Patent Application
20050194704
This application claims priority to an application entitled “apparatus and method for drawing optical fiber,” filed with the Korean Intellectual Property Office on Mar. 2, 2004 and assigned Serial No. 2004-13921, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an apparatus and a method for fabricating an optical fiber from an optical fiber preform and, m ore particularly, to an apparatus and a method for drawing an optical fiber.
2. Description of the Related Art
Optical fibers are advantageous in that they provide a high transmission rate and transmit/receive a large amount of optical signals. However, they are vulnerable to a polarization mode dispersion phenomenon, which disperses optical signals that are propagating inside the fiber. This increases a bit error rate of the optical signals and limits the capacity and rate for transmitting optical signals.
The polarization mode dispersion is caused by geometrical deformation in the optical fiber structure, residual stress therein, and the like. These factors cause a deformation in the optical fibers, the refractive index of which is changed irregularly. When the optical signals propagate through the abnormal areas, the refractive index of which is changed irregularly, and the angle and velocity of the components, which compose the optical signals, undergo irregular changes. Such changes in the angle and velocity of the components, which compose the optical signals, is one of the factors that cause the polarization mode dispersion phenomenon on the optical signals. The polarization mode dispersion is also caused by external environmental factors, such as changes in external temperature.
In an effort to minimize the polarization mode dispersion, it has been suggested to twist the optical fibers. Methods for twisting optical fibers involves rotating an optical fiber preform, from which optical fibers are drawn, as disclosed in International Patent Application WO 83/00232 of David et. al., entitled “Central electricity generating board.” A method wherein a drawn optical fiber is endowed with a rotational force using a rotating or vibrating device, which is positioned on a drawing path of the optical fiber, is well disclosed in a number of U.S. Pat. No. 5,298,047, entitled “Method of making a fiber having low polarization mode dispersion due to a permanent spin,” as well as U.S. Pat. No. 5,418,881; No. 5,704,960; No. 5,943,466; and No. 6,148,131 (the contents of which are hereby incorporated by reference). In addition, U.S. Pat. No. 6,189,343 of Franco Cocchini et. al., entitled “Apparatus and method for forming an optical fiber” (the contents of which are hereby incorporated by reference) discloses a method wherein an optical fiber, which is coated with an external coating, is made to incorporate a twist by rotating a coating device, which is adapted to coat a bare optical fiber (that is, an optical fiber which is not coated with a coating layer).
According to the above-mentioned methods, an optical fiber is made to incorporate a twist during a drawing process to suppress the polarization mode dispersion of the optical fiber. To this end, it is suggested to apply a helicity to the optical fiber so that it is made to incorporate twists having opposite directions, by repeatedly providing the optical fiber with a rotational force leftward and rightward about an axis along which the optical fiber is drawn.
However, such a method has a problem in that, if an optical fiber is subject to a repeated rotational force leftward and rightward for forming twists having opposite directions, the geometrical structure of the optical fiber tends to become unstable.
Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art and provides additional advantages, by providing a method of drawing an optical fiber, wherein the polarization mode dispersion of the optical fiber is suppressed and the geometrical structure thereof is improved.
In one aspect of the invention, there is provided a method for drawing an optical fiber by heating one end of an optical fiber preform and drawing an optical fiber from the heated preform. The method includes: a coating step for forming a plurality of coating layers, which have different viscosity, on the outer peripheral surface of a first optical fiber, which is drawn from the optical fiber preform; and a twisting step for drawing a second optical fiber, which has coating layers formed thereon in a direction slanted relative to the drawing axis of the first optical fiber to form a third optical fiber incorporating a twist.
The above features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. For the purposes of clarity and simplicity a detailed description of known functions and configurations incorporated herein will be omitted as it may make the subject matter of the present invention unclear.
According to the present invention, a method for drawing an optical fiber by heating one end of an optical fiber preform and drawing an optical fiber from the heated preform is provided. The method involves a coating step and a twisting step. In the coating step, a first optical fiber is coated. In the twisting step, the second optical fiber having coating layers is drawn with a predetermined angle slanted relative to the drawing axis of the first optical fiber to form a third optical fiber incorporating a twist.
The first optical fiber is an optical fiber just drawn from an optical fiber preform and includes a core, which is positioned in its center portion, and a clad, which surrounds the outer peripheral surface of the core. The second optical fiber includes coating layers, which are formed on the outer peripheral surface of the first optical fiber. The third optical fiber is obtained by making the second optical fiber incorporate a twist, which has the coating layers formed thereon.
In the coating step, the outer peripheral surface of the first optical fiber is coated with coating liquids having a different viscosity a number of times to obtain a second optical fiber, which has coating layers formed thereon. If a coating layer, which has the same viscosity as that of the first optical fiber, is formed on the outer peripheral surface of the first optical fiber, every twist that is applied to the second optical fiber, during the twisting step, is supposed to be applied to the clad. Accordingly, the coating layers should include a plurality of layers, which have a different viscosity, so that the degree of twist that is applied to the second optical fiber is regulated. By regulating the viscosity of each of the coating layers, the residual twist applied to the third optical fiber is regulated accordingly.
Each of the coating layers of the second optical fiber is formed using a coating liquid, the viscosity of which is gradually decreased as the layer is positioned farther from the center of the second optical fiber, respectively. As a result, the residual twist applied to the second optical fiber is increased, while the polarization mode dispersion thereof is decreased.
The polarization mode dispersion of optical fibers, which is a phenomenon caused by birefringence, is due to internal factors, including the non-circle ratio of a core, the difference in the refractive index, and the application of asymmetric stress during drawing, as well as external factors, including the optical fibers' bending, torsion, temperature, and humidity. Specifically, if the number of turns exceeds a critical point, the polarization mode dispersion is increased due to shear stress. According to a recent international standard, ITU-T, it is recommended to restrict the cable polarization mode dispersion link design value (Cable PMDg), regarding optical fibers of G.652.B and G.652.D, within 0.2 ps/{square root}{square root over (km)}. As such, stricter requirements are imposed on the polarization mode dispersion. If the number of turns exceeds 1.5 turn/M, it is difficult to fabricate a ribbon optical fiber by twisting it. Accordingly, it is important to maintain the residual twist of optical fibers appropriately in order to control the polarization mode dispersion according to the present invention.
Hereinafter, a spin that is applied to the second optical fiber will be referred to as a “residual twist,” and the number of residual twists per unit length that is applied to the third optical fiber will be referred to as “number of turns.”
The heating furnace 100 includes at least one heater 120, 130 for heating a lower portion of the optical fiber preform 110.
The coating unit 200 may be configured either as a wet-on-wet type or as a wet-on-dry type, according to how the coating layers, which are formed on the first optical fiber 160, are cured. The construction of each of the coating units 200 will now be described with reference to
The UV-curable polymer, as shown in
The spin wheel 330 is adapted to draw the second optical fiber 240 in a predetermined direction slanted relative to a drawing axis 401 of the first optical fiber 160, so that the second optical fiber 240 is made to incorporate a residual twist in a direction to obtain the third optical fiber 350. The spin wheel 330 is slanted at an angle clockwise or counterclockwise about the drawing axis 401, along which the first and second optical fibers 160, 240 are drawn, so that the second optical fiber 240 is made to incorporate a residual twist to obtain the third optical fiber 350.
The guide wheel 320 is positioned parallel to the drawing axis 401 between the spin wheel 330 and the coating unit 200 to guide the second optical fiber 240, which is inputted to the spin unit 330 from the coating unit 200, so that it does not to go out of its path along the drawing axis 401 due to the spin wheel 330. In other words, the guide wheel 320 guides the second optical fiber 240 to travel along the drawing axis 401 between the spin wheel 330 and the coating unit 200.
The auxiliary wheel 310 is positioned parallel to the drawing axis 401 between the guide wheel 320 and the coating unit 200, and is adapted to control excessive rotational force caused by an angle difference between the spin wheel 330 and the drawing axis 401.
As it is apparent in the foregoing, the present invention is advantageous in that it is possible to regulate the degree of twist applied to optical fibers, by coating the optical fibers with a plurality of coating liquids with different viscosity and selectively adjusting the viscosity of the coating liquids. In addition, it is easy to make the optical fibers incorporate a twist, since the twist is given in a predetermined direction. Furthermore, it is possible to fabricate optical fibers that have stable characteristics to compensate for the polarization mode dispersion.
While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-13921 | Mar 2004 | KR | national |
