KR100826046B1 - Method for measuring the residual twisting rate of a drawn optical fiber - Google Patents

Abstract

A method for measuring a residual twisting rate of a drawn optical fiber is provided to reduce a PMD(Polarization Mode Dispersion) by performing a precision detwisting process. A connecting process is performed to connect both ends of each of optical fibers(202,203,204) to two holders(201). The holders are horizontally positioned in a constant interval on a straight line. The holders approach each other in order to suppress twisting states of the optical fibers. A measuring process is performed to the twisted number of each of the optical fibers. The interval between the holders is 1/2 of the length of the optical fiber and more. The holders approach each other and contact with each other.

Description

METHODE FOR MEASURING THE RESIDUAL TWISTING RATE OF A DRAWN OPTICAL FIBER}

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.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view schematically showing a fiber optic cutting apparatus according to the prior art.

2 and 3 are perspective views showing a spin application device according to the prior art.

4 is a view for explaining a method of measuring the degree of coating twist of the optical fiber according to an embodiment of the present invention.

5 is a graph showing the correlation between the amount of spin of the optical fiber and the amount of twist of the coating according to an embodiment of the present invention.

<Explanation of symbols for important parts of the drawing>

201 ... Fiber Optic Holder 202, 203, 204 ... Fiber Optic

205 ... twist number

The present invention relates to an optical fiber, and more particularly to a method for measuring the amount of residual twist of drawn optical fiber.

Optical fibers, generally circular symmetrical structures, have two independent and canceled orthogonal polarization modes. However, in the optical fiber, the two modes propagate at different phase speeds, which causes a time delay. The time delay between these two polarization modes is called Polarization Mode Dispersion (PMD).

The PMD increases the bit-error rate by spreading the pulse of light transmitted through the optical fiber. Therefore, in the data transmission through the optical fiber, PMD acts as a major factor to limit the data transmission capacity, and is not preferable especially for the optical fiber operating over a long distance.

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 measures for reducing PMD are to manufacture optical fibers having a uniform circular cross section without mechanical stress and ovality, and it is difficult to completely remove mechanical stress and ovality of the optical fiber.

In order to reduce the PMD in this optical fiber, torsional deformation occurs in the optical fiber drawn at the outlet of the melting furnace. In other words, spin is applied to the optical fiber so that the optical fiber is twisted at a pitch smaller than its pulsation length. As a result, the optical pulses propagate between the slow and birefringent axes alternately when transmitted over the optical fiber to compensate for the relative delay and reduce the pulse spread.

As described above, the PMD of the optical fiber can be reduced by the spin applied in the cutting process. As a method of applying the spin in the cutting process, U.S. Patent No. 5,298,047 can swing the spin roller at a predetermined angle with respect to the cutting line axis. A method of generating twist in an optical fiber by applying a non-constant spin in a direction perpendicular to the cutting line axis.

The technique disclosed in US Patent No. 5,298,047 will be 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 melted at a sufficient temperature in the melting furnace 10, and a single strand of optical fiber 2 is formed from the neck-down portion of the optical fiber base material 1. Is withdrawn. Next, the drawn 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, and the spin applied optical fiber is directed to the capstan. At this time, the spin roller 16 is swinging (Canting) in a state inclined at a predetermined angle with respect to the cutting edge as shown in Figure 2, or as shown in Figure 3 spin roller 16 'with respect to the cutting edge Spin is applied to the optical fiber by linear reciprocating motion in the vertical direction.

On the other hand, PMD characteristics of the optical fiber are further improved when applying a unidirectional spin (Constant Spin) than the bidirectional spin. However, when the unidirectional spin is applied around the direction axis of the optical fiber during twisting, torsion is applied, and residual stress due to unidirectional twisting remains on the coating of the optical fiber wound on the bobbin, thereby deteriorating PMD quality. Problems such as kinks occur during handling or cabling. As in the above-mentioned US Patent No. 5,298,047, when the bidirectional spin is applied to the optical fiber, the optical fiber covering twist may remain within the minute length, but within one cycle length of the bidirectional, the coating twist becomes "0", which adversely affects the PMD. Although not known, the coating twists in the longitudinal direction when the unidirectional spin is applied to the optical fiber, which adversely affects the PMD.

Therefore, WO 2004/050573 proposes an apparatus for eliminating the coating twist of an optical fiber. WO2004 / 050573 provides an optical fiber guiding apparatus for applying a rotational force in a direction opposite to the twisting of a coating in order to apply a unidirectional spin about the direction of the edge of the optical fiber and to eliminate the twisting of the coating by the unidirectional spin. Discloses an apparatus that solves the problem of torsion of coatings. In addition, the Republic of Korea Patent No. 547755 (Spinning optical fiber manufacturing apparatus) discloses a method and apparatus for solving the twisting state of the optical fiber coating by applying a spin in the other direction after applying the spin in one direction to the coated optical fiber Doing.

By the way, in order to eliminate the coating twist of the optical fiber, it is necessary to accurately measure the amount of coating twist of the optical fiber, thereby eliminating the coating twist. WO 2004/050573 and Patent No. 547755 measure the amount of coating twist of the optical fiber. There is a problem in that it is not possible to solve the complete coating torsion only by applying the spin in the opposite direction to the mechanical torsion without any. In the process of releasing the coating twist of the optical fiber, if it is released less or in the opposite direction to which the unidirectional spin is applied, PMD of about 0.05 ps / km ^ 1/2 occurs than when the coating twist is completely removed (OFC'2003). , Vol. 1, WJ2 pp. 367-368).

On the other hand, US Patent No. 6,767,325 proposes a method for measuring the amount of spin twisted in the optical fiber itself is applied in the spin process. This method uses the eccentricity of the optical fiber core to measure the amount of spin of the optical fiber from the positional movement of the core rotating around the optical fiber center. However, since this method uses the eccentricity of the optical fiber, if the eccentricity of the optical fiber is low, the spin amount of the optical fiber cannot be measured, and even if the eccentricity is high, it takes a long time to measure the spin amount of the optical fiber. In addition, the amount of spin applied to the optical fiber after the cutting line can be measured, but there is a problem that the amount of twist remaining on the fiber coating cannot be measured.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to provide a method for simply measuring the amount of torsion remaining in the coating of an optical fiber.

It is another object of the present invention to provide a method for measuring the amount of spin applied to an optical fiber by measuring the amount of twisting of the coating of the optical fiber.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

The present invention for achieving the above object, a method for measuring the amount of twist remaining in the coating of the optical fiber, (a) connecting the two ends of the optical fiber to two holders that are kept in a straight line at a predetermined interval ; (b) approaching the two holders to one another until the optical fiber is no longer twisted; And (c) measuring the number of twists of the optical fiber.

In the step (a), it is preferable that the two holders are spaced at least 1/2 of the optical fiber length.

In addition, in the step (b), the two holders are preferably approached until they touch each other.

On the other hand, the present invention for achieving the above object is a method for measuring the amount of spin of the optical fiber, (a) connecting both ends of the optical fiber to two holders that are horizontally maintained in a straight line at a predetermined interval; (b) approaching the two holders to one another until the optical fiber is no longer twisted; (c) measuring the number of twists of the optical fiber; And (d) inferring the spin rate of the optical fiber based on the measured number of twists of the optical fiber.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art may easily implement the technical idea of the present invention. There will be. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

4 is a view for explaining a method of measuring the degree of coating twist of the optical fiber according to an embodiment of the present invention.

As shown in (a) of FIG. 4, first, two ends of two optical fibers are cut at a predetermined length (L, preferably about 1 m or more) of the optical fiber 202 manufactured by applying a bidirectional or unidirectional spin so as not to be twisted. It is fixed to each of the holders 201 and aligned. At this time, when the optical fiber 202 is fixed to the optical fiber holder 201, the optical fiber holder 201 maintains a constant length D so that no twist occurs. The length D between the optical fiber holders 201 is preferably L / 2 or more. In addition, the optical fiber holder 201 is preferably connected to the rail of a predetermined length to maintain parallel to each other.

Next, as shown in (b) of FIG. 4, the optical fiber holder 201 is brought closer and closer to each other while keeping the horizontal in a straight line. If there is no residual torsion in the coating, as shown by the dotted line, the optical fiber 203 has a constant U-shape and no torsion occurs. However, if there is a residual torsion in the coating, the optical fiber 204 is twisted and rotated like a solid line. Occurs.

On the other hand, as shown in (c) of FIG. 4, the number of twists 205 of the optical fiber 204 to which the twist occurs after the complete contact is made closer to the optical fiber holder 201. Dividing the measured number of twists 205 by the length L of the optical fiber 204 yields the unit twist number of the coating of the optical fiber 204.

Table 1 below is a result of measuring the amount of residual twist of the coating using the actual optical fiber according to the present invention described with reference to FIG. After taking samples of three optical fibers having an optical fiber length L of 1, 2, and 3, each optical fiber sample was connected to the optical fiber holder 201 to measure the number of twists of the optical fiber as shown in FIG. The number of twists of each optical fiber was divided by the length of the optical fibers to obtain the number of twists of the coating per unit length. In this experiment, the initial spacing D of the optical fiber holder 201 was 1/2 of the optical fiber length.

Sample number Fiber length (L) Initial interval (D) Optical fiber twist number Unit torsion number (turns / m) One One 0.5 2.2 2.2 2 2 1.0 4.0 2.0 3 3 1.5 6.0 2.0

As shown in Table 1, the number of twists of the coating per unit length measured in three optical fiber samples was measured to be equal to about 2.

On the other hand, according to the present invention by measuring the amount of twist of the coating of the optical fiber can be estimated the amount of spin (Spin Rate) applied to the optical fiber. That is, the amount of twisting of the coating of the optical fiber and the amount of spin of the optical fiber have a high correlation, and after measuring the amount of twisting of the coating of the optical fiber according to the present invention, the amount of twisting of the optical fiber can be inverted according to the correlation.

Table 2 below shows the relationship between the spin rate of the optical fiber and the amount of twist of the coating. The amount of spin of the optical fiber was measured by the method of US Pat. It is measured according to the invention.

Spin rate (turns / m) Sheath torsion (turns / m) 2.3 1.8 2.5 2.0 3.5 2.5 5.5 4.0 7.5 6.0

The correlation between the amount of spin of the optical fiber and the amount of torsion of the coating is calculated based on the data in [Table 2].

5 is a graph showing the correlation between the amount of spin of the optical fiber and the amount of twist of the coating according to an embodiment of the present invention. In FIG. 5, the points represent the data values of Table 2, where the data values of Table 2 are located on a line of y = 0.7697x and the correlation R ² is 0.9878, that is, about 99% correlation. Indicates. In other words, after measuring the number of twists of the coating of the optical fiber according to the present invention, if the amount of spin of the optical fiber is measured according to the relationship as shown in FIG. 5, the measured amount of spin has an accuracy of about 99%. It takes about 10 hours to measure the amount of spin for one sample of the optical fiber according to the method of US Pat. No. 6,977,325 described in the prior art, but after measuring the number of twists of the coating according to the present invention, the amount of spin is reversely estimated. The measurement can be made in 1 minute.

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.

As described above, the present invention can simply and quickly measure the amount of twist remaining in the coating of the optical fiber produced by applying spin. As a result, it is possible to reduce the PMD by performing a precise detwisting step. In addition, it is possible to estimate the amount of spin applied to the optical fiber in reverse from the amount of residual coating torsion in a short time.

Claims (4)

A method of measuring the amount of twist remaining in the coating of an optical fiber, (a) connecting both ends of the optical fiber to two holders which are leveled in a straight line at predetermined intervals; (b) approaching the two holders to one another until the optical fiber is no longer twisted; And (c) measuring the number of twists of the optical fiber; measuring the amount of residual twist of the optical fiber. The method of claim 1, In the step (a), The two holders, the method of measuring the amount of residual twist of the optical fiber, characterized in that for maintaining the interval at least 1/2 of the optical fiber length. The method according to claim 1 or 2, In step (b), And the two holders are approached until they touch each other. As a method of measuring the spin amount of an optical fiber, (a) connecting both ends of the optical fiber to two holders which are leveled in a straight line at predetermined intervals; (b) approaching the two holders to one another until the optical fiber is no longer twisted; (c) measuring the number of twists of the optical fiber; And (d) inversely estimating the spin rate of the optical fiber based on the measured number of twists of the optical fiber.

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