JPH11212042A - Production of faraday rotator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a bismuth-substd. rare earth iron garnet single crystal film having the coercive force to prevent the degradation in the coercive force by cutting with a dicing machine. SOLUTION: The process for producing the Faraday rotator consisting of cutting the bismuth-substd. rare earth iron garnet single crystal film having the characteristic to exhibit the coercive force even after an external magnetic field sufficiently larger than a satd. magnetic field is applied thereon and is then removed to a prescribed size is the process for producing the Faraday rotator which integrates an optical material by adhesion and fixation to the bismuth-substd. rare earth iron garnet single crystal film described above, then cuts the same by the dicing machine. As a result, the bismuth-substd. rare earth iron garnet single crystal film having the coercive force to prevent the degradation in the coercive force is obtd. Since the bismuth-substd. rare earth iron garnet single crystal film is integrated with the optical material as well, the assembly thereof is easy as well.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a bismuth-substituted rare earth iron garnet single crystal having coercive force (hereinafter referred to as BIG).
This is a method of manufacturing a Faraday rotator made of a film.Specifically, an optical material is bonded and fixed to a BIG film, which is an object to be cut, in advance, and this is cut by a dicing machine.
If these defects occur in the BIG film by suppressing chipping that occurs during cutting, and scratches on the surface that occur during handling, etc., the force that the BIG film retains magnetization in the absence of an external magnetic field decreases. That is, the coercive force of the BIG film is prevented from lowering.

[0002]

2. Description of the Related Art Chemical formula: (RBi) ₃ (FeM) ₅ O ₁₂ (where R is
Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
One or more selected from the group consisting of Yb and Lu, and M is one or more of Al and Ga. The bismuth-substituted rare earth iron garnet single crystal (BIG) film represented by) is industrially manufactured by a liquid phase epitaxial (LPE) method. Since the device exhibits a large Faraday effect, devices such as an optical isolator, an optical switch, and an optical circulator have been put to practical use one after another.

[0003] The Faraday effect is a kind of magneto-optical effect, and is a phenomenon in which the plane of polarization of light transmitted through a material exhibiting the Faraday effect (Faraday rotator) rotates. The phenomenon is a phenomenon that is not related to the direction of light entering and exiting the Faraday rotator but depends on the strength and direction of the external magnetic field applied to the Faraday rotator. BI
The case where the G film is used as a Friday rotator will be described with reference to the drawings. FIG. 1 shows a case of a BIG film having no hysteresis, and FIGS. 2 to 4 show a case of showing a hysteresis.
In particular, FIG. 4 shows the case of square hysteresis.

First, in FIG. 1, unless an external magnetic field is applied, the Faraday rotation angle of the Faraday rotator becomes zero [0].
That is, it is located at the origin o. When the external magnetic field gradually increases, the absolute value of the Faraday rotation angle [θf or -θf,
Positive for clockwise rotation and negative for counterclockwise]
It gradually increases through route a or route d [route o →
a → b or route o → d → e]. When the external magnetic field reaches a certain magnetic field strength, that is, the saturation magnetic field [Hs], the Faraday rotation angle becomes a saturated value [saturation magnetic field; point b or point e]
Becomes Even if the external magnetic field strength increases, the Faraday rotator is already magnetically saturated, so b → c
Or, only the transition from d to f does not change the magnitude of the Faraday rotation angle. Next, when the external magnetic field is gradually weakened, the reverse path, that is, c → b → a → o, or
Return to f → e → d → o and origin o.

A BIG film having a relatively large saturation magnetic field, for example,
The magnetization characteristics of the (HoTbBi) ₃ Fe ₅ O ₁₂ Faraday rotator with respect to an external magnetic field, that is, the relationship between the external magnetic field strength and the Faraday rotation angle, have a small hysteresis, as shown in FIG. However, in the case of a BIG film, particularly when a part of iron Fe is replaced by aluminum Al or gallium Ga, it is usually possible to manufacture a film in which the saturation magnetic field Hs is lowered according to the replacement amount, and magnetically depending on the replacement amount. The phenomenon that large hysteresis becomes large was found.

[0006] For example, (GdBi) ₃ (FeAlGa) ₅ O ₁₂ shows that the relationship between the external magnetic field strength and the Faraday rotation angle increases the external magnetic field as shown in FIG. 2 [path o → a →
b → c], when weakening [path c → b → b '→ a → o], the path is different. Here, this point b 'is
[Hc]. When the hysteresis becomes larger, the nucleation magnetic field Hc goes beyond the origin (o) and enters the minus side (FIG. 3). Further, in the case where the absolute value of the nucleation magnetic field Hc is larger than the absolute value of the saturation magnetic field Hs and falls on the minus side, there is also found one that draws a square hysteresis curve (FIG. 4).

[0007] In particular, in the case of FIG.
In some cases, only this rectangular loop is drawn, and the magnetic field required for reversing the magnetic direction is larger than the intrinsic saturation magnetic field Hs of the BIG film. In the BIG film showing a magnetic hysteresis loop as shown in FIG. 3 or FIG. 4, the bismuth-substituted rare earth iron garnet single crystal film is coercive in the absence of an external magnetic field. In FIGS. 3 and 4, the external magnetic field in the direction opposite to the magnetization direction of the magnetized BIG film causes
Magnetic field that changes the direction of magnetization of the IG film (= nucleation magnetic field Hc above)
Is defined as the coercive force.

[0008]

SUMMARY OF THE INVENTION The present inventors have found that a coercive force having a large coercive force can be manufactured by using a BIG film having a large coercive force from the viewpoint that an optical isolator or an optical circulator having a small assembly cost can be manufactured. We have developed a BIG film that draws a square hysteresis loop (Japanese Patent Application No. 8-140020). The BIG film has a large coercive force and its absolute value is more than the saturation magnetic field Hs in order to manufacture a compact and low-cost optical isolator or optical circulator without using permanent magnets and to operate it in various environments. It is desired to be large.

However, B which is sufficiently larger than the product size
Even those that show a sufficiently large coercive force in the state of the IG film, due to groove-like scratches on the surface due to chipping and handling that occur when cutting into the desired product shape,
We faced a serious problem that the coercive force was significantly reduced.
Chipping is a phenomenon in which the edge of the lower cut surface of the BIG film is chipped at the time of cutting, and it is extremely difficult to completely avoid this by cutting the hard and brittle BIG film with a dicing machine .

[0010]

That is, the present invention provides a bismuth-substituted rare earth iron garnet single crystal film having a characteristic that shows a coercive force even after the external magnetic field is removed by applying a sufficient external magnetic field larger than the saturation magnetic field. In a method of manufacturing a Faraday rotator, which is cut into a predetermined size, an optical material is bonded and fixed to the bismuth-substituted rare earth iron garnet single crystal film, and then the Faraday rotator cut with a dicing machine. It is a manufacturing method.

In the present invention, the coercive force characteristic B
As the IG film, a film that draws a square hysteresis loop by a magnetization process is preferable. Examples of the optical material to be bonded and fixed include a glass polarizing element, a birefringent plate, glass and a metal thin film mirror formed by depositing a metal on glass.

Hereinafter, the present invention will be described in detail. First, bismuth-substituted rare-earth iron garnet single crystals (BIG) exhibiting square hysteresis at room temperature are often mainly composed of rare earth ions Gd, Tb, and Ho, which have a large magnetic contribution.
(GdYBi) ₃ (FeGa) ₅ O ₁₂ , (TbBi) ₃ (FeGaAl) ₅ O ₁₂ (JP-A-08-1
40020), (TbHoBi) ₃ (FeGaAl) ₅ O ₁₂ (JP-A-08-186192). Also, BIG: (YLaBi) ₃ (FeGa) ₅ O ₁₂ , which is mainly a magnetic ion and mainly composed of La and Y, shows a square hysteresis when Ga is replaced in a large amount.

However, in general, a Faraday rotator
As a BIG, the temperature change of the Faraday rotation angle is large
BIG substituted with a large amount of Ga, such as (YLaBi) ₃ (FeGa) ₅ O _12, is not suitable. The operating temperature range (for example, -40 to 90
(° C), it is essential to have a sufficient coercive force in this temperature range. From these, (TbBi) ₃ (FeGaAl) ₅ O ₁₂ is most preferred in the present invention.

The BIG is appropriately used in combination with a glass polarizing element, a birefringent plate, a glass or a metal thin film mirror obtained by depositing a metal on glass, depending on the intended use. For example, in an optical isolator, a BIG is interposed between two polarizing elements or two birefringent plates whose polarization directions are inclined by 45 degrees. In an optical circulator or an optical switch, a BIG is interposed between a polarizing prism or a birefringent plate that separates an optical path according to a polarization direction and a λ / 2 retardation plate. In addition, a reflection plate is used for the Faraday mirror, and in the optical magnetic field sensor, the reflection plate and the polarizing element are arranged with the BIG interposed therebetween. By bonding and fixing the optical materials selected according to these purposes on both sides and cutting them with a dicing machine, without newly arranging these optical materials,
It is preferable because it can be used for the purpose. The method of manufacturing the Faraday rotator of the present invention is as described above. In the present invention, it is preferable to perform heat treatment after cutting, and then perform magnetizing treatment by applying an external magnetic field.

[0015]

[Effect] A Faraday rotator made of a bismuth-substituted rare earth iron garnet single crystal (BIG) film in which a decrease in coercive force was prevented was obtained. Since the target optical material is bonded and fixed to the BIG film, the target optical device can be easily and easily assembled.

[0016]

EXAMPLE 1 A 0.4 mm thick, 10 mm × 10 mm BIG film ((TbBi) ₃ (FeGaA) showing a coercive force of 420 (Oe) when magnetized by an external magnetic field of 5,000 (Oe)
l) ₅ O ₁₂ ) is sandwiched between glass plates with a thickness of 0.3 mm and 10 mm x 10 mm and fixed with an epoxy-based adhesive.
It was cut into 1 mm (81 pieces). A dicing saw manufactured by DISCO was used as a cutting machine, and the cutting was performed at a speed of 0.3 mm / sec with a diamond blade having a thickness of 100 μm. 1mm x 1m obtained
m After heat-treating 81 pieces at 150 ° C for 1 hour,
The magnet was magnetized by the external magnetic field of e), and the coercive force was measured. As a result, the value showing the smallest coercive force was 320 (Oe).

Example 2 In Example 1, a glass polarizing element having a thickness of 0.2 mm and 10 mm × 10 mm was used instead of a glass plate having a thickness of 0.3 mm and 10 mm × 10 mm.
(Corning Co., product name; Polar core) was used, except that the polarization direction was set to 45 degrees. As a result, the value showing the smallest coercive force was 300 (Oe).

Example 3 Example 2 was the same as Example 2, except that a 1 mm thick, 10 mm × 10 mm rutile polarizing element was used instead of the 0.2 mm thick, 10 mm × 10 mm glass polarizing element. The coercive force of the BIG film before cutting was 410 (Oe) when it was magnetized with an external magnetic field of 5,000 (Oe). As a result, the value showing the smallest coercive force was 330 (Oe).

Example 4 A 0.4 mm thick, 10 mm × 10 mm BIG film ((TbBi) ₃ (FeGaA) showing a coercive force of 460 (Oe) when magnetized by an external magnetic field of 5,000 (Oe)
l) ₅ O ₁₂ ) is sandwiched between a 1 mm thick, 10 mm × 10 mm glass plate and a glass surface of a 1 mm, 10 mm × 10 mm glass mirror with a metal thin film deposited on one side, and fixed with an epoxy adhesive The same procedures as in Example 1 were carried out except for using. As a result, the value showing the smallest coercive force was 290 (Oe).

Comparative Example 1 A 0.4 mm thick, 10 mm × 10 mm BIG film ((TbBi) ₃ (FeGaA) showing a coercive force of 450 (Oe) when magnetized by an external magnetic field of 5,000 (Oe)
l) The procedure of Example 1 was repeated except that ₅ O ₁₂ ) was used as it was for cutting. As a result, the value showing the smallest coercive force was 180 (Oe).

Comparative Example 2 In the bismuth-substituted rare earth iron garnet single crystal cut in Comparative Example 1, the surface of a sample having an average coercive force of 360 (Oe) was scratched with a glass cutter, and 150 ° C. , And the same magnetization treatment was performed. As a result, the coercive force was 120 (Oe), which was significantly reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an example of magnetic properties of a bismuth-substituted rare earth iron garnet single crystal that does not exhibit magnetic hysteresis.

FIG. 2 is a schematic diagram showing an example of magnetic properties of a bismuth-substituted rare earth iron garnet single crystal showing a somewhat large magnetic hysteresis loop.

FIG. 3 is a schematic diagram showing an example of magnetic properties of a bismuth-substituted rare earth iron garnet single crystal showing a large magnetic hysteresis loop.

FIG. 4 is a schematic diagram showing an example of magnetic properties of a bismuth-substituted rare earth iron garnet single crystal forming a square hysteresis loop for large magnetic hysteresis.

Claims (5)

[Claims] The method comprises cutting a bismuth-substituted rare earth iron garnet single crystal film having a characteristic exhibiting coercive force even after removing an external magnetic field by applying a sufficient external magnetic field larger than a saturation magnetic field to a predetermined size. In a method for manufacturing a Faraday rotator, an optical material is bonded and fixed to the bismuth-substituted rare earth iron garnet single crystal film, and then cut by a dicing machine. 2. A method for manufacturing a Faraday rotator according to claim 1, wherein said bismuth-substituted rare earth iron garnet single crystal film can form a square hysteresis loop by applying a sufficient external magnetic field larger than its saturation magnetic field. . 3. The method for producing a Faraday rotator according to claim 1, wherein the optical material to be bonded and fixed is a glass polarizing element. 4. The method for producing a Faraday rotator according to claim 1, wherein the optical material to be bonded and fixed is a birefringent plate. 5. The method for manufacturing a Faraday rotator according to claim 1, wherein the optical material to be bonded and fixed is glass or a metal thin film mirror formed by depositing metal on glass.