Dispersion slope compensating optical waveguide fiber

Details Dispersion slope compensating optical waveguide fiber Dispersion slope compensating optical waveguide fiber

2003-01-30

2004-12-07

Ullah, Akm Enayet (Department: 2874)

Optical waveguides

Optical fiber waveguide with cladding

Utilizing multiple core or cladding

C385S127000

Reexamination Certificate

active

06829422

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an optical waveguide fiber, and particularly to an optical waveguide fiber that compensates dispersion slope in a telecommunications link.
2. Technical Background
Dispersion compensation techniques in telecommunications systems or links have been used successfully. A technique useful in links already installed is one in which total dispersion (also called chromatic dispersion) is compensated by an appropriately designed waveguide fiber formed into a module that can be inserted into the link at an access point such as an end of the link. The compensating waveguide fiber can be designed to allow operation in, for example, the 1550 nm operating wavelength window of a link originally designed for the 1310 nm operating window.
A disadvantage of compensating with a module is that attenuation and nonlinear penalties are added to the link without increasing the useful link length. Also some of the refractive index profile designs for dispersion compensation are more difficult to manufacture and have higher attenuation than the fibers making up the link.
Another dispersion compensation scheme is to include both positive and negative dispersion fibers in the cables of the link. Each cable can contain both positive and negative total dispersion waveguide fibers, or the link can be formed using cables having only positive dispersion together with cables having only negative dispersion. The relatively high attenuation and low effective area of the negative dispersion fiber can be a problem in this scheme as it is in the dispersion compensating module solution. Also the cable inventory must be managed carefully, because replacing or repairing a cable involves tracking of another variable (the sign of the dispersion of fibers in the cable). In certain profile designs a mismatch of mode fields between the positive and negative total dispersion fibers exists and results in excessive splice or connecting losses.
There is therefore a need for a total dispersion compensating strategy in which the compensating fiber is a part of the link length and the problem of the compensating fiber producing excess link attenuation is addressed. Furthermore, a solution that includes introducing negative dispersion cabled fiber into the link must offer a benefit that offsets the cost of cable inventory management and that does not introduce excess splice loss into the link.
A further desired characteristic of a total dispersion compensation solution is that the compensation be effective over an extended bandwidth to facilitate use of wavelength division multiplexed link architectures.
DEFINITIONS
The following definitions are in accord with common usage in the art.
The refractive index profile is the relationship between refractive index or relative refractive index and waveguide fiber radius.
A segmented core is one that is divided into at least a first and a second waveguide fiber core portion or segment. Each portion or segment is located along a particular radial length, is substantially symmetric about the waveguide fiber centerline, and has an associated refractive index profile.
The radii of the segments of the core are defined in terms of the respective refractive indexes at respective beginning and end points of the segments. The definitions of the radii used herein are set forth in the figures and the discussion thereof.
Total dispersion, sometimes called chromatic dispersion, of a waveguide fiber is the sum of the material dispersion, the waveguide dispersion, and the inter-modal dispersion. In the case of single mode waveguide fibers the inter-modal dispersion is zero.
The sign convention generally applied to the total dispersion is as follows. Total dispersion is said to be positive if shorter wavelength signals travel faster than longer wavelength signals in the waveguide. Conversely, in a negative total dispersion waveguide, signals of longer wavelength travel faster.
The effective area is A
eff
=2Π(∫E
2
r dr)
2
/(∫E
4
r dr), where the integration limits are 0 to ∞, and E is the electric field associated with light propagated in the waveguide.
The relative refractive index percent, &Dgr;%=100×(n
i
2
−n
c
2
)/2n
i
2
, where n
i
is the maximum refractive index in region i, unless otherwise specified, and n
c
is the average refractive index of the cladding region. In those cases in which the refractive index of a segment is less than the average refractive index of the cladding region, the relative index percent is negative and is calculated at the point at which the relative index in most negative unless otherwise specified.
The term &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
i
−b
o
)]
&agr;
), where b
o
is the point at which &Dgr;(b)% is maximum, b
1
is the point at which &Dgr;(b)% is zero, and b is in the range b
i
≦b≦b
f
, where delta 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 pin array bend test is used to compare relative resistance of waveguide fibers to bending. To perform this test, attenuation loss is measured for a waveguide fiber with essentially no induced bending loss. The waveguide 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 waveguide fiber is caused to pass on opposite sides of adjacent pins. During testing, the waveguide fiber is placed under a tension just sufficient to make the waveguide conform to a portion of the periphery of the pins. The test pertains to macro-bend resistance of the waveguide fiber.
A waveguide fiber telecommunications link, or simply a link, is made up of a transmitter of light signals, a receiver of light signals, and a length of waveguide fiber having respective ends optically coupled to the transmitter and receiver to propagate light signals therebetween. A link can include additional optical components such as optical amplifiers, optical attenuators, optical switches, optical filters, or multiplexing or demultiplexing devices. One may denote a group of inter-connected links as a, telecommunications system.
SUMMARY OF THE INVENTION
One aspect of the present invention is a single mode optical waveguide fiber, having a core region and a surrounding clad layer. The reference to single mode waveguide fiber means that the fiber in cable form usually will carry only a single mode over the range of operating wavelengths. Persons skilled in the art understand that single mode operation also includes cases in which more than one mode is propagated but that the higher order modes may are strongly attenuated and so do not travel in the waveguide more than a few kilometers. The waveguide fiber in accord with the invention may also be used in a wavelength range where a few modes are propagated the full link length and the few modes are dispersion compensated. The core region includes at least three segments, a central segment beginning at the centerline of the waveguide fiber, and two annular segments surrounding the central segment. In one embodiment, the profile has four segments, a central segment, surrounded by a first, second and third annular segment. Each of the segments is characterized by a refractive index profile, a relative refractive index, and an inner and an outer radius. The respective segment characteristics are selected to provide a waveguide fiber having a total dispersion at 1550 nm in the range of −30 ps
m-km to −60 ps
m-km and preferably in the range of −30 ps
m-km to &

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