JP3521366B2 - Branch interference optical waveguide type magnetic field sensor - Google Patents

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 detecting a magnetic field using light, and more particularly to an optical magnetic field sensor using a branch interference type optical waveguide.

[0002]

2. Description of the Related Art Conventionally, the method of measuring the current of a distribution line or the like uses a ring-shaped magnetic core and a magnetic detection element such as a Hall element or a magnetoresistive element to detect a magnetic field, convert it into a current value, and output it. The method is generally used, but particularly in the field of handling high voltage, magnetic field sensors have come to be used because of their requirements such as high electrical insulation and no interference by various electromagnetic inductive properties. This method detects a magnetic field using a Faraday element having a Faraday effect in which the plane of polarization of light rotates when a magnetic field is applied in the traveling direction of light.

Further, due to the necessity of detecting a minute current or a minute magnetic field with high sensitivity, a magnetic field sensor has been developed which is composed of a substance having a magnetic birefringence effect as a substrate and a branching interference type waveguide formed on the surface thereof. Has been used and has been used.

Here, the magnetic field birefringence effect is an effect of producing a phase between polarized light parallel to the magnetic field and polarized light perpendicular to the magnetic field when a magnetic field is applied in a direction perpendicular to the traveling direction of light. When a magnetic field is applied in the in-plane direction of an optical waveguide made of a crystal having a birefringence effect and perpendicularly to the light traveling direction, the phase of TM-mode polarized light is shifted.

FIG. 5 shows an example of a conventional branched interference optical waveguide type magnetic field sensor in which a substrate having a magnetic birefringence effect is used as a substrate. On a substrate 20, an input optical waveguide 21, phase shift optical waveguides 23 and 24 branched and coupled from the input optical waveguide 21, and an output optical waveguide 22 in which the above two phase shift optical waveguides are joined and coupled are formed. . Input optical waveguide 21
The input optical fiber 26 is coupled to the incident end of the output optical waveguide 22 and the output optical fiber 27 is connected to the output end of the output optical waveguide 22. Here, the lengths of the two phase shift optical waveguides 23 and 24 are different from each other.

In FIG. 5, the incident light from the input optical fiber 26 is incident on the input optical waveguide 21, and then the energy is split into the phase shift optical waveguides 23 and 24. When a magnetic field is applied, the refractive index of light in the waveguide changes according to its strength. Therefore, two phase shift optical waveguides 2
A phase difference corresponding to the magnitude of the applied magnetic field is generated between the light waves propagating through 3, 24, and interference occurs in the output optical waveguide 22 where they join to change the light intensity. That is, the intensity of the output light emitted from the output optical fiber 27 changes according to the applied magnetic field intensity, and the intensity of the applied magnetic field can be measured by measuring the change in the optical intensity with a photodetector.

[0007]

The characteristic curve showing the relationship between the applied magnetic field intensity and the output light intensity of the magnetic field sensor is expressed as a periodic function having a maximum value and a minimum value as shown in A of FIG. To be done. Since the magnetic field sensor has the highest sensitivity and excellent linearity near the midpoint between the maximum value and the minimum value of the characteristic curve, it is desirable to use this portion as the center for measuring the magnetic field strength.

However, in reality, the characteristics of the manufactured magnetic field sensors are different from each other. This is because there are many factors that affect the characteristics of the optical probe during the manufacturing process, and it is difficult to strictly control these factors.

In the following, a point on the characteristic curve when the magnetic field to be detected is not applied is called an operating point, and a magnetic field between the maximum value and the minimum value of the optical output on the characteristic curve is called a bias magnetic field.

The operating point a of the characteristic curve A shown in FIG. 1 is near the minimum value of the output light intensity, and the bias magnetic field is c.
Is. When a magnetic field sensor having a finite bias magnetic field is used to detect a magnetic field, reliable magnetic field strength cannot be known unless the measured result is corrected. In addition, when a is the operating point, detection is performed using a region where the linearity of the characteristic curve is low. Therefore, not only the magnetic field detection sensitivity is low, but also the disadvantage that the dynamic range is narrow is inevitable.

In view of the above problems, the present invention provides a branch interference optical waveguide type magnetic field sensor having a characteristic curve having a controlled bias magnetic field, enables detection of a minute magnetic field, and improves sensitivity. is there.

[0012]

In order to solve the above problems, the present invention provides an input optical waveguide formed of a substance exhibiting a magnetic field birefringence effect, two phase shift optical waveguides branched from the input optical waveguide, In a branching interference type optical waveguide composed of an output optical waveguide into which two phase shift optical waveguides merge and enter, a permanent magnet is provided in the vicinity of any one of the two phase shift optical waveguides. A branch interference optical waveguide type magnetic field sensor is constructed.

Further, according to the present invention, the material, shape, size of the permanent magnet installed in the vicinity of the two phase shift optical waveguides,
A branch interference optical waveguide type magnetic field sensor in which at least one of the relative position with respect to the phase shift optical waveguide or the direction of magnetization is not equal to each other is configured.

[0014]

The magnetic field sensor of the present invention comprises a branch interference optical waveguide formed on the surface of a substrate made of a substance exhibiting a magnetic birefringence effect. The phase of the light guided through the optical waveguide changes depending on the strength of the magnetic field.

When a finite phase difference occurs between the two guided lights, they merge with each other and interfere with each other, and are emitted as light whose intensity changes according to the phase difference. However, as described above, it is extremely difficult to manufacture a branch interference type magnetic field sensor capable of controlling the phase difference between two guided lights.

Therefore, according to the present invention, a bias magnetic field is applied to the phase shift optical waveguide forming the magnetic field sensor by a means different from the magnetic field to be detected, and the magnetic field to be detected has a substantially operating point. , The point of half of the sum of the maximum value and the minimum value of the optical output is matched on the characteristic curve. That is, in FIG. 1, the characteristic curve A is moved in parallel to the characteristic curve B. As a result, in the characteristic curve B, the point where the output light intensity is between the maximum and the minimum is the operating point b.

At this time, the magnetic field sensor has the highest sensitivity and the excellent linearity, as described above.

[0018]

Embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 2 is a schematic plan view of a branch interference optical waveguide type magnetic field sensor 10 according to Embodiment 1 of the present invention. La, Ga on a gadolinium gallium garnet (Gd ₃ Ca ₅ O ₁₂ ) substrate having a (111) plane
The substituted yttrium iron garnet crystal 1 was epitaxially grown to prepare a single crystal thin film having in-plane magnetization.

Then, the photoresist in the branch interference optical waveguide pattern portion is removed by photolithography, and Ti is removed.
Is sputtered, the photoresist is removed by lift-off, and the rib type optical waveguide is etched by argon ion as a mask for etching. The input optical waveguide 2, the phase shift optical waveguides 3 and 4, and the output optical waveguide 5 were produced.
The width of each of the optical waveguides 2 to 5 is 5 to 10 μm, and the height is 0.5 to 0.8 μm.

Further, a SiO ₂ film was formed as a buffer layer by sputtering, and a barium-ferrite film to be a permanent magnet 6 having a width of 100 μm and a length of 3 mm was provided in the vicinity of one of the phase shift optical waveguides, and a direct current in the thickness direction was formed. It was magnetized in a saturated magnetic field.

A magnetic field was measured by the light intensity detected by a photodetector connected to this, and a minute magnetic field of 0.5 Oe could be detected.

(Embodiment 2) FIG. 3 is a schematic plan view of a branch interference optical waveguide type magnetic field sensor 10 according to Embodiment 2 of the present invention. In Example 2, a barium-ferrite film, which is a permanent magnet 6 having a width of 100 μm and a length of 2 mm, is provided near one of the phase shift optical waveguides, and a width of 100 μm and a length of 5 mm are provided near the other phase shift optical waveguide. A barium-ferrite film to be the permanent magnet 7 was provided, and a DC saturation magnetic field in the thickness direction was applied to magnetize in the same direction. The branch interference optical waveguide type magnetic field sensor 10 is installed in the vicinity of a conductor in which a current of 50 Hz is flowing, and the magnetic field is measured by the light intensity detected by a photodetector connected to this branch interference optical waveguide type magnetic field sensor 10, and the same as in the first embodiment. ,
It was possible to detect a minute magnetic field of 0.5 Oe.

(Third Embodiment) FIG. 4 is a schematic plan view of a branch interference optical waveguide type magnetic field sensor 10 according to a third embodiment of the present invention. Example 3 has a width of 100 μm, a length of 1.4 mm,
Barium-ferrite permanent magnets 6 and 7 having a thickness of 500 μm and magnetized in the thickness direction were arranged near the respective phase shift optical waveguides so that the magnetizations were opposite to each other.

The branch interference optical waveguide type magnetic field sensor 10 is installed in the vicinity of a conductor in which a current of 50 Hz is flowing, and the magnetic field is measured by the light intensity detected by a photodetector connected to the branch interference optical waveguide type magnetic field sensor 10. , 2, a minute magnetic field of 0.5 Oe could be detected.

The present invention discloses a technique for imparting a controlled phase difference between guided light beams passing through two phase shift optical waveguides.

In the above-mentioned embodiments, the substance using the La, Ga-substituted yttrium iron garnet crystal was described as an example of the substance exhibiting the magnetic birefringence effect, but the present invention is not limited to this. Other yttrium / iron / garnet crystals, heavy flint glass or the like may be used.

As a permanent magnet, a material other than barium ferrite such as manganese bismuth (MnB) is used.
i), platinum iron (Pt-Fe), etc. may be used.

Further, the shape and size of the permanent magnet, including the thickness, or the position between the permanent magnet and the phase shift optical waveguide is a factor that makes the magnetic field strengths applied to the two phase shift optical waveguides different from each other. . Therefore, the objective can also be achieved by adjusting each of these factors.

[0030]

As described above, according to the present invention, the operating point for the magnetic field to be detected and the half of the sum of the maximum value and the minimum value of the optical output of the magnetic field sensor are substantially matched. As a result, it is possible to detect a magnetic field based on the operating point b when the bias magnetic field is zero, and as a result, a minute magnetic field can be detected, realizing a highly sensitive branch interference optical waveguide type magnetic field sensor. Has a remarkable effect on.

[Brief description of drawings]

FIG. 1 is a characteristic curve showing a relationship between an applied magnetic field intensity and an output light intensity of a magnetic field sensor.

FIG. 2 is a schematic plan view of the branch interference optical waveguide type magnetic field sensor according to the first embodiment of the present invention.

FIG. 3 is a schematic plan view of a branch interference optical waveguide type magnetic field sensor according to a second embodiment of the present invention.

FIG. 4 is a schematic plan view of a branch interference optical waveguide type magnetic field sensor according to a third embodiment of the present invention.

FIG. 5 is a perspective view of an example of a conventional branch interference optical waveguide type magnetic field sensor.

[Explanation of symbols]

1 La, Ga Substituted Yttrium Iron Garnet Crystal 2 Input Optical Waveguide 3, 4 Phase Shift Optical Waveguide 5 Output Optical Waveguide 6, 7 Permanent Magnet 10 Branch Interference Optical Waveguide Magnetic Field Sensor 20 Substrate 21 Input Optical Waveguide 22 Output Optical Waveguide 23 , 24 Phase shift optical waveguide 26 Input optical fiber 27 Output optical fiber

Claims (2)

(57) [Claims] 1. An input optical waveguide formed of a substance exhibiting a magnetic birefringence effect, two phase shift optical waveguides branched from the input optical waveguide, and an output where the two phase shift optical waveguides merge and enter. At least one of the two phase shift optical waveguides in a branching interference optical waveguide comprising an optical waveguide
A branch interference optical waveguide type magnetic field sensor, wherein a permanent magnet is installed in the vicinity of the phase shift optical waveguide of the book. 2. At least one of the material, shape, size, relative position to the phase shift optical waveguide, or magnetization direction of the permanent magnets installed near the two phase shift optical waveguides is not equal to each other. The branched interference optical waveguide type magnetic field sensor according to claim 1.