阅读说明：本技术 一种基于七芯光子晶体光纤温度灵敏度测试方法 (Temperature sensitivity testing method based on seven-core photonic crystal fiber ) 是由 吴根柱 林春婷 卢俊城 魏文系 于 2021-09-17 设计创作，主要内容包括：本发明公开了一种基于七芯光子晶体光纤温度灵敏度测试方法。本发明首先利用有限元法计算七芯光子晶体光纤随温度变化的理论灵敏度,通过不断调整七芯光子晶体光纤的长度,使得理论灵敏度达到最高。然后将七芯光子晶体两端与单模光纤熔接,构成传感器头；一端的单模光纤与宽带光源光连接,另一端的单模光纤与光谱仪光连接,将所述的传感器头置于热源中。最后改变热源的温度,在选定的温度点记录光谱透射谱线图；选取其中的一组波谷,并获得不同温度点对应的波谷波长,对波谷波长与不同的温度点进行线性拟合,线性拟合后的斜率即为实际的七芯光子晶体光纤灵敏度。本发明通过模拟与实验结合去研究七芯光子晶体的温度传感特性,具有很大的参考价值。(The invention discloses a temperature sensitivity testing method based on a seven-core photonic crystal fiber. The method firstly utilizes a finite element method to calculate the theoretical sensitivity of the seven-core photonic crystal fiber along with the temperature change, and the theoretical sensitivity reaches the highest by continuously adjusting the length of the seven-core photonic crystal fiber. Then, welding two ends of the seven-core photonic crystal with the single-mode optical fiber to form a sensor head; the single-mode fiber at one end is optically connected with the broadband light source, the single-mode fiber at the other end is optically connected with the spectrometer, and the sensor head is placed in the heat source. Finally, changing the temperature of the heat source, and recording a spectral transmission line graph at the selected temperature point; and selecting a group of wave troughs, obtaining wave trough wavelengths corresponding to different temperature points, and performing linear fitting on the wave trough wavelengths and the different temperature points, wherein the slope after the linear fitting is the actual sensitivity of the seven-core photonic crystal fiber. The temperature sensing characteristic of the seven-core photonic crystal is researched by combining simulation and experiment, and the temperature sensing device has great reference value.)

1. A temperature sensitivity test method based on a seven-core photonic crystal fiber is characterized by comprising the following steps:

calculating the theoretical sensitivity of the seven-core photonic crystal fiber along with the temperature change by using a finite element method, and enabling the theoretical sensitivity to be highest by continuously adjusting the length of the seven-core photonic crystal fiber;

welding two ends of the seven-core photonic crystal with the single-mode optical fiber to form a sensor head; the single-mode optical fiber at one end is optically connected with the broadband light source, the single-mode optical fiber at the other end is optically connected with the spectrometer to form a temperature sensing device, and the sensor head is arranged in a heat source;

changing the temperature of a heat source, and recording a spectral transmission line graph at a selected temperature point; and selecting a group of wave troughs, obtaining wave trough wavelengths corresponding to different temperature points, and performing linear fitting on the wave trough wavelengths and the different temperature points, wherein the slope after the linear fitting is the actual sensitivity of the seven-core photonic crystal fiber.

2. The temperature sensitivity test method based on the seven-core photonic crystal fiber according to claim 1, characterized in that: the scanning wavelength of the spectrograph is set to be 1520nm-1610nm, and the central wavelength of the light source is 1550 nm.

3. The temperature sensitivity test method based on the seven-core photonic crystal fiber according to claim 2, characterized in that: the heat source is hot water, the initial temperature is 100 ℃, and a natural cooling mode is adopted.

4. The temperature sensitivity test method based on the seven-core photonic crystal fiber according to claim 3, characterized in that: the selected temperature points were 30 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃ and 80 ℃.

5. The seven-core photonic crystal fiber-based temperature sensitivity test method according to any one of claims 1 to 4, wherein: the calculations were performed using COMSOL software.

Technical Field

The invention relates to the field of temperature detection, in particular to a temperature sensitivity testing method based on a seven-core photonic crystal fiber.

Background

The temperature is an important parameter in the fields of marine environment monitoring, biological pharmaceutical industry, food detection, medicine, chemical industry and the like, and the application environment and the application prospect of the traditional electric temperature sensor in the market are greatly limited due to the problems that the detection precision is low, the response time is long, the anti-interference capability is weak, the thermistor is greatly influenced by the temperature and the like. The optical fiber is not influenced by an electromagnetic field, has stable sensing performance, higher measurement precision and quicker response time, and is widely applied to various fields and some extreme environments.

Seven-core Photonic Crystal Fiber (SCPCF) has 7 cores in a Photonic Crystal, the 7 cores being formed by introducing defects, i.e. reducing a number of air holes in the Photonic Crystal. Compared with single-core photonic crystals, the SCPCF has more fiber cores, extremely high design flexibility, less thermotropic beam distortion and larger effective mode area, so that a novel optical device suitable for various applications is possibly developed. And because the area of the mode field is large, the loss is reduced, the quality of the output light wave is high, and the performance of the temperature sensing device is better than that of a single-core photonic crystal.

However, the current research on the characteristics of the temperature sensor using the seven-core photonic crystal is particularly rare, and numerical simulation software is used. For example, Min Liu et al, in Seven-core photonic crystal fiber for discrete and structural mode mapping and temperature sensing, proposed that the mode intensity, effective mode area, waveguide dispersion and confinement loss of the liquid crystal permeated into the core are related to the temperature by using the finite element method to perform the measurement of temperature simulation experiment. This is the first study of SCPCF as a temperature sensor characterization but is limited to simulation software.

Disclosure of Invention

The invention aims to provide a method for combining theory and experiment, deeply explores the temperature sensing characteristic of a seven-core photonic crystal fiber and finds the optimal length of the seven-core photonic crystal so as to solve the problem of low temperature measurement sensitivity of the conventional photonic crystal.

The method specifically comprises the following steps:

the method comprises the steps of firstly, calculating the theoretical sensitivity of the seven-core photonic crystal fiber along with temperature change by using a finite element method, and enabling the theoretical sensitivity to be the highest by continuously adjusting the length of the seven-core photonic crystal fiber.

Welding two ends of the seven-core photonic crystal with the single-mode optical fiber to form a sensor head; the single-mode fiber at one end is optically connected with the broadband light source, the single-mode fiber at the other end is optically connected with the spectrometer to form a temperature sensing device, and the sensor head is arranged in a heat source.

Changing the temperature of a heat source, and recording a spectral transmission line graph at a selected temperature point; and selecting a group of wave troughs, obtaining wave trough wavelengths corresponding to different temperature points, and performing linear fitting on the wave trough wavelengths and the different temperature points, wherein the slope after the linear fitting is the actual sensitivity of the seven-core photonic crystal fiber.

Compared with the existing single-core photonic crystal temperature measurement method, the method has the following beneficial effects:

the seven-core photonic crystal has large mode field area, low loss and high output light wave quality, and the performance of the seven-core photonic crystal is better than that of a single-core photonic crystal when the seven-core photonic crystal is used as temperature sensing.

The two-core and seven-core photonic crystal fibers have more fiber cores, extremely high design flexibility, less thermotropic beam distortion and larger effective mode area, so that a novel optical device suitable for various applications is possibly developed.

And thirdly, the temperature sensing characteristic of the seven-core photonic crystal is researched by combining simulation and experiment for the first time, and the method has great reference value.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is an end view of a seven-core photonic crystal;

FIG. 2 is a schematic view of a temperature sensing device;

FIG. 3 is an interference spectrum plot for different temperatures;

FIG. 4 is a partial enlarged view of interference lines at different temperatures;

FIG. 5 is a graph of wavelength versus temperature;

in the figure: in FIG. 1, d is the diameter of the air hole of the seven-core photonic crystal, R is the distance between two air holes, and R is the diameter of the fiber core. In fig. 2, ASE is a broadband light source, OSA is a spectrometer, SMF is a single-mode fiber, and SCPCF is a seven-core photonic crystal.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

The embodiment comprises the following steps:

as shown in fig. 1, a geometrical structure diagram of an end face of the seven-core photonic crystal is constructed by utilizing COMSOL software, simulation calculation is carried out by utilizing the combination of electromagnetic waves and a thermal expansion module in solid mechanics, the effective refractive index difference between a base mode and a high-order mode of the seven-core photonic crystal is found by combining mode analysis, the relationship between the effective refractive index difference between the base mode and the high-order mode of the seven-core photonic crystal and the temperature is found by changing the temperature, the wave trough wavelength is calculated by the following formula, and the theoretical sensitivity is obtained by the ratio of the wave trough wavelength to the temperature.

Wherein the content of the first and second substances,is the effective refractive index of the fiber core in the seven-core photonic crystal,is the effective refractive index of the cladding in the seven-core photonic crystal, L is the length of the seven-core photonic crystal, and lambda_dipN is a trough wavelength, 0,1,2.

The length of the seven-core photonic crystal has great influence on the sensitivity, and if the length is too long or too short, the sensor is subjected to certain loss, so that the sensitivity is changed. In the COMSOL software, the length setting value of the seven-core photonic crystal is changed, the simulation calculation is carried out again, the sensitivity value of the length at the moment is calculated according to the formula, the length setting value is continuously changed, the sensitivity is compared, the highest sensitivity is searched, and the length is the optimal length at the moment.

The seven-core photonic crystal fiber is a photonic crystal fiber with 7 cores and air holes arranged in a regular hexagon, wherein the core diameter R is 4.3 mu m, the aperture R is 3.6 mu m, the hole spacing d is 4.3 mu m, and the cladding diameter is 125 mu m.

As shown in fig. 2, the fused SMF-SCPCF-SMF sensor head is placed in a beaker filled with hot water, wherein the single-mode fiber at one end is connected with ASE, and the other end is connected with OSA, thus forming a temperature sensing device. As the temperature of the hot water in the beaker dropped, a spectral transmission profile of the change in temperature was recorded every 10 ℃, as shown in fig. 3. A set of troughs from fig. 3 was selected as the study, as shown in fig. 4. The actual sensitivity is obtained by reading the valley wavelengths at different temperatures, processing the data, plotting the relationship between the valley wavelength and the temperature, and calculating the slope k as Δ λ/Δ T as shown in fig. 5.

The SMF-SCPCF-SMF sensing head is mainly a sensing structure of a section of seven-core photonic crystal fiber cascaded between two sections of single modes.

The COMSOL software is simulation software based on a finite element method, and is accurate in calculation and fast.

The center wavelength of the light source is 1550 nm.

The spectrometer described above is used to present a transmission line pattern of the sensing structure with the scanning wavelength set at 1520nm-1610 nm.

The initial temperature of the hot water is 100 ℃.

In conclusion, the method combining theory and experiment can solve the problems of low temperature measurement sensitivity, poor performance and the like of the existing photonic crystal, also achieves the characteristics of high temperature measurement linearity, strong stability and the like of the sensor manufactured by the method, and has good application value in the fields of marine environment monitoring, biological pharmaceutical industry, food detection and the like.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and modifications and variations of the present invention may occur to those skilled in the art. Any modification, improvement or the like made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.