AI Content Index › Liquid Crystals › VA Mode
VA Mode Nematic Liquid Crystal
Mode: Vertically Aligned (Homeotropic) | Highest Contrast Attenuator | Custom Manufactured
Highest Contrast
Thermally Stable Dark State
Ultra Extinction Ratio
VIS & NIR
To 90mm Aperture
VA Mode (Vertically Aligned) nematic liquid crystal devices deliver the highest contrast ratio of any LC mode. LC molecules are aligned perpendicular to the glass substrates (homeotropic alignment) with zero voltage applied — this creates zero residual birefringence and an exceptional dark state. The normal black mode configuration uses crossed linear polarizers on the outside substrates. As voltage is applied, molecules rotate from vertical to horizontal, achieving grey scale light transmission. The dark state is highly achromatic and thermally stable — the final contrast level is defined by the quality of the linear polarizers.
Highest
Contrast of Any LC Mode
Thermally Stable
Dark State
How VA Mode Works
In VA mode (also called homeotropic alignment), LC molecules with negative dielectric anisotropy are aligned perpendicular to the glass substrates — standing vertically. At zero voltage, light traveling along the optical axis of the cell encounters no birefringence because the molecular long axes are parallel to the light propagation direction. This is the dark state: with crossed polarizers, essentially no light passes.
As AC voltage is applied, the molecules tilt from vertical toward horizontal (driven by negative dielectric anisotropy — they align perpendicular to the field). The birefringence increases with tilt angle, allowing progressively more light through the crossed polarizers. This grey scale response enables smooth, analog attenuation from near-zero (dark state) to maximum transmission.
The dark state is inherently achromatic — no wavelength correction is needed — and thermally stable. This thermal stability is a major advantage over other LC modes in environments with temperature variation. Final contrast is ultimately limited by the extinction ratio of the linear polarizers used. NIR VA mode devices require two cells (double pass) plus NIR-appropriate linear polarizers.
Key Features
- Highest contrast ratio of any LC mode — defined by polarizer quality, not the LC itself
- Thermally stable dark state — major advantage in variable temperature environments
- Ultra extinction ratio over wavelength bandwidth — highly achromatic dark state
- Normal black mode — exceptional dark state at 0V with crossed polarizers
- Negative dielectric anisotropy LC fluid — special alignment layers required
- VIS devices: one cell + visible linear polarizers
- NIR devices: two cells + optional NIR linear polarizers (e.g. BVO NIR Ultra)
- Zero DC bias required — AC drive only to prevent LC degradation
- Custom apertures to 90mm — square or round
- Prototype to volume production (1–10,000 units)
Device Specifications (Custom — Contact BVO)
| Parameter | Details |
|---|
| LC Mode | Vertically Aligned (VA) / Homeotropic — negative dielectric anisotropy |
| Contrast | Highest of any LC mode — final level set by polarizer quality |
| Dark State | Normal black — 0V, crossed polarizers, zero residual birefringence |
| Dark State Stability | Thermally stable — low sensitivity to temperature variation |
| LC Fluid | Negative dielectric anisotropy — special alignment fluids required |
| VIS Configuration | One cell + visible linear polarizers |
| NIR Configuration | Two cells + optional NIR linear polarizers |
| Wavelength Range | Visible and NIR — custom to specification |
| Cell Thickness | ~1mm total (0.5mm thin glass substrates) |
| Max Aperture | 90mm |
| Shape | Square or round — custom geometry available |
| Characterization | Speed, insertion loss, contrast ratio (transmission vs voltage curve) |
| Volume | Prototype (1 unit) through high volume (10,000 units) |
| Zero DC Bias | Required — AC drive only |
Applications
Ultra High Contrast AttenuatorsPrimary application. Maximum extinction ratio variable attenuator for visible and NIR systems where contrast is the critical specification — not speed or achromaticity.
NIR High Contrast AttenuatorsTwo-cell NIR VA mode configuration with BVO NIR linear polarizers delivers exceptional contrast in NIR imaging and sensing systems.
Defense Optical SystemsUltra high contrast polarization-based attenuation for defense sensors, laser range finders, and electro-optic systems requiring maximum extinction in variable environments.
Laser Safety & Beam DumpsHigh contrast electronically controlled beam block where maximum extinction ratio in the dark state is essential for laser safety and system protection.
Thermally Demanding EnvironmentsVA dark state thermal stability makes it the preferred choice when temperature variation would degrade contrast in ECB or TN mode devices.
Scientific InstrumentationUltra contrast variable attenuation for spectroscopy, radiometry, optical coherence tomography, and any instrument requiring maximum extinction with analog grey scale control.
Contact Bolder Vision Optik
