JPH11116396A - Bismuth-substituted type garnet material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a bismuth-substituted type garnet material for an optical use, having low insertion loss, large Faraday rotation ability and small required applied magnetic field, and further to provide a method for producing the bismuth-substituted type garnet material. SOLUTION: This bismuth-substituted type garnet material for an optical use is obtained by growing a garnet single crystal membrane of the chemical formula Tb3-a-b Gda Bib Fe5-x Gax O12 [(a) is 0.02-0.55; (x) is 0.02-0.60; (b) is, 1.0-1.5] and consisting essentially of Tb, Ga, Bi, Fe and Ga on a neodium, gallium and garnet(NGG) substrate by a liquid phase growing method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bismuth (Bi) -substituted garnet material among optical garnet materials having a Faraday effect (rotational power), and more particularly to a liquid phase growth method (LPE method). Cultivated (TbGdBi)
₃ (FeGa) ₅ O ₁₂ garnet single crystal thick-film material and a method of manufacturing the same related.

[0002]

2. Description of the Related Art Hitherto, in optical communications, devices utilizing the Faraday effect have been developed and put into practical use. In optical communication using a semiconductor laser oscillator, oscillation may become unstable or stop when reflected light from an optical fiber cable or a connector returns to an oscillation unit. Therefore, an optical isolator utilizing the Faraday effect is used to block the reflected light and secure stable signal light oscillation.

[0003] A Bi-substituted (rare earth) iron garnet material having a large Faraday rotation ability is grown by an LPE method, a flux method or the like. In particular, a garnet single crystal (thick film) material grown by the LPE method is easy to manufacture, has low manufacturing costs, and is therefore excellent in productivity and can be manufactured at low cost.
Therefore, the rare earth iron garnet material is used as a Faraday rotator in an optical isolator used in the near infrared region.

[0004] An example of a liquid phase growth method of a Bi-substituted garnet material used for such a Faraday rotator for an optical isolator is performed as follows.

The flux components PbO, Bi ₂ O ₃ ,
B ₂ O ₃ and Tb ₂ which is a component that shifts to a garnet structure
O ₃ , Gd ₂ O ₃ , Fe ₂ O ₃ , Ga ₂ O _{3 and the} like are dissolved in a platinum crucible by heating to about 900 to 1100 ° C. to prepare a solution, and then the temperature is lowered, and garnet The components to be transferred to the structure are supercooled (supersaturated) and then maintained at a constant temperature. Then, the garnet substrate is immersed in the solution, and the garnet substrate is rotated for a long time to grow a thick film of the Bi-substituted garnet material on the garnet substrate.

Heretofore, in growing a TbBi-based garnet material which is a Bi-substituted garnet material, a substrate having a lattice constant close to the lattice constant of the crystal to be grown is used.
SGGG (samarium, gallium, gadolinium, garnet, lattice constant 12.495-12.498 angstroms) has been used.

Further, an NGG substrate (with a lattice constant of 12.509)
(About Å) has a large lattice constant difference from the bismuth-substituted garnet material, and it has been considered difficult to grow a garnet thick film using an NGG substrate. Therefore, N
Since a GG substrate cannot be used, a part of Tb is used as a measure for improving the Faraday rotation ability of a TbBi-based garnet material.
A technique has been used in which a TbBi-based garnet material having a composition substituted with holonium (Ho) or ytterbium (Yb) having a smaller ionic radius is grown on an SGGG substrate.

[0008] Among the Bi-substituted garnet materials, the (TbBi) ₃ Fe ₅ O ₁₂ garnet material has a relatively high Faraday rotation ability, a relatively small applied magnetic field to the garnet material, and a Faraday rotation. The temperature dependence of performance is also small.

The above-mentioned required applied magnetic field is the minimum magnetic field required for the reduction of the insertion loss of the garnet material to reach a saturated state, and is referred to as a saturation magnetic field Hs. Physically, it is a magnetic field necessary to align the direction of the magnetic field spin of the garnet material in one direction. Generally, the applied magnetic field is provided by a permanent magnet located around the garnet material.
As the permanent magnet, generally, a disc-shaped Sm ₂ Co ₁₇
A permanent magnet is used.

[0010]

The optical isolator exhibits a higher transmittance (lower insertion loss) in the light traveling direction, that is, in the forward direction, and has a higher light transmittance in the reverse direction, which is the reflection direction.
It is required to show lower transmittance. Therefore,
The Faraday rotator has a Faraday rotation angle of about 45
It has been required that the insertion loss in the forward direction at a moderate thickness be 0.3 dB or less. However, recently, with the development of communication technology, a Faraday rotator having a lower insertion loss has been demanded.

Therefore, the rotation angle of the Faraday rotator is about 4
The insertion loss at the garnet film thickness corresponding to 5 degrees is desirably 0.2 dB or less.

In the current state of the LPE method, the composition of the solution,
The growth condition of the garnet material is controlled by controlling the temperature, the lattice constant difference between the garnet substrate and the garnet material to be grown, and the number of rotations of the garnet substrate. It is very difficult to adjust by changing the factors independently.

On the other hand, in the LPE method, as described above, the precipitation of supersaturated components in the solution causes the B
Since it grows an i-substituted garnet material, it is extremely important to control the concentration of the supersaturated component. Depending on the temperature and the flow state of the solution, the composition and the state of the crystal of the garnet material to be grown change, and the properties of the material change. Deterioration, crystal defects and cracks may occur.

[0014] In particular, the main factor in the occurrence of cracks in the garnet material is that the thermal expansion coefficients of the garnet substrate and the garnet crystal are different. Therefore, as the thickness of the garnet material grown on the garnet substrate increases, the frequency of occurrence of cracks increases.

Therefore, the generation of cracks can be suppressed by improving the Faraday rotation capability of the garnet film and reducing the required film thickness. By the way, conventional Tb
In the Bi-based garnet material, the Faraday rotation ability is about 750 degrees / cm with respect to light having a wavelength of 1.55 μm,
In consideration of the processing allowance, it is desirable that the grown film thickness is about 700 μm. However, since the frequency of occurrence of cracks at this grown film thickness is high, the film thickness of the material is about 65%.
It is preferably 0 μm or less. Therefore, it is necessary to improve the Faraday rotation ability of the garnet thick film material to be grown by 10% or more.

That is, the Faraday rotation capability of the garnet thick film material is desirably 850 degrees / cm or more.

The garnet material has an Hs of about 900O.
If it is less than e, a commonly used Sm ₂ Co ₁₇ permanent magnet can be used without particularly increasing the diameter, but if Hs can be about 900 Oe or more, the diameter and the like of the permanent magnet can be reduced. It is necessary to use it after making it large.

Therefore, considering the characteristic variation of the permanent magnet, it is desirable that Hs of the garnet material is 850 Oe or less.

An object of the present invention is to provide an optical bismuth-substituted garnet material having a small insertion loss, a large Faraday rotation capability, and a small required applied magnetic field, and a method for producing the same.

[0020]

The present invention provides neodymium,
An optical bismuth-substituted garnet material formed by growing a garnet single crystal thick film containing Tb, Ga, Bi, Fe, and Ga as main components on a gallium and garnet (NGG) substrate by a liquid phase growth method.

Furthermore, the present invention, the composition of the garnet _{material, Tb 3-ab Gd a Bi} b Fe 5 -x Ga x O 12 comprising from 0.02 to 0.55 the a in chemical formula, 0.02 a x ~ 0.
The optical bismuth-substituted garnet material described above, wherein 60 and b are 1.0 to 1.5.

Further, the present invention is the method for producing the above-mentioned bismuth-substituted garnet material for optics, wherein the above-mentioned bismuth-substituted garnet material is heat-treated in a temperature range of 870 to 1130 ° C.

Further, the present invention is the above-mentioned method for producing an optical bismuth-substituted garnet material, wherein the oxygen content of the atmosphere in the above heat treatment is in the range of 5 to 100%.

As a result of various studies, the present inventor has found that it is possible to grow a garnet thick film on an NGG substrate even with a TbBi-based garnet material in a specific composition range. If the substrate for growing the garnet (thick film) material is an NGG substrate, the lattice constant of the grown garnet crystal can be increased, the content of Bi ₂ O ₃ can be improved, and the garnet (thick film) material can be improved. The Faraday rotation ability θ _F can be improved.

Further, the composition of the optical bismuth-substituted garnet material of the present _{invention, Tb 3-ab Gd a Bi} b Fe 5-x G
By the b in a _x O ₁₂ having a composition formula in the range of 1.0 to 1.5, excellent optical crystal of the crystal quality is obtained.

The inventor made various improvements, and as a result, T
b _3-ab Gd _a Bi a _{b Fe 5-x Ga x O} 1 a in ₂ a composition formula and from 0.02 to 0.55, and x and from 0.02 to 0.60, the b 1.0 to 1 By growing a TbBi garnet thick film material having a thickness of 1.5 on an NGG substrate, the TbBi
It has been found that the optical properties of garnet thick film materials are improved.

Here, the reason why a is set to 0.02 to 0.55 is that if a is less than 0.02, Hs becomes 850 Oe or more, insertion loss IL becomes 0.2 dB or more, and a becomes 0.55. Is exceeded, θ _F becomes 850 degrees / cm or less. The reason why b is set to 1.0 to 1.5 is that when b is less than 1.0, θ _F becomes 850 degrees / cm or less, and when b exceeds 1.5, crystal defects increase, and This makes it impossible to obtain a garnet film. The reason why x is set to 0.02 to 0.60 is that when x is less than 0.02, the insertion loss IL is 0.2.
When x exceeds 0.60, θ _F becomes 850.
This is because it is not more than degree / cm.

Further, according to the present invention, the garnet thick film material is prepared in an atmosphere having an oxygen concentration of 5 to 100% in a range of 870 to 11%.
The insertion loss is reduced by maintaining the temperature within a range of 30 ° C. for a predetermined time and performing a heat treatment.

The oxygen concentration in the heat treatment atmosphere is 5-10
The reason why the content is set to 0% is that if the content is less than 5%, correction of the ion balance of the constituent elements of the garnet thick film material becomes insufficient due to lack of oxygen, and the insertion loss becomes 0.2 dB or more.

On the other hand, the heat treatment temperature is 870 ° C. to 1130 ° C.
When the temperature is lower than 870 ° C., the homogenization of the crystal is insufficient, the insertion loss becomes 0.2 dB or more, and the
If the temperature exceeds ℃, the garnet thick film material is decomposed, and the insertion loss becomes 0.2 dB or more.

[0031]

EXAMPLES Next, examples and comparative examples of the bismuth-substituted garnet material for optics of the present invention will be described below.

(Example 1) Next, high-purity terbinium oxide (Tb ₂ O ₃ ), gadolinium oxide (Gd ₂ O ₃ ), ferric oxide (Fe ₂ O ₃ ), and gallium oxide (Ga ₂ O ₃₎ ), Bismuth oxide (Bi ₂ O ₃ ), lead oxide (PbO) and phosphorous oxide (B ₂ O ₃ ) as raw materials, and PbO-B
Using an i ₂ O ₃ -B ₂ O ₃ flux material, a garnet thick film having a thickness of about 550 μm is grown on an NGG substrate (12.509 Å) by the LPE method, and the optical bismuth substitution of the present invention is performed. A sample of the mold garnet material was obtained. When the composition of this sample was analyzed, the composition formula was Tb
Was _{1.7 Gd 0.2 Bi 1.1 Fe 4.9 Ga} 0.1 O 1 2.

Next, after removing the substrates of these samples, they were heat-treated at 1000 ° C. for 20 hours in an atmosphere containing about 40% oxygen. Next, the two surfaces of these samples were polished to adjust the thickness so that the Faraday rotation angle was about 45 degrees. In addition, the above-mentioned composition was obtained by performing EPMA analysis on each of the polished surfaces of these samples at 10 points, and calculating the average value.

Next, after subjecting these samples to a non-reflective coating treatment with a SiO ₂ film, a magnetic field of about 1 KOe was applied using an electromagnet.
The magnetic field Hs at which the transmittance reaches the saturation value, the insertion loss IL, and the Faraday rotation capability θ _F were determined. Table 1 shows the results.

Comparative Example High-purity terbinium oxide (T
b ₂ O ₃ ), gadolinium oxide (Gd ₂ O ₃ ), ferric oxide (Fe ₂ O ₃ ), gallium oxide (Ga ₂ O ₃ ), bismuth oxide (Bi ₂ O ₃ ), lead oxide (PbO), And oxidized phosphor (B
Powder ₂ O ₃₎ was used as a raw material, PbO-Bi ₂ O ₃ -
SGGG by LPE method using B ₂ O ₃ flux material
Substrate as formula composition on (lattice constant 12.496 Å) is _{Tb 1.9 Gd 0.2 Bi 0.9 Fe 4.} 9 Ga 0.1 O 12, and foster a garnet thick film of about 700 .mu.m, the bismuth-substituted optical Comparative Example A sample of the mold garnet material was obtained.

[0036]

In the garnet (thick film) material grown on the NGG substrate, the insertion loss IL is clearly smaller, and the Faraday rotation capability θ _F is significantly improved. On the other hand, H
Although s is slightly larger, Sm ₂ Co
_{Since 17} series magnets are generally used, they can be considered almost equivalent.

(Embodiment 2) In the same manner as in Embodiment 1, NG
On the G substrate composition formula _{Tb 1.9-a Gd a Bi 1.1} Fe 4 .9 Ga
_{Of 0.1} O ₁₂ , a is 0.05, _0.1 , 0.2, 0.3,
After making eight kinds of samples of the optical bismuth-substituted garnet material of the present invention at 0.4, 0.5, 0.6, and applying the same treatment as in Example 1, Hs, θ _F , I The L was measured. The result is shown in FIG.

In FIG. 1, the horizontal axis represents a, the vertical axis represents Hs,
θ _F and IL. As shown in FIG. 1, in the region where a is 0.02 or more, Hs is clearly 850 Oe or less.
Is 0.55 or less, θ _F is clearly 850 degrees / cm
That is, in the region where a is 0.02 or more, IL is clearly 0.2 dB or less. Therefore, when a is 0.
A range from 02 to 0.55 is useful.

(Embodiment 3) In the same manner as in Embodiment 1, NG
On a G substrate, a composition formula Tb _1.7 Gd _0.2 Bi _1.1 Fe _{5 -x} Ga
_{x of x} O ₁₂ is set to 0.05, 0.1, 0.2, 0.3, 0.3.
Eight samples of the optical bismuth-substituted garnet material of the present invention were obtained at 4, 0.5 and 0.6, and the same treatment as in Example 1 was carried out, after which Hs, θ _F , IL. Was measured. The result is shown in FIG.

In FIG. 2, x is shown on the horizontal axis, Hs is shown on the vertical axis,
θ _F and IL. As shown in FIG. 2, in the region where x is 0 or more, Hs is clearly 850 Oe or less, in the region where x is 0.6 or less, θ _F is clearly 850 degrees / cm or more, and x is 0 or less. In the region of .02 or more, IL is clearly 0.0.
It is 2 dB or less. Therefore, x is 0.02-0.60.
The range is useful.

(Embodiment 4) In the same manner as in Embodiment 1, NG
On the G substrate composition formula _{Tb 1.7 Gd 0.2 Bi 1.1 Fe 4} .9 Ga
_{A 0.1} O ₁₂ sample of the optical bismuth-substituted garnet material of the present invention was obtained. Next, 850 ° C., 90
0 ° C, 950 ° C, 1000 ° C, 1050 ° C, 1100
After changing the temperature to 7 stages of 1150 ° C. and holding in an oxygen atmosphere of about 40% for 20 hours, and performing a heat treatment,
Hs, θ _F and IL were measured.

In all the samples, Hs was 800 Oe or less and θ _F was 900 ° / cm or more. IL
FIG. 3 shows the results of the measurement. The horizontal axis of FIG. 3 shows the heat treatment temperature, and the vertical axis shows IL. As shown in FIG. 3, when the heat treatment temperature is in the range of 870 to 1130 ° C., the IL is clearly 0.2 dB or less. Therefore, 870 ° C.-113
A temperature range for the heat treatment at 0 ° C. is useful. Incidentally, the IL before the heat treatment (untreated) was 0.25 dB.

Example 5 A sample similar to that of Example 4 was subjected to an oxygen content of 0, 10, 20, 40,
The heat treatment temperature was changed to 7 stages of 60, 80 and 100%.
After heat treatment at 000 ° C. for 20 hours, Hs,
θ _F and IL were measured.

In all the samples, Hs was 800 Oe or less, and θ _F was 900 degrees / cm or more. IL
FIG. 4 shows the measurement results. The horizontal axis of FIG. 4 shows the oxygen content (oxygen concentration), and the vertical axis shows IL. As shown in FIG. 4, when the oxygen concentration in the atmosphere is 5% or more, I.I.
L. is equal to or less than 0.2 dB. Therefore, it is useful that the oxygen concentration in the heat treatment atmosphere is in the range of 5 to 100%.

[0046]

According to the present invention, an optical bismuth-substituted garnet material having a small insertion loss, a large Faraday rotation ability, and a small required applied magnetic field, and a method for producing the same can be obtained.

[Brief description of the drawings]

[1] formula Tb of optical bismuth-substituted garnet material of the present invention _{1.9-a Gd a Bi 1. 1} Fe 4.9 Ga 0.1 O 12 in Gd substitution amount a saturated applied magnetic field Hs, the Faraday rotation effect theta _F And the relationship between the insertion loss and the insertion loss IL (Example 2).

FIG. 2 shows a bismuth-substituted garnet material for optical use according to the present invention.
The composition formula Tb of_1.7Gd_0.2Bi_{1. 1}Fe_5-xGa_xO₁₂In
X and Hs, θ_F, IL.
FIG. (Example 3).

FIG. 3 is a view showing the relationship between the heat treatment temperature and the IL of the bismuth-substituted garnet material for optics of the present invention (Example 4).

FIG. 4 is a graph showing the relationship between the oxygen concentration in the heat treatment atmosphere and the IL of the bismuth-substituted garnet material for optical use of the present invention (Example 5).

Claims (4)

[Claims] 1. Neodymium, gallium, garnet (N
GG) Tb, Gd, B on the substrate by liquid phase epitaxy
An optical bismuth-substituted garnet material comprising a garnet single crystal thick film mainly composed of i, Fe and Ga. 2. The composition of the garnet material is Tb
_{3-ab Gd a Bi b Fe} 5-x Ga x O 12 comprising from 0.02 to 0.55 the a in chemical formula, 0.02 to 0.60 and x, be 1.0-1.5 and b The bismuth-substituted garnet material for optics according to claim 1, characterized in that: 3. A process for producing a bismuth-substituted garnet material for optical use, wherein the bismuth-substituted garnet material according to claim 1 or 2 is subjected to a heat treatment for maintaining the temperature in a temperature range of 870 to 1130 ° C. 4. The oxygen content of the atmosphere in the heat treatment is:
The method for producing an optical bismuth-substituted garnet material according to claim 3, wherein the garnet material is in a range of 5 to 100%.