Twisted Nematic (TN)

TN – Polarization Rotators


Twisted Nematic (TN) liquid crystals are the most common type of LC’s used in the display industry. TN cells are basically 90° polarization rotators. As linear polarized light enters the cell it rotates along the LC helical structure formed from the front glass substrate to back substrate. TN cells can be made in either a normally black mode or normally white mode. Normally black mode is a dark state with zero voltage applied with polarizers mounted to the outside of the substrates in parallel to each other. As voltage is applied light transmission increases as a function of voltage. Normally white mode has maximum transmission with zero voltage applied with the polarizers orthogonally mounted on the glass substrates. The light is attenuated as voltage increases. This mode achieves higher contrast as the dark state takes advantage of the crossed polarizer configuration.

TN’s advantages are low voltage requirements and they operate over a large wavelength range. TN cells can be manufactured uniformly in mass volumes with thin glass. If low transmitted wavefront distortion is required, precision cells can be manufactured with polished glass substrates.

TN Device Applications

Polarization Rotators


The most basic LC device. Input polarization rotated 90˚ with zero voltage. Increasing voltage to max unwinds the LC molecules imparting no rotation. TN devices can be optimized for NIR applications.

Achromatic High Contrast Attenuators


The workhorse of the display industry. High contrast attenuators first used in watches, are the cheapest and easiest cells to mass produce. Normal white mode 1000:1 contrast ratio capable over 200nm band.

LC Modulator - Stereoscopic Displays


TN modulators are commonly used in the stereoscopic display industry. Modulation of alternate linear polarization states in glasses simulate depth. The basis of modern 3D entertainment.

Laser Rangefinding

TN Liquid Crystal Devices
NIR polarization rotator

BVO TN components for rangefinders | construction and automotive Sub Heading

Precision twisted nematic (TN) 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 90˚ orthogonal
Transmitted Wavefront Distortion Polished glass devices: .25 waves over clear aperture
BBAR Coatings Optional coatings
Contrast Ratio 1000:1
Switching Speed 1 Milli Second (Rise Time) / 15 Milli Seconds (Fall Time) , Typical
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
BVO prototype twisted nematic liquid crystal devices can be made in most geometries and incorporate difficult specifications. Many designs can be turned quickly. High uniformity or faster response times are typical upgrade requests. TN devices do not require contrast compensation films. Achromatic high contrast attenuators can be provided with appropriate linear polarizers.

“off the shelf” Products – twisted nematic rotators and modulators

 

TN Liquid Crystal rotator

42.5mm x 39mm x 2.2mm

Active area: 36mm x 36mm

Medium format, TN liquid crystal cell

features
  • 0-5 Volts – 7.2 mSecond rise time, 18 mSecond fall time (due to back-flow)
  • 0-30 Volts – 82 microSecond rise time, 11 mSecond fall time
  • Thin device, 2.2mm thick
  • Analog grey scale as attenuator
  • Optic axis 0˚ to edge
  • Visible bandwidth
  • Low voltage requirements
  • Optional polarizers

Buy Now $295

 

NIR TN Liquid Crystal rotator

21mm x 20mm x 2.2mm

Active area: 18.5mm x 15mm

Near infrared TN LC cell and FPC connector

features
  • 400 – 1100nm broadband device
  • 2 millisecond rise time
  • 28 millisecond fall time
  • Thin device, 2.2mm thick
  • Analog grey scale as attenuator
  • Optic axis 0˚ to edge
  • Centered @ 850nm
  • 1000:1 contrast ratio
  • Optional polarizers

Buy Now $195

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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