Description:TECHNICAL FIELD
[1] The present disclosure relates generally to optical fibers and optical fiber
cables, and, more particularly, to a multicore optical fiber with a down doped
peripheral cladding.
BACKGROUND
[2] Multi-core optical fibers having a plurality of cores extending along the
multi-core optical fibers, in a cladding are available as an optical transmission line
which is capable to transmit information. Such multi-core optical fibers are
designed to have lower diameters. However, in a reduced diameter optical fiber,
an outside cladding thickness is very less. If the outside cladding is made up of a
pure silica glass material, the outside cladding will contribute more leakage loss
and micro bending loss. Especially in multi-core fiber, the outside cladding
thickness will be significantly low that makes the optical fiber impractical due to
leakage losses that further results in the multi-core optical fiber being impractical
for communication and/or data centre applications.
[3] While there are number of multicore optical fiber discloses technique to
reduce crosstalk and optimize the Mode Field Diameter (MFD) value. For
example, the prior art reference CN108181683A discloses a kind of low crosstalk
big mode field area multi-core optical fiber which includes multiple core regions
in which one core region is surrounded by a first clad region. The first clad region
is formed of silicon dioxide. A second clad region surrounds the first clad region
and the other core regions. The second clad region is doped with fluorine element.
Another prior art reference US20220283362A1 discloses a multicore optical fiber
including an inner glass region having multiple core regions surrounded by a
common outer cladding. The inner glass region further having at least one marker.
Each core region of the multicore optical fiber is comprised of a Germania-doped
silica core and a fluorine-doped silica trench. The reference discloses that the core
regions and the common outer cladding may be made of glass. Yet another prior
art reference US10031284B2 discloses a multicore fiber (MCF) comprising a core
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group consisting of eight or more cores. The MCF comprising an inner cladding
group consisting of inner claddings each of which individually surrounds a
corresponding core out of the eight or more cores, a trench group consisting of
trenches each of which individually surrounds a corresponding inner cladding out
of the inner claddings. The MCF comprises a common cladding individually
surrounding each of the trenches. The cores and the inner claddings are comprised
of GeO2-doped silica glass. The trenches are comprised of F-doped silica glass
and the common cladding is comprised of a silica-based glass.
[4] However, the prior art techniques falls short of effectively optimize the
Mode Field Diameter (MFD) value in a range as required and reduce the cross
talk in a reduced diameter multicore optical fiber. There always seems to be a
need to develop a multi-core optical fibre which would have an optimized design
with good macro-bend characteristics, less leakage loss, low attenuation, low
crosstalk, better strength, and reduced diameter. Thus, there is a need for a
technical solution that overcomes the aforementioned problems of conventional
multi-core optical fibers.
OBJECTIVE OF THE DISCLOSURE
[5] An objective of the present disclosure is to provide a multi-core optical
fiber that has a reduced leakage loss and reduced micro bending loss which is
necessary for a multi-core optical fiber due to low thickness of a peripheral
cladding layer of the multi-core optical fiber.
[6] Further, another objective of the present disclosure is to provide a
multi-core optical fiber that has an increased strength by virtue of a doping profile
of a peripheral cladding layer which is critical for a reduced diameter optical fiber.
[7] Furthermore, another objective of the present disclosure is to provide a
multi-core optical fiber that has a plurality of buffer layer made up of a pure silica
glass material and a plurality of trench layer along with the plurality of buffer
layer that may facilitate to achieve a delta value that is in reference to a core of the
multi-core optical fiber to require an optical signal to guide in the core to achieve
total internal reflection.
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[8] Furthermore, another objective of the present disclosure is to provide a
multi-core optical fiber that enables next-level cable designs and bend
performance, while streamlining field optical time domain reflectometer (OTDR)
testing protocols.
[9] Furthermore, another objective of the present disclosure is to provide a
reduced diameter multi-core optical fiber with low micro bending loss to
constitute an intermittently bonded multi-core fiber (MCF) ribbon which can be
incorporated in a multi-core optical fiber cable.
SUMMARY
[10] In an aspect of the present disclosure, a multi-core optical fiber is
disclosed. The multi-core optical fiber having a plurality of cores and a cladding
that surrounds the plurality of cores. The cladding has a peripheral cladding layer.
The peripheral cladding layer is down doped such that a leakage loss of the
multi-core optical fiber is less than 0.001 Decibel/Kilometer (dB/Km) at a
wavelength 1550 nanometres (nm).
BRIEF DESCRIPTION OF DRAWINGS
[11] 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.
[12] FIG. 1A illustrates a cross-sectional view of a multi-core optical fiber.
[13] FIG. 1B illustrates another cross-sectional view of the multi-core optical
fiber.
[14] FIG. 1C illustrates yet another cross-sectional view of the multi-core
optical fiber.
[15] FIG. 1D illustrates a cross-sectional view of a multi-core optical fiber
cable.
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[16] FIG. 2A illustrates a graph of a refractive index (RI) profile of the
multi-core optical fiber of FIG. 1A.
[17] FIG. 2B illustrates a graph of an experimental profile and a theoretical
profile of the multi-core optical fiber of FIG. 1A.
[18] FIG. 3A illustrates a graph of a cross talk versus pitch of the multi-core
optical fiber of FIG. 1A.
[19] FIG. 3B illustrates a graph of a cross talk versus pitch of the multi-core
optical fiber of FIG. 1A.
DEFINITIONS
[20] The term “core” as used herein defines a cylindrical structure present in an
optical fiber that is configured to guide an optical signal inside the optical fiber.
[21] The term “cladding layer” as used herein defines one or more layered
structure covering the core of an optical fiber from outside that is configured to
possess a lower refractive index than a refractive index of the core to facilitate
total internal reflection of the optical signal inside the optical fiber. Further, the
cladding layer of the optical fiber may include an inner cladding layer coupled to
an outer surface of the core of the optical fiber and an outer cladding layer
coupled to the inner cladding from outside.
[22] The term “multi-core optical fiber” as used herein defines an optical fiber
that includes multiple core regions, each capable of communicating the optical
signals between transceivers including transmitters and receivers which may
allow for parallel processing of multiple optical signals. The multi-core optical
fiber may be used for Wavelength Division Multiplexing (WDM) or multi-level
logic or for other parallel optics of spatial division multiplexing. The multi-core
optical fiber may advantageously be aligned with and connected to various
devices in a manner that allows for easy and reliable connection so that the
plurality of cores is aligned accurately at opposite terminal ends with like
communication paths in connecting devices. In general, the optical fibres are used
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in telecommunications to transmit telephone signals, internet communication,
cable television signals and the like.
[23] The term “marker” as used herein defines a structure used to identify
position of multiple cores of a multi-core optical fiber. The marker is arranged
along the optical fiber axis in parallel to the cores in a mid-cladding layer. The
refractive index of the marker is different and can be greater or lesser than the
refractive index of the mid-cladding layer.
[24] The term “refractive index” as used herein defines a measure of change of
speed of the optical signal 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 the optical signal from one
medium to another medium.
[25] The term “refractive index profile” as used herein is referred to as a
distribution of refractive indexes in an optical fiber from a core to an outmost
cladding layer of the optical f iber. 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 optical fiber and is higher than
the refractive index of the cladding layer. Further, the optical fiber may be
configured as a graded index fiber such that the refractive index of the core
gradually varies as a function of the radial distance from the centre of the core.
[26] The term “relative refractive index” as used herein is defined as
?% = 100× ???? , where ni is maximum refractive index in region i of an 2 -??2
2????2
optical fiber unless otherwise specified, and n is the average refractive index of an
undoped region of the optical fiber. As used herein, the relative refractive index is
represented by ? and its values are given in units of “%”, unless 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 as a trench region.
[27] The term “down doping” as used herein refers to adding doping materials
to facilitate decrease in a refractive index of a particular layer or part of an optical
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fiber. The materials configured to facilitate down doping are known as down
dopants.
[28] The term “up doping” as used herein refers to adding doping materials to
facilitate increase in a refractive index of a particular layer or part of an optical
fiber. The materials configured to facilitate up doping are known as up dopants.
[29] The term “undoped” as used herein refers to a region of an optical fiber
that contains a dopant not intentionally added to the region during fabrication, but
the term does not exclude low levels of background doping that may be inherently
incorporated during the fabrication process. Such background doping levels are
low in that they have an insignificant effect on the refractive index of the undoped
region.
[30] The term “reduced diameter optical fiber” as used herein refers to an
optical fiber as disclosed in the present disclosure having a diameter range of 80
micrometres (µm) to 110 µm (generally less than 125 µm) with a tolerance of +1
µm. Such optical fibers have very less peripheral clad thickness. The reduced
diameter optical fibre significantly increases the packing density of the optical
fibre cables.
[31] 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 Leakage loss is
calculated using finite element analysis method where the losses are calculated in
the optical fiber in straight condition.
[32] The term “bare fiber” as used herein refers to an uncoated fiber drawn by
melting a preform in draw tower. Further, the bare fiber is coated with a primary
coating and a secondary coating.
[33] The term “Mode Field Diameter (MFD)” as used herein refers to a
diameter of a spread of electric field distribution in propagation mode (light path).
An optical signal usually passes through a core of an optical fiber.. Generally, the
MFD is slightly greater than the core diameter.
[34] The term “Cable Cutoff” as used herein refers to a parameter of a
single-mode optical fiber. Specifically, an optical fiber cannot be a single-mode
fiber if it is used at a wavelength shorter than a cable cut-off wavelength, which is
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determined by optical fiber structure, involving refraction index distribution and
core diameter.
[35] The term “macro bend loss” as used herein refers to losses induced in
bends around mandrels (or corners in installations), generally more at a cable
level or for an optical fiber. 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.
[36] The term “micro bend loss” as used herein refers to a loss in an optical
fiber that relates to an optical 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 guided fundamental mode to lossy modes or cladding modes.
[37] The term “Coefficient of Thermal Expansion (CTE)” as used herein refers
to a rate at which a material expands with increase in temperature. More
specifically, this coefficient is determined at constant pressure and without a phase
change, i.e., the material is expected to still be in its solid or fluid form.
[38] The term “Zero Dispersion Wavelength (ZDW)” as used herein refers to a
wavelength at which a value of dispersion coefficient is zero. In general, ZDW is
a wavelength at which material dispersion and waveguide dispersion cancel one
another.
[39] The term “Attenuation” as used herein refers to a reduction in power of an
optical signal as it is transmitted. Specifically, the attenuation is caused by passive
media components such as cables, cable splices, and connectors.
[40] The term “Crosstalk” as used herein refers to a major impairment of
optical communication networks utilizing WDM transmission. Crosstalk in
optical networks occurs when the optical power associated with one channel starts
appearing in another channel or adjacent channel. In multi-core optical fibers, the
crosstalk arises from unwanted coupling between the multiple cores.
[41] The term “Ribbon optical fiber cable” as used herein refers to an optical
fiber cable that consists of coated optical fibers which are placed adjacent to each
other. Such an arrangement enables individual fibers to be aligned in a single row.
The cable ribbons are then impregnated with an acrylate UV curable resin and
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encapsulated in Mylar tape. As such, these multiple individual optical ribbons
allow stacking into a bundle with a matrix structure. They can then be stored in a
central core tube or in stranded multi-tubes in the cable core. Additionally, these
individual optical ribbons can be stored in two ways: inside a central core tube or
in stranded multi-tubes within the cable core.
[42] The term “intermittent bonded ribbon fibre cable” as used herein refers to
a ribbon fiber cable that 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 optical fiber cables
with higher packing density. Additionally, they can also undergo mass fusion fiber
cable splicing which is another advantage for manufacturers.
[43] The term “multi-core optical fiber ribbon” as used herein refers to an
optical fiber ribbon in which multiple multi-core optical fibers including the
multi-core optical fiber having the structure as disclosed in the present disclosure
are intermittently bonded.
[44] The term “multi-core optical fiber cable” as used herein refers to an optical
fiber cable that consists of coated multi-core optical fibers. The multi-core optical
fiber ribbon can also be placed in the multi-core optical fiber cable to design a
multi-core optical fiber cable with a greater fiber packing density.
DETAILED DESCRIPTION
[45] 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.
[46] Furthermore, it will be clear that the invention is not limited to these
alternatives only. Numerous modifications, changes, variations, substitutions and
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equivalents will be apparent to those skilled in the art, without parting from the
scope of the invention.
[47] The accompanying drawing is used to help easily understand various
technical features and it should be understood that the alternatives presented
herein are not limited by the accompanying drawing. As such, the present
disclosure should be construed to extend to any alterations, equivalents, and
substitutes in addition to those which are particularly set out in the accompanying
drawing. Although the terms first, second, etc. may be used herein to describe
various elements, these elements should not be limited by these terms. These
terms are generally only used to distinguish one element from another.
[48] FIG. 1A illustrates a cross-sectional view of a multi-core optical fiber 100.
The multi-core optical fiber 100 may be a reduced diameter multi-core optical
fiber with a peripheral cladding. Specifically, the multi-core optical fiber 100 may
be a reduced diameter multi-core optical fiber with a peripheral cladding that is
down doped. The multi-core optical fiber 100 may have a plurality of cores 102 of
which first through fourth cores 102a-102d are shown, a plurality of buffer layers
104 of which first through fourth buffer layers 104a-104d are shown, a plurality of
trench layers 106 (shown in FIG. 1B) of which first through fourth trench layers
106a-106d are shown, and a cladding 108. The multi-core optical fiber 100 may
further have a central axis 110 such that the plurality of cores 102 may be
arranged along the central axis 110 running longitudinally, i.e., generally parallel
to the central axis 110. The plurality of cores 102 may be arranged in a predefined
lattice on the cross-section of the multi-core optical fiber 100 that is perpendicular
to an axis extending parallelly along the central axis 110 of the multi-core optical
fiber 100. As illustrated, the predefined lattice is a square lattice. Alternatively, the
predefined lattice may be a hexagonal lattice. It will be apparent to a person
skilled in the art that the plurality of cores 102 are shown to be arranged in the
square lattice to make the illustrations concise and clear and should not be
considered as a limitation of the present disclosure. In various alternate aspects,
the plurality of cores 102 may be arranged in any type of the predefined lattice,
without deviating from the scope of the present disclosure.
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[49] Each core (i.e., the first through fourth cores 102a-102d) of the plurality of
cores 102 may be configured to guide an optical signal. Each core of the plurality
of cores 102 may be a cylindrical fiber that may run along a length of the
multi-core optical fiber 100 and may be made up of a material selected from at
least one of, a plastic, a pure silica glass, and the like. Preferably, each core of the
plurality of cores 102 may be made up of a silica glass doped with a suitable up
dopant. In other words, each core of the plurality of cores 102 may be up doped
with one or more up dopants that may increase a refractive index of the silica
glass. Suitable up dopants may be, but not limited to, Aluminum oxide (Al2O3),
Phosphorus pentoxide (P2O5), Titanium dioxide (TiO2), and the like. Preferably,
the up dopant used to increase the refractive index of each core of the plurality of
cores 102 may be one of, Germanium (Ge) and Chlorine (Cl). In some aspects of
the present disclosure, each core of the plurality of cores 102 may have a first
radius R1 and a first relative refractive index % ?1. Specifically, the first through
fourth cores 102a-102d may have the first radius R1. The first radius R1 of the
first through fourth cores 102a-102d may be in a range of 3 µm to 5 µm. In one
aspect of the present disclosure, the first radius R1 of each core of the plurality of
cores 102 may be equal. In another aspect of the present disclosure, the first radius
R1 of each core of the plurality of cores 102 may be different. In some aspects of
the present disclosure, the first relative refractive index % ?1 of each core of the
plurality of cores 102 may be in a range of 0.32 to 0.55.
[50] The plurality of buffer layers 104 (i.e., the first through fourth buffer
layers 104a-104d) may envelop the plurality of cores 102 (i.e., first through fourth
cores 102a-102d). Specifically, the plurality of buffer layers 104 may have the
first buffer layer 104a, the second buffer layer 104b, the third buffer layer 104c,
and the fourth buffer layer 104d. Specifically, the first buffer layer 104a may be
provided around an outer periphery of the first core 102a, the second buffer layer
104b may be provided around an outer periphery of the second core 102b, the
third buffer layer 104c may be provided around an outer periphery of the third
core 102c, and the fourth buffer layer 104d may be provided around an outer
periphery of the fourth core 102d. In some aspects of the present disclosure, the
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plurality of buffer layers 104 (i.e., the first through fourth buffer layers
104a-104d) may be undoped layers. In some aspects of the present disclosure, the
plurality of buffer layers 104 (i.e., the first through fourth buffer layers
104a-104d) may be undoped layers surrounding the plurality of cores 102 (i.e., the
first through fourth cores 102a-102d). Specifically, the plurality of buffer layers
104, by virtue of being undoped (i.e., made up of pure silica glass material) may
facilitate to achieve a delta in reference to each core of the plurality of cores 102
which is required for light to guide in core and to achieve total internal reflection.
The pure silica regions surrounding each core acts as a buffer 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.
[51] Further, the first through fourth buffer layers 104a-104d may facilitate in
providing a high effective area by increasing a Mode Field Diameter (MFD) of
the multi-core optical fiber 100. It will be apparent to a person skilled in the art
that the multi-core optical fiber 100 is shown to have four buffer layers (i.e., the
first through fourth buffer layers 104a-104d) to make the illustrations concise and
clear and should not be considered as a limitation of the present disclosure. In
various other aspects, the plurality of buffer layers 104 may have same number of
buffer layers as the number of cores of the plurality of cores 102 such that each
core of the plurality of cores 102 has at least one corresponding buffer layer of the
plurality of buffer layers 104, without deviating from the scope of the present
disclosure.
[52] In some aspects of the present disclosure, each buffer layer of the plurality
of cores 104 may have a second radius R2 and a second relative refractive index
% ?2. Specifically, the first through fourth buffer layers 104a-104d may have the
second radius R2. The second radius R2 of the first through fourth buffer layers
104a-104d may be in a range of 4 µm to 7 µm. In one aspect of the present
disclosure, the second radius R2 of each buffer layer of the plurality of buffer
layers 104 may be equal. In another aspect of the present disclosure, the second
radius R2 of each buffer layer of the plurality of buffer layers 104 may be
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different. In some aspects of the present disclosure, each buffer layer of the
plurality of buffer layers 104 may have a first thickness T1. Specifically, the first
through fourth buffer layers 104a-104d may have the first thickness T1. The first
thickness T1 of the first through fourth buffer layers 104a-104d may be in a range
of 1 µm to 2 µm. In one aspect of the present disclosure, the first thickness T1 of
each buffer layer of the plurality of buffer layers 104 may be equal. In another
aspect of the present disclosure, the first thickness T1 of each buffer layer of the
plurality of buffer layers 104 may be different. In some aspects of the present
disclosure, the second radius R2 first through fourth buffer layers 104a-104d may
be determined by an equation, i.e., R2 = R1 + T1. In some aspects of the present
disclosure, the second relative refractive index % ?2 of each buffer layer of the
plurality of buffer layers 104 may be in a range of -0.03 to 0.03. In one aspect of
the present disclosure, the second relative refractive index % ?2 of each buffer
layer of the plurality of buffer layers 104 may be 0.
[53] The first through fourth trench layers 106a-106d may be provided such
that the first trench layer 106a envelops an outer periphery of the first buffer layer
104a, the second trench layer 106b envelops an outer periphery of the second
buffer layer 104b, the third trench layer 106c envelops an outer periphery of the
third buffer layer 104c, and the fourth trench layer 106d envelops an outer
periphery of the fourth buffer layer 104d. As illustrated, the first through fourth
trench layers 106a-106d may be provided between the plurality of cores 102 and
the cladding 108. The MFD having a higher value may result into increase in
crosstalk due to an overlap between neighbouring cores of the plurality of cores
102. In general, the higher value of MFD with poor confinement of the mode may
result into increase in crosstalk. Moreover, the macro and micro bend may be
increased due to a lower distance between the plurality of cores 102 and a glass
boundary. Thus, the first through fourth trench layers 106a-106d may be provided
to control the crosstalk and the macro and micro bend of the multi-core optical
fiber 100. Specifically, the MFD may depend on a predefined radius of each
buffer layer of the first through fourth buffer layers 104a-104d and a predefined
radius of each trench layer of the first through fourth trench layers 106a-106d
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such that an effective area and the MFD of the multi-core optical fiber 100
increases with an increase in the radius of the first through fourth buffer layers
104a-104d and the first through fourth trench layers 106a-106d. Further, the first
through fourth buffer layers 104a-104d along with the first through fourth trench
layers 106a-106d may facilitate to increase a confinement of the optical signal,
while having a higher value of the MFD, lower crosstalk, and lower micro bend
and macro bend losses.
[54] Specifically, the role of the first through fourth trench layers 106a-106d is
to suppress the optical signal traveling to the cladding 108 and to focus the optical
signal into the first through fourth cores 102a-102d to reduce the crosstalk
between adjacent cores of the plurality of cores 102. Further, the first through
fourth trench layers 106a-106d may facilitate in fabrication of more densely
arranged cores in the multi-core optical fiber 100. In some aspects of the present
disclosure, the first through fourth trench layers 106a-106d may be made up of a
material such as, but not limited to, a plastic, a pure silica glass, and the like.
Preferably, each of the first through fourth trench layers 106a-106d may be made
up of a silica glass doped with a suitable down dopant. In other words, each of the
first through fourth trench layers 106a-106d made up of the silica glass may be
down doped with one or more down dopants that may decrease a refractive index
of the silica glass. In some aspects of the present disclosure, the first through
fourth trench layers 106a-106d may be down doped with Fluorine (F). It will be
apparent to a person skilled in the art that the first through fourth trench layers
106a-106d is shown to be down doped with Fluorine (F) to make the explanation
concise and clear and should not be considered as a limitation of the present
disclosure. In various other aspects, the first through fourth trench layers
106a-106d may be down doped with any suitable down dopant, without deviating
from the scope of the present disclosure. It will be apparent to a person skilled in
the art that the multi-core optical fiber 100 is shown to have four trench layers
(i.e., the first through fourth trench layers 106a-106d) to make the illustrations
concise and clear and should not be considered as a limitation of the present
disclosure. In various other aspects, the plurality of trench layers 106 may have
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same number of trench layers as the number of buffer layers of the plurality of
buffer layers 104 such that each buffer layer of the plurality of buffer layers 104
has at least one corresponding trench layer of the plurality of trench layers 106,
without deviating from the scope of the present disclosure.
[55] In some aspects of the present disclosure, each trench layer of the plurality
of trench layers 106 may have a third radius R3 and a third relative refractive
index % ?3. Specifically, the first through fourth trench layers 106a-106d may
have the third radius R3. The third radius R3 of the first through fourth trench
layers 106a-106d may be in a range of 9 µm to 14 µm. In one aspect of the
present disclosure, the third radius R3 of each trench layer of the plurality of
trench layers 106 may be equal. In another aspect of the present disclosure, the
third radius R3 of each trench layer of the plurality of trench layers 106 may be
different. In some aspects of the present disclosure, each trench layer of the
plurality of trench layers 106 may have a second thickness T2. Specifically, the
first through fourth trench layers 106a-106d may have the second thickness T2.
The second thickness T2 of the first through fourth trench layers 106a-106d may
be in a range of 5 µm to 7 µm. In one aspect of the present disclosure, the second
thickness T2 of each trench layer of the plurality of trench layers 106 may be
equal. In another aspect of the present disclosure, the second thickness T2 of each
trench layer of the plurality of trench layers 106 may be different. In some aspects
of the present disclosure, the third radius R3 of the first through fourth trench
layers 106a-106d may be determined by an equation, i.e., R3 = R2 + T2. In some
aspects of the present disclosure, the third relative refractive index % ?3 of each
trench layer of the plurality of trench layers 106 may be in a range of -0.41 to
-0.62.
[56] The cladding 108 may envelop an outer circumferential surface of the
plurality of trench layers 106 (i.e., the first through fourth trench layers
106a-106d). The cladding 108 may have an associated refractive index that may
be less than the refractive index of each core of the plurality of cores 102. For
example, when the refractive index of each core of the plurality of cores 102 is n1
and the refractive index of the cladding 108 is n2, then n2 is less than n1. The
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cladding 108 may have a mid-cladding layer 108a and a peripheral cladding layer
108b. Specifically, the mid-cladding layer 108a may envelop the outer
circumferential surface of the plurality of trench layers 106 (i.e., the first through
fourth trench layers 106a-106d) and the peripheral cladding layer 108b may
envelop an outer circumferential surface of the mid-cladding layer 108a. In some
aspects of the present disclosure, the mid-cladding layer 108a may be made up of
a pure silica glass material. In some aspects of the present disclosure, the
mid-cladding layer 108a may be made up of a down doped silica glass material
where concentration of down dopant is greater or lesser as compared to
concentration of the down dopant in the trench layers 106 and the peripheral
cladding layer 108b. Specifically, the mid-cladding layer 108a may be a host
material where one or more holes are drilled to insert one or more core rods (not
shown) to manufacture the multi-core optical fiber 100. Further, the mid-cladding
layer 108a may be required to achieve a refractive index difference with respect to
the plurality of cores 102 (i.e., an up doped region) to guide the optical signal in
each core of the plurality of cores 102.
[57] In some aspects of the present disclosure, the mid-cladding layer 108a may
have a fourth radius R4 and a fourth relative refractive index % ?4. The fourth
radius R4 of the mid-cladding layer 108a may be in a range of 35 µm to 46 µm. In
some aspects of the present disclosure, the mid-cladding layer 108a may have a
third thickness T3. The third thickness T3 of the mid-cladding layer 108a may be
in a range of 6 µm to 12 µm. In some aspects of the present disclosure, the fourth
radius R4 of the mid-cladding layer 108a is measured from the central axis 110 of
the multi-core optical fiber 100 and may be determined by an equation, i.e.,
??4 = ??1 + ??1 + ??2 + ??3 + ????????h . In some aspects of the present
2
disclosure, the fourth relative refractive index % ?4 of the mid-cladding layer
108a may be in a range of -0.03 to 0.03. In one aspect of the present disclosure,
the fourth relative refractive index % ?4 of the mid-cladding layer 108a may be 0.
[58] The peripheral cladding layer 108b may be an outermost cladding region
of the multi-core optical fiber 100. The peripheral cladding layer 108b may be
down doped by using a down dopant. In some aspects of the present disclosure,
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the down dopant used to down dope the peripheral cladding layer 108b may be
Fluorine (F). Specifically, the peripheral cladding layer 108b being down doped
by using the down dopant may facilitate to achieve a leakage loss that is less than
0.001 Decibel/Kilometer (dB/Km) at a wavelength 1550 nm for the multi-core
optical fiber 100. Further, doping the peripheral cladding layer 108b with Fluorine
(F) may lower a Coefficient of Thermal Expansion (CTE) value of the peripheral
cladding 108b. Specifically, a surface doping of Fluorine (F) in the peripheral
cladding layer 108b may facilitate to lower the CTE surface on the silica glass.
Thus, the low CTE on the surface may create compressive stress on the surface of
the peripheral cladding layer 108b that may further improve a mechanical
behaviour of the peripheral cladding layer 108b in terms of crack growth and
fatigue. In some aspects of the present disclosure, the down dopant (such as
Fluorine (F)) in the peripheral cladding layer 108b may be doped up to 10 mole%
(mol%) with the CTE value in a range of 6 x 10-7 to 1 x 10-7 C-1. In one aspect of
the present disclosure, the CTE may be less than 1 x 10-7 C-1.
[59] In some aspects of the present disclosure, the peripheral cladding layer
108b may have a fourth thickness T4 that may be in a range of 3 micrometres
(µm) to 6 µm. As discussed, the thickness of the peripheral cladding layer 108b is
less (i.e., in the range of 3 µm to 6 µm), therefore the peripheral cladding layer
108b may be down doped with the down dopant (i.e., Fluorine (F)) to improve a
leakage loss and a micro bending loss of the multi-core optical fiber 100. Further,
the peripheral cladding layer 108b, by virtue of being down doped by using the
down dopant may facilitate to increase a mechanical strength of the multi-core
optical fiber 100. In other words, the peripheral cladding layer 108b may provide
the additional mechanical strength to the multi-core optical fiber 100 (i.e., a
reduced diameter multi-core optical fiber) which is a critical concern to realize in
real time applications. In some aspects of the present disclosure, the peripheral
cladding layer 108b may have a fifth radius R5 and a fifth relative refractive index
% ?5. The fifth radius R5 of the peripheral cladding layer 108b is measured from
the central axis 110 of the multi-core optical fiber 100. The fifth radius R5 of the
peripheral cladding layer 108b may be in a range of 39 µm to 51 µm. In some
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aspects of the present disclosure, the fifth radius R5 of the peripheral cladding
layer 108b may be determined by an equation, i.e., R5 = R4 + T4. In some aspects
of the present disclosure, the fifth relative refractive index % ?5 of the peripheral
cladding layer 108b may be in a range of -0.07 to -0.21.
[60] The relative refractive index % (?i) of ith region of the multi-core optical
fiber 100 may be determined by an expression
??? (%) = (????)2-(??????)2
2.(??????)2 ( . 100)
where,
Ni is refractive index of ith region such that i=1 for cores 102, i=2 for buffer
layers 104, i=3 for trench layers 106, i=4 for mid-cladding layer 108a, and i=5 for
peripheral cladding layer 108b.
Nsi is refractive index of pure silica.
[61] The cladding 108 may have an associated outer cladding thickness (OCT)
that may have a predefined value depending on particular application attributes. In
an example, the OCT may be defined as a distance from the centre of any of the
core of the plurality of cores 102 to an interface of the cladding 108 without a
coating layer of the multi-core optical fiber 100. In some aspects of the present
disclosure, the OCT of the cladding 108 may be in a range of 18 µm to 33 µm.
The multi-core optical fiber 100 may further have a coating layer (not shown).
The coating layer may have one or more coatings. In some aspects of the present
disclosure, a thickness of the coating layer (not shown) may be in a range of 25
µm to 60 µm. In some aspects of the present disclosure, the coating layer may be
made up of an ultraviolet (UV) light curable resin. In some aspects of the present
disclosure, the coating layer may have the UV light curable acrylate mixture of
monomers, oligomers, photo initiators, and additives, such that the mixtures are
cured separately. In some aspects of the present disclosure, the one or more
coatings of the coating layer may be a colored coating.
[62] As illustrated, the multi-core optical fiber 100 has the first through fourth
cores 102a-102d. In some aspects of the present disclosure, the cladding 108 of
the multi-core optical fiber 100 may have a diameter that is equal to 80+/-1 µm
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such that a core to core spacing between each pair of adjacent cores of the first
through fourth cores 102a-102d is in a range of 20 µm to 30 µm. Further, when
the diameter of the cladding 108 of the multi-core optical fiber 100 is 80+/-1 µm,
the first relative refractive index % ?1 of the core 102 of the multi-core optical
fiber 100 may be in a range of 0.34 to 0.55, the first radius R1 of the of the core
102 may be in a range of 3 µm to 5 µm, the second relative refractive index % ?2
of the buffer layer 104 may be in a range of -0.03 to 0.03, the first thickness T1 of
the buffer layer 104 may be in a range of 1 µm to 2 µm, the third relative
refractive index % ?3 of the trench layer 106 may be in a range of -0.48 to -0.62,
the second thickness T2 of the trench layer 106 may be in a range of 5 µm to 7
µm, the fourth relative refractive index % ?4 of the mid-cladding layer 108a may
be in a range of -0.03 to 0.03, the third thickness T3 of the mid-cladding layer
108a may be in a range of 6 µm to 9 µm, and the fifth relative refractive index %
?5 may be in range of -0.07 to -0.21, and the fourth thickness T4 of the peripheral
cladding 108b may be in a range of 3 µm to 5 µm.
[63] In one aspect of the present disclosure, when the diameter of the cladding
108 of the multi-core optical fiber 100 is 80+/-1 µm, the first relative refractive
index % ?1 of the core 102 of the multi-core optical fiber 100 may be 0.38, the
first radius R1 of the of the core 102 may be 4 µm, the second relative refractive
index % ?2 of the buffer layer 104 may be 0, the first thickness T1 of the buffer
layer 104 may be 1.5 µm, the third relative refractive index % ?3 of the trench
layer 106 may be -0.55, the second thickness T2 of the trench layer 106 may 5
µm, the fourth relative refractive index % ?4 of the mid-cladding layer 108a may
be 0, the third thickness T3 of the mid-cladding layer 108a may be 8 µm, and the
fifth relative refractive index % ?5 may be -0.21, and the fourth thickness T4 of
the peripheral cladding 108b may be 5 µm.
[64] In another aspect of the present disclosure, when the diameter of the
cladding 108 of the multi-core optical fiber 100 is 80+/-1 µm, the first relative
refractive index % ?1 of the core 102 of the multi-core optical fiber 100 may be
0.45, the first radius R1 of the of the core 102 may be 4.5 µm, the second relative
refractive index % ?2 of the buffer layer 104 may be 0, the first thickness T1 of
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the buffer layer 104 may be 1.2 µm, the third relative refractive index % ?3 of the
trench layer 106 may be -0.6, the second thickness T2 of the trench layer 106 may
6 µm, the fourth relative refractive index % ?4 of the mid-cladding layer 108a
may be 0, the third thickness T3 of the mid-cladding layer 108a may be 7 µm, and
the fifth relative refractive index % ?5 may be -0.17, and the fourth thickness T4
of the peripheral cladding 108b may be 4 µm.
[65] In another aspect of the present disclosure, when the diameter of the
cladding 108 of the multi-core optical fiber 100 is 80+/-1 µm, the first relative
refractive index % ?1 of the core 102 of the multi-core optical fiber 100 may be
0.41, the first radius R1 of the of the core 102 may be 4.5 µm, the second relative
refractive index % ?2 of the buffer layer 104 may be 0, the first thickness T1 of
the buffer layer 104 may be 1.3 µm, the third relative refractive index % ?3 of the
trench layer 106 may be -0.6, the second thickness T2 of the trench layer 106 may
7 µm, the fourth relative refractive index % ?4 of the mid-cladding layer 108a
may be 0, the third thickness T3 of the mid-cladding layer 108a may be 8 µm, and
the fifth relative refractive index % ?5 may be -0.12, and the fourth thickness T4
of the peripheral cladding 108b may be 3 µm.
[66] In some aspects of the present disclosure, the cladding 108 of the
multi-core optical fiber 100 may have a diameter that is equal to 100+/-1 µm such
that a core to core spacing (i.e., a pitch) between each pair of adjacent cores of the
first through fourth cores 102a-102d is in a range of 25 µm to 35 µm. In one
aspect of the present disclosure, the plurality of cores 102 may have at least 4
cores (i.e., the first through fourth cores 102a-102d) such that the core to core
spacing (i.e., the pitch) of each pair of cores of the plurality of cores 102 may be
in a range of 20 µm to 35 µm. Further, when the diameter of the cladding 108 of
the multi-core optical fiber 100 is 100+/-1 µm, the first relative refractive index %
?1 of the core 102 of the multi-core optical fiber 100 may be in a range of 0.32 to
0.48, the first radius R1 of the of the core 102 may be in a range of 3 µm to 5 µm,
the second relative refractive index % ?2 of the buffer layer 104 may be in a
range of -0.03 to 0.03, the first thickness T1 of the buffer layer 104 may be in a
range of 1 µm to 2 µm, the third relative refractive index % ?3 of the trench layer
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106 may be in a range of -0.41 to -0.55, the second thickness T2 of the trench
layer 106 may be in a range of 5 µm to 7 µm, the fourth relative refractive index
% ?4 of the mid-cladding layer 108a may be in a range of -0.03 to 0.03, the third
thickness T3 of the mid-cladding layer 108a may be in a range of 10 µm to 12 µm,
the fifth relative refractive index % ?5 may be in range of -0.07 to -0.21, and the
fourth thickness T4 of the peripheral cladding 108b may be in a range of 4 µm to
6 µm.
[67] In one aspect of the present disclosure, when the diameter of the cladding
108 of the multi-core optical fiber 100 is 100+/-1 µm, the first relative refractive
index % ?1 of the core 102 of the multi-core optical fiber 100 may be 0.32, the
first radius R1 of the of the core 102 may be 4 µm, the second relative refractive
index % ?2 of the buffer layer 104 may be 0, the first thickness T1 of the buffer
layer 104 may be 2 µm, the third relative refractive index % ?3 of the trench layer
106 may be -0.45, the second thickness T2 of the trench layer 106 may be 6 µm,
the fourth relative refractive index % ?4 of the mid-cladding layer 108a may be 0,
the third thickness T3 of the mid-cladding layer 108a may be 12 µm, and the fifth
relative refractive index % ?5 may be -0.1, and the fourth thickness T4 of the
peripheral cladding 108b may be 6 µm.
[68] In another aspect of the present disclosure, when the diameter of the
cladding 108 of the multi-core optical fiber 100 is 100+/-1 µm, the first relative
refractive index % ?1 of the core 102 of the multi-core optical fiber 100 may be
0.45, the first radius R1 of the of the core 102 may be 4.5 µm, the second relative
refractive index % ?2 of the buffer layer 104 may be 0, the first thickness T1 of
the buffer layer 104 may be 1 µm, the third relative refractive index % ?3 of the
trench layer 106 may be -0.45, the second thickness T2 of the trench layer 106
may 6 µm, the fourth relative refractive index % ?4 of the mid-cladding layer
108a may be 0, the third thickness T3 of the mid-cladding layer 108a may be 11
µm, and the fifth relative refractive index % ?5 may be -0.14, and the fourth
thickness T4 of the peripheral cladding 108b may be 4 µm.
[69] In another aspect of the present disclosure, when the diameter of the
cladding 108 of the multi-core optical fiber 100 is 100+/-1 µm, the first relative
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refractive index % ?1 of the core 102 of the multi-core optical fiber 100 may be
0.45, the first radius R1 of the of the core 102 may be 4.5 µm, the second relative
refractive index % ?2 of the buffer layer 104 may be 0, the first thickness T1 of
the buffer layer 104 may be 1.3 µm, the third relative refractive index % ?3 of the
trench layer 106 may be -0.52, the second thickness T2 of the trench layer 106
may 7 µm, the fourth relative refractive index % ?4 of the mid-cladding layer
108a may be 0, the third thickness T3 of the mid-cladding layer 108a may be 12
µm, and the fifth relative refractive index % ?5 may be -0.15, and the fourth
thickness T4 of the peripheral cladding 108b may be 5 µm.
[70] The multi-core optical fiber 100 may further have (i) a crosstalk of less
than -30 Decibel (dB) at a wavelength of 1550 nanometres, (ii) a Zero Dispersion
Wavelength (ZDW) in a range of 1290 nm to 1350 nm, (iii) a cable cutoff (CC) of
less than 1260 nm, (iv) a Mode Field Diameter (MFD) of 8.1+/-0.5 µm at the
wavelength of 1550 nm. Preferably, the MFD may be in a range of 7.6 µm to 8.6
µm at the wavelength of 1550 nm, a macro bend loss of the multi-core optical
fiber 100 (i) at a wavelength of 1550 nm and a bend radius of 5 mm may be less
than or equal to 0.15 dB/turn, (ii) at a wavelength of 1625 nm and at a bend radius
of 5 mm may be less than or equal to 0.45 dB/turn, (iii) at a wavelength of 1550
nm and a bend radius of 7.5 mm may be less than or equal to 0.08 dB/turn, and
(iv) at a wavelength of 1625 and a bend radius of 7.5 mm may be less than or
equal to 0.025 dB/turn, and an attenuation may be (i) less than 0.35 dB/KM at
1310 nm wavelength and (ii) less than 0.25 dB/KM at 1550 nm wavelength.
[71] As discussed, the multi-core optical fiber 100 may have the coating layer.
In such a scenario, the coating layer may have a diameter that may be in a range
of 150 µm to 200 µm. In other words, a diameter of the multi-core optical fiber
100 with the coating layer is in the range of 150 µm to 200 µm. Further, without
the coating layer, the multi-core optical fiber 100 may have a diameter in a range
of 80 µm to 110 µm with a tolerance of + 1 µm.
[72] FIG. 1B illustrates another cross-sectional view of the multi-core optical
fiber 100. The mid-cladding layer 108a may have a marker 112. Specifically, the
marker 112 may facilitate to identify a position of the plurality of cores 102. As
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illustrated, the marker 112 may be disposed in the mid-cladding layer 108a along
the central axis 110 running longitudinally, i.e., generally parallel to the central
axis 110 and the plurality of cores 102. In some aspects of the present disclosure,
the marker 112 may have an associated refractive index that may be different from
the fourth relative refractive index % ?4 of the mid-cladding layer 108a. In some
aspects of the present disclosure, the refractive index of the marker 112 may be
greater than the fourth relative refractive index % ?4 of the mid-cladding layer
108a. In some aspects of the present disclosure, the refractive index of the marker
112 may be less than the fourth relative refractive index % ?4 of the mid-cladding
layer 108a.
[73] FIG. 1C illustrates yet another cross-sectional view of the multi-core
optical fiber 100. As discussed, the mid-cladding layer 108a may have the marker
112. As illustrated, the marker 112 may be disposed in the mid-cladding layer
108a. Specifically, the marker 112 may be disposed within a marker space 114.
Specifically, the marker space 114 may surround the first through fourth trench
layers 106a-106d and may be defined between a first and second distances D1 and
D2, respectively. In some aspects of the present disclosure, the marker 112 may be
disposed between the first distance D1 and the second distance D2 i.e., 20 µm to
37.5 µm from a central axis 110 of the multi-core optical fiber 100. In some
aspects of the present disclosure, the marker 112 may have a shape such as, but
not limited to, a circular shape, a cylindrical shape, an elliptical cylindrical shape,
a triangular cylindrical shape, and the like. Aspects of the present disclosure are
intended to include and/or otherwise cover any type of the shape of the marker
112 known to a person of ordinary skill in the art, without deviating from the
scope of the present disclosure.
[74] FIG. 1D illustrates a cross-sectional view of a multi-core optical fiber
cable 120. The multi-core optical fiber cable 120 may incorporate a bundle 124 of
multi-core optical fiber ribbon 122 in which a plurality of multi-core optical fibers
100 may be intermittently bonded. In one aspect of the present disclosure, the
multi-core optical fiber cable 120 may comprises one or more multi-core optical
fiber ribbons 122, one or more water blocking tapes 126, one or more water
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swellable yarns 128, one or more strength members 130, one or more rip cords
132, and an outer sheath 134.
[75] As discussed, the multi-core optical fiber 100 are reduced in diameter i.e.,
in a range of 80 to 110 µm, significantly increases a packing density of the
multi-core optical fiber cable 120. Specifically, the reduced diameter of the
multi-core optical fiber 100 may allow incorporation of higher number of the
multi-core optical fiber 100 in the multi-core optical fiber cable 120. In some
aspects of the present disclosure, the multi-core optical fiber ribbon 122
incorporated in the multi-core optical fiber cable 120 may be spirally twisted. In
some aspects of the present disclosure, the multi-core optical fiber cable 120 has
an attenuation of less than 0.4 dB/km at a wavelength 1310 nm. In another aspects
of the present disclosure the multi-core optical fiber cable 120 has an attenuation
of less than 0.3 dB/km at a wavelength1550 nm. In other aspects of the present
disclosure, a minimum average bending radius of the multi-core optical fiber
cable 120 is in a range of 10 to 15 times of a predefined diameter (generally 12.5
mm) of the multi-core optical fiber cable 120in the longitudinal direction.
[76] FIG. 2A illustrates a graph 200 of a refractive index (RI) profile of the
multi-core optical fiber 100 (as shown in FIG. 1A). X-axis and Y-axis of the graph
200 denotes various radiuses and thickness associated with the multi-core optical
fiber 100 and various relative refractive index percentages associated with the
multi-core optical fiber 100, respectively. The graph 200 has a curve 202 and a
central axis 204 of the plurality of core 102 As illustrated by the curve 202, near
the central axis of the plurality of core 102, the first relative refractive index % ?1
of the plurality of cores 102 (hereinafter interchangeably referred to and
designated as “the core 102”) is maximum. Further, as the first radius R1
associated with the core 102 increases i.e., moving away from the central axis 204
of the core 102, the first relative refractive index % ?1 of the core 100 dips.
Specifically, the first relative refractive index % ?1 of the core 102 may be
minimum near a transition point between the core 102 and the plurality of buffer
layers 104 (hereinafter interchangeably referred to and designated as “the buffer
layer 104”) (as shown in FIG. 1A). Further, as illustrated, the buffer layer 104
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may have the first thickness T1, the second radius R2 and the second relative
refractive index % ?2 that may be linear. Further, the second relative refractive
index % ?2 may be less than the first relative refractive index % ?1 of the core
102. Furthermore, as illustrated, the plurality of trench layers 106 (hereinafter
interchangeably referred to and designated as “the trench layer 106”) (as shown in
FIG. 1A) may have the second thickness T2, the third radius R3 and the third
relative refractive index % ?3. Further, the third relative refractive index % ?3
may be less than the second relative refractive index % ?2 of the buffer layer 104.
Furthermore, as illustrated, the mid-cladding layer 108a (as shown in FIG. 1A)
may have the third thickness T3, the fourth radius R4 and the fourth relative
refractive index % ?4 that may be linear. However, the fourth relative refractive
index % ?4 of the mid-cladding layer 108a may be greater than the third relative
refractive index % ?3 of the trench layer 106 and less than the second relative
refractive index % ?2 of the buffer layer 104. Furthermore, as illustrated, the
peripheral cladding layer 108b (as shown in FIG. 1A) may have the fourth
thickness T4, the fifth radius R5 and the fifth relative refractive index % ?5..
However, the fifth relative refractive index % ?5 of the peripheral cladding layer
108b may be greater than the third relative refractive index % ?3 of the trench
layer 106 and less than the fourth relative refractive index % ?4 of the
mid-cladding layer 108a. The first radius R1, the second radius R2 and the third
radius R3 are measured from the central axis 204 of the core 102. The fourth
radius R4 and the fifth radius R5 are measured form the central axis 110 of the
multi-core optical fiber 100.
[77] FIG. 2B illustrates a graph 204 of an experimental profile and a theoretical
profile of the multi-core optical fiber 100 (as shown in FIG. 1A). X-axis and
Y-axis of the graph 204 denotes various radiuses and thickness associated with the
multi-core optical fiber 100 and various refractive index percentages associated
with the multi-core optical fiber 100, respectively. The graph 204 has a first curve
206 and a second curve 208. As illustrated, the first curve 206 represents the
experimental profile of the multi-core optical fiber 100. Similarly, the second
curve 208 represents the theoretical profile of the multi-core optical fiber 100.
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Specifically, the second curve 208 of the graph 204 may be substantially similar to
the curve 202 of the graph 200 (as shown in FIG. 2A).
[78] FIG. 3A illustrates a graph 300 of a cross talk versus pitch of the
multi-core optical fiber 100 (as shown in FIG. 1A). X-axis and Y-axis of the graph
300 denotes various pitch associated with the multi-core optical fiber 100 and
various cross talks associated with the multi-core optical fiber 100, respectively.
As illustrated, the graph 300 has the first curve 302, the second curve 304, and the
third curve 306. Specifically, the first curve 302 is a cross talk versus pitch curve
of the multi-core optical fiber 100 when the diameter of the cladding 108 of the
multi-core optical fiber 100 is 100+/-1 µm, the first relative refractive index % ?1
of the core 102 of the multi-core optical fiber 100 may be 0.32, the first radius R1
of the of the core 102 may be 4 µm, the second relative refractive index % ?2 of
the buffer layer 104 may be 0, the first thickness T1 of the buffer layer 104 may
be 2 µm, the third relative refractive index % ?3 of the trench layer 106 may be
-0.45, the second thickness T2 of the trench layer 106 may be 6 µm, the fourth
relative refractive index % ?4 of the mid-cladding layer 108a may be 0, the third
thickness T3 of the mid-cladding layer 108a may be 12 µm, and the fifth relative
refractive index % ?5 may be -0.1, and the fourth thickness T4 of the peripheral
cladding 108b may be 6 µm.
[79] Specifically, the second curve 304 is a cross talk versus pitch curve of the
multi-core optical fiber 100, when the diameter of the cladding 108 of the
multi-core optical fiber 100 is 100+/-1 µm, the first relative refractive index % ?1
of the core 102 of the multi-core optical fiber 100 may be 0.45, the first radius R1
of the of the core 102 may be 4.5 µm, the second relative refractive index % ?2 of
the buffer layer 104 may be 0, the first thickness T1 of the buffer layer 104 may
be 1 µm, the third relative refractive index % ?3 of the trench layer 106 may be
-0.45, the second thickness T2 of the trench layer 106 may 6 µm, the fourth
relative refractive index % ?4 of the mid-cladding layer 108a may be 0, the third
thickness T3 of the mid-cladding layer 108a may be 11 µm, and the fifth relative
refractive index % ?5 may be -0.14, and the fourth thickness T4 of the peripheral
cladding 108b may be 4 µm.
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[80] Specifically, the third curve 306 is a cross talk versus pitch curve of the
multi-core optical fiber 100, when the diameter of the cladding 108 of the
multi-core optical fiber 100 is 100+/-1 µm, the first relative refractive index % ?1
of the core 102 of the multi-core optical fiber 100 may be 0.45, the first radius R1
of the of the core 102 may be 4.5 µm, the second relative refractive index % ?2 of
the buffer layer 104 may be 0, the first thickness T1 of the buffer layer 104 may
be 1.3 µm, the third relative refractive index % ?3 of the trench layer 106 may be
-0.52, the second thickness T2 of the trench layer 106 may 7 µm, the fourth
relative refractive index % ?4 of the mid-cladding layer 108a may be 0, the third
thickness T3 of the mid-cladding layer 108a may be 12 µm, and the fifth relative
refractive index % ?5 may be -0.15, and the fourth thickness T4 of the peripheral
cladding 108b may be 5 µm.
[81] FIG. 3B illustrates a graph 308 of a cross talk versus pitch of the
multi-core optical fiber 100 (as shown in FIG. 1A). X-axis and Y-axis of the graph
308 denotes various pitch associated with the multi-core optical fiber 100 and
various cross talks associated with the multi-core optical fiber 100, respectively.
As illustrated, the graph 308 has the first curve 310, the second curve 312, and the
third curve 314. Specifically, the first curve 310 is a cross talk versus pitch curve
of the multi-core optical fiber 100 when the diameter of the cladding 108 of the
multi-core optical fiber 100 is 80+/-1 µm, the first relative refractive index % ?1
of the core 102 of the multi-core optical fiber 100 may be 0.38, the first radius R1
of the of the core 102 may be 4 µm, the second relative refractive index % ?2 of
the buffer layer 104 may be 0, the first thickness T1 of the buffer layer 104 may
be 1.5 µm, the third relative refractive index % ?3 of the trench layer 106 may be
-0.55, the second thickness T2 of the trench layer 106 may 5 µm, the fourth
relative refractive index % ?4 of the mid-cladding layer 108a may be 0, the third
thickness T3 of the mid-cladding layer 108a may be 8 µm, and the fifth relative
refractive index % ?5 may be -0.21, and the fourth thickness T4 of the peripheral
cladding 108b may be 5 µm.
[82] Specifically, the second curve 312 is a cross talk versus pitch curve of the
multi-core optical fiber 100 when the diameter of the cladding 108 of the
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multi-core optical fiber 100 is 80+/-1 µm, the first relative refractive index % ?1
of the core 102 of the multi-core optical fiber 100 may be 0.45, the first radius R1
of the of the core 102 may be 4.5 µm, the second relative refractive index % ?2 of
the buffer layer 104 may be 0, the first thickness T1 of the buffer layer 104 may
be 1.2 µm, the third relative refractive index % ?3 of the trench layer 106 may be
-0.6, the second thickness T2 of the trench layer 106 may 6 µm, the fourth relative
refractive index % ?4 of the mid-cladding layer 108a may be 0, the third
thickness T3 of the mid-cladding layer 108a may be 7 µm, and the fifth relative
refractive index % ?5 may be -0.17, and the fourth thickness T4 of the peripheral
cladding 108b may be 4 µm.
[83] Specifically, the third curve 314 is a cross talk versus pitch curve of the
multi-core optical fiber 100 when the diameter of the cladding 108 of the
multi-core optical fiber 100 is 80+/-1 µm, the first relative refractive index % ?1
of the core 102 of the multi-core optical fiber 100 may be 0.41, the first radius R1
of the of the core 102 may be 4.5 µm, the second relative refractive index % ?2 of
the buffer layer 104 may be 0, the first thickness T1 of the buffer layer 104 may
be 1.3 µm, the third relative refractive index % ?3 of the trench layer 106 may be
-0.6, the second thickness T2 of the trench layer 106 may 7 µm, the fourth relative
refractive index % ?4 of the mid-cladding layer 108a may be 0, the third
thickness T3 of the mid-cladding layer 108a may be 8 µm, and the fifth relative
refractive index % ?5 may be -0.12, and the fourth thickness T4 of the peripheral
cladding 108b may be 3 µm.
[84] Thus, the multi-core optical fiber 100 of the present disclosure may have a
reduced leakage loss and reduced micro bending loss which is necessary for a
multi-core optical fiber due to low thickness of the peripheral cladding layer 108b
and cladding 108 of the multi-core optical fiber 100. Further, the multi-core
optical fiber 100 may have an increased strength by virtue of the peripheral down
doped cladding layer 108b which is critical for a reduced diameter optical fiber
such as the multi-core optical fiber 100. Furthermore, the buffer layer 104 that is
made up of a pure silica glass material may facilitate the multi-core optical fiber
100 to achieve a delta value (i.e., relative refractive index value) that is in
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reference to the core 102 to require the optical signal to guide in the core 102 to
achieve total internal reflection.
[85] 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. , Claims:I/We claim
1. A multi-core optical fiber (100) comprising:
a plurality of cores (102);
a cladding (108) that surrounds the plurality of cores (102), wherein the
cladding (108) comprising a peripheral cladding layer (108b), wherein the
peripheral cladding layer (108b) is down doped such that a leakage loss of the
multi-core optical fibre (100) is less than 0.001dB/Km at a wavelength 1550
nm.
2. The multi-core optical fiber (100) of claim 1, wherein the cladding (108)
further comprising a mid-cladding layer (108a), wherein the mid-cladding layer
(108a) is made up of pure silica glass.
3. The multi-core optical fiber (100) of claim 1, further comprising a
plurality of buffer layers (104) that surrounds the plurality of cores (102), wherein
the plurality of buffer layers (104 ) are undoped.
4. The multi-core optical fiber (100) of claim 1, further comprising a
plurality of trench layers (106) that surrounds the plurality of buffer layers (104),
wherein the plurality of trench layers (106) are down doped.
5. The multi-core optical fiber (100) of claim 1, wherein the plurality of
cores (102) are up doped with an up dopant, wherein the up dopant is one of
Germanium (Ge) and Chlorine (Cl).
6. The multi-core optical fiber of claim 1, wherein the peripheral cladding
layer (108b) is down doped with a down dopant, wherein the down dopant is
Fluorine (F).
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7. The multi-core optical fiber (100) of claim 1, wherein a diameter of the
multi-core optical fiber (100) without a coating layer is in a range of 80
micrometres (µm) to 110 µm with a tolerance of + 1 µm and a diameter of the
multi-core optical fiber (100) with a coating layer is in a range of 150 µm to 200
µm.
8. The multi-core optical fiber (100) of claim 1, wherein the peripheral
cladding layer (108b) has a thickness in a range of 3 µm to 6 µm.
9. The multi-core optical fiber (100) of claim 1, wherein at least one of:
a Mode Field Diameter (MFD) of the multi-core optical fiber (100) is in
a range of 7.6 µm to 8.6 µm at a wavelength of 1550 nm;
a macro bend loss of the multi-core optical fiber (100) (i) at a wavelength
of 1550 nm and a bend radius of 5 mm is 0.15 dB/turn, (ii) at a wavelength of
1625 nm and at a bend radius of 5 mm is 0.45 dB/turn, (iii) at a wavelength of
1550 nm and a bend radius of 7.5 mm is 0.08 dB/turn, and (iv) at a wavelength of
1625 and a bend radius of 7.5 mm is 0.025 dB/turn;
a Coefficient of Thermal Expansion (CTE) is in a range of 6 x 10-7 to 1 x
10-7 C-1; and
an attenuation is (i) less than 0.35 dB/KM at 1310 nm wavelength and
(ii) less than 0.25 dB/KM at 1550 nm wavelength.
10. The multi-core optical fiber (100) of claim 2, wherein the mid-cladding
layer (108a) comprising a marker (112) such that a refractive index of the marker
(112) is at least one of higher and lower with respect to a refractive index of the
mid-cladding layer (108a).
11. The multi-core optical fiber (100) of claim 2, wherein a marker (112) is
disposed at a distance between 20 µm to 37.5 µm from a central axis (110) of the
multi-core optical fiber (100), wherein a shape of the marker (112) is one of, a
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circular shape, a cylindrical shape, an elliptical cylindrical shape, and a triangular
cylindrical shape.
12. The multi-core optical fiber (100) of claim 1, wherein the multi-core
optical fiber (100) (100) has at least 4 cores such that a core to core spacing of
each pair of cores of the plurality of cores (102) is in a range of 20 µm to 35 µm.
13. The multi-core optical fiber (100) of claim 1, wherein a crosstalk of the
multi-core optical fiber (100) is less than -30dB at a wavelength of 1550 nm.
14. A multi-core optical fiber cable (120) incorporating one or more
multi-core optical fiber ribbon (122) in which a plurality of multi-core optical
fibers (100) of claim 1 are intermittently bonded, wherein the multi-core optical
fiber ribbon (122) is incorporated with spirally twisted.
15. The multi-core optical fiber cable (120) of claim 15, wherein the
multi-core optical fiber cable (120) has an attenuation of less than 0.4 dB/km at a
wavelength 1310 nm and the multi-core optical fiber cable (120) has an
attenuation of less than 0.3 dB/km at a wavelength1550 nm.
16. The multi-core optical fiber cable (120) of claim 15, wherein the
multi-core optical fiber cable (120) has a minimum average bending radius that is
10 to 15 times of a predefined diameter of the multi-core optical fiber cable (120)
in a fiber longitudinal direction.