CN112887083B - Phase encoding method, phase encoding device, and quantum key distribution system - Google Patents
Phase encoding method, phase encoding device, and quantum key distribution system Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
- H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
- H04L9/0852—Quantum cryptography
- H04L9/0858—Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/548—Phase or frequency modulation
- H04B10/556—Digital modulation, e.g. differential phase shift keying [DPSK] or frequency shift keying [FSK]
- H04B10/5561—Digital phase modulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
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Abstract
A phase encoding method, apparatus and quantum key distribution system, the method comprising: splitting an incident input optical pulse into two transmission sub-optical pulses transmitted through a first sub-optical path and a second sub-optical path; after the relative delay of the two paths of transmission sub-optical pulses, the two paths of transmission sub-optical pulses are combined into two paths of output optical pulses output through two output ports by using a beam combiner; randomly selecting one output light pulse or the other output light pulse of the two paths of output light pulses by using an optical switch for outputting; and randomly performing one of two kinds of phase modulation on at least one transmission sub-optical pulse of the two transmission sub-optical pulses or at least one output sub-optical pulse of the output optical pulses output by the optical switch by using a phase modulator. The method can realize four kinds of phase modulation, and the phase modulator driving circuit only needs to generate quarter wave voltage output, thereby reducing the output voltage requirement of the phase modulator driving circuit and being easy to realize high-speed phase modulation.
Description
Technical Field
The present invention relates to the field of optical transmission secret communication technology, and in particular, to a phase encoding method, a phase encoding device, and a quantum key distribution system using two-phase modulation.
Background
Quantum secret communication technology is the leading-edge hotspot field combining quantum physics and information science. Based on the quantum key distribution technology and the one-time secret code principle, the quantum secret communication can realize the safe transmission of information in a public channel. The quantum key distribution is based on the physical principles of quantum mechanics Hessenberg uncertainty relation, quantum unclonable theorem and the like, can safely share the key among users, can detect potential eavesdropping behaviors, and can be applied to the fields of national defense, government affairs, finance, electric power and the like with high safety requirements.
Currently, the coding scheme of quantum key distribution mainly adopts polarization coding and phase coding. Compared with polarization coding, phase coding adopts the phase difference of front and rear light pulses to code information, and can be stably maintained in the long-distance optical fiber channel transmission process. The actual quantum key distribution system mainly adopts the BB84 protocol or the evolved BB84 protocol, four different phases (such as 0 degree, 90 degrees, 180 degrees and 270 degrees) are required to be randomly generated by phase encoding, and generally, four different voltages are generated by a digital-to-analog converter (DAC) to drive an electro-optic phase modulator to encode corresponding four phase values.
However, there remains a need to provide a high-speed quantum key distribution system that can reduce the output voltage of a phase modulator drive circuit.
Disclosure of Invention
To achieve at least one of the above objects, the present invention provides a phase encoding method and apparatus and a corresponding quantum key distribution system as follows.
In one aspect, the present invention provides a phase encoding method, which is characterized in that the method includes:
Splitting an incident input optical pulse into two transmission sub-optical pulses transmitted through a first sub-optical path and a second sub-optical path;
After the two paths of transmission sub-optical pulses are relatively delayed, the two paths of transmission sub-optical pulses are combined into two paths of output optical pulses output through two output ports by using a beam combiner, and each path of output optical pulse in the two paths of output optical pulses is a pair of front-back adjacent output sub-optical pulses;
Receiving the two paths of output light pulses by using an optical switch and randomly selecting one path of output light pulse or the other path of output light pulse of the two paths of output light pulses to output;
During the transmission of two transmission sub-optical pulses via the first sub-optical path and the second sub-optical path after beam splitting or after the optical switch, one of two phase modulations is randomly performed on at least one transmission sub-optical pulse of the two transmission sub-optical pulses or on at least one output sub-optical pulse of the output optical pulses output by the optical switch by using a phase modulator, and the phases modulated by the two phase modulations are ninety degrees different.
Advantageously, in the above-mentioned phase encoding method, at least one output optical pulse of the two output optical pulses is randomly selected to output, and then four kinds of phase modulation can be finally achieved by two phase modulation modes, and the phase modulator only needs to modulate quarter wave voltage output, so that the output voltage of the phase modulator driving circuit can be reduced.
Preferably, the step of randomly performing one of two kinds of phase modulation on at least one of the two transmission sub-optical pulses or at least one of the output sub-optical pulses output by the optical switch by using a phase modulator includes:
And randomly carrying out 0-degree or 90-degree phase modulation on the at least one transmission sub-optical pulse or the at least one output sub-optical pulse.
Preferably, when the phase modulator uses 0 degree phase modulation, one output optical pulse output by the optical switch is 0 degree phase code, and the other output optical pulse output by the optical switch is 180 degree phase code; or alternatively
When the phase modulator uses 90-degree phase modulation, the one output optical pulse output by the optical switch is 90-degree phase code, and the other output optical pulse output by the optical switch is 270-degree phase code.
Preferably, the method further comprises: and controlling the polarization states of the light pulses in the beam splitting and beam combining processes so that the polarization states of the two paths of output light pulses are the same.
Preferably, the controlling the polarization state of the light pulse in the beam splitting and combining process includes:
and a polarization maintaining device is adopted in the beam splitting and combining process, so that the polarization state of the light pulse is kept unchanged in the beam splitting and combining process.
In another aspect, the present invention provides a phase encoding apparatus, comprising: beam splitters, beam combiners, optical switches and phase modulators, wherein,
The beam splitter is configured to split an incident one-way input light pulse into two-way transmission sub-light pulses transmitted via a first sub-light path and a second sub-light path;
the beam combiner is configured to combine the two transmission sub-optical pulses into two output optical pulses output through two output ports after the two transmission sub-optical pulses are relatively delayed, wherein each output optical pulse in the two output optical pulses is a pair of output sub-optical pulses adjacent to each other in front and back;
the optical switch is configured to receive the two output optical pulses and randomly select one output optical pulse or the other output optical pulse of the two output optical pulses to output;
The phase modulator is arranged on at least one sub-optical path of the first sub-optical path and the second sub-optical path behind the beam splitter or on an optical path connected with an output port of the optical switch, and is configured to transmit sub-optical pulses to at least one of the two transmission sub-optical pulses or randomly perform one of two kinds of phase modulation on at least one output sub-optical pulse of the output optical pulses output by the optical switch, and the phases modulated by the two kinds of phase modulation are ninety degrees different.
Preferably, the phase modulator is further configured to randomly perform 0 degree or 90 degree phase modulation on at least one of the at least one transmission sub-optical pulse or the output sub-optical pulse output by the optical switch.
Preferably, when the phase modulator uses 0 degree phase modulation, one output optical pulse output by the optical switch is a pair of front and rear adjacent output sub-optical pulses of 0 degree phase coding, and the other output optical pulse output by the optical switch is a pair of front and rear adjacent output sub-optical pulses of 180 degree phase coding; or alternatively
When the phase modulator uses 90-degree phase modulation, the one output optical pulse output by the optical switch is a pair of output sub-optical pulses adjacent to each other in front of and behind the 90-degree phase code, and the other output optical pulse output by the optical switch is a pair of output sub-optical pulses adjacent to each other in front of and behind the 270-degree phase code.
Preferably, the beam splitter, the beam combiner and the devices in the beam splitting and beam combining related optical paths are polarization maintaining optical devices.
Preferably, the phase encoding device adopts an optical path structure of an unequal arm Mach-Zehnder interferometer or an unequal arm Michelson interferometer.
Preferably, when the phase encoding device adopts an optical path structure of the unequal arm michelson interferometer, the beam splitter and the beam combiner are the same device, the beam splitter has a first input port, a second input port, a first output port and a second output port, and the phase encoding device further includes: an optical circulator and two mirrors, wherein,
The two reflectors are respectively arranged on two sub-optical paths of the beam splitter, which are connected with the first output port and the second output port, and are configured to respectively reflect the two transmission sub-optical pulses transmitted on the two sub-optical paths back to the beam splitter;
the first input port of the beam splitter is configured to receive the incident one-way input light pulse, and the optical circulator is configured to be positioned on an optical path of the beam splitter that is connected to the first input port; the optical circulator has a first port, a second port, and a third port, and an optical pulse input from the first port is output to the beam splitter via the second port of the optical circulator; the optical pulse output from the beam splitter to the second port of the optical circulator is output to one of the two input ports of the optical switch via the third port of the optical circulator, and the optical pulse output from the second input port of the beam splitter is transmitted to the other of the two input ports of the optical switch.
In yet another aspect, the present invention further provides a quantum key distribution system, which is characterized in that the quantum key distribution system includes the phase encoding device described in any one of the above.
By adopting the technical scheme, the phase encoding device and the quantum key distribution system have at least the following advantages:
Four kinds of phase modulation of 0 degree, 90 degree, 180 degree and 270 degree can be easily realized by randomly performing one of two kinds of phase modulation on at least one of the two transmission sub-optical pulses or on at least one of the two output optical pulses by using a phase modulator and randomly selecting any one of the two output optical pulses of the beam combiner or the other output optical pulse by using an optical switch. However, the driving circuit of the phase modulator only needs to generate quarter wave voltage output, so that the output voltage of the driving circuit of the phase modulator is reduced. In addition, compared with the method that four phases are generated directly through four voltage modulation phase modulators, the scheme only needs to modulate two levels of voltage, is easy to realize high-speed phase modulation, and provides a simple and easy-to-implement implementation scheme of a phase encoding device and a high-speed quantum key distribution system.
Drawings
FIG. 1 is a flow chart of a phase encoding method according to a preferred embodiment of the present invention;
FIG. 2 is a schematic diagram showing the construction of a phase encoding device according to a preferred embodiment of the present invention;
Fig. 3 is a schematic diagram showing the constitution of a phase encoding apparatus according to another preferred embodiment of the present invention;
fig. 4 is a schematic diagram showing the constitution of a phase encoding apparatus according to still another preferred embodiment of the present invention.
Detailed Description
Preferred embodiments of the present application are described in detail below with reference to the attached drawing figures, which form a part of the present disclosure and are used in conjunction with embodiments of the present application to illustrate the principles of the present application. For the purposes of clarity and simplicity, detailed descriptions of well-known functions and configurations incorporated herein by reference will sometimes be omitted so as not to obscure the present application.
Preferred embodiments of the present application are described in detail below with reference to the attached drawing figures, which form a part of the present disclosure and are used in conjunction with embodiments of the present application to illustrate the principles of the present application. For the purposes of clarity and simplicity, detailed descriptions of well-known functions and configurations incorporated herein by reference will sometimes be omitted so as not to obscure the present application.
Fig. 1 is a flow chart of a phase encoding method according to a preferred embodiment of the present invention.
The phase encoding method may be a phase encoding method using two high-speed phase modulations for a quantum key distribution system. Specifically, as shown in fig. 1, the phase encoding method may include the steps of:
S101: splitting an incident input optical pulse into two transmission sub-optical pulses transmitted through a first sub-optical path and a second sub-optical path;
S102: after the two paths of transmission sub-optical pulses are relatively delayed, the two paths of transmission sub-optical pulses are combined into two paths of output optical pulses output through two output ports by using a beam combiner, and each path of output optical pulse in the two paths of output optical pulses is a pair of front-back adjacent output sub-optical pulses;
S103: receiving the two paths of output light pulses by using an optical switch and randomly selecting one path of output light pulse or the other path of output light pulse of the two paths of output light pulses to output; and
S104: during the transmission of two transmission sub-optical pulses via the first sub-optical path and the second sub-optical path after beam splitting or after the optical switch, one of two phase modulations is randomly performed on at least one transmission sub-optical pulse of the two transmission sub-optical pulses or on at least one output sub-optical pulse of the output optical pulses output by the optical switch by using a phase modulator, and the phases modulated by the two phase modulations are ninety degrees different.
The execution sequence of the above-described method of the present application is not limited to the sequence or number shown in the drawings, but the execution sequence of the steps should be understood according to actual circumstances. For example, for step S104 in the above method, the step of performing phase modulation by using two phase modulation methods may be performed on at least one of the two transmission sub-optical pulses after beam splitting, or may be performed after beam combining, so the execution sequence of each step should be arranged according to the practical application. The application related to the method of the present application is not limited by the order in which the steps of the method are performed.
In addition, for simplicity, only the case where the phase modulator is disposed after the beam splitter is shown in the drawings, and the case where the phase modulator is disposed after the optical switch is not shown. Those skilled in the art will appreciate after reading this disclosure that the example of a phase encoder disposed after a beam splitter applies equally to the case of a phase modulator disposed after the optical switch.
Preferably, the one input light pulse may be polarized light having one phase. The beam splitter may then split the incoming one input light pulse by 50: the 50-beam splitting is performed by two transmission sub-optical pulses transmitted on two transmission sub-optical paths. In transmitting the two transmission sub-optical pulses, one transmission sub-optical pulse of the two transmission sub-optical pulses can be delayed relatively to the other transmission sub-optical pulse. Because the two paths of transmission sub-optical pulses have relative delay, the beam combiner is used for combining the two paths of transmission sub-optical pulses and outputting any path of output optical pulse to the optical switch, wherein the two paths of output optical pulses are two sub-optical pulses which are arranged in front of and behind each other in time, namely a pair of output sub-optical pulses which are adjacent in front of and behind each other.
Preferably, during transmission of two transmission sub-optical pulses after beam splitting or after the optical switch, a phase modulator is used to randomly perform one of two phase modulations on at least one transmission sub-optical pulse of the two transmission sub-optical pulses or on at least one output sub-optical pulse of a pair of output sub-optical pulses output by the optical switch, where the two phase modulations are ninety degrees out of phase. The phase modulation may include: and randomly carrying out 0-degree or 90-degree phase modulation on at least one output sub-optical pulse of the at least one transmission sub-optical pulse or the output optical pulse output by the optical switch. Or as long as the phases modulated by the two phase modulations differ by ninety degrees, two phase modulations of other different phase degrees can be randomly adopted for at least one of the transmission sub-optical pulses or the output sub-optical pulses outputted by the optical switch, for example, 90-degree or 180-degree phase modulations can be randomly carried out, or 180-degree or 270-degree phase modulations can be randomly carried out, which can be combined with the optical switch to realize that the quantum key distribution system finally obtains four phase coded optical pulses.
For example, by randomly performing phase modulation of 0 degrees or 90 degrees as described above using a phase modulator and randomly selecting one output light pulse or the other output light pulse of the two output light pulses to output using an optical switch, the quantum key distribution system can be made to obtain four kinds of phase-encoded output light pulses of 0 degrees, 90 degrees, 180 degrees, 270 degrees. The specific phase modulation procedure may be described below in connection with the phase encoding means. The phase encoding process described herein may refer to modulating the relative phase between two transmitted sub-optical pulses or modulating the relative phase between a pair of output sub-optical pulses. In addition, with respect to the four phase-encoded output light pulses of 0 degrees, 90 degrees, 180 degrees, and 270 degrees obtained last, the phase encoding may refer to a relative phase difference between a pair of output sub-light pulses adjacent to each other in front of and behind each other (or a pair of output sub-light pulses before and after each other).
In a preferred embodiment, when the phase modulator uses 0 degree phase modulation, one output light pulse outputted by the optical switch is a pair of output sub-light pulses adjacent to each other in front of and behind the 0 degree phase code, and the other output light pulse outputted by the optical switch is a pair of output sub-light pulses adjacent to each other in front of and behind the 180 degree phase code; or alternatively
When the phase modulator uses 90-degree phase modulation, the one output optical pulse output by the optical switch is a pair of output sub-optical pulses adjacent to each other in front of and behind the 90-degree phase code, and the other output optical pulse output by the optical switch is a pair of output sub-optical pulses adjacent to each other in front of and behind the 270-degree phase code.
With respect to the pair of output sub-optical pulses of the four phase encodings of 0 degrees, 90 degrees, 180 degrees, and 270 degrees obtained last, the four phase encodings of 0 degrees, 90 degrees, 180 degrees, and 270 degrees may refer to that the relative phase difference between the pair of output sub-optical pulses adjacent one after the other (or the pair of output sub-optical pulses before and after one after the other) in one output optical pulse is 0 degrees, 90 degrees, 180 degrees, or 270 degrees, respectively. For example, the pair of front and rear adjacent sub-optical pulses are phase-coded by 0 degrees, which may mean that the phase difference between the pair of front and rear adjacent sub-optical pulses is 0 degrees; the pair of front and rear adjacent sub-optical pulses are 180-degree phase encoded, which may mean that a phase difference between the pair of front and rear adjacent sub-optical pulses is 180 degrees. Similarly, the pair of front and rear adjacent sub-pulses of light are 90 degree phase encoded, which may mean that the phase difference between the pair of front and rear adjacent sub-pulses of light is 90 degrees; the pair of front and rear adjacent sub-optical pulses are 270-degree phase encoded, which may mean that a phase difference between the pair of front and rear adjacent sub-optical pulses is 270 degrees.
Preferably, the polarization states of the light pulses in the beam splitting and combining processes are controlled, so that the polarization states of the two transmission sub-light pulses transmitted by the first sub-light path and the second sub-light path are the same when the beam is combined into a pair of output sub-light pulses adjacent to each other.
Preferably, the controlling the polarization state of the light pulse in the beam splitting and combining process includes:
And adopting a polarization maintaining device in the beam splitting and combining process, and keeping the polarization states of the two paths of transmission sub-light pulses unchanged in the beam splitting and combining process.
Fig. 2 is a schematic diagram showing the constitution of a phase encoding apparatus according to a preferred embodiment of the present invention.
As shown in fig. 2, the phase encoding device may include the following components: a beam splitter 201, a phase modulator 202, a beam combiner 203, and an optical switch 204.
The beam splitter 201 may have an input port for receiving input pulses. The beam splitter 201 may be configured to split an incident one of the input light pulses into two transmitted sub-light pulses transmitted via the first sub-light path and the second sub-light path. The beam combiner 203 may be configured to combine the two transmission sub-optical pulses into two output optical pulses output via two output ports after the two transmission sub-optical pulses are relatively delayed, where each of the two output optical pulses is a pair of output sub-optical pulses that are adjacent to each other. The optical switch 204 may be configured to receive the two output optical pulses and randomly select one of the two output optical pulses or the other output optical pulse for output.
The phase modulator 202 may be disposed on either one of the first sub-optical path and the second sub-optical path after the beam splitter, or after the optical switch 204, the phase modulator 202 may be configured to randomly perform one of two phase modulations on at least one of the two transmission sub-optical pulses or at least one of the output sub-optical pulses output by the optical switch 204, the two phase modulations being ninety degrees out of phase.
In one embodiment, as shown in fig. 2, a phase modulator may be disposed on the first sub-optical path after splitting to randomly perform phase modulation, and delay the sub-optical pulse transmitted thereon on the second sub-optical path. Or a phase modulator can be arranged on the second sub-optical path after beam splitting to randomly perform phase modulation, and the sub-optical pulse transmitted on the first sub-optical path is delayed.
Alternatively, the phase encoding device may employ the structure of an unequal arm mach-zehnder interferometer (as shown in fig. 3) or an unequal arm michelson interferometer (as shown in fig. 4).
The terms "beam splitter" and "beam combiner" are used interchangeably herein, and a beam splitter may also be referred to as and function as a beam combiner, and vice versa. When the phase encoding device adopts a structure of an unequal arm michelson interferometer or an unequal arm faraday-michelson interferometer, the beam splitter and the beam combiner may be the same component.
Preferably, the phase modulator 202 may be further configured to randomly perform 0-degree or 90-degree phase modulation on at least one of the at least one transmitted sub-optical pulse or the output sub-optical pulse output by the optical switch 204.
Preferably, the phase encoding device may further comprise a laser connectable to the one of the input ports of the beam splitter for receiving input pulses.
In one embodiment, when the phase modulator uses 0 degree phase modulation, one output light pulse output by the optical switch is a pair of output sub-light pulses adjacent to each other before and after the 0 degree phase encoding, and the other output light pulse output by the optical switch is a pair of output sub-light pulses adjacent to each other before and after the 180 degree phase encoding.
Additionally or alternatively, when the phase modulator uses 90 degree phase modulation, the one output optical pulse output by the optical switch is a pair of output sub-optical pulses adjacent to each other in front of and behind the 90 degree phase code, and the other output optical pulse output by the optical switch is a pair of output sub-optical pulses adjacent to each other in front of and behind the 270 degree phase code.
Advantageously, in order to maintain the polarization state of the input light pulse unchanged during beam splitting and beam combining, the beam splitter 201, the beam combiner 203, and the devices used during beam splitting and beam combining may all employ polarization maintaining devices.
In some embodiments, the phase encoding device may employ an optical path structure of an unequal arm mach-zehnder interferometer or an unequal arm michelson interferometer.
Fig. 3 is a schematic diagram showing the constitution of a phase encoding apparatus according to a preferred embodiment of the present invention.
As shown in fig. 3, the phase encoding device is an unequal arm mach-zehnder interferometer structure, and specifically includes the following components: a beam splitter 303, a phase modulator 304, a beam combiner 305, and an optical switch 306. Preferably, beam splitter 303 is a polarization maintaining beam splitter and beam combiner 305 is a polarization maintaining beam combiner.
The splitter 303 may have a first input port 301 and a second input port 302. However, in this embodiment, the beam splitter need only receive one laser generated input light pulse received through one of the two input ports, and need not receive an incident input light pulse through the other input port.
The beam splitter 303 splits one input optical pulse incident via the one input port for receiving input pulses into two transmission sub-optical pulses. One path of transmission sub-optical pulse is modulated by the phase modulator 304 for 0 degree or 90 degrees, the other path of transmission sub-optical pulse is transmitted by the polarization maintaining optical fiber, and the two paths of transmission sub-optical pulses are combined into two paths of output optical pulses output through the first output port and the second output port by the beam combiner 305 after being delayed relatively. The phase modulator 304 may be inserted into either of the two arms of the mach-zehnder interferometer, i.e., any transmission sub-optical path after the beam splitter.
For example, when the phase modulator 304 modulates 0 degrees, one output optical pulse outputted through the first output port after beam combination by the beam combiner is a pair of output sub-pulses adjacent to each other before and after 0 degrees phase encoding, and the other output optical pulse outputted through the second output port is a pair of output sub-pulses adjacent to each other before and after 180 degrees phase encoding. Or when the phase modulator 304 modulates 90 degrees, one path of output light pulse output by the beam combiner through the first output port after beam combination is a pair of output sub-pulses adjacent to each other in front and behind the 90-degree phase coding, and the other path of output light pulse output by the second output port is a pair of output sub-pulses adjacent to each other in front and behind the 270-degree phase coding. Thereby, four phase-coded light pulses as required by the quantum key distribution protocol can be realized.
It will be appreciated that the beam splitter or combiner device itself may cause a 90 degree relative phase change between the sub-optical pulses after the beam splitting or combining process, i.e. a 90 degree relative phase change between the transmitted and coupled transmitted sub-optical pulses.
For example, when the phase modulator 304 modulates 0 degree and receives one input optical pulse incident through the port 301, the one input optical pulse is split by the beam splitter 303 to the first transmission sub-optical path above (transmission), and the optical pulse transmitted by the first transmission sub-optical path is split by the beam splitter 305 and then is assumed to be transmitted to the input port above the optical switch 306 (transmission), the phase of the output first sub-optical pulse is not changed during the splitting and the combining; however, if the one input optical pulse is split by the beam splitter 303 to the second transmission sub-optical path below (coupling transmission), and the optical pulse transmitted by the second transmission sub-optical path is supposed to be transmitted to the input port below the optical switch 306 after being split by the beam splitter 305 (coupling transmission), the phase of the output second sub-optical pulse is changed by 180 degrees during the beam splitting and beam combining (the phase is changed by 90 degrees during the beam splitting and beam combining), so that the front and rear adjacent pair of output sub-optical pulses in the one output optical pulse output by selecting the input port above the optical switch 306 is 180-degree phase encoded.
Similarly, according to the above calculation method, it can be deduced that when the phase modulator 304 modulates 90 degrees and receives an incident one of the input optical pulses through the port 301, a pair of output sub-optical pulses in one of the output optical pulses output by selecting the input port above the phase modulator through the optical switch 306 may undergo phase changes of 0 degrees and 270 degrees, respectively, so as to implement a pair of output sub-optical pulses adjacent to each other before and after 270 degrees of phase encoding.
Similarly, according to the above calculation method, it can also be deduced that when the phase modulator 304 modulates 0 degrees and receives an incident one of the input optical pulses through the port 301, a pair of sub-optical pulses in another one of the output optical pulses output by selecting the input port below the phase modulator through the optical switch 306 can undergo 90-degree and 90-degree phase changes, respectively, so as to implement a pair of output sub-optical pulses adjacent to each other before and after 0-degree phase encoding.
Similarly, according to the above calculation method, it can also be deduced that when the phase modulator 304 modulates 90 degrees and receives an incident one of the input optical pulses through the port 301, a pair of sub-optical pulses in another one of the output optical pulses output by selecting the input port below the phase modulator through the optical switch 306 can undergo 90-degree and 180-degree phase changes, respectively, so as to implement a pair of output sub-optical pulses adjacent to each other before and after 90-degree phase encoding.
Fig. 4 is a schematic diagram showing the constitution of a phase encoding apparatus according to still another preferred embodiment of the present invention.
As shown in fig. 4, the phase encoding device adopts an unequal arm michelson interferometer structure, and specifically comprises the following components: optical circulator 403, beam splitter 405, phase modulator 407, optical switch 409, and mirrors 406 and 408. In this embodiment, the beam splitter and beam combiner are the same device. The beam splitter 405 functions as both a beam splitter and a beam combiner, and is preferably a polarization maintaining device.
Two mirrors 406 and 408 are respectively disposed on two sub-optical paths of the beam splitter 405 connected to the first output port and the second output port, and are configured to reflect the two transmitted sub-optical pulses transmitted on the two sub-optical paths back to the beam splitter 405, respectively. A phase modulator 407 is placed on one of the two sub-paths after the beam splitter 405 or is inserted into either of the two arms of the michelson interferometer.
The first input port 401 of the beam splitter 405 is arranged to receive the incoming one input light pulse and the optical circulator 403 is arranged in the beam splitter 405 on an optical path connected to the first input port 401. The optical circulator 403 has a first port a, a second port B, and a third port C. The optical pulse input from the first port a is output to the beam splitter 405 via the second port B of the optical circulator 403; the optical pulse output from the beam splitter 405 to the second port B of the optical circulator 403 is output to one of the two input ports of the optical switch 409 via the third port C of the optical circulator 403, and the optical pulse output from the second input port of the beam splitter 405 is transmitted to the other of the two input ports of the optical switch 409.
Referring to fig. 4, a first input port 401 on the side of the beam splitter 405 is used as both an input and an output of the beam splitter; the second input port 402 on the same side is in fact used as only one of the two outputs of the splitter, not as an input. The two ports on the other side of the beam splitter 405 are connected with mirrors 406, 408, respectively. In operation, the first input port 401 is connected to a laser which, when illuminated, produces an input light pulse that is incident on the beam splitter 405.
The beam splitter 405 splits one input optical pulse into two transmission sub-optical pulses, one transmission sub-optical pulse is reflected by the reflecting mirror 406 after being relatively delayed, and the other transmission sub-optical pulse is reflected by the reflecting mirror 408 after being randomly subjected to phase modulation of 0 or 90 degrees by the phase modulator 407. Thus, the two reflected transmitted sub-pulses with a relative delay are combined into two output light pulses by the beam splitter 405 (which acts as a beam combiner at this time), and each output light pulse is a pair of output sub-light pulses adjacent to each other. The combined output optical pulse is input to the second port B of the optical circulator 403 and then transmitted to an input port of the optical switch 409 via the third port C of the optical circulator. The other output optical pulse after beam combination is directly transmitted to the other input port of the optical switch 409.
The two mirrors 406 and 408 may be quarter wave plate mirrors or 90 degree rotating faraday mirrors.
In another aspect, the present invention also provides a quantum key distribution system, which may include a phase encoding apparatus according to any one of the above.
According to the phase encoding method and the phase encoding apparatus of the above embodiments of the present invention described with reference to the drawings, four kinds of phase modulation of 0 degrees, 90 degrees, 180 degrees, 270 degrees can be easily achieved by randomly performing one of two kinds of phase modulation on at least one of the two transmission sub-optical pulses or on at least one of the two output optical pulses using a phase modulator and randomly selecting any one of the two output optical pulses of the beam combiner or the other output optical pulse to output using an optical switch. By the mode, the driving circuit of the phase modulator only needs to generate quarter wave voltage output, so that the output voltage of the driving circuit of the phase modulator is reduced, the edge of a faster phase modulation signal can be realized, and the implementation scheme of a simple and feasible high-speed phase encoding method and a quantum key distribution system is provided.
The technical means and technical effects adopted by the present invention to achieve the intended purpose should be more deeply and specifically understood by the description of the specific embodiments. In addition, the drawings are provided for reference and illustration only and are not intended to limit the invention.
Although the exemplary embodiments have been described in detail, the foregoing description is illustrative and not restrictive in all aspects. It should be understood that numerous other modifications and variations could be devised without departing from the scope of the exemplary embodiments, which fall within the scope of the invention. Accordingly, the scope of the invention should be assessed as that of the appended claims.
Claims (12)
1. A method of phase encoding, the method comprising:
Splitting an incident input optical pulse into two transmission sub-optical pulses transmitted through a first sub-optical path and a second sub-optical path;
After the two paths of transmission sub-optical pulses are relatively delayed, the two paths of transmission sub-optical pulses are combined into two paths of output optical pulses output through two output ports by using a beam combiner, and each path of output optical pulse in the two paths of output optical pulses is a pair of front-back adjacent output sub-optical pulses;
Receiving the two paths of output light pulses by using an optical switch and randomly selecting one path of output light pulse or the other path of output light pulse of the two paths of output light pulses to output;
During the period of transmitting two paths of transmission sub-optical pulses through a first sub-optical path and a second sub-optical path after beam splitting or randomly carrying out one of two kinds of phase modulation on at least one output sub-optical pulse in output optical pulses output by the optical switch, wherein the phases of the two kinds of phase modulation are ninety degrees different; and
Based on the selection of the optical switch and two phase modulations of the phase modulator, which differ by ninety degrees, four phase modulated output optical pulses are obtained.
2. The phase encoding method according to claim 1, wherein one of two kinds of phase modulation is randomly performed using the phase modulator, comprising:
and randomly carrying out 0-degree or 90-degree phase modulation on at least one output sub-optical pulse of the at least one transmission sub-optical pulse or the output optical pulse output by the optical switch.
3. The phase encoding method according to claim 1 or 2, characterized in that,
When the phase modulator uses 0-degree phase modulation, one path of output light pulse output by the optical switch is a pair of front and back adjacent output sub-light pulses with 0-degree phase encoding, and the other path of output light pulse output by the optical switch is a pair of front and back adjacent output sub-light pulses with 180-degree phase encoding; or alternatively
When the phase modulator uses 90-degree phase modulation, the one output optical pulse output by the optical switch is a pair of output sub-optical pulses adjacent to each other in front of and behind the 90-degree phase code, and the other output optical pulse output by the optical switch is a pair of output sub-optical pulses adjacent to each other in front of and behind the 270-degree phase code.
4. The phase encoding method according to claim 1, characterized in that the method further comprises: and controlling the polarization states of the light pulses in the beam splitting and beam combining processes, so that the polarization states of the two transmission sub-light pulses transmitted by the first sub-light path and the second sub-light path are the same when the beam is combined into two output light pulses.
5. The phase encoding method according to claim 4, wherein controlling the polarization state of the light pulses during beam splitting and combining comprises:
and a polarization maintaining device is adopted in the beam splitting and combining process, so that the polarization state of the light pulse is kept unchanged in the beam splitting and combining process.
6. A phase encoding apparatus, the apparatus comprising: beam splitters, beam combiners, optical switches and phase modulators, wherein,
The beam splitter is configured to split an incident one-way input light pulse into two-way transmission sub-light pulses transmitted via a first sub-light path and a second sub-light path;
the beam combiner is configured to combine the two transmission sub-optical pulses into two output optical pulses output through two output ports after the two transmission sub-optical pulses are relatively delayed, wherein each output optical pulse in the two output optical pulses is a pair of output sub-optical pulses adjacent to each other in front and back;
the optical switch is configured to receive the two output optical pulses and randomly select one output optical pulse or the other output optical pulse of the two output optical pulses to output;
The phase modulator is arranged on at least one sub-optical path of the first sub-optical path and the second sub-optical path behind the beam splitter or on an optical path connected with an output port of the optical switch, and is configured to randomly perform one of two kinds of phase modulation on at least one output sub-optical pulse of the output optical pulses output by the optical switch, wherein the phases of the two kinds of phase modulation are ninety degrees different; and
Based on the selection of the optical switch and the two phase modulations of the phase modulator that differ by ninety degrees, the phase encoding means is configured to obtain four phase modulated output optical pulses.
7. The phase encoding device of claim 6, wherein the phase modulator is further configured to randomly phase modulate at least one of the at least one transmitted sub-optical pulse or the output sub-optical pulse output by the optical switch by 0 degrees or 90 degrees.
8. The phase encoding apparatus according to claim 6 or 7, wherein when the phase modulator uses 0 degree phase modulation, one output light pulse outputted from the optical switch is a pair of output sub-light pulses adjacent to each other in front of and behind the 0 degree phase encoding, and the other output light pulse outputted from the optical switch is a pair of output sub-light pulses adjacent to each other in front of and behind the 180 degree phase encoding; or alternatively
When the phase modulator uses 90-degree phase modulation, one output light pulse output by the optical switch is a pair of output sub-light pulses adjacent to each other in front of and behind the 90-degree phase code, and the other output light pulse output by the optical switch is a pair of output sub-light pulses adjacent to each other in front of and behind the 270-degree phase code.
9. The phase encoding apparatus according to claim 6, wherein the beam splitter, the beam combiner, and devices in the optical path of the split and combined beams are polarization maintaining optical devices.
10. The phase encoding apparatus according to claim 6, wherein the phase encoding apparatus employs an optical path structure of an unequal arm mach-zehnder interferometer or an unequal arm michelson interferometer.
11. The phase encoding apparatus according to claim 10, wherein the beam splitter and the beam combiner are the same device when the phase encoding apparatus adopts an optical path structure of an unequal arm michelson interferometer, the beam splitter having a first input port, a second input port, a first output port, and a second output port, the phase encoding apparatus further comprising: an optical circulator and two mirrors, wherein,
The two reflectors are respectively arranged on two sub-optical paths of the beam splitter, which are connected with the first output port and the second output port, and are configured to respectively reflect the two transmission sub-optical pulses transmitted on the two sub-optical paths back to the beam splitter;
the first input port of the beam splitter is configured to receive the incident one-way input light pulse, and the optical circulator is configured to be positioned on an optical path of the beam splitter that is connected to the first input port; the optical circulator has a first port, a second port, and a third port, and an optical pulse input from the first port is output to the beam splitter via the second port of the optical circulator; the optical pulse output from the beam splitter to the second port of the optical circulator is output to one of the two input ports of the optical switch via the third port of the optical circulator, and the optical pulse output from the second input port of the beam splitter is transmitted to the other of the two input ports of the optical switch.
12. A quantum key distribution system comprising a phase encoding device according to any one of claims 6-11.
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