Optical waveguides – Optical fiber waveguide with cladding – With graded index core or cladding
Reexamination Certificate
2001-11-05
2004-03-23
Healy, Brian M. (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
With graded index core or cladding
C385S123000, C385S126000, C385S127000, C398S081000
Reexamination Certificate
active
06711332
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed to a dispersion compensating optical fiber and a transmission system including the same, and more particularly to a dispersion compensating optical fiber and transmission system in which the dispersion compensating fiber exhibits a negative dispersion and dispersion slope within the C-band (1525 nm to 1565 nm) to advantageously compensate for slope and dispersion in the transmission system.
BACKGROUND OF THE INVENTION
High data rates are becoming needed for the telecommunications industry. Thus, the search for high-performance optical fibers designed for long distance, high bit rate telecommunications in Dense Wavelength Division Multiplexing (DWDM) systems has intensified. However, these high data rates have penalties associated with them. In particular, dispersion is a significant problem for such systems, particularly those employing large effective area fibers, such as certain Non-Zero Dispersion Shifted Fibers (NZDSF). More specifically, positive dispersion builds as a function of the length of the transmission fiber (e.g., a NZDSF). Dispersion Compensating (DC) fibers included in a cable or in a Dispersion Compensating Module (DCM) have been designed that compensate for such dispersion in such optical transmission systems. These DC fibers generally have negative slope and negative dispersion such that a short length of the DC fiber may be used to compensate for the positive dispersion and positive slope of the longer transmission fiber, for example a NZDSF. For C-band operation between about 1525 nm and 1565 nm, the bend performance, attenuation, and dispersion properties (total dispersion and/or dispersion slope) of the DC fiber are very important. This is particularly true in DC fibers that will be included in a wound spool of a DCM. In particular, having very low total dispersion is advantageous as it allows for compensation with less DC fiber length. Low slope is desirable to compensate for the slope of the transmission fiber in a short length.
Thus, there is a need for a DC fiber that exhibits low attenuation, low bend loss, low dispersion and dispersion slope and is particularly effective at compensating for the dispersion and/or slope of certain Non-Zero Dispersion Shifted Fibers (NZDSF) over the C-band.
Definitions
The following definitions are in accordance with common usage in the art.
The refractive index profile is the relationship between refractive index and optical fiber radius.
A segmented core is one that has multiple segments, such as a first and a second segment (a central core and a moat, for example). Each core segment has a respective refractive index profile and maximum and minimum index therein.
The radii of the segments of the core are defined in terms of the beginning and end points of the segments of the refractive index profile or in terms of the midpoint of the segment in the case of a ring segment.
FIG. 2
illustrates the definitions of radii used herein. The same definitions are used for
FIGS. 3-6
as well. The radius R
1
of the center core segment
22
is the length that extends from the DC fiber's centerline (CL) to the point at which the profile crosses the relative refractive index zero as measured relative to the cladding
30
. The outer radius R
2
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, as measured relative to the cladding
30
. The radius R
3
is measured to the half height width where &Dgr;
3
% is half its maximum value of the ring segment
26
. The radius R
3
of segment
26
extends from the centerline (CL) to the midpoint
28
of a half-height line segment
27
. The midpoint
28
is formed by bisecting the segment
27
between the two intersection points with the ring segment at the half height position of &Dgr;
3
%. The radius R
4
is measured from the centerline (CL) to the point where the outermost portion of the ring segment
26
meets the zero refractive index point, as measured relative to the cladding
30
.
The effective area is defined as:
A
eff
=2&pgr;(∫E
2
r dr)
2
/(∫E
4
r dr), where the integration limits are 0 to ∞, and E is the electric field associated with the propagated light as measured at 1549 nm.
The term, &Dgr;%, represents a relative measure of refractive index defined by the equation,
&Dgr;%=100 (
n
l
2
−n
c
2
)/2
n
c
2
where n
l
is the maximum refractive index 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.,
30
) unless otherwise specified.
The term alpha profile, &agr;-profile refers to a refractive index profile, expressed in terms of &Dgr;(b) %, where b is radius, which follows the equation,
&Dgr;(
b
)%=[&Dgr;(
b
o
)(1-[|
b−b
o
|/(
b
1
−b
o
)]
&agr;
)]100
where b
o
is the maximum point of the profile and b
1
is the point at which &agr;(b)% is zero and b is in the range b
i
≦b≦b
f
, where &Dgr;% is defined above, b
i
is the initial point of the &agr;-profile, b
f
is the final point of the &agr;-profile, and &agr; is an exponent which is a real number. The initial and final points of the &agr;-profile are selected and entered into the computer model. As used herein, if an &agr;-profile is preceded by a step index profile, the beginning point of the &agr;-profile is the intersection of the &agr;-profile and the step profile. In the model, in order to bring about a smooth joining of the &agr;-profile with the profile of the adjacent profile segment, the equation is rewritten as;
&Dgr;(
b
)%=[&Dgr;(
b
a
)+[&Dgr;(
b
o
)−&Dgr;(
b
a
)]{(1-[|
b−b
o
|/(
b
1
−b
o
)]
&agr;
}]100,
where b
a
is the first point of the adjacent segment.
The pine array bend test is used to compare relative resistance of optical fibers to 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. 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 waveguide conform to a portion of the periphery of the pins.
SUMMARY OF THE INVENTION
The DC fiber in accordance with the invention disclosed and described herein is particularly well suited to compensating for dispersion and dispersion slope of certain NZDSF in the C-band.
According to an embodiment of the invention, a DC fiber is provided having a refractive index profile selected to provide a particular set of properties (attributes) that make it suited for transmission systems designed to operate in the C-band wavelength window of between about 1525 nm and 1565 nm.
The DC fiber in accordance with the invention is particularly suitable for compensating for build up of dispersion and/or dispersion slope in an NZDSF having a kappa of about 50. Thus, the DC fiber may be coupled to a NZDSF to form a transmission system and is designed to compensate for the dispersion and/or slope (and most preferably both) of the NZDSF, preferably across the entire C-band. The transmission system including the DC fiber may also preferably include optical amplifiers, filters, Wavelength Division Multiplexing operation, and other conventional system components. Preferably, the DC fiber is wound onto a spool and included in a Dispersion Compensating (DC) module.
In accordance with an embodiment of the invention, the total dispersion defined herein as the measurable dispersion (total dispersion equals chromatic dispersion
Hebgen Peter G.
Thompson David J.
Corning Incorporated
Healy Brian M.
Wayland Randall S.
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