Description:FORM 2
The Patent Act 1970
(39 of 1970)
&
THE PATENT RULES, 2003

COMPLETE SPECIFICATION
(SEE SECTION 10 AND RULE 13)

TITLE OF THE INVENTION

OPTICAL FIBER MANUFACTURING SYSTEM AND METHOD

APPLICANT:

Name : Sterlite Technologies Limited

Nationality : Indian

Address : 3rd Floor, Plot No. 3, IFFCO Tower,
Sector – 29, Gurugram, Haryana, 122002

The following specification particularly describes the invention and the manner in which it is to be performed:

TECHNICAL FIELD
[001] The present disclosure relates to the field of optical fibers, and more particularly, relates to an optical fiber manufacturing system and method.

BACKGROUND
[002] Optical fiber cables are a critical component of a modern communications network across the globe. As the data and data rate requirement increases, more optical fibers are required in the network to support higher capacity and speed. However, attributes such as attenuation and bend loss are a few significant factors aiding the degradation of signals. That is, an increase in attenuation disrupts the quality of the signals being transmitted in the optical fibers. Reducing one or more of the aforesaid factors would help reduce or eliminate the number of signal amplifications required in the network, which further reduce the network's cost and increase network’s efficiency. In the same context, a prior art reference “US9658394B2” teaches attenuation reduction in an optical fiber, wherein the optical fiber undergoes a heat treatment process after a drawing process at a constant temperature throughout a plurality of stages. Another prior art reference “CN102010123B” deals with an optical fiber having reduced attenuation, wherein a heat treatment process is done for a prolonged time. Another prior art reference “US7565820B2” proposes an optical fiber with reduced attenuation undergoing heat treatment process in two heating zones at different temperatures. Yet another prior art reference “US6851282B2” discloses attenuation reduction of an optical fiber through annealing process.
[003] While the prior arts cover various solutions for attenuation reduction, however, there still remains a scope for improvement.

OBJECT OF THE DISCLOSURE
[004] A primary object of the present disclosure is to provide an optical fiber manufacturing system and method.
[005] Another object of the present disclosure is to reduce attenuation in an optical fiber using an annealing process, conducted in an annealing furnace, following an optical fiber drawing process, wherein the annealing process is conducted at a constant temperature throughout a plurality of stages in order to improve relaxation time to prevent generation of thermal stress within the optical fiber.
[006] Another object of the present disclosure is to optimize the annealing process.

SUMMARY
[007] Accordingly, the present disclosure provides an optical fiber manufacturing system and method. The optical fiber manufacturing system comprises a main furnace for drawing an optical fiber from an optical fiber preform, wherein the main furnace has a temperature in a range between 2100-2500 degree Celsius. The optical fiber manufacturing system further comprises one or more annealing furnaces for annealing the optical fiber in a plurality of stages, wherein annealing temperature in each of the plurality of stages is constant, wherein constant refers to variation of up to 2%, wherein the optical fiber is annealed at a plurality of pre-defined constant temperatures. Complete length (L) of the plurality of stages is more than 2 meters and distance (d1) between each annealing furnace is less than 10 centimetres (cms).
[008] The optical fiber manufacturing method comprises drawing the optical fiber from the optical fiber preform using the main furnace, passing the optical fiber from the main furnace to each of the one or more annealing furnaces through an extension tube, holding the optical fiber in each of the plurality of stages for a time period and annealing the optical fiber in the plurality of stages in one or more annealing furnaces, wherein holding time in the plurality of stages for the optical fiber during annealing process is in a range of 0.06 to 0.36 seconds and a rate of moving the optical fiber between each of the plurality of stages is more than 1500 mm/minute.
[009] A manufactured annealed optical fiber has a macro-bend loss of less than 0.3 dB/Km at 1625 nm wavelength for 30 mm radius of curvature, a macro-bend loss of less than 1.5 dB/Km at 1625 nm wavelength at 10 mm radius of curvature, a macro-bend loss of less than 0.1 dB/Km at 1550 nm wavelength at 30 mm radius of curvature and a macro-bend loss of less than 0.5 dB/Km at 1550 nm wavelength at 10 mm radius of curvature, an average attenuation of less than 0.3211 dB/Km at 1310 nm wavelength, an average attenuation of less than 0.1819 dB/Km at 1550 nm wavelength and an average attenuation of less than 0.204 dB/Km at 1625 nm wavelength.
[0010] These and other aspects herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawing. 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
[0011] The invention is illustrated in the accompanying drawing, throughout which like reference letters indicate corresponding parts in the figure. The invention herein will be better understood from the following description with reference to the drawing, in which:
[0012] FIG. 1 illustrates an optical fiber manufacturing system.
[0013] FIG. 1a illustrates a closer view of an extension tube.
[0014] FIG. 1b illustrates a closer view of an annealing furnace.
[0015] FIG. 2 depicts a process sequence followed in the optical fiber manufacturing system.
[0016] FIG. 3 is a flow chart illustrating an optical fiber manufacturing method.
[0017] FIG. 4 is a flow chart illustrating the optical fiber manufacturing method.

DETAILED DESCRIPTION
[0018] 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 details so as not to unnecessarily obscure aspects of the invention.
[0019] 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.
[0020] The accompanying drawing is used to help easily understand various technical features and it should be understood that the alternatives presented herein are not limited by the accompanying drawing. 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 drawing. 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.
[0021] The proposed disclosure provides an optical fiber manufacturing system and method, where attenuation of an optical fiber is reduced using an annealing process, conducted in an annealing furnace, following an optical fiber drawing process, wherein the annealing process is conducted at a plurality of pre-defined constant temperatures throughout a plurality of stages in order to improve relaxation time to prevent generation of thermal stress within the optical fiber.
[0022] Now simultaneous reference is made to FIG. 1 through FIG. 2, in which FIG. 1 illustrates an optical fiber manufacturing system 100, FIG. 1a illustrates a closer view of an extension tube, FIG. 1b illustrates a closer view of an annealing furnace, and FIG. 2 depicts a process sequence 200 followed in the optical fiber manufacturing system 100.
[0023] The optical fiber manufacturing system 100 comprises a main furnace 102, an extension tube 106 and one or more annealing furnaces 110.
[0024] The main furnace 102 is used for preform drawing. The main furnace 102 is an induction furnace having graphite heating element with a heating coil, which heats glass preforms and converts the glass preform into an optical fiber of 125 microns in the presence of inert gases like Helium, Argon or Nitrogen to have uniform glass preform heating and to avoid oxidation of graphite heating element. The main furnace 102 is configured to receive an optical fiber preform 104 from its top end 114. The optical fiber preform 104 is a glass preform i.e., silica preform. The main furnace 102 further facilitates melting of the optical fiber preform 104 into an optical fiber 108. That is, the optical fiber 108 is drawn from a bottom end 116 of the main furnace 102, wherein the main furnace 102 has a temperature in a range between 2100-2500 degree Celsius intended for drawing of the optical fiber 108. The range of 2100-2500 degree Celsius is also suitable for drawing of the optical fiber 108 having increased diameter with a high draw line speed. Alternatively, the main furnace 102 may have any other suitable temperature for drawing of the optical fiber 108.
[0025] 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 other suitable category or the optical fiber may be a multi-core optical fiber. 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. The optical fiber comprises one or more cores and one or more clads, where a core is a light-carrying portion of the optical fiber using total internal reflection in which optical signal is confined and a clad is a region that prevents loss of signal by preventing any signal leakage from the core.
[0026] The bottom end 116 of the main furnace 102 is coupled with the extension tube 106 using a holding plate 118 (as shown in FIG. 1a). That is, the extension tube 106 is extended below the main furnace 102 to avoid sudden shock to the optical fiber 108 with room environmental conditions. Since, the optical fiber 108 is formed in the main furnace 102 at a very high temperature and exposing the optical fiber 108 to sudden change of temperature will result in a rapid quenching, hence the extension tube 106 is used to avoid sudden cooling and guide exhaust gases along the optical fiber 108 to have a slow cooling. The extension tube 106 may be fixedly or detachably coupled with the main furnace 102 from one end. The extension tube 106 may be made from glass, metal or any appropriate material or combination of materials known to a person having ordinary skill in the art. The extension tube 106 may have a cylindrical structure. Alternatively, the extension tube 106 may have any other suitable structure. The extension tube 106 may be incorporated with an air sealing mechanism. The extension tube 106 provides a passage for the optical fiber 108 being drawn from the main furnace 102. The extension tube 106 comprises a tubular body 106b with an insulation 106a. As shown in FIG. 1a, an inner diameter (ID) of the tubular body 106b is 80 mm, an outer diameter (OD) of the tubular body 106b is 82 mm, and a length (Le) of the extension tube 106 is 2 meters. Alternatively, the inner diameter, the outer diameter and the length (Le) of the extension tube 106 may vary. The insulation 106a may be a ceramic insulation having a thickness (T) of 1 inch applied for a length (Lc) of 1 meter on the tubular body 106b. Range of the thickness of the insulation 106a is 0.8 inch to 1.2 inch. If insulation 106a thickness is more than 1.2 inch, it leads to increased fiber break and attenuation due to release of metal particles inside the extension tube 106. Furthermore, length (Lc) of the 1 meter is optimised based on the furnace set-up requirements and fibre draw speed. It may be noted that length may vary according to the furnace set-up and fiber draw speeds such that length would be more for higher fibre draw speed. It may be noted that any other suitable insulation material may be used. Further, the thickness and length of the insulation 106a may vary.
[0027] Referring back to FIG. 1, the drawn optical fiber 108 from the main furnace 102 is fed to the one or more annealing furnaces 110 via the extension tube 106, wherein distance (d) between the extension tube 106 and a first annealing furnace 110a is at least 25 cms; for example between 25 cms and 55 cms. The distance (d) between the extension tube 106 and the first annealing furnace 110a is at least 25 cms in order to provide effective annealing, to avoid furnace particles entering into the one or more annealing furnaces 110 as well as to prevent sudden heat treatment of the optical fiber 108. In other words, benefit of maintaining the distance (d) from 25 cms is to decrease gas flow turbulence from the main furnace 102 to the first annealing furnace 110a as below 25 cms, due to the gas flow turbulence, the furnace particles cause contamination which may impact properties like attenuation of the optical fiber 108. Further, the distance (d) between bottom of the extension tube 106 and start (i.e., top end) of the first annealing furnace 110a is at least 25 cms to reduce thermal stress generation during the annealing process. The annealing process is used for cooling of the optical fiber 108 in a controlled manner to avoid rapid quenching as the rapid quenching generates thermal stress on the optical fiber 108, which influences fiber attenuation.
[0028] Each of the one or more annealing furnaces 110 (e.g., first annealing furnace 110a, second annealing furnace 110b, third annealing furnace 110c) has, but not limited to, an alumina tube 1101, a ceramic insulation 1102, a heating coil 1103, a thermocouple 1104 and a temperature controller 1105 as shown in FIG. 1b, wherein the heating coil 1103 is made of nichrome. The alumina tube 1101 is made of aluminium oxide (Al2O3) ceramic that provides electrical insulation and has a high chemical resistance and a low thermal expansion. The combination of the ceramic insulation 1102 and the heating coil 1103 provides optimal degrees of temperature uniformity in the one or more annealing furnaces 110. Further, the thermocouple 1104 is a sensor used to measure temperature in the one or more annealing furnaces 110 while the temperature controller 1105 controls the temperature of the one or more annealing furnaces 110. The thermocouple 1104 and the temperature controller 1105 maintain a requisite temperature in the one or more annealing furnaces 110. It may be noted that for illustration purposes, only the first annealing furnace 110a is shown in FIG. 1b. The second annealing furnace 110b and the third annealing furnace 110c comprise the same components and structure as the first annealing furnace 110a and excluded herein for sake of brevity.
[0029] The one or more annealing furnaces 110 facilitates annealing of the optical fiber 108 by holding the optical fiber 108 in a plurality of stages to provide an annealed optical fiber 112 with low attenuation, where an annealing temperature for the optical fiber 108 in each of the plurality of stages is constant and holding time in the plurality of stages (i.e., in the one or more annealing furnaces 110) for the optical fiber 108 during the annealing process is in a range of 0.06 - 0.36 seconds, wherein if the holding time is below 0.06 seconds, the cooling of the optical fiber 108 is expedited that will impact the fiber attenuation and if the holding time is above 0.36 seconds, the cooling of the optical fiber 108 slows down, therefore resulting in low fictive temperature, less density variation and reduced attenuation loss. The holding time is dependent upon draw line speed (meter per min (MPM)) such that lower the draw line speed higher would be the holding time. The holding time can be obtained using a formula T = L/V, where T is holding time, L is Length of furnace and V is draw line speed. Below table (Table 1) shows some example holding times (T) with respect to corresponding draw line speeds (V):
Length of furnace (L) 3 meters
Draw Line Speed (V)
(Meter per min (MPM)) Holding Time (T) (seconds)
3000 0.06
1850 0.10
1000 0.18
500 0.36
Table 1
[0030] Since the annealing process is conducted in the plurality of stages through the one or more annealing furnaces 110 (i.e., in the first annealing furnace 110a, the second annealing furnace 110b and the third annealing furnace 110c), where the annealing temperature is same in each of the plurality of stages due to which sudden thermal heating and cooling is avoided which is a major cause of thermal stress within the optical fiber 108. A rate of moving the optical fiber 108 between each of the plurality of stages is more than 1500 mm/minute, preferably in a range of 1500-2000 mm/minute, wherein the rate of moving the optical fiber 108 more than 2000 mm/minute results in increased fiber loss, which is mainly caused by change in Rayleigh scattering due to density fluctuation and the rate of moving the optical fiber 108 less than 1500 mm/minute results in less density fluctuation influence to the optical fiber 108. Alternatively, the holding time in the plurality of stages for the optical fiber 108 during annealing process and the rate of moving the optical fiber 108 between each of the plurality of stages may vary. Further, a time gap between each of the plurality of stages is dependent upon one or more factors. The one or more factors for determining the time gap between each of the plurality of stages include length (La) of each of the one or more annealing furnaces 110 and a time period for holding the optical fiber 108 in one stage from the plurality of stages in each of the one or more annealing furnaces 110, wherein the length (La) of each of the one or more annealing furnaces 110 is 1 meter. The length (La) of 1 meter is selected based on current space availability and draw speeds.
[0031] As mentioned earlier, the one or more annealing furnaces 110 facilitates annealing of the optical fiber 108 in the plurality of stages (i.e., in Annealing furnace 1 (first annealing furnace 110a), Annealing furnace 2 (second annealing furnace 110b), Annealing furnace 3 (third annealing furnace 110c)), where each of the one or more annealing furnaces 110 is maintained at the a plurality of pre-defined constant temperatures (i.e., annealing temperature or temperature) (e.g., 1050 degree Celsius) to prevent generation of stress in the optical fiber. That is, an entry and exit temperature of each of the one or more annealing furnaces 110 is maintained constant, wherein constant refers to variation of up to 2%. Further, complete length (L) of the plurality of stages is 3 meters and each of the one or more annealing furnaces 110 is installed/placed at a distance (d1) between 5-10 cms. If the distance (d1) is equal to 5 cms, then the annealing temperature will be maintained. Further, if the distance (d1) is below 5 cms, proper annealing will not occur due to the gas flow turbulence and if the distance (d1) is more than 10 cms, then the annealing of the optical fiber 108 in that portion will not happen, thereby influencing the attenuation loss due to thermal shock. If the length (L) of the plurality of stages is less than 3 meters, then holding time of fiber in the annealing furnace would be less resulting in higher attenuation and stress on fiber. The length (L) of 3 meters is designed based on fiber draw speed.
[0032] Herein, the annealing process is performed by increasing annealing time in an existing set up and by positioning each of the one or more annealing furnaces 110 with respect to exit/bottom end of the main furnace 102 as illustrated in FIG. 1. Typically, annealing is a process of heating a metal or alloy to an appropriate temperature for a certain time period and then slowly cooling the same. In other words, annealing is a heat treatment process that changes physical and sometimes also chemical properties of a material to increase ductility and reduce the hardness to make it more workable. The annealing process is optimized herein, thus may be termed as effective annealing. The effective annealing is done so as to reduce the relaxation time of the optical fiber that prevents generation of thermal stress within the optical fiber which can cause structural imperfection.
[0033] As the annealed optical fiber 112 manufactured through a heat treatment process, i.e., the annealing process, which leaves no imprint that will help in distinguishing it from an optical fiber manufactured from an optical fiber preform that has not undergone the annealing process. In an example, the annealing process is performed in three annealing furnaces at same/constant temperature that provides time for relaxation of the heated optical fiber and reduces thermal shock or sudden onset of stress due to sudden relaxation through the annealing process. Additionally, chlorine addition provides or acts as core viscosity reduction due to which core of the optical fiber becomes softer i.e., easier to flow to provide relaxation and ease in releasing of stress from the hot optical fiber preform.
[0034] Post annealing process, the annealed optical fiber 112 undergoes cooling process and coating process to obtain a coated optical fiber as depicted in FIG. 2. The annealed optical fiber 112 may have a diameter less than 250 microns.
[0035] Advantageously, the annealed optical fiber 112 manufactured by the proposed approach has a reduced attenuation. Optical attenuation or attenuation in fiber optics, also known as transmission loss, is the reduction in intensity or strength of the light beam (or signal) with respect to distance travelled through a transmission medium. Generally, attenuation varies with the wavelength of light/signal used and for a complete characterization of attenuation performance, a measure of attenuation over a wide range of wavelengths is required. The annealed optical fiber 112 has an average attenuation of less than 0.3211 dB/Km at 1310 nm wavelength, an average attenuation of less than 0.1819 dB/Km at 1550 nm wavelength and an average attenuation of less than 0.204 dB/Km at 1625 nm wavelength. Alternatively, the attenuation may vary.
[0036] Along with attenuation reduction in the annealed optical fiber 112, the proposed approach facilitates improving the quality of signal transmitted from the optical fiber. Further, the above combination of processes is effective for any category of optical fibers.
[0037] Further, the annealed optical fiber 112 has a macro-bend loss of less than 0.3 dB/Km at 1625 nm wavelength for 30 mm radius of curvature, a macro-bend loss of less than 1.5 dB/Km at 1625 nm wavelength at 10 mm radius of curvature, a macro-bend loss of less than 0.1 dB/Km at 1550 nm wavelength at 30 mm radius of curvature and a macro-bend loss of less than 0.5 dB/Km at 1550 nm wavelength at 10 mm radius of curvature. The macro-bend loss is defined by a loss occurred when an optical fiber cable is subjected to a significant amount of bending above a critical value of curvature.
[0038] FIG. 3 is a flow chart 300 illustrating an optical fiber manufacturing method. It may be noted that in order to explain the flow chart 300, references will be made to the elements explained in FIG. 1 through FIG 2.
[0039] At step 302, the method includes drawing the optical fiber 108 from the optical fiber preform 104 using the main furnace 102, wherein the main furnace 102 has the temperature in between 2100-2500 degree Celsius.
[0040] At step 304, the method includes annealing the optical fiber 108 in the plurality of stages in the one or more annealing furnaces 110. The annealing temperature in each of the plurality of stages is constant, wherein constant refers to variation of up to 2%. The optical fiber 108 is annealed at the plurality of pre-defined constant temperatures.
[0041] FIG. 4 is a flow chart 400 illustrating an optical fiber manufacturing method. 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 2.
[0042] At step 402, the method includes drawing the optical fiber 108 from the optical fiber preform 104 using the main furnace 102, wherein the main furnace 102 has the temperature in between 2100-2500 degree Celsius.
[0043] At step 404, the method includes passing the optical fiber 108 from the main furnace 102 to each of the one or more annealing furnaces 110.
[0044] At step 406, the method includes holding the optical fiber 108 in each of the plurality of stages for a time period to produce the annealed optical fiber 112.
[0045] At step 408, the method includes annealing the optical fiber 108 in the plurality of stages in the one or more annealing furnaces 110. The annealing temperature in each of the plurality of stages is constant, wherein constant refers to variation of up to 2%. The optical fiber 108 is annealed at the plurality of pre-defined constant temperatures.
[0046] The various actions, acts, blocks, steps, or the like of the flow charts 200, 300 and 400 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 invention.
[0047] Conditional language used herein, such as, among others, "can", "may", "might", “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.
[0048] 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.
[0049] 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.
, C , Claims:CLAIMS
We Claim:

1. An optical fiber manufacturing system (100) comprising:
a main furnace (102) for drawing an optical fiber (108) from an optical fiber preform (104), wherein the main furnace (102) has a temperature in a range between 2100-2500 degree Celsius; and
one or more annealing furnaces (110) for annealing the optical fiber (108) in a plurality of stages, wherein annealing temperature in each of the plurality of stages is constant, wherein constant refers to variation of up to 2%, wherein the optical fiber (108) is annealed at a plurality of pre-defined constant temperatures.

2. The optical fiber manufacturing system (100) as claimed in claim 1, wherein holding time in the plurality of stages for the optical fiber (108) during annealing process is in a range of 0.06 to 0.36 seconds.

3. The optical fiber manufacturing system (100) as claimed in claim 1, wherein a rate of moving the optical fiber (108) between each of the plurality of stages is more than 1500 mm/minute.

4. The optical fiber manufacturing system (100) as claimed in claim 1, wherein a complete length (L) of the plurality of stages is more than 2 meters and wherein distance (d1) between each annealing furnace is less than 10 cms.

5. An optical fiber manufacturing method comprising:
drawing an optical fiber (108) from an optical fiber preform (104) through a main furnace (102), wherein the main furnace (102) has a temperature in a range between 2100-2500 degree Celsius; and
annealing the optical fiber (108) in a plurality of stages in one or more annealing furnaces (110), wherein annealing temperature in each of the plurality of stages is constant, wherein constant refers to variation of up to 2%, wherein the optical fiber (108) is annealed at a plurality of pre-defined constant temperatures.

6. The optical fiber manufacturing method as claimed in claim 5, further comprising passing the optical fiber (108) from the main furnace (102) to each of the one or more annealing furnaces (110).

7. The optical fiber manufacturing method as claimed in claim 5, further comprising passing the optical fiber (108) from the main furnace (102) to each of the one or more annealing furnaces (110) through an extension tube (106).

8. The optical fiber manufacturing method as claimed in claim 5, further comprising holding the optical fiber (108) in each of the plurality of stages for a time period to produce an annealed optical fiber (112).

9. The optical fiber manufacturing method as claimed in claim 8, wherein the annealed optical fiber (112) has a macro-bend loss of less than 0.3 dB/Km at 1625 nm wavelength for 30 mm radius of curvature, a macro-bend loss of less than 1.5 dB/Km at 1625 nm wavelength at 10 mm radius of curvature, a macro-bend loss of less than 0.1 dB/Km at 1550 nm wavelength at 30 mm radius of curvature and a macro-bend loss of less than 0.5 dB/Km at 1550 nm wavelength at 10 mm radius of curvature and wherein the annealed optical fiber (112) has an average attenuation of less than 0.3211 dB/Km at 1310 nm wavelength, an average attenuation of less than 0.1819 dB/Km at 1550 nm wavelength and an average attenuation of less than 0.204 dB/Km at 1625 nm wavelength.

10. An annealed optical fiber (112) having a macro-bend loss of less than 0.3 dB/Km at 1625 nm wavelength for 30 mm radius of curvature, a macro-bend loss of less than 1.5 dB/Km at 1625 nm wavelength at 10 mm radius of curvature, a macro-bend loss of less than 0.1 dB/Km at 1550 nm wavelength at 30 mm radius of curvature and a macro-bend loss of less than 0.5 dB/Km at 1550 nm wavelength at 10 mm radius of curvature, wherein the annealed optical fiber (112) has an average attenuation of less than 0.3211 dB/Km at 1310 nm wavelength, an average attenuation of less than 0.1819 dB/Km at 1550 nm wavelength and an average attenuation of less than 0.204 dB/Km at 1625 nm wavelength, wherein the annealed optical fiber (112) is manufactured by annealing at a plurality of pre-defined constant temperatures, wherein constant refers to variation of up to 2%.