System for measuring half-wave voltage of phase modulator

Abstract

The utility model discloses a system for measuring the half-wave voltage of a phase modulator. The system comprises a laser generation module, an optical coupler, a first phase modulator, a second phase modulator, a first Faraday mirror, a second Faraday mirror, a signal generator, a photoelectric detector and an oscilloscope. The utility model discloses a system for measuring the half-wave voltage of a phase modulator, which is characterized in that a high-frequency periodic square wave electric signal is loaded to a second phase modulator through a signal generator, and the phase drift amount caused by unstable factors such as a light source, an optical device and an external environment can be regarded as perturbation in a small time period; the half-wave voltage of the second phase modulator is obtained by accurately calculating the variable quantity of the number of the peak (valley) values of the sine (cosine) waveform, so that the judgment on the light intensity extreme point of an interference pattern is avoided, the measurement precision is improved, and the key core application in the fields of quantum communication and quantum calculation is realized.

Description

TECHNICAL FIELD

[0001] The utility model relates to quantum network and optical fiber communication technical field, concretely relates to a system for measuring half wave voltage of phase modulator. BACKGROUND

[0002] Quantum key distribution (QKD) system transmits information through the phase loaded on the light pulse, and the key device is a phase modulator.

[0003] Half wave voltage is one of important indexes of the phase modulator, and refers to the voltage required for the phase change of 180 degrees of optical signal. The measurement precision of half wave voltage will directly affect the performance of QKD system, and the too large or too small half wave voltage value can cause the system bit error rate to rise and the key generation rate to reduce.

[0004] At present, the extreme value measurement method can be used to measure the half wave voltage of the phase modulator, and its principle is that the phase modulator is placed on the measuring arm of the interferometer, and only a direct current voltage is loaded. When gradually changing the size of the direct current voltage, the extreme point can be judged through the size of the output light intensity of the interferometer, and the absolute value of the difference between the direct current voltages corresponding to adjacent maximum and minimum is the half wave voltage.

[0005] The extreme value measurement method is very simple in principle, but is easily affected by unstable factors such as light source, optical device and external environment (vibration, temperature change), and phase drift is easily caused. Therefore, the interference pattern is difficult to stabilize for a long time, and further the positions of the maximum and minimum of the output light intensity of the interferometer are difficult to determine, and the measurement precision is not high enough. UTILITY MODEL CONTENTS

[0006] The utility model discloses in order to solve the problem that the measurement precision of the half wave voltage of the phase modulator is not high enough at present by using the extreme value measurement method, and proposes a system for measuring half wave voltage of phase modulator.

[0007] In order to achieve the above-mentioned purpose, the technical scheme adopted by the utility model is as follows:

[0008] A system for measuring half wave voltage of phase modulator, comprising laser generation module, optical coupler, first phase modulator, second phase modulator, first Faraday mirror, second Faraday mirror, signal generator, photodetector and oscilloscope;

[0009] The output end of the laser generation module, one end of the first phase modulator, the first port of the second phase modulator, and the input end of the photodetector are respectively connected with different ports of the optical coupler; the other end of the first phase modulator is connected with the first Faraday mirror, the second port of the second phase modulator is connected with the second Faraday mirror, the third port of the second phase modulator is connected with one output end of the signal generator, and the other output end of the signal generator and the output end of the photodetector are respectively connected with different input ends of the oscilloscope.

[0010] In the above scheme, the second phase modulator is loaded with a high-frequency periodic square wave electrical signal by the signal generator, and the phase drift caused by unstable factors such as light source, optical device, and external environment in a small time period is regarded as a perturbation; then the half-wave voltage of the second phase modulator is obtained according to the change amount of the number of peaks (valleys) of the sine (cosine) waveform in the oscilloscope, avoiding the judgment of the extreme value points of the interference pattern light intensity, and the measurement accuracy is relatively high.

[0011] Preferably, the laser generation module comprises a continuous laser, an optical isolator, and a polarization fiber connected in sequence; and the output end of the polarization fiber is connected with the optical coupler.

[0012] Preferably, the tail fibers of the optical isolator, the optical coupler, the first phase modulator, the second phase modulator, the first Faraday mirror, and the second Faraday mirror are all polarization maintaining fibers.

[0013] Preferably, the polarization direction of the polarization fiber is parallel to the induced principal axis direction of the crystal in the second phase modulator.

[0014] Preferably, the first Faraday mirror and the second Faraday mirror are of the same structure.

[0015] Preferably, the frequency range of the periodic square wave electrical signal generated by the signal generator is 100 KHz-300 MHz.

[0016] In the above scheme, the change amount of the number of peaks (valleys) of the sine (cosine) waveform is increased by increasing the amplitude of the high-frequency periodic square wave modulation signal, and a more accurate half-wave voltage value is obtained after averaging.

[0017] Preferably, the optical coupler is a 2×2 50:50 optical coupler.

[0018] Preferably, the first phase modulator and the second phase modulator are of the same structure.

[0019] Preferably, the first phase modulator and the second phase modulator are both electro-optic phase modulators.

[0020] Preferably, the first phase modulator and the second phase modulator are both lithium niobate phase modulators.

[0021] The utility model has the beneficial technical effect:

[0022] The utility model provides a system for measuring half-wave voltage of phase modulator, load high frequency periodic square wave electric signal to second phase modulator through signal generator, can regard the phase shift amount caused by light source, optical device and external environment etc. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is whole module connection schematic drawing of the utility model;

[0024] Figure 2 It is principle view of electro-optic phase modulation in the utility model;

[0025] Among them: 1, laser generation module;11, continuous laser;12, optical isolator;13, polarized optical fiber;2, optical coupler;3, first phase modulator;4, second phase modulator;5, first Faraday mirror;6, second Faraday mirror;7, signal generator;8, photodetector;9, oscilloscope. DETAILED DESCRIPTION

[0026] In order to make the utility model's purpose, technical scheme and advantage more clearly clear, the following is with example to the utility model further detailedly explained, but the utility model's scope of protection is not limited to the following specific embodiment.

[0027] Example 1

[0028] As Figure 1 Indicated, a system for measuring half-wave voltage of phase modulator, including laser generation module 1, optical coupler 2, first phase modulator 3, second phase modulator 4 (to be measured phase modulator), first Faraday mirror 5, second Faraday mirror 6, signal generator 7, photodetector 8 and oscilloscope 9;

[0029] The output end of the laser generation module 1, one end of the first phase modulator 3, the first port of the second phase modulator 4, and the input end of the photodetector 8 are respectively connected with different ports of the optical coupler 2; the other end of the first phase modulator 3 is connected with the first Faraday mirror 5, the second port of the second phase modulator 4 is connected with the second Faraday mirror 6, the third port of the second phase modulator 4 is connected with one output end of the signal generator 7, and the other output end of the signal generator 7 and the output end of the photodetector 8 are respectively connected with different input ends of the oscilloscope 9.

[0030] In the specific implementation process, the signal generator 7 loads a high-frequency periodic square-wave electrical signal on the second phase modulator 4, and the phase drift caused by unstable factors such as the light source, optical devices, and external environment in a small time period (0.1 ms) is regarded as a perturbation; then the half-wave voltage of the second phase modulator 4 is obtained according to the change amount of the number of peaks (valleys) of the sine (cosine) waveform in the oscilloscope 9, avoiding the judgment of the extreme value points of the interference pattern light intensity, and the measurement accuracy is relatively high.

[0031] More specifically, the laser generation module 1 comprises a continuous laser 11, an optical isolator 12, and a polarization optical fiber 13 connected in sequence; the output end of the polarization optical fiber 13 is connected with the optical coupler 2.

[0032] More specifically, the pigtail of the optical isolator 12, the optical coupler 2, the first phase modulator 3, the second phase modulator 4, the first Faraday mirror 5, and the second Faraday mirror 6 is a polarization maintaining optical fiber.

[0033] In the specific implementation process, the polarization state of light will randomly change when it is transmitted in a single-mode optical fiber with the change of external environment (vibration, temperature change), which will cause the instability of the interference fringes of the two light signals. The polarization maintaining optical fiber can stably transmit linearly polarized light, and then a stable sine (cosine) waveform can be obtained in the oscilloscope 9, facilitating observation and counting.

[0034] More specifically, the polarization direction of the polarization optical fiber 13 is parallel to the induced principal axis direction of the crystal in the second phase modulator 4.

[0035] In the specific implementation process, the electro-optic phase modulation system is composed of a polarizer and an electro-optic crystal, as shown in Figure 2 When the polarization direction of the polarizer is parallel to the induced principal axis x' (or y') of the crystal, the linearly polarized light incident on the crystal is no longer decomposed into x' and y' components, but is polarized in one direction along the x' (or y') axis, so that the external electric field does not change the polarization state of the outgoing light, but only changes its phase.

[0036] More specifically, the first Faraday mirror 5 and the second Faraday mirror 6 are of the same structure.

[0037] More specifically, the frequency range of the periodic square wave electrical signal generated by the signal generator 7 is 100KHz-300MHz.

[0038] The amplitude of the high frequency periodic square wave signal in this embodiment is not strictly constrained, and only needs to be greater than the half-wave voltage of the lithium niobate phase modulator.

[0039] More specifically, the optical coupler 2 is a 2x2 50:50 optical coupler.

[0040] More specifically, the first phase modulator 3 and the second phase modulator 4 are of the same structure.

[0041] More specifically, the first phase modulator 3 and the second phase modulator 4 are both electro-optical phase modulators.

[0042] More specifically, the first phase modulator 3 and the second phase modulator 4 are both lithium niobate phase modulators.

[0043] In the specific implementation process, the light emitted by the continuous laser 11 passes through the optical isolator 12 and the polarization fiber 13 in turn to obtain a polarized light, and the polarized light is further divided into two equal-intensity optical signals after entering the 2x2 50:50 optical coupler;

[0044] One of the optical signals passes through the first phase modulator 3, is reflected by the first Faraday mirror 5, passes through the first phase modulator 3 again to reach the optical coupler 2; the other optical signal enters the second phase modulator 4, is phase-modulated by the high frequency (100KHz-300MHz) periodic square wave electrical signal generated by the signal generator 7, is reflected by the second Faraday mirror 6, enters the second phase modulator 4 again, is phase-modulated again by the same high frequency periodic square wave electrical signal generated by the signal generator 7, and then enters the optical coupler 2.

[0045] The two optical signals meet and interfere with each other in the optical coupler 2, and then enter the photodetector 8 together, are converted into electrical signals by photoelectric conversion, and finally the electrical signals are input into the oscilloscope 9 for observation.

[0046] According to the number of cycles of the sine (cosine) waveform in the oscilloscope 9, by gradually changing the amplitude of the high-frequency periodic square wave signal loaded on the second phase modulator 4, when the number of peaks (valleys) of the sine (cosine) waveform on the oscilloscope 9 increases (decreases) by 1, the modulation square wave voltage value is recorded as V1; when the number of peaks (valleys) of the sine (cosine) waveform observed on the oscilloscope 9 increases (decreases) by n, the modulation square wave voltage value is recorded as Vn; then |Vn-V1| / (n-1) is the half-wave voltage of the second phase modulator 4. By increasing the amplitude of the high-frequency periodic square wave modulation signal to increase the amount of change in the number of peaks (valleys) of the sine (cosine) waveform, the more accurate half-wave voltage value is obtained after taking the average.

[0047] The embodiment is consistent with the rectangular wave modulation signal of the Faraday-Michelson phase encoding scheme in the actual quantum key distribution system. Therefore, the measured lithium niobate phase modulator half-wave voltage under the structure is used in the actual quantum key distribution system, and the minimum system error rate and the maximum interference contrast can be obtained.

[0048] According to the disclosure and teaching of the above description, those skilled in the art of the present application can also change and modify the above embodiments. Therefore, the present application is not limited to the specific embodiments disclosed and described above, and some modifications and changes of the present application should fall within the protection scope of the claims of the present application. In addition, although some specific terms are used in the specification, these terms are only for convenience and do not constitute any limitation on the present application.

Claims

1. A system for measuring half-wave voltage of a phase modulator, characterized by, The laser generating module, the optical coupler, the first phase modulator, the second phase modulator, the first Faraday mirror, the second Faraday mirror, the signal generator, the photodetector and the oscilloscope are included. The output end of the laser generating module, one end of the first phase modulator, the first port of the second phase modulator and the input end of the photodetector are connected with different ports of the optical coupler respectively; the other end of the first phase modulator is connected with the first Faraday mirror, the second port of the second phase modulator is connected with the second Faraday mirror, the third port of the second phase modulator is connected with one output end of the signal generator, and the other output end of the signal generator and the output end of the photodetector are connected with different input ends of the oscilloscope respectively.

2. The system for measuring half-wave voltage of a phase modulator according to claim 1, wherein, The laser generating module includes a continuous laser, an optical isolator and a polarization fiber connected in sequence; the output end of the polarization fiber is connected with the optical coupler.

3. The system for measuring half-wave voltage of a phase modulator according to claim 2, wherein, The pigtail of the optical isolator, the optical coupler, the first phase modulator, the second phase modulator, the first Faraday mirror and the second Faraday mirror is a polarization maintaining fiber.

4. The system for measuring half-wave voltage of a phase modulator according to claim 2, wherein, The polarization direction of the polarization fiber is parallel to the induced principal axis direction of the crystal in the second phase modulator.

5. The system for measuring half-wave voltage of a phase modulator according to claim 1, wherein, The first Faraday mirror and the second Faraday mirror are of the same structure.

6. The system for measuring half-wave voltage of a phase modulator according to claim 1, wherein, The frequency range of the periodic square wave electrical signal generated by the signal generator is 100KHz-300MHz.

7. The system for measuring half-wave voltage of a phase modulator according to claim 1, wherein, The optical coupler is a 2×2 50:50 optical coupler.

8. The system for measuring half-wave voltage of a phase modulator according to claim 1, wherein, The first phase modulator and the second phase modulator are of the same structure.

9. The system for measuring half-wave voltage of a phase modulator according to claim 1, wherein, The first phase modulator and the second phase modulator are both electro-optic phase modulators.

10. The system for measuring half-wave voltage of a phase modulator according to claim 1, wherein, The first phase modulator and the second phase modulator are both lithium niobate phase modulators.

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