Liquid Crystal Device Technology Based On Nematic Phase And Blue Phase

Liquid crystal(LC)is a kind of material with optical anisotropy and dielectric anisotropy.The working principle of most LC photonic devices is based on the reorientation of LC director induced by electric field,which causes the change of refractive index to modulate the amplitude or phase of incident light.At present,LC has been widely used in the fields of display,lens and light deflection.In the aspect of liquid crystal display(LCD),reflective liquid crystal display(RLCD)directly relies on ambient light to display images without built-in backlight.It will not be eroded by ambient light.Because of its good readability indoors and outdoors and low power consumption,transflective liquid crystal display(TRLCD)can be used in portable computers and mobile phones.In the aspect of LC lens,it has the focal length of incident light with the advantages of controllable voltage,compact structure,simple fabrication,good stability and low power consumption.It has attracted much attention in the fields of mobile camera,webcam,micro projector,glasses and two/three dimensional(2D/3D)switchable display.Although LC devices have many advantages,they also face some problems which need to be further solved by researchers.For the traditional transflective nematic liquid crystal display(TR-NLCD),it has high transmission efficiency,but the reflection efficiency of its reflection area(R area)is very low,which leads to the low utilization of external environment light when used outdoors.For the traditional transparent and reflective blue liquid crystal display(TR-BPLCD),its driving voltage is too high to be driven by thin film transistor(TFT),and the peak voltage of transmission area(T area)and reflection area(R area)can not match well.The traditional LC lens has a wide range of adjustable focal length,but its wide application is limited by its slow response speed and unstable response time caused by the uneven thickness of LC layer.Based on nematic liquid crystal(NLC)materials with low viscosity and large birefringence and polymer stabilized blue liquid crystal materials(BPLC)with large Kerr coefficient,four kinds of display devices are proposed,including a reflective blue liquid crystal display(R-BPLCD),two kinds of TR-BPLCD,one kind of TR-NLCD,two kinds of NLC lens and one kind of BPLC lens.Based on the BPLC lens,an BPLC light deflection device is proposed.The main research contents are as follows.(1)An R-BPLCD based on triangular dielectric layer is proposed.The upper glass substrate of the display has a complete planar indium tin oxide(ITO)electrode,and the inner surface of the lower glass substrate is coated with a diffuse reflection film to realize reflection.At the same time,it acts as a pixel electrode.The inner surface of the ITO glass substrate is etched with a triangular prism dielectric layer with high dielectric coefficient.The triangular prism dielectric layer acts as a conductive plate,which helps to obtain a structure similar to the corrugated electrode.The proposed R-BPLCD has a fairly strong and uniform horizontal electric field component in the LC layer,which helps to achieve a lower driving voltage.(2)A TR-BPLCD based on parallel wall electrodes is proposed.In order to make the phase retardation between the T area and the R area the same,we set the polymer wall in the T area to twice that of the reflection region,that is,the thickness of the LC layer in the T area is twice that of the R area.When the proposed TR-BPLCD works,the same voltage is applied to the wall pixel electrodes of the T area and the R area,and the same and uniform transverse electric field is generated between the wall electrodes of the two areas.The diffuse reflection film in the R area allows the ambient light to go back and forth twice.This setting can make the optical path difference of the TR-BPLCD in the two areas equal,and realize the driving of the same TFT.The voltage-dependent transmittance(VT)and voltage-dependent transmittance reflectance(VR)curves of the TR-BPLCD are well matched.Moreover,it has high transmittance in the T area and high reflectivity in the R area.(3)A TR-BPLCD with non-uniform dielectric bumps is proposed.The dielectric protrusion layer is plated on the in-plane conversion electrode,and the dielectric constant of the dielectric protrusion layer is higher than that of the BPLC material.When the voltage is applied to the TR-BPLCD,the potential drops very slowly in the dielectric protrusion layer.The thick dielectric protrusion layer increases the penetration depth of the electric field in the BPLC layer,which is conducive to reducing the working voltage of the TR-BPLCD.At the same time,it also suppresses the electrostrictive effect of the BPLC.The height of the dielectric bumps in the T area is higher than that in the R area,so that the same optical phase delay can be obtained in the T area and the R area.Compared with the traditional in-plane conversion electrode structure,the proposed TR-BPLCD has higher transmittance in the T area,higher reflectivity in the R area and lower operating voltage.(4)A TR-NLCD based on planar square electrode is proposed.The NLC layer of the proposed TR-NLCD adopts the vertical alignment(VA)mode.In order to realize the reflection,a diffuse reflection film is plated on the bottom of the lower glass substrate and staggered with the plane square electrode.When the proposed TR-NLCD works,a strong longitudinal electric field will be obtained in the T area with a square planar electrode,and a weak edge electric field will be obtained in the region with a diffuse reflection film.Therefore,the phase delay of light passing through the T area and the R area in the LC layer can be matched.The proposed TR-NLCD has the advantages of thin cell thickness,fast response speed and simple fabrication process.Moreover,the proposed TR-NLCD can achieve the same low peak voltage of the T region and the R region contribute to the realization of driving with a TFT.(5)A NLC lens array with a central common electrode over a low dielectric layer is proposed.The lower glass substrate of the lens array is plated with transparent strip ITO electrodes,and a low dielectric layer is plated between the strip ITO electrodes.In order to obtain gradient refractive index distribution,the ITO electrode is plated in the center of the upper surface of the low dielectric layer as the central common electrode,and the lower glass substrate is smoothed with high dielectric material.The LC thickness of the proposed NLC lens array is only 15μm,which means that the spherical aberration of the lens can be neglected and the response speed is faster.The focal length of the proposed NLC lens array can be continuously tuned to 0.988 mm with the increase of the applied electric field,and the ideal phase profile of the NLC lens array can be obtained in a large tuning range.(6)An electrically focused NLC lens array based on discontinuous common electrode is proposed.The lower glass substrate of the NLC lens has strip-shaped ITO electrodes as pixel electrodes,and the upper glass substrate has periodically arranged ITO electrodes as common electrodes.A single NLC lens is arranged between two strip ITO electrodes of the lower glass substrate.The center of each NLC lens corresponds to a gap of ITO electrode on the glass substrate.When the voltage is applied to the pixel electrode,an axisymmetric gradient refractive index distribution will be generated in the LC layer,resulting in the focusing effect.The LC layer thickness of the NLC lens is only 30μm,so the dynamic response time is fast.(7)A polarization independent BPLC lens array based on piezoresistive layer is proposed.The BPLC lens uses a low dielectric layer as a resistance film to share the voltage of the central electrode,and uses a high dielectric layer to smooth the phase distribution of the lens.When the same voltage is applied to the strip ITO electrode of the lower glass substrate,the longitudinal electric field generated in the BPLC layer changes gradiently from the edge of a single lens to the center of the lens,and the parabolic refractive index distribution is obtained according to the Kerr effect.The BPLC lens is a layer by layer device,so its fabrication process is simple.The simulation results show that the proposed BPLC lens array is polarization insensitive and has parabolic phase distribution in a large tuning range.(8)A BPLC light deflector based on polymer micro prism array is proposed.In order to realize the polarization independent properties of the BPLC light deflector,we will use the same dielectric coefficient of the BPLC material and polymer material to make the polymer micro prism array.The refractive index of the BPLC material is the same as that of the polymer material,so the direction of the incident light perpendicular to the surface of the BPLC light deflector does not change when no voltage is applied.After the voltage is applied,the refractive index of the BPLC material changes and the direction of the incident light deflects.