JPH0645932Y2 - Optical isolator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an optical isolator for preventing laser light emitted from a laser oscillator from returning to the inside of the oscillator.

<Prior Art> In an information control system using laser light, there is a phenomenon in which a part of the output light oscillated from the oscillator is reflected by the constituent elements of the system and returned to the oscillator to become return light, which disturbs the laser oscillation. An optical isolator is used to prevent this.

In this optical isolator, as shown in FIGS. 4 and 5, the incident light, which is oscillated by the oscillator and has an arbitrary elliptically polarized light in the direction of arrow A, becomes a plane polarized light when transmitted through the first polarizer 2. Is output. This plane-polarized light passes through the Faraday rotator 1 provided in the magnetic field applied in the direction of arrow B and is output as plane-polarized light rotated by 45 ° in the direction of arrow R. This plane-polarized light is Polarizer 2 '
The output light is plane-polarized light whose polarization plane direction does not change even when transmitted through. That is, the Faraday rotator 1 is rotated by 45 ° by Faraday rotation between the polarization plane of the incident light and the polarization plane of the output light regardless of the direction of the polarization plane, and the polarizers 2, 2 '
Transmits only the specific polarized light component unique to each of the polarizers 2 and 2'of the transmitted light, and absorbs the component perpendicular thereto.

Here, the output light returns and the laser light in the direction of arrow C is
As shown in the figure, the elliptically polarized return light passes through the second polarizer 2'and becomes plane polarized light, and this plane polarized light reaches the first polarizer 2 by rotating the plane of polarization by 45 ° by the Faraday rotator 1. .
However, in the first polarizer 2, the incident return light makes a difference of 90 ° with the polarization plane of the polarizer 2, so that it cannot pass through the polarizer 2 and does not return to the oscillator.

An example of this type of optical isolator is, as shown in FIG. 6, a cylindrical permanent magnet 3 for generating a magnetic field in the Faraday rotator 1.
The Faraday rotator 1 is formed in the through hole 7 of the center of the Faraday rotator 1 and the polarizers 2 and 2'are closely attached to both side surfaces thereof.

As another example of the optical isolator, as shown in FIG. 7, a Faraday rotator 1 is provided at the center, and ring-shaped permanent magnets 3 and 3'are attached to both side surfaces of the through holes 7 so that the centers of the permanent magnets 3 are in close contact with each other. Polarizers 2 and 2'are formed in close contact with both side surfaces thereof.

<Problems to be solved by the invention> In the conventional optical isolator, the components such as the Faraday rotator 1, the polarizer 2, and 2'are assembled with the contact surfaces in close contact.
There is a drawback that precision is required for processing that allows light to be correctly transmitted. In addition, since the parts used are fixed by heat adhesion, the optical isolator is damaged and deteriorated due to the strain stress generated by heating due to the difference in the thermal expansion coefficient of each part, resulting in a lack of reliability.

<Means for Solving the Problems> In the present invention, except for such drawbacks of the prior art, a plurality of claws are bent inward from the outer periphery of a cylindrical spacer made of a metal material, and the other end of the spacer claw is opened. Adhere one polarizer 2 on the inner surface and one Faraday rotator 1 on the outer surface,
Further, the optical isolator has one cylindrical permanent magnet 3 inserted from the open end.

<Operation> Here, when the output light in the forward direction from the optical isolator is received by a fiber having a polarization plane, and conversely, when the output light is polarized light and polarized perpendicular to the polarization plane, the optical fiber side and the laser The side polarizer 2 can be omitted, the number of parts is small, and the assembly is easy.

<Embodiment> An embodiment of the optical isolator of the present invention is shown in the exploded perspective view of FIG. 1 and the second longitudinal side view.

As shown in the drawing, a spacer 4 is formed by providing a plurality of claws 6 made of a non-magnetic metal material, one end of which is open in the axial direction and the other end of which is bent inward in the axial direction. The polarizer 2 is fixed to the spacer 4 around the optical axis 5 inside the claw 6 and the Faraday rotator 1 is fixed to the outside. Further, a cylindrical permanent magnet 3 in contact with the polarizer 2 of the spacer 4 and having a through hole 7 formed in the center thereof is provided with a through hole 7, a polarizer 2, and a Faraday rotator 1.
An optical isolator is formed by aligning and inserting the optical axes 5 of and into contact with each other. In order to make the optical axis 5 coincide with each other, the spacer 4 and the permanent magnet 3 and the polarizer 2 are not bonded and are freely rotated, and the reference light is transmitted to the position of the optical axis 5 to rotate the spacer 4. Fine adjustment is performed so that the polarizer 2 has the maximum performance as an optical isolator. After that, the permanent magnet 3 and the spacer 4 are bonded and fixed to finish the adjustment,
It becomes a high-performance optical isolator.

When the polarizer 2 and the Faraday rotator 1 are bonded to the spacer 4, the strain is absorbed by the deflection of the thin spacer 4 even if a heating and fixing process is added. Therefore, it is caused by the difference in the coefficient of thermal expansion. Will not be damaged by strain.

Further, in the present invention, when the output light in the forward direction from the optical isolator is received by a special fiber having a polarization plane, conversely, the output light is polarized and the return light having the polarization perpendicular to the polarization plane is affected by noise. In the case of the distributed feedback laser in which the disturbance of the oscillation mode is small, the function does not change even if the polarizers 2 on the optical fiber side and the laser side are omitted.

In general, the magnetic field on the optical axis 5 which is the center of rotation of the cylindrical permanent magnet 3 is always parallel to the optical axis 5 because the outer shape of the permanent magnet 3 is symmetrical. Here, as shown in FIG. 3, the permanent magnet 3 has an outer diameter of 4 mm, an inner diameter of 2 mm, and a length of 4 mm, and the vertical axis indicates the relative strength of the magnetic field G. The horizontal axis indicates the distance 0 m from the center of the permanent magnet 3.
The characteristic curve figure which simulated m is shown. As shown in the drawing, the relative strength G of the magnetic field with respect to the horizontal axis becomes maximum at the center D ₁ of the permanent magnet 3 and decreases as it approaches the end face D ₂ ,
The magnetic field strength becomes zero slightly outside D _2, and becomes negative relative strength outside, and tends to decrease again after increasing.
Therefore, in order to give a saturated magnetic field to the Faraday rotator 1, there are two positions on the optical axis 5, the inner X ₁ of the permanent magnet 3 and the outer X ₂ slightly apart from the end face. However, in the case of using the cylindrical permanent magnet 3 according to the present invention, since the external magnetic field is used, it is slightly smaller than the internal magnetic field, so that the permanent magnet 3 used is somewhat large. However, since the Faraday rotator 1 is installed outside the permanent magnet 3, it is easy to assemble and fine adjustment is possible.

<Effects of the Invention> As described above, according to the present invention, the Faraday rotator
It is only necessary to use one each of the polarizer 1, the permanent magnet 3, and the spacer 4, and the strain stress of the optical element such as the Faraday rotator 1, the polarizer 2 and the adhesive surface with the spacer 4 is reduced, and An optical isolator that is easy to assemble, allows fine adjustment after assembly, and has good performance is obtained.

[Brief description of drawings]

1 is an exploded perspective view of an optical isolator according to an embodiment of the present invention, FIG. 2 is a vertical sectional side view taken along the optical axis in FIG. 1, and FIG. 3 is an optical axis from the center of a permanent magnet in the present invention. Curve diagram showing the relationship between the relative strength of the external magnetic field
FIG. 4 is an exploded perspective view showing the operation of the optical isolator with respect to light in the forward direction, FIG. 5 is an exploded perspective view showing the operation with respect to light in the opposite direction to FIG. 4, and FIG. 6 is an example of a conventional optical isolator. FIG. 7 is a vertical sectional side view and an external front view of another example of the conventional optical isolator. Note 1: Faraday rotator, 2, 2 ': polarizer, 3, 3': permanent magnet,
4: Spacer, 5: Optical axis, 6: Claw, 7: Through hole.

Claims (1)

[Scope of utility model registration request] 1. A polarizer 2 is provided on the inner surface of a claw 6 of a cylindrical spacer 4 made of a non-magnetic material, one end of which has a plurality of claws 6 bent toward the central axis and the other end open. 1 on the outside
One Faraday rotator 1 is bonded and the spacer 4
An optical isolator having a cylindrical permanent magnet 3 inscribed therein.