High capacity optical waveguide fiber

Details High capacity optical waveguide fiber High capacity optical waveguide fiber

2002-10-25

2004-10-05

Tremblay, Mark (Department: 2876)

Optical waveguides

Optical fiber waveguide with cladding

C385S124000, C385S126000

Reexamination Certificate

active

06801699

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
An optical waveguide fiber is disclosed herein for high capacity telecommunications systems and particularly an optical waveguide fiber combining large effective area and resistance to bend induced attenuation.
2. Technical Background
Optical waveguide fibers designed for transmission of greater information capacity over long distances, preferably without use of electronic regenerators, typically reduce certain types of non-linear interactions of the signal by providing high effective area. In addition, the signal degrading effect commonly called four wave or four photon mixing, an effect that occurs in communications systems using wavelength division signal multiplexing, can be counteracted by control of the optical waveguide fiber total dispersion over the operating wavelength range. That is, the total dispersion is made to be non-zero over the operating wavelength range, thus altering the phase relationship among the signals in such a way that they do not interfere.
Through use of dispersion compensation strategies, a high capacity optical waveguide fiber can have a greater total dispersion magnitude over the operating window of a communication system. Thus, the design limitations are loosened somewhat, allowing a refractive index profile researcher to relax total dispersion requirements while improving other key fiber properties such as attenuation and resistance to bend induced attenuation.
An additional important factor in refractive index profile design of high capacity optical waveguide fibers is the simplicity of the profile as simplicity of design relates to manufacturing cost. For example, a core region that provides the desired properties but has fewer significant changes in refractive index along a radius will in general be easier to manufacture.
The present invention addresses the need for high capacity optical waveguide fiber designs which have a simpler refractive index profile structure and provide high effective area while maintaining low attenuation and providing excellent resistance to bend induced attenuation.
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 (percent) 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
=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 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. A positive relative index percent occurs where the refractive index is greater than the average refractive index of the cladding.
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
0
|/(b
1
−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 bend resistance of a waveguide fiber is expressed as induced attenuation under prescribed test conditions. Bend induced attenuation is also called bend loss herein. A bend test referenced herein is the pin array bend test that is used to compare relative resistance of waveguide fiber 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 in a serpentine path through the pin array and attenuation again measured. The loss induced by bending is the difference between these two measured attenuation values expressed 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. During testing, sufficient tension is applied to make the serpentine woven waveguide fiber conform to the portions of the pin surface at which there is contact between fiber and pin.
Another bend test referenced herein is the lateral load wire mesh test. In this test a prescribed length of waveguide fiber is placed between two flat plates. A #70 wire mesh is attached to one of the plates. A known length of waveguide fiber is sandwiched between the plates and a 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 is measured and expressed in dB/m. This increase in attenuation is the lateral load attenuation (or lateral load bend loss) of the waveguide.
A further test of the bend resistance of a waveguide fiber is one in which the fiber is wrapped a specified number of turns about a mandrel of a specified diameter. In each test condition the bend induced attenuation is expressed in units of dB/m, the length being determined by the number of turns of fiber and the mandrel diameter. The mandrel wrap test referenced herein is one in which induced attenuation is measured for 1 turn of waveguide fiber around a 20 mm diameter mandrel.
SUMMARY OF THE INVENTION
In one aspect, an optical waveguide fiber is disclosed herein which includes a central core region surrounded by and in contact with a clad layer. The central core region has a refractive index profile, a radius, and a centerline. The central core region has a portion with a refractive index profile configured to provide a local minimum relative refractive index percent on or near the centerline which is a fraction of the maximum relative refractive index percent of the central core region. In particular, the fraction formed by the ratio of the local minimum relative refractive index percent on or near centerline to the maximum value of relative refractive index percent in the central core region is in the range from 0.65 to 1.0. This fraction, together with the value of central core radius and maximum relative refractive index percent are chosen to provide an optical waveguide fiber having an effective area not less than 115 &mgr;m
2
at 1550 nm, a 20 mm mandrel wrap bend loss at 1550 nm not greater than 25 dB/m, and a lateral load wire mesh bend loss at 1550 nm not greater than 1.5 dB/m, preferably not greate

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