Optical waveguides – Accessories – External retainer/clamp
Reexamination Certificate
2002-06-26
2003-08-12
Dang, Hung (Department: 2873)
Optical waveguides
Accessories
External retainer/clamp
C385S136000
Reexamination Certificate
active
06606444
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
In assembling micro-optic structures and in particular those utilizing fiber optic waveguides, it is often necessary to control relative spatial alignments with extremely fine precision. Some optical components use optical fibers having a core region that carries a beam of light that is of the order of 10 microns in diameter (and even smaller in some cases). In order to assemble such a component the optical fibers have to be manipulated with a precision level on the order of {fraction (1/10)}
th
of a micron.
2. Prior Art
In the past, optical fiber components have been assembled using known 3-axis ball-bearing positioners. Anyone who has attempted to achieve stable alignment using single-mode optical fiber with such known kinds of positioners equipped with micrometer actuators will attest to the lack of required precision. Crossed roller and ball type stages inherently require preload which generates motional friction and have a resolution limit set by the randomness of the required drive force due to dust and surface variations associated with the frictional interfaces and the limited stiffness of actuator mechanisms.
Other designs of positioners offer frictionless movement with the use of flexure-based designs but often at the expense of overall mechanical stiffness. A single parallel cantilever pair will generate an arc-error in its trajectory. What is commonly done is to combine two cantilever pairs into a compound cantilever stage so as to have one compensate the other and provide perfect linear motion. Compound cantilever stages are very large for their available travel as conventional designs consist of two separate compound stages that are effectively joined at a centerline to maintain high off-axis stiffness. An example of such a positioner mechanism is shown in U.S. Pat. No. 4,686,440, issued Aug. 11, 1987 to Hatamura et al., in FIGS. 12 and 13. One of the objects of this invention is to provide a compound cantilever stage that is much smaller than the conventional design.
The majority of 3-axis positioning equipment is made up by staging single axis units one on top of each other using angle plates. This results in a structure that has diminished resolution and stiffness as one moves progressively further from the mounting frame of reference. In many designs the stiffness of the overall unit is inadequate to resist the forces required to operate the actuators. In these cases the operator must use a touch and release method where the signal is adjusted and the operator then has to release the actuator to witness the result. Another downfall of a 3-axis positioner made up of three individual orthogonally arranged stages is the fact that the actuators are also arranged in an XYZ configuration, i.e. each has an axis perpendicular to the other two actuators, making prolonged use strenuous due to the required hand movements.
An inherent limitation to the resolution of nearly all positioning systems lies in the use of what can be termed simple axial actuators. A micrometer head or a complex piezo micrometer head are examples of simple actuators as they produce a displacement that is used to control the movement of a translation stage in a direct ratio. For example, a 1 micron movement of the shaft of said actuator is used to produce a 1 micron movement of the corresponding translation stage. As a result all motional errors such as hysteresis or randomness of movement inherent in the actuator itself are passed on directly to the translation stage. The requirement for sub-micron resolution also necessitates the requirement for differential micrometer stages and stepper-motor driven lead screw drives in order to achieve the necessary resolution since a single thread micrometer under hand control cannot be easily adjusted at such fine a resolution. The general trend towards increased resolution and stability in positioning equipment has been driven by the increased use of small-core single-mode optical fibers over the larger core multimode optical fibers which require less precision in alignment manipulation. In order to remove the effect of operator induced forces a number of sub-micron resolution remote driven motor driven stages have emerged on the market. Even with fully automated positioning systems where a scan routine is carried out under computer control, some level of operator intervention is required for handling and loading the individual elements to be assembled. In many labor intensive assembly applications the cost of an automated system cannot be justified and would not be considered if an appropriate mechanical positioner were available.
Copending U.S. patent application No.671,143 as aforesaid, which is hereby incorporated by reference, describes and claims a 3-axis positioning device ideally suited for, but not limited to, the assembly of single-mode fiber optic components. The invention of this earlier application allows for all of the actuators to be placed in a common orientation to reduce hand fatigue and improve adjustment efficiency. That invention teaches a structure that provides for both coarse and fine movement while using a simple adjustment screw and a single micrometer head for each of at least two axes of movement. The structure also allows for the fine movement control to be a fraction of the travel of the micrometer head while increasing movement resolution. Another aspect of the invention of this earlier application includes means of translating motion from one axis of movement to another. In addition that invention teaches a linear compound flexure stage that provides for large travel and perfect linear motion with high stiffniess. In its ideal form that invention can provide for operator insensitive adjustment when aligning single-mode optical fibers with a resolution limit that is comparable to a closed-loop piezo driven translation stage.
The invention of the aforesaid copending application is a significant improvement over a conventional stacked 3-axis unit as the operator adjustment forces act only on a single stiff linear translation stage instead of the sum of the total of all stages. It is then possible to realize a positioning device that can operate under hand control at resolution and stiffness levels required for single-mode fiber optic alignments wherein the operator does not influence the measured optical signal level during adjustment of the unit. It is also possible with that invention to implement linear motor drive on the second and third axes without affecting the overall sensitivity to hand adjustment forces.
Another aspect of the aforesaid copending application is an orthogonal drive conversion system which serves to isolate the holding means of a positioner from manual forces applied to it. Another advantage of this orthogonal drive conversion is that it allows micrometer type actuators to be all aligned in one direction, thus decreasing operator strain.
Yet another aspect of the positioner of the aforesaid copending application is a compound cantilever stage that is one-half of the conventional design; the latter being a design which uses two separate compound stages that are effectively joined at a centerline to maintain high off-axis stiffness. Traditionally the one half arrangement is not used as the intermediate frame of reference would move in response to external loads placed on the system and limit off-axis stiffness. It can be shown however, that if the intermediate frame in a compound cantilever stage were to be forced to move one-half of the overall displacement, then high stiffness can be achieved while requiring only one half of the conventional compound cantilever design. An aspect of this earlier invention was to provide a forcing or control means to set the displacement of the intermediate frame of reference of a compound cantilever stage to one half of the output displacement. In its preferred form said control means is a beam connected to the parts by frictionless elastic elements.
SUMMARY OF THE INVENTION
In the copending application the compound
Harman Murray R.
Harman Stephen G.
Dang Hung
French David J.
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