Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
2002-04-19
2004-03-23
Lee, John D. (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S125000
Reexamination Certificate
active
06711333
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to a dispersion compensating optical waveguide fiber, a method of making the dispersion compensating optical waveguide fiber, and an optical communications link containing the dispersion compensating fiber and more particularly to a dispersion compensating optical waveguide fiber having a multiple core.
2. Technical Background
Optical telecommunication systems operating at very high bit rates typically require a low attenuation, large effective area optical waveguide fiber to achieve acceptable span lengths between electronic signal regenerator installations. The operating wavelength window extending from about 1450 nm to 1650 nm is attractive because of the low attenuation exhibited by silica based optical waveguide fibers over that wavelength range. To operate a system in this desired wavelength range, a transmission optical waveguide fiber was developed having a zero dispersion wavelength in or near this wavelength range. At the same time, the transmission optical waveguide fiber was designed to have large effective area in order to limit dispersion due to those non-linear effects that increasingly degrade the signal as signal power density increases.
A further advance in optical waveguide fiber design was made by locating the fiber zero dispersion wavelength outside the wavelength range over which the fiber was to be operated. By maintaining total dispersion magnitude greater than zero, preferably greater than about |0.5 ps
m-km|, the negative impact of the non-linear phenomenon, four wave mixing, was essentially eliminated.
However, because the total dispersion of the improved fiber was not zero over the operating wavelength window and desired span lengths were long, there was a need to compensate for the total dispersion accumulated over a span length. The concept of a dispersion compensating fiber, having a total dispersion opposite in sign to that of the transmission fiber, was explored and appropriate dispersion compensating fibers were developed and proven successful. The dispersion compensating fibers developed typically incorporated a core refractive index profile having two or more distinct segments, a design that is generally more costly to manufacture in comparison to a step index profile or a graded index profile having only one segment.
An additional requirement was placed upon the dispersion compensating fiber in that high data rate telecommunication systems generally employ wavelength division multiplexing. If the dispersion compensating optical waveguide fiber was to be effective, compensation had to be relatively uniform over the band of wavelengths of the multiplexed signals. That is, the slope of the total dispersion of the compensating fiber had to be adjusted to achieve uniform compensation over an operating band of wavelengths.
Although, the segmented core dispersion compensating fibers have served to improve system performance, the total dispersion of the compensating fibers exhibit considerable curvature over the preferred operating wavelength range. Work has therefore continued to design dispersion compensating optical waveguide fibers that exhibit the desired total dispersion, linearity of total dispersion over the operating window, and afford relatively low manufacturing cost.
SUMMARY OF THE INVENTION
One aspect of the invention is a multiple core, dispersion compensating optical waveguide fiber that includes a center region surrounded by a clad layer. The center region includes at least two optical waveguide fiber cores. An optical waveguide fiber core is defined as the structure that serves to confine light within the fiber. Each of the cores has a refractive index profile. At least two cores have refractive index profiles that are different from each other. The refractive index profiles of the respective cores and their relative positioning within the center region provide for coupling of light from one core to at least one other core. The multiple core optical waveguide fiber is configured to have negative total dispersion and negative total dispersion slope over a pre-selected wavelength range.
In an embodiment of this aspect of the invention, the pre-selected wavelength range extends from about 1525 nm to 1565 nm, and the total dispersion slope is more negative that −4.0 ps
m
2
-km over the pre-selected wavelength range. In this embodiment, the ratio of total dispersion to the total dispersion slope can be approximately 50 nm at 1550 nm. Additionally, in this embodiment the total dispersion is substantially linear (total dispersion slope is substantially constant) over the pre-selected wavelength range.
In another embodiment of this aspect of the invention, the center region includes at least seven structural elements arranged as six structural elements surrounding a centrally positioned structural element. The centrally positioned structural element has a refractive index profile which guides light and so it properly denoted a core. At least three of the surrounding structural elements are cores.
In another embodiment of this aspect of the invention, the center region contains at least seven structural elements of substantially equal diameter arranged as six structural elements surrounding a centrally positioned structural element configured to be a core. At least three of the surrounding structural elements are configured to be cores. The centrally positioned core and the three surrounding cores each contain a dopant material that serves to increase the relative refractive index percent of respective portions of the respective cores. When the dopant material causes the refractive index of the core portion to increase, the value of the relative refractive index percent of the doped portion is positive, as can be seen from the definition of relative refractive index percent given below. The remaining three surrounding structural elements have a uniform refractive index. The cores having a uniform refractive index can be fabricated without use of a dopant material, although a dopant material can be used to uniformly raise or lower the refractive index of the core relative to that of the clad layer. In the case where a structural element of the center region of the multiple core optical waveguide fiber has a relative refractive index percent equal to or less than that of the cladding layer, the structural element does not function to confine light to the fiber and so is denoted a spacing element. The six surrounding structural elements can advantageously be arranged so that each surrounding core containing a dopant material over a core portion is neighbored by two surrounding cores of uniform refractive index. The cores containing a dopant material over a core portion preferably have their portions of increased relative refractive index percent positioned to include and be symmetrically distributed about their respective centerlines. Preferably, the centrally positioned core has a portion having a relative refractive index percent (&Dgr;%) of approximately 2.0%, the portion having a diameter of approximately 3 &mgr;m. In the context of reference to the &Dgr;% and radius of the core or clad of an optical waveguide fiber, the term approximately generally means ±/−10% of the nominal value stated. This 10% tolerance will be understood to pertain to all relative refractive index percent and radius values stated throughout the specification. Also preferably, the surrounding cores containing a dopant material over a core portion each have a portion of relative refractive index percent of approximately 1.0%, the portion having a diameter of approximately 6.4 &mgr;m. The surrounding cores having a uniform relative refractive index percent over the core preferably have a relative refractive index percent of approximately 0.7%. Preferably in this embodiment each of the seven cores has an outside diameter of approximately 12 &mgr;m. As is described in more detail below, any of the core portions having a non-zero relative refractive index pe
West James A.
Wood William A.
Able Kevin M.
Chervenak William J.
Corning Incorporated
Lee John D.
Valencia Daniel
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