Optical transmission element and method for reducing...

Optical waveguides – Optical fiber waveguide with cladding

Reexamination Certificate

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C385S011000

Reexamination Certificate

active

06278828

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to an optical transmission element having at least one optical waveguide which comprises a given polarization-mode dispersion.
In practice, it can occur that some of the optical waveguides in optical transmission elements comprise an impermissibly high dispersion. As a result, in such optical waveguides their bandwidth for communication transmission can be too strictly limited. Particularly when what is known as a monomode fiber is utilized for the respective optical waveguide, its polarization-mode dispersion—that is, the transit time difference between its light waves, or modes, respectively, that are capable of dispersion (=natural waves)—can exceed an allowed limit value. This would lead to an impermissibly high impulse distribution of light signals that are to be transmitted in the respective optical waveguide.
U.S. Pat. No. 5,867,616 (see International PCT publication WO 97/06456) describes an optical waveguide in which, in order to reduce polarization-mode dispersion, imperfections—that is to say, birefringences-in the form of trenches are introduced into a preform of the optical waveguide during production.
International PCT publication WO 96/23739 teaches a method for producing an optical fiber. Manipulations are performed on the fiber by irradiation during the production process—that is to say, during the process of producing the preform from which the fibers are drawn.
U.S. Pat. No. 5,440,659 (see European published patent application EP 0 646 819 A1 teaches a method for producing a fiber-optic cable wherein a plurality of optical fibers are stranded together so as to effectuate a reduction of the polarization-mode dispersion.
SUMMARY OF THE INVENTION
The object of the invention is to provide an optical waveguide in transmission elements which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and wherein impermissibly high polarization-mode dispersion is reliably prevented to a large extent subsequent to the production thereof.
With the above and other objects in view there is provided, in accordance with the invention, an optical transmission element, comprising:
an optical waveguide having a given polarization-mode dispersion;
at least one outer protective layer applied to and completely surrounding the optical waveguide; and
a plurality of imperfections for reducing the given polarization-mode dispersion formed by additional material applications applied on an outer surface of the outer protective layer and distributed at irregular intervals along a length of the optical waveguide for purposefully effecting additional polarization-mode couplings for transmission light in an interior of the optical waveguide.
The term “optical waveguide” as used above includes one or more waveguides.
In accordance with an added feature of the invention, the material applications are color markings.
With the above and other objects in view there is also provided, in accordance with a variation of the invention, an optical transmission element, comprising:
an optical waveguide having a given polarization-mode dispersion;
at least one outer protective layer applied to and completely surrounding the optical waveguide; and
filling compound embedding the optical waveguide, the filling compound containing particles distributed along the optical waveguide at irregular intervals and forming imperfections along the optical waveguide for reducing the given polarization-mode dispersion, for purposefully effecting additional polarization-mode couplings for transmission light in an interior of the optical waveguide.
In accordance with an additional feature of the invention, an elongated winding material is wrapped around the optical waveguide or waveguides, the winding material forming a disturbing mechanism for effecting additional imperfections and thus additional dispersion-mode couplings in the optical waveguide(s).
In accordance with another feature of the invention, the optical waveguide is twisted with an irregularly varying twist length for effecting additional imperfections. In the alternative, the optical waveguide is stranded with an irregularly varying twist length for effecting additional imperfections.
In accordance with a further feature of the invention, there is provided an outer sheath forming a tube surrounding the optical waveguide or the plurality of optical waveguides.
In accordance with again an additional feature of the invention, the optical waveguide is post-processed with a number of imperfections guaranteeing at least 0.001%, and in particular between 0.01 and 1%, more dispersion-mode couplings than the optical waveguide substantially without imperfections.
By providing additional disturbing mechanisms along the longitudinal extent of the respective optical waveguide in a statistically distributed manner—whereby the imperfections effectuate purposeful additional polarization-mode couplings for transmission light in the interior of the optical waveguide from the outside—it is possible to subsequently reduce the polarization-mode dispersion of the respective optical waveguide. Thus, even optical waveguides whose polarization-mode dispersion was impermissibly high—for whatever reasons—prior to the use thereof in the respective optical transmission element can be subsequently brought to within an acceptable upper limit value. When all optical waveguides that are provided for use are post-processed in this way, then it is preventively ensured to a large extent that all the optical waveguides which are ultimately included in the finished optical transmission element also comprise a sufficient bandwidth. Intensive polarization-mode dispersion measurements for sorting and separating out optical waveguides that may comprise an impermissibly high polarization-mode dispersion and thus do not satisfy quality standards for communication transmission are thus largely avoided.
In accordance with again an added feature of the invention, the optical waveguide is a monomode fiber. When such a monomode or single-mode fiber is used for the respective optical waveguide, the originally given polarization-mode dispersion can be retroactively reduced in a particularly effective manner with the aid of the novel post-processing according to the invention.
There is also provided, in accordance with the invention, an optical cable provided with at least one optical transmission element according to the above and following summary.
As noted above, the novel optical transmission element may comprise at least one optical waveguide with the described polarization-mode dispersion, wherein, for the subsequent reduction of the given polarization dispersion of the respective optical waveguide thereof, the respective optical transmission element is stranded with a statistically varying twist length around a core element, thereby subsequently producing disturbance mechanisms which purposefully externally effectuate additional polarization-mode couplings for transmission light in the interior of the optical waveguide.
The invention also relates to an optical waveguide having an optical fiber onto which at least one all-round external protective layer has been applied and which comprises a predetermined polarization-mode dispersion; which is wherein imperfections have been subsequently introduced onto the outer protective layer in a statistically distributed manner in such a way that additional polarization-mode couplings are purposefully effectuated for transmission light in the optical fiber, whereby the predetermined polarization-mode dispersion of the optical fiber can be subsequently reduced.
With the above and other objects in view there is also provided, in accordance with the invention, a method for reducing the polarization-mode dispersion of optical waveguides. In order to reduce the predetermined polarization-mode dispersion of the respective optical waveguide afterward, imperfections are subsequently created along its length from the outside and are statisti

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