Benchtop Voltage Controller for Liquid Crystal Devices

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Figure 1.1  Back Panel of the LCC25 Liquid Crystal Controller

Features

• Square-Wave Output Voltage
  • Adjustable Amplitude: 0 to ±25 VAC
  • Frequency: 2,000 ± 5 Hz
• Maximum Output Current: 15 mA
• Three User-Set Operating Modes: Voltage 1, Voltage 2, or Modulation
• Internally or Externally Controlled Modulation Between Two Output Voltage Amplitudes
  • Internal: 0.5 to 150 Hz
  • External (0 to 5 V TTL Signal): 0.5 to 500 Hz
• Control Using Device Front Panel or via USB Input from a PC
• Settings can be Saved to Allow Stand-Alone Operation via Front Panel Controls
• Dimensions: 146 mm x 78 mm x 309 mm

The LCC25 liquid crystal controller is compatible with many of our liquid crystal (LC) devices (see Table 1.2). It produces a 2000 Hz square-wave AC voltage output with an amplitude that can be varied from 0 V_rms to ±25 V_rms. Nematic LC retarders must be driven with an AC voltage in order to prevent the separation and build up of charge, which can cause the device to burn out. In addition to the 2000 Hz AC drive voltage, the LCC25 controller automatically zeros the DC bias across the LC device to within 10 mV in order to counteract the buildup of charges.

Figure 1.4  A plot of the output voltage of the LCC25 Liquid Crystal Controller when the output voltage is being modulated between the two set voltages.

Figure 1.3  A plot of the output voltage of the LCC25 Liquid Crystal Controller when it is being operated in the constant voltage mode.

The AC output voltage amplitude can be set using the front panel controls, an external 0 - 5 VDC TTL input, or via the USB interface. Both the front panel and USB interface allow the user to select two voltage levels, Voltage 1 and Voltage 2. When the LCC25 is operated in the constant voltage mode, the output of the controller will be a 2000 Hz square wave with an amplitude equal to either of the two set voltage levels (Figure 1.3). Alternatively, in Modulation mode, the amplitude of the 2000 Hz square wave output will switch between Voltage 1 and Voltage 2 at a frequency that can be set internally (0.5 Hz to 150 Hz, see Figure 1.4) or triggered externally with 0 to 5 V TTL input (0.5 Hz to 500 Hz). The modulated mode can also be used to measure the response time of the LC retarder.

The USB interface can also be used to send line commands to the controller so that the LCC25 can be used in automated lab sequences. This enables operation through a terminal interface or control of the device using a written program.

Thorlabs also offers the KLC101 K-Cube^® Liquid Crystal Controller.

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Figure 3.1  Screenshot of the GUI interface in Modulation Mode

Software

Version 4.0.1

GUI Interface for controlling the Liquid Crystal Retarder Controller via a PC. To download, Click the button below.

Software for the LCC25 Controller

Graphical User Interface
The graphical user interface (GUI) included with the software provides access to all of the settings of the liquid crystal controller. For example, the user can select one of two user-defined voltages or a modulation mode that oscillates between these two voltages at a user-defined frequency. As shown in Figure 3.1, the GUI includes a plot of the output voltage with respect to time. Both the output and external input can be turned on and off via the GUI. In addition, advanced features allow the user to define a custom waveform by specifying the starting voltage, ending voltage, the voltage step size, and the dwell time. The waveform may be previewed on the screen before it is output to the retarder, and it may be saved so that the LCC25 can be restarted quickly in the future. The GUI is available as a stand-alone or LabVIEW based version for flexibility in implementation.

Custom Software Development
Users may also use the provided C/C++ and LabVIEW software development kits for implementing the liquid crystal retarder controller with other instruments. Sample C++ code and LabVIEW programs help to illustrate how the C commands and LabVIEW VIs can be utilized. Full documentation on the available commands is provided with the software.