JPS62140077A - Optical fiber magnetic sensor - Google Patents

Abstract

PURPOSE:To enable the measurement of a low magnetic field, by setting a fiber having a core comprising a crystalline Faraday material as a sensor part. CONSTITUTION:A sensor part 21 is constituted of a core comprising a crystalline Faraday material having a large Verdet's constant and a fiber comprising a clad coating said core and, as the Faraday material, BGO (bismuth germanium oxide) is used. The light from a light emitting source 27 is transmitted to a SELFOC lens 24 through an input optical fiber 25 to converge luminous flux and subsequently sent to a fiber type polarizer 22 and polarized to enter the sensor art 21. The polarized light transmitted to the sensor part 21 receives rotation at the polarizing surface thereof corresponding to the intensity of the magnetic field applied to said sensor part 21 to be sent to a fiber type analyzer 23 in said state. In the analyzer 23, the angle of rotation of the polarizing surface is converted in to luminous intensity and condensed at the SELFOC lens 24 to be transmitted to an output optical fiber 26 and sent to a light receiver 28 to obtain electric output. By this method, a low magnetic field can be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical fiber type magnetic sensor for detecting a magnetic field or a magnetic field formed by an electric current, particularly a weak magnetic field.

[Prior art and its problems]

Conventionally, the original 1# propagating in an isotropic material! Optical fiber magnetic field sensors are known that utilize the Faraday effect in which waves are rotated by a magnetic field. FIG. 2 shows an array of such fiber optic magnetic field sensors. The sensor in this example measures the magnetic field created by the current flowing through conductor A. The light from the light source 2 of transparent WaX is propagated through the input optical fiber 3 and guided to the polarizer 5 of the sensor body installed near the conductor A. Here, the light is polarized with a constant plane of polarization. It is sent to a sensor section 6 made of YTG (yttrium, iron, garnet).In this sensor section 6, the element undergoes a diagonal rotation comparable to the magnetic field.
The light is sent to two Ei photons 7 and 7 arranged in parallel, and after being separated into two lights whose polarization planes burn directly to each other, the light is reflected by a mirror 8 and output to an output optical fiber 9. The original receiver 10 measures the intensity of the light propagated through the output optical fiber 9. The deviation angle of the ball axis between the dimmer 5 and the analyzers 7, 7 is π
/4 radians (45°), and the polarization plane rotation angle is θ.
If Po is the original intensity input to the sensor unit 6, and Pr and Pz are the original intensities output from the analyzers 7, 7, then P1=Pocos2(θ-π/4) Pz=P o CO52 (θ1π/4).

The arithmetic circuit 11 calculates Pl and Pz as (Ps Pz
)/(Pt +P2), the output V (=PI P2/P1+P2) of this arithmetic circuit 11 becomes V=2θ in sio2θ (θ<1), and ■ is proportional to the rotation angle, that is, the magnetic field, and the magnetic field You can find the strength of

By the way, in such a case of C/f, if a low magnetic field is to be measured, it is necessary to increase the length of the sensor section 6 (the optical path length). In other words, the rotation angle θ is as follows:
This is because it is proportional to the optical path length e.

θ=V,, lH However, V is the Perde constant ridge and H is the strength of the magnetic field.

For this reason, a multiple reflection type optical fiber magnetic field sensor as shown in FIG. 3 has been proposed. This sensor is a plate-shaped YI
Reflectors M12, 12 are provided on both sides of the sensor section 6 made of G, etc., and light is sent from the incident prism 13 provided at the end of the sensor section 6 through the polarizer 5 at an incident angle such that total reflection occurs. The analyzer 7
The light is guided out from the exit prism 14 through the rays 5 and K is set to increase the optical path length.

However, even this type of sensor is 60 to 1o.

The limit is 15 to 5 times reflection due to the thickness of the sensor part 6.
It is only possible to obtain the optical path length of 0c+n Negarashi. Additionally, this sensor has the disadvantage that light tends to be attenuated due to multiple reflections.

Further, the optical path length sufficient to measure a magnetic field of, for example, 10e or 600e is as shown in the following table.

As described above, it has been virtually impossible to measure low magnetic fields with conventional sensors due to the optical path length.

[Means for solving problems]

Therefore, in this invention, a core made of crystalline faradaic material? By using the fiber provided as the sensor section, a long optical path length can be ensured, making it possible to measure low magnetic fields.

Figure 1 shows -91 of the optical fiber Mi air sensor of the present invention.
3, and the reference numeral 21 in the figure is a sensor section. This sensor section 21 has a large introduction to the Bellb constant &! The fiber consists of a core made of Faraday material and a cladding that covers this core. Crystalline faraday materials include BGO (bismuth kermanium oxide), B50 (bismuth silicon oxide)
, YIG (yttrium/iron garnet), cTbo
m ze Yo* atn3Is Ge1i (YSmL
uCa)a (FaGe)s Q2, La, Sm
.

A crystalline compound containing a lanthanide element such as C. is used. The core width is usually 50 to 300 prn4ff. As cladding, 5iO2s ki12o3
7. With a lower refractive index than cores such as 1: The thickness is about 2 to 60 μm. This fiber is produced by first creating a crystallized core using a method such as the EFG method using a die to pull up the above-mentioned melt of the crystalline compound using a JPC02 laser, and then sputtering the surface of this core. S i C that becomes the cladding
) x * A It is manufactured by providing a thin film such as #20s. The sensor section 21 made of such a fiber
The -bc optical path length) varies depending on the strength of the magnetic field to be measured and the Verdet constant of the Faraday material that forms the core, and is considered to be the length of the pressure, and for long lengths, it is possible to use a coil shape or a repeating shape using a reflective prism, or for short lengths. It can be formed into various shapes such as a straight line.

One end of a fiber polarizer 22 and a fiber photon 23 are connected to both ends of the sensor section 210. The fiber-type l-photon 22 and the fiber-type analyzer 23 are made by covering the surface of the core of a 5102 series fiber with a metal IV film such as aluminum. At the other end of each of the polarizer 22 and analyzer 23,
One end of the self-hook lens 24.24 for sunlight is attached. Furthermore, one end of an input optical fiber 25 and an output optical fiber 26 are connected to the other ends of these self-hock lenses 24, 24, respectively.

The input optical fiber 25 is naturally followed by the self-hock lens 24 which is followed by the analyzer 22. Furthermore, a light emitting diode (LE) is connected to the other end of the input optical fiber 25.
D), a light emitting source 27 such as a laser diode (LD),
A photodiode (P
D) or an avalanche photodiode (APD) is provided.

Thus, the light from the light source 27 is transmitted to the input optical fiber 2.
5, the light beam is transmitted to the cell-hock lens 24, where the light beam is focused and sent to the fiber polarizer 22, where it is polarized and then enters the sensor section 21. Sensor part 21
The plane of polarization of the transmitted polarized light is rotated according to the strength of the magnetic field applied here, and in this state, it is sent to the fiber analyzer 23. In the fiber analyzer 23, the rotation angle of the plane of polarization is converted into light intensity, and the selfoc lens 24
The light is collected and transmitted to an output optical fiber 26, and sent to a light receiver 28, so that an electrical output can be obtained.

[Effect]

In the optical 7-aiba air sensor having such a structure, the sensor section 21 is composed of a fiber having a core made of crystalline Faraday material.
The optical path length can be made sufficiently long as necessary, the rotation angle θ can be made large, and low magnetic fields can be measured.

In addition, since the polarizer and analyzer are fiber-shaped, the sensor body can be constructed entirely from fibers.
The structure is simple and the reliability is high.

Note that as the polarizer and analyzer, in addition to the fiber type, a prism type, a polarization constant fiber wound, etc. can be used. Alternatively, as shown in Figure 2, the light from the sensor section can be split into two using two prism-type photonic elements, the intensity of each output light can be determined, and similar calculation processing can be performed. You can also do it.

〔Example〕

(Example 1) Light emitting diode (LED) with a wavelength of 0.85 μm as a light source
, 8L-PIN photodiode in the receiver, core diameter 200pm, cladding diameter 25 in the input and output optical fibers.
A length obtained by forming a 25 μm thick cladding of 5102 by sputtering on the core of a BGO crystal with a diameter of 200 μm obtained by a pulling method using a CO2 laser method using a 0 μm Gradyrad index type silica fiber. The sensor part is made of 2In fiber. The sensor section had a length of approximately 1 m by folding a 2 m long fiber using a reflecting prism.

A prism-shaped polarizer and analyzer were connected to both ends of the sensor section, and further connected to input and output optical fibers via cell-hoc lenses to form a sensor.

When the maximum detection angle of the analyzer was set to 40', the hunting sensor was able to detect magnetic fields from 0.1 to 150 e.

(Example 2) A power-stabilized laser diode with a wavelength of 1.3 μm was used as the light source, an 8l-PIN photodiode was used as the receiver, polarization constant fibers were used as the input and output fibers, and the same was used for the polarizer and analyzer. A fixed polarization fiber was wound 10 times with a diameter of 30 mm, and was used as the fiber for the sensor section, using a core with a diameter of 70 μm made of crystalline YIG obtained by a pulling method using a CO2 laser, and a core of 70 μm in diameter by a sputtering method. Four magnetic sensors were fabricated using a 10 cm long fiber consisting of an 8102 cladding with a thickness of 3 μm. This magnetic sensor was capable of measuring magnetic fields of up to 600 e.

〔Effect of the invention〕

As explained above, in the optical fiber magnetic sensor of the present invention, the sensor part is composed of a fiber having a core made of crystalline Faraday material, so the optical path length of the sensor part is adjusted to be sufficient as necessary. It can be made long, making it possible to measure low magnetic fields. Further, the shape of the sensor portion can be formed into various shapes such as a coil shape or a straight shape, which increases the degree of freedom in measurement. Furthermore, if fiber-type polarizers and analyzers are used, all parts, including the input and output optical fibers, can be made of fibers, which has the advantage of simplifying the structure and improving AM performance. It will have the following.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of the optical fiber magnetic sensor of the present invention. FIG. 2 and FIG. 6 are both schematic configuration diagrams showing examples of conventional optical fiber magnetic sensors. 21... Sensor section, 22... Fiber type polarizer, 23... Fiber type analyzer, 24...
...Self-hock lens, 25 "...Input optical fiber, 26...Output optical fiber, 27
...Light source, 28...Receiver 0 m; 11° Fig. 1

Claims (1)

[Scope of Claims] A sensor body having a sensor section that detects the strength of a magnetic field as a change in the rotation angle of the plane of polarization using the Faraday effect, and an optical fiber connected to the sensor body that guides input light and output light. An optical fiber magnetic sensor comprising: an optical fiber magnetic sensor, characterized in that the sensor section is composed of a fiber having a core of a crystalline Faraday material.