CN108398403A - A kind of cone of wavelength modulation type four light fibre humidity transducer - Google Patents

Abstract

The invention relates to a wavelength-modulated four-cone optical fiber humidity sensor, which includes a light source, a four-cone optical fiber and a detector for detecting changes in the wavelength position of light. Both ends of the four-cone optical fiber are respectively connected to the light source and the detector. The four-cone structure of the four-cone optical fiber is coated with an optical gel layer of moisture-sensitive material. When the present invention detects humidity, when the air with different humidity is in contact with the agarose gel film, the refractive index of the agarose gel film will change, thereby affecting the transmission characteristics of light in the optical fiber, by measuring the wavelength of the interference peak/valley The corresponding humidity of the surrounding environment can be obtained by changing the position, and the optical fiber adopts a four-cone structure to accumulate phase difference, which enhances the change of interference during optical coupling. When ensuring the sensitivity of the measurement, there is no need to greatly lengthen the four-cone fiber cone waist The length of the part, its structural principle is simple and reliable, the process steps are simple, the operation and preparation are easy, the product stability is good, and the service life is long.

Description

A wavelength-modulated four-cone fiber optic humidity sensor

technical field

The invention relates to the technical field of making an optical fiber humidity sensor, and more specifically refers to a wavelength modulation type four-cone optical fiber humidity sensor.

Background technique

Fiber optic humidity sensors have many advantages over traditional capacitance-resistive humidity sensors. Such as: small size, good stability, anti-electromagnetic interference. Nowadays, fiber optic humidity sensors have been widely used, such as grain storage in agriculture, high temperature environment in boilers, industrial fields and so on. In recent years, the measurement methods of optical fiber humidity sensors mainly include the following: spectroscopy, light intensity modulation, changing surface reflectivity, Bragg and long-period gratings, interferometers, etc.

In recent years, many people have improved the characteristics of the sensor by coating moisture-sensitive materials on the surface of optical fibers. However, light intensity modulation sensors are easily affected by light source power fluctuations, such as patent number: CN 107561039 A, which uses a light intensity modulation method, which is easily affected by light source fluctuations. Sensors using Bragg fiber gratings are expensive.

In order to solve the above problems, the Chinese utility model patent with the authorized announcement number CN 203287311U discloses a transmission optical fiber humidity sensor based on biconical thin-core single-mode optical fiber, including the first single-mode optical fiber, biconical thin-core single-mode fiber The optical fiber, the second single-mode optical fiber and the humidity sensitive film are composed of four parts. The surface of the cone waist of the biconical thin-core single-mode fiber is coated with a moisture-sensitive film; the first single-mode fiber and the second single-mode fiber are respectively connected with a broadband light source and a fiber optic spectrometer. Although the sensor device can cause changes in the refractive index of the humidity-sensitive film according to changes in ambient humidity, thereby causing changes in the transmission spectrum characteristics of the sensor. According to the wavelength change of the characteristic peak in the transmission spectrum, the humidity value of the environment can be obtained. Although the sensor adopts the method of wavelength demodulation to overcome the influence of the light intensity stability of the light source, the sensor is based on the structure of the double cone thin core, and the single mode of the thin core must be drawn long enough, that is, the thin core is very thin, such as Otherwise, it is difficult to measure the change of the characteristic peak wavelength in the transmission spectrum of the sensor by a fiber optic spectrometer. In addition, the existing optical fiber humidity sensors usually work in the 1.3 micron or 1.5 micron waveband, but this waveband has no strong absorption of water molecules, and the sensitivity is not high.

Contents of the invention

The invention provides a wavelength-modulated four-cone optical fiber humidity sensor, aiming at overcoming the deficiencies of the prior art and providing an optical fiber humidity sensor with simple structure, low cost and high sensitivity.

The present invention adopts following technical scheme:

A wavelength-modulated four-cone optical fiber humidity sensor, including a light source, a four-cone optical fiber, and a detector for detecting changes in the wavelength position of light. Both ends of the four-cone optical fiber are respectively connected to the light source and the detector. The four-cone structure of the tapered optical fiber is coated with an optical gel layer of moisture-sensitive material.

Further, the light source is a width light source or a tunable light source, and the wavelength range of the light source is 1900nm-2400nm, preferably 2000nm, that is, a light source of two microns.

Further, the four-cone optical fiber is developed by using a single-mode optical fiber, including a core and a cladding, and the single-mode optical fiber is tapered to form a section of a four-cone structure, and the core of the four-cone structure is coated with the optical gel layer .

Further, the optical gel layer is an agarose gel film.

Further, the detector is a spectrometer.

As can be seen from the above description of the structure of the present invention, compared with the prior art, the present invention has the following advantages:

1. When the present invention detects humidity, when the air of different humidity is in contact with the agarose gel film, the refractive index of the agarose gel film will change, thereby affecting the transmission characteristics of light in the optical fiber. By measuring the interference peak/valley The change of the wavelength can calculate the corresponding humidity of the surrounding environment, which can not only avoid the test results from being affected by the stability of the light intensity of the light source, but also use the four-cone structure of the optical fiber to accumulate the phase difference and enhance the interference change during optical coupling. When the sensitivity is high, there is no need to greatly lengthen the length of the tapered part of the optical fiber. The structure and principle are simple and reliable, the process steps are simple, the operation is easy to prepare, the product is stable, and the service life is long.

2, the present invention adopts the light source of two micrometers, and the light of two micrometers has very strong water molecule absorption capacity, and is coated with the four-tapered optical fiber of agarose gel film, makes the loss spectrum of sensor output have several in 1900-2000nm band An approximately equidistant interference peak/valley, its wavelength change is very sensitive to humidity, a small change in humidity can produce obvious wavelength change, using this feature, can greatly improve the sensitivity of the humidity sensor.

Description of drawings

Fig. 1 is a structural block diagram of the present invention;

Fig. 2 is a schematic diagram of the structure of a four-tapered optical fiber;

Fig. 3 is the interference loss spectrum schematic diagram of the present invention with the change of external environment humidity;

FIG. 4 is a schematic diagram of a specific trough drifting with external humidity.

Detailed ways

The specific implementation manners of the embodiments of the present invention will be described below with reference to the accompanying drawings.

Referring to Figures 1 and 2, a wavelength-modulated four-cone optical fiber humidity sensor includes a light source 1, a four-cone optical fiber 2 and a detector 3 for detecting changes in the wavelength position of light. The detector 3 is preferably a spectrometer. Both ends of the four-cone fiber 2 are respectively connected to the light source 1 and the detector 3, and the four-cone structure of the four-cone fiber 2 is coated with an optical gel layer 4 of a moisture-sensitive material.

Referring to FIG. 1 and FIG. 2 , the light source 1 adopts a width light source 1 or a tunable light source 1 . The wavelength range of the light source 1 is 1900nm to 2400nm. In this embodiment, it is preferably 2000nm, that is, the light source 1 of two microns, and the light of two microns has a strong water molecule absorption capacity. Using this feature, the humidity sensor can be greatly improved. sensitivity.

Referring to Figures 1 and 2, the four-tapered optical fiber 2 is made of a common single-mode optical fiber tapered, and its manufacturing steps are as follows:

1. Take a 50cm commercially available single-mode optical fiber, the inner and outer core diameters are 9/125um, and its structure is composed of a core and a cladding.

2. Use a fiber stripper to strip the cladding with a length of 2-8cm.

3. Adopt the tapering method, such as melting and drawing the four-tapered optical fiber 2 with a four-tapered structure by using a carbon dioxide laser. The two cone waists of the four-taper fiber are both 50-70 microns, and the distance between the two cone waists is 10-30 microns.

4. An optical gel layer 4 of a moisture-sensitive material is coated on the bare four-cone structure fiber core.

Referring to Fig. 1 and Fig. 2, the optical gel layer 4 is made of a moisture-sensitive material, which may be a moisture-sensitive material film such as an agarose gel film, a PVA film, or a graphene oxide film. In this embodiment, an agarose gel film is preferred. The agarose gel film contains multiple hydroxyl groups, which can absorb water and combine the agarose gel with the optical fiber. The agarose gel will affect the effective refractive index of the optical fiber, and then affect the transmission characteristics in the optical fiber. Due to the simple and cheap fabrication method and high compatibility with fiber optic systems, agarose gel is an ideal material for quadruple cone fiber optic 2 sensing.

With reference to Fig. 1 to Fig. 4, the basic operating principle of the present invention is as follows:

The light emitted by the 2-micron light source 1 propagates in the four-cone fiber 2. When the light is transmitted from the core of the single-mode fiber to the first double-cone region of the four-cone structure, the incident light becomes equivalently two beams Light, that is, split into the light in the core and the light in the cladding and the optical gel layer 4 . When the two beams of light pass through the second biconical region, the phase difference is accumulated. When they are coupled back to the core of the single-mode fiber, interference will occur. The interference loss spectrum of the interference output shows several loss peaks/valleys. When the external environment humidity When the change occurs, the position of the loss peak/valley also changes, which is specifically manifested in the regular movement of the wavelength at a specific peak/valley position as the humidity changes. The wavelength λ change of the interference peak/valley and the humidity RH are shown in Figure 3, which is approximately linear, and its function is λ=λ0+a*RH (RH is the relative humidity, the unit is %, a is the sensitivity of the sensor, P0 is the sensor parameter). It can be seen from the above equation that λ is approximately linearly related to the humidity RH, and the relative humidity can be obtained by measuring the λ of a specific wavelength of the loss spectrum, that is, RH=(λ-λ0)/a. The sensitivity a of the sensor and the sensor parameter P0 are calibrated by experiments.

Referring to Fig. 1 and Fig. 2, in summary, when the present invention detects humidity, when the air of different humidity contacts the agarose gel contact film, the refractive index of the agarose gel film will change, thereby affecting the light in the optical fiber. By measuring the wavelength change of the interference peak/valley, the corresponding humidity of the surrounding environment can be obtained, and the optical fiber adopts a four-cone structure to accumulate the phase difference to enhance the interference change during optical coupling. While ensuring the measurement sensitivity, There is no need to greatly lengthen the length of the optical fiber taper waist, the structure principle is simple and reliable, the process steps are simple, the operation and preparation are easy, the product stability is good, and the service life is long.

The above is only a specific embodiment of the present invention, but the design concept of the present invention is not limited thereto, and any insubstantial changes made to the present invention by using this concept should be an act of violating the protection scope of the present invention.

Claims (6)

1. A wavelength-modulated four-cone optical fiber humidity sensor, characterized in that: comprise a light source, a four-cone optical fiber and a detector for detecting changes in the wavelength position of light, the two ends of the four-cone optical fiber are respectively connected to the light source and the detector The four-cone structure of the four-cone optical fiber is coated with an optical gel layer of moisture-sensitive material. 2. A wavelength-modulated four-cone fiber optic humidity sensor according to claim 1, characterized in that: the wavelength range of the light source is 1900nm-2400nm. 3. A wavelength-modulated four-cone optical fiber humidity sensor according to claim 1, characterized in that: the four-cone optical fiber adopts a single-mode optical fiber, and the single-mode optical fiber is drawn up to form a four-cone structure. The four-cone structure core is coated with the optical gel layer. 4. A kind of wavelength modulation type four-cone optical fiber humidity sensor according to claim 1, characterized in that: in the four-cone optical fiber four-cone structure, two cone waists are 50-70 microns, and between the two cone waists The distance is 10-30 microns. 5. A wavelength-modulated four-cone optical fiber humidity sensor according to claim 1, characterized in that: the optical gel layer is an agarose gel film. 6. A wavelength-modulated four-cone fiber optic humidity sensor according to claim 1, wherein the detector is a spectrometer.