Fast Tip-Tilt Stages / FSM Piezo Steering Mirrors (Active Optics)

PI's ultra fast steering mirror platforms are based on frictionless flexure guides and high-speed solid-state piezoelectric drives. These compact devices can provide integrated pitch and roll motion with a single moving mirror. They are faster than galvo-scanners and voice-coil driven beam steering systems (also available from PI) and can be used in both static and highly dynamic operation (e.g. scanning, tracking, drift and vibration cancellation).

Advantages of the PI steerable mirrors are: parallel kinematics design (coplanar multiaxis motion), fast response (sub-millisecond), high resolution (up to nanoradian range), long travel ranges (up to 3 degrees deflection). PI's parallel-kinematics multi-axis steering mirrors use only one platform/mirror for all axes. There is one common pivot point and no polarization rotation, an important feature for many precision optics applications.

Applications include scanning, image stabilization, laser welding, semiconductor test & manufacturing, laser beam steering, astronomy, two photon polymerization, medical applications. 

Download Whitepaper: Design, Performance and Tuning of Fast Piezo Tip/Tilt Platforms & Steering Mirrors 

Phase Shifters and Single Axis Steering Mirror Platforms

S-303 High Speed Phase Shifter
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S-303 High Speed Phase Shifter

Direct Metrology Option

  • Sub-millisecond dynamics
  • <0.1 nanometer resolution
  • High-linearity sensor option
  • Invar option
  • Aperture with open-loop versions
S-310/14 Z-Actuator – Phase Shifter
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S-310/14 Z-Actuator – Phase Shifter

With Aperture

  • 6/14µm piston motion
  • Sub-millisecond dynamics
  • Sub-nanometer resolution
  • Open loop
  • 10mm aperture
S-224 Fast Steering Mirror
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S-224 Fast Steering Mirror

Compact, 4mrad

  • Sub-microradian resolution
  • Sub-millisecond response
  • 4.4mrad optical beam deflection
  • Closed-loop option
  • Includes BK7 mirror

Tip / Tilt Mirror Platforms

Flexure Guided No Friction

The S-331 is a highly dynamic piezo-driven tip/tilt platform for compact mirrors up to ½” diameter. Its parallel kinematics design provides symmetrical performance for both axes along with a single pivot point. The platform is guided by backlash-free, frictionless flexure joints, a highly stiff design with zero wear. Closed-loop control with highly temperature stable metal foil strain gauges allows fast and linear motion.   The unit is driven with Mars-rover tested high performance PICMA® piezo actuators guarded by all-ceramic insulation for longer lifetime and protection from humidity.   S-331 tip/tilt mirror platforms are used in image processing, image stabilization, laser beam steering and tracking, scanning microscopy, materials processing, lithography, optical filters and switches.
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S-331 Tip/Tilt Mirror Platform

High Dynamics, for ½” Mirrors

  • 10mrad optical deflection
  • High dynamics: 0.8msec rise time
  • PKM: single pivot point
  • Closed-loop for high linearity
  • Up to 50nrad resolution
S-330 Fast Tip/Tilt Steering Mirror
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S-330 Fast Tip/Tilt Steering Mirror

Mirrors up to 50mm

  • Fixed orthogonal axes with a common pivot point
  • To 20mrad optical beam deflection
  • Up to 20nrad resolution
  • Closed-loop for high linearity
S-340 Fast Tip/Tilt Steering Mirror
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S-340 Fast Tip/Tilt Steering Mirror

Mirrors up to 100mm

  • Fixed orthogonal axes with a common pivot point
  • 4mrad optical beam deflection
  • Sub-microrad resolution
  • Closed-loop for high linearity
S-335 Tip/Tilt Mirror Platform
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S-335 Tip/Tilt Mirror Platform

Long Travel, Mirrors up 1”

  • 70mrad optical beam deflection
  • Up to 100nrad resolution
  • Closed-loop for high linearity
  • PKM = Equal dynamics for both axes
  • ID chip for auto calibrate

Long Travel & Custom Tip/Tilt Mirrors

N-480 Tip/Tilt Mirror Mount
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N-480 Tip/Tilt Mirror Mount

Piezo Motors, 16° Tilt Angle

  • Kinematic mount
  • High stability PiezoMike motors
  • For 0.5", 1" or 2" optics
  • 1µrad resolution
  • Vacuum versions to 10-9 hPa
Custom Example - Astronomy: Ultra-Stable, Piezo Mirror Mount
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Custom Example - Astronomy

Ultra-Stable, Piezo Mirror Mount

  • ±2° tip / tilt range with PiezoWalk motor
  • <0.5 arcsec angular resolution
  • <1 arcsec position repeatability
  • <20 arcsec static position stability
  • >110Hz resonant frequency 
Custom Tip/Tilt Mirrors
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Custom Example – Low Profile

Dynamic tip/tilt mirror (ΘXΘY)

  •  ±100µrad tip/tilt range
  •  Low profile design

Talk to our engineers about your custom steering mirror project.

Tip Tilt + Piston (Z) Mirror Platforms and Phase Shifters

S-325 Tip/Tilt Piston Mirror Platform
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S-325 Tip/Tilt Piston Mirror Platform

For 1” Mirrors

  • Tripod design: pitch, roll, piston
  • 10mrad optical beam deflection
  • 30µm piston (Z-motion)
  • Closed-loop for high linearity
  • PKM = Equal dynamics for All axes
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S-316 Tip/Tilt/Piston Platform

With 10mm Aperture

  • Tripod design: pitch, roll, piston
  • 2.4mrad optical beam deflection
  • 12µm piston (Z-motion)
  • Closed-loop for high linearity
  • PKM = Equal dynamics for all axes

Z and Z-Tip/Tilt Stages with Aperture

P-612 Piezo-Z Stage
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P-612 Piezo-Z Stage

Compact Z Stage, Aperture

  • 100µm motion
  • Compact: 60x60x27mm
  • For cost-sensitive applications
  • <1 nanometer resolution
  • PICMA® long-life piezo drives
P-541 Piezo-Z & Z-Tip-Tilt Stages
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P-541 Piezo-Z & Z-Tip-Tilt Stages

Low-Profile, 80x80mm Aperture

  • 100µm linear travel, 1 mrad tip/tilt
  • Lowest profile: 16.5mm
  • <1 nanometer resolution
  • Choice of feedback sensors
  • 80x80mm aperture
P-528 Piezo Z & Z/Tip/Tilt Stages
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P-528 Piezo Z & Z/Tip/Tilt Stages

Parallel Metrology

  • 50, 100, 200µm Z-motion
  • Up to 4 milliradian Z/tip/tilt
  • Precision trajectory control
  • Sub-nanometer resolution
  • Parallel capacitive metrology

Kinematics of Piezo Tip/Tilt Mechanisms

Steering Mirror Platforms

PI offers a large range of fast steering mirrors (FSM) from compact systems for laser beam steering up to large units used for astronomy.

Single-Axis Tilt Platforms
The most compact approach is based on a flexure guided platform driven by a single actuator.  For differentially driven platforms see “Tip/Tilt System with Differential Piezo Drive (Tetrapod) and improved Thermal Stability” below.

The platform is supported by one flexure and pushed by one linear piezo actuator. The flexure determines the pivot point and doubles as a preload for the Piezo actuator.

Single flexure, single piezo actuator (PZT) tilt mirror platform design. Advantages are the straightforward construction, compact dimensions and low costs. If thermal angular stability over a large temperature range is a critical issue, a differential piezo actuator drive system is recommended (see below).

Multi-Axis Piezo Steering Mirrors
Multi-axis piezo tip/tilt mirror platforms from PI are based on parallel kinematics with a single moving platform for all directions of motion. The common platform approach achieves higher linearity than can be attained by cascading single-axis mirrors in succession (e.g. with most galvo scanners).  The single platform design also avoids polarization rotation and is much more compact than a multi-stage approach.

High Dynamics and High Stability
Piezo-actuated tip/tilt mirrors and platforms are suitable both for highly dynamic operation, such as tracking, scanning, image stabilization, elimination of drift and vibration, and for static positioning of optical systems and samples.

Direct Drive and Motion Amplified Steering Mirrors
Piezo steering mirrors can provide very fast response times in the sub-millisecond range and resolutions down to nano radians.  Direct-driven units achieve higher dynamics, while designs that take advantage of on internal flexure motion amplifiers provide for larger optical beam deflection up to 100 mrad.

Tip/Tilt/Piston System - Tripod Piezo Drive
The platform is driven by three piezo actuators that are located in 120° angles to one another. By means of coordinate transformation, the motion can be split among the different actuators. In addition to tilting, the platform may also be used linearly in Z direction (piston motion), useful for phase shifting and correcting optical path length differences. 

Piezo actuator arrangement of a tripod Z/tip/tilt mechanism. Tilt angles and piston motion (Z) are calculated with these formulas:

θY = 2A-[(B+C)/2a];  θX = (B-C)/b;  Z = (A+B+C)/3

A, B, C = linear displacement of the relevant piezo actuators

Tip/Tilt System with Differential Piezo Drive (Tetrapod) and improved Thermal Stability
The platform is driven by a total of four piezo actuators - two pairs with the θX and θY tilt axes arranged orthogonally removing the need for coordinate transformation. Each pair is controlled differentially, i.e. one actuator extends while the other one retracts by the same amount. The advantage of this approach is the improved thermal stability over a wider temperature range compared to a simpler, two actuator design. Just as the tripod, the differential version guarantees an optimum angular stability over a large temperature range. For position controlled versions, the differential evaluation of two sensors per axis provides an improved linearity and resolution. 

Design principle of a differential piezo-actuator (PZT) steering mirror.  This construction features two piezo linear actuators (operated in push/pull mode) per axis, supporting the platform. The case can be machined from one solid metal block with FEA (Finite Element Analysis) designed wire EDM (Electric Discharge Machining) cut flexures. The flexures provide for zero friction/stiction and excellent guiding accuracy. The differential design exhibits excellent angular stability over a wide temperature range - temperature changes only affect the vertical position of the platform (piston motion) and have no influence on the angular position. After the operating voltage is removed the platform returns to the center position.

Dynamics of Piezo Tip/Tilt Mirror Mechanisms
The dynamics and maximum operating frequency of a piezo tip/tilt system strongly depends on its mechanical stiffness and resonant frequency. The properties of amplifier, controller and closed-loop position sensor / circuit are also important. To estimate the effective resonant frequency of the system – a combination of platform and mirror – the moment of inertia of the mirror substrate needs to be calculated:

Moment of inertia of a rotationally symmetric mirror

Moment of inertia of a rectangular mirror

m = mirror weight [g]

IM = moment of inertia of a mirror [g × mm²]

L = mirror length orthogonally to tilt axis [mm]

H = mirror thickness [mm]

R = mirror radius [mm]

T = distance of pivot point to platform surface [mm]

The resonant frequency of the system is calculated with resonant frequency of the platform (see technical data) and moment of inertia of the mirror substrate using the following formula: 

f' = resonant frequency of platform with mirror [Hz]

f0 = resonant frequency of platform without mirror [Hz]

I0 = moment of inertia of platform (see technical data) [g × mm²]

IM = moment of inertia of mirror [g × mm²]


Hexapods and Fast Steering Mirrors / Active Optics in Astronomical Telescopes

Resolution in large earthbound telescopes is limited by atmospheric turbulence and vibrations. During the last 35 years, PI has designed a number of large-aperture high bandwidth tip/tilt systems for image stabilization. Piezoelectrically driven active secondary mirrors can improve the effective resolution up to 1000% by correcting for these image shifts in real time, especially during long integrations with weak light sources.

Piezo-based solutions are key to precision in the World’s largest telescope, the ELT of the European Southern Observatory (ESO). This artist’s impression shows the European Extremely Large Telescope (E-ELT) in its enclosure. The E-ELT will be a 39-metre aperture optical and infrared telescope sited on Cerro Armazones in the Chilean Atacama Desert. PI provides the nanometer-precise actuation of the main mirror segments, as well as other piezo-based, highly customized motion solutions for precision-critical points of operation within the telescope. (Image: ESO/L. Calçada) Read about it: http://www.pi-usa.us/blog/hybrid-ultra-high-precision-positioning-actuators/
This fast tip / tilt platform corrects the image jitter at an M5 telescope mirror. A high bandwidth and extremely high resolution is essential to achieve a high image quality.
The image on the left represents a star without tip/tilt correction, the image on the right was obtained with fast tilt correction. (Source: http://arxiv.org/pdf/1606.00690.pdf)
View of the 8.2 m Subaru infrared telescope in Hawaii (from http://SubaruTelescope.org ), printed with permission of NAOJ.
Active tip/tilt mirror for the Subaru Telescope (Mauna Kea, Hawaii). Mirror diameter: 150 mm. Tip/tilt range: ±600 µrad. Resonant frequency: 610 Hz
Active tip/tilt mirror for the Subaru telescope, rear view.
Active tip/tilt mirror for the United Kingdom infrared telescope (UKIRT) on Mauna Kea, Hawaii with Secondary Hexapod 6-D alignment system. Mirror diameter: 314 mm Tip/tilt range: ±500 µrad Resonant frequency: 280 Hz
Active secondary mirror for NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii,with Hexapod 6-D alignment system. Mirror diameter: 244 mm Tip/tilt range: ±250 µrad Resonant frequency: 490 Hz
Active tip/tilt mirror system for the Keck Outrigger telescope in Hawaii. The units are controlled by a high-performance digital controller with a fiber optic interface (not shown). Mirror diameter: 250 mm Tip/tilt range: ±150 µrad Resolution: nanoradian range Position measurement: capacitive
Active secondary tip/tilt mirror for the 2.2 m ESO (European Southern Observatory) telescope in La Silla, Chile. Mirror diameter: 100 mm Tip/tilt range: ±400 µrad Resonant frequency: 900 Hz
Telescope structure with active secondary mirror (from "Progress Report on DISCO: A Project for Image Stabilization at the 2.2 m Telescope," F. Maaswinkel, S. D'Odorico and G. Huster, ESO, F. Bortoletto, Istituto di Astronomia, University of Padova, Italy).
Ultra-Stable Mirror Mounts for LINC-NIRVANA High Resolution Imager
This double piezo hexapod combines in one system the coarse and fine travel for alignment of the M2 mirror of a large telescope.

Momentum Compensation

Due to the inertia of the large mirrors and the high accelerations required to correct for image fluctuations, significant forces can be induced in the telescope structure, causing unwanted vibrations. PI has developed momentum compensation systems integrated into the tip/tilt platforms which cancel undesirable vibrations and thus offer significantly better stabilization than uncompensated systems.

 

More Information on PI Precsion Motion Control Products in Astronomy 

  • M-850.K102 Ultra-High-Load Hexapod for Astronomy