CN112887084A - 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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- H04B10/548—Phase or frequency modulation
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Abstract
A phase encoding method, a phase encoding device and a quantum key distribution system are provided, wherein the phase encoding method comprises the following steps: randomly receiving a first path of incident input optical pulse or a second path of incident input optical pulse from any one of a first input port and a second input port of the beam splitter respectively; splitting the first path of input light pulse or the second path of input light pulse into two paths of transmission sub light pulses respectively; combining two paths of transmission sub-optical pulses into one path of output optical pulse after relative delay, wherein the one path of output optical pulse is a pair of output sub-optical pulses which are adjacent in front and back; and (3) using a phase modulator to randomly perform one of two phase modulations on at least one transmission sub optical pulse in the two transmission sub optical pulses or at least one output sub optical pulse in a pair of output sub optical pulses. The method can realize four phase codes of the output light pulse by using two phase modulations, reduces the requirement of the output voltage of the phase modulator driving circuit, and is easy to realize high-speed phase modulation.
Description
Technical Field
The invention relates to the technical field of optical transmission secret communication, in particular to a phase encoding method, a phase encoding device and a quantum key distribution system using two phase modulations.
Background
The quantum secret communication technology is a leading-edge hotspot field combining quantum physics and information science. Based on quantum key distribution technology and one-time pad cipher principle, quantum secret communication can realize the safe transmission of information in public channel. The quantum key distribution is based on the physical principles of quantum mechanics Heisebauer uncertain relation, quantum unclonable theorem and the like, the key can be safely shared among users, potential eavesdropping behavior can be detected, and the quantum key distribution method can be applied to the fields of high safety requirements such as national defense, government affairs, finance, electric power and the like.
At present, the encoding scheme of quantum key distribution mainly adopts polarization encoding and phase encoding. Compared with polarization coding, phase coding adopts the phase difference of front and back 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 a BB84 protocol or an evolved BB84 protocol, phase encoding requires four different phases (such as 0 degree, 90 degrees, 180 degrees and 270 degrees) to be randomly generated, and a general method is to generate four different voltages through a digital-to-analog converter (DAC) to drive an electro-optical phase modulator to encode corresponding four phase values, which is limited by an analog bandwidth of the DAC.
Disclosure of Invention
The invention provides a phase encoding method and device and a corresponding quantum key distribution system.
In one aspect, the present invention provides a phase encoding method, including:
randomly receiving a first path of incident input optical pulse or a second path of incident input optical pulse from any one of a first input port and a second input port of the beam splitter respectively;
splitting the first path of input light pulse or the second path of input light pulse into two paths of transmission sub light pulses transmitted through a first sub light path and a second sub light path respectively;
combining the two paths of transmission sub-optical pulses into one path of output optical pulse after the two paths of transmission sub-optical pulses are delayed relatively, wherein the one path of output optical pulse output by combining is a pair of output sub-optical pulses which are adjacent in the front and back;
during the two paths of transmission sub-optical pulses are transmitted through a first sub-optical path and a second sub-optical path after beam splitting, or after the two paths of transmission sub-optical pulses are combined into a pair of output sub-optical pulses which are adjacent in the front and back, a phase modulator is used for carrying out one phase modulation of two phase modulations on at least one path of transmission sub-optical pulse in the two paths of transmission sub-optical pulses or at least one output sub-optical pulse in the pair of output sub-optical pulses which are adjacent in the front and back, and the phase of the two phase modulations are different by ninety degrees.
Advantageously, in the phase encoding method, the optical pulse is randomly incident on one of the two input ports of the beam splitter, and then four kinds of phase encoding can be finally achieved through two phase modulation modes, and the phase modulator only needs to modulate the quarter-wave voltage output, so that the output voltage of the phase modulator driving circuit can be reduced, and the problem of realizing the phase modulation voltage of the faster signal edge in the phase encoding quantum key distribution system can be solved.
Preferably, the randomly performing one of two phase modulations on at least one of the two transmission sub-optical pulses or at least one of the two output sub-optical pulses of the front-back adjacent pair of output sub-optical pulses by using a phase modulator includes:
and randomly performing 0-degree or 90-degree phase modulation on at least one transmission sub optical pulse or at least one output sub optical pulse.
Preferably, the first input port and the second input port of the beam splitter are connected to the first laser and the second laser, respectively, and the beam splitter randomly receives the optical pulses generated by any one of the first laser and the second laser through the first input port or the second input port at any one time.
Preferably, when the phase modulator uses 0-degree phase modulation, a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the first input port of the first input port and the second input port is combined and output are 0-degree phase-coded, and a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the second input port of the first input port and the second input port is combined and output are 180-degree phase-coded; and/or
When the phase modulator uses 90-degree phase modulation, a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the first input port of the first input port and the second input port is output after the input optical pulse is combined is 90-degree phase-coded, and a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the second input port of the first input port and the second input port is output after the input optical pulse is combined is 270-degree phase-coded.
Preferably, the method further comprises: and controlling the polarization state of the light pulse in the beam splitting and combining processes to ensure that the polarization states of two paths of transmission sub light pulses transmitted by the first sub light path and the second sub light path are the same when the combined beam is a pair of front and back adjacent output sub light pulses.
Preferably, the controlling the polarization state of the light pulse in the beam splitting and combining process includes:
and a polarization maintaining optical device is adopted in the beam splitting and combining process, and the polarization states of the two paths of transmission sub optical pulses are kept unchanged in the beam splitting and combining process.
In another aspect, the present invention provides a phase encoding apparatus, including: a beam splitter, a beam combiner and a phase modulator, wherein,
the beam splitter has a first input port and a second input port, and is configured to randomly receive an incident first path of input optical pulses or a second path of input optical pulses from any one of the first input port and the second input port, respectively, and split each of the incident first path of input optical pulses or the second path of input optical pulses into two paths of transmission sub optical pulses transmitted via a first sub optical path and a second sub optical path;
the beam combiner is configured to combine the two paths of transmission sub-optical pulses into one path of output optical pulse output through one output port after the two paths of transmission sub-optical pulses are relatively delayed, and the one path of output optical pulse output by the combined beam is a pair of output sub-optical pulses which are adjacent in the front and back;
the phase modulator is arranged on at least one of the first sub-optical path and the second sub-optical path after the beam splitter, or on an output optical path connected with the output port after the beam combiner, and the phase modulator is configured to perform one of two phase modulations on at least one of the two transmission sub-optical pulses or at least one of the front and back adjacent pairs of output sub-optical pulses at random, where the phases modulated by the two phase modulations are different by ninety degrees.
Preferably, the phase modulator is further configured to randomly perform 0-degree or 90-degree phase modulation on at least one transmission sub optical pulse or at least one output sub optical pulse.
Preferably, the phase encoding apparatus further comprises a first laser and a second laser, a first input port and a second input port of the beam splitter being connected to the first laser and the second laser respectively, the beam splitter being configured to randomly receive the optical pulses generated by either of the first laser and the second laser through the first input port or the second input port at any one time.
Preferably, when the phase modulator uses 0-degree phase modulation, a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the first input port of the first input port and the second input port is combined and output are 0-degree phase-coded, and a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the second input port of the first input port and the second input port is combined and output are 180-degree phase-coded; and/or
When the phase modulator uses 90-degree phase modulation, a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the first input port of the first input port and the second input port is output after the input optical pulse is combined is 90-degree phase-coded, and a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the second input port of the first input port and the second input port is output after the input optical pulse is combined is 270-degree phase-coded.
Preferably, the beam splitter, the beam combiner and the devices in the optical paths associated with splitting and combining beams 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 an unequal arm michelson interferometer, the beam splitter and the beam combiner are the same device, and the phase encoding device further includes: a light circulator and two mirrors, wherein,
the optical circulator is arranged on any input light path of the beam splitter; the optical circulator is provided with at least a first port, a second port and a third port, and optical pulses input from the first port are output to the beam splitter through 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 from the third port of the optical circulator;
the two reflectors are respectively arranged on the two sub-light paths behind the beam splitter and are configured to respectively reflect the two paths of transmitted sub-light pulses transmitted on the two sub-light paths back to the beam splitter.
In still another aspect, the present invention further provides a quantum key distribution system, which is characterized by comprising the phase encoding apparatus described in any one of the above.
By adopting the technical scheme, the phase encoding device and the quantum key distribution system have the advantages that:
one path of output optical pulse is randomly received at one of two input ports of a beam splitter, the phase coding difference of a pair of output sub optical pulses correspondingly generated by the two input ports is 180 degrees, and after the phase modulator randomly performs 0-degree or 90-degree phase modulation on at least one path of transmission sub optical pulse in the two paths of transmission sub optical pulses or at least one output sub optical pulse in the front and back adjacent pairs of output sub optical pulses, the 0-degree, 90-degree, 180-degree and 270-degree phase coding of the pair of output sub optical pulses can be realized. However, compared with a phase modulator using four kinds of phase modulation, the driving circuit of the phase modulator performing two-phase modulation only needs to generate a quarter-wave voltage output, and the output voltage of the driving circuit of the phase modulator is reduced. In addition, compared with the method that four phases are generated by directly modulating the phase modulator through four voltages, the scheme only needs to modulate the voltages of two levels, and is easy to realize high-speed phase modulation, so that the simple and feasible phase encoding device and high-speed quantum key distribution system realization scheme are provided.
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 of the structure of a phase encoder according to a preferred embodiment of the present invention;
FIG. 3 is a schematic diagram of the structure of a phase encoder according to another preferred embodiment of the present invention;
fig. 4 is a schematic structural diagram of a phase encoding apparatus according to still another preferred embodiment of the present invention.
Detailed Description
The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form a part of this disclosure and together with the embodiments of the invention serve to explain the principles of the invention. For the purposes of clarity and simplicity, detailed descriptions of well-known functions and constructions of the devices described herein are sometimes omitted so as not to obscure the invention.
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 kinds of phase modulation at high speed for a quantum key distribution system. Specifically, as shown in fig. 1, the phase encoding method may include the steps of:
s101: randomly receiving a first path of incident input optical pulse or a second path of incident input optical pulse from any one of a first input port and a second input port of the beam splitter respectively;
s102: splitting the first path of input light pulse or the second path of input light pulse into two paths of transmission sub light pulses transmitted through a first sub light path and a second sub light path respectively;
s103: combining the two paths of transmission sub-optical pulses into one path of output optical pulse after the two paths of transmission sub-optical pulses are delayed relatively, wherein the one path of output optical pulse output by combining is a pair of output sub-optical pulses which are adjacent in the front and back; and
s104: during the two paths of transmission sub-optical pulses are transmitted through a first sub-optical path and a second sub-optical path after beam splitting, or after the two paths of transmission sub-optical pulses are combined into a pair of output sub-optical pulses which are adjacent in the front and back, a phase modulator is used for carrying out one phase modulation of two phase modulations on at least one path of transmission sub-optical pulse in the two paths of transmission sub-optical pulses or at least one output sub-optical pulse in the pair of output sub-optical pulses which are adjacent in the front and back, and the phase of the two phase modulations are different by ninety degrees.
The execution order of the above-described methods of the present invention is not limited to the order shown in the drawings or the limitation of the numbers, but the execution order of the steps should be understood according to the actual situation. For example, in step S104 of the above method, since the step of performing phase modulation by using two phase modulation methods may be performed after splitting at least one of the two transmission sub-optical pulses, or after combining, the execution order of each step should be arranged according to the actual application. The invention related to the method of the present application is not limited by the order of execution of its method steps.
In addition, for the sake of simplicity, the drawings only show the case where the phase modulator is disposed on one of the sub-optical paths after the beam splitter, the case where the phase modulator is disposed on two sub-optical paths after the beam splitter, and the case where the phase modulator is disposed after the beam combiner. It will be understood by those skilled in the art after reading this disclosure that the situation where the phase encoder is placed on one of the sub-paths after the beam splitter is equally applicable to the situation where the phase modulator is placed on both sub-paths after the beam splitter and the situation where the phase modulator is placed after the beam combiner.
Preferably, the first path of input optical pulse and the second path of input optical pulse are polarized light respectively, and may be two paths of polarized light with different phases and the same polarization state, for example. In one embodiment, the first input port and the second input port of the beam splitter may be connected to a first laser and a second laser (not shown), respectively, and the first input optical pulse and the second input optical pulse generated by the first laser and the second laser may be in the same phase or different phases.
The beam splitter may randomly receive the optical pulses generated by either of the first and second lasers at any one time. In other words, at any one time, the beam splitter receives either the optical pulses generated by the first laser or the optical pulses generated by the second laser, rather than both lasers simultaneously. For example, randomly receiving one path of input optical pulses provided by one laser at one of the two input ports of the beam splitter may be achieved by randomly lighting one of the two lasers connected to the first input port or the second input port at any one time.
Subsequently, the beam splitter may transmit one incident path of input light pulse in a ratio of 50: the 50 split beams are two paths of transmission sub-optical pulses transmitted on two transmission sub-optical paths. Specifically, the beam splitter may split each of the first input optical pulse or the second input optical pulse into two transmission sub optical pulses transmitted through the first sub optical path and the second sub optical path. In other words, the beam splitter may split the first path of input optical pulse into two paths of transmission sub optical pulses transmitted through the first sub optical path and the second sub optical path, or may split the second path of input optical pulse into two paths of transmission sub optical pulses transmitted through the first sub optical path and the second sub optical path. In the two paths of transmission sub-optical pulses split by the beam splitter, one path of transmission sub-optical pulse in the two paths of transmission sub-optical pulses can be relatively delayed relative to the other path of transmission sub-optical pulse. Because two paths of transmission sub-optical pulses have relative time delay, one path of output optical pulse output after the two paths of transmission sub-optical pulses are combined by using the beam combiner is two sub-optical pulses which are in front and behind in time, namely a pair of output sub-optical pulses which are adjacent in front and behind.
Preferably, during the transmission of the two transmitted sub-optical pulses after splitting or after combining into a pair of output sub-optical pulses adjacent to each other in the front-back direction, the phase modulator is used to perform one of two phase modulations on at least one of the two transmitted sub-optical pulses or at least one of the pair of output sub-optical pulses adjacent to each other in the front-back direction, and the phases modulated by the two phase modulations are different by ninety degrees. For example, the randomly performing one of the two phase modulations may include: and randomly performing 0-degree or 90-degree phase modulation on at least one transmission sub optical pulse or at least one output sub optical pulse. Alternatively, as long as the phases modulated by the two phase modulations are different by ninety degrees, the two phase modulations of different phase degrees may be randomly applied to at least one transmission sub-optical pulse or at least one output sub-optical pulse, for example, the phase modulations may be randomly performed by 90 degrees or 180 degrees, or randomly performed by 180 degrees or 270 degrees, which can achieve that the quantum key distribution system finally obtains four phase-encoded optical pulses.
For example, one of the two input optical pulses is randomly received at one of the two input ports of the beam splitter, and during or after beam splitting by the beam splitter and the beam combiner, the phase modulator is used to randomly perform phase modulation of 0 degree or 90 degrees on at least one path of split transmission sub optical pulses or at least one output sub optical pulse after beam combining, so that the quantum key distribution system can obtain four phase-encoded output optical pulses of 0 degree, 90 degrees, 180 degrees and 270 degrees. Specific phase modulation processes may be described with reference to the phase encoding apparatus below. The phase encoding process described herein may refer to modulating the relative phase between two transmission sub optical pulses or modulating the relative phase between a pair of adjacent output sub optical pulses in one output optical pulse.
In a preferred embodiment, when the phase modulator uses 0-degree phase modulation, a pair of adjacent output sub optical pulses before and after the input optical pulse received by the first input port of the first input port and the second input port is combined and output is 0-degree phase-coded, and a pair of adjacent output sub optical pulses before and after the input optical pulse received by the second input port of the first input port and the second input port is combined and output is 180-degree phase-coded.
Additionally or alternatively, when the phase modulator uses 90-degree phase modulation, a pair of adjacent output sub optical pulses before and after the input optical pulse received by the first input port of the first input port and the second input port is combined and output are 90-degree phase-coded, and a pair of adjacent output sub optical pulses before and after the input optical pulse received by the second input port of the first input port and the second input port is combined and output are 270-degree phase-coded.
Regarding the finally obtained pair of output sub optical pulses with four phase codes of 0 degree, 90 degrees, 180 degrees and 270 degrees, the four phase codes of 0 degree, 90 degrees, 180 degrees and 270 degrees may refer to that the relative phase difference between a pair of adjacent output sub optical pulses (or a pair of adjacent output sub optical pulses) in one path of output optical pulse is 0 degree, 90 degrees, 180 degrees or 270 degrees, respectively. For example, the pair of adjacent front and back output sub optical pulses is phase-coded by 0 degree, which may mean that the phase difference between the pair of adjacent front and back output sub optical pulses is 0 degree; the pair of adjacent front and back output sub optical pulses are 180-degree phase-coded, which may mean that the phase difference between the pair of adjacent front and back output sub optical pulses is 180 degrees. Similarly, the pair of front and back adjacent output sub optical pulses is 90-degree phase-coded, which may mean that the phase difference between the pair of front and back adjacent output sub optical pulses is 90 degrees; the pair of adjacent front and back output sub optical pulses may be 270 degrees phase-coded, and the phase difference between the pair of adjacent front and back output sub optical pulses may be 270 degrees.
Preferably, the polarization states of the optical pulses in the splitting and combining processes are controlled, so that the polarization states of two paths of transmission sub optical pulses transmitted by the first sub optical path and the second sub optical path are the same when the combined optical pulse is a pair of output sub optical pulses adjacent to each other in front and back.
Preferably, the controlling the polarization state of the light pulse in the beam splitting and combining process includes:
and a polarization maintaining optical device is adopted in the beam splitting and combining process, and the polarization states of the two paths of transmission sub optical pulses are kept unchanged in the beam splitting and combining process.
Fig. 2 is a schematic structural diagram of a phase encoding apparatus according to a preferred embodiment of the present invention.
As shown in fig. 2, the phase encoding apparatus may include the following components: a beam splitter 203, a phase modulator 204 and a beam combiner 205.
The beam splitter 203 may have a first input port 201 and a second input port 202, and the beam splitter 203 may be configured to randomly receive an incident first input optical pulse or a second input optical pulse from any one of the first input port 201 and the second input port 202, respectively, and split the incident first input optical pulse or the incident second input optical pulse into two transmission sub optical pulses transmitted via a first sub optical path and a second sub optical path, respectively.
The combiner 205 may be configured to combine the two transmission sub-optical pulses into one output optical pulse output through one output port 206 after the two transmission sub-optical pulses are relatively delayed, where the combined output optical pulse is a pair of output sub-optical pulses adjacent to each other in the front-back direction.
The phase modulator 204 may be disposed on any one of the first sub-optical path and the second sub-optical path after the beam splitter (as shown in fig. 2); that is, the phase modulator 204 may be disposed on one or both of the first and second sub-optical paths after the beam splitter. Alternatively, the phase modulator may be located on an output optical path connected to an output port after the beam combiner (not shown). The phase modulator 204 is configured to randomly perform one of two phase modulations, which are different in phase by ninety degrees, on at least one of the two transmission sub-optical pulses or on at least one of a pair of output sub-optical pulses adjacent to each other in front and back on the one output optical path.
In one embodiment, as shown in fig. 2, a phase modulator may be disposed on the first split sub-optical path to perform two kinds of phase modulation at random, and the sub-optical pulses transmitted on the second sub-optical path may be delayed. Or, a phase modulator may be disposed on the second split sub-optical path to perform two kinds of phase modulation at random, and the sub-optical pulse transmitted on the first sub-optical path may be delayed. Or, a phase modulator is arranged on the same sub-optical path to randomly perform two kinds of phase modulation, and the sub-optical pulse transmitted on the phase modulator is delayed.
Alternatively, the phase encoding means 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).
Herein, the terms "beam splitter" and "beam combiner" are used interchangeably, and a beam splitter may also be used as a beam combiner, and vice versa. When the phase encoding device adopts the structure of the unequal arm michelson interferometer, the beam splitter and the beam combiner can be the same component.
Preferably, the phase modulator 204 is further configured to randomly phase modulate at least one transmission sub-optical pulse or at least one output optical pulse, for example, by 0 degrees or 90 degrees.
Preferably, the phase encoding device may further include a first laser and a second laser, and the first input port 201 and the second input port 202 of the beam splitter are respectively connected to the first laser and the second laser. (there is no relation between the first input optical pulse and the second input optical pulse, and the input from one port will make the final output pair of sub-output optical pulses 0 degree code, and the input from the other port will make the final output pair of sub-output optical pulses 180 degree code, not related to the laser.) the beam splitter 203 is configured to randomly receive the optical pulses generated by either of the first laser and the second laser through the first input port or the second input port at any one time. Randomly receiving one input optical pulse at one of the two input ports of the beam splitter 203 can be achieved by randomly lighting the laser connected to the corresponding input port.
In one embodiment, when the phase modulator uses 0-degree phase modulation, a pair of adjacent output sub optical pulses before and after a first input optical pulse received by a first input port of the first input port and the second input port is output after being combined is 0-degree phase-coded, and a pair of adjacent output sub optical pulses before and after a second input optical pulse received by a second input port of the first input port and the second input port is output after being combined is 180-degree phase-coded.
Additionally or alternatively, when the phase modulator uses 90-degree phase modulation, a pair of adjacent output sub optical pulses before and after the input optical pulse received by the first input port of the first input port and the second input port is combined and output are 90-degree phase-coded, and a pair of adjacent output sub optical pulses before and after the input optical pulse received by the second input port of the first input port and the second input port is combined and output are 270-degree phase-coded.
Advantageously, in order to keep the polarization state of the input light pulses unchanged during the splitting and combining processes, the beam splitter 203, the beam combiner 205, and the devices used during the splitting and combining processes may all adopt polarization maintaining optical devices.
In some embodiments, the phase encoding means 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 a configuration of a phase encoding apparatus according to a preferred embodiment of the present invention.
In the embodiment shown in fig. 3, the phase encoding device may be an unequal arm mach-zehnder interferometer structure, specifically including the following components: a beam splitter 303, a phase modulator 304 and a beam combiner 305. Preferably, the beam splitter 303 may be a polarization maintaining beam splitter, and the beam combiner 305 may be a polarization maintaining beam combiner.
The splitter 303 may have a first input port 301 and a second input port 302, and one of the first input port 301 and the second input port 302 is randomly selected to receive an incident path of optical pulses. In operation, the first input port 301 is connected to a first laser, the second input port 302 is connected to a second laser (not shown), and randomly receiving an incident optical pulse from one of the two input ports of the beam splitter 303 can be achieved by randomly lighting the laser connected to the corresponding input port.
The beam splitter 303 splits one input optical pulse incident from the first input port 301 or the second input port 302 into two transmitted sub optical pulses. For example, one of the two transmission sub optical pulses may be modulated by 0 degree or 90 degrees through the phase modulator 304, the other transmission sub optical pulse is transmitted through the polarization maintaining fiber and is relatively delayed, and the two relatively delayed transmission sub optical pulses are combined into one output optical pulse output through the first output port 306 or the second output port 307 through the beam combiner 305. Although two output ports are shown in fig. 3, only one output optical pulse output from one of the two output ports 306 and 307 of the beam combiner 305 may be selected. The phase modulator 304 may be inserted in either of the two arms of the mach-zehnder interferometer, i.e. in either of the transmission sub-paths after the beam splitter.
For example, when the phase modulator 304 modulates 0 degree, the first path of input optical pulse is split by the beam splitter 303 and then combined to form a pair of output sub-pulses that are adjacent to each other in front and behind and phase-coded by 0 degree, and the second path of input optical pulse is split by the beam splitter 303 and then combined to form a pair of output sub-pulses that are adjacent to each other in front and behind and phase-coded by 180 degree. Or, when the phase modulator 304 modulates 90 degrees, the first path of input optical pulse is split by the beam splitter 303 and then combined to form a pair of output sub-pulses which are adjacent to each other in front and at the back of 90-degree phase coding, and the second path of input optical pulse is split by the beam splitter 303 and then combined to form a pair of output sub-pulses which are adjacent to each other in front and at the back of 270-degree phase coding. Thereby, four types of phase-encoded optical pulses required by the quantum key distribution protocol for performing quantum communication can be realized.
It will be appreciated that the components of the beam splitter or combiner themselves may cause a 90 degree relative phase change between the sub-optical pulses after the splitting or combining process, i.e. a 90 degree relative phase change between the transmitted and coupled-in transmitted sub-optical pulses.
For example, when the phase modulator 304 modulates 0 degree and receives the first path of input optical pulse incident through the port 301, the first path of input optical pulse 301 is split by the beam splitter 303 to the upper first transmission sub optical path (transmission), and the optical pulse transmitted by the first transmission sub optical path is combined by the beam combiner 305 and is supposed to be transmitted to the upper output port 306 (transmission), so that the phase of the output first sub optical pulse is not changed in the beam splitting and combining processes; however, if the first input optical pulse 301 is split into the second transmission sub optical path (coupling transmission) below by the beam splitter 303, and the optical pulse transmitted by the second transmission sub optical path is supposed to be transmitted to the output port 306 above after being combined by the beam combiner 305 (coupling transmission), the phase of the output second sub optical pulse changes by 180 degrees in the splitting and combining process (the phase changes by 90 degrees in the splitting and combining process), so that the pair of adjacent sub optical pulses output through the output port 306 is a pair of adjacent output sub optical pulses before and after 180 degrees phase coding.
Similarly, it can be derived from the above calculation method that, when the phase modulator 304 modulates 90 degrees and receives the first input optical pulse through the port 301, the phase of a pair of sub optical pulses output through the output port 306 may be changed by 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 phase coding.
Similarly, it can also be derived from the above calculation method that when the phase modulator 304 modulates 0 degree and receives the second input optical pulse through the port 302, the phase of the pair of sub optical pulses output through the output port 306 may be changed by 90 degrees and 90 degrees, respectively, so as to realize a pair of adjacent output sub optical pulses before and after the phase encoding of 0 degree.
Similarly, it can also be derived from the above calculation method that when the phase modulator 304 modulates 90 degrees and receives the second incoming optical pulse through the port 302, the phase of the pair of sub optical pulses output through the output port 306 may be changed by 90 degrees and 180 degrees, respectively, so as to realize a pair of output sub optical pulses adjacent to each other before and after 90 degrees phase coding.
Fig. 4 is a schematic structural diagram of a phase encoding apparatus according to still another preferred embodiment of the present invention.
In the embodiment shown in fig. 4, the phase encoding apparatus adopts an unequal arm michelson interferometer structure, and specifically includes the following components: optical circulator 403, beam splitter 404, phase modulator 406, and mirrors 405 and 407. In this embodiment, the beam splitter and the beam combiner are the same device. The beam splitter 404 functions as both a beam splitter and a beam combiner, and is preferably a polarization maintaining optical device.
The splitter 404 has a first input port 401 and a second input port 402. The optical circulator 403 may be disposed on any input optical path of the beam splitter 404. The optical circulator 403 may have at least 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 404 via the second port B of the optical circulator; the optical pulse output from the beam splitter 404 to the second port B of the optical circulator is output from the third port C of the optical circulator.
The two mirrors 405 and 407 may be respectively disposed on two sub-optical paths behind the beam splitter 404, and are configured to respectively reflect two transmitted sub-optical pulses transmitted on the two sub-optical paths back to the beam splitter 404. The phase modulator 406 is arranged in one of the two sub-paths after the beam splitter or inserted into either of the two arms of the michelson interferometer.
Referring to fig. 4, a first input port 401 and a second input port 402 on one side of a beam splitter 404 are both input ends of the beam splitter, and one of the input ports is randomly selected to receive a corresponding path of input optical pulses. Mirrors 405 and 407 are connected to two ports on the other side of the beam splitter 404, respectively. During operation, the first input port 401 and the second input port 402 are respectively connected to the first laser and the second laser, and the first laser connected to the first input port 401 is randomly turned on, so that a first path of input optical pulse generated by the first laser is incident to the beam splitter 404. Alternatively, a second laser connected to the second input port 402 is randomly turned on, and a second input optical pulse generated by the second laser is input through the first port a of the optical circulator 403 and then output to the beam splitter 404 through the second port B of the optical circulator 403.
The beam splitter 404 splits the first path of input optical pulse or the second path of input optical pulse into two paths of transmission sub optical pulses respectively, one path of transmission sub optical pulse is reflected back by the reflector 405 after being subjected to relative delay, and the other path of transmission sub optical pulse is randomly subjected to 0-degree or 90-degree phase modulation by the phase modulator 406 and then reflected back by the reflector 407. In this way, the two reflected transmission sub-optical pulses with relative delays are combined into a pair of output sub-optical pulses adjacent to each other via the beam splitter 404 (which functions as a beam combiner), and then input to the second port B of the optical circulator 403, and then transmitted to the port 408 via the third port C of the optical circulator. Alternatively, the same result can be produced if the optical circulator 403 is placed on another input optical path of the beam splitter 404 connected to the first input port 401.
The two mirrors 405 and 407 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 the phase encoding apparatus according to any one of the above.
According to the phase encoding method and the phase encoding apparatus of the above-mentioned embodiments of the present invention described with reference to the drawings, four kinds of phase encoding of 0 degree, 90 degrees, 180 degrees and 270 degrees are finally realized by randomly receiving one path of input optical pulse at one of the two input ports of the beam splitter and then performing 0-degree or 90-degree random phase modulation by the phase modulator. Through the mode, the driving circuit of the phase modulator only needs to generate the quarter-wave voltage output, the output voltage of the driving circuit of the phase modulator is reduced, and therefore the faster phase modulation signal edge can be realized, and a simple and easy high-speed phase coding method and a realization scheme of a quantum key distribution system are provided.
The technical means and effects of the invention adopted to achieve the intended purposes should be more deeply and specifically understood through the description of the specific embodiments. Furthermore, the drawings are only for reference and illustration purposes and are not intended to limit the invention.
While the exemplary embodiments have been described in detail, the foregoing description is in all aspects illustrative and not restrictive. It should be understood that numerous other modifications and variations can be devised without departing from the scope of the exemplary embodiments, and that such modifications and variations fall within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.
Claims (14)
1. A method of phase encoding, the method comprising:
randomly receiving a first path of incident input optical pulse or a second path of incident input optical pulse from any one of a first input port and a second input port of the beam splitter respectively;
splitting the first path of input light pulse or the second path of input light pulse into two paths of transmission sub light pulses transmitted through a first sub light path and a second sub light path respectively;
combining the two paths of transmission sub-optical pulses into one path of output optical pulse after the two paths of transmission sub-optical pulses are delayed relatively, wherein the one path of output optical pulse output by combining is a pair of output sub-optical pulses which are adjacent in the front and back;
during the two paths of transmission sub-optical pulses are transmitted through a first sub-optical path and a second sub-optical path after beam splitting, or after the two paths of transmission sub-optical pulses are combined into a pair of output sub-optical pulses which are adjacent in the front and back, a phase modulator is used for carrying out one phase modulation of two phase modulations on at least one path of transmission sub-optical pulse in the two paths of transmission sub-optical pulses or at least one output sub-optical pulse in the pair of output sub-optical pulses which are adjacent in the front and back, and the phase of the two phase modulations are different by ninety degrees.
2. The phase encoding method according to claim 1, wherein the randomly performing one of two phase modulations on at least one of the two transmission sub-optical pulses or at least one of the two output sub-optical pulses of the front-back adjacent pair of output sub-optical pulses by using a phase modulator comprises:
and randomly performing 0-degree or 90-degree phase modulation on at least one transmission sub optical pulse or at least one output sub optical pulse.
3. The phase encoding method according to claim 1, wherein the first input port and the second input port of the beam splitter are connected to a first laser and a second laser, respectively, and the beam splitter randomly receives the optical pulses generated by any one of the first laser and the second laser through the first input port or the second input port at any one time.
4. The phase encoding method according to claim 1 or 2, wherein,
when the phase modulator uses 0-degree phase modulation, a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the first input port of the first input port and the second input port is output after the input optical pulse is combined is 0-degree phase coding, and a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the second input port of the first input port and the second input port is output after the input optical pulse is combined is 180-degree phase coding; and/or
When the phase modulator uses 90-degree phase modulation, a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the first input port of the first input port and the second input port is output after the input optical pulse is combined is 90-degree phase-coded, and a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the second input port of the first input port and the second input port is output after the input optical pulse is combined is 270-degree phase-coded.
5. The phase encoding method of claim 1, further comprising: and controlling the polarization state of the light pulse in the beam splitting and combining processes to ensure that the polarization states of two paths of transmission sub light pulses transmitted by the first sub light path and the second sub light path are the same when the combined beam is a pair of front and back adjacent output sub light pulses.
6. The phase encoding method of claim 5, wherein the controlling the polarization state of the optical pulses in the splitting and combining process comprises:
and a polarization maintaining optical device is adopted in the beam splitting and combining process, and the polarization states of the two paths of transmission sub optical pulses are kept unchanged in the beam splitting and combining process.
7. A phase encoding apparatus, characterized in that the apparatus comprises: a beam splitter, a beam combiner and a phase modulator, wherein,
the beam splitter has a first input port and a second input port, and is configured to randomly receive an incident first path of input optical pulses or a second path of input optical pulses from any one of the first input port and the second input port, respectively, and split each of the incident first path of input optical pulses or the second path of input optical pulses into two paths of transmission sub optical pulses transmitted via a first sub optical path and a second sub optical path;
the beam combiner is configured to combine the two paths of transmission sub-optical pulses into one path of output optical pulse output through one output port after the two paths of transmission sub-optical pulses are relatively delayed, and the one path of output optical pulse output by the combined beam is a pair of output sub-optical pulses which are adjacent in the front and back;
the phase modulator is arranged on at least one of the first sub-optical path and the second sub-optical path after the beam splitter, or on an output optical path connected with the output port after the beam combiner, and the phase modulator is configured to perform one of two phase modulations on at least one of the two transmission sub-optical pulses or at least one of the front and back adjacent pairs of output sub-optical pulses at random, where the phases modulated by the two phase modulations are different by ninety degrees.
8. Phase encoding apparatus according to claim 7, wherein the phase modulator is further configured to randomly phase modulate at least one of the transmission sub-optical pulses or at least one of the output sub-optical pulses by 0 degrees or 90 degrees.
9. The phase encoding apparatus of claim 7, further comprising a first laser and a second laser, a first input port and a second input port of the beam splitter being connected to the first laser and the second laser, respectively, the beam splitter being configured to randomly receive the optical pulses generated by any one of the first laser and the second laser through the first input port or the second input port at any one time.
10. The phase encoding device according to claim 8 or 9, wherein,
when the phase modulator uses 0-degree phase modulation, a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the first input port of the first input port and the second input port is output after the input optical pulse is combined is 0-degree phase coding, and a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the second input port of the first input port and the second input port is output after the input optical pulse is combined is 180-degree phase coding; and/or
When the phase modulator uses 90-degree phase modulation, a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the first input port of the first input port and the second input port is output after the input optical pulse is combined is 90-degree phase-coded, and a pair of adjacent output sub-optical pulses before and after the input optical pulse received by the second input port of the first input port and the second input port is output after the input optical pulse is combined is 270-degree phase-coded.
11. The phase encoding apparatus of claim 7, wherein the beam splitter, the beam combiner, and the devices in the optical paths associated with splitting and combining are polarization maintaining optical devices.
12. The phase encoding device according to claim 7, wherein the phase encoding device employs an optical path structure of an unequal arm Mach-Zehnder interferometer or an unequal arm Michelson interferometer.
13. The phase encoding apparatus of claim 12, wherein when the phase encoding apparatus adopts an optical path structure of an unequal arm michelson interferometer, the beam splitter and the beam combiner are the same device, and the phase encoding apparatus further comprises: a light circulator and two mirrors, wherein,
the optical circulator is arranged on any input light path of the beam splitter; the optical circulator is provided with at least a first port, a second port and a third port, and optical pulses input from the first port are output to the beam splitter through 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 from the third port of the optical circulator;
the two reflectors are respectively arranged on the two sub-light paths behind the beam splitter and are configured to respectively reflect the two paths of transmitted sub-light pulses transmitted on the two sub-light paths back to the beam splitter.
14. A quantum key distribution system, comprising a phase encoding apparatus according to any one of claims 7 to 13.
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