The Study Of OCB Liquid Crystal Grating’s Optical Characteristic

Nematic liquid crystal have birefringence characteristics and dielectric constant anisotropy,it can be control by low electricity field.And the LC grating made of nematic liquid crystal have the characteristics of light weight,small size,low power consumption,long life,low cost and low driving voltage.They have great potential for application in Flat Panel Display,space optical communication and sensors. At present,the application of liquid crystal grating has one defect that is the slow response speed,in addition,it is conform to practical application on the beam scanning,deflection,control and so an.This thesis designs a OCB liquid crystal grating structure,the grating is composed of two pieces of ITO glass substrate,the interdigital electrode is shaped on one substrate by photoetching,and another substrate is continuous electrode.By applying voltage to two substrate,the LC molecules arranged periodically.The incident light have phase difference after through the LC layer,it have diffraction phenomenon.This form a LC grating. OCB(optical compensation bending)mode is that the LC molecules is in bending state under the initial bias voltage,when it is applied with the driving voltage can be quickly changed from bending to vertical state,and that the OCB mode can restrain the backflow effect when LC molecules tuning, it significantly reduce the response time compared with from the parallel state to vertical state.The thesis research different condition to control pretilt angle with parallel orientation PI and vertical orientation PI and produce OCB liquid crystal grating and parallel liquid crystal grating samples with low degree of 5°～6 °,studied the coefficient of viscosity,thickness of cell and bias voltage.Studied the OCB LC grating and parallel LC grating under different conditions found that when choose low coefficient of viscosity liquid material can let the response time shorter,and the higher the initial bias voltage was,the faster the response speed,the thinner the thickness was,the shorter the response time.Under the same conditions,the response time of OCB liquid crystal grating significantly higher than the parallel one,is only a third of parallel grating response time.Measured the 0,1 and 2 order diffraction efficiency of OCB liquid crystal grating and parallel grating in different thickness of cell.With the increase of voltage 0 order diffraction efficiency drops,1 order and 2 order diffraction efficiency are rising then fell slightly.The diffraction efficiency of OCB mode in 1 order and 2 order are higher than parallel mode,the 1 order of 12 u m sample can reach 33%.With the decrease of the thickness of cell,the response time speed and the diffraction efficiency drops,it remains to be further optimized in order to get quick response samples of high diffraction efficiency.