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 gay 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 significantely 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	• polarization independent and polarization maintaining
• Attenuation is nearly wavelength independent in the visible (gray filter).	• Aperture up to 40 mm
• Attenuation from 0.2 to 10 -3	• No moving part
• Computer addressable	• Compact

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Ask for a quotation or for more information: info@arcoptix.com

Principle

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 function 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.

Specs

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.

Useable aperture	10 mm
Transmission for Model VA200 Model VA65	From 0.1 to 10-4 (at 633nm) From 0.5 to 1.5 ·10-2 (at 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	27x27x5 mm
Total size with housing	40x55x8 mm

Transmission curves for different applied voltages (Model VA65)

Custom Attenuators

Design and quotes for custom specifications such as attenuation range, switching time, active area, , total size, housing can directly be asked by sending us an email at info@arcoptix.com.

DOWNLOAD detailed description of the variable attenuator