Electroactive despeckle diffuser using polymer dispersed liquid crystal in-plane switched by interdigitated electrodes

Abstract

An electroactive despeckle diffuser (EADSD) is demonstrated using a polymer dispersed liquid crystal (PDLC) in-plane switched by two pairs of interdigitated electrodes whose directions are orthogonal. The mechanism underlying speckle suppression involves the time average of different speckle patterns during the exposure time of a detector, wherein the reorientation of LC molecules results in different speckle patterns. The introduction of interdigitated electrodes increases the diversity of the electric field in comparison with a conventional PDLC cell switched by a longitudinal electric field. Experimental results show that this device can reduce speckles more effectively owing to the more diverse electric field. The speckle reduction efficiency is approximately 55% when we drive the EADSD sample fabricated by 60 wt% E7: 40 wt% NOA65 under an exposure power of 6 mW/cm2 by bipolar triangle waveforms applied to the two pairs of interdigitated electrodes with frequencies of 20 Hz and peak voltage values of 150 V, and when the phase delay of the waveforms is 90° or 270°. The EADSD is static and does not require motors to achieve vibration, which make it a superior device for speckle reduction in laser displays.