JPH07199136A - Magneto-optic garnet - Google Patents

Abstract

(57) [Summary] [Objective] As a Faraday rotator for optical isolator for wavelength 1.55μm, transmittance is 99% or more, temperature dependence of Faraday rotation and saturation magnetization are small, and it can be grown by liquid phase epitaxial method. Provide a highly productive magneto-optical garnet. [Composition] A magneto-optical garnet used for a Faraday rotator such as an optical isolator and an optical switch, the chemical formula of which is TbxYyGdzBi _3-XYZ Fe ₅ O ₁₂
(However, 0.5 ≦ X <1.8, 0 ≦ Y <1.5, 0 ≦
Z <1.6, 0.3 ≦ 3-XYZ <2.4).

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 Faraday rotators such as optical isolators and optical switches.

[0002]

2. Description of the Related Art In order to eliminate reflection noise in optical fiber communication, an optical isolator utilizing the Faraday effect of a magneto-optical garnet single crystal under a saturated magnetic field has been put into practical use. As the Faraday rotator in the optical isolator, initially, a bulk Y ₃ Fe ₅ O ₁₂ single crystal grown by an infrared concentrated heating method or the like was used, but in recent years, a liquid phase epitaxial method having excellent productivity Thick film type single crystals grown in the most popular way. The chemical formulas of these thick film type magneto-optical garnet single crystals are R
_{3-X Bi X Fe 5 O} 12 (R is Y and Gd, rare earth elements Lu, etc.) represented by. Bi (bismuth) solidified in a single crystal has the effect of dramatically increasing the Faraday effect. The Bi amount and the Faraday rotation capability are almost proportional.

By the way, the characteristics required for the magneto-optical garnet for optical isolators are: (1) small absorption of light having wavelengths of 1.3 μm and 1.55 μm used in optical fiber communication; ) The Faraday rotation capability is large, the Faraday rotation is less dependent on the ambient temperature, and (3) the saturation magnetization is small. Bulk Y ₃ Fe ₅ O ₁₂ single crystal is a thick film type single crystal grown by a liquid phase epitaxial method because it has a low Faraday rotation ability, a large saturation magnetization, and a high manufacturing cost. It was replaced by.

On the other hand, thick-film type R _3-X Bi _X Fe ₅
Problems O ₁₂ is compared to Y ₃ Fe ₅ O ₁₂ single crystal was that a large environmental temperature dependence of the Faraday rotation.

For example, when R is Gd, the wavelength is 1.55
With respect to the light of μm, the temperature change rate of Faraday rotation near 20 ° C. is 1.8 × 10 ⁻³ / ° C.
_{In the 3} Fe ₅ O ₁₂ single crystal, the temperature change rate of Faraday rotation near 20 ° C. was 9.0 × 10 ⁻⁴ / ° C.

In a thick film type magneto-optical garnet single crystal (R _3-X Bi _X Fe ₅ O ₁₂ ), as a composition that solves this problem, the inventors of the present invention have reported that
Vol. 11, No. 2, 1987, pp. 157-160, Tb _3-X Bi _X Fe ₅ O ₁₂ (0.68 ≦ X ≦
1.18) is shown. In this composition, the temperature change rate of the Faraday rotation is Y ₃ Fe due to the effect of Tb.
_It is equivalent to ₅ O ₁₂ single crystal. And this composition satisfies the above-mentioned characteristics (1), (2) and (3) at a high level.

[0007]

By the way, the transmissivity of the magneto-optical garnet single crystal for an optical isolator is required to have a considerably high value in some cases. For example, when two optical isolators are used in a stacked manner, it is desired that the transmittance of each one is 99% or more.

However, the present inventors have found that the above-mentioned T
A Faraday rotator for wavelengths of 1.3 μm and 1.55 μm was measured with b _3-X Bi _X Fe ₅ O ₁₂ (0.68 ≦ X ≦ 1.18).
m was 100%, but it was 98% at a wavelength of 1.55 μm.

An object of the present invention is a Faraday rotator for an optical isolator for a wavelength of 1.55 μm, which has a transmittance of 99%.
As described above, it is an object of the present invention to provide a magneto-optical garnet which has a small temperature dependence of Faraday rotation and a saturation magnetization and which can be grown by a liquid phase epitaxial method with high productivity.

[0010]

According to the present invention, a magneto-optical garnet used in a Faraday rotator, comprising:
The chemical formula of the composition is Tb _x Y _y Gd _z Bi _3-XYZ Fe ₅
O ₁₂ (however, 0.5 ≦ X <1.8, 0 ≦ Y <1.5,
It is possible to obtain a magneto-optical garnet characterized by satisfying 0 ≦ Z <1.6, 0.3 ≦ 3-XYZ <2.4).

[0011]

EXAMPLES By the way, Tb _3-X Bi _X Fe ₅ O ₁₂ (0.
The fact that the transmittance of 68 ≦ X ≦ 1.18) at a wavelength of 1.55 μm is not 100% and is low is due to the optical absorption of Tb having a peak at a wavelength of 1.7 μm. Therefore, if Tb is not used, the transmittance at the wavelength of 1.55 μm can be improved, but this Tb has the effect of reducing the temperature dependence of the Faraday rotation angle, so this cannot be completely eliminated. Therefore, a part of this Tb can be replaced with another rare earth element, or Y which can replace Tb like other rare earth elements.
It is possible to replace with. However, in practice, the usable rare earth elements or Y elements are limited.

That is, the conditions required for the element to be used are (1) no light absorption at a wavelength of 1.55 μm, and (2) saturation when contained in R _3−x Bi _x Fe ₅ O _12. It is possible to reduce the magnetization.

Further, for the following reason, (3) T
It is also desired that the ion radius be smaller than b.

To improve the transmittance, Tb _3-X Bi _X Fe ₅
It is also effective to incorporate a large amount of Bi, which increases the Faraday effect, into O ₁₂ to reduce the thickness of the Faraday rotator.

However, in the liquid phase epitaxial method,
When a large amount of Bi is dissolved, since the ionic radius of Bi is considerably larger than Tb, the lattice constant of the thick film becomes large, and stress is generated due to the lattice constant mismatch with the non-magnetic garnet single crystal as the substrate. , Cracks occur. Therefore, Bi in the Tb _3-X Bi _X Fe ₅ O ₁₂ single crystal thick film that can be grown is grown.
There is a limit to the amount. Therefore, when a large amount of Bi is dissolved, an element having an ionic radius smaller than Tb must be replaced with a part of Tb.

However, these three items (1),
There is no element that simultaneously satisfies (2) and (3).

Therefore, the present inventor has decided to replace at least one of two elements, Y and Gd, which satisfy two of the above-mentioned three items.

That is, Y does not absorb light at a wavelength of 1.55 μm and has an ionic radius smaller than that of Tb. On the other hand, G
d is a wavelength of 1.55 μm and there is no light absorption.
Is characterized in that _3-X Bi _X Fe ₅ O when included in ₁₂ can be reduced saturation magnetization.

Accordingly, the present inventors have found that the chemical formula of the composition is Tb _X Y _Y Gd _Z Bi _3-XYZ Fe ₅ O ₁₂ (where 0.5≤X <1.8, 0≤Y <1.5 , 0 ≦ Z <
1.6, 0.3 ≦ 3-XYZ <2.4), a wavelength of 1.
When a Faraday rotator for an optical isolator for 55 μm is produced, its transmittance is 99% or more, and
The present invention has been completed by finding that the temperature dependence of the Faraday rotation angle and the saturation magnetization are small.

The present invention will be described below with reference to examples.

The compositions of Examples (1) to (5) are shown in Table 1 below.

[0022]

[Table 1]

Examples (1) to (5), Y _{3 Fe 5} O ₁₂ , G
The measured values of d _2.00 Bi _1.00 Fe 5 O ₁₂ and Examples 6- to 6- are shown in Table 2 below.

[0024]

[Table 2]

(Example 1) Using a melt having a composition shown in the column of Example 1 in Table 1 (total weight 5 kg), composition (GdCa)
_On a non-magnetic garnet single crystal substrate represented by ₃ (GaMgZr) ₅ O ₁₂ at a growth temperature of 800 ° C., Tb _0.72 Y _0.98
A magneto-optical garnet having a composition of Gd _0.10 Bi _1.20 Fe ₅ O ₁₂ was grown by a liquid phase epitaxial method. The Faraday rotation coefficient (Faraday rotation angle per unit length under a saturated magnetic field) absolute value at a wavelength of 1.55 μm of this magneto-optical garnet, and the temperature change rate of Faraday rotation,
The saturation magnetization was measured. Further, this magneto-optical garnet was processed into a Faraday rotator for an optical isolator for a wavelength of 1.55 μm, and the transmittance at a wavelength of 1.55 μm was measured. These measured values were used as a bulk Y ₃ Fe ₅ O ₁₂ single crystal and Gd _2.0 Bi _1.0 F grown by a liquid phase epitaxial method.
The results are shown in Table 2 together with the measured values of e ₅ O ₁₂ .

That is, Tb _0.72 Y _0.98 Gd _0.10 Bi
_1.20 Fe ₅ O ₁₂ is far superior to the Y ₃ Fe ₅ O ₁₂ single crystal in faraday rotation absolute value and saturation magnetization, and the Faraday rotation temperature change rate is smaller than that of Gd _2.0 Bi _1.0 Fe ₅ O ₁₂ . The value was close to that of a Y ₃ Fe ₅ O ₁₂ single crystal.
Further, the transmittance of the Faraday rotator for optical isolator for wavelength 1.55 μm made of Tb _0.72 Y _0.98 Gd _0.10 Bi _1.20 Fe ₅ O ₁₂ was 99.5%, which was a very high value.

(Example 2) A composition (GdCa) was obtained by using a melt having a composition shown in the column of Example 2 in Table 1 (total weight: 5 kg).
Tb _1.39 Y _0.41 at a growth temperature of 780 ° C. on a nonmagnetic garnet single crystal substrate represented by ₃ (GaMgZr) ₅ O _12.
A magneto-optical garnet having a composition of Gd _0.20 Bi _1.00 Fe ₅ O ₁₂ was grown by a liquid phase epitaxial method. The Faraday rotation coefficient (Faraday rotation angle per unit length under a saturated magnetic field) absolute value at a wavelength of 1.55 μm of this magneto-optical garnet, and the temperature change rate of Faraday rotation,
The saturation magnetization was measured. Further, this magneto-optical garnet was processed into a Faraday rotator for an optical isolator for a wavelength of 1.55 μm, and the transmittance at a wavelength of 1.55 μm was measured. These measured values are shown in Table 2.

That is, Tb _1.39 Y _0.41 Gd _0.20 Bi
_1.00 Fe ₅ O ₁₂ is far superior to the Y ₃ Fe ₅ O ₁₂ single crystal in faraday rotation absolute value and saturation magnetization, and the Faraday rotation temperature change rate is also smaller than Gd _2.0 Bi _1.0 Fe ₅ O ₁₂ , The value was close to that of a Y ₃ Fe ₅ O ₁₂ single crystal.
Further, the transmittance of the Faraday rotator for an optical isolator for wavelength 1.55 μm made of Tb _1.39 Y _0.41 Gd _0.20 Bi _1.00 Fe ₅ O ₁₂ was 99.0%, which was a very high value.

(Example 3) A composition (GdCa) was obtained by using a melt having a composition shown in the column of Example 3 in Table 1 (total weight: 5 kg).
_On a non-magnetic garnet single crystal substrate represented by ₃ (GaMgZr) ₅ O ₁₂ at a growth temperature of 830 ° C., Tb _0.50 Y _0.50
A magneto-optical garnet having a composition of Gd _1.40 Bi _0.60 Fe ₅ O ₁₂ was grown by a liquid phase epitaxial method. The Faraday rotation coefficient (Faraday rotation angle per unit length under a saturated magnetic field) absolute value at a wavelength of 1.55 μm of this magneto-optical garnet, and the temperature change rate of Faraday rotation,
The saturation magnetization was measured. Further, this magneto-optical garnet was processed into a Faraday rotator for an optical isolator for a wavelength of 1.55 μm, and the transmittance at a wavelength of 1.55 μm was measured. These measured values are shown in Table 2.

That is, Tb _0.50 Y _0.50 Gd _1.40 Bi
Compared with Y ₃ Fe ₅ O ₁₂ single crystal, _0.60 Fe ₅ O ₁₂ is far superior in Faraday rotation absolute value and saturation magnetization, and the Faraday rotation temperature change rate is also smaller than Gd _2.0 Bi _1.0 Fe ₅ O ₁₂ , The value was close to that of a Y ₃ Fe ₅ O ₁₂ single crystal.
Further, the transmittance of the Faraday rotator for optical isolator for wavelength 1.55 μm made of Tb _0.50 Y _0.50 Gd _1.40 Bi _0.60 Fe ₅ O ₁₂ was 99.0%, which was a very high value.

Example 4 A composition (GdCa) was obtained by using a melt (total weight: 5 kg) having the composition shown in the column of Example 4 in Table 1.
_On a non-magnetic garnet single crystal substrate represented by ₃ (GaMgZr) ₅ O ₁₂ at a growth temperature of 800 ° C., Tb _0.87 Y _0.93
A magneto-optical garnet having a composition of Bi _1.20 Fe ₅ O ₁₂ was grown by a liquid phase epitaxial method. Faraday rotation coefficient (Faraday rotation angle per unit length under a saturated magnetic field) of this magneto-optical garnet at a wavelength of 1.55 μm
The absolute value, the temperature change rate of Faraday rotation, and the saturation magnetization were measured. Furthermore, this magneto-optical garnet has a wavelength of 1.
It was processed into a Faraday rotator for an optical isolator for 55 μm, and the transmittance at a wavelength of 1.55 μm was measured. These measured values are shown in Table 2.

That is, Tb _0.87 Y _0.93 Bi _1.20 Fe ₅
O ₁₂ is compared to Y ₃ Fe ₅ O ₁₂ single crystal, the Faraday rotation absolute value, the saturation magnetization has much better, Faraday rotation temperature change rate Gd _2.0 Bi _1.0 Fe ₅ O ₁₂ smaller than, Y ₃ Fe _The value was close to that of a ₅ O ₁₂ single crystal. Also, T
The transmittance of the Faraday rotator for an optical isolator for wavelength 1.55 μm made of b _0.87 Y _0.93 Bi _1.20 Fe ₅ O ₁₂ was 99.5%, which was a very high value.

Example 5 A composition (GdCa) was prepared by using a melt having a composition shown in the column of Example 5 in Table 1 (total weight: 5 kg).
Tb _1.20 Gd at a growth temperature of 830 ° C. on a non-magnetic garnet single crystal substrate represented by ₃ (GaMgZr) ₅ O _12.
A magneto-optical garnet having a composition of _1.00 Bi _0.80 Fe ₅ O ₁₂ was grown by a liquid phase epitaxial method. The Faraday rotation coefficient (Faraday rotation angle per unit length under a saturated magnetic field) absolute value, the temperature change rate of Faraday rotation, and the saturation magnetization at a wavelength of 1.55 μm of this magneto-optical garnet were measured. Further, this magneto-optical garnet was processed into a Faraday rotator for an optical isolator for a wavelength of 1.55 μm, and the transmittance at a wavelength of 1.55 μm was measured. These measured values are shown in Table 2.

That is, Tb _1.20 Gd _1.00 Bi _0.80 Fe
₅ O ₁₂ has far more excellent Faraday rotation absolute value and saturation magnetization than the Y ₃ Fe ₅ O ₁₂ single crystal, and the Faraday rotation temperature change rate is smaller than that of Gd _2.0 Bi _1.0 Fe ₅ O ₁₂ , and Y ₃ The value was close to that of a Fe ₅ O ₁₂ single crystal. Also, T
The transmittance of the Faraday rotator for an optical isolator for wavelength 1.55 μm made of b _1.20 Gd _1.00 Bi _0.80 Fe ₅ O ₁₂ was 99.0%, which was a very high value.

Example 6 A magneto-optical garnet having the composition shown in the column of Example 6- to Table 2 in Table 2 was grown on a non-magnetic garnet single crystal substrate by a liquid phase epitaxial method. The wavelength of these magneto-optical garnets is 1.55 μm
The Faraday rotation coefficient (Faraday rotation angle per unit length under a saturated magnetic field) absolute value, the temperature change rate of Faraday rotation, and the saturation magnetization were measured. Further, this magneto-optical garnet was processed into a Faraday rotator for an optical isolator for a wavelength of 1.55 μm, and the transmittance at a wavelength of 1.55 μm was measured. These measured values are shown in Table 2.

Tb shown in the column of Example 6 in Table 2
_0.30 Y _1.00 Gd _1.00 Bi _0.70 Fe ₅ O ₁₂ has a Faraday rotation temperature change rate of 1.6 × 10 ⁻³ / ° C., and
It is larger than that of No. 5 and has a problem as a Faraday rotator for an optical isolator.

Tb shown in the column of Example 6 in Table 2
_1.90 Bi _1.90 Fe ₅ O ₁₂ has a transmittance of 98% as a Faraday rotator for an optical isolator for a wavelength of 1.55 μm.
As compared with Examples 1 to 5, the size was small and there was a problem as a Faraday rotator for an optical isolator.

Tb shown in the column of Example 6 in Table 2
_0.50 Y _1.60 Bi _0.90 Fe ₅ O ₁₂ has a saturation magnetization of 160
This is 0 G, which is larger than those of Examples 1 to 5, and there was a problem as a Faraday rotator for an optical isolator.

Tb shown in the column of Example 6 in Table 2
_0.50 Gd _1.70 Bi _0.80 Fe ₅ O ₁₂ has a Faraday rotation temperature change rate of 1.6 × 10 ⁻³ / ° C., which is larger than those of Examples 1 to 5, and is problematic as a Faraday rotator for optical isolators. It was

Tb shown in the column of Example 6 in Table 2
_1.00 Y _0.80 Gd _1.00 Bi _0.20 Fe ₅ O ₁₂ has a wavelength of 1.5
The absolute value of the Faraday rotation coefficient at 5 μm is 150d.
eg. / Cm, which is smaller than those of Examples 1 to 5, and
The transmittance as a Faraday rotator for an optical isolator for a wavelength of 1.55 μm was also 85%, which was smaller than that of Examples 1 to 5, and there was a problem as a Faraday rotator for an optical isolator.

Tb shown in the column of Example 6 in Table 2
_0.50 Y _0.05 Gd _0.05 Bi _2.50 Fe ₅ O ₁₂ has a wavelength of 1.5
The transmittance as a Faraday rotator for an optical isolator for 5 μm is 70.0%, which is smaller than those in Examples 1 to 5,
There was a problem as a Faraday rotator for optical isolators.

[0042]

As described above, according to the present invention, as a Faraday rotator for an optical isolator for a wavelength of 1.55 μm, a magneto-optical device having a transmittance of 99% or more and a temperature dependence of Faraday rotation and a small saturation magnetization. Garnet can be grown by a highly productive liquid phase epitaxial method, and its industrial utility value becomes great.

Claims (1)

[Claims] 1. A magneto-optical garnet for use in a Faraday rotator, the chemical formula of which is Tb _X Y _Y Gd _Z.
Bi _3-XYZ Fe ₅ O ₁₂ (where 0.5 ≦ X <1.
8,0 ≦ Y <1.5, 0 ≦ Z <1.6, 0.3 ≦ 3-X
-Y-Z <2.4).