Piezo Steering Mirrors | Active Optics

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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).

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

Read Article:Design, Performance, and Tuning of Fast Steering Mirrors based on Piezo Drives and Flexure Guides

Steering Mirror Fundamentals Steering Mirrors for Astronomy

Application video: Laser beam steering in eye surgery.

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.

Direct Metrology Option

Sub-millisecond dynamics
<0.1 nanometer resolution
High-linearity sensor option
Invar option
Aperture with open-loop versions

Details

With Aperture

6/14µm piston motion
Sub-millisecond dynamics
Sub-nanometer resolution
Open loop
10mm aperture

Details

Compact, 4mrad

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

Details

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.

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

Details

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

Details

Mirrors up to 100mm

Fixed orthogonal axes with a common pivot point
4mrad optical beam deflection
Sub-microrad resolution
Closed-loop for high linearity

Details

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

Details Article

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

Details

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

Dynamic tip/tilt mirror (ΘXΘY)

±100µrad tip/tilt range
Low profile design

Talk to our engineers about your custom steering mirror project.

More Custom Examples

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

Details

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

Details

Compact Z Stage, Aperture

100µm motion
Compact: 60x60x27mm
For cost-sensitive applications
<1 nanometer resolution
PICMA® long-life piezo drives

Details

Low-Profile, 80x80mm Aperture

100µm linear travel, 1 mrad tip/tilt
Lowest profile: 16.5mm
<1 nanometer resolution
Choice of feedback sensors
80x80mm aperture

Details

Parallel Metrology

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

Details

More Piezo Z-Stages

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]

I_M = 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]

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/

S-900K094 — 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) — The image on the left represents a star without tip/tilt correction, the image on the right was obtained with fast tilt correction. (Source: 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. — View of the 8.2 m Subaru infrared telescope in Hawaii (from 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).

N-510K013 — Ultra-Stable Mirror Mounts for LINC-NIRVANA High Resolution Imager

M-900K155 — This double piezo hexapod combines in one system the coarse and fine travel for alignment of the M2 mirror of a large telescope.

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