JP3135744B2 - Optical 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 a magneto-optical element having a Faraday effect and measuring the intensity of the magnetic field.

[0002]

2. Description of the Related Art In recent years, in the field of electric power in particular, as a method of measuring the intensity of a magnetic field generated around an electric wire using light, a current measuring device combining a magneto-optical element having a Faraday effect and an optical fiber has been proposed. It is being put to practical use. The method of detecting the current by measuring the magnetic field strength around the conductor where the current is flowing has characteristics such as good insulation because it uses light as a medium, and it does not receive electromagnetic induction noise. Application to equipment is considered.

FIG. 12 shows a principle diagram of a method for measuring a magnetic field using the Faraday effect. In FIG. 12, a magneto-optical element 4 is arranged in a magnetic field H. The light made linearly polarized by the polarizer 3 is passed through the magneto-optical element 4. The polarization plane is rotated in proportion to the magnetic field strength H by the Faraday effect. FIG. 12 shows a case where the Faraday rotation indicates a negative sign. The rotated linearly polarized light passes through the polarizer 3 and the analyzer 5 in which the transmitted polarization direction is changed by 45 degrees, and the magnitude of the rotation angle θ is converted into a change in the amount of light. In order to realize this magnetic measurement method, an optical magnetic field sensor generally configured as shown in FIG. 11 is used (National Technical Report)
Vol.38 No.2 P.127 (1992)).

In the optical magnetic field sensor configured as shown in FIG. 11, a multimode fiber having a core diameter of 80 μm is used for the optical fiber 9, and a 0.25 pitch self-focusing rod lens is used for the lenses 2 and 7. Further, the polarizer 3 and the analyzer 5
As a method, a polarizing beam splitter is used, and the optical path is 90
The total reflection mirror 6 is used to bend the lens. The polarizing beam splitter and the total reflection mirror are cubes with a side of 5 mm. The thickness of the ferrimagnetic garnet crystal used for the magneto-optical element 4 is 50 μm.

However, when a rare-earth iron garnet crystal, which is a ferrimagnetic material, is used for a magneto-optical element used in an optical magnetic field sensor, light transmitted through the crystal is diffracted by a multi-domain structure unique to the rare-earth iron garnet crystal. .
When the magnetic domain structure of the ferrimagnetic garnet crystal is a maize domain, diffracted light is observed as shown in FIG.
, The primary light 33, the secondary light 34,... In the optical magnetic field sensor configured as shown in FIG. 11, since the observation condition of the diffracted light at the emission side lens 7 is almost zero-order light observation, the output is represented by (Equation 1). Journal Journal Vol.14, No.4, P.642 (1990)).

[0006]

(Equation 1)

Here, θ _F is the Faraday rotation angle when the material is magnetically saturated, and is expressed as θ _F = FL. F is a material-specific Faraday rotation coefficient, and L is an optical path length (element length). M is the magnetization of the material when a magnetic field is applied, M _S is the magnetization when the material is magnetically saturated (saturation magnetization).

A magneto-optical element used in the above-described optical magnetic field sensor is represented by the following general formula (Formula 1), where the value of X is X = 1.3, the value of Y is Y = 0.1, and the value of Z is A rare earth iron garnet crystal having a value of Z = 0.1 and a value of W of W = 0.6 is disclosed (IEICE technical report OQE92-105).
(1992)). In this prior art, Y is Bi
By replacing with Gd or Gd, a magneto-optical element having good temperature characteristics is realized. The chemical formula of the crystal used in this conventional example is shown in (Formula 1).

[0009]

## STR1 ## _{Bi X Gd Y La Z Y 3-} (X + Y + Z) Fe 5-W Ga W O 12

[0010]

However, when an optical magnetic field sensor is constructed using this magneto-optical element,
As shown in FIG. 10, a linearity error of the magnetic field measurement of ± 2.0% or less in the range of 5.0 Oe to 190 Oe is shown, and there is a problem in the linearity of the optical magnetic field sensor.

As described above, when the rare earth iron garnet crystal is used for the magneto-optical element used in the optical magnetic field sensor,
When light is transmitted through a garnet crystal, which is a ferrimagnetic material,
Due to the multi-domain structure of the garnet crystal, light diffraction occurs, and the diffracted light transmitted through the crystal does not completely converge on the optical system on the emission side, so that there is a problem that the linearity with respect to the magnetic field intensity deteriorates.

The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide an optical magnetic field sensor having high linearity with respect to a magnetic field.

[0013]

According to the present invention, there is provided an optical system for receiving a higher order diffracted light than a conventional one using an output side optical fiber, and a polarizer is provided at least along a light traveling direction. And a magneto-optical element and an optical magnetic field sensor for detecting the magnetic field to be measured as an output light intensity by disposing an analyzer in which the transmission polarization directions are different from each other with respect to the polarizer. The core diameter of the second optical fiber provided across the analyzer is the same as that of the magneto-optical element.
A transmission type optical magnetic field sensor having a larger diameter than the core diameter of the first optical fiber provided with a polarizer on the other end face .

[0014]

When the (Equation 1) is expanded, it is expressed as (Equation 2).

[0015]

(Equation 2)

Here, M = χH, and χ is the magnetic susceptibility. Further, considering that the applied magnetic field is an AC magnetic field in (Equation 2) and substituting and transforming H = H ₀ sinωt, the output AC component V ₀ ac is expressed as (Equation 3).

[0017]

(Equation 3)

From equation (3), it can be seen that the expression representing the output includes the term sin2ωt, and its coefficient is multiplied by the square term H ₀ ² of the magnetic field strength. Therefore, for an alternating magnetic field, si
The presence of the second harmonic with respect to the fundamental wave of nωt causes the linearity distortion with respect to the magnetic field. Therefore, as the intensity H _{0 of the} applied magnetic field increases, the amplitude of the second harmonic increases in proportion to the square of H ₀ , and the output linearity deteriorates.

On the other hand, when a real image is observed so as to receive all high-order diffracted lights, the output from the sensor is expressed by the following equation.

[0020]

(Equation 4)

As can be seen from (Equation 4), when a real image is observed, it is considered that the effective value of the output is simply proportional to the applied magnetic field, and the nonlinearity of the output due to the presence of the second harmonic does not occur. Can be

According to the present invention, the optical system of the optical magnetic field sensor is configured to receive light diffracted by the rare-earth iron garnet crystal, which is a ferrimagnetic substance, up to higher-order light. Be improved.

[0023]

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

(Embodiment 1) FIG. 1 is a diagram showing a first embodiment of the present invention. In FIG. 1, the input side optical fiber 1 uses a multi-mode fiber having an optical fiber core diameter of 50 μm, and the output side optical fiber 8 uses a multi-mode fiber having an optical fiber core diameter of 200 μm. The entrance side lens 2 and the exit side lens 7 are 0.25 pitch self-focusing rod lenses. The polarizer 3 and the analyzer 5 are arranged on both opposing surfaces of the rare-earth iron garnet crystal, which is the magneto-optical element 4, with their transmission polarization directions inclined by 45 degrees. Further, a total reflection mirror 6 is arranged to bend the optical path by 90 degrees.

Light incident from the light source passes through the optical fiber 1, is converted into parallel light by the lens 2, becomes linearly polarized light by the polarizer 3, and the reflected light is incident on the magneto-optical element 4. At this time, the beam diameter of the light incident on the magneto-optical element 4 is 800
μm. The light incident on the magneto-optical element 4 is diffracted by the magneto-optical element 4 having a multi-domain structure as shown in FIG. 9, travels while diverging, and the analyzer 5 has only a 45-degree component with respect to the polarizer 3. And the traveling direction is bent by 90 degrees by the total reflection mirror 6. The light whose traveling direction is bent by 90 degrees is incident on the lens 7 and is condensed on the output side optical fiber 8. (BiGdLaY) ₃ (FeGa) ₅ O
_{Since 12} crystals were used, the diffraction angle θ per order of the diffracted light was 2.6 degrees for the wavelength of 880 nm.

When a multi-mode fiber having a core diameter of 200 μm, which is larger than the core diameter of 50 μm of the input side optical fiber 1 and used as the output side optical fiber 8 as in this embodiment,
The numerical aperture of the exit-side optical system becomes larger than the numerical aperture of the entrance-side optical system. Therefore, when an optical magnetic field sensor is formed by using an optical fiber having the same core diameter as the optical fiber 9 as shown in FIG. 11 of the conventional example, only the zero-order light is received. The order of the diffracted light that can be received by the side lens 7 is increased, and it is possible to receive up to the second order light.

Next, FIG. 7 shows an example of a current measuring device configured to evaluate a linearity error of the optical magnetic field sensor with respect to the magnetic field. The optical magnetic field sensor 24 is installed directly on the electric wire 30 or, as shown in FIG. 7, is arranged in a gap of a core 29 provided for increasing the measurement magnetic field. 2
Reference numeral 6 denotes an optical fiber forming an optical transmission line. Reference numeral 25 denotes an optical signal generating means, which is an LED having a wavelength of 0.8 μm
μm band and 1.5 μm band LDs are used. Here, the self-focusing rod lens used in the optical magnetic field sensor had an optimal length for different wavelengths so as to obtain parallel light. 27 is a detecting means for detecting the light transmitted through the optical magnetic field sensor 24 and converting the light into an electric signal.
Although a PIN-PD or the like is used, in this embodiment, since an LED in a 0.8 μm band is used, a Si PIN-PD is used. 2
8 is an electric circuit for signal processing.

FIG. 1 shows the structure of the current measuring device constructed as described above.
FIG. 8 shows the result of measuring the linearity error in the magnetic field range of 5.0 Oe to 200 Oe using the optical magnetic field sensor shown in FIG.
The frequency of the alternating magnetic field is 60 Hz. Further, the read data from FIG. 8 is summarized in (Table 1).

[0029]

[Table 1]

Compared to FIG. 10, which is the measured data of the conventional example, it can be seen that the linearity is improved. Therefore, by configuring the optical magnetic field sensor as shown in FIG. 1, the diffracted light is received to a higher order and the second light included in the output is received.
The signal intensity of harmonics can be reduced, and the linearity of the optical magnetic field sensor with respect to the magnetic field can be greatly improved.

(Embodiment 2) FIG. 2 shows a second embodiment.
The optical magnetic field sensor shown in FIG. 2 is different from the conventional example shown in FIG. 11 in that the incident side lens 10 has a 0.25 pitch self-focusing rod lens with a diameter of 1 mm, and the exit side lens 11 has a diameter of 3 mm or 5 mm.
The point is that a self-focusing rod lens of 0.25 mm in mm is arranged.

When a lens larger than the diameter of the incident side lens 10 is used as the exit side lens 11 as in the present embodiment, the numerical aperture of the exit side optical system is increased as in the first embodiment.
It becomes larger than the numerical aperture of the entrance side optical system. Therefore, the lenses 2 and 7 have the same diameter as shown in FIG.
In the case where the optical magnetic field sensor is constituted by using a self-focusing rod lens of 0.25 pitch, only the 0th order light is received. In the second embodiment, however, the order of the diffracted light that can be received by the exit lens 11 is increased. Higher order light can be received.

FIG. 2 shows a current measuring device constructed as shown in FIG.
The linearity error was measured in the magnetic field range of 5.0 Oe to 200 Oe using the optical magnetic field sensor shown in FIG. The frequency of the alternating magnetic field is 60
Hz. The measurement results are shown in (Table 1). Compared with the measurement result of the conventional example, it can be seen that the linearity is improved. Therefore, also in the second embodiment, by configuring the optical magnetic field sensor as shown in FIG. 2, it is possible to receive the diffracted light to a higher order and reduce the signal intensity of the second harmonic included in the output. Thus, the linearity of the optical magnetic field sensor with respect to the magnetic field can be greatly improved.

The self-focusing rod lens 1 shown in FIG.
Similar effects were observed when an aspheric lens capable of obtaining parallel light was used instead of 0 and 11 and the diameter of the exit lens was made larger than the diameter of the entrance lens.

(Embodiment 3) FIG. 3 shows a third embodiment.
The optical magnetic field sensor of FIG. 3 is different from the conventional example shown in FIG. 11 in that, in the conventional optical magnetic field sensor, the direction shown in FIG. This is the point that the Fresnel lens 12 is disposed in the first position. A Fresnel lens having a diameter of 3 mm and a numerical aperture of 0.3 was used. Therefore, the total number of zones of the Fresnel lens used for the wavelength of 880 nm is actually about 2.56 × 10 ⁵ .

In the case where the Fresnel lens is arranged immediately after the magneto-optical element in the traveling direction of the light so that the diverging light becomes parallel light as in this embodiment, the light is diffracted by the magneto-optical element 4. The light can be efficiently converted into parallel light. Therefore, when the optical magnetic field sensor shown in FIG. 11 of the conventional example is configured, only the zero-order light is received. However, in the third embodiment, the order of the diffracted light that can be received by the exit lens 7 is increased to higher-order light. It became possible to receive light.

Further, since the Fresnel lens has a smaller thickness than a plano-convex lens or the like, there is an advantage that the external shape of the optical magnetic field sensor does not become large when it is stored in a case. A similar effect was observed when a grating lens was used instead of the Fresnel lens.

The optical magnetic field sensor of the third embodiment shown in FIG. 3 was configured in the current measuring device shown in FIG. 7, and the linearity error was measured in a magnetic field range of 5.0 Oe to 200 Oe. The frequency of the alternating magnetic field is 60 Hz. The measurement results are similarly shown in (Table 1). Compared with the measurement result of the conventional example, it can be seen that the linearity is improved. Therefore, also in the third embodiment, by configuring the optical magnetic field sensor as shown in FIG. 3, it is possible to receive the diffracted light to a higher order and reduce the signal intensity of the second harmonic included in the output. Thus, the linearity of the optical magnetic field sensor with respect to the magnetic field can be greatly improved.

(Embodiment 4) FIG. 4 shows a fourth embodiment.
The optical magnetic field sensor shown in FIG. 4 differs from the conventional example shown in FIG. 11 in that spherical lenses 13 and 14 each having a diameter of 3 mm are arranged on the entrance side lens 10 and the exit side lens 11 to constitute a condensing optical system. Is a point. Here, when configuring the condensing optical system, the distance c between the incident-side optical fiber 9 and the incident-side spherical lens 13, the distance d between the incident-side spherical lens 13 and the polarizer 3, and the total reflection mirror 6 on the optical path. It is necessary to pay attention to the distance e between the emission-side spherical lens 14 and the distance f between the emission-side spherical lens 14 and the emission-side optical fiber 9, and in this embodiment, each distance is designed to be 1 mm. However, the polarizer 3, the analyzer 5, and the total reflection mirror 6 are 5 mm square cubes. When the material of the spherical lens is BK7 and the wavelength of the light source is 880 nm, the light beam diameter at the crystal position is 480 μm. When the condensing optical system is configured as in this embodiment, the crystal position is closer to the beam waist, and the beam diameter at the crystal position is smaller than before. As a result, higher-order light can be received by the emission-side spherical lens 14.

FIG. 4 shows a current measuring device constructed as shown in FIG.
The linearity error was measured in the magnetic field range of 5.0 Oe to 200 Oe using the optical magnetic field sensor shown in FIG. The frequency of the alternating magnetic field is 60
Hz. The measurement results are shown in (Table 1). Compared with the measurement result of the conventional example, it can be seen that the linearity is improved. Therefore, also in the fourth embodiment, by configuring the optical magnetic field sensor as shown in FIG. 4, it is possible to receive the diffracted light to a higher order and reduce the signal intensity of the second harmonic included in the output. Thus, the linearity of the optical magnetic field sensor with respect to the magnetic field can be greatly improved.

(Embodiment 5) FIG. 5 shows a fifth embodiment.
The optical magnetic field sensor of FIG. 5 is different from the conventional example shown in FIG. 11 in that the magneto-optical element 15 is arranged at an angle α to the optical axis. By arranging the magneto-optical element 15 at an angle to the optical axis, it is possible to reduce a diffraction effect generated in the magneto-optical element.

The rare earth iron garnet crystal, which is a ferrimagnetic material, has a multi-domain structure, and thus becomes a diffraction grating for light. Generally, when the incident angle of light on a diffraction grating is increased from zero, the diffraction effect of the diffraction grating is extremely reduced. Therefore, by inclining the magneto-optical element 15 with respect to the optical axis of the incident beam as in the present embodiment, the diffraction effect of the magneto-optical element can be reduced. In the present embodiment, the inclination angle α is set to the optimum value of 45 degrees in view of the sensitivity of the sensor and the light insertion loss. Using the optical magnetic field sensor shown in FIG. 5 in the current measuring device configured as shown in FIG.
The linearity error was measured in the magnetic field range from to 200 Oe. The frequency of the alternating magnetic field is 60 Hz. The measurement results are shown in (Table 1). Compared with the measurement result of the conventional example, it can be seen that the linearity is improved. Therefore, in the fifth embodiment, by eliminating the diffraction effect, it is possible to reduce the amplitude of the second harmonic, which causes linearity distortion, and to greatly improve the linearity of the optical magnetic field sensor with respect to the magnetic field. It became possible.

(Embodiment 6) FIG. 6 shows a sixth embodiment.
FIG. 6 shows a linear optical magnetic field sensor.
μm multimode fiber. The polarizer 18 and the analyzer 19 are laminated polarizer thin films, and are disposed on both surfaces of the magneto-optical element 4 with their transmission polarization directions inclined at 45 degrees. Magneto-optical element 4, polarizer 18, analyzer 19 are 3mm
Horns were used. The lens 20 is a self-focusing type rod lens, and 23 is a multimode fiber having a core diameter of 200 μm. Reference numerals 17 and 22 denote ferrules for fixing the fiber, and these parts are housed in a case 21.
The optical magnetic field sensor shown in FIG. 6 has a configuration obtained by combining the above-described embodiments.

The lens 20 can be a convex lens as long as the transmitted light can be focused on the end face of the optical fiber 23. Further, the core diameter of the optical fiber 23 is
In the case where the fiber diameter is larger than the core diameter of No. 6 and the fiber end faces are close to each other, a configuration in which the lens 20 is not provided is also possible.

The incident light a passes through the optical fiber 16, is linearly polarized by the polarizer 18, and is diffracted by the ferrimagnetic garnet crystal of the magneto-optical element 4. After the transmitted light is analyzed by the analyzer 19 for the 45-degree component, the light including the higher-order diffracted light is collected on the optical fiber 23 by the lens 20.

FIG. 6 shows a current measuring device constructed as shown in FIG.
The linearity error was measured in the magnetic field range of 5.0 Oe to 200 Oe using the optical magnetic field sensor shown in FIG. The frequency of the alternating magnetic field is 60
Hz. The measurement results are shown in (Table 1). Compared with the measurement result of the conventional example, it can be seen that the linearity is improved. Therefore, also in the sixth embodiment, by configuring the optical magnetic field sensor as shown in FIG. 6, it is possible to receive the diffracted light to a higher order and reduce the signal intensity of the second harmonic included in the output. Thus, the linearity of the optical magnetic field sensor with respect to the magnetic field can be greatly improved.

Therefore, the optical magnetic field sensor according to the present invention is shown in FIG.
When used as a current measuring device, an optical CT having a ratio error of ± 1% or less in the current measuring range of 0.025I to I with respect to the rated current value I can be configured. Become.

In this embodiment, the polarizer and the analyzer are polarization beam splitters. However, a Glan Thompson prism, a polarizing plate made of glass, or a laminated polarizer thin film can be used. In particular, an optical magnetic field sensor using a glass polarizer or a laminated polarizer thin film for a polarizer and an analyzer has a great advantage that the size can be reduced. It is also possible to replace the self-focusing rod lens with a lens capable of obtaining parallel light. Furthermore, it was possible to configure a linear optical magnetic field sensor without using a total reflection mirror.

The improvement of the linearity can be achieved not only with a light source in the 0.8 μm band but also with a 1.3 μm band which transmits a rare earth iron garnet crystal.
Other wavelengths in the μm band and 1.5 μm band were also observed.
In addition, it was confirmed that the magnetic field was measured not only at a frequency of 60 Hz but also from a DC magnetic field to about several hundred kHz with good linearity.

In the magneto-optical device of this embodiment, an example is shown in which a rare earth iron garnet crystal represented by the following formula (1) is used in order to consider the temperature characteristics of the optical magnetic field sensor. The configuration of the optical system can be applied to all optical magnetic field sensors using a garnet crystal, which is a ferrimagnetic material, as a magneto-optical element, and it is also possible to configure an optical magnetic field sensor by combining these embodiments.

[0051]

As is apparent from the above description, according to the present invention, it is possible to provide an optical magnetic field sensor having higher linearity with respect to a magnetic field than conventional ones.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram of an optical magnetic field sensor according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of an optical magnetic field sensor according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical magnetic field sensor according to a fourth embodiment of the present invention.

FIG. 5 is a configuration diagram of an optical magnetic field sensor according to a fifth embodiment of the present invention.

FIG. 6 is a configuration diagram of an optical magnetic field sensor according to a sixth embodiment of the present invention.

FIG. 7 is a schematic diagram of an embodiment of a current measuring device using the optical magnetic field sensor according to the present invention.

FIG. 8 is a diagram showing a linearity error of an output of a current measuring device using the photomagnetic field sensor according to the first embodiment of the present invention.

FIG. 9 is a diagram showing a linearity error of an output of a current measuring device using a conventional optical magnetic field sensor.

FIG. 10 is a schematic diagram illustrating a diffraction phenomenon of light by a ferrimagnetic garnet crystal.

FIG. 11 is a configuration diagram of a conventional optical magnetic field sensor.

FIG. 12 is a diagram illustrating a principle of measuring a magnetic field using the Faraday effect.

[Explanation of symbols]

a Incident light b Outgoing light c Distance between the incident side optical fiber 9 and the incident side spherical lens 13 d Distance between the incident side spherical lens 13 and the polarizer 3 e Distance between the total reflection mirror 6 and the emitting side spherical lens 14 f Outgoing side spherical lens Distance between 14 and output side optical fiber 9 1, 8, 9, 16, 23, 26 Optical fiber 2, 7, 10, 11, 20 Lens 3, 18 Polarizer 4, 15 Magneto-optical element 5, 19 Analyzer 6 All Reflecting mirror 12 Fresnel lens or grating lens 13, 14 Ball lens 17, 22, 38 Ferrule 21 Case 24 Optical magnetic field sensor 25 Light source 27 Light detection unit 28 Signal processing electric circuit 29 Core 30 Electric wire 31 Ferrimagnetic garnet crystal 32 0th-order light 33 Primary light 34 Secondary light 35 Tertiary light 36 Screen 37 Holder

Claims (5)

(57) [Claims] A polarizer, a magneto-optical element, and an analyzer having transmission polarization directions different from each other with respect to the polarizer are arranged at least along a traveling direction of light, and a magnetic field to be measured is output light intensity. In the optical magnetic field sensor to detect as , on one end surface of the magneto-optical element, sandwich the polarizer,
A first optical transmission line is provided, and the first
A second optical transmission line sandwiching the analyzer on the other end face
Is provided, and the transmission path diameter of the second optical transmission path is the first optical transmission path.
A transmission type optical magnetic field sensor, wherein the transmission type optical magnetic field sensor is larger than the transmission path diameter . 2. A magnetic field to be measured is output light intensity by disposing a polarizer, a magneto-optical element, and an analyzer having different transmission polarization directions with respect to the polarizer at least along a traveling direction of light. In the optical magnetic field sensor to detect as , on one end surface of the magneto-optical element, sandwich the polarizer,
A first lens is provided, and a first lens is provided in addition to the magneto-optical element.
A second lens is set on one end face with the analyzer
And the lens diameter of the second lens is smaller than the lens diameter of the first lens.
A transmission-type optical magnetic field sensor having a diameter larger than the diameter of the lens . 3. A device to be measured by arranging a polarizer, a magneto-optical element having a multi-domain structure, and an analyzer having transmission polarization directions different from each other with respect to the polarizer at least along a traveling direction of light. An optical magnetic field sensor for detecting a magnetic field as output light intensity, wherein a Fresnel lens or a grating is provided on an optical path between the magneto-optical element and the analyzer in a direction in which divergent light becomes parallel light. Magnetic field sensor. 4. A magnetic field to be measured is output by a polarizer, a magneto-optical element, and an analyzer having transmission polarization directions different from each other with respect to the polarizer, at least along a traveling direction of light. A first lens provided on one end face of the magneto-optical element with the polarizer interposed therebetween, and another end face of the magneto-optical element.
In a second lens provided across the analyzer
Is a light condensing optical system. 5. An optical magnetic field sensor according to claim 1, wherein said magneto-optical element is a ferrimagnetic garnet crystal.