from the beam splitter 703 are input to a polarization maintaining beam splitter 707 and are split into two sub optical pulses by the polarization maintaining beam splitter 707, sub optical pulses are transmitted to the reflection device 708 through the polarization maintaining fiber and are reflected back by the reflection device 708, another sub optical pulses are transmitted to the reflection device 709 through the polarization maintaining fiber and are reflected back by the reflection device 709, during which the phase modulators in the reflection device 708 and/or 709 perform phase modulation according to a quantum key distribution protocol, and the two sub optical pulses reflected back through relative delay are output through the port 710 after being combined by the polarization maintaining beam splitter 707.

Here, it should be noted that the splitter 704 is optional, and it is possible to directly output the optical pulses for time-bit decoding by the pre-splitter 703.

Next, the encoding and decoding apparatus of fig. 7 will be described by way of example for encoding.

The optical pulses input from the

ports

705 and 706 are combined by the beam splitter 704 and output to the pre-splitter 703, so as to realize time bit encoding, the optical pulses input from the port 710 are encoded by the polarization maintaining unequal arm michelson interferometer and output to the pre-splitter 703 by the polarization maintaining beam splitter 707, and two phase encodings are realized by the phase modulators in the modulation reflection devices 708 and/or 709, the ports 701 and of the pre-splitter 703 are used as the output ports of the device, and the optical pulses output by the beam splitter 704 and the optical pulses output by the polarization maintaining beam splitter 707 are combined by the beam splitter 703 and output by the

ports

701 or 702.

The splitter 704 is optional, it is possible to use the port of the splitter 703 connected to the splitter 704 directly as an input port for time bit encoding.

The kinds of direct current modulation quantum key distribution time bit-phase encoding and decoding device based on polarization orthogonal rotation reflection using the phase encoder and decoder of the present invention is shown in fig. 8, and comprises

beam splitters

803 and 804, optical circulator 807, polarization maintaining beam splitter 808, and polarization orthogonal rotation reflection device 809 and polarization orthogonal rotation reflection device 810 (hereinafter also referred to as reflection device 809 and reflection device 810, respectively).

Polarization maintaining beam splitter 808, two reflecting

devices

809 and 810, and two arms between polarization maintaining beam splitter 808 and the two reflecting devices constitute a polarization maintaining unequal arm michelson interferometer, i.e., a phase codec according to the present invention.

The following describes an example of the codec device of fig. 8 for decoding.

The splitter 803 acts as a pre-splitter with the side two ports 801 and of 802 acting as input ports for the device, the splitter 804 splits optical pulses from the splitter 803 for output by either

port

805 or 806 optical pulses input from the th port A of the optical circulator 807 are output by the second port B of the optical circulator 807, optical pulses input from the second port B of the optical circulator 807 are output by the third port C of the optical circulator 807. optical pulses input to the polarization maintaining unequal arm Michelson interferometer are decoded for output by port 811, or transmitted to the second port B of the optical circulator 807 via another output port of the polarization maintaining splitter 808 and output by the third port C of the optical circulator 807 for output by port 812.

When the optical fiber splitter 803 is in operation, an input optical pulse enters the beam splitter 803 through a port 801 or 802 of the beam splitter 803, and is split into two optical pulses by the beam splitter 803 for transmission, optical pulses from the beam splitter 803 are input to the beam splitter 804, and are output by a port 805 or 806 after being split by the beam splitter 804 for time bit decoding, another optical pulses from the beam splitter 803 are input through a third port a of the optical circulator 807 and are output to the polarization maintaining beam splitter 808 from a second port B of the optical circulator 807, the polarization maintaining beam splitter 808 splits the another optical pulses into two sub optical pulses, sub optical pulses are transmitted to a reflecting device 809 through a polarization maintaining optical fiber and are reflected back by the reflecting device 809, another sub optical pulses are transmitted to the reflecting device 810 through the polarization maintaining optical fiber and are reflected back by the reflecting device 810, and the dc phase modulators in the reflecting devices 809 and/or 810 perform dc phase modulation according to a quantum key distribution protocol, and the two relatively delayed sub optical pulses are output to a second port 811, and are output to a third port 808 or output by a second port C of the beam splitter 807 and are output.

Here, it should be noted that the splitter 804 is optional, and it is possible that the optical pulses are directly output by the pre-splitter 803 for time-bit decoding.

Next, the encoding and decoding apparatus of fig. 8 will be described by way of example for encoding.

Optical pulses input from the third port C of the optical circulator 807 are output from the second port B of the optical circulator 807, optical pulses input from the second port B of the optical circulator 807 are output from the third port a of the optical circulator 807, optical pulses input from the ports 805 and 806 are output to the pre-splitter 803 after being combined by the beam splitter 804, time-bit encoding is achieved, optical pulses input from the port 811 and optical pulses input from the third port C of the optical circulator 807 and output to the polarization-maintaining beam splitter 808 from the second port B of the optical circulator 807, optical pulses output from the polarization-maintaining beam splitter 808 to the second port B of the optical circulator 807 after being encoded by the polarization-maintaining unequal arm michelson interferometer and transmitted to the pre-splitter 803 from the third port B of the polarization-splitter 807 through the third port B of the polarization splitter 807, and output to the pre-splitter 803 through the third port a of the optical circulator 807, and output from the output port 802 of the optical circulator 801 and the optical pulse output port 802 of the optical circulator 803 after being combined by the polarization splitter 811, port 802 and the third port C of the polarization splitter 807, and the optical pulse encoding optical pulses output from the output port 802 and after being output from the optical circulator 803.

The splitter 804 is optional, it is possible to directly use the port of the splitter 803 connected to the splitter 804 as an input port for time bit encoding.

Herein, the terms "beam splitter" and "beam combiner" are used interchangeably, and a beam splitter may also be referred to and used as a beam combiner, and vice versa. Herein, the term "polarization maintaining fiber optical path" refers to an optical path formed by connecting polarization maintaining fibers or an optical path formed by transmitting optical pulses by using polarization maintaining fibers.

The phase codec or the corresponding codec device based on polarization orthogonal rotation reflection of the present invention as described above may be configured at the receiving end of the quantum key distribution system for decoding. In addition, the phase codec or the corresponding codec device based on polarization orthogonal rotation reflection of the present invention as described above may also be configured at the transmitting end of the quantum key distribution system for encoding.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments, as illustrated in the accompanying drawings.

Claims

Quantum key distribution phase codec comprising a beam splitter, two reflecting devices optically coupled to the beam splitter via two arms, respectively, wherein each of the reflecting devices is a polarization orthogonal rotating reflecting device, of the two reflecting devices or each of the reflecting devices comprises a polarizing beam splitter having an input port and two output ports and is coupled to a respective one of the two arms via the input port of the polarizing beam splitter, wherein the two output ports of each polarizing beam splitter are optically coupled to each other via a transmission optical path, at least of the reflecting devices comprising polarizing beam splitters are provided on their transmission optical paths with half-wave plates, the polarization direction of an optical pulse input to the half-wave plates is at an angle of 45 degrees to the fast or slow axis of the half-wave plates, and at least of the reflecting devices comprising polarizing beam splitters are provided on their transmission optical paths with phase modulators.
2. The phase codec of claim 1, wherein the two reflective devices are identically constructed polarization quadrature rotating reflective devices or differently constructed polarization quadrature rotating reflective devices.
3. The phase codec of claim 1, wherein the transmission optical path is a polarization maintaining optical path.
4. The phase codec of claim 1, wherein the beam splitter is a polarization maintaining beam splitter.
5. The phase codec of claim 1, wherein the two arms are each polarization-maintaining optical paths, and the optical devices on the two arms are polarization-maintaining optical devices and/or non-birefringent optical devices.
6, DC modulated quantum key distribution phase codec device, comprising a front splitter and two phase codecs according to any of claims 1-5, the two phase codecs being optically coupled to the front splitter via two sub-optical paths, respectively, wherein of the splitter of each phase codec not coupled to the ports of the two arms of the phase codec is optically coupled to a corresponding sub-optical path of the two sub-optical paths, each sub-optical path having optical circulators, wherein the phase modulators are DC phase modulators.
7, quantum key distribution time bit-phase codec device, characterized in that, the device comprises a front beam splitter and phase codecs according to of claims 1-5, the phase codecs is optically coupled to the front beam splitter via sub-optical paths, wherein of the beam splitter of the phase codecs, which are not coupled to the ports of the two arms, are optically coupled to sub-optical paths.
8, D.C. modulation quantum key distribution time bit-phase codec, characterized in that, the D.C. modulation quantum key distribution time bit-phase codec comprises a front beam splitter and phase codecs according to of any of claims 1-5, the phase codecs is optically coupled to the front beam splitter via sub-optical paths, wherein of the beam splitters of the phase codecs, which are not coupled to the ports of the two arms, are optically coupled to sub-optical paths, wherein optical circulators are arranged on the sub-optical paths, and the phase modulators are D.C. phase modulators.
9. The codec of claim 7 or 8, further comprising a splitter coupled to the front splitter via another sub-paths.
10, a quantum key distribution system, characterized in that the quantum key distribution system comprises:

the phase codec according to any of claims 1-5 or the codec according to any of claims 6-9, which is arranged at a receiving end of the quantum key distribution system for decoding, and/or

The phase codec according to any of claims 1-5 or the codec according to any of claims 6-9, provided at a transmitting end of the quantum key distribution system for encoding.