Optical fiber and optical fiber cable with ultra low bend loss

Abstract

The present invention relates to an optical fiber (100) having a core (102) and a cladding (104) surrounding the core (102) In particular, the core (102) has a first alpha value (α1) in a range of 4 to 8. And, the cladding (104) has first through third cladding layers (104a-104c). Further, the refractive index profile of the second cladding layer (104b) includes a trench region (402) such that a trench relative refractive index (Δ2) of the at least one trench region (402) decreases gradually from outer boundary (106) of the first cladding layer (104a) to a trench center (404) of the trench region (402). Furthermore, the refractive index profile increases gradually from the trench center (404) to an outer boundary of the second cladding layer (104b).

Description

“OPTICAL FIBER AND OPTICAL FIBER CABLE WITH ULTRA LOW BEND LOSS”FIELD OF INVENTION

[0001] This application claims the benefit of Indian Application No. “202311062255” titled “OPTICAL FIBER AND OPTICAL FIBER CABLE WITH ULTRA LOW BEND LOSS” fded by the applicant on 15 Sep 2023, which is incorporated herein by reference in its entirety. Embodiments of the present invention relate to the field of optical telecommunication systems, and more particularly, relates to an optical fiber and an optical fiber cable with ultra-low bend lossBACKGROUND OF INVENTION

[0002] Optical fiber is the leading alternative to traditional materials used for data signal communication such as copper wiring. Optical fiber is now widely utilized in a variety of electronic devices and systems to facilitate the high-speed communication of voice, video, and data signals at high bandwidths. Nowadays, optical fibers are widely used to transmit information or data in the form of light from one place to another. The optical fibers are disposed within the optical fiber cable. Fiber optic cables include one or more optical fibers or other optical waveguides that conduct optical signals, for example carrying voice, data, video, or other information.

[0003] Optical fibers are suitable in regional, metro, access, mobile, FTTH and 5G applications where high-density cables and accessories are being manufactured. Increasing adoption of FTTH and 5G architectures has led to wider application of bend-insensitive fibers because they ensure low losses in these high- density networks.

[0004] In recent years, fiber to the home (FTTh) and fiber to the desktop (FTTd) gradually become one development direction in the construction of communications networks and the construction of future optical fiber networks. Nowadays, conventional low water peak optical fibers (meeting ITU-T G.652C / D) have found wide applications in optical fiber access network and generally have abend radius of 30 mm. In the configuration process of FTTx optical fibers, cabling of optical fibers is often needed indoors and in narrow environments. Optical fibers are subject to high bending stresses at a small bend radius, and especially in practical applications, optical fibers are often wound in storage boxes that become increasingly small. Therefore, it becomes necessary to develop an optical fiber having high bending resistance performance to meet the requirements for FTTx network cabling and device miniaturization.

[0005] Based on the specifications of ITU-T and the specific use environments and conditions of the G.657.B3 optical fiber, the G.657.B3 optical fiber is basically used for short distance communication transmission and focuses more on macro-bending performance at a small bend radius, and the compatibility with the G.652.D standard is not mandatory. However, because the G.652.D has been widely used in the optical communication field for decades, the use habits of most of the customers, optical fiber cabling habits, and peer equipment are designed on the basis of the G.652 optical fiber design. Therefore, the development of a G.657.B3 optical fiber compatible with the G.652 optical fiber standard further facilitates promotion and use of optical communications.

[0006] Bend-insensitive optical fibers are used widely for high-speed optical networks such as FTTH and 5G architectures as they guarantee minimal losses in such dense networks. High density cables with small diameters enable service providers to maximize the number of fibers that can be installed in existing ducts or to minimize the size or even the need for new ducting and related infrastructure, which requires optical fiber with reduced (or low) glass diameter and low overall diameter. Dense-fiber technologies with extremely low bend loss maximizes the use of physical assets and provide flexibility to expand high-density networks in future.

[0007] Optical fibers with ultra-low bend sensitivity are crucial for highspeed optical networks like FTTH and 5G architectures. The current demand for high-density cables with small diameters necessitates reduced glass diameter and overall diameter in optical fibers.

[0008] US patent application “US9201192B2” discloses an ITU-G.657.B3 standard compliant optical fiber having a trench cladding layer and an outer cladding layer. The relative refractive index difference of the trench cladding layer changes gradually such that the lowest relative refractive index difference is achieved at an outermost interface between the trench cladding layer and an outer cladding layer. However, the suggested design of the optical fiber is very complex and difficult to manufacture. Further, the design does not meet the requirements of bend sensitivity while maintaining other optical parameters such as Mode Field Diameter (MFD), cable cut-off, and Zero Dispersion Wavelength (ZDW).

[0009] Other G.657.B3 optical fibers are primarily used for short-distance communication transmission and focus on macro-bending performance at a small bend radius and do not focus on ultra-low bend loss primarily.

[0010] Existing solutions, such as the one disclosed in US9201192B2, fall short in meeting bend sensitivity requirements while maintaining other vital optical parameters. Conventional G.657.B3 fibers focus primarily on macro-bending performance for short-distance communication, not ultra-low bend loss. Thus, there is a significant need for an optical fiber designed to prioritize ultra-low bend sensitivity.

[0011] The disclosed G.657.B3 fibers are complex to manufacture and fail to meet bend sensitivity requirements, making them unsuitable for high-density network applications. Additionally, conventional G.657.B3 fibers mainly focus on shortdistance communication with less emphasis on ultra-low bend loss, highlighting the need for an improved solution.

[0012] There, providing a solution that meets the evolving demands of high-density networks.

[0013] While the prior arts cover various solutions for the aforesaid drawbacks. However, there still is persistent need is for an optical fiber specifically designed to address the primary requirement of ultra-low bend sensitivity while ensuring optimal optical parameters bridging this gap. Thus, the present disclosure providesan optical fiber that fulfills the purpose of the optical fiber application with ultralow bend sensitivity.SUMMARY

[0014] Embodiments of the present invention relates to an optical fiber comprising a core having a first alpha value (al) in a range of 4 to 8 and a cladding comprising first through third cladding layers and surrounding the core. In particular, the refractive index profile of the second cladding layer comprises at least one trench region such that a trench relative refractive index (A2) of the at least one trench region decreases gradually from an outer boundary of the first cladding layer to a trench center of the at least one trench region and increases gradually from the trench center to an outer boundary of the second cladding layer.

[0015] In accordance with an embodiment of the present invention, the first cladding layer has a first clad diameter (D) and the core has a core diameter (d) and ratio of the first clad diameter (D) to the core diameter (d) is greater than 2.

[0016] In accordance with an embodiment of the present invention, at least one trench region has a second alpha value (a2) in a range of 5 to 8.

[0017] In accordance with an embodiment of the present invention, the optical fiber has a macro bend loss of less than or equal to(i) 0.2 decibel / turn (dB / turn) at a bend radius of 2.5 millimeter (mm) and a wavelength of 1550 nanometer (nm), and(ii) 0.5 dB / turn at a bend radius of 2.5 mm and a wavelength of 1625 nm.

[0018] In accordance with an embodiment of the present invention, the optical fiber further has a macro bend loss of less than or equal to(i) 0.15 dB / turn at a bend radius of 5 mm and a wavelength of 1550 nm, and(ii) 0.45 dB / turn at a bend radius of 5 mm and a wavelength of 1625 nm

[0019] In accordance with an embodiment of the present invention, the optical fiber comprising one or more coating layers surrounding the cladding. The absolutedifference between a third refractive index (N3) of the third cladding layer and a coating refractive index (N4) of the coating layer is less than or equal to 0.01.

[0020] In accordance with an embodiment of the present invention, the cladding is independent of traces of Chlorine (Cl). The concentration of traces of Chlorine (Cl) in the cladding is less than 1500 ppm.

[0021] In accordance with an embodiment of the present invention, the minimum value of the trench relative refractive index (A2) of the second cladding layer is in a range of -0.35% to -0.45%.

[0022] In accordance with an embodiment of the present invention, the second cladding layer has a trench radius (R2) in a range of 14 micrometer (pm) to 20 pm.

[0023] In accordance with an embodiment of the present invention, the mode field diameter (MFD) of the optical fiber is in a range of 8.2 pm to 9 pm. The cladding has a cladding diameter of less than or equal to 125 + 0.7 pm.

[0024] In accordance with an embodiment of the present invention, the one or more coating layers has a coating diameter less than or equal to 250 pm.

[0025] In accordance with an embodiment of the present invention, the optical fiber comprises a core and a cladding having at least one trench region such that a trench relative refractive index (A2) is minimum near center of the trench. The optical fiber is used in an optical fiber ribbon such that adjacent optical fibers are at least partially bonded.

[0026] The foregoing objectives of the present invention are attained by providing an optical fiber and an optical fiber cable with ultra-low bend loss.BRIEF DESCRIPTION OF THE DRAWINGS

[0027] So that the manner in which the above-recited features of the present invention is understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0028] The invention herein will be better understood from the following description with reference to the drawings, in which:

[0029] Fig. 1 is a pictorial snapshot illustrating an optical fiber with at least one trench region in accordance with an embodiment of the present invention;

[0030] Fig. 2 is a pictorial snapshot illustrating an optical fiber with two trench region in accordance with an embodiment of the present invention;

[0031] Fig. 3 is a representation illustrating a theoretically derived refractive index profile of the optical fiber in accordance with an embodiment of the present invention;

[0032] Fig. 4 is a representation illustrating an actual refractive index profile of the optical fiber derived through simulation in accordance with an embodiment of the present invention;

[0033] Fig. 5 is a pictorial snapshot illustrating the optical fiber coated with one or more coating layers in accordance with an embodiment of the present invention;

[0034] Fig. 6 is a pictorial snapshot illustrating the optical fiber cable in accordance with an embodiment of the present invention.

[0035] The optical fiber is illustrated in the accompanying drawings, which like reference letters indicate corresponding parts in the various figures. It should be noted that the accompanying figure is intended to present illustrations of exemplary embodiments of the present invention. This figure is not intended to limit the scope of the present invention. It should also be noted that the accompanying figure is not necessarily drawn to scale.DETAILED DESCRIPTION OF THE INVENTION

[0036] The principles of the present invention and their advantages are best understood by referring to figures. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the embodiment of the invention as illustrative or exemplary embodiments of the invention, specific embodiments in which the invention may be practiced are described in sufficient detail to enable those skilled in the art to practice the disclosed embodiments. However, it will be obvious to a person skilled in the art that the embodiments of the invention may be practised with or without thesespecific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to unnecessarily obscure aspects of the embodiments of the invention.

[0037] The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and equivalents thereof. 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. References within the specification to “one embodiment,” “an embodiment,” “embodiments,” or “one or more embodiments” are intended to indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention.

[0038] 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 and do not denote any order, ranking, quantity, or importance, but rather are used to distinguish one element from another. Further, the terms "a" and "an" herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items.

[0039] The conditional language used herein, such as, among others, "can," "may," "might," "may," “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and / or steps.

[0040] 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 notgenerally intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y, or at least one of Z to each be present.

[0041] The following brief definition of terms shall apply throughout the present invention:

[0042] The term “sheath” as used herein is referred to as an outermost layer or an outermost layer of the optical fiber cable that holds and protects the contents of the optical fiber cable.

[0043] The term “strength member” as used herein is referred to as a cable element made up of filaments or yarns that provides strength to the optical fiber cable.

[0044] The term “ribbon bundle” as used herein is referred to as a bundle of optical fiber ribbons.

[0045] The term “intermittently bonded fiber (IBR)” as used herein refers to an optical fiber ribbon having a plurality of optical fibers such that the plurality of optical fibers is intermittently bonded to each other by a plurality of bonded portions that are placed along the length of the plurality of optical fibers. The plurality of bonded portions is separated by a plurality of unbonded portions. An intermittently bonded ribbon fiber cable consists of fibers bonded using matrix material. As such, they lack a flat structure. The rollable ribbons in an intermittently bonded ribbon fiber are bundled together and have the appearance of a spider’s web. Hence, they are also called spider web ribbon fiber. Due to their loose fiber bundling, intermittently bonded ribbon cables are perfect for making optic fiber cables with higher packing density.

[0046] The term “core” as used herein refers to an inner most cylindrical structure present in the center of the optical fiber, that is configured to guide the light rays inside the optical fiber.

[0047] The term “cladding” as used herein refers to 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 thecore of the optical fiber and an outer cladding layer coupled to the inner cladding from the outside.

[0048] The term “trench” as used herein is 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.

[0049] 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.

[0050] The term “relative refractive index” as used herein is defined as ,where ni is the maximum refractive index in region i of an optical fiber unless otherwise specified, and n is the average refractive index of an undoped region of the optical fiber. As used herein, the values of the relative refractive index are given in units ofunless otherwise specified. In some cases where the refractive index of a region is less than the average refractive index of an undoped region, the relative refractive index percentage is negative, and the region is referred to as a trench region.

[0051] The term “refractive index profile” (also termed as relative refractive index profile) of the optical fiber as used herein is referred to as a distribution of refractive indexes in the optical fiber from the core to the utmost 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 varied as a function of the radial distance from the center of the core.

[0052] The term “down-doped” as used herein is referred to as addition of 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. Specifically, at least one down dopant as used herein is Fluorine.

[0053] The term “up-doped” as used herein is referred to as addition of 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 updopants. Specifically, the up dopant as used herein is one of Germanium and Chlorine.

[0054] The term “un-doped” as used herein is referred to as a material that is not intentionally doped, or which is pure silica. However, there are always chances of some diffusion of dopants in the region which is negligible.

[0055] The term “diameter of the optical fiber” as used herein is referred to as a diameter of a bare glass optical fiber excluding one or more coatings on the optical fiber.

[0056] The term “Mode Field Diameter (MFD)” as used herein is referred to as 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.

[0057] The term “pure silica region” as used herein is referred to as a region that helps in achieving the delta in reference to core which is required for light to guide in core and to achieve total internal reflection. The pure silica regions surrounding each core act as a buffer region (immediate cladding region), and these are required to optimize the MFD value in the required range as claimed in the present invention. In absence of this buffer region MFD becomes very low and will be out of range of the claimed value.

[0058] The term “micro bend loss” as used herein is referred to as a loss in an optical fiber that relates to a light signal loss associated with lateral stresses along a length of the optical fiber. The micro bend loss is due to coupling from the optical fiber’s guided fundamental mode to lossy modes or cladding modes.

[0059] The term “macro bend loss” as used herein is referred to as the 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 defined as large radius loss. The macro bend loss is measured as per IEC standards. The optical fiber with lower macro bend loss is required for better performance in optical network, especially during the cable termination.

[0060] The term “Zero Dispersion Wavelength (ZDW)” as used herein is referred to as a wavelength at which the value of a dispersion coefficient is zero. In general, ZDW is the wavelength at which material dispersion and waveguide dispersion cancel one another.

[0061] The term “attenuation” as used herein is referred to as reduction in power of a light signal as it is transmitted. Specifically, the attenuation is caused by Rayleigh scattering, absorption of the light signal, and the like. The attenuation in an optical fiber is measured with Optical Time Domain Reflectometer (OTDR) device as per IEC standards. The optical fiber disclosed in the present invention has low attenuation which helps in increasing the link length of an optical fiber and / or optical fiber cable.

[0062] 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 cutoff wavelength known as cable cut-off wavelength measured on 22 meters sample length of the optical fiber. If the cable cut-off value of an optical fiber is above 1260 nm, the optical fiber may not be compatible with typical telecommunication application and 1280 nm to 1310 nm window may not be used in a single mode operation for telecommunication application of the optical fiber.

[0063] The term “core peak” as used herein is referred to as the maximum refractive index value of the core of the optical fiber.

[0064] The term “core volume” as used herein is referred to as a volume acquired by the core with respect to the core radius. The core volume may have a magnitude in micrometers square (pm2) that may be determined by the following equation:where Rc is core radius and RO = 0.

[0065] The term “trench volume” as used herein is referred to as a volume acquired by region between the core radius and the trench radius. The trench volume may have a magnitude (in pm2) that may be determined as , where Rc is radius of core and R1 is trench radius (down doped cladding).

[0066] Fig. 1 is a pictorial snapshot illustrating an optical fiber with at least one trench region in accordance with an embodiment of the present invention. The optical fiber 100 may have a macro bend loss of less than or equal to (i) 0.2 decibel / turn (dB / tum) at a bend radius of 2.5 millimeter (mm) and a wavelength of 1550 nanometer (nm), and 0.5 dB / turn at a bend radius of 2.5 mm and a wavelength of 1625 nm. In alternative embodiments, the optical fiber 100 may further have a macro bend loss of less than or equal to 0.15 dB / tum at a bend radius of 5 mm and a wavelength of 1550 nm, and 0.45 dB / turn at a bend radius of 5 mm and a wavelength of 1625 nm.

[0067] The optical fiber 100 may have a zero-dispersion wavelength (ZDW) in a range of 1300 nm to 1324 nm. Further, the optical fiber 100 may have a mode field diameter (MFD) in a range of 8.2 pm to 9 pm. If the mode field diameter of an optical fiber is below 8.2 pm, the optical fiber may not be compatible for ultra-low bend insensitive application in telecom networks as per ITU recommendations. If the mode file diameter of an optical fiber is above 9 pm, the light confinement in the optical fiber is very poor which induces more bend losses such as macro bend and micro bending losses.

[0068] The optical fiber 100 may have a core 102 and a cladding 104 such that the cladding 104 surrounds the core 102. In particular, the core 102 has a core radius (Rc) from a central axis 101 and a core diameter (d). Further, the core 102 may have a core refractive index (N) and a core relative refractive index (Ac) such that thecore 102 may have an alpha profile with a first alpha value (al) in a range of 4 to 8. The optical fiber 100 may experience a higher value zero dispersion wavelength with respect to the ranges of zero dispersion wavelength disclosed in the present invention, if the first alpha value (al) is less than 4. The optical fiber 100 may experience a higher value of cable cutoff (CC) wavelength i.e., more than 1260 nm disclosed in the present invention, if the first alpha value (al) is greater than 8. If the cable cutoff of an optical fiber is more than 1260 nm, the optical fiber may not be compatible with typical telecommunication applications.

[0069] In accordance with an embodiment of the present invention, the relative refractive index profile of the core 102 may be the alpha profile such that the core refractive index ‘N’ may be derived from the first alpha value ‘ 1’ of the peak shaping parameter alpha. Further, the core refractive index ‘N’ may be dependent on a core peak with a maximum refractive index value ‘Nmax’ (i.e., a maximum value of the core refractive index ‘N’), the core radius ‘Rc’, the core relative refractive index difference ‘Ac’, and a radial position ‘r’ from a center of the optical fiber 100. In an exemplary aspect of the present invention, the core refractive index ‘N’ at the radial distance ‘r’ can be determined as:

[0070] In accordance with an embodiment of the present invention, the cladding (104) may have a cladding diameter 110 that may be less than or equal to 125 + 0.7 micrometer (pm). In an alternative aspect of the present invention, the cladding diameter may be between 80+ 0.7 pm to 125 + 0.7 pm.

[0071] The cladding 104 may have first through third cladding layers 104a- 104c such that the first cladding layer 104a surrounds the core 102, the second cladding layer 104b surrounds the first cladding layer 104a, and the third cladding layer 104c surrounds the second cladding layer 104b.

[0072] In accordance with an embodiment of the present invention, the cladding 104 may be independent of traces of Chlorine (Cl). In particular, a concentration of traces of Chlorine (Cl) in the cladding 104 may be less than 1500 ppm.

[0073] In accordance with an embodiment of the present invention, the optical fiber 100 may be drawn from a glass preform (not shown) which may have a refractive index profile concentration similar to the drawn optical fiber 100. Particularly, the glass preform, and optical fiber manufacturing process are efficiently designed and optimized with new techniques and process so that the cladding layer 104 has negligible amount of Chlorine traces. The glass preform manufacturing process includes an enhanced sintering technique to produce the optical fiber free form traces of Chlorine.

[0074] In accordance with an embodiment of the present invention, the first cladding layer 104a may have a buffer cladding region, and may extend from a radial distance of the core radius (Rc) from the central axis 101 to a first radius (Rl) from the central axis 101, from a central axis 101. In particular, the first radius (Rl) may be in a range of 7.3 pm to 10 pm. If the first radius (Rl) is below 7.3 pm, the optical fiber 100 may experience higher attenuation loss because more OH ion and impurities may diffuse in the core 102. If the first radius (Rl) is above 10 pm, the optical fiber 100 may not be able to achieve the claimed value of waveguide properties such as MFD and macro bend loss.

[0075] In accordance with an embodiment of the present invention, the first cladding layer 104a may have a first refractive index (Nl) and a first relative refractive index (Al). In particular, the first cladding layer 104a may either be undoped or slightly up-doped. Moreover, the first cladding layer 104a may have a first clad diameter (D) such that a ratio of the first clad diameter (D) to the core diameter (d) may be greater than 2. Further, ratio of the first clad diameter (D) to the core diameter (d) may be between 2 to 3. The ratio of the first clad diameter (D) to the core diameter (d) may be less than 3 to achieve good confinement of light in the optical fiber 100. The good light confinement decreases the zero dispersion towards the lower zero dispersion wavelength side and enhances the macro bend performance.

[0076] In accordance with an embodiment of the present invention, the ratio of the first clad diameter (D) to the core diameter (d) (i.e., D / d ratio) may be used in the disclosed range as per the present invention to manufacture the glass preform and then draw optical fiber 100 from the glass preform such that OH ion is negligible in core region irrespective of the process used for manufacturing of the cladding layer 104 over the core 102. If the D / d ratio is less than 2, OH ion, impurities, and moisture from the external environment may interact with the core region of glass preform and may lead to increase in attenuation loss. In some aspect of the present invention, if the ratio of diameter of the first cladding layer to the diameter of core region is less than 2, then the waveguide parameters such as MFD, ZDW, cable cutoff and macro bend value as claimed in the present invention may not be achieved.

[0077] In accordance with an embodiment of the present invention, the second cladding layer 104b may include at least one trench region (402). The at least one trench region 402 may have a second refractive index (N2) and a trench relative refractive index (A2) (hereinafter interchangeably referred to and designated as ‘second relative refractive index (A2)’) such that the trench relative refractive index (A2) may decrease gradually from an outer boundary 106 of the first cladding layer 104a to a trench center (404) of the at least one trench region 402, and may increase gradually from the trench center 404 to an outer boundary 108 of the second cladding layer 104b.

[0078] The second cladding layer 104b may extend from a radial distance of the first radius (Rl) from the central axis 101 to a trench radius (R2) (hereinafter interchangeably referred to and designated as ‘second radius (R2)’) from the central axis 101. In some aspects of the present invention the trench radius (R2) may be in a range of 14 micrometer (pm) to 20 pm.

[0079] In accordance with an embodiment of the present invention, the trench center 404 may be a central point of at least one trench region 402. Alternatively, the trench center may be an intermediate point nearest to the center of the trench region 402. The term center may not be limited to a fixed central point, it may vary within the range of a radial distance of the trench center 404 from the central axis 101 of the optical fiber 100.

[0080] In some aspects of the present invention, the radial distance of the trench center 404 from the central axis 101 may be in a range of 9 pm to 13 pm. In other words, a minimum value of alpha in the trench region 402 may be at the radial distance between 9 pm to 13 pm from the central axis 101 of the optical fiber 100.

[0081] In accordance with an embodiment of the present invention, the second cladding layer 104b may have an alpha profile.The second relative refractive index (A2) may have a second alpha value (a2) that may be in a range of 5 to 8. Further, a minimum value of the trench relative refractive index (A2) may be in a range of - 0.35% to -0.45%. If the trench relative refractive index (A2) is greater than -0.35%.

[0082] In accordance with an embodiment of the present invention, the optical fiber 100 may experience a higher value of bend loss with respect to the ranges of macro bend loss as disclosed in the present invention. In particular, the optical fiber 100 may experience a higher value of cable cutoff (CC) wavelength i.e., more than 1260 nm, if the trench relative refractive index (A2) is less than 0.45%. If the second alpha value (a2) and trench radius (R2) is not designed between the ranges disclosed in the present invention, the optical fiber 100 may not be able to achieve the ultralow bend loss along with good mode field diameter (MFD) which is the primary requirement of a bend insensitive optical fiber cable.

[0083] In accordance with an embodiment of the present invention, the relative refractive index profile of the second cladding layer 104b may be the alpha profile such that the second refractive index ‘N2’of the second cladding layer 104b may be derived from the second alpha value ‘2’ of the peak shaping parameter alpha. The second refractive index ‘N2’ may further be dependent on a minimum refractive index value ‘N2min’ (i.e., a minimum value of the refractive index ‘N2’ of the second cladding layer 104b), the first radius ‘Rl’, the second radius ‘R2’ of the second cladding layer 104b, the trench relative refractive index ‘ A2’ of the second cladding layer 104b, and the radial position ‘r’ from a center of the optical fiber 100. In an exemplary aspect of the present invention, the refractive index ‘N2’ at the radial distance ‘r’ can be determined as:

[0084] In accordance with an embodiment of the present invention, the third cladding layer 104c may extend from the second radius (R2) from the central axis 101 to a third radius (R3) from the central axis 101. In particular, the third cladding layer 104c may have a third refractive index (N3) and a third relative refractive index (A3). Moreover, the third cladding layer 104c may be un-doped. Further, the third radius (R3) may be greater than or equal to 40 pm and less than or equal to 63 pm.

[0085] In an exemplary aspect of the present invention, the optical fiber 100 may have the core relative refractive index (Ac) equal to 0.34%, the first alpha value (al) equal to 6, the core radius (Rc) equal to 3.8 pm, the first relative refractive index (Al) equal to zero, the first radius (Rl) equal to 8.3 pm, the second relative refractive index (A2) equal to -0.39%, the second alpha value (a2) equal to 7, the second radius (R2) equal to 16.4 pm, the third relative refractive index (A3) equal to zero, the third radius (R3) equal to 62.5 pm, the MFD equal to 8.35 pm at the wavelength of 1310 nm, the ZDW equal to 1321 nm, a cable cutoff (CC) wavelength of 1198 nm, the macro bend loss equal to 0.028 dB / turn at the wavelength of 1550 nm and the radius of 5mm, the macro bend loss equal to 0.059 dB / turn at the wavelength of 1625 nm and the radius of 5mm, the macro bend loss equal to 0.04 dB / tum at the wavelength of 1550 nm and the radius of 2.5 mm, and the macro bend loss equal to 0.073 dB / tum at the wavelength of 1625 nm and the radius of 2.5 mm.

[0086] In yet another exemplary aspect of the present invention, the optical fiber 100 may have the core relative refractive index (Ac) equal to 0.35%, the first alpha value (al) equal to 5, the core radius (Rc) equal to 3.52 pm, the first relative refractive index (Al) equal to zero, the first radius (Rl) equal to 7.92 pm, the second relative refractive index (A2) equal to -0.4%, the second alpha value (a2) equal to 7, the second radius (R2) equal to 15.97 pm, the third relative refractive index(A3)equal to zero, the third radius (R3) equal to 62.5 pm, the MFD equal to 8.45 pm at the wavelength of 1310 nm, the ZDW equal to 1320 nm, the cable cutoff (CC) wavelength of 1195 nm, the macro bend loss equal to 0.03 dB / turn at the wavelength of 1550 nm and the radius of 5mm, the macro bend loss equal to 0.061 dB / turn at the wavelength of 1625 nm and the radius of 5mm, the macro bend loss equal to 0.045 dB / turn at the wavelength of 1550 nm and the radius of 2.5 mm, and the macro bend loss equal to 0.076 dB / turn at the wavelength of 1625 nm and the radius of 2.5 mm.

[0087] In yet another exemplary aspect of the present invention, the optical fiber 100 may have the core relative refractive index (Ac) equal to 0.33%, the first alpha value (al) equal to 7, the core radius (Rc) equal to 3.6 pm, the first relative refractive index (Al) equal to zero, the first radius (Rl) equal to 7.9189 pm, the second relative refractive index (A2) equal to -0.4%, the second alpha value (a2) equal to 8, the second radius (R2) equal to 16 pm, the third relative refractive index (A3) equal to zero, the third radius (R3) equal to 62.5 pm, the MFD equal to 8.6 pm at the wavelength of 1310 nm, the ZDW equal to 1318 nm, the cable cutoff (CC) wavelength of 1190 nm, the macro bend loss equal to 0.032 dB / turn at the wavelength of 1550 nm and the radius of 5mm, the macro bend loss equal to 0.066 dB / turn at the wavelength of 1625 nm and the radius of 5mm, the macro bend loss equal to 0.048 dB / turn at the wavelength of 1550 nm and the radius of 2.5 mm, and the macro bend loss equal to 0.079 dB / tum at the wavelength of 1625 nm and the radius of 2.5 mm.

[0088] In yet another exemplary aspect of the present invention, the optical fiber 100 may have the core relative refractive index (Ac) equal to 0.36%, the first alpha value (al) equal to 6, the core radius (Rc) equal to 3.4 pm, the first relative refractive index (Al) equal to zero, the first radius (Rl) equal to 7.5 pm, the second relative refractive index (A2) equal to -0.41%, the second alpha value (a2) equal to 7, the second radius (R2) equal to 16.5 pm, the third relative refractive index(A3) equal to zero, the third radius (R3) equal to 62.5 pm, the MFD equal to 8.4 pm at the wavelength of 1310 nm, the ZDW equal to 1319 nm, the cable cutoff (CC) wavelength of 1220 nm, the macro bend loss equal to 0.024 dB / tum at thewavelength of 1550 nm and the radius of 5mm, the macro bend loss equal to 0.052 dB / turn at the wavelength of 1625 nm and the radius of 5mm, the macro bend loss equal to 0.038 dB / turn at the wavelength of 1550 nm and the radius of 2.5 mm, and the macro bend loss equal to 0.068 dB / tum at the wavelength of 1625 nm and the radius of 2.5 mm.

[0089] In yet another exemplary aspect of the present invention, the optical fiber 100 may have minimum and maximum values of the core relative refractive index (Ac) equal to 0.32% and 0.42%, respectively, minimum and maximum values of the first alpha value (al) equal to 4 and 8, respectively, minimum and maximum values of the core radius (Rc) equal to 3.4 pm and 4.5 pm, respectively, minimum and maximum values of the first relative refractive index (Al) equal to -0.05% and 0.05%, respectively, minimum and maximum values pf the first radius (Rl) equal to 7.3 pm and 10 pm, minimum and maximum values of the second relative refractive index (A2) equal to -0.45% and -0.35%, respectively, maximum and minimum values of the second alpha value (a2) equal to 5 and 8, respectively, minimum and maximum values of the second radius (R2) equal to 14 pm and 20 pm, minimum and maximum values of the third relative refractive index (A3) equal to -0.05% and 0.05%, respectively, minimum and maximum values of twice of the third radius (R3) (i.e., a cladding diameter) equal to (125-0.7) pm and (125+0.7) pm, minimum and maximum values of the MFD equal to (8.6-0.4) pm and (8.6+0.4) pm, respectively, at the wavelength of 1310 nm, minimum and maximum values of the ZDW equal to 1300 nm and 1324 nm, respectively, a maximum value of the cable cutoff (CC) wavelength of 1260 nm, a maximum value of the macro bend loss equal to 0.15 dB / turn at the wavelength of 1550 nm and the radius of 5mm, a maximum value of the macro bend loss equal to 0.45 dB / turn at the wavelength of 1625 nm and the radius of 5mm, a maximum value of the macro bend loss equal to 0.2 dB / turn at the wavelength of 1550 nm and the radius of 2.5 mm, and a maximum value of the macro bend loss equal to 0.2 dB / turn at the wavelength of 1625 nm and the radius of 2.5 mm.

[0090] Fig. 2 is a pictorial snapshot illustrating an optical fiber with two trench regions in accordance with an embodiment of the present invention. In particular,the optical fiber 100 may have two trench regions. Specifically, the second cladding layer 104b may be segregated into two sublayers (i.e., a first sublayer 104ba and a second sublayer 104bb) such that each sublayer of the first and second sublayers 104ba-104bb may have a trench region having one or more features same as the at least one trench region 402.

[0091] Further, the trench regions associated with each sublayer of the first and second sublayers 104ba-104bb may have the trench relative refractive index (A2) and an alpha profile.

[0092] In some aspects of the present invention, the trench regions may have the second alpha value (a2) that may be in the range of 5 to 8. Moreover, the minimum value of the trench relative refractive index (A2) may be in a range of -0.35% to - 0.45%.

[0093] Fig. 3 is a representation illustrating a theoretically derived refractive index profile of the optical fiber in accordance with an embodiment of the present invention.The theoretically derived refractive index profile 300 may showcase a variation of relative refractive index of the optical fiber 100 (presented on y-axis) with radial distance from the central axis 101 (presented on x-axis) that is derived theoretically. The optical fiber 100 may have the core 102 and the first through third cladding layers 104a- 104c. As derived theoretically, the core 102 may have the core relative refractive index (Ac) from the central axis 101 to the core radius (Rc). The refractive index profile of the core 102 may have the alpha profile with the first alpha value (al) such that the core relative refractive index (Ac) may increase from the central axis 101 unless the core relative refractive index (Ac) reaches the maximum value of the first alpha value (al) and then decreases till the core radius (Rc). The first cladding layer 104a may extend from the core radius (Rc) and the first radius (Rl) and may have the first relative refractive index (Al).

[0094] In particular, the refractive index profile of the first cladding layer 104a may have a decaying profile such that the first relative refractive index (Al) may decrease gradually from the core radius (Rc) to the first radius (Rl). Moreover, the second cladding layer 104b may have the second relative refractive index (A2). Further, the second cladding layer 104b may be evenly down-doped such that thesecond relative refractive index (A2) may have a constant value from the first radius (Rl) to the second radius (R2). Furthemore, the third cladding layer 104c may have the third relative refractive index (A3) and may be un doped such that the second relative refractive index (A2) may be zero from the second radius (R2) to the third radius (R3).

[0095] Fig. 4 is a representation illustrating an actual refractive index profile of the optical fiber derived through simulation in accordance with an embodiment of the present invention. The actual refractive index profile 400 may showcase an actual variation of the relative refractive index of the optical fiber 100 (presented on y- axis) with radial distance from the central axis 101 (presented on x-axis) that is derived practically.

[0096] The optical fiber 100 may have the core 102 and the first through third cladding layers 104a- 104c extending from the central axis 101 to the core radius (Rc), the first radius (Rl), the second radius (R2), and the third radius (R3), respectively. In particular, the core 102 may have the core relative refractive index (Ac) such that the refractive index profile of the core 102 may have the alpha profile with a first alpha value (al) in a range of 4 to 8. Moreover, the core relative refractive index (Ac) may increase from the central axis 101 unless the core relative refractive index (Ac) reaches the maximum value of the first alpha value (al), and then decreases till the core radius (Rc).

[0097] In some aspects of the present invention, the first cladding layer 104a may either be undoped or slightly up-doped such that the first relative refractive index (Al) may have either a zero value or a slightly positive value. Further, the first refractive index (Al) may decrease gradually from the core radius (Rc) to the first radius (Rl).

[0098] The second cladding layer 104b may include at least one trench region (402). The at least one trench region 402 may have a trench relative refractive index (A2) (hereinafter interchangeably referred to and designated as ‘second relative refractive index (A2)’) such that the trench relative refractive index (A2) may decrease gradually from an outer boundary 106 of the first cladding layer 104a (that may be at the radial distance equal to the first radius Rl from the central axis 101)to the trench center 404, and may increase gradually from the trench center 404 to an outer boundary 108 of the second cladding layer 104b (that may be at the radial distance equal to the second radius R2 from the central axis 101).

[0099] Further, the refractive index profile of the at least one trench region 402 may have the alpha profde with the second alpha value (a2) that may be in the range of 5 to 8. And, a minimum value of the trench relative refractive index (A2) may be in the range of -0.35% to -0.45%.

[0100] In some aspects of the present invention, the second cladding layer 104b may be slightly up-doped near the second radius (R2) such that the second relative refractive index (A2) may have a slight hump 406 near the second radius (R2). Further, the third cladding layer 104c may be undoped (i.e., pure silica region) such that the third relative refractive index (A3) may have a zero value.

[0101] Fig. 5 is a pictorial snapshot illustrating the optical fiber coated with one or more coating layers in accordance with an embodiment of the present invention. The one or more coating layers 502 may be surrounding the cladding layer 104. The one or more coating layers 502 may have a thickness of less than 65 pm and a coating refractive index (N4) such that an absolute difference between the third refractive index (N3) of the third cladding layer 104c and the coating refractive index (N4) of the coating layer 502 may be less than or equal to 0.01.

[0102] When the absolute difference between the third refractive index (N3) of the third cladding layer 104c and the coating refractive index (N4) of the coating layer 502 is less than or equal to 0.01 may result in lowering the Fresnel reflection at an interface of third cladding layer 104c and coating layer 502. If the absolute difference between the third refractive index (N3) of the third cladding layer 104c and the coating refractive index (N4) of the coating layer 502 deviates from the range disclosed in the present invention, this may lead to high Fresnel reflection towards the core 102 and may lead to more signal loss.

[0103] In some aspects of the present invention, a diameter of the optical fiber 100 that is coated by the one or more coating layers 502 may be less than or equal to 180 pm. In an exemplary aspect of the present invention, a diameter of the optical fiber 100 that is coated by the one or more coating layers 502 may bebetween 160 m to 180 pm. Further, the diameter of the optical fiber 100 that is coated by the one or more coating layers 502 may be less than or equal to 200 pm. Furthermore, the diameter of the optical fiber 100 that is coated by the one or more coating layers 502 may be less than 250 pm.

[0104] In accordance with an embodiment of the present invention, the one or more coating layers 502 may have a primary coating layer (not shown), a secondary coating layer (not shown), and a colored coating layer (not shown). In particular, the primary coating layer may have a coating thickness in a range of 10 pm to 30 pm, the secondary coating layer may have a coating thickness in a range of 10 pm to 30 pm, and the colored coating layer may have a coating thickness in a range of 4 pm to 8 pm.

[0105] In accordance with an alternative embodiment of the present invention, the one or more coating layers 502 may have the primary coating layer and the second coating layer such that the second coating layer may be colored.

[0106] In accordance with an embodiment of the present invention, a young’s modulus of the primary coating layer may be less than 0.6 Mega Pascal (MPa) and the secondary coating may be in a range of 1000 MPa to 1500 MPa.

[0107] Fig. 6 is a pictorial snapshot illustrating the optical fiber cable in accordance with an embodiment of the present invention. In particular, the optical fiber cable 600 may be a ribbon fiber cable. Moreover, the optical fiber cable 600 may be an intermittent bonded ribbon (IBR) fiber cable. Further, the optical fiber cable 600 may have a plurality of buffer tubes 602. Although FIG. 6 illustrates that the plurality of buffer tubes 602 has six buffer tubes (i.e., first through sixth buffer tubes 602a-602f), it will be apparent to a person skilled in the art that the scope of the present invention is not limited to it. In various other aspects, the plurality of buffer tubes 602 may have any number of buffer tubes, without deviating from the scope of the present invention. In such a scenario, each buffer tube of the plurality of buffer tubes 602 may be structurally and functionally similar to the first through sixth buffer tubes 602a-602f as described herein.

[0108] Further, the plurality of buffer tubes 602 may have a plurality of optical fiber ribbons 604 (hereinafter interchangeably referred to and designated as“plurality of IBRs 604”). Each optical fiber ribbon of the plurality of optical fiber ribbons 604 may have at least one pair of adjacent optical fibers of the plurality of optical fibers 100, that may be intermittently bonded. Although FIG. 6 illustrates that the plurality of buffer tubes 602 has twenty four IBRS (i.e., first through twenty fourth IBR 604a-604x), it will be apparent to a person skilled in the art that the scope of the present invention is not limited to it. In various other aspects, the plurality of buffer tubes 602 may have any number of IBRs, without deviating from the scope of the present invention. In such a scenario, each IBR of the plurality of IBRs 604 may be structurally and functionally similar to the first through twenty fourth IBR 604a-604x as described herein.

[0109] In particular, each buffer tube of the plurality of buffer tubes 602 has four IBRS (for example the first buffer tube 602a is shown to have the first through fourth IBR 604a-602d), it will be apparent to a person skilled in the art that the scope of the present invention is not limited to it. In various other aspects, each buffer tube of the plurality of buffer tubes 602 may have any number of IBRs, without deviating from the scope of the present invention. In such a scenario, each IBR of each IBR of the plurality of IBRs 604 may be structurally and functionally similar to the first through twenty fourth IBR 604a-604x as described herein.

[0110] In accordance with an embodiment of the present invention, each IBR 602 may have a plurality of optical fibers 100. In particular, each optical fiber of the plurality of optical fibers 100 may have one or more structural and functional properties same as the optical fiber 100. In some aspects of the present invention, each optical fiber of the plurality of optical fibers 100 may be the same as the optical fiber 100.

[0111] In accordance with an embodiment of the present invention, each optical fiber of the plurality of optical fibers 100 (hereinafter interchangeably referred to and designated as “the optical fiber 100”) may have the core 102 that may extend along the central axis 101 of the optical fiber 100, and the cladding 104 that may surround the core 102. The core 102 may have the first alpha value al that may be in the range of 4 to 8. The cladding 104 may have the first through third cladding layers 104a- 104c such that the refractive index profile of the secondcladding layer 104b may include at least one trench region 402. The trench relative refractive index (A2) of the at least one trench region 402 may decrease gradually from an outer boundary 106 of the first cladding layer 104a to a trench center 404 of the at least one trench region 402 and may increase gradually from the trench center 404 to the outer boundary 108 of the second cladding layer 104b.

[0112] In accordance with an embodiment of the present invention, the optical fiber cable 600 may further have a sheath 606 that surrounds the plurality of buffer tubes 602. Particularly, the sheath 606 may be adapted to act as an outermost covering for the optical fiber cable 600 such that the sheath 606 facilitates in reduction of abrasion and to provide the optical fiber cable 600 with extra protection against external mechanical effects such as crushing, and the like. Further, the sheath 606 may be made up of a material such as, but not limited to, a synthetic plastic material, a natural plastic material, and the like. Aspects of the present invention are intended to include and / or otherwise cover any type of material for the sheath 606, known to a person of ordinary skill in the art, without deviating from the scope of the present invention.

[0113] In accordance with an embodiment of the present invention, the sheath 606 may have a plurality of strength members 608 that may be partially or completely embedded in the sheath 606. In particular, the plurality of strength members 608 may be adapted to provide strength to the optical fiber cable 600 that may be required during an installation process of the optical fiber cable 600. Moreover, the strength members 608 may be adapted to provide the majority of structural strength and support to the optical fiber cable 600. Further, the strength members 608 may enhance the tensile strength of the optical fiber cable 600, which is highly desirable during the installation process. Although FIG. 6 illustrates that the plurality of strength members 608 has six strength members (i.e., first through sixth strength members 608a-608f), it will be apparent to a person skilled in the art that the scope of the present invention is not limited to it. In various other aspects, the plurality of strength members 608 may have any number of strength members, without deviating from the scope of the present invention. In such a scenario, each strength member of the plurality of strength members 608 may be structurally andfunctionally similar to the first through sixth strength members 608a-608f as described herein.

[0114] In accordance with an embodiment of the present invention, the optical fiber cable 600 may have one or more ripcords 610 that facilitate ripping, tearing, or opening up of the optical fiber cable 600. In particular, the one or more ripcords 610 may facilitate the ripping, tearing, or opening up of the optical fiber cable 600 to access the plurality of strength members 608 from the sheath 606. Although FIG. 6 illustrates that the one or more ripcords 610 has two ripcords (i.e., first and second ripcords shown as 610a and 610b, respectively), it will be apparent to a person skilled in the art that the scope of the present invention is not limited to it. In various other aspects, the one or more ripcords 610 may have any number of ripcords, without deviating from the scope of the present invention. In such a scenario, each ripcord of the one or more ripcords 610 may be structurally and functionally similar to the first and second ripcords 610a and 610b as described herein.

[0115] In accordance with an embodiment of the present invention, the optical fiber cable 600 may have a plurality of water swellable yarns 612 providing water resistance to the plurality of optical fibers 600 inside the optical fiber cable 600 by restricting penetration of water inside the optical fiber cable 600. Although FIG. 6 illustrates that the plurality WSYs 612 has six WSYs (i.e., first through sixth WSYs 612a-612f), it will be apparent to a person skilled in the art that the scope of the present invention is not limited to it. In various other aspects, the plurality WS Y s 612 may have any number of WSYs, without deviating from the scope of the present invention. In such a scenario, each WSY of the plurality WSYs 312 may be structurally and functionally similar to the first through sixth WSY 612a-612f as described herein.

[0116] The presented optical fiber introduces a design with specific alpha values for the core and cladding layers. The gradual variation in the trench relative refractive index in the second cladding layer contributes to achieving ultra-low bend sensitivity, surpassing the limitations of existing G.657.B3 fibers. Additionally, with ultra-low bend sensitivity, the optical fiber offers benefits like a macro bendloss below specified thresholds at different wavelengths and bend radii. The inclusion of coating layers with minimal refractive index differences enhances the overall performance and reliability of the optical fiber.

[0117] The specific alpha values for the core and cladding layers, a gradual variation in trench relative refractive index, and low macro bend loss synergistically ensures an ultra-low bend sensitivity while maintaining other essential optical parameters.

[0118] The combination of core and cladding alpha values, along with the gradual variation in trench relative refractive index, optimizes the optical fiber for ultra-low bend sensitivity. The optical fiber design ensures efficient light transmission through bends, reducing the risk of signal loss or degradation in high- density network applications.

[0119] Further, the optical fiber in optical fiber ribbons, both in bonded and intermittently bonded configurations. The reduced macro bend losses and ultralow bend sensitivity makes it ideal for various high-density network scenarios, maximizing the utilization of physical assets.

[0120] The optical fiber's innovative design addresses the long-felt need for ultra-low bend sensitivity in high-density networks. The optical fiber design parameters including specific alpha values and a gradual variation in trench relative refractive index, make it a versatile solution for various optical fiber applications, ensuring optimal performance and reliability.

[0121] While various aspects of the present invention have been illustrated and described, it will be clear that the present invention 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 invention, 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.

Claims

“OPTICAL FIBER AND OPTICAL FIBER CABLE WITH ULTRA LOW BEND LOSS”CLAIMSWe claim:

1. An optical fiber (100) comprising: a core (102) having a first alpha value (al) in a range of 4 to 8; and a cladding (104) that surrounds the core and comprising first through third cladding layers (104a- 104c), wherein a refractive index profile of the second cladding layer (104b) comprises at least one trench region (402) such that a trench relative refractive index (A2) of the at least one trench region (402) decreases gradually from an outer boundary (106) of the first cladding layer (104a) to a trench center (404) of the at least one trench region (402) and increases gradually from the trench center (404) to an outer boundary of the second cladding layer (104b).

2. The optical fiber (100) as claimed in claim 1, wherein the first cladding layer (104a) has a first clad diameter (D) and the core (102) has a core diameter (d), where a ratio of the first clad diameter (D) to the core diameter (d) is greater than 2.

3. The optical fiber (100) as claimed in claim 1, wherein the at least one trench region (402) has a second alpha value (a2) in a range of 5 to 8.

4. The optical fiber (100) as claimed in claim 1, wherein the optical fiber (100) further has a macro bend loss of less than or equal to(i) 0.2 decibel / turn (dB / turn) at a bend radius of 2.5 millimeter (mm) and a wavelength of 1550 nanometer (nm), and(ii) 0.5 dB / turn at a bend radius of 2.5 mm and a wavelength of 1625 nm.

5. The optical fiber (100) as claimed in claim 1, wherein the optical fiber (100) further has a macro bend loss of less than or equal to(i) 0.15 dB / turn at a bend radius of 5 mm and a wavelength of 1550 nm, and (ii) 0.45 dB / turn at a bend radius of 5 mm and a wavelength of 1625 nm.

6. The optical fiber (100) as claimed in claim 1, wherein the optical fiber (100) further comprising one or more coating layers (502) surrounding the cladding (104), wherein an absolute difference between a third refractive index (N3) of the third cladding layer (104c) and a coating refractive index (N4) of the coating layer (502) is less than or equal to 0.01.

7. The optical fiber (100) as claimed in claim 1, wherein the cladding (104) is independent of traces of Chlorine (Cl).

8. The optical fiber (100) as claimed in claim 1, wherein a concentration of traces of Chlorine (Cl) in the cladding (104) is less than 1500 ppm.

9. The optical fiber (100) as claimed in claim 1, wherein a minimum value of the trench relative refractive index (A2) of the second cladding layer (104b) is in a range of -0.35% to -0.45%.

10. The optical fiber (100) as claimed in claim 1, wherein the second cladding layer (104b) has a trench radius (R2) in a range of 14 micrometer (pm) to 20 pm.

11. The optical fiber (100) as claimed in claim 1, wherein a mode field diameter (MFD) of the optical fiber (100) is in a range of 8.2 pm to 9 pm.

12. The optical fiber (100) as claimed in claim 1, wherein the cladding (104) has a cladding diameter (110) of less than or equal to 125 + 0.7 pm.

13. The optical fiber (100) as claimed in claim 6, wherein the one or more coating layers (502) has a coating diameter (504) less than or equal to 250 pm.

14. The optical fiber (100) of claim 1, wherein the optical fiber (100) is used in an optical fiber ribbon (604) such that adjacent optical fibers are at least partially bonded.

15. An optical fiber (100) comprising a core (102); and a cladding (104) that surrounds the core, wherein cladding (104) comprising at least one trench region (402) such that a trench relative refractive index (A2) is minimum near center of trench.

16. The optical fiber (100) as claimed in claim 1, wherein the at least one trench region (402) has a second alpha value (a2) in a range of 5 to 8.

17. The optical fiber (100) as claimed in claim 1, wherein core (102) has a first alpha value (al) in a range of 4 to 8.

18. The optical fiber (100) as claimed in claim 1, wherein a minimum value of the trench relative refractive index (A2) of the second cladding layer (104b) is in a range of -0.35% to -0.45%.

19. The optical fiber (100) as claimed in claim 1, wherein a concentration of traces of Chlorine (Cl) in the cladding (104) is less than 1500 ppm.

20. The optical fiber (100) as claimed in claim 1, wherein optical fiber (100) has a macro bend loss of less than or equal to(i) 0.2 decibel / turn (dB / turn) at a bend radius of 2.5 millimeter (mm) and a wavelength of 1550 nanometer (nm), and (ii) 0.5 dB / turn at a bend radius of 2.5 mm and a wavelength of 1625 nm.

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