"; _cf_contextpath=""; _cf_ajaxscriptsrc="/cfthorscripts/ajax"; _cf_jsonprefix='//'; _cf_websocket_port=8578; _cf_flash_policy_port=1244; _cf_clientid='9D2E473B8E9983D332067A166E66326B';/* ]]> */
Open-Loop Piezo Controllers
Click for Details
Front Panel of 3-Channel Model
Click to Enlarge
Front Panel of Single-Channel Model
Thorlabs' Open-Loop Piezoelectric Controllers provide precise, low-noise output voltages for fine movement of piezoelectric actuators and stacks. Each output channel is independently controllable and provides a voltage ranging from 0 - 75 V, 0 - 100 V, or 0 - 150 V, depending upon the position of a switch on the back panel; the ability to choose a lower maximum voltage helps protect sensitive, low-voltage piezo devices. The voltage is output through BNC, and a 4-digit LED readout displays the value of the output voltage for each channel in real time. One BNC-to-SMC adapter (MDC40211) per channel is included in order to support actuators with SMC connectors.
Local and Remote Control Options
Master Scan Mode
Output Voltage: 0 - 150 V
External Voltage Control
Input Voltage: 0 - 10 V
External Computer Control
Type B USB Female
Click for Details
Piezo Controller as Part of a Closed-Loop System
Piezo Controller in a Beam Stabilization Setup
Active beam stabilization is often used to compensate for beam drift (unintended beam pointing deviations) in experimental setups. Drift can be caused by insecurely mounted optics, laser source instabilities, and thermal fluctuations within an optomechanical setup. In addition to correcting for setup errors, active stabilization is frequently used in laser cavities to maintain a high output power or used on an optical table to ensure that long measurements will take place under constant illumination conditions. Setups with long beam paths also benefit from active stabilization, since small angular deviations in a long path will lead to significant displacements downstream.
An example of a beam stabilization setup is shown in the schematic to the left. A beamsplitter inserted in the optical path sends a sample of the beam to a quadrant position sensor that monitors the displacement of the beam relative to the detector's center. (For optimal stabilization, the beamsplitter should be as close as possible to the measurement.) The quadrant detector outputs an error signal in X and Y that is proportional to the beam's position. Each error signal is fed into a channel of a piezoelectric controller that steers the beam back to the center of the quadrant sensor.
The setup illustrated here stabilizes the beam to a point in space. In order to stabilize the beam over a beam path, four independent output channels are required (i.e., at least two piezoelectric controllers), as are two mirror mounts with piezo adjusters, two position sensors, and two position sensor controllers. Suggested electronics for a beam stabilization setup are given in the table below.
External Control Using Serial Commands
Please note that firmware version 1.09 or later is required if using version 2 of the software. The firmware can be updated by clicking the Software link to the left.
Piezo Driver Bandwidth Tutorial
Knowing the rate at which a piezo is capable of changing lengths is essential in many high-speed applications. The bandwidth of a piezo controller and stack can be estimated if the following is known:
To drive the output capacitor, current is needed to charge it and to discharge it. The change in charge, dV/dt, is called the slew rate. The larger the capacitance, the more current needed:
For example, if a 100 µm stack with a capacitance of 20 µF is being driven by a BPC Series piezo controller with a maximum current of 0.5 A, the slew rate is given by
Hence, for an instantaneous voltage change from 0 V to 75 V, it would take 3 ms for the output voltage to reach 75 V.
Note: For these calculations, it is assumed that the absolute maximum bandwidth of the driver is much higher than the bandwidths calculated, and thus, driver bandwidth is not a limiting factor. Also please note that these calculations only apply for open-loop systems. In closed-loop mode, the slow response of the feedback loop puts another limit on the bandwidth.
The bandwidth of the system usually refers to the system's response to a sinusoidal signal of a given amplitude. For a piezo element driven by a sinusoidal signal of peak amplitude A, peak-to-peak voltage Vpp, and frequency f, we have:
A diagram of voltage as a function of time is shown to the right. The maximum slew rate, or voltage change, is reached at t = 2nπ, (n=0, 1, 2,...) at point a in the diagram to the right:
From the first equation, above:
For the example above, the maximum full-range (75 V) bandwidth would be
For a smaller piezo stack with 10 times lower capacitance, the results would be 10 times better, or about 1060 Hz. Or, if the peak-to-peak signal is reduced to 7.5 V (10% max amplitude) with the 100 µm stack, again, the result would be 10 times better at about 1060 Hz.
Triangle Wave Signal
For a piezo actuator driven by a triangle wave of max voltage Vpeak and minimum voltage of 0, the slew rate is equal to the slope:
Or, since f = 1/T:
Square Wave Signal
For a piezo actuator driven by a square wave of maximum voltage Vpeak and minimum voltage 0, the slew rate limits the minimum rise and fall times. In this case, the slew rate is equal to the slope while the signal is rising or falling. If tr is the minimum rise time, then
For additional information about piezo theory and operation, see the Piezoelectric Tutorials page.