JP2001044027A - Magnetic garnet single crystal and faraday rotator using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic garnet single crystal, where occurrence of crystal defect is suppressed and to provide a Faraday rotator improved in quenching ratio, related to a magnetic garnet single crystal and a Faraday rotator using it. SOLUTION: A magnetic garnet single crystal is used, which is grown by a liquid-crystal epitaxial growth method and is represented by a general expression BiaPbbA3-a-bFe5-c-dBcGedO12. Where A is at least one kind of element selected from among Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, B is at least one kind of element selected from among Ga, Al, Sc, Pt, and Si, and 0<a<3.0, 0<b<=2.0, 0<=c<=2.0, 0<d<=2.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic garnet single crystal and a Faraday rotator utilizing the magneto-optical effect using the same. A Faraday rotator using a magnetic garnet single crystal is used for a magneto-optical element such as an optical isolator, an optical circulator, or an optical attenuator.

[0002]

2. Description of the Related Art An optical isolator, an optical circulator, or an optical attenuator is widely used in optical communication and optical equipment using a semiconductor laser. One of the essential elements of these devices is a Faraday rotator. As the Faraday rotator, a single crystal of YIG (yttrium iron garnet) and a single crystal of bismuth (Bi) -substituted rare earth iron garnet are known. A Faraday rotator using a single crystal film has become mainstream.

[0003] For example, Kokoku 6-46604 and JP-grown by liquid phase epitaxial growth method, the general formula _{R 3- (a + b) Pb} a Bi b Fe 5-c M c O 12-d (R is M is at least one component selected from rare earth elements and elements that can be replaced with it, M is at least one component selected from elements that can be replaced with iron elements, and a is 0.01 to 0.2.
, B is a number from 0.5 to 2.0, c is 0.01 to 2.0
And d is a number from 0 to 1).
And groups IVA and IV in the periodic table as part of M in the above formula.
A bismuth-substituted rare earth iron garnet is described which contains a tetravalent element other than Pb belonging to Group B as an atomic ratio of the above general formula of 0.01 or more.

As disclosed in the above publication, by adding a group IV element, when growing a Bi-substituted rare earth iron garnet single crystal by a liquid phase epitaxial method, Pb ⁴⁺
Can be eliminated, whereby absorption loss when light is transmitted through the Bi-substituted rare earth iron garnet single crystal can be reduced.

[0005]

[Problems to be Solved by the Invention]
As shown in Examples disclosed in Japanese Patent No. 46604, when a single crystal epitaxial film is grown by a liquid phase epitaxial method by adding, for example, TiO ₂ as a group IV element, the obtained Bi-substituted rare earth iron garnet The effect of reducing the light absorption loss of the crystal epitaxial film is recognized. However, when the thickness of the obtained epitaxial film is about 200 μm or more, many crystal defects are found on the film surface. When such a crystal surface was polished to form a non-reflective film and a Faraday rotator for an optical isolator was fabricated, many defects were confirmed inside the Faraday rotator by infrared observation, and the extinction ratio Was also found to decrease.

The invention described in Japanese Patent Publication No. 46604/1994 has a technical problem of reducing the light absorption loss of a Bi-substituted rare earth iron garnet single crystal epitaxial film, suppressing the generation of crystal defects and improving the extinction ratio. It does not disclose anything about the task of making it work. If the generation of crystal defects in the Bi-substituted rare earth iron garnet single crystal epitaxial film can be suppressed, the extinction ratio of the Faraday rotator can be improved. The performance of the optical communication component can be improved.

An object of the present invention is to provide a magnetic garnet single crystal in which the occurrence of crystal defects is suppressed. Another object of the present invention is to provide a Faraday rotator having an improved extinction ratio.

[0008]

Therefore, the present inventors have studied to obtain a single crystal of about 200 μm or more without generating many crystal defects and to study an additive for achieving a reduction in light absorption. As a result, they have found that the use of Ge as an additive element has a great effect. That is, GeO
_{When 2} was added to grow a Bi-substituted rare earth iron garnet single crystal having a thickness of 200 μm or more, the number of crystal defects on the surface of the epitaxial film was significantly reduced, and the inside of the single crystal was observed with a polarizing microscope using infrared rays. However, no crystal defects were observed, and the light absorption loss could be reduced to almost zero (zero).

[0009] This object is grown by liquid phase epitaxial growth method, the general formula _{Bi a Pb b A 3-ab} Fe 5-cd B
_c Ge _d O ₁₂ (where A is Y, La, Ce, Pr, N
d, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
At least one element selected from m, Yb and Lu, B is at least one element selected from Ga, Al, Sc, Pt and Si, and a, b, c and d are each 0 <
a <3.0, 0 <b ≦ 2.0, 0 ≦ c ≦ 2.0, 0 <d
.Ltoreq.2.0). The magnetic garnet single crystal according to the present invention is characterized in that the film thickness is 200 μm or more. The above object is also achieved by a Faraday rotator formed of the magnetic garnet single crystal of the present invention.

The operation of the present invention will be described below. T
i ⁴⁺ and Ge ⁴⁺ are mainly Bi-substituted rare earth iron garnets
It is replaced by the lattice of the coordinated Fe site. However, since Ti ⁴⁺ has an ionic radius larger than that of Fe ³⁺ having six coordinations, the lattice of the Bi-substituted rare earth iron garnet is distorted. Therefore, when the epitaxial growth proceeds and the film becomes thicker, lattice distortion is accumulated, and many crystal defects occur. It is thought to occur. Since Ge ⁴⁺ has an ionic radius smaller than that of Fe ³⁺ having six coordinations, no distortion occurs in the garnet lattice, and it is considered that no crystal defects occur even when the epitaxial film is thickened. This Ge ⁴⁺
Wavelength of 1.13 μm and 1.5
When a Faraday rotator having a Faraday rotation angle of 45 degrees was produced using light of 5 μm, no defect inside the crystal was recognized, and 40 dB was obtained.
The following extinction ratio defects did not occur. The effect of GeO ₂ as such an additive is another GeO ₂
Similar effects can be expected by using a compound.

[0011] In the magnetic garnet single crystal of the present invention, a represents Bi content in the magnetic garnet. B
The i amount a is a factor that determines the rotational power (deg / μm) of the Faraday rotator, and the larger the Bi amount a, the larger the Faraday rotational power. The preferred Bi amount a of the magnetic garnet single crystal when used as a Faraday rotator is about 0.6 to
1.5. When the Bi amount a is 0.6 or less, the Faraday rotation ability becomes too small. When the Bi amount a is 1.5 or more, a phase other than garnet is precipitated, and normal epitaxial growth of the magnetic garnet may not be performed. However, a magnetic garnet having a Bi amount a of 0.6 or less can be experimentally manufactured at present, and the Bi amount a
Of 3.0 is also obtained. Therefore, the Bi amount a of the magnetic garnet single crystal for producing the Faraday rotator is set to 0 <a <3.0 in the present invention.

B represents the amount of Pb in the magnetic garnet. Since garnet having a Pb amount b of at least about 2.0 can exist in the state of a sintered body, 0 <b ≦ 2.0 is set in the present invention. c is Ca or Al
Represents the amount of nonmagnetic element that can be substituted for Fe.
When the amount c of the non-magnetic element exceeds about 2.0, the magnetic garnet changes from a ferrimagnetic substance to a paramagnetic substance, so that the Faraday rotation ability becomes extremely small and cannot be used as a rotor.
Therefore, in the present invention, the nonmagnetic element amount c is set to 0 ≦ c ≦ 2.0.
Is set to d represents the amount of Ge. In order to reduce the light absorption loss, it is necessary to make the amount of Pb, which is a divalent element, and the amount of Ge, which is a tetravalent element, almost equal.
The Ge amount d is set to 0 <d ≦ 2.0 similarly to the Pb amount.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiment of the present invention, a Bi-substituted rare earth iron garnet single crystal film having a thickness of 200 μm or more containing Ge is grown from a flux containing Pb. Using the obtained Bi-substituted rare earth iron garnet single crystal film, a Faraday rotator having a small light absorption loss, few crystal defects and a high extinction ratio can be stably manufactured.

[0014]

EXAMPLES [Examples] to [Example 3] will be described below along with Comparative Examples as specific examples of a magnetic garnet single crystal according to the present invention and a Faraday rotator using the same.

[Example 1] Yb ₂ was placed in a Pt crucible.
O ₃ (weight: 6.747 g), Gd ₂ O ₃ (weight: 6.62)
4 g), B ₂ O ₃ (weight: 43.214 g), Fe ₂ O
₃ (weight: 144.84 g), PbO (weight: 118)
9.6 g), Bi ₂ O ₃ (weight: 826.4 g), GeO
₂ Fill the material (weight 2.360g) and put it at about 1000 ° C
After melting and stirring to homogenize, the temperature was lowered at 120 ° C./h (hour), and the temperature was stabilized in a supersaturated state at 820 ° C. It has a size of 2 inches φ (Ca, M
g, Zr) A magnetic garnet single crystal film was epitaxially grown while rotating a single crystal substrate of gadolinium gallium garnet (hereinafter referred to as GGG) at 100 revolutions / minute (rpm) to obtain a single crystal film having a thickness of 495 μm.

The surface of this magnetic garnet single crystal film is mirror-finished, and the number of crystal defects on the surface is evaluated as 2 inches φ.
Twelve crystal defects were confirmed in the single crystal film of No. 1, and no crack was generated in the single crystal film. The composition of the single crystal film obtained by the fluorescent X-ray method was analyzed to _find that Bi _1.12 Gd _1.15 Yb _0.69 Pb _0.04
Fe _4.96 Pt _0.01 Ge _0.03 O ₁₂ . The magnetic garnet single crystal film was polished with light having a wavelength of 1.55 μm so that the Faraday rotation angle was 45 deg., And an anti-reflection film was provided on both surfaces to produce a Faraday rotator for a wavelength of 1.55 μm.

When this Faraday rotator was cut into 3 mm squares to evaluate internal crystal defects, Faraday rotability, insertion loss, temperature characteristics and extinction ratio, no defects were observed by a polarizing microscope using infrared rays. Is 400 μm, the Faraday rotation coefficient is 0.113 deg / μm, the insertion loss is 0.05 dB at the maximum and 0.01 dB at the minimum, and the temperature characteristic is 0.1 dB.
067 deg / ° C, extinction ratio is 45.1 dB at maximum and 4 at minimum
A value of 2.0 dB was obtained (see Table 1).

[0018]

[Table 1] Table 1 Composition and evaluation results of Bi-substituted rare earth iron garnet single crystal film

Example 2 Tb ₂ O was placed in a Pt crucible.
₃ (weight: 14.110 g), B ₂ O ₃ (weight: 46.4)
5 g), Fe ₂ O ₃ (weight: 148.82 g), PbO
(Weight: 1054.4 g), Bi ₂ O ₃ (weight: 965.
8g), filled with GeO ₂ (weight: 2.522 g), melted at about 1000 ° C., stirred and homogenized.
The temperature was lowered at a rate of ° C / h, and the temperature was stabilized under a supersaturated state of 833 ° C. It has a size of 2 inches φ (Ca, M
g, Zr) The magnetic garnet single crystal film was epitaxially grown while rotating the substituted GGG single crystal substrate at 100 rpm to obtain a single crystal film having a thickness of 460 μm.

The surface of this magnetic garnet single crystal film was in a mirror state, and when the number of crystal defects on the surface was evaluated, fifteen crystal defects were confirmed in the single crystal film of 2 inch φ, and no crack was generated in the single crystal film. . The composition of the single crystal film obtained by the X-ray fluorescence method was analyzed to _find that Bi _0.80 Tb _2.16 Pb _0.04 Fe _4.96
Pt _0.01 Ge _0.03 O ₁₂ . Further, this magnetic garnet single crystal film was polished with light having a wavelength of 1.31 μm so that the Faraday rotation angle was 45 deg, and a non-reflection film was provided on both surfaces to produce a Faraday rotator for a wavelength of 1.31 μm.

When this Faraday rotator was cut into 3 mm squares to evaluate internal crystal defects, Faraday rotability, insertion loss, temperature characteristics and extinction ratio, no defects were observed by a polarizing microscope using infrared rays. Is 352 μm, the Faraday rotation coefficient is 0.128 deg / μm, the insertion loss is 0.05 dB at the maximum and 0.02 dB at the minimum, and the temperature characteristic is 0.2 μm.
037 deg / ° C, extinction ratio is 45.8 dB at maximum and 4 at minimum
A value of 2.8 dB was obtained (see Table 1).

Example 3 Yb ₂ O ₃ (weight: 8.434 g) and Gd ₂ O ₃ (weight: 5.300) were placed in a Pt crucible.
g), B ₂ O ₃ (weight: 43.214 g), Fe ₂ O ₃ (weight: 144.84 g), PbO (weight: 1189.6)
g), Bi ₂ O ₃ (weight: 826.4 g) and GeO ₂ (weight: 2.360 g) were filled, melted at about 1000 ° C., stirred, homogenized, and then cooled at 120 ° C./h. The temperature was lowered and the temperature was stabilized under a supersaturated state of 804 ° C. Then, while rotating a (Ca, Mg, Zr) -substituted GGG single crystal substrate having a size of 2 inches φ at 100 rpm, a magnetic garnet single crystal film is epitaxially grown to a thickness of 35 mm.
A 0 μm single crystal film was obtained.

The surface of this magnetic garnet single crystal film was in a mirror state, and when the number of crystal defects on the surface was evaluated, ten single crystal defects were confirmed in the single crystal film of 2 inch φ, and no crack was generated in the single crystal film. . The composition of the single crystal film obtained by the fluorescent X-ray method was analyzed to _find that Bi _1.30 Gd _0.90 Yb _0.76 Pb _0.04
Fe _4.96 Pt _0.01 Ge _0.03 O ₁₂ . Further, this magnetic garnet single crystal film was polished with light having a wavelength of 1.31 μm so that the Faraday rotation angle was 45 deg., And a non-reflection film was provided on both sides to produce a Faraday rotator for a wavelength of 1.31 μm.

When this Faraday rotator was cut into 3 mm squares to evaluate internal crystal defects, Faraday rotability, insertion loss, temperature characteristics and extinction ratio, no defects were observed by observation with a polarizing microscope using infrared rays. Is 200 μm, the Faraday rotation coefficient is 0.225 deg / μm, the insertion loss is 0.03 dB at the maximum and 0.01 dB at the minimum, and the temperature characteristic is 0.2 μm.
063 deg / ° C, extinction ratio is 45.5 dB at maximum and 4 at minimum
A value of 3.1 dB was obtained (see Table 1).

[Comparative Example] Yb ₂ O ₃ (weight:
8.434 g), Gd ₂ O ₃ (weight: 5.300 g), B
₂ O ₃ (weight: 43.214 g), Fe ₂ O ₃ (weight: 14
4.84 g), PbO (weight: 1189.6 g), Bi
₂ O ₃ (weight: 826.4 g), TiO ₂ (weight: 1.8)
10 g), melted at about 1000 ° C., stirred and homogenized, then cooled at 120 ° C./h to 804 ° C.
The temperature was stabilized under supersaturated conditions. And 2 inches φ
The magnetic garnet single crystal film was epitaxially grown while rotating the (Ca, Mg, Zr) -substituted GGG single crystal substrate having the above-mentioned size at 100 rpm to obtain a single crystal film having a thickness of 355 μm.

The surface of this magnetic garnet single crystal film is dirty, and the number of crystal defects on the surface is evaluated.
In the single crystal film, 166 crystal defects were confirmed, and no crack was generated in the single crystal film. The composition of the single crystal film obtained by the fluorescent X-ray method was analyzed to _find that Bi _1.30 Gd _0.90 Yb _0.76 Pb _0.04
Fe _4.96 Pt _0.01 Ti _0.03 O ₁₂ . Further, this magnetic garnet single crystal film was polished with light having a wavelength of 1.31 μm so that the Faraday rotation angle was 45 deg, and a non-reflection film was provided on both surfaces to produce a Faraday rotator for a wavelength of 1.31 μm.

When this Faraday rotator was cut into 3 mm squares to evaluate internal crystal defects, Faraday rotation coefficient, insertion loss, temperature characteristics and extinction ratio, one or two defects were observed by a polarizing microscope using infrared rays. Accepted, film thickness 2
Faraday rotation coefficient is 0.225 deg / μ at 00 μm
m, insertion loss is 0.04 dB at the maximum and 0.02 dB at the minimum,
The temperature characteristic is 0.063 deg / ° C, and the extinction ratio is 38.
The minimum was 36.9 dB at 9 dB (see Table 1).

[0028]

As described above, according to the present invention, it is possible to obtain a magnetic garnet single crystal having not only a small light absorption loss but also few crystal defects. Further, a Faraday rotator having a high extinction ratio can be stably obtained.

Claims (3)

[Claims] 1. A grown by liquid phase epitaxial growth method, the general formula _{Bi a Pb b A 3-ab} Fe 5-cd B c Ge d O 12 (A in the formula, Y, La, Ce, Pr, Nd, Sm, E
u, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu
At least one element selected from the group consisting of
At least one element selected from l, Sc, Pt, and Si, a, b, c, and d are respectively 0 <a <3.0, 0 <
b ≦ 2.0, 0 ≦ c ≦ 2.0, 0 <d ≦ 2.0). 2. The magnetic garnet single crystal according to claim 1, wherein the thickness of the magnetic garnet single crystal is 200 μm or more. 3. A Faraday rotator made of the magnetic garnet single crystal according to claim 1 or 2.