Method of active fiber alignment with movable V-groove...

Details Method of active fiber alignment with movable V-groove... Method of active fiber alignment with movable V-groove...

2002-05-24

2004-01-27

Fulton, Christopher W. (Department: 2859)

Geometrical instruments

Gauge

Collocating

C033S533000

Reexamination Certificate

active

06681496

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention relates to alignment of an object with an external axis, and more particularly to active fiber alignment with movable V-groove precision control microstructures.
BACKGROUND OF THE INVENTION
Precision alignment of a component relative to an axis is encountered in numerous technologies, for example magnetic data storage, optical beam transmission, and nanotechnology. Fiber alignment is an important factor in optical fiber testing, assembly, and packaging. In many cases, an optical fiber is aligned to a waveguide, detector, laser, or another fiber. It may be a fiber pigtail (fiber(s) aligned and fastened to a device) or a fiber optic stub (short piece(s) of fiber with a ferrule and connector housing).
FIG. 1
represents isometrically the typical prior art means for aligning fibers before attachment, using fixed V-groove structure
10
. Fiber
12
is supported and positioned by fixed V-groove
11
having depth H
12
and sidewall width W
12
located at lateral distance W
10
from one edge of structure
10
having height H
10
and thickness T
10
. Typically the V-groove pattern is etched into silicon along preferred crystal orientations using KOH, a technique regularly used to make very high quality V-groove structures. Although the pitch between adjacent V-grooves, the slope and the depth H
12
of V-groove sidewalls
11
depend on the etching process, and the angle of the silicon V-groove wall depends on the silicon crystal orientation and the etch depth, these variations are nevertheless typically small (<1 micron). However, the overall structure height H
10
is imprecise, typically varying +/−10 microns or more from the mounting base to the fiber axis. Hence, the resulting fiber position varies almost independent of the depth and sidewall angle of the fabricated V-groove. Additionally, tolerances in the diameter and the concentricity of the cladding and core of the fiber to be aligned contribute to alignment variations. A further shortfall is that the mask needs to be closely aligned to the wafer crystal axis, or the groove will be wider than the mask opening. Another shortfall with silicon V-grooves is that they are typically very sharp at the bottom, promoting crack initiation. Moreover, the wet chemical etching requires long etching times, and small defects on the mask can produce large defects on the wafer.
As a consequence, prior art V-groove structures have tolerances in the range of tens of microns, much too large to achieve sub-micron alignment precision. Thus, the alignment burden is transferred to manipulating the V-groove structure and then applying excess bonding material, typically epoxy adhesive or solder, to fill residual gaps between the fiber cladding and the V-groove. In either case, there is an element of difficulty fixturing the fiber and bonding it to maintain the required micron scale alignment tolerances. Typically the fiber is glued into place in the groove, and then the whole groove assembly with the fiber attached is moved to get the best alignment, and then glued into place as a unit. The glue line underneath the V-groove block needs to fill in the variations in height, and so may be tens of microns thick and non-symmetrically distributed. Then the epoxy cures (typically at elevated temperature), it can shrink several per cent, causing misalignment. Also, the epoxy may take up moisture over time, making it change shape. Solder contracts less, but it typically needs even higher temperatures and is difficult to use. Thus, a pervasive problem is that the fiber moves when an adhesive cures and shrinks, solder cools, or welds forms a joint. This movement can be pre-compensated by deliberately misaligning before curing to allow for anticipated shrinkage, but satisfactory yields become an issue.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to a method to align an object with an external axis using movable V-groove microstructures and to maintain the object position after bonding. The alignment procedure is implemented using a microstructure device that can adjust and align the object position precisely relative to the external axis. This flexibly adjustable microstructure device improves on a standard silicon rigidly fixed V-groove, providing faster and easier alignment. The V-groove fabrication process is simple, fast, accurate and reproducible. The shape, depth, angle and the position can be controlled with high precision. The movable V-groove structure is inexpensive to fabricate and is small enough to be incorporated in the final package to maintain alignment accuracy stability during adhesive attachment. The bearing surfaces of the movable V-groove can be fabricated in a variety of shapes, including U-grooves, V-grooves, monotonic slopes, triangular, straight, concave, convex, and complex contours. The movable V-groove structure has the capability of flexibly fine-tuning alignment, providing a added precision relative to standard silicon fixed V-groove alignment. The method can be applied to the alignment of single optical fibers and multiple fiber arrays in optical systems, as well as magnetic data storage and retrieval, microscopy, microsurgery, and nanotechnology.
Advantageously, this method provides in-situ active fiber alignment, permitting the use of a much thinner and more consistent glue line under and/or alongside the mounting structure, minimizing post-cure motion. Adjusting the height of the fiber by moving blocks relative to one another achieves precision alignment using imprecise parts, since motion of the structures, and not the structural tolerances themselves, define the alignment precision. The self-fixturing microstructure device supports the fiber during active alignment, epoxy application, and epoxy curing, and then remains with the package. Therefore fiber alignment stability is maintained despite any material shrinkage after epoxy is cured. Combinations of the present microstructure assemblies together or with other structures can precisely position and align fibers and other objects in three dimensions.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.


REFERENCES:
patent: 3975830 (1976-08-01), Lopacki
patent: 6085430 (2000-07-01), Chen et al.
patent: 6513260 (2003-02-01), Krajec et al.
S.E. Shoal and A. D. Feinerman, Aligned Au-Si eutectic bonding of silicon structures, Microfabrication Applications Laboratory, Dept. of Electrical Engineering and Computer Science, U of Illinois at Chicago, Sep. 25, 1993,, published by J. Vac. Sci. Technol. A 12(a), Jan/Feb 1994, American Vacuum Society, pp. 19-22.
Ryoji Kaku, et al. “Si V-Groove Substrate for Optical Modules”, Central Research Laboratory, *Optoelectronics Development Division, Japan Aviation Electronics Industry, Ltd., 3-1-1, Musashino, Tokyo, Japan pp 13-17. (date unknown).
Carola Strandman and

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