JPH03280012A - Magneto-optical material - Google Patents

Abstract

PURPOSE:To obtain the magneto-optical material which has a large coefft. of Faraday rotation and small temp. coefft. by using Ho and Gd varying in the code of temp. coefft. as the rare earths of a magnetic garnet crystal film. CONSTITUTION:The magnetic garnet crystal film expressed by compsn. formula Ho3-x-yGdxBiyFe5O12 is grown on a nonmagnetic garnet substrate. In the formula, 0<x<3, 0<y<3. Namely, the coefft. of Faraday rotation is high and the exter nal saturation magnetic field is small if two kinds of the rare earths, Ho and Gd, which vary in the code of the temp. coefft. are combined. The growth of the magnetic garnet crystal film is, therefore, executed by immersing a garnet substrate into the melt of the prescribed compsn. formed by melting Fe2O3, Ho2O3, and Gd2O3 into a flux consisting of PbO, B2O3 and Bi2O3. The magneto- optical material which has the large coefft. of Faraday rotation, the small temp. coefft. and the small external saturation magnetic field and allows the miniaturization of the magnets to be used as parts is obtd. in this way.

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 circulators have been used as optical isolators for separating the light beam emitted from a semiconductor laser and returning light, or for guiding backscattered light from an optical fiber only to a light receiving diode in optical fiber loss measurement. Magneto-optical materials having a Faraday rotation effect are used as such.

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.

As this kind of magneto-optical material, rare earth iron garnet with Bi substitution (general formula B + x RE , Fe a
It is represented by O12, RE represents rare earth, and 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, replacing Fe with a non-magnetic element such as Al or Ga has been carried out (Japanese Patent Application Laid-open No. 20926/1983).

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 Problems] In order to achieve such an objective, the inventors of the present invention have conducted intensive research on combinations of two types of rare earths with different signs of temperature coefficients, and have found that when HO 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 is grown on a non-magnetic garnet substrate and consists of a magnetic garnet crystal film represented by the compositional formula %.

Here, the nonmagnetic garnet substrate is Gd or Ga.

012, Sm5Ga501z, NdaGasOta (hereinafter referred to as NGG), Ca-Mg-Zr substituted G d B
Ga 5O12 (hereinafter referred to as 5GGG) etc. are used, but the crystal film with the above composition has a lattice constant of 12.497A.
The lattice matching between the front and rear 5GGG substrates is the best.

The magnetic garnet crystal film is grown by liquid phase epitaxial method. That is, in the flux of PbO5BaOa, Bi, O, Fe, OB, Ho□O,, G d 20
A crystal film with a thickness of 500 μm or more can be grown on the substrate by immersing the garnet substrate in a melt of a predetermined composition made by melting the garnet.

With such a melt composition, the crystal film obtained has an extremely high Faraday rotation coefficient, so the thickness of the crystal film is considerably thinner than that of conventional magnetic garnet crystal films (
For example, 210 μm or less), and therefore the growth 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 (720° C.) for 10 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 Example 2 An NGG substrate was immersed in the same melt as in Example 1 for 10 minutes,
A 5 μm thick crystal film exhibiting a mirror surface was obtained on the substrate.

[Effect of the invention] As is clear from the above examples, according to the present invention,
By using Ho and Gd, which have different signs of temperature coefficients, as rare earths 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.
This can be realized at low cost and shortens the crystal growth time.

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.

Claims (1)

[Claims] Grown on a non-magnetic garnet substrate, with the composition formula Ho_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.