JPH03135513A - Optical isolator - Google Patents

Abstract

PURPOSE:To prevent isolation from deteriorating owing to variation and variance in the laser light wavelength by installing a wedgelike magnetooptic element which varies in thickness gradually at right angles to the optical axis in a member which is displaced by the rotating operation of a motor. CONSTITUTION:The magnetooptic element 1 which is equipped with a polarization separating element, a magnetooptic element, and a magnet and varies in thickness gradually perpendicularly to the optical axis is installed in the member which is displaced by the rotating operation of the motor. In such a case, the quantity of reflected light from the polarization separating element varies according to use ambient temperature and variance in laser light wavelength and the wedgelike magnetooptic element 1 is displaced perpendicularly to the optical axis corresponding to the variation in the quantity of reflected light. The thickness of the magnetooptic element c3 can be controlled by said displacement so that the angle of rotation of the polarizing direction of light passed through the magnetooptic element 3 is kept invariably to 45 deg., so even if the use temperature and laser light wavelength vary, reflected return light can be cut off completely at all times. Consequently, the optical isolator which provides high isolation is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical isolator used for removing reflected return light 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.

A conventional optical isolator includes, for example, a polarizer 31 . Magneto-optical element 30. Analyzer 32 and magnet 33
A configuration with

The principle of the optical isolator is as shown in Figure 5(a).
The light 34a traveling in the direction of the arrow 33 first passes through the polarizer 31 and becomes linearly polarized light 34b. Subsequently, when this linearly polarized light 34b passes through a magneto-optical element 30 having a Faraday effect in a saturation magnetic field H, its polarization direction becomes 45.
The light is rotated by a degree and becomes linearly polarized light 34c. Therefore, this linearly polarized light 34c can pass through the analyzer 32, whose direction in which light can pass is arranged at an angle of 45 degrees with the polarizer 31. Conversely, as shown in FIG. 5(b), the reflected return light 36a that has progressed as indicated by the arrow 35 first passes through the analyzer 32 and becomes linearly polarized light 36b. Subsequently, when this linearly polarized light 36b passes through the magneto-optical element 30 in the saturation magnetic field H, its polarization direction is further rotated by 45 degrees due to the non-reciprocity of the Faraday effect, and becomes linearly polarized light 36c. Therefore, this linearly polarized light 36c cannot pass through the polarizer 31 because it is perpendicular to the direction in which it can pass.

Based on the principle described above, by using an optical isolator, reflected return light can be prevented from returning to the semiconductor laser. However, in reality, there is a small amount of leakage light 36d, so the characteristics of the optical isolator are expressed as isolation (reverse direction loss) as shown in the following equation.

1=LOG(12/IO) Here, Io is the intensity of incident light in the opposite direction, and 2 is the intensity of leaked light in the opposite direction.

Magneto-optical elements for optical isolators include YIG (yttrium/iron/garnet), RIG (rare earth/iron/garnet),
garnet), BiRIG (bismuth-substituted rare earth, iron,
Garnet) and other single crystals with a garnet structure are generally used. The rotation angle θ of the polarization direction by such a magneto-optical element can be expressed as follows.

θ=VHL where V is Werde's constant, H is the strength of the magnetic field, and L is the thickness of the magneto-optical element.

Among these, the Weerde constant ■ has temperature dependence and wavelength dependence, and varies depending on the type and composition of the magneto-optical element. Therefore, magneto-optical elements are kept at a constant temperature (generally room temperature) in a saturated magnetic field.
The type 1 composition, thickness, etc. are designed so that the rotation angle of the polarization direction is 45 degrees for one wavelength. For example, when YIG is used as a magneto-optical element in a 1.3 μm optical isolator, the thickness thereof is approximately 2.0 mm.

However, with conventional optical isolators, the rotation angle of the polarization direction deviates from 45 degrees due to differences in the usage environment, temperature changes, and changes and variations in the laser light wavelength. This had the disadvantage that the isolation deteriorated due to the increased leakage light intensity. Therefore, in order to consistently obtain high isolation, there is a problem in that when using an optical isolator, a device that keeps the temperature constant, a device that keeps the laser light wavelength constant, etc. are required.

The present invention solves these problems, and aims to provide an optical isolator that can prevent deterioration of isolation due to differences in usage environments, temperature changes, and changes and variations in laser light wavelength. .

Means for Solving the Problems In order to solve the above problems, the present invention comprises a polarization separation element, a magneto-optical element, and a magnet, and has a wedge-shaped structure whose thickness gradually changes in a direction perpendicular to the optical axis. The magneto-optical element is disposed on a member that is displaced by the rotational movement of a motor, and the wedge-shaped magneto-optical element is displaceable in a direction perpendicular to the optical axis due to a change in reflected light from the polarization separation element. The present invention provides an optical isolator with the following characteristics.

Function: According to the optical isolator of the present invention, the amount of reflected light from the polarization separation element changes with variations in the operating environment temperature and the wavelength of the laser light, and the amount of light reflected from the polarization separation element changes.

The wedge-shaped magneto-optical element is displaced in a direction perpendicular to the optical axis. By such displacement, the thickness of the magneto-optical element can be controlled so that the rotation angle of the polarization direction of the light after passing through the magneto-optic element is always 45 degrees, so the operating temperature and laser light wavelength can be controlled. Even if it changes, it is possible to always completely block the reflected return light, and an optical isolator with high isolation can be obtained.

Embodiment FIGS. 1, 2, and 3 show an embodiment of the optical isolator according to the present invention. FIG. 1 is a cross-sectional view including the optical axis, and FIG. A' sectional view, Figure 3 is the 2nd
FIG. 3 is a diagram illustrating the operation of the optical isolator according to the present invention using a sectional view taken along line BB' in the figure.

First, a magneto-optic crystal cut into a cylindrical shape is cut diagonally into a wedge shape whose thickness gradually changes in the direction perpendicular to the optical axis, and then the light input and output surfaces are polished to a mirror surface, and the wedge is cut into a wedge shape. The magneto-optical element 1 has a shape.

On the other hand, it has a refractive index equal to that of the wedge-shaped magneto-optical element 1,
After cutting an optical material that does not have a magneto-optical effect into a similar wedge shape, the light entrance/exit surface is polished to a mirror surface to obtain a wedge-shaped optical element 2. After bonding these wedge-shaped magneto-optical element 1 and wedge-shaped optical element 2 so that the light incident surface and the light exit surface are parallel to each other to form a magneto-optical component 3,
An antireflection film is formed on the light entrance/exit surfaces 3a and 3b, and fixed in the permanent magnet 6. Furthermore, guides 10 and 11 for converting the rotational movement of the rotor 12 into a displacement movement of the permanent magnet 6 are attached to the permanent magnet 6, and the permanent magnet 6 is placed on a stand 9 for displacing the permanent magnet 6.

Next, a polarizer 4 with an anti-reflection film formed on the light incident/exit surfaces 4a and 4b and an analyzer 5 with an anti-reflection film formed on the light incident/exit surfaces 5a and 5b are attached to the polarizer holder 7 and the detector, respectively. Fix the photon holder during the day.

These polarizer 4 and analyzer 5 are at 45 degrees to each other,
Polarizer holder 7 and analyzer holder 8 are fixed in lower case 19 so as to be located on both sides of magneto-optical component 3. Here, in the usage environment of this optical isolator, the permanent magnet 6 is installed at a position where the leakage light intensity in the opposite direction is the smallest, that is, a position where the isolation is the highest. At this time, a light receiving element 15 for receiving the reflected component from the analyzer 5 and a rotor 12 for displacing the permanent magnet 6 are provided. After that, cover the upper case 20,
A cover 21 provided with a light passage hole 21a and a light passage hole 22
Attach the cover 22 provided with a.

Finally, the rotary motor 14 attached to the motor support stand 18
and rotor 12 are connected via a motor shaft 13. Thereafter, the light receiving element 15 and the rotary motor 14 are each connected to a rotation controller 16 to form an optical isolator.

Here, if the usage environment changes, for example, if the ambient temperature changes, the rotation angle of the polarization direction of the light that has passed through the wedge-shaped magneto-optical element 1 will deviate from 45 degrees, and it will not be able to pass through the analyzer 5. A polarized component is generated. This polarized component is
The reflected component from the analyzer 5 is received by the light receiving element 15 through the optical path 17. This reflected component increases as the rotation angle of the polarization direction deviates from 45 degrees, so the light receiving element 15
The magnitude of the deviation of the rotation angle of the polarization direction from 45 degrees can be detected based on the amount of light received at . After photo-electrically converting the amount of received light, the obtained electrical output is guided to the rotation controller 16, and a voltage corresponding to the amount of received light is introduced to the rotary motor 14, thereby controlling the rotation motor 14, motor shaft 139, rotor 12, etc.
can be rotated, and the permanent magnet 6 is rotated by the arrow 23
can be displaced in the direction of This allows the third
As shown in Figures +al, fbl, fc), the thickness of the wedge-shaped magneto-optical element 1 that corresponds to the optical axis 24 changes, making it possible to correct the rotation angle of the polarization direction to 45 degrees.

Further, even when the wavelength of the laser beam changes, the rotation angle of the polarization direction can be corrected to 45 degrees by the same effect.

In this way, according to the present invention, the rotation angle of the polarization direction can be adjusted or corrected to 45 degrees in accordance with differences in the usage environment, temperature changes, and changes and variations in the optical wavelength of the laser used. , an optical isolator with high isolation can be realized.

Although a wedge-shaped optical element is used in this embodiment, an optical isolator using only a wedge-shaped magneto-optical element is also possible.

Effects of the Invention As described above, according to the present invention, the wedge-shaped magneto-optical element can be adjusted in a direction perpendicular to the optical axis in accordance with differences in the usage environment, temperature changes, and changes and variations in the optical wavelength of the laser used. Because of the displacement, the thickness of the magneto-optical element can be controlled so that the rotation angle of the polarization direction of the light after passing through the magneto-optic element is always 45 degrees, making it possible to completely block reflected return light. Therefore, a high isolation optical isolator
The evening will come.

[Brief explanation of the drawing]

FIG. 1 is a sectional view including the optical axis of an optical isolator according to the present invention, FIG. 2 is a sectional view taken along line A-A' in FIG.
An explanatory diagram illustrating the operation of the optical isolator according to the present invention using a cross section taken along line B-B' in the figure, FIG. 4 is a block diagram of a conventional optical isolator, and FIG. 5 is a diagram showing the principle of the optical isolator. 1... Wedge-shaped magneto-optical element, 2...
Wedge-shaped optical element, 3...Magneto-optical component, 3a
, 3b, 4a4b, 5a, 5b... input/output surface,
4...Polarizer, 5...Analyzer, 6...
...Permanent magnet, 7...Polarizer holder, 8.
...Analyzer holder, 9...stand, 10.1
1...Guide, 12...Rotor, 13
...Motor shaft, 14...Rotating motor,
15... Light receiving element, 16... Rotation controller, 17... Optical path, 18... Motor support stand, 19... Lower case , 20...Top case, 21.22...Cover 21a, 22
a...Light passing hole, 24...Optical axis.

Claims (2)

[Claims] (1) The wedge-shaped magneto-optical element, which includes a polarization separation element, a magneto-optic element, and a magnet, and whose thickness gradually changes in a direction perpendicular to the optical axis, is installed on a member that is displaced by the rotational operation of a motor. An optical isolator characterized in that the wedge-shaped magneto-optical element can be displaced in a direction perpendicular to the optical axis by changes in reflected light from the polarization separation element. (2) As a magneto-optical element, an optical element having a refractive index equal to that of the wedge-shaped magneto-optical element and having no magneto-optic effect and a wedge-shaped magneto-optical element are used, with the light incident surface and the light exit surface being parallel to each other. 2. The optical isolator according to claim 1, further comprising a magneto-optical component that is integrated so as to have the following characteristics.