CN104237166A - Optical fiber fused taper-long-period fiber grating high-sensitivity refractive index sensor including transition zone and manufacture method of sensor - Google Patents

Abstract

The invention relates to a high-sensitivity refractive index sensor with a long-period grating of an optical fiber melting cone including a transition region, which includes a single-mode optical fiber, an optical fiber melting cone made of a single-mode optical fiber drawn by a hydrogen-oxygen flame, and a CO ₂ laser to write Long period fiber grating (LPFG) on a fiber fused cone. A large part of the optical field energy of the fiber fusion cone propagates outside the fiber in the form of evanescent waves. Based on the interaction between this part of the evanescent field outside the core and the environment, the refractive index changes of the surrounding environment can be sensed. Combining with the use of CO ₂ lasers, the writing range includes optical fibers The LPFG in the fusion cone transition zone is based on the coupling between the core fundamental mode and the cladding mode of the same direction transmission and due to the special tapered waveguide structure of the fiber fusion cone and the thin diameter characteristics of the cone waist, the change of the resonance wavelength to the external environment very sensitive. The present invention combines the advantages of the optical fiber fusion cone and the LPFG, and performs high-sensitivity sensing by measuring the change of the resonant wavelength of its transmission peak. significance.

Description

Optical fiber fused cone long-period grating high-sensitivity refractive index sensor including transition region and manufacturing method thereof

technical field

The invention relates to an optical fiber melting cone long-period grating high-sensitivity refraction index sensor including a transition region and a manufacturing method thereof, belonging to the field of optical fiber devices.

Background technique

Optical fiber devices are key devices for optical fiber communication and optical fiber sensing, and their development level largely determines the development of optical fiber communication and optical fiber sensing. Optical fiber sensors have strong anti-interference ability, good insulation, high safety, high sensitivity, light weight, small size and easy integration. Therefore, they are used in many industries such as aerospace (temperature measurement and pressure measurement of various parts of aircraft and spacecraft, etc.), Surface height measurement, etc.), power transmission (current measurement of high-voltage transmission network, etc.) and other fields have broad application prospects. With the rapid development of optical fiber communication and optical fiber sensing, the requirements for optical fiber devices are getting higher and higher. New optical fiber devices with the advantages of micro size, high sensitivity, and fast response have gradually become a research hotspot. Due to its superior performance, fiber grating has become one of the most representative and promising fiber passive devices at present. The development of new structure, new characteristics and multifunctional fiber grating has become an inevitable trend.

Long-period fiber grating (LPFG) has the advantages of small insertion loss, wide bandwidth, low back reflection, high response sensitivity to changes in the external environment, simple fabrication, and low cost, and has been widely used. In the field of sensing, due to the long period of LPFG, there is coupling between the core fundamental mode and cladding mode propagating in the same direction, and its resonance wavelength and peak value are very sensitive to changes in the external environment. Compared with ordinary single-mode fiber SMF (single mode fiber), a large part of the optical field energy of the fiber fusion cone propagates outside the core in the form of evanescent waves, and the light enters the transition region and continues to transmit forward. The radius of the transition zone decreases gradually. As the radius decreases, the light transmitted in the cladding gradually increases, the light transmitted in the core decreases gradually, and the light wave transmitted in the cone waist decays exponentially, forming a The evanescent wave, which is extremely sensitive to the change of the sensor, can be made into a high-sensitivity optical fiber sensor. After that, the light wave re-enters the transition zone and the single-mode zone for transmission, and the light gradually returns to the core from the cladding. Therefore, the basic research of fiber-cone composite devices is of great significance. The invention writes the LPFG on the fiber fusion cone, combines the advantages of the fiber fusion cone and the LPFG, and performs sensing by measuring the change of the resonant wavelength and the peak value of the transmission peak. Therefore, higher resolution, higher sensitivity, and wider range of sensing measurements can be achieved than ordinary LPFGs, while low-loss and high-performance sensing can be achieved by improving the process.

Contents of the invention

The purpose of the present invention is to improve the sensitivity of ordinary LPFG refractive index sensing, and provide a high-sensitivity refractive index sensor of optical fiber fusion taper long-period grating including transition region and its manufacturing method. The sensor enables higher resolution, higher sensitivity, and a wider range of refractive index sensing.

To achieve the above object, the present invention adopts the following technical solutions:

A fiber fusion cone long-period fiber grating high-sensitivity refractive index sensor including a transition region, including a single-mode fiber, a fiber fusion cone made of a single-mode fiber drawn by a hydrogen-oxygen flame, and a _CO2 laser written on the fiber fusion cone The LPFG above is characterized in that: in the optical fiber fusion cone, a large part of its light field energy propagates outside the core in the form of evanescent waves, and when this part of the evanescent field outside the core interacts with the environment, it can sense the surrounding environment The refractive index changes; the writing range includes the long-period fiber grating (LPFG) in the transition zone of the fiber taper. Due to the long period of the LPFG, there is coupling between the core fundamental mode and the cladding mode that are transmitted in the same direction, and its resonance wavelength and The peak value is very sensitive to changes in the external environment; LPFG is written on the fiber fuse, combining the advantages of the fiber fuse and LPFG to achieve low-loss and high-performance sensing characteristics. It is characterized in that the cladding diameter of the single-mode optical fiber (1) is about 100-150 μm, and the core diameter is about 7-10 μm; the total length of the fiber fusion cone transition region (2) and the waist region (3) of the fiber fusion cone The diameter of the waist (3) of the fiber optic fusion cone is 30-80 μm, and the length of the long-period fiber grating (4) is 15-20 mm.

For making the above-mentioned optical fiber fusion cone long-period grating refractive index sensor including the transition zone, the manufacturing process steps are as follows:

First, take a length of 1m 0.2m single-mode fiber (1), strip the middle part of the single-mode fiber (1) to a length of 10cm 1cm coating layer, and then taper it with a hydrogen-oxygen flame tapering machine to obtain the optical fiber fusion cone transition area (2) and the optical fiber fusion cone waist area (3); then the optical fiber fusion cone transition area (2 ) and the waist region of the fiber fusion cone (3) are fixed on the CO ₂ laser, and the two ends of the fiber fusion cone transition area (2) are respectively connected to the light source and the spectrometer through jumpers, and then focused on the cone waist of the fiber fusion cone through a microscope In the center of the area (3), use a computer to draw a long-period fiber grating (4) with a length of 15-20 mm, control the CO ₂ laser to write the long-period fiber grating (4), and obtain a better spectrum through the real-time online measurement of the spectrometer Long Period Fiber Bragg Gratings (4). So far, a fiber-cone long-period grating refractive index sensor including a transition region has been prepared.

Compared with the prior art, the present invention has the following obvious outstanding features and significant advantages:

(1) A large part of the optical field energy of the fiber fusion cone propagates outside the fiber in the form of evanescent waves, and the interaction between the evanescent field and the environment can realize high-sensitivity perception of changes in the refractive index of the surrounding environment;

(2) LPFG has the coupling between the core fundamental mode and the cladding mode that are transmitted in the same direction, and the resonant wavelength is very sensitive to changes in the external environment;

(3) The invented device has simple structure, stable and reliable performance, and can prepare different LPFG lengths and different fiber taper diameters according to requirements, with low cost and high repeatability, and it is easy to realize batch processing of devices.

How the invention works

Compared with the fiber grating refractive index sensor made by the conventional manufacturing method, the sensitivity of the long period fiber grating sensor including the transition region written on the fiber fusion cone is higher. Due to the long period of LPFG, there is coupling between the core fundamental mode and the cladding mode propagating in the same direction, and its resonance wavelength and peak are very sensitive to changes in the external environment, and have better sensitivity than Bragg gratings (expressed in temperature, Refractive index, bending, etc.). A large part of the optical field energy of the fiber fusion cone propagates outside the fiber in the form of evanescent waves. When this part of the evanescent field outside the core interacts with the environment, it can be used to make highly sensitive micro sensor. Therefore, it is of great significance to conduct basic research on the working principle, manufacturing process and application characteristics of composite devices based on fiber optic fusion cones. Write LPFG on the fiber taper (structure shown in Figure 1), combine the advantages of fiber taper and LPFG, and sense by measuring the change of the resonance wavelength and peak value of its transmission peak. Therefore, higher resolution, higher sensitivity, and wider range sensing than common LPFG can be achieved.

Description of drawings

Fig. 1 is a structure diagram of the optical fiber fusion cone long-period grating refractive index sensor including the transition region in the present invention. the

Fig. 2 is a schematic diagram of writing a long-period grating on a fiber fusion cone using a CO ₂ laser according to the present invention.

Figure 3 shows the movement of the LPFG transmission spectrum with a period of 500 μm and a period of 60 written on an ordinary single-mode fiber SMF-28 under the change of the external refractive index.

Figure 4 shows the movement of the LPFG transmission spectrum written on the cone waist with a diameter of 84 μm, a period of 500 μm, and a period of 60 when the external refractive index changes.

Detailed ways

Preferred embodiments of the present invention are described as follows in conjunction with the accompanying drawings:

Embodiment one:

Refer to Figure 1 for the content of this section, which includes the fiber optic fusion cone in the transition zone, the long-period fiber grating high-sensitivity refractive index sensor, including a single-mode fiber, the fiber fusion cone formed by the single-mode fiber through the hydrogen-oxygen flame fusion taper, CO ₂ The laser writes the long-period fiber grating on the fiber fusion cone, which is characterized in that: the fiber fusion cone part is made of hydrogen-oxygen flame heating and melting the taper, including the transition region and the waist region of the cone; the long-period fiber grating is made of CO ₂ laser writing, the writing area includes the transition area and the waist area of the fiber fusion cone. The strong evanescent field of the fiber taper produces high sensitivity characteristics to external environment changes; the coupling of the long-period fiber grating is the coupling between the fundamental mode of the fiber core and the cladding mode in the same direction, which is closely related to the effective refractive index of the cladding mode; However, changes in the external refractive index will lead to changes in the effective refractive index of the cladding mode, thereby affecting the coupling mode; the invention effectively combines the advantages of the two optical fiber devices to produce an optical fiber sensor device with high sensitivity to the refractive index.

Embodiment two:

This embodiment is basically the same as Embodiment 1, with special features: the cladding diameter of the single-mode optical fiber (1) is about 100-150 μm, and the core diameter is about 7-10 μm; the fiber-cone transition zone (2) The total length of the waist region (3) of the fiber optic fusion cone is 10-15 mm, the diameter of the waist (3) of the fiber optic fusion cone is 30-80 μm, and the length of the long-period fiber grating (4) is 15-20 mm.

Embodiment three:

The method for manufacturing the above-mentioned optical fiber fusion cone long-period fiber grating high-sensitivity refractive index sensor including the transition zone is used to manufacture the above-mentioned refractive index sensor, and its manufacturing process steps are as follows: first, take a length of 1m 0.2m single-mode fiber (1), strip the middle part of the single-mode fiber (1) to a length of 10cm 1cm coating layer, and then taper it with a hydrogen-oxygen flame tapering machine to obtain the optical fiber fusion cone transition area (2) and the optical fiber fusion cone waist area (3); then the optical fiber fusion cone transition area (2 ) and the waist region of the fiber fusion cone (3) are fixed on the CO ₂ laser, and the two ends of the fiber fusion cone transition area (2) are respectively connected to the light source and the spectrometer through jumpers, and then focused on the cone waist of the fiber fusion cone through a microscope In the center of the area (3), use a computer to draw a long-period fiber grating (4) with a length of 15-20 mm, control the CO ₂ laser to write the long-period fiber grating (4), and obtain a better spectrum through the real-time online measurement of the spectrometer Long Period Fiber Bragg Gratings (4). So far, a fiber-cone long-period fiber grating high-sensitivity refractive index sensor including a transition region has been prepared.

Embodiment four:

Referring to Fig. 1, the optical fiber fusion cone long-period fiber grating high-sensitivity refractive index sensor including the transition zone includes a single-mode fiber (1), and the fiber fusion cone transition zone formed by the single-mode fiber through the hydrogen-oxygen flame fusion taper (2) and the waist region of the fiber melting cone (3), CO ₂ laser writes long-period fiber gratings (4) on the fiber melting cone, the cladding diameter of the single-mode fiber (1) is about 125um, and the core diameter About 8.5um; the optical fiber fusion cone transition zone (2) and the cone waist region (3) of the fiber fusion cone are formed by ordinary single-mode optical fiber through hydrogen-oxygen flame fusion tapering, with a length of 10~15mm and a cone waist The diameter is 30~60μm, and the length of LPFG is 15~20mm;

Fig. 2 is a schematic diagram of writing a long-period fiber grating on a fiber fusion cone using a CO ₂ laser. Fig. 3 and Fig. 4 are respectively engraved on common single-mode optical fiber and taper waist diameter 84 μ m, period is 500 μ m period number is the movement situation of LPFG transmission spectrum that the period number is 60 in the external refractive index change situation, under the comparison, Fig. 4 shows the present invention The related optical fiber fusion cone long-period grating refractive index sensor including the transition region has higher sensing sensitivity.

Claims (3)

1. A high-sensitivity refractive index sensor with a fiber-cone long-period grating including a transition region, comprising a single-mode fiber (1) and a long-period grating written on a section of the fiber-cone in the single-mode fiber (1) (4), characterized in that: the long-period fiber grating (4) is written by a CO ₂ laser, and the writing area includes two transition areas (2) of the fiber fusion cone and a cone waist area (3); The optical fiber fusion cone transition region (2) and the optical fiber fusion cone waist region (3) are partially made by heating with a hydrogen-oxygen flame and melting the tapering. 2. A fiber-cone long-period fiber grating refractive index sensor including a transition zone according to claim 1, characterized in that the cladding diameter of the single-mode optical fiber (1) is about 100-150 μm, and the core diameter is about 7~10μm; the total length of the fiber fusion cone transition zone (2) and the fiber fusion cone waist area (3) is 10~15mm, the diameter of the fiber fusion cone waist (3) is 30~80μm, and the long-period optical fiber The grating (4) has a length of 15-20mm. 3. A manufacturing method of a fiber-optic fused-cone long-period grating high-sensitivity refractive index sensor comprising a transition zone, used to manufacture the fiber-optic fused-cone long-period grating high-sensitivity refractive index sensor comprising a transition zone according to claim 1, characterized in The manufacturing steps are as follows: 1) First, take a length of 1m 0.2m single-mode optical fiber (1), strip the middle part of the single-mode optical fiber (1) to a length of 10cm 1cm coating layer; 2) Then, tapering it with a hydrogen-oxygen flame tapering machine to obtain the optical fiber fusion cone transition area (2) and the tapered waist area (3) of the optical fiber fusion cone; 3) Next, fix the fiber cone transition zone (2) and the fiber cone waist zone (3) on the CO2 laser, and the two ends of the fiber cone transition zone (2) are respectively connected to the light source and the spectrometer through jumpers; 4) Finally, focus on the center of the lumbar region (3) of the fiber optic fusion cone through a microscope, use a computer to draw a long-period fiber grating (4) with a length of 15-20cm, and write the long-period fiber grating (4) by controlling the CO2 laser ; Through the real-time online measurement of the spectrometer, a better long-period fiber grating (4) is obtained.