JPH08290998A - Bismuth-substituted rare earth metal iron garnet single crystal - Google Patents

Abstract

PURPOSE: To obtain a bismuth-substituted magnetic garnet single crystal having low loss as a Faraday rotation element for optical isolator for 0.95-1.1μm wavelength. CONSTITUTION: A bismuth-substituted rare earth metal iron garnet single crystal expressed by the general formula, Pr3-x Bix Fe5-y My O12 (M is at least one kind of metal selected from In, Sc, Ga and Al; 0.8<=x<=1.8; 0<=y<=1.0) is grown on a non-magnetic garnet single crystal substrate having a lattice constant of 12.60Å to 12.70Å by a liquid epitaxy method. This process gives a bismuth- substituted magnetic garnet single crystal having low loss as a Faraday rotation element for an optical isolator for 0.95-1.1μm wavelength compared with conventional element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Faraday rotator for an optical isolator. More specifically, the present invention relates to a bismuth-substituted rare earth iron garnet single crystal suitable as a Faraday rotator for a wavelength band of 1 μm.

[0002]

2. Description of the Related Art Lasers are widely used as coherent light sources for optical application equipment or optical communication.
When the light emitted from the laser is reflected by an optical system or the like and returns to the laser again, there is a drawback that the laser oscillation becomes unstable. In particular, this is a big problem in semiconductor lasers and solid-state lasers.

In order to deal with this problem, an optical isolator is provided on the light output side of the laser and an optical path is set so that the light emitted from the laser does not return.
The optical isolator used for this purpose comprises a polarization element, a Faraday rotator, and a permanent magnet for magnetically saturating the Faraday rotator. As a Faraday rotator for optical isolators, liquid phase epitaxial (hereinafter "LP
E)) bismuth-substituted rare earth iron garnet single crystal with a thickness of several tens of μm or more (general formula R
_3-x Bi _x Fe ₅ O ₁₂ and R represents a rare earth) is used.

[0004]

Bismuth-substituted rare earth iron garnet single crystal is an excellent material that exhibits excellent transparency and a large Faraday effect in the near infrared region of 1.2 μm or more, and is actually used for long-distance optical fiber communication. Practical wavelength
The loss at 1.31 μm and 1.55 μm is less than 0.1 dB. However, it is shorter than 1.3 μm band
There is a problem that the light absorption loss increases at wavelengths around 1 μm. Wavelength of bismuth-substituted rare earth iron garnet single crystals currently in practical use, for example (HoTbBi) ₃ Fe ₅ O ₁₂
The loss at 1.064 μm is approximately 1 dB. 1μ
The large light absorption in the m band is due to the absorption peak of iron in the vicinity of 0.9 μm.

The 1 μm band is considered important because the oscillation wavelength of the solid-state laser belongs to this region. Specifically, the yttrium aluminum garnet (YAG) laser is 1.064 μm, and the gadolinium scandium gallium garnet (GSGG) laser is 1.061 μm. The output power of these solid-state lasers is very large, and therefore, if the absorption loss in the Faraday rotator is large, there is a serious problem that the Faraday rotator is damaged by the absorbed heat.

[0006]

The present inventors have found that the wavelength of 1 μm
The present invention has been completed through intensive studies to provide a low-loss bismuth-substituted rare earth iron garnet single crystal for the m band, specifically 0.95 μm to 1.1 μm. That is, the present invention is a bismuth-substituted rare earth iron garnet single crystal grown by a liquid phase epitaxial method on a nonmagnetic garnet single crystal substrate having a lattice constant of 12.60Å to 12.70Å, the general formula of which is Pr _{3-x. Bi x Fe 5-y M y} O 12 (M is at least one element selected in, Sc, Ga, from the group consisting of Al, 0.8 ≦
A bismuth-substituted rare earth iron garnet single crystal for a Faraday rotator, characterized in that x ≦ 1.8 and 0 ≦ y ≦ 1.0).

When practicing the present invention, the lattice constant of the substrate is
12.60Å to 12.70Å are preferred. The lattice constant of the bismuth-substituted rare earth iron garnet single crystal grown on the substrate must essentially match the lattice constant of the substrate, and in that sense, Pr _3-x Bi with a lattice constant of 12.60Å to 12.70 Å. _x Fe
_{5-y M y O 12 (} M is at least one element selected In, Sc, Ga, from the group consisting of Al, 0.8 ≦ x ≦ 1.8, 0
In other words, ≦ y ≦ 1.0) is preferable.
When the lattice constant of the substrate is 12.60 or less, the absorption loss in the 1 μm band is not so large as the loss level of the conventional bismuth-substituted rare earth iron garnet single crystal, which is not preferable.

When carrying out the present invention, the bismuth substitution amount x
Is preferably 0.8 or more and 1.8 or less. If x is less than 0.8, the Faraday effect decreases, which is not preferable.
If it exceeds 8, fine crystals are precipitated during crystal growth, and there is a disadvantage that a bismuth-substituted rare earth iron garnet single crystal having a predetermined thickness cannot be obtained. When practicing the invention, y
Is preferably 1 or less. If it exceeds 1, the temperature dependence of the Faraday rotation angle becomes large, and the Curie temperature is lowered, which is disadvantageous.

The flux components for liquid phase epitaxial growth of the present invention include lead oxide (PbO), bismuth oxide (Bi ₂ O ₃ ),
It is preferably composed of boron oxide (B ₂ O ₃ ). The liquid phase epitaxial growth temperature of the present invention is not particularly limited, but it is preferably selected appropriately within the range of 650 to 800 ° C. which is a generally-used bismuth-substituted garnet single crystal growth temperature. EXAMPLES Hereinafter, the present invention will be described specifically and in detail by way of Examples with respect to its embodiments and effects. The following examples are for specifically explaining the embodiments and the invention of the present invention. Is not intended to limit the scope of.

[0010]

【Example】

EXAMPLE 1 Lead oxide (PbO) was added to a platinum crucible having a capacity of 1,000 ml (milliliter).
2,000g, bismuth oxide (Bi ₂ O ₃ ) 2,300g, ferric oxide (Fe ₂
O ₃ ) 300 g, boron oxide (B ₂ O ₃ ) 90 g, praseodymium oxide
(Pr ₂ O ₃ ) 31 g and scandium oxide (Sc ₂ O ₃ ) 9 g were charged. This is installed in the predetermined position of the precision vertical tubular electric furnace,
The mixture was heated to 1000 ° C. to be melted, sufficiently stirred and uniformly mixed, and then cooled to a melt temperature of 751 ° C. to obtain a bismuth-substituted magnetic garnet single crystal growing melt.

Then, according to a conventional method, one surface of a (111) garnet single crystal [Sm ₃ (ScGa) ₅ O ₁₂ ] substrate having a lattice constant of 12.641 Å was brought into contact with the surface of the melt obtained here, and the melt Temperature
Epitaxial growth was performed for 4 hours while maintaining the temperature at 751 ° C. to obtain a bismuth-substituted iron garnet single crystal film having a thickness of 130 μm and a composition of Pr _1.6 Bi _1.4 Fe _4.8 Sc _0.2 O ₁₂ .
The thick film had a Faraday rotation coefficient of 3364 deg / cm 2 and a light absorption coefficient of 34 dB / cm 2 at a wavelength of 1.064 μm. Therefore, the figure of merit (= Faraday rotation coefficient / light absorption coefficient) is
The Faraday rotator (with the Faraday rotation angle
The optical absorption loss at 45 degrees is 0.45 dB. The composition analysis was based on plasma emission analysis (manufactured by Seiko Denshi Kogyo Co., Ltd., high frequency induction plasma emission emission spectrometer SPS 1200VR type).

Example 2 A platinum crucible having a capacity of 1,000 ml was charged with 2,000 g of lead oxide (PbO),
Bismuth oxide (Bi ₂ O ₃ ) 2,300 g, ferric oxide (Fe ₂ O ₃ ) 300
g, boron oxide (B ₂ O ₃ ) 83 g, praseodymium oxide (Pr ₂ O ₃ ).
31 g and indium oxide (In ₂ O ₃ ) 20 g were charged. This was placed in a predetermined position in a precision vertical tubular electric furnace, heated to 1000 ° C to melt it, stirred well and mixed uniformly, then cooled to a melt temperature of 766 ° C and bismuth-substituted magnetic. The melt was used for growing a garnet single crystal.

Then, according to a conventional method, one surface of a (111) garnet single crystal [La ₃ (ScGa) ₅ O ₁₂ ] substrate having a lattice constant of 12.662Å was brought into contact with the surface of the melt obtained here, and the melt Temperature
Epitaxial growth was performed for 7 hours while maintaining the temperature at 766 ° C. to obtain a bismuth-substituted magnetic garnet single crystal film having a thickness of 218 μm and a composition of Pr _2.0 Bi _1.0 Fe _4.7 In _0.3 O ₁₂ . The Faraday rotation coefficient at 1.064 μm of this thick film was 2350 deg / cm 2, and the light absorption coefficient was 28 dB / cm. Therefore, the figure of merit is 84deg / dB, and the optical absorption loss in the Faraday rotator is 0.54dB.

Example 3 In a platinum crucible having a capacity of 1,000 ml, 2,000 g of lead oxide (PbO),
Bismuth oxide (Bi ₂ O ₃ ) 2,300 g, ferric oxide (Fe ₂ O ₃ ) 300
g, boron oxide (B ₂ O ₃ ) 90 g, praseodymium oxide (Pr ₂ O ₃ ).
31 g and indium oxide (In ₂ O ₃ ) 42 g were charged. This was placed in a predetermined position in a precision vertical tubular electric furnace, heated to 1000 ° C to melt it, stirred well and mixed uniformly, then cooled to a melt temperature of 758 ° C and bismuth-substituted magnetic. The melt was used for growing a garnet single crystal.

Then, according to a conventional method, one surface of a (111) garnet single crystal [La ₃ (ScGa) ₅ O ₁₂ ] substrate having a lattice constant of 12.725Å was brought into contact with the surface of the melt obtained here, and the melt Temperature
Epitaxial growth was carried out for 4 hours while maintaining the temperature at 758 ° C, the thickness was 154 μm, and Pr _1.3 Bi _1.7 Fe _4.3 In _0.5 Ga _0.2 O
A bismuth-substituted magnetic garnet single crystal film having a composition of ₁₂ was obtained. The Faraday rotation coefficient at 1.064 μm of this thick film was 3660 deg / cm, and the light absorption coefficient was 25 dB / cm. Therefore, the figure of merit is 146 deg / dB, and the optical absorption loss in the Faraday rotator is 0.31 dB.

[0016]

According to the present invention, the wavelength is 0.95 μm to 1.1 μm.
It is possible to provide a low-loss bismuth-substituted magnetic garnet single crystal as a Faraday rotation element for an optical isolator of m.

Claims (1)

[Claims] 1. A bismuth-substituted rare earth iron garnet single crystal grown by a liquid phase epitaxial method on a non-magnetic garnet single crystal substrate having a lattice constant of 12.60Å to 12.70Å, the general formula of which is Pr _3-x Bi. _{x Fe 5-y M y O} 12 (M is an in, Sc,
A bismuth-substituted rare earth iron garnet single crystal for a Faraday rotator, which is at least one element selected from the group consisting of Ga and Al and has 0.8 ≦ x ≦ 1.8 and 0 ≦ y ≦ 1.0).