PROJECTION OF HOLOGRAMS FROM PHOTOREFRACTIVE OASLMs

Abstract

Liquid crystals doped with fullerenes and carbon nanotubes (CNTs) act as good optical nonlinear materials. We have used these materials to build optically addressed spatial light modulators (OASLMs). The devices comprise of single layer of doped liquid crystal acting as an active layer. Undoped LC devices with surfaces coated with fullerenes are also studied.Such OASLMs allow recording of phase holograms, and we record by imaging pre-calculated pre-recorded holograms. Writing is performed at normal incidence and reading at 45 o oblique incidence. Both, transmission and reflection modes of operation are used. Experimental results as well as comparison with commercially available OASLMs are presented.Keywords: optically addressed spatial light modulator (OASLM), holography, fullerene, carbon nanotube, liquid crystal, optical nonlinear materials, photorefractivity. IntroductionSpatial light modulators (SLMs) are devices that can record two-dimensional images and erase the previously recorded image. They are increasingly used in many applications including video and display applications 1 and real-time holography 2 . Electrically addressed SLMs are * or213@cam.ac.uk; phone +44 1223 748347; fax +44 1223 748348; http://www-g.eng.cam.ac.uk/photonics 2 expensive, and due to limitations on the driving circuitry the number of addressable pixels is limited. To simplify the system, one can address SLMs directly by light.Optically addressed spatial light modulators (OASLMs) are already commercially available (Hamamatsu † ). These devices are based on adjacent amorphous silicon and Liquid Crystal (LC) layers. They are relatively simple, but still hard to manufacture and can be used only in reflection at visible wavelengths. Dye-doped LC systems are highly promising materials for novel OASLMs based on photorefractive orientational effects. 3-9 Such devices are intrinsically photorefractive without the need of special layers or circuitry, therefore there are no strict technological limitations on the device area. They can be used in transmission as well as reflection, and measurements show that the resolution of 1-layer dye-doped-LC device can be better than that of the 2-layer amorphous silicon OASLM. 10 Target characteristics for photorefractive OASLMs are 2 phase modulation and fast switching (e.g. at least 20 ms for video applications). The devices are also expected to have low power consumption, low cost, high resolution (~ 10m) and good lifetime.Nematic liquid crystals doped with fullerenes 6,11,12 and carbon nanotubes 13,14 are recognised for their extraordinary large optical nonlinearities with nonlinear refractive index coefficient n 2 up to 20 cm 2 /W 11,12 . It is believed that the nonlinearities are due to the reorientation of the nematic director which occurs due to light-induced space-charge field formation aided by the dopant 6 .In this work we report performance of transmissive and reflective photorefractive OASLMs based on a single layer of fullerene or carbon nanotube doped nematic liquid crystals. Undoped L...

Characterization of carbon nanotube–thermotropic nematic liquid crystal composites

“…We tested 20μm and 100μm aligned films of CNT doped LCs and also CNT residue on filters 5 . However no CNT specific Raman signal could be detected in our equilibrated LC-CNT dispersions at concentrations of 10 -9 -10 -8 wt.…”

“…CNTs dispersed in thermotropic nematic LCs may form well-aligned systems [2,3]. Moreover, even small concentrations of CNTs in LC have been shown to lead to large nonlinear optical effects [4][5][6]. Enhancement of electro-optical as well as electrical and dielectric properties of the LC material has also been reported [7][8][9].…”

Tunable retarder made of pentaprisms and liquid crystal

“…Spatial solitons have also been created in a well-designed LC cell [95][96][97][98]. It has been found recently that carbon-nanotube doping enhances the photorefractive effect [19,99,100] or facilitates the electrically induced LC orientation [101][102][103].…”