Title: Dispersion compensating fiber for low slope transmission fiber and optical transmission line utilizing same
Abstract: A Dispersion Compensation (DC) fiber for low slope transmission fiber (such as a NZDSF) and transmission line including same. The DC fiber has a refractive index profile having a central core with a core delta (Δ1) value less than 1.8%, a moat surrounding the central core having a moat delta (Δ2) value greater than -0.9%, and a ring surrounding the moat having a positive ring delta (Δ3). The DC fiber's refractive index profile is selected to provide total dispersion less than -40 and greater than -87 ps/nm/km, and kappa of greater than 165 and less than 270 nm, all at 1550 nm. The DC fiber, when used in a transmission line, may provide low average residual dispersion across the C, L, and C+L when such lines include transmission fibers with a total dispersion between 4 and 10 ps/nm/km and a dispersion slope less than 0.045 ps/nm2/km at 1550 nm.
Patent Number: 6,975,801 Issued on 12/13/2005 to Bickham
| Inventors:
|
Bickham; Scott R. (Corning, NY)
|
| Assignee:
|
Corning Incorporated (Corning, NY)
|
| Appl. No.:
|
196076 |
| Filed:
|
July 15, 2002 |
| Current U.S. Class: |
385/124; 385/123 |
| Intern'l Class: |
G02B 006/16 |
| Field of Search: |
385/123-128
|
References Cited [Referenced By]
U.S. Patent Documents
| 4715679 | Dec., 1987 | Bhagavatula.
| |
| 5361319 | Nov., 1994 | Antos et al.
| |
| 5448674 | Sep., 1995 | Vengsarkar et al.
| |
| 5555340 | Sep., 1996 | Onishi et al.
| |
| 5568583 | Oct., 1996 | Akasaka et al.
| |
| 5673354 | Sep., 1997 | Akasaka et al.
| |
| 5748824 | May., 1998 | Smith.
| |
| 5838867 | Nov., 1998 | Onishi et al.
| |
| 5999679 | Dec., 1999 | Antos et al.
| |
| 6009221 | Dec., 1999 | Tsuda.
| |
| 6169837 | Jan., 2001 | Kato et al.
| |
| 6263138 | Jul., 2001 | Sillard et al.
| |
| 6345140 | Feb., 2002 | Sasaoka et al.
| |
| 6349163 | Feb., 2002 | Antos et al.
| |
| 6400877 | Jun., 2002 | Kato et al.
| |
| 6404967 | Jun., 2002 | Arai et al.
| |
| 6477306 | Nov., 2002 | Kato et al.
| |
| 2001/0055436 | Dec., 2001 | Sugizaki et al.
| |
| 2002/0012510 | Jan., 2002 | Jiang et al.
| |
| 2002/0018631 | Feb., 2002 | Arai et al.
| |
| 2002/0090186 | Jul., 2002 | Sillard et al.
| |
| Foreign Patent Documents |
| 1054275 | Nov., 2000 | DE.
| |
| 1130428 | Sep., 2001 | DE.
| |
| 1122562 | Aug., 2001 | EP.
| |
| 1004905 | Apr., 2002 | FR.
| |
| 1043609 | Oct., 2000 | GB.
| |
| WO 98/0494/1 | Feb., 1998 | WO.
| |
| WO 00/6705/3 | Nov., 2000 | WO.
| |
| WO 01/2582/8 | Apr., 2001 | WO.
| |
| WO 01/7348/6 | Oct., 2001 | WO.
| |
| WO 01/9293/1 | Dec., 2001 | WO.
| |
Other References
U.S. Appl. No. 10/098,889, filed Mar. 14, 2002, Bickham et al.
U.S. Appl. No. 60/357,539, filed Feb. 15, 2002, Bickham et al.
|
Primary Examiner: Williams; Joseph
Assistant Examiner: Dong; Dalei
Attorney, Agent or Firm: Wayland; Randall S.
Claims
1. A dispersion compensation fiber, comprising:
a refractive index profile including
a central core having a positive core delta (Δ
1) less than 1.8%,
a moat surrounding the central core having a negative moat delta (Δ
2)
greater than -0.9%, and
a ring surrounding the moat having a positive ring delta (Δ
3), the
refractive index profile selected to provide
a total dispersion less than -40 and greater than -87 ps/nm/km at 1550 nm; and
a kappa value defined as the total dispersion at 1550 nm divided by the dispersion
slope at 1550 nm of greater than 165 and less than 270 nm.
effective area of greater than 18 square microns at 1550 nm; and
pin array bend loss of less than 8 dB at 1550 nm.
2. The dispersion compensation fiber of claim 1 further comprising total dispersion
less than -40 and greater than -70 ps/nm/km at 1550 nm.
3. The dispersion compensation fiber of claim 1 further comprising dispersion
slope of between -0.2 and -0.45 ps/nm
2/km at 1550 nm.
4. The dispersion compensation fiber of claim 1 further comprising dispersion
slope of less than -0.3 and greater than -0.45 ps/nm
2/km at 1550 nm.
5. The dispersion compensation fiber of claim 1 further comprising kappa greater
than 175 and less than 230 nm at 1550 nm.
6. The dispersion compensation fiber of claim 1 wherein the core-moat ratio,
defined as an outer radius of the central core divided by an outer radius of the
moat, is greater than 0.3 and less than 0.45.
7. The dispersion compensation fiber of claim 1 wherein the core delta (Δ
1)
is less than 1.5%.
8. The dispersion compensation fiber of claim 7 wherein an outer core radius
(R
1) of the central core is between about 1.7 and 2.2 microns.
9. The dispersion compensation fiber of claim 1 wherein the moat delta (Δ
2)
is greater than -0.6%.
10. The dispersion compensation fiber of claim 9 wherein the moat delta (Δ
2)
is between -0.35% and -0.5%.
11. The dispersion compensation fiber of claim 9 wherein the outer moat radius
(R
2) is between about 4.4 and 5.5 microns.
12. The dispersion compensation fiber of claim 1 wherein the ring delta (Δ
3)
is between about 0.25% and 0.5%.
13. The dispersion compensation fiber of claim 12 wherein the ring radius (R
3)
to an approximate center of the ring is between about 6.5 and 8.5 microns.
14. The dispersion compensation fiber of claim 1 wherein a ring offset Ro defined as
is greater than 0.5 microns, where R
3 is the ring radius, R
2 is
the radius to an outer edge of the moat, and Wh is the width of the ring as measured
at a ring half delta value.
15. The dispersion compensation fiber of claim 14 wherein the ring offset Ro
is greater than 1.0 micron.
16. The dispersion compensation fiber of claim 14 wherein the ring offset Ro
is between 0.75 and 2.5 microns.
17. An optical transmission line, wherein the dispersion compensation fiber as
set forth in claim 1 is optically connected to a transmission fiber having:
a total dispersion between 4 and 10 ps/nm/km at 1550 nm, and
a positive dispersion slope of less than 0.045 ps/nm
2/km at 1550 nm.
18. The optical transmission line of claim 17 wherein the dispersion is between
4 and 8 ps/nm/km at 1550 nm.
19. The optical transmission line of claim 17 wherein the transmission fiber
comprises a kappa value defined as total dispersion at 1550 nm divided by dispersion
slope at 1550 nm of between 147 and 240 nm.
20. The optical transmission line of claim 17 wherein a High-to-Low average residual
dispersion for the transmission line over an entire C+L band having a wavelength
range from 1525 nm to 1625 nm is less than 0.12 ps/nm/km.
21. The optical transmission line of claim 17 wherein a High-to-Low average residual
dispersion for the transmission line over an entire C-band having a wavelength
range from 1525 nm to 1565 nm is less than 0.10 ps/nm/km.
22. The optical transmission line of claim 17 wherein a High-to-Low average residual
dispersion for the transmission line over an entire L-band having a wavelength
range from 1565 nm to 1625 nm is less than 0.10 ps/nm/km.
23. A dispersion compensation fiber, comprising:
a refractive index profile including
a central core having a positive core delta (Δ
1) less than 1.5%,
a moat surrounding the central core having a negative moat delta (Δ
2)
between -0.35% and -0.5%, and
a ring surrounding the moat having a positive ring delta (Δ
3), the
refractive index profile selected to provide
a total dispersion less than -40 and greater than -87 ps/nm/km at 1550 nm;
a dispersion slope of between -0.2 and -0.45 ps/nm
2/km at 1550 nm; and
a kappa value defined as the total dispersion at 1550 nm divided by the dispersion
slope at 1550 nm of greater than 165 and less than 270 nm.
effective area of greater than 18 square microns at 1550 nm; and
pin array bend loss of less than 8 dB at 1550 nm.
24. A dispersion compensation fiber, comprising:
a refractive index profile including
a central core having a positive core delta (Δ
1) less than 1.5%,
a moat surrounding the central core having a negative moat delta (Δ
2)
greater than -0.6%, and
a ring surrounding the moat having a positive ring delta (Δ
3),
a core-moat ratio, defined as an outer radius of the central core divided by
an outer radius of the moat, is greater than 0.3 and less than 0.45, and
the refractive index profile is selected to provide
a total dispersion less than -40 and greater than -87 ps/nm/km at 1550 nm;
a dispersion slope of between -0.2 and -0.45 ps/nm
2/km at 1550 nm; and
a kappa value defined as the total dispersion at 1550 nm divided by the dispersion
slope at 1550 nm of greater than 175 and less than 230 nm;
effective area of greater than 18 square microns at 1550 nm; and
pin array bend loss of less than 8 dB at 1550 nm.
25. A dispersion compensation fiber, comprising:
a refractive index profile including
a central core having a positive core delta (Δ
1) less than 1.8%,
a moat surrounding the central core having a negative moat delta (Δ
2)
greater than -0.9%, and
a ring surrounding the moat having a positive ring delta (Δ
3), the
refractive index profile selected to provide
a total dispersion less than -40 and greater than -87 ps/nm/km at 1550 nm;
a kappa value defined as the total dispersion at 1550 nm divided by the dispersion
slope at 1550 nm of greater than 165 and less than 270 nm;
effective area of greater than 18 square microns at 1550 nm;
pin array bend loss of less than 8 dB at 1550 nm; and
cutoff of less than 1732 nm.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to optical fiber, and more particularly
to dispersion compensation fiber and transmission lines including combinations
of NZDSF transmission fiber and dispersion compensation fiber.
2. Technical Background
Higher data rates and wider bandwidth systems are becoming needed for the
telecommunications industry. Thus, the search for high performance optical fibers
designed for long distance, high bit rate telecommunications that operate over
broad bandwidths has intensified. These high data rates and broad bandwidths, however,
have penalties associated with them. In particular, dispersion is a significant
problem in such systems. More specifically, positive dispersion builds along the
length of the high data rate transmission fiber. Dispersion Compensating (DC) fibers
included in cable or in Dispersion Compensation Modules (DCM's) have been designed
that compensate for such dispersion. These fibers generally have negative dispersion
slope and negative total dispersion, with the dispersion having a large negative
value such that a short length of the DC fiber compensates for the positive dispersion
and positive slope of the longer transmission portion. For C- and L-band operation
between 1525 nm and 1625 nm, the bend performance (both macro-bending and micro-bending)
and other properties, such as dispersion and kappa linearity (kappa being the ratio
of total dispersion divided by dispersion slope at a specific wavelength) of the
DC fiber are very important.
Thus, there is a need for a DC fiber which: (1) exhibits fairly linear properties
over the C- and L-bands in a wavelength range (1525 nm to 1625 nm); (2) retains
the usual high performance optical fiber characteristics such as high strength,
low attenuation and acceptable resistance to micro- and macro-bend induced loss,
and (3) is particularly effective at compensation for the dispersion of low slope
NZDSF transmission fibers across the C and L bands with low average residual dispersion.
SUMMARY OF THE INVENTION
DEFINITIONS
The following definitions are used herein.
Refractive Index Profile—The refractive index profile is the relationship
between refractive index and optical fiber radius (as measured from the fiber's
centerline) for the DC fiber.
Segmented Core—A segmented core is one that has multiple segments
in the physical core, such as a first and a second segment (a central core, a moat
and a ring, for example). Each core segment has a respective refractive index profile
and a maximum and minimum refractive index therein.
Radii—As shown in FIG. 3, the radii of the segments of the core
21 are defined in terms of the beginning and end points of the segments
of the refractive index profile of the fiber 20. FIG. 3 best illustrates
the definitions of radii R1, R2, and R3 used herein. The same
dimension conventions apply for defining the radii in the other refractive index
profiles described herein in FIGS. 4-10. The radius R1 of the central core
22 is the length that extends from the DC fiber's centerline CL to the point
at which the refractive index profile crosses the relative refractive index zero
23 as measured relative to the cladding 28. The outer radius R2
of the moat segment 24 extends from the centerline CL to the radius point
at which the outer edge of the moat crosses the refractive index zero 23,
as measured relative to the cladding 28. The radius R3 is measured
to the radius point at the approximate center of the ring 26. In particular,
R3 is measured to the center point 27 of the half height dimension
Wh. The half height dimension is the width Wh at the position Δ3/2,
as measured relative to the cladding 28.
Effective Area—The effective area is defined as:
where the integration limits are 0 to ∞, r is the fiber radius, and
E is the electric field associated with the propagated light as measured at 1550 nm.
Δ% or Delta (%)—The term, Δ% or Delta (%), represents
a relative measure of refractive index defined by the equation:
where n
i is the maximum refractive index (highest positive or lowest
negative) in the respective region i (e.g., 22, 24, 26), unless
otherwise specified, and n
c is the refractive index of the cladding
(e.g., 28) unless otherwise specified.
α-profile—The term alpha profile, α-profile
refers to a refractive index profile of the core 22, expressed in terms
of Δ(b)%, where b is radius, which follows the equation,
where b
o is the maximum point of the profile of the core and b
1
is the point at which Δ(b)% is zero and b is in the range b
i≦b≦b
f,
where Δ% is defined above, b
i is the initial point of the α-profile,
b
f is the final point of the α-profile, and α is an exponent
which is a real number. The initial and final points of the α-profile are
selected and entered into the computer model. As used herein, if an α-profile
is preceded by a step index profile, the beginning point of the α-profile
is the intersection of the α-profile and the step profile. In the model,
in order to bring about a smooth joining of the α-profile with the profile
of the adjacent profile segment, the equation is rewritten as;
where b
a is the first point of the adjacent segment.
Pin array macro-bending test—This test is used to compare relative resistance
of optical fibers to macro-bending. To perform this test, attenuation loss is measured
when the optical fiber is arranged such that no induced bending loss occurs. This
optical fiber is then woven about the pin array and attenuation again measured.
The loss induced by bending is the difference between the two attenuation measurements
in dB. The pin array is a set of ten cylindrical pins arranged in a single row
and held in a fixed vertical position on a flat surface. The pin spacing is 5 mm,
center-to-center. The pin diameter is 0.67 mm. The optical fiber is caused to pass
on opposite sides of adjacent pins. During testing, the optical fiber is placed
under a tension sufficient to make the optical fiber conform to a portion of the
periphery of the pins.
Lateral load test—Another bend test referenced herein is the lateral
load test that provides a measure of the micro-bending resistance of the optical
fiber. In this test, a prescribed length of optical fiber is placed between two
flat plates. A #70 wire mesh is attached to one of the plates. A known length of
optical fiber is sandwiched between the plates and the reference attenuation is
measured while the plates are pressed together with a force of 30 newtons. A 70
newton force is then applied to the plates and the increase in attenuation in dB/m
is measured. This increase in attenuation is the lateral load attenuation of the
optical fiber.
SUMMARY
In accordance with embodiments of the present invention, a Dispersion Compensating
(DC) fiber is provided having a refractive index profile including a central core
having a positive core delta (Δ1) less than 1.8%, a moat surrounding
the central core having a negative moat delta (Δ2) greater than -0.9%,
and a ring surrounding the moat having a positive ring delta (Δ3).
The DC fiber's refractive index profile is selected to provide a total dispersion
less than -40 and greater than -87 ps/nm/km at 1550 nm, and a kappa value, defined
as the total dispersion at 1550 nm divided by the dispersion slope at 1550 nm,
of greater than 165 and less than 270 nm.
In accordance with another embodiment of the invention, an optical transmission
line is provided, wherein the dispersion compensation fiber as set forth above
is optically coupled to a transmission fiber having a total dispersion between
4 and 10 ps/nm/km at 1550 nm, and a positive dispersion slope of less than 0.045
ps/nm
2/km at 1550 nm.
The DC fiber according to the invention has the advantage of having high effective
area (greater than 18 square microns at 1550 nm) while at the same time having
low bend loss. The high effective area allows for less coupling loss, low nonlinearities,
and reduced four wave mixing and cross phase modulation. In addition, the DC fiber
exhibits linear dispersion as a function of wavelength. Furthermore, the relatively
low core delta of the DC fiber may advantageously lead to lower attenuation because
of the lower dopant concentrations in the central core.
Additional features and advantages of the invention will be set forth
in the detailed description which follows, and in part will be readily apparent
to those skilled in the art from that description or recognized by practicing the
invention as described herein, including the detailed description which follows,
the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following
detailed description present embodiments of the invention, and are intended to
provide an overview or framework for understanding the nature and character of
the invention as it is claimed. The accompanying drawings are included to provide
a further understanding of the invention, and are incorporated in and constitute
a part of this specification. The drawings illustrate various embodiments of the
invention, and together with the description serve to explain the principles and
operations of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block depiction of a transmission line including a DC fiber in accordance
with the present invention.
FIG. 2 is a representative cross-sectional end view of embodiments of the DC
fiber in accordance with the present invention.
FIG. 3 is a graphic plot of a refractive index profile for one embodiment of
DC fiber in accordance with the present invention illustrating various dimensions
characterizing the fiber's refractive index profile.
FIGS. 4-10 are graphic plots of refractive index profiles for other embodiments
of DC fiber in accordance with the present invention.
FIG. 11 is a graphic plot of total dispersion as a function of wavelength for
the DC fibers of FIGS. 3-10 in accordance with the present invention.
FIG. 12 is a graphic plot of dispersion slope as a function of wavelength for
the DC fibers of FIGS. 3-10 in accordance with the present invention.
FIG. 13 is a graphic plot of kappa as a function of wavelength for the DC fibers
of FIGS. 3-10 in accordance with the present invention.
FIG. 14 is a graphic plot of average residual dispersion as a function of wavelength
for a transmission line including a DC fiber in accordance with the present invention.
FIG. 15 is a graphic plot of the refractive index of a low slope transmission
fiber with which the DC fiber in accordance with the present invention is designed
to be utilized.
FIG. 16 is a graphic plot of dispersion as a function of wavelength for a transmission
fiber of FIG. 15.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made in detail to the present preferred embodiment(s)
of the invention, examples of which is/are illustrated in the accompanying drawings.
Whenever possible, the same reference numerals will be used throughout the drawings
to refer to the same or like parts.
By way of example, and not to be considered limiting, an optical transmission
line
18 is illustrated in FIG. 1 having a length (preferably about 100 km)
of a transmission fiber
19, such as a low slope Non-Zero Dispersion Shifted
Fiber (NZDSF), optically coupled to a DC fiber
20 in accordance with embodiments
of the invention. One preferred transmission fiber
19 in the transmission
line
18 is low slope NZDSF
19, as is shown and described with reference
to FIGS. 15 and 16 herein. The transmission fiber
19 has a positive dispersion
between about 4 and 10 ps/nm/km at 1550 nm; and more preferably between 4 and 8
ps/nm/km at 1550 nm, and a positive dispersion slope of less than about 0.045 ps/nm
2/km
at 1550 nm. Kappa of the NZDSF transmission fiber
19 is preferably between
about 147 and 240 nm at 1550 nm. Kappa is defined herein as the total dispersion
of the fiber at 1550 nm divided by the dispersion slope of the fiber at 1550 nm.
In the transmission line
19, the DC fiber
20 compensates for build
up of dispersion resulting from passing a light signal through the transmission
fiber
19 (as indicated by arrow A). It should be recognized that although
the system is described herein as being unidirectional, that transmission lines
including the DC fiber
20 described herein may have signals passing in both directions.
In representative transmission lines
18, the built up dispersion of the
transmission fiber
19 (e.g., NZDSF) is compensated for by a shorter length
of DC fiber
20, having a length of between about 6 to 14 km in accordance
with the invention. The transmission line
18 may include a pre-amp
42
and power amp
44 or any other conventional amplifier arrangement. The line
18 may also include other conventional components such as a transmitter
40 and receiver
46. Optionally, the transmission line
18 may
couple to one or more additional lengths of NZDSF or other transmission fiber instead
of terminating at the receiver
46. Further additional components such as
filters, couplers, and amplifiers may also be included in the transmission lines.
The DC fibers
20 according to the invention have segmented core structures
as best illustrated in FIGS. 1-3 including, preferably, a central core
22
having a positive delta, a moat
24 having a negative delta, and a ring
26
having a positive delta (all deltas being measured relative to the cladding
28).
The family of DC fibers
20 shown in FIGS. 3-10 include a refractive index
profile with a physical core
21 having a central core
22 with a positive
maximum core delta (Δ
1) of less than 1.8%, a moat
24 surrounding
the central core
22 having a negative minimum moat delta (Δ
2)
greater than -0.9%, and a ring
26 surrounding the moat having a positive
ring delta (Δ
3). The refractive index profile of the DC fibers
20
is selected to provide a total dispersion less than -40 and greater than -87 ps/nm/km
at 1550 nm; and a kappa, defined as the total dispersion at 1550 nm divided by
the dispersion slope at 1550 nm, of greater than 165 and less than 270 nm. Dispersion
slope for the DC fiber
20 is preferably between about -0.20 and -0.45 ps/nm
2/km
at 1550 nm; more preferably less than -0.3 and greater than -0.45 ps/nm
2/km
at 1550 nm. Total dispersion, dispersion slope and kappa plots are illustrated
in FIGS. 11-13 for all the example DC fibers
20 in accordance with the invention.
In particular, all the DC fibers
20 in accordance with embodiments of
the
invention have a structure including (as shown in FIGS. 2 and 3) a core
21
having a central core
22 with a core delta (Δ
1) measured to
the highest point on the central core having a value less than 1.8%, a moat
24
surrounding the central core
22 having a moat delta (Δ
2) with
a minimum delta value less negative than -0.9% (measured to the lowest point in
the moat), and a ring
26 surrounding the moat
24 having a positive
ring delta (Δ
3) measured to the highest point on the ring. The core
22 preferably includes an α-profile where α is between about
2 and 5. The DC fibers
20 preferably also include a cladding
28 surrounding
the core
21 which is preferably silica, but may include other suitable dopants
(such as fluorine) as well. The cladding
28 of the DC fibers
20 is
preferably surrounded by a conventional polymer coating
30 (see FIG. 2),
such as a urethane acrylate coating. Preferably, the coating
30 exhibits
a low-modulus primary coating, and a high-modulus outer secondary coating, as is
known to those of skill in the art.
The DC fibers
20 in accordance with embodiments of the invention preferably
have a core-moat ratio (C-M Ratio), defined as the radius (R
1) to the outer
edge of the central core
22 (defined relative to the cladding reference
23) divided by a radius (R
2) to the outer edge of the moat
24
(defined relative to the cladding reference
23), of greater than 0.3 and
less than 0.45; and more preferably greater than 0.37 and less than 0.42.
By way of further clarification, the transmission line
18 (FIG. 1) include
a first section of positive dispersion, positive dispersion slope transmission
fiber
19, such as the NZDSF described above, and a DC fiber
20 in
accordance with the invention having a negative total dispersion and a negative
dispersion slope. The transmission line
18 described herein illustrates
very low average residual dispersions across the C-, L- and C+L bands. FIG. 14
illustrates average residual dispersion of a transmission line
18 including
a representative embodiment of the present invention DC fiber
20 described
in detail herein below. The DC fibers
20 in accordance with embodiments
of the invention may be housed in the form of a conventional Dispersion Compensating
Module (DCM), for example.
In accordance with the invention, and in more detail, a family of refractive
index
profiles of the dispersion compensation fiber
20 are described herein. FIG.
3 will be utilized to describe the refractive index structure of the family of
DC fibers
20. The refractive index profiles for the family of Dispersion
Compensation (DC) fibers
20 are provided in FIGS. 3-10. The DC fibers
20
each have a refractive index profile including a core
21 surrounded by a
cladding
28 which extends to the outermost glass periphery of the fiber.
The core
21 has a central core
22 having a core delta (Δ
1)
with a value less than 1.8%, a moat
24 surrounding the central core
22
having a moat delta (Δ
2) with a value less negative than -0.9%, and
a ring
26 surrounding the moat
24 having a positive ring delta (Δ
3).
The core-moat ratio of the DC fibers
20, defined as a radius (R
1)
to the outer edge of the central core
22 divided by a radius (R
2)
to the outer edge of the moat
24, is preferably greater than 0.3 and less
than 0.45. One particular advantage of the present invention DC fiber
20
is that the effective area is greater than 18 square microns at 1550 nm, while
the pin array bend loss at 1550 nm remains less than 8 dB.
Within the family of DC fibers
20 in accordance with the invention
as shown in FIGS. 4-8, a more preferred total dispersion range at a wavelength
of 1550 nm is less than -40 and greater than -70 ps/nm/km. The dispersion slope
within the family of DC fibers
20, as shown in FIGS. 3-10 ranges between
less than -0.2 and greater than -0.45 ps/nm
2/km at 1550 nm; and more
preferably less than -0.3 and greater than -0.45 ps/nm
2/km at 1550 nm.
Kappa for the family of DC fibers
20 at 1550 nm is more preferably greater
than 175 and less than 230 nm.
As is illustrated in FIG. 13, the family of DC fibers
20 have kappas that
are quite linear over the desired transmission bands, e.g., nearly flat over the
C-band (1525-1565 nm), and gradually ramping up in the L-band (1565-1625 nm), thereby
making them excellent candidates for providing low residual dispersion in transmission
lines
18. In particular, as is illustrated in FIG. 13, the DC fibers
20
have kappas that range between 150 and 450 nm over a wavelength range from 1525
to 1625 nm with some ranging between 150 and 250 nm over the C-and L-bands from
1525 to 1625 nm.
The structure of the family of DC fibers
20 in accordance with the invention
are shown in FIGS. 3-10 and are listed in Table 1 below as examples 1-8. FIG. 3
illustrates the radii dimensions R
1, R
2, R
3, the delta parameters
Δ
1, Δ
2, and Δ
3, the ring half width Wh (the
width measured at half the ring delta Δ
3/
2), and the ring offset
Ro. In particular, the conventions utilized to measure these parameters for FIG.
3 are shown only with reference to FIG. 3, but also apply to the refractive index
profiles of FIGS. 4-10.
For the family of DC fibers
20 of FIGS. 3-10 according to the invention,
the core delta (Δ
1) of the central core
22 is more preferably
less than 1.8%; and more preferably less than 1.5%. The core radius (R
1)
of the central core
22 is preferably between about 1.7 and 2.2 microns;
and more preferably between about 1.9 and 2.15 microns. Each of the DC fibers
20
includes a moat
24 having a negative moat delta (Δ
2). The moat
delta (Δ
2) for the family of DC fibers
20 is preferably greater
than -0.9%; more preferably greater than -0.6%; and most preferably between about
-0.35% and -0.5%. In accordance with embodiments of the invention, the outer moat
radius (R
2) of the moat
24 is preferably between 4.4 and 5.5 microns
from the DC fiber's centerline (CL). More preferably, the moat radius (R
2)
is between about 4.9 and 5.4 microns from the fiber's CL.
In accordance with further features of the invention, the refractive index profile
of the family of DC fibers
20 includes a ring
26 having a positive
ring delta (Δ
3). The ring delta (Δ
3) is preferably between
about 0.25% and 0.5%, and the ring radius (R
3), as measured to the approximate
center of the ring
26, is between about 6.5 and 8.5 microns; and more preferably
between 7.0 and 8.4 microns. The ring
26 has a ring half width (Wh) which
is preferably between about 1.6 to 2.2 microns; and more preferably between 1.7
and 2.0 microns. For this family of DC fibers
20, the ring
26 is
offset from the outer edge of the moat
24 by a defined ring offset Ro. The
ring offset Ro is determined as follows:
Ro for the family of DC fibers
20 is preferably greater than 0.5 microns;
more preferably greater than 1.0 micron; and most preferably between 0.75 and 2.5 microns.,
EXAMPLES
The present invention will be further clarified by the following examples that
are summarized in Table 1 below. Table 1 includes attributes (such as Total Dispersion
at 1550 nm, Dispersion Slope at 1550 nm, Kappa at 1550 nm, Pin Array at 1550 nm,
Lateral Load at 1550 nm, Effective Area at 1550 nm, and cutoff wavelength) and
refractive index structural parameters (Δ1, Δ2, Δ3,
R1, R2, R3, Ro, Wh, and Core-Moat (C-M) ratio) for the DC
fibers 20 in accordance with the invention corresponding to FIGS. 3-10.
Legends are included on each plot for identification of the examples.
| TABLE 1 |
| Dispersion Compensation Fiber Examples |
| |
|
Dis- |
|
|
|
|
|
|
|
|
|
|
|
Pin |
Lat. |
|
|
| |
|
persion |
Slope |
|
|
|
|
|
|
|
|
|
|
Array @ |
Load @ |
| |
|
(ps/ |
(ps/ |
Kappa |
Δ 1 |
Δ 2 |
Δ 3 |
R1 |
R2 |
R3 |
Ro |
Wh |
C-M |
1550 nm |
1550 nm |
Aeff |
λc |
| Ex. |
Legend |
nm/km) |
nm2/km) |
(nm) |
% |
% |
% |
(μm) |
(μm) |
(μm) |
(μm) |
(μm) |
Ratio |
(dB) |
dB/m |
(μm2) |
(nm) |
| 1 |
K167 |
-73 |
-0.44 |
167 |
1.25 |
-0.45 |
0.31 |
1.89 |
5.18 |
7.27 |
1.08 |
2.02 |
0.36 |
6.62 |
0.79 |
20.2 |
1699 |
| 2 |
K180 |
-67 |
-0.38 |
180 |
1.26 |
-0.48 |
0.33 |
1.92 |
4.99 |
7.04 |
1.12 |
1.87 |
0.39 |
4.33 |
0.44 |
19.7 |
1638 |
| 3 |
K185 |
-44 |
-0.23 |
185 |
1.09 |
-0.43 |
0.29 |
2.01 |
5.07 |
8.02 |
2.08 |
1.73 |
0.41 |
4.43 |
0.48 |
21.6 |
1671 |
| 4 |
K194 |
-68 |
-0.35 |
194 |
1.31 |
-0.45 |
0.32 |
2.04 |
4.95 |
7.38 |
1.55 |
1.76 |
0.41 |
6.49 |
0.72 |
21.1 |
1672 |
| 5 |
K211 |
-52 |
-0.25 |
211 |
1.44 |
-0.44 |
0.32 |
2.11 |
5.34 |
7.40 |
1.14 |
1.85 |
0.40 |
1.77 |
0.21 |
19.4 |
1677 |
| 6 |
K228 |
-64 |
-0.28 |
228 |
1.37 |
-0.41 |
0.30 |
2.00 |
5.15 |
7.38 |
1.24 |
1.98 |
0.39 |
2.78 |
0.36 |
20.4 |
1707 |
| 7 |
K253 |
-87 |
-0.33 |
253 |
1.51 |
-0.40 |
0.31 |
1.75 |
4.78 |
7.28 |
1.65 |
1.71 |
0.37 |
2.82 |
0.30 |
19.1 |
1642 |
| 8 |
K267 |
-72 |
-0.27 |
267 |
1.48 |
-0.37 |
0.32 |
1.73 |
4.55 |
7.02 |
1.47 |
2.01 |
0.38 |
0.34 |
0.05 |
18.2 |
1732 |
| TABLE 2 |
| Low slope NZDSF transmission fiber data |
| |
Dispersion (ps/nm/km) @ 1550 nm |
6.1 |
| |
Slope (ps/nm2/km) @ 1550 nm |
0.032 |
| |
Lambda Zero (nm) |
1395 |
| |
Kappa (nm) @ 1550 nm |
191 |
| |
FIG. 14 illustrates a plot 64 of modeled average residual dispersion
over the C and L bands (1525 to 1625 nm) for a transmission line 18 including
10 km of the DCF 20 designated K194 in Table 1 above and FIG. 6 herein,
and 100 km of the NZDSF 19 of Table 2. The profile plot for a preferred
transmission fiber 19 is shown in FIG. 15 whereas the dispersion plot for
that transmission fiber is illustrated in FIG. 16. As shown in FIG. 15, the preferred
transmission fiber 19 includes a central core 4, an annular moat
region 6, a ring 8, and a gutter 10. The core 4 and
the ring 6 are preferably germanium doped and have positive deltas relative
to the cladding 12 whereas the moat 6 and the gutter 10 are
fluorine doped and preferably have negative deltas in comparison to the cladding
12. Further description of this transmission fiber may be found in U.S.
Provisional Application No. 60/357,539 filed Feb. 15, 2002 entitled "Low Slope
Dispersion Shifted Optical Fiber," the disclosure of which is hereby incorporated
by reference herein. As illustrated in FIG. 14, the modeled High-to-Low average
residual dispersion 68 for the transmission line 18 in the C-band
is less than 0.10 ps/nm/km; in the L-band, the High-to-Low average residual dispersion
70 is less than 0.10 ps/nm/km; and in the C+L band less than 0.12 ps/nm/km.
In accordance with embodiments of the invention, transmission lines 18
including serially coupled lengths of transmission fiber 19 and DC fiber
20 include transmission fiber 19 having total dispersion ranging
from 4 to 10 ps/nm/km at 1550 nm; and more preferably between 4 to 8 ps/nm/km at
1550 nm. The dispersion slope of the transmission fiber 19 is preferably
less than 0.045 ps/nm
2/km at 1550 nm; and more preferably between 0.025
and 0.045 ps/nm
2/km at 1550 nm. Kappa for the transmission fiber 19
is preferably between 147 and 240 nm at 1550 nm.
The DC fibers 20 in accordance with them present invention may be drawn
from optical fiber preforms utilizing conventional draw methods and apparatus.
The optical fiber preform from which the present invention DC fibers 20
are drawn may be manufactured in accordance with any known method, such as any
known chemical vapor deposition method. Chemical vapor deposition methods include
OVD, MCVD, PCVD or the like. Most preferably, the DC fiber preform may be manufactured
by an OVD method wherein the preform portion corresponding to the central core
22 is first manufactured by depositing silicon oxide soot doped with germania
oxide onto a rotating tapered alumina mandrel to a desired diameter. The soot is
doped with the appropriate level of germania dopant to achieve the desired refractive
index profile for the central core segment including the appropriate Δ
1%.
The mandrel is then removed and the soot preform constituting the central core
22 is thoroughly dried in a preferably helium and chlorine containing environment
and then consolidated in a consolidating furnace including a helium atmosphere.
The consolidated central core blank is then redrawn into a single-segment core
cane of about 9 to 11 mm in diameter. During the redraw process, the centerline
aperture resulting from removal of the mandrel is closed through the application
of a vacuum or by other known methods.
Redrawn single-segment core cane then becomes the target deposition surface
for the application of further soot to form the preform portion corresponding to
the moat 24. Silica soot is deposited onto the cane to an appropriate diameter
for the moat and is then preferably dried within a consolidation furnace within
a helium- and chlorine-containing atmosphere in a consolidation furnace. The soot
preform is then doped with a suitable fluorine-containing gas, such as C
2F
6,
C
2F
2Cl
2, CF
4, SF
6, or SiF
4,
or the like, and subsequently consolidated and again redrawn into a two-segment
core cane. U.S. Pat. No. 4,629,485 to Berkey describes one such method for fluorine
doping an optical fiber preform.
This two-segment core cane material now becomes the deposition surface for the
preform portion corresponding to the ring 26. Germania-doped silica soot
is next deposited on the two-segment cane and is subsequently dried and consolidated
as herein before described. Again, the consolidated blank is redrawn and this time
becomes the final core cane including three segments corresponding to the central
core 22, moat 24, and ring 26 of the segmented physical core
21. Additional silica soot that comprises the cladding 28 is then
deposited on the final core cane to form the overclad soot blank. The overclad
soot blank is dried and consolidated and subsequently transferred to a draw furnace
where the present invention DC fiber 20 is drawn therefrom in accordance
with conventional draw methods.
It will be apparent to those skilled in the art that various modifications and
variations can be made to the present invention without departing from the spirit
and scope of the invention. Thus it is intended that the present invention cover
the modifications and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
*
