JPS59147320A - Optical non-reciprocal element - Google Patents

Abstract

PURPOSE:To obtain an optical non-reciprocal element which absorbs less light and has high Faraday rotation performance by providing a magnetooptic element having rare earth-iron garnet crystal among a polarizer, analyzer, and magnet. CONSTITUTION:The magnetooptic element which has rare earth-iron garnet crystal 11 shown by a formula (1.3<=x<=1.5 and 0<=y<=1.0) which is grown on an Sm3Ga5O12 substrate 11 by a liquid-crystal epitaxial method so that the direction of crystal growth and the optical axis are parallel to the polarization direction of incident light is provided among the polarizer 2, analyzer 2, and magnet 4. Consequently, low-strain crystal grown on the SmGG substrate with good grating comformity by the liquid-crystal epitaxial method is mass-produced securely in a short time to obtain the optical non-reciprocal element with a high isolation ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application In semiconductor laser light sources, reflected light returning to the laser active layer causes unstable operation and increased noise. Therefore, in order to operate a semiconductor laser stably, the laser ~
A nonreciprocal element is required to allow light from the laser to pass through, but to block light reflected from the laser. In the field of optical communications as well, stabilization of semiconductor lasers as light sources is strongly required in order to put high-speed modulation and analog modulation into practical use. As described above, the non-reciprocal element according to the present invention is used in many systems that use light, such as optical communication, optical recording/reproducing devices, and optical sensors.

A conventional configuration and its problems will now be described as an example of the use of non-reciprocal elements, and an isolator with a wavelength band of 8000A.

Generally, as shown in FIG. 1, an isolator consists of a polarizer, a magneto-optical crystal, a magnet, and an analyzer, and the polarizer and analyzer are arranged so that the polarization directions of the polarizer and the analyzer are 45 degrees. 1 is a polarizer, 2 is an analyzer, 3d is a magneto-optic crystal, 4 is a magnet,
5 is the ray in the incident direction.

6 indicates light and lines in the direction opposite to the incident direction.

In FIG. 1, light 5 having uniform polarization directions that has passed through the polarizer 1 in the forward direction is converted into θ-VH by the magneto-optic crystal 3.
t(V: rotation angle of unit length unit magnetic field, H: magnetic field, t=
The polarization direction is rotated by the optical path length in the crystal. When the magnetization of the magneto-optic crystal 3 is saturated, it can be expressed as θ-θpt, and θF is called the rotational power (rotation angle per unit length). V, H, t so that θ-45°
If you choose , the incident light can pass through the analyzer.

On the other hand, the light that passes through the analyzer 2 in the opposite direction and has a uniform polarization direction has its polarization plane further rotated by 45 degrees due to the non-reciprocity of the magneto-optic crystal 3, so that the polarizer and the polarization direction are perpendicular to each other. cannot pass. The element configured in this manner is an isolator, and the magneto-optic crystal 3 determines its characteristics.

The conventional isolator for the 8000-person band is magneto-optic crystal 3.
Since paramagnetic glass was used as the material, there were the following drawbacks.

Since paramagnetic glass has a small V, it requires a length of several tens of meters, and in order to make it smaller, it is necessary to attach mirrors to both ends of the paramagnetic glass and make it a reflective optical path, increasing t. The loss is also large.

Also, since it is paramagnetic, the magnetization does not saturate, and θ changes in response to changes in H, making it difficult to maintain θ-46°.
Isolator performance deteriorates. H not only changes depending on the temperature, but also varies slightly depending on the position of the crystal in the permanent magnet. In addition, 1. Our inverter for the wavelength band of 1.3 μm usually uses a ferrimagnetic material (that is, rare earth iron garnet YIG with saturation magnetization) as the magneto-optic crystal 3, but since this has large absorption in the aoooA band,
It could not be used as an isolator for the 8,000-person band.

The conventional thin film type non-reciprocal element is YIG on GGG substrate.
It has the disadvantage of a poor isolation ratio due to distortion caused by the difference in substrate and lattice constants.

Purpose of the Invention The present invention uses a magneto-optic crystal with low absorption and high Faraday rotation ability by selecting the composition of rare earth iron garnet, and further grows the crystal on an S mGG (Sm3Ga6012) substrate. The purpose of this study is to construct a non-reciprocal element using .

Structure of the Invention The rare earth iron garnet used in the present invention is (B i xLu
3-x) F e 5-y S cyol 2 (1-
3≦X≦1.5.0≦y≦1.0). Rare earth iron garnet is represented by the general formula Re3Fe6012 (Re is a rare earth atom) and has a structure in which rare earth atoms are formed by O atoms occupying 122 dodecahedral positions, and Fe atoms occupy octahedral and tetrahedral positions. If the rare earth atom is replaced with Bi, the Faraday rotation angle becomes sharper, and since the Fe atom at the octagonal position is the cause of absorption in the 8000A band, if γ kosai 1 is replaced with a rare earth atom, the absorption disappears.

In this way, since the Fe atoms at the octahedral positions are selectively substituted, the single crystal is grown using the LPE crystal growth method, which is advantageous for selectively replacing Fe atoms at octahedral positions, and can be mass-produced reliably in a short period of time and at low cost. The optimum substrate is S rrl 3G a 6012, which has a small difference in lattice constant from the crystal and has low absorption.

First, the substitution of Bi atoms with rare earth elements in order to increase the Faraday rotation angle will be explained.

As more Bi atoms are added, the rotation angle increases, but at the same time, the lattice constant of garnet also increases. As mentioned above, S
When considering growing a crystal on an mGG substrate by LPE, the lattice constant that can be grown by LPE is limited compared to the lattice constant of SmGG. Therefore, as many B as possible
In order to replace the i atom, it is appropriate to replace B13+ with Lu of L u3F e 6012 which has the smallest lattice constant among rare earth iron garnets.

Next, a description will be given of replacing Fe atoms at octahedral positions with rare earth atoms in order to reduce absorption.

As the rare earth ion to be substituted, 1 is selected, and Sc'+, which can selectively enter only the octahedral position, is selected. As the amount of Fe3+ to be replaced increases, one point of Curie decreases, so the amount of replacement of Sc'' is
, the crystal must be selected so that it is a ferrimagnetic material within the operating temperature range.

Therefore, the composition of a garnet crystal that satisfies the constraints of lattice constant and single Curie point, has a high Faraday rotation angle, and has low absorption is (B1xLu3-x)Fe5-ASCyO12(1,
3zxz1.6. o≦y21. ○).

Description of Examples Composition of mixed crystals such as oxides and fluorides as a flux solvent,
By selecting the components, B12O3゜Lu2O3
, Fe2O3, 5C203 (B
1 xL us -x) F e s' yS cy
We were able to single-crystallize ol 2 rare earth garnet.

When SmGG is used as a substrate, the Bi composition is B1-+, 4Lu1. e F
It was possible to replace up to e s○12 with Lu and perform epitaxial growth. Also, due to the composition of the Sc group, ○≦y
It was possible to replace Fe ions with ≦2 ox.

As an example, rare earth garnet grown on SmGG
(Bil, 4Lu1.6) [5cFe)
In the epitaxially grown film with Fe5O12 composition,
Faraday rotation angle 80Q○0/cT with grown film thickness 56μm
n, a Curie temperature of about 160°C was obtained.

FIG. 2 shows a cross-sectional view of an example of the structure of an isolator using this rare earth garnet. 1 and 2 indicate a polarizer and an analyzer, respectively, 1o is an SmGG substrate, 11 is a rare earth garnet crystal grown on it, 4 is a magnet, 6 is an incident light, 6
indicates reflected light. The rare earth garnet crystal 11 is arranged so that the crystal growth direction and the optical axis are parallel to the polarization direction of the incident light, so that the effect of birefringence due to strain is in the same direction.

Furthermore, polarizer 1, analyzer 2 and garnet crystal 1
0 was coated with an antireflection coating made of a dielectric multilayer film. As a result, when a semiconductor laser having a peak wavelength of 8,600 was used as a light source, an isolator was obtained that had an insertion loss of 2 dB and an isolation ratio of 40 dB based on the amount of light after passing through a polarizer.

Effects of the Invention According to the present invention, a magneto-optic crystal with high Faraday rotation ability and low absorption was obtained, and a non-reciprocal element with a high isolation ratio was obtained. In particular, lattice matching on the S mGG substrate (LP
By using E-growth, low-strain crystals could be reliably mass-produced in a short period of time.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram of the configuration of a general isolator, and FIG. 2 is a schematic diagram of the configuration of an isolator according to an embodiment of the present invention. 1...Polarizer, 2...Analyzer, 3...
Magneto-optical crystal, 4... Magnet, 6... Forward optical path, 6... Reverse optical path. Name of agent: Patent attorney Toshio Nakao and 1 other person1

Claims (4)

[Claims] (1) Between the polarizer, analyzer, and magnet, use the general formula % 02y21. A non-reciprocal element using a magneto-optical element having a rare earth iron garnet crystal indicated by ○). (2) The non-reciprocal element according to claim 1, wherein a crystal is formed on a Sm3G85012 substrate by a liquid phase Echlikinyar method. (3) The Makusho suspended optical non-reciprocal element according to claim 2, which uses a magneto-optical element as a Faraday rotation element. (4) The non-reciprocal element according to claim 3, wherein the growth surface of the Faraday rotation element is arranged parallel to the optical axis.