JPH0712907A - Optical magnetic field sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an optical magnetic field sensor that is small and lightweight, has a low manufacturing cost, and has a good insulating property and detects a lightning surge. In the device according to the present invention, light emitted from a light source 1 passes through an optical fiber 2, then passes through a lens 3 and a total reflection prism 4 in this order, and then enters a RIG film 5.
The light passes through the RIG film 5 while undergoing an intensity modulation according to the intensity of the magnetic field, is further deflected by the total reflection prism 6, and is focused on the optical fiber 8 by the lens 7.
The light is guided to the photodetector 9 by the optical fiber 8 and photoelectrically converted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical magnetic field sensor for measuring a change in magnetic field intensity by using the Faraday effect of a rare earth-iron garnet film, and more particularly to a lightning strike sensor for monitoring surge due to lightning strike.

[0002]

2. Description of the Related Art Since a lightning strike on a power supply line such as a power transmission line may lead to a serious accident, various power-saving devices for lightning strike are installed in a power receiving and transforming facility. Further, a lightning strike sensor for monitoring a surge caused by a lightning strike is used in order to grasp the operating condition of the above-mentioned security device. As a conventional lightning strike sensor, a coil wound around an iron core is used. This is a principle of reading a magnetic flux change outside the conductor caused by a current change of a conductor due to a lightning strike by electromagnetic induction.
It was decided by.

[0003]

However, the conventional lightning strike sensor as described above has a volume of about 20 cm × 20 cm × 20 cm.
Since it is large in size and heavy at about 10 kg, it is difficult to use, and the cost in the manufacturing process is high. Further, since the sensor itself is composed of a conductor, there is a problem that the insulation is poor.

In view of the above-mentioned problems of the prior art, the present invention is an optical magnetic field sensor (3300-) which is small and lightweight, has a low manufacturing cost, and has a good insulating property.
Applies to 100V).

[0005]

In order to achieve the above object, in the optical magnetic field sensor according to the present invention, the light emitted from the lens immediately after the incident side optical fiber is a total reflection prism, a rare earth element.
After passing through the iron garnet and the total reflection prism in this order, the light is guided to the optical fiber by a lens just before the light receiving side optical fiber.

[0006]

Therefore, in the device of the present invention, since the magnetic garnet film (hereinafter referred to as RIG film) is a perpendicular magnetization film having a labyrinthine magnetic domain, when light passes through the RIG film, a diffraction phenomenon occurs immediately after that. , 0th order light, 1st order light, 2nd order light ...
., Spreads in proportion to the n-th light (n is a natural number) and the order of the next light (however, when the magnetic field is 0, only odd-order light appears). This is because the magnetic domain serves as a phase grating. At this time, the diffraction angle φ of the nth-order light is expressed as 2 · d · sin (φ) = n · λ (1), where d is the width of a pair of magnetic domains having different magnetization directions. It can be seen that the diffraction angle increases as the order increases.

From the above equation (1), since the diffraction angle of the 0th order light is 0, it can be seen that the light travels straight even after passing through the RIG film. The relationship between the intensity I of the 0th-order light and the magnetic field H is that the saturation magnetic field of the RIG film is Hs and the Faraday rotation angle is θ.
Then, I = cos ² (θ) + (H ² / Hs ² ) · sin ² (θ) (2) Therefore, it can be seen from the above formula (2) that light is intensity-modulated by the magnetic field only by passing through the RIG film. However, since this phenomenon produces a light quantity proportional to the square of the magnetic field, there is a problem in using it for the purpose of measuring the magnitude of the magnetic field, but it is sufficient for lightning strike sensors that judge the presence or absence of the above magnetic field. It is possible.

[0008]

The present invention will be described below based on the illustrated embodiments. In FIG. 1, 1 is a light source, 2 is an optical fiber, 3 is a lens, 4 is a total reflection prism, 5 is a RIG film, 6 is a total reflection prism, 7 is a lens, 8 is an optical fiber, and 9 is a photodetector. . Since the optical magnetic field sensor according to the present invention is configured as described above, the light emitted from the light source 1 passes through the optical fiber 2 and then passes through the lens 3 and the total reflection prism 4 in this order to the RIG film 5. Incident. Where light is RI
The light passes through the G film 5 while undergoing the intensity modulation described by the above formula (2) according to the intensity of the magnetic field, is deflected by the total reflection prism 6, and is condensed on the optical fiber 8 by the lens 7. After that, the light is guided to the photodetector 9 by the optical fiber 8 and photoelectrically converted. The direction of the magnetic field to be detected is RI
It is parallel to the light ray passing through the G film 5. As described above, the magnetic field detecting portion of the optical magnetic field sensor according to the present invention is composed of the lens 3, the total reflection prism 4, the RIG film 5, the total reflection prism 6 and the lens 7, and even the largest component has a volume of at most 5 mm. Since it is about 5mm x 5mm, it will be a small and lightweight device.

Next, when actually manufacturing the above-mentioned device of the present invention, a light emitting diode having a wavelength of 0.85 μm is used for the light source 1, and a multimode fiber is used for the optical fibers 2 and 8.
Selfoc lenses are used for the lenses 3 and 7, and the RIG film 5 is used.
(YbTb) ₅ Fe ₃ O ₁₂ was used as the photodetector, and a Si photodetector was used as the photodetector 9. The lens 3, the total reflection prism 4,
The volume of the magnetic field detection unit composed of the RIG film 5 and the total reflection prism 6 is 3 cm × 2 cm × 1 cm, and its weight is about 10
It was 0g.

Furthermore, the relationship between the magnitude of the magnetic field and the output of the output photodetector of the optical magnetic field sensor according to the present invention was examined. In this case, the output of the photodetector 9 when a magnetic field of 1500 Oe was applied by an electromagnet. Was measured. The magnitude of the magnetic field was measured using a Gauss meter. The measurement result is as shown in FIG. 2, and it can be confirmed from this figure that the output of the photodetector is almost proportional to the square of the magnetic field as shown in the equation (2). The output is saturated at a magnetic field of about 1400 Oe or more because the saturation electric field of the RIG film is about 1400 Oe. Based on the above, the presence or absence of the fact of lightning strike
It became clear that the determination by N-OFF is sufficiently possible.

Further, when the optical magnetic field sensor according to the present invention is actually used as a lightning strike sensor, the magnetic field detecting portion is arranged in the vicinity of the conducting wire. At this time, the conducting wire is surrounded by an iron core with a gap, and the above-mentioned gap is provided in the gap. It is also possible to increase the magnetic flux density by arranging the magnetic field detection unit to improve the sensitivity.

[0012]

As described above, the optical magnetic field sensor according to the present invention is suitable for a lightning strike sensor because it is small in size and light in weight and excellent in insulation because it optically detects a magnetic field. Further, in the apparatus of the present invention, the light source and the photodetector can be kept sufficiently far away from the magnetic field detection section through the optical fiber, so that they are not easily affected by electromagnetic noise, and the measurement environment with a lot of electromagnetic noise can be used. It is also suitable for a sensor that determines the presence or absence of a magnetic field in a bad place.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical magnetic field sensor according to the present invention.

FIG. 2 is a relationship diagram between the output and the magnetic field of the optical magnetic field sensor according to the present invention.

[Explanation of symbols]

 1 light source 2,8 optical fiber 3,7 lens 4,6 total reflection prism 5 RIG (magnetic garnet) film 9 photodetector

Claims (1)

[Claims] 1. Light emitted from a lens immediately after an incident-side optical fiber passes through a total reflection prism, a rare earth-iron garnet, and a total reflection prism in this order, and then is guided to the optical fiber by a lens immediately before a light-receiving side optical fiber. An optical magnetic field sensor characterized in that.