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This software optimization process has
all been rendered obsolete by two innovations: first, an entirely firmware-based com-
mand that leverages internal position-wave-
form and synchronous data acquisition, and
then a single-frequency sinusoidal raster or
spiral scan that proceeds smoothly and continuously while avoiding exciting structural
resonances in mechanical elements like fibers
and tweezers. The result is an orders-of-mag-
nitude improvement in process throughput
(see Fig. 3).
Aiding in the quest for more alignment speed
are motion engines based on a parallel-kinematics design concept (see “Parallelism in the
design approach of multi-axis motion systems,”
page 48). By splitting the long travel motion
system and the high-speed scanner (analogous
to a multi-stage space rocket, where not all of
the mass needs to be accelerated the whole dis-
tance), additional performance can be found.
Putting it all together is where the advan-
tages of this fully modern architecture be-
comes evident. The single-frequency sinusoidal or spiral raster scan allows mapping of an entire coupling
region with high resolution in about 250–300 ms, complete
with the firmware-based fitting of a Gaussian to the observed
coupling. This allows especially fast scans to be performed
while still accurately localizing the main mode.
With the main mode localized at each coupling and each degree of freedom, the overall global consensus alignment across
all inputs and outputs can be achieved in a few hundred milliseconds, with all optimizations performed in parallel. If desired (for example, to accommodate drift if it occurs, perhaps
caused by heating from active elements, application of adhe-
sive, or other disturbances), quick global realignment or even
real-time tracking can then be performed.
Thus, to make silicon photonics devices profitably at scale,
automation becomes an essential element in process-design en-
gineering. Meeting this requirement, recent advances in fab-
class process automation subsystems include innovations in
one of the bedrock operations of photonics manufacturing—
the alignment process, which is common to process steps from
device characterization at the wafer level through final assembly and packaging.
1. S. Jordan, “Alignment: A Challenge for Test & Measurement,” https://goo.
Scott Jordan is PI’s Global Head of Photonics, senior director,
NanoAutomation Technologies, and PI Fellow at PI’s (Physik Instrumente)
Bay Area offfice in Sausalito, CA, and Stefan Vorndran is vice president
of marketing at PI‘s U.S. headquarters in Auburn, MA; e-mail: email@example.com; www.pi-usa.us.
FIGURE 3. Cascade Microtech’s CM300xi photonics-enabled engineering wafer probe
station integrates PI’s Fast Multichannel Photonics Alignment (FMPA) systems for high
throughput, wafer-safe, nanoprecision optical probing of on-wafer silicon photonics
devices. Both the six-axis hexapod positioner (top left) and the piezo XYZ scanner (black
cube mounted on the hexapod) are based on parallel-kinematics for improved dynamics
and precision. (Courtesy of Cascade Microtech, a FormFactor company)