JPH1192292A - Bismuth substituted type garnet single crystal thick film material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a bismuth substituted type garnet single crystal thick film material having a small insertion loss (<=0.2 dB) and slight in cracks during crystal growth, crystal defects and variability of characteristics and to provide a method for producing the material. SOLUTION: This bismuth substituted type garnet single crystal thick film material is an optical garnet material obtained by growing a garnet single crystal thick film comprising TbGaBiFeGa as a main component on a garnet substrate by a liquid phase growth method. SGGG is used as the growing substrate. The composition of the optical garnet material is shown by the chemical formula, Tb3-a-b Gda Bib Fe5-x Gax O12 , in which (a) is 0.03-0.50, (x) is 0.02-0.50 and (b) is 0.7-1.3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of bismuth (Bi) -substituted garnets among optical garnet materials having a Faraday rotation effect, and is grown by liquid phase growth (LPE) (TbGdBi) _3. (FeG
a) The present invention relates to a ₅ O ₁₂ -based garnet single crystal thick film material and an improvement in a manufacturing method thereof.

[0002]

2. Description of the Related Art Hitherto, devices using Faraday rotation in optical communication have been developed and put into practical use. In optical communication using a semiconductor laser oscillator, when reflected light from an optical fiber cable, a connector, or the like returns to the oscillation unit, the oscillation becomes unstable or stops. Therefore,
An optical isolator is used to block return light and secure a stable oscillation state.

A Bi-substituted garnet having a large Faraday rotation ability is grown by an LPE method, a flux method or the like, and is used as an isolator in the near infrared region.
In particular, the garnet thick film grown by the LPE method is excellent in productivity and can be manufactured at low cost, and thus the LPE method is mainly used at present.

It is desirable that the optical isolator exhibits a higher transmittance in the forward direction and a lower transmittance in the reverse direction with respect to the propagation of light. Therefore, as a garnet material, at a thickness where the Faraday rotation angle is about 450 deg, the insertion loss, which is the loss in the forward direction, is equal to 0.
It has been required to be less than 3 dB.

[0005]

However, recently, with the development of communication technology, further reduction in loss has been demanded. Therefore, the insertion loss is desirably 0.2 dB or less.

The above-mentioned LPE method grows a Bi-substituted garnet on a substrate by precipitating a supersaturated component in a solution. Therefore, it is extremely important to control the concentration of the supersaturated component, and the composition and crystallinity of the grown garnet change depending on the temperature and the flow state of the solution, and there are defects that change the material properties and generate cracks in crystal defects. In the current state of the LPE method, the crystal growth state is managed by controlling the temperature of the solution, the circuit of the substrate, and the like.

However, the TbBi-based garnet material containing Tb, Bi, and Fe as a main component has not reached a state where the crystal growth state can be sufficiently controlled. For this reason, growth cracks and crystal defects are generated, and characteristics are varied.

One of the main factors is that the dispersion of the lattice constant a of the SGGG substrate used for growth is about 0.00.
One angstrom is very large.
SGGG is (GdCa) ₃ (GaMgZr) ₅ O ₁₂ , and there is a possibility that the same site of the crystal lattice can be constituted by a plurality of elements. Therefore, in this crystal, it is inevitable that the dispersion of the lattice constant becomes large. It can be said that.

On the other hand, the lattice constant of TbBi-based garnet is preferably about 12.497 angstroms in terms of characteristics, and the commercially available growth substrate is SG.
GG only.

[0010] Therefore, TbBi using the SGGG substrate
In order to obtain a stable growth state in the production of a system-based garnet thick film, a garnet lattice arrangement corresponding to the variation in the lattice constant of the substrate must be obtained. The lattice constant in the same crystal system is determined primarily by the ionic radius occupying the lattice. In the above-described TbBi garnet containing only Tb, Bi, and Fe as main components, each lattice site is occupied by only one kind of atom.
It is impossible to realize variation in the lattice constant of garnet corresponding to the variation in the lattice constant of the substrate, resulting in the growth of garnet crystals, generation of crystal defects, and variation in characteristics.

Accordingly, the present invention provides a bismuth-substituted garnet single-crystal thick film material having a small insertion loss (less than 0.2 dB) and a small number of cracks, crystal defects, and variations in characteristics during crystal growth, and a method for producing the same. It is intended to do so.

[0012]

Means for solving the problem are as follows.

The present invention relates to an optical garnet material for growing a garnet single crystal thick film mainly composed of Tb, Gd, Bi, Fe and Ga on a garnet substrate by a liquid phase growth method. using the SGGG in the composition of the optical for garnet _{material, Tb 3- ab Gd a Bi b} Fe 5-x Ga
_{x =} O ₁₂ , a = 0.03-0.50, x = 0.0
A bismuth-substituted garnet single crystal thick film material characterized by 2 to 0.50, b = 0.7 to 1.3.

According to the present invention, a single crystal is formed in the range of 930 to 112.
The method for producing a bismuth-substituted garnet single crystal thick film material, wherein the heat treatment is performed at a temperature of 0 ° C.

The present invention is the method for producing a bismuth-substituted garnet single crystal thick film material, wherein the single crystal is heat-treated in an atmosphere having an oxygen content of 5 to 100%.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a bismuth-substituted garnet single crystal thick film material of the present invention and a method for producing the same will be described.

First, the insertion loss is 0.2d.
A liquid crystal growth method for a bismuth-substituted garnet of B or less can be obtained as follows.

In a platinum crucible, PbO, Bi ₂ O ₃ , B ₂
O _{3 and the} like are used as flux components, and garnet components (Tb ₂ O
_{3, Gd 2 O 3, Fe} 2 O 3, Ga 2 O 3 , etc.) of about 900 to 1
After dissolving at 100 ° C. to prepare a solution, the temperature is lowered to a supercooled state (supersaturated solution state). The garnet substrate is immersed in the solution and rotated for a long time to grow a thick Bi-substituted garnet film.

Among the Bi-substituted garnets, (Tb
Bi) ₃ Fe ₅ O ₁₂ -based garnet has features such as high Faraday rotation ability, a relatively small applied magnetic field to the garnet, and small temperature dependence of Faraday rotation.

The required applied magnetic field is the minimum saturation magnetic field (Hs) required for the insertion loss reduction of the garnet to reach a saturated state, and physically completely aligns the directions of the magnetic field spins in the garnet. This is the applied magnetic field required for

Generally, the applied magnetic field is supplied from a permanent magnet disposed around the garnet film.
If Hs is about 750 Oe or less, a standard Sm ₂ Co ₁₇ permanent magnet having relatively good temperature characteristics can be used, and it is not necessary to increase the diameter of the magnet. Hs was set to 750 Oe or less. Further, in order to maintain the characteristic of the TbBi material, which is good in the temperature dependence of the Faraday rotation angle of garnet,-
It was 0.05 deg / ° C. or more (0.05 deg / ° C. or less in absolute value). Therefore, as a constituent element of garnet, T
It has been found that the growth state of a garnet thick film is significantly improved by containing Gd and Ga having ionic radii slightly different from b and Fe as main components.
Further, in the composition of the garnet thick film, the content of Bi is determined by the content of Bi ₂ O _{3 and} the content of Tb _3-ab G under the production conditions of the present invention.
_{d a Bi b Fe 5-x} Ga x O 12 b = 0 in the formula made.
It was found that by setting the content in the range of 7 to 1.3, an optical crystal having good crystallinity can be obtained.

[0022] Standing on these aspects, as a result of various improvement, the composition of Bi substituted Tb garnet material thick film in the present invention is the _{Tb 3-ab Gd a Bi b} Fe 5-x Ga x O 12 having a composition , A = 0.03-0.50, x = 0.02-0.0.
By setting 50 and b = 0.7 to 1.3, the optical characteristics are improved.

Here, the reason for setting a = 0.03 to 0.50 is that Hs becomes 750 Oe or more when a is less than 0.03, and the temperature dependency of the Faraday rotation angle becomes absolute when a exceeds 0.50. This is because the value becomes 0.05 deg / ° C. or more. Also, the reason why b = 0.7 to 1.3 is that if b is less than 0.7, the Faraday rotation ability is reduced, the insertion loss at the used film thickness becomes 0.2 dB or more, and b = 1.3 is satisfied. If it exceeds, the number of crystal defects increases, and the insertion loss becomes 0.2 dB or more.

The reason for setting x = 0.02 to 0.50 is that
When x is less than 0.02, Hs becomes 750 Oe or more, and x
If it exceeds 0.50, the temperature dependence of the Faraday rotation angle becomes 0.05 deg / ° C. or more in absolute value.

Further, according to the present invention, the garnet film is heated in an atmosphere having an oxygen concentration of 5 to 100% at 930 to 1120 ° C.
By performing the heat treatment in the range, the insertion loss can be reduced. The reason why the oxygen concentration in the heat treatment atmosphere is set to 5% or more is 5%.
If the amount is less than%, the correction of the ion balance of the garnet element is insufficient due to the lack of oxygen, and the insertion loss becomes 0.2 dB or more.

On the other hand, the heat treatment temperature is 930 ° C. to 1120 ° C.
When the temperature is lower than 930 ° C., the homogenization of the composition is insufficient, and the insertion loss becomes 0.2 dB or more.
If it exceeds, the garnet film is decomposed and the insertion loss is 0.2
This is because it is not less than dB.

[0027]

Next, examples will be described.

(Embodiment 1) Hereinafter, Embodiment 1 of the present invention will be described.

High-purity terbinium oxide (Tb ₂ O ₃ );
Gadolinium oxide (Gd ₂ O ₃ ), ferric oxide (Fe
₂ O ₃ ), gallium oxide (Ga ₂ O ₃ ), bismuth oxide (B
i ₂ O ₃ ), lead oxide (PbO), and boron oxide (B
₂ O ₃ ) powder is used as a raw material and the flux is P
Using a bO—Bi ₂ O ₃ —B ₂ O ₃ system, an SGGG substrate [composition formula (GdCa) ₃ (GaMgZr) ₅
Using O _12], the composition ratio of _{Tb 2- a Gd a Bi 1 Fe} 4.9 G
With a _0.1 O ₁₂ , a = 0.05, _{0.1, 0.2} , 0.3, 0.3.
A single crystal garnet thick film of 4, 0.5, 0.6 was obtained. These films had a thickness of about 600 μm, a film surface of (888), and a lattice constant of about 12.495 Å.

Next, after removing the substrates of these samples, they were kept at 1050 ° C. for 20 hours in an atmosphere containing about 40% oxygen and heat-treated. Next, both surfaces of these samples were polished to obtain a sample plate having a thickness of about 350 μm. The above-mentioned composition was obtained by conducting EPMA analysis on each side of each of these samples at 10 points and obtaining an average value thereof.

Next, after subjecting these sample plates to a non-reflection coating treatment with a SiO ₂ film, a magnetic field of about 1 was applied using an electromagnet.
The voltage was applied up to KOe, and the saturation magnetic field Hs at which the transmittance at a wavelength of 1.31 μm reached a saturation value and the insertion loss IL were determined.

FIG. 1 shows the results. Hs is 750 Oe
In the following, a is 0.03 or more, and when IL is 0.2 dB or less, the area is a = 0.01 or more.

Next, when the Faraday rotation angle of these samples was measured, it was about 45 deg. The temperature dependence near room temperature was a = 0.5, -0.048 deg / ° C., and a =
At 0.6, it was -0.055 deg / ° C. From the above results, it can be said that the range of a = 0.03 to 0.50 is useful.

(Embodiment 2) Hereinafter, Embodiment 2 of the present invention will be described.

In the same manner as in Example 1, the composition ratio was Tb _1.8
Gd _0.2 Bi ₁ Fe _5-x Ga _x O ₁₂ , where a = 0.
After obtaining a garnet thick film of 1, 0.2, 0.3, 0.4, 0.5, 0.6, Hs, IL and Faraday rotation angle were measured.

FIG. 2 shows the results. Hs is 750 Oe
In the following, x is equal to or less than 0.02, and when the IL is equal to or less than 0.2 dB, the area is equal to or more than x = 0.01 dB.

The Faraday rotation angle is about 45 deg.
The temperature dependence at room temperature is -0.5 at x = 0.5.
049 deg / ° C, -0.057 deg / ° C at x = 0.6
Met. From the above results, it can be said that the range of x = 0.02 to 0.50 is useful.

(Embodiment 3) Hereinafter, Embodiment 3 of the present invention will be described.

In the same manner as in Example 1, the composition ratio was Tb _1.8
After obtaining a garnet film having a composition formula of Gd _0.2 Bi ₁ Fe _4.9 Ga _0.1 O ₁₂ , the heat treatment temperature was set to 900 ° C., 950 ° C., and 10 ° C.
After heat-treating at 00 ° C., 1050 ° C., and 1150 ° C. in an oxygen atmosphere of about 40% for 20 hours, Hs,
IL and Faraday rotation angle were measured.

In all the samples, Hs was 700 Oe or less, the Faraday rotation angle was about 45 deg, and the temperature dependence of the Faraday rotation was 0.045 deg / ° C. or less in absolute value.

FIG. 3 shows the results of IL. When the heat treatment temperature is in the range of 930 to 1120 ° C., the IL is significantly reduced, which is a useful heat treatment temperature range.

(Embodiment 4) Hereinafter, Embodiment 4 of the present invention will be described.

In the same manner as in Example 3, the heat treatment temperature was set at 10
50 ° C. and the oxygen content of the atmosphere is 0, 10, 20, 4
0,60,80,100% and after holding for 20 hours,
Hs, IL, and Faraday rotation angle were measured.

In all the samples, Hs was 700 Oe or less, the Faraday rotation angle was about 45 deg, and the temperature dependence of Faraday rotation was 0.045 deg / ° C. or less in absolute value.

FIG. 4 shows the results of IL. When the oxygen content in the atmosphere is in the range of 5 to 100%, the IL is remarkably reduced, which is a useful oxygen concentration range in the heat treatment atmosphere.

[0046]

As described above, the insertion loss is 0.2.
The present invention can provide an excellent bismuth-substituted garnet single-crystal thick film material and a method for producing the same, which are as small as dB or less and have extremely small cracks, crystal defects, and variations in characteristics during crystal growth.

[Brief description of the drawings]

FIG. 1 shows Tb _2-a Gd _a Bi ₁ Fe _4.9 G in Example 1.
diagram showing the relationship between the substitution amount a saturated applied magnetic field Hs and the insertion loss I.L. of Gd in a _0.1 O ₁₂ having a composition formula.

FIG. 2 shows Tb _1.8 Gd _0.2 Bi ₁ Fe _5-x in Example 2.
Diagram showing the relationship between the Ga substitution amount x and Hs and I.L. in Ga _x O ₁₂ having a composition formula.

FIG. 3 is a diagram showing a relationship between a heat treatment temperature and IL in Example 3.

FIG. 4 is a diagram showing the relationship between the oxygen concentration in a heat treatment atmosphere and IL in Example 4.

Claims (3)

[Claims] 1. An optical garnet material for growing a garnet single crystal thick film containing Tb, Gd, Bi, Fe, and Ga as main components on a garnet substrate by a liquid phase growth method. using the composition of the optical for garnet _{material, Tb 3-ab Gd a Bi} b Fe 5-x Ga x O
_{In the} chemical formula ₁₂ , a = 0.03 to 0.50, x = 0.02
Bismuth-substituted garnet single crystal thick film material characterized by being 0.5 to 1.3 and b = 0.7 to 1.3. 2. The method for producing a bismuth-substituted garnet single crystal thick film material according to claim 1, wherein a heat treatment for maintaining the single crystal at a temperature in a range of 930 to 1120 ° C. is performed. 3. A single crystal having an oxygen content of 5 to 100.
3. The method for producing a bismuth-substituted garnet single crystal thick film material according to claim 1, wherein the heat treatment is performed in an atmosphere in the range of%.