PI-Cell Shutter

pi-Cells for Ultra Fast Shutters


Pi-cells are used in applications requiring high speed switching. They are commonly used in 3D applications to avoid flicker effects, ultra fast shutters or switching components in tunable filters. The name comes from the twist of molecules, which is 180° formed by the parallel rubbing direction on each glass substrate. The fast speed is the result of fluid dynamics. When voltage is removed from a Pi-cell, the molecules feel very little torque to return to their low voltage state in a parallel configuration. A “holding” voltage at the desired low voltage state is required to maintain pure polarization switching. Pi-cells therefore operate between a high voltage (30V) and a low holding voltage (approx. 2V).

Parallel aligned cells also have naturally higher viewing angles due to the symmetrical molecular alignment at glass surface boundaries. High contrast is easily achieved with a film compensation layer to subtract residual birefringence at the surfaces.

pi-Cell Device Applications

Solid State Modulators


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.

Ultra Fast Shutters


Pi-cell LC shutters are constructed with crossed linear polarizers and optional compensator films. A push-pull configuration can be manufactured incorporating two thin cavity Pi-cells creating an ultra fast, self compensating optical shutter.

Augmented Reality

Pi-cell Liquid Crystal Devices
microsecond lc modulators

BVO Pi-cell LC components used in AR/VR head mounted displays Sub Heading

Precision pi-cell 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 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 200 Micro Seconds (Rise Time) / 1.3 Milli Seconds (Fall Time) , Typical
Bandwidth Visible or Near infrared (Dual cells required)
Temperature Range 10˚ C to 60˚ C
Damage Threshold 500 Watts/cm2 CW
.5 Joules/cm2 10nsec pulses @ 1064nm typical
BVO prototype Pi-cells can be made in most geometries and LC devices incorporating difficult specifications can be turned quickly. High uniformity, fast response times or compensation film stacks are typical upgrade requests. Liquid crystal shutters can be provided with appropriate linear polarizers.

“off the shelf” Products – pi-cell shutters and modulators

 

pi-Cell Liquid Crystal device

88mm x 56mm x 1.4mm
Active area: 65mm x 43mm

Large format, high speed liquid crystal modulator

features
  • 200 microsecond rise time
  • 1.5 millisecond fall time
  • Thin device, 1.4mm thick
  • Optic axis 45˚ to edge
  • 350nm retardance, clear of holding voltage
  • 2.0 Volts holding voltage
  • Optional compensator film

Buy Now $350

 

pi-Cell Liquid Crystal device

38mm x 35.6mm x 1.4mm
Active area: 36mm x 31mm

Medium format, high speed liquid crystal modulator

features
  • 200 microsecond rise time
  • 1.5 millisecond fall time
  • Thin device, 1.4mm thick
  • Optic axis 0˚ to edge
  • 350nm retardance, clear of holding voltage
  • 2.0 Volts holding voltage
  • Optional compensator film

Buy Now $195

 

pi-Cell Liquid Crystal Shutter

25.4mm x 26.2mm x 1.75mm
Active area: 21mm x 21mm

Fast shutter with polarizers and FPC connector

features
  • Liquid Crystal Light Valve
  • 50 microsecond rise time
  • 1.3 millisecond fall time
  • Thin device, 1.75mm thick
  • Polarizer transmission axis 45˚ to edge
  • 100:1 contrast ratio, 500:1 compensated
  • 2.0 Volts holding voltage, Typical
  • Optional compensator film

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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