JPH0251494A - Material for magneto-optical element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention provides an optical isolator using the Alladay effect;
This invention relates to magneto-optical materials used in optical circulators and the like.

(Conventional technology) In optical communication and optical measurement using semiconductor lasers as light sources,
An optical isolator is required to prevent reflected light from returning to the light source, and a magnetic garnet having a Faraday effect is used for the optical isolator. The requirements for Faraday rotator materials include ■) large Faraday rotation coefficient, 2) small temperature change in Faraday rotation angle, and 3)
There is no absorption in the wavelength range used, and 4) the magnetic field required for saturation is small, and a material that comprehensively satisfies these requirements is desired.

Conventionally, yttrium-iron-garnet YJe5O12 (Y I G) has been used for Faraday rotators. However, since YIG has a small Faraday rotation coefficient, the thickness required to obtain a Faraday rotation angle of 45 degrees is 2~
It will be as thick as 3 cranes. In recent years, Bi-substituted rare earth iron garnet has been proposed as a material to replace YIG.

This is because when the rare earth element of magnetic garnet is replaced with Bi, the Faraday rotation coefficient increases significantly in proportion to the amount of Bi replacement. Furthermore, by selecting a rare earth element, the material YbxTbyBi*-x-y has a small temperature change in the Faraday rotation angle and a small magnetic field required for saturation.
Fe5O12 has been proposed (Patent application 1318/1986)
96).

(Problem to be Solved by the Invention) Generally, the absorption of magnetic garnet at a wavelength of 0.4 to 1.0 μm is mainly caused by Fe'' ions occupying the 24d site of the oxygen tetrahedron and the 162 site of the oxygen octahedron. This is due to crystal field transition.In addition, there is a broad absorption of Fe2゜p e4 + caused by charge compensation of pb "pb" and pt'° ions mixed in from the flux and crucible material. The tail of absorption is wavelength 1.
3 μm and 1.55 μm, and the insertion loss at these wavelengths was large.

In the above (YbTbBi) Je5O12, this broad absorption appears prominently, and the wavelength is 1.3 μm and 1.55 μm.
Insertion loss in μm is 0.6 dB and 0.
It is as thick as 4 dB. Therefore, it has been difficult to fabricate an optical isolator with low loss (1 dB or less) using this material.

The object of the present invention is to obtain (YbTbBi) 3FesO+ z
By changing the composition ratio of rare earth elements in
The object of the present invention is to provide a high-performance Faraday rotator material with reduced insertion loss in the wavelength range of 0.8 to 1.6 μm, which is the wavelength range used in optical isolators and optical circulators.

(Means for solving the problem) (YbTbB i): +Fe50 + z,
Since Tb ions may exist stably in Tb'' as well as Tb'', it has been experimentally shown that the insertion loss is increased due to the additional broad absorption of Fe'' ions induced by Tb'' ions. This discovery led to the present invention. In order to solve the above problems, the magneto-optical element of the present invention has a T of (YbTbBi) 3FesO+ z
The insertion loss can be reduced by reducing the amount of b to reduce the absorption coefficient of the material itself, and by replacing a large amount of Bi to increase the Faraday rotation coefficient and reduce the thickness required to obtain the desired angle. It is characterized by its reduction. That is, the magneto-optical element material of the present invention has the high lattice constant G
On the GG substrate, the formula: YbTbyBiz□=.

It is an epitaxially grown former substituted rare earth iron garnet represented by Fe5 (L2), and in the above formula,
and y are x+y≦2.2. x>y and y-2.3x
+21K (21,62-a) (where a is the lattice constant of the substrate).

In YbxTb, Bit-x-yFe5O12,
and y are values determined by target values of the Faraday rotation coefficient and absorption coefficient and lattice constant matching with the substrate material.

First, in the above composition system, the Faraday rotation coefficient is proportional to the old substitution amount, and the target value of the Faraday rotation coefficient is -1000.
deg/c+n or more (wavelength 1.314 m), the B+ content per molecule needs to be 0.8/f,u or more. Based on this experimental result, 3-x-y≧
0.8, that is, x+y≦2.2. Next, the absorption coefficient is proportional to the amount of TbO, and in order to reduce loss due to absorption, it is necessary to make the molar ratio of Yb/Tb larger than 1. That is, X and y need to satisfy the relationship x>y. Furthermore, the lattice constants of the substrate and the film having the above composition must be matched. This matching condition is Yb3Fe5012. TbJe, 0+
z, is theoretically determined from the lattice constant of BiJesO+2, X, y, and the lattice constant of the substrate. That is, Yb3
The lattice constant of Fe50tz and TbJe5O12 is 12.
291 people, 12.477 people, B13Fe50+
The theoretical lattice constant of z is 12.620 people, so if the lattice constant of the substrate is 3 people, the formula for matching the lattice constant is: 12.291 x + 12.477y + 12.620
(3-x-y)-3a. From this formula, y =
-2,3x + 21x (12,62-a) is derived. a ranges from 12°47 to 12.53 people. Therefore, once the lattice constant of the substrate is determined, X and y are uniquely determined.

As mentioned above, the amounts of yb and Tb, that is, X and y are )<
+y≦2.2. x>y and y=-2,3x+21y(
12, 62-a) must be satisfied.

(Example) Grid window 912.498 people (GdCa) 3 as substrate
(GaHgZr) Yb+, by liquid phase epitaxial method using s0+2.

A magnetic garnet single crystal film having the chemical formula 7bo, 7Bi1.3FesO+z was grown. This liquid phase epitaxial method uses 2.84 g of melt-produced YbzOz
, Tbz032.70g, FezOz 46.06
g, Pb0174.10g, BizO: + 363
．． 45g and 820310.86g, these were melted at 920°C in a platinum crucible, the temperature was lowered to 810°C to create a supercooled state, and the above substrate was added to this melt at 1100°C.
The contact was made while rotating with rp. Growth rate is 0.
The film was grown to a thickness of 320 μm at a rate of 35 μm/min. The Faraday rotation coefficient and insertion loss of this garnet film are expressed as wavelength 1
．． When measurements were made at room temperature at 3 μm and 1.55 μm, the results shown in Table 1 were obtained. In the magnetic garnet film with this composition, the insertion loss is 1.3 μm at a wavelength of 1.3 μm.
．． 0.3dB and 0.2d at 55μm, respectively
B, which is half of the previous value, which is a big improvement.

(Effects of the Invention) According to the present invention, the insertion loss at wavelengths of 1.3 μm and 1.55 μm is 0.3 dB and 0.2 dB, respectively, which are half of the conventional values, and the characteristics are greatly improved. By using such materials, high-performance optical isolators and optical circulators can be manufactured.

Claims (1)

[Claims] (1) Formula: (GdCa)_3(GaMgZr)_5O_
A garnet single crystal substrate having a composition represented by 1_2, and a garnet single crystal substrate epitaxially grown on the substrate, with the formula:
5O_1_2, and x and y are x+y≦2.2,
A magnetic garnet single crystal film that satisfies the following conditions: x>y and y=-2.3x+21×(12.62-a) (a is the lattice constant of the above substrate, a value in the range of 12.47 to 12.53 Å) A material for magneto-optical elements consisting of.