Description:TECHNICAL FIELD
The present disclosure relates generally to optical fibers, and, more particularly, to an optical fiber with improved micro bending performance.
BACKGROUND
High density fibre optic cables are a viable solution for increase in data capacity demand. Space division multiplexing (SDM) schemes using multi core fibre and few mode fibres can be a promising solution for suture optical networks in maximizing a transmission capacity per fibre and in realization for high density data cables. However, such fibers require compatible fibre connectors and components, have higher fan-in/fan-out, require splicing, and are expensive.
Telecommunication systems for underground and undersea applications, require optical fibers that can transmit signals to longer distances without any degradation. However, the optical fiber attributes such as attenuation and bend loss can contribute to some degradation of the signals transmitted through the optical fiber.
The reference EP3978968A1 discloses an optical fiber with a small diameter and a preferable bending property. The optical fiber includes a core made of silica-based glass, a cladding that covers an outer circumference of the core and that is made of silica-based glass having a refractive index smaller than a maximum refractive index of the core, and a coating that covers an outer circumference of the cladding. The cladding has an outer diameter of 120 µm or smaller, a mode field diameter at a wavelength of 1310 nm is 8.6 µm to 9.2 µm, an effective cut-off wavelength is 1260 µm or smaller, and a bending loss at a wavelength of 1550 nm in a case of bending at a diameter of 20 mm is 0.75 dB or smaller.
The conventional optical fibers in the prior art experience leakage losses which induces high micro bend losses due to the reduced diameter of the optical fiber. Thus, there is a need for an optical fiber that overcomes the above stated disadvantages of conventional optical fibers.
SUMMARY
In an aspect of the present disclosure, an optical fiber is disclosed. The optical fiber has a silica region, a first coating, and a second coating. The first coating is adapted to cover an outer circumference of the silica region. The first coating has (i) a first diameter and (ii) a first Young’s modulus. The second coating is adapted to cover an outer surface of the first coating. The second coating has (i) a second diameter and (ii) a second Young’s modulus. The first coating and the second coating are adapted to cause a coating induced micro bend loss that is less than 2.2 x 103 N-1mm-8.5.
These and other aspects herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawing. It should be understood, however, that the following descriptions are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the invention herein without departing from the spirit thereof.

BRIEF DESCRIPTION OF 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.
The invention is illustrated in the accompanying drawing, throughout which like reference letters indicate corresponding parts in the figure. The invention herein will be better understood from the following description with reference to the drawing, in which:

FIG. 1A illustrates a cross-sectional view of an optical fiber.
FIG. 1B illustrates a graph of a refractive index (RI) profile of the optical fiber of FIG. 1A.
FIG. 1C illustrates a cross-sectional view of another optical fiber.
FIG. 1D illustrates a graph of a refractive index (RI) profile of the optical fiber of FIG. 1C.
FIG. 1E illustrates a cross-sectional view of yet another optical fiber.
FIG. 1F illustrates a graph of a refractive index (RI) profile of the optical fiber of FIG. 1E.
FIG. 1G illustrates a graph between leakage losses and diameter of the cladding of the optical fiber of FIG. 1E.
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 centre 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 “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 refractive index profile” of an 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 centre of the core.
The term “leakage loss” as used herein refers to a loss due to mode leak in an optical fiber that adds to an attenuation of the optical fiber.
The term “micro bend loss” as used herein refers to 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.
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 “coating induced micro bend loss” as used herein refers to losses caused by multiple coatings surrounding the cladding. The coating induced micro bend loss is only for coating part of the optical fiber while in general micro bend loss is a value for entire optical fiber.
The term “Zero Dispersion Wavelength (ZDW)” as used herein refers to a wavelength at which the value of dispersion coefficient is zero. In general, ZDW is the wavelength at which material dispersion and waveguide dispersion cancel one another.
FIG. 1A illustrates a cross-sectional view of an optical fiber 100. The optical fiber 100 may be designed to have improved micro bending performance. Specifically, the optical fiber 100 may be a reduced diameter fiber that has improved micro bending performance. The improved micro bending performance may be achieved by (i) reducing a leakage loss by waveguide refractive index profile and (ii) optimizing a thickness of coatings (as will be discussed herein). The optimised combination of fiber design and coatings may significantly improve optical loss from bends of the optical fiber 100 thus providing an optimised fiber product to minimize optical power loss and maximize network performance. The optical fiber 100 may have a silica region 102, a first coating 104, and a second coating 106. The silica region 102 may have traces of at least one carbon group element and at least one halogen group element. Specifically, the silica region 102 may have Germanium (GE) (i.e., a carbon group element) and Fluorine (F) (i.e., a halogen group element) in predefined concentrations.
The silica region 102 may have a core 108, a trench layer 110, and a cladding 112. The silica region 102 may have a diameter in a range of 60 µm to 100 µm. As illustrated, the optical fiber 100 may have a central axis 114 such that the core 108 may be arranged along the central axis 114 running longitudinally, i.e., generally parallel to the central axis 114. In other words, the core 108 may be positioned approximately at a centre of the optical fiber 100.
The core 108 may have a radius R1 and a refractive index ?1. The trench layer 110 may have a radius R2 and a refractive index ?2. The cladding 112 may have a radius R3 and a refractive index ?3. In an aspect of the present disclosure, the radius R1 of the core 108 may be in a range of 4.2 micrometres (µm) to 4.8 µm. Preferably, the radius R1 of the core 108 may be 4.5 µm. The refractive index ?1 of the core 108 may be in a range of 0.36 to 0.4. Preferably, the refractive index ?1 of the core 108 may be 0.39. Further, the radius R2 of the trench layer 110 may be in a range of 9 µm to 11 µm. Preferably, the radius R2 of the trench layer 110 may be 10.3 µm. The refractive index ?2 of the trench layer 110 may be in a range of -0.08 to -0.12. Preferably, the refractive index ?2 of the trench layer 110 may be -0.1. In some aspects of the present disclosure, the predefined concentrations of the Germanium (Ge) and Fluorine (F) is directly proportional to the refractive indexes ?1 and ?2 of the core 108 and the trench layer 110 respectively. For example, if the Ge concentration increases, the refractive index ?1 of the core 108 increases in an upward (i.e., positive) direction as compared to the refractive index of pure silica, because Ge is an up dopant. In another example, if F concentration increases, the refractive index ?2 of the trench layer 110 increases in a downward (i.e., negative) direction as compared to the refractive index of pure silica., because F is a down dopant. Furthermore, the radius R3 of the cladding 112 may be approximately 40 + 0.35 µm. Preferably, the radius R3 of the cladding 112 may be 40 µm.
In such an aspect of the present disclosure, at a wavelength of 1310 nanometres (nm), the optical fiber 100 may have a Mode Field Diameter (MFD) of approximately 8.6 + 0.4. Preferably, at the wavelength of 1310 nm, the optical fiber 100 may have the MFD of approximately 8.81. Further, the optical fiber 100 may have a Zero Dispersion Wavelength in a range of 1300 to 1324 nm. Preferably, the ZDW of the optical fiber 100 may be 1302 nm. Furthermore, the optical fiber 100 may have a Cable Cut off (CC) that may be less than 1260 nm. Preferably, the CC of the optical fiber 100 may be 1234 nm. The optical fiber 100, at a wavelength of 1550 nm and with a bend radius of 7.5 mm, 1 turn, may have a macro bend loss that is less than or equal to 0.5 dB. Preferably, the optical fiber 100, at the wavelength of 1550 nm and with the bend radius of 7.5 mm, 1 turn, may have the macro bend loss of 0.177 dB. Similarly, the optical fiber 100, at the wavelength of 1625 nm and with the bend radius of 7.5 mm, 1 turn, may have the macro bend loss that is less than or equal to 1 dB. Preferably, the optical fiber 100, at the wavelength of 1625 nm and with the bend radius of 7.5 mm, 1 turn, may have the macro bend loss of 0.449 dB. The optical fiber 100, at the wavelength of 1550 nm and with a bend radius of 10 mm, 1 turn, may have the macro bend loss that is less than 0.1 dB. Preferably, the optical fiber 100, at the wavelength of 1550 nm and with the bend radius of 10 mm, 1 turn, may have the macro bend loss of 0.02 dB. Similarly, the optical fiber 100, at the wavelength of 1625 nm and with the bend radius of 10 mm, 1 turn, may have the macro bend loss that is less than 1 dB. Preferably, the optical fiber 100, at the wavelength of 1625 nm and with the bend radius of 10 mm, 1 turn, may the macro bend loss of 0.076 dB. The optical fiber 100, at the wavelength of 1550 nm and with a bend radius of 15 mm, 10 turns, may have the macro bend loss that is less than 0.03 dB. Preferably, the optical fiber 100, at the wavelength of 1550 nm and with the bend radius of 15 mm, 10 turns, may have the macro bend loss of 0.002 dB. Similarly, the optical fiber 100, at the wavelength of 1625 nm and with the bend radius of 15 mm, 10 turns, may have the macro bend loss that is less than 0.1 dB. Preferably, the optical fiber 100, at the wavelength of 1625 nm and with the bend radius of 15 mm, 10 turns, may the macro bend loss of 0.014 dB. The optical fiber 100, at the wavelength of 1550 nm, may have leakage losses that may be less than 0.001 Decibels/Kilometres (dB/km). Preferably, the optical fiber 100, at the wavelength of 1550 nm, may have leakage losses of 0.000000871 dB/km. At a wavelength of 1550 nm, the optical fiber 100 may have a leakage loss that may be less than the leakage loss at the wavelength of 1625 nm. Specifically, at the wavelength of 1625 nm, the leakage loss may be less than 0.001 dB/km. Preferably, the optical fiber 100, at the wavelength of 1625 nm, may have leakage losses of 0.000001564 dB/km.
The first coating 104 may cover an outer circumference of the silica region 102. Specifically, the first coating 104 may cover an outer circumference of the cladding 112. The second coating 106 may cover an outer circumference of the first coating 104. The first coating 104 may have a first diameter D1 and a first Young’s modulus. In some aspects of the present disclosure, the first diameter D1 may be in a range of 116 µm to 155 µm and the first Young’s modulus may be in a range of 0.0001 Gigapascal (GPa) to 0.0004 GPa. Preferably, the first Young’s modulus may be 0.0002 GPa. The second coating 106 may have a second diameter D2 and a second Young’s modulus. In some aspects of the present disclosure, the second diameter D2 may be in a range of 140 µm to 180 µm and the second Young’s modulus may be in a range of 1.3 GPa to 3 GPa. Preferably, the second Young’s modulus may be 2.2 GPa. Specifically, by virtue of the second coating 106 having the second diameter D2, the optical fiber 100 may have the second diameter D2 that is less than or equal to 180 µm. Preferably, the second diameter D2 is 160 µm. In some aspects of the present disclosure, a ratio of the second diameter to the first diameter may be in a range of 1.05 to 1.45.
The first coating 104 and second coating 106 may be adapted to induce a micro bend loss in the optical fiber 100. The micro bend loss induced by the first coating 104 and second coating 106 may be given by coating induced micro bend loss that may be determined by an equation as given below:
(K_p^2)/(?BR?_g^2 * ?DR?_s^0.375 *?BR?_s^0.625 )
K_p=(E_P D_g)/t_p
?BR?_g = p/4 E_g (D_g/2)^2
?DR?_s = E_p+(t_s/R_s )^3 E_s
?BR?_s = p/4 E_s (R_s^4-R_p^4 )^2
where, K is spring constant (MPa),
BR is bending rigidity (MPa.mm4),
DR is deformation resistance (MPa),
T is thickness(mm),
R and D is Radius (mm) and Diameter (mm), respectively,
E is Young’s modulus (MPa), and
Subscripts g, p, s denote glass region, first coating (primary coating), and second coating, respectively.
where, K_p represents spring constant of the first (primary) coating which is the ratio of product of Young’s modulus of first (primary) coating and diameter of glass region to the thickness of the first (primary) coating.
?BR?_g represents bending rigidity or bending resistance of the glass region which is a function of Youngs modulus of the glass region and diameter of the glass region.
?DR?_s represents deformation rigidity or deformation resistance of the second coating upon external force. It is a function of Young’s modulus of the first (primary) coating, thickness of the second coating and Young’s modulus of the second coating.
?BR?_s represents bending rigidity or bending resistance of the second coating which is a function of Young’s modulus of the second coating, radius of first and second coating.
In an exemplary aspect of the present disclosure, when the radius R3 of the cladding 112 is 40 µm, the diameter D1 of the first coating 104 is in a range of 145 µm to 155 µm, the diameter D2 of the second coating 106 is 180 µm, the first Young’s modulus associated with the first coating 104 is 0.0002 GPa, and the second Young’s modulus associated with the second coating 106 is 2.2 GPa, in such an aspect of the present disclosure, a coating induced micro bend loss of the optical fiber 100 is 0.05 x 103 N-1mm-8.5. In another exemplary aspect of the present disclosure, when the radius R3 of the cladding 112 is 40 µm, the diameter D1 of the first coating 104 is in a range of 145 µm to 155 µm, the diameter D2 of the second coating 106 is 180 µm, the first Young’s modulus associated with the first coating 104 is 0.0004 GPa, and the second Young’s modulus associated with the second coating 106 is 1.3 GPa, in such an aspect of the present disclosure, the coating induced micro bend loss of the optical fiber 100 is 0.25 x 103 N-1mm-8.5. In yet another exemplary aspect of the present disclosure, when the radius R3 of the cladding 112 is 40 µm, the diameter D1 of the first coating 104 is in a range of 130 µm to 140 µm, the diameter D2 of the second coating 106 is 160 µm, the first Young’s modulus associated with the first coating 104 is 0.0002 GPa, and the second Young’s modulus associated with the second coating 106 is 2.2 GPa, in such an aspect of the present disclosure, the coating induced micro bend loss of the optical fiber 100 is 0.12 x 103 N-1mm-8.5. In yet another exemplary aspect of the present disclosure, when the radius R3 of the cladding 112 is 40 µm, the diameter D1 of the first coating 104 is in a range of 130 µm to 140 µm, the diameter D2 of the second coating 106 is 160 µm, the first Young’s modulus associated with the first coating 104 is 0.0004 GPa, and the second Young’s modulus associated with the second coating 106 is 1.3 GPa, in such an aspect of the present disclosure, the coating induced micro bend loss of the optical fiber 100 is 0.65 x 103 N-1mm-8.5. In yet another exemplary aspect of the present disclosure, when the radius R3 of the cladding 112 is 40 µm, the diameter D1 of the first coating 104 is in a range of 116 µm to 126 µm, the diameter D2 of the second coating 106 is 140 µm, the first Young’s modulus associated with the first coating 104 is 0.0002 GPa, and the second Young’s modulus associated with the second coating 106 is 2.2 GPa, in such an aspect of the present disclosure, the coating induced micro bend loss of the optical fiber 100 is 0.4 x 103 N-1mm-8.5. In yet another exemplary aspect of the present disclosure, when the radius R3 of the cladding 112 is 40 µm, the diameter D1 of the first coating 104 is in a range of 116 µm to 126 µm, the diameter D2 of the second coating 106 is 140 µm, the first Young’s modulus associated with the first coating 104 is 0.0004 GPa, and the second Young’s modulus associated with the second coating 106 is 1.3 GPa, in such an aspect of the present disclosure, the coating induced micro bend loss of the optical fiber 100 is 2.2 x 103 N-1mm-8.5. Specifically, the first coating 104 and the second coating 106 may be adapted to induce the micro bend loss (i.e., coating induced micro bend loss) that may be less than 2.2 x 103 N-1mm-8.5. The first coating 104 and the second coating 106 employed for protection of the silica region 102 may have a significant role in the micro bending sensitivity of the optical fiber 100. The micro bend loss of the optical fiber 100 may decrease by combining the first coating 104 (i.e., a primary coating) having a lower Young’s modulus with the second coating 106 (i.e., a secondary coating) having a higher Young’s modulus to enhance micro bending performance.
FIG. 1B illustrates a graph 116 of a refractive index (RI) profile of the optical fiber 100. X-axis and Y-axis of the graph 116 denotes various radiuses associated with the optical fiber 100 (as shown in FIG. 1A) and various refractive indexes (RI) associated with the optical fiber 100, respectively. The graph 116 has a curve 118. As illustrated by the curve 118, near the centre of the optical fiber 100 i.e., when the radius R1 of the core 108 (as shown in FIG. 1A) is minimal, the refractive index ?1 of the core 108 peaks. Further, as the radius R1 of the core 108 increases i.e., moving away from the centre of the optical fiber 100, the refractive index ?1 of the core 108 dips. Specifically, the refractive index ?1 of the core 108 is maximum near the centre of the optical fiber 100 and minimum near a transition point between the core 108 and the trench layer 110 (as shown in FIG. 1A). Further, as illustrated, the trench layer 110 may have a linear refractive index ?2 that may be less than the refractive index ?1 of the core 108. Furthermore, as illustrated, the cladding 112 (as shown in FIG. 1A) may have a linear refractive index ?3. However, the refractive index ?3 of the cladding 112 may be greater than the refractive index ?2 of the trench layer 110.
FIG. 1C illustrates a cross-sectional view of another optical fiber 120. The optical fiber 120 may be designed to have improved micro bending performance. Specifically, the optical fiber 120 may be a reduced diameter fiber that has improved micro bending performance. The improved micro bending performance may be achieved by (i) reducing a leakage loss by waveguide refractive index profile and (ii) optimizing a thickness of coatings (as will be discussed herein). The optimised combination of fiber design and coatings may significantly improve optical loss from bends of the optical fiber 100 thus providing an optimised fiber product to minimize optical power loss and maximize network performance. The optical fiber 120 may have a silica region 122, a first coating 124, and a second coating 126. The silica region 122 may have a diameter in a range of 60 µm to 100 µm. The silica region 122 may have traces of at least one carbon group element and at least one halogen group element. Specifically, the silica region 122 may have Germanium (GE) (i.e., a carbon group element) and Fluorine (F) (i.e., a halogen group element) in predefined concentrations. In an aspect of the present disclosure, the silica region 122 may have a core 128, a buffer layer 130, a trench layer 132, and a cladding 134. The optical fiber 120 may have a central axis 136 such that the core 128 may be arranged along the central axis 136 running longitudinally, i.e., generally parallel to the central axis 136. In other words, the core 128 may be positioned approximately at a centre of the optical fiber 120. The core 128 may be a cylindrical fiber that may run along a length of the optical fiber 120 and may be configured to guide an optical signal. The buffer layer 130 may cover an outer circumference of the core 128, the trench layer 132 may cover an outer circumference of the buffer layer 130, and the cladding 134 may cover an outer circumference of the trench layer 132.
The core 128 may have a radius R4 and a refractive index ?4. The buffer layer 130 may have a radius R5 and a refractive index ?5. The trench layer 132 may have a radius R6 and a refractive index ?6, and the cladding 134 may have a radius R7 and a refractive index ?7. In one aspect of the present disclosure, for the core 128, the radius R4 may be in a range of 3.5 µm to 4.2 µm and the refractive index ?4 may be in a range of 0.35 to 0.45. For the buffer layer 130, the radius R5 may be in a range of 3.5 µm to 4.2 µm and the refractive index ?5 may be in a range of -0.05 to 0.05. For the trench layer 132, the radius R6 may be in a range of 6.5 µm to 8 µm and the refractive index ?6 may be in a range of -0.28 to -0.35. For the cladding 134, the radius R7 may be 40 + 0.35 µm and the refractive index ?7 may be in a range of -0.05 to 0.05. In some aspects of the present disclosure, the predefined concentrations of the Germanium (Ge) and Fluorine (F) is directly proportional to the refractive indexes ?4 and ?6 of the core 128 and the trench layer 132 respectively. For example, if the Ge concentration increases, the refractive index ?4 of the core 128 increases in an upward (i.e., positive) direction as compared to the refractive index of pure silica, because Ge is an up dopant. In another example, if F concentration increases, the refractive index ?6 of the trench layer 132 increases in a downward (i.e., negative) direction as compared to the refractive index of pure silica., because F is a down dopant. In relation to the above aspects of the disclosure, the MFD of the optical fiber 120 at a wavelength of 1310 nm may be equal to 8.6 + 0.4 µm, the ZDW of the optical fiber 120 may be in a range of 1300 nm to 1324 nm, the CC of the optical fiber 120 may be less than or equal to 1260 nm. Further, at a wavelength of 1550 nm and with a bend radius of 7.5 mm, 1 turn, a macro bend loss in the optical fiber 120 may be less than or equal to 0.2 dB and at a wavelength of 1625 nm and with the bend radius of 7.5 mm, 1 turn, the macro bend loss in the optical fiber 120 may be less than or equal to 0.5 dB. At the wavelength of 1550 nm and with a bend radius of 10 mm, 1 turn, the macro bend loss in the optical fiber 120 may be less than or equal to 0.1 dB and at the wavelength of 1625 nm and with the bend radius of 10 mm, 1 turn, the macro bend loss in the optical fiber 120 may be less than or equal to 0.2 dB. At the wavelength of 1550 nm and with a bend radius of 15 mm, 10 turns, the macro bend loss in the optical fiber 120 may be less than or equal to 0.03 dB and at the wavelength of 1625 nm and with the bend radius of 15 mm, 10 turns, the macro bend loss in the optical fiber 120 may be less than or equal to 0.1 dB/turn. The first coating 124 and the second coating 126 may be structurally and functionally similar to the first coating 104 and the second coating 106, respectively (as discussed above in FIG. 1A). Specifically, the first coating 124 and the second coating 126 may be adapted to induce the micro bend loss (i.e., coating induced micro bend loss) that may be less than 2.2 x 103 N-1mm-8.5. The first coating 124 and the second coating 126 employed for protection of the silica region 122 may have a significant role in the micro bending sensitivity of the optical fiber 120. The micro bend loss of the optical fiber 120 may decrease by combining the first coating 124 (i.e., a primary coating) having a lower Young’s modulus with the second coating 126 (i.e., a secondary coating) having a higher Young’s modulus to enhance micro bending performance.
The first coating 124 and second coating 126 may be adapted to induce a micro bend loss in the optical fiber 120. The micro bend loss induced by the first coating 124 and second coating 126 may be given by coating induced micro bend loss that may be determined by an equation as given below:
(K_p^2)/(?BR?_g^2 * ?DR?_s^0.375 *?BR?_s^0.625 )
K_p=(E_P D_g)/t_p
?BR?_g = p/4 E_g (D_g/2)^2
?DR?_s = E_p+(t_s/R_s )^3 E_s
?BR?_s = p/4 E_s (R_s^4-R_p^4 )^2
where, K is spring constant (MPa),
BR is bending rigidity (MPa.mm4),
DR is deformation resistance (MPa),
T is thickness(mm),
R and D is Radius (mm) and Diameter (mm), respectively,
E is Young’s modulus (MPa), and
Subscripts g, p, s denote glass region, first coating (primary coating), and second coating, respectively.
where, K_p represents spring constant of the first (primary) coating which is the ratio of product of Young’s modulus of first (primary) coating and diameter of glass region to the thickness of the first (primary) coating.
?BR?_g represents bending rigidity or bending resistance of the glass region which is a function of Youngs modulus of the glass region and diameter of the glass region.
?DR?_s represents deformation rigidity or deformation resistance of the second coating upon external force. It is a function of Young’s modulus of the first (primary) coating, thickness of the second coating and Young’s modulus of the second coating.
?BR?_s represents bending rigidity or bending resistance of the second coating which is a function of Young’s modulus of the second coating, radius of first and second coating.
FIG. 1D illustrates a graph 138 of a refractive index (RI) profile of the optical fiber 120 (as shown in FIG. 1C). X-axis and Y-axis of the graph 138 denotes various radiuses associated with the optical fiber 120 and various refractive indexes (RI) associated with the optical fiber 120, respectively. The graph 138 has a curve 140. As illustrated by the curve 140, near the centre of the optical fiber 120 i.e., the refractive index ?4 of the core 128 is maximum. Further, as the radius R4 of the core 128 increases i.e., moving away from the centre of the optical fiber 120, the refractive index ?4 of the core 128 dips. Specifically, the refractive index ?4 of the core 128 may be minimum near a transition point between the core 128 and the buffer layer 130 (as shown in FIG. 1C). Further, as illustrated, the buffer layer 130 may have a linear refractive index ?5 that may be less than the refractive index ?4 of the core 128. Furthermore, as illustrated, the trench layer 132 (as shown in FIG. 1C) may have a linear refractive index ?6 that may be less than the refractive index ?5 of the buffer layer 130. Furthermore, as illustrated, the cladding 134 (as shown in FIG. 1A) may have a linear refractive index ?7. However, the refractive index ?7 of the cladding 134 may be greater than the refractive index ?6 of the trench layer 132 and less than the refractive index ?5 of the buffer layer 130.
FIG. 1E illustrates a cross-sectional view of yet another optical fiber 142. The optical fiber 142 may be designed to have improved micro bending performance. Specifically, the optical fiber 142 may be a reduced diameter fiber that has improved micro bending performance. The improved micro bending performance may be achieved by (i) reducing a leakage loss by waveguide refractive index profile and (ii) optimizing a thickness of coatings (as will be discussed herein). The optimised combination of fiber design and coatings may significantly improve optical loss from bends of the optical fiber 142 thus providing an optimised fiber product to minimize optical power loss and maximize network performance. The optical fiber 142 may have a silica region 144, a first coating 146, and a second coating 148. The silica region 144 may have a diameter in a range of 60 µm to 100 µm. The silica region 144 may have traces of at least one carbon group element and at least one halogen group element. Specifically, the silica region 144 may have Germanium (GE) (i.e., a carbon group element) and Fluorine (F) (i.e., a halogen group element) in predefined concentrations. In an aspect of the present disclosure, the silica region 144 may have a core 150, a buffer layer 152, a trench layer 154, and a cladding 156.
The optical fiber 142 may have a central axis 158 such that the core 150 may be arranged along the central axis 158 running longitudinally, i.e., generally parallel to the central axis 158. In other words, the core 150 may be positioned approximately at a centre of the optical fiber 142. The core 150 may be a cylindrical fiber that may run along a length of the optical fiber 142 and may be configured to guide an optical signal. The buffer layer 152 may cover an outer circumference of the core 150, the trench layer 154 may cover an outer circumference of the buffer layer 152, and the cladding 156 may cover an outer circumference of the trench layer 154.
In an aspect of the present disclosure, for simulation of the leakage losses in the optical fiber 142 at different values of diameter of the cladding 156, the optical fiber 142 may be fabricated with below mentioned input parameters. In an exemplary aspect of the present disclosure, for the core 150, the radius R8 may be in a range of 3.8 µm to 4.2 µm, the refractive index ?8 may be in a range of 0.35 to 0.45 and a core alpha may be in a range of 4 to 7. For the buffer layer 152, the radius R9 may be in a range of 8 µm to 9 µm and the refractive index ?9 may be in a range of -0.05 to 0.05. For the trench layer 154, the radius R10 may be in a range of 14 µm to 15.5 µm, the refractive index ?10 may be in a range of -0.0028 to -0.0035, and a trench alpha may be in a range of 5 to 8. For the cladding 156, the radius R11 may be in a range of 79.3 µm to 80.7 µm, the refractive index ?11 may be in a range of -0.02 to 0.02. In some aspects of the present disclosure, the predefined concentrations of the Germanium (Ge) and Fluorine (F) is directly proportional to the refractive indexes ?8 and ?10 of the core 150 and the trench layer 154 respectively. For example, if the Ge concentration increases, the refractive index ?8 of the core 150 increases in an upward (i.e., positive) direction as compared to the refractive index of pure silica, because Ge is an up dopant. In another example, if F concentration increases, the refractive index ?10 of the trench layer 154 increases in a downward (i.e., negative) direction as compared to the refractive index of pure silica., because F is a down dopant. In relation to the above aspect of the disclosure, the MFD of the optical fiber 142 at a wavelength of 1310 nm may be equal to 8.6 +0.4 µm, the ZDW of the optical fiber 142 may be in a range of 1300 nm to 1324 nm, the CC of the optical fiber 142 may be less than or equal to 1260 nm. Further, at a wavelength of 1550 nm and with a bend radius of 7.5 mm, 1 turn, a macro bend loss in the optical fiber 142 may be less than or equal to 0.2 dB and at the wavelength of 1625 nm and with the bend radius of 7.5 mm,1 turn, the macro bend loss in the optical fiber 142 may be less than or equal to 0.5 dB. At the wavelength of 1550 nm and with a bend radius of 10 mm,1 turn, the macro bend loss in the optical fiber 142 may be less than or equal to 0.1 dB and at the wavelength of 1625 nm and with the bend radius of 10 mm, 1 turn, the macro bend loss in the optical fiber 142 may be less than or equal to 0.2 dB. At the wavelength of 1550 nm and with a bend radius of 15 mm, 10 turns, the macro bend loss in the optical fiber 142 may be less than or equal to 0.03 dB and at the wavelength of 1625 nm and with the bend radius of 15 mm, 10 turn, the macro bend loss in the optical fiber 142 may be less than or equal to 0.1 dB. The first coating 146 and the second coating 148 may be structurally and functionally similar to the first coating 104 and the second coating 106, respectively (as discussed above in FIG. 1A). Specifically, the first coating 146 and the second coating 148 may be adapted to induce the micro bend loss (i.e., coating induced micro bend loss) that may be less than 2.2 x 103 N-1mm-8.5. The first coating 146 and the second coating 148 employed for protection of the silica region 144 may have a significant role in the micro bending sensitivity of the optical fiber 142. The micro bend loss of the optical fiber 142 may decrease by combining the first coating 146 (i.e., a primary coating) having a lower modulus with the second coating 148 (i.e., a secondary coating) having a higher modulus to enhance micro bending performance.
The first coating 146 and second coating 148 may be adapted to induce a micro bend loss in the optical fiber 142. The micro bend loss induced by the first coating 146 and second coating 148 may be given by coating induced micro bend loss that may be determined by an equation as given below:
(K_p^2)/(?BR?_g^2 * ?DR?_s^0.375 *?BR?_s^0.625 )
K_p=(E_P D_g)/t_p
?BR?_g = p/4 E_g (D_g/2)^2
?DR?_s = E_p+(t_s/R_s )^3 E_s
?BR?_s = p/4 E_s (R_s^4-R_p^4 )^2
where, K is spring constant (MPa),
BR is bending rigidity (MPa.mm4),
DR is deformation resistance (MPa),
T is thickness(mm),
R and D is Radius (mm) and Diameter (mm), respectively,
E is Young’s modulus (MPa), and
Subscripts g, p, s denote glass region, first coating (primary coating), and second coating, respectively.
where, K_p represents spring constant of the first (primary) coating which is the ratio of product of Young’s modulus of first (primary) coating and diameter of glass region to the thickness of the first (primary) coating.
?BR?_g represents bending rigidity or bending resistance of the glass region which is a function of Youngs modulus of the glass region and diameter of the glass region.
?DR?_s represents deformation rigidity or deformation resistance of the second coating upon external force. It is a function of Young’s modulus of the first (primary) coating, thickness of the second coating and Young’s modulus of the second coating.
?BR?_s represents bending rigidity or bending resistance of the second coating which is a function of Young’s modulus of the second coating, radius of first and second coating.
FIG. 1F illustrates a graph 160 of a refractive index (RI) profile of the optical fiber 142 (as shown in FIG. 1E). X-axis and Y-axis of the graph 160 denotes various radiuses associated with the optical fiber 142 and various refractive indexes (RI) associated with the optical fiber 142, respectively. The graph 160 has a curve 162. As illustrated by the curve 162, near the centre of the optical fiber 142, the refractive index ?8 of the core 150is maximum. Further, as the radius R8 of the core 150 increases i.e., moving away from the centre of the optical fiber 142, the refractive index ?8 of the core 150 dips. Specifically, the refractive index ?8 of the core 150 may be minimum near a transition point between the core 150 and the buffer layer 152 (as shown in FIG. 1E). Further, as illustrated, the buffer layer 152 may have a linear refractive index ?9 that may be less than the refractive index ?8 of the core 150. Furthermore, as illustrated, the trench layer 154 (as shown in FIG. 1E) may have a linear refractive index ?10 that may be less than the refractive index ?9 of the buffer layer 152. Furthermore, as illustrated, the cladding 156 (as shown in FIG. 1E) may have a linear refractive index ?11. However, the refractive index ?11 of the cladding 156 may be greater than the refractive index ?10 of the trench layer 154 and less than the refractive index ?9 of the buffer layer 152.
FIG. 1G illustrates a graph 164 between leakage losses and diameter of the cladding 156 of the optical fiber 142. X-axis and Y-axis of the graph 164 may denote the leakage losses and the diameter of the cladding 156, respectively. The graph 164 may have a first curve 166 and a second curve 168. Specifically, the first curve 166 may represent the leakage loss in the optical fiber 142 (as shown in FIG. 1E) at the wavelength of 1550 nm when the diameter (i.e., R11x2) of the cladding 156 is 100 µm. Similarly, the second curve 168 may represent the leakage loss in the optical fiber 142 at the wavelength of 1625 nm when the diameter of the cladding 156 is 100 µm. Specifically, when the diameter of the cladding 156 is 100 µm, the leakage loss in the optical fiber 142 at the wavelength of 1625 nm may be greater than the leakage loss in the optical fiber 142 at the wavelength of 1550 nm. The leakage loss in the optical fiber 142 at the wavelength of 1625 nm may be 0.000000758 dB/km. Thus, the optical fiber 142 may have good confinement of mode in the core 150 at the wavelength of 1550 nm with the cladding 156 having the diameter of 100 µm.
Thus, the optical fiber 100, 120, and 142 of the present disclosure may be a reduced diameter fiber such that the diameter D2 of the optical fiber 100, 120, and 142 is less than or equal to 180 µm. The reduced diameter optical fiber 100, 120, and 142 may demonstrate good micro bend performance. Specifically, by virtue of the first coating 104, 124, 146 and the second coating 106, 126, 148, the optical fiber 100, 120, and 142 may demonstrate a micro bend loss that is less than 2.2 x 103 N-1mm-8.5.
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:I/We claim

An optical fiber (100, 120, 142) comprising:
a silica region (102, 122, 144);
a first coating (104, 124, 146) adapted to cover an outer circumference of the silica region (102, 122, 144), wherein the first coating (104, 124, 146) has (i) a first diameter and (ii) a first Young’s modulus; and
a second coating (106, 126, 148) adapted to cover an outer surface of the first coating (104, 124, 146), wherein the second coating (106, 126, 148) has (i) a second diameter is less than or equal to 180 µm and (ii) a second Young’s modulus;
wherein the first coating (104, 124, 146) and the second coating (106, 126, 148) are adapted to cause a coating induced micro bend loss that is less than 2.2 x 103 N-1mm-8.5, wherein the coating induced micro bend loss is determined by an equation:
(K_p^2)/(?BR?_g^2 * ?DR?_s^0.375 *?BR?_s^0.625 )
wherein,
K_p = (E_P D_g)/t_p ,
?BR?_g = p/4 E_g (D_g/2)^2,
?DR?_s = E_p+(t_s/R_s )^3 E_s,
?BR?_s = p/4 E_s (R_s^4-R_p^4 )^2,
wherein, K is spring constant (MPa),
BR is bending rigidity (MPa.mm4),
DR is deformation resistance (MPa),
T is thickness(mm),
R and D is Radius (mm) and Diameter (mm), respectively,
E is Young’s modulus (MPa), and
Subscripts g, p, s denote glass, first coating, and second coating, respectively.

The optical fiber (100, 120, 142) of claim 1, wherein at least one of, (i) the silica region (102) comprising a core (108), a trench layer (110), and a cladding (112), and (ii) the silica region (122) comprising a core (128), a buffer layer (130), a trench layer (132), and a cladding (134), and (iii) the silica region (144) comprising a core (150), a buffer layer (152), a trench layer (154), and a cladding (156).

The optical fiber (100, 120, 142) of claim 1, wherein the first Young’s modulus is in a range of 0.0001 Gigapascal (GPa) to 0.0004 GPa, and wherein the second Young’s modulus is in a range of 1.3 GPa to 3 GPa.

The optical fiber (100, 120, 142) of claim 1, wherein a ratio of the second diameter to the first diameter is in a range of 1.05 to 1.45.

The optical fiber (100, 120, 142) of claim 1, wherein (i) the optical fiber (100) has a macro bend loss of less than or equal to 0.5 dB at a wavelength of 1550 nm, a bend radius of 7.5 mm, 1 turn, and a macro bend loss of less than or equal to 1 dB at a wavelength1625 nm, a bend radius of 7.5 mm, 1 turn, and (ii) the optical fiber (120, 142) has a macro bend loss of less than or equal to 0.2 dB at a wavelength of 1550 nm, a bend radius of 7.5 mm, 1 turn and a macro bend loss of less than or equal to 0.5 dB at a wavelength of 1625 nm, a bend radius of 7.5 mm, 1 turn.

The optical fiber (100, 120, 142) of claim 1, wherein (i) the optical fiber (100) has a macro bend loss of less than or equal to 0.1 dB at a wavelength of 1550 nm, a bend radius of 10 mm, 1 turn, and a macro bend loss of less than or equal to 1 dB at a wavelength1625 nm, a bend radius of 10 mm, 1 turn, and (ii) the optical fiber (120, 142) has a macro bend loss of less than or equal to 0.1 dB at a wavelength of 1550 nm, a bend radius of 10 mm, 1 turn and a macro bend loss of less than or equal to 0.2 dB at a wavelength of 1625 nm, a bend radius of 10 mm, 1 turn.

The optical fiber (100, 120, 142) of claim 1, wherein a macro bend loss at a bend radius of 15 mm, 10 turns, and at a wavelength of 1550 nm and 1625 nm is 0.03 dB and less than 0.1 dB, respectively.

The optical fiber (100, 120, 142) of claim 1, wherein a leakage loss at a wavelength 1550 nm is less than a leakage loss at a wavelength 1625 nm, wherein the leakage loss at the wavelength of 1550 nm is less than 0.001 Decibels/Kilometres (dB/km).

The optical fiber (100, 120, 142) of claim 1, wherein a diameter of the silica region (102, 122, 144) is in a range of 60 µm to 100 µm.

The optical fiber (100, 120, 142) of claim 1, wherein the silica region (102, 122, 144) has traces of at least one carbon group element and at least one halogen group element.

The optical fiber (100, 120, 142) of claim 1, wherein (i) a refractive index ?1 of a core (108) is in a range of 0.36 to 0.4, (ii) a refractive index ?4 of a core (128) is in a range of 0.35 to 0.45, and (iii) a refractive index ?8 of a core (150) is in a range of 0.35 to 0.45

The optical fiber (100, 120, 142) of claim 1, wherein (i) a refractive index ?2 of a trench layer (110) is in a range of -0.08 to -0.12, (ii) a refractive index ?6 of a trench layer (132 is in a range of -0.28 to -0.35, and (iii) a refractive index ?10 of a trench layer (154) is in a range of -0.0028 to -0.0035.

The optical fiber (100, 120, 142) of claim 1, wherein a Zero Dispersion Wavelength (ZDW) is in a range of 1300 nm to 1324 nm.