Large effective area optical fiber

Details Large effective area optical fiber Large effective area optical fiber

2001-11-28

2003-08-26

Ullah, Akm E. (Department: 2874)

Optical waveguides

Optical fiber waveguide with cladding

C065S385000

Reexamination Certificate

active

06611647

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
A single mode optical waveguide fiber for use in telecommunication systems and more particularly, a waveguide fiber which reduces non-linear dispersion effects, combines bend resistance, low polarization mode dispersion (PMD), low attenuation, and large effective area features desired, for example, in underground and undersea applications is disclosed herein.
2. Technical Background
Optical amplifier technology and wavelength division multiplexing techniques are typically required in telecommunication systems that require high power transmissions for long distances. Undesirable non-linear effects become more pronounced for higher powers and/or longer distances. The definition of high power and long distances is most meaningful in the context of a particular telecommunication system wherein a bit rate, a bit error rate, a multiplexing scheme, and perhaps optical amplifiers are specified. Additional actors, known to those skilled in the art, have impacted upon the definition of high power and long distance. However, for most purposes, high power could be considered to be an optical power greater than about 10 mW. In some applications, single power levels of 1 mW or less are still sensitive to non-linear effects, so that the effective area is still an important consideration in such lower power systems. A long distance could be considered to be an application in which the distance between optical regenerators or repeaters or amplifiers is in excess of 50 km or more. Regenerators are to be distinguished from repeaters that make use of optical amplifiers. Repeater spacing, especially in high data density systems, can be less than half the regenerator spacing. To provide a suitable waveguide for a multiplex transmission, the total dispersion should be low, but not zero, and have a low dispersion slope over the window of operating wavelength.
Generally, an optical waveguide fiber having a large effective area (A
eff
) reduces non-linear optical effects, including self-phase modulation, four-wave-mixing, cross-phase modulation, and non-linear scattering processes, all of which can cause degradation of signals in high powered systems. In general, a waveguide fiber having a segmented core can provide a large effective area while limiting the non-linear optical effects.
The mathematical description of these non-linear effects includes the ratio, P/A
eff
, where P is the optical power. For example, a non-linear optical effect can be described by an equation containing the term, exp [P×L
eff
/A
eff
], where L
eff
is effective length. Thus, an increase in A
eff
produces a decrease in the non-linear contribution to the degradation of a light signal. On the other hand, an increase in effective area of an optical waveguide fiber typically results in an increase in microbending induced losses which attenuate signal transmission through a fiber. The microbending losses become increasingly significant over long distances or spacing between regenerators, amplifiers, transmitters and/or receivers.
Optical amplifier technology and/or wavelength division multiplexing techniques are typically employed in communication systems which require one gigabyte per second and higher transmission rates. Thus waveguide fiber manufacturers have designed waveguides that are less susceptible to non-linear effects induced by higher power signals or by four wave mixing in multiplexing systems. Preferred waveguide fibers have low linear dispersion and low attenuation as well. Furthermore, fiber polarization mode dispersion (PMD) may be a major contributor to overall system PMD. Therefore, a suitable waveguide fiber should also have low PMD. Lower fiber PMD can also provide upgrade paths for high bit rate transmission (e.g. 40 Gbs and higher) in existing or upgraded systems. In addition, the waveguide fiber preferably displays these properties over a particular extended wavelength range in order to accommodate wavelength division multiplexing used for multiple channel transmission.
SUMMARY OF THE INVENTION
One aspect of the optical waveguide fiber disclosed herein relates to a relatively large effective area single mode optical waveguide fiber that offers low microbending sensitivity. The fibers disclosed herein preferably include a single segment core. The core region is described by a refractive index profile, a relative refractive index percent, and an outer radius. The optical waveguide fiber further includes a clad layer surrounding and in contact with the core. Unless indicated otherwise, the effective area described herein corresponds to a wavelength of about 1550 nmn.
Preferably, the effective area of the fibers disclosed herein is greater than or equal to about 90 &mgr;m
2
, and exhibits microbending of less than or equal to about 3.0 dB/m, more preferably less than or equal to about 2.0 dB/m, even more preferably less than or equal to about 1.5 dB/m, even still more preferably less than or equal to about 1.0 dB/m, yet still more preferably less than or equal to about 0.8 dB/m, and even still more preferably less than or equal to about 0.5 dB/m.
The core region and cladding layer preferably define a step-index refractive index profile. Preferably, the fibers disclosed herein has a maximum relative index &Dgr;
1
% of between about 0.20% and about 0.35%, more preferably between about 0.24% and about0.33%, even more preferably between about 0.26% and about0.32%, and still more preferably between about 0.27% and about0.31%. Preferably, the core radius of the fibers disclosed herein, measured at half the maximum or peak relative index, is between about 4.0 &mgr;m and about 7.0 &mgr;m, more preferably between about 4.5 &mgr;m and about 6.5 &mgr;m, and still more preferably is between about 5.0 &mgr;m and about 6.2 &mgr;m.
The fibers disclosed herein further preferably comprise a primary coating surrounding the cladding and a secondary coating, also known as an outer primary coating, surrounding the primary coating. The primary coating is preferably selected to have a modulus of elasticity of less than about 5 MPa, more preferably less than about 3 MPa, and even more preferably less than about 1.5 MPa. Preferably, the modulus of elasticity of the secondary coating is greater than 700 Mpa, more preferably greater than 800 Mpa, and even more preferably over 900 MPa.
Preferably, the fibers disclosed herein comprise a core region of silica which is up-doped with germania, and a cladding of silica. Preferably, the cladding contains no down-dopants. Even more preferably, the cladding contains no fluorine. Most preferably, the cladding comprises pure or substantially pure silica.
In another aspect, the optical waveguide fiber disclosed herein relates to a relatively large effective area single mode optical waveguide fiber having a step-index profile. Preferably, the effective area of the fibers disclosed herein is greater than or equal to about 90 &mgr;m
2
. In one or more preferred embodiments, the effective area is between about 90 &mgr;m
2
and about 115 &mgr;m
2
, more preferably between about 95 &mgr;m
2
and about 110 &mgr;m
2
.
Preferably, the fibers disclosed herein have a maximum relative index &Dgr;
1
% of between about 0.20% and about 0.35%, more preferably between about 0.24% and about 0.33%, still more preferably between about 0.26% and about 0.32%, and yet more preferably between about 0.27% and about 0.31%. Preferably, the core radius of the fibers disclosed herein, measured at half the maximum or peak relative index, is between about 4.0 &mgr;m and about 7.0 &mgr;m, more preferably between about 4.5 &mgr;m and about 6.5 &mgr;m, even more preferably between about 5.0 &mgr;m and about 6.2 &mgr;m.
Preferably, the fibers disclosed herein comprise a core region of silica which is up-doped with germania, and a cladding of silica. Preferably, the cladding contains no down-dopants. Even more preferably, the cladding contains no fluorine. Most preferably, the cladding comprises pure, or substantially pure, silica.
The fibers disclosed herein pre

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