CN100593727C - Apparatus based on magnetofluid refraction index changing and detecting magnetic variation - Google Patents

Abstract

The invention discloses an apparatus for testing magnetic variation based on the refractive index change of magnetofluid, including a first light source output device, a transmission apparatus, a magnetic field testing device and a first receiving detecting device. The magnetic field testing device includes a refractive index testing device, an electric magnet, a long cycle optical fiber grating and a magnetofluid sample. The long cycle optical fiber grating is arranged in the capillary pipe filled with magnetofluid, and then arranged between two magnetic poles of the electric magnet. A transmission apparatus is used to connect the first light source output device, the magnetic field testing device and the first receiving detecting device, the light output from the first light source output device spreads in the transmission apparatus, the light signal passing through the magnetic field testing device is then received by the first receiving detecting device. The inventive apparatus fortesting magnetic variation based on the refractive index change of magnetofluid under the function of magnetic field in the normal temperature, has very high sensitivity, reaching 0.0025nm/Gs, and the operating region of the apparatus can be from 0Gs to 1500Gs.

Description

Device for detecting changes in magnetic field based on changes in the refractive index of ferrofluid

technical field

The invention relates to a detection device in the field of physical optoelectronic technology, in particular to a device for detecting changes in a magnetic field based on a change in the refractive index of a magnetic fluid under the action of a magnetic field.

Background technique

In optical communication, tunable optical fiber devices are very useful. Long-period fiber gratings can couple light from the fiber core to the cladding. It is sensitive to the refractive index of the material cladding it, so it can be used for tunable filtering and band rejection. Theoretically and experimentally, people have studied how to change the optical properties of LPFGs by changing the refractive index of the outer cladding of LPFGs. The change of the refractive index of the outer cladding of the LPFG can be realized by liquid droplets placed on the periphery of the LPFG in the capillary. There are various methods to manipulate droplets, such as: electrochemical effects, electrocapillary pressure, and electrowetting excitation methods, etc. Through the electrowetting pumping and the circulation of the fluid cavity, the optical properties of the LPFG can be dynamically adjusted, so that it has the characteristics of a switch and a filter.

Magnetic fluid (or called: magnetic liquid, ferrofluid, ferrofluid, magnetic colloid, magnetic fluid) is a stable colloidal system formed by nano-scale strong magnetic particles dispersed in a certain liquid. It has both solid The magnetism of the substance and the fluidity of the liquid are a new type of functional material, which has been paid more and more attention by people. Its application has penetrated into electronics, energy, national defense and military industry, metallurgical machinery, chemical environmental protection, instrumentation, medical and health care, etc. , the effect is very significant. It was not until the end of the 20th century that scholars studied the new optical properties of magnetic fluids (such as: optical transmittance, magnetochromic effect, thermo-optic effect, etc.). In recent years, with the rapid development of integrated optics and photonic devices, and the discovery of the potential application of magnetic fluid in the field of optics, some researchers have begun to pay attention to the optical properties of magnetic fluid, and proposed photonic devices based on magnetic fluid, such as optical switches, Optical modulators, magnetic or electric field sensors, tunable gratings and coarse wavelength division multiplexers, etc.

After searching the literature of the prior art, it was found that "Origin and applications of magnetically tunable refractive index of magnetic fluid films" published by S.Y.Yang et al. in "Applied Physics Letters" (Journal of Applied Physics) in 2004, (Magneto-induced refractive index of magnetic fluid film Adjustable origin and application), this paper proposes for the first time to comprehensively propose the use of the characteristics of the change of the refractive index difference of the magnetic fluid film with the size of the magnetic field for optical sensing. The modulation phenomenon of the experimental scheme of the cladding is not very obvious, and the transmission loss is only 1.13%. It is difficult to meet the requirements of high-precision magnetic field measurement, and it is difficult to have too many applications in real life.

Contents of the invention

The present invention aims at the deficiencies of the prior art, and provides a device for detecting changes in the magnetic field based on the change of the refractive index of the magnetic fluid, so that the purpose of adjusting the optical properties of the long-period fiber grating can be achieved through the method that the magnetic field acts on the magnetic fluid. The refractive index of ferrofluids can be tuned by applying an external magnetic field. When the magnetic fluid with proper refractive index is coated on the outer layer of the LPFG, the optical properties of the LPFG can be adjusted, and then the functions of filter and optical switch can be realized.

The present invention is realized through the following technical solutions, and the present invention includes: a first light source output device, a transmission device, a magnetic field testing device and a first receiving and detecting device. The magnetic field test device includes a refractive index test device, an electromagnet, a long-period fiber grating, and a magnetic fluid sample. The long-period fiber grating is placed behind the capillary filled with magnetic fluid, and placed between the two magnetic poles of the electromagnet. The first light source output device, the magnetic field testing device, and the first receiving and detecting device are connected by a transmission device. The light output by the first light source output device propagates almost without loss in the transmission device. After passing through the magnetic field testing device, the optical signal is received by the first receiver. The detection device receives. The refractive index testing device and the ferrofluid sample are connected together. The connections between all the above components are realized by optical fiber.

The first light source output device is an amplified spontaneous radiation light source.

The transmission device is a standard communication wavelength single-mode optical fiber.

The first receiving and detecting device is a spectrum analyzer.

The refractive index testing device is composed of a second light source output device, a coupler, and a second receiving and detecting device, and is used to measure the change of the refractive index of the ferrofluid sample under a magnetic field. These components are connected by optical fibers, and the coupler in the refractive index test device guides the incident light to the end face of the optical fiber, and uses the optical fiber to collect the back reflected light. The input end of the coupler is connected to the second light source output device, and the input end of the coupler guides the incident light to the fiber-magnetic fluid sample interface at the end face of the fiber, and the reflected light power is detected by the second receiving and detecting device.

The second light source output device is a laser with stable output power and communication band.

The second light source detection device is an optical power meter in the communication band.

When the present invention works, the long-period optical fiber grating is put into the capillary, and magnetic fluid is injected into the capillary, so that the long-period optical fiber grating is placed in the magnetic fluid environment. Because the central attenuation wavelength of the long period fiber grating is quite sensitive to the change of its surrounding refractive index. Therefore, when a magnetic field is present, the refractive index of the ferrofluid sample changes, causing the detected central attenuation wavelength to shift. In this way, the change of the refractive index of the magnetic fluid under the action of a magnetic field can be detected through the detected central wavelength drift value. In addition, the magnitude of the applied magnetic field can be detected by means of a refractive index testing device. Thus, the effect of accurately detecting the magnetic field is achieved.

The invention realizes the application of the change of the refraction index of the magnetic fluid under the action of the magnetic field in the detection of the magnetic field under normal temperature conditions. In the working range, its sensitivity is extremely high, reaching 0.0025nm/Gs. The invention is suitable for small-scale high-precision temperature measurement or accurate temperature discrimination in the normal temperature range, and has a simple structure and is easy to integrate.

Description of drawings

Fig. 1 is a schematic diagram of the structure of the present invention.

Detailed ways

The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings: this embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following the described embodiment.

As shown in FIG. 1 , this embodiment is a device for detecting changes in magnetic field based on changes in the refractive index of magnetic fluid: a first light source output device 1 , a transmission device 2 , a magnetic field testing device, and a first receiving and detecting device 9 .

The magnetic field testing device includes a refractive index testing device, an electromagnet 3 , a long period fiber grating 4 , and a magnetic fluid sample 5 . The long-period fiber grating 4 is placed behind the capillary filled with the magnetic fluid 5 and placed between the two magnetic poles of the electromagnet 3 . The transmission device 2 is used to connect the first light source output device 1, the magnetic field testing device, and the first receiving and detecting device 9. The light output by the first light source output device 1 propagates almost without loss in the transmission device 2. After passing through the magnetic field testing device, the light The signal is received by the first reception detection means 9 .

The refractive index testing device is composed of a second light source output device 7, a coupler 6, and a second receiving and detecting device 8, and is used to measure the refractive index change of the ferrofluid sample under a magnetic field. The optical fiber coupler 6 in the refractive index testing device guides the incident light to the end face of the optical fiber, and uses the optical fiber to collect the retroreflected light. The input end of the coupler 6 is connected to the second light source output device 7, and the input end of the coupler guides the incident light to the optical fiber-magnetic fluid sample 5 interface at the end face of the optical fiber, and the second receiving and detecting device 8 detects and receives the light power reflected back. .

All the above components are connected by optical fibers.

The first light source output device 1 is an amplified spontaneous emission light source.

The transmission device 2 is a single-mode optical fiber.

The first receiving and detecting device 9 is a spectrum analyzer.

The electromagnet device 3 is an electromagnet whose magnetic field can be changed by the magnitude of the supply current.

The long-period fiber grating 4 is a long-period fiber grating with a grating period of 400 μm and a central wavelength of 1540.5 nm in air.

The magnetic fluid 5 is a water-based magnetic fluid with a density of 1.2 g/ml.

The coupler 6 is a 3dB coupler.

The second light source output device 7 is a laser with a power of 1 mW and a center wavelength of 1550 nm.

The second receiving and detecting device 8 is a communication band 1550nm optical power meter.

When this embodiment works, the long-period fiber grating 4 is put into the capillary, and the magnetic fluid 5 is injected into the capillary, so that the long-period fiber grating 4 is placed in the environment of the magnetic fluid 5 . Since the central attenuation wavelength of the long-period fiber grating 4 is quite sensitive to changes in the surrounding refractive index. Therefore, when a magnetic field exists, the refractive index of the sample of the magnetic fluid 5 changes, so that the detected central attenuation wavelength shifts. The change of the refractive index of the magnetic fluid 5 under the action of the magnetic field can be detected through the detected central wavelength drift value. In addition, the magnitude of the applied magnetic field can be detected by means of a refractive index testing device. Thus, the effect of accurately detecting the magnetic field is achieved. In this embodiment, a long-period fiber grating 4 with a grating period of 400 μm and a central wavelength of 1540.5 nm in air is first selected, and placed in a water-based magnetic fluid 5 with a density of 1.2 g/ml, and the magnetic field is changed by an external magnetic field device During the process, the center attenuation wavelength received by the receiving and detecting device 9 changes significantly. The center of the working area of the device is around 25 degrees Celsius, and the sensitivity reaches 0.0025nm/Gs. The experimental results are consistent with the theoretical predictions. In this embodiment, the refractive index of the magnetic fluid 5 is changed by applying a magnetic field, thereby changing the center wavelength position of the long-period fiber grating 4 from 1528.4 nm to 1532.2 nm, and the detected magnetic field ranges from 0 to 1500 Gs. The experimentally obtained relationship between the magnetic field and the central wavelength is:

λ＝[n _co -(-5.49121×10 ^-6 ×H+1.43255)]×Λ.

This embodiment realizes the application of the change of the refractive index of the magnetic fluid under the action of the magnetic field in the detection of the magnetic field under the condition of normal temperature. In the working range, its sensitivity is extremely high, reaching 0.0025nm/Gs. The invention is suitable for small-scale high-precision temperature measurement or accurate temperature discrimination in the normal temperature range. And the structure is simple and easy to integrate.

Claims (7)

1. A device for detecting magnetic field changes based on the refractive index of the magnetic fluid, comprising: a first light source output device, a transmission device, a magnetic field testing device and a first receiving and detecting device, wherein the magnetic field testing device includes a refractive index testing device device, electromagnet, long-period fiber grating and ferrofluid sample, the long-period fiber grating is placed behind the capillary tube containing the ferrofluid, and placed between the two magnetic poles of the electromagnet, the first light source output device, the magnetic field testing device and the first The receiving and detecting devices are connected by a transmission device, the light output by the first light source output device propagates in the transmission device, and the optical signal is received by the first receiving and detecting device after passing through the magnetic field testing device, and the refractive index testing device and the ferrofluid sample are connected together , the connections between all the above components are realized by optical fiber. 2. The device for detecting changes in the magnetic field based on changes in the refractive index of the magnetic fluid according to claim 1, wherein the refractive index testing device is composed of a second light source output device, a coupler and a second receiving and detecting device, and these components They are all connected by optical fiber. The coupler guides the incident light to the end face of the optical fiber, and uses the optical fiber to collect the retroreflected light. The input end of the coupler is connected to the second light source output device, and the input end of the coupler guides the incident light to the optical fiber. On the optical fiber-magnetic fluid sample interface at the end face, the reflected optical power is detected and accepted by the second receiving and detecting device. 3 . The device for detecting changes in magnetic field based on changes in the refractive index of the magnetic fluid according to claim 2 , wherein the second light source output device is a communication band laser. 4 . 4 . The device for detecting changes in magnetic field based on changes in the refractive index of ferrofluid according to claim 2 , wherein the second light source detection device is an optical power meter in a communication band. 5 . The device for detecting changes in magnetic field based on changes in the refractive index of ferrofluid according to claim 1 , wherein the first light source output device is an amplified spontaneous emission light source. 6 . 6 . The device for detecting changes in magnetic field based on changes in the refractive index of ferrofluid according to claim 1 , wherein the transmission device is a single-mode optical fiber used in the communication band. 7 . The device for detecting changes in magnetic field based on changes in the refractive index of ferrofluid according to claim 1 , wherein the first receiving and detecting device is a spectrum analyzer.

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