U.S. patent application number 10/689636 was filed with the patent office on 2004-11-11 for optical fiber and optical transmission line.
Invention is credited to Kawasaki, Mitsuhiro, Oonuma, Hiroaki, Uchida, Yohei.
Application Number | 20040223714 10/689636 |
Document ID | / |
Family ID | 18903230 |
Filed Date | 2004-11-11 |
United States Patent
Application |
20040223714 |
Kind Code |
A1 |
Kawasaki, Mitsuhiro ; et
al. |
November 11, 2004 |
Optical fiber and optical transmission line
Abstract
The optical fiber includes a center core portion, a side core
portion and clad portion, which has a dispersion value of 14-20
ps/nm/km at a wavelength of 1550 nm, a dispersion slope of
0.05-0.08 ps/nm.sup.2/km at a wavelength of 1550 nm and a
transmission attenuation of 0.2 dB/km or less at a wavelength of
1550 nm, wherein the relative refractive index difference .DELTA.1
between the center core portion and the clad portion is 0.25-0.50%,
the relative refractive index difference .DELTA.2 between the side
core portion and the clad portion is 0.05-0.30%, an inequality
.DELTA.2 <.DELTA.1 is satisfied, the ratio a/b between an outer
diameter a of the center core portion and an outer diameter b of
the side core portion is 0.3-0.7, and the effective core area Aeff
at a wavelength of 1550 nm is 90 .mu.m.sup.2 or larger.
Inventors: |
Kawasaki, Mitsuhiro;
(Chiyoda-Ku, JP) ; Uchida, Yohei; (Chiyoda-Ku,
JP) ; Oonuma, Hiroaki; (Chiyoda-ku, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
18903230 |
Appl. No.: |
10/689636 |
Filed: |
October 22, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10689636 |
Oct 22, 2003 |
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10072996 |
Feb 12, 2002 |
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6665482 |
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Current U.S.
Class: |
385/123 |
Current CPC
Class: |
G02B 6/0286 20130101;
G02B 6/02019 20130101; G02B 6/02266 20130101; G02B 6/03633
20130101; G02B 6/02271 20130101; G02B 6/0228 20130101 |
Class at
Publication: |
385/123 |
International
Class: |
G02B 006/16 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2001 |
JP |
2001-040663 |
Claims
1-4. (Canceled)
5. An optical fiber which has a dispersion value of 14 ps/nm/km or
higher and 20 ps/nm/km or less at a wavelength of 1550 nm, a
positive dispersion slope of 0.05 ps/nm.sup.2/km or higher and 0.08
ps/nm.sup.2/km or less at a wavelength of 1550 nm, a transmission
attenuation of 0.2 dB/km or less at a wavelength of 1550 nm, and an
effective core area Aeff of 90 .mu.m.sup.2 or larger at a
wavelength of 1550 nm.
6. The optical fiber according to claim 5, wherein the effective
core Aeff at a wavelength of 1550 nm is 100 .mu.m.sup.2 or
larger.
7. The optical fiber according to claim 5, further comprising a
center core portion, a side core portion and clad portion in order
from an inner side, wherein a relative refractive index difference
.DELTA.1 of the center core portion with respect to the clad
portion is positive, a relative refractive index difference
.DELTA.2 of the side core portion with respect to the clad portion
is positive, and an inequality .DELTA.1>.DELTA.2 is
satisfied.
8. The optical fiber according to claim 6, further comprising a
center core portion, a side core portion and clad portion in order
from an inner side, wherein a relative refractive index difference
Al of the center core portion with respect to the clad portion is
positive, a relative refractive index difference .DELTA.2 of the
side core portion with respect to the clad portion is positive, and
an inequality .DELTA.1>.DELTA.2 is satisfied.
9. An optical transmission line comprising: a plurality of optical
fibers, each of which configured to transmit an optical signal,
wherein at least one of said plurality of optical fibers has a
dispersion value of 14 ps/nm/km or higher and 20 ps/nm/km or less
at a wavelength of 1550 nm, a positive dispersion slope of 0.05
ps/nm.sup.2/km or higher and 0.08 ps/nm.sup.2/km or less at a
wavelength of 1550 nm, a transmission attenuation of 0.2 dB/km or
less at a wavelength of 1550 nm, and an effective core area Aeff of
90 .mu.m.sup.2 or larger at a wavelength of 1550 nm.
10. An optical transmission line of claim 9, wherein the effective
core Aeff of said at least one of the plurality of optical fibers
at a wavelength of 1550 nm is 100 .mu.m.sup.2 or larger.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2001-040663, filed Feb. 16, 2001, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an optical fiber and an
optical transmission line used suitably in a wavelength division
multiplexing (WDM) optical communications.
[0004] 2. Description of the Related Art
[0005] As a technique for increasing the transmission capacity in
the optical transmission using optical fibers, the WDM (wavelength
division multiplexing) optical transmission has become a focus of
attention recently, and many intensive studies have been conducted
on optical fibers which are employed suitable in the WDM optical
transmission.
[0006] Incidentally, well-known examples of the optical fiber which
can be used for the WDM optical transmission are a single mode
optical fiber (SMF) having a zero dispersion near a wavelength of
1.3 .mu.m and a dispersion shift type optical fiber which does not
have a zero dispersion in a wavelength band in use (NZDSF); however
these types of optical fibers have a problem of non-linearity.
Under these circumferences, there is a demand of developing a new
type of optical fiber.
[0007] More specifically, in order to solve the problem of
non-linearity, an optical fiber has been developed, in which the
dispersion value is set fully away from zero and the effective core
area Aeff is enlarged. Examples of such an optical fiber is
discussed in Collection of Lecture Notes C-3-76 and C-3-77 for the
Electronics Society Convention 1999 held by the Institute of
Electronics, Information and Communication Engineers.
[0008] However, those types of optical fibers discussed in Lecture
Notes C-3-76 and C-3-77, each exhibits a dispersion value of more
than 20 ps/nm/km, and therefore the cumulative amount of
dispersions of fibers when an optical transmission line is formed
of these fibers, increases. With such an increased amount of
dispersion, the transmission line cannot be appropriately used for
a long-distance WDM optical transmission.
BRIEF SUMMARY OF THE INVENTION
[0009] An object of the present invention is to provide an optical
fiber which has a dispersion value maintained at a similar level to
that of the conventional SMF and is more suitable for the WDM
optical transmission than-the conventional SMF.
[0010] Another object of the present invention is to provide an
optical transmission line comprising the above-described optical
fiber, which is suitable for the WDM optical transmission.
[0011] According to an embodiment of the present invention, there
is provided an optical fiber comprising a center core portion, a
side core portion and a clad portion in an order from an inner
side, which has a dispersion value of 14 ps/nm/km or higher and 20
ps/nm/km or less at a wavelength of 1550 nm, a dispersion slope of
0.05 ps/nm.sup.2/km or higher and 0.08 ps/nm.sup.2/km or less at a
wavelength of 1550 nm and a transmission attenuation of 0.2 dB/km
or less at a wavelength of 1550 nm, wherein a relative refractive
index difference .DELTA.1 between the center core portion and the
clad portion is 0.25% or larger and 0.50% or less, a relative
refractive index difference .DELTA.2 between the side core portion
and the clad portion is 0.05% or larger and 0.30% or less, an
inequality .DELTA.2<.DELTA.1 is satisfied, a ratio a/b between
an outer diameter a of the center core portion and an outer
diameter b of the side core portion is 0.3 or higher and 0.7 or
less, and an effective core area Aeff at a wavelength of 1550 nm is
90 .mu.m.sup.2 or larger.
[0012] According to another embodiment of the present invention,
there is provided an optical transmission line comprising a
plurality of optical fibers, configured to transmit optical
signals, wherein at least one of the plurality of optical fibers is
the above-described optical fiber.
[0013] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be leaned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0014] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the invention, and together with the general description given
above and the detailed description of the embodiments given below,
serve to explain the principles of the invention.
[0015] FIG. 1 is a diagram schematically showing an example of the
refractive index profile of an optical fiber according to an
embodiment of the present invention; and
[0016] FIG. 2 is a diagram schematically showing an optical
transmission system comprising an optical fiber according to the
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Specific embodiments of the present invent-ion will now be
described with reference to accompanying drawings.
[0018] FIG. 1 is a diagram schematically showing an example of the
refractive index profile of an optical fiber according to an
embodiment of the present invention. FIG. 1 illustrates a
refractive index profile 1 of a center core portion having an outer
diameter a, a refractive index profile 2 of a side core portion
having an outer diameter b, and a refractive index profile 3 of a
clad portion.
[0019] As can be seen in FIG. 1, there is a maximum relative
refractive index difference .DELTA.1 between the center core
portion 1 and the clad portion 3 and there is a relative refractive
index difference .DELTA.2 between the side core portion 2 and the
clad portion 3.
[0020] It should be noted here that with regard to the optical
fiber according to the embodiment, the relative refractive index
difference .DELTA.2 between the side core portion 2 and the clad
portion 3 is defined as follows.
[0021] That is:
[0022] (1) In the case where there is no local maximum point of the
refractive index in the side core portion 2, the relative
refractive index difference .DELTA.2 is taken by the value where
the slope of the refractive index profile curve is at minimum.
[0023] (2) In the case where there is a local maximum point of the
refractive index in the side core portion 2, the relative
refractive index difference .DELTA.2 is taken by the value of the
relative refractive index difference between the local maximum
point of the refractive index in the side core portion and the clad
portion 3. Or in the case where there are a plurality of local
maximum points of the refractive index, it is taken by the value of
the relative refractive index difference between the maximum value
of the local maximum points of the refractive index in the side
core portion 2 and the clad portion 3. It should be noted here that
there is a local minimum point when there is a local maximum point
of the refractive index in the side core portion 2. Here, when the
local minimum value of the relative refractive index differences
(that is, the local minimum values of the refractive index) between
the side core portion 2 and the clad portion 3 is 0.5 times or more
as large as .DELTA.2, the side core portion 2 is formed as one
region.
[0024] Further, the border between the center core portion 1 and
the side core portion 2 is defined at a point where when the curve
of the refractive index profile of the center core portion 1 is
approximated by an .alpha. curve, the .alpha. curve crosses with
the line of the relative refractive index difference being zero. It
should be noted that the .alpha. curve can be expressed by the
following formula:
.DELTA.n(r)=.DELTA.n(0).multidot.{1-(2r/a).alpha.}
[0025] where .DELTA.n(r) represents the relative refractive index
difference at a distance "r" from the center, .DELTA.n(0)
represents the maximum relative refractive index difference, "a"
represents the outer diameter of the center core portion and "r"
represents the distance from the center.
[0026] Further, the border between the side core portion and the
clad portion is defined at a point where the relative refractive
index difference becomes {fraction (1/10)} of the relative
refractive index difference .DELTA.2 between the side core portion
and the clad portion, and a line extending in the direction where
the relative refractive index difference changes crosses with the
line of the relative refractive index difference being zero.
[0027] In the refractive index profile of the optical fiber
according to the embodiment shown in FIG. 1, the relative
refractive index difference .DELTA.1 between the center core
portion and the clad portion is 0.25% to 0.50%, and more
preferably, it should be in a range of 0.33% to 0.40%. If the
relative refractive index difference .DELTA.1 is less than 0.25%,
the dispersion value rises to 20 ps/nm/km or more, whereas if it
exceeds 0.50%, Aeff drops to 90 .mu.m.sup.2 or less, which is not
preferable.
[0028] The relative refractive index difference .DELTA.2 between
the side-core portion-and the clad portion is 0.05% to 0.30%, and
more preferably, it should be in a range of 0.15% to 0.20%. If the
relative refractive index difference .DELTA.2 is less than 0.05%,
bending attenuation becomes large, whereas if it exceeds 0.30%,
cut-off wavelength exceeds 1550 nm, which is not preferable.
[0029] The relationship between .DELTA.1 and .DELTA.2 should be
.DELTA.2<.DELTA.1 and if .DELTA.2.gtoreq..DELTA.1, desired
properties are not obtained, which is not preferable.
[0030] In the optical fiber having a refractive index profile as
described above, the ratio a/b between the outer diameter a of the
center core portion and the outer diameter "b" of the side core
portion should be in a range of 0.3 to 0.7, and more preferably it
should be in range of 0.4 to 0.6. If the a/b ratio is less than
0.3, cut-off wavelength becomes large, whereas if it exceeds 0.7,
bending attenuation becomes large, which is not preferable.
[0031] The effective core area Aeff at a wavelength of 1550 nm
should be 90 .mu.m.sup.2 or more, and more preferably it should be
100 .mu.m.sup.2 or more. If the effective core area Aeff at a
wavelength of 1550 nm is less than 90 .mu.m.sup.2, non-linear
effect becomes prominent.
[0032] In the optical fiber according to the embodiment described
above, the dispersion value at a wavelength of 1550 nm should be in
a range of 14 ps/nm/km to 20 ps/nm/km, and more preferably it
should be in a range of 14 ps/nm/km to 16 ps/nm/km. If it is tried
to attain the dispersion value less than 14 ps/nm/km at a
wavelength of 1550 nm, refractive index profile becomes complicate
and productivity becomes worse, whereas if it exceeds 20 ps/nm/km,
waveform is distorted, which is not preferable.
[0033] The dispersion slope at a wavelength of 1550 nm should be in
a range of 0.05 ps/nm.sup.2/km to 0.08 ps/nm.sup.2/km, and more
preferably it should be in a range of 0.05 ps/nm.sup.2/km to 0.07
ps/nm.sup.2/km. If it is tried to attain the dispersion slope less
than 0.05 ps/nm.sup.2/km at a wavelength of 1550 nm, refractive
index profile becomes complicate and productivity becomes worse,
whereas if it exceeds 0.08 ps/nm.sup.2/km, transmission wavelength
intervals must be widened, which is not preferable.
[0034] The transmission attenuation at a wavelength of 1550 nm
should be 0.2 dB/km or less, and more preferably it should be 0.19
dB/km or less. If the transmission attenuation at a wavelength of
1550 nm exceeds 0.2 dB/km, distance between amplifiers becomes
short, which is not preferable.
[0035] In order to achieve an optical fiber suitable for WDM
optical transmission, it is necessary that the waveform distortion
due to the four wave mixing should be suppressed, the distortion of
the waveform due to the self phase modulation/cross-phase
modulation should be suppressed and the distortion of the waveform
due to dispersion should be suppressed.
[0036] The optical fiber according to the embodiment, which
satisfies the above-described conditions, meets the above-described
requirement and it is very much suitable for the WDM optical
transmission. With use of the optical fiber, it is possible to
obtain an optical transmission line suitable for the WDM optical
transmission.
[0037] FIG. 2 is a diagram illustrating an optical transmission
system including an optical transmission line with the optical
fiber according to the embodiment of the present invention. FIG. 2
shows an optical transmitter 11, optical amplifiers 12a, 12b, . . .
, positive dispersion optical fibers 13a, 13b, . . . , negative
dispersion optical fibers 14a, 14b, . . . , such as DCFs, and an
optical receiver 15.
[0038] The structure itself of the system shown in FIG. 2 is
similar to that of the conventional system; however, a part of the
system, specifically, optical fibers 13a, 13b, . . . , are of the
fibers according to the embodiment of the present invention. With
this structure, it becomes possible to remarkably improve the
transmission properties. And then, it is possible to obtain an
optical transmission line suitable for the WDM optical
transmission.
[0039] Examples of the present invention will now be presented, and
the invention will be explained in more detail.
EXAMPLES
[0040] The optical fiber having the refractive index profile shown
in FIG. 1, was examined in terms of the change in properties at a
wavelength of 1550 nm, when the parameters (.DELTA.1, .DELTA.2,
a/b) were varied. It should be noted that the refractive index of
the center core portion 1 was set such that it could be
approximated with a curve of .alpha.=2 and the side core portion
had no maximum points of the refractive index.
[0041] The outer diameter "b" of the side core portion 2 can be set
in a range of 10 to 40 .mu.m, and preferably it should be in a
range of 18 to 30 .mu.m. In this embodiment, the outer diameter "b"
of the side core portion 2 was set to an optimal value within a
range of 18 to 30 .mu.m. It should be noted that the outer diameter
"a" of the center core portion should preferably be in a range of 8
to 12 .mu.m.
[0042] The results of the examination are presented in TABLE 1
below. In TABLE 1, the units for the values of .DELTA.1 and
.DELTA.2 are in %, the unit for the dispersion value is in
ps/nm/km, the unit for the dispersion slope is in ps/nm.sup.2/km,
the unit for the transmission attenuation is in dB/km, the unit for
Aeff is in .mu.m.sup.2. For reference, a cutoff wavelength
.lambda.c (unit in nm) is presented as well in the table.
1 TABLE 1 Dispersion Dispersion Transmission .DELTA. 1 .DELTA. 2
a/b value slope attenuation Aeff .lambda.c Example 0.37 0.07 0.50
17.1 0.063 0.186 102 1320 1 Example 0.36 0.05 0.43 17.0 0.062 0.184
97 1260 2 Example 0.38 0.10 0.57 16.9 0.064 0.190 103 1460 3
Comparative 0.26 0.00 -- 21.9 0.068 0.195 133 1580 Example
[0043] As can be understood from TABLE 1 above, the optical fibers
of Examples 1 to 3 each have a refractive index profile which is
within the range defined by the present invention, and therefore
they have the properties (the dispersion value is 20 ps/nm/km or
less) suitable for the WDM optical transmission. By contrast, the
optical fiber according to the comparative example has a refractive
index profile which is out of the range defined by the present
invention, and therefore its dispersion value exceeds 20 ps/nm/km.
Further, its cutoff wavelength shifts to long wavelength side.
Therefore, it is not suitable for the WDM optical transmission at a
wavelength of near 1550 nm.
[0044] In the meantime, an optical transmission line was made of
optical fibers according to Example 1 and line-type dispersion
compensation optical fibers having such a length at which the
dispersion can be substantially perfectly compensated. Of the
optical fibers according to Examples 2 and 3 as well as that of
Comparative Example, similar optical transmission lines were built.
Then, the transmission test was carried out on these lines under
conditions that an optical signal having 10 Gbps per wave was used
as the WDM optical signal and 16 waves were arranged at the same
intervals in a range of 1530 to 1560 nm in wavelength.
[0045] As a result, it was found that the optical transmission
lines which were made of the optical fibers according to Examples 1
to 3 exhibited properties such as bit error rate of 10.sup.-9 or
less, which are suitable for the WDM optical transmission, whereas
the optical transmission line made of the optical fiber according
to the Comparative Example exhibited bit error rate exceeding
10.sup.-9 and did not show suitable properties for the WDM optical
transmission.
[0046] It should be noted here that the optical transmission line
of the present invention is not limited to that discussed above,
but can be remodeled into various versions. For example, the
optical transmission line can be made of a dispersion compensation
type fiber module in place of the line-type dispersion compensation
optical fiber.
[0047] Additional advantages arid modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *