Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2001-08-23
2003-06-03
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S232000, C204S242000, C204S297010, C204S297100, C204S297140
Reexamination Certificate
active
06572743
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the preparation of terminal portions of optical fibers to be bonded, typically by soldering, into ferrules, connectors, laser diodes and related modules and devices. More particularly the present invention relates to the application of adherent metallic coatings to the ends of optical fibers to facilitate bonding of fiber ends at interfaces between the fiber ends and optoelectronic and related devices and modules including laser diodes. Adherent metallic coatings according to the present invention provide improved soldered joints having increased durability during repeated solder reflow to establish and maintain optimum alignment between light carrying optical fibers and optoelectronic packages and related devices to which they connect.
BACKGROUND OF THE INVENTION
The use of optical fiber communication networks has grown to provide an alternative to coaxial cable systems. Optical fiber communication networks include optoelectronic modules for transmitting and receiving signals. In a typical arrangement, optical fibers direct optical signals to and from a suitably packaged optoelectronic device. A common structure includes an optical fiber solder sealed inside a nose tube that is brazed to the sidewall of the package. This type of hybrid electrical-optical package arrangement is commonly referred to as a “fiber-pigtailed” hybrid package. The process for interfacing the fiber to the package is called “pigtailing.”
An efficient optical fiber communications network requires proper alignment between an optical fiber and an optical subassembly. In an optoelectronic receiver, a fiber is aligned with an optical detector, typically a PIN photodiode. Light signal generation requires an optoelectronic transmitter using a light emitting diode (LED) or laser diode aligned with a suitable waveguide, such as an optical fiber. An optical fiber, correctly aligned, minimizes the amount of light attenuation within a subassembly.
The manufacture of an optoelectronic hybrid package requires precise alignment of a fiber optic member with an LED, a laser diode, or a photodetector. Alignment may thereafter be maintained using means to lock optical fibers inside optoelectronic packages. A variety of materials have been used to bond optical fibers to selected substrates including metal alloy solders. During their lifetime microelectronic solder joints show three key failure modes of overload failure, due to handling; thermal fatigue failure, during service; and dimensional changes, particularly for optoelectronic devices. The microstructure of the solder has an impact on each of the three failure modes after formation of the soldered bond. Changes in microstructure of a particular soldered bond may occur because of the composition of the solder, the chemical nature of the substrate and the manufacturing process used to form the solder joint (see Proceedings of Symposium for Process Design & Reliability of Solders & Solder Interconnections, Feb. 10-13, 1997, pages 49-58). Such changes may result in creep within a soldered joint connecting an optical fiber to an optoelectronic device.
Problems may occur with alignment and coupling efficiency to and from an optical fiber when there is movement due to creep in a joint used to lock an optical fiber inside an optoelectronic package. For this reason a need may exist for periodic adjustment of alignment between optical fibers and optically active devices. Realignment of optical fibers has been investigated in a variety of ways using soldered joints to hold optical fibers in required alignment with optical devices. United States Patent U.S. Pat. No. 4,119,363 describes hermetic sealing of an optical fiber inside a metal tube using solder. The solder, upon solidifying and cooling squeezes against the fiber and forms a hermetic seal. After passing the tube-fiber assembly through a hole in the wall of a device package and aligning the fiber with the device, a solder bond holds the tube to the wall to maintain optimum alignment within the device package.
United States Patents, U.S. Pat. No. 5,692,086 and U.S. Pat. No. 6,164,837 use commercially available gold sleeved optical fibers to be held in alignment with optical devices inside optoelectronic packages.
Optical fibers held in place by soldered joints may be realigned by solder reflow to soften the solder thereby allowing the optical fiber to be repositioned. In some cases, the reflow process introduces microstructural changes leading to embrittlement and eventually failure of the joint.
Soldered connections, in the form of optical fiber splices, terminations and hermetic seals, may include a thin metallic layer over the surface of an optical fiber adjacent to the position at which the splice, termination or seal will be made. Metal coating of terminal ends of optical fibers facilitates solder bonding and attachment of one optical fiber to another optical fiber, to a laser diode, to a ferrule and to connection points of optoelectronic devices.
United States Patent, U.S. Pat. No. 4,033,668 describes a method for joining a first glass member, such as an optical fiber, to a second member by means of solderable splices and terminations, which additionally can form hermetic seals. The splice, termination or seal may be formed after coating the peripheral surface of the glass member with a thin adhering metallic layer. After properly positioning the coated glass member, formation of a splice termination or seal with a corresponding member, may use heated solder to flow around the joint to form a bond between the members when cooled. When the second member is also formed of glass, a thin adhering metallic layer, similarly formed on the peripheral surface thereof, provides a solder receptive surface in the area of the intended joint. Metal may be applied to terminal portions of e.g. optical fibers by dipping them into a paste containing conductive metal particles.
United States Patent U.S. Pat. No. 5,100,507 addresses finishing techniques for lensed optical fibers. The process of finishing an optical fiber places an integral lens and a metallized outer coating on the end of an optical fiber. Metal may be deposited on the ends of optical fibers using known sputtering techniques. Materials deposited in this way include titanium, platinum and gold. Application of metal close to the lensed end of an optical fiber allows the formation of a soldered connection very close to the tip of the fiber. This limits subsequent movement of a lensed fiber relative to an aligned optical device.
Prior description of soldered connections involves individual processing of metallized ends of optical fibers. Optical fiber handling represents a challenge for the optical fiber industry. Manufacturing operations may include a number of steps requiring handling of long and short lengths of optical fiber. These lengths of optical fiber are fragile filaments requiring Careful handling and more efficient processes to accelerate the production of optical fibers, for communication links and related devices. With a growing demand for optical fiber systems and devices, there is a need for processing a plurality of optical fibers simultaneously.
SUMMARY OF THE INVENTION
The present invention provides a galvanic cell designed for precision application of metal to an array of nonconductors previously processed, by known electroless metal plating techniques, to produce a conductive layer on at least a portion of the nonconductor. The electrolytic plating equipment and process permit simultaneous electrolytic plating of a plurality of optical fiber tails, taking advantage of the conductive electroless metal fiber coatings as the cathodes of the electroplating cell. During operation of the electrolytic plating cell, pure metal such as nickel may be applied to increase the thickness of a previously deposited electroless metal layer thereby adding metal to e.g. an optical fiber that may subsequently be hermetically sealed in an optoelectronic package. Experimental refinement optionally accompanied by numerical mo
Lentz David J.
Miller Michael N.
Yu Steven Y.
3M Innovative Properties Company
Ball Alan
Mutschler Brian L
Nguyen Nam
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