ECB Nematic Liquid Crystal Devices
- Liquid crystal variable retarder
- True zero order to multi-wave retardance
- Liquid crystal variable attenuator
- Visible / NIR bandwidths
- Small volume precision LC optics
- Large volume inexpensive LC optics
- Very low current devices (milli amps)
- 0-20 Volts RMS, AC
- 2 KHz carrier frequency, square wave
- DC Driving-Zero DC bias between +/- voltages required
- Low capacitance (nano farads)
- 90% internal transmittance
ECB Nematic | Summary
Electronically controlled birefringence is one of the most versatile nematic modes where the retardance of set wavelengths can be controlled in analog fashion. ECBs have maximum retardance at 0 Volts and switch towards minimum retardance as voltage is increased. The birefringence change is a function of the LC tilt angle (also called the polar angle) defined as the angle created by the substrate normal and the molecule’s long axis.
ECB Device Applications
Liquid Crystal Variable Retarder – Wavelength Specific
Tune unique retardance for each specific wavelength. Setting the retardance to halfwave for a specific wavelength creates a plane polarization rotator. Setting the retardance to quarterwave of a wavelength creates a circular polarization.
Phase Control – OPL Change
The optical path length (OPL) of an input plane polarized wave can be changed through voltage control. Accomplished by aligning the linear polarization with the slow axis of the variable retarder. Increasing the voltage tilts the LC molecule, changes the index and the input polarization experiences a phase change.
Liquid Crystal Variable Attenuator
A solid state, voltage controlled analog device capable of 1000:1 contrast ratio. LCVAs can create grey scale or complete light extinction. High extinction devices generally require compensator plate to correct for LC surface pinning common to ECB mode devices.
ECB Nematic | Precision LC Devices
ECB precision components are handmade devices which often incorporate difficult specifications. High uniformity, faster response times or simple patterned apertures are typical upgrade requests. An example of a common precision ECB LC device would have the following specifications.
Glass Fused Silica Thickness 6-8mm (no compensator) standard, optional alternatives Outer Dimensions Up to 75mm OD Clear Aperture (CA) cell outer diameter – 6mm (gaskets and landings) = CA Buffing Anti-parallel Transmitted Wavefront Distortion .25 waves / 25mm or better over clear aperture BBAR Coatings BBAR VIS (400-900nm),BBAR NIR (900-1700nm), V-Coat Internal Transmittance 400-450nm – 85% (ITO absorption), 450-1000nm – 92% Contrast Ratio 500:1 standard , 1000:1 compensated Switching Speed Low as 15-20mSec, 10-90% full cycle (function of cell gap thickness) Bandwidth Visible or Near infrared Temperature Range 10˚ C to 50˚ C Damage Threshold 500 Watts/centimeter2 CW
.5 Joules/ centimeter2 squared 10nsec pulses @ 1064nm typical
ECB Nematic | OEM Volume LC Devices
OEM volume components can leverage the power of numbers to decrease cost. BVO builds proof of concept prototypes and then rolls into large volume production using overseas vendors. Result is components for much less.Nematic liquid crystal cells can be delivered as raw cells or post laminated with linear polarizers. Custom AR coated glass caps can be added to protect and increase transmission.Large volume liquid crystal components easily approach the cost of passive components making electronically tunable solid state devices appropriate for OEM systems.