Claims:CLAIMS
We Claim:

1. An optical fiber draw tower (100) configured to melt a preform (104) into an optical fiber (106), the optical fiber draw tower (100) comprising:
a top end zone (108) and a bottom end zone (110), wherein the preform (104) is inserted at the top end zone (108) and is melted into the optical fiber (106) that exits from the bottom end zone (110), wherein a fluid is inserted into the optical fiber draw tower (100) from the top end zone (108); and
a plurality of air knives (112) that distorts an optical fiber path such that partially uncooled optical fiber deviates from a vertical path and follows a bended path, wherein a bended path length is greater than a vertical path length, wherein the bended path length is defined by laminar flow for at least 70% of the bended path length.

2. The optical fiber draw tower (100) as claimed in claim 1, wherein the plurality of air knives (112) is a plurality of openings arranged such that to cause distortion on the vertical path of the optical fiber (106) in the optical fiber draw tower (100), wherein the plurality of openings is a combination of one or more of a suction and pumping of the fluid.

3. The optical fiber draw tower (100) as claimed in claim 1, wherein the plurality of air knives (112) modifies mass flow of the fluid in a predefined manner to modify the optical fiber path inside the optical fiber draw tower (100).

4. The optical fiber draw tower (100) as claimed in claim 1, wherein the plurality of air knives (112) is arranged such that the fluid enters or exits the optical fiber draw tower (100) at an angle of 0-89 degrees with respect to the vertical path.

5. The optical fiber draw tower (100) as claimed in claim 1, wherein the bended path length is at least 10% greater than the vertical path length of the optical fiber (106).

6. The optical fiber draw tower (100) as claimed in claim 1, wherein the bended path length for a single partial turn is defined by:
OA=OU=OQ=r
AQ=2?=2r cos??
where A = entrance path (202) of the optical fiber (106) and Q = exit path (204) of the optical fiber (106).

7. The optical fiber draw tower (100) as claimed in claim 1, wherein the bended path length for multiple partial turns is defined by:
?_(i=1)^N¦?h_i+ ?_(i=1)^N¦??_i= H_T ? ?
?_(i=1)^N¦?L_i=H_T (1+p)?
where p = desired fractional increase in draw path length, N = number of turn segments required to cover a vertical drop (304), HT = available tower height, Li = length of the optical fiber (106) entering ith turn, Li+1 = length of the optical fiber (106) exiting the ith turn and hi = corresponding vertical drop of path entering the ith turn; and
cos??= (2H_T)/(NW_T ) [1-(1+p)sin?? ]
where p = desired fractional increase in draw path length, N = number of turn segments required to cover the vertical drop (304), HT = available tower height and WT = available tower width.

8. A method of drawing an optical fiber (106) in an optical fiber draw tower (100), the method comprising:
drawing the optical fiber (106) from a preform (104); and
modifying a vertical path length of the optical fiber (106) by subsequent partial turns, wherein a bended path length is defined by laminar flow for at least 70% of the bended path length, thereby modifying the vertical path length of the optical fiber (106) into the bended path length.

9. The method as claimed in claim 8, wherein the bended path length for a single partial turn is defined by:
OA=OU=OQ=r
AQ=2?=2r cos??
where A = entrance path (202) of the optical fiber (106) and Q = exit path (204) of the optical fiber (106).

10. The method as claimed in claim 8, wherein the bended path length for multiple partial turns is defined by:
?_(i=1)^N¦?h_i+ ?_(i=1)^N¦??_i= H_T ? ?
?_(i=1)^N¦?L_i=H_T (1+p)?
where p = desired fractional increase in draw path length, N = number of turn segments required to cover a vertical drop (304), HT = available tower height, Li = length of the optical fiber (106) entering ith turn, Li+1 = length of the optical fiber (106) exiting the ith turn and hi = corresponding vertical drop of path entering the ith turn; and
cos??= (2H_T)/(NW_T ) [1-(1+p)sin?? ]
where p = desired fractional increase in draw path length, N = number of turn segments required to cover the vertical drop (304), HT = available tower height and WT = available tower width.

11. The method as claimed in claim 8, wherein modifying the vertical path length of the optical fiber (106) by the subsequent partial turns further comprising:
applying external force to uncooled optical fiber at one or more predefined zones (114, 116, 118) in the optical fiber draw tower (100); and
altering path of a fluid at the one or more predefined zones (114, 116, 118) in the optical fiber draw tower (100) due to application of the external force causing the uncooled optical fiber to deviate from the vertical path into a bended path.

12. The method as claimed in claim 11, wherein applying the external force to the uncooled optical fiber comprising at least one of adding or removing fluid mass from the optical fiber draw tower (100) in the one or more predefined zones (114, 116, 118) such that the optical fiber (106) bends subsequently in partial turns, thereby modifying the vertical path length to a bended path length.
, Description:TECHNICAL FIELD
The present disclosure relates to an optical fiber manufacturing equipment and more particularly, relates to an optical fiber draw tower facilitating in-tower optical fiber bending and an optical fiber processing method.

BACKGROUND
During optical fiber manufacturing, glass preforms are heated at a high temperature and drawn at a high draw down ratio and a high draw speed to produce an optical fiber due to which the glass preforms do not reach an equilibrium state, thereby resulting in the optical fiber with high fictive temperature which is undesirable as the same results in increased attenuation (aka “signal loss”).
One way to address the aforesaid drawbacks is modifying fiber processing conditions that can allow manufacturing the optical fiber with lower fictive temperature. In the same context, a prior art reference “US20190256400” discloses an optical fiber with low attenuation, where the optical fiber is produced under conditions that reduce fictive temperature. Another prior art reference “US10696580” teaches an optical fiber with low fictive temperature along with a system and method for making the optical fiber.
However, the fictive temperature is not reduced to a satisfactory/desired level due to a short residence time, due to which structure of the glass preforms do not reach a required equilibrium state as well as decrease in the fictive temperature is also small. Further, the existing solutions utilize a turn or fold mechanism and mechanically moves the path of the draw outside a draw tower assembly, that is, one cannot draw the optical fiber within required fictive temperature and attenuation values without dimensionally changing the existing draw tower set-up, which in turn, makes the fiber drawing process costly due to requirement of additional equipments.
Therefore, there exists a need for an improved technique which solves the aforesaid drawbacks and allows easy manufacturing of optical fibers in restricted space (i.e., within an available volume of the draw tower) without encroaching outside space of the draw tower and with increased residence time and reduced fictive temperature and attenuation.

OBJECT OF THE DISCLOSURE
A principal object of the present disclosure is to provide an optical fiber draw tower facilitating in-tower optical fiber bending and an optical fiber processing and drawing method.
Another object of the present disclosure is to enable easy manufacturing of optical fibers in restricted space (i.e., within an available volume of the optical fiber draw tower) without encroaching outside space of the draw tower and with increased residence time and reduced fictive temperature and attenuation.

SUMMARY
Accordingly, the present disclosure provides an optical fiber draw tower. The optical fiber draw tower is configured to melt a preform into an optical fiber and facilitate in-tower optical fiber bending. The optical fiber draw tower comprises a top end zone and a bottom end zone, wherein the preform is inserted at the top end zone and is melted into the optical fiber that exits from the bottom end zone, wherein a fluid is inserted into the optical fiber draw tower from the top end zone. The optical fiber draw tower further comprises a plurality of air knives that distorts an optical fiber path such that partially uncooled optical fiber deviates from a vertical path and follows a bended path, wherein a bended path length is greater than a vertical path length, wherein the bended path length is defined by laminar flow for at least 70% of the bended path length.
The plurality of air knives is a plurality of openings arranged such that to cause distortion on the vertical path of the optical fiber in the optical fiber draw tower, wherein the plurality of openings is a combination of one or more of a suction and pumping of the fluid. The plurality of air knives modifies mass flow of the fluid in a predefined manner to modify the optical fiber path inside the optical fiber draw tower. The plurality of air knives is arranged such that the fluid enters or exits the optical fiber draw tower at an angle of 0-89 degrees with respect to the vertical path. The bended path length is at least 10% greater than the vertical path length of the optical fiber.
Accordingly, the present disclosure provides a method of drawing an optical fiber in an optical fiber draw tower. The method comprises drawing the optical fiber from a preform and modifying a vertical path length of the optical fiber by subsequent partial turns, wherein a bended path length is defined by laminar flow for at least 70% of the bended path length, thereby modifying the vertical path length of the optical fiber into the bended path length. The vertical path length of the optical fiber is modified by the subsequent partial turns by applying external force to uncooled optical fiber at one or more predefined zones in the optical fiber draw tower and by altering path of a fluid at the one or more predefined zones in the optical fiber draw tower due to application of the external force which causes the uncooled optical fiber to deviate from the vertical path into a bended path. Applying the external force to the uncooled optical fiber comprises at least one of adding or removing fluid mass from the optical fiber draw tower in the one or more predefined zones such that the optical fiber bends subsequently in partial turns, thereby modifying the vertical path length to a bended path length.
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
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:
FIG. 1 illustrates an optical fiber draw tower according to the present disclosure.
FIG. 2 is an example illustration showing a single partial turn for an optical fiber.
FIG. 3 is an example illustration showing multiple partial turns for the optical fiber.
FIG. 4 is a flow chart representing a method of drawing the optical fiber.

DETAILED DESCRIPTION
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.
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.
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.
In opening, simultaneous reference is made to FIG. 1 through FIG. 3, in which FIG. 1 illustrates an optical fiber draw tower 100 according to the present disclosure, FIG. 2 is an example illustration 200 showing a single partial turn for an optical fiber and FIG. 3 is an example illustration 300 showing multiple partial turns for the optical fiber.
The optical fiber draw tower 100 may also be referred to as a draw tower. The optical fiber draw tower 100 is configured to melt a preform 104 into an optical fiber 106 and defined by a top end zone 108 and a bottom end zone 110, where the preform 104 is inserted at the top end zone 108 and is melted into the optical fiber 106 that exits from the bottom end zone 110. The temperature at the top end zone 108 is in range 950 to 1050 degree Celsius. The temperature at the bottom end zone 110 is in range 750 degree Celsius to 800 degree Celsius.
The preform 104 is a glass preform i.e., silica preform. Further, the optical fiber 106 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, 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.
Further, a fluid is inserted into the optical fiber draw tower 100 from the top end zone 108. The fluid may be liquid or air. The fluid may be N2 (nitrogen) or other suitable fluid.
The optical fiber draw tower 100 comprises, but not limited to, a preform insertion device 102 and a plurality of air knives 112. The preform insertion device 102 may also be referred to as a preform holding device. The preform insertion device 102 is configured to hold and insert the preform 104 inside the optical fiber draw tower 100 and is installed near the top end zone 108 of the optical fiber draw tower 100.
The plurality of air knives 112 is a plurality of air bearings. The plurality of air knives 112 is arranged along with height 124 of the optical fiber draw tower 100. The plurality of air knives 112 is configured to distort an optical fiber path such that partially uncooled optical fiber deviates from a vertical path and follows a bended path as shown in FIG. 1, where the vertical path is defined by gravitational force and a bended path length is greater than a vertical path length. In an example, the bended path length is at least 10% greater than the vertical path length of the optical fiber 106, leading to at least 10% increase in residence time of the optical fiber 106. Typically, residence time is the total time that the optical fiber 106 has spent inside the optical fiber draw tower 100. Further, the bended path length is defined by laminar flow for at least 70% of the bended path length.
The plurality of air knives 112 is configured to guide semi-cooled fiber in a non-linear path in a vertical resultant fiber draw direction. The plurality of air knives 112 includes a plurality of openings arranged such that to cause distortion on the vertical path of the optical fiber in the optical fiber draw tower (100). The plurality of openings is a combination of one or more of a suction and pumping of the fluid. The plurality of openings either pump-in and suck-out fluid causing distortion in fluid flow path, while maintaining the laminar flow, which causes increase in path length without increasing space requirements.
The plurality of air knives 112 arranged such that the fluid enters or exits the optical fiber draw tower 100 at an angle of 0-89 degrees with respect to the vertical path. The plurality of air knives 112 modifies mass flow of the fluid in a predefined manner to modify the optical fiber path inside the optical fiber draw tower 100 and exerts a force to displace the optical fiber 106 of mass less than 37 km for 1 kg glass, where the optical fiber 106 may have a diameter of 250 microns or less. The plurality of air knives 112 modifies the vertical path length taken by the optical fiber 106 (in melted state) due to gravity by subsequent partial turns as depicted in FIG. 1. Such modification in the vertical path length is done by applying external force to the optical fiber (uncooled optical fiber) at one or more predefined zones 114, 116, 118 in the optical fiber draw tower 100 and by altering path of the fluid at the one or more predefined zones 114, 116, 118 in the optical fiber draw tower 100 due to application of the external force which causes the optical fiber in uncooled state to deviate from the vertical path into the bended path. The external force to the optical fiber in uncooled state is applied by at least one of adding or removing fluid mass from the optical fiber draw tower 100 in the one or more predefined zones 114, 116, 118 such that the optical fiber bends subsequently in the partial turns.
The plurality of air knives 112 guides the slanted path along with gravity. The optical fiber 106 drawn from the preform 104 is conveyed through the plurality of air knives 112, where a first air knife from the plurality of air knives 112 directs the optical fiber 106 to a second air knife, the second air knife directs the optical fiber 106 to a third air knife and so on so forth. In other words, the optical fiber 106 is directed from a first set of air knives of the plurality of air knives 112 to a second set of air knives of the plurality of air knives 112 that facilitate controlled cooling of the optical fiber 106. The optical fiber 106 is directed from the first set of air knives to the second set of air knives in an alternate manner and at predefined angles such that a bending angle of the first set of air knives is different than a bending angle of the second set of air knives that results in multiple partial turns 120 to the optical fiber 106.
The multiple partial turns 120 are step turns in a sequence, which may be implemented between 10-90 degrees in the optical fiber draw tower 100. Advantageously, sum of partial turns increases the residence time of the optical fiber 106. The multiple partial turns 120 can be achieved by optimizing fluid flow with the optical fiber draw tower 100, where the fluid flow in the optical fiber draw tower 100 is directed from top to bottom. One example of optimization technique includes use of multiple inlets and outlets (i.e., the plurality of openings) along the height 124 of the optical fiber draw tower 100 for the fluid flow. Other optimization techniques may also be used.
Due to the aforementioned arrangement, length of the optical fiber 106 exiting a turn is +1 the length of optical fiber 106 entering the turn. For the same, referring to FIG. 2 and FIG. 3 that depict the single partial turn and multiple partial turns 120 respectively, which is further explained below using equations:
Equation 1 – Bended path length for the single partial turn:
OA=OU=OQ=r
AQ=2?=2r cos??…………….(1)
Where A = entrance path of the optical fiber shown using reference numeral 202 and Q = exit path of the optical fiber shown using reference numeral 204.
Equation 2 - Bended path length for the multiple partial turns 120 within an idealized tower frame border, i.e., available tower width 308:
?_(i=1)^N¦?h_i+ ?_(i=1)^N¦??_i= H_T ? ?
?_(i=1)^N¦?L_i=H_T (1+p)?…………….(2)
Where p = desired fractional increase in draw path length, N = number of turn segments required to cover a vertical drop 304 and HT = available tower height. Further, Li is length of the optical fiber entering the ith turn as depicted using reference numeral 302, Li+1 is length of the optical fiber exiting the ith turn as depicted using reference numeral 306 and hi is corresponding vertical drop of path entering the ith turn as depicted using reference numeral 304.
Equation 3 - Bended path length for the multiple partial turns 120 within the idealized tower frame border, i.e., available tower width 308:
cos??= (2H_T)/(NW_T ) [1-(1+p)sin?? ]…………….(3)
Where p = desired fractional increase in draw path length, N = number of turn segments required to cover the vertical drop 304, HT = available tower height and WT = available tower width.
The above equations show the constraint if the optical fiber production is restricted to a horizontal dimension of WT given a vertical drop of hi and a desired fractional increase of p in the path length.
After exiting the plurality of air knives 112, the optical fiber 106 may be directed for further controlled cooling or directed to other processing units for coating, spooling, for example.
Advantageously, the plurality of air knives 112 with bending angle less than 90 degrees can be accommodated in existing draw tower constrains that allows sequential turning of the optical fiber 106 at predefined angles i.e., less than 90 degrees in a predefined draw tower volume which further increases the residence time and annealing/dwell time within a standard draw tower height and width as shown using the above equations. Resultantly, one can achieve the optical fiber 106 within required fictive temperature and attenuation values (for example, 0.17 dB/km-0.18dB/km) without dimensionally changing the existing draw tower set-up. In general, the fictive temperature is the temperature at which corresponding liquid structure and properties of glass are frozen in upon cooling and the attenuation corresponds to signal loss.
FIG. 4 is a flow chart representing a method of drawing the optical fiber 106 in the optical fiber draw tower 100. It may be noted that in order to explain the flow chart 400, references will be made to the elements explained in FIG. 1 through FIG. 3.
At step 402, the method includes drawing the optical fiber 106 from the preform 104.
At step 404, the method includes modifying the vertical path length of the optical fiber 106 by subsequent partial turns, wherein the bended path length is defined by laminar flow for at least 70% of the bended path length, thereby modifying the vertical path length of the optical fiber 106 into the bended path length. In this step, the plurality of air knives 112 modifies the vertical path length taken by the optical fiber 106 (in melted state) due to gravity by subsequent partial turns as depicted in FIG. 1. Such modification in the vertical path length is done by applying external force to the optical fiber (uncooled optical fiber) at the one or more predefined zones 114, 116, 118 in the optical fiber draw tower 100 and by altering path of the fluid at the one or more predefined zones 114, 116, 118 in the optical fiber draw tower 100 due to application of the external force which causes the optical fiber in uncooled state to deviate from the vertical path into the bended path. The external force to the optical fiber in uncooled state is applied by at least one of adding or removing the fluid mass from the optical fiber draw tower 100 in the one or more predefined zones 114, 116, 118 such that the optical fiber bends subsequently in the partial turns.
It may be noted that the flow chart 400 is explained to have above stated process steps; however, those skilled in the art would appreciate that the flow chart 400 may have more/less number of process steps which may enable all the above stated implementations of the present disclosure.
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.
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-described 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.
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.
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.
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.