Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
2002-03-14
2004-06-29
Lee, John D. (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S123000, C385S125000, C385S126000
Reexamination Certificate
active
06757468
ABSTRACT:
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 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 can 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 for such systems. 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 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. This is particularly true in DC fibers that will be included in a wound spool of a DCM, but also for cabled DC fiber utilized in dispersion managed systems.
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 transmission fibers across the C, L and C+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 for the DC fiber.
Segmented Core—A segmented core is one that has multiple segments in the core, 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 refractive index therein.
Radii—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
illustrates the definitions of radii R
1
, R
2
, and R
3
used herein. The same dimension conventions apply for defining the radii in
FIGS. 4-15
,
28
-
30
and
43
as well. The radius R
1
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 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
23
, as measured relative to the cladding
28
. The radius R
3
is measured to the radius point at which a tangent to the outer edge
27
of the ring
26
meets the refractive index zero
23
, as measured relative to the cladding
28
. The width of the ring
26
is defined as the distance from R
3
to the bisecting point of a tangent of the inward portion
29
of the ring with the refractive index zero
23
, as measured relative to the cladding
28
.
Effective Area—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 1550 nm.
&Dgr;% or Delta (%)—The term, &Dgr;% or Delta (%), represents a relative measure of refractive index defined by the equation,
&Dgr;%=100(
n
i
2
−n
c
2
)/2
n
i
2
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.
&agr;-profile—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
l
−b
o
)]
&agr;
)]100
where b
o
is the maximum point of the profile and b
l
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
l
−b
o
)]
&agr;
}]100,
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 compensation fiber is provided having a refractive index profile including a core having a central core with a core delta (&Dgr;
1
) having a value greater than 1.5%, a moat surrounding the central core having a moat delta (&Dgr;
2
) having a value less negative than −0.65%, and a ring surrounding the moat having a positive ring delta (&Dgr;
3
). The refractive index profile of the DC fiber is selected to provide a total dispersion less than −87 and greater than −167 ps
m/km at 1550 nm; a dispersion slope more negative than −0.30 ps
m
2
/km at 1550 nm; and a kappa value defined as the total dispersion at 1550 nm divided by t
Bickham Scott R.
Donlagic Denis
Corning Incorporated
Lee John D.
Lin Tina M
Wayland Randall S.
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