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 |
“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
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
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
volume manufacturing
• 1mm thick cells, custom design mass production
• large panels up to 450mm x 350mm
• 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
Optical Finesse LC Drivers
RECOMMENDED DRIVERS
Click to learn more about Optical Finesse Liquid Crystal Drivers. BVO’s recommended driver manufacturer.
LCC2-33 Analog Contoller
uLC400-30 DigitalController