Variable attenuator

The Arcoptix electrical adjustable variable attenuator is a worldwide unique liquid crystal device that permits to control precisely the attenuation of a free space traveling beam with a simple applied voltage. The variable gray filter functions for polychromatic or monochromatic light as well as for unpolarized or polarized white light. It does not significantly alter the spectrum of the incident light and functions almost equally for wavelengths between 350nm and 700nm. The ARCoptix variable attenuator can so be considered as an ideal variable gray filter in the visible. Notice that this is not the case for usual liquid crystal attenuators that are designed to attenuate efficiently only a single wavelength! Also in the off state, the ARCoptix attenuator shows a higher transmission (for unpolarized light) than usual attenuators and it does not alter significantly the Polarization state of the light (Polarization maintaining element).

White light transmission of the variable attenuator WA65 for decreasing applied bias.
The Arcoptix variable attenuator has the unique property to be adjusted in milliseconds with a simple square wave bias between 0 and 10V and can so be easily computer controlled via the ARCoptix LC driver (with external voltage control). No need to change filters mechanically or to rotate a filter wheel. This device is ideal for application where the intensity needs to be dynamically and continuously controlled.
  • Voltage adjustable in milliseconds
  • Attenuation is nearly wavelength
    independent in the visible (gray filter)
  • Attenuation from 0.2 to 10³
  • Computer addressable
  • Polarization independent and
    Polarization maintaining
  • Aperture up to 40 mm
  • No moving part
  • Compact

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The variable attenuator is based on a combination of two cells filled a specially developed mixture of liquid crystals with dichroic molecules. The two cells act as a polarizer and analyzer with a kind of variable dichroicity (or specific Polarization absorption). By applying a bias, the optical axes on these two cells can be tilted and the absorption of the light that propagate normally to the cells is reduced.

The dichroic molecules of the two cells are tilted forward when a bias is applied to the cell.
The absorption of the dichroic molecules has been optimized for the visible spectrum and functions ideally between 400 and 650nm. As it is also the case for many sheet polarizers. Since the two cells have equal thickness and the two optical axis are perpendicular, the birefringence is perfectly compensated and the Polarization state of the light is not altered.
For an attenuator with a 10mm aperture, the specs are given by the table below. For a more detailed information (calibration curves, transmission curves, ...), please download the PDF file.
Features Variable Attenuator
Useable aperture 10 mm
Transmission for
Model VA200
Model VA65

From 0.1 to 10-4 (@ 633nm)
From 0.5 to 1.5 ·10-2 (@ 633nm)
Transmission uniformity Better than 0.3%
Voltage range 0-20 V (square wave)
Wavelength range 350-700 nm (optimal performances
between 400 and 650nm
Temperature range 10° - 50° C
Cell size 27mm x 27mm x 5mm
Total size with housing 40mm x 55mm x 8mm

Transmission curves for different applied voltages (Model VA65)

DOWNLOADDetailed description of the variable attenuator