Patent Application
20050163434
The present invention relates to manufacturing an optical fiber, and more particularly to method and apparatus for applying a spin to an optical fiber in order to manufacturing an optical fiber having an ultra-low Polarization Mode Dispersion (PMD).
A single mode optical fiber with a circular symmetric structure theoretically has two orthogonal polarization modes which are independent and compensated each other. Generally, an electric field of the light propagating through an optical fiber can be considered as linear overlap of such two peculiar polarization modes. In the single mode optical fiber in fact, compensation of the two polarization modes is generated due to defective factors such as symmetric lateral stress or eccentricity of a circular core. These two modes are propagated at different phase rates, hence two modes have different propagation constants (β1 and β2). This difference of propagation constants is called double refraction (Δβ), and the increase of double refraction means the increase of rate difference between two polarization modes. Differential time delay between two polarization modes is called Polarization Mode Dispersion (hereinafter, referred to as “PMD”). The presence of PMD is one of factors causing difficulty in high-speed transmission or analog data transmission.
There is known a method directed to lowering PMD by making the optical fiber be twisted with a pitch far less than its beat length so that the polarization modes can be gradually compensated due to relative delay between the modes.
WO83/00232 and Japanese Patent Laid-open Publication H8-59278 disclose a method of drawing an optical fiber with rotating an optical fiber preform at a high speed.
In addition, Japanese Patent Laid-open Publication H7-69665 discloses a method of drawing an optical fiber preform, which is twisted with a short pitch.
However, in these methods, the optical fiber is twisted to one direction, so an elastic torque stress is accumulated in the optical fiber. In addition, since a rotating speed of the preform should be rapidly increased for equivalence to the rapidity of a drawing speed, the above methods are not commercially practical.
U.S. Pat. Nos. 5,298,047 and 5,418,881 disclose a method of applying a torque to an optical fiber so that a spin imparted on the optical fiber has non-constant spatial frequency (spins/m) by canting a guide roller contacted with the coated optical fiber at a certain angle with respective to a drawing axis or linearly reciprocating the guide roller to a direction perpendicular to the drawing axis.
U.S. Pat. Nos. 5,943,466 and 6,240,748 disclose a method of generating a torque to an optical fiber strand by guiding the optical fiber strand, after forming a coating layer on an optical fiber, with a canting guide roller, which is reciprocating so that a tilt of its rotary axis is changed, and then guiding the optical fiber strand with a guide roller of which a rotary axis is fixed. Particularly, '466 and '748 are characterized in that the spin function generating a torque to the optical fiber strand is substantially not a sine function, but a time-varying complex function having at least two peak values such as a frequency-modulated sine function or an amplitude-modulated sine function.
The above conventional techniques are described in more detail with reference to
First,
An optical fiber preform 11 is slowly supplied to a furnace 12, and an optical fiber 13 is drawn from a neck-down portion of the preform. A bare optical fiber drawn as above (or, an uncoated optical fiber) is provided through a diameter monitor 14 to a coating device 15 where a coating polymer is coated on the bare optical fiber relatively cooled. If this coated optical fiber passes through a concentric coating monitor 16, the optical fiber then passes through a hardening device 17. The hardening device 17 typically has a UV lamp. At a downstream of the hardening device 17, a coating diameter monitor 18 and a following guide means (i.e., rollers 21, 22 and 23) and a drive means (i.e., capstan) are provided. The guide roller 21 gives a first contact point which is contacted with the optical fiber for the first time. At this point, the optical fiber is protected by the polymer coating which is already hardened. The capstan 24 gives a draw force, and the optical fiber from the capstan 24 is typically advanced to a take-up means (e.g. a take-up spool).
The guide roller 21 cants with being inclined a predetermined angle to a drawing axis or linearly reciprocates to a direction perpendicular to the drawing axis in order to provide a spin to the optical fiber. At this time, the spin function is substantially a sine function or a frequency-modulated or amplitude-modulated sine function.
Referring to
In addition, since a contact surface of the guide roller 21 forms a flat plane without any slope, the contacted optical fiber can be slipped on the contact surface as the roller moves. This slipping obstructs twist of the optical fiber which is caused by a frictional force, so the optical fiber cannot be provided with a regular spin.
Moreover, the coated optical fiber passing through the coating device is contacted with the guide roller 21 for the first time. Thus, in order to increase a spatial frequency of the spin (i.e. a spin rate [spins/m]) applied to the optical fiber, an amplitude of the guide roller 21 should be grown large. However, as the amplitude of the guide roller 21 increase, a vibration of the optical fiber also becomes increased and the regularity of coating is further deteriorated.
Therefore, there is needed to develop a spin applying device which may not only vibrate the guide roller with an amplitude capable of obtaining the regularity of coating but also ensure a high spin rate.
There have been proposed various attempts to solve the problem of the prior art.
Korean Patent No. 10-230463 by Samsung Electronics discloses an optical fiber drawing device in which many support rollers are arranged for supporting an optical fiber not to escape from its original position between the guide rollers and a coating device so that the optical fiber is not deviated from a drawing axis with a certain deviation as the guide rollers providing a torque to the optical fiber moves. However, the patented technique of Samsung Electronics is lack of practicality in a commercial aspect since the mechanism for restraining movement of the optical fiber is too complex.
In addition, U.S. Pat. No. 6,324,872 by Blaszyk et al. discloses a spin applying device in which a V-shaped support roller is positioned between a coating device and a guide roller for applying a spin. However, Blaszyk et al. failed to suggest or imply that the slipping of the optical fiber can be prevented and the spin rate can be controlled by suitably designing a structure of a guide roller and a position relation between the support roller and the guide roller.
EP 0 729 919 A1 by Onishi et al. discloses a structure in which a pair of guide rollers are arranged at an upper portion of a canting roller in order to restrain movement of an optical fiber within a certain deviation so that the optical fiber does not escape from the drawing axis.
However, like Blaszyk et al., Onishi et al. failed to suggest or imply that the slipping of the optical fiber can be prevented and the spin rate can be controlled by suitably designing a configuration of a guide roller and a position relation between the support roller and the guide roller.
U.S. Patent Laid-open Publication No. 2001/20374 by Roba et al. and Japanese Patent Laid-open Publication No. 2000-247675 disclose a technique of restraining the slipping of the optical fiber by designing a contact surface of a roller, which provides an alternating torque to the optical fiber, in a V shape. However, these conventional arts also failed to suggest or imply a position relation between the support roller and the guide roller for controlling a spin rate, and mechanism for providing a torque to the optical fiber and overall configuration of the spin applying device are different from the present invention.
The present invention provides a method of manufacturing an optical fiber which may ensure a high spin rate even while driving a roller with a low amplitude for obtaining regularity of coating.
In addition, the present invention designs the structure of the roller so that an optical fiber contacted with a contact surface of the roller, which applies a spin to the optical fiber, is not slipped.
The present invention also provides a method of restraining movement of the optical fiber so that a vibration generated at a point where a twist is induced to the optical fiber is not transferred to a coating device.
Inventors have found that, a moving velocity or an amplitude of the roller should be increased to improve a spin rate of the optical fiber, in a spin applying mechanism which induces a torque to the optical fiber by linearly reciprocating the driving roller, contacted with the coated optical fiber, to a direction perpendicular to a drawing axis. However, increasing the moving velocity or amplitude of the roller has various limitations, and particularly the increase of the amplitude causes the optical fiber to be deviated greatly from the coating center, so the regularity of coating is seriously deteriorated. Thus, the inventors conceived an idea that the spin rate can be controlled by means of positioning a separate guide roller between the driving roller and the coating device and then adjusting a distance between the guide roller and the driving roller. In other words, if the driving roller vibrates with a constant amplitude, a vibration angle (or, an angle between a drawing axis and an optical fiber positioned between the driving roller and the guide roller) becomes large and the spin rate of the optical fiber is increased as the distance is shortened. On the contrary, as the distance is lengthened, the vibration angle of the optical fiber is decreased and the spin rate of the optical fiber is reduced.
In order to realize the above idea, the present invention provides an apparatus for applying a spin to an optical fiber, which is installed between a coating device for coating the optical fiber drawn from an optical fiber preform and a bobbin for taking up the coated optical fiber, which includes a driving roller which is linearly reciprocating to a direction perpendicular to a drawing axis in contact with the coated optical fiber so as to give a rotary force in a circumferential direction to the coated optical fiber; a roller driving means for vibrating the driving roller to a direction perpendicular to the drawing axis; and a guide roller contacted with the coated optical fiber in an area between a lower end of the coating device and an upper end of the driving roller, the guide roller guiding the contacted optical fiber in a longitudinal direction so that the optical fiber is not deviated more than a predetermined range on the basis of the drawing axis.
At this time, a distance (l) between the driving roller and the guide roller in a drawing axis direction is set to satisfy a predetermined spin rate (spins/m).
Thus, in case an amplitude of the driving roller is constant, the spin rate applied to the optical fiber can be controlled by adjustment of the distance.
In addition, there is also provided a method for manufacturing an optical fiber, which includes the steps of (A) heating an optical fiber preform; (B) drawing a bare optical fiber from the heated preform; (C) coating at least one coating layer on the drawn bare optical fiber, and (D) applying a torque to the coated optical fiber so that the optical fiber drawn from the preform is rotated on the basis of a longitudinal direction thereof.
At this time, the step (D) further includes the steps of (a) guiding the coated optical fiber so that the optical fiber is not deviated more than a predetermined range from a drawing axis below an optical fiber coating point; (b) giving a torque to the optical fiber by contacting the coated optical fiber to a driving roller which vibrates on the basis of a axis substantially parallel to the drawing direction below a guiding point; and (c) controlling an angle (θ) between the vibrating optical fiber and the drawing axis by adjusting an amplitude (A) of the driving roller and a distance (l) between the guiding point and the vibrating point.
Thus, a spin rate (spins/m) of the optical fiber generated by rotation can be adjusted by controlling the angle (θ) between the vibrating optical fiber and the drawing axis.
Preferably, a contact surface of the driving roller has an approximate V shape in order to prevent the optical fiber, which contacts with the driving roller according to vibrations of the driving roller, from slipping on the contact surface. Particularly, a curved surface can be formed at a central valley of the contact surface so as to receive the contacted optical fiber therein.
In addition, for the purpose of obtaining the regularity of coating, the vibration of the contacted optical fiber corresponding to the vibration of the driving roller should be transferred to a coating point so that the optical fiber may not be deviated more than a predetermined range from a coating center.
In this aspect, the present invention arranges a guide roller, of which a contact surface has an approximate V shape, between the coating device and the driving roller. Thus, though the optical fiber at an upper end of the driving roller deviates more than a predetermined range from the drawing axis, the optical fiber can be substantially coincident with the coating center at a lower end of the coating device.
In addition, the present invention also provides an optical fiber manufacturing apparatus in which the above-mentioned spin applying apparatus is arranged between a coating device and a take-up bobbin. With this configuration, the present invention allows easy manufacture of an optical fiber having ultra-low PMD without the use of expensive additional equipment. In particular, a spin spatial frequency (i.e., spin ratio) can be easily controlled as desires by adjustment of the distance between the driving roller and the guide roller of the spin applying apparatus.
These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings:
a to 6c are vertical sectional views respectively showing a guide roller, a driving roller and a support guide roller which may be used in the spin applying device of the present invention;
a to 8c are enlarged vertical sectional views for illustrating that the optical fiber contacting with a contact surface of the driving roller is twisted due to a frictional force on the contact surface of the driving roller;
a and 9b show a correlation between a distance (l) from the guide roller to the driving roller and a vibration angle (θ) when an amplitude of the driving roller is constant; and
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
The optical fiber manufacturing apparatus 100 heats an optical fiber preform 101 in a furnace 102 to a high temperature, and then draws a bare optical fiber 103 from a neck-down portion of the preform which is softened. The drawn bare optical fiber 103 is passing through an outer circumference measurer 104 and cooled in a cooling device 105, and then coated with an ultraviolet hardening resin at least one time in a coating device 106. The coated optical fiber coated in the coating device 106 is then hardened in a hardening device 107 and then transferred to a spin applying device 110.
The optical fiber is twisted with a predetermined spin rate in the spin applying device 110 and then traveled through a driving device (i.e., capstan) 108, which controls a drawing speed of the optical fiber, to a take-up device (i.e., a take-up bobbin) 109.
The spin applying device 110 according to the present invention includes a guide roller 111, a driving roller 112 positioned below the guide roller in a drawing direction, and a driving tool 115 for linearly reciprocating the driving roller in an arrowed direction perpendicular to the drawing axis. The guide roller 111 and the driving roller 112 become rotated on the center of their rotary axes (i.e., axes perpendicular to the drawing axis) as the optical fiber moves along the drawing axis since the guide roller 111 and the driving roller 112 are contacted with the drawn optical fiber 103.
In addition, the guide roller 111 and the driving roller 112 are spaced apart to a drawing axis direction, and contacted with the optical fiber with being faced to each other on the basis of the drawing axis.
A drawing direction of the optical fiber contacted with the driving roller 112 should be substantially coincident with a drawing direction of an optical fiber drawn at a lower end of the coating device 106 and a drawing direction of an optical fiber contacted with the guide roller 111. In other words, rotary axes of the guide roller 111 and the driving roller 112 are on the same plane, and parallel to each other on the plane. Thus, the optical fiber passing through the coating device 106 to the driving roller 112 does not experience any path change as for its drawing direction.
Particularly, it is preferred that the guide roller 111 is contacted with the coated optical fiber for the first time at an area between the coating device 106 and the driving roller 112.
In addition, though it is shown in the drawing that the driving roller 112 linearly reciprocates with a constant amplitude L on the center of the drawing axis, the present invention is not limited to that example. In other words, the driving roller 112 can be vibrated on the center of an axis, which is substantially not coincident with the drawing axis.
The spin applying device 110 of the present invention may also include a separate support guide roller positioned at a downstream of the driving roller 112, i.e., between the driving roller 112 and the capstan 108, for guiding the coated optical fiber 103 to the take-up bobbin 109 so as to be coincident with the drawing axis.
Of course, it is also possible to arrange a plurality of support guide rollers between the driving roller and the capstan.
An optimized example configuring the spin applying device 110 with two guide rollers and one driving roller is well shown in
Referring to
The driving roller 112 is positioned between the guide rollers 111 and 113 and contacted with the optical fiber with being faced to the guide rollers 111 and 113 on the basis of the drawing axis.
Vertical sectional views of the driving roller and the guide roller are shown in
Referring to
Thus, a radius R1 of the curved portion should be larger than a diameter of the received optical fiber. If the radius of the curved surface is smaller than the diameter of the optical fiber, the optical fiber is contacted with the inclined surfaces 111b and 11c, which may damages surfaces of the optical fiber or exerts unnecessary stress to the optical fiber.
In addition, the radius R1 of the curved portion is preferably smaller than a linear reciprocating distance of the driving roller. If the radius of the curved portion is greater than the linear reciprocating distance of the driving roller, it becomes difficult to form a vibration angle θ described later and the optical fiber can be slipped.
The tilt angle φ1 should be set suitably so that the optical fiber is not only safely guided without any damage on its coating but also not deviated more than a predetermined range from a coating center due to vibration.
If the tilt angle φ1 is too small, the optical fiber can be damaged, while if too great, the coating can be irregular.
Referring to
Thus, a radius R2 and R3 of the curved portion should be larger than a diameter of the received optical fiber. If the radius of the curved surface is smaller than the diameter of the optical fiber, the optical fiber is contacted with the inclined surfaces 112b, 112c and 113b, 113c, which may damages surfaces of the optical fiber or exerts unnecessary stress to the optical fiber.
In addition, the radius R2 of the curved portion is preferably smaller than a linear reciprocating distance of the driving roller. If the radius R2 of the curved portion is greater than the linear reciprocating distance of the driving roller, it becomes difficult to form a vibration angle θ described later and slipping of the optical fiber can be appeared.
The tilt angle φ2 should be set suitably so that the optical fiber is not only safely guided without any damage on its coating but also stably twisted without slipping according to vibration of the driving roller while the optical fiber is moving along the inclined surfaces. If the tilt angle φ2 is too small, the optical fiber can be damaged, while if too great, the optical fiber cannot be twisted stably.
In addition, the tilt angle φ3 should be set suitably to induce vibration of the driving roller stably without damaging the coating of the optical fiber.
As an example of the present invention, it is preferred that the tilt angle φ1 and the radius R1 of the curved surface of the guide roller are smaller than the tilt angle φ2 and +3 and the radius R2 and R3 of the curved surface of the driving roller 112 and the support guide roller 113.
The guide roller 111, the driving roller 112 and the support guide roller 113 are fixed to a frame 114, and a rotary shaft of the driving roller 112 is connected to a crank 115b installed to a base 115c. On the base 115c, installed are a motor 115a and the crank 115b for converting a rotary motion of the motor 115a into a linear reciprocating motion.
Thus, the rotary motion generated by driving the motor 115a is converted into a linear reciprocating motion due to the crank 115b, and the driving roller 112 connected to the crank 115b is thus vibrated to an arrowed direction on the drawing.
Now, a mechanism of axially twisting the optical fiber contacted with the driving roller as the driving roller vibrates is described with reference to
First, if the driving roller 112 is moved to an arrowed direction shown in
To the contrary, if the driving roller 112 moves to an arrowed direction shown in
Thus, if the driving roller linearly reciprocates (i.e., vibrates) on the basis of the drawing axis with a constant amplitude and a constant vibration frequency, there are generated alternating spins to the optical fiber in clockwise/counterclockwise directions.
A spin rate (the spin number per unit length [spins/m]) of the optical fiber depends on the tilt angle φ2, amplitude, vibration rate and drawing speed of the driving roller. Particularly, if the amplitude of the driving roller is increased, the optical fiber can be deviated too much from the drawing axis, which deteriorates regularity of coating.
Thus, there is needed a way to control the spin rate of the optical fiber as desired, without deteriorating the coating regularity while the tilt angle, the vibration rate and the drawing speed of the driving roller are determined to certain values.
a and 9b shows a method of controlling a spin rate of the optical fiber by adjusting a length (l) between the guide roller 111 and the driving roller 112 according to the present invention.
As shown in
If the amplitude (L) is constant, the spin rate increases as the vibration angle (θ) is increased. Thus, if the amplitude (L) is constant and the length (l) between the driving roller and the guide roller is increased, the vibration angle (θ) is reduced and the spin rate is decreased.
Comparing the case of
Thus, while other spin control factors such as a drawing speed, a vibration rate and an amplitude are determined, the spin rate (spins/m) of the optical fiber can be controlled as desired by suitably adjusting the distance (l) between the driving roller and the guide roller.
In addition, the present invention may restrain movement of the optical fiber so that vibration of the optical fiber generated by the driving roller 112 is not transferred to the coating device 106 by means of positioning the guide roller 111 above the driving roller 112 as shown in
As described above, the present invention ensures the regular coating by positioning the guide roller of an approximate V shape at an upstream of the driving roller for applying alternating torques to the optical fiber, and also controls the spin rate of the optical fiber by adjusting the distance between the guide roller and the driving roller.
In addition, since the guide roller and the driving roller have an approximately V-shaped section, the present invention may reduce slipping of the optical fiber on a contact surface and helps the optical fiber to be twisted more easily.
The present invention has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002/52299 | Aug 2002 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR02/02017 | 10/31/2002 | WO |
