Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
2002-09-09
2004-10-19
Glick, Edward J. (Department: 2882)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S128000
Reexamination Certificate
active
06807351
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 L-band (1570 nm to 1620 nm).
BACKGROUND OF THE INVENTION
Higher 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 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. More specifically, positive dispersion builds as a function of the length of the high data rate transmission fiber. Dispersion Compensating (DC) fibers included in cable or in Dispersion Compensating Modules (DCM's) have been designed that compensate for such dispersion. These fibers generally have negative slope and negative dispersion such that a short length of the DC fiber compensates for the positive dispersion and positive slope of the longer transmission portion. A good example of a DC fiber may be found in commonly assigned U.S. patent application Ser. No. 09/802,696 filed on Mar. 9, 2001. For L-band operation between 1570 nm and 1620 nm, the bend performance and dispersion properties (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.
Thus, there is a need for a DC fiber which: (1) is single moded over the L-band wavelength range (1570 nm to 1620 nm) when included in a DCM; and (2) retains the usual high performance optical fiber characteristics such as high strength, low attenuation and acceptable resistance to bend induced loss, and (3) is particularly effective at compensating for the dispersion of Non-Zero Dispersion Shifted Fibers (NZDSF) in the L-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 at least a first and a second segment such as a central core and a moat, for example. Each core segment has a respective refractive index profile and maximum and minimum index.
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. 3-5
. 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 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 where &Dgr;
3
% is half its maximum value of the ring segment
26
. The half-height width of ring segment
26
is measured at the half &Dgr; % value of 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
26
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 1595 nm.
The effective diameter, D
eff
, is defined as:
D
eff
=(2/&pgr;
1/2
)
A
eff
1/2
The profile volume is defined as 2 &pgr;∫&Dgr; % r dr. The profile volume of the central core segment
22
extends from the waveguide centerline, R=0, to the radius R
1
. The profile volume of the ring segment
26
extends from the radius R
2
to the last point of the ring segment at radius R
4
. The units of the profile volume are % &mgr;m
2
because relative index is dimensionless. The profile volume units, % &mgr;m
2
, will be referred to simply as units throughout this document.
The term, &Dgr; %, represents a relative measure of refractive index defined by the equation,
&Dgr; %=100(
n
i
2
−n
c
2
)/2
n
c
2
where n
i
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 &Dgr;(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 pin 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 L-band.
According to an embodiment of the invention, a DC fiber is provided which has a segmented core of at least three segments, each segment characterized by having a refractive index profile, a relative index &Dgr; %, and radius dimensions. The DC fiber's overall refractive index profile structure is selected to provide a particular set of properties (attributes) that make it suited for transmission systems designed to operate in the L-band wavelength window having a midpoint at about 1595 nm, and a wavelength band between about 1570 nm and 1620 nm. The DC fiber in accordance with the invention is particularly suitable for compensating for build up of dispersion and/or dispersion slope in NZDSF's. Thus, the DC f
Hebgen Peter G.
Qi Gang
Zhang Lu
Glick Edward J.
Suchecki Krystyna
Wayland Randall S.
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