Description:TECHNICAL FIELD
The present disclosure relates to the field of optical fibers and, in particular, relates to an optical fiber drawing apparatus and a method thereof.

BACKGROUND
Optical fibers are usually drawn from a glass preform (a cylindrical blank made up of glass). Currently, multiple glass preforms are joined together using oxy hydrogen or propane burner to form a large size glass preform and drawn in a draw furnace. If the multiple glass preforms are not joined together, there is an increase in time during the optical fiber drawing process generally because of a preform changeover time. The preform changeover time involves removing the glass preform, cleaning the draw furnace, inserting new glass preform. To reduce the steps of drawing the optical fiber, the preforms are joined together. Conventional techniques face major problem during drawing of this large size glass preform i.e., multiple joined glass preforms. Whenever the large size glass preform is drawn, there is sudden increase in bare fiber diameter near the preform joint between two adjacent preforms. This stuck the die that controls the coating diameter of the optical fiber and the optical fiber breaks. This sudden change in bare fiber diameter near the preform joint is due to the presence of high concentration of hydroxyl ion (OH) diffused during glass joining process and significantly alter the glass properties such as viscosity, stress, attenuation, etc. One of the techniques to manufacture a large sized preform is described in US20220286204A1. The reference discloses stacking of multiple rods inside cladding tubes which is done using a generic rod in cylinder (RIC) process. Another reference US7641969B2 discloses assembling of the optical fiber preform by inserting core rod segments axially end to end inside of a first glass overclad tube. Prior techniques require multiple clad tubes or a single tube, which is costly, in which core rods are inserted to achieve the required optical performance (such as attenuation, waveguide parameters) of the optical fiber. By stacking of core rods in one or more clad tubes in prior methods limits the overall size of the preform and the overall length of the fiber which can be drawn continuously without break during the draw process. When core rods or glass rods having lower value of ratio of clad portion diameter (D) to the core portion diameter (d) (D/d) are stacked in one or more tubes, there is very high chances of diffusion of impurities in the core regions and subsequently an increase in concentration of OH ions.
In light of the above stated discussion, there is a need for an efficient and effective way to manufacture a large-sized preform which overcomes the above stated disadvantages.

SUMMARY
In an aspect of the present disclosure, a method for drawing an optical fiber is disclosed. The method has a step of stacking at least two glass sub-preforms of a plurality of glass sub-preforms inside a hollow cylindrical glass tube to form a master glass preform such that the master glass preform comprises a top end and a bottom end, Each of the at least two glass sub-preforms is defined by a first end and a second end, where the first end of a successive glass sub-preform is stacked on the second end of a previous glass sub-preform such that the successive glass sub-preform rests on the previous glass sub-preform. The method further has a step of melting the bottom end of the master glass preform in a furnace to draw an optical fiber, where a temperature of the furnace is at least 16500 C, where the optical fiber is drawn continuously.

BRIEF DESCRIPTION OF DRAWINGS
Having thus described the disclosure in general terms, reference will now be made to the accompanying figures, wherein:
FIG. 1 illustrates a schematic view of an optical fiber drawing apparatus.
FIG. 2 illustrates a flowchart that depicts a method for manufacturing a glass sub-preform.
FIG. 3 illustrates a flowchart that depicts a method for drawing the optical fiber.
FIG. 4 illustrates a cross-sectional view of the optical fiber.
FIG.5 illustrates an exemplary representation of the relative refractive index profile.
It should be noted that the accompanying figures are intended to present illustrations of exemplary embodiments of the present disclosure. These figures are not intended to limit the scope of the present disclosure. It should also be noted that accompanying figures are not necessarily drawn to scale.
DEFINITIONS
The term “optical fiber” as used herein refers to a light guide medium that provides high-speed data transmission. The light moving through the glass core region of the optical fiber relies upon the principle of total internal reflection, where the glass core region has a higher refractive index (n1) than the refractive index (n2) of the cladding region of the optical fiber.
The term “draw, drawing, drawn” with context to the optical fiber as used herein refers to obtainment of the optical fiber from a multi-layer, pure glass cylinder, called as a glass preform. The glass preform is hung at a top end of a furnace and inserted inside the furnace at a predefined preform feed speed. Further, the glass preform is melted until the glass flows under a low pulling tension. A draw capstan pulls the optical fiber from the bottom of the glass preform in the furnace, while the glass preform feed drive above the furnace maintains material flow equilibrium through the furnace. The glass fiber is cooled, coated in protective polymers, cured under ultraviolet lights, and wound onto spools.
The term “glass preform” as used herein refers to a rod/solid body of glass that is melted and drawn to form an optical fiber. The cylindrical glass preform is designed to have the desired refractive index profile for the optical fiber.

DETAILED DESCRIPTION
The detailed description of the appended drawings is intended as a description of the currently preferred aspects of the present disclosure, and is not intended to represent the only form in which the present disclosure may be practiced. It is to be understood that the same or equivalent functions may be accomplished by different aspects that are intended to be encompassed within the spirit and scope of the present disclosure.
Moreover, although the following description contains many specifics for the purposes of illustration, anyone skilled in the art will appreciate that many variations and/or alterations to said details are within the scope of the present technology. Similarly, although many of the features of the present technology are described in terms of each other, or in conjunction with each other, one skilled in the art will appreciate that many of these features can be provided independently of other features. Accordingly, this description of the present technology is set forth without any loss of generality to, and without imposing limitations upon, the present technology.
FIG. 1 illustrates a schematic view of an optical fiber drawing apparatus 100 (hereinafter referred to as “the apparatus 100”). The apparatus 100 may be adapted to facilitate drawing of long length (in kilometers) optical fiber i.e., an optical fiber 101 in an online process and in an offline process. The optical fiber 101 that may be drawn from the apparatus 100 such that the optical fiber 101 may be in compliance to ITU standard. Specifically, the apparatus 100 may be adapted to manufacture a large sized glass preform that may be formed in both the online process and the offline process. In the online process, the large sized glass preform may be formed in a draw furnace and in an immediate subsequent step, the optical fiber 101 may be drawn from the large sized glass preform. Specifically, a complete volume of the large sized glass preform may be drawn without any break in the optical fiber. In the offline process, the large sized glass preform may be formed in a separate furnace and then the large sized glass preform may be transferred in the draw furnace for drawing the optical fiber.
In some aspects of the present disclosure, the optical fiber 101 may have an outer glass diameter that may be in a range between 60 microns (µm) and 125 µm with a tolerance value of + 0.7 µm.
The apparatus 100 may have a vacuum pump 102, a holding tube 104, a spacer plate 106, a hollow cylindrical glass tube 108, a furnace 110, and a handle holder 112. The hollow cylindrical glass tube 108 may have a plurality of glass sub-preforms 114a-114n (hereinafter collectively referred to and designated as “the glass sub-preforms 114”). The furnace 110 may have a first opening 118, a second opening 120, a pair of induction coils 122a and 122b (hereinafter collectively referred to and designated as “the induction coils 122”), a susceptor 124, and a collapsed region 125.
The vacuum pump 102 may be disposed at an upper side of the apparatus 100. Specifically, the vacuum pump 102 may be disposed at an upper side of the hollow cylindrical glass tube 108. The vacuum pump 102 may be adapted to create vacuum in the hollow cylindrical glass tube 108 from the upper side of the hollow cylindrical glass tube 108.
The holding tube 104 is used to hold the core rods and spacer plate in place under the application of vacuum. If holding tube is not there, then there is chances that the core rods will move up under application of vacuum.
The spacer plate 106 may be disposed between the holding tube 104 and one of the glass sub-preforms 114. The spacer plate 106 has a plurality of grooves and is placed over the hollow cylindrical tube and glass sub-preforms 114. This plate act as air passage to suck the air present between core rods and sub preforms.
The handle holder 112 may be used to lift the entire assembly (i.e., master glass preform assembly 116) and insert it inside furnace 110 vertically.
The hollow cylindrical glass tube 108 may hold the glass sub-preforms 114. In other words, the glass sub-preforms 114 may be inserted in the hollow cylindrical glass tube 108.
Each glass sub-preform of the glass sub-preforms 114 may have a first end 126 and a second end 128. The glass sub-preforms 114 may be stacked on one above the other to form a master glass preform 130. Specifically, the glass sub-preforms 114 and the hollow cylindrical glass tube 108 may together form a master glass preform assembly 116. The master glass preform 130 may have a top end 132 and a bottom end 134. The top end 132 may be positioned near to the upper side of the hollow cylindrical glass tube 108. The bottom end 134 may be positioned near to a lower side of the hollow cylindrical glass tube 108. Specifically, the first end 126 of a successive glass sub-preform of the glass sub-preforms 114 may be stacked on the second end 128 of a previous glass sub-preform of the glass sub-preforms 114 such that the successive glass sub-preform of the glass sub-preforms 114 rests on the previous glass sub-preform of the glass sub-preforms 114. The term “successive” as used herein context of the glass sub-preform refers to a glass sub-preform that lies on above side in the hollow cylindrical glass tube 108 and away from the furnace 110. The term “previous” as used herein context of the glass sub-preform refers to a glass sub-preform that lies on below side in the hollow cylindrical glass tube 108 and near to the furnace 110. For example, the first end 126 of the glass sub-preform 114a of the glass sub-preforms 114 may be stacked on the second end 128 of the glass sub-preform 114b of the glass sub-preforms 114 such that the glass sub-preform 114a of the glass sub-preforms 114 rests on the glass sub-preform 114b of the glass sub-preforms 114.
In some aspects of the present disclosure, each glass sub-preform of the glass sub-preforms 114 may be made up of a type 3 silica material. The type 3 silica material may be produced by burning SiCl4 in a hydrogen-oxygen flame. Aspects of the present disclosure are intended to include and/or otherwise cover any type of known and later developed material for each glass sub-preform of the glass sub-preforms 114, without deviating from the scope of the present disclosure.
In some aspects of the present disclosure, a mating portion at the second end 128 of the previous glass sub-preform and the first end 126 of the successive glass sub-preform has negligible hydroxide (OH) ion. In other words, the mating portion at the second end 128 of the previous glass sub-preform and the first end 126 of the successive glass sub-preform has a hydroxide (OH) infusion of less than or equal to 1 parts per million (ppm). For example, the mating portion at the second end 128 of the glass sub-preform 114b of the glass sub-preforms 114 and the first end 126 of the glass sub-preform 114a of the glass sub-preforms 114 has negligible hydroxide (OH) ion.
In some aspects of the present disclosure, the second end 128 of the previous glass sub-preform and the first end 126 of the successive glass sub-preform are of a flat circular shape.
In some aspects of the present disclosure, the hollow cylindrical glass tube 108 may be made up of a type 2 silica material or a type 2 quartz material. In some aspects of the present disclosure, the hollow cylindrical glass tube 108 may be made up of a type 1 silica material or a type 1 quartz material. The type 2 silica and/or type 1 silica material may be a low-quality silica material that may act as an outer cladding. Since, the type 2 silica and/or type 1 silica material is the low-quality silica material, therefore, cost for manufacturing the hollow cylindrical glass tube 108 may be advantageously reduced and overall glass volume may be advantageously increased. The type 2 silica and type 1 silica material may be produced by fusing quartz crystal powder in a high temperature flame.
The hollow cylindrical glass tube 108 may have very less thickness that negligibly affects optical properties of the glass sub-preforms 114. Aspects of the present disclosure are intended to include and/or otherwise cover any type of known and later developed material for the hollow cylindrical glass tube 108, without deviating from the scope of the present disclosure.
The hollow cylindrical glass tube 108 may be inserted into the furnace 110. Specifically, the bottom end 134 may be inserted into the collapsed region 125 through the first opening 118 of the furnace 110.
In some aspects of the present disclosure, each glass sub-preform of the glass sub-preforms 114 may have a solid cylindrical shape. Each glass sub-preform of the glass sub-preforms 114 may have a glass cladding formed of one or more cladding layers and one or more glass cores. The glass cladding of each glass sub-preform may have a clad diameter (D) and the glass core of each glass sub-preform may have a core diameter (d) such that a ratio of the clad diameter (D) to the core diameter (d) may be greater than 8. Specifically, the ratio of the clad diameter (D) to the core diameter (d) may be kept greater than 8 to prevent reaching of impurities up to the core that may be diffused in the clad. The one or more glass cores and the one or more glass cladding may be made up of silica with less than 0.1% metallic impurity.
In some aspects of the present disclosure, the clad diameter (D) may be in a range between 65 mm and 175 mm.
In some aspects of the present disclosure, each glass sub-preform of the glass sub-preforms 114 may have a preform length that may be in a range between 1 meter (m) and 3 m.
In some aspects of the present disclosure, the hollow cylindrical glass tube 108 may have a tube length (L1) that may be in a range between 5 m and 10 m. The hollow cylindrical glass tube 108 may have an outer diameter (D1) that may be in a range between 100 millimeters (mm) and 200 mm. The hollow cylindrical glass tube 108 may have an inner diameter (D2) that may be in a range between 70 mm and 180 mm. Aspects of the present disclosure are intended to include and/or otherwise cover any value of the tube length (L1), the outer diameter (D1), the inner diameter (D2).
In some aspects of the present disclosure, the hollow cylindrical glass tube 108 may have a glass cladding (i.e., secondary clad). The hollow cylindrical glass tube 108 may be made up of a silica material with greater than 0.1% of metallic impurity.
The furnace 110 may be disposed below the hollow cylindrical glass tube 108. The first opening 118 may be disposed above the second opening 120 such that the first opening 118 aligns with the second opening 120. The collapsed region 125 may lie within the first opening 118. The induction coils 122 may be disposed near to the first opening 118. The susceptor 124 may extend from the first opening 118 to the second opening 120. The furnace 110 may be adapted to melt the bottom end 134 of the master glass preform 130. Specifically, the induction coils 122 of the furnace 110 may be adapted to produce heat in the furnace. The induction coils 122 may be adapted to provide induction heating to the bottom end 134 of the master glass preform 130. The susceptor 124 may facilitate proper heating of the bottom end 134 of the master glass preform 130. In some aspects of the present disclosure, the at least two glass sub-preforms of the plurality of glass sub-preforms 114 and the hollow cylindrical glass tube 108 which forms the master glass preform assembly 116 may be collapsed in the furnace 110 to form the master glass preform 130. Specifically, the master glass preform assembly 116 may be collapsed in the collapsed region 125 of the furnace. The collapsing may facilitate fusion/binding of the at least two glass sub-preforms of the glass sub-preforms 114. Specifically, the bottom end 134 of the master glass preform 130 may be collapsed in the collapsed region 125 while the induction coils 122 melts the bottom end 134. The collapsing of the bottom end 134 may be facilitated by virtue of creation of vacuum inside the hollow cylindrical glass tube 108 through the vacuum pump 102. The collapsing may be accelerated by the vacuum inside the hollow cylindrical glass tube. The bottom end 134 of the cylindrical glass tube 108 may be converted into a conical shape so that the glass sub-preforms rests near the conical shape of the cylindrical glass tube 108. The optical fiber 101 may be continuously drawn from the bottom end 134 upon heating the bottom end 134. The optical fiber 101 may be continuously drawn out from the second opening 120 of the furnace 110. Upon drawing the optical fiber 101 from the second opening 120, the optical fiber 101 may be cured by ultra-violet radiation (UV radiation). Specifically, the optical fiber 101 with coatings may be cured by a UV curing system. The UV curing system may use UV radiation to cure one or more coatings and color codes on the optical fiber 101 to protect the optical fiber 101 from cracking. Thus, the UV curing system may advantageously make the optical fiber 101 resistant to abrasion and scratches. Upon curing, the optical fiber 101 may be winded on a take-up spool.
In some aspects of the present disclosure, the first and second openings 118 and 120 may have a cylindrical shape. Aspects of the present disclosure are intended to include and/or otherwise cover the first and second openings 118 of any shape, without deviating from the scope of the present disclosure.
In some aspects of the present disclosure, the first and second openings 118 and 120 may have irises that may be adapted to change a diameter of the first and second openings 118 and 120.
In some aspects of the present disclosure, each induction coil of the induction coils 122 may be a high-voltage electric element.
In some aspects of the present disclosure, the susceptor 124 may be made up of a material, including but not limited to, graphite. Aspects of the present disclosure are intended to include and/or otherwise cover any type of known and later developed material, without deviating from the scope of the present disclosure.
In some aspects of the present disclosure, the furnace 110 may be kept at a temperature that may be in a range between 15000 C and 18000 C. In some aspects of the present disclosure, the furnace 110 may be kept at a temperature that may be 16500 C. In some other aspects of the present disclosure, the furnace 110 may be kept at a temperature above than 1900 0 C, where the bottom end 134 may be softened and elongated with a teardrop-shaped drip. This teardrop-shaped drip may be pulled to draw the optical fiber 101 from the second opening 120 of the furnace 110.
FIG. 2 illustrates a flowchart that depicts a method 200 for manufacturing a glass sub-preform. Specifically, FIG. 2 illustrates the method 200 for manufacturing of one of the glass sub-preform of the glass sub-preforms 114. Each glass sub-preform of the glass sub-preforms 114 may be manufactured without welding. The method 200 may include following steps for manufacturing of one of the glass sub-preform of the glass sub-preforms 114.
At step 202, a core rod soot i.e., a silica soot may be manufactured. Specifically, the core rod soot may be manufactured through one of, outside vapor deposition (OVD) technique, vapor axial deposition (VAD), modified chemical vapor deposition (MCVD), and the like. During manufacturing of the core rod soot by the OVD technique in an OVD machine, silica vapors may be deposited over a rotating mandrel. In some aspects of the present disclosure, the silica vapors may have a plurality of dopants. Aspects of the present disclosure are intended to include and/or otherwise cover any type of technique for manufacturing of the core rod soot.
At step 204, one or more core rods (hereinafter collectively referred to as “the core rods”) may be manufactured from the core rod soot. Specifically, the core rod soot may be sintered and soaked to manufacture the core rods. Upon deposition of the silica vapors on the rotating mandrel, the rotating mandrel may be pulled out from the OVD machine such that the deposited silica vapors may be sintered and collapsed in a sintering furnace and soaked in a soaking furnace. The soaked silica glass may be drawn into the core rods in a draw furnace.
At step 206, each core rod of the core rods may be deposited with a cladding layer (i.e., primary clad) to form a soot preform. Specifically, each core rod of the core rods may be deposited with the cladding layer of the silica soot. Each core rod of the core rods may be deposited by way of an outside vapor deposition (OVD) technique to form the soot preform.
At step 208, the soot preform may be sintered in a sintering furnace. Specifically, the soot preform may be sintered in the sintering furnace to manufacture each glass sub-preform of the glass sub-preforms 114.
At step 210, instead of the steps 206 and 208, the core rods may be inserted and stacked inside one or more cladding tubes to form the glass sub-preforms 114. The glass sub-preforms 114 and the hollow cylindrical glass tube 108 may together form the master glass preform assembly 116. Each cladding tube of the one or more cladding tubes may be a primary clad silica tube.
At step 212, after step 210 i.e., upon the core rods being inserted inside the one or more cladding tubes, the glass sub-preform assembly 116 may be collapsed to form each glass sub-preform of the glass sub-preforms 114. Specifically, upon collapsing, each glass sub-preform of the glass sub-preforms 114 may be formed. Each glass sub-preform of the glass sub-preforms 114 may be formed such that a core rod of the core rods may be surrounded by the primary clad. The glass sub-preforms 114 may then be inserted into the hollow cylindrical glass tube 108 to form the master glass preform 130.
The method 200 as described hereinabove may be used to manufacture any number of glass sub-preforms i.e., the method 200 may be used to manufacture the glass sub-preforms 114.
FIG. 3 illustrates a flowchart that depicts a method 300 for drawing the optical fiber 101. The method 300 may include following steps to draw the optical fiber 101.
At step 302, the apparatus 100, by way of the hollow cylindrical glass tube 108, may be adapted to hold the glass sub-preforms 114. In other words, glass sub-preforms 114 may be inserted in the hollow cylindrical glass tube 108. The glass sub-preforms 114 may be stacked on one above the other to form the master glass preform 130. The top end 132 may be positioned near to the upper side of the hollow cylindrical glass tube 108. The bottom end 134 may be positioned near to a lower side of the hollow cylindrical glass tube 108. Specifically, the first end 126 of a successive glass sub-preform of the glass sub-preforms 114 may be stacked on the second end 128 of a previous glass sub-preform of the glass sub-preforms 114 such that the successive glass sub-preform of the glass sub-preforms 114 rests on the previous glass sub-preform of the glass sub-preforms 114. The term “successive” as used herein context of the glass sub-preform refers to a glass sub-preform that lies on above side in the hollow cylindrical glass tube 108 and away from the furnace 110. The term “previous” as used herein context of the glass sub-preform refers to a glass sub-preform that lies on below side in the hollow cylindrical glass tube 108 and near to the furnace 110.
At step 304, the apparatus 100, by way of the furnace 110, the bottom end 134 may be collapsed online. In other words, the bottom end 134 may be melted. The apparatus 100, by way of the furnace 110, may be adapted to perform online collapsing of the bottom end 134 of the master glass preform 130. Specifically, the induction coils 122 of the furnace 110 may be adapted to produce heat in the furnace. The induction coils 122 may be adapted to provide induction heating to the bottom end 134 of the master glass preform 130. The susceptor 124 may facilitate proper heating of the bottom end 134 of the master glass preform 130. The master glass preform assembly 116 may be collapsed in the collapsed region 125 of the furnace. Specifically, the bottom end 134 of the master glass preform 130 may be collapsed in the collapsed region 125 while the induction coils 122 melts the bottom end 134. The collapsing of the bottom end 134 may be facilitated by virtue of creation of vacuum inside the hollow cylindrical glass tube 108 through the vacuum pump 102.
At step 306, instead of the step 304, the bottom end 134 of the master glass preform 130 may be collapsed offline. The master glass preform 130 may have a core, a primary clad, and a secondary clad.
At step 308, the optical fiber 101 may be continuously drawn from the bottom end 134 upon heating the bottom end 134. The optical fiber 101 may be drawn with type 1 primary clad and type 2 secondary clad.
FIG. 4 illustrates a cross-sectional view of the optical fiber 101. The optical fiber 101 may have a core region 402, a primary cladding region 404, a secondary cladding region 406. The core region 402 may have a core radius that may be in a range between 4 µm and 5 µm. The primary cladding region 404 may have a primary cladding radius that may be in a range between 30 µm and 55 µm. The secondary cladding region 406 may have a secondary cladding radius that may be in a range between 40 µm and 63 µm.
In some aspects of the present disclosure, the core region 402 may be formed from a material, including but not limited to, un-doped silica, co-doped silica, and up-doped silica. Aspects of the present disclosure are intended to include and/or otherwise cover any type of known and later developed materials for the core region 402, without deviating from the scope of the present disclosure.
In some aspects of the present disclosure, the primary cladding region 404 may have at least two cladding layers 408 and 410. The at least two cladding layers 408 and 410 may be formed of a silica material such that at least one of the at least two cladding layers 408 and 410 may be one of, (i) up-doped, (ii) down-doped, and (iii) un-doped.
FIG.5 illustrates an exemplary representation of the relative refractive index profile 500. Specifically, FIG. 5 illustrates the exemplary representation of the refractive index profile 500 of the optical fiber 101. The relative refractive index profile 500 may have first through third relative refractive index profiles 502, 504, and 506, respectively. Specifically, the first relative refractive index profile 502 may correspond to the relative refractive index profile of the optical fiber 101 such that the core region 402 may be an up-doped region and the primary and secondary cladding regions 404 and 406 may be down-doped regions. The second relative refractive index profile 504 may correspond to the relative refractive index profile of the optical fiber 101 such that the core region 402 may be an un-doped silica region (i.e., the core region 402 may be manufactured from the pure silica) and the primary and secondary cladding regions 404 and 406 may be the down-doped regions. The third relative refractive index profile 506 may correspond to the relative refractive index profile of the optical fiber 101 such that the core region 402 may be a co-doped region and the primary and secondary cladding regions 404 and 406 may be the down-doped regions.
In some aspects of the present disclosure, the relative refractive index profile 500 may have an abrupt jump 508 (i.e., an abrupt change 508) in a relative refractive index of the relative refractive index profile 500. Specifically, the relative refractive index profile 500 may have the abrupt jump 508 in the relative refractive index at an interface 505 of the primary cladding region 404 and the secondary cladding region 406. The abrupt jump in the relative refractive index at the interface 505 may be defined as an increase or decrease (i.e., a discontinuity in the relative refractive index profile with respect to the adjacent cladding regions 404 and 406) in relative refractive index with respect to pure silica. The relative refractive index at the interface 505 may be in a range of -0.05% to 0.05%. In some aspects of the present disclosure, the relative refractive index at the interface 505 is greater than a relative refractive index of the secondary cladding region 406. In some aspects of the present disclosure, the relative refractive index at the interface 505 is less than a relative refractive index of the secondary cladding region 406. In some aspects of the present disclosure, the relative refractive index at the interface 505 is greater than a relative refractive index of the primary cladding region 404. In some aspects of the present disclosure, the relative refractive index at the interface 505 is less than a relative refractive index of the primary cladding region 404.
In some aspects of the present disclosure, the relative refractive index profile 500 may have a cladding relative refractive index profile. Specifically, the primary cladding region 404 may have the cladding relative refractive index profile. The cladding relative refractive index profile may have at least one down doped region that may be disposed on one of, (i) an inner region and (ii) an outer region. Aspects of the present disclosure are intended to include and/or otherwise cover drawing of the optical fiber 101 having any type of relative refractive index profile 500.
Thus, the apparatus 100 may facilitate increase in production volume and reduction in cost because of multiple preforms loaded together without any time spent on welding and cooling the joint. In other words, by virtue of stacking of the glass sub-preforms 114, there is no need for welding and cooling the joint of the multiple preforms. This increases the production volume and reduces the cost and time. The apparatus 100 may facilitate to save changeover time and furnace ramping up and ramping down time. The apparatus 100 may facilitate stacking of the glass sub-preforms 114 such that the mating portion at the second end 128 of the previous glass sub-preform and the first end 126 of the successive glass sub-preform has negligible hydroxide (OH) ion. In some aspects of the present disclosure, the mating portion at the second end 128 of the previous glass sub-preform and the first end 126 of the successive glass sub-preform has hydroxide (OH) ion less than 1 ppm. The apparatus 100 require a low-quality clad tube i.e., the hollow cylindrical glass tube 108 which saves huge production costs.
The foregoing descriptions of specific embodiments of the present technology have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present technology to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present technology and its practical application, to thereby enable others skilled in the art to best utilize the present technology and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present technology.
While several possible embodiments of the invention have been described above and illustrated in some cases, it should be interpreted and understood as to have been presented only by way of illustration and example, but not by limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments.
, Claims:We Claim(s):
1. A method (300) for drawing an optical fiber (101), the method (300) comprising:
stacking (302) at least two glass sub-preforms of a plurality of glass sub-preforms (114a-114n) inside a hollow cylindrical glass tube (108) to form a master glass preform (130) such that the master glass preform (130) comprises a top end (132) and a bottom end (134), where each of the at least two glass sub-preforms is defined by a first end (126) and a second end (128), where the first end (126) of a successive glass sub-preform is stacked on the second end (128) of a previous glass sub-preform such that the successive glass sub-preform rests on the previous glass sub-preform; and
melting (304) the bottom end (134) of the master glass preform (130) in a furnace (110) to draw an optical fiber (101), where a temperature of the furnace (110) is at least 16500 C, where the optical fiber (101) is drawn continuously.

2. The method (300) of claim 1, where each of the at least two glass sub-preforms has a solid cylindrical shape such that each of the at least two glass sub-preforms has a clad diameter (D) and a core diameter (d), where a ratio of the clad diameter (D) to the core diameter (d) is greater than 8.

3. The method (300) of claim 1, where the hollow cylindrical glass tube (108) is made up of a silica material with greater than 0.1% of metallic impurity and one or more glass core and one or more glass cladding is made of silica with less than 0.1% metallic impurity.

4. The method (300) of claim 1, where the hollow cylindrical glass tube (108) is made up of a type 2 silica material and each of the at least two glass sub-preforms is made up of a type 3 silica material.

5. The method (300) of claim 1, where for forming the master glass preform (130), the method comprising collapsing the at least two glass sub-preforms of the plurality of glass sub-preforms (114a-114n) and the hollow cylindrical glass tube (108) in the furnace (110).

6. The method (300) of claim 1, where a mating portion at the second end (128) of the previous glass sub-preform and the first end (126) of the successive glass sub-preform has a hydroxide (OH) infusion of less than 1 parts per million (ppm).

7. The method (300) of claim 1, where to form the at least two glass sub-preforms comprising:
depositing a cladding layer of a silica soot on a core rod by way of an outside vapor deposition (OVD) technique to form a soot preform; and
sintering the soot preform in a sintering furnace to manufacture each of the at least two glass sub-preforms.

8. The method (300) of claim 1, where to form the at least two glass sub-preforms comprising:
stacking one or more core rods inside one or more cladding tubes to form a glass sub-preform assembly; and
collapsing the glass sub-preform assembly to form the at least two glass sub-preforms.

9. The method (300) of claim 1, where the optical fiber (101) has an outer glass diameter that is in a range between 60 microns (µm) and 125 µm with a tolerance value of + 0.7 µm.

10. The method (300) of claim 1, where the optical fiber (101) comprises a core region (402), a primary cladding region (404), and a secondary cladding region (406), where a core radius of the core region (402) is in a range between 4 µm and 5 µm, a primary cladding radius of the primary cladding region (404) is in a range between 20 µm and 55 µm, and a secondary cladding radius of the secondary cladding region (406) is in a range between 30 µm and 63 µm.

11. The method (300) of claim 1, the optical fiber (101) is defined by a relative refractive index profile (500) such that an interface (505) of the primary cladding region (404) and the secondary cladding region (406) has an abrupt change (508) in a relative refractive index.

12. The method (300) of claim 1, where the second end (128) of the previous glass sub-preform and the first end (126) of the successive glass sub-preform are of a flat circular shape.

13. The method (300) of claim 1, where the hollow cylindrical glass tube (108) has a tube length (L1) that is in a range between 5 meters (m) and 10 m, an outer diameter (D1) that is in a range between 100 millimeters (mm) and 200 mm, and an inner diameter (D2) that is in a range between 70 mm and 180 mm, where each of the at least two glass sub-preforms has a preform length (L2) that is in a range between 1 m and 3 m and a clad diameter (D) is in a range between 65 mm and 175 mm.

14. The method (300) of claim 9, where the core region (402) is formed from one of, (i) un-doped silica material, (ii) a co-doped silica material, and (iii) an up-doped silica material.

15. The method (300) of claim 9, where the primary cladding region (404) comprising a cladding relative refractive index profile that has at least one down doped region disposed on one of, (i) an inner region and (ii) an outer region.

16. The method (300) of claim 9, where the primary cladding region (404) comprising at least two cladding layers (408, 410), where the at least two cladding layers (408, 410) are formed of a silica material such that at least one of the at least two cladding layers (408, 410) is one of, (i) up-doped, (ii) down-doped, and (iii) un-doped.