Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2002-02-04
2003-12-09
Patel, Tulsidas (Department: 2839)
Optical waveguides
With optical coupler
Particular coupling structure
C385S052000
Reexamination Certificate
active
06661955
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to optical devices, and more particularly to optical element alignment assemblies and methods of making the same.
2. Description of the Related Art
An optical component, such as a mirror, lens or fiber, in an optical instrument or device, such as an optical switch, should be accurately located/positioned with respect to another optical component in order for the optical instrument or device to function properly. Thus, optical devices may require their components to be placed with exacting tolerances to fulfill design objectives.
Conventional passive alignment assemblies for MicroElectroMechanical System (MEMS) devices are typically planar in nature and only align local elements, e.g., a fiber and ball lens collimator, where the two components are within a few millimeters of each other. Alignments over larger distances (e.g., greater than five millimeters), and three-dimensional optical systems typically use conventionally machined components. Such assemblies often fail to align optical components with high intrinsic precision.
SUMMARY OF THE INVENTION
Components generally need to be located in three dimensions, i.e., distributed in a volume of space, and have three rotations specified and/or controlled. Components located in a plane (two dimensions) with three or fewer rotations specified and/or controlled are a subset of the general case. Other design objectives may include: (1) locate components without induced strains, either from the process of mounting or through bulk temperature changes of constituent parts, and/or (2) support components as rigidly as possible.
In accordance with the present invention, alignment assemblies and methods of using and making the assemblies are provided. An important advantage of several embodiments of the invention is to completely orient one body with respect to another body to a high degree of precision by providing (1) precise mating features between bodies and connecting elements, and (2) precise distances between these features on all bodies and connecting elements.
In one embodiment, the alignment assemblies are passive, kinematic or non-kinematic, and micromachined. “Passive alignment” means the various parts or devices to be assembled have mating features such that when these features are engaged with each other, the correct alignment (typically optical) is attained. In some instances, the engagement of these mating features permanently controls the alignment. In other instances, some type of fixture will hold the parts with their mating features engaged while some additional fixation, e.g., glue or bolt, is added to make the engagement permanent.
For comparison, in “active” alignment, two parts or devices are maneuvered with respect to each other by some motion control mechanism, e.g., a motorized motion stage, shim set, etc., in one or more directions or degrees-of-freedom (DOF) until some metric, e.g., light through-put, optical beam quality, etc., is within a specified tolerance. At that point, the two parts are fixed rigidly with respect to each other by some means, e.g., glue, solder, bolt.
As defined and used herein, “kinematic mounting” relates to attaching two bodies, which may be called a base assembly or a payload assembly, together by forming a structural path and creating stiffness between the two bodies in six, and only six, independent degrees of freedom (“DOFs”) or directions. Each degree of freedom (DOF) kinematically controlled between two bodies is also a position defined, i.e., a specific value of that DOF, as a linear measurement, may be maintained. Six DOFs are desired because the location of any object in space is defined by three orthogonal coordinates, and the attitude of the object is defined by three orthogonal rotations.
A kinematic support has the advantage of being stiff, yet any strains or distortions in the base assembly are not communicated to the payload assembly. Thus, any sensitive optical alignments are not altered in the payload assembly if the base assembly undergoes deformation due to applied loads or bulk temperature changes.
In one embodiment, it is desirable to tailor a DOF based on the configuration of a “pseudo-kinematic” support. “Pseudo-kinematic” means that although there may be many DOFs connecting at least two bodies, such as two micromachined passive alignment assemblies, in a practical attachment scheme, the DOFs can be tailored such that only six DOFs have a relatively high stiffness, and substantially all other DOFs have a relatively low stiffness.
Thus, true “kinematic” support means only 6 stiff DOFs connecting two parts, and no other stiffness paths exist. “Pseudo-kinematic” means there are 6 DOFs with relatively high stiffness, and possibly many more with much lower stiffness (typically two to three orders of magnitude less). In some applications, it is desirable to have pseudo-kinematic DOFs with relatively low stiffness to be two to three orders of magnitude lower than DOFs with relatively high stiffness.
DOFs with different levels of stiffness may be accomplished using a flexure system to relieve stiffness in unwanted DOFs. Depending on the cross-sectional properties of elements in the flexure system, connecting elements between two bodies may attain the desired stiffness connectivities.
The alignment assemblies and methods of making the assemblies according to the invention may provide a number of advantages. For example, the micromachined passive alignment assemblies may be made with high intrinsic precision. Micromachining processes may form three-dimensional structures from a substrate wafer with high accuracy. In several embodiments, one micromachined passive alignment assembly may be oriented and spaced with respect to another assembly (e.g., with connecting elements) with lithographic precision, e.g., three-dimensional translational positioning to less than one micron and three-dimensional angular positioning to less than five arcseconds for an assembly with a 50-mm characteristic dimension.
The methods according to the invention may construct mating surfaces on micromachined passive alignment assemblies, such as a base assembly and a payload assembly, to control six independent DOFs between the assemblies and allow complete, high-precision specification of position and attitude. In some applications, it is desirable to have micromachined connecting elements with counterpart mating surfaces to mate with the mating surfaces on the base and payload assemblies.
The accuracy of micromachined passive alignment assemblies may be fully realized if there is a positive contact between a pair of mating features. Thus, some form of preload or force may be applied to maintain compressive contact between the pair of mating features. An external force may be applied to preload mating surfaces to contact each other prior to gluing. Glues that shrink on cure may be used to maintain the preload across mating surfaces after assembly.
In addition to or instead of an external force, any of the structural elements being assembled may have an internal flexure assembly that applies an internally-reacted force (preload). The internal flexure assembly may seat mating surfaces without a deadband. In one embodiment, the internal flexure assembly comprises a set of double parallel motion flexures, a preloader stage, and a hole on one side of the preloader stage for inserting a separate preloader pin. When the preloader pin is inserted into the hole of the internal flexure assembly, the preloader stage deflects and exerts a force on the pin, which exerts a preload against a mating surface. After the micromachined passive alignment assemblies are assembled, the mating surfaces may be glued or bonded if desired.
A connecting element may be configured to restrain the base assembly and the payload assembly with one or more desired DOFs. In some embodiments, a “degenerate” support or connecting element may be used where less than six constrained DOFs between a base and payload are desired. The degenerate su
Calvet Robert J.
Gutierrez Roman C.
Tang Tony Kai
Fish and Richardson P.C.
Patel Tulsidas
Siwave, Inc.
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