Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
  • C03B37/01—Manufacture of glass fibres or filaments
  • C03B37/02—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
  • C03B37/01—Manufacture of glass fibres or filaments
  • C03B37/02—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor
  • C03B37/025—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor from reheated softened tubes, rods, fibres or filaments, e.g. drawing fibres from preforms
  • C03B37/0253—Controlling or regulating
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2205/00—Fibre drawing or extruding details
  • C03B2205/06—Rotating the fibre fibre about its longitudinal axis
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2205/00—Fibre drawing or extruding details
  • C03B2205/40—Monitoring or regulating the draw tension or draw rate
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2205/00—Fibre drawing or extruding details
  • C03B2205/42—Drawing at high speed, i.e. > 10 m/s
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2205/00—Fibre drawing or extruding details
  • C03B2205/44—Monotoring or regulating the preform feed rate
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2205/00—Fibre drawing or extruding details
  • C03B2205/60—Optical fibre draw furnaces
  • C03B2205/72—Controlling or measuring the draw furnace temperature

Definitions

• the present invention relates to optical waveguide fibers, and more particularly, to methods for drawing an optical fiber from an optical fiber perform whereby the fiber exhibits a more uniform mode filed diameter (MFD) and reduced polarization mode dispersion (PMD)
• MFD uniform mode filed diameter
• PMD reduced polarization mode dispersion
• a glass core preform which typically comprises S ⁇ O 2 , the axial portion of which is doped with a compound such as GeO 2 to increase the refractive index
• the doped region will provide the light transmission portion or core of the fiber
• the blank As fiber is drawn from a blank, the blank is fed into the furnace, and fiber diameter is closely monitored. Control of fiber diameter is generally accomplished by varying certain operating parameters at the draw tower.
• a fiber diameter measuring device is located just below the furnace outlet to measure the fiber diameter. The measured diameter is compared to a nominal diameter value and a signal is generated to either increase the tractor speed (thus decreasing the fiber diameter), or decrease the tractor speed (thus increasing the fiber diameter. )
• the control system would increase the tractor speed and, at the same time, decrease the rate at which the blank was fed into the draw furnace.
• This control philosophy reflected the belief that when operating a fiber draw process at a speed greater than 8-9 meters/sec, it was necessary to vary the blank downfeed rate when draw speed was varied to maintain a more constant fiber diameter.
• Spinning optical fiber as it is drawn causes internal geometric and/or stress asymmetries of the fiber to rotate about the fibers axis along the length of the axis; however, spinning the fiber does not address the underlying problems in the glass that cause PMD, nor does spinning entirely eliminate PMD or address the issue of MFD uniformity.
• the present invention is directed to a method for the high speed drawing of optical fiber that alleviates one or more of the problems due to limitations and disadvantages of the related prior art.
• the principal advantage of the present invention is the provision of a method for controlling the diameter of a drawn optical fiber while reducing PMD in the fiber and maintaining uniform MFD when drawing the fiber at high speed.
• the method comprises drawing fiber at a high speed while keeping the blank downfeed rate constant. It is believed that constant downfeed rate avoids oscillation of the blank root in the furnace which causes variability in the core shape during fiber formation. Such variations are believed to contribute to poor PMD and MFD in the final fiber.
• the invention is a method for reducing polarization mode dispersion in drawn optical fiber comprising the steps of feeding an optical fiber preform of a predetermined size into a furnace at a predetermined downfeed rate, drawing an optical fiber from the optical fiber preform at a draw rate of at least 10 meters per second. and varying the draw rate to maintain a substantially constant fiber diameter while maintaining the predetermined downfeed rate constant.
• the draw rate is greater than 14 meters per second and most preferably, greater than 20 meters per second.
• the downfeed rate is constant for a first zone or range of draw speeds and is then changed to a different constant downfeed rate for a second zone or range of draw speeds. As the draw speed varies in each zone, the downfeed rate remains constant within each zone. In addition, the downfeed rate may be different for each zone.
• the method may also include the step of decreasing the downfeed rate as the draw rate changes from one zone to another having a higher rate of draw Sfte ⁇ ds, or increasing the downfeed rate as the draw rate changes from one to another having a lower range of draw speeds.
• the invention may also include the step of spinning the fiber as it is being drawn to further reduce PMD.
• a method for drawing optical fiber from an optical fiber preform comprising the steps of feeding the optical fiber preform of a predetermined size into a draw furnace at a constant downfeed rate and drawing optical fiber from the optical fiber preform at a draw rate of at least 10 meters per second.
• the method further comprises the steps of measuring the drawn fiber diameter and generating a signal representative of the measured diameter and comparing the generated signal to a nominal fiber diameter. A second signal representative of the difference of the comparison is generated and used to vary the draw rate to adjust the drawn fiber diameters.
• the method also includes the step of sensing the draw rate to determine if it is within a zone of predetermined speeds and changing the downfeed rate to another predetermined rate if the sensed draw rate is outside of the zone.
• the downfeed rate is constant for a first zone or range of draw speeds and is then changed to a different constant downfeed rate for a second zone or range of draw speeds.
• the downfeed rate is maintained constant within each zone and as the draw rate is varied between the plurality of zones, the downfeed rate is change accordingly.
• the method according to this embodiment may include the further step of spinning the optical fiber as it is drawn.
• FIG. 1 is a schematic diagram of a fiber drawing apparatus.
• the present invention is directed to method for reducing polarization mode dispersion in drawn optical fiber wherein an optical fiber preform of a predetermined size is fed into a furnace at a predetermined downfeed rate.
• the downfeed rate is kept constant throughout the entire draw process in order to minimize oscillation of the preform root in the furnace in order to maintain MFD uniformity and reduce PMD in the drawn optical fiber.
• Fig. 1 illustrates a well known optical fiber draw system, designated generally by reference numeral 1.
• Preform 10 disposed vertically in muffle 11 of a draw furnace.
• Preform 10 includes a handle (not shown) that attaches to a holding device (not shown) in a known manner.
• the holding device is part of preform feed drive 22, which controls the rate at which preform 10 is fed into the furnace.
• Heating element 12 supplies heat to at least the bottom portion of preform 10.
• the temperature of heating element 12 is controlled by temperature controller 49 in a known manner.
• preform feed drive 22 feeds preform 10 into the furnace.
• the end portion of preform 10 commonly referred to as the root, melts and fiber 14 is drawn from root portion 13 of perform 10 by tractor 20.
• fiber 14 After leaving muffle 11 , fiber 14 passes through diameter monitor 15 which produces a signal that is used in a feedback control loop to regulate the speed of tractor 20 and preform feed drive 22, as well as to regulate temperature in the furnace through temperature controller 49. After diameter monitor 15, fiber 14 passes through a cooling tube 17 and a coater 18 by which a curable protective coating is applied to fiber 14. The coated fiber may also pass through a coating curing apparatus and if desired additional coaters (not shown).
• the feedback control of perform feed drive 22, tractor drive 21 and temperature controller 49 can be implemented by known control algorithms. Tractor drive 21 is provided with an input from control algorithm 48 which is part of draw control computer 47. Given the demand for optical fiber, it is advantageous to run tractor 20 at a rate of at least 10 meters per second. Preferably, tractor 20 produces a draw speed of greater than 14 meters/second, and more preferably greater than 20 meters per second.
• the present invention is directed to a method for reducing polarization mode dispersion in drawn optical fiber comprising the step of feeding a glass preform and drawing an optical fiber at a speed greater than 10 meters/second.
• the size of preform 10 can be measured by weight or by its diameter.
• the downfeed rate of perform 10 is selected based on the size of perform 10.
• the downfeed rate once selected, remains constant throughout the fiber drawing process.
• the downfeed rate may remain constant within a predetermined zone or range of draw speeds. There may be any number of zones of draw speeds and the range of draw speeds within each zone may also vary. However, each zone has a predetermined downfeed rate associated with it and the downfeed rate remains constant within the given zone.
• control algorithm 48 If the draw speed, which is controlled through tractor drive 21 , increases or decreases out of a specific zone of draw speed, a signal is sent from control algorithm 48 to preform feed drive 22 to change the downfeed rate to the appropriate downfeed rate for the particular zone of draw speed.
• Control algorithm 48 is set up so that as the tractor speed changes from one zone to another, the downfeed rate changes by small increments until the predetermined downfeed rate is reached. This allows the downfeed rate to adjust back to the original rate quickly if the tractor speed were to suddenly return to the original zone.
• the method may comprise the further steps of sensing the draw rate to determine if it is within a zone of predetermined speed and varying the downfeed rate if the sensed draw rate is outside of the zone.
• a draw rate sensor (not shown) continually monitors draw rate at draw control computer 47. If the draw speed changes from one zone to another, control algorithm 48 sends a signal to preform feed drive 22 to increase or decrease the downfeed rate to the predetermined constant rate associate with the zone of draw speed.
• the present inventive method also includes the step of varying the draw rate in response to the measured fiber diameter to maintain a substantially constant fiber diameter while maintaining the predetermined downfeed rate constant. In order to maintain a constant fiber diameter, fiber 1 is constantly monitored by diameter monitor 15.
• Diameter monitor 15 produces a signal representative of the measured fiber diameter. That signal is sent to draw control computer 47. At draw computer 47, the measured signal is compared to a predetermined nominal fiber diameter value. A second signal is generated based on any difference between the measured fiber diameter value. The second signal sent to the tractor drive 21 and the tractor speed is varied to maintain a constant fiber diameter. This process is carried out hundreds of times per minute and the downfeed rate remains constant throughout the draw process during all ranges of tractor speed.
• control algorithm 48 is set up to maintain the preform downfeed rate constant even as the tractor speed varies to maintain fiber diameter. It is believed that this control mechanism reduces or perhaps eliminates oscillations in the draw control loop that can cause variations in the core shape during fiber formation, and results in reduced PMD and improves MFD uniformity.
• EXAMPLE 1 An unspun optical fiber was produced using a draw system similar to that illustrated in Fig. 1. The tractor speed was allowed to vary up to a maximum of 19 meters per second to maintain a constant fiber diameter, while the downfeed rate was kept constant at about 2.75 millimeters per minute. The resulting fiber was tested for PMD and MFD uniformity. The results as compared to a fiber drawn under a standard process (i.e. variable downfeed rate), are shown in Table 1 below:
• EXAMPLE 2 A fiber was drawn using an apparatus similar to that depicted in Fig. 1 The fiber was also spun during the draw process. The downfeed rates were set according to the zone embodiment of the present invention as describe above to achieve a 15.5 meters per second nominal draw speed. The drawn fiber was tested and the results of PMD and MFD uniformity were compared to a fiber drawn using a standard draw process. Several different runs were undertaken and the results are shown in Table 2 below.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Manufacture, Treatment Of Glass Fibers (AREA)

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Publications (1)

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• 1998
  • 1998-09-10 KR KR1020007003205A patent/KR20010024306A/ko not_active Application Discontinuation
  • 1998-09-10 CN CN98809377A patent/CN1119301C/zh not_active Expired - Fee Related
  • 1998-09-10 CA CA002301033A patent/CA2301033A1/en not_active Abandoned
  • 1998-09-10 JP JP2000512784A patent/JP2001517598A/ja active Pending
  • 1998-09-10 EP EP98946905A patent/EP1030823A4/en not_active Withdrawn
  • 1998-09-10 AU AU93817/98A patent/AU738625B2/en not_active Ceased
  • 1998-09-10 WO PCT/US1998/018785 patent/WO1999015470A1/en not_active Application Discontinuation
  • 1998-09-10 ID IDW20000757A patent/ID24850A/id unknown
  • 1998-09-10 BR BR9812674-1A patent/BR9812674A/pt not_active IP Right Cessation

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Non-Patent Citations (1)

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