JPH0533769B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a magneto-optical element used in an optical isolator or circulator using the Faraday effect.

Conventional technology When the rare earth sites of rare earth iron garnet represented by Re ₃ Fe ₅ O ₁₂ (Re is a rare earth atom) are replaced with Bi atoms, the Faraday rotation ability increases with the amount of Bi substitution. Many substituted rare earth iron garnets are produced.

The limit of Bi substitution amount for each rare earth element was reported by Shinagawa et al. in Japan Journal of Applied Physics, Vol. 13, No. 10.
1663 pages (1984) (JAPAN.J.APPL.PHYS.vo1
13. No. 10, P. 1663 (1984). According to this study, as shown in Figure 3, the lattice constant of Bi-substituted rare earth iron garnet increases with the amount of Bi substitution, but there is no correlation between the limit of Bi substitution and the size of the lattice constant of the base material garnet. When Gd ₃ Ga ₅ O ₁₂ is used as the material garnet, the Bi substitution amount is maximum, and the substitution amount at that time is BixLu _3-x Fe ₅ O ₁₂ (x
= 1.4).

Figure 3 is by Shinagawa et al., Japan Journal of Applied Physics, Vol. 13, No. 10.
1663 pages (1984) (JAPAN.J.APPL.PHYS.vo1
13.No.10, P.1663 (1984))
The relationship between the amount of Bi substitution in the sintered rare earth iron garnet represented by BixRe _3-x Fe ₅ O ₁₂ (Re is rare earth) and the lattice constant of the Bi-substituted rare earth iron garnet and the limit of Bi substitution in each rare earth iron garnet are shown. In the graph shown in Figure 3, the horizontal axis is the amount of Bi substitution x, the left side of the vertical axis is the lattice constant, the right side is the lattice constant of each rare earth iron garnet (the scale is on the left), and the dashed line and the x mark in the center are the Bi substitution limit. It shows. Also,
Only for BixLu _3-x Fe ₅ O ₁₂ , other Bi-substituted rare earth iron garnets reported by Shinagawa et al., especially BixYb _3-x
The lattice constant was added by analogy with the lattice constant of Lu ₃ Fe ₅ O ₁₂ with reference to Fe ₅ O ₁₂ , and the Bi substitution limit was determined by extrapolating the Bi substitution limit curve. .

Bi conventionally used as magneto-optical elements
Substituted rare earth iron garnet single crystal was published by Tamaki et al. in Japanese Journal of Applied Magnetics Vol. 8, No. 2, P. 125 (1984).
by the stirred scooping flux method reported in , and by Koshizuka et al. in the Journal of the Japanese Society of Applied Magnetics.
Vol. 8, No. 2, P. 129 (1984) by liquid phase epitaxial growth, and the amount of Bi substitution in both of them is that the former composition is Bi _1.15.
Gd _1.85 Fe ₅ O ₁₂ , the latter has a composition of Yb _2.25 Pr _0.34 Bi _0.73
Fe _3.66 Ga _1.02 O ₁₂ and the Bi substitution limit reported by Shinagawa et al. mentioned above did not occur.

However, recently, J-P.
) (APPLIED OPTICS vol 23.No.8, P.1184
(1984)), and Hibiya et al.
4, there are some liquid-phase epitaxial growth methods that exceed the Bi substitution limit reported by Shinagawa et al.

Problems to be Solved by the Invention There are reports of rare earth iron garnets substituted with a large amount of Bi exceeding the above Bi substitution limit to be made into single crystals by heat treatment from amorphous amorphous laminated by a sputtering method. Since a material with good crystallinity is required to obtain a high isolation ratio, it is preferable to use a material grown by liquid phase epitaxial growth.

In liquid phase epitaxial growth, the lattice constant of a film that can be grown on the substrate is controlled by the lattice constant of the substrate. According to the report by Shinagawa et al. mentioned above, the lattice constant of Bi-substituted rare earth iron garnet increases with the Bi substitution amount, and the smaller the lattice constant of the base material garnet, the lower the lattice constant of Bi-substituted rare earth iron garnet with the same Bi substitution amount. becomes smaller. This situation can be seen from Figure 3.

Therefore, in order to obtain garnet substituted with as much Bi as possible on the same substrate, it is desirable that the lattice constant of the base material garnet be as small as possible.
Among the rare earth iron garnets, Lu ₃ Fe ₅ O ₁₂ has the smallest lattice constant of 12.28 Å, but the Bi substitution limit of these base metal Bi-substituted rare earth iron garnets is shown in Figure 3 reported by Shinagawa et al. is not described, so we can _change the lattice constant of BixLu _3-x Fe ₅ O ₁₂ (0x3) by passing through the lattice constant of Lu _{3 Fe 5} O ₁₂ , _12.28Å , and Assuming that it is a straight line parallel to the change in lattice constant, the BixLu _3-x
Extrapolate the Bi substitution limit curve for each rare earth iron garnet toward the straight line of change in the lattice constant of Fe ₅ O ₁₂ ,
The Bi substitution amount at the intersection point was taken as the Bi substitution limit. According to this, the Bi substitution limit amount of BixLu _3-x Fe ₅ O ₁₂ is x = 1.0
So far, there has been no example of growing Bi-substituted rare earth iron garnet exceeding the Bi substitution limit of BixLu _3-x Fe ₅ O ₁₂ mentioned above.

In addition, in liquid phase epitaxial growth, due to the difference in thermal expansion coefficient between the substrate and the grown film, the grown film may crack when the temperature is lowered from the growth temperature to room temperature, or even if it does not crack, losses due to strain increase. Since the extinction ratio deteriorates, it is necessary to grow at as low a temperature as possible.

The present invention enables a large amount of Bi to be replaced by Lu ₃ Fe ₅ O ₁₂ by selecting the mixing ratio of the melt for liquid phase epitaxial growth.
Bi-substituted rare earth iron garnet is grown by liquid phase epitaxial growth, which has high Faraday rotation ability at wavelengths in the 1.3 μm region and low optical power loss.
The purpose of this study is to demonstrate a growth method that can produce a magneto-optic crystal with a high extinction ratio without cracking.

Means for Solving the Problems In order to solve the above problems, the present invention uses a mixed liquid consisting of B ₂ O ₃ , PbO, Bi ₂ O ₃ , Fe ₂ O ₃ and Lu ₂ O ₃ as a melt, PbO + Bi The molar ratio of ₂ O ₃ and B ₂ O ₃ is PbO
+Bi ₂ O ₃ :B ₂ O ₃ =x: 1 (30≧x≧10) is used, and Sm ₃ which has a large lattice constant and is transparent to wavelengths of 0.8 μm or 1.3 μm is used as a garnet substrate. Fe ₅ O ₁₂ or Ca−Mq−Zr substituted Gd ₃
Using Ga ₅ O ₁₂ , in order to minimize distortion of the grown film due to the difference in expansion coefficient between the substrate and the grown film.
By liquid phase epitaxial growth at a low temperature of 800℃ or less, the composition becomes Bi _x Lu _3-x Fe ₅ O ₁₂ (however, 1.0≦
The present invention provides a method for manufacturing a magneto-optic crystal in which x≦3.0).

Function The present invention works as follows using the manufacturing method described above. Since the lattice constant of Lu ₃ Fe ₅ O ₁₂ , which is the base metal garnet, is the smallest among the rare earth iron garnets, Sm ₃ Ga ₅ O ₁₂ or Ca-
BixLu _3-x with a large amount of Bi atom substitution when grown by liquid phase epitaxial growth on Mq-Zr substituted Gd ₃ Ga ₅ O ₁₂ substrate
Fe ₅ O ₁₂ (however, 1.0≦x≦3.0) is obtained, and the Faraday rotation ability has an absolute value of approximately 1.3 μm at the wavelength used.
2800deg/cm or more, the absolute value is approximately 2800deg/cm at 0.8μm
cm or more and 0.8 μm, it is possible to obtain a high absolute value of about 3000 deg/cm or more. Therefore, when used as a magneto-optical element, it can be made thin, and a high extinction ratio due to low absorption loss and low distortion can be obtained. Furthermore, as shown in the production method of the present invention, the molar ratio of PbO + Bi ₂ O ₃ and B ₂ O ₃ in the melt is PbO + Bi ₂
By setting O ₃ :B ₂ O ₃ =x:1 (30>x>10), (1) low temperature growth becomes possible, and (2) the amount of Bi substitution can be increased. For this reason, (1) the growth temperature is low, so the strain caused by the difference in thermal expansion coefficient between the substrate and the grown film is small when the temperature is returned to room temperature after growth, so it is less likely to crack; and (2) the amount of Bi substitution is large. , it has a high Faraday rotation ability, and the film thickness required for a Faraday rotator, which is usually enough to obtain a Faraday rotation angle of 45 degrees, can be reduced to about half of the conventional film thickness. It is possible to prevent crystal cracking for two reasons: (1) cracking due to the difference in lattice constant between the substrate and the grown film at room temperature caused by the difference in expansion coefficient can be prevented; (2) High Faraday rotation ability due to high Bi substitution; and thin film thickness as a Faraday rotator to reduce loss of optical power of transmitted light. Therefore, the characteristics of the magneto-optical element can be made high Faraday rotation ability, low loss, and high extinction. Moreover, since Sm ₃ Fe ₅ O ₁₂ or Ca-Mg-Zr substituted Gd ₃ Ga ₅ O ₁₂ is used as the substrate, the wavelength of light Sm ₃ Fe ₅ O ₁₂ is 0.8 μm, Ca-
0.8 μm and 1.3 μm for Mg−Zr substituted Gd ₃ Ga ₅ O ₁₂
Bands commonly used in optical communications can be used.

Example As an example, liquid phase epitaxy was performed using a melt mixed with Bi ₂ O ₃ , PbO, B ₂ O ₃ , Fe ₂ O ₃ and Lu ₂ O ₃ and whose mixing molar ratio takes the value shown in the following formula. This figure shows a magneto-optical element grown in a single layer.

Fe ₂ O ₃ /Lu ₂ O ₃ =10 PbO+Bi ₂ O ₃ /B ₂ O ₃ =15 Fe ₂ O ₃ +Lu ₂ O ₃ /Fe ₂ O ₃ +Lu ₂ O ₃ +B ₂ O ₃ +Bi ₂ O ₃ +PbO=0 .
1 Bi ₂ O ₃ /PbO=1.0 Example 1 A garnet film epitaxially grown on a Sm ₃ Fe ₅ O ₁₂ substrate with a lattice constant of 12.439 Å at a growth temperature of 690°C has a composition of Bi _1.3 Lu _1.7 Fe ₅ O _12. The absolute values of Faraday rotation ability are 9600°/cm, 3200°/cm and
It was 2100°/cm.

Example 2 Ca-Mg-Zr substituted Gd ₃ Ga ₅ with lattice constant of 12.497 Å
The garnet film epitaxially grown on an O ₁₂ substrate at a growth temperature of 665°C has a composition of Bi _1.5 Lu _1.5 Fe ₅ O ₁₂
The absolute value of the Faraday rotation ability when the wavelength used is 0.8 μm, 1.15 μm, and 1.3 μm, respectively, is
They were 11500°/cm, 3900°/cm, and 2800°/cm.

Example 3 Ca-Mg-Zr substituted Gd ₃ Ga ₅ with lattice constant of 12.497 Å
The garnet film epitaxially grown on an O ₁₂ substrate at a growth temperature of 640°C has a composition of Bi _1.8 Lu _1.2 Fe ₅ O ₁₂
The wavelengths used are 0.8μm, 1.15μm and
The absolute value of Faraday rotation ability at 1.3μm is 13000°/
cm, 4800°/cm, and 3800°/cm. Also,
The film thickness necessary to obtain a Faraday of 45 degrees at a wavelength of 1.3 μm was 118 μm.

FIGS. 1 and 2 respectively show the relationship between the Faraday rotation ability and the lattice constant with respect to the Bi composition x of the magneto-optical element BixLu _3-x Fe ₅ O ₁₂ obtained in this example. Figure 1 is a graph showing the relationship between the Faraday rotation ability at a wavelength of 1.3 μm and the Bi composition x of the magneto-optical element with the composition BixLu _3-x Fe ₅ O ₁₂ of this example, and Figure 2 is the graph of the composition of this example The relationship between the lattice constant and the Bi composition x of a BixLu _3-x Fe ₅ O ₁₂ magneto-optical element is shown.

Note that the present invention is not limited to the magnetic garnet film grown by liquid phase epitaxial growth from the melt of the above embodiment, but also covers any magnetic garnet film grown from any melt that satisfies the claims of the present invention. It is sufficient if the composition is BixLu _3-x Fe ₅ O ₁₂ (1.0≦x≦3.0).

Effects of the Invention The production method of the present invention produces a composition BixLu _3-x Fe ₅ O ₁₂ that was previously considered impossible (however, 1.0≦x≦3.0)
It is possible to obtain high Faraday rotation ability,
The film thickness for the Faraday rotator could be made thinner. In addition, the required film thickness is thinner and the growth temperature is approximately 100°C lower than conventional methods, which reduces the effects of cracking and distortion during growth due to the difference in thermal expansion coefficient between the substrate and the grown film. It was particularly effective for thick film growth in liquid phase epitaxial growth of Faraday rotators, which conventionally had problems such as cracking. Further, when the composition of the present invention was grown by the manufacturing method of the present invention, a magneto-optical element with a Faraday rotation ability of 3000°/cm or more at the wavelength of 1.3 μm could be obtained. The film thickness of the Faraday rotator that provides a Faraday rotation angle of 45 degrees in this device was 150 μm or less, and if it was epitaxially grown on both sides of the substrate, the film thickness on one side would be 75 μm or less. Moreover, the optical wavelength is 0.8 μm, which is commonly used for optical communication.
1.3 μm, Sm ₃ Ga ₅ O ₁₂ is 0.8 μm, Ca−Mg
-Zr-substituted Gd ₃ Ga ₅ O ₁₂ uses substrates with low absorption of both 0.8 μm and 1.3 μm, so when used as a magneto-optical element in optical communication components, it is configured so that light also passes through the substrate. It can also be used as

Therefore, by using the manufacturing method of the present invention, it was possible to obtain a magneto-optical element with high Faraday rotation ability, low loss, and high extinction ratio.

[Brief explanation of the drawing]

Figure 1 shows the composition of an embodiment of the present invention.
Figure 2 shows the relationship between the Faraday rotation ability at a wavelength of _1.3 μm and the Bi composition x of a magneto-optical element of BixLu 3 _{- x} Fe ₅ O _{12 .}
Figure 3 shows the relationship between the lattice constant and the Bi composition x of the magneto-optical element.
JAPAN.J.APPL.PHYS.vol 13.No.10, P.1663
(1984) announced the composition BixRe _3-x Fe ₅ O ₁₂ (Re
1 is a diagram showing the relationship between the amount of Bi substitution in a sintered rare earth iron garnet (represented by rare earth metal) and the lattice constant of the Bi-substituted rare earth iron garnet, and the Bi substitution limit of each rare earth iron garnet.

Claims (1)

[Claims] 1 Bi _x Lu _3-x Fe ₅ O ₁₂ (1.0≦x
≦3.0), wherein the melt for growing the Bi _x Lu _3-x Fe ₅ O ₁₂ is Bi ₂ O. ₃ , PbO, B ₂ O ₃ , Fe ₂ O ₃ and Lu ₂ O ₃ are mixed, and the mixing molar ratio of PbO + Bi ₂ O ₃ and B ₂ O ₃ in the melt is PbO + Bi ₂ O ₃ :B ₂ O ₃ = y: 1 (however, 30≧
y≧10). 2 Fe ₂ O ₃ , Lu ₂ O ₃ , Bi ₂ O ₃ and the components of the melt
PbO, and Fe ₂ O ₃ + Lu ₂ O ₃ and Bi ₂ O ₃ + PbO + B ₂ O ₃
The mixing molar ratio of +Fe ₂ O ₃ +Lu ₂ O ₃ is Fe ₂
O ₃ :Lu ₂ O ₃ =a: 1 (5≦a≦30), Bi ₂ O ₃ :PbO
= b: 1 (0.5≦b<1.5), and Fe ₂ O ₃ + Lu ₂ O ₃ :
Bi ₂ O ₃ +PbO+B ₂ O ₃ +Fe ₂ O ₃ +Lu ₂ O ₃ =c:1
The method for manufacturing a magneto-optical element according to claim 1, wherein (0.75≦c≦1.3). 3. The method for manufacturing a magneto-optical element according to claim 1, wherein the liquid phase epitaxial growth temperature is 800° C. or lower. 4. The method for manufacturing a magneto-optical element according to claim 1, wherein the garnet substrate is Gd ₃ Ga ₅ O ₁₂ . 5. The method for manufacturing a magneto-optical element according to claim 1, wherein the garnet substrate is Sm ₃ Ga ₅ O ₁₂ . 6 Garnet substrate is Ga-Mg-Zr substituted Gd ₃ Ga ₅
The method for manufacturing a magneto-optical element according to claim 1, wherein the magneto-optical element is _O12 .