JP2012036031A - Garnet type single crystal for faraday rotator and optical isolator using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a garnet type single crystal for a Faraday rotator that has a large Verdet constant, can fully suppress the occurrence of cracks and can be made larger; and an optical isolator using the single crystal.SOLUTION: The garnet type single crystal for a Faraday rotator is represented by the following general formula: (TbL)(ScMN)AlO(In the formula, M represents a quadrivalent ion, N represents a bivalent ion, L represents at least one kind chosen from the group consisting of M, N and Sc, and x, y, w and z satisfy the following formulae. 0<x<0.3, 0<y<0.3, 0<x+y<0.6, 0≤z<0.3, 0≤w<0.5).

Description

  The present invention relates to a garnet-type single crystal for a Faraday rotator and an optical isolator using the same.

  The optical isolator has a Faraday rotator that rotates the polarization plane of incident light by applying a magnetic field, and has recently been used not only for optical communication but also for laser processing machines.

Conventionally, as a Faraday rotator used in such an optical isolator, a terbium gallium garnet single crystal (TGG: Tb ₃ Ga ₅ O ₁₂ ), a terbium aluminum garnet single crystal (TAG: Tb ₃ Al). ₅ O ₁₂ ), terbium / scandium / aluminum / garnet type single crystal (TSAG: Tb ₃ Sc ₂ Al ₃ O ₁₂ ) and the like are known (Non-patent Documents 1 and 2 below and Patent Document 1).

JP 2002-293893 A

Journal of Crystal Growth 306 (2007) p. 195-199 Cryst. Res. Technol. 34 (1999) 5-6, p. 615-619

  However, with TGG, it is difficult to increase the size of a single crystal because of the rapid evaporation of gallium oxide as a raw material component during the growth of the single crystal, and the yield is poor. This is a factor that makes it difficult to reduce costs. Moreover, since TGG has a small Verde constant, it is necessary to manufacture a Faraday rotator using a large crystal in order to obtain a Faraday rotator exhibiting a large Faraday rotation angle, and it has been difficult to reduce the size of the Faraday rotator.

  Moreover, although TAG has a larger Verde constant than TGG, it is difficult to grow a large single crystal as compared with TGG, and it has not yet been put into practical use.

  Furthermore, although TSAG has a larger Verde constant than TGG and can grow a large single crystal compared to TAG, cracks are more likely to occur than TGG, making it difficult to increase the size of the single crystal.

  The present invention has been made in view of the above circumstances, has a large Verde constant, can sufficiently suppress generation of cracks, and can be increased in size, and a garnet-type single crystal for a Faraday rotator and light using the same An object is to provide an isolator.

In order to solve the above-mentioned problems, the present inventors have the following general formula described in Patent Document 1 described below:
_{(Tb 3-x Sc x)} Sc 2 Al 3 O 12
As a result of diligent research focusing on the single crystal represented by the formula, it was found that the above problem can be solved by substituting a part of hexacoordinated Sc with a tetravalent ion and a divalent ion. The present invention has been completed.

That is, the present invention is a garnet-type single crystal for a Faraday rotator represented by the following general formula (1).
_{(Tb 3-z L z)} (Sc 2-x-y M x N y) Al 3 O 12-w (1)
(Wherein M represents a tetravalent ion, N represents a divalent ion, L represents at least one selected from the group consisting of M, N and Sc, and x, y, z and w satisfy the following formula: .
0 <x <0.3
0 <y <0.3
0 <x + y <0.6
0 ≦ z <0.3
0 ≦ w <0.5)

  The garnet-type single crystal of the present invention has a large Verde constant. For this reason, the Faraday rotator obtained by using this single crystal can be miniaturized while exhibiting a large Faraday rotation angle. Moreover, according to the garnet-type single crystal of the present invention, the generation of cracks can be sufficiently suppressed and the size can be increased. For this reason, when a Faraday rotator is cut out from the single crystal of the present invention, a large amount of Faraday rotator can be obtained.

  Regarding the reason why the above effect can be obtained, the present inventors presume as follows. That is, the present inventors speculate that the reason why the single crystal of the present invention has a large Verde constant is because the single crystal of the present invention has a basic structure of TSAG having a large Verde constant. Yes. In addition, the reason why it is possible to realize a large single crystal in which generation of cracks is sufficiently suppressed is that a part of hexacoordinated Sc in TSAG is replaced with tetravalent ions and divalent ions. The present inventors speculate that the garnet structure is extremely stabilized.

In the general formula (1), x, y, z and w are the following formulas:
x = y
0 ≦ z <0.2
0 ≦ w <0.3
0 <x <0.1
It is preferable to satisfy. In this case, compared with the case where x, y, z, and w do not satisfy the above formula, the electrical neutral condition is easily satisfied, and the stability of the crystal is further improved.

  Moreover, this invention is an optical isolator which has a Faraday rotator, Comprising: The said Faraday rotator is an optical isolator comprised by the said garnet-type single crystal for Faraday rotators.

  In this optical isolator, the Faraday rotator is composed of the garnet-type single crystal, and the garnet-type single crystal has a large Verde constant. For this reason, the Faraday rotator can be reduced in size while exhibiting a large Faraday rotation angle. For this reason, according to the optical isolator of the present invention, it is possible to reduce the size. In the optical isolator of the present invention, the Faraday rotator is composed of the garnet-type single crystal, and a large amount of the Faraday rotator can be obtained from the single crystal. Therefore, the cost of the Faraday rotator can be reduced. . Therefore, according to the optical isolator of the present invention, the price can be reduced.

  According to the present invention, there is provided a garnet-type single crystal for a Faraday rotator that has a large Verde constant, can sufficiently suppress generation of cracks, and can be increased in size, and an optical isolator using the same.

It is a figure which shows one Embodiment of the optical isolator which concerns on this invention. It is process drawing which shows the process of growing the garnet-type single crystal for Faraday rotators which concerns on this invention using a crystal growth apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing an embodiment of an optical isolator according to the present invention. As shown in FIG. 1, the optical isolator 10 includes a polarizer 1, an analyzer 2, and a Faraday rotator 3 disposed between the polarizer 1 and the analyzer 2. Here, the polarizer 1 and the analyzer 2 are arranged so as to form an angle of 45 °, for example, so that their transmission axes are not parallel to each other.

  For example, a magnetic field B is applied to the Faraday rotator 3 along the direction from the polarizer 1 to the analyzer 2, that is, the incident direction of the light L, and the Faraday rotator 3 is applied with the magnetic field B. Thus, the polarization plane of the light L that has passed through the polarizer 1 is rotated so as to pass through the transmission axis of the analyzer 2.

  Here, the Faraday rotator 3 will be described in detail.

The Faraday rotator 3 is composed of a garnet-type single crystal for a Faraday rotator represented by the following general formula (1).
_{(Tb 3-z L z)} (Sc 2-x-y M x N y) Al 3 O 12-w (1)
(Wherein M represents a tetravalent ion, N represents a divalent ion, L represents at least one selected from the group consisting of M, N and Sc, and x, y, z and w satisfy the following formula: .
0 <x <0.3
0 <y <0.3
0 <x + y <0.6
0 ≦ z <0.3
0 ≦ w <0.5)

Here, the single crystal represented by the general formula (1) represents a terbium / scandium / aluminum / garnet type single crystal. When the single crystal represented by the general formula (1) is based on Tb ₃ Sc ₂ Al ₃ O ₁₂ , a part of Sc is tetravalent due to a part of (Sc _2−xy M _x N _y ). of shows to be replaced by ion M and divalent ions _{N, (Tb 3-z L} z) a portion of Tb by portions of the at least one selected from the group consisting of M, N and Sc It can be substituted with.

  M can be used without any particular limitation as long as it is a tetravalent ion. As M, for example, Si, Ge, Sn, Ti, Zr, or Hf is used. These may be used alone or in combination of two or more. Among them, as M, Si is most preferable because it is stable and inexpensive among tetravalent ions.

  N can be used without particular limitation as long as it is a divalent ion. For example, Ca, Mg, Be, Sr, Ba, Zn, or Ni is used as N. These may be used alone or in combination of two or more. Among these, as N, Ca is most preferable because it is stable and inexpensive among divalent ions.

  L may be at least one selected from the group consisting of M, N, and Sc, may be M, N, or Sc alone, or may be two or more selected from M, N, and Sc. May be.

  The garnet-type single crystal represented by the general formula (1) has a large Verde constant. For this reason, the Faraday rotator 3 can be downsized while exhibiting a large Faraday rotation angle. Therefore, it is possible to reduce the size of the optical isolator 10. Moreover, the garnet-type single crystal represented by the general formula (1) can sufficiently suppress the occurrence of cracks and can be increased in size. For this reason, when the Faraday rotator 3 is cut out from the single crystal, a large amount of Faraday rotator can be obtained. For this reason, the price of the Faraday rotator 3 can be reduced, and the price of the optical isolator 10 can also be reduced.

  In the general formula (1), x satisfies the formula 0 <x <0.3. If x does not satisfy this equation, the generation of cracks cannot be sufficiently suppressed. x is preferably 0.01 or more because tetravalent ions are more stably present at the 6-coordination position and the generation of cracks can be more sufficiently suppressed.

  In the general formula (1), y satisfies the formula 0 <y <0.3. If y does not satisfy this equation, the occurrence of cracks cannot be sufficiently suppressed. y is preferably 0.01 or more, since divalent ions are more stably present at the 6-coordinate position and the generation of cracks can be more sufficiently suppressed.

  In the general formula (1), x and y satisfy the formula 0 <x + y <0.6. If x + y does not satisfy this equation, the generation of cracks cannot be sufficiently suppressed. (X + y) is preferably 0.02 to 0.4 because each ion of M and N exists more stably at the 6-coordinate position and can more sufficiently suppress the occurrence of cracks.

  In the general formula (1), z satisfies the formula 0 ≦ z <0.3. If z does not satisfy this formula, the garnet-type single crystal does not have a large Verde constant, and it is impossible to obtain a large single crystal in which the occurrence of cracks is sufficiently suppressed. z is preferably 0 to 0.2 from the viewpoint of sufficiently suppressing the occurrence of cracks, and in particular, z is preferably 0.

  In the general formula (1), w satisfies the formula 0 ≦ w <0.5. If w does not satisfy this equation, oxygen defects become excessive, the garnet-type single crystal does not have a large Verde constant, and a large single crystal in which the occurrence of cracks is sufficiently suppressed cannot be obtained. It is preferable that w is 0 because there is no oxygen defect in the single crystal. When w is not 0, the number of oxygen atoms is smaller than 12, which is the number of oxygen atoms in the garnet-type crystal, but this is due to a defect in the single crystal.

In the general formula (1), x, y, z and w are represented by the following formula:
x = y
0 ≦ z <0.2
0 ≦ w <0.3
0 <x <0.1
Are preferably satisfied simultaneously. In this case, there is an advantage that the crystal is more stabilized and a larger crystal can be grown as compared with the case where x, y, z, and w do not satisfy the above formula.

  Next, a method for manufacturing the Faraday rotator 3 will be described.

  First, a crystal growth apparatus for growing a garnet-type single crystal constituting the Faraday rotator 3 will be described with reference to FIG. FIG. 2 is a process diagram showing a process of growing a garnet-type single crystal for a Faraday rotator according to the present invention using a crystal growing apparatus. As shown in FIG. 2, the crystal growing apparatus 20 mainly includes an iridium crucible 21, a ceramic cylindrical container 22 that accommodates the crucible 21, and a high-frequency coil 23 that is wound around the cylindrical container 22. I have. The high-frequency coil 23 is for generating an induced current in the crucible 21 and heating the crucible 21.

  Next, a method for growing the single crystal using the crystal growth apparatus 20 will be described.

First, Tb ₄ O ₇ powder, Sc ₂ O ₃ powder, Al ₂ O ₃ powder, MO ₂ powder and NO powder are prepared.

Then, the composition of which should be encouraged single crystal, i.e., if x in the general formula (1), y, z and w are determined, on the basis of its composition, _Tb 4 _{O 7} powder, _Sc 2 _{O 3} powder The blending ratio of Al ₂ O ₃ powder, MO ₂ powder and NO powder is determined. At this time, Tb ₄ O ₇ powder, Sc ₂ O ₃ powder, Al ₂ O ₃ powder, MO ₂ powder and NO powder are as follows.

That, _Tb 4 _{O 7} blending ratio of the powder is usually, _Tb 4 _{O 7} powder, _Sc 2 _{O 3} powder, _Al 2 _{O 3} powder, based on the total moles of MO ₂ powder and NO powder, 20 to 24 mol% And

The mixing ratio of Sc ₂ O ₃ powder is usually 22 to 31 mol% based on the total number of moles of Tb ₄ O ₇ powder, Sc ₂ O ₃ powder, Al ₂ O ₃ powder, MO ₂ powder and NO powder. .

The mixing ratio of the Al ₂ O ₃ powder is usually 40 to 46 mol% based on the total mole of the Tb ₄ O ₇ powder, Sc ₂ O ₃ powder, Al ₂ O ₃ powder, MO ₂ powder and NO powder.

The mixing ratio of the MO ₂ powder is usually greater than 0 mol% and not more than 5 mol%, based on the total mol of Tb ₄ O ₇ powder, Sc ₂ O ₃ powder, Al ₂ O ₃ powder, MO ₂ powder and NO powder. To do.

The mixing ratio of the NO powder is usually greater than 0 mol% and not more than 5 mol% based on the total mol of Tb ₄ O ₇ powder, Sc ₂ O ₃ powder, Al ₂ O ₃ powder, MO ₂ powder and NO powder. .

Then, obtain the _Tb 4 _{O 7} powder blending ratio determined as described above, _Sc 2 _{O 3} powder, _Al 2 _{O 3} powder, the mixed powder was dry-mixed to MO ₂ powder and NO powder.

  Next, the mixed powder is packed in the crucible 21.

  Subsequently, a current is applied to the high frequency coil 23. Then, the crucible 21 is heated, the mixed powder is melted in the crucible 21, and the melt 24 is obtained. Subsequently, a rod-shaped seed crystal 25 is prepared, the tip of the seed crystal 25 is immersed in the melt 24, and then the seed crystal 25 is pulled up at a predetermined pulling speed while rotating at a predetermined rotation speed.

  At this time, as the seed crystal 25, for example, a garnet single crystal such as yttrium, aluminum, and garnet (YAG) can be used.

  The rotation speed of the seed crystal 25 is preferably 3 to 50 rpm, more preferably 3 to 10 rpm.

  The pulling rate of the seed crystal 25 is preferably 0.1 to 3 mm / h, more preferably 0.2 to 1 mm / h.

  The pulling of the seed crystal 25 is preferably performed in an inert gas atmosphere, and nitrogen is usually used as the inert gas. The pulling of the seed crystal 25 is usually performed under atmospheric pressure.

  When the seed crystal 25 is pulled up in this way, a bulk single crystal 26 represented by the general formula (1) can be obtained at the tip of the seed crystal 25. At this time, by growing the single crystal 26 to have the composition represented by the general formula (1), the generation of cracks in the process of growing the single crystal 26 is sufficiently suppressed, and the generation of cracks is suppressed. It is possible to obtain a large single crystal 26 that is sufficiently suppressed.

  Then, the Faraday rotator 3 is cut out from the bulk single crystal 26. At this time, since a large single crystal 26 is obtained, a large amount of the Faraday rotator 3 can be obtained. In addition, since the single crystal 26 has the composition represented by the general formula (1), it is possible to sufficiently suppress the occurrence of cracks during cutting. For this reason, the Faraday rotator 3 can be stably obtained from the single crystal 26.

  Hereinafter, the content of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

Example 1
First, Tb ₄ O ₇ powder (purity 99.99%), Sc ₂ O ₃ powder (purity 99.99%), Al ₂ O ₃ powder (purity 99.99%), SiO ₂ powder (purity 99.99%) , CaO powder (purity 99.99%) was prepared, and these powders were dry-mixed to obtain a mixed powder. At this time, based on the total number of moles of Tb ₄ O ₇ powder, Sc ₂ O ₃ powder, Al ₂ O ₃ powder, SiO ₂ powder and CaO powder, Tb ₄ O ₇ powder, Sc ₂ O ₃ powder, Al ₂ O _The blending ratios of ₃ powder, SiO ₂ powder and CaO powder were 22.9 mol%, 29.8 mol%, 45.8 mol%, 0.76 mol% and 0.76 mol%.

  Subsequently, the mixed powder was packed in a cylindrical crucible 21 having a diameter of 50 mm and a depth of 50 mm.

  Next, a current was applied to the high-frequency coil 23 to heat the crucible 21 to melt the mixed powder, and a melt 24 was obtained. Subsequently, a 3 × 3 × 70 mm square bar-shaped seed crystal 25 made of YAG (yttrium, aluminum, garnet) is prepared, and the tip of the seed crystal 25 is immersed in the melt 24. It was pulled up at a pulling speed of 1 mm / hr while rotating at a rotation speed of. At this time, nitrogen was poured into the cylindrical container 22 at a flow rate of 2 L / min, and the seed crystal 25 was pulled up in a nitrogen atmosphere under atmospheric pressure. Thus, a transparent single crystal having a diameter of about 2.5 cm and a length of about 5 cm was obtained.

When the X-ray diffraction was performed on the single crystal thus obtained, a peak of Tb ₃ Sc ₂ Al ₃ O ₁₂ was confirmed. Further, as a result of structural analysis by single crystal X-ray diffraction on the obtained single crystal, a part of Tb is substituted with Sc, a part of Sc is substituted with Si and Ca, and a part of oxygen atoms is substituted. It was confirmed to be missing.

Furthermore, about the said single crystal, the chemical analysis by ICP (inductively coupled plasma) was performed, and the composition (atomic ratio of Tb, Sc, Al, Si, Ca, and O) of the single crystal was confirmed. Specifically, the chemical analysis by ICP was performed as follows. That is, first, 50 mg was cut out from the lower end of the straight body of the single crystal to obtain a cut piece. Next, the cut piece was put into a platinum crucible, and then 250 mg of lithium tetraborate was added. Subsequently, the platinum crucible was accommodated in a high-temperature heating furnace and heated at 1030 ° C. for 2 hours to melt the cut piece. Thereafter, the platinum crucible was allowed to cool, and then the cut piece was placed in a 50 ml beaker, and further 20 ml of HCl was added. Next, the beaker was placed on a hot plate and heated gently to dissolve each elemental component (Tb, Sc, Al, Si and Ca) in HCl from the cut piece. At this time, the volume of the solution obtained in the beaker was made up to 50 ml, and this solution was subjected to chemical analysis by ICP. As a result, it was confirmed that a single crystal having a composition of (Tb _2.98 Sc _0.02 ) (Sc _1.96 Si _0.02 Ca _0.02 ) Al ₃ O _11.9 was obtained.

(Example 2)
First, Tb ₄ O ₇ powder (purity 99.99%), Sc ₂ O ₃ powder (purity 99.99%), Al ₂ O ₃ powder (purity 99.99%), SiO ₂ powder (purity 99.99%) , CaO powder (purity 99.99%) was prepared, and these powders were dry-mixed to obtain a mixed powder. At this time, based on the total number of moles of Tb ₄ O ₇ powder, Sc ₂ O ₃ powder, Al ₂ O ₃ powder, SiO ₂ powder and CaO powder, Tb ₄ O ₇ powder, Sc ₂ O ₃ powder, Al ₂ O _The blending ratios of ₃ powder, SiO ₂ powder and CaO powder were 22.7 mol%, 28.8 mol%, 45.5 mol%, 1.5 mol% and 1.5 mol%.
Subsequently, the mixed powder was packed in a cylindrical crucible 21 having a diameter of 50 mm and a depth of 50 mm.

  Thereafter, a single crystal was grown in the same manner as in Example 1. Thus, a transparent single crystal having a diameter of about 2.5 cm and a length of about 5 cm was obtained.

When the X-ray diffraction was performed on the single crystal thus obtained, a peak of Tb ₃ Sc ₂ Al ₃ O ₁₂ was confirmed. Further, as a result of structural analysis by single crystal X-ray diffraction on the obtained single crystal, a part of Tb is substituted with Sc, a part of Sc is substituted with Si and Ca, and a part of oxygen atoms is substituted. It was confirmed to be missing.

Further, when the single crystal was subjected to chemical analysis by ICP in the same manner as in Example 1, (Tb _2.97 Sc _0.03 ) (Sc _1.92 Si _0.04 Ca _0.04 ) Al ₃ O It was confirmed that a single crystal having a composition of _11.9 was obtained.

(Example 3)
First, Tb ₄ O ₇ powder (purity 99.99%), Sc ₂ O ₃ powder (purity 99.99%), Al ₂ O ₃ powder (purity 99.99%), SiO ₂ powder (purity 99.99%) , CaO powder (purity 99.99%) was prepared, and these powders were dry-mixed to obtain a mixed powder. At this time, based on the total number of moles of Tb ₄ O ₇ powder, Sc ₂ O ₃ powder, Al ₂ O ₃ powder, SiO ₂ powder and CaO powder, Tb ₄ O ₇ powder, Sc ₂ O ₃ powder, Al ₂ O The respective blending ratios of ₃ powder, SiO ₂ powder and CaO powder were 22.3 mol%, 26.9 mol%, 44.8 mol%, 3 mol% and 3 mol%.

  Subsequently, the mixed powder was packed in a cylindrical crucible 21 having a diameter of 50 mm and a depth of 50 mm.

  Thereafter, a single crystal was grown in the same manner as in Example 1. Thus, a transparent single crystal having a diameter of about 2.5 cm and a length of about 5 cm was obtained.

When the X-ray diffraction was performed on the single crystal thus obtained, a peak of Tb ₃ Sc ₂ Al ₃ O ₁₂ was confirmed. Further, as a result of structural analysis by single crystal X-ray diffraction on the obtained single crystal, a part of Tb is substituted with Sc, a part of Sc is substituted with Si and Ca, and a part of oxygen atoms is substituted. It was confirmed to be missing.

Further, when the single crystal was subjected to chemical analysis by ICP in the same manner as in Example 1, (Tb _2.95 Sc _0.05 ) (Sc _1.82 Si _0.09 Ca _0.09 ) Al ₃ O It was confirmed that a single crystal having a composition of _11.9 was obtained.

(Comparative Example 1)
First, Tb ₄ O ₇ powder (purity 99.99%), Sc ₂ O ₃ powder (purity 99.99%) and Al ₂ O ₃ powder (purity 99.99%) were prepared, and these powders were dry mixed. A mixed powder was obtained. At this time, _Tb 4 _{O 7} powder, the _Sc 2 _{O 3} powder and _Al 2 _{O 3} powder based on the total moles of, _Tb 4 _{O 7} powder, _Sc 2 _{O 3} powder and _Al 2 _{O 3} powder each blending ratio of 20.8 mol%, 34 mol% and 45.2 mol%.

  Subsequently, the mixed powder was packed in a cylindrical crucible 21 having a diameter of 50 mm and a depth of 50 mm.

  Thereafter, a single crystal was grown in the same manner as in Example 1. Thus, a transparent single crystal having a diameter of about 2.5 cm and a length of about 5 cm was obtained.

When the X-ray diffraction was performed on the single crystal thus obtained, a peak of Tb ₃ Sc ₂ Al ₃ O ₁₂ was confirmed. Further, as a result of structural analysis by single crystal X-ray diffraction for the obtained single crystal, a part of Tb was replaced with Sc, a part of Sc was replaced with Al, and a part of oxygen atoms was lost. It was confirmed that

Furthermore, when the single crystal was subjected to chemical analysis by ICP in the same manner as in Example 1, (Tb _2.88 Sc _0.12 ) (Sc _1.96 Al _0.04 ) Al ₃ O _11.9
It was confirmed that a single crystal having the following composition was obtained.

(Comparative Example 2)
First, Tb ₄ O ₇ powder (purity 99.99%) and Ga ₂ O ₃ powder (purity 99.99%) were prepared, and these powders were dry-mixed to obtain a mixed powder. At this time, based on the total moles of _Tb 4 _{O 7} powder and _Ga 2 _{O 3} powder, _Tb 4 _{O 7} powder and _Ga 2 _{O 3} powder each mixture ratio of 34.8 mol% and 65.2 mol% It was.

  Subsequently, the mixed powder was packed in a cylindrical crucible 21 having a diameter of 50 mm and a depth of 50 mm.

  Thereafter, a single crystal was grown in the same manner as in Example 1. Thus, a transparent single crystal having a diameter of about 2.5 cm and a length of about 5 cm was obtained.

When the X-ray diffraction was performed on the single crystal thus obtained, a peak of Tb ₃ Ga ₅ O ₁₂ was confirmed. Further, as a result of structural analysis by single crystal X-ray diffraction for the obtained single crystal, it was confirmed that a part of Tb was substituted with Ga and a part of oxygen atoms was missing.

Further, the single crystal was subjected to chemical analysis by ICP in the same manner as in Example 1. As a result, (Tb _2.98 Ga _0.02 ) Ga ₅ O _{11.9 was obtained.}
It was confirmed that a single crystal having the following composition was obtained.

[Characteristic evaluation]
(Faraday rotation angle)
For the single crystals of Examples 1 to 3 and Comparative Examples 1 and 2 obtained as described above, Faraday rotation angles at wavelengths of 633 nm, 1064 nm, and 1303 nm were measured.

  At this time, the Faraday rotation angle was measured as follows. That is, first, the analyzer was rotated to a quenching state without placing a single crystal between the polarizer and the analyzer. Next, the single crystals of Examples 1 to 3 and Comparative Examples 1 and 2 were cut into a 3.5 × 3.5 × 20 mm square bar shape, which was placed between a polarizer and an analyzer, Light was incident in a state where a magnetic flux density of 0.42 T was applied along the longitudinal direction of the crystal, and the analyzer was rotated again to be in a quenching state. Then, the difference between the rotation angle of the analyzer before sandwiching the single crystal between the polarizer and the analyzer and the rotation angle of the analyzer after sandwiching the single crystal is calculated, and this angular difference is calculated as the Faraday rotation angle. It was. At this time, the Faraday rotation angle was measured for the wavelength of the light source at 633 nm, 1064 nm, and 1303 nm, respectively. The results are shown in Table 1.

(Presence of cracks)
About the single crystal of Examples 1-3 and Comparative Examples 1-2, the presence or absence of the crack immediately after a growth was investigated visually. Further, from the single crystals of Examples 1 to 3 and Comparative Examples 1 and 2, a crystal lump having a thickness of about 2 cm was cut out by an inner peripheral cutting machine equipped with an electrodeposited diamond blade, and the presence or absence of cracks at the time of cutting in the single crystal was visually observed. We investigated in. The results are shown in Table 1.

  From the results shown in Table 1, it was found that the single crystals of Examples 1 to 3 showed a large Faraday rotation angle in all wavelength regions of 633 nm, 1064 nm, and 1303 nm as compared with the single crystal of Comparative Example 2. From this, it was found that the single crystals of Examples 1 to 3 had a large Verde constant in all wavelength regions of 633 nm, 1064 nm, and 1303 nm as compared with the single crystal of Comparative Example 2.

  Moreover, about the single crystal of Examples 1-3, although it was a large-sized single crystal of about 2.5 cm in diameter and about 5 cm in length, a crack was not seen in both immediately after growth and at the time of cutting. . In contrast, the single crystal of Comparative Example 1 was a large single crystal having a diameter of about 2.5 cm and a length of about 5 cm, but cracks were observed both immediately after growth and at the time of cutting.

  From the above, it was confirmed that the garnet-type single crystal for a Faraday rotator of the present invention has a large Verde constant, can sufficiently suppress generation of cracks, and can be increased in size.

DESCRIPTION OF SYMBOLS 1 ... Polarizer 2 ... Analyzer 3 ... Faraday rotator 10 ... Optical isolator

Claims (3)

A garnet-type single crystal for a Faraday rotator represented by the following general formula (1):
_{(Tb 3-z L z)} (Sc 2-x-y M x N y) Al 3 O 12-w (1)
(Wherein M represents a tetravalent ion, N represents a divalent ion, L represents at least one selected from the group consisting of M, N and Sc, and x, y, z and w satisfy the following formula: .
0 <x <0.3
0 <y <0.3
0 <x + y <0.6
0 ≦ z <0.3
0 ≦ w <0.5) In the general formula (1), x, y, z and w are the following formulas:
x = y
0 ≦ z <0.2
0 ≦ w <0.3
0 <x <0.1
The garnet-type single crystal for a Faraday rotator according to claim 1, wherein An optical isolator having a Faraday rotator,
An optical isolator in which the Faraday rotator is formed of a garnet-type single crystal for a Faraday rotator according to claim 1 or 2.

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