JPH0450120A - Magnetic optical material - Google Patents

Abstract

PURPOSE:To obtain a magnetic optical material having a high coefficient of Faraday rotation and a low temperature coefficient, comprising a magnetic garnet crystal film shown by a specific composition formula grown on a nonmagnetic garnet substrate. CONSTITUTION:This magnetic optical material comprises a magnetic garnet crystal film shown by the composition formula Er3-x-yGdxBiyGe5O12 (0<x3 and 0<y<3) grown on a nonmagnetic garnet substrate. Consequently, since the coefficient of Faraday rotation is extremely high, the thickness of crystal film can be considerably thinned in comparison with an existing magnetic garnet crystal film and growing time can be shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical material used for optical isolators, optical circulators, etc.

[Prior Art] Conventionally, optical isolators have been used to separate the light beam emitted from a semiconductor laser from the returning light, or to guide backscattered light from an optical fiber only to a light receiving diode in optical fiber loss measurement. A magneto-optical material having a Faraday rotation effect is used as a circulator.

The Faraday rotation effect is a phenomenon in which when a magneto-optical material is placed in a magnetic field, the plane of polarization of light traveling in the direction of the magnetic field rotates. The conditions are that the coefficient (rotation angle per unit length) is large, that the Faraday rotation coefficient has little temperature dependence, and that insertion loss is small.

This kind of magneto-optical material is a rare earth iron garnet substituted with Bi (general formula Bi, RE-Fe).

0.2, RE represents rare earth, x
y=3) has been developed. Such an iron garnet crystal can be grown on a garnet substrate by a liquid phase epitaxial method, and the Faraday rotation coefficient improves as the amount of Bi substitution increases. In order to replace a large amount of Bi, it has been proposed to replace Fe with a non-magnetic element such as Al5Ga (Japanese Unexamined Patent Publication No. 20926/1982).

On the other hand, since Bi has a large ionic radius, as the amount of Bi increases, the difference in lattice constant with the substrate increases, resulting in poor lattice matching. For this reason, lattice matching with the substrate is achieved by using rare earth elements with a small ionic radius (JP-A-63-291028, JP-A-1-1999).
No. 217313).

[Problems to be Solved by the Invention] However, when Fe is replaced with a nonmagnetic element, there is a problem that the temperature characteristics of the resulting magneto-optical material deteriorate. In addition, the rare earths that form rare earth iron garnet are 1
Although these species or a mixture of two or more species are used, each has different temperature characteristics (the sign of the temperature coefficient), and if only one species is used or the combination is inappropriate, the temperature coefficient of the Faraday rotation coefficient will become large. , cannot be put to practical use as a magneto-optical element.

The purpose of the present invention is to provide a magneto-optical material with a large Faraday rotation coefficient and a small temperature coefficient by combining two types of specific rare earth elements. Furthermore, the external saturation magnetic field is small, making it possible to miniaturize the magnet used as a component. The purpose is to provide a magneto-optical material that

[Means for Solving the Problem] In order to achieve the above object, the inventors of the present invention have conducted extensive research on combinations of two types of rare earths with different signs of temperature coefficients, and have found that when Er and Gd are combined as rare earths. The inventors discovered that the Faraday rotation coefficient is extremely high and the external saturation magnetic field is small, leading to the present invention.

That is, the magneto-optical material of the present invention consists of a magnetic garnet crystal film grown on a non-magnetic garnet substrate and represented by the compositional formula %.

Here, the nonmagnetic garnet substrate is GdaGa.

012, Sm5Ga, O+z, NdaGa60+2 (hereinafter referred to as NGG), Ca-Mg-Zr substituted GdxGas
O12 (hereinafter referred to as 5GGG) etc. are used, but the crystal film with the above composition is 5GG with a lattice constant of around 12.497A.
It has the best lattice matching with the G substrate.

The magnetic garnet crystal film is grown by liquid phase epitaxial method. That is, PbO1B*Os.

In the flux of Bi*Os, Fe*Oss ErtO
By immersing a garnet substrate in a melt of a predetermined composition made by melting ssG d *Os, a crystal film with a thickness of 500 μm or more can be grown on the substrate.

With such a melt composition, the Faraday rotation coefficient of the obtained crystal film is extremely high, so the thickness of the crystal film can be made considerably thinner (for example, 202 μm or less) compared to conventional magnetic garnet crystal films. Therefore, the breeding time can be shortened.

The obtained crystal film is used as a magneto-optical element such as an optical isolator after removing all or part of the substrate as necessary.

[Example] The present invention will be explained in detail below.

Example 1 A 5GGG substrate was immersed in a melt having the composition shown in Table 1 (735° C.) for 5 minutes to obtain a 5 μm thick crystal film exhibiting a mirror surface on the substrate.

Table 2 shows the composition of the obtained crystal film, the Faraday rotation coefficient at a wavelength of 1.3 μm, and the external saturation magnetic field.

Table 1 Table 2 Example 2 An NGG substrate was immersed in the same melt as in Example 1 for 5 minutes to obtain a 5 μm thick crystal film exhibiting a mirror surface on the substrate.

[Effects of the Invention] As is clear from the above embodiments, according to the present invention,
By using Er and Gd, which have different signs of temperature coefficients, as rare earth elements in the magnetic garnet crystal film, it is possible to obtain a magneto-optical material with an extremely large Faraday rotation coefficient and a small temperature coefficient.

Therefore, an extremely thin crystal film can be used as a magneto-optical element such as an optical isolator, which reduces the size of the element.
Cost reduction can be achieved and crystal growth time can be shortened.

Further, since the magneto-optical material of the present invention has a small external saturation magnetic field, the magnet used as a component can be made small, and the entire device can be made smaller.

Agent Patent Attorney Moritani - Yu

Claims (1)

[Claims] Grown on a non-magnetic garnet substrate, having the composition formula Er_3
＿−＿x＿−＿yGd_xBi_yFe_5O_1_2
(However, 0<x<3, 0<y<3) A magneto-optical material comprising a magnetic garnet crystal film represented by the following formula.