ECB Nematic

ECB – Analog Variable Retarder


Electronically controlled birefringence (ECB) is one of the most versatile nematic modes where the retardance of set wavelengths can be controlled in analog fashion. ECB’s 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 to the molecule’s long axis.

ECB Device Applications

Liquid Crystal Variable Retarders


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.

Liquid Crystal Variable Attenuator


LCVA’s are solid state, voltage controlled analog attenuators capable of 1000:1 contrast ratio. High extinction devices generally require compensator plate to correct for LC surface pinning common to ECB mode devices.

Phase Control - OPL Change


The optical path length (OPL) of input polarization can be changed through voltage control. This is accomplished by aligning linear polarization with the slow axis of the variable retarder and modulating voltage.

semiconductor Lithography Systems

ECB Liquid Crystal Devices
liquid crystal variable retarder

BVO ECB LC components used in laser writer mask alignment system Sub Heading

Precision ECB LC Devices
BVO Developmental Liquid Crystal Lab

Glass Eagle XG Display Glass or Polished Fused Silica
Thickness 1-2mm thick: Thin devices made with standard display glass
6-8mm thick: Low wavefront distortion devices made with fused silica
Outer Dimensions Maximum Size – 90mm | Minimum size – 12mm
Clear Aperture (CA) 2mm internal gasket & 2mm landing
Buffing Anti-parallel
Transmitted Wavefront Distortion Polished glass devices: .25 waves over clear aperture
BBAR Coatings Optional coatings
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 60˚ C
Damage Threshold 500 Watts/cm2 CW
.5 Joules/cm2 10nsec pulses @ 1064nm typical
ECB precision components are handmade devices incorporating difficult specifications. High uniformity, fast response times or compensation film stacks are typical upgrade requests. Liquid crystal attenuators provided with appropriate linear polarizers for respective bandwidth.

“off the shelf” Products – ECB Tunable Retarder

Buy Now $495

Ready for the lab

Prefilled liquid crystal cells, wired and ready to ship

features
  • Low wavefront distortion
  • No spacers in clear aperture
  • Low scattering device
  • Full wave retardance @ 700nm
  • < 2% non-uniformity over clear aperture
  • Optional compensator film

Voltage vs Retardance

Voltage vs retardance curve of an ECB liquid crystal variable retarder. High uniformity cell capable of 700nm retardance. Click to enlarge.

volume manufacturing

   • 1mm thick cells, custom design mass production 

   • large cells ≥ 100mm possible

   • aoi , contrast enhancement films value add

   • AR coated caps optional

   • high speed shutters

   • custom flex cable

   • lowest cost option

OEM volume components leverage the power of numbers to decrease cost. BVO builds proof of concept prototypes, verifies cell integration and after approval moves into production. BVO and customer work together to meet cost target.

Liquid Crystal Specifications & Drivers

Liquid Crystal Cell Drive Specs

  • 2 KHz carrier frequency, square wave
  • AC Drive, 0-30 Volts RMS, 50/50 duty cycle
  • DC Drive, Bipolar DC-balanced square wave
    Zero DC bias between +/- voltages required
  • Very low current devices, 15 milli amps Typical
  • Low capacitance, 35 nano farads Typical
Don’t Let This Happen To You – Zero DC Bias is Essential !
Optical Finesse LC Drivers

OF-logo
RECOMMENDED DRIVERS

Click to learn more about Optical Finesse Liquid Crystal Drivers. BVO’s recommended driver manufacturer.


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