阅读说明：本技术 光纤干涉仪臂长差测试系统及测试方法 (Optical fiber interferometer arm length difference testing system and testing method ) 是由 叶蕾 叶青 蔡海文 翟荣辉 王照勇 卢斌 于 2020-04-22 设计创作，主要内容包括：一种基于随机相位噪声分离技术的光纤干涉仪臂长差测试系统及测试方法,该系统包括：扫描激光器、单频激光器、测试光路、待测光纤干涉仪、信号采集模块、信号处理系统。测试光路是由1个2*2光纤耦合器,1个光纤环形器,2个波分复用器(WDM)组成；待测光纤干涉仪为1副迈克逊干涉仪,由1个2*2光纤耦合器、1卷光纤线圈和2个法拉第反射镜组成；信号采集模块功能主要包括光电转换,模拟信号采集和信号模数转换；信号处理系统功能包括扫数据采集模块控制、光纤干涉仪臂长差数字信号处理。本发明能在噪声和振动环境下实现光纤干涉仪臂长差的高精度测试。(A test system and a test method for the arm length difference of an optical fiber interferometer based on a random phase noise separation technology are provided, the system comprises: the device comprises a scanning laser, a single-frequency laser, a test light path, an optical fiber interferometer to be tested, a signal acquisition module and a signal processing system. The test optical path consists of 12 x 2 optical fiber coupler, 1 optical fiber circulator and 2 Wavelength Division Multiplexers (WDM); the optical fiber interferometer to be measured is 1 Michelson interferometer, which consists of 12 x 2 optical fiber coupler, 1 coil of optical fiber coil and 2 Faraday reflectors; the signal acquisition module mainly has the functions of photoelectric conversion, analog signal acquisition and signal analog-to-digital conversion; the signal processing system comprises a scanning data acquisition module for controlling and an optical fiber interferometer arm length difference digital signal processing. The invention can realize high-precision test of the arm length difference of the optical fiber interferometer in a noise and vibration environment.)

1. A fiber interferometer arm length difference testing system is characterized by comprising: the device comprises a scanning laser (1), a single-frequency laser (2), a test light path (3), a data acquisition module (5) and a signal processing system (6); the test optical path (3) comprises a 2-by-2 optical fiber coupler (7), an optical fiber circulator (8), a first wavelength division multiplexer (9) and a second wavelength division multiplexer (10);

linear wavelength scanning light output by the scanning laser (1) and single wavelength light output by the single-frequency laser (2) are combined through the 2 x 2 optical fiber coupler (7), input through a first port of the optical fiber circulator (8), input into the optical fiber interferometer (4) to be tested through a second port, reflected by the optical fiber interferometer (4) to be tested, wherein one path returns along the original path, input through a second port of the optical fiber circulator (8), output to the first wavelength division multiplexer (9) through a third port of the optical fiber circulator (8), and the other path is directly input into the second wavelength division multiplexer (10); interference signals output by the first wavelength division multiplexer (9) and the second wavelength division multiplexer (10) are converted into digital signals by the data acquisition module (5), and then signal demodulation is carried out by the signal processing system (6).

2. The fiber optic interferometer arm length difference testing system of claim 1, wherein: the scanning laser is a narrow linewidth wavelength linear scanning laser.

3. The fiber optic interferometer arm length difference testing system of claim 1, wherein: the single-frequency laser is a narrow-linewidth single-frequency laser, and the wavelength is not in the wavelength scanning working range of the scanning laser.

4. The fiber optic interferometer arm length difference testing system of claim 1, wherein: the working wavelength of the first wavelength division multiplexer (9) and the working wavelength of the second wavelength division multiplexer (10) are the same as the wavelength of the single-frequency laser (2).

5. The fiber optic interferometer arm length difference testing system of claim 1, wherein: the optical fiber interferometer to be measured is a Michelson optical fiber interferometer or a Mach-Zehnder optical fiber interferometer.

6. The fiber optic interferometer arm length difference testing system of claim 1, wherein: the data acquisition module comprises a photoelectric conversion module, an analog signal acquisition module and a signal analog-to-digital conversion module in sequence.

7. The fiber optic interferometer arm length difference testing system of claim 1, wherein: the signal processing system comprises acquisition module control and optical fiber interferometer interference signal digital processing.

8. A method for testing the arm length difference of an optical fiber interferometer by using the arm length difference testing system of any one of claims 1 to 7, the method comprising the steps of:

step 1: one path of interference signal output by the optical fiber interferometer (4) to be detected is divided into a first interference signal I after sequentially passing through an optical fiber circulator (8) and a first wavelength division multiplexer (9)₁And a second interference signal I₂Said first interference signal I₁Is generated by the output light of a scanning laser (1) through an optical fiber interferometer (4) to be measured and is expressed asThe second interference signal I₂Is generated by the output light of the single-frequency laser (2) through the optical fiber interferometer (4) to be measured and is expressed asWherein A is₁And A₂Is the amplitude of the interference signal, n is the refractive index of the fiber, L is the arm length difference of the fiber interferometer, c is the speed of light,α is the phase noise, the phase difference between two output ends of the interferometer;

the other path of interference signal output by the optical fiber interferometer (4) to be measured is divided into a third interference signal I by a second wavelength division multiplexer (10)₃And a fourth interference signal I₄Said third interference signal I₃Is generated by the output light of a scanning laser (1) through an optical fiber interferometer (4) to be measured and is expressed asSaid fourth interference signal I₄Is generated by the output light of the single-frequency laser (2) through the optical fiber interferometer (4) to be measured and is expressed asWherein B is₁And B₂Is the amplitude of the interference signal;

step 2: 4 paths of interference signals form digital signals after passing through a data acquisition module (5) and then are input into a signal processing system (6);

and step 3: the signal processing system (6) performs signal processing on the 4 paths of interference signals, and the signal processing system specifically comprises the following steps:

①, the 4 interference signals are normalized to obtain a normalized interference signal I'₁～I′₄The mathematical expressions are respectively:

calculating a difference value F, wherein the formula is as follows:

③, FFT conversion is carried out on the difference value F to obtain a frequency value corresponding to the maximum value of the signal spectrum amplitudeAnd obtaining the arm length difference L of the optical fiber interferometer.

Technical Field

The invention relates to the technical field of optical fiber interferometers, in particular to a test system and a test method for improving the arm length difference test precision of an optical fiber interferometer in a vibration or noise environment.

Technical Field

The optical fiber sensor based on the optical fiber interferometer structure has excellent sensitivity and dynamic range, and can be used for detecting information such as underwater acoustic signals, strain, temperature and the like. Particularly, the optical fiber sensor based on the Michelson interferometer and the Mach-Zehnder interferometer is widely applied to the field of optical fiber sensing due to the characteristic of easy multiplexing.

Because the optical fiber interferometer adopts the optical coherence principle, the maximum arm length difference is limited by the coherence length of a light source, and the size of the arm length difference of the interferometer directly determines the noise level of an interference signal output by the interferometer; in addition, when the optical fiber interferometer is multiplexed on a large scale, the arm length difference of the interferometer influences the time sequence control precision of output signals of the interferometer, so that the arm length difference of the optical fiber interferometer needs to be accurately tested in the development process of the optical fiber interferometer, data support is provided for strict control of the arm length difference of the interferometer, and the application requirement of the actual optical fiber interferometer is met. Compared with a white light interferometry, an interferometer interference spectrum calculation method and an optical time domain reflectometer technology, the optical frequency domain reflectometer technology (OFDR) is more suitable for high-precision testing of arm length difference of a common optical fiber interferometer due to the characteristics of a testing range for testing hundreds of meters in magnitude, micrometer-scale spatial resolution, no testing dead zone and the like. The OFDR technology is researched by scientific researchers at home and abroad for many years, and the technology is relatively mature, for example, an OBR4600 instrument developed by Lunaninnovation company in the United states can realize the spatial resolution of 40 mu m in a test range of 70 m.

On the other hand, in the OFDR technology, a beat frequency signal between two paths of transmission signals of an interferometer is detected, a frequency value of the beat frequency signal is obtained in a frequency domain, and an arm length difference value of the corresponding optical fiber interferometer is obtained by utilizing a linear relation between the frequency of the beat frequency signal and two arm time delay differences. When noise or vibration exists in the external environment, particularly for the optical fiber interferometer with a long arm length difference (such as tens of meters) or the test arm wound on the sensitization component (such as an elastic body), random phase noise is easily generated along the test arm, when the strength of the phase noise reaches a certain degree, the beat frequency spectrum of the interferometer is widened, at the moment, the beat frequency and the time delay difference do not form a simple linear relation any more, and the precision of the measured arm length difference cannot be guaranteed through conventional calculation. For the problem of random noise generated by external environment noise or vibration in the OFDR testing technology, the research is less at present, and no relevant results are shown.

Therefore, in order to realize high-precision testing of the arm length difference of the optical fiber interferometer in a noise or vibration environment, a novel arm length difference testing system and a novel arm length difference testing method need to be designed.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a system and a method for testing the arm length difference of an optical fiber interferometer.

The technical solution of the invention is as follows:

the utility model provides a fiber interferometer arm length difference test system which characterized in that includes: the device comprises a scanning laser, a single-frequency laser, a test light path, a data acquisition module and a signal processing system; the test light path comprises a 2 x 2 optical fiber coupler, an optical fiber circulator, a first wavelength division multiplexer and a second wavelength division multiplexer;

linear wavelength scanning light output by the scanning laser and single wavelength light output by the single-frequency laser are combined through the 2 x 2 optical fiber coupler, input through the first port of the optical fiber circulator and then input into the optical fiber interferometer to be tested through the second port, and are reflected by the optical fiber interferometer to be tested, wherein one path returns along the original path, and is output to the first wavelength division multiplexer through the third port of the optical fiber circulator after being input through the second port of the optical fiber circulator, and the other path is directly input into the second wavelength division multiplexer; interference signals respectively output by the first wavelength division multiplexer and the second wavelength division multiplexer are converted into digital signals by the data acquisition module, and then signal demodulation is carried out by the signal processing system.

The scanning laser is a narrow linewidth wavelength linear scanning laser.

The single-frequency laser is a narrow-linewidth single-frequency laser, and the wavelength is not in the wavelength scanning working range of the scanning laser.

The working wavelength of the first wavelength division multiplexer and the working wavelength of the second wavelength division multiplexer are the same as the wavelength of the single-frequency laser.

The optical fiber interferometer to be measured is a Michelson optical fiber interferometer or a Mach-Zehnder optical fiber interferometer.

The data acquisition module comprises a photoelectric conversion module, an analog signal acquisition module and a signal analog-to-digital conversion module in sequence.

The signal processing system comprises acquisition module control and optical fiber interferometer interference signal digital processing.

A method for testing the arm length difference of an optical fiber interferometer by using the arm length difference testing system of the optical fiber interferometer comprises the following steps:

step 1: one path of interference signal output by the optical fiber interferometer to be detected is divided into a first interference signal I after sequentially passing through the optical fiber circulator and the first wavelength division multiplexer₁And a second interference signal I₂Said first interference signal I₁Is generated by scanning the output light of the laser through the fiber interferometer to be measured, and is expressed asThe second interference signal I₂Is generated by the output light of the single-frequency laser through the fiber interferometer to be measured and is expressed asWherein A is₁And A₂Is the amplitude of the interference signal, n is the refractive index of the fiber, L is the arm length difference of the fiber interferometer, c is the speed of light,α is the phase noise, the phase difference between two output ends of the interferometer;

the other path of interference signal output by the optical fiber interferometer to be measured is divided into a third interference signal I by a second wavelength division multiplexer₃And a fourth interference signal I₄Said third interference signal I₃Is generated by scanning the output light of the laser through the fiber interferometer to be measured, and is expressed asSaid fourth interference signal I₄Is generated by the output light of the single-frequency laser through the fiber interferometer to be measured and is expressed asWherein B is₁And B₂Is the amplitude of the interference signal;

step 2: 4 paths of interference signals form digital signals after passing through a data acquisition module and are input into a signal processing system;

and step 3: the signal processing system performs signal processing on the 4 paths of interference signals, and the signal processing system specifically comprises the following steps:

① normalizing the 4 paths of interference signals to obtain a normalized interference signal I₁'-I4', the mathematical expressions are respectively:

calculating a difference value F, wherein the formula is as follows:

③ FFT conversion is carried out to F, and a frequency value corresponding to the maximum value of the signal spectrum amplitude is obtainedThe arm length of the optical fiber interferometer can be obtainedThe difference L.

Compared with the prior art, the invention has the beneficial effects that: based on the OFDR technology, the dual-laser detection technology and the random phase noise separation algorithm are adopted, the influence of the random phase noise of the optical fiber on the spectrum broadening of the interference signal is eliminated, and the testing precision of the arm length difference of the optical fiber interferometer in a vibration or noise environment is improved.

Drawings

FIG. 1 is an overall framework diagram of the arm length difference testing system of the fiber interferometer of the present invention.

Fig. 2 is a schematic diagram of a test optical path structure in an embodiment of the present invention.

FIG. 3 is a flow chart of digital signal processing of the arm length difference of the fiber interferometer in the embodiment of the present invention.

FIG. 4 shows an interference signal I carrying random phase noise corresponding to a scanning laser in an embodiment of the present invention₁And interference signal I₃。

FIG. 5 shows an interference signal I carrying random phase noise corresponding to a single-frequency laser in an embodiment of the present invention₂And interference signal I₄。

FIG. 6 is a plot of a reflected beat frequency spectrum carrying random phase noise in an example of the present invention.

FIG. 7 is a plot of the reflected beat frequency spectrum after random phase noise cancellation in an example of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings and examples. However, the following examples are only for explaining the present invention, and the scope of the present invention is not limited by the following examples.

The invention discloses an optical fiber interferometer arm length difference testing system, which comprises a scanning laser 1, a single-frequency laser 2, a testing light path 3, an optical fiber interferometer 4 to be tested, a data acquisition module 5 and a signal processing system 6 as shown in figure 1.

The scanning laser is a narrow linewidth wavelength wide range scanning laser as shown in fig. 1, the coherence length is larger than 100m, and the wavelength scanning range is larger than 5 nm.

The single-frequency laser is a narrow-linewidth single-frequency laser as shown in fig. 1, the coherence length is greater than 100m, and the working wavelength is 1548 nm.

The test optical path is shown in fig. 2 and comprises 12 × 2 optical fiber coupler 7, 1 optical fiber loop 5, and 2 WDM9 and 10.

The operating wavelength of the WMD is approximately 1548 nm.

The optical fiber interferometer to be measured is a pair of Michelson interferometers, the arm length difference is about 9m, and the phase difference of two output ends of the interferometer is about 90 degrees.

The data acquisition module has the functions of photoelectric conversion, analog signal acquisition and 12-bit signal analog-to-digital conversion, and the sampling rate is greater than 20 MHz.

And the signal processing system is used for carrying out digital signal processing on the digital signals input from the data acquisition module.

The signal processing system comprises acquisition module control and optical fiber interferometer interference signal digital processing.

The control of the scanning laser comprises the steps that the wavelength range of the laser is set to be 1536-1540 nm, the scanning speed of the laser is set to be 40nm/s, and the output power of the laser is set to be 8 mW.

The data acquisition module controls the sampling rate to be set to be 20MHz/s, the sampling trigger type to be set to be rising edge trigger, and the sampling data volume to be set to be 1M.

The method for testing the arm length difference of the optical fiber interferometer by the arm length difference testing system of the optical fiber interferometer is characterized by comprising the following steps:

step 1: one path of interference signal output by the optical fiber interferometer to be detected is divided into a first interference signal I after sequentially passing through the optical fiber circulator and the first wavelength division multiplexer₁And a second interference signal I₂Said first interference signal I₁Is generated by scanning the output light of the laser through the fiber interferometer to be measured, and is expressed asThe second interference signal I₂Is produced by single-frequency laser output light passing through an optical fiber interferometer to be measuredRaw, is represented asWherein n is 1.4681, L is approximately equal to 9m, α is 90 °;

the other path of interference signal output by the optical fiber interferometer to be measured is divided into a third interference signal I by a second wavelength division multiplexer₃And a fourth interference signal I₄Said third interference signal I₃Is generated by scanning the output light of the laser through the fiber interferometer to be measured, and is expressed asSaid fourth interference signal I₄Is generated by the output light of the single-frequency laser through the fiber interferometer to be measured and is expressed as

Step 2: 4 paths of interference signals form digital signals after passing through a data acquisition module (5) and are input into a signal processing system;

and step 3: the signal processing system performs signal processing on the 4 paths of interference signals, and the signal processing system specifically comprises the following steps:

① normalizing the 4 paths of interference signals to obtain a normalized interference signal I₁′～I₄', the mathematical expressions are respectively:

calculating a difference value F, wherein the formula is as follows:

③ FFT conversion is carried out to F, and a frequency value corresponding to the maximum value of the signal spectrum amplitude is obtainedAnd obtaining the arm length difference L of the optical fiber interferometer.