JPH0277719A - Magneto-optical garnet for temperature compensation - Google Patents

Abstract

PURPOSE:To provide the magneto-optical garnet for temp. compensation of a thin film having a large effect of temp. compensation by forming the single crystal of magnetic garnet having a specific compsn. on a single crystal substrate of (CaGd)3(MgZrGa)5O12 by liquid phase epitaxy and combining this magnetic garnet with a thin film for polarization. CONSTITUTION:This magneto-optical garnet is formed by growing the single crystal of the magnetic garnet having the prescribed compsn. on the single crystal substrate of the (CaGd)3(MgZrGa)5O12 by the liquid phase epitaxy and the compsn. thereof is expressed by the general formula HO3-x-yGdxBiyFe5-zGazO12 (where 0.8<=x<=1.3, 0.7<=y<=1.2, 1.2<=z<=1.7). The temp. coefft. of the Faraday rotation coefft. of this film approaches from the plus positive side to 0 and, therefore, the film is combined with the magnetic garnet which is generally used for polarization and has the temp. coefft. of the Faraday rotation coefft. approaching from the negative side to zero, by which the production of the Faraday rotating element having nearly the specified angle of Faraday rotation in spite of a change in temp. as a whole is enabled. The thin combination is formable of both of the film for polarization and the film for temp. compensation.

Description

[Detailed Description of the Invention] [Summary of the Invention] The Faraday rotation angle of the magneto-optic garnet changes with changes in the ambient temperature, but by combining magneto-optic garnets 1 to 1 for temperature compensation that cancel out this temperature characteristic, It has been attempted to construct a Faraday rotation element in which the overall Faraday rotation angle is approximately constant within a certain temperature range, but when combining such magneto-optic garnets, the thickness of each film has not been previously reported. It is now possible to fabricate a much thinner combination than when using a temperature compensation film.

[Industrial Application Field] The present invention relates to a Faraday rotation element used in optical isolators, optical circulators, and the like.

[Prior Art] Semiconductor lasers are widely used as coherent light sources in optical applications and optical communications, but when the light beam emitted from the semiconductor laser is reflected by an optical system and returns to the semiconductor laser, There is a problem that laser oscillation becomes unstable.

In order to deal with this problem, an optical isolator is provided on the optical output side of the semiconductor laser, and an optical path is set so that the light emitted from the semiconductor laser does not return.

In recent years, a Faraday rotation coefficient has been conventionally used as a magneto-optical element material for an optical isolator to separate the light beam emitted from such a half-retentive laser and the reflected light beam by the Faraday rotation effect. <,
Moreover, many bismuth-substituted iron garnet thick films produced by liquid phase epitaxial (LPE) method, which can be mass-produced, have been reported.

For example (GdBi) 3 (FeAIGa) 50□2
"Summary of the 8th Japanese Society of Applied Magnetics Academic Lectures" (19
84-) On page 31, (YbTbBi)3Fe, ○I
2 is “Summary of the 10th Academic Lectures of the Japanese Society of Applied Magnetics” (
1986), page 88.

However, in general, the Faraday rotation coefficient in bismuth-substituted iron garnet changes with changes in the temperature of the surrounding environment, which greatly affects isolation. In the case of Anki's (YbTbBi)3FesO+2, 1
．． Taking values in the 3 μm to 1.55 μm band as an example, the Faraday rotation coefficient approaches from - to O on one side, and its rate of change is 0.13% per 1°C. Converting this to isolation' using equation (1), if an isolator set at room temperature is used at 60°C, isolation is 2.
9, (iB) and the performance decreases significantly.

Is = 10 X log (1/5in2(△θ)
) (1) Here, ■S is isolation, △θ
represents the angle of deviation of the Faraday rotation angle from 45+Jeg.

Therefore, we combined magnetic garnet, which has a characteristic that the Faraday rotation coefficient approaches 0 from the + side as the temperature rises, as a temperature compensation material, and kept the Faraday rotation angle almost constant even if the temperature changed overall. is used.

As a temperature compensation film, (GdB i) 3 (FeAI Ga) 5 described in the above-mentioned "10th Japanese Society of Applied Magnetics, Academic Conference Abstracts J (198'6), page 88" is used.
O1□ and the like have been proposed.

In this case, a polarizing film (a film that rotates the plane of polarization more than a temperature compensation film), that is, (YbTbB
]) When a Faraday rotation element is constructed with only 3Fes 012, its film thickness is 231 μm at a wavelength of 1.3 μm.
m, whereas temperature compensation film (GdBi) 3 (F
eAIGa) 50.2 to form a temperature-independent Faraday rotation element, the polarizing film should be 483μ
It is reported that a film thickness of 367 μm is required for temperature compensation.

[Problems to be Solved by the Invention] When films having different temperature characteristics of Faraday rotation angle are combined as described above, both the temperature compensation film and the polarizing film need to be considerably thick.

However, the LPE method has a problem in that the thicker the film, the more difficult it is to obtain high-quality crystals.

The present invention has been made in order to solve the above-mentioned problems, and is a magneto-optical device for temperature compensation that has a large temperature compensation effect, in which the thickness of the polarizing film and the film thickness for temperature compensation are both as thin as possible. The purpose is to provide garnet.

[Means for solving the problems] The present invention provides (CaGd)3 CWigZrGa)s0
12 A magnetic garnet single crystal grown by liquid phase epitaxial method on a single crystal substrate, with the general formula HO2-x-y G
d,, B 1 y F es-20a2012 (However, 0.8≦X≦1.3, 0.7≦y≦1.2.1
．． The present invention is a temperature-compensating magneto-optical garnet for compensating for temperature changes in the Faraday rotation angle in a bismuth-substituted magnetic garnet for use in Faraday rotation elements, characterized by having a composition expressed by 2≦2≦1.7).

[Action] “General formula I (03-M'y cd, BiyFes 2
Ga201□ (however, 0.8≦X≦1.3, 0.
Since the temperature coefficient of the Faraday rotation coefficient of the bismuth-substituted magnetic garnet film expressed as 7≦y≦1.2, 1.2≦2≦1.7 approaches 0 from the + side, it is generally used for polarization. The temperature coefficient of the Faraday rotation coefficient is 0 from one side.
By combining it with a magnetic garnet that approaches , it is possible to create a Farabout rotation element whose Faraday rotation angle remains almost constant even when the overall temperature changes.

There are three methods of combining a polarizing film and a temperature compensating film as shown below, and the same effect is expected in any of them.

1) First, either a temperature compensation film or a polarization film is grown by liquid phase epitaxial growth on a substrate, and the remaining film is grown on top of that film.

2) A temperature compensation film or a polarization film is grown on the substrate by liquid phase epitaxial growth, and one film remaining on the opposite side of the substrate is grown.

3) The temperature compensation film and the polarization film are separately produced by liquid phase epitaxial growth and bonded together.

In the present invention, both the thickness of the polarizing film and the thickness of the temperature compensation film are much thinner than in the case where a conventionally reported temperature compensation film is used.

[Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 5GGG with (111) plane immersed in the melt shown in Table 1
((CaGd) 3 (MgZrCa) , 01□)
HOo with a mirror thickness of 140 μm was grown on the substrate by liquid phase epitaxial growth at 777° C. for 5 hours.

o Gd+, o B I +, o F e3. e Ga
A magnetic garnet single crystal film having a composition of +, 2012 was obtained.

The Faraday rotation coefficient of this temperature compensation film is 1.55 at wavelength.
It was +590d, eg/cm for μm light. 1st
The figure shows the temperature change in the Faraday rotation coefficient of this temperature compensation film. The rate of change of the Faraday rotation coefficient per 1°C near room temperature is extremely large at 0.75%.

Here, the polarizing film contains the above (YbTbB i) 3Fe
5O1□ (Faraday rotation coefficient--1947deg/c
Let us assume a case where this is used in combination with a temperature compensation film and used as a Faraday rotation element for an optical isolator.

The required rotation angle of the plane of polarization is 45 after passing through the two films.
deg, but the optimal combination to obtain a stable element with little change in characteristics over a wide temperature range is
．． For 3 μm, the polarizing film is 280 μm and the temperature compensation film is 110 μm.
dB+)3 (F eA I Ga) s When combined with 0+2, polarizing film 483 μm, temperature compensation 367
The film thickness is much thinner than the μm combination (described above).

Example 2 The polarizing film contains H O+ and 2 T, which have excellent temperature characteristics.
bo.

s B jl, 2 Fe5O12 (77 rad one rotation coefficient -1360 deg/cm, temperature change rate 0.11%) was used.

FIG. 2 shows the temperature change in the Faraday rotation angle of a Faraday rotation element manufactured by separately growing a temperature compensation film and a polarization film by liquid phase epitaxial growth and then bonding them together. △θ is 0 in the range of -10℃ to 60℃
．． 5 or less, and according to equation (1), it is clear that isolation of 40 dB or more is maintained. Here, as a comparative example, FIG.
012 shows changes in rotation angle due to temperature. In this case, the temperature range in which isolation of 40 dB or more is maintained, that is, the temperature range in which 1Δθ] is 0.5 deg or less is 1
The range is extremely narrow, ranging from 6 to 34 degrees Celsius.

[Effect of the invention] By combining the film with a large temperature compensation effect of the present invention and a polarizing film, both temperature compensation and polarization can be stabilized over a wide temperature range with a combination of film thicknesses that are much thinner than those previously reported. It is possible to fabricate a Faraday rotation element that operates as follows.

[Brief explanation of the drawing]

Figure 1 shows Ho+, a Gd+, o B i +, o F
e3. Figure 2 shows the temperature characteristics of the Faraday rotation coefficient of e Ga, -20, garnet film, Figure 2 is HOl, 2 T
bo, 6B11.2 F es 0+2 garnet membrane and HO+-o G d I. o B i +, o F e3. s Ga 1.20+
Figure 3 shows temperature changes in the rotation angle of the polarization plane of light transmitted through a Faraday rotator in which two garnet films are combined.
The figure shows a temperature change in the rotation angle of the polarization plane of light transmitted through a Faraday rotation element of (HoTbBi)3Fes012 garnet film. Patent Applicant Mitsubishi Gas Chemical Co., Ltd. Agent Patent Attorney Sadafumi Kobori Figure 1 Temperature (℃) Figure 2 Temperature ('C) Figure 3 Temperature (℃)

Claims (2)

[Claims] (1) (CaGd)_3(MgZrGa)_5O_1_
2 A magnetic garnet single crystal grown by liquid phase epitaxial method on a single crystal substrate, with the general formula Ho_3_-_x_-_
yGd_xBi_yFe_5_-_zGa_zO_1_
2 (however, 0.8≦x≦1.3, 0.7≦y≦1.2
, 1.2≦z≦1.7) A magneto-optical garnet for temperature compensation for compensating for temperature changes in Faraday rotation angle in bismuth-substituted magnetic garnet for use in Faraday rotation elements. (2) A garnet film formed by combining the temperature compensating garnet of claim 1 with a polarizing garnet.