CN110620612B - Test light path and QKD system - Google Patents
Test light path and QKD system Download PDFInfo
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- CN110620612B CN110620612B CN201811457468.8A CN201811457468A CN110620612B CN 110620612 B CN110620612 B CN 110620612B CN 201811457468 A CN201811457468 A CN 201811457468A CN 110620612 B CN110620612 B CN 110620612B
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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
- H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
- H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
- H04B10/079—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
- H04B10/0795—Performance monitoring; Measurement of transmission parameters
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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
- H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
- H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
- H04B10/079—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
- H04B10/0795—Performance monitoring; Measurement of transmission parameters
- H04B10/07955—Monitoring or measuring power
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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
- H04B10/70—Photonic quantum communication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- 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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Abstract
The invention discloses a test light path and a QKD system, which are characterized in that a first optical power beam splitter is used for acquiring an optical signal emitted by a source end coding light path, the optical signal can be divided into two paths according to a set beam splitting ratio, two output ports of the optical signal respectively output one path of optical signal, the attenuation of the optical signal can be realized, the first output port of the optical signal can be used for providing an attenuated light signal for a subsequent light path, the second output port of the optical signal outputs one path of optical signal for carrying out optical parameter measurement on the input optical signal, the detection, the test and the calibration of the light path are completed, the first optical power beam splitter can be used for carrying out the detection, the test and the calibration of the light path while the attenuation of the optical signal is realized, a plurality of different light path modules are not required to be adopted for realizing different functions, and the structure of the test light path is simple.
Description
Technical Field
The invention relates to the technical field of optical communication, in particular to a test optical path and a QKD system.
Background
Quantum key distribution (QuantumKey Distribution, QKD) techniques are therefore of great interest, as they are capable of producing a perfectly consistent unconditionally secure key between two communicating parties. Quantum key distribution (QuantumKey Distribution, QKD) differs fundamentally from classical key systems in that it uses a single photon or entangled photon pair as the carrier for the key, guaranteeing the non-eavesdroppability, non-hackability of the process by the three fundamental principles of quantum mechanics (hessian-parcels, measurement collapse theory, quantum unclonable law), thus providing a more secure key system.
Since the BB84 scheme in 1984 is proposed, various theoretical schemes related to the quantum key distribution technology are perfected day by day, and technology implementation is mature gradually, so that a quantum communication system and a quantum communication method based on the quantum key distribution technology are put to practical use.
In the prior art, a quantum communication system needs to test and calibrate parameters of an optical signal through a test optical path, and the existing test optical path has a complex structure.
Disclosure of Invention
In order to solve the problems, the technical scheme of the invention provides a test light path and a QKD system, and the test light path has a simple structure.
In order to achieve the above object, the present invention provides the following technical solutions:
a test optical path for a QKD system, the QKD system including a source-side encoded optical path, the test optical path comprising:
a first optical power splitter having a first output port, a second output port, and at least one input port;
an input port of the first optical power beam splitter is used for connecting the source end coding optical path so as to acquire an optical signal emitted by the source end coding optical path; the first optical power beam splitter divides the optical signals emitted by the source end coding optical path into two paths of optical signals according to a set beam splitting ratio, and the two paths of optical signals are respectively output through a first output port and a second output port; one path of optical signal output by the second output port is used for measuring optical parameters, and the first output port is used for connecting with a subsequent optical path to provide optical signals for the subsequent optical path.
Preferably, in the above test optical path, the test optical path further includes: at least one second optical power splitter having a first input port, a second input port, a first output port, and a second output port;
when one second optical power beam splitter is arranged, the first input port of the second optical power beam splitter is connected with the first output port of the first optical power beam splitter, and the first output port of the second optical power beam splitter is used for connecting the subsequent optical path;
when the second optical power splitters are provided with the plurality of second optical power splitters, the plurality of second optical power splitters are cascaded, a first input port of the second optical power splitter of a first stage is connected with a first output port of the first optical power splitter, and a first output port of the second optical power splitter of a last stage is used for being connected with the subsequent optical path; for any two adjacent second optical power splitters, the first input port of the second optical power splitter of the subsequent stage is connected with the first output port of the second optical power splitter of the previous stage.
Preferably, in the above test optical path, a second input port of the second optical power splitter connected to the subsequent optical path is used for inputting an external test signal.
Preferably, in the above test optical path, the loss of the external test signal input by the second input port of the second optical power splitter connected to the subsequent optical path after passing through the first output port is less than or equal to 3dB.
Preferably, in the above test optical path, for the second optical power splitter, for an optical signal incident on the first input port, the intensity of one optical signal output by the first output port is less than or equal to the intensity of one optical signal output by the second output port.
Preferably, in the above test optical path, for the first optical power splitter, for an optical signal incident on the first input port, the intensity of one optical signal output by the first output port is less than or equal to the intensity of one optical signal output by the second output port.
Preferably, in the above test optical path, the first optical power splitter has a first input port and a second input port, where the first input port is used to connect to the source end coding optical path;
the beam splitting ratio of the first optical power beam splitter is the same as the beam splitting ratio of the second optical power beam splitter.
The present invention also provides a QKD system comprising: a source-side coded light path and a test light path as claimed in any preceding claim.
Preferably, in the QKD system, the source-side encoding optical path is a polarization state preparation optical path, and is configured to emit polarized light in four polarization states, where two polarization directions are perpendicular to each other and two other polarization directions are perpendicular to each other.
Preferably, in the QKD system, the test optical path acquires an optical signal emitted from the source-side encoded optical path, and sends the attenuated optical signal to a subsequent optical path, where the subsequent optical path includes: a variable optical attenuator and a filter;
and the optical signals output by the test optical path sequentially pass through the variable optical attenuator and the filter.
As can be seen from the above description, in the test optical path and the QKD system provided by the present invention, the optical signal emitted from the source end encoding optical path is obtained through the first optical power beam splitter, the optical signal can be divided into two paths according to the set beam splitting ratio, two output ports thereof respectively output one path of optical signal, so that attenuation of the optical signal can be achieved, one path of attenuated optical signal after attenuation can be provided for the subsequent optical path through the first output port thereof, one path of optical signal output by the second output port thereof is used for performing optical parameter measurement on the input optical signal, and detection, test and calibration of the optical path are completed, and the optical path can be detected, tested and calibrated through the first optical power beam splitter while realizing optical signal attenuation, without adopting a plurality of different optical path modules to realize different functions, and the test optical path has a simple structure.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic structural diagram of a test optical path according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of another test light path according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a QKD system according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Since the output light intensity of the QKD system is very weak, taking the decoy BB84 scheme as an example, the output power is-86.1 dBm under the condition of 40MHz repetition frequency, in the QKD system, the output light intensity modulation needs to be realized by matching a fixed light attenuator (for example, a pluggable fixed light attenuator) with a mode of a tunable light attenuator, and the problems of poor repeatability and stability generated by cascading of multistage tunable light attenuators are avoided by using the fixed light attenuator. In the prior art, a scheme of testing a separation module or even a single device is adopted in the optical parameter testing process of the QKD system, a series of key parameters such as insertion loss and the like are tested and calibrated for different modules of the QKD system, and then the modules of the QKD system are subjected to fitting calibration of the outlet light intensity. In addition, under the abnormal condition of the modules of the QKD system, resolution is needed to be conducted to check and analyze one by one, and the problem root is determined.
In the existing test light path, the precision problem of the existing optical power meter is limited, a scheme of testing a separation module and even a single device is adopted, a series of key parameter tests and calibrations such as insertion loss are carried out on the modules of different QKD systems, and the form of calibrating the output light intensity of the modules of the QKD systems is complicated in the operation process, and the parameter calibrations such as separation loss and the like have certain difference with the whole system test process; in addition, when the problem module is checked, module separation work is needed, the specific problem points are determined after the separation modules are detected one by one, the detection complexity is increased to a certain extent, and the problem checking analysis cannot be carried out on the optical link at all due to the fact that the attenuation is large in the scheme of adopting the fixed optical attenuator to carry out intensity attenuation.
The embodiment of the invention provides a test light path based on a conventional optical passive power beam splitter, which integrates attenuation, detection and test functions, avoids incapability of realizing the test and detection functions caused by large attenuation of a link, greatly simplifies light intensity calibration and light link problem investigation and detection difficulty, and has a simple light path structure.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Referring to fig. 1, fig. 1 is a schematic structural diagram of a test optical path provided in an embodiment of the present invention, where the test optical path is used in a QKD system, and the QKD system includes a source-side encoding optical path 12, where the source-side encoding optical path 12 is configured to provide an optical signal to the test optical path, and where the source-side encoding optical path 12 may be a polarization state preparation optical path, and is configured to emit polarized light, as shown in fig. 1, where the test optical path includes: the first optical power splitter SMC1, the first optical power splitter SMC1 has a first output port smc1_d1, a second output port smc1_d2 and at least one input port. In the embodiment shown in fig. 1, the first optical power splitter SMC1 has two input ports, namely, a first input port smc1_d1 and a second input port smc1_d2.
One input port of the first optical power splitter SMC1 is used for connecting with the source coding optical path 12 to obtain an optical signal emitted from the source coding optical path 12, in the manner shown in fig. 1, the first input port smc1_d1 is connected with the source coding optical path 12, and the second input port smc1_d2 may be an empty port and not connected with other elements; the first optical power beam splitter SMC1 divides the optical signal emitted from the source end coding optical path 12 into two paths of optical signals according to a set beam splitting ratio, and the two paths of optical signals are output through a first output port smc1_d1 and a second output port smc1_d2 respectively; one path of optical signal output by the second output port smc1_d2 is used for performing optical parameter measurement, for example, the second output port smc1_d2 is used as a test end, and can be connected with other optical paths, and the optical signal can be subjected to parameter measurement through other optical paths, so that the optical signal input by the first optical power beam splitter is subjected to parameter measurement, the detection and the test of the input optical signal are realized, and the first output port smc1_d1 is used for being connected with a subsequent optical path 11 to provide the optical signal for the subsequent optical path 11.
In the test optical path, the optical signal emitted by the source end coding optical path 12 is obtained through the first optical power beam splitter SMC1, the optical signal can be divided into two paths according to a set beam splitting ratio, two output ports of the optical signal respectively output one path of optical signal, attenuation of the optical signal can be achieved, one path of attenuated optical signal after attenuation can be provided for a subsequent optical path 11 through the first output port smc1_d1, one path of optical signal output by the second output port smc1_d2 is used for carrying out optical parameter measurement on the input optical signal, detection, test and calibration of the optical path are completed, the optical path can be detected, tested and calibrated while the optical signal attenuation is achieved through the first optical power beam splitter SMC1, a plurality of different optical path modules are not required to be adopted for achieving different functions, and the test optical path is simple in structure.
For the same incident optical signal, the intensities of the two optical signals output by the two output ports in the first optical power splitter SMC1 may be the same or different.
In the embodiment of the present invention, for the same incident optical signal, two paths of optical signal intensities output by two output ports of the first optical power beam splitter SMC1 are set to be different. For the first optical power splitter SMC1, for the optical signal incident on the first input port smc1_d1 thereof, the intensity of the optical signal outputted by the first output port smc1_d1 of the first optical power splitter SMC1 is set to be smaller than or equal to the intensity of the optical signal outputted by the second output port smc1_d2 thereof. In this way, a weaker optical signal can be made to enter a subsequent optical path, facilitating the formation of weak coherent light suitable for QKD systems. The optical signal intensities of the two output ports can be set by setting the splitting ratio of the first optical power splitter SMC 1.
The subsequent optical path 11 includes: a variable optical attenuator and a filter; and the optical signals output by the test optical path sequentially pass through the variable optical attenuator and the filter. At this time, the first output port smc1_d1 of the first optical power splitter SMC1 is connected to the variable optical attenuator.
In the manner shown in fig. 1, only one first optical power splitter SMC1 is provided, and the second input port smc1_d2 thereof can be used as a test input port for inputting an external test signal to perform a subsequent optical path test, in the manner that when the test optical path has a plurality of optical power splitters, the second input port smc1_d2 of the first optical power splitter SMC1 can be emptied, and the second input port of the last optical power splitter in the test optical path is selected as a test port to input the external test signal.
Referring to fig. 2, fig. 2 is a schematic structural diagram of another test optical path provided in an embodiment of the present invention, where the test optical path further includes, on the basis of fig. 1: at least one second optical power splitter SMC2, the second optical power splitter SMC2 having a first input port smc2_d1, a second input port smc2_d2, a first output port smc2_d1 and a second output port smc2_d2.
In the embodiment shown in fig. 2, only one second optical power splitter SMC2 is shown, in which case the test optical path has one of the second optical power splitters SMC2, the first input port smc2_d1 of the second optical power splitter SMC2 being connected to the first output port smc1_d1 of the first optical power splitter SMC1, the first output port smc2_d1 being used for connecting the subsequent optical path 11.
In other modes, when a plurality of second optical power splitters SMC2 are provided, the plurality of second optical power splitters SMC2 are cascaded, a first input port smc2_d1 of a first stage of the second optical power splitters SMC2 is connected to a first output port smc1_d1 of the first optical power splitter SMC1, and a first output port smc2_d1 of a last stage of the second optical power splitters SMC2 is used to connect the subsequent optical path 11; for any adjacent two of the second optical power splitters SMC2, the first input port smc2_d1 of the second optical power splitter SMC2 of the subsequent stage is connected to the first output port smc2_d1 of the second optical power splitter SMC2 of the previous stage.
On the one hand, the number of the optical power splitters cascaded between the source end coded optical path 12 and the subsequent optical path 11 can be increased by arranging the second optical power splitter SMC2, so that the attenuation amplitude can be increased, and an optical signal with the set attenuation amplitude can be obtained by adjusting the number of the optical power splitters between the source end coded optical path 12 and the subsequent optical path 11. On the other hand, the second input port smc2_d2 of the second optical power splitter SMC2 connected to the subsequent optical path 11 may be configured to input an external test signal, so that the external test signal input by the second input port smc2_d2 of the second optical power splitter SMC2 is split into two paths by the second optical power splitter SMC2 according to a set splitting ratio, and is output through two output ports thereof, and the optical parameter measurement can be performed on the external test signal through the subsequent optical path 11, so as to implement the detection, the test and the calibration of the optical path.
For the second optical power splitter SMC2 connected to the subsequent optical path 11, after the external test signal input by the second input port smc2_d2 passes through the first output port smc2_d1, the loss is less than or equal to 3dB, and more preferably, the loss is less than 1dB, so as to better implement detection, test and calibration of the optical path between the second input port smc2_d2 and the output port of the QKD system.
In the same manner as shown in fig. 1, the subsequent optical path 11 may include: a variable optical attenuator and a filter; when one second optical power beam splitter SMC2 is provided, the optical signal output by the first output port smc2_d1 of the second optical power beam splitter SMC2 sequentially passes through the variable optical attenuator and the filter; when there are a plurality of the second optical power splitters SMC2, an optical signal output from the first output port smc2_d1 of the second optical power splitter SMC2 of the last stage sequentially passes through the variable optical attenuator and the filter.
In the test optical path, for the second optical power beam splitter SMC2, for the optical signal incident on the first input port smc2_d1, the intensity of one optical signal output by the first output port smc2_d1 is smaller than or equal to the intensity of one optical signal output by the second output port smc2_d2. In this way, the attenuation amplitude of the optical signal output by the first output port smc2_d1 is larger than that of the optical signal incident by the first input port smc2_d1, so that the test optical path has larger attenuation amplitude, and weak coherent light can be conveniently realized.
As described above, the first optical power splitter SMC1 has the first input port smc1_d1 and the second input port smc1_d2, and the first input port smc1_d1 is used for connecting the polarization state preparation optical path 12. The beam splitting ratio of the first optical power beam splitter SMC1 is the same as the beam splitting ratio of the second optical power beam splitter SMC2, and the two have the same structure and the same beam splitting ratio, so that the optical path layout is convenient to set. It is also possible to set the splitting ratio of all the optical power splitters not to be identical.
In the test optical path, for any optical power splitter, when the same optical signal is incident, the two paths of optical signals output by the two output ports have different power, the target optical signal is input through the first input port, the first output port outputs the optical signal of the first power, the second output port outputs the optical signal of the second power, and when the same target optical signal is input through the second input port, the second output port outputs the optical signal of the first power, and the first output port outputs the optical signal of the second power. At this time, the first power is different from the second power.
In the embodiment of the invention, the first optical power beam splitter SMC1 and the second optical power beam splitter SMC2 are both passive power beam splitters, and the implementation mode is simple without electric signal control.
The working principle of the test optical path shown in fig. 2 is described below with reference to specific beam splitting ratios.
Setting the beam splitting ratio of all the optical power beam splitters to be the same in the test optical path to be 99:1, namely, after the optical signals are input through the first input port, 99% of the optical signals are output through the second output port, 1% of the optical signals are output through the first output port, and when the optical signals are input through the second input port, 99% of the optical signals are output through the first output port, and 1% of the optical signals are output through the second output port.
Thus, after the optical link of the source-side encoded optical path 12 is connected to the first input port smc1_d1 of the first optical power splitter SMC1, 1% of the optical signal enters the input port smc2_d1 of the second optical power splitter SMC2 through the first output port smc1_d1, 99% of the optical signal is output from the second output port smc1_d2 of the first optical power splitter SMC1, 1% of the optical signal input through the first input port smc2_d1 of the second optical power splitter SMC2 is output through the first output port smc2_d1 of the second optical power splitter SMC2, and is further transmitted to the subsequent optical path 11, and 99% of the optical signal input through the first input port smc2_d1 of the second optical power splitter SMC2 is output through the second output port smc2_d2 of the second optical power splitter.
In the whole test light path, the first output port of each optical power beam splitter outputting 1% of optical signals is connected with the subsequent stage component, so that the large attenuation of the initial incident optical signals can be realized, the requirements of large attenuation values required by different light paths can be realized by adjusting the number of the optical power beam splitters, the cascade number of the optical power beam splitters is selected according to the actual attenuation values required by different light paths, the large attenuation value with set amplitude is realized, and the use of a fixed optical attenuator in the prior art is replaced.
The attenuation loss from the first input port smc1_d1 of the first optical power beam splitter SMC1 to the second output port smc1_d2 of the first optical power beam splitter SMC1 is set to be less than 1dB, so that the second output port smc1_d2 can acquire an optical signal with larger power, and the optical path detection, test and calibration functions from the source end coded optical path 12 to the first optical power beam splitter SMC1 can be conveniently realized.
When the second optical power beam splitter SMC2 is set to input an external test signal through the second input port smc2_d2, the attenuation loss from the second input port smc2_d2 to the first output port smc2_d1 is less than 1dB, so that when the external test signal is input through the second input port smc2_d2, the first output port smc2_d1 can acquire a light signal with higher power, and the functions of optical path detection, test and calibration from the second input port smc2_d2 to the output port of the QKD system can be conveniently realized.
In the test optical path, the implementation form of the optical power beam splitter is not limited to a 99:1 beam splitter, and also comprises a beam splitter with a special customized beam splitting ratio, a cascade connection form among beam splitters with different beam splitting ratios, or other embodiments such as space optics.
Compared with the prior art, the test light path has the following beneficial effects:
the integrated calibration and test functions of the QKD system module are realized, the analysis and positioning efficiency of the abnormal module is improved, and the integrated module problem positioning and detection are especially aimed at.
On the basis of realizing the calibration and test functions of the optical link, the single-stage or multi-stage beam splitter cascade connection mode can be adopted to realize the fixed attenuation of different amplitudes, and the use of a fixed optical attenuator is replaced.
Aiming at weak coherent optical communication in the technical field of quantum communication, the requirements on the precision of an optical power meter under the test condition of a greatly attenuated link are reduced.
Based on the above embodiments, another embodiment of the present invention also provides a QKD system, as shown in fig. 3.
Referring to fig. 3, fig. 3 is a schematic structural diagram of a QKD system according to an embodiment of the present invention, including: source side encoder path 12 and test path 21. The test optical path 21 is the test optical path described in any of the above embodiments. The QKD system of fig. 3 is schematically illustrated with respect to the test optical path of fig. 2, and the test optical path of fig. 1 may be used.
In the manner shown in fig. 3, the test beam path 21 has a second optical power splitter SMC2, the first output port smc2_d1 of which is connected to the subsequent beam path 11.
The test optical path 21 obtains the optical signal emitted from the source end encoding optical path 12, and sends the attenuated optical signal to the subsequent optical path 11, where the subsequent optical path 11 includes: a variable optical attenuator VOA and a Filter; the optical signal output from the test optical path 21 sequentially passes through the variable optical attenuator VOA and the Filter.
It should be noted that, in the embodiment of the present invention, the implementation manner of the subsequent optical path 11 is not limited to including the variable optical attenuator VOA and the Filter, and the specific structure of the subsequent optical path 11 may be designed according to the measurement and detection functions required to be implemented by the subsequent optical path 11.
The source-end encoding optical path 12 is a polarization state preparation optical path, and is used for emitting polarized light of four polarization states, wherein the four polarization states are P-state, N-state, H-state and V-state respectively, two polarization directions are perpendicular to each other, the other two polarization directions are perpendicular to each other, specifically, the P-state and N-state polarization directions are perpendicular, and the H-state and V-state polarization directions are perpendicular.
In the mode shown in fig. 3, taking the polarization encoding of the decoy BB84 protocol as an example, the source-end encoding optical path 12 is a polarization-state preparation optical path, two sets of orthogonal states of polarization encoding H/V, P/N are prepared, and the two sets of orthogonal states are input to the first input port smc2_d1 of the second optical power beam splitter SMC2 with the beam splitting ratio of 99:1 through the first input port smc1_d1 of the first optical power beam splitter SMC1 with the beam splitting ratio of 99:1, so that a large attenuation of about 40dB is realized, and the first output port smc2_d1 of the second optical power beam splitter SMC2 is connected to an I/O port through a link formed by an adjustable optical attenuator VOA, a Filter and other optical passive devices, so that the output light intensity of the I/O port is ensured to be at a single photon level.
As described above, the attenuation loss from the first input port smc1_d1 of the first optical power splitter SMC1 to the second output port smc1_d2 thereof is set to be less than 1dB, so as to facilitate the optical path detection, test and calibration functions from the source-side coded optical path 12 to the first optical power splitter SMC1, and the attenuation loss from the second input port smc2_d2 to the first output port smc2_d1 thereof is set to be less than 1dB when the second input port smc2_d2 inputs an external test signal to the second optical power splitter SMC2, so as to facilitate the VOA attenuation calibration and filter center wavelength detection functions from the second input port smc2_d2 to the QKD system I/O port optical path.
Compared with the prior art, the QKD system adopts the test light path in the embodiment, and forms the test light path through a conventional optical passive beam splitter cascade connection mode (the number N of the optical passive beam splitters is more than or equal to 1), so that the test light path integrating attenuation, detection and test functions is realized, the incapability of realizing the test and detection functions caused by large link attenuation is avoided, and the light intensity calibration and the optical link problem investigation and detection are greatly simplified. The QKD system is not limited to a decoy BB84 polarization coding scheme, and is also applicable to coding modes under any other protocols and the related technical fields of optical communication.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the QKD system of the embodiment, since it corresponds to the test optical path of the embodiment, the description is relatively simple, and the relevant points will be described with reference to the corresponding parts of the test optical path.
It is further noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such article or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in an article or apparatus that comprises such element.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (8)
1. A test optical path for a QKD system, the QKD system including a source-side encoded optical path, the test optical path comprising:
a first optical power splitter having a first output port, a second output port, and at least one input port;
an input port of the first optical power beam splitter is used for connecting with an output end of the source end coding optical path so as to obtain an optical signal emitted after being coded by the source end coding optical path; the first optical power beam splitter divides the optical signals emitted by the source end coding optical path into two paths of optical signals according to a set beam splitting ratio, and the two paths of optical signals are respectively output through a first output port and a second output port; one path of optical signal output by the second output port is used for measuring optical parameters, and the first output port is used for connecting a subsequent optical path to provide optical signals for the subsequent optical path;
the test optical path further includes: at least one second optical power splitter having a first input port, a second input port, a first output port, and a second output port; the second input port of the second optical power beam splitter connected with the subsequent optical path is used for inputting an external test signal, the external test signal is divided into two paths according to a set beam splitting ratio through the second optical power beam splitter, the two paths of the external test signal are respectively output through the two output ports of the second optical power beam splitter, and the optical parameter measurement is carried out on the external test signal through the subsequent optical path;
when one second optical power beam splitter is arranged, the first input port of the second optical power beam splitter is connected with the first output port of the first optical power beam splitter, and the first output port of the second optical power beam splitter is used for connecting the subsequent optical path;
when the second optical power splitters are provided with the plurality of second optical power splitters, the plurality of second optical power splitters are cascaded, a first input port of the second optical power splitter of a first stage is connected with a first output port of the first optical power splitter, and a first output port of the second optical power splitter of a last stage is used for being connected with the subsequent optical path; for any two adjacent second optical power beam splitters, the following stage of the second optical power beam splitter
The first input port of the second optical power splitter is connected with the first output port of the second optical power splitter of the previous stage.
2. The test optical path of claim 1, wherein the external test signal input at the second input port of the second optical power splitter connected to the subsequent optical path passes through the first output port with a loss of less than or equal to 3dB.
3. The test optical path of claim 1, wherein for the second optical power splitter, for an optical signal incident on its first input port, the intensity of an optical signal output by its first output port is less than or equal to the intensity of an optical signal output by its second output port.
4. The test optical path of claim 1, wherein for the first optical power splitter, for an optical signal incident on its first input port, the intensity of an optical signal output by its first output port is less than or equal to the intensity of an optical signal output by its second output port.
5. The test optical path of claim 1, wherein the first optical power splitter has a first input port for connecting the source coded optical path and a second input port;
the beam splitting ratio of the first optical power beam splitter is the same as the beam splitting ratio of the second optical power beam splitter.
6. A QKD system, comprising: a source coded light path and a test light path as claimed in any one of claims 1 to 5.
7. The QKD system of claim 6, wherein the source-side encoded optical path is a polarization state preparation optical path configured to emit four polarization states of polarized light, two of the four polarization states being orthogonal to each other and the other two of the four polarization states being orthogonal to each other.
8. The QKD system of claim 6 or 7, wherein the test optical path acquires the optical signal exiting the source-side encoded optical path and transmits the attenuated optical signal to a subsequent optical path comprising: a variable optical attenuator and a filter;
and the optical signals output by the test optical path sequentially pass through the variable optical attenuator and the filter.
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| CN208924245U (en) * | 2018-11-30 | 2019-05-31 | 科大国盾量子技术股份有限公司 | A kind of optical system for testing and QKD system |
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