Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Optical fiber – waveguide – or preform
Reexamination Certificate
2000-10-20
2002-07-02
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Optical fiber, waveguide, or preform
C219S121720, C264S001260, C264S001370, C264S002700, C264S482000
Reexamination Certificate
active
06413450
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to optical fibers. More particularly, the present invention is directed toward segmentation of optical fibers suitable for use with data communication.
To minimize insertion loss, the loss of optical energy when coupling data links in fiber-optic communication systems, it is important to correctly match the aperture through which optical energy is transmitted with the aperture through which optical energy is detected. As a result the areas of the apertures must be correctly sized and aligned.
The ideal interconnection of one fiber to another would have two fibers that are optically and physically identical and held by a connector that aligns the fibers so that the interconnection does not exhibit any influence on light propagation therethrough. Formation of the ideal interconnect is impractical for several reasons. These include variations in fiber properties, tolerances in the connector, as well as and in cost and ease of use.
Commercially available interconnection devices have typical insertion losses from between 0.2 dB to 4 dB. This range of insertion loss results from several factors that maybe divided into those related to fibers and those related to interconnection devices. Fibers intrinsically contribute loss to an interconnection and any fiber has variations that are produced during manufacture. These variations exist not only among different lots of fibers, but also within a length of a single fiber, as well. The main variations in these cases are in the core and cladding diameters and fiber numerical aperture (NA). The core ellipticity, cladding ellipticity, and core-to-cladding eccentricity exacerbate the problems associated with variations in the core and cladding diameters. Losses caused by diameter variations, NA variations, eccentricity, and ellipticity are intrinsic to the fiber and the total loss contributed by these intrinsic factors can range from less than 0.2 dB to over 2 dB, depending on how well two fibers match.
Connector-related losses may also arise even when there are no intrinsic variations in the fibers. These types of losses arise when two fibers are not aligned on their center axes and lateral or axial displacement can be, and usually is, the greatest cause of loss in the connection. For example, a 0.5 dB loss that is due to a displacement, equal to 10% of the core diameter, will require tolerances to be maintained on each connector (fiber) that is within 2.5 &mgr;m. Tolerances of this magnitude are difficult to achieve. Add to this, the losses that are also induced due to angular misalignment, and the total tolerances that must be maintained in the termination process, proper fiber and/or connector end preparation becomes problematic.
The considerations discussed above with respect to fiber-to-fiber interconnections apply equaling to fiber-source and fiber-detector interconnections, as well. The result is that the requirements that should be achieved to provide efficient optical coupling necessitate end-finishing or termination processes that strives to provide lossless propagation of optical energy. To that end, it is desired to provide the end of a fiber that functions as either a transmission or reception aperture with a smooth finish free of such defects that may change the geometrical propagation patterns of optical energy passing therethrough. These defects include hackles, burrs, and fractures.
Preparation of conventional glass optical fibers employs score-and-break techniques or mechanical polishing techniques. The score-and-break technique provides an optical fiber with an arc that is scored. Tension is applied to that optical fiber so that the score propagates across the width of the optical fiber, segmenting the same. This technique is capable of producing excellent end finishes. Repeatability, however, is difficult, lowering yields and increasing the cost of the finished optical fibers. In addition, a great amount of skill is required to properly control both the depth of the scoring and the amount of tension during breaking. The aforementioned control may be frustrated by intrinsic fiber variations. Finally, the difficulty in controlling both the depth of scoring and breaking tension increases as the length of the optical fiber becomes shorter.
Polishing, compared to scribing-and-breaking, has the advantage of consistent results, but is a much more costly technique. Polishing is typically performed after a connector, or ferrule, has been attached to the optical fiber. Polishing a bare optical fiber is impractical. Usually, a polishing fixture is provided that controls the polishing to a fixed dimension, e.g., usually within 0.3 &mgr;m.
Polymer-based optical fibers may be segmented with a sharp, and preferably hot, blade. As with the polishing technique mentioned above with respect to glass optical fibers, segmenting is performed on polymer-based optical fibers after a connector has been attached. Polymer-based optical fibers may also be polished, but with great difficulty.
In addition to providing a smooth end finish, the preparation procedure should provide the optical fiber with a cleaved end, i.e., the end of the optical fiber should be planar and lying in a plane with the longitudinal axis of the optical fiber extending orthogonally thereto. Otherwise, an angle may exist between the axes of juxtaposed fibers and fibers-devices, referred to as tilting. Tilting can cause additional, and sometimes quite severe, losses in addition to those mentioned previously. While tilting loss can be controlled to some degree by proper end preparation and positioning of adjacent fiber ends, it should not be completely ignored. Often alignment mechanisms are employed to reduce the effects of tilting. Such alignment mechanisms includes lenses that may be effectively coupled and aligned, (with minimum loss, to the end of the optical fiber).
Referring to
FIG. 1
, a fiber-to-fiber arrangement
10
employing lensed optical fibers
12
and
14
is shown. The lenses are shown as
12
a
and
14
a
, at the ends of the optical fibers
20
and
22
, respectively. The lenses
12
a
and
14
a
are typically spherical and refract optical energy, shown as
12
b
and
14
b
, propagating therethrough to facilitate control of the path of light therebetween. In this manner, the lateral and axial alignment between the optical fibers
12
and
14
may be relaxed. However, the fibers
12
and
14
should be accurately placed and aligned behind the lenses in order to actually see any real or significant benefits to the overall loss considerations (e.g., low losses). Moreover, such conditions are most often achieved without the aid of non-integral support elements such as lenses, when the appropriately prepared fiber ends are perpendicular to the fiber axis. One manner in which to form lenses
12
a
and
14
a
is discussed below with respect to a source-fiber arrangement.
Referring to
FIG. 2
, shown is a source-fiber arrangement in which a lens is formed on one end of an optical fiber. The fiber-source arrangement
16
includes an optical fiber
18
composed of a core
18
a
and a cladding
18
b
. A lens
20
is
30
formed at an end of a fiber core. Were the optical fiber
18
formed from silica glass, the lens
20
would be formed in the following manner: First, while a portion of the silica glass optical fiber
18
is heated by heating means such as a burner, a tensile force is applied to the fiber in the longitudinal direction thereof, whereby the heated portion extends. When the outer diameter of the heated portion has decreased to a predetermined diameter, the optical fiber
18
is cut at the diameter-reduced portion, and then the cut end is again heated for fusion. In the heating step, the extreme end
22
of the optical fiber
18
, including the core
18
a
in the center thereof, becomes spherical in shape due to surface tension, and this spherical end functions as a lens. Thus, the lensed optical fiber
18
has a taper portion
24
extending from the extreme end
22
to an outer peripheral edge which
Brooks Kenneth C.
Megladon Manufacturing Group
Vargot Mathieu D.
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