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).

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.

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 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.