Research On Video-rate Holographic Displays Based On Doped Liquid Crystal

Three-dimensional?3D?display technology has attracted worldwide attention and been developed vigorously.Usually,3D displays are classified into two types according to principles of stereopsis.One type is based on binocular parallax with glasses/helmet stereoscopic displays or with parallax barriers or lens array.With the development of liquid crystal display,these techniques are relatively mature and have become commercial productions.The other type,including holographic display,integral imaging display and volumetric display,is based on 3D scene reconstruction.Compared to stereoscopic display of3D images,these techniques are true 3D displays that provide more depth perceptions.So,the discomfort and fatigue can be avoided effectively.These techniques are currently under active research and lack in commercial productions.Among these 3D display techniques,holographic display is considered as anultimate goal to provide realistic image of a real object or a scene,because it has the ability to reconstruct both the intensity and wave front information of a true nature of an object or a scene,allowing the observer to perceive the light as it would be scattered by the real object itself without the need for a special eyewear.Therefore,many research groupshave begun to study the holographic displays of real3D images.Large-size and static holographic displays,including full-parallax holographic stereograms created using special holographic recording materials,and very small-sized and dynamic holographic displays based on current commercially available spatial light modulators,have been realized by some companies and scientific research institutes.However,limited to the computational processing power capacities and VLSI technology,DH is difficult to realize the video-rate image reconstruction.In fact,the real-time holographic display is an important and challenging problem to solve and a variety of technologies have addressed this challenge.Optical purely reconstruction based on the dynamic recording materials might be an effective way for the video-rate holographic display without post data processing.My thesis focuses on the studies of the key problem of“How to realize dynamic holographic display”and investigate the photorefractive materials for the dynamic holographic display,which are discussed as follows:1.Video-rate holographic display using azo-dye-doped liquid crystalA a real-time holographic video at a refresh rate of 25 Hz is reconstructed by an azo dye?DR1?doped nematic LC cell without any applied electric field.The performance of the proposed device is underlined by the response time,including both recording and erasing time.Its dependence on the recording intensity,polarization direction,and polarization state has been experimentally revealed.By adjusting the above parameters,response time can be measured up to 1.3 ms,sufficiently fast for the video-rate display applications.By angular multiplexing technique,dynamically multiplexed holographic videos are realized.Moreover,the reconstructed RGB images are merged into a color image,which illustrates the possibility of a color holographic three-dimensional display by holographic multiplexing of the LC cell.We have experimentally investigated the dependence of the properties of the holographic gratings on the ambient temperature in the DR1 doped LCs.The results indicate that the diffraction efficiency of the DR1-doped LC is seriously affected by the temperature while the response time is relatively stable.2.High-efficiency Video-rate Holographic Display Using Quantum Dot Doped Liquid Crystal.We have achieved a real-time holographic video display of R,G,B with a refresh rate of60 Hz in the ZnS/InP QD-doped LC.Compared with DR1 doped LCs,the maximum diffraction efficiency is measured up to 30%and the doping of QDs endows the LC with much better photorefractive characteristics.The build-up time of the grating is of the order of several to tens of milliseconds,fast enough for the video-rate display applications.The temperature and recording laser power dependence of the photorefractivity is also investigated.The results show that the optical Freedericksz transition decreases as the laser power increases.And the response time is dependent on the temperature,the fastest one is up to 3.4 ms.3.High photosensitivity Video-rate Holographic Display in ZnS/InP Doped Liquid Crystal with ZnSe film.In this chapter,we perform detailed investigation on a real-time holographic display with ZnSe layer assisting ZnS/InP-doped LC.The combination of these methods is more effective to increase the photorefractive sensitivity than single method.The diffraction efficiency of 12%and response time of 4 ms are obtained at intensities as low as 0.8 mW/cm².The nonlinear index coefficient n₂ is as high as 2.1 cm²/W.The photosensitivity S of the hybrid device is measured up to 2.2 cm³/J,which is improved by a factor of 150.The dependences of the diffraction efficiency and response time on recording light power in the LC and externally applied voltage are studied by experimental means.This work indicates that QD-doped LC could be a promising candidate towards future video-rate dynamic 3D holographic display.