CN109116272B - Large-bandwidth magnetic field sensor based on tapered fiber bragg grating and preparation method - Google Patents

Abstract

In view of the problem that the bandwidth of the optical signal obtained by the magnetic field sensor in the prior art is relatively narrow, the present invention proposes a large-bandwidth magnetic field sensor based on a tapered fiber grating and a preparation method, including a capillary glass tube, a tapered fiber grating and a magnetic fluid; it is characterized in that: the tapered fiber grating includes a light entry section, a stretch section, a light exit section for deriving the light wave, and a plurality of fiber gratings connected in sequence for receiving incident light waves; wherein, the stretch section includes sequentially connected The first circular truncated section, the cylindrical section and the second circular truncated section; wherein, the fiber grating is evenly arranged in the middle of the capillary glass tube and the fiber grating is written on the variable diameter section of the second circular truncated section. The present invention has a simple structure, and the present invention obtains a larger optical signal bandwidth by arranging the fiber grating on the variable diameter section of the second circular truncated section.

Description

A kind of large bandwidth magnetic field sensor based on tapered fiber grating and preparation method

technical field

The invention belongs to the field of optical fiber sensing in information technology, in particular to a large-bandwidth magnetic field sensor based on tapered fiber grating (TFBG: taper Fiber Bragg grating), which can effectively increase the bandwidth of optical signals, and a preparation method thereof.

Background technique

There are magnetic fields or information related to magnetic fields in many places in nature and human society. In today's information society, magnetic field sensors have become an indispensable basic element in information technology and information industry. At present, people have developed magnetic field sensors using various physical, chemical and biological effects, which have been widely used in scientific research, production and social life, and undertake the task of exploring various information.

The earlier magnetic field sensors were gradually developed with the progress of magnetic measuring instruments. Among the many magnetic measurement methods, most of them convert the magnetic field information into electrical signals for measurement. In magnetometry, the "probe" or "sampling device" is the magnetic field sensor. Traditional magnetic field sensors include magnetic force method, electromagnetic induction method, electromagnetic effect method, magnetic resonance method, etc., which are mostly based on energized coils or metal and semiconductor structures. With the rapid development of information industry, industrial automation, transportation, power electronic technology, office automation, household appliances, medical instruments, etc. and the popularization of electronic computer applications, a large number of sensors are required to measure and control non-electrical parameters. . It is precisely based on the above requirements that the optical fiber magnetic field sensor has been focused on and researched and developed.

Moreover, compared with traditional electrical magnetic field sensors, optical fiber sensors have the advantages of small size, low power consumption, and easy network transmission.

At present, fiber-optic magnetic field sensors have been gradually put into practical use, and the use of magnetic fluid to modulate optical signals is one of the main methods. Magnetic fluid is a new type of functional material, and its evaporation rate is related to the carrier liquid. At the same time, when there is an external magnetic field, the solid particles inside the magnetic fluid will aggregate and orient along the direction of the external magnetic field, thereby causing magnetic fluid. The refractive index changes.

The specific method is as follows: an optical fiber magnetic field sensor (CN207352076U) based on dual-core optical fiber microchannel and magnetic fluid, which uses dual-core optical fiber to form interference, and uses magnetic fluid to control one interference arm for detection; The magnetic field sensor of the sensor head (CN207281263U) uses magnetic fluid to coat the fiber grating corroded by HF acid, and detects the magnetic field according to the change of the refractive index of the magnetic fluid.

Also, for example, a magnetic field sensor and measurement method based on photonic crystal fiber and grating (CN201711260749.X), nano-gold grating is processed on the side of photonic crystal fiber by etching method, and then metal grating is coated with magnetic fluid, according to the surface, etc. The excitation of the exciton is used to detect the magnetic field.

And, a magnetic field sensor (CN107064827A) based on grapefruit-type optical fiber and fiber Bragg grating, filling magnetic fluid into the grapefruit-type fiber, and using the reflection characteristic wavelength of the fiber grating to reflect the signal, thereby obtaining the magnetic field signal.

In the above-mentioned patent, limited by the characteristics of fiber Bragg gratings, the bandwidth of the optical signals obtained by these magnetic field sensors is relatively narrow, and the energy only exists in a small wavelength range after the light is modulated by the magnetic field; and the disappearance of ordinary fiber gratings The field is small and the interaction energy with the magnetic fluid is small.

SUMMARY OF THE INVENTION

Aiming at the problem that the bandwidth of the optical signal obtained by the magnetic field sensor in the prior art is relatively narrow, the present invention proposes a large bandwidth magnetic field sensor based on a tapered fiber grating and a preparation method, which can effectively increase the bandwidth and enhance the The interaction with the magnetic fluid forms a more compact optical fiber magnetic field sensor.

In order to achieve the above-mentioned purpose, the technical scheme adopted in the present invention is: a large-bandwidth magnetic field sensor based on tapered fiber grating, comprising a capillary glass tube, a tapered fiber grating coaxially sealed and arranged in the capillary glass tube, and a tapered fiber grating arranged in the capillary glass tube. The glass tube is filled with magnetic fluid; the tapered fiber grating includes a light input section for receiving incident light waves, a stretching section, a light output section for exporting light waves, and several fiber gratings connected in sequence;

Wherein, the stretching section is arranged in the capillary glass tube, and the light entry section and the light exit section extend to the outside of the capillary glass tube;

The stretching section includes a first circular truncated section, a cylindrical section and a second circular truncated section connected in sequence; and the large diameter end of the first circular truncated section corresponds to and is connected to the light entry section; the small diameter end of the first circular truncated section is connected to the cylindrical section. One end of the segment corresponds to and is connected to; the small diameter end of the second circular truncated segment corresponds to and is connected to the other end of the cylindrical segment; the large diameter end of the second circular truncated segment corresponds to and is connected to the light-emitting segment;

Wherein, the fiber grating is evenly arranged in the middle of the capillary glass tube, and the fiber grating is written on the variable diameter section of the second circular truncated section.

The outer side of the capillary glass tube is coaxially provided with an aluminum tube for preventing the volatilization of the magnetic fluid; the aluminum tube is sealed with the light entry section and the light exit section.

The inner diameter of the aluminum tube is 0.7-1.0 mm, the outer diameter is 0.9-1.2 mm, and the length is 5-6 cm.

The first circular truncated segment and the second circular truncated segment have the same taper ratio, and the taper ratio is 0.24-0.4; the length of the fiber grating is 2-3 mm.

The inner diameter of the capillary glass tube is 0.3-0.5 mm, the outer diameter is 0.5-0.7 mm, and the length is 3-4 cm.

A method for manufacturing a large-bandwidth magnetic field sensor based on a tapered fiber grating as above, comprising the following steps:

A. The single-mode fiber is melted and stretched by the phase mask method, and then the fiber grating is written on the variable diameter section of the second truncated cone segment of the tapered fiber grating by the phase mask method, and finally the tapered fiber grating is obtained;

B. Place the capillary glass tube horizontally, and coaxially place the tapered fiber grating obtained in step A in the middle of the capillary glass tube to form a combination of the capillary glass tube and the tapered fiber grating;

C. The combination of the capillary glass tube obtained in step B and the tapered fiber grating is subjected to capillary action to absorb the magnetic fluid to obtain a liquid-filled glass tube with openings at both ends;

D. The liquid-filled glass tube with the openings at both ends obtained in step C is left to stand for 15-20min horizontally, and the air in the capillary glass tube is removed. The segment, the cylindrical segment and the second circular truncated segment are sealed in the capillary glass tube to obtain a detection head for detecting the magnetic field strength;

Wherein, the method for curing the first UV-curable adhesive seal is to irradiate with a UV lamp for 100-150 s;

E. The outer side of the detection head obtained in step D is coaxially provided with a casing to prevent the volatilization of the magnetic fluid, and the casing is sealed by a second UV-curing glue seal.

The working principle of the present invention is as follows: the present invention selects and writes the fiber grating on the variable diameter section of the second circular truncated section, that is, the position of the waist region of the stretching section, in order to detect the change of the magnetic field strength in a larger bandwidth range. At the same time, the dumbbell-shaped stretched segment contains intermodal interference peaks in the reflection spectrum. The direction of the changing magnetic field strength of the ferrofluid can be obtained from the inter-mode interference signal. At the same time, the sensitivity of the present invention can be further improved.

In the stretching section, the refractive index of the cladding and the core will decrease with the decrease of the fiber diameter during the drawing process, and at the same time, two gradual waist regions and a gentle transition region are formed. When the light wave is incident from one end of the stretched section, a part of the light wave will be transmitted to the surrounding structure of the fiber due to the change of the waveguide structure. At this time, the stretched section becomes a new core, and the external environment becomes the cladding. When the magnetic field changes the external environment, the refractive index of the magnetic fluid changes, thereby obtaining the loss of the reflected light signal and realizing the measurement of the magnetic field strength.

The beneficial effects of the present invention are: the present invention transmits light waves through the stretching section, and the fiber grating is arranged in the variable diameter section of the second circular truncated section. When the refractive index of the magnetic fluid changes under the action of the magnetic field, the magnetic fluid acts and couples with the evanescent field of the tapered fiber grating, resulting in a change in the output signal of the fiber grating. Signal contrast increases with increasing magnetic field strength. The present invention has a simple structure, and the present invention obtains a larger optical signal bandwidth by arranging the fiber grating on the variable diameter section of the second circular truncated section.

Description of drawings

Figure 1 is a schematic structural diagram of the present invention.

Figure 2 shows a magnetic field monitoring system using the present invention.

FIG. 3 is a comparison diagram of the reflection spectrum of the present invention and the reflection bandwidth of a general uniform fiber grating.

Figure 4 shows the reflection spectrum recorded by the spectrum analyzer under the condition of changing the external magnetic field.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings.

The technical scheme adopted by the present invention is: as shown in Figure 1, a large bandwidth magnetic field sensor based on tapered fiber grating includes a capillary glass with an inner diameter of 0.3-0.5mm, an outer diameter of 0.5-0.7mm and a length of 3-4cm Tube 4, tapered fiber grating 3 coaxially sealed in capillary glass tube 4 and magnetic fluid 5 filled in capillary glass tube 4; tapered fiber grating 3 includes incoming light for receiving incident light waves connected in sequence segment 301, stretching segment 302, light exit segment 303 for deriving light waves, and several fiber gratings 304;

Wherein, the stretching section 302 is arranged in the capillary glass tube 4, and the light entry section 301 and the light exit section 303 extend to the outside of the capillary glass tube 4;

The stretching section 302 includes a first circular truncated section 3021, a cylindrical section 3022 and a second circular truncated section 3023, which are connected in sequence; and the large diameter end of the first circular truncated section 3021 corresponds to and is connected to the light entry section 301; the first circular truncated section The small diameter end of 3021 corresponds to and is connected to one end of the cylindrical segment 3022; the small diameter end of the second circular truncated segment 3023 corresponds to and is connected to the other end of the cylindrical segment 3022; the large diameter end of the second circular truncated segment 3023 corresponds to and is connected to the light exit segment 303 Preferably, the first circular truncated section 3021 and the second circular truncated section 3023 have the same taper ratio, and the taper ratio is 0.24-0.4, so that the stretching section 302 is in a dumbbell shape.

Wherein, the fiber grating 304 is uniformly arranged in the middle of the capillary glass tube 4 and the fiber grating 304 is written on the variable diameter section of the second circular truncated section 3023; the length of the fiber grating 304 is 2-3 mm.

In order to prevent the volatilization of the magnetic fluid 5, an aluminum tube 8 for preventing the volatilization of the magnetic fluid 5 is coaxially arranged on the outside of the capillary glass tube 4; the aluminum tube 8 is sealed with the light entry section 301 and the light exit section 303; The aluminum tube 8 is sealed with the light-in section 301 and the light-out section 303 by UV-curing glue sealing, and the glue is irradiated with a UV lamp to solidify the glue.

A method for manufacturing a large-bandwidth magnetic field sensor based on a tapered fiber grating as above, comprising the following steps:

A. The single-mode fiber is melted and stretched by the phase mask method, and then the fiber grating 304 is written on the variable diameter section of the second circular truncated section 3023 of the tapered fiber grating 3 by the phase mask method, and finally the tapered fiber grating is obtained. 3;

B. the capillary glass tube 4 is placed horizontally, and the tapered fiber grating 3 obtained in step A is coaxially placed in the middle of the capillary glass tube 4 to form a combination of the capillary glass tube 4 and the tapered fiber grating 3;

C. the combination of the capillary glass tube 4 obtained in step B and the tapered fiber grating 3 is drawn through capillary action to absorb the magnetic fluid 5 to obtain a liquid-filled glass tube with openings at both ends;

D. The liquid-filled glass tube with openings at both ends obtained in step C is left to stand for 15-20min horizontally, and the air in the capillary glass tube 4 is removed, and then, the two ends of the capillary glass tube 4 are sealed by the first UV curing glue 6 , 7 seal the first circular truncated section 3021, the cylindrical section 3022 and the second circular truncated section 3023 in the capillary glass tube 4 to obtain a detection head for detecting the magnetic field strength;

Wherein, the method for curing the first UV-curable glue seals 6 and 7 is to irradiate with a UV lamp for 100-150 s;

E. A casing for preventing the volatilization of the magnetic fluid 5 is coaxially arranged on the outer side of the detection head obtained in the step D, and the casing is sealed by the second UV-curing glue seals 9 and 10 .

It should be clarified that: the sealing method of the second UV-curable adhesive seals 9 and 10 in the E step is the same as that in the D step.

To be clear: Please refer to Figure 1 for the description of the directionality in this paper.

Specific embodiment 1: as shown in Fig. 1, a large-bandwidth magnetic field sensor based on tapered fiber grating consists of a capillary glass tube 4 with an inner diameter of 0.4mm, an outer diameter of 0.6mm, and a length of 3.5cm, and a coaxial seal is arranged on the capillary The tapered fiber grating 3 in the glass tube 4 and the magnetic fluid 5 filled in the capillary glass tube 4 are composed; wherein, the tapered fiber grating 3 consists of a light entry section 301 and a stretching section that are connected in sequence for receiving incident light waves. 302. The light-emitting section 303 for deriving light waves and five fiber gratings 304 are composed; wherein, the magnetic fluid 5 is water-soluble Fe ₄ O ₃ , model EMG605;

Wherein, the stretching section 302 is arranged in the capillary glass tube 4, and the light entry section 301 and the light exit section 303 extend to the outside of the capillary glass tube 4;

The stretching section 302 is composed of a first circular truncated section 3021, a cylindrical section 3022 and a second circular truncated section 3023 connected in sequence; and the large diameter end of the circular truncated section 3021 corresponds to and is connected to the light entry section 301; the first circular truncated section 3021 The small diameter end of the second circular truncated segment 3023 corresponds to and is connected to one end of the cylindrical segment 3022; the small diameter end of the second circular truncated segment 3023 corresponds to and is connected to the other end of the cylindrical segment 3022; the large diameter end of the second circular truncated segment 3023 corresponds to and is connected to the light exit segment 303 ; Preferably, the first circular truncated section 3021 and the second circular truncated section 3023 have the same taper ratio, and the taper ratio is 0.24-0.4, so that the stretching section 302 is in the shape of a dumbbell.

The fiber grating 304 is uniformly arranged in the middle of the capillary glass tube 4, and the fiber grating 304 is written on the variable diameter section of the second circular truncated section 3023; the length of the fiber grating 304 is 2.5 mm.

At the same time, an aluminum tube 8 is coaxially arranged on the outer side of the capillary glass tube 4; the aluminum tube 8 is airtightly arranged with the light entry section 301 and the light exit section 303; when airtight, ultraviolet curing glue is used to seal the aluminum tube 8 and the light entry section 301 , The light-emitting section 303 is glue-sealed, and the glue is irradiated with an ultraviolet lamp for 150s.

2, the present invention is in use, such as a magnetic field monitoring system, in addition to the large bandwidth magnetic field sensor of the present invention, also includes a broadband light source module 11, a three-terminal circulator 14, a spectrum analyzer 12 and a magnetic field generator 13; The fiber grating 304 is located in the magnetic field of the magnetic field generator 13; the input end of the three-terminal circulator 14 is connected to the broadband light source module 11; ; The other output end of the three-terminal circulator 14 is connected to the spectrum analyzer 12 .

It should be clarified that the principle of the above magnetic field monitoring system is: the light wave of the broadband light source module 11 is transmitted to the light output section 303 through the light input section 301 of the tapered fiber grating 3, and the light wave is reflected by the magnetic fluid 5 and the fiber grating 304 and passes through the light output section again. 303 is transmitted to the light exit section 303, and transmitted from the three-terminal circulator 14 to the spectrum analyzer 12, so as to detect the optical signal.

As shown in FIG. 3 , the reflection spectrum of the present invention has a larger reflection bandwidth than a general uniform fiber grating.

As shown in Fig. 4, the reflection spectrum of the present invention is recorded by a spectrum analyzer under the condition of changing the external magnetic field.

In combination with the above content, the present invention also has the following advantages: the present invention adopts the structure of the dumbbell-shaped stretching section 302, so that the sensing part of the present invention is more integrated and the volume is smaller.

The invention overcomes the problem of narrow measurement bandwidth of most fiber grating magnetic field sensors in the prior art, and can measure the response of the magnetic field in a larger bandwidth range.

The present invention utilizes the inter-mode interference signal formed by the action of the tapered fiber grating 3 and the magnetic fluid 5, and the contrast of the interference fringes increases with the change of the magnetic field intensity.

In the present invention, the aluminum tube 8 is encapsulated outside the capillary glass tube 4 for a second time. Under the premise of not affecting the magnetic field, not only the optical fiber sensing unit is effectively protected, but also the volatilization of the magnetic fluid 5 is effectively prevented. Stability of the present invention.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (5)

1. A large-bandwidth magnetic field sensor based on a tapered fiber grating comprises a capillary glass tube (4), a tapered fiber grating (3) coaxially and hermetically arranged in the capillary glass tube (4) and a magnetic fluid (5) filled in the capillary glass tube (4); the method is characterized in that: the tapered fiber grating (3) comprises a light inlet section (301) for receiving incident light waves, a stretching section (302), a light outlet section (303) for leading out the light waves and a plurality of fiber gratings (304) which are connected in sequence;

the drawing section (302) is arranged in the capillary glass tube (4), and the light inlet section (301) and the light outlet section (303) extend to the outside of the capillary glass tube (4);

the stretching section (302) comprises a first circular table section (3021), a cylindrical section (3022) and a second circular table section (3023) which are connected in sequence; the large-diameter end of the first circular platform section (3021) corresponds to and is connected with the light inlet section (301); the small-diameter end of the first circular platform section (3021) corresponds to and is connected with one end of the cylindrical section (3022); the small-diameter end of the second circular platform section (3023) corresponds to and is connected with the other end of the cylindrical section (3022); the large-diameter end of the second circular platform section (3023) corresponds to and is connected with the light emitting section (303), the first circular platform section (3021) and the second circular platform section (3023) have the same taper ratio, and the taper ratio is 0.24-0.4;

the length of the fiber bragg grating (304) is 2-3 mm, the fiber bragg grating (304) is uniformly arranged in the middle of the capillary glass tube (4), and the fiber bragg grating (304) is inscribed in the diameter-changing section of the second circular table section (3023).

2. The large bandwidth tapered fiber grating-based magnetic field sensor according to claim 1, wherein: an aluminum pipe (8) for preventing the magnetic fluid (5) from volatilizing is coaxially arranged at the outer side of the capillary glass pipe (4); the aluminum pipe (8) is hermetically arranged with the light inlet section (301) and the light outlet section (303).

3. The large bandwidth tapered fiber grating-based magnetic field sensor according to claim 2, wherein: the inner diameter of the aluminum pipe (8) is 0.7-1.0 mm, the outer diameter is 0.9-1.2 mm, and the length is 5-6 cm.

4. The large bandwidth tapered fiber grating-based magnetic field sensor according to claim 1, wherein: the inner diameter of the capillary glass tube (4) is 0.3-0.5mm, the outer diameter is 0.5-0.7mm, and the length is 3-4 cm.

5. A method for manufacturing a large bandwidth magnetic field sensor based on a tapered fiber grating according to claim 1, wherein: the method comprises the following steps:

A. melting and stretching the single-mode fiber by a phase mask method, and then writing the fiber grating (304) on the reducer section of the second circular platform section (3023) of the tapered fiber grating (3) by the phase mask method to finally obtain the tapered fiber grating (3);

B. horizontally placing the capillary glass tube (4), and coaxially placing the tapered fiber bragg grating (3) obtained in the step A in the middle of the capillary glass tube (4) to form a combined body of the capillary glass tube (4) and the tapered fiber bragg grating (3);

C. absorbing the magnetic fluid (5) by the combination of the capillary glass tube (4) and the conical fiber bragg grating (3) obtained in the step B through capillary action to obtain a liquid-filled glass tube with two open ends;

D. horizontally standing the liquid-filled glass tube with the two open ends obtained in the step C for 15-20min, removing air in the capillary glass tube (4), and then sealing the first circular table section (3021), the cylindrical section (3022) and the second circular table section (3023) in the capillary glass tube (4) at the two ends of the capillary glass tube (4) through first ultraviolet curing glue seals (6, 7) to obtain a detection head for detecting the magnetic field intensity;

wherein, the first ultraviolet curing glue seal (6, 7) is cured by irradiating for 100-150 s through an ultraviolet lamp;

and C, coaxially arranging a shell for preventing the magnetic fluid (5) from volatilizing outside the detection head obtained in the step D, and sealing the shell by second ultraviolet curing glue seals (9, 10).

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