STEFAN VORNDRAN & SCOTT JORDAN AUTOMATED
AUTOMATED ALIGNMENT BOOSTS FIBRE THROUGHPUT
The development of automated fibre aligners has made a significant dierence to what could be a tedious task. So how has this technology progressed from the first devices; and what is possible with today’s technology? By Stefan Vorndran and Scott Jordan of Physik Instrumente.
SCOTT JORDAN
I n the recent past, joining fibre endfaces with the analogue phase demodulation hill- climbing technique worked for clean, quasi-Gaussian couplings that were already near optimal alignment. However, this approach locks in on local maxima and flat spots that occur in multimode couplings, with imperfect devices, or far from optimum alignment. Nevertheless, instrumentation based on this principle has still been popular. This is despite the fact that the equipment can be bulky and provide too little travel range for fully automated fibre alignment. The first digital gradient search technique was introduced in the early 1990s to allow fibre optic devices to be e ciently aligned using motorised linear stages of the day, which were low in speed, resolution and synchronisation capabilities compared to today’s piezoelectric nanopositioners. Flexibility was an advantage of this class of automatic fibre aligners, plus the massive motorised positioners on which these systems were built were a good match for the industrial era of photonics. However, the architectures mentioned above did not cover angular alignment. Three new types of photonic devices made angular alignment a mainstream concern: 1) Planar waveguides emerged as key players in switching and modulating in photonic networks; 2) Angular alignment needed to be automated. Optical switches based on steering of collimated beams necessitated throughput-optimised gimballing alignment of collimators and other optical elements; 3) Confocal optical trains in photonic packages had sensitive angular alignment needs. These needs, in addition to unabated alignment requirements for high-throughput transverse alignment, drove the introduction of Physik Instrumente’s (PI) F-206 hexapod six-axis fibre alignment system. This instrument combined six ultra-precision actuators with a stictionless kinematic flexure coupling.
long-travel hexapods to be deployed for high-throughput industrial alignment applications. Building on established designs featuring high stiness, highly triangulated geometries, these systems oer travel ranges of several centimeters while accommodating loads of many kilograms. These designs are suitable for use in any mounting orientation and oer up to 50 percent higher acceleration than previously possible. In addition to integrating optical metrology with the hexapods’ six degrees of freedom plus two additional linear or rotary axes of motion, their powerful new controllers integrate data recorders for precise correlation of optical power with position. 100x100mm scans can be achieved in as little as 650msec with these speedy mechanisms. Interfacing options have also expanded and improved, with standard TCP/ IP and USB ports oering high-speed communications and compatibility with factory automation architectures. New, optional remote-control pad/displays oer hands-o manual operation. The software suite oers GUI setup and configuration tools, as well as Windows and Linux libraries and a comprehensive, well-documented, native and open- source LabVIEW library. As the telecom boom crested in the early 2000s, Physik Instrumente
Compact and swift, it integrated a fast photodetector and a flexible assortment of sophisticated digital algorithms for autonomous fibre alignment automation in up to six degrees of freedom. It has been refined over a decade with updates to its mechanics, controller design and software. A key advantage of the hexapod parallel kinematic approach is the ability to cast the rotational pivot point anywhere in space. This is defined by their bearings and fixturing structures and cannot readily be moved around. With the hexapod, process engineers gained the capability to place the rotation point about an optical sweet-spot with a single software command, a significant advantage for alignment of complex fibre-optic components. Examples include: a) For multichannel waveguide alignments, the rotation can be about the first optical channel; b) In collimator-collimator alignments, the rotation can be centred on either collimator’s face; c) For COT alignment, the alignment can pivot about its focal point, which might be buried inside a package and only blindly accessible by tweezers. Hexapod options Recent advances in hexapod design and controls have now enabled a host of robust, high-load,
By integrating six degrees of freedom, F-206 facilitates complex alignments like this 10-DOF waveguide MUX/ DEMUX packaging.
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| ISSUE 11 | Q4 2017
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