JPH04358119A - Optical attenuator - Google Patents

Abstract

PURPOSE:To simplify the structure and to easily vary the attenuation quantity by varying an external magnetic field by using a perpendicularly magnetized magnetooptic material in the variable impressed magnetic field. CONSTITUTION:This optical attenuator attenuates transmitted light by diffracting incident light by impressing the variable magnetic field from an electromagnet 2, etc., to a magnetooptic element 1 which has multiple magnetic domain structure in the absence of the impressed magnetic field and generate mutually different mgnetism components parallel to the incident light in adjacent magnetic domains. This optical attenuator functions as an optical modulator by using a means which can impress a modulating magnetic field. This magnetooptic element 1 preferably uses bismuth substituted rare earth iron garnet, etc. In general, diffraction loss is maximum when no magnetic field is pressed and decreases by the movement of a magnetic wall as the impressed magnetic field increases. The multiple magnetic domain structure of the element turns into single magnetic domain structure above a saturated magnetic field, so no diffraction is caused. In this case, the intensity of direct light is adjusted with the diffraction loss by the magnetooptic element 1, so a polarizer can be omitted, which is advantageous in structure.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel optical attenuator and optical modulator using magneto-optical elements.

0002

2. Description of the Related Art An optical attenuator is a device for adjusting the intensity of light entering a light receiving element or a photographing element to an optimum value. In optical communications, the loss that enters the transmission path varies greatly due to splicing, connections, relays, branches, etc., and the light intensity that enters the light receiving device also fluctuates greatly due to loss in the optical fiber itself.
Optical attenuators are very often used to bring these optical intensities into the dynamic range of a receiving device. Furthermore, optical attenuators are often used for purposes such as evaluating and calibrating the performance and reliability of other communication equipment and optical measuring instruments.

Conventionally, ND filters have been used as optical attenuators, and fixed attenuators with a constant amount of attenuation and variable attenuators with variable attenuation are known. FIG. 2 shows a generally used variable attenuator consisting of a movable damping section 5 and a collimator section 3. The attenuation section of such a variable attenuator consists of a step variable attenuation plate 6 and a continuous variable attenuation plate 7, as shown in FIG. , the latter has a range larger than this step width (for example, 0 to 15 dB)
An ND filter whose attenuation amount changes continuously depending on the rotation angle is installed to cover the following.

However, the optical attenuator using the above-mentioned ND filter has a complicated structure because the attenuation amount is set by mechanically rotating the filter. Furthermore, since there are moving parts in the optical system, there is a problem with reliability.

As another type of optical attenuator, a variable attenuator using magneto-optic effect is known (Utility Model Application No. 63-1).
28522). This variable attenuator has the advantage that there are no moving parts because the amount of attenuation is adjusted by an external magnetic field. However, in order to adjust the light intensity by extracting a specific polarized light component, it is necessary to arrange polarizing prisms on both sides of the magneto-optical element, resulting in a complicated structure.

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel optical attenuator in which the amount of attenuation can be easily adjusted without the need for moving parts, and the structure of the entire attenuator can be simplified.

[0007]

[Means for Solving the Problems] As a result of intensive study and research in order to solve the above problems, the present inventors have found that by using a magneto-optical material with perpendicular magnetization in a variable applied magnetic field, a magnetic field can be detected based on the diffraction phenomenon. We have discovered that the amount of light passing through the material can be adjusted appropriately, and have completed the optical attenuator of the present invention.

That is, the present invention provides a magneto-optical element which has a multi-domain structure when no magnetic field is applied, and in which magnetization components parallel to the direction of propagation of light in the magnetic domains differ from each other in adjacent magnetic domains, and the magneto-optical element. The present invention provides an optical attenuator comprising means for applying a magnetic field of variable strength to the optical attenuator.

The magneto-optical element used in the present invention is a material that has a multi-domain structure when no magnetic field is applied, and the magneto-optical element is made of a material that has a multi-domain structure, and the magneto-optical element absorbs the incident light so that adjacent magnetic domains have different magnetization vector components in the traveling direction of the incident light. placed against. Regarding the arrangement of the magneto-optical element with respect to the incident light, as shown in FIG. 1, it is preferable that the magnetization directions in adjacent magnetic domains are parallel to the incident light and parallel to each other, but as shown in FIGS. 5 and 6. The magneto-optical element itself having perpendicular magnetization can also be arranged obliquely with respect to the incident light. Furthermore, a plurality of magneto-optical elements can be stacked and used for purposes such as adjusting the amount of optical attenuation.

[0010] Examples of materials that have a multi-domain structure without applying a magnetic field as described above include Bi-substituted rare earth iron garnet materials, rare earth iron garnets, orthoferrites produced by the LPE method, etc. However, the material is not particularly limited to these materials, and various materials having a multi-domain structure can be used within the range that can achieve the purpose of the present invention. By cutting these materials so that the axis of easy magnetization is perpendicular to the surface, a thin film with perpendicular magnetization can generally be obtained, which can be used as the element of the present invention. In particular, in the case of the Bi-substituted rare earth iron garnet film produced by the LPE method, it has perpendicular magnetization as it is without any special treatment due to growth-induced magnetic anisotropy, achieving the objective of the present invention. It is preferable to do so. In addition, this Bi-substituted rare earth iron garnet material has a large Faraday rotation ability, so it is suitable from the viewpoint that a large rotation loss can be obtained with a small thickness.

When light is transmitted through the above magneto-optical material, the polarization plane of the transmitted light has a different Faraday rotation angle depending on the magnetization component of each magnetic domain, so the material acts as a diffraction grating. Some light is diffracted. In the optical system shown in FIG. 1, this diffracted light is not received by the receiving optical fiber, and as a result, the light incident on the optical fiber is attenuated.

As a means for applying a magnetic field of variable strength to the magneto-optical element used in the present invention, an electromagnet is used to electrically control the amount of attenuation of light, and as a simple means, an electromagnet whose position is movable is used. Permanent magnets can be used, but are not particularly limited thereto. The magnetic field applying means is preferably arranged so that the magnetic field is applied parallel to the magnetization component, as shown in FIG.

Furthermore, the optical attenuator of the present invention can be used as an optical modulator by using means capable of applying a modulated magnetic field in place of the above magnetic field applying means. Furthermore, it can also be used as a variable modulation frequency optical modulator by using means that can apply a magnetic field at a variable modulation frequency.

The attenuator of the present invention can freely attenuate the intensity of the light emitted from the magneto-optical element by appropriately adjusting the magnetic field intensity by the magnetic field applying means arranged as described above. The arrangement of the attenuator of the present invention with respect to the light source may be various as shown in the embodiments, but is not particularly limited thereto. Further, for input/output, optical fibers are particularly suitable for use as optical attenuators, but the present invention is not limited thereto and can be used for various purposes.

[0015]

[Operation] Diffraction loss from a magneto-optical element having a multi-domain structure as described above changes through the movement of domain walls due to the applied magnetic field, so the amount of attenuation of light can be varied by changing the intensity of the applied magnetic field. Can be adjusted. Generally, the diffraction loss is maximum when the applied magnetic field is 0, and as the applied magnetic field increases, the diffraction loss decreases due to the movement of the domain walls. And above the saturation magnetic field,
Since the multi-domain structure of the element changes to a single-domain structure, diffraction no longer occurs. In addition, the Faraday rotation angle of saturation is 90°
Therefore, when the applied magnetic field is 0, all light is calculated to be diffracted. To increase the amount of attenuation, set the rotation angle to 90
In addition to making it close to °, it can also be achieved by stacking a large number of elements. As described above, in the present invention, since the intensity of light is directly adjusted by the diffraction loss caused by the magneto-optical element, a polarizer can be omitted, which is advantageous in terms of structure.

Examples of the present invention are shown below, but the present invention is not limited thereto.

[0017]

【Example】

Example 1 FIG. 1 shows an optical system using a specific example of the optical attenuator of the present invention. The optical system is composed of a magneto-optical material 1 which has a multi-domain structure when no magnetic field is applied, a magnetic field applying means 2, collimator lenses 3 and 3', and optical fibers 4 and 4'. In the above system, the magnetic field applying means 2 is a cylindrical permanent magnet whose position is movable, and the magnetic field applying means 2 applies a magnetic field parallel to the direction of magnetization of the magneto-optical material 1. Collimator lenses 3 and 3' are arranged on both sides of the element 1 on the optical axis of the optical fiber, so that the lens 3 converts the light emerging from the fiber 4 into a parallel beam, and the lens 3' converts the parallel beam into the fiber 4. It works to focus light on '. Bi1.4 Y1 produced by LPE method as magneto-optical material 1
．． A material of 6 Fe5 O12 was used. This material had perpendicular magnetization. The thickness of this material is 400μm
And so. In this system, by gradually increasing the magnetic field strength from 0, the diffraction loss from the magneto-optic material 1 decreases, and the amount of light incident on the optical fiber 4' increases. The loss of the optical attenuator without applying a magnetic field was 12 dB. When the magnetic field is gradually applied, the loss gradually decreases to about 1.
The loss was 2 dB under a magnetic field of 5 kOe. Even if a larger magnetic field was applied, the loss remained at 2 dB.

Embodiment 2 FIG. 2 is a diagram showing an optical system using another specific example of the optical attenuator of the present invention. The structure is similar to that of the optical system of Example 1, except that the magneto-optic material 1 is inserted directly between the fiber ends and there is no collimator lens. This aspect is suitable for a system that does not particularly require a lens, and allows for a simpler structure.

Embodiment 3 FIG. 3 shows an optical system arrangement that can prevent return reflection from the fiber end surface by arranging the end surface of the optical fiber and the magneto-optical element obliquely in the specific example shown in FIG. show.

Embodiment 4 FIG. 4 shows an embodiment in which a plurality of magneto-optical materials are stacked in the arrangement shown in FIG. 3, and is a suitable arrangement when it is desired to further increase the amount of attenuation.

[0021]

The optical attenuator of the present invention has an extremely simple structure, and the amount of attenuation can be easily varied by changing the external magnetic field. Furthermore, since the optical system does not have any moving parts, the reliability of the device is high.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an optical system using a specific example of an optical attenuator of the present invention.

FIG. 2 shows a variable attenuator consisting of a conventional movable damping part 5 and a collimator part 3;

3 is an enlarged view of the attenuation section of the optical attenuator shown in FIG. 2. FIG.

FIG. 4 is a diagram illustrating an optical system using another embodiment of the optical attenuator of the present invention in which a magneto-optic material is inserted directly between fibers.

FIG. 5 is a diagram showing an optical system using a specific example of the optical attenuator of the present invention in which an optical fiber end face and a magneto-optical element are arranged obliquely.

FIG. 6 is a diagram showing an optical system using a specific example of the optical attenuator of the present invention in which a plurality of magneto-optic materials are stacked on the optical axis.

[Explanation of symbols]

1 Magneto-optical materials 2 Magnetic field application means 3, 3’ collimator lens 4, 4’ optical fiber 5 Attenuation section 6. Step variable damping plate 7 Continuously variable damping plate

Claims (5)

[Claims] 1. A magneto-optical element which has a multi-domain structure when no magnetic field is applied, and in which magnetization components parallel to the traveling direction of light in the magnetic domains differ from each other in adjacent magnetic domains, and a magneto-optical element having a variable intensity. and means capable of applying a magnetic field. 2. A magneto-optical element that has a multi-domain structure when no magnetic field is applied, and in which magnetization components parallel to the traveling direction of light in the magnetic domains are different from each other in adjacent magnetic domains; and means capable of applying a magnetic field. 3. The optical attenuator according to claim 1, further comprising a plurality of said magneto-optical elements stacked in the direction of propagation of light. 4. An optical attenuator for optical fibers using the optical attenuator according to claim 1 between optical fibers. 5. The optical attenuator or optical modulator according to claim 1, wherein a Bi-substituted rare earth iron garnet film produced by the LPE method is used as the magneto-optical element.