KR20080044678A - Edge mode of single mode optical fiber for reducing polarization mode dispersion and optical fiber manufactured by this method - Google Patents

Abstract

The present invention relates to a edge method of a single mode optical fiber for reducing the polarization mode dispersion and an optical fiber manufactured by the method. According to the present invention, a method of cutting a single mode optical fiber for reducing polarization mode dispersion may include: (a) heating the optical fiber base material with a melting furnace, and cutting the optical fiber necked down at the outlet of the melting furnace at a predetermined speed; And (b) applying a spin to the optical fiber by a sine function by a spin application device provided on the edge path of the optical fiber, wherein the amount of spin finally applied to the optical fiber satisfies the following equation. The spin frequency of the spin application device for the predetermined cutting speed and the cutting distance is adjusted.

Description

Single mode optical fiber drawing method for polarization mode dispersion reduction and Optical fiber 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 device configuration diagram schematically showing an optical fiber cutting apparatus according to the prior art.

2 and 3 are partially enlarged perspective views illustrating a state in which spin is applied to an optical fiber by the spin application device of FIG. 1.

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

5 is a graph illustrating the final degree of return of the optical fiber by the spin and twist in accordance with a preferred embodiment of the present invention.

<Description of main reference numerals in the drawings>

101 ... optical fiber base material 102 ... melting furnace

103 or optical fiber 104 ... coating device

Curing device 103 '... sheathed fiber

106.Spin-applied device 107 ... Capstan

108 ... winding bobbin

The present invention relates to a method of cutting a single mode optical fiber for reducing polarization mode dispersion (PMD), and more particularly, a method of cutting a fiber for reducing polarization mode dispersion of an optical fiber and an optical fiber manufactured by the method. It is about.

In general, the frequency response of transmission and reception in an optical fiber is limited by various dispersion modes such as color dispersion, transmission dispersion, and flat dispersion. Nowadays, the development of many device technologies such as laser diodes with a fairly precise beam width has solved some of the color dispersion and transmission dispersion, but the polarization dispersion mode remains a difficult problem to solve.

Theoretically, a circular symmetric single mode optical fiber has two independent and mutually canceling orthogonal polarization modes. In addition, the electric field of light propagating through the optical fiber can be called a linear superposition of these two polarization eigenmodes. In practice, a single-mode fiber is offset by both incomplete polarization modes due to symmetrical lateral stresses or eccentricity of the circular core. These two modes propagate at different phase velocities, which causes the two polarization modes to propagate at different propagation constants β ₁ and β ₂ . This difference in propagation constants is called birefringence (Δβ), and the increase in birefringence means an increase in the speed difference between the two polarization modes.

Here, the differential time delay between two polarization modes is called polarization mode dispersion (hereinafter, abbreviated as "PMD"). PMD spreads a pulse of light transmitted through an optical fiber to increase the bit-error rate. Let's go. Thus, in data transmission over optical fibers, PMDs act as a major factor in limiting the capacity of data, and are undesirable in signal transmission systems, especially for optical fibers operating over long distances.

In order to ensure the transmission and reception performance of the optical fiber, it is essential to minimize the attenuation of the PMD and thus the dispersion of the signal. The most preferable countermeasure for the PMD is the optical fiber having a uniform circular cross section without mechanical stress and ovality. It is difficult to completely remove the mechanical stress and ovality of the optical fiber.

To reduce the PMD in this optical fiber, an artificial twisting strain is applied to the optical fiber drawn at the outlet of the melting furnace. In other words, spin is applied to the optical fiber, causing the optical fiber to be twisted at a pitch smaller than its pulsation length. As a result, when an optical pulse is transmitted through the optical fiber, the optical pulse propagates alternately between the slow and birefringent axes, thereby compensating for the relative delay and reducing the pulse spread. This is equivalent to making the local effective refractive index for a pulse equal to the average refractive index on both axes, and the average is applied over the pulse length of the optical fiber.

As an example of the prior art of applying spin in an optical fiber edge process to reduce the PMD of an optical fiber, US 5,298,047 can rotate the spin roller at an angle with respect to the optical fiber edge, or linearly reciprocate in a direction perpendicular to the edge line axis. Disclosed is a method of applying twist to a fiber by applying a non-constant spin including forward and reverse directions so that the spin imparted to the optical fiber has a non-constant spatial frequency.

The technique disclosed in US 5,298,047 is described in more detail with reference to FIGS. 1 to 3 as follows.

First, as shown in FIG. 1, the optical fiber base material 1 is heated to a high temperature by the melting furnace 10 so that the lower end portion of the optical fiber base material 1 is softened, so that the cross-sectional area is gradually reduced, wherein one strand of the optical fiber is the optical fiber base material. The edge is drawn from the neck-down portion of (1). Next, the optical fiber passes through the diameter monitor 11, the coating apparatus 12, the coating concentricity monitor 13, the curing apparatus 14, and the coating diameter monitor 15. Thereafter, the optical fiber passes through the spin roller 16 and spin, that is, the optical fiber twist is applied, the optical fiber is applied to the capstan 17. At this time, as shown in FIG. 2, the spin roller 16 is swinging (Canting) in an inclined state at an angle with respect to the edge line axis (reciprocating AB section about the rotation axis 0), or as shown in FIG. Likewise, the spin roller 16 'provides spin to the optical fiber by linearly reciprocating in a direction perpendicular to the edge line axis. At this time, the spin function is a substantial sine function or amplitude modulation or frequency modulation sine function.

However, in US 5,298,047, the twisted optical fiber of the same size / counter direction as the spin applied to the optical fiber before being wound on the bobbin is applied to the optical fiber to which the spin is applied, and the final return angle of the optical fiber is the sum of the spin and the twisting. As such, no consideration is given to the inability to achieve the desired PMD reduction if the twisting offsets the spin due to inadequate process conditions. US 5,298,047 only describes that PMD can be reduced only by spin rates of 4 turn / m or more without twisting considerations.

On the other hand, WO2004 / 050573 proposed an apparatus for eliminating the twisting of the coating coating layer during unidirectional spin application. Specifically, WO2004 / 050573 applies a unidirectional spin about an axis in the cutting line direction in order to manufacture an optical fiber having an improved PMD, and in order to solve the twist of the coating coating layer by the unidirectional spin, An apparatus for solving the problem of twisting a coating coating layer by using an optical fiber guiding device that applies rotational force in a direction opposite to twisting is disclosed. However, the apparatus disclosed in WO2004 / 050573 is mechanically complex and has many limitations in actual implementation, and there is a problem in that the cost is large and the practicality is degraded in order to additionally configure the existing equipment.

The present invention was devised to solve the above problems, and by adjusting the spin frequency of the spin application device applied in the cutting process of the optical fiber, the polarization mode dispersion characteristics of the optical fiber are independent of the cutting line distance and the cutting speed of the optical fiber. An object of the present invention is to provide a method of cutting a single mode optical fiber for reducing polarization mode dispersion and an optical fiber manufactured by the method.

In order to achieve the object as described above, the cutting method of a single mode optical fiber for reducing the polarization mode dispersion according to the present invention, (a) heating the optical fiber base material in the melting furnace, and a predetermined speed of the optical fiber necked down at the outlet of the melting furnace Edge cutting; And (b) applying a spin to the optical fiber by a sine function by a spin application device provided on the edge path of the optical fiber, wherein the amount of spin finally applied to the optical fiber satisfies the following equation. The spin frequency of the spin application device for the predetermined cutting speed and the cutting distance is adjusted.

Θ: spin amount [turn / m] finally applied to the optical fiber, h: edge distance [m] of the optical fiber, vf: edge speed [mpm] of the optical fiber, ω: spin frequency [rpm] ]to be.)

In the present invention, the spin application device alternately applies the spin in the clockwise and counterclockwise directions while oscillating at a predetermined angle with respect to the edge line axis.

In the present invention, the spin application device applies spin in both directions, forward and reverse, while linearly reciprocating in a direction perpendicular to the cutting line axis.

Preferably, the amount of spin finally applied to the optical fiber, the edge line distance of the optical fiber, the edge speed of the optical fiber, and the spin frequency of the spin application device may have a polarization mode dispersion value of 0.5 ps / km ^1/2 or less at a wavelength of 1310 μm. Have it.

In addition, the optical fiber has a polarization mode dispersion value of 0.5 ps / km ^1/2 or less at a wavelength of 1310 μm by adjusting the spin frequency of the spin applying apparatus irrespective of the edge distance and the edge speed of the optical fiber.

According to another aspect of the present invention, there is provided a single mode optical fiber having reduced polarization mode dispersion produced by the edge line method.

Preferably, the polarization mode dispersion value at a wavelength of 1310 μm of the optical fiber satisfies a value of 0.5 ps / km ^1/2 or less.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. 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.

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

Referring to FIG. 4, the optical fiber cutting apparatus is a melting furnace 102 for melting the optical fiber base material 101 and cutting it into the bare optical fiber 103, and drawing at the outlet of the melting furnace 102. A coating device 104 for coating at least one coating layer on the fiber optic 103, a curing device 105 for curing the coated coating layer, and spin application for applying spin to the coating optical fiber 103 'coated with the coating layer. The device 106 includes a capstan 107 for controlling the edge velocity of the optical fiber, and a winding bobbin 108 for winding the optical fiber to which the spin is applied.

The melting furnace 102, the coating device 104, the curing device 105, and the spin application device 106 are sequentially mounted on the draw tower, although not shown in FIG. 4, the melting furnace 102 and the coating device. Between the 104, a diameter control device for controlling the diameter of the filament fiber 103 and a cooling device for cooling the filament fiber 103 may be sequentially installed.

In an embodiment of the present invention, the optical fiber base material 101 is heated to a high temperature in the melting furnace 102. Then, the lower end portion of the optical fiber base material 101 is softened so that the cross-sectional area is reduced, and it is edged from the neck-down point of the optical fiber base material 101 to the spiral fiber 103. The stranded fiber 103 is converted into the coated optical fiber 103 'by the coating device 104 and the curing device 105.

At this time, the flux of the fiber filament 103 and the coated optical fiber 103 'is controlled by the capstan 107, the flux satisfies a range free from manufacturing errors including the shaking phenomenon of the optical fiber and the coating bubble, Obviously, it matches the flux of the optical fiber finally wound on the winding bobbin 108 on the edge of the edge.

The coated optical fiber 103 'drawn from the curing device 105 is edged to the optical fiber to which the spin is applied by the spin application device 106 that applies the spin. At this time, the spin applying device 106 is provided on the cutting line path of the optical fiber and rotates at the same time as the rotation axis, or a linear motion in a direction perpendicular to the cutting line axis to spin in a sine function to the optical fiber Is authorized.

However, since the coated optical fiber 103 'to which spin is applied is not completely cured, the force to return to its original form still remains and the coated optical fiber 103' to which spin is applied by this force is In the process of finally winding the winding bobbin 108 on the edge line past the capstan 107, the coated optical fiber 103 'is the same size as the spin and twisting in the opposite direction occurs. Therefore, the final degree of return of the coated optical fiber 103 'is determined by the relative magnitude of the spin amount and the twist amount.

5 is a graph illustrating the final degree of return of the optical fiber by spin and twisting according to a preferred embodiment of the present invention.

Referring to FIG. 5, since the spin is applied to the sine function by the spin applying device 106, the degree of return of the coated optical fiber 103 ′ shows a waveform of the sine function (110). On the other hand, the degree of return of the coated optical fiber 103 'by the twisting action draws the waveform of the cosine function (120).

Here, the degree 130 of the optical fiber is finally returned is determined by the sum of the degree 110 of the optical fiber is rotated by the spin and the degree 120 of the optical fiber is rotated by twisting. If the process conditions are not appropriate and the twisting offsets the spin, there is a problem that the PMD reduction effect is not obtained.

Accordingly, in the present invention, the spin conditions satisfying the following Equation 1 are selected so that the spin is not canceled by twisting, and the PMD is increased regardless of the edge speed and the edge distance of the optical fiber without increasing the spin size. Reduction effect can be obtained. This will be described later through Experimental Examples to be described later. Here, "θ" is the degree to which the optical fiber is finally turned, and the unit is turn / m, "h" is the edge distance of the optical fiber, the unit is m, "vf" is the edge velocity of the optical fiber, and the unit is mpm, and "ω" Is the spin frequency of the spin application unit, in rpm.

Referring to Equation 1, the magnitude of the degree (θ) at which the optical fiber is finally turned is determined by the edge line distance (h) of the optical fiber, the edge line speed (vf) of the optical fiber, and the spin frequency (ω) of the spin application device. When the spin frequency applied by the spin application device is adjusted according to the optical fiber edge distance and the edge speed so that the value is greater than 1, the effect of canceling the spin due to twisting does not occur and thus the PMD reduction effect can be obtained.

Table 1 below shows the cutting edge distance of the optical fiber to 20 m or 30 m at three speeds of 1000 mpm, 1400 mpm, and 1800 mpm in a manufacturing error-free range including optical fiber shaking and coating bubbles. When spin frequencies having 10 rpm, 30 rpm, and 50 rpm values are applied to the edge condition of, it is experimental data showing the PMD reduction state of the optical fiber together with the satisfaction of Equation 1 above. At this time, "0" indicated in Table 1 to the edge condition is an indication that satisfy the condition of Equation (1), on the other hand, the optical fiber is the PMD value 0.5ps ^/ km ^1/2 or less in the preferred wavelength 1310㎛ It shows that it has a PMD reduction state.

division Edge distance h (m) Cutting speed Vf (mpm) Spin Device Frequencyω (rpm) Equation 1 Satisfaction PMD Reduction Status Example 1 20 1000 10 0 0 Example 2 20 1000 30 0 0 Example 3 20 1000 50 X X Example 4 20 1400 10 X X Example 5 20 1400 30 0 0 Example 6 20 1400 50 0 0 Example 7 20 1800 10 X X Example 8 20 1800 30 0 0 Example 9 20 1800 50 0 0 Example 10 30 1000 10 0 0 Example 11 30 1000 30 X X Example 12 30 1000 50 0 0 Example 13 30 1400 10 0 0 Example 14 30 1400 30 0 0 Example 15 30 1400 50 X X Example 16 30 1800 10 X X Example 17 30 1800 30 0 0 Example 18 30 1800 50 X X

As shown in Table 1, Examples 1 and 2 in which the edge velocity (Vf) of the optical fiber is 1000 mpm and the spin frequency is 10 and 30 rpm, the edge conditions satisfy the equation (1) and the PMD reduction state is also good, Example 3 having a cutting line speed Vf of 1000 mpm and a spin frequency of 50 rpm shows that the cutting line conditions do not satisfy Equation 1, and the PMD reduction state is also poor.

In Examples 5 and 6 in which the edge velocity (Vf) of the optical fiber is 1400 mpm and the spin frequencies are 30 and 50 rpm, the edge condition satisfies Equation 1 and PMD reduction is good, but the edge velocity (Vf) is 1400 mpm. And the spin frequency of 10 rpm, it can be seen that the edge condition not only satisfies Equation 1, but also the PMD reduction state is poor.

In Examples 8 and 9 in which the edge velocity (Vf) of the optical fiber is 1800 mpm and the spin frequencies are 30 and 50 rpm, the edge condition satisfies Equation 1 and PMD reduction is good, but the edge velocity (Vf) is 1800 mpm. And the spin frequency of 10 rpm, it can be seen that the edge condition does not satisfy the equation (1) as well as poor PMD reduction state. Meanwhile, referring to Examples 10 to 18 having a cutting line distance of 30 m, Examples 10 and 12 having a cutting edge speed (Vf) of an optical fiber of 1000 mpm and a spin frequency of 10 and 50 rpm showed that the cutting edge condition satisfied Equation 1 and PMD. The reduction state is also good, but Example 11, in which the edge speed Vf is 1000 mpm and the spin frequency is 30 rpm, shows that the edge condition does not satisfy Equation 1, and the PMD reduction state is also poor.

In Examples 13 and 14 in which the edge velocity (Vf) of the optical fiber is 1400 mpm and the spin frequencies are 10 and 30 rpm, the edge condition satisfies Equation 1 and PMD reduction is good, but the edge velocity (Vf) is 1400 mpm. And the spin frequency of 50 rpm can be seen that the edge condition does not satisfy Equation 1, and the PMD reduction state is also poor.

In Example 17, in which the edge velocity (Vf) of the optical fiber was 1800 mpm and the spin frequency was 30 rpm, the edge condition satisfies Equation 1 and the PMD reduction state was good, but the edge velocity (Vf) was 1800 mpm and the spin frequency was In Examples 16 and 18 at 10 and 50 rpm, it can be seen that the edge condition not only satisfies Equation 1 but also a poor PMD reduction state.

As can be seen from Table 1, the following equation 1 is satisfied under the condition that the cutting line distance (h) 20 to 30 m, the cutting speed (Vf) 1000 to 1800 mpm, spin frequency (ω) 10 to 50 rpm If you select the edge condition to perform the optical fiber cutting process, it can be manufactured as a single mode optical fiber that can reduce the PMD.

Table 2 below shows the numerical value of the difference between the failure rate and the case of manufacturing the optical fiber in the embodiment according to the present invention.

existing Invention Input (km) Bad (km) Defective rate Input (km) Bad (km) Defective rate 12,000 450 3.8% 9,300 50 0.5%

As shown in Table 2, in manufacturing the optical fiber manufacturing process of the prior art, 450 km of defects are generated during the manufacturing of 12,000 km of optical fiber, which is converted into a defective rate of 3.8%. However, when the present invention is applied, it can be seen that a defect of 50 km occurs during manufacture of an optical fiber of 9,300 km, and when converted into the defective rate, the defect rate of 0.5% is significantly improved than that of the prior art.

Although the present invention has been described above by means of limited embodiments and drawings, the present invention is not limited thereto and will be described below by the person skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of the claims.

According to the present invention, a single mode optical fiber having a reduced polarization mode dispersion can be manufactured by selecting an optimal spin condition for each cutting line condition without increasing the size of the spin in the spin applying apparatus in the cutting process of the optical fiber. In addition, it is possible to implement an optimal edge condition capable of reducing the PMD only by adjusting the frequency of the spin applying device without adding a complicated device.

Accordingly, by reducing the PMD, it is possible to solve the problem of poor optical fiber due to the PMD.

Claims (7)

In the method for producing a single-mode optical fiber having a reduced polarization mode dispersion by cutting the optical fiber base material consisting of a core portion having a high refractive index and a clad portion surrounding the core portion, (a) heating the optical fiber base material in the melting furnace, and drawing the optical fiber necked down at the outlet of the melting furnace at a predetermined speed; And (b) applying a spin to the optical fiber with a sine function by a spin application device provided on a cutting line path of the optical fiber; And the spin frequency of the spin application device for a predetermined edge speed and edge distance is adjusted so that the amount of spin finally applied to the optical fiber satisfies the following equation.

Θ: spin amount [turn / m] finally applied to the optical fiber, h: edge distance [m] of the optical fiber, vf: edge speed [mpm] of the optical fiber, ω: spin frequency [rpm] ]to be.) The method of claim 1, The spin applying apparatus is a single mode optical fiber edge line method for reducing the polarization mode dispersion, characterized in that for applying a spin alternately clockwise and counterclockwise while swinging at a predetermined angle with respect to the edge line axis. The method of claim 1, The spin applying apparatus is a single mode optical fiber edge line method for reducing the polarization mode dispersion, characterized in that for applying a spin in both the direction of the forward and reverse direction while linearly reciprocating in a direction perpendicular to the edge line axis. The method of claim 1, The amount of spin finally applied to the optical fiber, the edge distance of the optical fiber, the edge speed of the optical fiber, and the frequency of the spin application device are such that the optical fiber has a polarization mode dispersion value of 0.5 ps / km ^1/2 or less at a wavelength of 1310 μm. Single mode optical fiber edge method for reducing polarization mode dispersion. The method according to claim 1 or 3, Reduction of polarization mode dispersion, characterized in that the optical fiber has a polarization mode dispersion value of 0.5 ps / km ^1/2 or less at a wavelength of 1310 μm by adjusting the frequency of the spin application device regardless of the edge distance and the edge speed of the optical fiber. Mode fiber optic edge line method. A single mode optical fiber having reduced polarization mode dispersion produced by the method of any one of claims 1 to 4. The method of claim 5, And a polarization mode dispersion value at a wavelength of 1310 μm of the optical fiber satisfies a value of 0.5 ps / km ^1/2 or less.

Images