CN105241848A - Liquid refractive index and temperature dual-parameter sensor, and preparation method thereof - Google Patents

Abstract

The invention discloses a liquid refractive index and temperature dual-parameter sensor and a manufacturing method thereof, comprising an input optical fiber, an output optical fiber, a capillary and a drop-shaped curved optical fiber grating structure, and the input optical fiber and the output optical fiber are respectively welded to the water-drop-shaped curved optical fiber grating structure. At both ends, the input fiber and the output fiber go out from the same side of the capillary. The water drop-shaped curved fiber grating structure is close to the capillary, and the water drop-shaped curved fiber grating structure is fixed to the capillary side; Fiber Bragg grating: based on the different responses of the fiber Bragg grating transmission trough and the interference trough caused by the drop-shaped curved fiber structure to temperature and refractive index, the dual-parameter measurement of refractive index and temperature is realized. Compared with the prior art, the sensor of the invention has the advantages of compact structure, simple manufacture, low cost, high sensitivity and the like.

Description

A dual-parameter sensor of liquid refractive index and temperature and its manufacturing method

technical field

The invention relates to the fields of optical fiber sensing and biochemistry, in particular to an all-fiber refractive index and temperature dual-parameter sensor based on a curved fiber grating (FBG) and a manufacturing method thereof.

Background technique

Optical fiber sensors have received extensive attention and research in recent years because of their advantages such as small size, high sensitivity, anti-electromagnetic interference, and long sensing distance. Refractive index and temperature are two important parameters of liquids, and their real-time and accurate simultaneous measurement is of great significance in the fields of biology and chemistry. Usually, because the mode field in the FBG is confined inside the fiber core, it is sensitive to changes in external temperature but insensitive to changes in refractive index. In order to realize the refractive index measurement of FBG, one method is to use acidic solution to corrode the cladding of FBG, and reduce the cladding of FBG to make the evanescent field of the core mode field interact with the external liquid, resulting in the reflection wavelength of FBG Drift with the change of the refractive index of the external liquid, the refractive index is sensed by detecting the change of the FBG resonance wavelength; another method is to use laser to etch the cladding of the FBG gate region to form a D-shaped cross-sectional structure. The evanescent field can be brought into contact with the external liquid to realize the measurement of the refractive index. However, in the production process of these existing sensors, either dangerous and complicated corrosion processes or special optical fiber etching equipment and techniques are required, which increase the difficulty and cost of sensor production and hinder the practical application of such sensors. . Therefore, it is particularly important to make FBG dual-parameter fiber optic sensors with simple structure, easy fabrication and low cost.

Contents of the invention

Aiming at the above-mentioned prior art and existing problems, the present invention proposes a liquid refractive index and temperature dual-parameter sensor and its manufacturing method, by monitoring the change of the center wavelength of the two troughs in the transmission spectrum to monitor the refractive index and temperature of the external liquid. The temperature is measured simultaneously.

The present invention proposes a liquid refractive index and temperature dual-parameter sensor, the sensor includes an input optical fiber 1, an output optical fiber 2, a capillary 4 and a drop-shaped curved fiber grating structure 6, and the input optical fiber 1 and the output optical fiber 2 are respectively welded on the water-drop-shaped curved The two ends of the fiber grating structure 6, the input fiber 1 and the output fiber 2 pass through the same side of the capillary 4, the water drop-shaped curved fiber grating structure 6 is close to the capillary 4, and the side of the water drop-shaped curved fiber grating structure 6 close to the capillary 4 is fixed to the capillary 4 ; The curved fiber grating structure 6 includes a section of fiber Bragg grating 5 whose coating is removed;

The sensor realizes dual-parameter measurement of refractive index and temperature based on the different responses of the transmission trough of the fiber Bragg grating 5 and the interference trough caused by the drop-shaped bent optical fiber structure 6 to temperature and refractive index.

The present invention also proposes a method for manufacturing a liquid refractive index and temperature dual-parameter sensor, the method comprising the following steps:

Strip off the coating layer of the curved fiber grating grating area and clean it with alcohol to form a fiber Bragg grating 5; pass the input optical fiber 1 and output optical fiber 2 welded at both ends of the curved optical fiber grating through the same side of the capillary, and the input optical fiber 1 is connected to the broadband The light source, the output optical fiber 2 is connected to the spectrometer to monitor the transmission spectrum in real time, slide the capillary towards the end of the curved fiber grating, and form a water drop-shaped curved fiber structure 6 in the curved fiber grating area, and observe the transmission spectrum at the same time until an obvious interference trough is produced; finally, the capillary 4 approaches Fix the bent fiber grating with glue on one side.

Compared with the prior art, the sensor of the invention has the advantages of compact structure, simple manufacture, low cost, high sensitivity and the like.

Description of drawings

Fig. 1 is the structure schematic diagram of liquid refractive index and temperature dual-parameter sensor of the present invention;

Figure 2 is a schematic diagram of the transmission spectrum of the sensor in an environment with an external refractive index of 1.0 and a temperature of 20°C;

Figure 3 is a schematic diagram of the variation of the transmission spectrum of the sensor with the external temperature;

Fig. 4 is a schematic diagram of the change of the central wavelength of trough 1 and trough 2 with the external temperature;

Fig. 5 is a schematic diagram of the variation of the transmission spectrum of the sensor with the external refractive index;

Fig. 6 is a schematic diagram of the change of the central wavelength of trough 1 and trough 2 with the external refractive index;

Reference signs: 1. Input optical fiber, 2. Output optical fiber, 3. Fixing glue, 4. Capillary tube, 5. Fiber Bragg grating (FBG); 6. Bending fiber (FBG) grating structure.

detailed description

The technical solution of the present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

The present invention will be further described below in conjunction with accompanying drawing and embodiment:

As shown in Figure 1, the sensor of the present invention is mainly made of input optical fiber 1, output optical fiber 2, capillary 4 and curved fiber grating (FBG) structure 5, wherein input optical fiber 1, output optical fiber 2 are welded on the curved fiber grating structure 5 respectively At both ends, the input optical fiber 1 and the output optical fiber 2 pass through the capillary 4 until the curved fiber grating structure 5 is close to the capillary 4, and the side of the water drop-shaped curved fiber grating structure 5 close to the capillary 4 is fixed by the fixing glue 3 and the capillary 4, and bent The fiber grating structure 5 includes a section of fiber Bragg grating whose coating layer has been removed.

The common commercial FBG used in this example, its input optical fiber 1 and output optical fiber 2 are standard single-mode optical fiber (CorningSMF-28); the fixing glue 3 is made of UV curing glue; the capillary 4 has an inner diameter of 0.5mm and a length of 3mm The glass tube; the length of the fiber grating (including the FBG gate region) whose coating layer has been removed in the curved fiber grating structure 5 is 25 mm, and the radius of curvature of the drop-shaped structure is 4.5 mm. FBG is the abbreviation of FiberBraggGrating, that is, Fiber Bragg Grating.

The specific manufacturing process of the sensor is as follows: firstly, peel off the coating layer of the curved fiber grating FBG grid area and clean it with alcohol; Optical fiber 1 is connected to a broadband light source, output optical fiber 2 is connected to a spectrometer to monitor the transmission spectrum in real time, slide the capillary towards the FBG end, form a drop-like structure in the FBG area, and observe the transmission spectrum at the same time, until an obvious interference trough is produced; finally, on the side of the capillary close to the FBG Glue to fix. (3) The response curves of FBG transmission troughs and curved structure interference troughs to changes in refractive index and temperature were calibrated through experiments. The calibrated sensor can be used to simultaneously measure the external refractive index and temperature.

The sensor of the present invention can be regarded as a combination of an FBG and a water drop-shaped curved structure (as shown in FIG. 1 ). For a broadband input optical signal, the output spectrum is the superposition of the transmission spectra of the FBG and the curved structure. For ease of analysis, the two can be discussed separately:

(1) For FBG, since the forward-transmitted core mode at the Bragg wavelength is almost completely coupled into the backward-transmitted core mode, its transmission spectrum appears to form a sharp trough at the Bragg wavelength;

(2) For a drop-shaped curved structure, due to the bending of the optical fiber, a part of the core mode enters the cladding, and reflection occurs at the interface between the cladding and the outside world, thereby forming a whispering gallery mode. When the mode is transmitted in the curved part, part Coupled back to the core, interference occurs between the core mode and the whispering gallery mode at the output fiber, forming one or more wide valleys on the output spectrum;

To sum up, two types of troughs appear on the transmission spectrum of the sensor of the present invention: one is caused by FBG, and the other is caused by a drop-shaped curved structure. The central wavelength of these two types of troughs will change linearly with the change of the external refractive index or temperature, but their slopes are different. Perform simultaneous measurements.

As shown in Figure 2, it can be seen that the sharp trough (trough 1) at 1539.2nm is caused by FBG, and the other two wider troughs are caused by the curved structure. Select the trough 1 and trough 2 shown in the figure as the monitoring objects, measure the changes of their central wavelength with temperature and refractive index respectively, and calibrate the sensor.

As shown in Figure 3, when the external refractive index is kept at 1.0, the central wavelengths of trough 1 and trough 2 both move to the long-wave direction with the increase of temperature, but the magnitude of the movement is different.

As shown in FIG. 4 , it can be seen that the central wavelengths of both trough 1 and trough 2 vary linearly with temperature, and the slope of the curve represents the sensitivity of the corresponding central wavelength to temperature change. It can be seen that the sensitivity of the central wavelength of the transmission valley generated by the sample sensor FBG and the drop-shaped curved structure to the external temperature change is 9.8pm/°C and 31.7pm/°C respectively; y is the strain amount, indicating the change of the central wavelength of the valley . In the figure, x is an independent variable, representing the size of the outside temperature; R represents the fitting coefficient of linear fitting.

As shown in Figure 5, the external temperature is maintained at 20°C, and the transmission spectrum of the sensor changes with the external refractive index. It can be seen that the central wavelengths of trough 1 and trough 2 both move to the long-wave direction with the increase of the external refractive index.

As shown in FIG. 6 , the central wavelength of the trough 1 and the trough 2 vary with the external refractive index, and both have a good linear relationship. The fitting results show that the sensitivities of FBG and curved structure to the center wavelength of the trough to the change of the external refractive index are 0.5050nm/RIU and 165.9276nm/RIU (RIU is the unit refractive index), respectively. In the figure, y is the strain variable, indicating the variation of the center wavelength of the trough; x is the independent variable, indicating the magnitude of the external refractive index; R is the linear correlation coefficient.

After the sensor is calibrated, the response of the two valleys of the sensor to temperature and refractive index changes can be expressed in the following matrix form:

Among them, ΔT and Δn represent the variation of external temperature and refractive index, and Δλ ₁ and Δλ ₂ represent the variation of the central wavelength of trough 1 and trough 2, respectively. The numbers in the formula are the sensitivity parameters determined by the above calibration process. According to the above formula, as long as the changes in the central wavelengths of the two troughs are measured, the corresponding changes in temperature and refractive index can be calculated, thereby realizing the simultaneous measurement of temperature and refractive index.

In summary, it can be seen that the sensor in the present invention has the ability to measure the refractive index and temperature at the same time, and the sensor has the advantages of low manufacturing cost, simple and compact structure, and high sensitivity.

Claims (2)

1. a liquid refractivity and temperature dual sampling device, it is characterized in that, this sensor comprises input optical fibre (1), output optical fibre (2), kapillary (4) and drops curved fiber optical grating construction (6), input optical fibre (1), output optical fibre (2) is welded on the two ends of drops curved fiber optical grating construction (6) respectively, input optical fibre (1), output optical fibre (2) passes from kapillary (4) the same side, drops curved fiber optical grating construction (5) is near kapillary (4), drops curved fiber optical grating construction (5) is fixed near kapillary (4) side and kapillary (4), curved fiber optical grating construction (6) comprises the Fiber Bragg Grating FBG (5) that a section is removed coat,

The interference trough that this sensor causes based on described Fiber Bragg Grating FBG (5) transmission trough and described drops curved fiber structure (6) responds temperature and the different of refractive index, realizes refractive index and temperature two parameter measurement.

2. liquid refractivity and a temperature dual sampling device method for making, it is characterized in that, the method comprises the following steps:

The coat in curved fiber grating grid region is divested and cleans with alcohol, as Fiber Bragg Grating FBG (5); The input optical fibre (1), the output optical fibre (2) that are welded on curved fiber grating two ends are passed from kapillary (4) the same side, input optical fibre (1) connects wideband light source, output optical fibre (2) connects spectrometer Real-Time Monitoring transmission spectrum, to curved fiber grating end slip kapillary (4), fiber grating (5) is caused to bend, form drops curved fiber optical grating construction (6), observing transmission spectrum simultaneously, significantly interfering trough to producing; Finally fix near curved fiber grating side point glue at kapillary (4).