Liquid Crystal Variable Waveplates (Retarders)

Liquid Crystal Variable Waveplates (Retarders) are constructed using precision polished, optically flat fused silica windows spaced a few microns apart. The cavity is filled with nematic liquid crystal material and sealed. This assembly ensures excellent transmitted wavefront quality and low beam deviation, required for many demanding applications. Uncompensated retarders can vary from 30nm - ½λ retardance while compensated retarders can operate from 0 – ½λ.

The long axis of the liquid crystal molecules defines the extraordinary, or slow, index. With no voltage present, the molecules lie parallel to the windows and maximum retardance is obtained. When voltage is applied across the liquid crystal layer, the molecules tip towards the direction of the applied electric field. As voltage increases, the effective birefringence decreases, causing a reduction in retardance.

The basic liquid crystal controller allows a single retarder to be controlled manually. The 4 channel digital liquid crystal controller can operate up to four retarders at once using a computer interface. A LabVIEW™ virtual instruments driver is included with the digital controller. The digital controller also features advanced software and capability for temperature monitoring and control on one channel.

Basic Liquid Crystal Controller Specifications

• Output Voltage: 2kHz AC square λ adjustable 0-25V RMS; 50% duty cycle, minimal DC bias
• Voltage Resolution: 3mV
• Internal Modulation: 0.7-150Hz
• External Modulation: TTL input: 12V maximum DC-1 kHz

4 Channel Digital Liquid Crystal Controller Specifications

• Fundamental Drive Waveform: 2kHz AC square λ Modulation: 0-10V RMS
• Modulation Waveforms: External modulation input (0-5 V); Sinusoidal, triangle, square, sawtooth, transient nematic effect
• Modulation Resolution: 1mV (0.155mV using LabVIEW™ subroutines)
• DC Offset: <5mV
• PC Controller Communications Interface: USB or RS232
• LC cell to Controller Connections: SMA-SMB connections, 2m length
• Sync Output: TTL, 1μs pulse, user specified phase
• Temperature Control: Active heating/passive cooling to within ±1°C of nominal set point