JPH11337893A - Magneto-optic garnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magneto-optic garnet with which a desired Faraday rotation angle can be obtd. without using a cylindrical magnet by specifying the compsn. of the magneto-optic garnet. SOLUTION: Eu and Ho are used as rare earth elements, and Fe is partly replaced with at least one element of Ga, Al and Sc. Namely, a magneto-optic garnet having a compsn. expressed by the chemical formula of Rx Bi3-x Fe(5- A) MAO12 is used. In the formula, R is at least one of Eu and Ho, X satisfies 1.5<=X<=2.7, M is at least one of Ga, Al and In, and A satisfies 0.6<=A<=1.4. In the graph showing the relation between the intensity of the magnetic field applied on the magneto-optical garnet having >=250 Oe coercive force and the Faraday rotation angle, the relation shows a so-called hysteresis curve in which the Faraday rotation angle qF is const. over >=250 (Oe) magnetic field applied and when a magnetic field of <=-250 (Oe) is applied, the Faraday rotation angle qF is also to be the same negative value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical garnet used for an optical isolator, an optical circulator, and a Faraday rotator for an optical switch used for near-infrared light.

[0002]

2. Description of the Related Art Conventionally, for example, a semiconductor laser is often used as a light source of an optical device for performing optical communication, optical measurement, magneto-optical recording, etc. due to its coherence. But,
When a part of the light emitted from the semiconductor laser is returned to the laser itself, wavelength fluctuation and noise are generated. Therefore, an optical isolator using a Faraday element that generates a Faraday rotation (non-reciprocal optical rotation in a magnetic field) angle of 45 degrees in order to block the return light has been put to practical use.

[0003] Different materials are used for the Faraday element depending on the wavelength of the light source. For example, at wavelengths of 1.31 μm and 1.55 μm, which are wavelengths of optical communication, a magnetic garnet (a garnet containing iron in a component) single crystal is used as a Faraday rotator.

Among them, especially, low-cost LPE (liq
uid phase epitaxial) method (GdBi)
₃ (FeA1Ga) of ₅ O ₁₂ having a composition magnetic garnet single crystal thick films are widely used.

[0005]

The above (GdBi)
A magnetic garnet single crystal thick film such as ₃ (FeAlGa) ₆ O ₁₂ is a ferromagnetic material, and the relationship between the applied magnetic field and the Faraday rotation angle is as shown in FIG.

That is, an external magnetic field of Hs or more shown in FIG. 2 is applied in parallel with the traveling direction of light to obtain a Faraday rotation angle of 45 degrees.

Specifically, by covering the outer periphery of the magnetic garnet single crystal thick film with a cylindrical permanent magnet, the garnet is saturated to form a single magnetic domain, and a Faraday rotation angle of 45 degrees is obtained.

However, covering with a cylindrical permanent magnet has the disadvantage that not only is the cylindrical magnet expensive, but also the parts themselves become large.

Therefore, one technical problem of the present invention is to provide a magneto-optical garnet that can obtain a desired Faraday rotation angle without using a cylindrical magnet.

Another technical problem of the present invention is that
An object of the present invention is to provide a magneto-optical garnet capable of realizing miniaturization and cost reduction of an optical isolator.

[0011]

Means for Solving the Problems The present inventors used Eu and Ho as rare earth elements in a magneto-optical garnet,
By replacing at least one of Ga with Al and at least one element of Sc, it is possible to obtain a Faraday rotation angle of 45 degrees without increasing the coercive force and using a cylindrical permanent magnet. Have been found, and the present invention has been accomplished.

That is, according to the present invention, the chemical formula: R _x Bi
_3-x Fe _(5-A) M _A O ₁₂ (where R is Eu and Ho
And at least one of 1.5 ≦ X ≦ 2.7, and M is at least one of Ga and Al, In and has a composition represented by 0.6 ≦ A ≦ 1.4). Thus, a magneto-optical garnet is obtained.

In the present invention, the coercive force is 250
If it is less than (Oe), in the absence of a permanent magnet, Faraday rotation is reversed by an external disturbance magnetic field, which causes deterioration of magneto-optical characteristics. Therefore, in a garnet for an isolator that does not use a permanent magnet, the coercive force is desirably 250 (Oe) or more.

[0014]

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

The magneto-optical garnet according to the present invention has the chemical formula: R _x Bi _3-x Fe _(5-A) M _A O ₁₂ (where R is E
at least one of u and Ho, and 1.5 ≦ X ≦
2.7, and M is at least one of Ga, Al, and In, and has a composition represented by 0.6 ≦ A ≦ 1.4).

In the composition of the present invention represented by the above chemical formula, the coercive force is increased only when the composition range x of R is 1.3 or more and the composition range A of M is 0.6 ≦ A ≦ 1.4. 25
0 (Oe) or more.

Further, when the composition range 3-x of Bi of the present invention is less than 0.3, the Faraday rotation speed is low, so that the thickness becomes large, which is not practical as a Faraday rotator. On the other hand, B
When the composition range (3-x) of i exceeds 1.5, defects occur in the single crystal and the magnetic characteristic optical characteristics deteriorate. Therefore,
The composition range 3-x of Bi is preferably in the range of 0.3 to 1.5. In addition, when comprehensively considering the coercive force, crystal thickness, and crystal defects, the R concentration x of the present invention is 1.3 ≦ x ≦ 2.
It is necessary to be within 7 ranges.

FIG. 1 is a diagram showing the applied magnetic field strength and the Faraday rotation angle of a magneto-optical garnet having a coercive force of 250 (Oe) or more according to the embodiment described below. FIG.
As shown in (2), by applying a magnetic field of 250 (Oe) or more, the Faraday rotation angle θF becomes constant,
It can be seen that when a magnetic field of 50 (Oe) or more is applied, the Faraday rotation angle .theta.F also draws a so-called hysteresis curve having the same negative value.

(First Embodiment) Eu ₂ O ₃ , Ho ₂ O ₃ , Fe ₂ O ₃ , 99.99% pure as starting materials
Ga ₂ O ₃ , In ₂ O ₃ and flux as Bi ₂ O
₃ , PbO and B ₂ O ₃ were used and blended to have the component compositions shown in Table 1 below to grow a magneto-optical garnet thick film.
Polishing was performed at a wavelength of 1.31 and 1.55 μm to a thickness at which the Faraday rotation angle was 45 degrees. The coercive force Hc at that time is shown.

[0020]

[Table 1]

As is clear from Table 1 above, it can be seen that the garnet having the composition of the present invention has a coercive force that can be put to practical use. (Sample Nos. 3, 4, 5, 6, 7) 3 ~
Good magneto-optical characteristics were obtained by incorporating the garnet No. 7 into the magnetless isolator.

(Second Embodiment) Tb ₂ O ₃ , Eu ₂ O ₃ , Ho ₂ O ₃ , 99.99% pure as starting materials
Fe ₂ O ₃ , Al ₂ O ₃ , In ₂ O ₃ and Bi ₂ O ₃ , PbO, B ₂ O ₃ were used as fluxes, and were blended so as to have the composition shown in Table 2 below. The membrane was grown. The garnet was further polished to a thickness at which the Faraday rotation angle was 45 degrees at 1.31 and 1.55 μm. The coercive force Hc at that time is shown in Table 2 below.

[0023]

[Table 2]

As is clear from Table 2 above, it can be seen that the garnet having the composition of the present invention has a practically usable coercive force. (Sample Nos. 10, 11, 12, 13, 1
4) No. Good magneto-optical characteristics were obtained by incorporating the garnets 10, 11, 12, 13, and 14 into the magnetless isolator.

(Third Embodiment) Tb ₂ O ₃ , Eu ₂ O ₃ , Ho ₂ O ₃ , 99.99% pure as starting materials
Fe ₂ O ₃ , In ₂ O ₃ and Bi as flux
_A thick film of magneto-optical garnet was grown by using ₂ O ₃ , PbO, and B ₂ O ₃ and blending them to have the component compositions shown in Table 3 below. Further, the garnet was polished to a thickness at which the Faraday rotation angle was 45 degrees at 1.31 and 1.55 μm. The coercive force Hc at that time is shown in Table 3 below.

[0026]

[Table 3]

As is clear from Table 3 above, it can be seen that the garnet having the composition of the present invention has a practical coercive force. (Sample Nos. 17, 18, 19, 20, 21, 21)
No. By incorporating the garnets 17, 18, 19, 20, 21 into the magnetless isolator, good magneto-optical characteristics were obtained.

[0028]

As described above, by using the magneto-optical garnet according to the present invention, it is possible to provide a practical optical isolator without a permanent magnet, and the optical isolator can be reduced in size and cost. Was.

[Brief description of the drawings]

FIG. 1 is a diagram showing an applied magnetic field strength and a Faraday rotation angle of a garnet having a coercive force of 250 Oe or more in the first to third embodiments of the present invention.

FIG. 2 is a diagram showing an applied magnetic field strength of (GdBi) ₃ (FeA1Ga) ₅ O ₁₂ and a Faraday rotation angle.

Claims (2)

[Claims] 1. The chemical formula, R _x Bi _3-x Fe _(5-A) M _A O
₁₂ (where R is at least one of Eu and Ho, 1.5 ≦ X ≦ 2.7, and M is Ga and Al,
In at least one of In and 0.6 ≦ A ≦ 1.4)
A magneto-optical garnet having a composition represented by the following formula: 2. The magneto-optical garnet according to claim 1, wherein the coercive force is at least 250 (Oe).