The present disclosure relates to an optical fiber draw furnace and more particularly, relates to a flexible sealing assembly for an optical fiber draw furnace and a method of manufacturing an optical fiber.
BACKGROUND
[0002] A glass preform produced by an Outside Vapor Deposition (OVD) process has a diameter variation along its length, meaning higher the diameter of the glass preform, more is the diameter variation. To draw such glass preform having the diameter variation, there is a high probability of disturbance of sealing apparatus, due to which oxygen may enter inside an optical fiber draw furnace (i.e., furnace) that can deteriorate furnace health and affect mechanical and optical parameters of an optical fiber produced from that glass preform.
[0003] One way to address the aforesaid drawback is using felt rings in accordance with a minimum diameter of the glass preform. However, the existing felt rings have limitations of flexibility and less elasticity which is not sufficient to tackle high diameter variation of glass preforms greater than 5mm.
[0004] Therefore, there exists a need to develop a sealing assembly which solves the aforesaid drawbacks.
OBJECT OF THE DISCLOSURE
[0005] A principal object of the present disclosure is to provide a flexible sealing assembly for an optical fiber draw furnace (interchangeably "drawing furnace" or "furnace") and a method of manufacturing an optical fiber.
[0006] Another object of the present disclosure is to provide a sealing assembly that can keep adjusting as per a preform diameter.
SUMMARY
[0007] Accordingly, the present disclosure provides an optical fiber draw furnace. The optical fiber draw furnace comprises a vertical hollow body having a top end and a bottom end, wherein a glass preform is hung near the top end,

wherein the glass preform is melted to form an optical fiber and the optical fiber exits the vertical hollow body from the bottom end. The optical fiber draw furnace further comprises a flexible sealing assembly placed near the top end.
[0008] The flexible sealing assembly comprises a first plurality of curved ring sections arranged in a circular arrangement and a plurality of tension loaders exerting continuous radially inward force on at least one curved ring section. Each curved ring section is defined by same radius of curvature. Each curved ring section of the first plurality of curved ring sections is separated from each other, wherein the first plurality of curved ring sections is radially movable such that the first plurality of curved ring sections creates a seal between the glass preform and the vertical hollow body while axial movement of the glass preform, where diameter of the glass preform varies. The first plurality of curved ring sections is arranged such that a central passage is formed to enable entry of the glass preform, wherein each curved ring section is placed such that a first gap exists between adjacent curved ring sections.
[0009] The flexible sealing assembly further comprises a plurality of flexible dielectric ring sections attached to the first plurality of curved ring sections such that the plurality of flexible dielectric ring sections presses against the glass preform for sealing. The flexible sealing assembly further comprises a second plurality of curved ring sections coaxial to the first plurality of curved ring sections. The second plurality of curved ring sections is placed such that there is an offset between the first gap between each curved ring section of the first plurality of curved ring sections and a second gap between each curved ring section of the second plurality of curved ring sections. The offset is between 30 to 70 degrees.
[0010] Accordingly, the present disclosure provides a method of manufacturing an optical fiber. The method comprises holding a glass preform near a top end of an optical fiber draw furnace and melting the glass preform of a diameter greater than 80mm to form the optical fiber having a diameter less than 260 microns. The method further comprises feeding the glass preform into the optical fiber draw furnace, wherein the glass preform is periodically or

continuously pushed into the optical fiber draw furnace as lower end of the glass preform is melted into the optical fiber and a continuous radially inward force is exerted by a first plurality of curved ring sections creating a seal between the glass preform and a vertical hollow body, wherein the first plurality of curved ring sections is radially movable and each curved ring section is defined by same radius of curvature.
[0011] The method further comprises cooling the optical fiber and applying one or more coatings on the optical fiber.
[0012] These and other aspects herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the invention herein without departing from the spirit thereof.
BRIEF DESCRIPTION OF FIGURES
[0013] The invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the drawings. The invention herein will be better understood from the following description with reference to the drawings, in which:
[0014] FIG. 1 illustrates a perspective view of a flexible sealing assembly for an optical fiber draw furnace.
[0015] FIG. 2 illustrates an exploded view of the flexible sealing assembly for the optical fiber draw furnace.
[0016] FIG. 3 illustrates curved ring sections and flexible dielectric ring sections for the flexible sealing assembly.
[0017] FIG. 4 illustrates movement of the curved ring sections and the flexible dielectric ring sections in the flexible sealing assembly.
[0018] FIG. 5 illustrates an example optical fiber draw furnace.
[0019] FIG. 6 is a flow-chart illustrating a method of manufacturing an optical fiber.

[0020] FIG. 7 is a flow-chart illustrating a method of manufacturing the optical fiber.
DETAILED DESCRIPTION
[0021] In the following detailed description of the invention, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be obvious to a person skilled in the art that the invention may be practiced with or without these specific details. In other instances, well known methods, procedures and components have not been described in detail so as not to unnecessarily obscure aspects of the invention.
[0022] Furthermore, it will be clear that the invention is not limited to these alternatives only. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art, without parting from the scope of the invention.
[0023] The accompanying drawings are used to help easily understand various technical features and it should be understood that the alternatives presented herein are not limited by the accompanying drawings. As such, the present disclosure should be construed to extend to any alterations, equivalents and substitutes in addition to those which are particularly set out in the accompanying drawings. Although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are generally only used to distinguish one element from another.
[0024] In opening, simultaneous reference is made to FIG. 1 through FIG. 4, in which FIG. 1 illustrates a perspective view of a flexible sealing assembly 100 for an optical fiber draw furnace 500, FIG. 2 illustrates an exploded view of the flexible sealing assembly 100 for the optical fiber draw furnace 500, FIG. 3 illustrates curved ring sections and flexible dielectric ring sections for the flexible sealing assembly, FIG. 4 illustrates movement of the curved ring sections, and the flexible dielectric ring sections in the flexible sealing assembly and FIG. 5 illustrates an example optical fiber draw furnace 500.

[0025] The furnace sealing assembly 100 and its components may be composed of graphite, aluminium, steel or other suitable material or combination of materials. The furnace sealing assembly 100 comprises a cooling section 102, a felt holding section 104, an inlet 106, an outlet 108, a first plurality of curved ring sections 110, a second plurality of curved ring sections 112, a plurality of tension loaders 114, a plurality of apertures 116, a seal cover 118 and a plurality of flexible dielectric ring sections 120.
[0026] The cooling section 102 may have a three-cylinder structure having a top cylindrical element 128, a middle cylindrical element 130 and a bottom cylindrical element 132, wherein the top cylindrical element 128, the middle cylindrical element 130 and the bottom cylindrical element 132 are stacked and joined to form the cooling section 102. The cooling section 102 may comprise the inlet 106 and the outlet 108, on the top cylindrical element 128, configured for water which help in preventing heat transfer to the plurality of flexible dielectric ring sections 120. The top cylindrical element 128 may have an inner diameter of about 115+0.5mm and a height of about 64+0.5mm. Similarly, the middle cylindrical element 130 may have an inner diameter of about 115+0.5mm, an outer diameter of 190+0.5mm and a height of about 23+0.5mm. The bottom cylindrical element 132 may have similar dimensions as the top cylindrical element 128. The present disclosure is not limited to these dimensions. Other suitable dimensions are also possible. The cooling section 102 may be configured for cooling a glass preform 504.
[0027] The felt holding section 104 may be placed at a top portion of the cooling section 102. The felt holding section 104 may be configured to hold the plurality of flexible dielectric ring sections 120 which is further attached to the first plurality of curved ring sections 110 and the second plurality of curved ring sections 112. The plurality of flexible dielectric ring sections 120 is attached to the first plurality of curved ring sections 110 and the second plurality of curved ring sections 112 such that the plurality of flexible dielectric ring sections 120 presses against the glass preform 504 for sealing. The felt holding section 104 may have an inner diameter of about 190+0.5mm, an outer diameter of about

222+0.5mm and a height of about 78+0.5mm. The present disclosure is not limited to these dimensions. Other suitable dimensions are also possible.
[0028] The felt holding section 104 comprises the first plurality of curved ring sections 110 and the second plurality of curved ring sections 112 which is covered using the seal cover 118. The seal cover 118 may have an inner diameter of 115+0.5mm, an outer diameter of 222+0.5mm and a height of about 30+0.5mm. The present disclosure is not limited to these dimensions. Other suitable dimensions are also possible. The first plurality of curved ring sections 110 is arranged in a circular arrangement. The first plurality of curved ring sections 110 is arranged such that a central passage 122 is formed to enable entry of the glass preform 504. Each curved ring section 110 is defined by same radius of curvature and is placed such that a first gap 124 exists between adjacent curved ring sections as shown in FIG. 3. Similarly, the second plurality of curved ring sections 112 is arranged in a circular arrangement. The second plurality of curved ring sections 112 is arranged such that the central passage 122 is formed to enable entry of the glass preform 504. Each curved ring section 112 is defined by same radius of curvature and is placed such that a second gap 126 exists between adjacent curved ring sections as shown in FIG. 3. The second plurality of curved ring sections 112 is placed coaxially to the first plurality of curved ring sections 110 as shown in FIG. 1 and FIG. 2. Further, the second plurality of curved ring sections 112 is placed such that there is an offset between the first gap 124 between each curved ring section of the first plurality of curved ring sections 110 and the second gap 126 between each curved ring section of the second plurality of curved ring sections 112. The offset is between 30 to 70 degrees.
[0029] In other words, the first plurality of curved ring sections 110 and the second plurality of curved ring sections 112 form a circular seal unit which are placed co-axially such that separating slits of the first plurality of curved ring sections 110 is placed at 30 to 70 degree offset with respect to separating slits of the second plurality of curved ring sections 112. Advantageously, multiple curved ring sections help to eliminate diameter variations placed at smaller intervals along a preform length. Each of the first plurality of curved ring sections 110 and

the second plurality of curved ring sections 112 may have an inner diameter of about 140+0.5mm, an outer diameter of about 170+0.5mm and a height of about 25+0.5mm. The present disclosure is not limited to these dimensions. Other suitable dimensions are also possible.
[0030] Each of the first plurality of curved ring sections 110 and the second plurality of curved ring sections 112 is a three-part curved ring section, which when placed offset to each other as mentioned above, provides flexibility in movement to the furnace sealing assembly 100 depending on the diameter variations. The offset arrangement provides flexibility in movement of the first plurality of curved ring sections 110, the second plurality of curved ring sections 112 and the plurality of flexible dielectric ring sections 120 as per the diameter variations (or preform diameter variations) at various location present along a preform length. Such movement is shown in FIG. 4 using dashed circles and line, where each curved ring section of the first plurality of curved ring sections 110 and the second plurality of curved ring sections 112 moves between the two dashed circles (i.e., inner dashed circle and outer dashed circle). Due to absence of the offset, the diameter variations in adjacent portions of the glass preform 504 might go uncorrected. Each curved ring section of the first plurality of curved ring sections 110 and the second plurality of curved ring sections 112 gets adjusted by spring tension mechanism depending upon preform size variations. For example, considering large size and triple joint preforms which have diameter variations at small interval lengths, each curved ring section of the first plurality of curved ring sections 110 and the second plurality of curved ring sections 112 helps to detect the diameter variations at small intervals.
[0031] The plurality of tension loaders 114 is secured in the plurality of apertures 116 present on the felt holding section 104 using a plurality of connecting means, such as nut-spring, for example, to apply spring tension mechanism. Of course, other connecting means are known, foreseeable, and unforeseeable, and each of these is readily apparent to those of skill in the art upon reading the present disclosure. The plurality of tension loaders 114 is configured to exert continuous radially inward force on at least one curved ring

section. Due to such force, the first plurality of curved ring sections 110 and the second plurality of curved ring sections 112, in which each curved ring is separated from each other, is radially movable such that the first plurality of curved ring sections 110 and the second plurality of curved ring sections 112 create a seal between the glass preform 504 and a vertical hollow body 506 (as shown in FIG. 5) in the optical fiber draw furnace 500 (as shown in FIG. 5) while axial movement of the glass preform 504, where diameter of the glass preform 504 may vary.
[0032] The vertical hollow body 506 is a cylindrical hollow body that has a top end 508 and a bottom end 510, wherein the glass preform 504 is hung near the top end 508 and then is melted to form an optical fiber 502. The optical fiber 502 exits the vertical hollow body 506 from the bottom end 510. The flexible sealing assembly 100 is placed near the top end 508.
[0033] The above arrangement of the flexible sealing assembly 100 prevents unwanted dissipation of heat from the optical fiber draw furnace 500 which further prevents furnace health deterioration and oxidisation of the plurality of flexible dielectric ring sections 120, thereby preventing preform deformities like optical fiber with uneven geometric properties.
[0034] Advantageously, the flexible sealing assembly 100 enables drawing of preforms having up to 18+10mm diameter variations due to flexibility in the movement of the plurality of flexible dielectric ring sections 120 attached to the first plurality of curved ring sections 110 and the second plurality of curved ring sections 112. The flexible sealing assembly 100 allows drawing of triple joint preforms without affecting furnace health due to separation of the flexible sealing assembly 100 from heat zone and thus an optical fiber with better mechanical and optical parameters can be produced. Unlike conventional complicated compressor assemblies, the flexible sealing assembly 100 incorporates easy to use spring tension mechanism, which provides required flexibility in the movement of the plurality of flexible dielectric ring sections 120 as per preform diameter variations.

[0035] FIG. 6 is a flow-chart illustrating a method of manufacturing an optical fiber 502. It may be noted that in order to explain the flow-chart 600, references will be made to the elements explained in FIG. 1 through FIG. 5.
[0036] Generally, an optical fiber refers to a medium associated with transmission of information over long distances in the form of light pulses. The optical fiber uses light to transmit voice and data communications over long distances when encapsulated in a jacket/sheath. The optical fiber may be of ITU.T G.657.A2 category. Alternatively, the optical fiber may be of ITU.T G.657.A1 or G.657.B3 or G.652.D or a multi-core or other suitable category. The ITU.T, i stands for International Telecommunication Union-Telecommunication Standardization Sector, is one of the three sectors of the ITU. The ITU is the United Nations specialized agency in the field of telecommunications and is responsible for studying technical, operating and tariff questions and issuing recommendations on them with a view to standardizing telecommunications on a worldwide basis. The optical fiber may be a bend insensitive fiber that has less degradation in optical properties or less increment in optical attenuation during multiple winding/unwinding operations of an optical fiber cable.
[0037] At step 602, the method includes holding the glass preform (aka "cylindrical glass preform") 504 near the top end 508 of the optical fiber draw i furnace 500.
[0038] At step 604, the method includes melting the glass preform 504, wherein the glass preform 504 may have a diameter greater than 80mm to form the optical fiber 502 having a diameter less than 260 microns.
[0039] At step 606, the method includes feeding the glass preform 504 into the optical fiber draw furnace 500. During the feeding step, the glass preform 504 is periodically or continuously pushed into the optical fiber draw furnace 500 as lower end of the glass preform 504 is melted into the optical fiber 502 and a continuous radially inward force is exerted by the first plurality of curved ring sections 110 and the second plurality of curved ring sections 112 that create a seal i between the glass preform 504 and the vertical hollow body 506. The first plurality of curved ring sections 110 and the second plurality of curved ring

sections 112 are radially movable as shown in FIG. 4 and each curved ring section is defined by same radius of curvature.
[0040] FIG. 7 is a flow-chart illustrating a method of manufacturing the optical fiber 502. It may be noted that in order to explain the flow-chart 700, references will be made to the elements explained in FIG. 1 through FIG. 4.
[0041] At step 702, the method includes holding the glass preform (aka "cylindrical glass preform") 504 near the top end 508 of the optical fiber draw furnace 500.
[0042] At step 704, the method includes melting the glass preform 504, wherein the glass preform 504 may have a diameter greater than 80mm to form the optical fiber 502 having a diameter less than 260 microns.
[0043] At step 706, the method includes feeding the glass preform 504 into the optical fiber draw furnace 500. During the feeding step, the glass preform 504 is periodically or continuously pushed into the optical fiber draw furnace 500 as lower end of the glass preform 504 is melted into the optical fiber 502 and a continuous radially inward force is exerted by the first plurality of curved ring sections 110 and the second plurality of curved ring sections 112 that create a seal between the glass preform 504 and the vertical hollow body 506. The first plurality of curved ring sections 110 and the second plurality of curved ring sections 112 are radially movable as shown in FIG. 4 and each curved ring section is defined by same radius of curvature.
[0044] At step 708, the method includes cooling the optical fiber 502 and at step 710, the method includes applying one or more coatings on the optical fiber 502.
[0045] It may be noted that the flow-chart 600 and 700 are explained to have above stated process steps; however, those skilled in the art would appreciate that the flow-chart 600 and 700 may have more/less number of process steps which may enable all the above stated implementations of the present disclosure.
[0046] The various actions act, blocks, steps, or the like in the flow chart and sequence diagrams may be performed in the order presented, in a different order or simultaneously. Further, in some implementations, some of the actions,

acts, blocks, steps, or the like may be omitted, added, modified, skipped, or the like without departing from the scope of the present disclosure.
[0047] It will be apparent to those skilled in the art that other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention. While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above-de scribed embodiment, method, and examples, but by all embodiments and methods within the scope of the invention. It is intended that the specification and examples be considered as exemplary, with the true scope of the invention being indicated by the claims.
[0048] Conditional language used herein, such as, among others, "can", "may", "might", "may", "e.g.", and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain alternatives include, while other alternatives do not include, certain features, elements and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more alternatives or that one or more alternatives necessarily include logic for deciding, with or without other input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular alternative. The terms "comprising," "including," "having," and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term "or" is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term "or" means one, some, or all of the elements in the list.
[0049] Disjunctive language such as the phrase "at least one of X, Y, Z," unless specifically stated otherwise, is otherwise understood with the context as

used in general to present that an item, term, etc., may be either X, Y, or Z, or any combination thereof (e.g., X, Y, and/or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain alternatives require at least one of X, at least one of Y, or at least one of Z to each be present.
[0050] While the detailed description has shown, described, and pointed out novel features as applied to various alternatives, it can be understood that various omissions, substitutions, and changes in the form and details of the devices or algorithms illustrated can be made without departing from the scope of the disclosure. As can be recognized, certain alternatives described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others.

CLAIMS
We Claim:

1. An optical fiber draw furnace (500), comprising:
a vertical hollow body (506) having a top end (508) and a bottom end (510), wherein a glass preform (504) is hung near the top end (508), wherein the glass preform (504) is melted to form an optical fiber (502), wherein the optical fiber (502) exits the vertical hollow body (506) from the bottom end (510); and
a flexible sealing assembly (100) placed near the top end (508), the flexible sealing assembly (100) comprising:
a first plurality of curved ring sections (110) arranged in a circular arrangement, wherein each curved ring section is defined by same radius of curvature; and
a plurality of tension loaders (114) exerting continuous radially inward force on at least one curved ring section, wherein each curved ring section of the first plurality of curved ring sections (110) is separated from each other, wherein the first plurality of curved ring sections (110) is radially movable such that the first plurality of curved ring sections (110) creates a seal between the glass preform (504) and the vertical hollow body (506) while axial movement of the glass preform (504), where diameter of the glass preform (504) varies.
2. The optical fiber draw furnace (500) as claimed in claim 1 further comprising a plurality of flexible dielectric ring sections (120) attached to the first plurality of curved ring sections (110) such that the plurality of flexible dielectric ring sections (120) presses against the glass preform (504) for sealing.
3. The optical fiber draw furnace (500) as claimed in claim 1, wherein the first plurality of curved ring sections (110) is arranged such that a central passage (122) is formed to enable entry of the glass preform (504), wherein each curved

ring section is placed such that a first gap (124) exists between adjacent curved ring sections.
4. The optical fiber draw furnace (500) as claimed in claim 1 further comprising a second plurality of curved ring sections (112) coaxial to the first plurality of curved ring sections (110).
5. The optical fiber draw furnace (500) as claimed in claim 1 further comprising a second plurality of curved ring sections (112) such that there is an offset between a first gap (124) between each curved ring section of the first plurality of curved ring sections (110) and a second gap (126) between each curved ring section of the second plurality of curved ring sections (112).
6. The optical fiber draw furnace (500) as claimed in claim 5, wherein the offset is between 30 to 70 degrees.
7. An optical fiber (502) manufactured by any of claims 1 to 6.
8. A method of manufacturing an optical fiber (502), the method comprising:
holding a glass preform (504) near a top end (508) of an optical fiber draw furnace (500);
melting the glass preform (504) of a diameter greater than 80mm to form the optical fiber (502) having a diameter less than 260 microns; and
feeding the glass preform (504) into the optical fiber draw furnace (500), comprising:
periodically or continuously pushing the glass preform (504) into the optical fiber draw furnace (500) as lower end of the glass preform (504) is melted into the optical fiber (502); and
exerting continuous radially inward force by a first plurality of curved ring sections (110) creating a seal between the glass preform (504) and a vertical hollow body (506), wherein the first

i

plurality of curved ring sections (110) is radially movable and each curved ring section is defined by same radius of curvature.
9. The method as claimed in claim 8 further comprising cooling the optical fiber
(502).
10. The method as claimed in claim 8 further comprising applying one or more
coatings on the optical fiber (502).