JPH03135515A - Optical isolator - Google Patents

Abstract

PURPOSE:To obtain the optical isolator to be used for plural wavelengths automatically by fixing a step-shaped magnetooptic element in a magnetic circuit material and making it rotatable on an axis parallel to an optical axis except the optical axis in a plane perpendicular to the optical axis. CONSTITUTION:The step-shaped magnetooptic element 7 is fixed in the magnetic circuit material and enabled to rotate on the axis 10 parallel to the optical axis except the optical axis in the plane perpendicular to the optical axis. In such a case, the step-shaped magnetooptic element 7 which is stepped in thickness corresponding to wavelengths is rotated on the axis 10 parallel to the optical axis except the optical axis in the plane perpendicular to the optical axis to vary the thickness of the magnetooptic element on the optical path, thus obtaining the optical isolator which handles the wavelengths. Further, the wavelength of reflected light from a polarization separating element is measured and supplied to a rotation control machine to rotate the magnetooptic element and handle the light wavelength. Consequently, the optical isolator to be used for the wavelengths automatically is obtained.

Description

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

Conventional technology When a semiconductor laser is used as a light source in an optical signal transmission system such as optical communication, a part of the light emitted from the semiconductor laser is reflected at the transmission line or at each connection of the transmission optical components, causing the semiconductor laser to emit light. This causes oscillation characteristics to become unstable and noise to increase. An optical isolator is generally used to prevent this reflected return light from returning to the semiconductor laser.

Conventionally, this type of optical isolator includes a polarizer 1, a magneto-optical element 2, an analyzer 3, and a magnet 4, as shown in FIG. 6, for example. The emitted light 6 from the semiconductor laser passes through the polarizer 1 and becomes linearly polarized light, and when it passes through the magneto-optical element 2, its polarization direction is rotated by 46 degrees, and then passes through the analyzer 3, which is arranged at an angle of 45 degrees with the polarizer 1. do. On the contrary, the reflected return light 6
passes through the analyzer 3 and becomes linearly polarized light, and the magneto-optical element 2
Upon passing, the polarization direction is further rotated by 45 degrees due to the non-reciprocity of the Faraday effect, and since it is orthogonal to the polarizer 1, linearly polarized light cannot pass through. Based on the principle described above, it is possible to prevent the reflected return light 6 from returning to the semiconductor laser.

Generally, the rotation angle θ of the polarization direction by the magneto-optical element is expressed as θ=VHL V: Guelde constant H: strength of magnetic field L: thickness of the magneto-optical element. Among these, the Werde constant V is wavelength dependent,
It is temperature dependent and varies depending on the type and composition of the magneto-optic crystal. Therefore, the magneto-optical element is kept at a constant temperature (
The type, composition, thickness, etc. of the crystal are designed so that the rotation angle of the polarization direction is 45° for one wavelength at room temperature (generally).

Problems to be Solved by the Invention Conventional optical isolators are designed to handle only one wavelength. Optical isolators that can handle multiple wavelengths need to increase the magnetic field strength in the unsaturated magnetic field region. By changing the rotation angle of the polarization direction by 45
A method of correcting to
JP-A-69-181319) and the like have been proposed.

The present invention is intended to solve these problems, and aims to provide an optical isolator that can handle multiple wavelengths and has a high isolation ratio.

Means for Solving the Problems In order to solve the above problems, the present invention includes a polarization separation element, a magneto-optical element, and a magnetic circuit material, and fixes the stepped magneto-optic element in the magnetic circuit material. At the same time, it can be rotated around an axis parallel to the optical axis excluding the optical axis in a plane perpendicular to the optical axis, and further fixed in the magnetic circuit material by changing the wavelength of the reflected light from the polarization separation element. The stepped magneto-optical element is configured to automatically rotate around an axis parallel to the optical axis excluding the optical axis within a plane perpendicular to the optical axis.

Effect: According to the optical isolator of the present invention, the thickness of the magneto-optical element in the optical path portion can be changed depending on the wavelength of the light used, so an optical isolator that can handle multiple wavelengths can be obtained. .

Furthermore, by measuring the wavelength of the reflected light from the polarization separation element, it is possible to automatically rotate the magneto-optical element within a plane perpendicular to the optical axis and around an axis parallel to the optical axis, excluding the optical axis. This means that an optical isolator that can handle multiple wavelengths can be obtained.

Embodiment FIG. 1 shows the configuration of an optical isolator according to the present invention. A magneto-optic crystal (for example, YIG) is designed to have a thickness that corresponds to two types of optical wavelengths, and a stepped magneto-optical element 7 having a thickness corresponding to the first wavelength and a thickness corresponding to the second wavelength is attached to the magnet 4.
Fix it inside. The emitted light 5 from the semiconductor laser passes through a polarizer 8 (hereinafter referred to as the first polarizer) corresponding to the first wavelength and becomes linearly polarized light, and the stepped magneto-optical element 7 has a thickness corresponding to the first wavelength. The polarization direction of the light is rotated by 46 degrees when it passes through a section designed for ). Conversely, the reflected return light is the first
The linearly polarized light passes through the analyzer 9, and when it passes through the stepped magneto-optical element 7, the polarization direction is further rotated by 46 degrees due to the non-reciprocity of the Faraday effect, and the linearly polarized light is now perpendicular to the first polarizer 8. Can't pass.

However, when a semiconductor laser with a different second wavelength is used, the rotation angle of the polarization direction by the stepped magneto-optical element 7 deviates from 46°, and thus the amount of light passing through the first analyzer 9 decreases. Furthermore, even when the reflected return light passes through the stepped magneto-optical element 7, the rotation angle of the polarization direction deviates from 46°, so the amount of light passing through the first polarizer 8 increases, resulting in a deterioration of the isolation ratio. It turns out.

Therefore, the magnet 4 to which the stepped magneto-optical element 7 is fixed is placed in a plane perpendicular to the optical axis so that the part designed to have a thickness corresponding to the second wavelength is located on the optical path. The magnet is rotated 180° around the 1° rotation axis of the magnet parallel to the optical axis. Then, as shown in FIG. 2, the part of the stepped magneto-optical element 7 designed to have a thickness corresponding to the second wavelength will be located on the optical path, and at the same time, the polarizer 1 corresponding to the second wavelength will be located on the optical path.
1 (hereinafter referred to as a second polarizer) and an analyzer 12 (hereinafter referred to as a second analyzer) corresponding to the second wavelength are located on the optical path. Therefore, the emitted light 6 from the semiconductor laser having the second wavelength passes through the second polarizer 11 to become linearly polarized light, and passes through a portion of the stepped magneto-optical element 7 designed to have a thickness corresponding to the second wavelength. In this case, the polarization direction is 45°
It is rotated and passes through a second analyzer 12 arranged at an angle of 45° with the second polarizer 11 . On the contrary, the reflected return light passes through the second analyzer 12 and becomes linearly polarized light, and when it passes through the stepped magneto-optical element 7, the polarization direction is further rotated by 45 degrees due to the non-reciprocity of the Faraday effect, and the polarization direction is further rotated by 45 degrees. 11, linearly polarized light cannot pass through, resulting in a high isolation ratio. Here, 13 is a polarizer holder, and 14 is an analyzer holder.

Furthermore, as shown in FIG. 3, a light receiving element 16 is installed in order to measure the optical wavelength of the semiconductor laser being used. The reflected light from the analyzers 9 and 12 is measured by the light receiving element 15, and a voltage with a power corresponding to the wavelength of the light is guided to the rotation controller 16. It can be rotated around an axis parallel to the optical axis excluding the optical axis.

Now, if we are using a semiconductor laser with the first wavelength,
The emitted light 5 from the semiconductor laser passes through the first polarizer 8, the stepped magneto-optical element 7, and the first analyzer 9, and the reflected light passes through the first analyzer 9 and the stepped magneto-optical element 7. However, the light cannot pass through the first polarizer 8, resulting in a high isolation ratio. However, when the light emitted from the semiconductor laser of the second wavelength is incident on this optical isolator, the rotation angle of the polarization direction by the stepped magneto-optical element 7 deviates from 46° due to the difference in the designed thickness with respect to the wavelength, and the aisle ratio increases. deteriorates. Here, if a light receiving element 15 for measuring the light wavelength is provided, the reflected light from the first analyzer 9 is guided to the light receiving element 16, and the rotation controller 16 moves the holder 17 in a plane perpendicular to the optical axis. can be rotated around an axis parallel to the optical axis, excluding the optical axis. Then, as shown in Figure 4,
On the optical path are a second polarizer 11, a portion of the stepped magneto-optical element 7 designed to have a thickness corresponding to the second wavelength, and a second analyzer 1.
2, the angle of rotation of the polarization direction by the stepped magneto-optical element 7 is 46°, and a high isolation ratio can be obtained.

Note that by arranging a magneto-optical element having steps of thickness corresponding to three or more wavelengths, an optical isolator that can handle three or more wavelengths can be obtained.

Effects of the Invention As described above, according to the present invention, step-shaped magneto-optical elements having thicknesses corresponding to the optical wavelengths of the semiconductor lasers used are arranged in a plane perpendicular to the optical axis. Rotate around an axis parallel to the optical axis, excluding the optical axis,
By changing the thickness of the magneto-optical element on the optical path, an optical isolator that can handle multiple wavelengths can be obtained.

Furthermore, by measuring the wavelength of the reflected light from the polarization separation element and guiding it to a rotation controller, which rotates the magneto-optical element to correspond to the optical wavelength, an optical isolator that can automatically handle multiple wavelengths can be obtained. It happens.

[Brief explanation of the drawing]

1 and 2 are block diagrams of an optical isolator according to the present invention, FIGS. 3 and 4 are block diagrams of an optical isolator equipped with a rotation controller among the optical isolators according to the present invention, and FIG. 6 is a block diagram of a conventional optical isolator. FIG. 1 is a configuration diagram showing the configuration and principle of an optical isolator. 4... Magnet, 6... Emitted light, 7...
...Stepped magneto-optical element, 8, 11...Polarizer, e, 12...Analyzer, 1o...Rotation axis of magnet, 13... ...Polarizer holder, 14...
...Analyzer holder, 16... mark, light receiving element, 16.
... Rotation control machine, 17 ... Holder.

Claims (2)

[Claims] (1) comprising a polarization separation element, a magneto-optical element, and a magnetic circuit material, in which the magneto-optical element is fixed in a step-like manner in the magnetic circuit material, and light excluding the optical axis in a plane perpendicular to the optical axis; An optical isolator characterized by being configured to be able to rotate around an axis parallel to the axis. (2) Due to the change in the wavelength of the reflected light from the polarization separation element, the stepped magneto-optical element fixed in the magnetic circuit material is centered on an axis parallel to the optical axis excluding the optical axis in a plane perpendicular to the optical axis. The optical isolator according to claim 1, wherein the optical isolator is configured to rotate.