SUCCESS STORY – Automatic Testing of Photonics Components-- Steffen Arnold --Automatic Testing of Photonics Components
Fast, Accurate, and Suitable for Industry

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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SUCCESS STORY – Automatic Testing of Photonics Components-- Steffen Arnold --Silicon photonics sets the pace on the fiber optic data
highway. Cloud computing, server farms, big data, fastInternet access as well as a large number of other computersupported services that demand high transmission speeds,
benefit from data rates in the TBit/s range.

Precision Fiber Alignment:
Multi-Channel Fiber Adjustment inReal Time

However, a number of challenges must be overcome for
production and testing of the latest generation of silicon
photonics wafers. Automated solutions must function reliably
under industrial conditions and work around-the-clock withgreat accuracy. At the same time, individual solutions arerequired because the wafer can make very different demandson the testing and production equipment.

As solution supplier for drive technology and precision
positioning systems, PI (Physik Instrumente) has taken a close
look at this and developed a new complete system for fast
fiber alignment, which can align, test, and optimize the light
input and output at each input and output coupling point inless than one second (Fig. 1).

Silicon photonics (SiP) uses standard, easily scalable processes
optimized for mass production of semiconductor
components. With SiP, electronic logic circuits (such as thoseused for computing) and optical transceivers are integrated
into the same wafer. The resulting low-power microchips arethen able to transmit data at bandwidths in the Tbit/s range
and with low heat generation.
However, because the value of a packaged SiP circuit goes up
significantly compared to the raw circuit on a wafer, it iscritical to introduce wafer-level testing of each circuit before
dicing and packaging. Optical inputs and outputs must betested. The precision required to do this is several orders ofmagnitude higher than is possible with traditional electrical
wafer probing equipment.
Inputs and outputs need to be aligned precisely to the opticalfibers connected to the test equipment. That is definitely nota trivial matter, because optical waveguides in silicon wafers
normally have a core diameter of only 150 to 200 nm, and to
avoid losses, alignment equipment must have at least 10times higher resolution.
Managing this type of automation task is therefore aconsiderable challenge: Maximum precision during handling,
positioning and adjusting is just as necessary as the highest
possible speed for meeting the demands made by industrialproduction.

Fig. 1

Industry-suited complete systems for wafer probing in silicon
photonics

This guarantees fast data throughput rates during industrial
production. The system consists of two compact identical
positioning units which, with a small footprint of 100 ×100 mm require very little installation space. The heart of thesystem is the application-specific controller with a variety ofbuilt-in alignment and tracking algorithms required for opticalalignment and therefore lightens the burden on the higher
level control.
The host computer communicates with the controller via
Ethernet, USB 2.0 or an RS-232 interface. The system comeswith a high-performance software package that allows theuser to quickly develop applications under Windows, Linux,and OS/X.

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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SUCCESS STORY – Automatic Testing of Photonics Components-- Steffen Arnold --Coarse and Fine Adjustment
Positioning is done in two phases: A three-axis positioning
stage driven by closed-loop DC motors takes care of the initialtask of coarse adjustment; it travels to the respective
coupling point over travel ranges of several tens ofmillimeters with an accuracy of up to 50 nm.
An additional three-axis positioning unit is then responsible
for fine positioning of the fibers. The system is driven by piezo
actuators and achieves resolutions of 1 nm with response
times in the microsecond range and travel ranges of
100 × 100 × 100 µm.
The high-performance piezo actuators are integrated into
guiding systems with FEA-optimized flexure joints and arefree of both friction and backlash. Because actuators, guides,
and sensor work without wear, the systems are extremely
reliable and durable, and are therefore perfectly suitable forindustrial requirements in multiple-shift operation (24 hours
and seven days a week).

The accuracy would suffer because additional guiding errors
would reduce the overall precision. Instead, a more elegant
and performant solution is to combine the above-describedfine positioner with a hexapod parallel-kinematic positioning
system. Because, in contrast to serial kinematics, all actuators
in parallel-kinematic systems act directly on the same
platform and therefore, it is not possible for guiding errors toaccumulate as is the case with "stacked" systems and thisincreases the accuracy considerably.
Hexapods, which have six-axis parallel kinematics, also havefurther advantages for fiber alignment. Due to their low
moving mass, they provide much higher dynamics (Fig. 2). The
arbitrary center of rotation or pivot point is another feature,
which can be programmed by a single command.

More Degrees of Freedom
During wafer probing or packaging, the one or otherchallenge can arise depending on the application: If forexample, the fibers need to be positioned at different angles
or if tilting angular errors need to be compensated, more axes
are required. Serial stacking of additional axes on thepositioning stage is basically possible, but the limitations
outweigh the advantages of this approach.

Fig. 3This parallel-kinematic six-axis positioning system is also ideal for
fiber alignment

The compact H-811 Hexapod (Fig. 3) for example, offers travel
linear ranges up to 34 mm and rotational travel up to 42°. The
piezo-based fine positioner integrates with the hexapod
platform. For different travel ranges or load requirements,
other parallel-kinematic positioning systems are available,
which can be combined with the fine positioner.

Fig. 2Wafer level alignment with a two-side 6-axis Hexapod and apiezo scanning stage for fine alignment

The minimum incremental motion of 0.1 µm / 2 µrad, andvelocities of 10 µm/s to 10 mm/s. This planar parallel
positioning system is based on three XY stages driving one
platform through three fixed struts. This design allows more
flexibility and longer travel ranges on the XY plane.

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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SUCCESS STORY – Automatic Testing of Photonics Components-- Steffen Arnold --High-Performance Software

Simulation tools, for example, help to calculate theworkspace, or objects can be integrated to avoid collisions.

Irrespective of which positioning system is worthy of
consideration for the application, all algorithms necessary forfiber optic alignment are already integrated in the digitalcontroller.

A mobile app enables wireless monitoring and control.
Development libraries and example applications simplify
implementation and a number of common programming
languages and software environments are supported (C, C++,Python, Visual C++, Visual Basic and Delphi or LabVIEW,
MATLAB, μManager, EPICS, TANGO as well as all
programming environments that support loading of DLLs).

In addition, the digital motion controllers from PI are suppliedwith an extensive software package (Fig. 4), which covers all
application aspects, from easy start-up, to the convenient
control of the system via the graphical interface, and fast andtransparent integration into external programs. A virtualcontroller allows development of application programs
without the need to have all of the components at hand.

Fig. 4This allows realization of "tailored" industrial applications
related to wafer probing and packaging in silicon photonics.

An example of real-time system control

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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SUCCESS STORY – Automatic Testing of Photonics Components-- Steffen Arnold --Author

Dipl.-Phys. Steffen Arnold, Head of "Marketing and Products"
at PI (Physik Instrumente)

About PI
In the past four decades, PI (Physik Instrumente) with
headquarters in Karlsruhe, Germany has become the leading
manufacturer of nanopositioning systems with accuracies in
the nanometer range. With four company sites in Germany
and fifteen sales and service offices abroad, the privately
managed company operates globally. Over 850 highly
qualified employees around the world enable the PI Group tomeet almost any requirement in the field of innovativeprecision positioning technology. All key technologies aredeveloped in-house. This allows the company to control every
step of the process, from design right down to shipment:
precision mechanics and electronics as well as positionsensors.
The required piezoceramic elements are manufactured by its
subsidiary PI Ceramic in Lederhose, Germany, one of the
global leaders for piezo actuator and sensor products.
PI miCos GmbH in Eschbach near Freiburg, Germany, is a
specialist for positioning systems for ultrahigh vacuum
applications as well as parallel-kinematic positioning systems
with six degrees of freedom and custom-made designs.

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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