Optical waveguides – Accessories – External retainer/clamp
Reexamination Certificate
2001-06-21
2003-12-30
Ullah, Akm Enayet (Department: 2874)
Optical waveguides
Accessories
External retainer/clamp
C385S094000, C385S120000
Reexamination Certificate
active
06671450
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to an apparatus and method to connect multiple optical fibers to a package, and more specifically to an apparatus and method to metallize optical fibers, reinforce metallized optical fibers, and hermetically seal the connection of metallized optical fibers to a package.
BACKGROUND OF THE INVENTION
In many optical and electro-optical and optical packages and systems (e.g., computer systems, programmable electronic systems, telecommunication switching systems, control systems, and so forth) the reliable connection of multiple optical fibers to a package is desired, but difficult to achieve due to the fragile nature of the optical fibers and the water permeability of the polymer coating (e.g., urethane acrylate and equivalent polymers) surrounding each optical fiber. The migration of water into a package through the polymer coating surrounding each optical fiber has a detrimental effect on the operation and reliability of the components inside the package.
One solution for connecting one or more optical fibers to a package is to remove the polymer coatings surrounding each optical fiber and coat the bare optical fiber with a solderable metal, such as nickel or lead-tin solder. Then each optical fiber is soldered into an opening of a package with sufficient-solder to completely seal the optical fiber opening of the package. Prior art solutions are typically addressed to metal-coating each optical fiber on the very end of a bare optical fiber, one at a time.
However, this process introduces several new problems. One problem is that the optical fiber becomes very brittle and easy to break after the polymer coating is removed, since the polymer coating supplied mechanical support to the optical fiber. Another serious problem is created when the optical fiber is coated with a solderable metal, because the thermal shock of being coated with hot metal frequently degrades the optical and mechanical properties of the optical fiber. Furthermore, it is usually necessary to deposit multiple metal-coatings (creating multiple thermal shocks) on an optical fiber to achieve sufficient metal adhesion to the optical fiber. Additionally, it is extremely difficult to solder individual metal-coated optical fibers to package openings without breaking off the weakened metal-coated end of the optical fiber. Finally, it is also extremely difficult to solder multiple individual metal-coated optical fibers one-at-a-time, without the previously soldered optical fibers coming loose and shifting in position. Since the positioning of optical fibers is extremely critical to the optical coupling efficiency of the connection, even a shift between an optical fiber and a component exceeding 0.5 micron can be detrimental to the operation of an optical or electro-optical device.
FIG. 1
illustrates one approach for handling package connections in an electro-optical or optical system
100
. Electro-optical system
100
shows an example of package
102
with ribbon cable
104
conventionally routed into the package
102
through opening or junction
106
.
FIG. 2A
shows an example of a cross section of an individual fiber
200
from ribbon
104
in cross-section
2
A—
2
A from FIG.
1
. As seen in a conventional assembly, individual fiber
202
may be typically surrounded by polymer coating
204
that is coated with a metal sleeve
206
and soldered into a wall at junction
106
of package
102
. Polymer coating
204
may provide a path for the migration of water into package
102
and the eventual failure of components within electro-optical system
100
. If coating
204
were removed from optical fiber
202
, optical fiber
202
may become extremely brittle and easy to break during the process of soldering metal sleeve
206
to package
102
.
Even if every opening is properly sealed by solder, the fragility of the optical fibers
202
near the soldered connections and the lack of mechanical reinforcement make it easy to break the optical fibers
202
when forces are imparted to the ribbon
104
. The prior art metallization on the end of an optical fiber makes it difficult to mechanically clamp or reinforce the optical fiber near the soldering point. Mechanical clamping and reinforcement would be greatly facilitated by the extension of each optical fiber into a package. This would allow the optical fiber and package opening to be soldered some distance away from the end of the optical fiber. Then clamping and reinforcement could support the optical fiber on the outside of the package opening, as well as support the optical fiber on the inside of the package opening.
Furthermore, most optical and electro-optical systems may require several groups of optical fibers (e.g., bundled in ribbons of optical fibers) connected to one or more packages. The conventional method of connecting separate optical fibers to a package also has the disadvantage of requiring several package openings. Each package opening provides another point of entry for water into the package. Therefore, it would be preferable to minimize the number of package openings by connecting multiple optical fibers through one package opening to the components inside the package.
It would also be desirable to have the capability to selectively metallize multiple optical fibers in a bundled configuration along any segment of the bundle without breaking the optical fibers. The selective metallization would make it easier to reliably connect multiple optical fibers in a bundled (e.g., ribbon or cabled) configuration to a package using solder to seal the package opening to avoid moisture and gas migration into the package. It would also be desirable to provide an apparatus and method to reduce the stress on metallized optical fibers created by hermetically sealing the connection of metallized optical fibers to a package.
SUMMARY OF THE INVENTION
It is difficult to route optical fibers through a package opening for a component package. In such a case, metallized fibers may be used at the junction point where the fibers extend through the package wall to aid in sealing the package. However these fibers become very fragile and easy to break. Accordingly, apparatus and methods to metallize, reinforce, and hermetically seal multiple optical fibers are described herein.
A ribbon of optical fibers ranging from one to several dozen individual fibers may be placed into a fixture as described herein which preferably exposes only a select portion of the mid-span segment. The exposed portion may correspond to the geometry of the length of the ribbon segment to be stripped and metallized, as described below. The exposed segment of ribbon may be stripped of polymer coatings surrounding each of the individual fibers through a variety of methods, preferably by acid etching or alternatively by laser etching, etc. Then, a variety of metallic coatings may be deposited onto the bare segment of the optical fibers, preferably while the ribbon is still disposed within the fixture. The metallic coatings may comprise one to several layers, e.g., an adhesion layer, a solderable layer, and a protection layer.
Once metallized, the segment of optical fibers may then be positioned onto a metallic plate and soldered onto the plate for reinforcement of the metallized segment. Epoxy may additionally be deposited onto the fibers and plate to further affix the assembly. The plate and metallized segment may then be fed through a package opening. Once properly positioned within an opening, flux and additional solder may be melted around the gap defined between the plate and fiber assembly and the package opening. In addition to the solder, epoxy may also be applied over the solder to help protect the solder and additionally seal the package. This may result in a hermetic seal of the package preferably having a package leak rate less than about, e.g., 10
−9
AtmCC/sec (air) which is lower than an industry Mil-spec. standard of 10
−6
AtmCC/sec (air). The hermetic seal may also provide protection of the package interior from marine and
Garcia Rickquel B.
Guardado Maria G.
Khan Mohammad Zubair
Connelly-Cushwa Michelle R.
Lightwave Microsystems Corporation
Morrison & Foerster / LLP
Ullah Akm Enayet
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