An Optical Alignment Robot System

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Abstract
We have designed and built a robot system for the automated alignment of optical fibers. A generalized alignment problem consists of a photodetector and electro-optical circuitry contained in a package. This is a difficult task that requires very high precision (1gm) translational movement with little backlash, and high speed manipulation (> 5 mm/sec). The robot system has closed-loop computer control and intelligent feedback to allow active alignment of the system, i.e., the optical components need to be manipulated while monitoring the output of the optical system. High-precision adjustments are needed in three dimensions, with sub-micron step increments. The robot system consists of an xy stage and an x-y-z translation stage, with closed-loop feedback control. As the optical fiber is inserted into the package, the optical fiber comes in close proximity to the photodetector. The alignment of the optical fiber to the photodetector occurs by a device which grasps the optical fiber. The fiber is translated in three dimensions within the package. The optical power coupled into the fiber serves as the control signal. Optimum alignment time can be achieved in < 10 s despite the complications caused by localized minima, with -40 dB of peak coupling power. The purpose of this paper is to discuss the general problem of precision alignment.

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