Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
1999-05-18
2001-02-13
Ullah, Akm E. (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C257S084000, C385S092000
Reexamination Certificate
active
06186674
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to optical sub-assemblies. More particularly it relates to the mounting of optical sub-assemblies (OSA's) in a package using means that provide sufficient resiliency to prevent or minimize distortion of the OSA and maintain proper optical alignment within the OSA when the package is subjected to mechanical stress, in particular, that caused by bolting the package to a rigid external platform and the like.
BACKGROUND OF THE INVENTION
Current pump laser packages typically include an optical sub-assembly that comprises a laser chip and an optical fiber that acts as a wave guide, both of which are mounted on a platform in proper optical alignment with each other. Often, the method employed to effect this alignment will depend on the degree of precision required (less precision is required for surface emitting lasers than for edge emitting lasers). For sub-assemblies comprising surface emitting lasers, where less precision is required, the alignment may be effected passively (e.g., using solder bumps and wettable pads, as taught, for example, in U.S. Pat. No. 5,499,312).
Bumps of solder (and other materials) have been used also to provide electrical conductivity in optical devices. Such use is disclosed, for example, in U.S. Pat. No. 5,689,279.
For applications where greater precision of alignment is required, as is the case for edge emitting laser chips, the alignment is effected actively, by activating the laser and moving it relative to the optical wave guide until maximum transmission is achieved. Once the alignment of laser to fiber is achieved, both the laser and the optical fiber are fixed to a platform, which is, in turn, mounted on a base, typically using solder to form a rigid joint. The fiber also is fixed to the package by using either welding or a solder joint to form a hermetic seal. The package base, in turn, is generally bolted to a rigid external platform. Such active alignment and bonding techniques are described in U.S. Pat. No. 5,700,987, the contents of which are hereby incorporated herein by reference.
The joint between the optical sub-assembly platform and the base serves as the main means for dissipating heat generated by the laser when it is being operated. Because of other structural requirements, the portion of the platform supporting the laser and the portion to which the fiber sheath is attached usually are formed of different materials. For example, the portion of the platform on which the laser chip is mounted can be beryllium oxide (BeO) whereas the portion of the platform to which the optical fiber sheath is attached may be Kovar. Also, the package base to which the optical sub-assembly platform is joined typically is made of yet another material, for example, copper/tungsten (CuW). Each of these materials has a different coefficient of expansion from that of the other materials. Upon heating or cooling of the package, the differential expansion or contraction causes stresses that tend to distort the sub-assembly platform. Any such distortion would tend to cause misalignment of the laser and fiber, thereby reducing the efficiency of the device. Similarly, stresses that tend to cause misalignment by distorting the sub-assembly are typically created when the package base is bolted to an external platform.
In copending parent application Ser. No. 09/153,386, the contents of which are hereby incorporated herein by reference, there is a description of resilient mounting means comprising resilient solder bumps, typically of the order of 625 microns thick, that are used to attach the sub-assembly platform to the package base. Said mounting means, which replace the rigid solder connection of the typical prior art optical sub-assembly, provide similar heat transfer from the platform to the base as was provided by the rigid prior art mounting means, while, at the same time, providing sufficient resiliency in the connection between the base and the platform to minimize stress on the platform and thereby prevent or minimize misalignment between the optical laser beam and the lens of the optical fiber. (The stress that otherwise would be transferred to the platform from the base could result from differential expansion or contraction due to temperature changes in the device or from forces arising from bolting or otherwise attaching the package base to a rigid external platform.)
SUMMARY OF THE INVENTION
The present invention provides alternative resilient mounting means for an optical sub-assembly so as to minimize distortion during bolting of the package to a rigid metal plate or other housing, said means comprising cut-outs in the package base. The invention thereby provides improved retention of alignment between the optical laser beam and the optical fiber lens on the sub-assembly by minimizing stresses on the sub-assembly platform. This enhanced alignment of the sub-assembly, in turn, enhances the efficiency of the device of which the sub-assembly is a part. Preventing misalignment is particularly important for optical sub-assemblies that employ edge-emitting laser devices. Thus, the tolerances for such devices are of the order of 0.2 to 0.3 microns.
In accordance with a first embodiment of the present invention, the package base on which the sub-assembly is mounted is modified to provide the requisite resiliency. More particularly, as described in greater detail hereafter, cut-out means are provided near the foot of the package base so that the stresses otherwise associated with affixing the package base, at the foot thereof, to an external plate or housing are minimized. In accordance with a second embodiment, the package base cut-out feature is used in combination with the resilient bump expedient disclosed and claimed in application Ser. No. 09/153,386 now allowed.
REFERENCES:
patent: 5333225 (1994-07-01), Jacobowitz et al.
patent: 5432358 (1995-07-01), Nelson et al.
patent: 5499312 (1996-03-01), Hahn et al.
patent: 5511140 (1996-04-01), Cina et al.
patent: 5537504 (1996-07-01), Cina et al.
patent: 5631991 (1997-05-01), Cohen et al.
patent: 5689279 (1997-11-01), Nelson et al.
patent: 5700987 (1997-12-01), Basavanhally
patent: 5990560 (1999-11-01), Coult et al.
patent: 6001664 (1999-12-01), Swirhun et al.
N. Basavanhally, “Application of soldering technologies for opto-electronic component assembly”, ASME Int. Electronic Packaging Conference, New York: ASME, 1993, pp. 1149-1155.
Y.C. Lee and N. Basavanhally, “Soldering engineering for optoelectronic packaging”, J. Metals, Jun. 1994.
N.R. Basavanhally, M.F. Brady, and D. Bruce Buchholz, “Optoelectronic Packaging of Two-Dimensional Surface Active Device”, IEEE Transactions on Components, Packaging, and Manufacturing Technology—Part B, vol. 19, No. 1.
Lucent Technologies - Inc.
Synnestvedt & Lechner LLP
Ullah Akm E.
LandOfFree
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