CN209930263U - Unequal-arm interferometer measuring device based on polarization selection - Google Patents
Unequal-arm interferometer measuring device based on polarization selection Download PDFInfo
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Abstract
The application provides a not waiting for arm interferometer measuring device and test method based on polarization selection, measuring device wherein, when being used for waiting for not waiting for arm interferometer performance test, light source module is used for outputting periodic pulse light, through the polarization modulation of polarization modulation module, then only contains interference pulse in the messenger signal to be measured through the analysis polarization module, at last through the direct measurement light intensity value of power meter to calculate the parameter value that is used for evaluating waiting for not waiting for arm interferometer performance according to the light intensity value. Therefore, the light source of the measuring device adopts a common periodic light source, the power meter is adopted in the measuring device for measuring, and compared with the existing measuring device adopting a wide-spectrum light source and a spectrometer, the cost is greatly reduced. The test module of this application is because the power meter that uses, can audio-visual accurate reaction measuring result, and the current measuring device adopts the spectrum appearance, needs to utilize experience estimation method or meter algorithm to obtain the contrast according to the spectrogram that measures.
Description
Technical Field
The application relates to the field of optical communication equipment testing, in particular to an unequal-arm interferometer measuring device based on polarization selection.
Background
Quantum key distribution systems typically employ phase encoding, temporal phase encoding, and the like, wherein phase encoding schemes are often implemented using unequal-arm interferometers. While the interference effect of the unequal arm interferometer will significantly affect the error rate (signal-to-noise ratio) of the quantum key distribution system. In order to ensure that the interference of quantum optical signals passing through the unequal arm interferometer reaches a high contrast ratio, and the error rate (signal-to-noise ratio) of the quantum key distribution system is within a certain acceptable range (for example, not more than 3%), the contrast ratio is usually used as one of parameters for evaluating the interference effect of the unequal arm interferometer.
There are two main ways to obtain contrast in the existing solutions. The first way is to estimate according to the arm length difference of the unequal arm interferometer; the second mode is to establish a coherence calculation model of the unequal arm interferometer to be measured according to the arm length difference of the unequal arm interferometer and obtain the contrast of the unequal arm interferometer to be measured according to the coherence.
The two modes comprise the following specific steps: taking white light interference as an example, a measuring device of the to-be-measured unequal arm interferometer shown in fig. 1 is firstly established, and the measuring device comprises a wide-spectrum light source, a standard unequal arm interferometer and a spectrometer. When the method is used for measuring the arm length difference, the unequal arm interferometer to be measured is connected between the light source and the standard unequal arm interferometer. The specific method comprises the following steps: calculating the arm length difference DeltaL of the to-be-measured unequal arm interferometer according to the test result of the spectrometer (as shown in figure 2)DUTArm length difference DeltaL from standard unequal arm interferometerSTDThe calculation formula is as follows:
When | Δ LDUT-ΔLSTDWhen the | result is less than a certain threshold (e.g., 100 microns), it is determinedAnd if not, judging that the arm length difference of the to-be-detected unequal arm interferometer is unqualified. Completing the arm length difference Delta L of the to-be-measured unequal arm interferometerDUTArm length difference DeltaL from standard unequal arm interferometerSTDAfter the difference value measurement, it is a common practice to:
(1) empirical estimation method
According to experience, for quasi-monochromatic light, assuming that the central spectrum is square, when the error of the arm length difference of the unequal arm interferometer to be measured is less than 100 micrometers, the contrast of the interferometer is greater than 100:1 (typical empirical value). By this method, it can only be roughly obtained that the contrast of the inequality arm interferometer to be measured exceeds a certain value (e.g., 100), but it cannot be determined in particular.
(2) Measurement calculation method
Firstly, evaluating the spectral distribution of a quantum light source of a quantum key distribution system, wherein the light source is a quantum light source, and the test result is the spectral distribution G (omega) of the quantum light source, wherein omega is frequency.
For light wave with a certain frequency omega in the quantum light source, the electric vector is E (omega, r, t)
E(ω,r,t)＝E0(r)exp[-i(ωt+φ0)]
When the light wave passes through the to-be-detected unequal arm interferometer and the standard unequal arm interferometer to reach the detector, the electric vector of the light wave is E1(ω,r,t)＝E0(r)exp[-i(ωt+φ0+φ1)]
E2(ω,r,t)＝E0(r)exp[-i(ωt+φ0+φ2)]
The intensity of the light received at the detector is
I(ω)＝[E1+E2]*[E1+E2]*
Definition of
I1(ω)＝[E1]*[E1]*
I2(ω)＝[E2]*[E2]*
The total light intensity generated by the quantum light source on the detector can be obtained by integrating the frequency
I＝∫0 +∞I(ω)G(ω)dω
Calculating degree of coherence (degree of coherence) gamma12As follows
Wherein (phi)1-φ2) Can be calculated from the measurement results of white light interference.
By the method, the degree of coherence of the to-be-measured unequal arm interferometer can be roughly calculated, but the result still has an error with the true value of the degree of coherence of the to-be-measured unequal arm interferometer, and the error factors include:
errors introduced by the measurement instrument: for example, limited by the operating wavelength range of the broad spectrum light source, the spectral flatness, when | Δ LDUT-ΔLSTDWhen | is smaller, the test result of the spectrometer is an approximately flat spectral distribution, and accurate λ cannot be obtained at this time1、λ2. The computational model cannot be accurately traced
The characteristics of the to-be-measured unequal arm interferometer, for example, the problem of inconsistent insertion loss of the to-be-measured unequal arm interferometer is not considered, and inconsistent insertion loss of the to-be-measured unequal arm interferometer reduces the coherence of the to-be-measured unequal arm interferometer, so that the computed coherence is higher than the real coherence. Therefore, an accurate contrast cannot be obtained depending on the degree of coherence.
In summary, both the empirical estimation method and the measurement calculation method require the use of a broad spectrum light source and a spectrometer, so that there are two main disadvantages: (1) the price of an ideal wide-spectrum light source and a spectrometer is very expensive, so that the price of the existing measuring device of the to-be-measured unequal-arm interferometer is very expensive; (2) the contrast for evaluating the performance of the to-be-measured unequal arm interferometer cannot be directly measured by the spectrometer, but the arm length difference of the unequal arm needs to be calculated according to a spectrogram measured by the spectrometer, and then experience estimation or measurement is carried out according to the arm length difference to calculate the contrast, in addition, only the result of the measurement of the spectrometer with the frequency spectrum of the light source wide enough is accurate, so that the performance of the to-be-measured unequal arm interferometer cannot be intuitively and accurately reflected by the measurement result.
Interpretation of terms:
the quantum light source is a light source of which the frequency spectrum is basically consistent with that of a light source adopted by an actual quantum key distribution system;
the contrast ratio is defined as the ratio I of the light intensity of two output ports of the measuring device1/I2In which I1The large value of the light intensities of the two output ports is taken.
Disclosure of Invention
The application provides an unequal arm interferometer measuring device based on polarization selection to solve the problems that the measuring device for the performance of the unequal arm interferometer to be measured in the existing scheme is expensive and the test result is not intuitive and accurate.
The application provides an unequal arm interferometer measuring device based on polarization selection, which comprises a light source module, a polarization modulation module, an analyzing module, a standard unequal arm interferometer and a measuring module;
the polarization modulation module is arranged between the standard unequal arm interferometer and the measurement module, and the unequal arm interferometer to be measured is placed between the polarization modulation module and the measurement module;
the standard unequal-arm interferometer is a standard unequal-arm interferometer, and the polarization analyzing module is positioned on a light path between the polarization modulation module and the measuring module;
the light source module is used for outputting periodic pulsed light, and the periodic pulsed light passes through the unequal arm interferometer to be detected, the standard unequal arm interferometer, the polarization modulation module and the polarization analysis module to obtain a signal to be detected only containing interference pulses;
the measuring module comprises a power meter, and the power meter is used for measuring the light intensity value of the signal to be measured according to the received signal to be measured.
Preferably, the input end of the standard unequal arm interferometer is used for placing the to-be-measured unequal arm interferometer between the output end of the light source module and the input end of the standard unequal arm interferometer;
or the standard unequal arm interferometer is placed between the output end of the standard unequal arm interferometer and the input end of the polarization modulation module.
Preferably, the polarization modulation module is configured to make the polarization direction of the incoherent pulse perpendicular to the polarization direction of the interference pulse, and the polarization direction of the interference pulse is the same as the optical axis direction of the polarization analysis module.
Preferably, the BSs in the unequal arm interferometer to be tested and the standard unequal arm interferometer are both 50:50 beam splitters.
Preferably, the measuring module is further configured to evaluate the encoding and decoding performance of the optical quantum phase state of the inequality interferometer to be measured according to the light intensity value or the contrast value.
Preferably, the measuring device further comprises a phase shifter and a phase shifter control unit;
the phase shifter is arranged on one arm light path of the standard unequal arm interferometer, and the phase shifter control unit adjusts the phase shifter according to the parameter value measured by the measuring module and is used for compensating the influence of the external environment.
According to the scheme, the application has the following beneficial effects:
the application provides an unequal arm interferometer measuring device based on polarization selection and a test method thereof, wherein the measuring device is used for testing the performance of an unequal arm interferometer to be tested, a light source module is used for outputting periodic pulse light, the polarization modulation is carried out through a polarization modulation module, then only interference pulses are contained in a signal to be tested through the polarization selection of a polarization detection module, non-interference items influencing the accuracy of a measuring result are eliminated, finally, a light intensity value is directly measured through a power meter, and a parameter value used for evaluating the performance of the unequal arm interferometer to be tested is calculated according to the light intensity value. Therefore, compared with the prior art, the measuring device of the application has the following advantages:
(1) the device light source of this application adopts ordinary periodic light source, adopts the power meter to measure among the measuring device, current measuring device adopts wide spectrum light source and spectrum appearance to measure, and the wide spectrum light source price that a frequency spectrum is wider also needs tens of thousands RMB, a spectrum appearance needs hundreds of thousands RMB, the ordinary price of this application measuring device's periodic light source and power meter is also several hundreds of RMB, for the measuring device of current adoption wide spectrum light source and spectrum appearance, the cost reduces greatly.
(2) The test module of this application is owing to the power meter that uses to through the polarization modulation of polarization modulation module, then only contain interference pulse in the selection messenger signal to be measured through polarization again, eliminate the noninterference item that influences the measuring result accuracy, need not consider the insertion loss scheduling problem of the unequal arm interferometer that awaits measuring, can directly obtain accurate audio-visual parameter value that is used for evaluating the unequal arm interferometer performance that awaits measuring according to the light intensity value that measures. The existing measuring device adopts a spectrometer, the output is a spectrum, the performance of the to-be-measured unequal arm interferometer cannot be visually represented, the contrast is obtained by an empirical estimation method or a measuring meter algorithm according to the measured spectrogram, and the contrast obtained by the existing scheme is limited by the working wavelength range of a wide-spectrum light source and the influence of the spectrum flatness. Therefore, compared with the existing measuring device, the measuring device can intuitively and accurately reflect the measuring result.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a diagram of a conventional measurement device for measuring the performance of an unequal arm interferometer to be measured;
FIG. 2 is a spectrum measured by a conventional measuring apparatus;
FIG. 3 is a schematic diagram of a polarization selection-based measurement apparatus according to the present application;
FIG. 4 is a waveform diagram of an optical pulse passing through a corresponding module before non-coherent terms are eliminated according to the present application;
FIG. 5 is a schematic diagram of waveforms obtained after eliminating non-coherent terms by polarization modulation and polarization selection according to the present application;
FIG. 6 is a schematic diagram of another polarization selection-based measurement apparatus according to the present application;
FIG. 7 is a schematic structural diagram of a measuring device for compensating environmental disturbances according to the present application.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present application more comprehensible, the present application is described in further detail with reference to the accompanying drawings and the detailed description.
The application provides an unequal arm interferometer measuring device based on polarization selection, which comprises a light source module, a polarization modulation module, an analyzing module, a standard unequal arm interferometer and a measuring module; the polarization modulation module is arranged between the standard unequal arm interferometer and the measurement module, and the unequal arm interferometer to be measured is placed between the polarization modulation module and the measurement module; the standard unequal-arm interferometer is a standard unequal-arm interferometer, and the polarization analyzing module is positioned on a light path between the polarization modulation module and the measuring module; the light source module is used for outputting periodic pulsed light, and the periodic pulsed light passes through the unequal arm interferometer to be detected, the standard unequal arm interferometer, the polarization modulation module and the polarization analysis module to obtain a signal to be detected only containing interference pulses; the measuring module comprises a power meter, and the power meter is used for measuring the light intensity value of the signal to be measured according to the received signal to be measured.
Therefore, compared with the prior art, the measuring device of the present application has:
(1) the device light source of this application adopts ordinary periodic light source, adopts the power meter to measure among the measuring device, current measuring device adopts wide spectrum light source and spectrum appearance to measure, and the wide spectrum light source price that a frequency spectrum is wider also needs tens of thousands RMB, a spectrum appearance needs hundreds of thousands RMB, the ordinary price of this application measuring device's periodic light source and power meter is also several hundreds of RMB, for the measuring device of current adoption wide spectrum light source and spectrum appearance, the cost reduces greatly.
(2) The test module of this application is owing to the power meter that uses to through the polarization modulation of polarization modulation module, then only contain interference pulse in the polarization selection messenger signal to be measured of rethread polarization detection module, eliminate the noninterference item that influences the measuring result accuracy, need not consider the insertion loss scheduling problem of the unequal arm interferometer that awaits measuring, can directly obtain accurate audio-visual parameter value that is used for evaluating the unequal arm interferometer performance that awaits measuring according to the light intensity value that measures. The existing measuring device adopts a spectrometer, the output is a spectrum, the performance of the to-be-measured unequal arm interferometer cannot be visually represented, the contrast is obtained by an empirical estimation method or a measuring meter algorithm according to the measured spectrogram, and the contrast obtained by the existing scheme is limited by the working wavelength range of a wide-spectrum light source and the influence of the spectrum flatness. Therefore, compared with the existing measuring device, the measuring device can intuitively and accurately reflect the measuring result.
The position between the output end of the light source module and the input end of the standard unequal arm interferometer is used for placing the to-be-measured unequal arm interferometer; or the standard unequal arm interferometer is placed between the output end of the standard unequal arm interferometer and the input end of the polarization modulation module.
The positions of the to-be-measured unequal arm interferometer and the standard unequal arm interferometer are shown in the schematic diagrams of fig. 3 and fig. 6, the working flow of specifically eliminating incoherent items through polarization selection is illustrated by taking the output end of the light source module and the input end of the standard unequal arm interferometer as an example, the light source module sends out a light pulse, and the light pulse is split and then respectively passes through the long arm L of the to-be-measured unequal arm interferometer1And a short arm S1The waveform is then formed as S in FIG. 41And L1Two waveforms. If the incoherent term is not canceled, then waveform L1Respectively passing through long arms L of standard unequal-arm interferometers after beam splitting2And a long arm S2The resulting waveform is shown as L in FIG. 41S2And L1L2Wave form S1Respectively passing through long arms L of standard unequal-arm interferometers after beam splitting2And a long arm S2The resulting waveform is S as shown in FIG. 41S2And S1L2. Therefore, the waveform that can satisfy the coherence is L1S2And S1L2Therefore, the waveform output by the standard unequal-arm interferometer contains an incoherent term in addition to a coherent term. Therefore, the measurement result without eliminating the incoherent term contains the incoherent term, which results in that the performance of the to-be-measured unequal arm interferometer cannot be accurately evaluated.
Therefore, as shown in the schematic diagram of fig. 5, the polarization modulation module is configured to make the polarization direction of the incoherent pulse perpendicular to the polarization direction of the interference pulse, and the polarization direction of the interference pulse is the same as the optical axis direction of the polarization analysis module. That is, the analyzer in the analyzer module allows only polarized light in a certain vibration direction to pass through, when the polarization direction of the polarized light and the polarization direction of the incoherent term pulse transmitted by the analyzer are modulated to be consistent with the optical axis direction of the analyzer module, the polarized light can completely pass through the analyzer, and if the polarization direction of the polarized light is perpendicular to the optical axis direction of the analyzer module, the polarized light cannot pass through the analyzer.
BS in the test unequal-arm interferometer and BS in the standard unequal-arm interferometer are both beam splitters of 50:50, and the beam splitters of 50:50 ensure that light intensity at two output ends of a standard interferometer module is lossless.
The measuring module is also used for evaluating the encoding and decoding performance of the optical quantum phase state of the to-be-measured inequality arm interferometer according to the light intensity value or the contrast value. The measuring device of the application can judge the optical fiber interferometer to be measured according to the maximum value or the minimum value measured by the power meter, for example, the larger the maximum value or the smaller the minimum value is, the better the encoding and decoding performance of the optical quantum phase state of the optical fiber interferometer to be measured is. Of course, the measuring means may also be measured separatelyComparing the light intensities of the two output ends to obtain an accurate contrast value I1/I2In which I1And obtaining a specific measurement value of the unequal arm interferometer to be measured by taking a large value in the light intensities of the two output ports, wherein the specific measurement value can be specified through a contrast value.
In actual use, the measuring device may also be affected by the external environment, i.e. the arm length of the interferometer is affected by changes in the external environment, such as: external ambient temperature, vibration. In order to compensate the influence of the external environment, a phase shifter is added in the standard interferometer module for active feedback. Specifically, the method comprises the following steps: the testing device of the present application further includes a phase shifter and a phase shifter control unit, as shown in the schematic diagram of fig. 7; the phase shifter is arranged on one arm light path of the standard unequal arm interferometer, and the phase shifter control unit adjusts the phase shifter according to the parameter value measured by the measuring module to obtain the change relation of the parameter value.
Specifically, each time the phase shifter adjusts the arm length difference of the standard unequal arm interferometer according to the control instruction of the phase shifter control unit, the measuring module measures a parameter value, and the change relation of the parameter values can reflect the influence of the external environment on the testing device. Therefore, the phase shifter is adjusted by the phase shifter control unit according to the change relation of the obtained parameter value, and the length of the optical path of the arm is adjusted to compensate the influence of the external environment.
In addition, the light source module of this application outputs periodic pulsed light, includes: controlling the light pulse light emitting frequency output by the light source module to be f, wherein f is different from the arm length difference delta L of the standard unequal arm interferometerSTDThe relationship of (1) is:
wherein c is the speed of light in vacuum, and n is the refractive index of the material used for preparing the standard unequal-arm interferometer. The interference of the output periodic light is ensured.
The present application has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to limit the application. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the presently disclosed embodiments and implementations thereof without departing from the spirit and scope of the present disclosure, and these fall within the scope of the present disclosure. The protection scope of this application is subject to the appended claims.
Claims (6)
1. An unequal arm interferometer measuring device based on polarization selection is characterized by comprising a light source module, a polarization modulation module, an analyzing module, a standard unequal arm interferometer and a measuring module;
the polarization modulation module is arranged between the standard unequal arm interferometer and the measurement module, and the unequal arm interferometer to be measured is placed between the polarization modulation module and the measurement module;
the polarization analyzing module is positioned on an optical path between the polarization modulation module and the measuring module;
the light source module is used for outputting periodic pulsed light, and the periodic pulsed light passes through the unequal arm interferometer to be detected, the standard unequal arm interferometer, the polarization modulation module and the polarization analysis module to obtain a signal to be detected only containing interference pulses;
the measuring module comprises a power meter, and the power meter is used for measuring the light intensity value of the signal to be measured according to the received signal to be measured.
2. The interferometer measurement device of claim 1, wherein the input end of the standard interferometer is connected to the output end of the light source module, and the output end of the light source module is connected to the input end of the standard interferometer;
or the standard unequal arm interferometer is placed between the output end of the standard unequal arm interferometer and the input end of the polarization modulation module.
3. The polarization selection-based interferometer measuring device according to claim 1, wherein the polarization modulation module is configured to make the polarization direction of the incoherent pulse perpendicular to the polarization direction of the interference pulse, and the polarization direction of the interference pulse is the same as the optical axis direction of the polarization analysis module.
4. The polarization selection-based interferometer measuring device of claim 1, wherein the BS of the under-test interferometer and the BS of the standard interferometer are both 50:50 beam splitters.
5. The interferometer measurement device of claim 1, wherein the measurement module is further configured to evaluate the encoding and decoding performance of the photonic qubit state of the inequality interferometer under test according to the intensity value or the contrast value.
6. The polarization selection based interferometer measurement device of any one of claims 1-5, wherein the measurement device further comprises a phase shifter and a phase shifter control unit;
the phase shifter is arranged on one arm light path of the standard unequal arm interferometer, and the phase shifter control unit adjusts the phase shifter according to the parameter value measured by the measuring module and is used for compensating the influence of the external environment.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113324485A (en) * | 2021-05-26 | 2021-08-31 | 国开启科量子技术(北京)有限公司 | Arm length difference measuring system of unequal arm interferometer |
| CN113595630A (en) * | 2021-08-09 | 2021-11-02 | 国开启科量子技术(北京)有限公司 | Two-arm insertion loss calibration device and system for unequal-arm interferometer |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113324485A (en) * | 2021-05-26 | 2021-08-31 | 国开启科量子技术(北京)有限公司 | Arm length difference measuring system of unequal arm interferometer |
| CN113595630A (en) * | 2021-08-09 | 2021-11-02 | 国开启科量子技术(北京)有限公司 | Two-arm insertion loss calibration device and system for unequal-arm interferometer |
| CN113595630B (en) * | 2021-08-09 | 2022-04-01 | 国开启科量子技术(北京)有限公司 | Two-arm insertion loss calibration device and system for unequal-arm interferometer |
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