Two Novel LCOS Structures For Holographic Video Display

Holographic video display is a true three-dimensional display technology, it is considered to be the future alternative for high-definition television. The core device of holographic video technology is the spatial light modulator (SLM), it is different from the current liquid crystal display and it requires the capability of modulation on 2π phase at least. SLM is now widely studied by mainly acoustic optical modulator (AOM), digital micro mirror device (DMD) and liquid crystal on silicon (LCOS). LCOS integrates the advantage of modern flat panel display technology and complementary metal oxide semiconductor (CMOS) technology, it is considered to be an alternative device of the holographic display technology in the future. However, although CMOS technology has reached the scale of sub-micron, the smallest pixel size of the LCOS for holographic display which can be bought on the market is 6.4μm. The reason for this problem is, the current LCOS structure use the different optical paths of liquid crystal (LC) to achieve the purpose of the phase modulation, the thickness of liquid crystal can not be reduced while the pixel size is reduced. Unfortunately, according to diffraction theory, the LCOS provides a small view angle, it can not meet the needs of a wide field for holographic display. According to theoretical calculations, LCOS feature sizes should be fairly light wavelength scale. Currently, studies show that if the LCOS pixel sizes directly reduce to the theory size requirements will lead the ratio of pixel dimensions with liquid crystal layer thickness to be too small. This makes the electric field between the adjacent pixels in LCOS mutual interference that could cause fringe field; it decline the phase modulation and diffraction efficiency of LCOS.In order to break the limitations of existing structure, we explore the use of surface plasmon (SP) technology. SP (otherwise known as surface plasmon polaritons (SPP)) is a charge density wave which propagates on metal-dielectric interface that is caused by the interaction of free electrons on metal surface and photons, it is a new light control technology with advantages of near-field enhancement and tunable, etc. The physical properties of SP can be described by the Maxwell equations and can also be calculated by the method of numerical simulation. SP has the characteristics that conventional dielectric can not be achieved.This paper presents two novel LCOS structures based on SP technology, expect to solve the fringe field effect and low diffraction efficiency problem in current LCOS, attempting to break the current problems in LCOS. This paper mainly includes some researches in the following areas.1) Analyzing the problems of that LCOS devices currently used for holographic video display, pointing out the current LCOS which be used for holographic display can not meet the needs of wide view angle.2) Aiming at the problem of fringe field effect in LCOS devices, this paper proposed a LCOS structure model based on surface plasmon resonance (SPR). The SP is sensitive to surrounding mediums, we modulate the refractive index of LC to achieve the modulation of the light based on the traditional structure of Kretschmann model. Numerical analysis results show that the LCOS structure based on SPR can reduce the LC layer thickness to reduce the influence of fringe field effect.3)Because the SP has the ability to break the diffraction limiting, this paper study the dispersion characteristics of metal-dielectric-metal (MDM), which can be viewed as gap surface plasmon (GSP). This study puts forward to introducing metasurface into LCOS cell structure to increase the diffraction efficiency of LCOS. We use TechWiz LCD to calculate the LC molecules director distribution and use FDTD Solutions to analyze the optical properties. The results show, when the type and thickness of the dielectric metal used is determined, the GSP composed of different metal widths with unusual light scattering can effectively realize the phase control. Using the sub-wavelength scale structures to adjust the light field can effectively improve the diffraction efficiency of hologram reconstruction.