Claims:CLAIMS
We claim:

1. An optical fiber, comprising:
a core extending along a central axis of the optical fiber, wherein the core is up-doped with at least a first up-dopant and a second up-dopant;
an inner cladding surrounding the core, wherein the inner cladding is up-doped with at least the second up-dopant; and
an outer cladding surrounding the inner cladding, wherein the outer cladding is un-doped.

2. The optical fiber of claim 1, wherein the core, the inner cladding, and the outer cladding has a refractive index ?1, a refractive index ?2, and a refractive index ?3, respectively, such that the refractive index ?1 is greater than the refractive index ?2 and the refractive index ?2 is greater than the refractive index ?3.

3. The optical fiber of claim 1, wherein the core has a relative refractive index ?1% that is in range 0.2 % to 0.4 %, wherein the inner cladding has a relative refractive index ?2% that is in range 0.01 % to 0.05 %, and wherein the outer cladding has a relative refractive index ?3% that is equal to 0%.

4. The optical fiber of claim 1, wherein the core up-doped with first and second up-dopants, the inner cladding up-doped with the second up-dopant, and the un-doped outer cladding 106 generates a Refractive Index (RI) profile that is defined by a core peak and an inner cladding peak, wherein the core peak is greater than the inner cladding peak.

5. The optical fiber of claim 4, wherein the core peak and the inner cladding peak has a peak radial distance therebetween, wherein the radial distance is in a range of 9 micrometres (µm) to 10 µm.
6. The optical fiber of claim 1, wherein the core and the inner cladding has the second up-dopant in first and second concentrations, respectively, wherein the first concentration is less than the second concentration.

7. The optical fiber of claim 8, wherein the first concentration of the second up-dopant in the core is in a range of 41% to 43% and the second concentration of the second up-dopant in the inner cladding 104 is in a range of 57% to 59%.

8. The optical fiber of claim 1, wherein concentration of the first up-dopant in the core is in a range of 0.25% to 0.3%.

9. The optical fiber of claim 1, wherein the core and the inner cladding has the second up-dopant in a first and second volumes, wherein the first volume is less than the second volume.

10. The optical fiber of claim 9, wherein the first volume of the second up-dopant in the core is in a range of 1850 ppm to 2100 ppm and the second volume of the second up-dopant in the inner cladding is in a range of 2490 ppm to 2800 ppm.

11. The optical fiber of claim 9, wherein the volume of the first up-dopant (i.e., Ge) in the core may be in a range of 2500 Parts Per Million (ppm) to 3000 ppm

12. The optical fiber of claim 1, wherein the relative refractive index ?2% of the inner cladding is radially distributed with a maximum value ?2max and a minimum value ?2min, wherein the maximum value ?2max is 0.03 and the minimum value ?2min is 0.02.

13. The optical fiber of claim 1, wherein (i) an attenuation of the optical fiber at a wavelength of 1625 nanometres (nm) is less than 0.2, wherein the attenuation of the optical fiber at a wavelength of 1550 nm is less than 0.18, and wherein the attenuation of the optical fiber at a wavelength of 1310 nm is less than 0.32, (ii) a macro bend loss of the optical fiber for 10 turns, 30mm Mandrel diameter and at a wavelength of 1625 nm is less than 0.3 db/km, wherein the macro bend loss in the optical fiber for 1 turn, 20mm Mandrel diameter at the wavelength of 1625 nm is less than 1.5 db/km, wherein the macro bend loss of the optical fiber for 10 turn, 30mm Mandrel diameter at a wavelength of 1550 nm is less than 0.1 db/km, and wherein the macro bend loss of the optical fiber for 1 turns, 20mm Mandrel diameter at the wavelength of 1550 nm is less than 0.5 db/km, and (iii) a cable cutoff of the optical fiber is in a range of 1186nm to 1194 nm.

14. The optical fiber of claim 1, wherein the core has a radius R1 that is in range of 4 µm to 4.5 µm, wherein the inner cladding has a radius R2 that is in a range of 14 µm to 15 µm, and wherein the outer cladding has a radius R3 that is in range 61.5 µm to 62.5 µm.

15. The optical fiber of claim 13, wherein the radius R1, the radius R2, and the radius R3 is given by an average ratio (R3 - R1) / (R2 - R1), wherein the average ratio is in a range of 5.52 µm to 5.75 µm.

16. The optical fiber of claim 1, wherein the core has a thickness T1 and the inner cladding has a thickness T2 such that the thickness T2 is greater that the thickness T1.
, Description:FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13)

TITLE OF THE INVENTION
“OPTICAL FIBER WITH AN ATTENUATION REDUCTION REFRACTIVE INDEX (RI) PROFILE”
APPLICANTS:
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 performed.
TECHNICAL FIELD
[0001] The present disclosure relates generally to optical fibers, and, more particularly, to an optical fiber with an attenuation reduction Refractive Index (RI) profile.
BACKGROUND
[0002] Telecommunication systems for underground and undersea applications, require optical fibers that can transmit signals to longer distances without any degradation. However, the optical fiber attributes such as attenuation and bend loss can contribute to some degradation of the signals transmitted through the optical fiber. The increased attenuation can disrupt quality of the signals which is being transmitted in the optical fiber. Moreover, a part of the degradation of optical performance of the optical fiber may be attributed to stress in the optical fiber, a part of which may be inherited from the stress in a glass preform from which the optical fiber was drawn.

[0003] Prior art, WO2018093451 discloses an optical fiber with low attenuation where a core of the optical fiber is up-doped and chlorine (Cl) is present in an outer cladding of the optical fiber. However, the optical fiber does not reduce stress in an optical fiber preform and hence the optical fiber (while drawings). Further, prior art, US9658394B2 discloses a single mode optical fiber having a core made from silica and less than or equal to about 6.5 weight % germania and having a maximum relative refractive index ?1MAX. The core of optical fiber is up-doped and an inner cladding is down doped. However, the optical fiber is not optimized to reduce stress in an optical fiber preform and hence the fiber (while drawings). Furthermore, the prior art, US2018031761A1 discloses an attenuation reduction through adding chlorine in a core of an optical fiber. Furthermore, prior art CA2630557A1 discloses a method of producing an optical fiber where fluorine is doped in an inner cladding during consolidation process. However, the optical fiber of CA2630557A1 is not optimized to reduce stress in an optical fiber preform and hence the optical fiber (while drawings).
[0004] Thus, there is a need for a technical solution that allows an optimized fabrication of an optical fiber that can reduce stress in an optical fiber preform and hence the optical fiber while reducing the attenuation of the optical fiber.
SUMMARY
[0005] In an aspect of the present disclosure, an optical fiber is disclosed. The optical fiber has a core extending parallelly along a central axis of the optical fiber The core is up-doped with first and second up-dopants. Further, the optical fiber has an inner cladding surrounding the core. The inner cladding is up-doped with the second up-dopant. Furthermore, the optical fiber has and an outer cladding surrounding the inner cladding. The outer cladding is un-doped. The optical fiber has an attenuation of less than 0.2 at a wavelength of 1625 nanometres (nm), and the attenuation of less than 0.18 at a wavelength of 1550 nm, and the attenuation of less than 0.32 at a wavelength of 1310 nm. The optical fiber further has a cable cutoff in a range of 1186 nanometres (nm) to 1194 nm.
BRIEF DESCRIPTION OF DRAWINGS
[0006] The following detailed description of the preferred aspects of the present disclosure will be better understood when read in conjunction with the appended drawings. The present disclosure is illustrated by way of example, and not limited by the accompanying figures, in which like references indicate similar elements.

[0007] FIG. 1 illustrates a cross-sectional view of an optical fiber.

[0008] FIG. 2 illustrates a graph representing a Refractive Index (RI) profile of the optical fiber of FIG. 1.

DETAILED DESCRIPTION
[0009] 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.

Definitions:
[0010] As used herein the term “core” of an optical fiber as used herein is referred to as the inner most cylindrical structure present in the center of the optical fiber, that is configured to guide the light rays inside the optical fiber.

[0011] The term “Cladding” of an optical fiber as used herein is referred to as one or more layered structure covering the core of an optical fiber from the outside, that is configured to possess a lower refractive index than the refractive index of the core to facilitate total internal reflection of light rays inside the optical fiber. Further, the cladding of the optical fiber may include an inner cladding layer coupled to the outer surface of the core of the optical fiber and an outer cladding layer coupled to the inner cladding from the outside.

[0012] The term “refractive index” as used herein is referred to as the measure of change of speed of light from one medium to another and is particularly measured in reference to speed of light in vacuum. More specifically, the refractive index facilitates measurement of bending of light from one medium to another medium.

[0013] The term “relative refractive index” as used herein is referred to as the ratio of refractive index of one medium to the refractive index of other medium.

[0014] The term refractive index profile” of the optical fiber as used herein is referred to as the distribution of refractive indexes in the optical fiber from the core to the outmost cladding layer of the optical fiber. Based on the refractive index profile, the optical fiber may be configured as a step index fiber. The refractive index of the core of the optical fiber is constant throughout the fiber and is higher than the refractive index of the cladding. Further, the optical fiber may be configured as a graded index fiber, wherein the refractive index of the core gradually varies as a function of the radial distance from the center of the core.

[0015] The term “core peak” as used herein is referred to as the maximum refractive index value of the core of the optical fiber. The core peak is more significant in the graded index fiber as for the step index fiber, the refractive index of the core is same throughout.

[0016] The term “Cladding peak” as used herein is referred to as the maximum value of the refractive index of the one or more layers of cladding of the optical fiber.

[0017] The term “up-doping” as used herein is referred to as adding doping materials to facilitate increase in the refractive index of a particular layer or part of optical fiber. The materials configured to facilitate up-doping are known as up-dopants.

[0018] The term “down-doping” as used herein is referred to as adding doping materials to facilitate decrease in the refractive index of a particular layer or part of optical fiber. The materials configured to facilitate down-doping are known as down-dopants.

[0019] Concentration of Up dopant:
The term “first concentration” as used herein is referred to as the percentage of the up-dopant materials present in the core that facilitate an increase in refractive index of the core of the optical fiber.
The term “second concentration” as used herein is referred to as the percentage of the up-dopant material present in the inner cladding that is configured to facilitate an increase in the refractive index of the inner cladding of the optical fiber.
The term “first volume” as used herein is referred to as the count of the up-dopant present per million of the elements of the core, i.e., concentration of the up-dopant in the core in (ppm), that is configured to facilitate an increase in refractive index of the core of the optical fiber.
The term “second volume” as used herein is referred to as the count of the up-dopant present per million of the elements of the inner cladding i.e., concentration of the up-dopant in the inner cladding in (ppm), that is configured to facilitate an increase in refractive index of the core of the optical fiber.

[0020] FIG. 1 illustrates a cross-sectional view of an optical fiber 100. The optical fiber 100 may be fabricated to have reduced attenuation without increasing macro bend losses. As illustrated in FIG. 1. the optical fiber 100 may have a core 102, an inner cladding 104, and an outer cladding 106. Further, the optical fiber 100 may have a central axis 108 such that the core 102 may be arranged along the central axis 108 running longitudinally, i.e., generally parallel to the central axis 108. The optical fiber 100 may have a Refractive Index (RI) profile (shown later in FIG. 2) that may be generated by virtue of the core 102 being up doped with Germanium (Ge) and Chlorine (Cl), the inner cladding 104 being up doped with Cl and the outer cladding being undoped and made up of pure silica. Specifically, by up doping the core 102 and the inner cladding 104 with Cl, the RI profile having an upward peak in the inner cladding region may be generated, that may further facilitate the optical fiber 100 to have reduced attenuation without increasing macro bend losses.

[0021] The core 102 may be a cylindrical fiber that may run along a length of the optical fiber 100 and may be configured to guide an optical signal. The core 102 may be made up of a material selected from at least one of, a pure silica glass, Silicon tetrachloride (SiCl4), Germanium tetrachloride (GeCl4), Chlorine gas (Cl2), and the like. Preferably, the core 100 may be made up of a silica glass doped with a first up-dopant and a second up-dopant. Aspects of the present disclosure are intended to include and/or otherwise cover any type of the material for the core 102, including known, related, and later developed materials. Specifically, the core 102 may be up-doped with the first and second up-dopants that may increase values of net refractive index of the optical fiber 100 and may further facilitate to control macro bend losses. The first and second up-dopants may be Germanium (Ge), and Cl2, respectively. In some aspects of the present disclosure, a concentration (i.e., a weight percentage (wt. %)) of the first up-dopant in the core 102 may be in a range of 0.25% to 0.3%. Preferably, the concentration of the first up-dopant in the core 102 may be 0.3%. Further, the second up-dopant may have a first concentration in the core 102. In some aspects of the present disclosure, the first concentration (i.e., a weight percentage (wt. %)) of the second up-dopant in the core 102 may be in a range of 41% to 43%. Preferably, the first concentration of the second up-dopant in the core 102 may be 42%. In some aspects of the present disclosure, a volume of the first up-dopant (i.e., Ge) in the core 102 may be in a range of 2500 Parts Per Million (ppm) to 3000 ppm. Preferably, the volume of the first up-dopant (i.e., Ge) in the core 102 may be 3000 ppm. Further, the second up-dopant may have a first volume in the core 102. The first volume of the second up-dopant may be in a range of 1850 ppm to 2100 ppm. Preferably, the first volume of the second up-dopant (i.e., Cl2) in the core 102 may be 1950 ppm. The second up-dopant may have a second volume in the inner cladding 104. The second volume of the second up-dopant may be in a range of 2490 ppm to 2800 ppm. Preferably, the second volume of the second up-dopant (i.e., Cl2) in the inner cladding 104 may be 2680 ppm.

[0022] Specifically, the second up-dopant (i.e., Cl2) may be used to up dope the core 102 as Cl2 can facilitate in reduction of stress in an optical fiber preform and hence in the optical fiber 100. In other words, the second up-dopant (i.e., Cl2) may act as a core viscosity reduction agent such that the core 102 becomes softer (i.e., easy to flow to provide relaxation and ease in releasing of stress from the hot optical fiber preform and resultant optical fiber.

[0023] The core 102 may have a radius R1, a thickness T1 (shown later in FIG. 2), and a refractive index ?1. In some aspects of the present disclosure, the radius R1 may be in a range of 4 micrometres (µm) to 4.5 µm. Preferably, the radius R1 may be 4 µm. In some aspects of the present disclosure, the thickness T1 may be less than 4.5 µm. Preferably, the thickness T1 may be equal to the radius R1. In some aspects of the present disclosure, the refractive index ?1 may be in a range of 4.4 to 5.4 Further, the core 102 may have a core alpha in a range of 3 to 5. Furthermore, the core 102 may have a Mode Field Diameter (MFD) in a range of 8.85 to 9.2. Specifically, the refractive index ?1 in the range of 4.4 to 5.4, the core alpha in the range of 3 to 5, and the MFD in the range of 8.85 to 9.2 may facilitate the optical fiber 100 to demonstrate desirable parameters. The desirable parameters may be, but not limited to, low attenuation, low MFD, high cutoff, low dispersion, and low macro bending loss, and the like.

[0024] To the contrary, when the core 102 has the refractive index ?1 that is not within the range of 4.4 to 5.4, the core alpha that is not in the range of 3 to 5, and the MFD that is not in the range of 8.85 to 9.2, the optical fiber 100 may demonstrate undesirable parameters such as high attenuation, high MFD, less power in a core region, low cutoff, high macro bending loss, high dispersion, and poor lightening in confined space.

[0025] The inner cladding 104 may be surrounding the core 102. The inner cladding 104 may be made up of a material selected from at least one of, a pure silica glass, a doped silica glass, and the like. In some aspects of the present disclosure, the inner cladding 104 may be made up of a combination of SiCl4 and Cl2. Preferably, the inner cladding 104 may be made up of a silica glass doped with the second up-dopant. Aspects of the present disclosure are intended to include and/or otherwise cover any type of the material for the inner cladding 104, including known, related, and later developed materials. Specifically, the inner cladding 104 may be up-doped with the second up-dopant that may increase values of net refractive index of the optical fiber 100 and may further facilitate to control macro bend losses in the optical fiber 100. Further, the core 102 and the inner cladding 104 may be doped with the second up-dopant (i.e., Cl2) to avoid generation of stress in the optical fiber 100.

[0026] In some aspects of the present disclosure, the inner cladding 104 may have the second up-dopant in a second concentration. In some aspects of the present disclosure, the second concentration (i.e., a weight percentage (wt. %)) of the second up-dopant (i.e., Cl2) in the inner cladding 104 may be in a range of 57% to 59%. Preferably, the second concentration of the second up-dopant (i.e., Cl2) in the inner cladding 104 may be 58%. In some aspects of the present disclosure, the inner cladding 104 may have the second up-dopant in a second volume. The second volume of the second up-dopant in the inner cladding 104 may be in a range of 2490 ppm to 2800 ppm. Preferably, the second volume of the second up-dopant in the inner cladding 104 may be 2680 ppm.

[0027] In some aspects of the present disclosure, the first concentration may be lower than the second concentration. In other words, the second concentration of the second up-dopant in the inner cladding 104 may be higher as compared to the first concentration of the second up-dopant in the core 102. Specifically, the second concentration may be higher as compared to the first concentration to accommodate the consolidation of the inner cladding 104 that happens prior to the consolidation of the core 102. The addition of the second up-dopant (i.e., Cl2) in the core 102 and in the inner cladding 104 may further reduce the stress in the optical fiber preform and hence in the optical fiber 100, thus generating a peak surrounding an inner clad region (shown later in FIG. 2). Specifically, the addition of the second up-dopant may reduce viscosity that may facilitate to avoid causing stresses between the core 102 and the inner cladding 104 of the optical fiber 100. Further, the addition of the second up-dopant in the core 102 and the inner cladding 104 may increase the value of net refractive index of the optical fiber 100 that may further facilitate to control the macro-bend loss of the optical fiber 100. Specifically, the addition of the second up-dopant may facilitate to control the macro-bend loss to less than 0.1 Decibel/Kilometres (dB/Km) at a wavelength of 1550 nanometres (nm) at 30mm Mandrel diameter for 10 turns and the macro-bend loss may be controlled to less than 0.3 dB/Km at a wavelength of 1625 nm for 30 mm Mandrel diameter for 10 turns.

[0028] The addition of the first dopant in the core 102 may facilitate to increase the refractive index of the core 102. However, a concentration of the first dopant is not increased in the optical fiber 100 to control attenuation. Thus, the attenuation in the optical fiber 100 may be controlled only through the addition of the first and second up-dopants in the core 102 and the addition of the second up-dopant in the inner cladding 104 and keeping the overall concentration of the first up-dopant in the optical fiber 100 consistent. In some aspects of the present disclosure, at a wavelength of 1310, the attenuation of the optical fiber 100 may be controlled to a value that may be in a range of 0.32 to 0.324. In some other aspects of the present disclosure, at a wavelength of 1550, the attenuation of the optical fiber 100 may be controlled to a value that may be in a range of 0.179 to 0.184.

[0029] The inner cladding 104 may have a radius R2, a thickness T2 (shown later in FIG. 2), and a refractive index ?2. Specifically, the radius R2 of the inner cladding 104 may be in a range of 14 µm to 15 µm. Preferably, the radius R2 of the inner cladding 104 may be 14.5um. In some aspects of the present disclosure, the second up-dopant may be doped in the inner cladding 104 in a way such that the concentration of the second up-dopant in the inner cladding 104 varies along the radius R2 of the inner cladding 104. Further, the thickness T2 of the inner cladding 104 may be equal to a difference between a numerical value of the radius R2 of the inner cladding 104 and a numerical value of the radius R1 of the core 102 (i.e., T2 = R2 - R1). In some aspects of the present disclosure, the thickness T2 of the inner cladding 104 may be greater than the thickness T1 of the core 102. Specifically, the thickness T2 of the inner cladding 104 may be in a range of 10 µm to 10.5 µm.

[0030] Further, the inner cladding 104 may have a relative refractive index ?2% that may be in a range of 0.01 to 0.05. The relative refractive index ?2% of the inner cladding 104 may be radially distributed along the central axis 108 of the optical fiber 100. Further, the relative refractive index ?2% of the inner cladding 104 may have a maximum value ?2max and a minimum value ?2min (as shown later in FIG. 2). Specifically, the relative refractive index ?2% may be less than the relative refractive index ?1% of the core 102. Similarly, the refractive index ?2 of the inner cladding 104 may be less than the refractive index ?1 of the core 102. In other words, the refractive index ?1 of the core 102 may be higher than the refractive index ?2 of the inner cladding 104 such that the optical signal that propagates through the core 102 and that strikes a boundary between the core 102 and the inner cladding 104 at an angle that may be smaller than a critical angle will reflect into the core 102 by total internal reflection.

[0031] The outer cladding 106 may surround the inner cladding 104. The outer cladding 106 may be made up of a material selected from at least one of, a pure silica glass, and the like. Preferably, the outer cladding 106 may be made up of a silica glass that may be undoped. The outer cladding 106 may have a radius R3, a thickness T3, and a refractive index ?3. In some aspects of the present disclosure, the radius R3 may be in a range of 61.5 µm to 62.5 µm. Further, the thickness T3 of the outer cladding 106 may be in a range of 46.5 µm to 48.5 µm. The refractive index ?3 may be equal to 0 such that the refractive index ?1 of the core 102 may be greater than the refractive index ?2 of the inner cladding 104 and the refractive index ?2 of the inner cladding 104 may be greater than the refractive index ?3 of the outer cladding 106. In some aspects of the present disclosure, the radius R1, the radius R2, and the radius R3 may have a predefined ratio. Specifically, the predefined ratio may be in a range of 5.52 µm to 5.75 µm and may be given by the equation (R3 - R1) / (R2 - R1). For example, when the radius R1 is 4 µm, the radius R2 is 14 µm , and the radius R3 is 62.5 µm.

[0032] In one aspect of the present disclosure, the core 102 may have the refractive index ?1 that is between 4.4 to 5.4, the relative refractive index ?1% between 0.33 to 0.36, the radius R1 between 4.4 to 4.6, the core alpha between 3.58 to 4.65, and the MFD between 8.85 to 9.2. Correspondingly, the inner cladding 104 may have the relative refractive index ?2% between 0.02 to 0.03 and the radius R2 between 14 µm to 15 µm. Correspondingly, the outer cladding 106 may have the relative refractive index ?3% of 0 and the radius R3 between 61.5 µm to 62.5 µm. The optical fiber 100 fabricated based on the above numerical values may have a cable cutoff between 1186 nm to 1194 nm. For example, an optical fiber with the refractive index ?1 of 4.4, the relative refractive index ?1% of 0.33, the radius R1 of 4.5, the core alpha of 3.7, the MFD of core 102 of 9.2, the relative refractive index ?2% of 0.02, the radius R2 14 µm, the relative refractive index ?3% of 0 may demonstrate a cable cutoff of 1186 nm.

[0033] In one aspect of the present disclosure, the optical fiber 100 fabricated based on the above numerical values may demonstrate an attenuation of 0.321 Decibel/Kilometers (dB/km) at a wavelength of 1310 nm, an attenuation of 0.182 dB/km at a wavelength of 1550 nm, and an attenuation of 0.202 dB/km at a wavelength of 1625 nm. Further, the optical fiber 100 fabricated based on the above numerical values may demonstrate a MFD of 8.89 µm at a wavelength of 1310 nm. Furthermore, the optical fiber 100 fabricated based on the above numerical values may have a cutoff wavelength of 1295 nm.

[0034] In one aspect of the present disclosure, the optical fiber 100 fabricated based on the above numerical values may demonstrate a MFD in a range of 8.7 to 9.5, a cutoff wavelength in a range of 1160 nm to 1360 nm, and a zero-dispersion in a range of 1300 nm to 1323 nm. For example, when the MFD is 8.9, the optical fiber 100 demonstrates the cutoff of 1294 nm and the zero-dispersion of 1317 nm. Similarly, when the MFD is 8.92, the optical fiber 100 demonstrates the cutoff of 1286 nm and the zero-dispersion of 1316 nm.

[0035] In one aspect of the present disclosure, the optical fiber 100 fabricated based on the above numerical values may experience a macro bend loss of less than 0.3 db/Km for 10 turns, 30mm Mandrel diameter at a wavelength of 1625 nm. Specifically, the optical fiber 100 may experience the macro bend loss of less than 0.1 db/km for 10 turns, 30mm Mandrel diameter at the wavelength of 1550 nm. Further, the optical fiber 100 fabricated based on the above numerical values may experience the macro bend loss of less than 1.5 db/km for 1 turn, 20 mm Mandrel diameter at a wavelength of 1625 nm. Specifically, the optical fiber 100 may experience the macro bend loss of less than 0.5 db/km for 1 turn, 20 mm Mandrel diameter, at the wavelength of 1550 nm. Furthermore, the optical fiber 100 fabricated based on the above numerical values may experience the macro bend loss of less than 0.1 db/km for 10 turns, 30 mm Mandrel diameter at a wavelength of 1550 nm. Specifically, the optical fiber 100 may experience the macro bend loss of less than 0.1 db/km for 10 turns, 30 mm Mandrel diameter at the wavelength of 1550 nm. Furthermore, the optical fiber 100 fabricated based on the above numerical values may experience the macro bend loss of less than 0.5 db/km for 1 turns, 20mm Mandrel diameter at the wavelength of 1550 nm. Specifically, the optical fiber 100 may experience the macro bend loss of less than 0.5 db/km for 1 turns, 20mm Mandrel diameter at the wavelength of 1550 nm.

[0036] FIG. 2 illustrates a graph 200 representing the RI profile of the optical fiber 100. The graph 200 is a radius versus relative refractive index graph such that an x-axis of the graph 200 represents values of the radius R1, the radius R2, and the radius R3 of the core 102, the inner cladding 104, and the outer cladding 106, respectively, and a y-axis of the graph 200 represents values of the relative refractive index ?1%, the relative refractive index ?2%, and the relative refractive index ?3% of the core 102, the inner cladding 104, and the outer cladding 106, respectively. The graph 200 has a curve 202 that represent the RI profile of the optical fiber 100. As illustrated in FIG. 2, the core 102 doped with the first and second up-dopants, the inner cladding 104 doped with the second up-dopant, and the undoped outer cladding 106 generates the RI profile. As shown by the curve 202, the refractive index ?1 of the core 102 has a maximum value that is given by ?1max. As illustrated in FG. 2, the core 102 defines a core region such that the refractive index ?1 of the core 102 is realized in the core region (i.e., within the radius R1 of the core 102). Further, the inner cladding 104 defines an inner cladding region such that the refractive index ?2 of the inner cladding 104 is realized in the inner cladding region (i.e., within the radius R2 of the inner cladding 104). Further, the outer cladding 106 may define an outer cladding region such that the refractive index ?3 of the outer cladding 106 is realized in the outer cladding region (i.e., within the radius R3 of the outer cladding 104).

[0037] As illustrated in the FIG. 2, the curve 202 transitions from of the core region to the inner cladding region, thus generating the RI profile that is defined by a core peak 204 and an inner cladding peak 206. As shown by the curve 202, the core peak 204 is greater than the inner cladding peak 206. Further, a peak radial distance Rd between the core peak 204 and the inner cladding peak 206 may be in a range of 9 µm to 10 µm. Specifically, the peak radial distance Rd between the core peak 204 and the inner cladding peak 206 may be between (T1min + T2min) to (T1max + T2max). For example, when T1min is 4.4 µm, T2min is 4.6 µm, T1max is 4.6 µm, and T2max is 5.4 µm, the radial distance between the core peak 204 and the inner cladding peak 206 is 4.4 + 4.6 to 4.6 + 5.4 i.e., 9 µm to 10 µm. Specifically, a low numerical value of the peak radial distance Rd (i.e., 9 µm to 10 µm) and the difference in the refractive indexes ?1 and ?2 may facilitate in reduction of attenuation due to reduction in the relative refractive index between the core 102 and the inner cladding 104.

[0038] As illustrated in the FIG. 2, the refractive index ?2 of the inner cladding 104 may have the maximum value i.e., ?2max and the minimum value i.e., ?2min. Specifically, the curve 202 may transition from the core region to the inner cladding region when the refractive index ?2 of the inner cladding 104 is at the minimum value i.e., ?2min. Further, the curve 202 may transition from the inner cladding region to the outer cladding region when the refractive index ?2 of the inner cladding 104 is at the maximum value i.e., ?2max. In some aspects of the present disclosure, the maximum value i.e., ?2max of the refractive index ?2 is 0.03 and the minimum value i.e., ?2min of the refractive index ?2 is 0.02. Further, as shown by the curve 202, the refractive index ?3 of the of the outer cladding 106 is 0 along the thickness T3.

[0039] FIG. 3 illustrates a graph 300 depicting concentration profiles of first up dopant and second up dopant in the core 102, inner cladding 104, and the outer cladding 106 along with a resultant refractive index profile, according to an aspect of the present disclosure.

[0040] The graph 300 may depict a concentration profile of the first up dopant and the second up dopant in the core 102, inner cladding 104, and the outer cladding 106. The graph 300 may include a first curve 302, a second curve 304, and a third curve 306. The first curve 302 may depict a concentration profile of the first up dopant in the core 102, the inner cladding 104, and the outer cladding 106. Specifically, the first curve 302 depicts the core peak 204 that may be realized due to the up doping of the core 102 with the first up dopant (i.e., Cl) that may further facilitate the optical fiber 100 to have reduced attenuation without increasing macro bend losses. Further, the first curve 302 depicts that at a transition point 308 when the concentration profile transitions from the core 102 to the inner cladding 104, a first diffusion zone is formed that includes traces of the first up dopant diffusing from the core 102 to the inner cladding 104.

[0041] Specifically, the second curve 304 may depict the inner cladding peak 206 that may be realized due to the up doping of the inner cladding 104 with the first up dopant (i.e., Cl) that may further facilitate the optical fiber 100 to have reduced attenuation without increasing macro bend losses. Further, the second curve 304 depicts that at a transition point 310 when the concentration profile transitions from the inner cladding 104 to the outer cladding 106, a second diffusion zone is formed that includes traces of the first up dopant diffusing from the inner cladding 104 to the outer cladding 106.

[0042] Specifically, the third curve 306 may depict a resultant refractive index profile in the core 102, the inner cladding 104, and the outer cladding 106. The third curve 306 may be an actual resultant refractive index profile generated due to the up doping of the core 102 and the inner cladding 104 with the first and second up dopants (as discussed in FIG. 2). As illustrated in the FIG. 3, an ideal refractive index profile is shown, that depicts a step function.

[0043] Thus, the optical fiber 100 of the present disclosure may demonstrate reduced stresses and reduction in the attenuation.

[0044] Further, the up doping of the core 102 with Ge and Cl2 and the up doping of the inner cladding 104 with Cl2 may facilitate to control the micro-bend losses and macro-bend loss in the optical fiber 100. Specifically, the up doping of the core 102 with the first up-dopant (i.e., Ge) and the second up-dopant (i.e., Cl2) and the up doping of the inner cladding 104 with the second up-dopant (i.e., Cl2) may result in a net increase in the refractive index of the optical fiber 100 and thus facilitates to improve the attenuation in the optical fiber 100 without causing hindrance in micro-bending.

[0045] Further, the up doping of the inner cladding 104 with the second up-dopant (i.e., Cl2) may reduce stresses in the optical fiber 100 due to reducing viscosity facilitating stress reduction between the core and the inner cladding 104.

[0046] Further, the up doping of the core 102 with the first and second up-dopants and the up doping of the inner cladding 104 with the second up-dopant (i.e., Cl2) may facilitate to improve the travelling of the optical signal within the optical fiber 100.

[0047] While various aspects of the present disclosure have been illustrated and described, it will be clear that the present disclosure is not limited to these aspects only. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the spirit and scope of the present disclosure, as described in the claims. Further, unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements.