JP2004168657A - Magnetic garnet single crystal and faraday rotator using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic garnet single crystal in which crystal defects do not occur and a Faraday rotator improved in extinction ratio. <P>SOLUTION: The magnetic garnet single crystal is grown by a liquid phase epitaxial growing method and has a general formula denoted as Bi<SB>a</SB>Pb<SB>b</SB>A<SB>3-a-b</SB>Fe<SB>5-c-d</SB>B<SB>c</SB>Pt<SB>d</SB>O<SB>12</SB>(wherein A is at least an element selected from among Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; B is at least an element selected from among Ga, Al, Sc, Ge and Si; 0<a<3.0; 0<b≤2.0; 0≤c≤2.0; and 0<d≤2.0). <P>COPYRIGHT: (C)2004,JPO

Description

  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.

Optical isolators, optical circulators, or optical attenuators are widely used in optical communication and optical equipment using semiconductor lasers. 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.

For example, Japanese Patent Kokoku 6-46604, 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 and rare earth elements At least one component selected from elements that can be substituted therewith, M is at least one component selected from elements that can be substituted for iron, a is a number from 0.01 to 0.2, b is a number of 0.5 to 2.0, c is a number of 0.01 to 2.0, and d is a number of 0 to 1), and one of M in the above formula A bismuth-substituted rare earth iron garnet is described, which contains, as a part, a tetravalent element other than Pb belonging to the groups IVA and IVB of the periodic table in an atomic ratio of the above general formula of 0.01 or more.

As disclosed in the above publication, Pb ⁴⁺ can be eliminated when a Bi-substituted rare earth iron garnet single crystal is grown by a liquid phase epitaxial method by adding a group IV element, whereby Bi substitution can be performed. It becomes possible to reduce the absorption loss when light passes through the rare earth iron garnet single crystal.

By the way, as shown in Examples disclosed in Japanese Patent Publication No. 6-46604, when a single crystal epitaxial film was grown by liquid phase epitaxial method by adding, for example, TiO ₂ as a group IV element, the obtained result was obtained. The effect of reducing the light absorption loss of the Bi-substituted rare earth iron garnet single crystal epitaxial film is recognized. However, when the thickness of the obtained epitaxial film is about 200 μm or more, many crystal defects are confirmed 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 observation using infrared rays, and the extinction ratio Was also found to decrease.

  The invention described in Japanese Patent Publication No. 6-46604 has a technical problem of reducing light absorption loss of a Bi-substituted rare earth iron garnet single crystal epitaxial film, and has a problem of suppressing generation of crystal defects and improving an extinction ratio. Is not disclosed at all. 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 generation of crystal defects is suppressed.
Another object of the present invention is to provide a Faraday rotator having an improved extinction ratio.

Therefore, the present inventors have studied to obtain a single crystal having a size 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, it has been found that the use of Pt capable of stably forming a tetravalent structure similar to that of a group IV element has a great effect as an additional element. That is, when PtO ₂ or Pt was dissolved in a flux 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. Observation with a polarizing microscope revealed that no crystal defects were observed, and that the light absorption loss was almost zero.

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 Pt d O 12 (A in the formula, Y, La, Ce, Pr , Nd, Sm , Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, at least one element selected from the group consisting of Ga, Al, Sc, Ge, and Si; , B, c, and d are represented by 0 <a <3.0, 0 <b ≦ 2.0, 0 ≦ c ≦ 2.0, and 0 <d ≦ 2.0, respectively. Achieved by garnet single crystals.
The magnetic garnet single crystal according to the present invention is characterized in that the film thickness is 200 μm or more. Further, it is preferable that 0.5 ≦ b / d ≦ 2.0.
Further, the above object is achieved by a Faraday rotator formed of the magnetic garnet single crystal according to the present invention.

The operation of the present invention will be described below. Ti ⁴⁺ and Pt ⁴⁺ are replaced by hexacoordinate Fe sites in the lattice of Bi-substituted rare earth iron garnet. 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 strained. Therefore, when the epitaxial growth proceeds and the film thickness becomes large, the lattice strain is accumulated and many crystal defects occur. It is thought to occur. It is considered that since Pt ⁴⁺ has an ionic radius smaller than that of Fe ³⁺ having six coordinations, no distortion occurs in the garnet lattice, and no crystal defects occur even when the epitaxial film becomes thick. When a Faraday rotator having a Faraday rotation angle of 45 degrees was produced with light having wavelengths of 1.31 μm and 1.55 μm using the single crystal obtained by substituting Fe ³⁺ with Pt ⁴⁺ , no defect inside the crystal was observed, and it was reduced to 40 dB or less. Such an extinction ratio defect no longer occurs. The effect of PtO ₂ and Pt as such additives can be expected to be the same even when other Pt compounds are used.

  In the magnetic garnet single crystal of the present invention, a represents the amount of Bi in the magnetic garnet. The Bi amount a is a factor that determines the rotation capability (deg / μm) of the Faraday rotator, and the larger the Bi amount a, the larger the Faraday rotation capability. The preferred Bi amount a of the magnetic garnet single crystal when used as a Faraday rotator is about 0.6 to 1.5. If the Bi amount a is 0.6 or less, the Faraday rotation ability becomes too small. If 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 under the present circumstances, and a magnetic garnet having a Bi amount a of 3.0 is also obtained by the vacuum film forming technique. 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 represents the amount of nonmagnetic elements that can be substituted for Fe such as Ca and Al. 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.

d represents the amount of Pt. In order to reduce the light absorption loss, the amount of Pb, which is a divalent element, and the amount of Pt, which is a tetravalent element, need to be substantially the same, so that the amount of Pt d is 0 <d ≦ similarly to the amount of Pb. 2.0 is set.
Further, it is preferable that the relationship of 0.5 ≦ b / d ≦ 2.0 is obtained from the relationship with the light absorption loss (insertion loss). For example, in Example 1 described below, the Pb amount b is 0.04 and the Pt amount d is 0.04, so that Pb amount b / Pt amount d = 1. The insertion loss of the Faraday rotator at this time is 0.01 to 0.05 dB. Further, for example, in the second embodiment, since the Pb amount b is 0.04 and the Pt amount d is 0.02, Pb amount b / Pt amount d = 2. At this time, the insertion loss of the Faraday rotator is 0.06 to 0.10 dB. The value generally required for the insertion loss of the Faraday rotator for the optical isolator is 0.10 dB. The composition in which the Pb amount b and the Pt amount d are the same has the smallest insertion loss, the ratio of the Pb amount b and the Pt amount d is different, and the insertion loss is large. Therefore, in order to satisfy the insertion loss of 0.10 dB which is a general required value, a condition of 0.5 ≦ b / d ≦ 2.0 is required.

  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.

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

Hereinafter, [Examples 1] to [Example 4] will be described together with comparative examples as specific examples of the magnetic garnet single crystal according to the present invention and the Faraday rotator using the same.
[Example 1]
In a crucible made of Pt, Yb ₂ O ₃ (weight: 6.747 g), Gd ₂ O ₃ (weight: 6.624 g), B ₂ O ₃ (weight: 43.214 g), Fe ₂ O ₃ (weight: 1444.84 g), PbO (weight: 1189.6 g), Bi ₂ O ₃ (weight: 826.4 g), PtO ₂ (weight: 5.121 g), and melted at about 1000 ° C. After the homogenization, the temperature was lowered at 120 ° C./h (hour), and the temperature was stabilized in a supersaturated state of 820 ° C. Then, while rotating a (Ca, Mg, Zr) -substituted gadolinium gallium garnet (hereinafter referred to as GGG) single crystal substrate having a size of 2 inches φ at 100 revolutions / minute (rpm), a magnetic garnet single crystal film is epitaxially grown. A 505 μm thick 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 inches φ, and no crack was generated in the single crystal film. When the composition of the single crystal film obtained by the fluorescent X-ray method was analyzed, it was Bi _1.12 Gd _1.15 Yb _0.69 Pb _0.04 Fe _4.96 Pt _0.04 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 a non-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 recognized by polarization microscopy using infrared rays, and the film thickness was 400 μm. The Faraday rotation coefficient was 0.113 deg / μm, the insertion loss was 0.01 dB at the maximum of 0.05 dB, the temperature characteristic was 0.067 deg / ° C., and the extinction ratio was 42.1 dB at the maximum of 45.6 dB. (See Table 1).
In the first embodiment, the insertion loss of the Faraday rotator is 0.01 to 0.05 dB, which satisfies the general required value of 0.10 dB or less. At this time, the Pb amount b is 0.04 and the Pt amount d is 0.04, so that Pb amount b / Pt amount d = 1, which is within the range of 0.5 ≦ b / d ≦ 2.0. .

表１ Ｂｉ置換希土類鉄ガーネット単結晶膜の組成と評価結果

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

[Example 2]
The Pt crucible Yb ₂ O _{3 (weight: 6.747g), Gd 2 O 3} ( _{weight: 6.624g), B 2 O 3} ( _{weight: 43.214g), Fe 2 O 3} ( weight: 144.84g) , PbO (weight: 1189.6 g), Bi ₂ O ₃ (weight: 826.4 g), and PtO ₂ (weight: 2.556 g) were melted at about 1000 ° C., stirred, and homogenized. The temperature was lowered at 120 ° C./h, and the temperature was stabilized under a supersaturated state of 820 ° C. Then, a magnetic garnet single crystal film was epitaxially grown while rotating a (Ca, Mg, Zr) -substituted GGG single crystal substrate having a size of 2 inches φ at 100 rpm to obtain a single crystal film having a thickness of 500 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, 15 crystal defects were confirmed in the single crystal film of 2 inch φ, and no crack was generated in the single crystal film. When the composition of the single crystal film obtained by the fluorescent X-ray method was analyzed, it was Bi _1.12 Gd _1.15 Yb _0.69 Pb _0.04 Fe _4.98 Pt _0.02 O ₁₂ . Further, this 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 a non-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 recognized by polarization microscopy using infrared rays, and the film thickness was 400 μm. The Faraday rotation coefficient was 0.113 deg / μm, the insertion loss was 0.16 dB at the maximum and the minimum was 0.06 dB, the temperature characteristic was 0.064 deg / ° C., and the extinction ratio was 44.9 dB at the maximum and 41.6 dB at the minimum. (See Table 1).
In the second embodiment, the insertion loss of the Faraday rotator is 0.06 to 0.10 dB, which satisfies an insertion loss of 0.10 dB or less, which is a general required value. At this time, the Pb amount b is 0.04 and the Pt amount d is 0.02, so that the Pb amount b / Pt amount d = 2, which is within the range of 0.5 ≦ b / d ≦ 2.0. .

[Example 3]
In a Pt crucible, Yb ₂ O ₃ (weight: 10.677 g), Gd ₂ O ₃ (weight: 7.403 g), B ₂ O ₃ (weight: 48.68 g), Fe ₂ O ₃ (weight: 205.58 g) , PbO (weight: 430.5 g) and Bi ₂ O ₃ (weight: 1605.8 g) were filled, melted at about 1050 ° C., stirred, homogenized, and cooled at 120 ° C./h to 885. The temperature was stabilized in a supersaturated state at ° 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 was epitaxially grown to obtain a 620 μm-thick single crystal film.

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, 18 single crystal films having a diameter of 2 inches were found to have 18 crystal defects and no crack was generated in the single crystal film. When the composition of the single crystal film obtained by the fluorescent X-ray method was analyzed, it was Bi _1.16 Gd _1.08 Yb _0.72 Pb _0.04 Fe _4.97 Pt _0.03 O ₁₂ . The Pt contained in the magnetic garnet was eluted from the Pt crucible into the Pb-containing flux. The 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 rotation coefficient, insertion loss, temperature characteristics and extinction ratio, no defects were observed by polarized light microscopy using infrared rays. The Faraday rotation coefficient was 0.188 deg / μm, the insertion loss was 0.03 dB at the maximum of 0.07 dB, the temperature characteristic was 0.064 deg / ° C., and the extinction ratio was 41.9 dB at the maximum of 45.6 dB. (See Table 1).
In the third embodiment, the insertion loss of the Faraday rotator is 0.03 to 0.07 dB, which satisfies a general required value of 0.10 dB or less. At this time, the Pb amount b is 0.04 and the Pt amount d is 0.03, so that Pb amount b / Pt amount d ≒ 1.33, which falls within the range of 0.5 ≦ b / d ≦ 2.0. ing.

[Example 4]
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: 144.84 g) in a Pt crucible , PbO (weight: 1189.6 g), Bi ₂ O ₃ (weight: 826.4 g), and PtO ₂ (weight: 5.121 g) were filled, melted at about 1000 ° C., stirred, and homogenized. Thereafter, the temperature was lowered at 120 ° C./h, and the temperature was stabilized under a supersaturated state of 804 ° C. Then, a magnetic garnet single crystal film was epitaxially grown while rotating a (Ca, Mg, Zr) substituted GGG single crystal substrate having a size of 2 inches φ at 100 rpm to obtain a single crystal film having a thickness of 360 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, 10 crystal defects were confirmed in the single crystal film of 2 inch φ, and no crack was generated in the single crystal film. When the composition of the single crystal film obtained by the fluorescent X-ray method was analyzed, it was Bi _1.30 Gd _0.90 Yb _0.76 Pb _0.04 Fe _4.96 Pt _0.04 O ₁₂ . The 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 rotation coefficient, insertion loss, temperature characteristics and extinction ratio, no defects were observed by a polarizing microscope using infrared rays. The Faraday rotation coefficient was 0.225 deg / μm, the insertion loss was 0.01 dB at the maximum of 0.04 dB, the temperature characteristic was 0.063 deg / ° C., and the extinction ratio was 42.1 dB at the maximum of 45.7 dB. (See Table 1).
In the fourth embodiment, the insertion loss of the Faraday rotator is 0.01 to 0.04 dB, which satisfies the general required value of 0.10 dB or less. At this time, the Pb amount b is 0.04 and the Pt amount d is 0.04, so that Pb amount b / Pt amount d = 1, which is within the range of 0.5 ≦ b / d ≦ 2.0. .

[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: 144.84 g) in a Pt crucible , PbO (weight: 1189.6 g), Bi ₂ O ₃ (weight: 826.4 g), and TiO ₂ (weight: 1.810 g) were charged, melted at about 1000 ° C., stirred, and homogenized. Thereafter, the temperature was lowered at 120 ° C./h, and the temperature was stabilized under a supersaturated state of 804 ° C. Then, a magnetic garnet single crystal film was epitaxially grown while rotating a (Ca, Mg, Zr) -substituted GGG single crystal substrate having a size of 2 inches at 100 rpm to obtain a single crystal film having a thickness of 355 μm.

The surface of this magnetic garnet single crystal film was rough, and the number of crystal defects on the surface was evaluated. As a result, 166 crystal defects were confirmed in the single crystal film of 2 inch φ, and no crack was generated in the single crystal film. When the composition of the single crystal film obtained by the fluorescent X-ray method was analyzed, it was Bi _1.30 Gd _0.90 Yb _0.76 Pb _0.04 Fe _4.96 Pt _0.01 Ti _0.03 O ₁₂ . The 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 the Faraday rotator was cut into 3 mm squares to evaluate internal crystal defects, Faraday rotation coefficient, insertion loss, temperature characteristics and extinction ratio, one to two defects were observed by polarization microscope observation using infrared rays. At a film thickness of 200 μm, the Faraday rotation coefficient is 0.225 deg / μm, the insertion loss is 0.02 dB at a maximum of 0.04 dB, the temperature characteristic is 0.063 deg / ° C., and the extinction ratio is 36.9 dB at a maximum of 38.9 dB. (See Table 1).
In this comparative example, the insertion loss of the Faraday rotator is 0.02 to 0.04 dB, which satisfies a general required value of 0.10 dB or less. This is because the present comparative example is included in the invention disclosed in Japanese Patent Publication No. 6-46604.

Claims (4)

Grown by liquid phase epitaxial growth method,
Formula _{Bi a Pb b A 3-ab} Fe 5-cd B c Pt d O 12
(A in the formula is at least one element selected from Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and B is Ga, At least one element selected from Al, Sc, Ge, and Si, a, b, c, and d are respectively 0 <a <3.0, 0 <b ≦ 2.0, and 0 ≦ c ≦ 2.0. , 0 <d ≦ 2.0)
A magnetic garnet single crystal, characterized by being represented by: The magnetic garnet single crystal according to claim 1,
A magnetic garnet single crystal having a thickness of 200 μm or more. A magnetic garnet single crystal according to claim 1 or 2,
A magnetic garnet single crystal, wherein 0.5 ≦ b / d ≦ 2.0. A Faraday rotator made of the magnetic garnet single crystal according to claim 1.