Lock around the clock!
Frequency combs can act as precise reference for optical frequencies, as well as for
seeding phase-stable laser amplifers.
TOP TICA offers complete solutions including
the frequency comb, wavelength conversion, beat detection and stabilization units for
cw-lasers. The fber-based comb provides
the convenience of fber lasers with a new
level of robustness and ultra-low noise performance. This laser creates a completely
new frequency comb experience, it is made
to lock around the clock.
Frequency Combs TOPTICA
frep-locking bandwidth > 400 kHz
RMS phase stability < 40 mrad
frep and fCEO perfectly decoupled
Dr. Felix Rohde, Product Management
Parallelism in the design approach
of multi-axis motion systems
When faced with a multi-axis motion application, the traditional way is to stack multiple
single-axis motion stages. As applications become more complex, so do the equivalent
stacks of stages—and advantages such as simplicity can turn into disadvantages when it
comes to performance.
A parallel kinematics design provides a more effective approach to multi-axis motion
and brings several advantages (see Fig. 1):
Dynamics/stiffness. With conventional
multi-axis systems, the bottom stage in a
stack carries the mass of the entire stack
and so on up to the top stage, which car-
ries only the application load. Dynamics suf-
fers because of the overall moved mass and
tuning becomes a laborious, axis-by-ax-
is process, with different settings for each
axis and consequently different responsive-
ness. Hexapods provide very high stiffness
because all six struts work in parallel on
one common lightweight motion platform.
Consequently, the dynamics are higher and
tuning settings are very close for all axes.
Rotation-centerpoint flexibility. Stacked
stages place the center of their tip/tilt and rotation mo-
tions at the geometric centers of each rotation stage
and goniometer bearing. Sometimes, they coincide at a
desired point in space (for example, at the focal point of
a lens) via custom adapter plates and fixtures, but this
takes time and effort, and is inflexible should application
requirements change. With hexapod multi-axis systems,
the center of rotation can be changed by a single soft-
ware command on the fly.
No moving cables. Managing cables deserves more
attention than it often gets. Cables can be a conduit
for vibration that can impact an entire application. As a
stage moves, any cable being dragged along can contribute to parasitic motions and other errors. These issues scale with the number of axes in a user-stacked
system. Parallel kinematics avoid moving cables and
the other issues altogether.
Parasitic errors. Stacked axes interact in complicated ways. For example, runout in the x-axis can cause
unwanted motion in the y- and z-axes; angular deviation of an axis similarly imparts motion in the travel-di-rections of the other axes, with magnitude proportional
to the distance to the moving axis. And in stacks, that
multiplicative lever arm can be large.
What works on a larger scale for long-travel posi-
tioners can also be implemented for motion with sub-nanometer resolution and sub-mil-
limeter travel ranges. Piezo flexure positioners rely on motion based on the piezoelectric
effect. An embedded piezo ceramic transducer changes its dimensions analogous to an
applied voltage and a wire-EDM cut flexure arrangement amplifies the motion while pro-
viding frictionless guidance at the same time (see Fig. 2).
FIGURE 1. Parallel-kinematics positioners
such as hexapods have multiple advantages
over traditional stacks of single-axis stages.
Higher stiffness, lower inertia, and faster
response are critical to precision alignment
applications. (Courtesy of PI)
FIGURE 2. The NanoCube
includes a parallel kinematics
XYZ piezo scanner, with 100
µm motion and subnanometer
resolution (Model P-616). It is
similar to the arrangement of six
struts in the hexapod in that it
uses three internal actuators in a
parallel arrangement to affect the
motion-output platform (silver).
Integrated position sensors
provide feedback to a high-bandwidth closed-loop controller
for absolute position information
in real time. (Courtesy of PI)