Research On LCoS-like Phase Modulation Device Model Based On Sub-wavelength Grating Structure

Holographic video display technology based on diffraction reconstruction can generate realistic 3D scenes,which is considered as one of the most promising 3D display technologies.Its core component is spatial light modulator(SLM).At present,the widely used liquid crystal on silicon(LCoS)is still far from the huge spatial bandwidth product required to achieve diffraction reconstruction,especially the pixel size(mainstream manufacturers have already achieved a minimum of 3.74 ?m).If continue to use the optical delay physical mechanism of LCoS to further reduce the the pixel unit size of structure directly,the edge field effect enhancement?phase modulation may not reach 2? and process limitations and many other problems will be encountered.In recent years,due to the advantages of unique slot waveguide mode resonance ? the ability to manipulate light effectively ? flexible design and easy manufacturing,the sub-wavelength metal grating structure with surface plasmon(SPP)effect has provided the possibility of realizing micro-nano optical devices.However,the current application development are most concentrated in the passive components,the study of active device is still in the stage of simulation.In order to develop the requirements of active SLM for holographic video display,this thesis grafts the sub-wavelength metal grating structure with the traditional LCoS liquid crystal unit structure and discusses a LCoS-like phase modulation device model(called G-LCoS)for realizing the high active space bandwidth product of SLM,the simulation results show that this device can achieve active 0-2? phase modulation.This thesis conducts research from theoretical simulations and practical experiments,hoping to provide a new solution for the technical problems faced by holographic video displays.The main research works of this thesis are summarized as follows:(1)The model of G-LCoS device based on sub-wavelength grating structure is studied.In response to the requirements of ultra-thin active phase modulator,the structure of subwavelength metal grating is grafted with the traditional liquid crystal unit structure of LCoS to replace the LCoS top electrode,active liquid crystal as a medium between layers of adjustable electric materials.Using the synergistic effect of SPP and Fabry-Perot(F-P)resonance in the sub-wavelength grating slit to modulate the phase modulation to study a different from traditional LCoS modulation mechanism of novel sub-wavelength grating device structure.(2)A simulation platform is built based on TechWiz?CST and FDTD Solutions.The effects of different pixel pitch and liquid crystal layer thicknesses on the basic phase modulation performance of the device and fringe field effects were studied.The simulation results show that the pixel pitch and the thickness of the liquid crystal layer affect the fringe field effect of the structure.At the same time,the phase modulation result is close to 2? when the pixel pitch is 300 nm and the thickness of the intermediate medium layer is 600 nm in a 1um pixel unit.(3)Based on the interference principle,the phase modulation of G-LCoS is tested.The GLCoS device structure are made by reference of the traditional LCoS process.Due to the particularity of the sub-wavelength grating structure,the cleaning?packaging and filling processes of G-LCoS were analyzed.By analyzing various phase test methods,we design and build a new optical path test system experimental platform in this thesis.The external voltage is applied to complete the phase modulation measurement of the G-LCoS device,and maximum phase value of the modulation amount is 1.2?.Compared with the traditional LCoS,the experimental results show that the device can achieve 70.58% of the commercial device phase modulation capacity.