JPH0375614A - Optical isolator - Google Patents

Abstract

PURPOSE:To obtain the optical isolator which can deal with plural wavelengths by displacing magneto-optical elements for the respective light wavelengths in the direction perpendicular to the optical axis in correspondence to the light wavelength of a semiconductor laser to be used to dispose the magneto-optical elements on the optical axis. CONSTITUTION:This optical isolator is provided with polarizers 11, 13, analyzers 12, 14, the magneto-optical elements 7, 8 disposed between these two elements, and a magnetic circuit constituting element 9. The plural magneto-optical elements 7, 8 designed to correspond to the different light wavelengths are provided in the magnetic circuit constituting element 9 so as to array in one direction on the plane perpendicular to the optical axis. The constitution to allow the plural magneto-optical elements 7, 8 to be displaced perpendicularly to the optical axis and in the direction where the magneto-optical elements 7, 8 array. The constitution to detect the reflected light wavelengths from the polarizers 11, 13 or analyzers 12, 14 and to rotate the plural magneto-optical elements 7, 8 on the basis of the detected values is adopted. The optical isolator which can deal with the plural wavelengths with the simple constitution is obtd. in this way.

Description

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

Conventional technology Conventionally, when a semiconductor laser is used as a light source in an optical signal transmission system such as optical communication, a portion of the light emitted from the semiconductor laser is reflected at the transmission path or at each connection of the transmission optical components. It is known that this causes instability of the oscillation characteristics of the semiconductor laser and an increase in noise. and,
In order to prevent such reflected return light from returning to the semiconductor laser, an optical isolator is generally used.

For example, as shown in FIG. 5, this optical isolator includes a polarizer 4. Magneto-optical element (also called Faraday element) 3.
An analyzer 5 and a cylindrical magnet 6 that fixes the magneto-optical element 3 so that the magneto-optical element 3 is positioned between the polarizer 4 and the analyzer 5, which are polarization separation elements. Configured with the necessary features. Then, the emitted light l from the semiconductor L/-zer (not shown) passes through the polarizer 4 and becomes linearly polarized light, and when passing through the magneto-optical element 3, the polarization direction is rotated by 45 degrees, and the polarizer 4 and 45 It passes through an analyzer 5 arranged at an angle of . Conversely, the reflected return light 2 passes through the analyzer 5 and becomes linearly polarized light, and when passing through the magneto-optical element 3, the polarization direction is further changed to 4 due to the non-reciprocity of the Faraday effect.
It is rotated by 5 degrees and is perpendicular to polarized light 4, so linearly polarized light cannot pass through. Based on the principle described above, it is possible to prevent the reflected return light 2 from returning to the semiconductor laser.

In general, the rotation angle θ of the polarization direction by the magneto-optical element is expressed as: θ=VHL (2)=Wuelde constant H: Magnetic field strength L: Thickness of the magneto-optical element. In this, the Werde constant V is wavelength dependent,
It has temperature dependence and also differs depending on the type and composition of the magneto-optic crystal that constitutes the magneto-optical element.

Therefore, the crystal type 1 composition, thickness, etc. of a magneto-optical element are designed so that the rotation angle of the polarization direction is 45° for one wavelength at a constant temperature (generally room temperature) in a saturated magnetic field. .

Problems to be Solved by the Invention Recently, among such optical isolators, an optical isolator that can handle a plurality of wavelengths has become desired. As an optical isolator that can handle multiple wavelengths, the rotation angle of the polarization direction can be changed by 45° by changing the magnetic field strength in the saturation magnetic field region.
A method has been proposed to correct the
817 Publication 1 JP-A-59-181319) is
The problem was that the magnetic field strength was unstable and the rotation angle was unstable.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide an optical isolator that has a simple configuration and can handle a plurality of wavelengths.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention includes a polarizer, an analyzer, a magneto-optical element placed between these two elements, and a magnetic circuit component, and is compatible with different wavelengths of light. A plurality of said magneto-optical elements designed to The structure is vertical and can be displaced in the direction in which the magneto-optical elements are lined up. Further, the wavelength of reflected light from the polarizer or analyzer is detected, and the plurality of magneto-optical elements are displaced based on the detected value.

Effects According to the optical isolator of the present invention configured as described above, different magneto-optical elements can be moved on the optical axis depending on the wavelength of the light used, so that light that can handle multiple wavelengths can be used. An isolator will be obtained. Also,
By measuring the wavelength of reflected light from a polarizer or analyzer and moving multiple magneto-optical elements along the optical axis based on the measured values, an optical isolator that can automatically handle multiple wavelengths can be created. This will be obtained.

Embodiment FIG. 1 shows the configuration of an optical isolator according to the present invention. First, magneto-optic crystals of the same type and composition are designed to have a thickness corresponding to two wavelengths, and a magneto-optic element (hereinafter referred to as the first magneto-optic element) 7 corresponding to the first wavelength is formed. Magneto-optical elements (hereinafter referred to as second magneto-optical elements) 8 corresponding to the second wavelength are arranged in a plane perpendicular to the optical axis and fixed in a cylindrical magnet 9. Then, the emitted light 10 from the semiconductor laser passes through a polarizer 11 corresponding to the first wavelength (hereinafter referred to as the first polarizer) to become linearly polarized light, and when passing through the first magneto-optical element 7, the polarization direction is rotated 456 times,
The reflected light passes through an analyzer (hereinafter referred to as the first analyzer) 12 corresponding to the first wavelength, which is arranged at an angle of 45'' with the first polarizer 11. Conversely, the reflected return light passes through the first analyzer 12. When passing through the first magneto-optical element 7, 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 first polarizer 11, the linearly polarized light cannot pass through.

However, when using semiconductor lasers with different wavelengths, the rotation angle of the polarization direction by the first magneto-optical element 7 is 45°.
As a result, the amount of light passing through the first analyzer 12 decreases. Further, the reflected return light is transmitted to the first magneto-optical element 7.
Since the rotation angle of the polarization direction also deviates from 45 degrees when passing through the first polarizer 11, the amount of light passing through the first polarizer 11 increases, and as a result, the isolation ratio deteriorates.

Therefore, the first magneto-optical element 7 and the second magneto-optical element 8, which are arranged in one direction in a plane perpendicular to the optical axis, are arranged in two directions perpendicular to the optical axis so as to be on the optical axis. The magnet 9 is moved in the direction of displacement direction A in which the magneto-optical elements 7 and 8 are lined up. By doing so, the second magneto-optical element 8 corresponding to a different second wavelength is located on the optical axis as shown in FIG. ) 13 and an analyzer corresponding to the second wavelength (hereinafter referred to as the second wavelength)
14, which is assumed to be an analyzer, is now located on the optical axis. Therefore, the emitted light 10a from the semiconductor laser of the second wavelength is
It passes through the second polarizer 13 and becomes linearly polarized light, and when it passes through the second magneto-optical element 8, its polarization direction is rotated by exactly 45 degrees.
It passes through an analyzer 14. Then, the reflected return light passes through the second analyzer 14 and becomes linearly polarized light, and the second magneto-optical element 8
When passing through, the polarization direction is further rotated by 45 degrees due to the non-reciprocity of the Faraday effect, and since it is perpendicular to the second polarizer 13, linearly polarized light cannot pass through, resulting in a high isolation ratio. Further, in FIGS. 1 and 2, 15 and 16 are a polarizer holder and an analyzer holder.

Next, another embodiment of the present invention will be described with reference to FIGS. 3 and 4. Here, as shown in FIGS. 3 and 4, a light receiving element 17 is installed to measure the optical wavelength of the semiconductor laser used. The reflected light from the analyzers 12 and 14 is measured by the light receiving element 17, and a voltage with a power corresponding to the wavelength of the light is guided to the displacement controller 18, thereby moving the holder 19 in the direction perpendicular to the optical axis ( The structure is such that it can be displaced in the displacement direction A). Therefore, by arranging the two magneto-optical elements 7 and 8 fixed in the magnet 9 side by side in the direction in which the holder 19 is displaced, the magneto-optical element 7 or 8 corresponding to the measured light wavelength is placed on the optical axis. can be moved to

Now, if we are using a semiconductor laser with the first wavelength,
The emitted light 10 from the semiconductor laser is transmitted through a first polarizer 11. First magneto-optical element7. The reflected return light passes through the first analyzer 12. The light passes through the first magneto-optical element 7 but cannot pass through the first polarizer 11, resulting in a high isolation ratio. However, when light is emitted from the semiconductor laser of the second wavelength, the rotation angle of the polarization direction by the first magneto-optical element 7 deviates from 45@, so that the isolation ratio deteriorates. Here, if a light receiving element 17 for measuring the light wavelength is provided, the reflected light from the first analyzer 12 is guided to the light receiving element 17, and the displacement controller 18 moves the holder 19 perpendicular to the optical axis to the magneto-optical element 7. , 8 are lined up so that the second magneto-optical element 8 is aligned with the optical axis as shown in FIG. As a result, on the optical axis, the second polarizer 13 degrees, the second magneto-optical element 8. Since the second analyzer 14 is located, the rotation angle of the polarization direction by the second magneto-optical element 8 is 45 degrees, resulting in a high isolation ratio. Furthermore, when light is emitted from the semiconductor laser of the first wavelength in the state shown in FIG. Displace the holder 19 by the controller 18,
The first magneto-optical element 7 can be moved so as to be on the optical axis.

In the embodiments shown in FIGS. 3 and 4, the reflected light from the first and second analyzers 12 and 14 is guided to the light receiving element 17, and based on the measured value, the displacement controller 18
, thereby displacing the magnet 9 to create the first. Second
The magneto-optical elements 7.8 of 1. are moved so that they are on the optical axis. The reflected light from the second polarizer 11.13 is guided to the light receiving element, and based on the measured value, the reflected light from the first polarizer 11.13 is guided to the light receiving element.
The second magneto-optical element 7.8 may be moved so as to be on the optical axis.

Further, in the above embodiment, the first. The second magneto-optical elements 7 and 8 are fixed to a magnet 9, and the magnet 9 is moved in the displacement direction A.
By displacing the first degree second magneto-optical element 7
. The structure is such that the magnet 9 is fixed and the first. It is also possible to have a configuration in which only the second magneto-optical elements 7 and 8 are moved so that they are on the optical axis.

Furthermore, the magnet 9 in the embodiment includes magneto-optical elements 7 and 8.
Any magnetic circuit constituent element that can apply a unidirectional saturation magnetic field to the magnetic circuit may be used, and it can also be composed of a coil or the like.

Note that in the present invention, by arranging magneto-optical elements that can handle 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, the magneto-optical elements corresponding to the respective optical wavelengths are displaced in the direction perpendicular to the optical axis in accordance with the optical wavelengths of the semiconductor lasers used. Since the magneto-optical element can be placed on the optical axis, an optical isolator that can handle multiple wavelengths can be obtained. Furthermore, by measuring the wavelength of reflected light from a polarizer or analyzer that is a polarization separation element, and automatically arranging a magneto-optical element corresponding to the light wavelength on the optical axis based on the measured value. , an optical isolator that can automatically handle multiple wavelengths can be obtained.

[Brief explanation of drawings]

1 and 2 are block diagrams showing one embodiment of the optical isolator according to the present invention, FIGS. 3 and 4 are block diagrams showing other embodiments of the optical isolator according to the present invention, and FIG. 5 is a block diagram showing a conventional optical isolator. FIG. 2 is a configuration diagram showing an optical isolator of FIG. 7...Magneto-optical element corresponding to the first wavelength, 8.
...Magneto-optical element corresponding to the second wavelength, 9...
... Magnet, 10, 10a... Outgoing light, 11.
... Polarizer corresponding to the first wavelength, 12 ...
- Analyzer corresponding to the first wavelength, 13... Polarizer corresponding to the second wavelength, 14... Analyzer corresponding to the second wavelength, 15... Polarized light Child holder, 16...
...Analyzer holder, 17... Light receiving element, 1
8...Displacement controller, 19...Holder.

Claims (2)

[Claims] (1) A polarizer, an analyzer, a magneto-optical element placed between these two elements, and a magnetic circuit component, and a plurality of magneto-optical elements designed to correspond to different wavelengths of light are connected along the optical axis. The magneto-optical elements are arranged in the magnetic circuit component so as to be arranged in one direction in a plane perpendicular to the optical axis, and the magneto-optical elements can be displaced in the direction perpendicular to the optical axis in which the magneto-optical elements are arranged. optical isolator. (2) Detect the wavelength of reflected light from a polarizer or analyzer,
2. The optical isolator according to claim 1, wherein the plurality of magneto-optical elements are displaced based on the detected value.