JPS63118677A - Detection of magnetic field by optical fiber magnetic field sensor - Google Patents

Abstract

PURPOSE:To improve the variance of Verdet's constant due to temperature by making two light beams different in wavelength incident on an optical fiber magnetic field sensor and detecting the Faraday rotation angle for each wavelength. CONSTITUTION:Light beams from a light source 1 which emits light having a wavelength lambda1 and a light source 2 emits light having a wavelength lambda2 are made incident on an optical fiber 4 through a multiplexer 3. They are converted to parallel rays of light by a rod lens 5 and are turned by a rectangular prism 6 and are made incident on a polarizing prism 7. The incident light is converted to linear light and is made incident on a Faraday rotating element 8. The exit light is divided into (x) and (y) components by a polarizing beam splitter prism 9. Light of the (y) component is made incident on an optical fiber 11 by a rod lens 10 and is inputted to a demultiplexer 12. This light is divided to light beams having wavelengths lambda1 and lambda2 again by the demultiplexer 12, and they are made incident on detectors 13 and 14. Light of the (x) component is turned by a rectangular prism 15 and is converted to parallel rays of light by a rod lens 16 and is made incident on an optical fiber 17 and is inputted to a demultiplexer 18. This light is divided into light beams having wavelengths lambda1 and lambda2 again by the demultiplexer 18, and they are made incident on detectors 19 and 20.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magnetic field detection method using an optical fiber magnetic field sensor for measuring current, etc. in a high voltage line.

(Prior art) In recent years, optical fibers have been used for measurement and control, taking advantage of their advantages such as electrical insulation, resistance to electromagnetic induction, and environmental resistance. Optical fiber type magnetic field sensors combined with crystals having optical or magneto-optical effects are expected to be applied in a wide range of industrial fields, mainly the electric power field, and are being developed and commercialized.

FIG. 3 shows an example of a conventional optical fiber type magnetic field sensor.

In this sensor, the light incident from the light emitting element 1 is transmitted through the optical fiber 2.
The light passes through the rod lens 3, is converted into parallel light, is bent by the right angle prism 4, and enters the polarizing prism 5.

In this polarizing prism 5, the incident light is converted into linearly polarized light and enters the Faraday rotation element 6. The plane of polarization of the linearly polarized light passing through the Faraday rotation element 6 is rotated by an angle shown by θ=VdH1 in proportion to the length l of the element and the strength H of the magnetic field (Vd is the Verdet constant).

The light emitted from the Faraday rotation element 6 is divided into an X component and an X component by a polarizing beam splitter prism 7, and the
The light of I & minute is incident on the optical fiber 9 by the rod lens 8 and guided to the detector 10, and the TL output P1 is detected by the detection WIO.
is converted to The X component light is bent by a right angle prism 11, made into parallel light by a rod lens 12, guided to a detector 14 through an optical fiber 13, and converted into an electrical output P2 by the detector 14. These electrical outputs P, P2 are respectively expressed by the following equations.

P+ = 2 cog2 (45°10) P2 = 2
5in2 (45@10) If you perform the following signal processing on this P, , P2, F= CP+ -P2) /
CP+ +P2 )=coa (2θ+900) =srn2 θ 8=20 (however, θ<<1), and the magnetic field H
An output voltage proportional to can be obtained.

The optical fiber magnetic field sensor measures the strength of the magnetic field H using the Faraday effect based on changes in the optical signal.

(Problems with the Prior Art) The conditions necessary for the Faraday rotation element 6 used in these magnetic field sensors are as follows.

B. The temperature characteristics of the Verdet constant are small.

B. The Verdet constant is large.

C. Good light transmittance.

For example, in the case of lead glass, it is said that there is theoretically no temperature characteristic of the Verdet constant, but the value of the Verdet constant is 0.04 (
i+iu 10e-cm) (wavelength 0-8 pm).

On the other hand, in the case of ferromagnetic YIG, the Verdet constant value is 9 (sin
10e cm) (wavelength 1.3 gm), which is 200 times larger, but its temperature characteristics are extremely large.

As shown in Figure 4, an example of its temperature characteristics is -20 to 1
It exists at about 16% at 20°C.

Since the Faraday rotation angle is θ=VdH1, the temperature L1
What is the Verdet constant at Vd (t+) and temperature? When the Verdet constant at is Vd (tz), the respective Faraday rotation angles θl and θ2 are expressed as θ+ =Vd(t+)Hl θ2 =Vd(F)Hl.

Therefore, if only θ is detected and the temperature is not detected,
θ2 = Vd (t+)H' 1.In order to reduce these effects, the temperature change in the Faraday rotation angle and the temperature change in the magnetic field cancel each other out. By finding a Faraday rotator element 6 having a composition such that the temperature change of the Verdet constant can be improved, for example, in some companies (Tbo, uYa, a+) 3 Fe soum [
A composition of 1' ((YTb)IGX) has been developed, which has a temperature of ±1% at -20 to 120°C, as shown in Figure 4.
and good temperature characteristics.

(Objective of the Invention) An object of the present invention is to make it possible to improve the temperature change in the Verdet constant without having to adjust the W composition as in the conventional method.

(Means for solving the problem) The magnetic field detection method using the optical fiber magnetic field sensor of the present invention is as follows:
Inject two different wavelengths of input 1 and 2 into an optical fiber magnetic field sensor, detect the rotation angle of 7 degrees at each wavelength of input 1 and input 2, and calculate the temperature of the Faraday rotator element 8 from the ratio of both rotation angles. The temperature is corrected to detect the strength of the magnetic field.

(Operation of the Invention) FIG. 1 shows an embodiment of the optical fiber magnetic field sensor of the present invention.

In FIG. 1, light from a light source 1 that emits λ-multiplexed light and a light source 2 that emits λ-multiplexed light enter a multiplexer 3 and then enter an optical fiber 4. The light is then made into parallel light by the rod lens 5, bent by the right angle prism 6, and incident on the polarizing prism 7. This polarizing prism 7 converts the incident light into linearly polarized light,
It enters the Faraday rotation element 8. The plane of polarization rotates by O in proportion to the strength H of the magnetic field. This emitted light is divided into an X component and a y component by a polarizing beam splitter prism 9.

The y-component light enters the optical fiber 11 through the rod lens 10 and enters the demultiplexer 12. In the 0 demultiplexer 12, it is again divided into wavelength input 1 and wavelength input 2, and enters the detectors 13 and 14.

The X component light is bent by a rectangular prism 15, converted into parallel light by a rod lens 16, enters an optical fiber 17, and enters a demultiplexer 18.
and enters the detector 19.20.

In other words, the present invention described above can be applied to a conventional magnetic field sensor.
The Faraday rotation at each wavelength is detected by passing two wavelengths (input 2). The wavelength dependence of Faraday rotation is shown in FIG. 5, and the Faraday rotation angle at each wavelength can be written as follows since the Verdet constant has temperature characteristics.

θ input l = vd input 1 (t)・H fist 1θ input 2 = v
d input 2 (t)·H-1 Now, if we take the ratio of the Faderer rotation angles at each wavelength, we get the following equation (see Figure 2).

K = θ input 2 / θ input 1 = Vd input 2 (t) / Vd input I (1) (t: temperature) Therefore, this ratio is independent of the magnetic field strength H, and K is t
Therefore, if you measure the value of K by changing the temperature t by - degrees, you can conversely calculate the value of Faderer rotating element 8 from the value of K.
The easiest thing to do is to find the temperature t.

If the temperature of the Faderer rotation element 8 is determined in this manner, Vd input 1 (t) can be determined from the equation θ input 1=vd input 1 (t)·HIll. Since the length l of the element is already known and the θ input l can be measured, it is naturally possible to measure the magnetic field strength H as well.

Therefore, the present invention is not affected by the temperature characteristics of the Faderer rotating element 8, which was a problem in the prior art, so there is no need to use a Faderer rotating material whose temperature characteristics are reduced by specially adjusting the m-constituent.

For example, materials such as YIG, Bi:YIG, etc., which have a large Verdet constant but have conventionally had problems in temperature characteristics, can also be used.

In Fig. 1, if the light sources 1 and 2 are made to emit light alternately, the demultiplexer 12.18 can be omitted, and in this way, the two detectors 13.14 can also be reduced to one. The two detectors 19 and 20 can also be reduced to one.

(Effects of the Invention) The magnetic field detection method of the present invention has the following effects (1) Since the Faderer rotating element 8 is not affected by temperature characteristics, the composition of the rotating element 8 is specially adjusted. There is no need to use a Faraday rotation material with low temperature characteristics, and therefore a material with poor temperature characteristics can be used as the Faraday rotation element 8 of the optical fiber magnetic field sensor.

(2) Since the temperature at the installation location of the optical fiber magnetic field sensor is also measured in a circular motion, it is suitable for monitoring abnormal heating of cables, etc., for example.

4. Brief explanation of the figures Figure 1 is an explanatory diagram showing an example of the present invention, Figure 2 is an explanatory diagram showing the relationship between the ratio of Verdet constants and temperature, and Figure 3 is an explanation of a conventional optical fiber magnetic field sensor. FIG. 4 is an explanatory diagram of the temperature characteristics of Faraday rotation material.

FIG. 5 is an explanatory diagram of the wavelength dependence of a Faraday rotation material.

input l, λ2 is the wavelength 8 is Faraday rotation element

Claims (1)

[Claims] Two different wavelengths are incident on an optical fiber magnetic field sensor, the Faraday rotation angle of each wavelength is detected, the temperature of the Faraday rotation element is determined from the ratio of both rotation angles, and the temperature is corrected to determine the strength of the magnetic field. A magnetic field detection method using an optical fiber magnetic field sensor, characterized in that: