Research On Phase Modulation Model Of Multi-wavelength Metal Grating Structure

The core device of holographic video display is the spatial light modulator(SLM).The existing SLM designs are based on classic optical principles,which cannot meet the large spatial bandwidth product and large field of view required for holographic video display.Therefore,we need to use the latest development of plasmonics and micro-nano technology to solve the core problems faced by holographic video display.However,most of the current micro-nano light field control devices are passive,which is very challenging for the research and technology development of active micro-nano SLM devices.Different from the existing Liquid Crystal on Silicon(LCoS)SLM that uses the principle of optical path difference,our group has produced a proof-of-principle device:sub-wavelength metal grating Liquid Crystal on Silicon(G-LCoS).The upper electrode of G-LCoS is a resonance structure of Surface Plasmon Polaritons(SPP)and Fabry-Pérot(F-P),which induces a phase modulation of zero-order reflection.The box forms an SLM to achieve active 0?2p dynamic phase modulation.Because the device involves a complex parameter space,based on the previous single-wavelength theoretical model,the multi-wavelength characteristics of the incident angle and the refractive index of the liquid crystal in the liquid crystal cell are mainly studied without changing the geometry of the model.The main contents of this thesis are as follows:(1)The dispersion characteristics of surface plasmons of gold and aluminum materials and the influence of their incident angle changes on G-LCo S are studied.A numerical simulation platform is established based on commercial software such as CST Studio Suite and Matlab to discuss the phase modulation characteristics of the metal grating structure and the reflected intensity of incident light by the refractive index of the liquid crystal layer and the angle of incident light.The experimental results show that when the incident light wavelength is in the range of 589.10 nm to 596.13nm(frequency 502.9THz to 508.9THz),increasing the refractive index of the intermediate dielectric layer can increase the reflection phase modulation of the sub-wavelength metal grating structure model to close and have higher reflection intensity.When the incident angle is incident on the sub-wavelength metal grating structure at a small angle,within the range of the incident light wavelength from645.41 nm to 653.85nm(frequency 458 THz to 464THz),as the angle increases,the amount of phase modulation decreases.When testing the device in this wavelength range,try to make the incident light enter the upper glass substrate of the device perpendicularly to ensure that the phase modulation of the reflected light is close to 2p.(2)The multi-wavelength phase modulation characteristic test work for G-LCo S devices,including the preparation process of the sub-wavelength metal grating structure G-LCo S device and the establishment of a test experimental system.Firstly,the process of orientation anchoring of the liquid crystal,alignment and sealing of the upper and lower substrates,cell thickness detection and liquid crystal filling are analyzed and improved.Secondly,it analyzes the phase test method of G-LCo S,and uses the improved Michelson interference method to build an optical path test experimental platform to measure the multi-wavelength phase modulation characteristics of the G-LCo S structure device.In the experiment,RGB three-color lasers were used to test and analyze the phase modulation performance of G-LCo S.The preliminary experimental results show that the prepared G-LCo S device has a phase modulation amount of 1.1p,1.66p and 1.28p for three different wavelengths,respectively,which can reach the expected 55%,83% and 64% phase modulation capabilities.It laid the foundation for the following device preparation and experimental testing.