CN111982346B - A high-sensitivity fiber-optic temperature sensor - Google Patents

Abstract

The invention discloses a high-sensitivity optical fiber temperature sensor, which comprises an introduction optical fiber, a capillary collimating tube and an optical sheet. The optical sheet and the capillary collimation tube are directly connected, and the optical fiber is inserted into the capillary collimation tube and connected, wherein the two end faces of the optical sheet form an F-P cavity, and the optical fiber and the optical sheet are introduced to form an F-P cavity. The import fiber is used to import the light source signal and transmit the reflected light. When the temperature is changed, the capillary collimator and the optical sheet thermally expand, so that the change of the two F‑P cavities leads to a change in the spectrum, resulting in ultra-high temperature sensitivity. In addition, the cost of the optical sheet and the capillary collimation tube is low, the fabrication is simple, and complex fabrication processes and expensive equipment are not required, which can reduce the fabrication cost of the sensor.

Description

A high-sensitivity fiber-optic temperature sensor

technical field

The invention belongs to the technical field of optical fiber sensor manufacturing, and in particular relates to a high-sensitivity optical fiber temperature sensor.

Background technique

The advantages of fiber optic sensors, such as high sensitivity, anti-electromagnetic interference, good reliability, and abundant raw materials, have attracted widespread attention. Common fiber sensors include fiber gratings, fiber Sagnac interferometers, fiber Mach-Zehnder interferometers (MZI), and fiber Fabry–Perot resonators. Among them, the vernier effect produced by the fiber Fabry-Perot resonator can be used to amplify the sensitivity of the sensor, so it has received extensive attention. For example, in 2009, Dai and Jin et al. respectively proposed a vernier effect optical sensor based on a tandem optical fiber structure, and used the wavelength demodulation method to achieve ultra-high sensitivity measurement of refractive index. In 2014, Zhang et al. proposed to use the large mode field characteristics of hollow-core photonic crystal fiber (HC-PCF) to embed two sections of HC-PCF into single-mode fiber (SMF) to form a vernier effect fiber sensor with a cascaded FPI structure. Compared with a single FPI, the sensitivity of magnetic field measurement is increased by about 29 times. In 2015, Shao et al. proposed a vernier effect fiber optic temperature sensor with a series Sagnac interferometer. Compared with a single Sagnac interferometer, its sensitivity was increased by about 9 times, but The size of the entire sensor is large (the length of a single Sagnac interference ring is about 2 m), which makes it difficult to achieve temperature measurement with high spatial resolution. However, the materials and equipment required for the above-mentioned sensors are relatively expensive, and the production process is relatively complicated, which is not conducive to mass production of the sensors.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a high-sensitivity optical fiber temperature sensor, the optical fiber temperature sensor has significantly improved sensitivity to temperature, can be used in the field of precision measurement, and has the advantages of low cost, simple structure, and easy preparation. The method is simple and easy to implement.

The technical solution adopted by the present invention to solve the technical problem is as follows: a high-sensitivity optical fiber temperature sensor is provided, which includes an optical fiber, a capillary collimating tube and an optical sheet, an optical sheet is fixed at one end of the capillary collimating tube, and the optical fiber is removed from the The other end of the capillary collimator is inserted, wherein the two end faces of the optical sheet form an F-P cavity, and the optical fiber and the optical sheet form an F-P cavity. When the light beam enters the sensor, three reflected light beams are generated on the fiber end face and the two end faces of the optical sheet. These three reflected lights will form two F-P interferences, that is, the two reflected lights of the interface between the optical fiber and the optical sheet and the capillary collimator will form an F-P interference, and the two reflected lights of the optical sheet itself will form an F-P interference. One end face of the sheet is used simultaneously by two F-P interferences. The Vernier effect occurs when the free spectral ranges of the two F-P interferences are close in size. Optical fibers are used to introduce light source signals and transmit reflected light. When the temperature changes, the capillary collimator and the optical sheet thermally expand, so that the change of the two F-P cavities leads to the change of the spectrum, thus obtaining the ultra-high temperature sensitivity.

According to the above technical solution, the optical fiber is collimated by the capillary collimating tube, and the optical fiber is attached to the capillary collimating tube.

The difference between the inner diameter of the capillary collimating tube and the outer diameter of the optical fiber is less than 5%, which has the effect of collimation. At least one end of the capillary collimation tube is flat, and this end is used for attaching the optical sheet.

According to the above technical solution, the optical sheet is fixed at one end of the capillary collimating tube by means of adhesive bonding or resistance welding or pressure welding or laser welding.

According to the above technical solution, the optical sheets are polished on both sides and are parallel to each other.

According to the above technical solution, the optical sheet is a transparent sheet.

According to the above technical solution, the material of the optical sheet is quartz or sapphire wafer or glass, which is an optical material whose refractive index differs from that of the optical fiber by 0.2.

The present invention also provides a method for preparing a high-sensitivity optical fiber temperature sensor, which comprises the following steps. Step 1: ultrasonically clean the capillary collimation tube and the optical sheet with alcohol, and then clean the flat end face of the capillary collimation tube and the optical The sheets are closely attached, and the capillary collimation tube and the optical sheet are connected; in step 2, the optical fiber is inserted into the capillary collimation tube, and the spectrum is observed in real time. When the preset spectrum appears, the optical fiber and the capillary collimation tube are fixed; Step 3: Put the fabricated optical fiber temperature sensor into a high temperature furnace to test the temperature sensitivity and temperature response curve of the optical fiber temperature sensor.

The beneficial effects that the present invention produces are:

(1) When the temperature changes, the capillary collimator and the optical sheet will be thermally expanded, resulting in a very obvious shift in the spectrum, and high sensitivity can be obtained.

(2) Optical sheets and capillary collimators are inexpensive, and the cost of the sensor is extremely low.

(3) The processing technology of the optical sheet is very mature, and the length of the two F-Ps can be better controlled, which is conducive to mass production.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments, in which:

1 is a schematic structural diagram of an optical fiber temperature sensor according to an embodiment of the present invention;

Fig. 2 is the spectrogram of the optical fiber sensor;

Fig. 3 is the spectrogram of the optical fiber sensor at 310 ℃;

Fig. 4 is the spectrogram of the optical fiber sensor at 315 ℃;

Fig. 5 is the spectrogram of the optical fiber sensor at 320°C;

Fig. 6 is the spectrogram of the optical fiber sensor at 325°C;

Fig. 7 is the spectrogram of the optical fiber sensor at 330°C;

Figure 8 is a measurement diagram of the same wave trough position drift of the sensor when the temperature changes.

Among them, 1-capillary collimating tube; 2-optical sheet; 3-connection point; 4-optical fiber.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1:

As shown in FIG. 1 , in an embodiment of the present invention, a high-sensitivity optical fiber temperature sensor is provided, including an optical fiber, a capillary collimator, and an optical sheet. An optical sheet is fixed at one end of the capillary collimator, and the optical fiber is removed from the capillary. The other end of the collimating tube is inserted, wherein the two end faces of the optical sheet form an F-P cavity, and the optical fiber and the optical sheet form an F-P cavity. When the light beam enters the sensor, three reflected light beams are generated on the fiber end face and the two end faces of the optical sheet. These three reflected lights will form two F-P interferences, that is, the two reflected lights of the interface between the optical fiber and the optical sheet and the capillary collimator will form an F-P interference, and the two reflected lights of the optical sheet itself will form an F-P interference. One end face of the sheet is used simultaneously by two F-P interferences. The Vernier effect occurs when the free spectral ranges of the two F-P interferences are close in size. Optical fibers are used to introduce light source signals and transmit reflected light. When the temperature changes, the capillary collimator and the optical sheet thermally expand, so that the change of the two F-P cavities leads to the change of the spectrum, thus obtaining the ultra-high temperature sensitivity. The optical fiber is collimated by the capillary collimating tube, and the optical fiber is attached to the capillary collimating tube. The difference between the inner diameter of the capillary collimating tube and the outer diameter of the optical fiber is less than 5%, which has the effect of collimation. At least one end of the capillary collimation tube is flat, and this end is used for attaching the optical sheet. Use adhesive bonding or resistance welding or pressure welding or laser welding to fix the optical sheet at one end of the capillary collimator. Optical flakes are polished on both sides and parallel to each other. The material of the optical sheet is quartz or sapphire wafer or glass, which is an optical material whose refractive index differs from that of the optical fiber by 0.2.

Embodiment 2:

A ceramic ferrule is used as a capillary collimation tube, the ceramic ferrule is placed in a beaker, alcohol is added to the beaker, and ultrasonic waves are used to clean it for 3 mins. Then pour out the alcohol, add new alcohol, and repeat the cleaning 3 times. After the ceramic ferrule is cleaned, use a heating plate to heat it to evaporate the alcohol remaining in the ceramic ferrule.

Then, the glass flake with a thickness of 180um was taken out, and the glass flake was cleaned by the same method. Place the cleaned glass sheet horizontally on a clean platform, and then place one end of the ceramic ferrule on the glass sheet for use.

Mix the two-component high temperature adhesive DB5014 in a ratio of 1:1. And drop the prepared high-temperature adhesive on the connection between the ceramic ferrule and the glass sheet. After that, it is cured according to the curing method of high temperature adhesive.

Then insert the optical fiber with the jumper into the ceramic ferrule, and connect the jumper to the demodulator to observe the spectral change of the sensor in real time. When the spectrum becomes the spectrum in Figure 2, drop the high-temperature adhesive on the connection between the ceramic ferrule and the optical fiber, and cure. At this point the sensor fabrication is complete.

Figure 1 shows a schematic diagram of the structure of a highly sensitive optical fiber temperature sensor. Figure 2 shows the spectrogram of the fiber optic sensor.

Figures 3 to 7 show the spectrograms of the optical fiber sensor at 310°C-325°C, and Figure 8 is a measurement diagram of the same wave trough position drift of the sensor according to the embodiment of the present invention when the temperature changes.

It should be understood that, for those skilled in the art, improvements or changes can be made according to the above description, and all these improvements and changes should fall within the protection scope of the appended claims of the present invention.

Claims (1)

1. A method for preparing high-sensitivity optical fiber temperature sensor is characterized in that the optical fiber temperature sensor comprises an optical fiber, a capillary collimator and an optical sheet, wherein the optical sheet is fixed at one end of the capillary collimator, and the optical fiber is inserted into the other end of the capillary collimator, wherein an F-P cavity is formed on two end faces of the optical sheet, and the optical fiber and the optical sheet form the F-P cavity; aligning the optical fiber by a capillary collimator, attaching the optical fiber to the capillary collimator, and fixing an optical sheet at one end of the capillary collimator by using an adhesive bonding or resistance welding or pressure welding or laser welding mode; the preparation method comprises the following steps that firstly, the capillary collimator and the optical sheet are ultrasonically cleaned by alcohol, then the smooth end surface of the capillary collimator is tightly attached to the optical sheet, and the capillary collimator and the optical sheet are connected with the optical sheet; inserting the optical fiber into the capillary collimator, observing the spectrum in real time, and fixing the optical fiber and the capillary collimator when a preset spectrum appears; and step three, placing the manufactured optical fiber temperature sensor into a high-temperature furnace, and testing the temperature sensitivity and the response curve of the optical fiber temperature sensor to the temperature.

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