KR20190054599A - Polarization maintaining optical fiber - Google Patents

Abstract

The present invention relates to an optical fiber maintaining polarization, which comprises: a cladding unit; an oval-shaped elliptical core positioned at the center of the cladding unit; and a plurality of air holes formed in the cladding unit with respect to the long axis of the elliptical core.

Description

[0001] POLARIZATION MAINTAINING OPTICAL FIBER [0002]

The present invention relates to a polarization maintaining optical fiber. More particularly, the present invention relates to a polarization maintaining optical fiber comprising an elliptical core and a plurality of air holes.

A light wave can be defined as an electric field and a magnetic field that are perpendicular to the traveling direction and vibrate perpendicularly to each other. Light traveling in a conventional single-mode optical fiber changes its polarization state with changes in external environmental conditions.

On the other hand, the polarization maintaining optical fiber has anisotropy in the stress distribution in the single mode optical fiber, thereby breaking the degeneracy between the two orthogonal modes propagating in the optical fiber to make difference in the propagation constant, thereby eliminating the coupling between modes. As a result, when light that matches a certain polarized wave enters the polarization maintaining optical fiber, the polarized light is propagated while maintaining only the polarized wave.

The polarization maintaining optical fiber can be fabricated in the form of a panda type optical fiber by introducing a high refractive index around the optical fiber core or by inserting another stress axis, or by using an elliptical core so that the long and short axes of the core have relatively different refractive indices.

However, in the case of the panda-type optical fiber, expensive manufacturing cost is required. In the case of the optical fiber having the elliptical core, the manufacturing cost is comparatively low, but the polarizing retention is relatively low as compared with the panda type optical fiber. In order to compensate for these problems, the side of the optical fiber is polished to use the D-shaped optical fiber. However, since the connection loss is large when the optical fiber is connected to the optical fiber and the cladding side of the optical fiber is polished, .

Korean Patent Publication No. 10-2008-0041428 (published on May 13, 2008)

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polarization maintaining optical fiber which is easy to manufacture, minimizes connection loss when connected to a general optical fiber, and has excellent polarization maintaining characteristics.

In order to improve the polarization maintaining property of a polarization maintaining optical fiber having an elliptical core and to compensate for the connection loss of a polarization maintaining optical fiber having a D-shape shape and a connection with another optical fiber, Maintaining polarization maintaining characteristics and lowering the connection loss with a general optical fiber.

The present invention relates to a cladding portion, An oval-shaped elliptical core located at the center of the cladding portion; And a plurality of air holes formed in the cladding portion with respect to a long axis of the elliptical core.

In one embodiment, the plurality of air holes include first air holes formed closest to a straight line extending the long axis of the elliptical core, and second air holes formed above the first air holes do.

In addition, third air holes formed above the second air holes may further include the second air holes.

The elliptical core may be provided with an air hole forming portion in which the first air holes are not formed.

The distance between the major axis of the elliptical core and the lower end of the second air holes may be greater than a predetermined value.

In addition, the loss of the optical fiber can be controlled by controlling the ratio of the total cross-sectional area of the air holes to the total cross-sectional area of the optical fiber.

The polarization maintaining optical fiber according to the present invention is excellent in polarization maintaining property, easy to manufacture, and easy to connect with a general optical fiber.

Conventional panda-type optical fibers have a disadvantage in that the manufacturing process is complicated due to having a stress axis having a large difference in refractive index. However, the polarization maintaining optical fiber according to the present invention has advantages of being easy to manufacture and economical because it does not use stress axis.

In addition, in the case of the conventional panda-type optical fiber, there is a disadvantage that the durability is degraded due to an environmental change such as an external sudden temperature change, but the present invention solves this disadvantage.

1 is a cross-sectional view of a polarization maintaining optical fiber according to a preferred embodiment of the present invention.
2 is a view showing a numerical relationship of a polarization maintaining optical fiber according to a preferred embodiment of the present invention.
FIG. 3 is a graph showing a change in refractive index according to a fill factor in a polarization maintaining optical fiber according to a preferred embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to designate the same or similar components throughout the drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. In addition, the preferred embodiments of the present invention will be described below, but it is needless to say that the technical idea of the present invention is not limited thereto and can be variously modified by those skilled in the art.

1 is a cross-sectional view of a polarization maintaining optical fiber according to a preferred embodiment of the present invention.

The basic principle of the polarization maintaining optical fiber is that the optical fiber has different polarization ratios along the vertical direction and the horizontal direction so that the polarization axis is aligned in either direction so that the incident light maintains the polarization direction while advancing the optical fiber. Accordingly, the polarization maintaining optical fiber is required to have different refractive indices along the vertical direction and the horizontal direction.

The polarization maintaining optical fiber according to the present invention comprises a cladding portion 10, an elliptic core 20 formed at the center of the cladding portion 10, a plurality of air holes 30 formed at one side of the long axis of the elliptical core 20 ).

Referring to FIG. 1, the elliptical core 20 is elongated in the horizontal direction so that the effective refractive index in the vertical direction is smaller than the effective refractive index in the horizontal direction. In addition, by forming the air holes 30 at one side of the elliptical core 20, the effective refractive index in the vertical direction can be made smaller than the effective refractive index in the horizontal direction. This difference in effective refractive index between the vertical direction and the horizontal direction can be further increased by the elliptical core 20 and the air hole 30. [

The polarization maintaining optical fiber according to the present invention can have a higher polarization characteristic than a polarization maintaining optical fiber of a general elliptical core, and the outer shape of the entire cladding can be circular, thereby solving the disadvantage of the D-shaped optical fiber.

In one embodiment, the air holes 30 may be formed in a plurality of rows at one side of the long axis of the elliptical core 20. [ 1, the first air holes 30-1 closest to the long axis of the elliptical core 20 and the second air holes 30 (1) formed in order above the first air holes 30-1 -2, third air holes 30-3, and fourth air holes 30-4. The number of rows of air holes 30 and the number of air holes in each row can be increased or decreased as needed. In addition, the first through fourth air holes 30-1, 30-2, 30-3, and 30-4 are arranged so that each row forms a straight line, but each row may be arranged as an arc.

In the air holes, the width to the left and right of the first air holes 30-1 is the largest, and the width decreases toward the upper side.

In the case of the first air holes 30-1, an air hole may not be formed just above the elliptical core 20. [ Accordingly, the air hole non-formed portion 40 is provided just above the elliptical core 20. [

2 is a view showing a numerical relationship of a polarization maintaining optical fiber according to a preferred embodiment of the present invention.

In the polarization maintaining optical fiber according to the present invention, the ratio of the size of the elliptical core 20 to the size of the cladding portion 10, the ratio of the major axis length 2a to the minor axis length 2b of the elliptical core 20, The distance d from the straight line extending from the long axis of the elliptic core 20 to the center of the first air holes 30-1 and the straight line extending from the long axis of the elliptic core 20 The distance D from the first air holes 30-2 to the lower ends of the second air holes 30-2, and the ratio of the area occupied by the air holes 30, and the like.

The distance D from the upper portion of the elliptical core 20 to the second air holes 30-2 disposed apart through the air hole formed portion 40 is equal to the distance d and the distance between the first air holes 30-1 D + t / 2 + g according to the distance g between the upper end of the first air holes 30-2 and the lower end of the second air holes 30-2 and the diameter t of the air hole.

When the D value becomes smaller, the light passing through the core is scattered toward the second air holes 30-2, thereby increasing the loss of the optical fiber. Accordingly, D is preferably larger than the predetermined value.

<Examples>

The optical fiber was fabricated with the following numerical values.

- Diameter of cladding part: 125 탆

- Diameter of air hole (t): 8.2 탆

- Number of air holes: 24

- gaps between the air holes (g): 6.45 탆

(1) Loss due to change in D value

Referring to FIG. 2, D = d + 4.1 + 6.45. When d is smaller than a predetermined value according to the change of d, the loss of the optical fiber increases in the Y-axis direction and the connection loss of the optical fiber increases. In this embodiment, it was confirmed that the loss was significantly reduced when d was 8.4 탆 or more.

(2) Fill factor (f)

In the present invention, the fill factor is defined as ((the sum of the cross sectional areas of all the air holes) / (the total cross sectional area of the optical fiber)) x 100%.

FIG. 3 is a graph showing a change in refractive index according to a fill factor in a polarization maintaining optical fiber according to a preferred embodiment of the present invention.

3, when the fill factor is from 0 to about 9, the refractive index (B: birefringence) of the polarization maintaining optical fiber is decreased, and then the refractive index is increased until 10, but when the fill factor is 10 to 12, appear.

In the numerical value according to the embodiment, the fill factor is 10.3%, and a stable refractive index can be maintained.

It will be apparent to those skilled in the art that various modifications, substitutions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. will be. Therefore, the embodiments disclosed in the present invention and the accompanying drawings are intended to illustrate and not to limit the technical spirit of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments and the accompanying drawings . The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

10: cladding portion
20: Oval core
30: air hole

Claims (6)

Cladding portion;
An oval-shaped elliptical core located at the center of the cladding portion; And
A plurality of air holes formed in the cladding portion with respect to a long axis of the elliptic core,
/ RTI &gt; The method according to claim 1,
Wherein the plurality of air holes include first air holes formed closest to a straight line extending the long axis of the elliptical core and second air holes formed above the first air holes. 3. The method of claim 2,
And third air holes formed above the second air holes. 3. The method of claim 2,
And an air hole unformed portion in which the first air holes are not formed is provided directly above the elliptical core. 3. The method of claim 2,
Wherein a distance from a long axis of the elliptical core to a lower end of the second air holes is larger than a predetermined value. The method according to claim 1,
Wherein the loss of the optical fiber is controlled as the ratio of the total cross-sectional area of the air holes to the total cross-sectional area of the optical fiber is controlled.

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