JP2002529357A - Method and apparatus for manufacturing optical fiber - Google Patents

Abstract

Abstract: A filament in tube and stick in tube process for forming optical fibers has been described. A solid or monolith core feed (110) is disposed within the hollow cladding structure (112) to form a loosely filled cladding structure. The filled cladding structure is heated to a drawing temperature approximately equal to the softening point of the cladding structure. The feedstock (110) melts and fills the heated portion of the cladding structure to form a filled core. This core can then be drawn into an optical fiber or optical cane. The optical cane is then consolidated with additional cladding and can be drawn into a fiber. Feedstocks (110) and cladding structures (112) having various coefficients of expansion may be used. The resulting fiber can be easily designed to be fused to an existing installed fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

FIELD OF THE INVENTION The present invention relates generally to optical fiber waveguides and improvements in their manufacture. More specifically, the present invention relates to a fiberized filament-in-tube (filam
A novel method and apparatus for forming optical fiber waveguides by ent in tube and stick in tube methods.

BACKGROUND optical fiber waveguide of the invention, has become increasingly play an important role in the communication. For application to many different systems, a variety of optical fiber types must be available with respect to dimensions, refractive index profiles, operating wavelengths, materials, and the like. further,
Active devices such as amplifiers, lasers, switches and dispersion compensators are increasingly needed. In addition, the fiber optic cables must be connected to each other without being too difficult to implement. It is important that these connection techniques be readily applicable at the site where the cable connection is made. In many applications, it is particularly important to easily connect a new fiber to a fiber that is already in place. In other words, it is often not an option to remove all existing fibers and replace them with new fibers having different characteristics.

[0003] Various techniques have been used to manufacture optical fibers. In one method (see US Pat. No. 3,659,915), a rod of core material is placed in a tube of low index cladding material to form a tight concentric fit. The core material must be uniform in cross section and have a smooth surface. The temperature is then increased and the rod and tube are drawn to the desired cross-sectional area. The optical fiber obtained by this process will not be ideal for communication due to excessive loss and dispersion.

[0004] Another method (see US Pat. No. 5,651,083) involves inserting a core material into a molten cladding material to form a preform. Insertion of the core occurs quickly so that the core does not soften or melt in the process. Next, the obtained preform is drawn into an optical fiber. ZBLA manufactured in this manner
Fluoride glass such as N cannot be fusion-spliced to silica fiber, easily devitrifies, and has poor durability.

[0005] One of the more important methods used in soot making, which is used to make low loss optical fibers, is a chemical vapor deposition (CVD) process. In one embodiment of the CVD process, a relatively pure chemical (such as silicon tetrachloride) is passed through the manifold with oxygen. They are then mixed and fed into a burner running under a rapidly rotating mandrel or high purity fused silica tube. As a result, silicon is oxidized to silica on a mandrel or silica tube.
The deposit may be doped with various materials. The resulting preform is generally consolidated and then drawn into an optical fiber. This process is an external CVD or OVD process. Internal or MCVD processes are also known CVD processes.

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for producing various optical fibers by a fiberized filament-in-tube and stick-in-tube method. In one aspect, the present invention involves filling a glass tube with a glass filament or stick of a desired material, and then drawing or drawing the glass tube at an elevated temperature. The material in the tube melts at the drawing temperature and fills the tube to form a continuous core. The loosely-fitted feedstock can be fed automatically or melt down by gravity to maintain a constant depth of the molten feedstock and produce a homogeneous and reproducible product. The feed may be comprised of a core material or a core / cladding material. Similarly, the tube may have additional core material (eg,
(Which can be used to form the outer core region), core / cladding material, or cladding material. The present invention can be used to draw optical fibers directly (filament-in-tube) or to produce core canes or core clad canes that are subsequently coated with additional material before being drawn into the optical fiber. (Stick-in-tube).

According to the present invention, almost any glass that can be produced by chemical (sol-gel, vapor phase growth, etc.) or physical (batch and melt) techniques can be economically produced in the form of continuous clad filaments. Due to the quenching allowed by this technique,
Glass and glass ceramics, which were previously unstable, can be formed as stable fibers.

[0008] A more complete understanding of the present invention, as well as further features and advantages, will be apparent from the following detailed description and the accompanying drawings.

DETAILED DESCRIPTION The present invention provides a method and apparatus for making various optical fibers by the fiberized filament-in-tube and stick-in-tube methods as discussed in more detail below. Before addressing the invention in detail with reference to the drawings, various general aspects and advantages are first generally addressed. First, a glass or crystalline stick of the desired core composition should be obtained. Regardless of whether the stick has a circular, square or triangular or other different cross section, it only needs to fit within the cladding tube to be used therewith. Unlike the known rod-in-tube method, the method of the present invention requires the core to be tightly concentrically fitted into the cladding tube as the core filament melts and conforms to the cladding wall. There is no. Similarly, the lumen of the tube need not be circular, but may be rectangular, elliptical, or any other non-circular shape capable of forming a fiber with a non-circular core. In the present invention, the core glass or stick conforms to the shape of the inner diameter of the tube when a rectangular tube lumen is used, so that the core glass deforms into the shape of the tube, thereby forming a shape during consolidation. Form a rectangular core region. A fiber having a substantially rectangular core can be manufactured by using a tube having a rectangular inner diameter. After drawing the fiber, the core remains substantially rectangular in cross section (the corners of the rectangle are somewhat rounded). Using the method of the present invention disclosed herein, a fiber having a rectangular core was made. These fibers exhibited a numerical aperture (NA) of greater than about 0.35, and in particular achieved a numerical aperture of about 0.45. Such high NA fibers typically have a large amount of modifier required for such refractive index changes, which can cause the core material to crystallize, crack, or sag during manufacture, resulting in CVD Cannot be manufactured using techniques. Such a fiber with a rectangular core can be used to efficiently couple light from a stripe laser diode. For example, a typical high power striped laser diode emits a beam having a substantially 100 μm × 1 μm rectangular geometry. Thus, a beam having this geometry is provided by a fiber formed according to the present invention to have a core geometry substantially similar to that of a laser beam.
Captured more efficiently.

[0010] Other non-circular lumens, including oval, may be used. These lumens can be used to form polarization maintaining fibers. Similarly, a tube having a non-circular cross-section can be used to produce a non-circular fiber. In each of these embodiments where a non-circular inner or outer diameter is to be maintained, a high drawing speed is preferred to cause the fiber or core cane to at least substantially maintain the inner or outer diameter, or both shapes. . In particular,
In certain preferred embodiments used to produce fibers or core canes having either a non-circular core or non-circular fiber outer diameter, or both, the preform draw rate and temperature are determined by the resulting fiber or The core cane is maintained so as to at least substantially maintain the inner and outer shape of the tube. Such a result is promoted by maintaining the temperature (when producing a core cane) drawing or redrawing, the temperature such that the viscosity of the tube is maintained greater than about 10 ⁷ poises.

The method of the present invention, unlike conventional rod-in-tube techniques, does not require that the core stick be uniform in cross section and have a smooth surface.

FIG. 1 is a cross-sectional view of an apparatus 100 suitably used to implement a filament-in-tube method for drawing optical fibers according to the present invention. First, the cladding tube 112, having an outer diameter of 57 mm and an inner diameter of 2 mm in the preferred embodiment, along with the inner wall 118, is purged with a dry gas, for example, chlorine (Cl ₂ ) or chlorine mixed with an inert gas. Removes unwanted moisture. In a preferred embodiment, a core feed or filament 110 having a diameter of 1.5 mm
Place in 112. The feedstock or filament 110 is preferably an elongate monolithic rod of material, but a plurality of elongate rods can be stacked on top of one another in a cladding tube 112 to form a feedstock. The use of multiple rods is particularly well suited for the production of dispersion managed fibers. Clad tube 1
12 and core filament 110 form a filled cladding tube having an open centerline 122 that is heated by furnace 114, as described further below. Furnace 114
It is operated at a draw temperature above the melting temperature of the core filament 110, but only softens the cladding tube 112. As the cladding tube 112 softens, the core filament 110 melts at its drawing temperature and the core melt 12 contained within the cladding tube 112
Form a 0. It is currently preferred that the drawing temperature be equal to or higher than the liquidus temperature of the core filament to remove crystals in the core melt 120. As used herein, melt means that the core filament 110 flows and fills or deforms the inside of the cladding tube 112 such that a filled cladding structure is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a suitable apparatus for performing a filament-in-tube method for drawing an optical fiber according to the present invention.

FIG. 2 is a cross-sectional view of a suitable apparatus for performing a stick-in-tube method for drawing optical fibers according to the present invention.

FIG. 3 shows a suitable device for coating an optical cane formed according to the invention, which will be drawn into an optical fiber according to the invention.

FIG. 4 is a graph showing the loss as a function of wavelength for a 5 meter long optical fiber manufactured by the filament-in-tube method of the present invention.

FIG. 5 is a graph showing a refractive index profile of a core clad cane manufactured according to the present invention.

FIG. 6 is a graph showing the loss as a function of wavelength for optical fibers manufactured by the stick-in-tube method of the present invention.

FIG. 7 is a graph showing loss and mode field diameter as a function of fiber length for an optical fiber made according to the present invention.

[Procedure amendment]

[Submission date] July 11, 2001 (2001.7.11)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

Title: Method and apparatus for manufacturing optical fibers

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

FIELD OF THE INVENTION The present invention relates generally to optical fiber waveguides and improvements in their manufacture. More specifically, the present invention relates to a fiberized filament-in-tube (filam
A novel method and apparatus for forming optical fiber waveguides by ent in tube and stick in tube methods.

BACKGROUND optical fiber waveguide of the invention, has become increasingly play an important role in the communication. For application to many different systems, a variety of optical fiber types must be available with respect to dimensions, refractive index profiles, operating wavelengths, materials, and the like. further,
Active devices such as amplifiers, lasers, switches and dispersion compensators are increasingly needed. In addition, the fiber optic cables must be connected to each other without being too difficult to implement. It is important that these connection techniques be readily applicable at the site where the cable connection is made. In many applications, it is particularly important to easily connect a new fiber to a fiber that is already in place. In other words, it is often not an option to remove all existing fibers and replace them with new fibers having different characteristics.

[0003] Various techniques have been used to manufacture optical fibers. In one method (see US Pat. No. 3,659,915), a rod of core material is placed in a tube of low index cladding material to form a tight concentric fit. The core material must be uniform in cross section and have a smooth surface. The temperature is then increased and the rod and tube are drawn to the desired cross-sectional area. The optical fiber obtained by this process will not be ideal for communication due to excessive loss and dispersion.

[0004] Another method (see US Pat. No. 5,651,083) involves inserting a core material into a molten cladding material to form a preform. Insertion of the core occurs quickly so that the core does not soften or melt in the process. Next, the obtained preform is drawn into an optical fiber. ZBLA manufactured in this manner
Fluoride glass such as N cannot be fusion-spliced to silica fiber, easily devitrifies, and has poor durability.

[0005] One of the more important methods used in soot making, which is used to make low loss optical fibers, is a chemical vapor deposition (CVD) process. In one embodiment of the CVD process, a relatively pure chemical (such as silicon tetrachloride) is passed through the manifold with oxygen. They are then mixed and fed into a burner running under a rapidly rotating mandrel or high purity fused silica tube. As a result, silicon is oxidized to silica on a mandrel or silica tube.
The deposit may be doped with various materials. The resulting preform is generally consolidated and then drawn into an optical fiber. This process is an external CVD or OVD process. Internal or MCVD processes are also known CVD processes.

[0006] Current CVD methods for producing optical fibers are limited to compositions consisting almost entirely of silica. Only an appropriate amount of rare earth elements can be contained without forming clusters or crystallization. Volatile components such as alkalis and halogens cannot be easily introduced due to their tendency to evaporate during lay down.
Other important glass modifiers, such as alkaline earths, cannot be included due to the lack of high vapor pressure CVD precursors. Even if the glass soot can be deposited by CVD, it must then be consolidated, which can lead to crystallization and loss of glass components with a high vapor pressure.

Another manufacturing technique, known as the cullet-in-tube method, has recently been developed. This technique is assigned to the assignee of the present invention and is incorporated herein by reference in its entirety.
No. 08 / 944,932, filed Oct. 2, 2014. In the cullet-in-tube process, the core cullet feedstock (generally 100-5,00
Having a particle size in the range of 0 μm) is introduced into the cladding structure. The ends of the core / cladding structure are heated in a furnace to near the softening temperature of the cladding and drawn into an optical fiber. This method overcomes some of the shortcomings of typical CVD processes, allowing the cladding composition to consist of pure SiO ₂ and the core composition to consist of a multi-component glass.

[0008] However, there is a need for a method and apparatus for producing optical fibers from a variety of glass and glass-ceramic compositions that overcomes the shortcomings of known methods and is more practical, efficient and economical than conventional methods. Have been.

As an example, a disadvantage of various prior art CVD techniques is that the compositions that can be produced using current CVD methods are very limited. Only an appropriate amount of rare earth elements can be contained without forming clusters. Volatile components such as alkalis and halogens cannot be introduced in appreciable amounts due to their tendency to evaporate during laydown. Other important glass modifiers, such as alkaline earths, are difficult to include due to the lack of high vapor pressure CVD precursors. Even if the glass soot can be deposited by CVD, it must then be consolidated, which can lead to loss or crystallization of the glass component with the high vapor pressure.

[0010] Disadvantages of the general rod-in-tube technique include the requirement that the core and cladding be very similar. Both the coefficient of expansion and the viscosity temperature profile must be similar, or the final product will crack or break upon cooling.

[0011] The present invention also relates to an optical fiber having a numerical aperture greater than about 0.35. Such fibers that are glass and that comprise a core and cladding region doped with a rare earth element selected from the group consisting of ytterbium, neodymium, and erbium can be used in a fiber laser. Such a fiber laser can be manufactured by coupling a pump source to a high NA fiber. Using the methods disclosed herein, numerical apertures of about 0.40 or greater (eg, 0.45) have been achieved.

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for producing various optical fibers by a fiberized filament-in-tube and stick-in-tube method. In one aspect, the present invention involves filling a glass tube with a glass filament or stick of a desired material, and then drawing or drawing the glass tube at an elevated temperature. The material in the tube melts at the drawing temperature and fills the tube to form a continuous core. The loosely-fitted feedstock can be fed automatically or melt down by gravity to maintain a constant depth of the molten feedstock and produce a homogeneous and reproducible product. The feed may be comprised of a core material or a core / cladding material. Similarly, the tube may have additional core material (eg,
(Which can be used to form the outer core region), core / cladding material, or cladding material. The present invention can be used to draw optical fibers directly (filament-in-tube) or to produce core canes or core clad canes that are subsequently coated with additional material before being drawn into the optical fiber. (Stick-in-tube).

According to the present invention, almost any glass that can be produced by chemical (sol-gel, vapor phase growth, etc.) or physical (batch and melt) techniques can be economically produced in the form of continuous clad filaments. Due to the quenching allowed by this technique,
Glass and glass ceramics, which were previously unstable, can be formed as stable fibers.

A more complete understanding of the present invention, as well as further features and advantages, will be apparent from the following detailed description and the accompanying drawings.

DETAILED DESCRIPTION The present invention provides a method and apparatus for making various optical fibers by the fiberized filament-in-tube and stick-in-tube methods as discussed in more detail below. Before addressing the invention in detail with reference to the drawings, various general aspects and advantages are first generally addressed. First, a glass or crystalline stick of the desired core composition should be obtained. Regardless of whether the stick has a circular, square or triangular or other different cross section, it only needs to fit within the cladding tube to be used therewith. Unlike the known rod-in-tube method, the method of the present invention requires the core to be tightly concentrically fitted into the cladding tube as the core filament melts and conforms to the cladding wall. There is no. Similarly, the lumen of the tube need not be circular, but may be rectangular, elliptical, or any other non-circular shape capable of forming a fiber with a non-circular core. In the present invention, the core glass or stick conforms to the shape of the inner diameter of the tube when a rectangular tube lumen is used, so that the core glass deforms into the shape of the tube, thereby forming a shape during consolidation. Form a rectangular core region. A fiber having a substantially rectangular core can be manufactured by using a tube having a rectangular inner diameter. After drawing the fiber, the core remains substantially rectangular in cross section (the corners of the rectangle are somewhat rounded). Using the method of the present invention disclosed herein, a fiber having a rectangular core was made. These fibers exhibited a numerical aperture (NA) of greater than about 0.35, and in particular achieved a numerical aperture of about 0.45. Such high NA fibers typically have a large amount of modifier required for such refractive index changes, which can cause the core material to crystallize, crack, or sag during manufacture, resulting in CVD Cannot be manufactured using techniques. Such a fiber with a rectangular core can be used to efficiently couple light from a stripe laser diode. For example, a typical high power striped laser diode emits a beam having a substantially 100 μm × 1 μm rectangular geometry. Thus, a beam having this geometry is provided by a fiber formed according to the present invention to have a core geometry substantially similar to that of a laser beam.
Captured more efficiently.

Other non-circular shaped lumens, including elliptical, may be used. These lumens can be used to form polarization maintaining fibers. Similarly, a tube having a non-circular cross-section can be used to produce a non-circular fiber. In each of these embodiments where a non-circular inner or outer diameter is to be maintained, a high drawing speed is preferred to cause the fiber or core cane to at least substantially maintain the inner or outer diameter, or both shapes. . In particular,
In certain preferred embodiments used to produce fibers or core canes having either a non-circular core or non-circular fiber outer diameter, or both, the preform draw rate and temperature are determined by the resulting fiber or The core cane is maintained so as to at least substantially maintain the inner and outer shape of the tube. Such a result is promoted by maintaining the temperature (when producing a core cane) drawing or redrawing, the temperature such that the viscosity of the tube is maintained greater than about 10 ⁷ poises.

The method of the present invention, unlike conventional rod-in-tube technology, does not require that the core stick be uniform in cross section and have a smooth surface.

The core stick can be manufactured by conventional crucible melting and casting, drawing, sol-gel, or some other technique. The stick is then loaded into the cladding tube. The composition of the fiber cladding tube is not limited and is pure SiO ₂
To multi-component glass. The only requirement is that the core glass melt below the softening point of the cladding tube, and the difference in thermal expansion between the core and the cladding is such that the resulting fiber upon cooling can be crushed as detailed below. It is not big.

After the cladding tube has been loaded, it can be drawn down into a cane for the fiber or overcladding. The loading tube is heated to soften the clad glass for elongation. As the cladding tube softens during drawing, the core stick melts and clarifies (bubble removal), conforming to the cladding tube wall and forming an interface determined by the cladding tube inner surface. Outer diameter of tube (O
D) The ratio of inner diameter (ID) to the inner diameter (ID) can be controlled by the pressure (positive or negative) applied to the molten core outside the cladding tube, but will be about the same as the OD / ID ratio of the fiber or cane. The draw temperature can also be used to control the core diameter, as higher draw temperatures result in smaller core diameters for the same given fiber OD. This control represents a substantial advantage over conventional preforms where this ratio is fixed once the blank is manufactured. The higher temperature used to draw the cladding tube (200 for pure SiO ₂ cladding)
0 ° C.) helps to homogenize the core melt and remove harmful water in the glass. In addition, a vacuum may be applied to the centerline to improve water removal and fining.

The use of a centerline opened during the initial drawing process allows atmospheric control of the melt at the drawing temperature. An oxidizing atmosphere as well as a reducing atmosphere can be introduced over the melt to control the redox state of the core material and to maintain the reduced metal core or superconductor in the dielectric cladding. Multiple concentric or balanced cores may also be manufactured by this method, where one core carries optical information and the other carries electrical information. For example, a stress rod (eg, a B ₂ O ₃ -doped SiO ₂ glass rod) can be placed in a lumen opened in the wall of the tube. Such stress rods can be manufactured by CVD, consolidated into glass, and then placed in a lumen opened in the side wall of the tube. Alternatively, the stress rod may be comprised of non-CVD formed glass (eg, molten glass) and may be located within the lumen of the tube sidewall. In each case, after the glass stress rods have been placed within the lumen of the tube sidewall on the opposite side of the tube, the core glass feed is further introduced into the inside diameter of the tube, as described herein. You can supply it. The resulting preform may then be drawn to produce a polarization maintaining fiber. Alternatively, instead of a stress rod, using two conductive wires (also inserted into holes drilled in the side wall of the tube), an electro-optic switch (eg, to change the refractive index of the core) (A voltage can be applied between two wires).

The diameter of the core can also be adjusted by controlling the pressure in the tube above the core. Control of this type of process is not available with any of the current preform fiberization methods, and in the present invention such control greatly facilitates the formation of certain tube and core glass combinations. For example, for thinner tubes, such vacuum assistance may not be important. However, for some tubes with thinner walls, or where the core glass has a greater melting depth within the tube, such a vacuum may be drawn into the tube from above the core glass and applied to the tube wall. Can offset the force of the molten glass pushing outwardly, thereby helping to maintain the internal shape of the tube wall.

A controlled glass composition and thermal history can also be used to generate a gradient index profile. Since the core is melted and the cladding is softened, the diffusion process is relatively fast, so that a gradient index profile can be generated in situ. By proper selection of the cladding material, the manufactured fibers can be fused to conventional fibers, making them very practical in today's fiber networks and facilitating device fabrication.

A complex refractive index profile can be generated by the stick-in-tube method. For example, the first cladding tube may have an index of refraction between the core and over cladding tubes to control the numerical aperture of the fiber, or to manipulate the dispersion and mode field diameter of the fiber. It may include a refractive index moat and a ring inserted into the. Very fine structures can be achieved because the first draw reduces the radial dimension of the refractive index profile by a factor of 6-8 and the second draws their dimension by a further 400-500.

The present invention will be described in more detail with reference to the accompanying drawings. Here, some currently preferred embodiments of the present invention are shown. However, the present invention
It may be embodied in various forms and should not be regarded as limited to the presently preferred embodiments described herein. Rather, Applicants provide these embodiments so that this disclosure will be thorough and complete, and will convey the scope of the invention to those skilled in the art, who can readily apply these teachings to various embodiments and applications. .

For example, while the present invention has been described primarily with reference to optical fiber waveguides, those skilled in the art will recognize that optical products contemplated by the present invention include, but are not limited to, planar amplifiers. , Couplers, fiber lasers, Faraday rotators, filters, optical isolators, and nonlinear waveguide fibers. Further, when considering the production of continuous clad filaments for conductive conduits, superconductive wires are obtained. Electro-optical and photonic crystal compositions are also contemplated.

FIG. 1 is a cross-sectional view of an apparatus 100 suitably used to implement a filament-in-tube method for drawing optical fibers according to the present invention. First, the cladding tube 112, having an outer diameter of 57 mm and an inner diameter of 2 mm in the preferred embodiment, along with the inner wall 118, is purged with a dry gas, for example, chlorine (Cl ₂ ) or chlorine mixed with an inert gas. Removes unwanted moisture. In a preferred embodiment, a core feed or filament 110 having a diameter of 1.5 mm
Place in 112. The feedstock or filament 110 is preferably an elongate monolithic rod of material, but a plurality of elongate rods can be stacked on top of one another in a cladding tube 112 to form a feedstock. The use of multiple rods is particularly well suited for the production of dispersion managed fibers. Clad tube 1
12 and core filament 110 form a filled cladding tube having an open centerline 122 that is heated by furnace 114, as described further below. Furnace 114
It is operated at a draw temperature above the melting temperature of the core filament 110, but only softens the cladding tube 112. As the cladding tube 112 softens, the core filament 110 melts at its drawing temperature and the core melt 12 contained within the cladding tube 112
Form a 0. It is currently preferred that the drawing temperature be equal to or higher than the liquidus temperature of the core filament to remove crystals in the core melt 120. As used herein, melt means that the core filament 110 flows and fills or deforms the inside of the cladding tube 112 such that a filled cladding structure is obtained.

According to one preferred embodiment of the present invention, during the process of core is melted, deformed to the inside of the tubular shape, the core is preferably less than 10 ⁶ poise, more preferably, 1
0 less than ⁴ poise, and most preferably, a viscosity of less than 1000 poise, the cladding structure, clad maintains a sufficient viscosity to substantially maintain its interior shape. Most preferably, the cladding tube 112 exhibits a viscosity greater than 10 ^7.6 poise at this temperature.
This ensures that both the rod and the tube have viscosities that differ by less than about 10 times at the temperature at which the fiber is drawn or the cane is drawn.
A more general method of the prior art where the viscosities of the core and cladding are generally adapted (
For example, the present invention is distinguished from rods and tubes or CVD). Next, the optical fiber 116 is drawn. During melting, the core filament 110 is preferably clarified, conforms to the inner wall 118 of the cladding tube 112, forms an interface defined by the inner wall 118, and completely fills the inside of the cladding tube 112.

The glass clad tube 112 has a viscosity at its softening point of about ^107.6 poise. For some types of SiO ₂ this occurs at a temperature of about 2000 ° C. The cladding material should be selected such that at a temperature at which the core material fills the interior of the cladding tube, it has a viscosity greater than 10 ⁷ poise, preferably greater than 10 ^7.6 poise, and most preferably greater than 10 ⁸ poise. . However, at the same temperature, 69.86 mol% of silica (SiO ₂ ), 18.63 mol% of aluminum oxide (Al ₂ O ₃ ), 4.66 mol% of sodium oxide (Na ₂ O) and 6.85 mol% of fluoride Core 120, such as lanthanum (La ₂ F ₆ ), has a viscosity of about 10 poise, which is seven orders of magnitude smaller than cladding 112. The core 120 may suitably have a viscosity of less than about 10 ^4.5 poise. In contrast, a typical rod-in-tube process generally employs both core and cladding materials having substantially the same viscosity.

One of the important advantages of the present invention is that the core filament 110 can be manufactured by any method (conventional crucible melting and casting, drawing, sol-gel, etc.) into any shape (circle, square, triangle, etc.). It is. The only physical requirement is the core filament
110 fits within the inner wall of the cladding tube 112. Therefore, less versatile process control is not required during the manufacture of the core filament 110. In addition, the bottom is melted to maintain a constant depth of the molten core 120, creating a homogeneous and reproducible optical fiber 116, so that the loosely conforming core filament 110 can be automatically fed down. , Or downward. Core filament 110
Has a melting temperature lower than the softening temperature of the cladding tube 112, as described above, and the difference in thermal expansion between the core filament 110 and the cladding tube 112 is so large that the fiber 116 is crushed when cooled. Absent. The composition of the cladding tube 112 is preferably is a silicate glass, the person skilled in the art, the composition of the cladding tube 112 is not substantially limited, can range from a pure SiO ₂ by multi-component glass It will be understood that this is not a problem.

FIG. 2 is a cross-sectional view of an apparatus 200 that may suitably be used to perform a stick-in-tube method of drawing optical fiber according to the present invention. A one meter long SiO ₂ clad tube 212 (55 mm outer diameter and 6 mm inner diameter) is purged with a drying gas to remove unwanted moisture. A core stick 210 having a diameter of 5 mm is placed in the cladding tube 212 to form a filled cladding tube. Furnace filling clad tube 2
Heat to 1700 ° C. by 14 to soften cladding tube 212 in preparation for elongation. As the cladding tube 212 softens, the core stick 210 melts and then
An optical core cane 216 of m outer diameter is drawn in a standard fashion. As used herein, the term "cane" or "core cane" refers to an optical fiber precursor element that includes a core glass material where additional cladding must be added to the core cane before it is drawn into the optical fiber. Such additional cladding may be applied, for example, by inserting the cane into a glass cladding sleeve, or by depositing additional core and / or cladding glass by external or other methods. . During melting, the core stick 210 is refined and conforms to the inner wall of the cladding tube 212, forming an interface defined by the inner surface of the cladding tube 212.

[0031] In this embodiment, where the core sticks and tubes are first drawn into the core cane, the cladding tube 212 preferably has a drawing temperature (eg,
The silica some form has a viscosity of about 1700 ° C.) to about 10 ⁸ poises, core stick 2
10 has a viscosity of less than about 10 ⁴ poise at its draw temperature.

In the embodiment of the invention shown in FIG. 2, the resulting core cane 216 is then placed in an overclad tube 220. Furnace filling overclad tube 220
Heat by 222 softens the overclad tube 220 in preparation for elongation.
As the overclad tube 220 softens, the cane 216 softens and the optical fiber 224
Is drawn.

In a typical method of forming a fiber using the stick-in-tube process of the present invention, a molar composition of 70.0 SiO ₂ -11.25 Al ₂ O ₃ -7.5 Ta ₂ O ₅ -10
The core glass of CaO-2CaF ₂ -0.05Er ₂ O ₃ batched of high purity powder,
The batch was mixed and calcined at 400 ° C. for 12 hours to dry and then melted at 1650 ° C. for 4 hours in a covered high purity silica crucible. The melt was agitated with a fused silica rod to promote homogeneity, then cooled to 1500 ° C. and drawn up from the melt onto a 4-5 mm diameter stick.

[0034] A 5 mm diameter stick of core glass was then produced using an external process, a 1 meter long 55 mm outer diameter (OD) and a 6 mm inner diameter (I
Inserted into a consolidated SiO ₂ blank with D). The tube was purged with dry He gas to remove unwanted moisture and heated to 1800 ° C. to soften the SiO ₂ blank and draw it down into a 6 mm diameter core / clad cane, Flame cut into metric pieces. Then, a 1 meter long piece is
It mounted on a VD lathe, and overclad with SiO ₂ soot, 32: yield 1 of the desired cladding diameter / core diameter. Then, overclad cane was heated from 1440 ° C to 15 ° C.
Consolidation was performed up to 00 ° C. to form a monolithic SiO ₂ blank with a core. The blank is then placed in a graphite resistance furnace for 1 hour.
It was heated to 950-2000 ° C. and drawn at a speed of 2 m / s into a standard 125 micrometer diameter fiber. The resulting fiber having an Er-doped core is suitable for use as an optical amplifier.

FIG. 3 is a drawing of an apparatus 300 used to overcladd optical canes by an alternative CVD process and draw optical fibers according to the present invention. The cane 216 manufactured according to the embodiment of the present invention shown in FIG. 2 is cut into 1 meter long pieces. Then, the cane 216 cut and mounted on CVD lathe 332, and overclad with SiO _2, to obtain the desired ratio between the diameter of the cladding diameter and the core, to form a overclad optical cane 330. Next, overclad cane 330
Consolidate at a temperature between 1400 ° C. and 1500 ° C. to form a monolithic SiO ₂ blank 336. The end of the monolithic blank 336 is then heated in a furnace 338 to a drawing temperature of 1950-2000 ° C. and an optical fiber 340 having a standard 125 micrometer diameter is used.
Draw a line.

FIG. 4 is a graph 400 illustrating loss as a function of wavelength over a 5 meter range for an optical fiber made according to the present invention. Low loss optical fiber (0.07dB at 1310nm)
/ M) show the same loss per meter from start to finish over a range of 2000 meters. The core of this optical fiber was successfully doped with erbium ions, Ef ³⁺ , as evidenced by absorption hands at 980 and 1500 nm. Furthermore, when 980 nm laser light was pumped into the fiber, Er ³⁺ fluorescence was observed from the optical fiber. FIG. 4 shows that 2d by using the method of the present invention.
It shows that fibers exhibiting a background attenuation of less than B / m can be manufactured with rare earth dopants therein.

FIG. 5 is a graph showing the refractive index profile of a core cane made according to the present invention using the core glass composition described above with respect to FIG. Core cane is 2.74
The core of the cane has a diameter of 0.21 mm and a core / cladding thickness ratio of about 0.077. As can be seen from FIG. 5, this core exhibited a refractive index delta of about 0.11 (for the silica core), or about 6.76 percent (for the undoped silica cladding). Observed
The maximum delta of 6.76 percent is significantly higher than that seen for typical CVD manufactured fibers. The cane was then overclad and drawn into a 10,000 m homogeneous optical fiber. The total core diameter square deviation over a total length of 10,000 m was ± 0.25 μm, as compared to the cullet-in-tube method, which produced a square deviation of ± 4 μm. Thus, fibers made according to the present invention exhibit at least an order of magnitude improvement. Further, SiO _{2 is} used as a cladding material.
By using, the obtained optical fiber can be fusion-spliced using a conventional fusion splicer. When splicing a fiber made according to the present invention to an SMF-28 optical fiber, a fusion loss of less than 0.5 dB is achieved, and
When fused to an S-980 optical fiber, the fusion loss was less than 0.2 dB.

FIG. 6 is a graph 600 showing the loss as a function of wavelength over a 5 meter range for an optical fiber made according to the present invention. By depositing pure silica followed by germania-doped silica, followed by pure silica cladding regions
Tubes were manufactured. The soot preform obtained was consolidated to form a tube. A core glass rod of the same type as described above with respect to FIG. 2 was then inserted into the glass tube and drawn into the fiber. In this case, the resulting multi-component core consisted of a central high refractive index region surrounded by silica moat, which was surrounded by a ring of SiO ₂ doped with germanium oxide (GeO ₂ ). This shows that complex refractive index profiles with background attenuation of less than 0.5 dB / m can be created.

FIG. 7 is a graph 700 showing loss and mode field diameter as a function of fiber length for optical fibers made according to the present invention. FIG. 7 expands the mode field diameter by using an increased index ring outside the central high index region of the core, thereby reducing the mode field diameter to one core with the increased index. It shows that it can be expanded beyond what would be achieved by use. As shown by FIG. 7, losses for various lengths and minimum square deviations in mode field diameter are achieved.

The method of the present invention has various advantages. The method of the present invention greatly expands the composition range of fiberization that has not previously been achieved by conventional CVD techniques that have been used to manufacture optical fibers. With a new composition having high rare earth solubility,
Improved gain flatness and improved optical properties can be easily manufactured in fiber form. The method of the present invention accommodates large differences in thermal expansion between core filament 110 or core stick 210 and cladding tube 112 or cladding tube 212. This is because if the stress due to thermal expansion mismatch is much smaller than in a larger sized rigid monolithic preform, the core filament 110 or core stick 210 will be in a fiber or cane form until the core filament 110 or core stick 210 is in the form of a fiber or cane.
This is because 110, 210 is not tightly coupled to claddings 112, 212, and these stresses vary inversely with the square of the radius of the fiber, preform, or the like. Thus, a large number of apertured fibers used as efficient couplers and lasers can be manufactured by the method of the present invention.

The method of the present invention allows atmospheric control of the core melts 120, 220 at the drawing temperature. An open centerline may be used to control the redox state, and any of an oxidizing, reducing or chemically reactive atmosphere may be introduced. The diameter of the core can be adjusted by controlling the pressure on the core filament 110 or core stick 210, as allowed by the drawing temperature. The higher the draw temperature, the smaller the core diameter for the same given fiber outer diameter (OD), which is in contrast to conventional preforms where this ratio is fixed once the blank is manufactured. It is. For example, these elements can be used to adjust the core diameter by ± 50% using the present invention. As described above, the ratio of OD to inner diameter (ID) is
It can be controlled by the positive or negative pressure applied to the molten cores 120, 220 with respect to the cladding tube 112 or the cladding tube 212, but it is almost the same as the ratio of OD to ID of the optical fiber. Further, the high temperatures used to draw the optical fibers 116, 216
It serves to homogenize the core melts 120, 220 and release harmful moisture present in the core melts 120, 220.

While the above description includes details that enable one of ordinary skill in the art to practice the invention, such description is indeed illustrative, and many modifications and changes will be made to the benefit of these teachings. It will be apparent to those skilled in the art that As an example,
While it is presently preferred that the core feed, such as the core feed 110, be a solid rod, the core feed can be hollow or divided into several large blocks. In addition, the term feedstock refers to a thin filament, a thick stick, a plurality of elongated filaments bundled for insertion into a tube, or an axial direction for insertion into a tube, which is suitably fed down during melting. It is intended to include an elongate filament or stick or the like with one over the other. On the other hand, the feedstock as defined herein is preferably neither a powder nor a cullet. Further, the feedstock can be formed from the core material alone or from the core material with the cladding material disposed thereon. Any of these embodiments may then be placed in a tube formed from the cladding material. Similarly, the tube may be formed from a core or cladding material. Thus, it is also conceivable to produce a preform having a plurality of concentric rings of core and cladding material, each having the same or different optical properties as the other rings in the preform. Further, although not presently preferred, the preform may be formed, cooled, stored, and then subsequently reheated and drawn. Further, the term optical fiber includes any fiber or fiber component used in applications including, but not limited to, optical waveguides, single mode fibers, multimode fibers, amplifiers, electro-optic fibers, couplers, lasers, etc. Should be interpreted as

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a suitable apparatus for performing a filament-in-tube method for drawing an optical fiber according to the present invention.

FIG. 2 is a cross-sectional view of a suitable apparatus for performing a stick-in-tube method for drawing optical fibers according to the present invention.

FIG. 3 shows a suitable device for coating an optical cane formed according to the invention, which will be drawn into an optical fiber according to the invention.

FIG. 4 is a graph showing the loss as a function of wavelength for a 5 meter long optical fiber manufactured by the filament-in-tube method of the present invention.

FIG. 5 is a graph showing a refractive index profile of a core clad cane manufactured according to the present invention.

FIG. 6 is a graph showing the loss as a function of wavelength for optical fibers manufactured by the stick-in-tube method of the present invention.

FIG. 7 is a graph showing loss and mode field diameter as a function of fiber length for an optical fiber made according to the present invention.

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──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GE, GH, GM , HR, HU, ID, IL, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, UZ, VN, Y U, ZW (72) Inventor Digineca, Matthew Jay United States 14830 Corning Ellison Road, New York 2378 (72) Inventor Soloski, John W. United States of America New York 14840 Hammondsport Route 54 8488 Bee (72) Inventor Wilson, Otis El Jr. United States of America New York 14845 Lindley Liberty Paul Road 115 (72) Inventor Jost, Kevin Jay United States of America New York 14870 Painted Post Victory Highway 561 F-term (reference) 4G021 BA00

Claims (2)

[Claims] 1. A method of manufacturing an optical fiber, comprising: positioning a solid, elongated feedstock in a hollow tube; deforming the tube and at least a portion of the feedstock into the shape of the tube. Heating to a temperature sufficient to reduce the outer diameter of the tube, wherein the feedstock has a softening point less than the softening point of the tube. 2. The method according to claim 1, wherein said tube has a clad structure.