CN113376105A

CN113376105A - Optical fiber humidity sensor

Info

Publication number: CN113376105A
Application number: CN202110803528.2A
Authority: CN
Inventors: 孙小燕; 曾理; 董欣然; 张立木; 胡友旺; 段吉安
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2021-07-15
Filing date: 2021-07-15
Publication date: 2021-09-10

Abstract

The invention discloses an optical fiber humidity sensor, which is characterized in that a layer of MOFs coating is prepared on the surface of a Mach-Zehnder interference structure formed by a single-mode optical fiber, a thin-core optical fiber and a single-mode optical fiber (STS), so that the spectrum of the structure can be obviously changed along with the change of the environmental humidity. Compared with the existing humidity sensor, the humidity sensor has the advantages of small volume, high sensitivity, electromagnetic interference resistance, no need of a power supply, capability of working for a long time in a severe environment and the like. The optical fiber humidity sensor provided by the invention is suitable for the fields of biomedicine, industrial production, food storage and the like which need continuous humidity monitoring.

Description

Optical fiber humidity sensor

Technical Field

The invention belongs to the technical field of optical fiber sensing, and particularly relates to an optical fiber humidity sensor.

Background

Humidity is used as an important physical parameter, plays an important role in the fields of biological medicine, industrial production, food storage and the like, and has important guiding significance for accurately acquiring environmental humidity for a long time in the process of generating life. Traditional electricity humidity transducer is difficult to be suitable for with adverse circumstances, and optical fiber sensor has corrosion-resistant, anti-electromagnetic interference, need not the advantage of power supply, can satisfy the long-time measurement demand under adverse circumstances such as inflammable and explosive, forceful electric magnetic interference, has irreplaceable advantage.

Various optical fiber humidity sensors with different structures have been proposed at present, but most of them have the disadvantages of complex manufacture, low sensitivity, slow response speed and the like. MOFs are a class of metal organic framework compounds. The crystalline porous material with the periodic network structure can effectively adsorb water molecules in the air, so that the refractive index of the crystalline porous material is changed, and if the crystalline porous material is coated on the surface of an optical fiber sensing structure, a high-sensitivity optical fiber humidity sensor can be manufactured.

Disclosure of Invention

Technical problem to be solved

In order to solve the above problems in the prior art, the present invention aims to provide an optical fiber humidity sensor with simple manufacture and high sensitivity.

(II) technical scheme

The invention provides an optical fiber humidity sensor, which comprises a broadband light source, a spectrometer and a sensing head, and is characterized in that: the sensing head consists of a single mode fiber, a fine core fiber and MOFs coatings. A section of thin core optical fiber is welded between two sections of single mode optical fibers, and MOFs is coated on the surface of the thin core optical fiber with the coating layer removed; when humidity is tested, one end of the single-mode optical fiber at two ends of the fine core is connected with a broadband light source to serve as an input optical fiber, and the other end of the single-mode optical fiber is connected with a spectrometer to serve as an output optical fiber.

(III) advantageous effects

Compared with the prior art, the invention has the beneficial effects that:

(1) the sensor is simple in manufacturing process, and can be manufactured by only welding the thin-core optical fiber without the coating layer between two sections of single-mode optical fibers and then soaking the thin-core optical fiber into a pre-prepared MOFs reagent for standing for 48 hours

(2) The sensor has extremely high humidity sensitivity

(3) The sensor does not damage the optical fiber in the manufacturing process, and the mechanical strength of the optical fiber structure is ensured.

Drawings

The features and advantages of the present invention will be more clearly understood by reference to the accompanying drawings, which are illustrative and not to be construed as limiting the invention in any way, and in which:

FIG. 1 is a schematic structural diagram of a MOFs coated single mode fiber-fine core fiber-single mode fiber humidity sensor;

FIG. 2 is a schematic view of a humidity sensor feature of the present invention;

FIG. 3 is a graph of the spectral shift of the interference peak of the humidity sensor of the present invention at different humidities;

FIG. 4 is a graph of a fit of the interference peak of the humidity sensor of the present invention as a function of humidity.

In the figure: 1. input end single mode fiber, 2, thin core fiber, 3, output end single mode fiber, 4, broadband light source, 5, spectrometer, 6, fiber humidity sensor

Detailed Description

The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples.

The manufacturing method of the optical fiber humidity sensor comprises the following specific steps: firstly, stripping a coating layer of the thin-core optical fiber 2, and cutting the thin-core optical fiber into 45mm long by using an optical fiber cutter; secondly, welding one end of the single-mode optical fiber with an input end single-mode optical fiber 1 by using an optical fiber welding machine, and welding the other end of the single-mode optical fiber with an output end single-mode optical fiber 3 by using an optical fiber welding machine; and thirdly, immersing the single-mode-fine core-single-mode fiber structure manufactured in the second part into the prepared MOFs reagent, standing at room temperature for 48 hours, taking out and airing, and finishing the manufacture.

When the humidity is tested, the single-mode fiber 1 at the input end is connected to the broadband light source 4, the single-mode fiber 3 at the output end is connected to the spectrometer, and the fiber humidity sensor 6 is arranged in an environment to be tested. The MOFs coating has hygroscopicity, can absorb water in air, enables the refractive index to change, influences the coupling between a fundamental mode and a high-order mode in the fine-core optical fiber, and causes the wavelength of an interference peak of a transmission spectrum of the device to shift; the change of the humidity to be measured can be demodulated by measuring the change of the output spectrum of the humidity sensor.

FIG. 3 is a diagram showing the shift of interference peak spectrum with humidity change in the humidity change range of 82.1% -87.5% at room temperature; the interference peak shifts to the long wavelength direction along with the gradual increase of the environmental humidity; FIG. 4 is a graph of interference peak shift as a function of humidity, and the sensor has a sensitivity of 1220 pm/% RH and a correlation coefficient of 0.9972 in the relative humidity range of 82.1% -87.5%. From the experimental results, the optical fiber humidity sensor has extremely high humidity sensitivity and linearity.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations fall within the scope defined by the appended claims.

Claims

1. The optical fiber humidity sensor is characterized by comprising a single-mode optical fiber, a fine-core optical fiber and MOFs coatings; a small section of thin core optical fiber is welded between the two sections of single mode optical fibers, and the MOFs coating is coated on the surface of the thin core optical fiber; one section of the two sections of single mode fibers is used as an input fiber, and the other section of the two sections of single mode fibers is used as an output fiber. When humidity is tested, the single-mode optical fiber at the input end is connected to a broadband light source, and the single-mode optical fiber at the output end is connected to a spectrometer.

2. The single mode optical fiber of claim 1 having a model number SMF 28 and said fine core optical fiber having a model number 460 HP.

3. The fine core optical fiber according to claim 1, wherein the length of the fine core optical fiber is between 25mm and 80mm, and the coating layer is removed.

4. The MOFs coatings of claim 1 having a thickness of 100 to 500 μ ι η.