KR100642378B1 - A device for decreasing pmd by changing pressure around optical fiber and apparatus for making an optical fiber having low polarization mode dispersion by using the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the manufacture of optical fibers, and more particularly to an apparatus for reducing polarization mode dispersion (PMD) of an optical fiber.

The present invention comprises a means for cutting the optical fiber base material to form a bare optical fiber; Means for irregularly deforming the optical fiber by forming an irregular irregular pressure on the longitudinal and / or circumferential surface of the bare optical fiber; Means for coating at least one coating layer around the irregularly deformed optical fiber; A capstan for controlling the cutting speed of the optical fiber; It relates to an optical fiber manufacturing apparatus comprising a winding bobbin for winding the optical fiber passed through the capstan to the bobbin.

Optical fiber, PMD, pressure change

Description

A device for improving polarization mode dispersion using a pressure change around an optical fiber and an optical fiber manufacturing apparatus using the same.

The following drawings attached to this specification are illustrative of preferred embodiments of the present invention, and together with the detailed description of the invention to serve to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings It should not be construed as limited to

1 is a schematic diagram of a typical prior art optical fiber edge device.

2 is a schematic diagram illustrating an optical fiber cutting apparatus of a preferred embodiment according to the present invention.

Figure 3a is an exploded perspective view of a rotary pressure device of a preferred embodiment according to the present invention, Figure 3b is a plan view of the Figure 3a.

Figure 4 is an exploded perspective view of a rotary pressing apparatus of another preferred embodiment according to the present invention.

<Description of the symbols for the main parts of the drawings>

101: optical fiber preform 102: cutting line

103: filament fiber 104: outer diameter measuring instrument

105: cooling device 106: coating device

107: curing device 108: driver

109: winding device 110: rotary tubular member

120: rotary drive

The present invention relates to the manufacture of optical fibers, and more particularly, to a method and apparatus for reducing polarization mode dispersion (PMD) of an optical fiber.

Theoretically, a single mode optical fiber with circular symmetry has two independent, mutually canceling orthogonal polarization modes. In general, the electric field of light propagating through an optical fiber can be seen as a linear superposition of these two polarization eigenmodes. In practice, single-mode optical fibers are canceled out of these two polarization modes by incomplete elements such as symmetrical lateral stresses or eccentricity of circular cores. These two modes propagate with different phase velocities, thereby propagating the two polarization modes with different propagation constants β ₁ and β ₂ . This difference in propagation constants is referred to as birefringence (Δβ), and the increase in birefringence means an increase in the speed difference between the two polarization modes. The differential time delay between two polarization modes is called polarization mode dispersion (hereinafter abbreviated as "PMD"), the presence of which makes it difficult to transmit high speed or analog data.

It is known to reduce the PMD by twisting the optical fiber to a pitch much smaller than its beat length so that gradual compensation is achieved due to the relative delay between polarization modes.

WO83 / 00232 and Japanese Unexamined Patent Application Publication No. 8-59278 disclose a method of cutting an optical fiber base material while rotating it at high speed.

In addition, Japanese Laid-Open Patent Publication No. 7-69665 discloses a method of cutting the optical fiber base material by twisting it with a short pitch.

However, these methods are commercially impractical because the twisting of the optical fiber in a unidirectional direction embeds an elastic torsional stress in the optical fiber and dramatically increases the rotational speed of the base material to correspond to the increase in the cutting speed.

U.S. Pat.Nos. 5,298,047 and 5,418,881 are also applied to an optical fiber by swinging a guide roller in contact with the coated optical fiber at an angle with respect to the edge axis or by linearly reciprocating in a direction perpendicular to the edge axis. A method of providing twist in an optical fiber so that the spin has a non-uniform spatial frequency (spins / m) is disclosed.

U.S. Patent Nos. 5,943,466 and 6,240,748 describe optical fiber element wires by guiding the optical fiber element wires after forming the coating layer on the optical fiber with a rocking guide roller reciprocating to change the inclination of the rotation axis, and then guiding the optical fiber element wires with a guide roller having a fixed rotation axis. Disclosed is a method of generating torsion. In particular, the '466 and' 748 is a time-varying complex function (frequency modulation sine function or amplitude modulation) that is not substantially a sinusoidal function of generating twist in the optical fiber element wire, but has at least two maximum values different in magnitude. Sine function).

The above prior art will be described in more detail with reference to FIG. 1.

First, FIG. 1 is a schematic configuration diagram of an optical fiber manufacturing apparatus 10 disclosed in the above-described US patents.

The optical fiber base material 11 is slowly supplied to the melting furnace 12, and the optical fiber 13 is withdrawn from the neck-down portion of the base material. The drawn optical fiber (i.e., uncovered optical fiber) is fed to the coating apparatus 15 through the diameter monitor 14, where the coating polymer is coated on the relatively cooled state of the optical fiber. After the coated optical fiber passes through the coating concentricity monitor 16, the optical fiber passes through the curing apparatus 17. Typically the curing device 17 has a UV lamp. Downstream of the curing apparatus 17 is provided a coating diameter monitor 18 and subsequent guide means (ie rollers 21, 22, 23) and drive means (ie capstans). The guide roller 21 is the first point of contact with which the optical fiber first comes into contact, at which point the optical fiber is protected by an already cured polymer coating. Darw force is provided by the capstan 24, and the optical fiber from the capstan 24 typically goes to a winding means (e.g., TAKE-UP SPOOL).

The guide roller 21 can spin in a state inclined at an angle with respect to the edge axis, or provide a spin to the optical fiber by linear reciprocating motion in a direction perpendicular to the edge axis. In this case, the spin function may be a substantially sinusoidal function or an amplitude modulation or frequency modulation sinusoidal function.

As such, conventionally, physical contact is used to apply spin to the optical fiber. Such physical contact is likely to weaken the coating property of the optical fiber and cause breakage of the optical fiber. In addition, the addition of rotational force through contact imparts mechanical defects to the optical fiber surface, weakening the strength of the optical fiber.

Therefore, recently, a method of reducing PMD by periodically changing the shape of the optical fiber core without contacting the optical fiber by using a laser light (US Patent No. 5,992,181) or a heat source (European Patent No. 1,318,369) has been proposed. have.

It is an object of the present invention to provide an apparatus capable of unevenly changing the core shape of an optical fiber without physical contact with the optical fiber.

Other objects and advantages of the invention will be described below and will be appreciated by the embodiments of the invention. Furthermore, the objects and advantages of the present invention can be realized by means and combinations indicated in the appended claims.

The present inventors can create irregular deformations in the optical fiber by periodically or aperiodically applying non-constant pressure to the longitudinal and / or circumferential surfaces of the fringed fiber being edged, thereby reducing the PMD characteristics. I found it possible.

In order to implement the technical principle, the present inventors have developed a rotary pressurizing device and an optical fiber manufacturing apparatus using the rotary pressurizing device as follows.

One aspect according to the present invention is provided between the edge line for drawing out the bare optical fiber from the optical fiber base material and the coating device for forming a coating layer on the bare optical fiber irregularities in the interior of the bare optical fiber Claims are made for a rotary pressurizing device for changing.

In this apparatus, a hollow is formed therein, the hollow having a diameter larger than at least the diameter of the spiral fiber extending long along the edge of the optical fiber to pass through the spiral fiber, and the central axis of the hollow and the edge axis are substantially A tubular member which coincides and the distance from said central axis to said hollow surface is not constant; Rotation driving means for rotating the tubular member about the central axis. Accordingly, by rotating the tubular member about the central axis, irregular pressure can be formed on the surface of the optical fiber descending along the edge line.

In addition, another aspect of the present invention includes a means for cutting the optical fiber base material to form spiral fiber; Means for irregularly deforming the optical fiber by forming an irregular irregular pressure on the longitudinal and / or circumferential surface of the bare optical fiber; Means for coating at least one coating layer around the irregularly deformed optical fiber; A capstan for controlling the cutting speed of the optical fiber; Claims are made for an optical fiber manufacturing apparatus including a winding bobbin for winding an optical fiber passing through the capstan to a bobbin.

At this time, the means for irregularly deforming the optical fiber, the hollow is formed therein larger than the diameter of at least the spiral fiber extending along the edge of the optical fiber in order to pass through the spiral fiber, the hollow A tubular member whose central axis and the edge axis substantially coincide, and whose distance from the central axis to the hollow surface is not constant; Rotation driving means for rotating the tubular member about the central axis.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 shows a schematic configuration of an optical fiber manufacturing apparatus 100 according to the present invention.

After the base material 101 for manufacturing the optical fiber is heated to a high temperature in the furnace 102, the bare optical fiber 103 is drawn from the neck-down point of the softened base material. The drawn fiber optics 103 are deformed in the rotary pressing apparatuses 110 and 120 via the outer diameter measuring instrument 104, and the shape of the deformed optical fiber is fixed while being cooled by the cooling apparatus 105. The cooled fibrous fiber is coated at least once with an ultraviolet curable resin in the coating device 106. The coated optical fiber coated in the coating device 106 is cured in the curing device 107 and then passed through a drive device (ie, capstan) 108 that controls the cutting speed of the optical fiber (ie, winding bobbin) 109. It is transferred to) and is picked up.

The rotary pressurizing device includes a rotary tubular member 110 as shown in FIGS. 3A and 4 and a rotary drive device 120 for rotating the tubular member 110 about a cutting line axis.

The rotary tubular member 110 has a hollow 111 for accommodating the optical fiber therein, and extends along a cutting line axis X of the optical fiber in a predetermined length. It is preferable that the central axis X of the tubular member 110 and the edge line of the optical fiber coincide with each other. In addition, the tubular member 110 is rotated in a clockwise or counterclockwise direction by the rotary drive device 120.

The tubular member 110 has an inlet 112 through which the optical fiber 103 is introduced and an outlet 113 through which the optical fiber is drawn out. Therefore, the optical fiber 103 drawn from the melting furnace 102 is introduced into the tubular member 110 through the inlet 112 to experience an irregular pressure change, and then discharged through the outlet 113.

The distance (L ₁ , L ₂ ) between the central axis (X) and the inner surface (surface of the hollow) of the tubular member 110 should not be constant. That is, the distances (L ₁ , L ₂ ) to the central axis (X) and the inner surface of the tubular member 110 should not coincide with each other at least two or more points. For example, the cross section of the hollow 111 preferably has an oval shape as shown in FIG. 3B or a rectangle as shown in FIG. 4. In addition, the minimum diameter L ₂ of the hollow 111 should be at least larger than the diameter of the filamentary fiber 103 to sufficiently accommodate the filamentary fiber 103.

When the cross section of the tubular member 110 is elliptical (or rectangular) as shown in FIG. 3B (or FIG. 4), the tubular member 110 rotates because the lengths of the long axis L ₂ and the short axis L ₁ are not equal to each other. As a result, the pressure formed between the surface of the optical fiber 103 and the inner surface of the tubular member 110 is different from each other in the circumferential direction and / or the longitudinal direction of the optical fiber. That is, the pressure at a specific point in the longitudinal direction of the optical fiber and the pressure acting on another point in the longitudinal direction are different from each other. For example, the pressure P ₂ formed between the spiral fiber and the hollow in the uniaxial (minimum diameter) direction is greater than the pressure P ₁ formed between the spiral fiber and the hollow in the major axis (maximum diameter) direction.

As such, when different pressures are applied to each part of the optical fiber, internal deformation generated by the pressure is also uneven. In other words, the internal characteristics of the optical fiber are changed irregularly to reduce the polarization mode dispersion (PMD) characteristics.

In addition, the tubular member 110, as shown in Figure 3a it is possible to gradually reduce the maximum diameter (or minimum diameter) of the hollow along the line axis or to design the same as shown in FIG. That is, by setting the maximum diameter (and minimum diameter) of the inlet 112 of the tubular member 110 to be larger than the maximum diameter (and the minimum diameter) of the outlet 113, it is also possible to further strengthen the pressure change in the longitudinal direction. (See FIG. 3A).

The rotary drive device 120 is for rotating the tubular member 110 about a cutting line axis, and a motor (not shown in the drawing) for generating a rotational driving force, and a rotational transmission for transmitting the rotational driving force of the motor to the tubular member. Device (not shown in the figure). For example, the rotation transmission device may be composed of a pair of pulleys and a power transmission belt.

The rotary drive unit 120 rotates the tubular member 110 at a constant or irregular rotation speed in the clockwise or counterclockwise direction. In particular, the rotation drive device 120 preferably changes the rotational speed of the tubular member 110 periodically or aperiodically to enhance the change in pressure acting on the surface of the optical fiber.

3B and 4 illustrate an example in which the hollow shape of the tubular member is oval or rectangular, but the present invention is not necessarily limited to this example. That is, any form can be accommodated as long as the nonuniformity inside the core can be increased by generating a local pressure difference around the optical fiber descending along the edge line.

Hereinafter, the mechanism for reducing the PMD of the optical fiber will be described based on the above-described configuration of the rotary pressure device.

When the helical fiber drawn from the optical fiber edge 102 is received into the hollow 111 of the tubular member through the inlet 112 of the rotating tubular member 110, the tubular member 110 is rotated to The pressure changes locally. That is, a greater pressure is applied to a region coupled with the minimum diameter of the hollow than a region coupled with the maximum diameter of the hollow, and the optical fiber before cooling is deformed in response to the applied pressure. In addition, the temperature change of the nano-unit occurs along with the pressure change, which causes a slight difference in the cooling rate. Through this process, the core of the optical fiber is compressed periodically or non-periodically to have a slightly pressed shape, which increases the nonuniformity inside the core, thereby reducing the polarization mode dispersion value as a whole.

<Example>

A tubular member having an elliptical hollow having a long axis of 10 mm and a short axis of 5 mm is installed between the edge line and the coating apparatus, and after passing through the filament fiber at a flux of 25 m / s through the tubular member, the polarization mode dispersion value is measured. It was. As a result of the measurement, the polarization mode dispersion value of the optical fiber according to the present embodiment was 0.03ps to 0.05ps.

This value is much lower than 0.1 ps to 0.2 ps, which is the PMD value of the optical fiber without spin, and is comparable to 0.03 to 0.05 ps, the PMD of the optical fiber which is periodically spinned at 2 to 20 spin / m.

In the above, preferred embodiments of the present invention have been described with reference to the accompanying drawings. Herein, the terms or words used in the present specification and claims should not be interpreted as being limited to the ordinary or dictionary meanings, and the inventors properly define the concept of terms in order to explain their own invention in the best way. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that it can. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

According to the present invention, it is possible to reduce the PMD in a non-contact manner without physically contacting the optical fiber or applying twist stress to the outside of the optical fiber.

Moreover, it becomes possible to implement | achieve the apparatus which reduces PMD of an optical fiber more cheaply and simply.

Claims (15)

A device for irregularly changing the characteristics of the inner optical fiber is provided between the line for drawing out the optical fiber from the optical fiber base material and the coating device for forming a coating layer on the optical fiber, This device is In order to penetrate and pass through the bare optical fiber, a hollow is formed to extend along a line axis of the optical fiber, the hollow having a minimum diameter larger than the diameter of the fiber is formed therein, and the central axis and the line axis of the hollow are substantially A tubular member which is coincident, and whose distance from said central axis to said hollow surface is not constant; Rotational drive means for rotating said tubular member about said central axis; Due to this, an irregular pressure is formed in at least a portion of the surface of the optical fiber descending along the edge axis by rotating the tubular member about the central axis. The method of claim 1, And the hollow cross section is elliptical. The method of claim 1, And the hollow cross section is rectangular. The method of claim 2 or 3, The maximum diameter, the minimum diameter of the inlet of the splicing fiber and the maximum diameter, the minimum diameter of the outlet of the splicing fiber is different from each other. The method of claim 4, wherein And the diameter of the hollow becomes smaller along the cutting edge. According to claim 1, wherein the rotary drive device A motor for generating a rotational driving force, And rotational transmission means for transmitting the rotational driving force of the motor to the tubular member. The method of claim 1, And the rotational speed of the tubular member is not constant. Means for cutting the optical fiber base material to form bare optical fibers; Means for irregularly deforming the optical fiber by forming an irregular irregular pressure on the longitudinal and / or circumferential surface of the bare optical fiber; Means for coating at least one coating layer around the irregularly deformed optical fiber; A capstan for controlling the cutting speed of the optical fiber; And a winding bobbin for winding the optical fiber passing through the capstan to the bobbin. The method of claim 8, wherein the means for irregularly deforming the optical fiber is In order to penetrate and pass through the spiral fiber, a hollow is formed to extend along the edge of the optical fiber, and a hollow having a minimum diameter larger than the diameter of the fiber is formed therein. And a tubular member in which the distance from the central axis to the hollow surface is not constant; And rotation driving means for rotating the tubular member about the central axis. The method of claim 9, And the hollow cross section is elliptical. The method of claim 9, And the hollow cross section is rectangular. The method of claim 10 or 11, The maximum diameter, the minimum diameter of the inlet of the splicing fiber and the maximum diameter, the minimum diameter of the outlet of the splicing fiber is different from each other. The method of claim 12, And the diameter of the hollow becomes smaller along the cutting edge. The method of claim 9, wherein the rotary drive device A motor for generating a rotational driving force, And rotational transmission means for transmitting the rotational driving force of the motor to the tubular member. The method of claim 9, And the rotational speed of the tubular member is not constant.

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