WO2020182059A1

WO2020182059A1 - Quantum key distribution phase encoder/decoder, corresponding encoding/decoding device and system

Info

Publication number: WO2020182059A1
Application number: PCT/CN2020/078060
Authority: WO
Inventors: 许华醒
Original assignee: 中国电子科技集团公司电子科学研究院
Priority date: 2019-03-08
Filing date: 2020-03-05
Publication date: 2020-09-17
Also published as: CN110460384B; CN110460384A

Abstract

Provided in the present invention are a quantum key distribution phase encoder/decoder and a corresponding encoding/decoding device and system. The phase encoder/decoder comprises: a beam splitter, and two polarization orthogonal rotation reflection devices optically coupled with the beam splitter through two arms respectively, wherein either or each of the two reflection devices comprises a polarization beam splitter having an input port and two output ports, and is coupled to a corresponding arm via the input port, and the two output ports of each polarization beam splitter are coupled through a transmission optical path, which is formed by twisting a polarization-maintaining fiber 90 degrees, and at least one reflection device comprising a polarization beam splitter is provided with a phase modulator on its transmission optical path. According to the present invention, encoding/decoding interference can be stably carried out on input light pulses in any polarization state, solving the problem that a system cannot stably work due to polarization induced fading in phase encoding and time bit-phase encoding quantum key distribution application, and at the same time reducing the loss at the interferometer.

Description

Quantum key distribution phase codec, corresponding codec device and system

Technical field

The present invention relates to the technical field of optical transmission secure communication, in particular to a quantum key distribution phase codec based on polarization orthogonal rotating reflection, a corresponding codec device and a quantum key distribution system including the phase codec.

Background technique

Quantum secure communication technology is a frontier hotspot in the combination of quantum physics and information science. Based on quantum key distribution technology and the principle of one-time encryption, quantum secure communication can realize the secure transmission of information in public channels. Quantum key distribution is based on the Heisenberg uncertainty relationship of quantum mechanics, quantum unclonability theorem and other physical principles. It can realize the secure sharing of keys between users, and can detect potential eavesdropping behaviors. It can be applied to national defense, government affairs, and Finance, electric power and other high security information transmission fields.

Terrestrial quantum key distribution is mainly based on fiber channel transmission. Because the phase encoding uses the phase difference between the front and rear optical pulses to encode information, it can be stably maintained during long-distance fiber channel transmission, so it is based on the phase encoding and time bit of the unequal arm interferometer -Phase encoding is the main encoding scheme for quantum key distribution applications. However, fiber production has non-ideal conditions such as non-circular symmetry of the cross-section and uneven distribution of the core refractive index along the radial direction. In addition, the fiber is affected by temperature, strain, and bending in the actual environment, which will produce random birefringence effects. Therefore, after the optical pulse is transmitted through the long-distance fiber and the two-arm fiber of the unequal-arm interferometer, there is a problem of polarization-induced fading when the phase-decoding interference is performed through the unequal-arm interferometer, which leads to unstable decoding interference and bit error rate. Elevated. If the correction equipment is used, it will increase the complexity and cost of the system, and it is difficult to achieve stable applications for strong interference situations such as overhead optical cables and road bridge optical cables.

In the prior art, a unequal-arm Faraday-Michelson interferometer is proposed, which can make the optical pulse be affected by the random birefringence of the fiber channel and the polarization state change caused by it, while still maintaining a stable output of the interference result. However, this kind of interferometer has a large loss, and the insertion loss of the phase modulator is one of the main factors causing the large loss. Specifically, when the phase modulator is placed on one arm of the interferometer, the light pulse will pass through the phase modulator twice due to the back and forth transmission, which causes the interferometer to have a large loss and the system efficiency is low.

For quantum key distribution phase encoding and time bit-phase encoding schemes, how to perform interference decoding stably and efficiently is a hot spot and difficult problem for quantum secure communication applications based on existing optical cable infrastructure.

Summary of the invention

The main purpose of the present invention is to propose a quantum key distribution phase codec based on polarization orthogonal rotating reflection, a corresponding codec device including the phase codec, and a quantum key distribution system to solve phase coding and time bit -The problem of instability of phase decoding interference caused by polarization-induced fading in phase encoding quantum key distribution applications, while reducing the loss at the interferometer.

The present invention provides at least the following technical solutions:

1. A quantum key distribution phase codec, comprising: a beam splitter, and two reflection devices optically coupled to the beam splitter via two arms, wherein each of the reflection devices is polarization orthogonal rotation A reflection device, one or each of the two reflection devices includes a polarization beam splitter having an input port and two output ports, and is coupled to the two through the input port of the polarization beam splitter The two output ports of each polarization beam splitter are optically coupled to each other via a transmission optical path, and at least one reflection device including a polarization beam splitter is provided with a phase modulator on its transmission optical path. A reflection device including a polarization beam splitter: the transmission light path is formed by a polarization-maintaining fiber twisted by 90 degrees, so that the optical pulses output by the two output ports are coupled to the slow axis of the polarization-maintaining fiber for transmission or uniformity. It is coupled to the fast axis of the polarization maintaining fiber for transmission.

2. The phase codec according to claim 1, wherein the two reflecting devices are polarization orthogonal rotating reflecting devices of the same structure, or polarization orthogonal rotating reflecting devices of different structures.

3. The phase codec according to claim 1, wherein the 90-degree twisted polarization-maintaining fiber comprises a 90-degree twisted or (90+n*180)-degree twisted polarization-maintaining fiber, where n is an integer.

4. The phase codec according to scheme 1, wherein the beam splitter is a polarization maintaining beam splitter.

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

6. A DC modulation quantum key distribution phase codec device, comprising a pre-splitter and two phase codecs according to any one of schemes 1-5, the two phase codecs are respectively Two sub-optical paths are optically coupled to the front beam splitter, wherein one of the ports of the beam splitter of each phase codec that is not coupled to the two arms of the phase codec is optically coupled to all In the corresponding sub-optical paths of the two sub-optical paths, each of the sub-optical paths is provided with an optical circulator, wherein the phase modulator is a DC phase modulator.

7. A quantum key distribution time bit-phase codec device, comprising a pre-splitter and a phase codec according to any one of the schemes 1-5, the phase codec passing through a sub-optical path Optically coupled to the pre-splitter, wherein one of the ports of the beam splitter of the phase codec that is not coupled to the two arms is optically coupled to the one sub-optical path.

8. A DC modulation quantum key distribution time bit-phase codec device, comprising a pre-splitter and a phase codec according to any one of the schemes 1-5, the phase codec is The sub-optical path is optically coupled to the pre-splitter, wherein one of the ports of the beam splitter of the phase codec that is not coupled to the two arms is optically coupled to the one sub-optical path, wherein the one An optical circulator is arranged on the sub-optical path, and the phase modulator is a DC phase modulator.

9. The coding and decoding device according to claim 7 or 8, further comprising a beam splitter coupled to the pre-splitter via another sub-optical path.

10. A quantum key distribution system, including:

The phase codec according to any one of the solutions 1 to 5 or the codec device according to any one of the solutions 6 to 9, which is arranged at the receiving end of the quantum key distribution system for decoding; and /or

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

Through the creative structure of the present invention, the input optical pulse of any polarization state can be stably coded and decoded, thereby achieving unexpected beneficial effects. With the solution of the present invention, stable interference output at the phase decoding interferometer can be realized for input optical pulses of any polarization state, which solves the problem of polarization-induced fading in the application of phase encoding and time bit-phase encoding quantum key distribution, which causes the system to be unstable The problem of work. In addition, since the phase modulator is placed in the reflection device of the interferometer, the optical pulse only needs to be transmitted through the phase modulator once, thereby reducing the loss at the interferometer. The present invention provides a highly effective anti-polarization-induced fading phase encoding and time bit-phase encoding quantum key distribution decoding scheme that is easy to implement and apply.

Description of the drawings

Fig. 1 is a schematic diagram of the composition structure of a quantum key distribution phase encoder and decoder based on polarization orthogonal rotating reflection according to a preferred embodiment of the present invention;

2 is a schematic diagram of the composition structure of a quantum key distribution phase codec based on polarization orthogonal rotating reflection according to another preferred embodiment of the present invention;

3 is a schematic diagram of the composition structure of a polarization orthogonal rotating reflection device that can be used in the phase codec of the present invention;

4 is a schematic diagram of the composition structure of another polarization orthogonal rotating reflection device that can be used in the phase codec of the present invention;

5 is a schematic diagram of the composition structure of another polarization orthogonal rotating reflection device that can be used in the phase codec of the present invention;

6 is a schematic diagram of the composition structure of a DC modulation quantum key distribution phase encoding and decoding device based on polarization orthogonal rotating reflection according to a preferred embodiment of the present invention;

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

FIG. 8 is a schematic diagram of the composition structure of a DC modulation quantum key distribution time bit-phase encoding and decoding device based on polarization orthogonal rotating reflection according to a preferred embodiment of the present invention.

detailed description

The preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings, wherein the accompanying drawings constitute a part of the application and are used together with the embodiments of the present invention to explain the principle of the present invention. For the purpose of clarity and simplification, when it may obscure the subject of the present invention, detailed descriptions of the known functions and structures of the devices described herein will be omitted.

The quantum key distribution phase codec based on polarization orthogonal rotating reflection according to a preferred embodiment of the present invention is shown in FIG. 1 and includes the following components: a beam splitter 101 and two

reflecting devices

102 and 103.

The two

reflecting devices

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

According to the present invention, the two

reflection devices

102 and 103 are both polarization orthogonal rotating reflection devices, and at least one of the two reflection devices includes a phase modulator.

Here, the polarization orthogonal rotating reflection device refers to a polarization orthogonal rotating reflection of the two orthogonal polarization states of the reflected light pulse, that is, when reflecting the incident light pulse, each of the light pulses is orthogonal A reflection device that transforms the polarization state into a polarization state orthogonal to it. For example, suppose that the two orthogonal polarization states are the x polarization state and the y polarization state, respectively. The x polarization state transmitted along the optical path to a polarization orthogonal rotating reflector is transformed into a polarization orthogonal rotating reflector at the reflector. The polarization state orthogonal to it is the y polarization state, and the y polarization state transmitted along the optical path to the reflection device is converted into the polarization state orthogonal to it, that is, the x polarization state after being reflected by the polarization orthogonal rotation at the reflection device.

Here, a polarization orthogonal rotating reflection device including a phase modulator may be referred to as a "polarization orthogonal rotating reflection device with a phase modulation function".

The beam splitter 101 is used for splitting an incident input optical pulse of any polarization state into two optical pulses for transmission along two arms respectively.

The two arms are used to respectively transmit the two optical pulses.

Each phase modulator is used to phase-modulate the light pulse passing through it in accordance with the quantum key distribution protocol. The phase modulation performed by the phase modulator is determined by the quantum key distribution protocol and depends on the specific application. For example, in one possible application, the phase modulator can randomly modulate a 0 degree phase or a 90 degree phase. In the case where each of the two reflecting

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 specific application.

The phase modulator can be a single polarization phase modulator or a birefringent phase modulator. The single polarization phase modulator applies phase modulation to one polarization state and cuts off the other polarization state. The birefringent phase modulator is adapted to apply different adjustable phase modulations to two orthogonal polarization states passing therethrough. For example, the birefringent phase modulator may be a lithium niobate phase modulator, and by controlling the voltage applied to the lithium niobate crystal, the phase modulation of the two orthogonal polarization states passing through the lithium niobate phase modulator can be modulated. Control and adjust.

The

reflection devices

102 and 103 are respectively used to reflect the two optical pulses transmitted from the beam splitter 101 via the two arms back to the beam splitter 101 to be combined and output by the beam splitter 101.

Since the two

reflection devices

102 and 103 are polarization orthogonal rotating reflection devices, for each of the two optical pulses: when the optical pulse is reflected by the corresponding reflection device of the two reflection devices, the The two orthogonal polarization states of the path light pulse are reflected by polarization orthogonal rotation, so that after reflection by the corresponding reflecting device, each orthogonal polarization state of the path light pulse is transformed into a polarization state orthogonal to it. In this way, for the phase codec in Figure 1, the polarization orthogonal rotating reflection at the polarization orthogonal rotating reflector is used, and the x-polarization state of the input optical pulse is passed through the beam splitter during the beam splitter to combine the beam splitter. The phase difference transmitted by the two arms is exactly equal to the phase difference transmitted by the two arms when the y-polarization state of the optical pulse is split by the beam splitter to combine the beam by the beam splitter.

The present invention proposes three creative polarization orthogonal rotating reflection device configurations, namely, the following configuration 1, configuration 2, and configuration 3.

According to configuration 1, the polarization orthogonal rotating reflection device includes a polarization beam splitter having an input port and two output ports, and the two output ports of the polarization beam splitter are optically coupled to each other via a transmission optical path, and the transmission A half-wave plate is arranged on the optical path, and the angle between the polarization direction of the light pulse input to the half-wave plate and the fast axis or the slow axis of the half-wave plate is 45 degrees. When the polarization orthogonal rotating reflection device with configuration 1 is used in the phase codec of the present invention, the reflection device can be coupled to all by coupling the input port of its polarization beam splitter to one arm of the phase codec. The arm.

According to configuration 2, the polarization orthogonal rotating reflection device includes a polarization beam splitter having an input port and two output ports, and the two output ports of the polarization beam splitter are optically coupled to each other via a transmission optical path, the The transmission light is formed by a polarization-maintaining fiber. The slow axis and the fast axis of the polarization-maintaining fiber respectively maintain the two orthogonal polarization states of the light pulse input to the polarization-maintaining fiber for stable transmission—that is, the polarization state does not change, and the polarization component The two output ports of the beamer and the polarization-maintaining fiber are 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 both are coupled to the polarization-maintaining fiber The fast axis of the optical fiber is used for transmission. Here, 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 both are coupled to the fast axis of the polarization-maintaining fiber for transmission. The polarization-maintaining fiber can be twisted by 90 degrees. Or it can be achieved by twisting (90+n*180) degrees, where n is an integer. Regardless of whether the polarization-maintaining fiber is twisted or not, the light pulse input from the slow axis of the polarization-maintaining fiber is always transmitted along the slow axis (steady transmission along the slow axis), and the light pulse input from the fast axis of the polarization-maintaining fiber is always along the fast axis. Axis transmission (steady transmission along the fast axis). When the polarization orthogonal rotating reflection device with configuration 2 is used in the phase codec of the present invention, the reflection device can be coupled to all by coupling the input port of its polarization beam splitter to one arm of the phase codec. The arm.

According to configuration 3, the polarization orthogonal rotating reflection device includes a polarization beam splitter having an input port and two output ports, and the two output ports of the polarization beam splitter are optically coupled to each other via a transmission optical path, the polarization beam splitter The transmission optical route is formed by polarization-maintaining fibers with an odd number of 90-degree fusion splices, and each 90-degree fusion splice is formed by aligning the slow axis of the polarization-maintaining fiber and the fast axis of the polarization-maintaining fiber. When the polarization orthogonal rotating reflection device with configuration 3 is used in the phase codec of the present invention, the reflection device can be coupled to all by coupling the input port of its polarization beam splitter to one arm of the phase codec. The arm.

For the polarization orthogonal rotating reflection device of any one of the above configuration 1, configuration 2 and configuration 3, a phase modulation can be inserted in the transmission optical path between the two output ports of the polarization beam splitter in the polarization orthogonal rotating reflection device Device.

Returning to the phase codec of FIG. 1, at least one of the

reflection devices

102 and 103 may be a polarization orthogonal rotating reflection device adopting one of the above-mentioned construction 1, construction 2, and construction 3. When one of the

reflection devices

102 and 103 is a polarization orthogonal rotating reflection device that uses one of the above-mentioned configuration 1, configuration 2 and configuration 3, the other reflection device may be the above-mentioned configuration 1, configuration 2 and configuration 3. One of the polarization orthogonal rotating reflection devices may also be a polarization orthogonal rotating reflection device of other structures. The polarization orthogonal rotating reflection device of the other configuration may be, for example, a quarter wave plate mirror. The "quarter wave plate mirror" includes a reflector and a quarter wave plate, the reflector being formed integrally with the quarter wave plate at the rear end of the quarter wave plate, wherein The angle between the polarization direction of the light pulse input to the quarter wave plate and the fast axis or the slow axis of the quarter wave plate is 45 degrees. The quarter wave plate reflector can be realized by coating a reflector on the crystal surface of the quarter wave plate, or by coating a reflector on the end face of a polarization maintaining fiber with a phase difference of 90 degrees in the fast and slow axis transmission.

When only one of the

reflection devices

102 and 103 is a polarization orthogonal rotating reflection device adopting one of the above-mentioned configuration 1, configuration 2, and configuration 3, the one reflection device includes a phase modulator. When the two reflection devices of the

reflection devices

102 and 103 each adopt the polarization orthogonal rotating reflection device of any one of the above-mentioned configuration 1, configuration 2 and configuration 3, one or both of the two reflection devices may include phase modulation Device.

For the phase codec of FIG. 1, one or two reflection devices selected from the configuration of configuration 1, configuration 2 and configuration 3 can be adopted by adjusting the length of the two arms and/or adjusting the two

reflection devices

102 and 103 The transmission optical path realizes the relative delay of the above two optical pulses.

In the case that the reflection device adopts a configuration selected from configuration 1, configuration 2, and configuration 3, the two arms of the phase codec can be configured as polarization maintaining optical paths, and the optical devices on the two arms can be configured as polarization Maintain optical devices and/or non-birefringent optical devices. In this way, for each of the two optical pulses obtained by splitting: the two orthogonal polarization states of the optical pulse can be kept unchanged during the splitting of the beam by the beam splitter to the reflection of the corresponding reflecting device, and at all The reflection of the corresponding reflecting device remains unchanged during the beam combining period of the beam splitter. Generally, the polarization maintaining optical path can be a free space optical path or a polarization maintaining fiber optical path. Herein, "non-birefringent optical device" refers to an optical device having the same refractive index for different polarization states (for example, two orthogonal polarization states). In addition, polarization maintaining optical devices can also be referred to as polarization maintaining optical devices.

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

A phase codec according to another preferred embodiment of the present invention is shown in Fig. 2 and includes the following components: a polarization-maintaining beam splitter 203, a polarization orthogonal rotating reflector 204, and a polarization orthogonal rotating reflector 205 (also below These are respectively referred to as reflecting device 204 and reflecting device 205).

One of the two

ports

201 and 202 on the side of the polarization-maintaining beam splitter 203 is used as the input port of the phase codec. The polarization-maintaining beam splitter 203 and the reflecting

devices

204 and 205 constitute a unequal-arm Michelson interferometer, and the two arms in between are the optical paths of the polarization-maintaining fiber. At least one of the reflection device 204 and the reflection device 205 includes a phase modulator. The

port

201 or 202 of the polarization-maintaining beam splitter 203 can be used as the output port of the phase codec.

During operation, the 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. One of the two optical pulses is transmitted to the reflecting device 204 via the polarization-maintaining fiber and reflected by the reflecting device 204, and the other optical pulse is transmitted to the reflecting device 205 via the polarization-maintaining fiber and is reflected by the reflecting device 205, and is reflected in the meantime. The phase modulator in the device 204 and/or 205 performs phase modulation according to the quantum key distribution protocol. The two optical pulses reflected back with a relatively delay are combined by the polarization-maintaining beam splitter 203 and output by the

port

201 or 202.

In the case where one of the input port and the output port of the polarization-maintaining beam splitter 203 is the same port, the phase codec may also include an optical circulator. The optical circulator may be located at the front end of the polarization maintaining beam splitter 203. An incident light pulse of any polarization state can be input from the first port of the optical circulator and output from the second port of the optical circulator to the polarization-maintaining beam splitter 203. The combined 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 shows a schematic diagram of the composition structure of a polarization orthogonal rotating reflection device with phase modulation function that can be used in the phase codec of the present invention.

The polarization orthogonal rotating 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.

The polarization beam splitter 302 includes three ports: port A, port B, and port C. Port A, port B, and port C may be called input ports, first output ports, and second output ports, respectively. One port 301 of the polarization beam splitter 302, namely port A, serves as an input port and an output port of the device. Port B and port C of the polarization beam splitter 302 are connected by a polarization maintaining fiber 303. The optical pulses output by the port B and the port C of the polarization beam splitter 302 are both coupled to the slow axis transmission of the polarization maintaining fiber 303 or both are coupled to the fast axis transmission of the polarization maintaining fiber. The phase modulator 304 is inserted into the optical path of the polarization maintaining fiber 303 connecting the port B and the port C of the polarization beam splitter 302.

In operation, the input optical pulse is input to the polarization beam splitter 302 through the port 301, that is, the port A of the polarization beam splitter 302. The input light pulse can be regarded as composed of two orthogonal polarization states, and the two orthogonal polarization states can be denoted as x polarization state and y polarization state respectively. The polarization beam splitter 302 polarizes and splits the input optical pulse into the first optical pulse of the x-polarization state and the second optical pulse of the y-polarization state to be output by the port B and the port C of the polarization beam splitter 302 respectively. The first optical pulse of the x-polarization state output from the port B of the polarization beam splitter 302 is coupled to the slow axis transmission of the polarization-maintaining fiber 303, and is input into the phase modulator 304 from the port D of the phase modulator 304 for phase modulation. The first optical pulse after phase modulation is output by port E of the phase modulator 304 and transmitted along the slow axis of the polarization-maintaining fiber 303 to port C of the polarization beam splitter 302. At port C, the first optical pulse is The slow axis of the polarization fiber 303 is coupled to the polarization beam splitter 302, and the polarization state of the first optical pulse coupled to port C of the polarization beam splitter 302 is the y polarization state; the first optical pulse of the y polarization state is split by the polarization. The port A of the beamer 302 is output. That is, the x-polarization component of the input optical pulse input by the port A is converted into the y-polarization state when it is output by the port A after being reflected by the reflecting device. The second optical pulse of the y-polarization state output from the port C of the polarization beam splitter 302 is coupled to the slow axis transmission of the polarization maintaining fiber 303, and is input into the phase modulator 304 from the port E of the phase modulator 304 for phase modulation. The second optical pulse after phase modulation is output by port D of the phase modulator 304 and transmitted along the slow axis of the polarization-maintaining fiber 303 to port B of the polarization beam splitter 302. At port B, the second optical pulse is The slow axis of the polarization fiber 303 is coupled to the polarization beam splitter 302, and the polarization state of the second optical pulse coupled to the port B of the polarization beam splitter 302 is the x polarization state; the second optical pulse of the x polarization state is split by the polarization The port A of the beamer 302 is output. That is, the y polarization state component of the input optical pulse input by the port A is converted into the x polarization state when output by the port A after being reflected by the reflecting device. The first optical pulse input to the phase modulator 304 from port D and the second optical pulse input to the phase modulator 304 from port E are input to the phase modulator 304 in the same polarization state and undergo the same phase modulation to achieve polarization-independent phase modulation. And when the two orthogonal polarization states of the input light pulse are reflected and output by the reflecting device, each orthogonal polarization state is transformed into a polarization state orthogonal to it. The polarization maintaining fiber 303 is used to perform polarization orthogonal rotation on the two orthogonal polarization states, so that the phase between the x polarization state and the y polarization state of the input optical pulse is between the y polarization state and the x polarization state of the output optical pulse. The phase remains the same.

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

Both port B and port C of the polarization beam splitter 302 can be coupled to the fast axis of the polarization maintaining fiber 303, and the above result is not affected at this time.

FIG. 4 shows a schematic diagram of the composition structure of another polarization orthogonal rotating reflection device with phase modulation function that can be used in the phase codec of the present invention.

The polarization orthogonal rotating 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 fusion splice 405.

The polarization beam splitter 402 includes three ports: port A, port B, and port C. Port A, port B, and port C may be called input ports, first output ports, and second output ports, respectively. One port 401 of the polarization beam splitter 402, namely port A, serves as an input port and an output port of the device. Port B and port C of the polarization beam splitter 402 are connected by a polarization maintaining fiber 403. The optical pulse output from the port B of the polarization beam splitter 402 is coupled to the slow axis of the polarization maintaining fiber 403 and the optical pulse output from the port C of the polarization beam splitter 402 is coupled to the fast axis of the polarization maintaining fiber 403, or is split by polarization. The optical pulse output from the port B of the beamer 402 is coupled to the fast axis of the polarization maintaining fiber 403 and the optical pulse output from the port C of the polarization beam splitter 402 is coupled to the slow axis of the polarization maintaining fiber 403. The polarization-maintaining fiber 403 includes a 90-degree fusion splice point 405, which is formed by aligning the slow axis of the polarization-maintaining fiber and the fast axis of the polarization-maintaining fiber. The phase modulator 404 is inserted into the optical path of the polarization maintaining fiber 403 connecting the port B and the port C of the polarization beam splitter 402.

In operation, the input optical pulse is input to the polarization beam splitter 402 through the port 401, that is, the port A of the polarization beam splitter 402. The input light pulse can be regarded as composed of two orthogonal polarization states, and the two orthogonal polarization states can be denoted as x polarization state and y polarization state respectively. The polarization beam splitter 402 polarizes and splits the input optical pulse into the first optical pulse of the x-polarization state and the second optical pulse of the y-polarization state to be output by the port B and the port C of the polarization beam splitter 402 respectively. The first optical pulse of the x-polarization state output from the port B of the polarization beam splitter 402 is coupled to the slow axis transmission of the polarization maintaining fiber 403, and is input into the phase modulator 404 from the port D of the phase modulator 404 for phase modulation. The first optical pulse after phase modulation is output from port E of the phase modulator 404 and transmitted along the slow axis of the polarization-maintaining fiber 403 to the 90-degree fusion splice point 405. Axis is transmitted to the port C of the polarization beam splitter 402. At port C, the first optical pulse is coupled to the polarization beam splitter 402 by the fast axis of the polarization maintaining fiber 403; the first optical pulse is coupled to the port C of the polarization beam splitter 402. The polarization state of the path optical pulse is the y polarization state, and the first path of the optical pulse in the y polarization state is output from the port A of the polarization beam splitter 402. That is, the x-polarization state component of the input optical pulse input by the port A is converted into the y-polarization state when it is output by the port A after being reflected by the device. The second optical pulse of the y-polarization state output by the port C of the polarization beam splitter 402 is coupled to the fast axis transmission of the polarization-maintaining fiber 403, and is transmitted along the fast axis of the polarization-maintaining fiber 403 to the 90-degree fusion splice point 405, passing through 90° After the degree fusion splice 405 is transmitted along the slow axis of the polarization-maintaining fiber 403 to the port E of the phase modulator 404, the port E of the phase modulator 404 is input to the phase modulator 404 for phase modulation. The second optical pulse after phase modulation is output from port D of the phase modulator 404 and transmitted along the slow axis of the polarization-maintaining fiber 403 to port B of the polarization beam splitter 402. At port B, the second optical pulse is The slow axis of the polarization fiber 403 is coupled to the polarization beam splitter 402; the polarization state of the second optical pulse coupled to the port B of the polarization beam splitter 402 is the x polarization state, and the second optical pulse of the x polarization state is split by the polarization. The port A of the beamer 402 is output. That is, the y polarization state component of the input optical pulse input by the port A is converted into the x polarization state when it is output by the port A after being reflected by the device.

The first optical pulse input to the phase modulator 404 from port D and the second optical pulse input to the phase modulator 404 from port E are input to the phase modulator 404 with the same polarization state and undergo the same phase modulation to achieve polarization-independent phase modulation. When the two orthogonal polarization states of the input light pulse are reflected and output by the reflecting device, each orthogonal polarization state is transformed into a polarization state orthogonal to it.

Although only one 90-degree fusion splice point 405 is shown in FIG. 4, this is only exemplary, and the polarization-maintaining optical fiber 403 may include any odd number of 90-degree fusion splice points. Each 90-degree fusion splice point is formed by aligning the slow axis of the polarization maintaining fiber and the fast axis of the polarization maintaining fiber. In the case that the polarization-maintaining fiber 403 contains more than one odd number of 90-degree fusion splices, the above results are not affected, only the first optical pulse and the second optical pulse output by the port B and port C of the polarization beam splitter 402 When each of the optical pulses is transmitted along the polarization-maintaining fiber 403, it is converted more times between transmission along the slow axis of the polarization-maintaining fiber and transmission along the fast axis of the polarization-maintaining fiber, and the number of conversions is equal to the number of 90-degree fusion splices.

The polarization-maintaining fiber 403 containing an odd number of 90-degree fusion splices is used to perform polarization orthogonal rotation on the two orthogonal polarization states, so that the phase between the x polarization state and the y polarization state of the input optical pulse is equal to the y of the output optical pulse. The phase between the polarization state and the x polarization state remains the same.

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

When the port B of the polarization beam splitter 402 is coupled to the fast axis of the polarization maintaining fiber 403 and the 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 sequence of the phase modulator 404 and the 90-degree welding point 405 are changed, and the above results are not affected.

FIG. 5 shows a schematic diagram of the composition structure of another polarization orthogonal rotating reflection device with phase modulation function that can be used in the phase codec of the present invention.

The polarization orthogonal rotating reflection device with phase modulation function shown in FIG. 5 includes the following components: a polarization beam splitter 502, a phase modulator 503, and a half-wave plate 504.

The polarization beam splitter 502 includes three ports: port A, port B, and port C. Port A, port B, and port C may be called input ports, first output ports, and second output ports, respectively. One port 501 of the polarization beam splitter 502, namely port A, serves as an input port and an output port of the device. Port B and port C of the polarization beam splitter 502 are connected through a transmission optical path; more specifically, the port B of the polarization beam splitter 502 is connected to the port D of the phase modulator 503 through the transmission optical path, and the port E of the phase modulator 503 is connected through the transmission optical path. The optical path is connected to the half-wave plate 504, and the half-wave plate 504 is connected to the port C of the polarization beam splitter 502 through the transmission optical path. Transmission optical path between port B of polarization beam splitter 502 and port D of phase modulator 503, transmission optical path between port E of phase modulator 503 and half-wave plate 504, half-wave plate 504 and polarization beam splitter 502 The transmission optical paths between the ports C are polarization maintaining optical paths, such as polarization maintaining optical fiber optical paths. The polarization direction of the polarization state of the light pulse input into the half-wave plate 504 from the ports on both sides of the half-wave plate 504 and the slow axis or the fast axis of the half-wave plate 504 include an angle of 45 degrees.

In operation, the input optical pulse is input to the polarization beam splitter 502 through the port 501, that is, the port A of the polarization beam splitter 502. The input light pulse can be regarded as composed of two orthogonal polarization states, and the two orthogonal polarization states can be denoted as x polarization state and y polarization state respectively. The polarization beam splitter 502 polarizes and splits the input optical pulse into the first optical pulse of the x-polarization state and the second optical pulse of the y-polarization state to be output by the port B and the port C of the polarization beam splitter 502 respectively. The first optical pulse of the x-polarization state output from the port B of the polarization beam splitter 502 is transmitted to the phase modulator 503, and the port D of the phase modulator 503 is input to the phase modulator 503 and undergoes phase modulation. The first optical pulse after phase modulation is output to the half-wave plate 504 from the port E of the phase modulator 503. After the first optical pulse is polarized orthogonally rotated by the half-wave plate 504, its polarization state is converted from the x polarization state to the y polarization state. The first optical pulse of the y polarization state output by the half-wave plate 504 is transmitted to the port C of the polarization beam splitter 502, and the port C of the polarization beam splitter 502 is input to the polarization beam splitter 502, and the polarization beam splitter 502 The port A output. In this way, the x-polarization state component of the input optical pulse input by the port A is converted into the y-polarization state when it is output by the port A after being reflected by the device. The second optical pulse of the y polarization state output from the port C of the polarization beam splitter 502 is transmitted to the half-wave plate 504, and the polarization state of the second optical pulse after the polarization orthogonal rotation by the half-wave plate 504 is converted into x polarization state. The second optical pulse of the x-polarization state output by the half-wave plate 504 is transmitted to the port E of the phase modulator 503, and the port E of the phase modulator 503 is input to the phase modulator 503 and undergoes phase modulation. The second optical pulse after phase modulation is output from port D of phase modulator 503 to port B of polarization beam splitter 502, and input to polarization beam splitter 502 from port B of polarization beam splitter 502, and is split by polarization The port A of the converter 502 is output. In this way, it is realized that the y polarization state component of the input optical pulse input by the port A is converted into the x polarization state when it is output by the port A after being reflected by the device. The half-wave plate 504 is used to perform polarization orthogonal rotation on the two orthogonal polarization states, 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 Keep it the same.

The first optical pulse input to the phase modulator 503 from port D and the second optical pulse input to the phase modulator 503 from port E are input to the phase modulator 503 in the same polarization state and undergo the same phase modulation to achieve polarization-independent phase modulation. When the two orthogonal polarization states of the input light pulse are reflected and output by the reflecting device, each orthogonal polarization state is transformed into a polarization state orthogonal to it.

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

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

The phase codec of the present invention can be used as a component of a DC modulation quantum key distribution phase codec device, can be used as a component of a quantum key distribution time bit-phase codec device, and can also be used as a DC modulation quantum key Key distribution time bit-a component of the phase codec device.

A DC modulation quantum key distribution phase codec device based on polarization orthogonal rotating reflection using the phase codec of the present invention is shown in FIG. 6, and includes the following components: pre-splitter 603, optical circulator 604 And 610, polarization-maintaining

beam splitters

605 and 611, and polarization orthogonal

rotating reflection devices

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

reflection devices

606, 607, 612, and 613, respectively).

The polarization-maintaining beam splitter 605, the two

reflection devices

606 and 607, and the two arms between the polarization-maintaining beam splitter 605 and the two reflection devices constitute the first polarization-maintaining unequal-arm Michelson interferometer, which is according to the present invention The first phase codec. The two arms of the first phase codec are polarization maintaining fiber optics. At least one of the

reflection devices

606 and 607 includes a DC phase modulator.

Similarly, the polarization-maintaining beam splitter 611, the two reflecting

devices

612 and 613, and the two arms between the polarization-maintaining beam splitter 611 and the two reflecting devices constitute a second polarization-maintaining unequal-arm Michelson interferometer, namely The second phase codec according to the present invention. The two arms of the second phase codec are polarization maintaining fiber optic paths. At least one of the

reflection devices

612 and 613 includes a DC phase modulator.

Hereinafter, the coding and decoding device in FIG. 6 is used for decoding as an example to describe it.

One of the two

ports

601 and 602 on the side of the pre-splitter 603 serves as the input port of the device. The first port A and the second port B of the optical circulator 604 are respectively connected to an output port of the pre-beam splitter 603 and an input port of the polarization-maintaining beam splitter 605. The optical pulse input to the first phase codec is decoded and then output by one output port 608 of the polarization-maintaining beam splitter 605, or through another output port of the polarization-maintaining beam splitter 605 (that is, all of the polarization-maintaining beam splitter 605). The one input port) is transmitted to the second port B of the optical circulator 604 and output from the third port C of the optical circulator 604. The first port A and the second port B of the optical circulator 610 are respectively connected to the other output port of the pre-beam splitter 603 and one input port of the polarization-maintaining beam splitter 611. The optical pulse input to the second phase codec is decoded and then output by one output port 614 of the polarization-maintaining beam splitter 611, or through another output port of the polarization-maintaining beam splitter 611 (that is, all of the polarization-maintaining beam splitter 611). The one input port) is transmitted to the second port B of the optical circulator 610 and output from the third port C of the optical circulator 610.

During operation, the optical pulse enters the beam splitter 603 through the

port

601 or 602 of the beam splitter 603 and is split by the beam splitter 603 into a first optical pulse and a second optical pulse. The first optical pulse is input through the first port A of the optical circulator 604 and output to the polarization-maintaining beam splitter 605 from the second port B of the optical circulator 604. The polarization maintaining beam splitter 605 splits the input first optical pulse into two first sub optical pulses. One first sub-light pulse is transmitted to the reflection device 606 via the polarization-maintaining fiber and reflected back by the reflection device 606, and the other first sub-light pulse is transmitted to the reflection device 607 via the polarization-maintaining fiber and is reflected back by the reflection device 607, during which the reflection device The DC phase modulator in 606 and/or 607 performs DC phase modulation according to the quantum key distribution protocol. The two first sub-light pulses that have been reflected back with relative delay are combined by the polarization-maintaining beam splitter 605 and output by port 608, or output to the second port B of the optical circulator 604 and transmitted to the optical circulator 604 The third port C is output by port 609. The second optical pulse is input through the first port A of the optical circulator 610 and output to the polarization maintaining beam splitter 611 through the second port B of the optical circulator 610. The polarization-maintaining beam splitter 611 splits the input second optical pulse into two second optical sub-pulses. One second sub-light pulse is transmitted to the reflection device 612 via the polarization-maintaining fiber and reflected back by the reflection device 612, and the other second sub-light pulse is transmitted to the reflection device 613 via the polarization-maintaining fiber and is reflected back by the reflection device 613, during which the reflection device The DC phase modulator in 612 and/or 613 performs DC phase modulation according to the quantum key distribution protocol. The two second sub-light pulses that have been reflected back with relatively delay are combined by the polarization-maintaining beam splitter 611 and then output by the port 614, or output to the second port B of the optical circulator 610 and transmitted to the optical circulator 610 The third port C is output by port 615. Wherein, the DC phase modulator in the reflection device 606 and/or 607 performs DC phase modulation according to the quantum key distribution protocol, and/or the DC phase modulator in the reflection device 612 and/or 613 performs DC phase modulation according to the quantum key distribution protocol The phase modulation causes the DC phase modulation of one of the first unequal-arm Michelson interferometer and the second unequal-arm Michelson interferometer to differ by 90 degrees from the other.

Next, the coding and decoding device of FIG. 6 is used for coding as an example to describe it.

One port 608 of the polarization maintaining beam splitter 605, the third port C of the optical circulator 604, one port 614 of the polarization maintaining beam splitter 611, and the third port C of the optical circulator 610 are used as input ports of the device. The first port A and the second port B of the optical circulator 604 are respectively connected to one port of the pre-beam splitter 603 and the other port of the polarization-maintaining beam splitter 605. The optical pulse input from the third port C of the optical circulator 604 is input to the first phase codec via the second port B of the optical circulator 604. The optical pulses input from the one port 608 of the polarization maintaining beam splitter 605 and the third port C of the optical circulator 604 are encoded by the first phase codec and output by the polarization maintaining beam splitter 605 to the optical circulator 604. The second port B is transmitted from the first port A of the optical circulator 604 to the pre-splitter 603. The first port A and the second port B of the optical circulator 610 are respectively connected to the other port of the pre-beam splitter 603 and the other port of the polarization-maintaining beam splitter 611. The optical pulse input from the third port C of the optical circulator 610 is input to the second phase codec via the second port B of the optical circulator 610. The optical pulses input from the one port 614 of the polarization-maintaining beam splitter 611 and the third port C of the optical circulator 610 are encoded by the second phase codec and output by the polarization-maintaining beam splitter 611 to the optical circulator 610. The second port B is transmitted from the first port A of the optical circulator 610 to the pre-splitter 603. One of the two

ports

601 and 602 on the side of the pre-splitter 603 (the left side in FIG. 6) is used as the output port of the device. Optical pulses input from the one port 608 of the polarization maintaining beam splitter 605, the third port C of the optical circulator 604, the one port 614 of the polarization maintaining beam splitter 611, and the third port C of the optical circulator 610 After encoding, four kinds of phase encoding are realized respectively, and the encoded optical pulses are combined by the beam splitter 603 and output by the

port

601 or 602.

A quantum key distribution time bit-phase codec device based on polarization orthogonal rotating reflection using the phase codec of the present invention is shown in Fig. 7, and includes the following components:

beam splitters

703 and 704, polarization maintaining splitters The beamer 707, and polarization orthogonal rotating reflection devices 708 and 709 (hereinafter also referred to as reflection device 708 and reflection device 709, respectively).

The polarization-maintaining beam splitter 707, the two

reflection devices

708 and 709, and the two arms between the polarization-maintaining beam splitter 707 and the two reflection devices constitute a polarization-maintaining unequal-arm Michelson interferometer, which is the phase according to the present invention. Codec. The two arms are polarization maintaining fiber optic paths. At least one of the

reflection devices

708 and 709 includes a phase modulator.

Hereinafter, the codec device of FIG. 7 is used for decoding as an example to describe it.

The beam splitter 703 serves as a front beam splitter, and one of the two

ports

701 and 702 on one side thereof is used as the input port of the device. The beam splitter 704 splits one optical pulse from the beam splitter 703 and outputs it through the

port

705 or 706. The optical pulse input to the PM unequal-arm Michelson interferometer is decoded and output from the port 710.

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

port

701 or 702 of the beam splitter 703, and is divided into two optical pulses for transmission by the beam splitter 703. One optical pulse from the beam splitter 703 is input to the beam splitter 704, and is split by the beam splitter 704 and then output through the

port

705 or 706 to realize time bit decoding. Another optical pulse from the beam splitter 703 is input to the polarization-maintaining beam splitter 707, and is split into two sub-light pulses by the polarization-maintaining beam splitter 707. One sub-light pulse is transmitted to the reflection device 708 through the polarization-maintaining fiber and reflected by the reflection device 708, and the other sub-light pulse is transmitted to the reflection device 709 through the polarization-maintaining fiber and is reflected back by the reflection device 709, during which the reflection device 708 and/or The phase modulator in 709 performs phase modulation in accordance with the quantum key distribution protocol. The two sub-light pulses reflected back with a relatively delay are combined by the polarization-maintaining beam splitter 707 and then output by the port 710.

Here, it should be noted that the beam splitter 704 is optional. It is possible for the pre-splitter 703 to directly output the above-mentioned optical pulse for time bit decoding.

Next, the coding and decoding apparatus of FIG. 7 is used for coding as an example to describe it.

The

ports

705 and 706 of the beam splitter 704 and the port 710 of the polarization maintaining beam splitter 707 serve as input ports of the device. The optical pulses input from the

ports

705 and 706 are combined by the beam splitter 704 and output to the pre-beam splitter 703 to realize time bit encoding. The optical pulse input from port 710 is encoded by the polarization-maintaining unequal-arm Michelson interferometer, and then output to the pre-beam splitter 703 by the polarization-maintaining beam splitter 707, during which it passes through the phase modulator in the modulating reflector 708 and/or 709 Realize two kinds of phase encoding. One of the

ports

701 and 702 of the pre-splitter 703 serves as the output port of the device. The beam splitter 703 combines the optical pulse output from the beam splitter 704 and the optical pulse output from the polarization-maintaining beam splitter 707, and then outputs the optical pulse through the

port

701 or 702.

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

A DC modulation quantum key distribution time bit-phase codec device based on polarization orthogonal rotating reflection using the phase codec of the present invention is shown in Fig. 8, and includes the following components:

beam splitters

803 and 804, optical ring The shaper 807, the polarization-maintaining beam splitter 808, and the polarization orthogonal rotating reflecting device 809 and the polarization orthogonal rotating reflecting device 810 (hereinafter also referred to as reflecting device 809 and reflecting device 810, respectively).

The polarization-maintaining beam splitter 808, the two

reflection devices

809 and 810, and the two arms between the polarization-maintaining beam splitter 808 and the two reflection devices constitute a polarization-maintaining unequal-arm Michelson interferometer, that is, the phase according to the present invention Codec. The two arms are polarization maintaining fiber optic paths. At least one of the

reflection devices

809 and 810 includes a DC phase modulator.

Hereinafter, the coding and decoding device of FIG. 8 is used for decoding as an example to describe it.

The beam splitter 803 serves as a front beam splitter, and one of the two

ports

801 and 802 on one side thereof serves as the input port of the device. The beam splitter 804 splits one optical pulse from the beam splitter 803 and outputs it through the

port

805 or 806. The optical pulse input from the first port A of the optical circulator 807 is output from the second port B of the optical circulator 807, and the optical pulse input from the second port B of the optical circulator 807 is output from the third port C of the optical circulator 807. Output. The optical pulse input to the unequal-arm Michelson interferometer is decoded and output by port 811, or it is transmitted to the second port B of the optical circulator 807 through another output port of the polarization-maintaining beam splitter 808 and from the optical circulator The third port C of 807 is output from port 812 after output.

In operation, the input optical pulse enters the beam splitter 803 through the

port

801 or 802 of the beam splitter 803, and is split into two optical pulses for transmission by the beam splitter 803. One optical pulse from the beam splitter 803 is input to the beam splitter 804, and is split by the beam splitter 804 and then output by the

port

805 or 806 for time bit decoding. Another optical pulse from the beam splitter 803 is input through the first port A of the optical circulator 807 and output from the second port B of the optical circulator 807 to the polarization-maintaining beam splitter 808. The polarization maintaining beam splitter 808 splits the other optical pulse into two sub optical pulses. One sub-light pulse is transmitted to the reflection device 809 via the polarization-maintaining fiber and reflected by the reflection device 809, and the other sub-light pulse is transmitted to the reflection device 810 via the polarization-maintaining fiber and is reflected by the reflection device 810, during which the reflection device 809 and/or The DC phase modulator in 810 performs DC phase modulation according to the quantum key distribution protocol. The reflected two relatively delayed sub-light pulses are combined by the polarization-maintaining beam splitter 808 and output by the port 811, or are transmitted to the second port B of the optical circulator 807 and are transmitted by the third port of the optical circulator 807 After C is output, it is output by port 812.

Here, it should be noted that the beam splitter 804 is optional. It is possible for the pre-splitter 803 to directly output the above-mentioned optical pulse for time bit decoding.

Next, the coding and decoding device of FIG. 8 is used for coding as an example to describe it.

The

ports

805 and 806 of the beam splitter 804, the port 811 of the polarization-maintaining beam splitter 808, and the third port C of the optical circulator 807 are used as input ports of the device. The optical pulse input from the third port C of the optical circulator 807 is output from the second port B of the optical circulator 807, and the optical pulse input from the second port B of the optical circulator 807 is output from the first port A of the optical circulator 807. Output. The optical pulses input from the

ports

805 and 806 are combined by the beam splitter 804 and output to the pre-beam splitter 803 to realize time bit encoding. The optical pulse input from the port 811 and the optical pulse input from the third port C of the optical circulator 807 and output from the second port B of the optical circulator 807 to the polarization-maintaining beam splitter 808 are passed through the polarization-maintaining unequal-arm Michelson After the interferometer is encoded, the polarization-maintaining beam splitter 808 outputs to the second port B of the optical circulator 807 and transmits to the pre-beam splitter 803 via the first port A of the optical circulator 807. The optical pulses input from the port 811 of the polarization-maintaining beam splitter 808 and the third port C of the optical circulator 807 are encoded to realize two kinds of phase encoding respectively. One of the

ports

801 and 802 of the beam splitter 803 serves as the output port of the device. The beam splitter 803 combines the optical pulses output from the beam splitter 804 and the optical pulses output from the first port A of the optical circulator 807 and then outputs them through the

port

801 or 802.

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

Herein, the terms "beam splitter" and "beam combiner" can be used interchangeably, and beam splitters can also be referred to and used as beam combiners, and vice versa. In this article, "polarization-maintaining fiber optical path" refers to the optical path that uses polarization-maintaining fiber to transmit light pulses or the optical path formed by polarization-maintaining fiber connection.

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

Through the description of the specific embodiments, it should be possible to have a more in-depth and specific understanding of the technical means and effects adopted by the present invention to achieve the intended purpose. However, the attached drawings are only for reference and explanation, and are not used to describe the present invention. limit.

Claims

A quantum key distribution phase codec, comprising: a beam splitter, and two reflection devices optically coupled to the beam splitter via two arms, wherein each of the reflection devices is a polarization orthogonal rotating reflection device At least one of the two reflecting devices includes a polarization beam splitter having an input port and two output ports, and is coupled to a corresponding one of the two arms through the input port of the polarization beam splitter, wherein The two output ports of each polarization beam splitter are optically coupled to each other via the transmission optical path, at least one reflection device including a polarization beam splitter is provided with a phase modulator on its transmission optical path, and for at least one reflection device including the polarization beam splitter Device: The transmission light is formed by a polarization-maintaining fiber twisted by 90 degrees, so that the optical pulses output by the two output ports are coupled to the same axis of the polarization-maintaining fiber for transmission.
The phase codec according to claim 1, wherein the two reflection devices are polarization orthogonal rotating reflection devices of the same structure.
The phase codec according to claim 1, wherein the two reflection devices are polarization orthogonal rotating reflection devices with different configurations.
The phase codec according to claim 1, wherein the same axis of the polarization maintaining fiber is a slow axis of the polarization maintaining fiber.
The phase codec according to claim 1, wherein the same axis of the polarization maintaining fiber is a fast axis of the polarization maintaining fiber.
The phase codec according to claim 1, wherein the polarization-maintaining fiber twisted by 90 degrees comprises a polarization-maintaining fiber twisted by (90+n*180) degrees, wherein n is an integer.
The phase codec according to claim 1, wherein the beam splitter is a polarization maintaining beam splitter.
The phase codec according to claim 1, wherein each of the two arms is a polarization maintaining optical path, and the optical devices on the two arms are polarization maintaining optical devices.
A quantum key distribution system includes:

The phase codec according to claim 1, which is arranged at the receiving end of the quantum key distribution system for decoding; or

The phase codec according to claim 1, which is arranged at the transmitting end of the quantum key distribution system for encoding.