JPH0646604B2 - Bismuth-substituted magnetic garnet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical isolator utilizing the Faraday effect,
The present invention relates to a bismuth-substituted magnetic garnet suitable as a magneto-optical element such as an optical circulator and an optical switch.

Faraday rotators are used in optical isolators, optical circulators, optical switches, etc. For such elements, the loss when light is transmitted, that is, the insertion loss of the element, should be minimized. Is required.

By the way, as the Faraday rotator, it is preferable to use a bismuth-substituted garnet having a large Faraday rotation angle for downsizing of the element, but when manufacturing this by a liquid phase epitaxial method, a flux mainly composed of PbO is used. Therefore, it is unavoidable that lead is mixed in the grown crystal film, but since lead is one of the causes of light absorption loss, the light absorption loss due to this is inevitable.

On the other hand, it is known to increase the bismuth substitution amount in order to obtain a magnetic garnet having a large Faraday rotation angle and excellent temperature characteristics. However, in order to increase the bismuth substitution amount, lower the growth temperature. Since it is necessary, the amount of lead mixed inevitably increases, and the light absorption loss tends to increase more and more.

In order to reduce the light absorption loss in such a bismuth-substituted garnet and enhance the function as a Faraday rotator, a method of heat treatment in an oxidizing atmosphere has been used up to now (Japanese Patent Laid-Open No. 58-58).
-10718 gazette), when growing garnet on a gadolinium gallium garnet substrate by a liquid phase epitaxial method using a mixture of PbO, Bi ₂ O ₃ , Fe ₂ O ₃ and Lu ₂ O ₃ , A method of reducing light absorption by adding (Japanese Patent Laid-Open No. 56-22699), a magnetic garnet is formed by using a flux consisting of Bi ₂ O ₃ and a garnet constituent element alone, without using a flux mainly composed of PbO. A method has been proposed in which light absorption is reduced by adding divalent ions during epitaxial growth (JP-A-61-150303).

However, in order to reduce the light absorption loss by heat treatment in an oxidizing atmosphere, it is difficult to select the treatment conditions and it is not practical, and when CaO is added, the bismuth substitution amount is small and the Faraday rotation angle is sufficient. Can't be big. Furthermore, if a flux containing no PbO is used, it is difficult to obtain a garnet film having good crystallinity.

Problems to be Solved by the Invention The present invention has been made for the purpose of providing a bismuth-substituted magnetic garnet film having a large amount of bismuth substitution, good crystallinity, a large Faraday rotation angle, and low light absorption loss. It is a thing.

Means for Solving the Problems The inventors of the present invention have conducted extensive studies on reducing light absorption loss in a bismuth-substituted magnetic garnet film containing a relatively large amount of bismuth, and as a result, a flux mainly composed of PbO has been obtained. When a bismuth-substituted magnetic garnet is produced by a liquid phase epitaxial growth method using Pd, the optical absorption loss of this is due to the coexistence of Pb ²⁺ and Pb ^4+. However, the addition of divalent metal ions or tetravalent metal ions is effective for eliminating either Pb ²⁺ or Pb ^4+. To do
It was found that the addition of tetravalent metal ions is preferable to the addition of divalent metal ions, and the present invention has been completed based on this finding.

That is, the present invention has the general formula _{R 3- (a + b) Pb} a Bi b Fe 5-c M c O 12-d ··
(I) (wherein R is at least one component selected from rare earth elements and elements substitutable therewith, M is at least one component selected from elements substitutable with iron element) , A
Is a number of 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 a part of M in the above formula. As the atomic ratio of the above general formula, a tetravalent element other than Pb belonging to Group IVA and Group IV of the periodic table is expressed as
A bismuth-substituted magnetic garnet containing at least 01 is provided.

The garnet of the present invention has a composition represented by the above general formula (I), and R in this is a component selected from rare earth elements and elements substitutable for them. Examples of such a metal include cerium, praseodymium, neodymium,
Examples include promesium, samarium, europium, gadolinium, terbium, dysprosium, yttrium, holmium, erbium, thulium, ytterbium, lutecium, hafnium and zirconium.

These metals may be contained alone, or 2
It may be contained as a combination of two or more species.

In the magnetic garnet of the present invention, lead derived from the flux component in the manufacturing process is contained, and the content thereof is usually in the range of 0.01 to 0.2 as the atomic ratio a. Further, the content of bismuth in this magnetic garnet needs to be selected so that the atomic ratio b is in the range of 0.5 to 2.0. If this value is less than 0.5, the amount of bismuth substitution is insufficient and the Faraday rotation angle cannot be increased, and if this value is greater than 2.0, stable crystal growth cannot be achieved.

Next, M in the general formula (I) is a component contained by optionally substituting with iron in order to improve the physical properties of the magnetic garnet. Examples of such components include aluminum and gallium. , Scandium, indium, silicon, germanium, titanium, tin, manganese, vanadium, antimony, and the like. It is necessary that the content of M be 2.0 or less as the atomic ratio c, and if this value exceeds 2.0, the original characteristics of magnetic garnet will be impaired.

The magnetic garnet film of the present invention is characterized in that a specific tetravalent element is contained as a part of M in the composition of the general formula (I). As the tetravalent element that is a part of this M,
Elements other than lead belonging to Group IVA and Group IVB of the periodic table are used. Examples of such elements include tetravalent elements such as silicon, germanium, titanium, tin and zirconium. The tetravalent element is responsible for the light absorption increases, to destroy the coexistence of Pb ²⁺ and Pb ^4+, Pb ²⁺
As a matter of course, Pb ⁴⁺ cannot be used because it is contained only for the sake of ^limitation .

Thus, in the present invention, the light absorption loss is reduced by containing the tetravalent element for the following reason.

That is, when a magnetic garnet film is formed by a liquid phase epitaxial method using a flux mainly composed of PbO, lead is mixed into this, but this mixed lead is
It exists as a mixed state of divalent and tetravalent ones, and this is one of the causes of light absorption loss. In this case, if only one of divalent or tetravalent is used, the light absorption is reduced. The absorption loss can be reduced. By the way, when a magnetic garnet is produced by a normal method using a platinum crucible, the amount of divalent compounds is higher than that of tetravalent compounds because Pt ⁴⁺ is mixed, so it is necessary to convert it to only one of them. Rather than adding divalent elements to make them all tetravalent,
It is advantageous to add all tetravalent elements by adding tetravalent elements. Therefore, in the present invention, part of M is replaced with a tetravalent element other than Pb ⁴⁺ , and substantially all the lead is changed to Pb ²⁺ , whereby the light absorption loss is efficiently reduced.

To produce the bismuth-substituted magnetic garnet of the present invention,
Prepare a melt by adding rare earth oxide (R ₂ O ₃ ), iron oxide and other necessary garnet components to flux components such as PbO, B ₂ O ₃ and Bi ₂ O ₃ while maintaining a supercooled state. , A single crystal substrate such as a gadolinium / gallium / garnet substrate is dipped, and while it is rotated, it is epitaxially grown on the surface of the substrate. In this case, it is important to select the composition of the melt, and garnet cannot be obtained unless the molar ratio of Fe ₂ O ₃ / R ₂ O ₃ is 10 to 30, for example. Although the film composition, especially the amount of bismuth mixed in, depends on the growth temperature and the rotation speed of the substrate, the growth temperature is usually 700 to 900 ° C. and the rotation speed of the substrate is 30 to 200 rpm.

EFFECTS OF THE INVENTION The bismuth-substituted magnetic garnet film of the present invention has the advantages that the Faraday angle is large and the crystallinity is good, and since the light absorption loss is very low, an optical isolator and an optical circulator utilizing the Faraday effect are provided. It is suitable as a magneto-optical element used for an optical switch or the like.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples.

The light absorption loss in the examples is a light absorption loss (dB) measured for light having a wavelength of 1.3 μm at a film thickness with a Faraday rotation angle of 45 °.

Reference Example 1 A melt having the basic composition shown below was used and the lattice constant was 12.4.
By performing liquid phase epitaxial growth on a Ca, Mg, Zr-substituted gadolinium gallium garnet substrate of 69 A at a temperature of 800 to 820 ° C, Bi _1.3 Yb _0.7 Gd Fe ₅ O ₁₂ A bismuth-substituted magnetic garnet film having a composition was formed.

Reference Example 2 A melt having the composition shown below was used and the lattice constant was 12.469A.
Liquid phase epitaxial growth on Ca, Mg, Zr-substituted gadolinium-gallium-garnet substrates at temperatures of 740 to 780 ℃ removes Bi _0.7 Y
A bismuth-substituted magnetic garnet film having a composition of b _0.8 Gd _1.5 Fe ₅ O ₁₂ was formed.

Example 1 TiO ₂ was added to the melt of Reference Example 1 at different ratios, and epitaxial growth was performed on the garnet substrate in the same manner as in Reference Example 1. The relationship between the compounding ratio of TiO ₂ and the light absorption loss at this time is shown as a graph in FIG.

As is clear from this figure, the molar ratio of TiO ₂ / Fe ₂ O ₃ is 0.04
The absorption loss was close to 0 dB in the vicinity.

Next, a garnet film having excellent crystallinity was obtained by growing a thick film up to a film thickness of 400 μm using this molar ratio.

For comparison, when the optical absorption loss was measured in the case where TiO ₂ was not added, a very large value of 2.0 dB was shown.

Example 2 SiO ₂ was added to the melt of the reference example in different proportions, and epitaxial growth was performed on the garnet substrate in the same manner as in the reference example. The relationship between the compounding ratio of SiO ₂ and the light absorption loss at this time is shown as a graph in FIG.

As is clear from this figure, the optical absorption loss was almost 0 dB when the SiO ₂ / Fe ₂ O ₃ molar ratio was around 0.07.

Next, this SiO ₂ / Fe ₂ O ₃ having a thickness of 0.07 was grown as a thick film and then polished to obtain a garnet film having a thickness of 260 μm. A graph showing wavelength characteristics of this product is shown by a solid line in FIG. The Faraday rotation angle of this product at 1.3 μm is 44.
It was 7 °.

Further, for comparison, a graph showing wavelength characteristics of those not containing SiO ₂ is also shown in FIG. 3 by a broken line. The Faraday rotation angle at 1.3 μm of this product was 38.8 °.

Example 3 SnO ₂ was added to the melt of Reference Example 1 in different proportions to prepare Reference Example 1
Epitaxial growth was performed on the garnet substrate in the same manner as in. The relationship between the compounding ratio of SnO ₂ and the light absorption loss at this time is shown as a graph in FIG.

As is clear from this figure, the SnO ₂ / Fe ₂ O ₃ molar ratio is 0.00
At around 8, the optical absorption loss was about 0.3 dB.

Further, when a thick film was grown with this composition, deterioration of crystallinity was not recognized as compared with the case of no addition.

Example 4 TiO ₂ was added to the melt of Reference Example 2 so that the molar ratio of TiO ₂ / Fe ₂ O ₃ was 0.015, and thick film growth was performed. The absorption loss was 0.2 dB per 45 ° Faraday rotation angle.

The optical absorption loss of the film when TiO ₂ was not added showed a large value of 0.8 dB.

Comparative Example MgO was added to the melt of Reference Example 1 at different ratios, and epitaxial growth was performed on the garnet substrate in the same manner as in Reference Example 1. The relationship between the mixing ratio of MgO and the light absorption loss at this time is shown in the graph of FIG.

As is clear from this figure, even if a large amount of MgO / Fe ₂ O ₃ molar ratio of 0.12 or more is added, the light absorption loss does not decrease so much, and in the case of adding a small amount, the opposite effect is obtained. It is expected that the optical absorption loss will be reduced by adding a larger amount of MgO, but this is not practical because the crystallinity is significantly deteriorated as the amount of addition is increased.

So far, the explanation has been given for light with a wavelength of 1.3 μm.
The same tendency is exhibited for wavelengths of m to 0.9 μm and 1.1 μm to 1.6 μm. As an example, at a wavelength of 0.8 μm, at a thickness where the Faraday rotation angle is 45 ° at a molar ratio of SiO ₂ / Fe ₂ O ₃ = 0.07, a light absorption loss of 2 dB is obtained, which is compared with 8 dB without addition. It has been greatly improved.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the compounding ratio of TiO ₂ and light absorption loss in the present invention, FIG. ₂ is a graph showing the relationship between the compounding ratio of SiO ₂ and light absorption loss, and FIG. FIG. 4 is a graph showing wavelength characteristics relating to Examples and Comparative Examples of the present invention.
Graph showing the relationship between the compounding ratio of SnO ₂ and light absorption loss, No. 5
The figure is a graph showing the relationship between the mixing ratio of MgO and the light absorption loss.

Claims (1)

[Claims] 1. A compound represented by the general formula: R _{3- (a + b)} Pb _a Bi _b Fe _5-c M _c O _12-d (wherein R is at least selected from rare earth elements and elements substitutable therewith). One component, M is at least one component selected from elements substitutable with iron element, a
Is a number of 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 a part of M in the above formula A bismuth-substituted magnetic garnet, characterized in that it contains a tetravalent element other than Pb belonging to groups IVA and IVB of the periodic table in an atomic ratio of 0.01 or more in the above general formula.