JPS61113026A - Medium for magnetooptic element - Google Patents

Abstract

PURPOSE:To grow a thick film having >=45 deg. Faraday rotation angle in the wavelength region of 0.8mum band and 1.3-1.7mum band by specifying the compsn. of a bismuth-substd. iron garnet film. CONSTITUTION:The magnetic garnet film having the compsn. which contains elements Bi, Gd, Fe, R (R=Lu, Yb, Y, Tm), M (M=Ga, Al, Ge) and the balance O and unavoidable impurities and is x=0.4-0.8, y=0-0.1, z=0-0.1 in the chemical formula (Bi1-x-yGdxRy)3(Fe1-zMz)5O12 is grown by a liquid phase epitaxial method on a substrate. PbO, Bi2O3, Fe2O3, Ge2O3, B2O3, R2O3 and M2O3 (R=Lu, Yb, Tm, Y, etc., M=Ga, Al, Ge, etc.) are used as the molten mixture for growing the thick film by an LPE method. The compsn. and temp. of the molten liquid are so controlled that the growth rate attains >=0.5mum/min and the substrate is immersed into the molten liquid for 60-240 minutes, by which the film having >=30mum thickness and exhibiting the specular surface is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a medium for magneto-optical elements used in optical isolators and optical circulators essential for optical application equipment, optical communications, and the like.

[Prior Art] In optical equipment that uses a semiconductor laser as a light source, when reflected light from an end face of an optical connector or the like returns to the laser of the light source, the oscillation mode changes, causing noise. Optical isolators are used to block this return light. Lead glass and paramagnetic glass are used as optical isolators for wavelengths of 0.8 p and m bands, but their Faraday rotation coefficients are orders of magnitude smaller than those of ferromagnetic materials, and the rotation of the plane of polarization necessary for the device is In order to obtain this, it is necessary to cause multiple reflections and increase the optical path length to 10 cm or more. Therefore, it is inevitable that the device becomes larger, and the manufacturing cost is high due to the need for precision processing, making it difficult to obtain isolators for consumer devices.

Yttrium iron garnet single crystal is used in the wavelength range of 1.3 to 1.7 μm, which is important in optical communications. This single crystal is grown by a flux method or a traveling solvent floating zone method, and the end face of the single crystal cut into a cylindrical shape is optically polished.

It takes a long time (10 days or more) to grow a large single crystal, and defects such as flux inclusions often occur, resulting in low yields and high costs.Furthermore, it takes a relatively long time to saturate magnetization. It also has disadvantages, such as requiring a large magnetic field (~3 kOe), making the device large.

In this way, the optical isolators currently used are 0.8
There are many problems in both the gm band and the 1.3 to 1.7 JL11 band, and it is desired to develop a small, high performance, low cost optical isolator.

Bismuth-substituted iron garnet single crystals are currently attracting attention as a medium for small, high-performance optical isolators.

This bulk single crystal has already been grown using an improved flux method, but due to the large size and non-uniformity of the amount of bismuth substitution,
Problems remain in terms of cost and performance, such as low yield and the need for precision processing. For this reason, it is desired to establish conditions for growing a high-quality bismuth-substituted iron garnet thick film (thickness such that the Faraday rotation angle is 45 degrees at the wavelength of the light used) by the liquid phase epitaxial (LPE) method.

Usually, LP using PbO-B203-Bi203 as a solvent
In the E method, the film growth rate is 0.1 to 2 p-m/m.
It is in.

It is thought that if the growth time is increased, the film thickness will increase in proportion to the time, but in general, when the film thickness exceeds 307 zm, facet growth and flux inclusion occur during the growth, making it difficult to grow a good quality film. This prevents the film surface from exhibiting a mirror surface. Particularly in the case of bismuth-substituted iron garnet films, it is necessary to increase the degree of supersaturation in order to incorporate a large amount of bismuth and to lower the growth temperature, making it even more difficult to grow thick films with mirror surfaces.

[Objective] The object of the present invention is to control the 0.8 pm band and the 1.3-1.
An object of the present invention is to provide a medium for a magneto-optical element comprising a bismuth-substituted iron garnet film having an appropriately determined composition so as to enable the growth of a thick film with a Faraday rotation angle of 45 degrees or more in the 7 μm wavelength range.

[Structure of the Invention] In order to achieve such an object, the present invention consists of a magnetic garnet film with a thickness of 30 g or more grown on a substrate by a liquid phase epitaxial method, and containing elements Bi, Gd, Fe,
R (R=Lu, Yb, Y, Tm), M (M”Ga, A
n, Ge), residual ○ and unavoidable impurities, and its chemical formula (Bi Gd R) (Fe M
) 0, ×=1−x−y! y 3
1z z 5120.4~o, e, y* 0~0.1.
It is characterized by having a composition of z=0 to 0.1.

Here, as a molten mixture for growing a thick film by the LPE method, PbO, Bi2O3, Fe2O3, Gd2O
3゜B2O3, R2O3 and M2O5 (Rrowu, Yb
, Tm, Y, etc., =Ga, AJI, Ge, etc.) are used. These relative molar ratios (R parameters) are
Shown in the table.

Table 1 m- for thick film growth of bismuth-substituted iron garnet
Relative molar ratio of m As a substrate, the lattice constant is 12.508
NGG (Nd3Ga5012) which is A or 5-G (iG[(GdMgC) whose lattice constant is 12.497
a) A (GaZr)5012] substrate is used. Lattice mismatch between film and substrate is within ±0.005, growth rate is 0.5
By adjusting the composition and temperature of the melt so that it is at least p, m/min and immersing the substrate in the melt for 60 to 240 minutes, a film having a thickness of at least 301 Lm and exhibiting a mirror surface can be obtained.

[Example] The present invention will be described in detail below with reference to the drawings.

Example of film production under the above conditions and wavelength 0.81L
The magneto-optical properties at m are shown.

Example 1゜Among the molten mixture, AJI,.03 was used as M2O3 (R203 was not used), and the relative molar ratio was R1=1.
2. R2'0.011. R3=7.25. R
4=0.12°R5=0. A mixture was used in which R6 = 1.8.

(Bind) (Fe
AJl)5012 membrane was obtained. At a wavelength of 0.8 μm, the light absorption coefficient α of this film is α = 124 cm-', and the Faraday rotation coefficient θf is IθfI = 4800 deg/Cm.
The magneto-optical figure of merit is 8. ? deg/dB.

Example 2゜Yb2O was used as RO (M2O3 was not used), and its relative molar ratio was R1 = 15. R2=O, RA=7
．． 25. Ra' 0.11. Rs”0.1.
A mixture was used in which R6 = 1.8. 5-GG
(BiGdYb)31e50□2 with a thickness of 8Qp,m was obtained by immersing the G substrate in a melt at 803°C for 80 minutes.
A membrane was obtained. In this case, α=17 at wavelength Q, 8gn+
5cm', lθfl = 5350deg/Cl
11, and the magneto-optical figure of merit was 7.9 deg/dB.

Example 3: Using A9.0 as MO (R203 is for inconvenience),
The relative molar ratio is R,=12. R2=0.022
．． R3=7.25. R4=0.12. Rs =
A mixture in which O, R6 = 1.8 was used. 5-GGG
A film with a thickness of 140 μm was obtained by immersing the substrate in the melt at 845° C. for 80 minutes. Wavelength 0.8
p, m, a = 180cm”, Iθfl = 5500d
eg/am, and the magneto-optical figure of merit is f3. llde
g/dB.

All of the thick films obtained in Examples 1 to 3 had mirror surfaces, and the surface irregularities measured by a roughness meter were 2.00 Å or less. This indicates that it is possible to further increase the thickness by increasing the soaking time of the substrate.

FIG. 1 is a micrograph of a cross section of a thick film. It can be seen that the crystal is of good quality, although the film does not have defects such as inclusion bonds. The reason why the film surface is not straight is due to incomplete polishing. .

FIG. 2 shows the structure of an optical isolator made using thick film media according to the present invention. Here, 1 is a bismuth-substituted iron garnet thick film according to the present invention, 2 is a polarizing beam splitter disposed on both sides of this thick film 1, and 3 is a thick film 1, a beam splitter, and a ritter so as to apply a magnetic field to the thick film 1. A permanent magnet, for example a SmCo magnet (H=1
．． 8kOe) Yes.

This medium 1 has the NGO substrate of Example 1 removed by polishing, and has a Faraday rotation coefficient of 0.8Ii and 4 in the m band.
It was prepared by polishing it to a 5 degree angle. The characteristics of this medium are shown in Table 2.

2nd table thickness 9thickness d for various properties of the film
90IL growth temperature TG 8
40°C saturation temperature Ts 883°C temperature T, 300°C compensation temperature Tcosp -98°C saturation magnetic field Hs
5100e Farade one rotation coefficient θ(-
5020 deq/cm absorption loss α1 580
dB/cm The Curie temperature of this medium was 300°C and the compensation temperature was -98°C. Since the Faraday rotation coefficient at a wavelength of 3.78 Bm is approximately 5000 deg/am, the film thickness required for 45 deg rotation is 90 p.
It was m. Since the magnetic field required to saturate the magnetization of this medium is as small as 5100e, it is possible to saturate the magnetization with a smaller magnet than the permanent magnet 3 used in FIG. The characteristics of the isolator are that the wavelength is 9.78 g.
m, insertion loss is 13.3 dB, isolation is 18
It was dB. In order to improve these characteristics, it is essential to improve the magneto-optical figure of merit of the medium.
(FeAu) Wavelength 0.8 g in 5012 film
A film with a figure of merit of 10 deg/dB was obtained.

Furthermore, it has been found that by subjecting this film to reduction treatment, the absorption loss can be lowered and the figure of merit can be improved to 14 deg/dB. Therefore, with current technology, the insertion loss is 4 dB.
Hereinafter, it is also possible to create an element with an isolation of 20 dB or more.

Although the optical isolator has been described above, it is clear that the thick film according to the present invention is also suitable as a medium for other magneto-optical elements that use 45 degrees of Faraday rotation, such as optical circulators.

[Effects] As described above in detail, according to the present invention, it is possible to grow a high-quality bismuth-substituted iron garnet thick film having a thickness of 39 pm or more by the LPE method. The thick film medium of the present invention is effective for producing magneto-optical elements such as optical isolators and optical circulators, which are small in size, have high performance, are low in cost, and can also be expected to reduce the number of peripheral devices.

[Brief explanation of drawings]

Figure 1 shows (B+Gd) (Fe
Ajj) 50+. A micrograph showing the crystal structure of a cross section of the thick film, and FIG. 2 is a diagram showing an example of the configuration of an optical isolake using a magnetic garnet thick film.

Claims (1)

[Claims] The thickness grown on the substrate by liquid phase epitaxial method is 3.
Consists of a magnetic garnet film of 0 μm or more, containing elements Bi and G.
d, Fe, R (R=Lu, Yb, Y, Tm), M (M=
Ga, Al, Ge), including residual O and unavoidable impurities, and has the chemical formula (Bi_1_-_x_-_yGd_x
R_y)_3(Fe_1_-_zM_z)_5O_1_
2, x=0.4-0.8, y=0-0.1, z
1. A medium for a magneto-optical element, characterized in that it has a composition of =0 to 0.1.