JPS5977409A - Optical isolator - Google Patents

Abstract

PURPOSE:To eliminate birefringence due to the dynamic strain of crystal and to obtain an isolator having high precision by using a magnetic garnet monocrystal of a Faraday rotator used for an optical isolator released from the growth substrate of this monocrystal by gringing without being strained. CONSTITUTION:In an optical isolator composed of polarizers 1-1, 1-2, Selfoc lenses 2-1, 2-2, Faraday rotators 3-1, 3-2, and magnetic field impressing magnets 5-1, 5-2, a crystal of magnetic garnet (Bi0.95Yb2.1Fe3.8Ga1.1Pb0.03O12) grown on a GGG substrate in a liquid phase and released from the substrate by strain- free grinding is used for the rotator materials 3-1, 3-2, and it is bonded to a transparent substrate 4 to reinforce it. As a result, dynamic strain is removed by the difference in the space of lattice planes of the substrate crystal and the magnetic garnet crystal, birefringence is eliminated, and accordingly, an incident light 10-1 is sufficiently intercepted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to optical isolators, and in particular to high-performance optical isolators obtained by improving the optical properties of magnetic garnet crystals for Faraday rotation materials.

[Prior art]

Magnetic garnet is an excellent Faraday rotation material used in optical isolators because it has a large Faraday effect. A liquid phase growth method is an easy method for obtaining this magnetic garnet crystal. However, in general, in the liquid phase growth method, there is a difference between the lattice constant of the crystalline material that serves as the substrate and the lattice constant of the crystalline film grown on the substrate. The optical distortion causes optical birefringence. This birefringence deteriorates the properties in Faraday rotation.

When Bi is mixed into magnetic garnet, the Faraday rotation ability increases by an order of magnitude. G () G (Gd5GasOtz
) When forming a magnetic garnet crystal film containing J3i on a substrate, various elements are mixed so that the lattice constant becomes close to that of the substrate crystal. The composition of the formed film is, for example, B i O, 63Tm 2,3 pe3,6Gal, 2
Pbo, 620+2, or B i6.9s Yb2. +
Fea, s G a +, + Pbo, o3012. The crystal film thicknesses are 13 μm and 5.3 μm, respectively. The lattice constant difference at this time is -o, oio.

-0,044 people. FIG. 1 shows the power of the polarization component of the output light perpendicular to the polarization plane of the input light when linearly polarized light is incident on these two materials.

In the sample used in Figure 1, birefringence exists in the crystal, so linearly polarized light becomes elliptically polarized light and 10
There was a drawback that power was not transferred to the 0% orthogonal component.

Therefore, if such a magnetic garnet film is used in an optical isolator, highly accurate characteristics cannot be obtained.

[Purpose of the invention]

An object of the present invention is to provide an optical isolator with improved isolation characteristics by eliminating birefringence that tends to occur in magnetic garnet crystals for Faraday rotation materials manufactured by liquid phase growth.

[Summary of the invention]

The structure of the present invention to achieve the above object is to detach a magnetic garnet single crystal from a growth substrate by strain-free grinding.

When a Faraday rotation material crystal M (magnetic garnet) is formed on a substrate garnet, optical birefringence occurs due to the difference in lattice constant between the crystal film and the substrate crystal. Optical birefringence is caused by mechanical strain due to the difference in lattice spacing between the crystal film and the substrate crystal. Therefore, if the mechanical strain that causes birefringence is removed by removing the substrate by strain-free grinding, a magnetic garnet crystal of optically good quality can be obtained.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

FIG. 2 shows the configuration of an optical isolator as an embodiment of the present invention. Polarizer (1-1, 1-2), self-off lens (2-1, 2-2) and Faraday rotation material (
3-1, 3-2) and applied magnetic field magnet (5-1, 5-2)
It is composed of various parts.

The above Faraday rotation material is a liquid-phase grown magnetic garnet (B i llLa5 Y bz, + F ea, s
The crystal 1 is obtained by removing the substrate from Ga+, +Pbo, oac)+2) by strain-free polishing, and is bonded to a transparent substrate 4 for reinforcement.

Only linearly polarized light 10 from the light source is transmitted through the polarizer 1-1. This directly a-polarized light is converted into parallel light by a self-off lens and enters the Faraday rotation material 3-1. The plane of polarization of the incident linearly polarized light is rotated by 45 degrees in the Faraday rotation material 3-1.3-2. And Self Off Lens 2
The light passes through the polarizer 1-2, which is stopped by -2 and then tilted by 45 degrees, without any loss. Note that the thickness of the Faraday rotation material is 0.
If it is 5 to 3 μm, the intensity of the applied magnetic field is 45 degrees, and the applied magnetic field intensity is 45 degrees. Fafu rotating material 3-2゜3-
1, the light is further rotated by 45 degrees to become linearly polarized light perpendicular to the polarizer 1-2. Therefore, the light 11 incident from the opposite direction is blocked by the polarizer 1-2 and does not reach the light source. In this way, the unidirectional coupling element optical isolator functions.

If birefringence exists in the magnetic garnet crystal, which is a Faraday rotation material, as shown in FIG. 1, the incident light from the opposite direction becomes elliptically polarized light instead of linearly polarized light, resulting in a poor degree of shielding. In this case, the magnetic garnet obtained by strain-free grinding showed very good characteristics. Wavelength 1.15μm
The ratio of the light output from the light source to the light output from the opposite direction (extinction ratio) was 30 dB.

〔Effect of the invention〕

According to the present invention, birefringence that tends to occur in magnetic garnet crystals for Faraday rotation materials manufactured by liquid phase growth can be reduced.
The substrate crystal is removed by strain-free grinding,
By using it as a Faraday rotation element, the optical isolator characteristics were significantly improved. Since birefringence does not occur, 100% linear polarization was maintained when the plane of polarization was rotated by the Faraday effect. As a result, the optical isolator can sufficiently prevent the incident light from the opposite direction from returning to the light source, making it possible to obtain an extinction of 30 dB.

[Brief explanation of the drawings] Figure 1 shows actual measured values of the component power of the output light perpendicular to the polarization plane of the incident light when linearly polarized light is incident on the crystal, expressed as a ratio to the input light power. FIG. 1 is a configuration diagram of an optical isolator as an embodiment of the present invention. 1-1.1-2...Polarizer, 2-1.2-2...Self-off lens, 3-1.3-2...Faraday rotation material (magnetic garnet), 4...Reinforcement Substrate, 5-1゜5-2... Magnet for applying external magnetic field, 10-1.10-2
...Light from the light source, 11...Light entering the light source from the opposite direction. Agent Patent Attorney Toshiyuki Usuda T 1 Figure 2 Figure 51

Claims (1)

[Claims] In an optical isolator constructed by using a magnetic garnet single crystal as a Faraday rotation element, and arranging a polarizer and an analyzer whose optical axes are opposed to each other at 45 degrees before and after the magnetic garnet single crystal, the magnetic garnet single crystal can be grinded without distortion from the growth substrate. An optical isolator with a structure that allows for easy separation.