JPH06281902A - Magneto-optical element material - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a magneto-optical element material comprising a magnetic garnet single crystal film formed by the LPE method, which has a reduced absorption in the wavelength band of 0.93 to 1.05 μm and has a high figure of merit. [Structure] On a non-magnetic garnet substrate having a composition represented by the chemical formula Gd ₃ (ScGa) ₅ O ₁₂ , the composition formula is represented by R _3-xy Gd _x Bi _y Fe ₅ O ₁₂ , and a liquid phase epitaxial method is used. It is a magneto-optical element material having a grown magnetic garnet single crystal film for use wavelengths of 0.93 to 1.05 μm band. However, R is one or more kinds of rare earth elements selected from Sm, Nd, Pr, and La, the gadolinium amount x is 0 ≦ x <1.5, and the bismuth substitution amount y is 1.2 ≦ y.
≦ 1.7 and 1.2 ≦ x + y <3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a wavelength of 0.93 to 1.0.
The magneto-optical element material used in the 5 μm band will be described in more detail. A liquid phase epitaxial method (hereinafter referred to as “LPE
Method)) as a magnetic garnet single crystal substrate using a non-magnetic garnet substrate having a composition represented by the chemical formula Gd ₃ (ScGa) ₅ O ₁₂ . This magneto-optical element material is
It is useful for optical isolators that utilize the Faraday effect.

[0002]

2. Description of the Related Art In optical communication, transmission quality deteriorates when reflected return light enters a semiconductor laser which is a light source. Therefore, an optical isolator utilizing the Faraday effect is used. The magnetic garnet single crystal has the Faraday effect and is the central material of the optical isolator. Currently, the wavelength bands used for optical communication are 1.3 μm and 1.55 μm. In recent years, magnetic garnet single crystals applied to this wavelength band are mainly bismuth-substituted rare earth iron garnets by the LPE method using a substrate (plate-shaped seed crystal). The reason is that the LPE method is excellent in mass productivity. As a typical substrate, lattice constant a = 12.4
There is 96Å of (CaGd) ₃ (ZrMgGa) ₅ O ₁₂ .

In the case of bismuth substitution type rare earth iron garnet, the Faraday effect increases in proportion to the bismuth substitution amount, and as a result, the figure of merit F (deg / dB) increases.
Therefore, a large amount of bismuth substitution has been attempted. The figure of merit is expressed by F = θ _F / α, where θ _F is the Faraday rotation coefficient (d
eg / cm) and α are absorption coefficients (dB / cm 2). in this case,
Since the crystal lattice constant increases in proportion to the bismuth substitution amount, a substrate having a large lattice constant a is used. For example, a = 12.509Å Nd ₃ Ga ₅ O ₁₂ , a = 12.5
15 Å Tb ₃ (ScGa) ₅ O ₁₂ , a = 12.56 Å Gd
_{There is 3} (ScGa) ₅ O ₁₂ . All of them are intended to replace a large amount of bismuth to increase the Faraday effect, that is, to increase the Faraday rotation coefficient.

[0004]

By the way, in recent years, a fiber type optical amplifier capable of directly amplifying an optical signal has been actively developed. The 1.3 μm band includes praseodymium-doped fiber, and the 1.55 μm band includes erbium-doped fiber. An optical isolator for pumping light is required for practical use of each. The excitation light wavelength of the praseodymium-doped fiber is 1.017 μm, and the excitation light wavelengths of the erbium-doped fiber are 0.98 μm and 1.48 μm. Therefore, 0.98 μm, 1.017 μm, and 1.48 μm band optical isolators are required, and magnetic garnet single crystals suitable for each wavelength are required accordingly.

Among them, the 1.48 μm band magnetic garnet single crystal is currently manufactured by diverting the existing 1.55 μm band magnetic garnet single crystal. On the other hand, 0.98 μm, 1.
A magnetic garnet single crystal suitable for the 017 μm band has not yet been put to practical use. Even if an existing 1.3 μm band magnetic garnet single crystal is used in this wavelength band, the light absorption is large and the characteristics are deteriorated, so that it cannot be used.

An object of the present invention is to have a wavelength of 0.93 to 1.05.
It is an object of the present invention to provide a magneto-optical element material which exhibits good characteristics in the μm band and is composed of a magnetic garnet single crystal film formed by the LPE method.

[0007]

The present invention is based on Gd ₃ (Sc
Ga) ₅ O ₁₂ has a composition formula of R _3-xy Gd _x Bi _y F on a non-magnetic garnet substrate having a composition represented by a chemical formula.
e ₅ O ₁₂ However, R is one or more kinds of rare earth elements selected from Sm, Nd, Pr and La 0 ≦ x <1.5 1.2 ≦ y ≦ 1.7 1.2 ≦ x + y <3 , A magneto-optical element material having a magnetic garnet single crystal film grown by the LPE method for a wavelength band of 0.93 to 1.05 μm. Here, the non-magnetic garnet substrate may be Nd, Cr-doped.

When iron garnet is used for the Faraday element of the 0.98 μm, 1.017 μm band optical isolator, Fe ³⁺
Since the intrinsic absorption has a peak near 0.9 μm, there is a problem that the absorption is large. In the magnetic garnet single crystal obtained by the flux method, the absorption peak shifts to the shorter wavelength side when the lattice constant of the crystal is increased. Therefore, in the present invention, L
As a substrate for the PE method, Gd ₃ (ScG) having a large lattice constant
a) A non-magnetic garnet substrate represented by the chemical formula ₅ O ₁₂ is used, and thereby the lattice constant of the magnetic garnet single crystal formed is increased.

In the present invention, gadolinium is optionally used in the paper by Shinagawa et al., Japanese Journal of Applied Physics.
This is because gadolinium can form the most solid solution of bismuth from ournal of Applied Physics, Vol. 13 (1974) p. 1663. The gadolinium substitution amount x is set to 0 or more and less than 1.5 in order to match the lattice constant with the substrate. Further, the reason that the substitution amount y of bismuth is specified to be 1.2 or more and 1.7 or less is based on the experimental results shown below. .7
This is because if it exceeds, the difference in the coefficient of thermal expansion with the substrate becomes large and cracks occur.

By the way, when a crystal is grown by the LPE method,
It is constrained to match the lattice constants of the substrate and the film. Therefore, if the bismuth substitution amount of 1.2 to 1.7 is determined, in order to match the lattice constant with the Gd ₃ (ScGa) ₅ O ₁₂ substrate within that range, the paper by B.STROCKA et al. [Phil
ips J. Res. 33 (1978) 186], the R must be a rare earth element having an ionic radius of europium (Eu) or more. For example, the lattice constant a =
In order to match the lattice constant with the 12.561Å Gd ₃ (ScGa) ₅ O ₁₂ substrate, if R = Eu and x = 0, Eu _1.3
Bi _1.7 Fe ₅ O ₁₂ , and when R = Gd, Gd _1.1
It becomes Bi _1.9 Fe ₅ O ₁₂ . However, Europium is 2
Since both valence and trivalence are stable, Fe ⁴⁺ may be generated. When Fe ⁴⁺ is generated, 0.93 to 1.
The absorption at 05 μm becomes large, which is not preferable. Therefore, R is one or more selected from samarium, neodymium, praseodymium, and lanthanum.

[0011]

[Operation] When Gd ₃ (ScGa) ₅ O ₁₂ having a large lattice constant is used as the non-magnetic garnet substrate used in the LPE method and a bismuth-substituted iron garnet single crystal conforming to it is grown, the lattice constant of the formed single crystal is increased. Becomes larger,
As a result, the absorption peak near 0.9 μm of the single crystal film shifts to the short wavelength side. Therefore, 0.93 to 1.
The absorption reduction effect occurs in the band of 05 μm, and the figure of merit is improved.

[0012]

EXAMPLES Hereinafter, experimental examples and comparative examples will be described. In Experimental Examples 1 to 7, the same substrate [lattice constant a = 12.561] was used.
Å Nd, Cr-doped Gd ₃ (ScGa) ₅ O ₁₂ ] was used. In the comparative example, the lattice constant a = 12.496Å (CaGd)
₃ (MgZrGa) ₅ O ₁₂ was used. 9 raw materials
It was melted at 50 ° C. for 10 hours and stirred at the same 950 ° C. for 3 hours. After that, the temperature was lowered to the single crystal growth temperature according to the material, and L
A magnetic garnet single crystal was grown by the PE method. The raw materials used in each experimental example and comparative example, the single crystal growth temperature, the film thickness and composition of the grown magnetic garnet are as follows. The substrates used in Experimental Examples 1 to 7 are doped with Nd and Cr, but the doping amount is about 1/100 of the main component, and the doping has no particular meaning.

(Experimental Example 1) Raw materials: Gd ₂ O ₃ , La ₂ O ₃ , Fe ₂ O ₃ , Bi ₂ O
₃ , PbO, B ₂ O ₃ single crystal growth temperature: 850 ° C. Magnetic garnet single crystal film thickness: 130 μm Magnetic garnet single crystal composition: Gd _1.5 La _0.5 Bi
_1.0 Fe ₅ O ₁₂ (Experimental Example 2) Raw material: Sm ₂ O ₃ , Fe ₂ O ₃ , Bi ₂ O ₃ , PbO,
B ₂ O ₃ single crystal growth temperature: 800 ° C. Magnetic garnet single crystal film thickness: 125 μm Magnetic garnet single crystal composition: Sm _1.8 Bi _1.2 Fe ₅
O ₁₂ (Experimental Example 3) Raw material: Gd ₂ O ₃ , Nd ₂ O ₃ , Fe ₂ O ₃ , Bi ₂ O
₃ , PbO, B ₂ O ₃ single crystal growth temperature: 760 ° C. Magnetic garnet single crystal film thickness: 120 μm Magnetic garnet single crystal composition: Gd _1.0 Nd _0.6 Bi
_1.4 Fe ₅ O ₁₂ (Experimental Example 4) Raw material: Gd ₂ O ₃ , Pr ₂ O ₃ , Fe ₂ O ₃ , Bi ₂ O
₃ , PbO, B ₂ O ₃ single crystal growth temperature: 740 ° C. Magnetic garnet single crystal film thickness: 140 μm Magnetic garnet single crystal composition: Gd _1.1 Pr _0.4 Bi
_1.5 Fe ₅ O ₁₂ (Experimental Example 5) Raw material: Gd ₂ O ₃ , La ₂ O ₃ , Fe ₂ O ₃ , Bi ₂ O
₃ , PbO, B ₂ O ₃ single crystal growth temperature: 720 ° C. Magnetic garnet single crystal film thickness: 145 μm Magnetic garnet single crystal composition: Gd _1.2 La _0.1 Bi
_1.7 Fe ₅ O ₁₂ (Experimental Example 6) Raw material: Gd ₂ O ₃ , Fe ₂ O ₃ , Bi ₂ O ₃ , PbO,
B ₂ O ₃ single crystal growth temperature: 700 ° C. Magnetic garnet single crystal film thickness: 135 μm Magnetic garnet single crystal composition: Gd _1.1 Bi _1.9 Fe ₅
O ₁₂ In this case, however, after the completion of the single crystal growth, cracks occurred during cooling, the interface of the magnetic garnet single crystal grown with the substrate. (Experimental Example 7) Raw materials: Tb ₂ O ₃ , Fe ₂ O ₃ , Bi ₂ O ₃ , PbO,
B ₂ O ₃ single crystal growth temperature: 680 ° C. Magnetic garnet single crystal film thickness: 120 μm Magnetic garnet single crystal composition: Tb _0.9 Bi _2.1 Fe ₅
O ₁₂ However, also in this case, cracks occurred at the interface between the substrate and the grown magnetic garnet single crystal during cooling after the completion of single crystal growth. (Comparative Example) raw material _{... Gd 2 O 3, Lu 2} O 3, Fe 2 O 3, Bi 2 O
₃ , PbO, B ₂ O ₃ substrate ... (CaGd) ₃ (MgZrGa) ₅ O ₁₂ single crystal growth temperature ... 730 ° C. magnetic garnet single crystal film thickness ... 145 μm magnetic garnet single crystal composition ... Gd _1.1 Lu _0.6 Bi
_1.3 Fe ₅ O ₁₂ Lu is used to match the lattice constant with the substrate.

With respect to the magnetic garnet single crystals produced in Experimental Examples 1 to 5 and Comparative Example, the absorption coefficient α (dB / cm) in each wavelength band of 0.85 μm to 1.31 μm was measured. The results are shown in Table 1. In the magnetic garnet single crystals of Experimental Examples 6 and 7, incident light was scattered due to cracks at the interface and did not pass therethrough, and therefore measurement was impossible.

From Table 1, the wavelength is 0.93 to 1.05 μm.
It is understood that the absorption coefficient of the magnetic garnet single crystals of Experimental Examples 1 to 5 is smaller than the absorption coefficient of the magnetic garnet single crystal of the comparative example within the range of m. That is, when Gd ₃ (ScGa) ₅ O ₁₂ having a large lattice constant is used as the substrate, the grown magnetic garnet single crystal is 0.93 to
The absorption coefficient decreases in the wavelength band of 1.05 μm.

[0016]

[Table 1]

Next, the Faraday rotation coefficient θ _F (deg / cm) at a wavelength of 0.98 μm of each sample was measured, and the performance index F (de
g / dB) was calculated. The results are shown in Table 2. In addition, the absorption coefficient α (dB / cm 2) and the bismuth substitution amount y (atm / fu) are also described.

From Table 2, the magnetic garnet single crystal of Experimental Example 1 has a small absorption coefficient α but a Faraday rotation coefficient θ _F.
Therefore, the figure of merit F was smaller than that of the magnetic garnet single crystal of the comparative example. Since the Faraday rotation coefficient is proportional to the bismuth substitution amount, the bismuth substitution amount y needs to be 1.2 atm / fu or more.

[0019]

[Table 2]

As described above, the samples of Experimental Examples 6 and 7 had cracks at the interface. As a result of various studies on it, it was found that the cause of the crack was due to the difference in the coefficient of thermal expansion between the substrate and the magnetic garnet single crystal grown on the substrate. FIG. 1 shows the relationship between the bismuth substitution amount y and the coefficient of thermal expansion β in Experimental Examples 1 to 7. Where the coefficient of thermal expansion β
Is a value defined by the following equation. β = Δt / t ₀ = [(thickness at 300 ° C.) − (thickness at 100 ° C.)] / (thickness at 100 ° C.) × [1/200] From FIG. 1, as the bismuth substitution amount y increases, It can be seen that the difference in the coefficient of thermal expansion between the substrate and the magnetic garnet single crystal becomes large. The broken line shows the coefficient of thermal expansion of the substrate.
This is irrelevant to the bismuth substitution amount y, but is shown as a straight line for convenience. Bismuth substitution amount of Experimental Example 6 y = 1.9 at
Above m / fu (indicated by x), the coefficient of thermal expansion β is large, and it is considered that cracks occur due to the increased stress. Therefore, the bismuth substitution amount is appropriately 1.7 atm / fu or less.

[0021]

INDUSTRIAL APPLICABILITY As described above, the present invention provides Gd ₃ (ScG
a) A non-magnetic garnet substrate having a large lattice constant of the chemical formula ₅ O ₁₂ is used, and R _3-xy Gd _x Bi _y Fe _{5 is formed} on the substrate.
Since the magnetic garnet single crystal film having a composition formula of O ₁₂ was grown by the LPE method, the wavelength was 0.
The figure of merit was improved in the 93 to 1.05 μm band, and a material usable as an optical isolator in that band was obtained. As a result, it becomes possible to put the 1.3 μm band using the praseodymium-doped fiber and the pumping light optical isolator of the fiber type optical amplifier in the 1.55 μm band using the erbium-doped fiber into practical use.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a Bi substitution amount y and a coefficient of thermal expansion β.

Claims (2)

[Claims] 1. A nonmagnetic garnet substrate having a composition represented by the chemical formula Gd ₃ (ScGa) ₅ O ₁₂ has a composition formula of R _3-xy Gd _x Bi _y Fe ₅ O ₁₂ where R is Sm,
One or more rare earth elements selected from Nd, Pr, and La 0 ≦ x <1.5 1.2 ≦ y ≦ 1.7 1.2 ≦ x + y <3, and magnetic properties grown by liquid phase epitaxial method Working wavelength with garnet single crystal film 0.93-1.0
Magneto-optical element material for 5 μm band. 2. A nonmagnetic garnet substrate having a composition represented by a chemical formula of Gd ₃ (ScGa) ₅ O ₁₂ is Nd,
The magneto-optical element material according to claim 1, which is doped with Cr.