JPS63107900A - Material for magneto-optical element - Google Patents

Abstract

PURPOSE:To obtain a material for a magneto-optical element having superior magneto-optical characteristics at 0.8mum band wavelength by growing magnetic garnet having a specified compsn. contg. Y, Gd, Bi, Fe, O, and Ga or Al on a specified single crystal substrate. CONSTITUTION:Magnetic garnet represented by formula II (where L is Ga and/or Al, x=0.2-0.4, y=0.9-1.3 and z=0-0.5) is grown on a single crystal substrate represented by formula I by a liq. phase epitaxy to >=30mum thickness to obtain a material for a magneto-optical element. Since a formed thick film of >=30mum thickness and the substrate match in lattice constant, the film has a specular surface and such superior characteristics as >=8,000deg/cm Faraday rotation coefft. and >=20deg/dB performance index.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a material for magneto-optical elements used in optical isolators, optical circulators, etc. that utilize the Faraday rotation effect.

[Prior art and its problems]

Semiconductor lasers are widely used as light sources in optical applications and optical communications, but there is a major problem in that laser oscillation becomes unstable when reflected light returns to the semiconductor laser.

Optical isolators are used to block this returning light. In the wavelength band of 1.3 to 1.7 μm, yttrium
Bulk single crystal wavelength of iron/garnet (YIG) 0.8μ
In the m-band, paramagnetic glass is used as a Faraday rotation material for optical isolators, but a material with a larger Faraday rotation coefficient is desired in order to miniaturize the device and reduce manufacturing costs.

Garnet with a solid solution of chloride is known as a material with a large Faraday rotation coefficient. This material has already been manufactured as a bulk single crystal using an improved flux method, but there are problems such as difficulty in mass production and the need for precision machining to create devices, so this material is used in Faraday rotary devices. As long as it is used, it cannot be expected to reduce the cost of the optical isolator. For this reason, a method for producing a bismuth-substituted iron garnet thick film using a liquid phase epitaxial (LPE) method, which is excellent in mass production and easy to process, is being considered.

For example, the 8th Japanese Society of Applied Magnetics Academic Lecture Abstracts (19
84,11) NdzGasO+t(
(GdBi) 3 (Fe
AIGa) sO+ z thick films have been reported.

The Faraday rotation coefficient IM of this thick film at a wavelength of 0.8 μm is 7500 deg/cm, and the figure of merit 1eFl/α (
The optical absorption coefficient α (dB/cm) is an excellent value of 23 deg/dB. When making an optical isolator using this thick film, it is necessary to rotate the polarization plane by 45 degrees.
A thick film of 0 μm is required, and the loss due to light absorption is 36χ.

By the way, when growing such a thick film on a garnet substrate by the LPE method, it is necessary to reduce the difference in lattice constant between the substrate and the film. When the difference in lattice constants is large, defects due to the difference in lattice constants are likely to occur in the film, especially when growing a thick film (thus, good quality film growth is inhibited and the film surface cannot exhibit a mirror surface).

In the above (GdBi) s (FeAIGa) Sol film, by using an NGG substrate with a lattice constant of 1 & 12.509, lattice matching was achieved and a thick film could be grown.

However, NGG substrates have large optical absorption by Nd'+ ions at wavelengths below 0.9 μm, so when using the grown thick film for magneto-optical materials in the 0.8 μm band, the NGG on the substrate must be completely removed by polishing. Must.

Moreover, since the film thickness is several tens of microns, precise machining is required and the film remaining after polishing is extremely difficult to handle. Therefore, when the purpose is to provide a magneto-optical material for the 0.8 μm band, it is desirable to use a substrate that does not absorb light in this wavelength range and to fabricate the device with the substrate attached.

Garnet single crystal substrates that meet this purpose and can currently be produced industrially have a lattice constant of 12.496±0.
003 (CaGd)3(MgZrGa)sO+z
(S-GGG) and GdxG with a lattice constant of 12.383
There is asO+g (GGG).

A 0-magnetic PE method Bi-substituted iron garnet thick film grown using this 5-GGG substrate for the 0 and 8 μm band is described in JP-A-61-113026 (Bit-X-Y
GdX Ry)+(Fe+-Jz)s, o+z (However, R=Lu, Yb, Y, Tm; M=Gas
A1% Ge; X=0.4-0.8, y=o
~0.1, Z=0~0.1) thick films have been reported, but I(lIFI・~5500deg/cm−1eFl/
α = ~9 deg/dB, which is a practical problem.

On the other hand, there has been no report on the production of a practically practicable old massively substituted magnetic garnet thick film using a GGG substrate with a small lattice constant.

[Object of the present invention]

The object of the present invention is to provide a thick film grown on a non-magnetic garnet single crystal substrate that is transparent in the 0.8 μm wavelength range, with a Faraday rotation angle of 45 degrees or more in the wavelength range, and with excellent magneto-optical properties. An object of the present invention is to provide a magneto-optical material exhibiting the following properties.

[Structure of the invention]

The inventors of the present invention have made the following findings as a result of intensive study to achieve such an objective.

That is, from the Pb0-BizOs-BzOz system melt,
Y2-, -yGd xBiyFes-zLzO+z (L is Ga, AI or a combination thereof, X・0.2
J, 4, y=0.9~1.3, z=0~0.5) as (CaGd) :l (MgZrGa) so + z
When grown on a single crystal substrate, the film surface exhibited a mirror surface due to good lattice constant matching between the film and the substrate, and furthermore, the Faraday rotation coefficient was 8000 deg/cm or more, and the figure of merit was 2.
A thick film of 30 μm or more and exhibiting excellent characteristics of 0 deg/dB or more was obtained.

The Faraday rotation coefficient of this BiW iron garnet is B
Since it increases almost in proportion to the amount of i direct conversion, it is necessary to harden as much Bi as possible. However, if Bi is dissolved in a solid solution of y 1.4 or more, the lattice constant of the film becomes large and lattice matching with the substrate cannot be achieved, and the resulting film cannot exhibit a mirror surface. .

The purpose of replacing Fe with AI or Ga, which has a small ionic radius, is to achieve lattice matching with the film and to control the magnitude of the saturation magnetic field of the film, but as the amount of AI or Ga replacement increases, Since problems such as a decrease in the Faraday rotation coefficient or an increase in the temperature dependence of the Faraday rotation coefficient, a value of 2.0 to 0.5 is preferable.

Table 1 shows the melt composition for growing a Bi haze-exchanged garnet film in terms of the relative molar ratio (R parameter) of the solution mixture.

Table 1 Relative molar ratio of molten mixture Examples will be described below.

Note that the Faraday rotation coefficient 1□□□ and the light absorption coefficient α are both measurement results at a wavelength of 0.78 μm.

〔Example〕

Example 1 A melt having the composition shown in Example 1 in Table 2 was given a lattice constant of 12.
496 (CaGd) x (MgZrGa) sO
By soaking the tz substrate at 750"C for 90 minutes,
Yl with a thickness of 45 μm, 5Gdo, Ji l+ zF
A film was grown using ea, 1A1o, z(L). The lattice constant of the film was 12.498, and no defects due to the difference in lattice constant with the substrate were observed, and a mirror surface was observed.

The Faraday rotation coefficient of this film is 11,700 de
g/cm, optical absorption coefficient α is 478 dB/cm, magneto-optical figure of merit! The mark/α was 24.5 deg/dB, indicating extremely excellent properties as a material for magneto-optical elements.

Example 2 (CaGd)s was added to the melt having the composition shown in Example 2 in Table 2.
By soaking the (MgZrGa)so+z substrate at 760 °C for 120 min, Yl, tG with a thickness of 60 pm was obtained.
do, Ji 1. oFe4. A qGa6+1012 film was grown. The lattice constant of the film was 12.493, and no defects due to the difference in lattice constant with the substrate were observed, and the film exhibited a mirror surface.

In this case, I is 10,200deg/cm, cr=
440dB/cm.

The IEI was t/α·23.2 deg/dB, showing extremely excellent properties as a material for magneto-optical elements.

Next, we attempted to measure the isolation (ratio of reverse loss to forward loss) of this thick film.

That is, among the films grown on both sides of the substrate, one film is removed by polishing and the remaining film is set to a Faraday rotation angle of 4.
A thick film is adjusted by chemical etching so that it forms a 5 degree angle, and then an anti-reflection film is applied to each of the film surface and the substrate surface.
Isolation was measured using a Glan-Thompson prism and a Hi-Sm-Co magnet.

As a result, an extremely good isolation value of 35 dB was obtained.

Under the thick film growth conditions of Examples 1 and 2, it is possible to further increase the thickness by further increasing the time during which the substrate is immersed in the melt.

Comparative Example 1 In the melt of Comparative Example 1 in Table 2, (CaGd) x (MgZ
rGa) s.

, 2 substrates were immersed at 770°C for 60 minutes to form a Gd2. aBi +, oFe4. s^
lo and ffi membranes were grown. The lattice constant of the film is 12.51
There were two people involved, and many defects were observed due to misalignment with the substrate.

Table 2 Melt composition for growing bismuth-converted iron garnet film [Effects of the invention] According to the present invention, a thick film of 30.17 m or more and a surface roughness of 30. Exhibits a mirror surface and has a Faraday rotation angle of 8000 deg/cm or more,
A high-performance bismuth-substituted iron garnet thick film with a figure of merit of 20 deg/dB or more can be obtained.

The material of the present invention is suitable as a material for magneto-optical elements such as optical isolators and optical circulators in the 0.8 μm wavelength range.

Patent applicant: Mitsubishi Gas Chemical Co., Ltd. Agent: Patent Attorney Sadafumi Kohori Procedural correction divination (voluntary) January 5, 1986

Claims (1)

[Claims] (CaGd)_3(MgZ
rGa)_5O_1_2 30 grown on a single crystal substrate
It is made of magnetic garnet with a thickness of μm or more, and its composition formula is Y_3_-_x_-_yGd_xBi_yFe_
5_-_2L_2O_1_2 (L is Ga, Al, or a combination thereof, x=0.
2 to 0.4, y = 0.9 to 1.3, z = 0 to 0.5)