JPH10301070A - Faraday rotation angle variable device - Google Patents

Abstract

(57) [Problem] To enable a Faraday rotation angle to be varied, to be easily controlled by one electromagnet, and to be downsized. SOLUTION: A Faraday element 10 in which a plurality of types of magnetic garnet single crystal films 12a and 12b having different coercive forces are arranged to overlap in the optical axis direction, and a single electromagnet for applying a magnetic field in the optical axis direction to the Faraday element And controlling the magnetic field applied to the Faraday element by the electromagnet to change the algebraic sum of the Faraday rotation angle. Depending on the magnitude of the magnetic field applied by the electromagnet, the magnetization direction of one or more kinds of magnetic garnet single crystal films is reversed, thereby changing the total Faraday rotation angle of all the magnetic garnet single crystals constituting the Faraday element. It has become. This Faraday rotation angle variable device can also be used for an optical switch or an optical attenuator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a magnetic recording medium having two different
Using a Faraday element in which at least one kind of magnetic garnet single crystal films are arranged so as to overlap in the direction of the optical axis, the magnetic field applied to the Faraday element is controlled by an electromagnet to change the algebraic sum of the Faraday rotation angle to a desired angle. The present invention relates to a Faraday rotation angle variable device, an optical switch using the same, and a step variable optical attenuator.

[0002]

2. Description of the Related Art An optical communication system and an optical measurement system require an optical switch for spatially switching the traveling direction of light or an optical attenuator for adjusting the amount of transmitted light.

For example, in an optical communication system requiring high system reliability, multiplexed devices and transmission lines are switched by an optical switch in order to avoid communication failure due to failure of the devices and transmission lines. Various structures of the optical switch have been proposed, but a typical example is a method in which switching is caused by switching the polarization direction by a magnetic field.

FIG. 8 shows an example of a conventional optical switch. In this configuration, the 45-degree Faraday rotator 70 and the half-wave plate 74 are arranged between the symmetrically arranged first and second composite polarizing prisms 76 and 78. Here, the Faraday rotator 70 has a configuration in which a Faraday element (magnetic garnet single crystal having a predetermined thickness) 71 and an electromagnet 72 are combined, and the composite polarizing prisms 76 and 78 are a parallelogram prism and a right triangle prism. In this configuration, a polarization separation film 79 is interposed therebetween.

The light incident from the port is separated into P-polarized light and S-polarized light by the first composite polarizing prism 76. The polarization direction of each polarized light is -45 by the Faraday rotator 70.
Then, the light is rotated by +45 degrees by the half-wave plate 74, so that the light is canceled and the polarization direction is not changed, and the light is coupled to the port. When the magnetic field applied by the electromagnet 72 is reversed, the light incident from the port is rotated by +45 degrees by the Faraday rotator 70 and further +45 degrees by the half-wave plate 74, so that the polarization direction is 90 degrees in total. It will rotate and couple to the port. In this way,
Light incident from the port can be sent to either the port or the port by controlling the applied magnetic field by the electromagnet 72.

Next, FIG. 9 shows an example of a conventional optical attenuator, and FIG. 10 schematically shows an example of the structure of a Faraday rotation angle varying device used therein. Each collimating lens 8
Input fiber 88 and output fiber 89 having 6,87
A polarizer 80 made of a wedge-shaped birefringent crystal (for example, rutile), a Faraday rotation angle varying device 84, and an analyzer 82 made of a wedge-shaped birefringent crystal are arranged on the optical axis in this order. (See Japanese Patent Application Laid-Open No. 6-51255). Here, the Faraday rotation angle varying device 84 includes a Faraday element (magnetic garnet single crystal) 90 and
It consists of a combination of a permanent magnet 91 and an electromagnet 92 that apply a magnetic field from two different directions. The magnetic moment of the magnetic garnet single crystal is oriented in the direction of the synthetic magnetic field formed by the constant magnetic field generated by the permanent magnet 91 and the variable magnetic field generated by the electromagnet 92, and the Faraday rotation angle changes accordingly.

For example, when the birefringent crystals constituting the polarizer 80 and the analyzer 82 are arranged so that the optical axes are parallel to each other, the following operation is performed. The light emitted from the input fiber 88 and converted into a parallel beam by the first lens 86 is separated by the polarizer 80 into ordinary light o and extraordinary light e. The polarization directions of the ordinary light o and the extraordinary light e are orthogonal to each other. Then, when each light passes through the Faraday rotation angle varying device 84,
The direction of polarization rotates depending on the magnitude of the magnetic moment perpendicular to the optical axis, and is separated by the analyzer 82 into ordinary light o ₁ and extraordinary light e ₁ , and ordinary light o ₂ and extraordinary light e ₂ , respectively. Normal light o ₁ and abnormal light e ₂ emitted from the analyzer 82 is parallel to each other, by the second lens 87 is coupled to the output fiber 89 (indicated by a solid line), abnormal light e ₁ and normal light emitted from the analyzer 82 o ₂ are not parallel to each other but spread,
Does not couple to the output fiber 89 even though it passes through the lens 87 (shown by a broken line).

When the magnetic field applied by the electromagnet 92 is 0, the Faraday rotation angle is 90 degrees (the magnetic moment is parallel to the optical axis).
, And the order ordinary o emitted from the polarizer 80 is emitted as abnormal light e ₁ from the analyzer 82, the abnormal light e emitted from the polarizer 80 is emitted from the analyzer 82 as ordinary light o _2,
Even though the light passes through the second lens 87, it is not coupled to the output fiber 89. On the other hand, if the magnetic field applied by the electromagnet 92 is sufficiently large, the Faraday rotation angle approaches 0 degree and the polarizer 8
The ordinary light o emitted from 0 is emitted as it is as ordinary light o ₁ from the analyzer 82 and the extraordinary light e emitted from the polarizer 80.
Is emitted from the analyzer 82 as it is as the extraordinary light e ₂ , so that both lights are parallel and all are coupled to the output fiber 89 by the second lens 87. Thus, the electromagnet 92
In accordance with the strength of the applied magnetic field, the magnetic moment rotates and the Faraday rotation angle changes in the range from 0 degrees to about 90 degrees, and accordingly, the amount of light coupled to the output fiber 89 differs, It will function as an optical attenuator.

When the birefringent crystals of the polarizer 80 and the analyzer 82 are arranged so that their optical axes are orthogonal to each other, the amount of transmitted light becomes maximum when the Faraday rotation angle is 90 degrees, contrary to the above. In the case of 0 degree, the transmitted light amount becomes minimum.

[0010]

In the case of an optical switch, 1
In order to rotate the polarization direction by exactly 45 degrees by using a half-wave plate, the optical axis thereof must be exactly 22.5 degrees with respect to the incident light.
It is necessary to incorporate it at an angle. The half-wave plate is made of, for example, a quartz plate, and is attached to a side surface of the electromagnet. 1
The / 2 wavelength plate defines the angle of the optical axis with respect to the outer side when the crystal body is cut into rectangular plate-like sides, but the optical axis alignment is performed so that there is no mounting error when attaching to the side surface of the electromagnet. Accuracy is required, and assembly work is complicated.

In the case of an optical attenuator, since a magnetic field is applied to the Faraday element from two directions, at least two magnets are required, and the configuration and control are complicated and the size is increased. Assuming that one magnet is a permanent magnet as described above, even if a magnetic field is applied perpendicularly to the traveling direction of light by the electromagnet, the magnetic moment is directed in the direction in which the magnetic field of the electromagnet and the permanent magnet are combined. Is not from 0 to 90 degrees. This is because a component parallel to the light traveling direction always remains. This problem can be solved by using both magnets as electromagnets, but there is a disadvantage that control becomes complicated.

An object of the present invention is to provide a variable Faraday rotation angle device which can be easily controlled and reduced in size. Another object of the present invention is to provide an optical switch that is easy to manufacture because it is unnecessary to align the optical axis of a half-wave plate, which is complicated and requires precision. Still another object of the present invention is to provide an optical attenuator which is easy to control and can be miniaturized, is hardly affected by changes in temperature and wavelength, and can obtain a Faraday rotation angle difference of 90 degrees.

[0013]

SUMMARY OF THE INVENTION The present invention provides a Faraday element in which a plurality of types of magnetic garnet single crystal films having different coercive forces are arranged so as to overlap in the optical axis direction, and a magnetic field in the optical axis direction is applied to the Faraday element. A single electromagnet to
A Faraday rotation angle varying device that changes an algebraic sum of Faraday rotation angles by controlling a magnetic field applied to the Faraday element by the electromagnet. Depending on the magnitude of the magnetic field applied by the electromagnet, the magnetization direction of one or more kinds of magnetic garnet single crystal films is reversed, thereby changing the total Faraday rotation angle of all the magnetic garnet single crystals constituting the Faraday element. It has become.

The thickness of each magnetic garnet single crystal film may be set so as to have the same Faraday rotation angle,
You may combine so that it may become a completely different Faraday rotation angle. Magnetic garnet single crystal films having different compositions may be combined, or magnetic garnet single crystal films having the same composition may be used. Even if the same composition and the same wafer are cut into chips, a certain degree of variation occurs in the coercive force, so that a desired combination can be realized by selecting according to the coercive force. The coercive force can also be adjusted by a subsequent heat treatment or the like. Furthermore, the number of magnetic garnet single crystal films to be combined is arbitrary, and may be arranged so as to be in close contact with each other, or may be arranged at intervals. This Faraday rotation angle varying device can be used as an Faraday rotation angle varying device of an optical switch Faraday rotator or a step variable optical attenuator.

[0015]

FIG. 1 shows an example of a Faraday rotation angle varying device. As a Faraday element 10, two types of magnetic garnet single crystal films 12a and 12b having different coercive forces are used.
Here is an example of using. Two magnetic garnet single crystal films 1
2a and 12b are arranged so as to overlap in the direction of the optical axis, and an electromagnet 14 for applying a magnetic field in the direction of the optical axis is provided outside thereof.
Place. As shown in FIG. 2, the coercive force of each magnetic garnet single crystal film 12a, 12b is defined as Ha, Hb (however, Ha
<Hb), and all have a square magnetic hysteresis. The thickness of each magnetic garnet single crystal film 12a, 12b is set to a thickness at which the absolute value of the Faraday rotation angle at the time of magnetic saturation becomes 45 degrees.

In this structure, when an external magnetic field + H ₂ (where H ₂ > Hb) is applied to the Faraday element 10 by the electromagnet 14, both magnetic garnet single crystal films 12a, 12a
b is magnetized in the + direction, and the entire Faraday rotation angle is +90.
Degree. From that state, the external magnetic field −H ₁ (where Ha <
When H ₁ <Hb) is applied, the magnetic garnet single crystal film 1
Since the magnetization of only 2a is inverted, the algebraic sum of the Faraday rotation angle is 0 degree. Further, from this state, when applying an external magnetic field -H _2, the algebraic sum of the Faraday rotation angle since the magnetization is also reversed magnetic garnet single crystal film 12b becomes -90 °.

As apparent from this description, it is possible to realize a desired Faraday rotation angle by controlling the magnetic field applied by the electromagnet by selecting the thicknesses of the magnetic garnet single crystal films having different coercive forces and by combining them. it can.

FIG. 3 shows an example of the optical switch. The Faraday rotation angle varying device 24 is provided between the symmetrically arranged first and second composite polarizing prisms 20 and 22.
Are arranged. Here, the Faraday rotation angle varying device 24 has the same configuration as that shown in FIG. 1, and has a configuration in which the Faraday element 10 composed of two types of magnetic garnet single crystal films 12a and 12b having different coercive forces and the electromagnet 14 are combined. is there. Both composite polarizing prisms have the same structure,
In this configuration, a parallelogram prism 25 and a right triangle prism 26 are joined via a polarization separation film 27 therebetween.

First, the magnetic field (+ H ₂ or more) shown in FIG.
2a and 12b are magnetized in the + direction. At this time, the polarization direction is +90 by both magnetic garnet single crystal films.
Rotate degrees. When a magnetic field (−H ₁ ) is applied by the electromagnet 14, the magnetization of only one magnetic garnet single crystal film 12a is inverted and only the polarization direction is rotated by −45 degrees, so that the sum of the magnetic garnet single crystal film 12b and the other magnetic garnet single crystal film 12b is increased. Has a Faraday rotation angle of 0 degrees. Next, when a magnetic field (+ H ₁ ) is applied by the electromagnet 14, the magnetic garnet single crystal 12a
Is again inverted, and the algebraic sum of Faraday rotation angles is +9.
0 degrees. In this way, the algebraic sum of the Faraday rotation angle of the Faraday element 10 by controlling the one of the magnetic field + H ₁ or -H ₁ by the electromagnet 14 is +90 degrees and 0
It will switch every time.

It is assumed that the total Faraday rotation angle of the Faraday element 10 is controlled to 0 degree by the electromagnet 14. Light incident from the port is separated into P-polarized light and S-polarized light by the polarization separation film 27 of the first composite polarizing prism 20. The transmitted P-polarized light is transmitted through a Faraday rotation angle varying device 24.
, The polarization direction does not rotate but remains P-polarized light, and passes through the polarization separation film 27 of the second composite polarization prism 22. On the other hand,
The S-polarized light reflected by the polarization splitting film 27 of the first composite polarizing prism 20 also remains S-polarized without rotating the polarization direction in the Faraday rotation angle varying device 24, and the polarization splitting film of the second composite polarizing prism 22 It is reflected at 27. In this way, the incident light from the port is coupled to the port (see FIG. 3). Next, the electromagnet 14 is switched to the Faraday element 2.
The total Faraday rotation angle of No. 4 is controlled to 90 degrees. Light incident from the port is separated into P-polarized light and S-polarized light by the polarization separation film 27 of the first composite polarizing prism 20. Penetrated P
The polarization direction of the polarized light is 9 by the Faraday rotation angle varying device 24.
Rotate by 0 degree to become S-polarized light, and the second composite polarizing prism 2
The light is reflected by the second polarization separation film 27. On the other hand, the S-polarized light reflected by the polarization splitting film 27 of the first composite polarizing prism 20 is turned into P-polarized light by rotating the polarization direction by 90 degrees by the Faraday rotation angle varying device 24, and the polarization separation of the second composite polarizing prism 22 is performed. It passes through the membrane 27. In this way, incident light from the port couples to the port. Therefore, by controlling the applied magnetic field by the electromagnet 14, the optical path can be switched.

In the above example, the composite polarizing prism has a polarization separating film interposed between a parallelogram prism and a right-angled triangular prism, but a parallelogram prism is used instead of the right-angled triangular prism. Alternatively, a polarization separation film may be interposed between the two parallelogram prisms. With such a configuration, the outgoing light ports (ports and ports) can be taken out in the same direction, and there is an advantage that the device can be downsized.

FIG. 4 shows an example of the optical attenuator. A Faraday rotation angle varying device 34 is arranged between the polarizer 30 and the analyzer 32, each made of a wedge-shaped birefringent crystal and arranged symmetrically, and these are collimated lenses 36 and 37, respectively.
Is installed between the input fiber 38 and the output fiber 39 having Here, the Faraday rotation angle varying device 34 is composed of a Faraday element 40 in which many kinds of magnetic garnet single crystal films having different coercive forces and exhibiting a square magnetization hysteresis are combined so as to be overlapped in the optical axis direction.
A single electromagnet 44 for applying a magnetic field in the direction of the optical axis to 0. By controlling the magnetic field applied to the Faraday element 40 by the electromagnet 44, the algebraic sum of the Faraday rotation angle is changed and the amount of transmitted light is discrete. This is a configuration for switching to. The polarizer 30 and the analyzer 32 have the same shape made of, for example, rutile, and their optical axes are in a plane perpendicular to the plane of the paper, and are arranged such that their slopes are parallel and located outside.

It is assumed that each magnetic garnet single crystal film is set to a thickness such that the Faraday rotation angle at the time of magnetization saturation is 15 degrees, for example. When a sufficiently large external magnetic field in the + direction is applied, all the magnetic garnet single crystal films are magnetized in the same direction, and the total Faraday rotation angle is +
90 degrees. Thereafter, when a small reverse (-) magnetic field is applied to reverse the magnetization direction of the magnetic garnet single crystal film having the smallest coercive force, the algebraic sum of the Faraday rotation angle becomes +60 degrees. In this way, by controlling the direction and strength of the external magnetic field by the electromagnet, the magnetization direction of each magnetic garnet single crystal film is switched, and the algebraic sum of the Faraday rotation angle can be changed within a range of -90 to +90 degrees. It becomes possible to change step by step every time.

For example, when the directions of the optical axes of the birefringent crystals of the polarizer 30 and the analyzer 32 are parallel, the following operation is performed. Light emitted from the input fiber 38 and converted into a parallel beam by the first lens 36 is separated by the polarizer 30 into ordinary light o and extraordinary light e. The polarization directions of the ordinary light o and the extraordinary light e are orthogonal to each other. Then, when each of the light passing through the Faraday rotation angle varying device 34, depending on the Faraday rotation angle to rotate the polarization direction by the same angle, normal light o ₁ and abnormal light e ₁ by each analyzer 32, normal light o ₂ and separating the abnormal light e _2. The ordinary light o ₁ and the extraordinary light e emitted from the analyzer 32
₂ are parallel to each other and are coupled to an output fiber 39 by a second lens 37 (shown by solid lines).
Does not bind to also output fiber 39 for extending not parallel to one another extraordinary ray e ₁ and normal light o ₂ emitted through the second lens 37 from (shown in phantom).

[0025] by controlling the magnetic field applied by the electromagnet 44 when the Faraday rotation angle to 0 degrees, normal light o emitted from the polarizer 30 as it is emitted from the analyzer 32 as ordinary light o _1, abnormal emitted from the polarizer 30 Since the light e is emitted from the analyzer 32 as it is as the extraordinary light e ₂ , both lights are parallel and are all coupled to the output fiber 39 by the second lens 37. On the other hand, when the applied magnetic field by the electromagnet 44 is controlled to make the entire Faraday rotation angle 90 degrees, all the ordinary light o emitted from the polarizer 30 is emitted from the analyzer 32 as the extraordinary light e ₁ and emitted from the polarizer 30. Since all the extraordinary light e emitted from the analyzer 32 as ordinary light o ₂ , the second
Does not couple to the output fiber 39 even though the lens 37 passes through. If the Faraday rotation angle is changed in the range from 0 degrees to about 90 degrees by controlling the applied magnetic field by the electromagnet in this way, the amount of light coupled to the output fiber 39 changes accordingly, that is, the attenuation changes. And functions as an optical attenuator.

When the birefringent crystals of the polarizer 30 and the analyzer 32 are arranged so that the optical axes thereof are orthogonal to each other, the amount of transmitted light is reduced when the algebraic sum of the Faraday rotation angles is 90 degrees. It becomes maximum, and the transmitted light amount becomes minimum at 0 degree. In this example, a wedge-shaped birefringent crystal is used as the polarizer and the analyzer, but a parallel plate-shaped birefringent crystal may be used. In this case, both parallel plate-shaped birefringent crystals have the same thickness, the optical axes are orthogonal to each other, and each optical axis is provided to be inclined with respect to the optical path.

[0027]

【Example】

[Example 1] Two types of magnetic garnet single crystal films (referred to as crystal a and crystal b) were produced by the LPE method (liquid phase epitaxial growth method). At the time of film formation, PbO—Bi ₂ O ₃ —B ₂ O ₃ was used for the flux, and (CaGd) ₃ (MgZrGa) ₅ O having a diameter of about 25 mm was used for the substrate.
₁₂ (lattice constant: 12.496 ± 0.003 °) was used. First, the formed magnetic garnet single crystal film is 5 × 8
mm and then the substrate was removed by polishing to the desired thickness and then cut to 2 × 7 mm. Various characteristics of the obtained magnetic garnet single crystal films are shown below, and the relationship between the Faraday rotation angle and the magnetic field is shown in FIG. The wavelength used is 1310
nm. As can be seen from FIG. 5, the relationship between the Faraday rotation angle and the magnetic field of these magnetic garnet single crystal films has a square hysteresis. <Crystal a> Film composition: Tb _0.7 Y _0.7 Bi _1.6 Fe _4.0 Ga _1.0 O ₁₂ Growth temperature: 723 ° C. Coercive force: 150 Oe Shape: 2 mm × 7 mm × 0.26 mm <Crystal b> Film composition: Tb _1.0 Y _0.6 Bi _1.4 Fe _4.2 Ga _0.8 O ₁₂ Growth temperature: 735 ° C. Coercive force: 300 Oe Shape: 2 mm × 7 mm × 0.29 mm

Using these two types of magnetic garnet single crystals, an optical switch as shown in FIG. 3 was assembled. Introduction +
A magnetic field of 400 Oe was applied to keep both magnetic garnet single crystal films in a state of magnetization saturation. -200 Oe with electromagnet
When a magnetic field of + is applied, the light incident from the port is coupled to the port, and then when a magnetic field of +200 Oe is applied by the electromagnet, the light incident from the port is coupled to the port and can be confirmed to function as an optical switch. Was.

Example 2 When one of the magnetic garnet single crystals (crystal a) of Example 1 was heat-treated at 1000 ° C. for 2 hours in the air, the coercive force was reduced to 5 Oe (this is called crystal c). . Fig. 6 shows the relationship between Faraday rotation angle and magnetic field.
Shown in The wavelength used is 1310 nm. When an optical switch was formed using both magnetic garnet single crystal films (crystal b and crystal c), it was confirmed that the optical switch functions as an optical switch as in Example 1.

Example 3 A magnetic garnet single crystal film was manufactured by the LPE method. PbO-Bi in flux
₂ O ₃ -B ₂ O ₃ and a substrate (C
aGd) ₃ (MgZrGa) ₅ O ₁₂ (lattice constant: 12.
496 ± 0.003 °). The formed magnetic garnet single crystal film was first cut into 3 × 3 mm, then the substrate was removed by polishing to a desired thickness, and heat-treated at 1000 ° C. in the air for 2 hours. Further, on both sides of the magnetic garnet single crystal film, a SiO ₂ single layer film (thickness: 22) was used to prevent reflection.
00 ± 200 °) and then cut to 1 × 1 mm. Among the many chips obtained, 6 with different coercive force
Seed magnetic garnet single crystals were selected. The thickness of each chip is 0.095 mm. In general, chips cut from one wafer have a certain degree of variation in coercive force, and the coercive force changes even when heat treatment is performed. Each magnetic garnet single crystal film (they are made of crystal A, ..., crystal F
FIG. 7 shows the relationship between the Faraday rotation angle and the magnetic field. The wavelength used is 1310 nm. The optical attenuator shown in FIG. 4 was assembled by using these six magnetic garnet single crystal films side by side. The angle between the optical axes of the birefringent crystals of the polarizer and the analyzer was a right angle.

After applying a sufficiently large magnetic field in the + direction by the electromagnet to magnetize all the Faraday elements in the optical axis direction,
The Faraday rotation angle was varied by controlling the magnetic field applied by the electromagnet. Table 1 shows the relationship between the applied magnetic field, the Faraday rotation angle, and the amount of attenuation. It was confirmed that this configuration operated as a step-variable optical attenuator. The attenuation amount 1 when the Faraday rotation angle is +90 degrees or -90 degrees
dB is due to absorption loss of the magnetic garnet single crystal film, reflection loss at the end face, and the like.

[0032]

[Table 1]

Example 4 An optical attenuator shown in FIG. 4 was assembled using a magnetic garnet single crystal film having the same composition and coercive force as in Example 3 above. However, the thickness of each magnetic garnet single crystal film was changed, and the Faraday rotation angles were adjusted such that the crystals A and F were 40 degrees, the crystals B and E were 3 degrees, and the crystals C and D were 2 degrees.

After applying a sufficiently large magnetic field in the + direction by the electromagnet to magnetize all the Faraday elements in the optical axis direction,
The Faraday rotation angle was varied by controlling the magnetic field applied by the electromagnet. Table 2 shows the relationship between the applied magnetic field, the Faraday rotation angle, and the attenuation. It was confirmed that this configuration operated as a step-variable optical attenuator. The attenuation amount 1 when the Faraday rotation angle is +90 degrees or -90 degrees
dB is due to absorption loss of the magnetic garnet single crystal film, reflection loss at the end face, and the like.

[0035]

[Table 2]

[0036]

According to the present invention, there is provided a Faraday rotation angle varying device having a configuration in which a plurality of magnetic garnet single crystal films having different coercive forces are superposed as described above, and configured to apply only a magnetic field in the optical axis direction. Therefore, there is an advantage that control is easy and the size can be reduced. In particular, when incorporated in an optical switch, the half-wave plate conventionally used for switching the polarization direction between 0 degree and 90 degrees is unnecessary, and the optical axis alignment of the half-wave plate, which is complicated and requires precision, is unnecessary. Therefore, it becomes easy to manufacture. Also, when applied as an optical attenuator, only one electromagnet is required, which not only reduces the size, but also facilitates control, and when the polarization direction is 0 degrees, it is hardly affected by changes in temperature or wavelength. Since the polarization direction can be rotated by 90 degrees, an optical attenuator having a Faraday rotation angle difference of 90 degrees can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a Faraday rotation angle varying device according to the present invention.

FIG. 2 is an explanatory diagram of the operation.

FIG. 3 is an explanatory view showing an example of the optical switch according to the present invention.

FIG. 4 is an explanatory diagram showing an example of a variable step optical attenuator according to the present invention.

FIG. 5 is an explanatory diagram showing one embodiment of a magnetic field-Faraday rotation angle characteristic of a Faraday rotation angle variable device used for an optical switch.

FIG. 6 is an explanatory diagram showing another embodiment of the magnetic field-Faraday rotation angle characteristic of the Faraday rotation angle variable device used for the optical switch.

FIG. 7 is an explanatory diagram showing one embodiment of a magnetic field-Faraday rotation angle characteristic of a Faraday rotation angle variable device used for an optical attenuator.

FIG. 8 is an explanatory diagram showing an example of a conventional optical switch.

FIG. 9 is an explanatory view showing an example of a conventional optical attenuator.

FIG. 10 is an explanatory diagram showing an example of a Faraday rotation angle variable device used for the device.

[Explanation of symbols]

 Reference Signs List 10 Faraday element 12a, 12b Magnetic garnet single crystal film 14 Electromagnet

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[Procedure amendment]

[Submission date] August 19, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction contents]

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a magnetic recording medium having two different
Using a Faraday element in which at least one kind of magnetic garnet single crystal films are arranged so as to overlap in the direction of the optical axis, the magnetic field applied to the Faraday element is controlled by an electromagnet to change the algebraic sum of the Faraday rotation angle to a desired angle. Faraday rotation angle variable device, optical switch using the same, step variable
It relates to a mold optical attenuator.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

For example, when the birefringent crystals constituting the polarizer 80 and the analyzer 82 are arranged so that the optical axes are parallel to each other, the following operation is performed. The light emitted from the input fiber 88 and converted into a parallel beam by the first lens 86 is separated by the polarizer 80 into ordinary light o and extraordinary light e. The polarization directions of the ordinary light o and the extraordinary light e are orthogonal to each other. Then, when each light passes through the Faraday rotation angle varying device 84,
The polarization direction is rotated depending on the magnitude of the magnetic moment in the direction parallel to the optical axis, and is separated by the analyzer 82 into ordinary light o ₁ and extraordinary light e ₁ , and ordinary light o ₂ and extraordinary light e ₂ , respectively. Normal light o ₁ and abnormal light e ₂ emitted from the analyzer 82 is parallel to each other, by the second lens 87 is coupled to the output fiber 89 (indicated by a solid line), abnormal light e ₁ and normal light emitted from the analyzer 82 o ₂ are not parallel to each other but spread,
Does not couple to the output fiber 89 even though it passes through the lens 87 (shown by a broken line).

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

When the magnetic field applied by the electromagnet 92 is 0, the Faraday rotation angle is 90 degrees (the magnetic moment is parallel to the optical axis).
, And the order ordinary o emitted from the polarizer 80 is emitted as abnormal light e ₁ from the analyzer 82, the abnormal light e emitted from the polarizer 80 is emitted from the analyzer 82 as ordinary light o _2,
Even though the light passes through the second lens 87, it is not coupled to the output fiber 89. On the other hand, if the magnetic field applied by the electromagnet 92 is sufficiently large, the Faraday rotation angle approaches 0 degree and the polarizer 8
The ordinary light o emitted from 0 is emitted as it is as ordinary light o ₁ from the analyzer 82 and the extraordinary light e emitted from the polarizer 80.
Is emitted from the analyzer 82 as it is as the extraordinary light e ₂ , so that both lights are parallel and all are coupled to the output fiber 89 by the second lens 87. Thus, the electromagnet 92
The Faraday rotation angle changes in the range from 90 degrees to about 0 degrees according to the strength of the applied magnetic field, and the amount of light coupled to the output fiber 89 changes accordingly. Function as an optical attenuator.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

The thickness of each magnetic garnet single crystal film may be set so as to have the same Faraday rotation angle,
You may combine so that it may become a completely different Faraday rotation angle. Magnetic garnet single crystal films having different compositions may be combined, or magnetic garnet single crystal films having the same composition may be used. Even if the same composition and the same wafer are cut into chips, a certain degree of variation occurs in the coercive force, so that a desired combination can be realized by selecting according to the coercive force. The coercive force can also be adjusted by a subsequent heat treatment or the like. Furthermore, the number of magnetic garnet single crystal films to be combined is arbitrary, and may be arranged so as to be in close contact with each other, or may be arranged at intervals. The Faraday rotation angle varying device can be used as a Faraday rotation angle varying device Hikarisu <br/> acme switch and step variable optical attenuator.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

[0015]

FIG. 1 shows an example of a Faraday rotation angle varying device. As a Faraday element 10, two types of magnetic garnet single crystal films 12a and 12b having different coercive forces are used.
Here is an example of using. Two magnetic garnet single crystal films 1
2a and 12b are arranged so as to overlap in the direction of the optical axis, and an electromagnet 14 for applying a magnetic field in the direction of the optical axis is provided outside thereof.
Place. As shown in FIG. 2, the coercive force of each magnetic garnet single crystal film 12a, 12b is defined as Ha, Hb (however, Ha
<Hb), all having square magnetic hysteresis
And The thickness of each magnetic garnet single crystal film 12a, 12b is set to a thickness at which the absolute value of the Faraday rotation angle at the time of magnetic saturation becomes 45 degrees.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction contents]

First, the magnetic field (+ H ₂ or more) shown in FIG.
2a and 12b are magnetized in the + direction. At this time, the polarization direction is +90 by both magnetic garnet single crystal films.
Rotate degrees. When a magnetic field (−H ₁ ) is applied by the electromagnet 14, the magnetization of only one magnetic garnet single crystal film 12a is inverted and only the polarization direction is rotated by −45 degrees, so that the sum of the magnetic garnet single crystal film 12b and the other magnetic garnet single crystal film 12b is increased. Has a Faraday rotation angle of 0 degrees. Next, when a magnetic field (+ H ₁ ) is applied by the electromagnet 14, the magnetic garnet single crystal film 12
The magnetization of a is reversed again and the algebraic sum of the Faraday rotation angle is +
90 degrees. In this way, the algebraic sum of the Faraday rotation angle of the Faraday element 10 by controlling the one of the magnetic field + H ₁ or -H ₁ by the electromagnet 14 will be switched to +90 degrees and 0 degrees.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction contents]

It is assumed that the total Faraday rotation angle of the Faraday element 10 is controlled to 0 degree by the electromagnet 14. Light incident from the port is separated into P-polarized light and S-polarized light by the polarization separation film 27 of the first composite polarizing prism 20. The transmitted P-polarized light is transmitted through a Faraday rotation angle varying device 24.
, The polarization direction does not rotate but remains P-polarized light, and passes through the polarization separation film 27 of the second composite polarization prism 22. On the other hand,
The S-polarized light reflected by the polarization splitting film 27 of the first composite polarizing prism 20 also remains S-polarized without rotating the polarization direction in the Faraday rotation angle varying device 24, and the polarization splitting film of the second composite polarizing prism 22 It is reflected at 27. In this way, the incident light from the port is coupled to the port (see FIG. 3). Next, the electromagnet 14 is switched to switch the Faraday element 1.
The total Faraday rotation angle of 0 is controlled to 90 degrees. Light incident from the port is separated into P-polarized light and S-polarized light by the polarization separation film 27 of the first composite polarizing prism 20. Penetrated P
The polarization direction of the polarized light is 9 by the Faraday rotation angle varying device 24.
Rotate by 0 degree to become S-polarized light, and the second composite polarizing prism 2
The light is reflected by the second polarization separation film 27. On the other hand, the S-polarized light reflected by the polarization splitting film 27 of the first composite polarizing prism 20 is turned into P-polarized light by rotating the polarization direction by 90 degrees by the Faraday rotation angle varying device 24, and the polarization separation of the second composite polarizing prism 22 is performed. It passes through the membrane 27. In this way, incident light from the port couples to the port. Therefore, by controlling the applied magnetic field by the electromagnet 14, the optical path can be switched.

[Procedure amendment 8]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

FIG. 2

[Procedure amendment 9]

[Document name to be amended] Drawing

[Correction target item name] Fig. 5

[Correction method] Change

[Correction contents]

FIG. 5

[Procedure amendment 10]

[Document name to be amended] Drawing

[Correction target item name] Fig. 6

[Correction method] Change

[Correction contents]

FIG. 6

[Procedure amendment 11]

[Document name to be amended] Drawing

[Correction target item name] Fig. 7

[Correction method] Change

[Correction contents]

FIG. 7

Claims (4)

[Claims] A Faraday element in which a plurality of types of magnetic garnet single crystal films having different coercive forces are arranged so as to overlap in the optical axis direction, and a single electromagnet for applying a magnetic field in the optical axis direction to the Faraday element. And a Faraday rotation angle varying device that changes an algebraic sum of Faraday rotation angles by controlling a magnetic field applied to the Faraday element by the electromagnet. 2. A plurality of types of magnetic garnet single crystal films having different coercive forces are arranged so as to be overlapped in the optical axis direction between first and second composite polarizing prisms each having a polarization splitting film provided therein and arranged symmetrically. A Faraday rotation angle varying device including a Faraday element that has been applied and a single electromagnet that applies a magnetic field in the optical axis direction to the Faraday element is disposed, and the Faraday rotation is performed by controlling the magnetic field applied to the Faraday element by the electromagnet. An optical switch, wherein an optical path is switched by changing an algebraic sum of angles to either 0 degree or ± 90 degrees. 3. A first magnetic garnet single-crystal film having a square hysteresis, a large coercive force and a Faraday rotation angle of ± 45 degrees when a saturation magnetic field is applied, and a Faraday element having a smaller coercive force. 3. The optical switch according to claim 2, wherein a Faraday rotation angle of the second magnetic garnet single crystal film is combined with an electromagnet in combination with a second magnetic garnet single crystal film having a Faraday rotation angle of ± 45 degrees when a magnetic field is applied. 4. A Faraday element in which a plurality of types of magnetic garnet single crystal films having different coercive forces are arranged so as to be overlapped in the optical axis direction between a polarizer and an analyzer, each of which is made of a wedge-shaped birefringent crystal and arranged symmetrically. A Faraday rotation angle varying device comprising a single electromagnet for applying a magnetic field in the direction of the optical axis to the Faraday element, and controlling the magnetic field applied to the Faraday element by the electromagnet to thereby produce an algebraic sum of Faraday rotation angles. The step-variable optical attenuator is characterized in that the transmitted light quantity is changed discretely by changing the light intensity.