JPH0413113A - Optical isolator - Google Patents

Abstract

PURPOSE:To compensate variation in angle of Faraday rotation due to wavelength variation and temperature variation and to obtain high isolation by fitting a magnet for magnetic field application with a rotary shaft which passes the nearly center part of a Faraday rotator and rotates on an axis perpendicular to the optical axis. CONSTITUTION:The magnet 5 for magnetic field application is fitted with the rotary shaft 57 which passes through the Faraday rotator 3 nearly in the center and rotates on the axis perpendicular to the optical axis l. Then the magnet 5 for magnetic field application is rotated on the rotary shaft 57. The direction of a magnetic field applied to the Faraday rotator 3 is changed, a component of magnetism of the Faraday rotator 3 in the direction of the optical axis lis changed, and the angle of rotation of light in the Faraday rotator 3 can be changed. Consequently, even if wavelength variation or temperature variation occurs, the angle of Faraday rotation is corrected into a constant value and the high isolation is obtained at all times.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical isolator used in light emitting devices and optical circuit networks for optical communications, and particularly relates to an optical isolator that can reduce wavelength dependence and temperature dependence. It is something.

[Conventional technology]

Conventional optical isolators can be installed just in front of a light emitting source such as a laser diode, and allow the emitted light emitted from the light emitting source to enter and pass therethrough, while at the same time eliminating the return light generated by reflection, scattering, etc. of the transmitted emitted light. It has a function to remove so that it does not return to the light emitting source.

FIG. 4 shows a conventional optical isolator 80 of this type.

As shown in the figure, this optical isolator 80 includes a plate-shaped Faraday rotator 82 disposed between a cubic polarizer 81 and an analyzer 83, and a plate-shaped Faraday rotator 82 between the polarizer 81, the Faraday rotator 82, and the analyzer. A cylindrical magnetic field applying magnet 84 is disposed around the outer periphery of the magnet 83 so as to wrap around the magnet 83.

For the light incident from the left side of the figure, only the light having a predetermined plane of polarization is transmitted by the polarizer 81, and the plane of polarization of the light is rotated by 45@ by the Faraday rotator 82.
In this state, the light passes through the analyzer 83 and is emitted toward a desired optical component.

On the other hand, from the right side of the optical isolator 80, return light generated by reflection, scattering, etc. enters.

Of this returned light, 4
Only light having a polarization plane rotated by 5° passes through the analyzer 83, and the Faraday rotator 82 allows the polarization plane to be further rotated by 45°.

In the end, only light having a plane of polarization rotated by 90 degrees with respect to the plane of polarization of the polarizer 81 will enter the polarizer 81, but this light cannot pass through the polarizer 81 and is mostly reflected there. (Depending on the type of polarizer, it may be absorbed), so the returned light is reliably removed.

[Problem to be solved by the invention]

By the way, as mentioned above, the Faraday rotator 82 has the function of rotating the plane of polarization of light by a predetermined angle, but the degree of rotation angle depends on the thickness of the Faraday rotator 82, the strength of the magnetic field applied to the Faraday rotator 82, and the incidence It depends on the wavelength of light and temperature.

Therefore, when the wavelength of the incident light changes or the temperature of the environment in which the optical isolator 80 is used changes, the Faraday rotation angle changes, and as a result, the returned light is transmitted to the polarizer 81. This deviates from the crossed nicol condition of the analyzer 83, and the isolation decreases.

The decrease in isolation becomes a factor that increases noise in the optical signal when the optical isolator 80 is used in combination with a light emitting element.

The present invention has been made in view of the above points, and its purpose is to provide an optical isolator that can exhibit stable performance by providing means for correcting changes in Faraday rotation angle due to wavelength changes and temperature changes. It's about doing.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention arranges a polarizer 2, a Faraday rotator 3, and an analyzer 4 in series in this order with respect to the optical axis of the incident light. In an optical isolator 1, a magnetic field applying magnet 5 is provided on the outer periphery of the Faraday rotator 3 to apply a magnetic field in the direction of the optical axis! At the same time, a rotating shaft 57 that rotates around an axis perpendicular to the optical axis p is attached.

[Effect]

In the optical isolator 1 described above, by rotating the magnetic field applying magnet 5 about the rotating shaft 57, the direction of the magnetic field that can be applied to the Faraday rotator 3 can be changed, thereby changing the direction of the optical axis of the Faraday rotator 3. ! The directional component can be changed, and the rotation angle of the light in the Faraday rotator 3 can be changed.

Therefore, even if the Faraday rotation angle changes due to wavelength changes or temperature changes, the rotation angle can be corrected to the original state by rotating the magnetic field applying magnet 5.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail based on the drawings.

FIG. 1 is a perspective view showing the optical isolator 1 of this embodiment, and FIG. 2 is a view of the optical isolator 1 viewed from the direction of incident light.

As shown in both figures, this optical isolator 1 has a polarizer 2, a Faraday rotator 3, and an analyzer 4 arranged along the optical axis of the incident light! The polarizer 2, the Faraday rotator 3, and the analyzer 4 are arranged in series in this order, and the optical axis is set on both sides of the polarizer 2, Faraday rotator 3, and analyzer 4. It is constructed by disposing a magnetic field applying magnet 5 (consisting of two magnet plates 51 and 53 and their supporting member 55) that applies a magnetic field in the same direction.

Each component will be explained below.

The polarizer 2 is formed into a square plate-like body, and a dichroic polarizer is used in this embodiment. Note that this polarizer 2 may be constituted by another polarizing element such as a polarizing beam splitter.

The Faraday rotator 3 is also formed into a square plate-like body, and the plane of polarization of light incident perpendicularly to the Faraday rotator 3 is 45.
° Constructed in rotating thickness.

Further, the analyzer 4 uses a dichroic polarizer having the same shape and structure as the polarizer 2. This analyzer 4 is fixedly set at a position where its polarization plane is shifted from the polarization plane of the polarizer 2 by 45@ around the optical axis 2. Note that this analyzer 4 may also be constructed from other polarizing elements such as a polarizing beam splitter.

The magnetic field applying magnet 5 is composed of two magnet plates 51.53 made of rectangular plate-shaped bodies and a support member 55 that fixes the two magnet plates 51.53 together.

Here, the optical axes of the magnet plates 51 and 53 are connected to the Faraday rotator 3, respectively. magnetized to apply a directional magnetic field.

The support member 55 is made of a metal plate having a substantially U-shape, and a rotating shaft 57 for rotatably supporting the support member 55 is attached to the longitudinal direction of the support member 55.

This rotating shaft 57 has its axis passing through the center of the Faraday rotator 3 and the optical axis! It is placed perpendicular to the

Therefore, the entire magnetic field applying magnet 5 can rotate around an axis perpendicular to the optical axis P.

That is, by rotating the magnetic field applying magnet 5 around this rotating shaft 57, the direction of the magnetic field applied to the Faraday rotator 3 can be changed, and the optical axis of magnetization of the Faraday rotator 3! The angle of polarization of the light incident on the Faraday rotator 3 can be changed by changing the angle of rotation θF of the polarization plane of the light incident on the Faraday rotator 3.
can change.

Here, the operation of this optical isolator 1 will be explained.

Normally, the magnet plates 51, 53 are as shown in FIGS. 1 and 2.
They are arranged so that their longitudinal direction is parallel to the optical axis of the incident light.

The light having a predetermined plane of polarization transmitted through the polarizer 2 is
The plane of polarization is rotated by 45 degrees by the Faraday rotator 3, and the light passes through the analyzer 4 as it is.

On the other hand, regarding the return light incident from the analyzer 4 side, only the light having a predetermined polarization plane passes through the analyzer 4, and the Faraday rotator 3
Since the plane of polarization is further rotated by 45 degrees, the light enters the polarizer 2 with the plane of polarization rotated by 90 degrees. Therefore, the returned light cannot pass through the polarizer 2 and can be completely removed.

By the way, if the wavelength of the incident light changes for some reason,
By changing the temperature of the Faraday rotator 3, the Faraday rotation angle θ of the light by the Faraday rotator 3 is changed.
F may change.

In this case, the Faraday rotation angle can be corrected to 45° by rotating the magnet plates 51, 53 by a predetermined angle about the rotating shaft 57.

FIG. 3 is a diagram showing a mechanism for correcting the Faraday rotation angle.

As shown in the figure, light enters and exits perpendicularly to the plane of the Faraday rotator 3.

On the other hand, the direction of magnetization of this Faraday rotator 3 almost coincides with the direction of the magnetic field applied to it, so if the angle formed between the applied magnetic field and the optical axis i is θr, then the component of magnetization in the direction of light propagation (optical axis !direction component) is M−CO5θr M: magnitude of magnetization of the Faraday rotator 3.

Therefore, the Faraday rotation angle θF is defined by the following equation.

θF w=v−t −M−cosθr Here, ■= Wave wavelength Humidity temperature dependent material specific coefficient t: Thickness of Faraday rotator 3 As can be seen from this equation, as the wavelength and temperature change, V Even if the value changes, the Faraday rotation angle θF can be maintained at a predetermined value by changing θr by rotating the magnetic field applying magnet 5.

That is, even if the wavelength or temperature changes, the Faraday rotation angle θF can be easily corrected by simply rotating the magnetic field applying magnet 5 by a predetermined angle.

In the above embodiments, the magnetic field applying magnet 5 is composed of two magnet plates 51 and 53, but the magnetic field applying magnet 5 may be constructed as a cylindrical member as shown in FIG. Various modifications are possible.

That is, the magnet for applying a magnetic field can be arranged around the outer periphery of the Faraday rotator to apply a magnetic field in the direction of the optical axis to the Faraday rotator, and the magnet can pass approximately through the center of the Faraday rotator and has an axis perpendicular to the optical axis. Any structure may be used as long as it has a rotating shaft that rotates around the center.

It goes without saying that the polarizer, Faraday rotator, and analyzer may have any shape and structure as long as they are arranged in this order.

Further, in the above embodiment, the rotation angle of the Faraday rotator was set to 45 degrees, but it goes without saying that this rotation angle can be changed in various ways as necessary.

〔Effect of the invention〕

As explained in detail above, according to the optical isolator according to the present invention, the direction of the magnetic field applied to the Faraday rotator can be changed simply by rotating the magnetic field applying magnet around the rotation axis. The angle of rotation of the light in the child can be changed. Therefore, even if a wavelength change or a temperature change occurs, the Faraday rotation angle can be corrected to a constant value, and an optical isolator that always has high isolation can be realized.

Furthermore, conventionally, different optical isolators were required for light of different wavelengths, but according to the present invention, the optimum isolation for light of different wavelengths can be achieved by simply rotating the magnetic field applying magnet 5. It can be set to the state of Therefore, there is an advantage that only one type of optical isolator is required for light of different wavelengths.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an optical isolator 1 according to an embodiment of the present invention, FIG. 2 is a view of the optical isolator 1 seen from the direction of incident light, and FIG. 3 shows a mechanism for correcting the Faraday rotation angle. Figure 4 shows a conventional optical isolator 80.
FIG. In the figure, 1... optical isolator, 2... polarizer, 3...
...Faraday rotator, 4...analyzer, 5...magnet for applying magnetic field, 57...rotating shaft or inside! ...The optical axis.

Claims (1)

[Claims] A polarizer, a Faraday rotator, and an analyzer are arranged in series in this order with respect to the optical axis of incident light, and the outer periphery of the Faraday rotator is provided with an optical axis connected to the Faraday rotator. In an optical isolator provided with a magnetic field applying magnet that applies a magnetic field in a direction, the magnetic field applying magnet has a rotating shaft that passes approximately through the center of the Faraday rotator and rotates about an axis that is perpendicular to the optical axis. An optical isolator characterized by having a.