CN107612690B

CN107612690B - Phase decoding method and device and quantum key distribution system

Info

Publication number: CN107612690B
Application number: CN201711018889.6A
Authority: CN
Inventors: 许华醒; 谢海永; 廖勇; 莫小范; 程旭升
Original assignee: Electronic Science Research Institute of CTEC
Current assignee: Electronic Science Research Institute of CTEC
Priority date: 2017-10-26
Filing date: 2017-10-26
Publication date: 2021-05-07
Anticipated expiration: 2037-10-26
Also published as: CN107612690A; WO2019080530A1

Abstract

The invention provides a phase decoding method, a phase decoding device and a quantum key distribution system, wherein the method comprises the following steps: the method comprises the steps of polarizing and splitting an incident path of input light pulse into a first path of transmission light pulse and a second path of transmission light pulse; respectively carrying out phase decoding on the first path of transmission light pulse and the second path of transmission light pulse, and obtaining two paths of sub-output light pulses after each path of transmission light pulse is subjected to phase decoding; and polarizing and combining any path of sub output optical pulses of the first path of transmission optical pulses after phase decoding and any path of sub output optical pulses of the second path of transmission optical pulses after phase decoding into one path of output optical pulses. The invention can effectively solve the influence of the random change of the polarization state of the light pulse on the stability of the system and realize the stable phase decoding of the interference immunity of the transmission optical fiber environment. In addition, the invention adopts the unequal arm Mach-Zehnder interference ring, and the optical pulse only needs to pass through the phase modulator once during decoding, thereby greatly reducing the insertion loss of a receiving end and remarkably improving the system efficiency.

Description

Phase decoding method and device and quantum key distribution system

Technical Field

The invention relates to the technical field of optical transmission secret communication, in particular to a phase decoding method, a phase decoding device and a quantum key distribution system.

Background

In the phase coding quantum key distribution system based on the unequal-arm interference ring, in the transmission process of optical pulse in an optical fiber quantum channel, due to the non-ideal conditions of non-circular symmetry of the cross section, nonuniform distribution of the refractive index of a fiber core in the radial direction and the like in the manufacture of the optical fiber, and the influence of temperature, strain, bending and the like on the optical fiber in the actual environment, a double refraction effect is generated, the polarization state of the optical pulse when reaching a receiving end is randomly changed, the output result of the phase decoding interference ring is unstable, and the deterioration is obvious along with the increase of the distance of the. In the prior art, an unequal-arm Faraday-Michelson interference ring is provided, which can prevent the polarization state of an optical pulse from being influenced by random birefringence of an optical fiber channel and keep the interference result to be stably output. However, such an interferometric ring has a large loss, wherein the insertion loss of the phase modulator is one of the main factors causing the large loss, and when the phase modulator is disposed in one arm of the interferometric ring, the optical pulse will pass through the phase modulator twice due to the back-and-forth transmission, so that the loss of the interferometric ring is large, and the system efficiency is low.

Disclosure of Invention

The invention mainly aims to provide a phase decoding method, a phase decoding device and a quantum key distribution system, which are used for solving the problem of low insertion loss polarization-independent phase decoding in a phase coding quantum key distribution system and establishing a quantum key distribution system with high-efficiency environmental interference immunity based on unequal-arm Mach-Zehnder interference rings.

To achieve the above object, the present invention provides a phase decoding method, comprising:

the method comprises the steps of polarizing and splitting an incident path of input light pulse into a first path of transmission light pulse and a second path of transmission light pulse;

respectively carrying out phase decoding on the first path of transmission light pulse and the second path of transmission light pulse, and obtaining two paths of sub-output light pulses after each path of transmission light pulse is subjected to phase decoding;

and polarizing and combining any path of sub output optical pulses of the first path of transmission optical pulses after phase decoding and any path of sub output optical pulses of the second path of transmission optical pulses after phase decoding into one path of output optical pulses.

Optionally, the performing phase decoding on the first path of transmission light pulse and the second path of transmission light pulse respectively includes:

splitting one path of transmission light pulse into two paths of sub-transmission light pulses, and combining the split two paths of sub-transmission light pulses into two paths of sub-output light pulses;

in the process of phase decoding one path of transmission light pulse, the polarization state of the light pulse is controlled, so that the polarization states of two paths of sub-transmission light pulses before the two paths of sub-output light pulses are combined into two paths of sub-transmission light pulses are the same.

Optionally, the method further includes:

and in the process from polarization beam splitting to polarization beam combining, controlling the polarization state of the optical pulse so as to ensure that the polarization states of the two paths of sub-output optical pulses are orthogonal to each other during the polarization beam combining.

Optionally, the controlling the polarization state of the light pulse includes:

by using a polarization-preserving device, the polarization state of the optical pulses is maintained constant.

In addition, to achieve the above object, the present invention provides a phase decoding apparatus comprising: a polarization beam splitter, two phase decoders, and one or two polarization beam combiners;

the polarization beam splitter is used for polarization beam splitting of an incident input light pulse into a first transmission light pulse and a second transmission light pulse;

the two phase decoders are used for respectively carrying out phase decoding on the first path of transmission light pulse and the second path of transmission light pulse, and each path of transmission light pulse obtains two paths of sub-output light pulses after the phase decoding;

the polarization beam combiner is used for polarization beam combining of any path of sub output optical pulses after the phase decoding of the first path of transmission optical pulses and any path of sub output optical pulses after the phase decoding of the second path of transmission optical pulses into one path of output optical pulses.

Optionally, the phase decoder is specifically configured to:

and splitting one path of transmission light pulse into two paths of sub-transmission light pulses, and combining the split two paths of sub-transmission light pulses into two paths of sub-output light pulses.

Optionally, the polarization beam splitter, the phase decoder, the polarization beam combiner, and the discrete devices and waveguide devices used for conducting light are all polarization control type devices, so as to control the polarization state of the light pulse, so that the polarization states of the two paths of sub-transmission light pulses before the two paths of sub-output light pulses are combined into two paths of sub-transmission light pulses are the same, and the polarization states of the two paths of sub-output light pulses during polarization beam combination are orthogonal to each other.

Optionally, the polarization beam splitter, the phase decoder, the polarization beam combiner, and the discrete devices and waveguide devices used for guiding light are all polarization-maintaining devices, so as to maintain the polarization state of the light pulse unchanged.

Optionally, the phases modulated by the two phase decoders coincide.

Optionally, the two phase decoders use unequal-arm mach-zehnder interference rings or unequal-arm michelson interference rings.

Optionally, when the two phase decoders adopt an unequal-arm michelson interference ring and the input port and the output port of the unequal-arm michelson interference ring are the same port, the polarization beam combiner and the polarization beam splitter are the same device, and at this time, the apparatus further includes: optical circulator

The optical circulator is positioned at the front end of the polarization beam splitter; the optical pulse input by the first port of the optical circulator is output to the polarization beam splitter from the second port of the optical circulator; the optical pulses output from the polarizing beam splitter to the second port of the optical circulator are output from the third port of the optical circulator.

In addition, to achieve the above object, the present invention also provides a quantum key distribution system, including: the single photon source, the phase encoder, the quantum channel, the single photon detector and the introduced phase decoding device;

the single photon source is used for generating single photon light pulses;

the phase encoder is used for carrying out phase encoding on the single photon light pulse generated by the single photon source;

the quantum channel is used for transmitting single photon light pulse;

the phase decoding device is used for carrying out phase decoding on the single-photon optical pulse transmitted by the quantum channel according to a quantum key distribution protocol;

the single-photon detector is used for detecting the single-photon optical pulse output by the phase decoding device and distributing the quantum key according to the detection result and a quantum key distribution protocol.

Optionally, the phase encoder adopts any one of the following: unequal arm Mach-Zehnder interference rings, unequal arm Michelson interference rings, unequal arm Faraday-Michelson interference rings, and the phase decoding device described above.

By adopting the technical scheme, the invention at least has the following advantages:

the phase decoding method, the device and the quantum key distribution system polarize and split an incident path of input optical pulse into a first path of transmission optical pulse and a second path of transmission optical pulse, respectively perform phase decoding on the two paths of transmission optical pulses, obtain two paths of sub output optical pulses after the phase decoding of each path of transmission optical pulse, polarize and combine any path of sub output optical pulse after the phase decoding of the first path of transmission optical pulse and any path of sub output optical pulse after the phase decoding of the second path of transmission optical pulse into one path of output optical pulse. The phase decoding is to split one path of transmission light pulse into two paths of sub-transmission light pulses and to combine the split two paths of sub-transmission light pulses into two paths of sub-output light pulses. And controlling the polarization state of the optical pulse, so that the polarization states of two paths of sub-transmission optical pulses before two paths of sub-output optical pulses are combined into a beam are the same, and the polarization states of the two paths of sub-output optical pulses are orthogonal to each other during polarization beam combination. Generally, when an optical pulse is transmitted through an optical fiber quantum channel, the polarization state of the optical pulse transmitted to a receiving end is randomly changed due to environmental influence, and the working stability of a quantum secret communication system is influenced. The invention can effectively solve the influence of the random change of the polarization state of the input optical pulse on the stability of the system and realize the stable phase decoding of the interference immunity of the transmission optical fiber environment. In addition, the invention has no restriction on the type of the interference ring adopted by the phase decoder, and can be suitable for the most common unequal arm Mach-Zehnder interference ring, so that the optical pulse only needs to pass through the phase modulator once during decoding, the insertion loss of a receiving end is greatly reduced, and the system efficiency is remarkably improved. The invention provides a technical scheme of a stable and efficient quantum key distribution system with low insertion loss. The method is simple and easy to realize.

Drawings

FIG. 1 is a flow chart of a phase decoding method according to a first embodiment of the present invention;

FIG. 2 is a schematic diagram of a phase decoding apparatus according to a second embodiment of the present invention;

FIG. 3 is a schematic diagram of a phase decoding apparatus according to a third embodiment of the present invention;

FIG. 4 is a schematic diagram of a phase decoding apparatus according to a fourth embodiment of the present invention;

FIG. 5 is a schematic diagram of the structure of an unequal arm Mach-Zehnder interference ring according to a fifth embodiment of the present invention;

FIG. 6 is a schematic structural diagram of an unequal-arm Michelson interference ring according to a sixth embodiment of the present invention;

FIG. 7 is a schematic diagram illustrating a structure of an unequal-arm Faraday-Michelson interference ring according to a seventh embodiment of the present invention;

fig. 8 is a schematic structural diagram of a quantum key distribution system according to an eighth embodiment of the present invention.

Detailed Description

The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form a part hereof, and which together with the embodiments of the invention serve to explain the principles of the invention. For the purpose of clarity and simplicity, a detailed description of known functions and configurations in the devices described herein will be omitted when it may obscure the subject matter of the present invention.

A first embodiment of the present invention, a phase decoding method, as shown in fig. 1, specifically includes the following steps:

step S101: and the polarization beam splitting of the incident input light pulse is carried out to form a first path of transmission light pulse and a second path of transmission light pulse.

Specifically, the polarization state of the incident input optical pulse may be any polarization state, and the polarization states of the first path of transmission optical pulse and the second path of transmission optical pulse after polarization splitting are orthogonal to each other.

Step S102: and respectively carrying out phase decoding on the first path of transmission light pulse and the second path of transmission light pulse, and obtaining two paths of sub-output light pulses after each path of transmission light pulse is subjected to phase decoding.

Specifically, the performing phase decoding on the first path of transmission light pulse and the second path of transmission light pulse respectively includes:

Step S103: and polarizing and combining any path of sub output optical pulses of the first path of transmission optical pulses after phase decoding and any path of sub output optical pulses of the second path of transmission optical pulses after phase decoding into one path of output optical pulses.

Further, the method further comprises:

Further, the controlling the polarization state of the light pulse includes:

by using the polarization-maintaining device, the polarization state of the optical pulse is maintained to be constant all the time; alternatively, the polarization state of the optical pulses is subjected to a known modulation.

A second embodiment of the present invention, a phase decoding apparatus, as shown in fig. 2, specifically includes the following components: a polarization beam splitter 201, two phase decoders 202, and two polarization beam combiners 203.

1) The polarization beam splitter 201 is configured to polarizedly split one incident input optical pulse into a first transmitted optical pulse and a second transmitted optical pulse.

2) And the two phase decoders 202 are respectively arranged on two light paths between the polarization beam splitter 201 and the polarization beam combiner 203, and are used for respectively performing phase decoding on the first transmission light pulse and the second transmission light pulse, and each transmission light pulse obtains two paths of sub-output light pulses after the phase decoding.

Specifically, the phase decoder 202 is configured to:

Further, the phases modulated by the two phase decoders 202 coincide.

Further, the two phase decoders 202 employ either an unequal arm mach-zehnder interferometer ring or an unequal arm michelson interferometer ring.

3) And the polarization beam combiner 203 is configured to combine any path of sub-output optical pulses after the phase decoding of the first path of transmission optical pulses and any path of sub-output optical pulses after the phase decoding of the second path of transmission optical pulses into one path of output optical pulses in a polarization manner.

Specifically, two sub-output optical pulses input to the polarization beam combiner 203 synchronously reach the polarization beam combiner 203 and are combined into one output optical pulse.

Further, when the two phase decoders 202 both use the unequal-arm michelson interference rings and the input port and the output port of the unequal-arm michelson interference rings are the same port, the polarization beam combiner 203 and the polarization beam splitter 201 are the same device, and at this time, the apparatus further includes: an optical circulator;

the optical circulator is positioned at the front end of the polarization beam splitter 201; the optical pulse input by the first port of the optical circulator is output to the polarization beam splitter 201 from the second port of the optical circulator; the optical pulse output from the polarization beam splitter 201 to the second port of the optical circulator is output from the third port of the optical circulator.

Furthermore, the polarization beam splitter 201, the phase decoder 202, the polarization beam combiner 203, and the discrete devices and waveguide devices used for transmitting light are all polarization control type devices, so as to control the polarization state of the light pulse, so that the polarization states of the two paths of sub-transmission light pulses before the two paths of sub-output light pulses are combined into two paths of sub-transmission light pulses are the same, and the polarization states of the two paths of sub-output light pulses during polarization beam combination are orthogonal to each other. The eigenstate of the orthogonal basis of the polarization beam combiner 203 is consistent with the orthogonal polarization state of the two sub-output light pulses during polarization beam combination.

Preferably, the polarization beam splitter 201, the phase decoder 202, the polarization beam combiner 203, and the discrete devices and waveguide devices used for guiding light are all polarization-maintaining devices to maintain the polarization state of the light pulse unchanged.

As shown in fig. 2, the phase decoding apparatus of the present embodiment includes two polarization beam combiners, but in practical applications, only one polarization beam combiner may be provided as needed.

A third embodiment of the present invention is a phase decoding apparatus, as shown in fig. 3, which specifically includes the following components: a polarization beam splitter 301, two

phase decoders

302 and 303, and two

polarization beam combiners

304 and 305.

The polarization beam splitter 301 polarizes and splits one input optical pulse into two transmitted optical pulses. One path of transmission light pulse is subjected to phase decoding by a phase decoder 302 to obtain two paths of sub-output light pulses; the other path of transmission light pulse is subjected to phase decoding by the phase decoder 303 to obtain the other two paths of sub-output light pulses. One path of sub-output optical pulse of the phase decoder 302 and one path of sub-output optical pulse of the phase decoder 303 are combined into one path of output through a polarization beam combiner 304; the other path of sub-output optical pulses of the phase decoder 302 and the other path of sub-output optical pulses of the phase decoder 303 are combined into one path of output by the polarization beam combiner 305. The two sub-output light pulses arrive synchronously at

polarization combiners

304 and 305, respectively. The phase decoder 302 and the phase decoder 303 modulate the phases in unison. In the phase decoding device, the polarization beam splitter, the polarization beam combiner and devices on a light path between the polarization beam splitter and the polarization beam combiner are all polarization control type devices.

A fourth embodiment of the present invention provides a phase decoding apparatus, as shown in fig. 4, which specifically includes the following components: an optical circulator 401, a polarization beam splitter 402, two

phase decoders

403 and 404, and a polarization beam combiner 405.

The optical pulses are input through a first port a of the optical circulator 401 and output through a second port B of the optical circulator 401 to the polarization beam splitter 402. The polarization beam splitter 402 polarizes and splits one input optical pulse into two transmitted optical pulses. One path of transmission light pulse is subjected to phase decoding through a phase decoder 403 to obtain two paths of sub-output light pulses; the other path of transmission light pulse is subjected to phase decoding by the phase decoder 404 to obtain the other two paths of sub-output light pulses.

Phase decoders

403 and 404 use an unequal arm michelson interference loop, with the input and output ports of the two phase decoders being identical. One path of sub-output optical pulses of the phase decoder 403 and one path of sub-output optical pulses of the phase decoder 404 are combined into one path by the polarization beam splitter 402 and output to the second port B of the optical circulator 401, and output by the third port C of the optical circulator 401; the other path of sub-output optical pulses of the phase decoder 403 and the other path of sub-output optical pulses of the phase decoder 404 are combined into one path of output by the polarization beam combiner 405. The two sub-output light pulses arrive synchronously at the polarization beam splitter 402 and the polarization beam combiner 405, respectively. The phase decoder 403 and the phase decoder 404 have the same modulated phase. In the phase decoding device, the polarization beam splitter, the polarization beam combiner and devices on a light path between the polarization beam splitter and the polarization beam combiner are all polarization control type devices.

In a fifth embodiment of the present invention, an unequal arm mach-zehnder interference ring, as shown in fig. 5, specifically includes the following components: two 2 x 2

3dB splitters

503 and 506, a delay line 504, and a phase modulator 505.

One of two

ports

501 and 502 on one side of a 3dB splitter 503 serves as an input terminal of a phase encoder, one of two

ports

507 and 508 on the other side of the 3dB splitter 506 serves as an output terminal of the phase encoder, and a delay line 504 and a phase modulator 505 are respectively inserted into two arms of a mach-zehnder interference ring. During operation, light pulses enter the beam splitter 503 through the

port

501 or 502 of the beam splitter 503 and are transmitted in two paths, one path is delayed through the delay line 504, the other path is subjected to phase modulation through the phase modulator 505, and the relatively delayed light pulses transmitted on the two light paths are combined into one path of light pulse through the beam splitter 506 and output through the

port

507 or 508. When the delay line 504 and the phase modulator 505 are located on the same arm of the mach-zehnder interferometer ring, the results are not affected. In the unequal arm Mach-Zehnder interference ring, the 3dB beam splitter, the delay line, the phase modulator and devices on a light path between the two 3dB beam splitters are all polarization control devices or polarization maintaining devices.

In a sixth embodiment of the present invention, an unequal-arm michelson interference ring, as shown in fig. 6, specifically includes the following components: a 2 x 2 3dB splitter 603, two

mirrors

605 and 607, a phase modulator 606, and a delay line 604.

Two

ports

601 and 602 on one side of the 3dB splitter 603 are respectively used as an input end and an output end of the phase encoder, one of the two ports on the other side of the 3dB splitter 603 is sequentially connected to the delay line 604 and the mirror 605, and the other port on the same side is sequentially connected to the phase modulator 606 and the mirror 607. During operation, light pulses enter the beam splitter 603 through the port 601 of the beam splitter 603 and are split into two paths of light pulses for transmission, one path of light pulses is delayed by the delay line 604 and is reflected by the mirror 605, the other path of light pulses is subjected to phase modulation by the phase modulator 606 and is reflected by the mirror 607, and the reflected light pulses transmitted on the two light paths are combined into one path of light pulses through the beam splitter 603 and are output through the port 602. When the delay line 604 and the phase modulator 606 are connected in series at the same port, the above result is not affected. The optical pulse is input from port 602, output from port 601, and the result is the same when the

port

601 or 602 is simultaneously input and output. In the unequal-arm Michelson interference ring, the 3dB beam splitter, the delay line, the reflecting mirror, the phase modulator and devices on a light path between the 3dB beam splitter and the two reflecting mirrors are all polarization control type devices or polarization maintaining type devices.

In a seventh embodiment of the present invention, an unequal-arm faraday-michelson interference ring, as shown in fig. 7, specifically includes the following components: a 2 x 2 3dB splitter 703, two 90 degree rotating faraday mirrors 705 and 707, a delay line 704, and a phase modulator 706.

Two

ports

701 and 702 on one side of the 3dB splitter 703 are respectively used as an input end and an output end of the phase encoder, one of the two ports on the other side of the 3dB splitter 703 is sequentially connected to a delay line 704 and a 90-degree rotating faraday mirror 705, and the other port on the same side is sequentially connected to a phase modulator 706 and a 90-degree rotating faraday mirror 707. During operation, optical pulses enter the beam splitter 703 through the port 701 of the beam splitter 703 and are transmitted in two paths, one path is delayed by the delay line 704 and reflected by the 90-degree rotating faraday mirror 705, the other path is phase-modulated by the phase modulator 706 and then reflected by the 90-degree rotating faraday mirror 707, and the reflected optical pulses transmitted on the two optical paths are combined into one path through the beam splitter 703 and output through the port 702. When the phase modulator 704 and the delay line 706 are connected in series at the same port, the above result is not affected. The optical pulse is input from port 702, output from port 701 and the result is the same when the

port

701 or 702 is input and output simultaneously.

An eighth embodiment of the present invention provides a quantum key distribution system, as shown in fig. 8, which specifically includes the following components: a single photon source 801, a phase encoder 802, a quantum channel 803, two

single photon detectors

805 and 806, and a phase decoding apparatus 804 as described above.

A single photon source 801 for generating single photon light pulses.

And a phase encoder 802 for phase encoding the single photon light pulses generated by the single photon source 801.

And a quantum channel 803 for transmitting single photon optical pulses.

A phase decoding device 804 for performing phase decoding on the single-photon optical pulse transmitted through the quantum channel 803 according to a quantum key distribution protocol;

and the single-

photon detectors

805 and 806 are configured to detect the single-photon optical pulse output by the phase decoding device 804, and perform quantum key distribution according to a detection result and a quantum key distribution protocol.

The single photon source 801 emits a single photon light pulse to enter the phase encoder 802, the phase encoder 802 performs phase encoding on the single photon light pulse, the light pulse after the phase encoding is transmitted to the phase decoding device 804 through the quantum channel 803, the phase decoding device 804 performs phase decoding on the incident single photon pulse, and the light pulse output by the phase decoding device 804 is sent to the single photon detector 805 or the single photon detector 806. The phase encoder 802 and the phase decoder 804 respectively perform phase encoding and decoding on the optical pulses according to a quantum key distribution protocol, and perform key distribution according to the quantum key distribution protocol.

Specifically, the phase encoder 802 employs any one of the following: unequal arm Mach-Zehnder interference rings, unequal arm Michelson interference rings, unequal arm Faraday-Michelson interference rings, and the phase decoding device described above.

The quantum channel 803 may be an optical waveguide, an optical fiber, free space, a discrete optical element, a planar waveguide optical element, a fiber optical element, or a light propagation channel combining any two or more of the above.

The phase decoding method, the phase decoding device and the quantum key distribution system introduced in the embodiment of the invention polarize and split an incident path of input optical pulse into a first path of transmission optical pulse and a second path of transmission optical pulse, respectively perform phase decoding on the two paths of transmission optical pulses, obtain two paths of sub-output optical pulses after the phase decoding of each path of transmission optical pulse, polarize and combine any path of sub-output optical pulse after the phase decoding of the first path of transmission optical pulse and any path of sub-output optical pulse after the phase decoding of the second path of transmission optical pulse into one path of output optical pulse. The phase decoding is to split one path of transmission light pulse into two paths of sub-transmission light pulses and to combine the split two paths of sub-transmission light pulses into two paths of sub-output light pulses. And controlling the polarization state of the optical pulse, so that the polarization states of two paths of sub-transmission optical pulses before two paths of sub-output optical pulses are combined into a beam are the same, and the polarization states of the two paths of sub-output optical pulses are orthogonal to each other during polarization beam combination. Generally, when an optical pulse is transmitted through an optical fiber quantum channel, the polarization state of the optical pulse transmitted to a receiving end is randomly changed due to environmental influence, and the working stability of a quantum secret communication system is influenced. The invention can effectively solve the influence of the random change of the polarization state of the input optical pulse on the stability of the system and realize the stable phase decoding of the interference immunity of the transmission optical fiber environment. In addition, the invention has no restriction on the type of the interference ring adopted by the phase decoder, and can be suitable for the most common unequal arm Mach-Zehnder interference ring, so that the optical pulse only needs to pass through the phase modulator once during decoding, the insertion loss of a receiving end is greatly reduced, and the system efficiency is remarkably improved. The invention provides a technical scheme of a stable and efficient quantum key distribution system with low insertion loss. The method is simple and easy to realize.

While the invention has been described in connection with specific embodiments thereof, it is to be understood that it is intended by the appended drawings and description that the invention may be embodied in other specific forms without departing from the spirit or scope of the invention.

Claims

1. A method of phase decoding, the method comprising:

any path of sub output optical pulse after the phase decoding of the first path of transmission optical pulse and any path of sub output optical pulse after the phase decoding of the second path of transmission optical pulse are polarized and combined into one path of output optical pulse;

the method further comprises the following steps:

in the process from polarization beam splitting to polarization beam combining, the polarization state of the light pulse is controlled so that the polarization states of the two paths of sub-output light pulses are orthogonal to each other during the polarization beam combining; the controlling the polarization state of the light pulse comprises:

2. The phase decoding method according to claim 1, wherein the phase decoding the first path of transmission optical pulse and the second path of transmission optical pulse respectively includes:

3. A phase decoding apparatus, characterized in that the apparatus comprises: a polarization beam splitter, two phase decoders, and one or two polarization beam combiners;

the polarization beam combiner is used for polarization beam combining of any path of sub output optical pulse after the phase decoding of the first path of transmission optical pulse and any path of sub output optical pulse after the phase decoding of the second path of transmission optical pulse into one path of output optical pulse;

4. The phase decoding device according to claim 3, wherein the phase decoder is specifically configured to:

5. The phase decoding device according to claim 3, wherein the polarization beam splitter, the phase decoder, the polarization beam combiner, and the discrete devices and waveguide devices used for the guided light are all polarization-controlled devices to control the polarization state of the light pulse, so that the polarization states of the two sub-transmission light pulses before being combined into the two sub-output light pulses are the same.

6. The phase decoding device according to any one of claims 3 to 5, wherein the polarization beam splitter, the phase decoder, the polarization beam combiner, and the discrete devices and waveguide devices for guiding light are polarization-maintaining type devices to maintain the polarization state of the light pulse unchanged.

7. Phase decoding arrangement according to claim 3, characterized in that the phases modulated by the two phase decoders coincide.

8. The phase decoding arrangement of claim 3, wherein the two phase decoders employ either unequal arm Mach-Zehnder interferometer rings or unequal arm Michelson interferometer rings.

9. The phase decoding apparatus of claim 8, wherein when the two phase decoders use an unequal-arm michelson interference loop and the input port and the output port of the unequal-arm michelson interference loop are the same port, the polarization beam combiner and the polarization beam splitter are the same device, and when the apparatus further comprises: an optical circulator;

10. A quantum key distribution system, comprising: a single photon source, a phase encoder, a quantum channel, a single photon detector and a phase decoding apparatus as claimed in any one of claims 3 to 9;

the single photon source is used for generating single photon light pulses;

the quantum channel is used for transmitting single photon light pulse;

11. A quantum key distribution system according to claim 10, wherein the phase encoder employs any one of: an unequal arm Mach-Zehnder interference ring, an unequal arm Michelson interference ring, an unequal arm Faraday-Michelson interference ring, or a phase decoding device according to any one of claims 3 to 9.