KR20010024306A - Draw constant downfeed process - Google Patents

Abstract

The optical fiber 14 is drawn out from the mall article 10 fed to the furnace at a constant speed. The optical fiber 14 is drawn by the tractor 20 at a speed of at least 10 m per second, and the tractor 20 measures the fiber diameter measured by the diameter monitor 15 during the drawing process in order to keep the diameter of the fiber relatively constant. According to this, the drawing speed of the fiber 14 is changed. Maintaining a constant downfeed rate of the full article at high draw rates of more than 20 m per second does not adversely affect the drawing process and reduces vibrations in the pull control loop that can cause deformation of the core shape during fiber formation. It is believed that removal will result in reduced PMD and improve MFD uniformity.

Description

DRAW CONSTANT DOWNFEED PROCESS}

In optical fiber fabrication, glass core malleables, typically comprising SiO ₂ , are fabricated and the axial portions of the malleables are doped with composites such as GeO ₂ to increase the refractive index. When fibers are drawn from the glass malleable, the doped regions provide a core or light transmission of the fibers.

The foregoing process is well known in the art, and further details are omitted. In order to obtain an optical fiber, the glass preform or blank is fed to a drawing furnace heated to a melting temperature, and a small glass mass falls along with the trailing fibers from the root of the preform. The fiber is fed from the malleable to the tractor capstan assembly that draws the fiber and then wound onto a spool.

As the fiber is drawn from the malleable, the malleable is fed to the furnace and the fiber diameter is precisely monitored. In general, the diameter adjustment of the fibers is accomplished by changing certain working parameters in the draw tower. Typically, the fiber diameter measuring device is located just below the exit of the furnace to measure the diameter of the fiber. The measured diameter is compared with the nominal diameter value and a signal is generated for increasing (reducing the fiber diameter) or decreasing (increasing the fiber diameter) the tractor speed.

By the 1970s and mid-1980s, the primes for drawing fibers were relatively small. The drawing speed did not exceed about 8 or 9 meters per second. Due to this size and draw speed, the fiber diameter was controlled by varying the speed of the tractor while maintaining the furnace temperature and the rate of delivery of the goods.

In the mid-1980s, increasing the drawing speed resulted in the development and introduction of new process control methods. In particular, when the drawing speed reaches 10 m / s, those skilled in the art gave up the use of constant speed downfeed. In particular, in order to properly control at high drawing speeds, i.e., drawing speeds of up to or exceeding about 10 m / s, changes in drawing speeds, changes in the feeding speeds of malleable goods conveyed downward to the drawing furnaces and actual diameters of fibers Or in response to an error signal indicating that the measured diameter is not equal to the desired diameter, it was believed to rely on a cascade or two-level process control method. For example, if the measured fiber diameter is larger than the desired fiber diameter, the control system speeds up the tractor and, at the same time, reduces the speed of the rolled goods being fed to the drawing furnace. This control principle reflects that when the fiber drawing process is performed at a speed of 8 to 9 m / s or more, it is necessary to change the downward feed rate of the malleable product when the drawing speed is changed to maintain a constant fiber diameter. do.

While this two-stage control process essentially makes the fiber diameter constant, other side effects have been found. Vibration in the draw control loop, in particular fluctuations in the malleable downfeed rate, can cause a change in core shape during the fiber forming process. This is especially serious in the vicinity of the malleable material where the fibers are drawn. Vibration at the proximal end in the furnace affects its shape when the core is molded at the proximal end, resulting in poor PMD and non-uniform MFD.

For telecommunication fiber optics, the PMD should be as small as possible and the MFD should be kept as uniform as possible. Several solutions for solving the above problems have been proposed. For example, pending US Patent Application Nos. 08 / 858,836 and 08 / 784,574, and PCT Application Nos. PCT / US97 / 02541, provide for rotation of fibers when they are drawn to reduce PMD. Various apparatus and methods are disclosed. By spinning the fiber upon drawing, the internal structure and / or stress imbalance of the fiber rotates along the length of the axis about the axis of the fiber, but rotating the fiber solves the important problem in glass causing PMD or It does not remove completely and does not achieve MFD uniformity.

In view of these problems, it is desirable to provide a method for maintaining or increasing MDF uniformity and reducing PMD. This is essential when drawing the optical fiber at a high draw rate, i.

Accordingly, the present invention relates to a fiber optic high speed drawing method that solves one or more problems due to the limitations in the art. The main advantage of the present invention is to provide a diameter control method of a drawn optical fiber that maintains a uniform MFD while reducing the PMD of the fiber when drawing the fiber at high speed. The method includes drawing the fibers at high speed while maintaining a constant downfeed rate of the malleable product. The constant downfeed rate suppresses the proximal near-vibration vibrations in the furnace which cause deformation of the core shape during fiber forming. This deformation causes poor PMD and MFD in the final fiber.

In order to achieve the above object, the present invention provides the steps of feeding the optical fiber malle of a predetermined size to the furnace at a predetermined downward feed rate, drawing the optical fiber from the optical fiber malle at a draw rate of at least 10 m / s and the predetermined It provides a method for reducing polarization mode dispersion in a drawn optical fiber comprising varying the draw rate to maintain a constant fiber diameter while maintaining a constant downward feed rate. Preferably, the draw rate is at least 14 m / s, most preferably at least 20 m / s.

In a preferred embodiment, the downfeed rate is constant in the first draw speed region or section and is changed to another constant downfeed rate in the second draw speed region or section. When the drawing speed is changed in each region, the downward feed rate is kept constant in each region. In addition, the downward dispatch rate may be different in each area. Further, the method may further comprise reducing the downfeed rate when the draw rate changes from one region to another region having a higher draw speed interval or another region having the draw rate from one region having a lower draw speed interval. It may include increasing the downfeed rate when changed to. The method may also include spinning the fiber as it is drawn to further reduce the PMD.

According to another embodiment of the present invention, there is provided a method of drawing an optical fiber from an optical fiber malleable product, the method comprising the steps of feeding an optical fiber malle of a predetermined size to the draw furnace at a constant downward feed rate, wherein Drawing at a draw rate of 10 m / s. The method may further comprise measuring a diameter of the drawn fiber, generating a signal indicative of the measured diameter and comparing the generated signal with a nominal fiber diameter. A second signal indicative of the comparison difference is generated, which is used to change the draw rate to control the drawn fiber diameter. The method also includes detecting a draw rate to determine whether the draw rate is within a predetermined velocity range, and if the detected draw rate is not within the region, changing to another predetermined draw rate. Include. The downward dispatch rate is constant in the first drawing speed region or section, and is changed to another constant downfeed rate in the second drawing speed region or section. Preferably, the downfeed rate is kept constant in each area, and the downfeed rate changes accordingly when the draw rate is changed in a plurality of areas. The method according to the present embodiment further includes rotating the optical fiber when the optical fiber is drawn.

TECHNICAL FIELD The present invention relates to optical waveguide fibers, and more particularly to a method for drawing optical fibers from optical fiber malleables that exhibit reduced polarization mode dispersion (PMD) and more uniform mode pile diameter (MFD).

1 is a schematic view of a fiber drawing device.

The present invention relates to a method for reducing polarization mode dispersion in drawn optical fiber, wherein an optical fiber malle of a predetermined size is fed to a furnace at a predetermined downfeed rate. Preferably, in order to reduce the PMD of the drawn optical fiber and maintain the MFD uniformity, the downward feed rate is kept constant in the entire drawing process to minimize vibration of the near-mold in the furnace.

1 shows a well known fiber optic drawing system, indicated by reference numeral 1. The malleable product 10 is vertically arranged inside the muffle 11 of the drawing furnace. The malleable product 10 includes a handle (not shown) attached to a fixing device (not shown) in a known manner. The fixing device is part of the malleable feeding drive 22 which controls the speed at which the malleable 10 is fed to the furnace. The heater 12 supplies heat to at least the bottom of the malleable product 10. The temperature of the heater 12 is controlled in a known manner by the temperature controller 49. After going through a known start-up process, the article delivery drive 22 feeds the article 10 to the furnace. When the rolled product 10 is fed to the furnace, the end of the rolled material 10, usually called the root, is melted, and the fiber 14 is drawn out by the tractor 20 from the root 13 of the rolled material 10. do.

After leaving the muffle (11), the fibers are used in a feedback control loop to adjust the speed of the premature feeding drive (22) and the tractor (20) as well as to control the temperature from the furnace to the temperature controller (49). After passing through the diameter monitor 15, the fiber 14 passes through a cooling tube 17 and a coating machine for coating the curable protective film on the fiber 14 (fiber 14). 18). The coated fibers may also be passed through a coating curing apparatus and, if desired, an additional coater (not shown). The feedback control of the malleable feed drive 22, tractor drive 21, and temperature controller 49 may be implemented by known control algorithms. The tractor drive 12 is provided with input from a control algorithm 48 which is part of the drawing control computer 47. Considering the demand of the optical fiber, it is preferable to operate the tractor 20 at least 10 m / s. Preferably, the tractor 20 provides a drawing speed of at least 14 m / s, more preferably at least 20 m / s.

The present invention relates to a method for reducing polarization mode dispersion of a drawn optical fiber, comprising feeding a glass malleable material and drawing the optical fiber at a speed of 10 m / s or more. The size of the roll 10 can be measured by weight or diameter. The lower rate of delivery of the malleable goods may be selected based on the size of the malleable product 10. Preferably, the downfeed rate selected once remains constant throughout the fiber drawing process. Optionally, the downfeed rate may be kept constant within a predetermined draw speed region or section. There may be any number of drawing speed ranges, and the drawing speed section within each area may vary. However, each region has a predetermined downfeed rate associated with it, and the downfeed rate remains constant within a given region.

If the drawing speed controlled through the tractor drive 21 increases or decreases out of a specific drawing speed range, it is transferred from the control algorithm 48 to change the lower feeding rate to a lower feeding rate suitable for the specific drawing speed range. A signal is sent to the character feeding drive 22. The control algorithm 48 is set such that the downfeed rate increases a small amount until the predetermined downfeed rate is reached when the tractor speed is changed from one area to another. This allows the downfeed rate to be quickly adjusted back to the original feed rate when the tractor speed suddenly returns to its original area.

According to another feature of the invention, the method comprises the steps of detecting a draw rate to determine whether the draw rate is within a predetermined velocity range, and if the detected draw rate leaves the range, It may further comprise the step of changing. In this embodiment, the draw rate sensor (not shown) will continuously monitor the draw rate in the draw control computer 47. When the drawing speed is changed from one area to another area, the control algorithm 48 may apply to the premature delivery drive 22 to increase or decrease the downfeed rate at a predetermined constant feed rate associated with the drawing speed area. Will send a signal.

In addition, the present invention includes the step of changing the draw rate corresponding to the measured fiber diameter in order to maintain a constant downfeed rate while maintaining a constant fiber diameter. In order to maintain a constant fiber diameter, the fibers 14 are continuously monitored by the diameter monitor 15. The diameter monitor 15 generates a signal indicating the diameter of the measured fiber. The signal is sent to the draw control computer 47. In the drawing computer 47, the measured signal is compared with a predetermined nominal fiber diameter value. A second signal is generated based on the difference from the measured fiber diameter value. The second signal is sent to the tractor drive 21, and the tractor speed is changed to maintain a constant fiber diameter. This process is carried out hundreds of times per minute and the downfeed rate remains constant throughout the drawing process at all tractor speed sections.

It is also advantageous to rotate the fibers as they are drawn. Rotation of the fiber was found to further reduce PMD. Various methods and devices have been developed for rotating fibers as they are drawn. With respect to apparatus and methods used to rotate the fibers, pending US patent applications Ser. Nos. 08 / 858,836 and 08 / 784,574, PCT Application No. PCT / US97, incorporated herein for further understanding. / 02541 and US Pat. No. 5,298,047.

The advantages according to the invention are very numerous. In conventional drawing systems, the fiber diameter was adjusted by the tractor speed. The control loop includes two stage process control in drawing. When the tractor speed changes, the downfeed rate responds to the tractor speed change. While not wishing to be limited by other theories or explanations with respect to the cause of action of the present invention, this causes vibration of the root portion 13 in the furnace. The vibration in the vicinity of the malleable product 10 in the furnace causes a deformation in the core shape of the drawn optical fiber, the deformation of the core shape leads to a high non-uniformity of PMD and MFD, both adversely affect the fiber performance.

The present invention helps to reduce the malleable vibration by providing a constant downfeed rate during the drawing process. In contrast to the well known two-stage control method for drawing fibers at high speed, the control algorithm 48 is set to keep the gutter downfeed rate constant even when the tractor speed is varied to maintain the fiber diameter. This control mechanism is believed to reduce or eliminate vibrations in the pull-out loop that causes changes in the core shape during the fiber forming process, resulting in reduced PMD and improving MFD uniformity.

The invention is further illustrated by the following examples for illustration.

Example 1

Unrotated fiber was fabricated using a drawing system similar to that shown in FIG. 1. In order to maintain a constant fiber diameter, the tractor speed can be varied up to 19 m / s, while the constant downfeed rate was maintained at about 2.75 mm / min. Final fibers were tested for PMD and MFD uniformity. The results compared to the fibers drawn by the standard process (ie variable downfeed rate) are shown in Table 1 below.

Constant downlink rate % PMD reduction 71% Improved% MFD Uniformity 83%

As a result, PMD was greatly reduced and MFD was improved in the drawing process according to the present invention as compared to standard processes.

Example 2

Fibers were drawn using a device similar to that shown in FIG. The fibers were also spun during the drawing process. As described above, according to an embodiment of the present invention, the downward feed rate was set to be 15.5 m per second nominal drawing speed. The drawn fibers were tested and the PMD and MFD uniformity results were compared to the drawn fibers using standard drawing processes. Some differences were ignored and the results are shown in Table 2 below.

Constant downlink rate % PMD reduction 80% Improved% MFD Uniformity 76%

As shown in Table 2, PMD was significantly reduced in the fibers drawn according to the present invention as compared to the fibers drawn according to standard processes. In addition, MFD uniformity was also greatly improved.

Those skilled in the art will appreciate that various changes and modifications can be made to the method of the present invention without departing from the scope of the appended claims and their equivalents.

Claims (16)

Feeding the optical fiber rolls of a predetermined size to the furnace at a predetermined downward feed rate; Drawing an optical fiber from the optical fiber mallet at a draw rate of at least 10 m / s; And And varying the draw rate to maintain a constant fiber diameter while maintaining the predetermined downfeed rate constant. The method of claim 1, wherein the draw rate is 14 m / s or more. The method of claim 1, wherein the draw rate varies between about 14 and 20 m / s. The method of claim 1, wherein the draw rate varies between about 14 and 20 m / s. 5. The method of claim 4, further comprising defining at least one draw rate region. 6. The method of claim 5, wherein when the draw speed is varied in each region, the downward feed rate remains constant within each region. 7. The method of claim 6, wherein the downfeed rate is different in each region. 8. A method according to claim 7, wherein the downfeed rate is reduced when the draw rate is changed from one region to another region having a higher draw rate interval. . 8. The method of claim 7, wherein the downward feed rate increases as the draw rate changes from one region to another region having a lower draw speed interval. . 10. The method of claim 1, wherein the fiber is rotated as it is drawn. Feeding the optical fiber rolls of a predetermined size to the drawing path at a predetermined downward feed rate; Drawing an optical fiber from the optical fiber mallet at a draw rate of at least 10 m / s; Measuring the diameter of the drawn optical fiber and generating a signal indicative of the measured diameter; Comparing the generated signal with a nominal fiber diameter value and generating a second signal representing the comparison difference; Sensing the draw rate to determine whether the draw rate is within a predetermined velocity range; Varying the draw rate based on the second signal to adjust the diameter of the drawn fiber; And Varying the downward feed rate when the detected draw rate leaves the region. 12. The method of claim 11, further comprising rotating the optical fiber when the optical fiber is drawn. 12. The method of claim 11, wherein the draw rate comprises a plurality of regions, each region comprising a predetermined draw speed interval. 14. The method of claim 13, wherein the downfeed rate changes when the draw rate varies between the plurality of regions. 15. The method of claim 14, wherein the downfeed rate is kept constant in each region. Feeding the optical fiber rolls of a predetermined diameter to the furnace at a constant downward feed rate; Drawing an optical fiber from the optical fiber mallet at a draw rate of at least 10 m / s; And And varying said draw rate to maintain a constant fiber diameter.