JP2000221448A - Optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously realize miniaturization, lightening in weight and the reduction of cost by constituting a permanent magnet for applying magnetic field to a Faraday rotator of ferrite sintered magnet. SOLUTION: This optical isolator consists of two polarizing elements, the Faraday rotator and the permanent magnet, and the permanent magnet is constituted of the ferrite sintered magnet 41 such as Ba ferrite or Sr ferrite. It is not matter whether the magnet 41 is an isotropic magnet or an anisotropic magnet. The cross section perpendicular to the magnetization direction of the magnet 41 can be formed in cylindrical shape, square frame shape or recessed shape. The magnet 41 satisfying relation 0<S1/2/t<=5.5 is used in the optical isolator assuming that the length in the magnetization direction is (t) and the cross section is S. The ratio Hm/4πMs of a value expressing maximum magnetic field intensity Hm generated in space inside the magnet 41 by the unit of oersted to a value expressing the saturation magnetization 44πMs of the Faraday rotator by the unit of gauss is set to >=0.7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for optical communication equipment, optical information processing equipment, etc., and transmits light in one direction only.
The present invention relates to an optical isolator that is an optical element that blocks light in a reverse direction.

[0002]

2. Description of the Related Art When light emitted from a light source is transmitted using an optical system, light reflected at an end face of an optical element in the optical system returns to the light source. For example, in optical communication, light emitted from a laser light source is converged by a coupling lens and collected on an end face of an optical fiber. When the optical isolator is not used, a part is reflected on the end face of the optical fiber and returns to the laser light source. The light returned to the laser light source is generally different in phase and polarization direction from the light emitted from the laser light source, which may disturb the laser oscillation, generate noise in the emitted light, or even stop the laser oscillation. is there.

[0003] An optical isolator is used to block such return light. Optical isolators have high return light blocking characteristics (isolation, extinction ratio),
It is required that transmission loss (insertion loss) of incident light be low.

FIG. 6 is a sectional view showing the structure of an optical isolator. In FIG. 6, the optical isolator includes a Faraday rotator 3, two polarizing elements 1, a permanent magnet 4, a holder 2, and a housing 5. The Faraday rotator 3 and the polarizing element 1 are fixed to the housing 5 via the holder 2 and the permanent magnet 4 by an adhesive, solder, laser welding, or the like.

In the optical isolator shown in FIG. 6, the magnetic material constituting the Faraday rotator 3 needs to have a magnetic field intensity enough to magnetize the magnetic material in one direction, so that the permanent magnet 4 requires a certain volume.

[0006]

Since the permanent magnet 4 of the optical isolator has a structure including the Faraday rotator 3, the outer diameter of the optical isolator corresponds to at least the thickness of the permanent magnet 4. It becomes extra large by the amount. Optical isolators, like other optical components,
There is a demand for further reduction in size, weight, and cost. The use of high-performance rare earth permanent magnets is effective for miniaturization, but has been left as an issue for cost reduction.

An object of the present invention is to provide an optical isolator that is simultaneously reduced in size, weight, and cost.

[0008]

An optical isolator according to the present invention comprises two polarizing elements, a Faraday rotator, and a permanent magnet.
It is composed of a sintered ferrite magnet such as Sr ferrite. The ferrite sintered magnet may be an isotropic magnet or an anisotropic magnet. The cross section perpendicular to the magnetization direction of the sintered ferrite magnet may be a cylindrical shape, a square frame shape, a concave shape, or the like.

In the optical isolator according to the present invention, when the length t in the magnetization direction and the sectional area are S, 0 <S ^1/2.
By using a ferrite sintered magnet satisfying the relationship of /t≦5.5, high isolation can be obtained.

Further, in the optical isolator according to the present invention, the maximum magnetic field strength Hm generated in the space inside the sintered ferrite magnet in units of Oersted (Oe) and the saturation magnetization 4πMs of the Faraday rotator are represented by Gauss (G). )), A high isolation can be obtained by setting the ratio of the values expressed in units of Hm / 4πMs to 0.7 or more.

In the optical isolator of the present invention, a GdBi garnet thick film or a TbBi garnet thick film produced by a liquid phase epitaxial method is used as a Faraday rotator.

[0012]

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

The Faraday rotator of the optical isolator according to the present invention includes a GdBi-based garnet thick film and a T film formed by a liquid phase epitaxial growth method (hereinafter referred to as an LPE method).
A bBi-based garnet thick film is used. The GdBi-based garnet thick film and the TbBi-based garnet thick film are characterized by having easy magnetization in the film thickness direction and having a lower saturation magnetization than other rare earth garnet thick films. If a part of Fe in the GdBi-based garnet thick film and the TbBi-based garnet thick film crystal is replaced with Al or Ga, the saturation magnetization 4πMs can be further reduced to 500G or less. As a result, the intensity of the applied magnetic field for saturating the magnetization of the Faraday rotator can be reduced, and it is not necessary to enhance the characteristics of the permanent magnet for applying the magnetic field, and the cost of the optical isolator can be reduced. The saturation magnetization 4πMs of the Faraday rotator is 5
If it is 00G or less, the applied magnetic field strength required for the magnetization of the Faraday rotator made of a garnet thick film can be reduced without using an expensive rare-earth permanent magnet without using a remarkable increase in volume. And can easily be obtained.

In the present invention, the material of the permanent magnet is defined as a sintered ferrite magnet because the powdered metallurgy method makes it possible to easily achieve a dense and stable high magnet property, and also has a sufficient mechanical strength. Is obtained. These ferrite sintered magnets can be anisotropic magnets in addition to isotropic magnets. Although isotropic magnets have relatively low magnet properties, they are expected to improve the fluidity of the powder in the molding process, so that the degree of freedom of the shape of the molded body is extremely high and can be manufactured at low cost. On the other hand, anisotropic magnets have a lower degree of freedom in formability than isotropic magnets, but have improved magnet properties, and can be reduced in size and weight.

In the present invention, a sintered magnet of Ba-based ferrite or Sr-based ferrite is used as the permanent magnet for applying a magnetic field. These ferrite sintered magnets are made of Ba
Since it is an oxide containing O, SrO, and Fe ₂ O ₃ as main components, it is extremely chemically stable as compared with rare earth permanent magnets and the like.
There is no need to perform corrosion or oxidation prevention treatment. Since raw materials of Ba-based ferrite and Sr-based ferrite are inexpensive, they are useful in realizing a low-cost optical isolator.

Therefore, the sintered ferrite magnet can also serve as a housing for the optical isolator. The optical isolator of the present invention is configured to include an optical element including a polarizing element and a Faraday rotator in a space inside a sintered ferrite magnet. Needless to say, this configuration can be arranged in a housing made of stainless steel or the like, as in a conventional optical isolator.

[0017]

EXAMPLES The present embodiment will be described in detail below with reference to examples.

Example 1 A garnet thick film was formed by the LPE method.
Produced by High purity gadolinium oxide (Gd
₂O₃), Ferric oxide (Fe₂O₃), Gallium oxide
(Ga₂O₃), Aluminum oxide (Al₂O₃),acid
Bismuth (Bi)₂O₃), Lead oxide (PbO) and acid
Boron boride (B₂O₃) Powder and PbO-Bi₂
O₃-B₂O ₃Using the system as flux, the NGG substrate (grating
(Constant 12.5094 angstroms).
Bo (Gd_1.9Bi_1.1) (Fe_4.3Al_0.4G
a_{0. 3}) O₁₂GdBi garnet thick film represented by
Was grown to a thickness of about 600 μm.

Further, terbinium oxide (Tb ₂ O ₃ ) is used instead of gadolinium oxide, and Sb is used instead of the NGG substrate.
GGG substrate (Lattice constant: 12.496 angstroms)
(Tb _2.0 Bi) by the LPE method using
_{1.0) (Fe 4.1 Al 0 .4} Ga 0.5) was grown TbBi garnet thick film is represented by _{O 12.} These GdBi garnet thick films and TbBi garnet thick films each contained ₃ wt% or less of B ₂ O ₃ and PbO.

After each removal of the substrate, these garnet thick films were heat treated at a temperature of 1050 ° C. in a 50% oxygen atmosphere. By measuring magnetic properties using a vibrating magnetometer, these garnet thick films were found to have a saturation magnetization (4πM
s) was 100 to 150 G, and it was confirmed that the film had easy magnetization in the film thickness direction. The Faraday rotation ability of these garnet thick films at a wavelength of 1.55 μm is about 1
000 deg / cm.

Each garnet thick film was adjusted so that the Faraday rotation angle at a wavelength of 1.55 μm was about 45 deg (film thickness of about 450 μm), cut after AR coating treatment, and the length of one side was 1.3 mm. Into a square Faraday rotator. An optical element was manufactured by arranging the polarization planes of each other so as to be 45 deg, and sandwiching a Faraday rotator between two glass polarizers.

FIG. 1 is a configuration diagram of an optical isolator constituted by mounting an optical element on an isotropic cylindrical ferrite sintered magnet. The permanent magnet is an isotropic cylindrical ferrite sintered magnet 41 having an outer diameter of 4 mm, an inner diameter of 2 mm, and a height of 2 mm.
(Sr-based ferrite, Ba-based ferrite). The optical element 6 is mounted on the inner cylindrical portion of the isotropic cylindrical ferrite sintered magnet 41, and a magnetic field of about 10 kOe is applied using an electromagnet to raise the isotropic cylindrical ferrite sintered magnet 41 to a high level. The optical isolator was manufactured by magnetizing in the vertical direction.

The magnetic properties of the isotropic cylindrical ferrite sintered magnet 41 used in the present embodiment are as follows: Sr ferrite has Br of 2200 G, iHc of 3000 Oe, and Ba ferrite has Br of 2000 G and iHc of 2500 Og.
e. In addition, an isotropic ferrite sintered magnet has an advantage in that the powder filling is better than that of an anisotropic ferrite sintered magnet, so that there is little deformation due to sintering.

The characteristics of the optical isolator according to this embodiment are as follows.
At a wavelength of 1.55 μm, there is no difference due to the type of the garnet thick film and the material of the ferrite sintered magnet, and the isolation is about 45 dB and the insertion loss is about 0.2 dB.
Was good.

(Embodiment 2) FIG. 2 is a structural view of an optical isolator constituted by mounting an optical element on an isotropic square frame ferrite sintered magnet. The optical isolator according to the present embodiment is configured such that the same optical element 6 manufactured in the first embodiment is directly mounted inside a square frame of an isotropic square frame-shaped ferrite sintered magnet 42. The isotropic square frame-shaped ferrite sintered magnet 42 has an outer dimension of 2.5 mm × 2.5 m.
m, inner dimensions 1.5 mm × 1.5 mm, thickness 2 mm, magnetized in the thickness direction.

The characteristics of the optical isolator according to this embodiment are as follows.
At a wavelength of 1.55 μm, the isolation is about 45
The dB and the insertion loss were about 0.2 dB, which was good and independent of the type of the garnet thick film and the material of the sintered ferrite magnet.

(Embodiment 3) FIG. 3 is a structural view of an optical isolator in which an optical element is mounted on an isotropic concave ferrite sintered magnet. Concave ferrite sintered magnet 43
Are the square frame-shaped ferrite sintered magnets 42 used in Example 2.
The cross section has a concave shape as if one side was removed. The optical isolator according to the present embodiment is configured by mounting the same optical element 6 as manufactured in the first embodiment, as it is, inside the square frame of the concave shaped ferrite sintered magnet 43.
The isotropic concave ferrite sintered magnet 43 has an outer dimension of 2.5 mm × 2.5 mm, a width of 1.5 mm and a depth of 1.8 mm.
With a thickness of 2 mm and magnetized in the thickness direction.

The characteristics of the optical isolator according to this embodiment are as follows.
At a wavelength of 1.55 μm, the isolation is about 45
The dB and the insertion loss were about 0.2 dB, which was good and independent of the type of the garnet thick film and the material of the sintered ferrite magnet.

(Embodiment 4) This embodiment shows an optical isolator using an anisotropic magnet as a sintered ferrite magnet. The same optical element produced in Example 1 is directly attached to anisotropic sintered ferrite magnets of various shapes. Anisotropic cylindrical ferrite magnets, square frame ferrite magnets, and concave ferrite magnets are used for each optical isolator in the same manner as in the first, second, and third embodiments. I have. The shape and size of each ferrite sintered magnet are as follows. Anisotropic cylindrical ferrite magnet: outer diameter 3 mm, inner diameter 2 mm, height 2 mm, anisotropic square frame ferrite magnet: outer dimension 2.0 mm x 2.0 mm, inner dimension 1.5 m
m × 1.5 mm, thickness 2 mm, anisotropic concave ferrite magnet: outer dimensions 2.0 mm × 2.0 mm, width 1.5 m
m, with a 1.7 mm deep groove, 2 mm thick. These anisotropic ferrite sintered magnets are magnetized in the height direction or the thickness direction, and are smaller in size than the isotropic ferrite sintered magnets used in Examples 1 to 3. ing.

The characteristics of the anisotropic sintered ferrite magnet used in this embodiment are as follows.
0G, iHc is about 2000 Oe, Sr ferrite
Br was about 4000 G and iHc was about 3000 Oe.

The characteristics of the optical isolator according to this embodiment are as follows.
At a wavelength of 1.55 μm, the type of garnet thick film (G
Regardless of the material and shape of the dBi-based or TbBi-based) and sintered ferrite magnets, the isolation was about 45 dB and the insertion loss was about 0.2 dB, which was good.

(Embodiment 5) FIG. 4 is a diagram showing isolation using the cross-sectional area S of the sintered ferrite magnet and the length t in the magnetizing direction as parameters. According to the optical isolator having the same configuration as that of each of the above embodiments, S ^1/2 / t is 5.
If it exceeds 5, the isolation sharply decreases. From these results, it is useful to provide an optical isolator having S ^1/2 / t of 5.5 or less.

The size of the optical element used in this embodiment is 0.7.
The outer dimensions of the sintered ferrite magnet are 1.0 to 5.0 mm, the thickness is 1.0 to 7.0 mm, and S
^1/2 / t is 0.2 to 6.0.

Here, S^1/2/ T = 0 is ferrite
Since there is no sintered magnet, S ^1/2/ T = 0 includes
No. Effectively S^1/2In the region where / t = 0.1 or more
Be practical. S^1/2When /t=5.5 is exceeded,
The isolation of the isolator is significantly deteriorated. S
^1/2When /t=5.5 or less, the ferrite sintered magnet
High magnetic field strength and homogeneity
Solation is secured.

(Example 6) FIG. 5 is a diagram showing an isolation in which the ratio Hm / 4πMs between the maximum magnetic field strength Hm generated in the space in the sintered ferrite magnet and the saturation magnetization 4πMs of the garnet thick film is used as a parameter. It is. The unit of the maximum magnetic field strength Hm is Oersted (Oe), and the saturation magnetization is 4π.
When the unit of Ms is represented by Gauss (G), respectively, Hm
When / 4πMs = less than 0.7 Oe / G, the isolation sharply decreases. When Hm / 4πMs is 0.7 or more, the alignment of the magnetic moment of the garnet thick film is improved, and high isolation is obtained. from this result,
It can be seen that an optical isolator with Hm / 4πMs = 0.7 or more is useful.

The Faraday rotator of the optical isolator of this embodiment has a 4πMs of 30 to 500 G and a wavelength of 1.55 μm.
The Faraday rotation capability at m is 800-1200 deg
/ Cm, G showing each value of Hm / 4πMs of 0.4 to 2.5.
A dBi garnet thick film was used.

The sintered ferrite magnet can also serve as the housing of the optical isolator as it is, thereby significantly reducing cost and size. An optical isolator using a rectangular frame-shaped or concave-shaped ferrite sintered magnet also facilitates automatic mounting in surface mounting. In addition, the optical isolator using the concave shaped ferrite sintered magnet has an advantage that the mounting of the optical element to the ferrite sintered magnet becomes extremely easy during the manufacturing process of the optical isolator.

It should be noted, the polarizer need not be limited to a glass polarizer, rutile, may be used birefringent material such as YVO _4. The ferrite sintered magnet for applying a magnetic field is not limited to a single sintered body, and may be configured by combining a plurality of sintered magnets.

[0039]

As described above, according to the present invention,
By using a ferrite sintered magnet as the permanent magnet for applying a magnetic field, an optical isolator that is reduced in size, weight, and cost can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical isolator of the present invention in which an optical element is mounted on an isotropic cylindrical ferrite sintered magnet.

FIG. 2 is a configuration diagram of an optical isolator of the present invention in which an optical element is mounted on an isotropic square frame ferrite sintered magnet.

FIG. 3 is a configuration diagram of an optical isolator of the present invention in which an optical element is mounted on an isotropic concave ferrite sintered magnet.

FIG. 4 is a diagram showing isolation using a bottom area S and a thickness t of a sintered ferrite magnet as parameters.

FIG. 5 is a view showing an isolation using a ratio Hm / 4πMs between a maximum magnetic field intensity Hm generated in a void portion in a ferrite sintered magnet and a saturation magnetization 4πMs of a garnet thick film as a parameter.

FIG. 6 is a configuration sectional view of an optical isolator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polarizing element 2 Holder 3 Faraday rotator 4 Permanent magnet 5 Housing 6 Optical element 41 Cylindrical ferrite sintered magnet 42 Square frame ferrite sintered magnet 43 Concave ferrite sintered magnet

Claims (9)

[Claims] 1. An optical isolator having two polarizing elements, a Faraday rotator disposed between the polarizing elements, and a permanent magnet for applying a magnetic field to the Faraday rotator, wherein the permanent magnet is a sintered ferrite magnet. An optical isolator comprising: 2. The optical isolator according to claim 1, wherein said ferrite sintered magnet is Ba ferrite or Sr ferrite, and is an isotropic magnet. 3. The optical isolator according to claim 1, wherein said ferrite sintered magnet is Ba ferrite or Sr ferrite, each of which is an anisotropic magnet. 4. The optical isolator according to claim 1, wherein the sintered ferrite magnet has a cylindrical shape. 5. A cross section perpendicular to the magnetization direction of the ferrite sintered magnet has a square frame shape.
An optical isolator according to claim 3. 6. The optical isolator according to claim 1, wherein a cross section perpendicular to a magnetization direction of the sintered ferrite magnet has a concave shape. 7. When the length of the ferrite sintered magnet in the magnetizing direction is t and the sectional area is S, 0 <S ^1/2 / t ≦
7. The method according to claim 1, wherein said value is 5.5.
An optical isolator according to any one of the above. 8. The Faraday rotator includes a GdBi garnet thick film produced by a liquid phase epitaxy method,
The optical isolator according to any one of claims 1 to 7, wherein the optical isolator is a TbBi garnet thick film. 9. A maximum magnetic field strength Hm generated in a space in the ferrite sintered magnet whose unit is expressed by Oersted and a saturation magnetization 4π of the Faraday rotator whose unit is expressed by Gauss.
The optical isolator according to any one of claims 1 to 8, wherein a ratio with respect to Ms, Hm / 4πMs, is 0.7 or more.