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 IMMEDIATE FLUORINE CLADDING”
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
The present disclosure relates generally to optical fibers, and, more particularly, to an optical fiber with an immediate fluorine cladding adjacent to the core.
BACKGROUND
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. Single mode fibers of G.652.D/G657A2 generally face major challenges in 400G transmission in territorial long haul communication systems due to non-linear effects, mainly in submarine application. Single mode fibers of G654E/G654C is specifically characterized by cut-off shifted, low attenuation, low latency, higher Optical Signal to Noise Ratio (OSNR) as compared to G.652.D/G657A2. Also, single mode fibers of G654E have large effective area and large Mode Field Diameter (MFD) as compared to G.652.D/G657A2.
The prior art reference CN106772788A discloses a kind of cut off wavelength displacement single-mode fiber. The single mode fiber has a sandwich layer, an inner cladding for coating successively, a depressed cladding, a middle covering and a surrounding layer. The single mode fiber of CN106772788A provides properties such as low decay, large effective area and low bend loss, and can realize the controllability of fiber cut off wavelength. However, CN106772788A does not talk about trench and core volumes, mode field diameter (MFD) of the single mode fiber.
The prior art reference US20170003445A1 discloses an optical fiber with large effective area, low bending loss and low attenuation. The optical fiber includes a core, an inner cladding region, and an outer cladding region. The core region includes a spatially uniform up dopant to minimize low Rayleigh scattering and a relative refractive index and radius configured to provide large effective area. The inner cladding region features a large trench volume to minimize bending loss. The core may be doped with Cl and the inner cladding region may be doped with F. The prior art reference US20130071080A1 discloses a trench-assisted optical fiber, optimized for figure-of-merit (FOM) performance, having a core region having a longitudinal axis, a shelf region surrounding said core region, a cladding region surrounding said shelf region, said core and shelf and cladding regions configured to support and guide the propagation of signal light in a fundamental transverse mode in said core and shelf regions in the direction of said axis, the cladding region including an inner trench and an outer trench.
There is a need of an optical fiber which provides higher cut-off wavelength, large effective area, large Mode Field Diameter (MFD), low attenuation, low latency, and higher Optical Signal to Noise Ratio (OSNR). Therefore, a technical solution that overcomes the technical shortcomings of the traditional single mode optical fibers is required.
SUMMARY
In an aspect of the present disclosure, an optical fiber is disclosed. The optical fiber that has a core that is up doped with an up dopant. The up dopant is Germanium (Ge). The optical fiber further has a cladding that has inner and outer claddings. The inner cladding is down doped with a down dopant and is disposed adjacent to the core and the outer cladding is at least one of, undoped and down doped. The optical fiber has (i) a Mode Field Diameter (MFD) in a range of 9.5 µm to 13.0 µm and (ii) a Cable Cut off of less than 1530 nm.
BRIEF DESCRIPTION OF DRAWINGS
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.
FIG. 1 illustrates a cross-sectional view of an optical fiber.
FIG. 2A illustrates a graph that represents a Refractive Index (RI) profile of the optical fiber of FIG. 1 with an outer cladding being down doped with a down dopant.
FIG. 2B illustrates an enlarged sectional view of the graph of FIG. 2A that represents a RI profile of a core of the optical fiber of FIG. 1 with the outer cladding being down doped with the down dopant.
FIG. 2C illustrates another enlarged sectional view of the graph of FIG. 2A that represents a RI profile of an inner cladding of the optical fiber of FIG. 1 with the outer cladding being down doped with the down dopant.
FIG. 2D illustrates another enlarged sectional view of the graph of FIG. 2A that represents a RI profile of the outer cladding of the optical fiber of FIG. 1 with the outer cladding being down doped with the down dopant.
FIG. 2E illustrates an enlarged sectional view of the graph of FIG. 2A that represents a RI profile of an inner cladding-outer cladding interface of the optical fiber of FIG. 1 with the outer cladding being down doped with the down dopant.
FIG. 3A illustrates a graph that represents a RI profile of the optical fiber of FIG. 1 with the outer cladding being undoped.
FIG. 3B illustrates an enlarged sectional view of the graph of FIG. 3A that represents a RI profile of a core of the optical fiber of FIG. 1 with the outer cladding being undoped.
FIG. 3C illustrates an enlarged sectional view of the graph of FIG. 3A that represents a RI profile of an inner cladding of the optical fiber of FIG. 1 with the outer cladding being undoped.
FIG. 3D illustrates an enlarged sectional view of the graph of FIG. 3A that represents a RI profile of the outer cladding of the optical fiber of FIG. 1 with the outer cladding being undoped.
FIG. 3E illustrates an enlarged sectional view of the graph of FIG. 3A that represents a RI profile of an inner cladding-outer cladding interface of the optical fiber of FIG. 1 with the outer cladding being undoped.

DETAILED DESCRIPTION
The detailed description of the appended drawings is intended as a description of the currently preferred aspects of the present disclosure and is not intended to represent the only form in which the present disclosure may be practiced. It is to be understood that the same or equivalent functions may be accomplished by different aspects that are intended to be encompassed within the spirit and scope of the present disclosure.
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.
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 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.

Definitions:

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.
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.
The term “inner cladding” of the optical fiber as used herein is referred to as a layer surrounding to the core of the optical fiber.
The term “outer cladding” of the optical fiber as used herein is referred to as a layer surrounding the inner cladding of the optical fiber.
The term “trench layer” as used herein referred to as a down doped region with a higher down dopant concentration to decrease the refractive index of the down doped region with respect to pure silica and increase the relative refractive index of the core region.
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.
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.
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.
The term “Mode Field Diameter (MFD)” as used herein refers to the size of the light-carrying portion of the optical fiber. For single-mode optical fibers, this region includes the optical fiber core as well as a small portion of the surrounding cladding glass of the optical fiber. The selection of desired MFD helps to describe the size of the light-carrying portion of the optical fiber.
The term “macro bend loss” as used herein refers to losses induced in bends around mandrels (or corners in installations), generally more at the cable level or for fibers. The macro bend loss occurs when the fiber cable is subjected to a significant amount of bending above a critical value of curvature. The macro bend loss is also called as large radius loss.
The term “cable cut-off wavelength” as used herein refers to a wavelength above which a single-mode fiber will support and propagate only one mode of light. The optical fiber transmits a single mode of optical signal above a pre-defined cut-off wavelength known as cable cut-off wavelength.
The term “effective area” as used herein refers to an optical effective area. A large effective area is always preferred in the optical fiber for an efficient optical transmission.
The term “latency” as used herein is referred to as a time delay that occurs when transmitting a light signal over a length of the optical fiber.
The term “attenuation” as used herein is referred to as the reduction in power of a light signal as it is transmitted. Specifically, the attenuation is caused by passive media components such as cables, cable splices, and connectors.
The term “Optical Signal to Noise Ratio (OSNR)” as used herein is referred to as the ratio of signal power to noise power, over a specific spectral bandwidth, at any point in an optical link.
The term “core peak” as used herein is referred to as the maximum refractive index value of the core of the optical fiber.
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.
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.
The term “undoped” (or unintentionally doped) means that a region of the optical fiber contains a dopant not intentionally added to the region during fabrication, but the term does not exclude low levels of background doping that may be inherently incorporated during the fabrication process. Such background doping levels are low in that they have an insignificant effect on the refractive index of the undoped region.
FIG. 1 illustrates a cross-sectional view of an optical fiber 100. The optical fiber 100 may be Outside Vapor Deposition (OVD) manufactured optical fiber that has an immediate fluorine cladding that induces G654C/E properties in the optical fiber 100. Specifically, the optical fiber 100 is a G.654.E fiber that is a cut-off wavelength shift single-mode optical fiber. The optical fiber 100 may be complied with the G.654.E standard issued by International Telecommunications Union – Telecommunications Sector (ITU-T), that is latest revision of "ITU-T Recommendation G.654 - Characteristic of a Cut-Off Shifted Single-mode Optical Fiber and Cable". The former revisions of ITU-T G.654 standard include G.654.A, G.654.B, G.654.C and G.654.D that describes optical fibers typically used in submarine applications. As illustrated in FIG. 1, the optical fiber 100 may have a core 102, and a cladding 104. Further, the optical fiber 100 may have a central axis 106 such that the core 102 and the cladding 104 are arranged along the central axis 106 running longitudinally, i.e., generally concentric to the central axis 106. The cladding 104 may have an inner cladding 108 and an outer cladding 110. 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 an up dopant, the inner cladding 108 being down doped with a down dopant, and the outer cladding 110 being one of, undoped (i.e., made up of pure silica) and down doped with a down dopant.
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. Specifically, the core 102 may be a confinement region of the optical fiber 100. 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), and the like. Preferably, the core 102 may be made up of a silica glass doped with the 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/or later developed materials, without deviating from the scope of the present disclosure. Specifically, the core 102 may be up-doped with the up-dopant that may increase values of net refractive index of the optical fiber 100 and may further facilitate to control macro bend losses. Preferably, the up dopant may be Germanium (Ge). The up dopant Germanium (Ge) may be preferred over other up dopant for example chlorine (Cl) to achieve a required refractive index of the core 102. To achieve the required refractive index of the core 102 by using the up dopant chlorine (Cl) is a complex process and a high pressure chamber is required. Aspects of the present disclosure are intended to include and/or otherwise cover any type of the up dopant for the core 102, without deviating from the scope of the present disclosure. In some aspects of the present disclosure, the core 102 may have traces of chlorine (Cl) and fluorine (F). There is no measurable impact of these traces in the core 102. Specifically, concentrations of Cl and F in the core 102 may be less than 2500 parts per million (ppm) and 1500 ppm, respectively. The traces of chlorine (Cl) and fluorine (F) may be used to up dope the core 102 as the chlorine (Cl) and the fluorine (F) can facilitate in reduction of stress in an optical fiber preform and hence in the optical fiber 100. In other words, the traces of the chlorine (Cl) and the fluorine (F) 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). In some aspects of the present disclosure, the core 102 may have a core radius R1 that may be in a range of 4.5 micrometres (µm) to 6.5 µm. Further, the core 102 may have a core volume that is defined as a volume acquired by the core 102 with respect to the core radius R1. The core volume may have a magnitude in micrometres square (µm2) that may be determined by the following equation:
= ?_R0^R1¦?? (r) rdr?
In some aspects of the present disclosure, the magnitude of the core volume of the core 102 as determined by the above equation may be in a range of 5% µm2 to 5.5% µm2. In one example, the core volume of the core 102 may be 5.25% µm2.
The cladding 104 having the inner cladding 108 and the outer cladding 110 may be a layer made up of a material having a lower refractive index, and in immediate contact with the core 102 which is made up of a material of higher refractive index. The inner cladding 108 may surround the core 102. Specifically, the inner cladding 108 may be disposed adjacent to the core 102. In some aspects of the present disclosure, an end of the inner cladding 108 that is adjacent to the core 102 (i.e., at an intersection of the core 102 and the inner cladding 108) may be substantially deeper when compared to an end of the core 102 adjacent to the inner cladding 108 (i.e., at an intersection of the core 102 and the inner cladding 108). The deeper end of the inner cladding 108 at the intersection of the core 102 and the inner cladding 108 may form a trench layer 108a that has a non-step single trench shape. The non-step single trench shape is preferred over stepped trench because manufacturing process of the optical fiber with non-step trench is less complex and less time consuming as compared to the manufacturing process of the optical fiber comprising stepped trench. In some aspects of the present disclosure, the trench layer 108a may have a trench radius R2 (i.e., inner cladding radius) that may be in a range of 22 µm to 25 µm. In some aspects of the present disclosure, the trench layer 108a may have a trench volume that may be defined as a volume acquired by region between the core radius R1 and the trench radius R2. The trench volume may have a magnitude in µm2 that may be determined by the following equation:
= ?_R1^R2¦?? (r) rdr?
In some aspects of the present disclosure, the magnitude of the trench volume of the trench layer (i.e., the inner cladding 108) as determined by the above equation may be in a range of 48% µm2 to 55% µm2. In one example, the trench volume of the trench layer 108a may be equal to 48.59% µm2. In some aspects of the present disclosure, the trench layer 108a may have a trench delta that may be in a range of 0.22% to 0.32%. Preferably, the trench layer may have the trench delta of 0.24%. The trench delta may be determined by the following equation:
? (%)=(n1^2-n2^2)/(2*n1^2 )*100

Where, ? is trench delta,
n1 is refractive index of trench layer,
n2 is refractive index of pure silica.
In one example, a refractive index n1 of the trench layer 108a may be equal to 1.44332 and a refractive index of pure silica may be equal to 1.44692, the trench delta ? (%) may be determined using above equation is 0.25%.
The inner cladding 108 may be made up of a material such as, but not limited to, a silica glass. In some aspects of the present disclosure, the inner cladding 108 may be made up of a combination of Silicon tetrachloride (SiCl4) and Cl. Preferably, the inner cladding 108 may be made up of a silica glass doped with the down dopant. Aspects of the present disclosure are intended to include and/or otherwise cover any type of the material for the inner cladding 108, including known, related, and later developed materials. Specifically, the inner cladding 108 may be down doped with the down dopant that may decrease values of net refractive index of the inner cladding 108 and may further facilitate to control macro bend losses in the optical fiber 100.
The outer cladding 110 may surround the inner cladding 108. The outer cladding 110 may be made up of a material such as but not limited to, a silica glass. In some aspects of the present disclosure, the outer cladding 110 may be made up of a silica glass that may be undoped. In some other aspects of the present disclosure, the outer cladding 110 may be made up of a silica glass that may be down doped with a down dopant. In some aspects of the present disclosure, the down dopant used to dope the outer cladding 110 may be similar to the down dopant used to down dope the inner cladding 108. In some other aspects of the present disclosure, the down dopant used to dope the outer cladding 110 may be different than the down dopant used to down dope the inner cladding 108. The outer cladding 110 may have an outer cladding radius R3 that is in a range of 62.15 µm to 62.85 µm.
In some aspects of the present disclosure, the optical fiber 100 may have a total profile volume. The total profile volume may have a magnitude in µm2 that may be determined by the following equation:
= ?_R0^R3¦?? (r) rdr?
In some aspects of the present disclosure, the magnitude of the profile volume as determined by the above equation may be in a range of 50% µm2 to 60.50% µm2. The profile volume may be determined by surface integrating the relative refractive index as a function of radial change. In one example, the total profile volume may be determined with integration limits of core center to outer cladding radius R3 (0 to 62.5 µm). In some aspects of the present disclosure, the trench volume of the trench layer 108a may be in a range of 45.00% µm2 to 55.00% µm2. In some aspects of the present disclosure, the trench layer 108a may have a trench delta that may be in a range of 0.22% to 0.32%. In some aspects of the present disclosure, a ratio of the core volume to the trench volume is in a range of 0.082% to 0.11%. The minimum value in the range of the ratio of the core volume to the trench volume may be determined by dividing minimum value of the core volume by maximum value of the trench volume. For example, the minimum value of core volume may be 5% µm2 and the maximum value of the trench volume may be 55.00% µm2, the minimum value of the ratio of the core volume to the trench volume may be 0.09%. The maximum value in the range of the ratio of the core volume to the trench volume may be determined by dividing maximum value of the core volume by minimum value of the trench volume. For example, the maximum value of core volume may be 5.5% µm2 and the minimum value of the trench volume may be 45.00% µm2, the maximum value of the ratio of the core volume to the trench volume may be 0.12%. Specifically, the core volume in the range of 5% µm2 to 5.5% µm2, the trench volume in the range of 45% µm2 to 55% µm2, and the profile volume in the range of 50% µm2 to 60.50% µm2 may facilitate to get G654E/C parameters in the optical fiber 100. The G654E/C parameters may be, but not limited to, MFD at 1550 nm in range of 9.5 to 13.0, Cable Cut off of less than 1530 nm, Attenuation at 1550 nm of less than 0.17 dB/Km, Dispersion in range of about 17 picosecond per nanometer-kilometer (ps/(nm.Km)) to 23 ps/(nm.Km) at wavelength of about 1550 nm. When the outer cladding 110 is undoped, a Macro bend loss at a wavelength of 1625 nm, 60 mm diameter and 100 turns of the optical fiber 100 is less than 0.5 Decibel (dB). When the outer cladding 110 is down doped, a Macro bend loss at a wavelength of 1625 nm, 60 mm diameter and 100 turns of the optical fiber is less than 0.1 dB.
In an exemplary scenario, when the optical fiber 100 has the outer cladding 110 that is down doped with the down dopant (i.e., F), the core radius R1 is in a range of 5.5 µm to 6.5 µm, a maximum refractive index ?1max of the core 102 is in a range of 0.38% to 0.45%. Preferably, the core radius R1 is 5.92 µm, the maximum refractive index ?1max of the core 102 is 0.41%. The inner cladding radius R2 is in a range of 22 µm to 25 µm, a maximum refractive index ?2max of the inner cladding 108 is in a range of 0.26% to 0.32%. Preferably, the inner cladding radius R2 is 22.5 µm, the maximum refractive index ?2max of the inner cladding 108 is 0.28%. The outer cladding radius R3 is in a range of 62.15 µm to 62.85 µm, a maximum refractive index ?3max of the outer cladding 110 is in a range of 0.10% to 0.20%. Preferably, the outer cladding radius R3 is 62.5 µm, the maximum refractive index ?3max of the outer cladding 110 is 0.15%. The core volume is in a range of 5% µm2 to 5.5% µm2, the trench volume is in a range of 48% µm2 to 55% µm2, and the total profile volume is in a range of 53% µm2 to 60.5% µm2. In one example, the core volume is 5.01% µm2, the trench volume is 49.15% µm2, and the total profile volume is 54.16% µm2.
In another exemplary scenario, when the optical fiber 100 has the outer cladding 110 that is undoped, the core radius R1 is in a range of 4.5 µm to 5.5 µm, the maximum refractive index ?1max of the core 102 is in a range of 0.38% to 0.45%. Preferably, the core radius R1 is 5 µm and the maximum refractive index ?1max of the core 102 is 0.42%. The inner cladding radius R2 is in a range of 22 µm to 25 µm, the maximum refractive index ?2max of the inner cladding 108 is in a range of 0.22% to 0.26%. Preferably the cladding radius R2 is 23.5 µm and the maximum refractive index ?2max of the inner cladding 108 is 0.24%. The outer cladding radius R3 is in a range of 62.15 µm to 62.85 µm, the maximum refractive index ?3max of the outer cladding 110 is in a range of -0.05% to 0.05%. Preferably, the cladding radius R3 is 62.5 µm and the maximum refractive index ?3max of the outer cladding 110 is 0. The core volume is in a range of 5% µm2 to 5.5% µm2, the trench volume is in a range of 45% µm2 to 50% µm2, and the total profile volume is in a range of 50% µm2 to 55.5% µm2. In one example, the core volume is 5.25% µm2, the trench volume is 48.59% µm2, and the total profile volume is 53.84% µm2.
FIG. 2A illustrates a graph 200 that represents a Refractive Index (RI) profile of the optical fiber 100 with the outer cladding 110 being down doped with the down dopant. 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 108 (i.e., the trench layer 108a), and the outer cladding 110, respectively, and a y-axis of the graph 200 represents values of the refractive index ?1, the refractive index ?2, and the refractive index ?3 of the core 102, the inner cladding 108 (i.e., the trench layer 108a), and the outer cladding 110, respectively. The graph 200 has a curve 202 that represent the RI profile of the optical fiber 100. As illustrated in FIG. 2A, the core 102 being up doped with the up dopant, the inner cladding 108 being down doped with the down dopant, and the down doped outer cladding 110 generates the RI profile. As illustrated in FG. 2A, 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 108 (i.e., the trench layer 108a) defines a trench region such that the refractive index ?2 of the inner cladding 108 (i.e., the trench layer 108a) is realized in the trench region (i.e., within the radius R2 of the inner cladding 108). Further, the outer cladding 110 may define an outer cladding region such that the refractive index ?3 of the outer cladding 110 is realized in the outer cladding region (i.e., within the radius R3 of the outer cladding 110).
As illustrated, the curve 202 illustrates that a value of the refractive index ?1 is maximum at a core peak 204 in the core region that is up doped by the up dopant (i.e., GE). Further, the curve 202 transitions from the core region to the trench region which is down doped with the down dopant (i.e., F) such that the curve 202 dips in the trench region (i.e., the region defined by R2 – R1). Specifically, the curve 202 illustrates that a value of the refractive index ?2 is minimum at an inner cladding dip point 206 in the trench region that is down doped by the down dopant (i.e., F). The curve 202 further transitions from the trench region to the outer cladding region defined by the outer cladding 110 that is down doped with the down dopant such that the curve 202 peaks to an outer cladding peak 208a at an inner cladding-outer cladding interface 208b that is lesser than the core peak 204. In other words, the curve 202 transitions from the core region to the trench region and further from the trench region to the outer cladding region (i.e., the region defined by R3 – R2) thus generating the RI profile that is defined by the core peak 204 and the outer cladding peak 208a at the inner cladding-outer cladding interface 208b. The graph 200 further has a straight line 210 that defines the refractive index of pure silica. As illustrated, the curve 202 dips after the inner cladding-outer cladding interface 208b that defines that the refractive index ?3 of the outer cladding 110 decrease gradually and is less than the refractive index of pure silica which is due to the fact the outer cladding 110 is down doped using the down dopant.
FIG. 2B illustrates an enlarged sectional view of the graph 200 that represents a RI profile of the core 102 of the optical fiber 100 with the outer cladding 110 being down doped with the down dopant. As illustrated, the core 102 defines the 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). The curve 202 illustrates that the value of the refractive index ?1 is maximum at the core peak 204 in the core region that is up doped by the up dopant (i.e., GE). In one example, the core volume of the core 102 may be 5.25% µm2. The core volume may be determined by surface integrating the relative refractive index as a function of radial change. In one example, the core volume may be determined with integration limits of core center to core radius R1 (0 to 5.35 µm).
Further, the curve 202 transitions from the core region to the trench region which is down doped with the down dopant (i.e., F) such that the curve 202 dips in the trench region (i.e., the region defined by R2 – R1).
FIG. 2C illustrates another enlarged sectional view of the graph 200 that represents a RI profile of the inner cladding 108 of the optical fiber 100 with the outer cladding 110 being down doped with the down dopant. As illustrated, the inner cladding 108 (i.e., the trench layer 108a) defines the trench region such that the refractive index ?2 of the inner cladding 108 (i.e., the trench layer 108a) is realized in the trench region (i.e., within the radius R2 of the inner cladding 108). The deeper end of the inner cladding 108 at the intersection of the core 102 and the inner cladding 108 may form a trench layer 108a that has a non-step single trench shape as illustrated by the curve 202. The non-step single trench shape is preferred over stepped trench because manufacturing process of the optical fiber with non-step trench is less complex and less time consuming as compared to the manufacturing process of the optical fiber comprising stepped trench. Specifically, the curve 202 illustrates that the value of the refractive index ?2 is minimum at the inner cladding dip point 206 in the trench region that is down doped by the down dopant (i.e., F). The non-step trench shape of the trench layer 108a comprising only one dip point 206.
FIG. 2D illustrates another enlarged sectional view of the graph 200 that represents a RI profile of the outer cladding 110 of the optical fiber 100 with the outer cladding 110 being down doped with the down dopant. The outer cladding 110 may define the outer cladding region such that the refractive index ?3 of the outer cladding 110 is realized in the outer cladding region (i.e., within the radius R3 of the outer cladding 110). The curve 202 further transitions from the trench region to the outer cladding region defined by the outer cladding 110 that is down doped with the down dopant such that the curve 202 peaks to an outer cladding peak 208a at an inner cladding-outer cladding interface 208b that is lesser than the core peak 204. In other words, the curve 202 transitions from the core region to the trench region and further from the trench region to the outer cladding region (i.e., the region defined by R3 – R2) thus generating the RI profile that is defined by the core peak 204 and the outer cladding peak 208a at the inner cladding-outer cladding interface 208b. The graph 200 further has the straight line 210 that defines the refractive index of pure silica. As illustrated, the curve 202 dips after the inner cladding-outer cladding interface 208b that defines that the refractive index ?3 of the outer cladding 110 decrease gradually and is less than the refractive index of pure silica which is due to the fact the outer cladding 110 is down doped using the down dopant.
FIG. 2E illustrates an enlarged sectional view of the graph of FIG. 2A that represents a RI profile of the inner cladding-outer cladding interface 208b of the optical fiber 100 with the outer cladding 110 being down doped with the down dopant. The curve 202 transitions from the trench region to the outer cladding region defined by the outer cladding 110 that is down doped with the down dopant such that the curve 202 peaks to the outer cladding peak 208a at the inner cladding-outer cladding interface 208b that is lesser than the core peak 204. In other words, the curve 202 transitions from the core region to the trench region and further from the trench region to the outer cladding region (i.e., the region defined by R3 – R2) thus generating the RI profile that is defined by the core peak 204 and the outer cladding peak 208a at the inner cladding-outer cladding interface 208b. The graph 200 further has a straight line 210 that defines the refractive index of pure silica.
FIG. 3A illustrates a graph 300 that represents a RI profile of the optical fiber 100 with the outer cladding 110 being undoped. The graph 300 is a radius versus relative refractive index graph such that an x-axis of the graph 300 represents values of the radius R1, the radius R2, and the radius R3 of the core 102, the inner cladding 108 (i.e., the trench layer 108a), and the outer cladding 110, respectively, and a y-axis of the graph 200 represents values of the refractive index ?1, the refractive index ?2, and the refractive index ?3 of the core 102, the inner cladding 108 (i.e., the trench layer 108a), and the outer cladding 110, respectively. The graph 300 has a curve 302 that represent the RI profile of the optical fiber 100. As illustrated, the core 102 being up doped with the up dopant, the inner cladding 108 being down doped with the down dopant, and the undoped outer cladding 110 generates the RI profile. As illustrated, 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 108 (i.e., the trench layer 108a) defines a trench region such that the refractive index ?2 of the inner cladding 108 (i.e., the trench layer 108a) is realized in the trench region (i.e., within the radius R2 of the inner cladding 108). Further, the outer cladding 110 may define an outer cladding region such that the refractive index ?3 of the outer cladding 110 is realized in the outer cladding region (i.e., within the radius R3 of the outer cladding 110).
As illustrated, the curve 302 illustrates that a value of the refractive index ?1 is maximum at a core peak 304 in the core region that is up doped by the up dopant (i.e., GE). Further, the curve 302 transitions from the core region to the trench region which is down doped with the down dopant (i.e., F) such that the curve 302 dips in the trench region (i.e., the region defined by R2 – R1). Specifically, the curve 302 illustrates that a value of the refractive index ?2 is minimum at an inner cladding dip point 306 in the trench region that is down doped by the down dopant (i.e., F). The curve 302 further transitions from the trench region to the outer cladding region (i.e., the region defined by R3 – R2) defined by the outer cladding 110 that is undoped such that the curve 302 peaks to an outer cladding peak 308a at an inner cladding outer cladding interface 308b that is lesser than the core peak 304. The graph 300 further has a straight line 310 that defines the relative refractive index of the pure silica. The curve 302 transitions from the trench region to the outer cladding region defined by the outer cladding 110 and follows the straight line 310 which is due to the fact the outer cladding 110 is undoped. The outer cladding 110 has traces of the down dopant that is near the inner cladding-outer cladding interface 308b. Preferably, the traces of the down dopant near the near the inner cladding-outer cladding interface 308b is negligible.
FIG. 3B illustrates an enlarged sectional view of the graph 300 that represents a RI profile of the core 102 of the optical fiber 100 with the outer cladding 110 being undoped. As illustrated, the core 102 defines the 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). As illustrated, the curve 302 illustrates that the value of the refractive index ?1 is maximum at the core peak 304 in the core region that is up doped by the up dopant (i.e., GE).
FIG. 3C illustrates another enlarged sectional view of the graph 300 that represents a RI profile of the inner cladding 108 of the optical fiber 100 with the outer cladding 110 being undoped. The inner cladding 108 (i.e., the trench layer 108a) defines the trench region such that the refractive index ?2 of the inner cladding 108 (i.e., the trench layer 108a) is realized in the trench region (i.e., within the radius R2 of the inner cladding 108). The deeper end of the inner cladding 108 at the intersection of the core 102 and the inner cladding 108 may form a trench layer 108a that has a non-step single trench shape as illustrated by the curve 302. The non-step single trench shape is preferred over stepped trench because manufacturing process of the optical fiber with non-step trench is less complex and less time consuming as compared to the manufacturing process of the optical fiber comprising stepped trench. Further, the curve 302 transitions from the core region to the trench region which is down doped with the down dopant (i.e., F) such that the curve 302 dips in the trench region (i.e., the region defined by R2 – R1). Specifically, the curve 302 illustrates that the value of the refractive index ?2 is minimum at the inner cladding dip point 306 in the trench region that is down doped by the down dopant (i.e., F). The non-step trench shape of the trench layer 108a comprising only one dip point 306.
FIG. 3D illustrates yet another enlarged sectional view of the graph 300 that represents a RI profile of the outer cladding 110 of the optical fiber 100 with the outer cladding 110 being undoped. The outer cladding 110 may define the outer cladding region such that the refractive index ?3 of the outer cladding 110 is realized in the outer cladding region (i.e., within the radius R3 of the outer cladding 110). The curve 302 further transitions from the trench region to the outer cladding region (i.e., the region defined by R3 – R2) defined by the outer cladding 110 that is undoped such that the curve 302 peaks to the outer cladding peak 308a at the inner cladding outer cladding interface 308b that is lesser than the core peak 304. The graph 300 further has the straight line 310 that defines the relative refractive index of the pure silica. The curve 302 transitions from the trench region to the outer cladding region defined by the outer cladding 110 and follows the straight line 310 which is due to the fact the outer cladding 110 is undoped.
FIG. 3E illustrates yet another enlarged sectional view of the graph 300 that represents a RI profile of the inner cladding-outer cladding interface 308a of the optical fiber 100 with the outer cladding 110 being undoped. The curve 302 further transitions from the trench region to the outer cladding region (i.e., the region defined by R3 – R2) defined by the outer cladding 110 that is undoped such that the curve 302 peaks to the outer cladding peak 308a at the inner cladding outer cladding interface 308b that is lesser than the core peak 304. The graph 300 further has the straight line 310 that defines the relative refractive index of the pure silica. The curve 302 transitions from the trench region to the outer cladding region defined by the outer cladding 110 and follows the straight line 310 which is due to the fact the outer cladding 110 is undoped.
Thus, the optical fiber 100 of the present disclosure has a fluorine doped cladding (i.e., the inner cladding 108) adjacent to the core 102 that brings G654E and G654C properties in the optical fiber 100. Further, the optical fiber 100 with an immediate inner cladding 108 that is down doped with fluorine may induce G654E and G654C category optical fiber properties in the optical fiber 100 with predefined core volume and trench volume thus providing good confinement and improved bending loss.
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.
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.
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.
, Claims:Claims
1. An optical fiber (100) comprising:
a core (102) that is up doped with an up dopant; and
a cladding (104) having inner and outer claddings (108, 110), wherein the inner cladding (108) is down doped with a down dopant and is disposed adjacent to the core (102) and the outer cladding (110) is at least one of: undoped and down doped, wherein the optical fiber (100) has (i) a Mode Field Diameter (MFD) in a range of 9.5 µm to 13.0 µm and (ii) a Cable Cut off of less than 1530 nm.

2. The optical fiber (100) of claim 1, wherein the up dopant is Germanium (Ge).

3. The optical fiber (100) of claim 1, wherein (i) the core (102) has a core radius R1 in a range of 4.5 micrometres (µm) to 6.5 µm, (ii) the inner cladding (108) has an inner cladding radius R2 in a range of 22 µm to 25 µm, and (iii) the outer cladding (110) has an outer cladding radius R3 in a range of 62.15 µm to 62.85 µm.

4. The optical fiber (100) of claim 1, wherein the outer cladding (110) has traces of down dopant near an inner cladding-outer cladding interface (308b).

5. The optical fiber (100) of claim 1, wherein the core (102) has traces of the down dopant such that concentrations of the down dopant is less than 2500 parts per million (ppm).

6. The optical fiber (100) of claim 5, wherein the down dopant is at least one of Chlorine (Cl) and Fluorine (F) such that concentrations of Cl and F are less than 2500 parts per million (ppm) and 1500 ppm, respectively.

7. The optical fiber (100) of claim 1, wherein the outer cladding (110) is made of pure silica.

8. The optical fiber (100) of claim 1, wherein the inner cladding (108) has a trench layer (108a), wherein the trench layer (108a) is defined by a non-step single trench shape, wherein the trench layer (108a) is such that an end of the inner cladding (108) that is adjacent to the core (102) is deeper than an end of the core (102) adjacent to the inner cladding (108)

9. The optical fiber (100) of claim 1, wherein the inner cladding (108) has a trench delta in a range of 0.22% to 0.32%.

10. The optical fiber (100) of claim 1, wherein an attenuation of the optical fiber (100) is less than 0.17 dB/KM.

11. The optical fiber (100) of claim 1, wherein a ratio of the core volume to the trench volume is in a range of 0.082 to 0.11.

12. The optical fiber (100) of claim 1, wherein, at least one of, (i) the core (102) has a core volume in a range of 5% µm2 to 5.5% µm2, and (ii) the trench layer (108a) has a trench volume in a range of 48% µm2 to 55% µm2.

13. The optical fiber (100) of claim 1, wherein a total profile volume of the optical fiber (100) is in a range of 50% µm2 to 60.50% µm2.

14. The optical fiber (100) of claim 1, wherein (i) when the outer cladding (110) is undoped, macro bend loss of the optical fiber (100) at a wavelength of 1625 nm, a bend diameter of 60 millimeters (mm), 100 turns of the optical fiber (100) is less than 0.5 Decibel (dB) and (ii) when the outer cladding (110) is down doped, a macro bend loss of the optical fiber (100) at a wavelength of 1625 nm, a bend diameter of 60 mm, 100 turns of the optical fiber (100) is less than 0.1 dB.