Optical waveguides – Accessories – External retainer/clamp
Reexamination Certificate
2001-10-01
2004-03-09
Prasad, Chandrika (Department: 2839)
Optical waveguides
Accessories
External retainer/clamp
Reexamination Certificate
active
06704488
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical fibers, and in particular to a packaging and assembly platform capable of accurately and easily connecting one or more optical fibers to one or more optical components having functions, such as optical detection, optical signal branching, optical multiplexing, optical switching, optical modulation and/or optical transmission. The present invention also describes optical modules comprising one or more optical components and such one or more packaging and assembly platforms.
DESCRIPTION OF THE PRIOR ART
As disclosed in U.S. Pat. No. 6,222,967, “Packaging Platform, optical modules using the platform, and methods for producing the platform and the module,” an optical component using a planar optical waveguide circuit, connection between an optical waveguide and an optical fiber requires alignment precision of the order of microns. Simplifying this connection is very important in reducing the manufacturing cost. An optical component which processes fast signals also involves fine electrical wiring, and thus requires a fan-out structure for electrical connection. An optical device generally needs sealing to achieve reliability. In an optical module having structures for a fiber pigtail and electrical wiring, it is necessary to seal large capacity regions above these structures. This has caused problems relating to packaging capacity and sealing effect.
Moreover, optical modules may have to implement many different types of components which can include lenses, individual gratings, thin film filters, isolators and/or other components which would need to be aligned and secured.
It is disclosed in the aforementioned patent that an improvement in the prior art of packaging and assembling optical components can be made by forming a packaging platform containing patterns which could be used to align optical waveguide components. It is further disclosed that this packaging platform could be made by injection molding or transfer molding. One class of materials discussed which could be used to create the packaging platform is synthetic resins. One specific class of synthetic resin discussed consisted of a thermosetting resin which contained inorganic fillers such as Talc, Mica, Calcium Carbonate, clay, alumina, alumina silicate, silica, zinc oxide, carbon, aluminum hydroxide, asbestos fiber, glass fiber and carbon fiber.
The aforementioned patent also mentions the use of ceramic as a packaging platform material, but no specific ceramic material is disclosed and no process for producing a module using ceramic was disclosed. Ceramic materials such as Alumina are mentioned, but only as an inorganic filler to a synthetic resin. In fact, the term ceramic is an extremely broad term used to include structural clay products, whitewares (dishes), refractories, glasses, abrasives and even cements. Most of these materials are not suitable for mounting and/or packaging optical, optoelectronic and/or electronic components. One type of ceramic material is fabricated using one or more powders, which are wet or dry pressed into a desired shape using either a hot or cold die. These materials are not discussed in the aforementioned patent.
Moreover, in embodiment 17 in the aforementioned patent, where the use of ceramic as a packaging platform is disclosed, the problem of shrinkage of the ceramic during firing or sintering is mentioned, which caused a deformation in the substrate. This deformation prevented the precise alignment of optical fibers or waveguides or other optical components. In order to resolve this, features were made by precision dicing into the ceramic substrate after firing or sintering, which were used for alignment in the transverse direction.
Thus features formed by injection or transfer molding of ceramic materials for the use of aligning optical fibers or waveguides or optical components were not disclosed in the aforementioned patent.
In addition, many aspects of sintered ceramic substrate formation were not discussed in the patent which would further inhibit the accurate formation of features in ceramic substrates after sintering. One such aspect includes so called ‘grain growth’ during sintering. In the case of Alumina ceramic substrates, this grain growth is essentially the assembly of A12O3 crystal-like structures which can extend outward from the surface of the molded pre-fired material. These grains can be greater than 1 micron in size and even greater than 10 microns in size. This deformation of the substrate would be in addition to the substrate shrinkage after sintering, making the tolerance of +−0.1 micron or +−1.0 micron difficult to achieve.
In addition, in the practice and implementation of such a packaging platform, the meaning of the dimensional tolerance of, for example, +−1.0 micron is not made clear in the aforementioned patent. This tolerance is presumed to be an overall tolerance of the platform, not a specific tolerance quantifying the dimensional accuracy of features on said platform which may be 10-100 microns apart. This is an important point since different deformation mechanisms will play different roles in the accuracy of the alignment of two optical components depending upon the size and distance between the components. For example, grain growth after sintering may impact the achievable alignment tolerance between two optical components located approximately 2 to 10 microns apart or 10 to 100 microns apart much more than shrinkage (or bow) after sintering.
Another factor not discussed in the aforementioned patent is the impact of binders which are typically (but not always) added to ceramic powders used to make ceramic substrates. These binders are used to keep the transfer molded pre-fired ceramic substrate or part's shape until the substrate or part has been fired or sintered. During the firing process, the binder is ‘burned off’ or thermally removed from the substrate or part and the formation of grain boundaries during firing play a key role in the structural stability of the substrate or part after firing.
Another factor not discussed in the aforementioned patent is the stability of the packaging platform to variations in ambient temperature. Many synthetic resins exhibit deformations in their physical geometry due to expansion and contraction of the material as the ambient temperature is changed. In the case of optical waveguide to waveguide coupling, this thermal deformation is critical to the stability of optical coupling. In fiber optic modules such as uncooled laser diodes, the change in optical coupling as a function of ambient temperature due to the change in the physical geometry of the package is typically referred to as the tracking error and can be greater than +−1.0 dB. Thus it is desirable to form a packaging platform of a thermally stable material.
Yet another factor not discussed in the aforementioned patent is the cost effectiveness of using molded ceramics.
Several approaches have been explored to reduce the cost of packaging and assembling optical and optoelectronic modules. The work contained in U.S. Pat. No. 6,222,967 is an example of one approach. In addition to just packaging and assembly of optical and optoelectronic modules and components, much work has focused on the further integration of electronic devices with optical and optoelectronic devices to further reduce the cost of more complex optical, optoelectronic and electronic assemblies. One approach for doing this includes the use of a Silicon substrate (a so called ‘Silicon optical bench’) which contains features for aligning optical and optoelectronic components. The cost, complexity and limitations of both these approaches have limited the wide spread implementation of this technology.
What is required is a packaging and assembly approach which addresses the issues of optical and optoelectronic component alignment, the integration of electronic devices and the need for a simple assembly process containing not only fewer and simpler steps, but implementing fewer
Catchmark Jeffrey M.
Lavallee Guy P.
Colesanti Anthony
Colesanti & Associates
Prasad Chandrika
LandOfFree
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