Products :

Liquid crystal switchable gratings

The unique ARCoptix’s liquid crystal switchable grating permits to deflect a beam within tens of milliseconds. The binary grating can be switched on and off electrically. Theremore the grating can be adapted to any wavelength between 400nm and 2000nm by simply adjusting the applied bias.

Upper image shows the none deviated beam when the LC grating is switched of and the lower image shows the beam deviated in the 1 and -1 diffraction order

• Simple
• Non mechanical parts
• Robust
• Inexpensive
• Wavelength adjustable
• Electrically addressable
• Low absorption

By applying a bias of about 2V rms (depending of the wavelength) with about 1KHz frequency the grating can be switched on and the central beam (upper image) is deviated equally in the 1 and -1 diffraction order (lower image). The deviation angle of the beam (below 4°) is imposed by the pitch of the grating. When switching of the the grating the beam returns in center within tens of milliseconds.

The binary grating is ideal for application where active beam steering with modest deviation angles are requested. 

Housing Liquid crystal cell

In stock elements

Model Aperture Deviation angle Bias OFF/ON Binary grating 40 15 mm 1° 0V/2.1V Binary grating 80 15 mm 0.5° 0V/2.1V

Principle

The binary switchable grating is composed of a nematic liquid crystal layer sandwiched between to glass substrates with a ITO transparent structured electrode on their surface. According to the schematic representation below, the electrode of the lower substrate cover the entire aperture and the electrode of the upper surface has a grating pattern. By applying a bias on the grating electrode, an electrical field is created inside the LC layer and the LC molecules are inclined with a certain tilt angle. This tilt angle modifies the apparent extraordinary index of the LC layer and a binary (slightly smoothed) phase modulation is created over the whole aperture of the device.

By applying a bias on the electrode the LC molecules are inclined and a binary phase modulation diffracted the incoming light

If the device is illuminated with coherent light with a linear polarization parallel to the optical axis (in order to experience the extraordinary index) the light is deviated into the 1 and -1 diffraction order with a theoretical diffraction efficiency of 40%. Practically a diffraction efficiency of about 35% is obtained. When the grating is switched off the alignment of the LC molecules is uniform and there is no phase modulation. Then the light passes trough the device without being deviated.

By using more complex electrode patterns gratings with 3 or 4 levels can be produced. Such gratings present higher diffraction efficiencies of respectively 65% and 90%.

Specs

Wavelength range 400-1800 nm Active area 15 mm x 15 mm Diffraction efficiency (1st order/zero order) > 35% Transmission > 85% Retarder material Nematic Liquid-Crystal Substrates Glass Wavefront distortion < l/4 Temperature range 10°-35° Total size (with housing) 4 cm x 6 cm x 1 cm

Custom gratings

By adapting the electrode design, custom gratings with higher diffraction efficiency (up to 90%) or specific deviation angles (maximal 4°) can be designed for specific wavelength. Production prices of this device decrease drastically when higher volumes are ordered.

Please contact a ARCtix engineer for more information: info@arcoptix.com