JPH0654744B2 - Manufacturing method of bismuth substituted magnetic garnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to, for example, a magnetic garnet applied to an optical isolator, and particularly to a 0.8 μm wavelength band (0.8 μm wavelength band
A wavelength range of about 0.75 to 0.85 μm centering on a wavelength of 0.8 μm is generally referred to, and this specification also refers to this wavelength range.) Bismuth (Bi) substitution with reduced light absorption Magnetic garnet and its manufacturing method.

[Conventional technology]

For example, semiconductor lasers are widely used for various purposes including recording and / or reading of information on optical disks and magneto-optical disks.

However, when a semiconductor laser is used in this way, there is a disadvantage such as mode hopping noise when there is return light, so that the light emitted from the semiconductor laser should not return to the semiconductor laser as much as possible. In addition, there is an increasing need for an optical isolator that blocks this return light.

This optical isolator comprises a Faraday rotator element (1) and a polarizer (2) and an analyzer (3), as shown in the schematic structure of FIG. Faraday rotator (1)
The magnetic field is applied by the magnet (4) in the optical axis direction so that the plane of polarization of the linearly polarized light incident from the light source (5) such as a semiconductor laser through the polarizer (2) is rotated by 45 °. The axial direction of the analyzer (3) is selected so that the Faraday rotator (1) can pass the polarized light rotated by 45 ° so that the light passing therethrough irradiates the illuminated surface. Has been done. Then, in this case, when there is reflected light from the irradiated surface (6), that is, return light, this return light again passes through the analyzer (3) and the Faraday rotation element (1), and again at this time. Rotated 45 ° Polarizer (2)
Head to. Therefore, the returning light toward the polarizer (2) has its polarization plane rotated by 90 ° with respect to the incident light in the forward direction, and cannot pass through the polarizer (2). I can't go to (4). As described above, the optical isolator has a light transmitting property in one direction, that is, the forward direction, but has a blocking effect in the opposite direction.

As described above, the optical isolator has a function of blocking light in the reverse direction, but in order to reduce the light loss in the forward direction, it is desired that the Faraday rotator itself has as high a light transmittance as possible. To increase this light transmittance,
The thickness t of the Faraday rotator is desired to be as small as possible, but this thickness t requires a certain thickness in order to obtain the required angle of rotation, in the example above 45 °. .

The forward loss L (dB) during 45 ° rotation is (However, α is given by the light absorption coefficient and F is the Faraday rotation ability.) Therefore, in order to make L small, one having a small light absorption coefficient α is required.

This light absorption coefficient α depends on the wavelength and is 1.3
For long wavelength bands such as the μm wavelength band, Y
The Faraday rotator made of IG (yttrium, iron, garnet) has been able to achieve satisfactory results.

However, as a light source of the above-mentioned optical disc or magneto-optical disc, a semiconductor laser of 0.8 μm wavelength band such as AlGaAs type semiconductor laser is in the direction to be used, and the Faraday rotation about this 0.8 μm wavelength band is used. Development of elements is desired.

On the other hand, as a method of growing a magnetic garnet used for such a Faraday rotation element, that is, a rare earth iron garnet, a method of obtaining a crystal film by liquid phase epitaxy, that is, GGG (gadolinium gallium garnet) in a raw material melt is used. The method of growing a magnetic garnet film on this substrate by dipping the substrate and pulling up this substrate is excellent in mass productivity.In this case, the melt of this liquid phase epitaxy contains flux Is added. This flux is usually P
bO is used. However, when this PbO 2 is used as a flux, it is unavoidable that a part of Pb ²⁺ is mixed in the grown crystal film, which makes it difficult to reduce light absorption loss. It has been reported that the light absorption can be lowered by controlling the growth temperature of the crystal film even in the case of using PbO flux (Journal of Applied Physic.
s) Vol.45 P 2867 ~ 2873 July 1974) By the way,
Again, this is not effective in the 0.8 μm wavelength band.

Therefore, in order to prevent Pb ^{2+ from} being mixed in, a Bi-substituted magnetic garnet film, that is, a part of the rare earth element, was prepared by liquid phase epitaxy using a melt containing only Bi ₂ O ₃ as a flux.
It is possible to grow a magnetic garnet film substituted with Bi (Journal of Electrochemical Society) Vol.
123 P 1248 to 1249 1976).

However, in reality, even if the Bi-substituted magnetic garnet is grown by such a method, the light absorption cannot be sufficiently reduced. This is because the composition of Bi-substituted magnetic garnet is
For example (T ▲ m ³⁺ _2.3 ▼ B ▲ i ³⁺ _0.7 ▼) (F ▲ e ³⁺ _4.0 ▼ G ▲ a ³⁺
_1.0 ▼) O ₁₂ … (2) is actually T ▲ m ³⁺ _2.3 ▼ B ▲ i ³⁺ _0.7 ▼ F ▲ e ³⁺ _{4.0-2 δ} ▼ G ▲ a ³⁺ _{1.0
^{▼ ▲ O 2- 12- δ ▼ ...}} (3) 2 -valent Fe ions by the generation of oxygen vacancies as shown by the thereby is believed that light absorption occurs occurred.

In addition, as a method for obtaining a garnet film having magnetic anisotropy by liquid phase epitaxy, it was reported that CaCO ₃ was added to the flux (Material Research Bulltein VOL.11, PP337-346).
, 1976), but in this case, the flux is Bi ₂ O ₃
CeO ₂ / K ₂ O, SiO ₂ / Na ₂ O, or the like is added together with Bi ₂ O ₃ , not alone, and the light absorption has not been investigated.

[Problems to be solved by the invention]

As described above, there is a problem that the Bi-substituted magnetic garnet obtained by the conventional method has not obtained sufficiently small light absorption in the 0.8 μm wavelength band.

The present invention is to eliminate such problems,
A Faraday rotator element of an optical isolator that has a high transmittance in the 0.8 μm wavelength band and prevents a returning light when a semiconductor laser in the 0.8 μm wavelength band is used as a light source in a recording / reproducing apparatus for an optical disk, a magneto-optical disk, etc. The present invention provides a Bi-substituted magnetic garnet suitable for use as the above and a method for producing the same.

[Means for solving problems]

In the present invention, in a bismuth-substituted magnetic garnet formed by liquid phase epitaxial growth using a melt composed of Bi ₂ O ₃ and garnet constituent elements only, And a Bi-substituted magnetic garnet having the following composition. Then, select x such that 0.5 ≦ x ≦ 2.0,
y is selected in the range of 0 ≦ y ≦ 2, and 2δ is selected in the range of ± 15% around the value at which the light absorption in the 0.8 μm wavelength band is minimum.

In the present invention, in order to grow the above-mentioned bismuth-substituted magnetic garnet, a magnetic garnet is grown on a garnet substrate having small light absorption by liquid phase epitaxial growth from a melt composed of Bi ₂ O ₃ and garnet constituent elements only. Therefore, in this liquid phase epitaxial growth, the content of one or more IIA group element ions such as Ca and Be in the melt is close to the amount that gives the minimum light absorption in the 0.8 μm wavelength band. So add.

Thus, in the present invention, finally, for example, T ▲ m ³⁺ _{2.3-2 δ} ▼ B ▲ i ³⁺ _0.7 ▼ C ▲ a ²⁺ _{2 δ} ▼ F ▲ e ³⁺ _4.0
▼ G ▲ a ³⁺ _1.0 ▼ ▲ O _{12- δ} ▼ ... (4) Bi-substituted magnetic garnet is obtained.

[Action]

According to the present invention, for example, as seen in the above equation (4), F
constitutes a Bi-substituted magnetic garnet e ²⁺ is absent, due to the presence of Fe ²⁺ by such
It is possible to avoid an increase in light absorption in the 0.8 μm wavelength band.

〔Example〕

Example 1 A Bi-substituted magnetic garnet film was grown on a GGG substrate by liquid phase epitaxial growth. In this case, the melt used is The composition of the grown film was Tm _{2.3-2 δ} Bi _0.7 Ca _{2 δ} (Fe Ga) ₅ O ₁₂ when CaCO ₃ was added to the melt and the deviation coefficient between Tm and Ca was assumed to be the same. Was added. In this case, the grown crystal film has a thickness of 40 to 50 μm. This thickness is the initial GGG
It was calculated by measuring the weight change of the substrate.
Then, in that composition, 2δ is 0.005 and 0.02 respectively.
Crystal films, that is, Bi-substituted crystal films were grown, respectively, by changing to 5, 0.05, 0.06, 0.07, 0.08, 0.12. FIG. 2 shows the results of measuring the electrical resistivity ρ by the Seebeck effect for the crystal films of each of these compositions. This gives 2δ =
The resistance ρ shows a maximum at 0.07, and the conductivity type is n
It was found that the type was changed to the p-type. This is x
= 0.07, Fe ²⁺ ion is replaced by Ca ²⁺ ion,
It is considered that the composition became electrical compensation. Moreover, FIG.
The results of measuring the absorption coefficient α of each composition with respect to the wavelength λ = 0.81 μm are shown. The absorption coefficient α is 60 when x = 0.07.
It can be seen that it shows the minimum value of cm ^-1 . this is,
In the charge compensation composition, the absorption coefficient gone light absorption by Fe ²⁺ for Fe ²⁺ is absent α is expected to decrease (Journal of Aburaido Physics (Jour
nal of Applied Physics) Vol. 41 P 1211 ~ 1217,197
0). When 2δ is sufficiently larger than 0.07, it becomes p-type and the electrical resistivity ρ decreases, and the absorption coefficient also increases, which is ^presumably because Fe ⁴⁺ is generated from excess Ca ²⁺ ions. From this, 2δ = 0.07 ± 0.01, that is, Ca ²⁺
It can be said that 0.06 to 0.08 mol / fu (per molecular formula) is a desirable range in which a low absorption coefficient can be obtained.

In addition, the phenomenon of the above-described Example 1 is common to the rare earth iron garnet using only Bi ₂ O ₃ as the flux, and therefore, other rare earths are used as rare earths instead of Tm, and Ga that replaces Fe is used. Even when other trivalent Al is used instead, the same effect can be expected by adding Ca ²⁺ . In this case, since the deviation coefficient of Ca ²⁺ generally varies depending on the composition of the melt, the amount of Ca ²⁺ that gives the minimum absorption coefficient is considered to be different from that in Example 1, but Ca ²⁺
A minimum is always obtained by selecting the amount, and if Ca ^{2+ of} ± 15% before and after the amount of Ca ²⁺ that gives this minimum is added,
It was confirmed that a significant reduction in light absorption could be obtained.

Comparative Example Liquid phase epitaxy was performed on a GGG substrate using a melt having the following composition to grow a crystal film.

At this time, the film thickness was 46.6 μm, the light absorption coefficient α was 300 cm ⁻¹ , and the electrical resistivity ρ was 1.39 × 10 at the wavelength λ = 0.81 μm.
^The conductivity type measured by the Seebeck effect was ⁵ Ω · cm and was n-type. Such high light absorption and low resistivity are considered to be due to generation of Fe ²⁺ ions due to oxygen vacancy.

Example 2 A crystal film having a thickness of 96 μm on each side was grown on both sides of a GGG substrate by a melt having the following composition, and then punched out to a diameter of 6 mm to produce the Faraday rotator (1) described in FIG. did.

At this time, the Frayday rotation angle is 45 °, and the Faraday rotation capability is F.
Was 0.23 ° / μm, and the light absorption coefficient α was 59 cm ⁻¹ . Using the Faraday rotator (1) to construct the optical isolator explained in Fig. 1, the optical absorption loss in the forward direction is 5 dB,
The isolation (extinction ratio) was 34 dB. In addition, since the thickness t can be further reduced by forming a grown film having a larger Faraday rotation capability F, the forward direction
The loss of light in the 1.8 μm wavelength band can be made smaller.

〔The invention's effect〕

As described above, according to the present invention, it is possible to obtain a Bi-substituted magnetic garnet having a small light absorption in the 0.8 μm wavelength band. Therefore, by using this as a Faraday rotator element of an optical isolator, for example, When a semiconductor laser is used, the returned light is blocked and a stable operation is performed in the semiconductor laser, and a high transmittance for forward light, that is, a low optical loss can be achieved. It can be used as a recording / reproducing light source system for various kinds of information such as, and has a great practical advantage.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical isolator to which the Bi-substituted magnetic garnet according to the present invention can be applied, and FIGS. 2 and 3 are measurement curve diagrams of the resistivity ρ and the optical absorption coefficient α used for explaining the present invention. (1) is a Faraday rotation element, (2) is a polarizer, (3) is an analyzer, (4) is a magnet, (5) is a light source, and (6) is a surface to be illuminated.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshiro Yamada 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo, Sony Corporation (56) References JP-A-56-22699 (JP, A) JP-A-SHO 57-50407 (JP, A)

Claims (1)

[Claims] 1. A liquid phase epitaxial growth method using a melt composed only of Bi ₂ O ₃ and a magnetic garnet constituent element. And x is 0.5 ≦ x ≦ 2.0, y is 0 ≦ y ≦ 2, and 2δ is 0.8 μ.
A method for producing a bismuth-substituted magnetic garnet, which comprises obtaining a bismuth-substituted magnetic garnet selected within a range of ± 15% around a value at which the light absorption in the m wavelength band is minimal.