Description:TECHNICAL FIELD
[1] The present disclosure relates generally to optical fibers, and, more
particularly, to an optical fiber with a large effective area.
BACKGROUND
[2] An optical fiber communication system uses light as the carrier of
information from a source to a destination via a guided fiber cable (glass or
plastic). A communication system's information-carrying capacity is directly
proportional to its bandwidth; that is, the wider the bandwidth, the greater the
information-carrying capacity. Light frequencies used in fiber optical systems
range from 104 to 4 x 1014 Hz, resulting in higher information-carrying capacity.
[3] An effective area is a quantitative measure of the area which a waveguide
or fiber mode effectively covers in the transverse dimensions. The effect of
nonlinearities can be reduced by designing a fiber with a large effective area. It is
evident that nonzero-dispersion fibers have a small value of the chromatic
dispersion in the 1.55 µm band to minimize the effects of chromatic dispersion.
However, such fibers have smaller effective areas, and thus face enormous
amount of non-linearity and its associated challenges.
[4] A prior art reference "US20150226914A1" disclosed an optical fiber with
a core and cladding portions. The core is doped with an up dopant (chlorine), and
it is surrounded by a first and second cladding. The second cladding has a higher
refractive index than the first cladding.
[5] Using Chlorine as an up dopant in the core region of the optical fiber leads
to low relative refractive index in the core region. The low refractive index results
in a low effective area which increases nonlinear effects in the optical fiber. The
nonlinear effects generate spurious (unwanted) signals and increase noise which is
not desirable.
[6] A prior art "US20210214266A1" discloses an optical fiber with a core and
cladding portions. An optical fiber preform is used to produce the optical fiber.
The optical fiber preform is manufactured by combining silica and Germania
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precursors (Germanium dioxide). During the manufacturing of the optical fiber
preform, the silica to germanium dioxide ratio varies from 1:1 to approximately
100:1, resulting in a gradual decrease in germanium dioxide concentration in the
core portion. The core of the optical fiber is doped with Germanium, but the
cladding is not pure silica. The prior art showcased step index fibers with a low
effective area, resulting in an increase in nonlinearity which causes spurious
signals and increases noise in data transmission. Such a condition is undesirable
for optical signal transmission. A confinement versus mode field in the core (with
a constant refractive index 1.446) of a step-index fibers for a fundamental mode
(LP01) at 1550nm is shown in FIG.1(A). Mode field intensities of the step-index
fibers for a fundamental mode (LP01) at 1550nm is shown in FIG. 1(B).
[7] Thus, there is a need for an optical fiber that overcomes the above stated
disadvantages of conventional optical fiber.
OBJECTIVE OF THE DISCLOSURE
[8] As mentioned, there is a need for a technical solution that overcomes the
aforementioned problems of conventional optical fibers. Thus, an objective of the
present disclosure is to provide an optical fiber with large effective area. To
achieve the large effective area, the optical fiber has an exponentially decaying
Refractive Index (RI) profile of the core and an undoped cladding. Further, an
objective of the present disclosure is to provide an optical fiber having a higher
confinement of mode field. Furthermore, an objective of the present disclosure is
to provide an optical fiber with reduced nonlinear effects (i.e., less spurious
signals and low noise).
SUMMARY
[9] In an aspect of the present disclosure, an optical fiber is disclosed having a
core and a cladding, such that the core extends substantially parallel and along a
central axis of the optical fiber and the cladding concentrically surrounds the core.
The core has at least 83-mole percent (mol %) of Silicon dioxide (SiO2) and at
most 17-mole percent (mol %) of an up dopant. In some aspects of the present
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disclosure, the up dopant used in the core is Germanium (Ge). The cladding has at
least 99-mole percent (mol %) of Silicon dioxide (SiO2) and less than 1-mole
percent (mol %) of metallic impurity.
BRIEF DESCRIPTION OF DRAWINGS
[10] 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.
[11] FIG. 1A illustrates a refractive index profile of an optical fiber of a prior
art.
[12] FIG. 1B illustrates a variation of a mode field intensity value of an optical
fiber of the prior art.
[13] FIG. 2 illustrates a cross-sectional view of an optical fiber.
[14] FIG. 3 illustrates a graph that represents a refractive index (RI) profile of
the optical fiber of FIG. 2.
[15] FIG. 4 illustrates a graphical relation of the RI profile with different
regions of the optical fiber of FIG. 2.
[16] FIG. 5 illustrates a graph that represents an effect of a slope variation ‘a’
(alpha) in a first segment of a core of the optical fiber of FIG. 2 on a mode field
diameter (MFD) and an effective area of the optical fiber of FIG. 2.
[17] FIG. 6 illustrates a graph that represents an effect of a slope variation ‘a’
(alpha) in the first segment of the optical fiber of FIG. 2 on a value of a chromatic
dispersion at a wavelength of 1550 nm.
[18] FIG. 7 illustrates a graph that represents a confinement value versus a
mode field value of the core of the optical fiber of FIG. 2 for a fundamental mode
(LP01) at a wavelength of 1550 nm.
[19] FIG. 8 illustrates a graphical variation of a mode field intensity value of
the optical fiber of FIG. 2.
DEFINITIONS
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[20] 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.
[21] 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
surrounding the outer surface of the core of the optical fiber and an outer cladding
layer surrounding the inner cladding from the outside.
[22] The term “Mole percent (mol%)” as used herein refers to a number of
moles of a given material (i.e., Ge) in a composite (i.e., SiO2+Ge) to the total
number of moles in the composite (Ge + SiO2). The mole percent (mol %) of a
component can be obtained by multiplying a mole fraction of the component by
numeric value one hundred.
[23] The term “up doped” as used herein refers to adding doping materials to
facilitate an increase in a refractive index of a particular layer or a part of the
optical fiber. The materials configured to facilitate up doping are known as “up
dopants”.
[24] “The term “refractive index” as used herein refers to a 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 is
used to measure bending of light from one medium to another medium.
[25] The term “refractive index (RI) profile” as used herein refers to the
distribution of refractive indexes in the optical fiber from the core to the
outermost cladding layer of the optical fiber. Based on the refractive index profile,
the optical fiber may be configured as a step index fiber or a graded index fiber.
The refractive index of a core of a step index fiber is constant throughout the
optical fiber and is higher than the refractive index of the cladding. Further, the
refractive index of the core is gradually varied as a function of the radial distance
from the center of the core for a graded index fiber.
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[26] The term “down doping” as used herein refers to adding doping materials
to facilitate the decrease in the refractive index of a particular layer or part of an
optical fiber. The materials configured to facilitate down doping are known as
“down dopants”.
[27] The term “undoped or unintentionally doped” as used herein refers a
region of the optical fiber contains one or more dopants 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 because of diffusion. Such background doping levels are very low and
have an insignificant effect on the refractive index of an undoped region.
[28] The term “effective area” as used herein refers to a quantitative measure of
an area that a waveguide or fiber mode effectively covers in a number of
transverse dimensions.
[29] The term “mode field diameter” (MFD) as used herein refers to size of a
light-carrying portion of the optical fiber. For single-mode optical fiber, the MFD
may include a core of the single-mode optical fiber as well as a small portion of a
cladding surrounding the core of the single-mode optical fiber. The selection of
desired MFD helps to describe the size of the light-carrying portion of the optical
fiber.
[30] The term “chromatic dispersion” as used herein refers to a phenomenon
that depicts a phase velocity and a group velocity of light propagating in a
transparent medium depend on an optical frequency. The dependency of the phase
velocity and the group velocity on the optical frequency results mostly from the
interaction of light with electrons of the medium and is related to absorption of
light in some spectral regions.
[31] The term “chromatic dispersion slope” as used herein refers to the total
dispersion varying along the length of a waveguide or the optical fiber.
[32] 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 optical fibers. The macro bend loss occurs when the fiber cable is
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subjected to a significant amount of bending above a critical value of curvature.
The macro bend loss is also called large radius loss.
[33] The term “cut-off wavelength” as used herein refers to a wavelength above
which a single-mode fiber supports and propagates only one mode (i.e., LP01) of
light. The cabled optical fiber transmits a single mode of optical signal above a
predefined cut-off wavelength.
[34] The term “attenuation” as used herein refers to an amount of light lost
between an input and an output. Total attenuation is the sum of all losses. Optical
losses of fiber are usually expressed in decibels per kilometre (dB/Km). The
losses can be scattering related losses, micro bending losses, macro bending losses
and the like.
[35] The term “Micro bend loss” as used herein refers to small-scale bends in
the optical fiber, often from pressure exerted on the optical fiber itself as well as
being pressed by other components of an optical communication system.
[36] The term “Scattering related losses” as used herein refers to losses that are
caused by the interaction of light with density fluctuations within a fiber. Density
changes are produced when optical fibers are manufactured. During
manufacturing, the regions of higher and lower molecular density areas, relative
to the average density of the fiber are created. Light traveling through the fiber
interacts with the density areas, the light is then partially scattered in all
directions.
DETAILED DESCRIPTION
[37] 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.
[38] 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.
[39] 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.
[40] FIG. 2 illustrates a cross-sectional view of an optical fiber 200. The optical
fiber 200 may have an effective area of greater than or equal to 100 micrometre
square (µm2). The optical fiber 200 may have a core 202 and a cladding 204 such
that the core 202 may extend substantially parallel and along a central axis 206 of
the optical fiber 200. The cladding 204 may concentrically surround the core 202.
In some aspects of the present disclosure, the effective area of the optical fiber
200 may be in a range of 100-176 µm2. Preferably, the effective area of the optical
fiber 200 may specifically be 110 µm2.
[41] The optical fiber 200 may further have a mode field diameter (MFD) in a
range of 11 µm to 15 µm. Preferably, the MFD of the optical fiber 200 may be
12.15 µm.
[42] Further, the optical fiber 200 may have a chromatic dispersion of less than
or equal to 23.5 picoseconds per nano meter wavelength change and kilometre
propagation distance (ps/(Km.nm) at a wavelength of 1550 nanometres (nm). In
some aspects of the present disclosure, the chromatic dispersion of the optical
fiber 200 may specifically be 17.73 ps/(Km.nm) at the wavelength of 1550 nm.
[43] Furthermore, the optical fiber 200 may have a chromatic dispersion slope
of less than or equal to 0.07 ps/(Km.nm2). Preferably, the chromatic dispersion
slope of the optical fiber 200 may be 0.065 ps/(Km.nm2).
[44] Furthermore, the optical fiber 200 may have a macro bend loss of less than
or equal to 10 dB/Km at a bend radius 30 mm and wavelength of 1550 nm.
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Preferably, the macro bend loss for the optical fiber 200 may be 4.17dB/Km at the
bend radius 30 mm and the wavelength of 1550 nm. Specifically, low macro bend
loss (i.e., 4.17 dB per Km at 30 mm bend radius) may provide high confinement
of mode filed in the core 202.
[45] Furthermore, the optical fiber 200 may have a cutoff wavelength of less
than or equal to 1530 nm. In some aspects of the present disclosure, the cutoff
wavelength of the optical fiber 200 may specifically be 1516 nm.
[46] The core 202 may have at least 83 mole percent (mol%) of Silicon dioxide
(SiO2) and at most 17 mol% of at least one up dopant. In an aspect of the present
disclosure, the at least one up dopant of the core 202 may be Germanium (Ge)
such that the core 202 may have at least 83 mol% of SiO2 and at most 17 mol% of
Ge. In some aspects of the present disclosure, the at least one up dopant may be in
the form of Germanium Dioxide (GeO2). In an aspect of the present disclosure,
the concentration of GeO2 may be expressed in terms of the refractive index as
?? = 529. 329 1 - (??????)2
( ??1)2
???
???
where,
C is the GeO2 concentration in mol%,
Nsi is refractive index of cladding 204 (pure silica),
N1 (i.e., refractive index of the core 202)
[47] The optical fiber 200 having SiO2 up doped with GeO2 may result in a
higher refractive index difference in the core 202 of the optical fiber 200.
Specifically, GeO2 is a glass network former material and thus forms natural glass
and having GeO2 as up dopant may result in increased effective area. Specifically,
a low effective area of the optical fiber 200 may increase nonlinear effects (that
may generate spurious signals and increase noise) in the optical fiber 200. Thus,
the high effective area may result in low noise in a signal and minimum spurious
signal. Aspects of the present disclosure are intended to include and/or otherwise
cover any type of the up dopant for the core 202, including known, related, and
later developed materials (similar to Ge and GeO2) that may facilitate to achieve
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high effective area of the optical fiber 200, and thus must not be considered as a
limitation to the present disclosure.
[48] The core 202 may have a core radius R1. The core radius R1 may be in a
range of 4.45 µm to 15 µm. Preferably, the core radius R1 may be 4.5 µm. The
core 202 may further have a first refractive index N1 and a first relative refractive
index ?1. In some aspects of the present disclosure, the first refractive index N1
may have a maximum value N1max (i.e., a peak refractive index of the core 202)
that may be in a range of 1.447 to 1.47. Preferably, the maximum value of the first
refractive index N1max may be 1.4495. In some aspects of the present disclosure,
the first relative refractive index ?1 may have a maximum value ?1max (i.e., a
peak relative refractive index of the core 202) (as shown in FIG. 3) that may be in
a range of 2.05 x 10-3 to 17.5 x 10-3. Preferably, the maximum value of the first
relative refractive index ?1max may be 3.77 x 10-3. In an aspect of the present
disclosure, a region of the core 202 having the maximum relative refractive index
?1max may have a doping concentration of the up dopant in a range of 2-17 mol%.
Preferably, the doping concentration in the region of the core 202 having the
maximum relative refractive index ?1max may be 3.7 mol%.
[49] In some aspects of the present disclosure, the core radius R1 may be
segmented into a first segment S1 and a second segment S2. The core 202 may
have an exponentially increasing refractive index in the first segment S1 and an
exponentially decaying refractive index in the second segment S2.
[50] The cladding 204 may concentrically surround the core 202 such that the
cladding 204 has at least 99 mol% of Silicon dioxide (SiO2) and less than 1 mol%
of metallic impurity. In some aspects of the present disclosure, the cladding 204
may be undoped and/or unintentionally doped and may be made up of 100% pure
silica. The cladding 204 may have a cladding radius R2. The cladding 204 may
further have a second refractive index N2 and a second relative refractive index
?2. In some aspects of the present disclosure, the second refractive index N2 may
be in a range of 1.444 and 1.44404. Preferably, the second refractive index N2
may be 1.44402. In some aspects of the present disclosure, the second relative
refractive index ?2 may be in a range of 0 to 1.3 x 10-5. Preferably, the second
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relative refractive index ?2 may be 0. The relative refractive index ?i of an ith
region such as i=1 for core 202 and i=2 for cladding 204 of the optical fiber 200
may be determined as:
??? = (????)2-(??????)2
2(????)2
where
Ni is refractive index of ith region, and
Nsi is refractive index of pure silica.
[51] FIG. 3 illustrates a graph 300 that represents a refractive index (RI) profile
of the optical fiber 200 of FIG. 2. The graph 300 is a radius versus relative
refractive index graph such that an x-axis of the graph 300 represents a radial
distance from the central axis 206 and a y-axis of the graph 300 represents a
variation in the relative refractive indexes of the optical fiber 200. The graph 300
includes a reference line 304 that is pure silica, and a refractive index of the pure
silica may be 1.44402. As discussed, the optical fiber 200 may have the core 202
segmented into the first segment S1 and the second segment S2. The first
segment S1 may extend from the central axis 206 to a first radial distance ‘a’. The
core 202 adjacent to the central axis 206 may have the first refractive index value
of N(0) and a relative refractive index (?dip) at the central axis 206. In other
words, the core 202 may have a centerline dip adjacent to the central axis 206. In
some aspects the refractive index value at the centerline dip may be in a range of
1.44402 to 1.449. In some aspects of the present disclosure, the normalized
refractive index difference (?dip) may be dependent on the refractive index value
N(0) adjacent to the central axis 206 and the maximum value of the first refractive
index N1max. In an exemplary aspect of the present disclosure, the value of ?dip
may be determined as:
??????? = (??1??????)2-(??(0))2
2(??1??????)2 .
[52] The first segment S1 may further have the exponentially increasing
refractive index from the central axis 206 to the first radial distance ‘a’. In some
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aspects of the present disclosure, the refractive index in the first segment S1 may
be dependent on the maximum value of refractive index N1max, the normalized
refractive index difference (?dip) at the central axis 206, a radial distance ‘x1’,
the first radial distance ‘a’ and a slope variation ‘a’ (alpha). In an exemplary
aspect of the present disclosure the refractive index at a point ‘x1’ in the first
segment S1 of the core 202 can be determined as:
??(??1) = ??1?????? 1 - 2??????? 1 - ??1 .
?? ( )a
[53] In some aspects of the present disclosure, ‘a’ (alpha) may be defined as a
variation of slope in the refractive index (RI) profile of the core 202 from the
central axis 206 to the first radial distance ‘a’ (i.e., x1= 0 to x1= a). The value of
the slope variation ‘a’ (alpha) may be in a range of 0.1 to 20. Preferably, the value
of the slope variation ‘a’ (alpha) may be 3.5.
[54] In some aspects of the present disclosure, the first segment S1 may have a
normalized refractive index difference in a range of 0.0006 to 0.018. Preferably,
the relative refractive index in the first segment S1 may be 0.00427.
[55] The second segment S2 may extend from the first radial distance ‘a’ to a
second radial distance ‘a+b’ from the central axis 206. The second segment S2
may have the exponentially decaying refractive index from the first radial distance
‘a’ to the second radial distance ‘a+b’. In an exemplary aspect of the present
disclosure, the refractive index ‘N(x2)’ at any point ‘x2’ in the second segment S2
of the core 202 (i.e., the exponentially decaying refractive index between the first
radial distance ‘a’ and the second radial distance ‘a+b’) can be determined as:
??(??2) = [??(??) - ??(??)] ??
??-1 ( ) exp ?????? -(??+??)
?? ( ) + ?? ??(??)-??(??)
??-1 .
where
‘a’ is the first radial distance,
N(a) is refractive index of the core at the first radial distance ‘a’ that is equal to
the maximum refractive index N1max of the core 202,
‘e’ is an exponential constant equal to a value 2.71828, and
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‘w’ is a radial distance from the central axis 206 where the refractive index N(w)=
N1max/e.
[56] In some aspects of the present disclosure, the optical fiber 200 may have a
smooth core-cladding interface 302 at the second radial distance ‘a+b’ from the
central axis 206. The refractive index at the core-cladding interface 302 may be in
a range of 1.444 to 1.44404 at a wavelength of 1550 nm. Preferably, the refractive
index at the core-cladding interface 302 may be 1.44402. The cladding 204 may
have a constant relative refractive index value ?2 from the second radial distance
‘a+b’ to the cladding radius R2 of the cladding 204. In some aspects of the present
disclosure, the second radial distance ‘a+b’ may be equal to the core radius R1 of
the core 202. The relative refractive index ?2 of the cladding 204 may be in a
range of 0 to 1.3 x 10-5 at a wavelength of 1550 nm. Preferably, the relative
refractive index ?2 of the cladding 204 may be 0. The RI profile of the optical
fiber 200 is illustrated by way of a first half portion of the RI profile of the optical
fiber 200, however, it will be apparent to a person skilled in the art that the other
half of the RI profile of the optical fiber 200 also possesses same structural and
functional characteristics, and thus must not be considered as a limitation of the
present disclosure.
[57] FIG. 4 illustrates a graphical relation 400 of the RI profile with different
regions of the optical fiber 200. The graph 400 is a radial distance versus
refractive index graph of the optical fiber 200. The x-axis of the graph 400
represents values of the radial distance from the central axis 206, and the y-axis
represents the value of the refractive index of the optical fiber 200. In some
aspects of the present disclosure, the first relative refractive index ?1 may have
the maximum value ?1max (i.e., a peak refractive index of core 202) in the range of
2.05 x 10-3 to 17.5 x 10-3. Preferably, the maximum value of the first relative
refractive index ?1max may be 3.77 x 10-3. In an aspect of the present disclosure,
the region of the core 202 having the maximum relative refractive index ?1max
may have a doping concentration in a range of 2-17 mol%. Preferably, the doping
concentration in the region of the core 202 having the maximum relative
refractive index ?1max may be 3.7 mol%.
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[58] The core 202 may have the centerline dip at the central axis 206. In some
aspects of the present disclosure, the first refractive index at the centerline dip
(i.e., at the central axis 206) may have a refractive index value of N(0) that may
be in a range of 1.44402 to 1.449. In some aspects of the present disclosure, the
first segment S1 may extend from the central axis 206 to a first radial distance ‘a’
from the central axis 206. In some aspects of the present disclosure, the first
segment S1 may have a thickness value in a range of 0.05 to 1 micrometre (µm).
Preferably, the thickness value of the first segment S1 (i.e., ‘a’) may be 0.69 µm.
In some aspects of the present disclosure, the first segment S1 may have the
exponentially increasing refractive index from the central axis 206 to the first
radial distance ‘a’.
[59] The second segment S2 may extend from the first radial distance ‘a’ to the
second radial distance ‘b’. The second segment S2 may have a thickness value ‘b’
in a range of 4.4 to 14 µm. Preferably, the thickness value ‘b’ of the second
segment S2 may be 8.625 µm.
[60] In some aspects of the present disclosure, the radius R1 of the core 202
may be in the range of 4.45 to 15 µm. In some aspects of the present disclosure, a
ratio of the thickness of the second segment S2 (i.e., ‘b’) to the thickness of the
first segment S1 (i.e., ‘a’) may be in the range of 4.4 to 280. Preferably, the ratio
of ‘b/a’ may be 12.5. High ratio of b/a may help in exponential decrease in the
refractive index over a long radial distance, which may makes a manufacturing
process of the optical fiber 200 easy. The refractive index in the second segment
S2 of the core 202 may be exponentially decaying.
[61] The core-cladding interface 302 may lie at the end of the second segment
S2 of the core 202 and may have a refractive index ‘Nint’ value that may be in a
range of 1.444 and 1.44404 and a relative refractive index ?int may be in range of
0 to 1.3 x 10-5. Preferably, the refractive index value ‘Nint’ for the core-cladding
interface 302 may be 1.44402 and the relative refractive index ?int may be 0.
[62] In some aspects of the present disclosure, the cladding 204 may have a
thickness 402 (i.e., R2-R1) in a range of 47.5 to 58.05 µm. The cladding 204 may
further have a cladding radius R2. In some aspects of the present disclosure, the
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cladding radius R2 may be in the range of 51.95 to 63.05 µm. Furthermore, the
cladding 204 may have the second relative refractive index ?2 between the core
radius R1 and the cladding radius R2. In some aspects of the present disclosure,
the second relative refractive index ?2 may lie between 0 to 1.3 x 10-5. Preferably,
the second relative refractive index may be 0.
[63] FIG. 5 illustrates a graph 500 that represents an effect of the slope
variation ‘a’ (alpha) in the first segment S1 of the core 202 of the optical fiber 200
on a mode field diameter (MFD) and an effective area of the optical fiber 200.
The graph 500 is an ‘a’ (alpha) value versus MFD, and ‘a’ (alpha) value versus
the effective area graph. The x-axis of the graph 500 represents values of the
variation of slope ‘a’(alpha), and a first y-axis represents the value of MFD of the
optical fiber 200, whereas a second y-axis represents the value of the effective
area of the optical fiber 200. A variation in the value of the MFD with respect to
change in the variation of slope ‘a’ is represented as 502. A variation in the value
of the effective area with respect to change in the variation of slope‘a’ (alpha) is
represented as 504. In some aspects of the present disclosure, increasing the
variation of slope‘a’ decreases the MFD and the effective area of the optical fiber
200.
[64] FIG. 6 illustrates a graph 600 that represents an effect of a slope variation
‘a’ (alpha) in the first segment of the optical fiber 200 on a value of the chromatic
dispersion at the wavelength of 1550 nm. The graph 600 is an ‘a’ (alpha) value
versus dispersion value graph such that the x-axis of the graph 600 represents
values of the variation of slope ‘a’ (alpha), and the y-axis represents the value of
dispersion at 1550 nm wavelength. In some aspects of the present disclosure, the
variation of a material dispersion with respect to change in the ‘a’ (alpha) value is
represented as 602. The variation of a total dispersion with respect to change in
the ‘a’ (alpha) value is represented as 604. The variation of a waveguide
dispersion with respect to change in the ‘a’ (alpha) value is represented as 606. In
some aspects of the present disclosure, increasing the value of the variation of
slope ‘a’ (alpha) may decrease the dispersion at the wavelength of 1550nm. In
some aspects of the present disclosure, the value of ‘a’ (alpha) may be in a range
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of 0.1 to 20. In some aspects of the present disclosure, the value of ‘a’ (alpha)
equals to zero may represent a condition where dip may have a vertical fall from
‘?1max’ to ‘?(0)’ at the central axis 206.
[65] FIG. 7 illustrates a graph 700 that illustrates a confinement value versus
the mode field value of the core 202 of the optical fiber 200 for the fundamental
mode (LP01) at the wavelength of 1550 nm. The graph 700 is radial distance from
the central axis 206 versus MFD graph such that the x-axis of the graph 700
represents values of radial distance from the central axis 206, and the y-axis
represents the value of MFD of the core 202 of the optical fiber 200 for the
fundamental mode (LP01) at the wavelength of 1550 nm. In some aspects of the
present disclosure, the MFD of the optical fiber 200 for the fundamental mode
(LP01) at the wavelength of 1550 nm is shown as 702. A confinement region for
the optical fiber 200 is shown as 704. The MFD of the optical fiber 200 for the
fundamental mode (LP01) at the wavelength of 1550 nm may have higher
confinement as compared to the MFD of the step-index fiber (prior art) as shown
in FIG. 1A. In one aspect of the present disclosure, high relative refractive index
may increase the confinement region of the fundamental mode field in the optical
fiber and may increase the optical cutoff wavelength and may reduce the bending
loss. In another aspect of the present disclosure, high relative refractive index may
increase a Rayleigh scattering of light in the optical fiber 200, which may result in
an increase in the attenuation at the wavelength of 1550 nm.
[66] FIG. 8 illustrates a graphical variation 800 of a mode field intensity value
of the optical fiber 200. In some aspects of the present disclosure, the mode field
intensity of the optical fiber 200 for the fundamental mode (LP01) at the
wavelength of 1550 nm may be highly confined in the second segment S2 (i.e.,
the exponentially decaying refractive index profile of the core 202) as compared
to the variation of the mode field intensity for the fundamental mode (LP01) at the
wavelength of 1550 nm of the step-index fiber (prior art) as shown in FIG. 1B.
[67] Thus, the optical fiber 200 of the present disclosure may provide a higher
confinement of mode field inside the core 202, thereby may increase the effective
area and may reduce nonlinear effects of the optical fiber 200 (i.e., less spurious
16/21
signals and low noise). In some aspects of the present disclosure, the undoped or
unintentionally doped cladding 204 may result in reduced manufacturing cost of
the optical fiber 200 as the cost of fluorination may be reduced for the optical
fiber 200.
[68] 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.
[69] , Claims:CLAIMS
I/We Claim:
1. An optical fiber (200) comprising:
a core (202) having at least 83 mole percent (mol%) of Silicon dioxide
(SiO2), wherein the core (202) has at least one up dopant;
a cladding (204) that concentrically surrounds the core (102), wherein
the cladding (204) has at least 99 mole percent (mol%) of Silicon dioxide
(SiO2);
wherein, the optical fiber (200) has (i) an effective area is greater than
or equal to 100 micrometers square (µm2), (ii) a mode field diameter
(MFD) in a range of 11 micrometer (µm) to 15 µm, and (iii) a chromatic
dispersion of less than or equal to 23.5 Picoseconds per nanometer
wavelength change and kilometer propagation distance (ps/(Km.nm) at a
wavelength of 1550 nm.
2. The optical fiber (200) as claimed in claim 1, wherein the at least one up
dopant is Germanium (Ge).
3. The optical fiber (200) as claimed in claim 1, wherein the core (202) and
the cladding (204) interfaces at a core-cladding interface (302) such that a
concentration of the up dopant at the core-cladding interface (302) is less
than 17 mol%.
4. The optical fiber (200) as claimed in claim 1, wherein the cladding (204)
is made up of pure silica with less than 1% metallic impurity.
5. The optical fiber (200) as claimed in claim 1, wherein (i) the core (202)
has a core radius (R1) that is in a range of 4.45 µm to 15 µm and (ii) the
cladding (204) has a cladding thickness (402) that is in a range of 47.5 µm
to 58.05 µm.
6. The optical fiber (200) as claimed in claim 1, wherein (i) the core (202)
has a maximum relative refractive index (?1max) in a range of 2.05 x 10-3
to 17.5 x 10-3, (ii) the cladding (204) has a relative refractive index (?2) in
a range of 0 to 1.3 x 10-5, and (iii) the core-cladding interface (302) has a
relative refractive index (?int) in a range of 0 to 1.3 x 10-5.
7. The optical fiber (200) as claimed in claim 1, wherein (i) a chromatic
dispersion value of the optical fiber (200) is 20.87 ps/Km.nm at a
wavelength of 1600 nano meter (nm) and (ii) the chromatic dispersion
value is 14.39 ps/Km.nm at a wavelength of 1500 nm.
8. The optical fiber (200) as claimed in claim 1, wherein (i) a cutoff
wavelength of the optical fiber (200) is less than or equal to 1530 nm and
(ii) a macro bend loss of the optical fiber (200) is less than or equal to 10
dB/KM at a bend radius 30 mm and a wavelength of 1550 nm.
9. The optical fiber (200) as claimed in claim 1, wherein the core (202)
extends substantially parallel and along a central axis (206) of the optical
fiber (200), wherein the core (202) has a refractive index (RI) profile that
is defined by a centerline dip at the central axis (206) such that a
refractive index at the centerline dip is in a range of 1.44402 to 1.449.
10. The optical fiber (200) as claimed in claim 1, wherein the refractive index
(RI) profile of the core (202) is an exponential decay refractive index
profile which is determined by an equation:
??(??2) = [??(??) - ??(??)] ??
??-1 ( ) exp ?????? -(??+??)
?? ( ) + ?? ??(??)-??(??)
??-1 .
where x2 is a radial distance from the center axis 206 between a first
radial distance ‘a’ and a second radial distance ‘a+b’ of the core 202;
N(a) is refractive index of the core at the first radial distance ‘a’ that is
equal to the maximum refractive index N1max of the core 202;
‘e’ are exponential constant equal to a value 2.71828; and
‘w’ is a radial distance from the central axis 206 where the refractive
index N(w)= N1max/e.