JPS61179413A - optical isolator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical isolator used in fields such as optical communication, optical measurement, and optical recording.

Conventional technology Conventionally, magneto-optical elements used in optical isolators include:
For use wavelength 1.371Zm, Y3Fe5O12°0.
Paramagnetic Faraday glass has been used for 8 μm.

However, the rare earth site of rare earth iron garnet is Bi
Since atomic substitution increases the Faraday rotation ability, optical isolators using various Bi-substituted rare earth iron garnets as magneto-optical elements have recently been reported. For example, the Japanese Society of Applied Magnetics Bi Vol s
yvh2. Growth using the stirring scooping flux method reported in P125 (1984) 1.15 1.85
This is an optical isolator using Fe5O12 as a BiGd element with magnetic optical elements. Also, Applied Magnetics Society 5c+ Vol 8 tK 2, P 129
(1984), Yb Pr Bi G was grown by the liquid phase epitaxial method reported in (1984).
dFe 02.25 0.34 0.73
There is a report on an optical isolator using 1.85 5 12 as a magneto-optical element in a waveguide type.

In addition, there are several reports on Bi-substituted garnet grown by liquid phase epitaxial growth as magneto-optical elements for optical isolators.

Problems to be Solved by the Invention In the optical isolator of the prior art described above, the amount of Bi substitution in the Bi-substituted glass used as a magneto-optical element is small, and the Faraday rotation ability, which increases with the amount of Bi substitution, is also small. If the amount of Bi substitution is increased, the Faraday rotation ability increases, and the magneto-optical element that obtains the Faraday rotation angle of 45° necessary for use in an optical isolator can be made smaller. By shortening the optical path length in the magneto-optical element, the turbulence of linearly polarized light can be reduced and the isolation ratio can be improved. The stirred scooping flux method has poor fractionation, and if mass production and cost reduction are desired, liquid phase epitaxial growth, which has good fractionation and can grow in a short time, is suitable. Furthermore, in liquid phase epitaxial growth, if the thickness of the grown magnetic garnet film exceeds 150 μm, it is difficult to obtain a homogeneous film without defects. In order to be able to use a thin garnet film that is easy to grow for an optical isolator, it is necessary to increase the amount of Bi 2 substitution.

In liquid phase epitaxial growth, it is necessary to reduce the difference in lattice constant between the substrate and the grown film in order to obtain a homogeneous film without distortion and defects in the grown film, but when rare earth iron garnet is replaced with Bi, the amount of Bi replaced is reduced. Accordingly, the lattice constant of Bi-substituted rare earth iron garnet increases. If the grown film is distorted, the extinction ratio of the grown film decreases, which causes a decrease in the isolation run ratio when used in an optical isolator.

The structure of an optical isolator is such that light propagates using a liquid-phase epitaxially grown magnetic garnet, which is a magneto-optical element, as a waveguide, or a structure in which light passes in a direction perpendicular to the surface direction of the substrate. Coupling loss at the optical fiber part of an optical isolator such as a fiber is large.

Further, there is a problem in that the operation of the semiconductor laser, which is the light source, becomes unstable due to reflected light from each component that constitutes the optical isolator.

It is an object of the present invention to solve the above-mentioned problems and provide a high-performance optical isolator that is lightweight, compact, easily mass-produced, has a high isolation ratio, and has low loss at a low price.

Means for Solving the Problems In order to solve the above problems, the present invention uses Lu3Fe5Q12, which has the smallest lattice constant among rare earth iron garnets, as a rare earth iron garnet base material for Bi substitution,
Transparent Gd Ga O lattice constant is 3312' in the 0.8 μm band, 1.3 μm band, and 1.5 μm band, and the wavelength is O, a μm band, 1.3 μm band, and 1.5 μm.
Ca-Mg-Zr substituted Gd5G transparent to m light
a5Q12 or even larger lattice constant, 0.
Transparent N in 8 μm band, 1.3 μm band, and 1.5 μm band
Composition grown by liquid phase epitaxial growth using d3G a 3O12 as a substrate ix Lu 3-, Fe501
2 (however, 1.Q≦x≦3.0), a high isolation ratio, low retardation magnetic garnet thin film is used as a magneto-optical element, and the light incident direction is parallel to the plane direction of the substrate, The object is to obtain a high-performance optical isolator that is lightweight, compact, easily mass-produced, has a high isolation ratio, and has low loss.

Effect of the Invention With the above-described configuration, the present invention can obtain a magnetic garnet film with a large amount of Bi substitution without increasing the difference in lattice properties with the substrate, and can be made thin as a magneto-optical element for an optical inlator. This makes it possible to obtain an optical isolator that is lightweight, compact, easily mass-produced, has a high isolation ratio, and has low loss.

EXAMPLE A semiconductor laser module with an optical inulator will be described below as an example of the present invention with reference to FIG. In FIG. 1, 1 is a semiconductor laser, and 2 is a lens that condenses light emitted from the semiconductor laser 1 and couples it to an optical fiber 3. 4 is Ca-Mg- with a lattice constant of 12.497A
A Zr-substituted Gd3Ga5O12 substrate is used, and 5 is a (B iL u ) s Fe so12 film grown on one side thereof by liquid phase epitaxial growth without mismatching of lattice constants. 6 is a permanent magnet for applying a saturation magnetic field to (B t L u ) 3F e s 012, 7 is a semiconductor laser 1
This is a polarizer arranged in a direction rotated by 46° from the polarizing power of the linearly polarized light emitted from = j9J.

The composition of (BiLu)3Fe601□ 5 is B 12.
oLu 1. .

F li) s 012 , and the wavelength used is O, Sμ
Faraday rotation ability at m is approximately 14000 deg/Cn
1, the film thickness is approximately 32 μm in order to obtain a Faraday rotation angle of 45°. Also (BiLu)3Fe5
0125 is magnetized by the permanent magnet 6 in a direction parallel to the surface direction of the film.

The linearly polarized light emitted from the semiconductor laser 1 is focused by the lens 2, and (B iL u ) s F e so 1
25, the polarization direction is rotated by 46°, and Ca
The light passes through the -Mg-Zr substituted Gd3Ga5O12 substrate 4, passes through a polarizer 7 whose polarization directions are parallel to each other, and is coupled to the optical fiber 3.

On the other hand, among the returned light from the optical fiber 3, the linearly polarized light that has passed through the polarizer is Ca-Mg-Zr substituted Gd
3Ga5O12 substrate 4, (B IL u )3
When passing through Fes○1°5, due to the non-reciprocity of the Faraday effect, the polarization direction is further rotated by 45°,
The light returns to the semiconductor laser 1 in a state where the polarization direction of the light emitted from the semiconductor laser 1 and the polarization direction of the return light from the optical fiber 3 to the semiconductor laser 1 are orthogonal to each other. Since the polarization direction of the returned light is perpendicular to the polarization direction of the light emitted from the semiconductor laser 1, the returned light does not cause noise in the semiconductor laser 1.

As described above, an optical isolator that controls the return light to the semiconductor laser 1 and suppresses the noise of the semiconductor laser caused by the return light is realized, and the isolation ratio of the optical isolator of the above embodiment is as high as 39 dB. value was obtained.

In addition, in an optical isolator, light reflected back to the semiconductor laser from the ends of each used component such as a polarizer, lens, and magneto-optical element can cause characteristic deterioration, but in this example, (1) the lens 2 Since the configuration is such that the light emitted from the semiconductor laser 1 is condensed onto the optical fiber 3,
Compared to a configuration in which parallel light rays pass through each used component, the amount of light that returns to the semiconductor laser 1 among the reflected light from each used component is smaller.

(2) Each part used is coated with an anti-reflection coating.
Ca-Mg-Zr-substituted Gd3Ga5O12 substrate 4
Since reflection at the interface between (B iL u ) 3F e so1゜6 and the refractive index cannot be avoided, (B iL u ) 3F e 60125 can be changed to C
Liquid phase epitaxial growth is performed only on one side of the a-Mg-Zr substituted Gd3Ga5O12 substrate 4, and the growth surface is placed on the semiconductor laser 1 side. By adopting the above configuration, it is possible to eliminate the process of polishing and removing the substrate, and the light reflected at the interface passes through (BiLu)3F@601° and returns to the semiconductor laser 1, so the polarization direction is rotated. Since the polarization direction is perpendicular to the polarization direction of the semiconductor laser 1, it does not cause noise.

This can be avoided by the above two points.

Next, another embodiment of the present invention will be described.

(1) As shown in Fig. 2, Ca-Mg-Zr substituted Gd3
A mismatched lattice constant (
B l 2. o L u 1. o F e s 0
An optical isolator for a wavelength of 1.3 μm using a magneto-optical element obtained by liquid-phase epitaxial growth of each of No. 12 to 60 μm.

(2 Ca -Mg -Z r-substituted Gd5Ga6o
1゜(BiLu)3Fe6o12 on one side of the substrate
An optical isolator for a wavelength of 1.3 μm using a μm liquid-phase Evita crystal grown as a magneto-optical element.

(3) 4' of B11.3Lu1.7Fe5012 on one side of the Sm3Fe5O12 substrate without mismatch of lattice constants.
An optical isolator for a wavelength of 0.8 μm using a 7 μm liquid-phase epitaxially grown magneto-optical window.

(4) Mismatched lattice constants on both sides of the Sm3Fe5O12 substrate (Bl c 3Lu1.7 F eso12
were grown by liquid phase epitaxial growth of 23°7/1 m each and used as a magneto-optical element with a wavelength of 0.8 μm.
optical isolator for. In this case, the time required to grow the magneto-optical element was 46 minutes, and since a 3-inch substrate was used,
More than 400 magneto-optical elements could be obtained from those grown on the above substrate.

It should be noted that the present invention does not apply to those shown in the above embodiments, but as long as it uses the magneto-optical element described in the claims, it can be applied to any substrate, any growth line (cow may be used, and still exposed to light). The isolator may have any configuration.

Effect of the invention As described above, according to the present invention, it is lightweight.

A compact, mass-producible optical isolator with high isolation ratio and low loss was obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of an embodiment of an optical isolator according to the present invention, and FIG. 2 is a sectional view showing the structure of a second embodiment of the invention. 1... Semiconductor laser, 2... Lens,
3...Optical fiber, 4- ・-Ca-Mg
-Z r-substituted Gd3Ga5O12 substrate, 6...
(BiLu)3Fe6012.6...Permanent magnet, 7...Polarizer.

Claims (8)

[Claims] (1) Composition BixL_u_3_-_xFe_5O_1_2(
An optical isolator characterized by using a magneto-optical element made of magnetic garnet (1.0≦x≦3.0). (2) The optical isolator according to claim 1, wherein the epitaxial growth is liquid phase epitaxial growth. (3) Garnet crystal substrate is Gd_3Ga_5O_1_
2. The optical isolator according to claim 1, wherein: (4) Garnet crystal substrate is Sm_3Fe_5O_1_
2. The optical isolator according to claim 1, wherein: (5) Garnet crystal substrate is Ca-Mg-Zr substituted Gd
_3Ga_5O_1_2 The optical isolator according to claim 1, wherein the optical isolator is made of _3Ga_5O_1_2. (6) Garnet crystal substrate Nd_3Ga_3O_1_2
The optical isolator according to claim 1, characterized in that: (7) The optical isolator according to claim 1, wherein the direction of light incidence is parallel to the surface direction of the substrate. (8) A magneto-optical element in which magnetic garnet is epitaxially grown on only one side of a substrate is used, and the side of the magneto-optical element on which light from a light source is incident is arranged so that the magnetic garnet is on the side. Optical isolator according to range 1.