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Piezo Mechanisms in Optics and Laser Technology
By Stefan Vorndran, Scott Jordan and Steffen Arnold, Physik Instrumente L.P. T
he delivery of a laser beam requires precise motion of optical components. Piezo mecha- nisms provide just this. Piezoelectric systems are currently the gold standard of motion control,
complex systems, such as flexure guided tip-tilt steering mirrors, or piezo scanning stages, which are used in laser scanning microscopy. For longer travel ranges, the devices come in high-force, high- resolution “piezo walk” type designs, high-speed ultrasonic, traveling wave motors, as well as com- pact, low-cost stick-slip (inertial) drives. Piezo devices are maintenance-free, vacuum
compatible, lubricant-free, and do not have gears and other moving components like conventional positioning systems. This allows them to have long lifetime and provide high reliability, as well as speed and precision — ideal conditions for use in laser control applications. Today’s digital servo algorithms have further increased the perform- ance of such piezo-based systems and made it easy to adapt the mechanics to changing requirements.
F-131 XYZ coarse/fine fiber alignment system.
because of their speed and precision. Laser sys- tems engineers have a large toolbox of options at their disposal, ranging from highly stable actua- tors for static fine-tuning to fast piezo auto-focus- ing devices, as well as high-speed, integrated, multi-axis beam steering systems based on piezo- flexure mechanisms.
Not All Piezo Drives Are Created Equal Piezo actuators and motors are based on the
same physical principle — molecular level motion with intrinsically unlimited resolution. However, some commercially available basic designs fit cer- tain applications better than others. Piezo stack actuators are short travel devices, less than 0.2mm (0.008in) travel, which are able to provide picome- ter resolution and high acceleration of up to 10,000-g. Often, they are used for laser cavity tun- ing and switching, and also incorporated in more
Laser Scanning in Fluorescence Microscopy In laser scanning microscopy, the laser beam
needs to be controlled and focused to cause fluores- cence in a sample. Galvo scanners have tradition- ally been used to steer the system, but piezo scan- ners are more precise, have faster response times, and can provide multiple motion axes in one device. Along with a reduced size, they also elimi- nate polarization rotation effects. Piezo devices are used in most fields of super-resolution micro- scopies where resolution can be far below the dif- fraction limit. Piezo-driven tip/tilt mirrors and platforms are useful here. PI’s S-334 tip/tilt scan- ner allows dynamic and precise steering motions of an integrated mirror in two orthogonal axes around a common pivot point. The frictionless piezo drives and flexure guides allow higher accel- erations than do conventional drives. Also, a com- pact controller was specially designed for this type of mechanism and combines the functions of a multi-channel servo and driver.
Telecommunications and Photonics Alignment
Telecommunication relies heavily on fiber
optic data transmission of modulated laser light. Bandwidth requirements constantly increase, which has created a need for better and faster pro- duction of fiber optic components. To align most single-mode fiber optic components, nanometer resolution is required. A compact multi-axis piezo mechanism, such as the company’s NanoCube{R}
February, 2016
M-663 miniature linear stage, driven by an ultrasonic piezo motor.
positioner, together with a fast controller and align and tracking algorithms can align fiber optic com- ponents in a matter of a few seconds. In the past, this task could take up to several minutes. The piezo scanner provides 100µm of fine travel and can be combined with motorized positioning stages for coarse positioning as well. Piezo scanners are also used in free-space optical communication to keep laser transmitters and receivers aligned dynamically.
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