CN103163493A - Reflective type magnetic field sensor based on magnetic fluid and fiber gratings - Google Patents

Abstract

The invention discloses a reflective type magnetic field sensor based on a magnetic fluid and fiber gratings. The sensor comprises a broadband light source, an optical fiber circulator, the fiber gratings, the magnetic fluid and a wavemeter, wherein a port 1, a port 2 and a port 3 of the optical fiber circulator are respectively connected with the broadband light source, the fiber gratings and the wavemeter, the ptical fiber circulator couples reflected light of the fiber gratings and fresnel reflected light of truncated tail filbers to an output end, due to the character that magnetism filled in the magnetic fluid in capillary tube can lead to a variable refractive index, the variation of a magnetic field changes the refractive index of the tail fibers, as proved by experiments, the variable quantity of a side-mode suppression ratio of fiber bragg gratings has a good linear relation with the variable quantity of an external magnetic field, and therefore the reflective type magnetic field sensor based on the magnetic fluid and the fiber gratings is obtained. The reflective type magnetic field sensor based on the magnetic fluid and the fiber gratings is simple to manufacture, low in cost, and capable of being applied on line, and is expected to be applied to sensing fields, such as chemistry and biology.

Description

Reflective magnetic field sensor based on magnetic fluid and fiber grating

Technical field

The invention belongs to technical field of optical fiber sensing, be specifically related to a kind of reflective magnetic field sensor based on magnetic fluid and fiber grating.

Background technology

Magnetic-field measurement is one of important branch of Techniques in Electromagnetic Measurement.Nowadays magnetic field measurement technology has been widely used in the fields such as geophysics, space science, biomedicine, military affairs, industry.Optical fiber sensing technology is compared with traditional sensors, has anti-electromagnetic interference (EMI), corrosion-resistant, the light path pliability is good, highly sensitive, dynamic range large, be easy to realize the advantage such as telemeasurement and caused widely and pay close attention to.

Magnetic liquid is that a kind of it had both had the magnetic of solid matter, had again the mobility of liquid by nano level ferromagnetism particle dispersion formed stable colloidal dispersion in base fluid, is a kind of novel functional material.Now have the fibre optic magnetic field sensor based on the magneto-optic effect of magnetic liquid, as people such as J.J.Chieh 2005, propose in " Dynamic response ofoptical-fiber modulator by using magnetic fluid as cladding layer " literary composition of delivering on " Journal ofApplied Physics ", after fiber optical corrosive, utilize magnetic fluid as the covering of optical fiber, the characteristic that the output intensity of optical fiber changes with the magnetic field size variation realizes the optical fiber magnetic field sensing, but the optical fiber after the bad control of the corrosion of optical fiber and corrosion is fragile.Simultaneously, fibre optic magnetic field sensor based on the mangneto variable refractive index phenomenon of magnetic liquid, as putting in the optical fibre Fabry-perot interferometer interference cavity magnetic fluid diaphragm or the pickup arm of Mach-Zehnder interferometer, realize magnetic field sensing by the phase place that changes transmission light, utilize in addition the fibre optic magnetic field sensor of magnetic fluid coating long period fiber grating formation etc., but its manufacture difficulty is large, integrated level is low.The present invention utilizes the mangneto variable refractive index character of magnetic fluid, the fiber end face of fiber grating end is cut put down and immerse in magnetic fluid, because the Fresnel reflection rate of fiber grating end changes with external magnetic field, the side mode suppression ratio of Fiber Bragg Grating FBG changes with the difference of external magnetic field, thereby obtains the reflective magnetic field sensor based on magnetic fluid and fiber grating.The present invention makes simply, cost is low, can use online, is expected to be used in the sensory fields such as chemistry, biology.

Summary of the invention

The invention provides a kind of reflective magnetic field sensor based on magnetic fluid and fiber grating, utilized the character of the mangneto variable refractive index of magnetic fluid, the measurement that the side mode suppression ratio by Fiber Bragg Grating FBG changes has realized the measurement of magnetic field intensity.

Technical scheme of the present invention is as follows:

Key component of the present invention is the sensing part of sensor, namely invades the fiber grating in magnetic fluid, and the fiber grating end is cut flat.The present invention mainly is comprised of wideband light source, fiber optical circulator, fiber grating, magnetic fluid and wavemeter.1,2,3 three port of fiber optical circulator respectively with wideband light source, fiber grating, wavemeter is connected.Fiber optical circulator couples light to output terminal with reflected light and the fiber grating end face reflection of fiber grating, and wavemeter is observed the variation of its output spectrum side mode suppression ratio.Character due to the mangneto variable refractive index that pours into magnetic fluid in kapillary, changes of magnetic field has changed the Fresnel reflection rate of fiber grating end, the side mode suppression ratio of Fiber Bragg Grating FBG can change with the difference of external magnetic field, thereby obtains the reflective magnetic field sensor based on magnetic fluid and fiber grating.The measurement of the side mode suppression ratio by Fiber Bragg Grating FBG can realize the sensing measurement of tested magnetic field intensity.

Advantage of the present invention is: (1) transducing part of the present invention is fiber grating, and its distal optical fiber end face is cut and put down and immerse in magnetic fluid, and required fiber lengths is short, and is highly sensitive; (2) the present invention makes simply, cost is low, can use online.

Description of drawings

Fig. 1 is the structural representation based on the reflective magnetic field sensor of magnetic fluid and fiber grating

Fig. 2 is the spectrogram of magnetic field when being respectively 382Oe, 1576Oe, 2190Oe

Embodiment

Below in conjunction with accompanying drawing, the present invention is further described.

As shown in Figure 1, a kind of reflective magnetic field sensor based on magnetic fluid and fiber grating comprises that wideband light source 1, fiber optical circulator 2, fiber grating 3, magnetic fluid 4 and wavemeter 5 form.1,2,3 three port of fiber optical circulator respectively with wideband light source, fiber grating, wavemeter is connected.

The present invention is based on following principle:

Fiber optical circulator couples light to output terminal with the Fresnel reflection of Fiber Bragg Grating FBG reflected light and fiber grating end, and when the coherent length that the distance of fiber grating and fiber grating end is longer than light source, the reflectivity of bragg wavelength is

I _out(λ _B)＝R _FBG(λ _B)I _m+[1-R _FBG(λ _B)] ²R _FI _in≈R _FBG(λ _B)I _m (1)

Reflectivity away from bragg wavelength is

I _out(λ)＝R _FBG(λ)I _in+[1-R _FBG(λ)] ²R _FI _in (2)

I wherein _inIt is the light intensity of incident light.The side mode suppression ratio of Fiber Bragg Grating FBG

$\mathrm{SMSR}={10\log }_{10}\left\{\frac{I_{\mathrm{out}}\left({\mathrm{\λ}}_B\right)}{I_{\mathrm{out}}\left(\mathrm{\λ}\right)}\right\}={10\log }_{10}\left(\frac{R_{\mathrm{FBG}}\left({\mathrm{\λ}}_B\right)+[1-R_{\mathrm{FBG}}{\left({\mathrm{\λ}}_B\right)}^2]}{R_{\mathrm{FBG}}\left(\mathrm{\λ}\right)+{[1-R_{\mathrm{FBG}}\left(\mathrm{\λ}\right)]}^2{R}_F}\right)$

Work as R _FBG≈ 0, R _FBG(λ _B) enough large,

$\mathrm{SMSR}={10\log }_{10}\left[\frac{R_{\mathrm{FBG}}\left({\mathrm{\λ}}_B\right)}{R_F}\right]$

Wherein,

n _cAnd n _fBe respectively the refractive index of single-mode fiber core and the refractive index of magnetic fluid.

When sensor is in different magnetic field intensitys, due to the refractive index of magnetic fluid in kapillary to residing magnetic-field-sensitive, so can change the Fresnel reflection rate R of fiber grating end by magnetic fluid _FThereby, causing that the side mode suppression ratio of Fiber Bragg Grating FBG changes, the measurement of the side mode suppression ratio by Fiber Bragg Grating FBG can demodulate the change information of magnetic field intensity.

Fig. 2 is the spectrogram of magnetic field intensity when being respectively 382Oe, 1576Oe, 2190Oe, can find out that side mode suppression ratio reduces with the increase of intensity.Record by experiment, during less than 2400Oe, this variable in the variable quantity of side mode suppression ratio and magnetic field has good linear relationship.

Utilize the present invention can realize that the key of magnetic field sensing is: the magnetic fluid that pours in kapillary has mangneto variations in refractive index effect, the variation of external magnetic field has changed the Fresnel reflection rate of fiber grating end, thereby the side mode suppression ratio that causes Fiber Bragg Grating FBG changes, and has realized the measurement in magnetic field.

In the present embodiment, the optical fiber of inscribing fiber grating is standard single-mode fiber (YOFC-MKD-101, mode field diameter is 9.9～10.9 μ m@1550nm), and the bragg wavelength of fiber grating is 1548.6nm, and three dB bandwidth is 0.16nm.The distance of fiber grating and general single mode fiber tail end is 3-cm, and magnetic fluid is water base Fe ₃O ₄, its density is 1.2g/mL.

Claims (1)

1. the reflective magnetic field sensor based on magnetic fluid and fiber grating, comprise wideband light source, fiber optical circulator, fiber grating, magnetic fluid and wavemeter.It is characterized in that: 1,2,3 three port of fiber optical circulator is connected with wideband light source, fiber grating and wavemeter respectively, and the fiber end face of fiber grating end is cut and put down and immerse in magnetic fluid.

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