Preparation Of Electro-controlled Polymer Dispersed Liquid Crystal Based On Dual Interdigitated Electrodes And Its Application In Speckle Suppression

In comparison with conventional light source,lasers are promising light sources which have obvious advantages such as high brightness,wide color gamut,long lifetime.However,lasers have high coherence owing to its narrow linewidth of emission spectrum.When a laser illuminates a rough surface of an object,a granular pattern with uniform bright and dark distribution is generated and the granule is named “speckle”.The existence of speckles severely degrades quality of projection image,which is a critical issue must be solved in the field of laser displays.The common dynamic speckle reduction methods involve vibrating or rotating diffusers,using micro-scanning mirror,vibrating screens,etc.Dynamic speckle reduction is achieved by time-averaging uncorrelated speckle patterns during the integration time of a detector or human eyes.In general,the dynamic speckle reduction methods introduce devices such as mechanical motor and voice coil motor,which increases the optical expansion.Because of the mechanical vibration of the above devices,the lifetime and stability of the projection system are greatly reduced.Therefore,static speckle reduction devices have more application prospects.Liquid crystal is a promising filling material for static speckle reduction devices owing to its superior photoelectric properties.In this paper,according to the dynamic speckle reduction methods,we design and fabricate a static diffuser based on the polymer dispersed liquid crystal(PDLC)switched by dual interdigitated electrodes and successfully achieve speckle suppression.The diffuser is named as electroactive despeckle diffuser(EADSD).When the EADSD is working,a diverse electric field can be generated and reorient the LC directors.Speckle contrast can be reduced because uncorrelated speckle patterns are yielded and time-averaged in the integration time.The EADSD does not require mechanical motor,which can significantly reduce the optical expansion of the projection system and enhance the stability of projection system.The main content of this article includes the following two aspects:1.Design and fabrication of EADSD based on PDLC.By considering the limitation of electric field in a conventional PDLC cell and the mechanism of dynamic speckle reduction,we design and fabricate EADSD with dual interdigitated electrodes whose directions are orthogonal.The EADSD can generate a more diverse electric field because of the special electrodes,which is conductive to speckle reduction.2.Experiment of speckle reduction using the EADSD based on PDLC.We set up a speckle measurement system.By studying the effects of speckle reduction efficiency of EADSD on different exposure powers and driving conditions,we finally obtain the optimized speckle reduction condition,where speckle contrast reduces from 0.71 initially to 0.32 and speckle suppression efficiency is up to 55%.