JPH11268993A - Bismuth substitution type garnet thick membrane material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bismuth substitution type garnet thick membrane material that avoids the absorption intrinsic to TbBi garnet at >= about 1.6 μm wavelength and is improved in the changing rate of θF depending on temperature, its production method and additionally provide a Faraday rotary element which is used in the range of >1.5 μm wavelength. SOLUTION: In the garnet thick membrane for optical purposes that is grown by the liquid-phase growing process on the garnet substrate and mainly comprises Tb, Ha, Bi, Fe, and Al, the composition of the garnet thick membrane is represented by the formula: Tb3-x-y Hox Biy Fe5-z Alz O12 (0<x<=0.45, 0.90<=y<=1.50, 0.05<=z<=0.45) and platinum oxide (PtO2 ) is included in the garnet thick membrane in amount of 0-3.5 wt.% where zero is excluded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical garnet material having a Faraday rotation effect, and more particularly to a bismuth (Bi) -substituted garnet and a method for producing the same, and particularly to a liquid phase growth method (LPE method). (Tb, H
The present invention relates to an o, Bi) ₃ (Fe, Al) ₅ O ₁₂ based garnet single crystal thick film material and a method for producing the same.

[0002]

2. Description of the Related Art Hitherto, devices using Faraday rotation in optical communication have been developed and put into practical use. Also, in optical communication using semiconductor lasers, when reflected light from an optical fiber cable, a connector, or the like returns to the oscillation unit, the oscillation becomes unstable or stops. Therefore, an optical isolator is used to block return light and secure a stable oscillation state.

A Bi-substituted rare earth iron garnet having a large Faraday rotation is grown by an LPE method, a flux method, or the like, and is used as an isolator in the near infrared region. In particular, a garnet thick film grown by the LPE method has excellent productivity, and is currently mostly produced by this method.

[0004] Commercially available Bi-substituted garnet thick films produced by the LPE method are classified into GdBi-based and TbBi-based garnets. In the former, the lattice constant of the crystal is large, so that on the NGG substrate (lattice constant, about 12.509 angstroms), and in the latter, the lattice constant of the crystal is small, so that the SGGG substrate (lattice constant, about 12.496 angstroms). It is said that by growing above, a thick film can be stably grown, which is common sense in production.

A commercially available GdBi-based garnet material requires a small applied magnetic field, but is inferior in temperature characteristics (a narrow usable temperature range in a low temperature range and a large temperature change rate).

On the other hand, TbBi-based garnet materials have good temperature characteristics, but have the drawback of requiring a high applied magnetic field.

[0007] Further, the TbBi material uses an SGGG substrate in which the variation in lattice constant is essentially large due to the type of constituent elements, so that crystal defects and strains are liable to occur and homogeneity is inferior to that of the GdBi material. There is a trend.

[0008]

However, the trend in the market is to use TbBi-based garnets having good temperature characteristics.

The present invention relates to the improvement of a TbBi-based garnet thick film. When the basic composition of the TbBi-based garnet material is grown on an SGGG substrate which is considered to be suitable for the growth, the composition of the garnet becomes Tb _2.2 Bi _0.8 Fe ₅ O.
_{It is around 12} .

The optical characteristics of this TbBi-based garnet thick film are such that the Faraday rotation capability (θ _F ) is about 750 deg / c.
m, temperature change rate of Faraday rotation near room temperature (θ
_{F / T} ) is about 0.04 deg / ° C., and the insertion loss (IL) is
0.10~0.30dB, H _s is about 800Oe. However, with respect to this crystal, production of a film having a thickness of about 500 μm or more is not easy because cracks and crystal defects occur.

For this reason, companies that manufacture TbBi-based garnets take a method of reducing the problem caused by increasing the film thickness by improving θ _F.

The method is based on the basic composition of TbBi.
By substituting a part of Tb with Ho or Yb,
It increases the Bi composition value with garnet, but these are grown on an SGGG substrate as before.

Accordingly, in order to increase the number of Bi ions having a large ion radius, it is necessary to replace a large amount of Ho or Yb having a small ion radius.

[0014] Ho-based garnet and Yb garnet material, since significantly higher saturation magnetization (4 [pi] Ms) is at near room temperature compared to the Tb-based garnet, H _s of TbHoBi based garnet material and TbYbBi garnet material, 1
It will be about 000-1200 Oe. In addition, good temperature characteristics, which were characteristics of the Tb-based garnet material, tend to deteriorate.

As literatures on TbBi-based garnet films by the LPE method, see the Journal of the Japan Society of Applied Magnetics, Vol.
2, 1987, P157 and JP-A-60-208730,
JP-A-2-131216 and the like can be mentioned.
The content relating to the present invention has not been suggested.

Therefore, the technical problem of the present invention is that TbBi
Are those systems garnet repelling absorption essentially have to have a wavelength of about 1.6μm or more, an improved bismuth-substituted garnet thick film material of the temperature change rate of the theta _f the GdBi garnet and a manufacturing method thereof To provide.

Another technical object of the present invention is to provide a Faraday rotator used in a wavelength band exceeding about 1.5 μm among wavelengths.

[0018]

Means for Solving the Problems The present inventors have proposed SGGG.
TbBi on an NGG substrate with a larger lattice constant than the substrate
By growing a garnet-based material, the amount of substitution with rare earth elements having a small ionic radius such as Ho or Yb is reduced to a small amount,
By increasing the composition value, H _s (related to 4πMs) was suppressed, and an attempt was made to improve the TbBi-based garnet.

As a result, the TbHoBi-based garnet material has a specific solution (melt) composition, including a method of replacing a part of Fe with a small amount of Al in the TbHoBi-based garnet material. , Ho substitution amount significantly lower, and, H _s is 1000Oe following (conventional Tb
The HoBi material has found conditions for obtaining a material of about 1200 Oe).

The required characteristic θ _F at a wavelength of 1.55 μm as a TbBi-based garnet material is 800 deg /
cm or more, the H _s 1000Oe below, 0.07d the θ _{F / T}
This was carried out by setting the IL to 0.2 dB or less, and preferably 0.1 dB or less at a Faraday rotation angle of about 45 deg or less.

As a result, Tb, Ho, Bi, F
e, in a garnet thick film containing Al as a main component, platinum oxide (PtO ₂ ) is contained in the garnet in an amount of 0 to 3.5 wt%.
(But not including 0), it was found that IL was clearly reduced.

That is, according to the present invention, Tb, Ho, Bi, F grown on a garnet substrate by a liquid phase growth method.
a garnet thick film containing e and Al as main components, wherein the composition of the garnet thick film is represented by a general formula: Tb _3-xy Ho _x Bi _y
Fe _5-z Al _z O ₁₂ (provided that 0 <x ≦ 0.45, 0.90 ≦
y ≦ 1.50, 0.05 <z ≦ 0.45), and platinum oxide (PtO ₂ ) in the garnet thick film is 0 to
A bismuth-substituted garnet thick film material containing 3.5 wt% (but not including 0) is obtained.

According to the present invention, a Faraday rotator substantially consisting of the garnet thick film is obtained.

Further, according to the present invention, there is provided a method for producing a bismuth-substituted garnet thick film material in which the garnet thick film is grown on a neodymium gallium garnet (NGG) substrate.

Further, according to the present invention, there is provided a method for producing a bismuth-substituted garnet thick film material which is subjected to a heat treatment for maintaining the garnet thick film in a range of 950 to 1130 ° C.

Further, according to the present invention, there is obtained a method for producing a bismuth-substituted garnet thick film material in which the oxygen content of the atmosphere in the heat treatment is in the range of 10 to 100%.

Here, in the present invention, PtO _{2 is set} to 0 to
The reason why the content was set to 3.5 wt% (not including 0) was that even if a small amount of PtO ₂ was contained, the effect of reducing IL was recognized.
When the content exceeds 3.5 wt%, a remarkable increase in IL due to mismatch of ion balance is observed.

In the present invention, the TbHo having the above composition
Growing Bi-based garnets on NGG substrates is done by SG
Compared to GG substrate development, a Bi composition value can be easily increased, because it reduces the substitution of Yb and Ho causing a high H _s.

Further, in the present invention, the garnet thick film is formed in an atmosphere having an oxygen concentration of 10 to 100% in the atmosphere of 950 to 11%.
By performing heat treatment in a temperature range of 30 ° C., a reduction in IL is realized.

The oxygen concentration in the heat treatment atmosphere is 5-10.
The reason why the content is set to 0% is that if the content is less than 5%, correction of the ion balance of garnet constituent elements becomes insufficient due to lack of oxygen, and IL increases.

The reason why the heat treatment temperature is set in the range of 950 to 1130 ° C. is that if the heat treatment temperature is lower than 950 ° C., the homogenization of the crystal is insufficient, and the insertion loss hardly decreases. This causes insertion loss to increase significantly.

The liquid phase growth method of the Bi-substituted garnet used for such an optical isolator material is performed as follows.

In a platinum crucible, PbO, Bi ₂ O ₃ , B
The ₂ O ₃ or the like as the flux component, garnet component (Tb ₂
O ₃ , Ho ₂ O ₃ , Fe ₂ O ₃ , Al ₂ O ₃ )
After dissolving at 1100 ° C to make a solution (melt),
The temperature is lowered to a supersaturated solution state. By immersing the garnet substrate in the solution (melt) and rotating for a long time,
A Bi-substituted garnet thick film is grown.

The lattice constant of the grown garnet single crystal is constrained to be substantially the same as the lattice constant of the substrate, and the composition ratio of atoms is determined.

Therefore, it is extremely important to control the concentration of the supersaturated component, and the composition and crystallinity of the grown garnet change depending on the temperature and the flow state of the solution (melt), thereby causing a change in the material properties and the occurrence of crystal defects and cracks. .

In the current state of the LPE method, the crystal growth state is managed by controlling the composition of the solution, the temperature, the lattice constant difference from the substrate, the number of rotations of the substrate, and the like.

However, the optimum state of breeding is limited to an extremely narrow range, and it is almost impossible to adjust the factors independently by changing them. In particular, the main factor for the occurrence of cracks in the garnet crystal thick film is that the growth substrate and the garnet have different lattice constants and thermal expansions.

Accordingly, as the thickness of the garnet to be grown increases, the frequency of cracks increases, and the Faraday rotation performance of the garnet film is improved, and reducing the required thickness reduces the effect of reducing the occurrence of cracks. And industrially beneficial.

Regarding the characteristics shown in the present invention, since the garnet insertion loss (IL) relates to attenuation in the traveling direction of light, the smaller the better, the better the Faraday rotation capability θ _F is. As the temperature coefficient θ _{F / T} of the Faraday rotation becomes closer to 0, the temperature stability becomes better.

Further, a saturation applied magnetic field (saturation magnetic field H _s ) which is a minimum magnetic field required for the reduction of insertion loss to reach saturation.
The lower is, the lower the characteristics of the permanent magnet used for the magnetization of the garnet film can be, and the smaller and lighter can be realized.

[0041] Therefore, I.L. Reduction of, improvement of θ _F, θ _{F / T}
Reduction in decline, H _s is, industrial, be beneficial.

[0042]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) High-purity terbium oxide (Tb ₂ O ₃ ), holmium oxide (Ho ₂ O ₃ ), ferric oxide (Fe ₂ O ₃ ), aluminum oxide (Al ₂ O ₃₎ ),
Using powders of bismuth oxide (Bi ₂ O ₃ ), lead oxide (PbO) and boron oxide (B ₂ O ₃ ) as raw materials, PbO
Using a Bi ₂ O ₃ -B ₂ O ₃ flux as a flux, the main component ratio was Tbd _1.8 Ho _0.1 Bi _1.1 Fe _4.7 Al _0.3 O ₁₂ on an NGG substrate (lattice constant: 12.509 angstroms).
TbHoB having a composition containing about 1.0 wt% of PtO ₂
An i-type garnet film was grown to a thickness of about 600 μm.

A garnet thick film having a thickness of about 600 μm was grown on an SGGG substrate (with a lattice constant of 12.496 angstroms) by using the same solution (melt).

Next, these samples were removed and both surfaces were polished, and a Faraday rotation at a wavelength of 1.55 μm was performed for about 4 hours.
The thickness was adjusted to 5 deg.

The above composition was obtained by conducting EPMA analysis on each of the five surfaces of each of these samples at five points and calculating the average value.

Next, after subjecting these sample plates to a non-reflection coating treatment with a SiO ₂ film, a magnetic field of about 1.
5 kOe, and at a wavelength of 1.55 μm, the minimum applied magnetic field at which the transmittance reaches saturation (the saturation magnetic field H
_s ), insertion loss IL, Faraday rotation ability θ _F , and temperature change rate θ _{F / T} of θ _F near room temperature were determined. Table 1 shows the results.

[0048]

From Table 1, it can be seen that the garnet thick film grown on the NGG substrate is clearly superior in IL, θ _F and θ _{F / T.} Although H _s is slightly higher, practically is the difference to the extent that not a problem at all.

Therefore, it can be said that the growth on the NGG substrate is clearly beneficial.

(Second Embodiment) In the same manner as in the first embodiment, the main component ratio is set to Tb _1.5 H on an NGG substrate.
In _{o 0 .2 Bi 1.3 Fe 4.8 Al} 0.2 O 12, the PtO ₂ 0, 1.
A TbHoBi-based garnet thick film having a composition containing 0, 2.0, 3.0, 4.0, and 5.0 wt% was grown to a thickness of about 600 µm, and then a sample was prepared and measured.

[0052] Consequently, for all samples, H _s is about 850Oe, θ _F is about 1200deg _/ cm, θ _F / _T was about 0.06deg / ℃.

FIG. 1 shows the relationship between IL and PtO ₂ content. From Figure 1, by the inclusion of PtO _2, I.L. Decreases in a region where PtO ₂ exceeds 3.5wt%, I.L.
It can be seen that is significantly increased.

Therefore, the content of PtO ₂ is from 0 to 3.5 w
It can be said that the range of t% (not including 0) is useful. Further, desirably, PtO ₂ is in the range of 0.4 to 3.5 wt%, so that IL can be reduced to 0.1 dB or less.

(Third Embodiment) As in the first embodiment, the main component ratio is Tb _2.0 YHo _0.1 Bi _0.9 F
e in _{4 .9} Al _0.1 O _12, and a thickness of about 700μm growing a garnet thick film containing PtO ₂ to about 0.5 wt%.

Next, this sample was placed in an atmosphere of about 50% oxygen concentration at 950 ° C., 1000 ° C., 1050 ° C., 110 ° C.
It was kept at each of 0 ° C., 1130 ° C., and 1150 ° C. for 10 hours and heat-treated.

Next, both surfaces of these samples were polished, and the Faraday rotation at a wavelength of 1.55 μm was about 45 °.
It was measured after adjusting to a thickness of deg.

[0058] Consequently, for all samples, H _s is about 800 Oe, theta _F is about 900deg _/ cm, θ _F / _T was about 0.05 deg / ° C..

FIG. 2 shows the results of IL and heat treatment temperature. From FIG. 2, it can be seen that when the heat treatment temperature is in the range of 950 to 1130 ° C., the effect of reducing the IL by the heat treatment is recognized.

Therefore, it can be said that heat treatment in a temperature range of 950 to 1130 ° C. is useful.

(Fourth Embodiment) In the same manner as in the third embodiment, the main component ratio is Tb _1.3 Ho _0.3 Bi _1.4 Fe
A garnet thick film containing about 3.0 wt% of PtO ₂ was grown to a thickness of about 600 μm with _4.6 Al _0.4 O ₁₂ .

Next, this sample was heated at a temperature of 1050 ° C.
The oxygen concentration of the atmosphere is 0, 10, 20, 40, 60, 8
After setting the temperature to 0,100% and holding and heat-treating for 20 hours, a sample was prepared and measured.

[0063] Consequently, for all samples, H _s is about 900 Oe, theta _F is about 1300deg _/ cm, θ _F / _T was about 0.06deg / ℃.

FIG. 3 shows the relationship between IL and the heat treatment temperature.
FIG. 3 shows that the heat treatment has an effect of reducing the IL when the oxygen concentration in the heat treatment atmosphere is in the range of 10 to 100%.

Therefore, it can be said that a 10-100% oxygen concentration in the heat treatment atmosphere is useful.

[0066]

As described above, according to the present invention, the absorption at a wavelength of about 1.6 μm or more inherently possessed by TbBi-based garnets is avoided.
i system improved bismuth-substituted garnet thick film materials and manufacturing method thereof rate of temperature change theta _F garnet can be provided.

Further, according to the present invention, it is possible to provide a Faraday rotator used in a wavelength band exceeding about 1.5 μm among wavelengths.

[Brief description of the drawings]

FIG. 1 shows the content and insertion loss of PtO ₂ in a TbHoBi-based garnet thick film according to a second embodiment of the present invention.
L.).

FIG. 2 is a diagram showing a relationship between a heat treatment temperature and an insertion loss (IL) of a TbHoBi-based garnet thick film according to a third embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between oxygen concentration in a heat treatment atmosphere of a TbHoBi-based garnet thick film and insertion loss (IL) according to a fourth embodiment of the present invention.

Claims (5)

[Claims] 1. A garnet thick film mainly composed of Tb, Ho, Bi, Fe, and Al grown on a garnet substrate by a liquid phase growth method, wherein the garnet thick film has a general formula: Tb _3-xy Ho _x Bi _y Fe _5-z Al _z O
₁₂ (However, 0 <x ≦ 0.45, 0.90 ≦ y ≦ 1.50,
0.05 ≦ z ≦ 0.45), and the garnet thick film contains 0 to 3.5% by weight (but not including 0) of platinum oxide (PtO ₂ ). Bismuth substitution type garnet thick film material. 2. A Faraday rotator substantially consisting of the garnet thick film according to claim 1. 3. The method for producing a bismuth-substituted garnet thick film material according to claim 1, wherein the garnet thick film is grown on a neodymium gallium garnet (NGG) substrate. 4. The method according to claim 1, wherein the garnet thick film is 950-113.
4. The method for producing a bismuth-substituted garnet thick film material according to claim 1, wherein a heat treatment is performed at a temperature of 0 ° C. 5. The method according to claim 4, wherein the oxygen content of the atmosphere in the heat treatment is in the range of 10 to 100%.