Research On Liquid Crystal Phase Modulator Based On Deep Sub-wave Length Grating Structure

The holographic video display is considered to be one of the most promising 3Ddisplay because of its ability to display realistic 3D objects.The core device of the holographic video display is represented by the LCoS Spatial light modulator.The challenge for Spatial light modulator based dynamic holographic video display is the need for large space bandwidth product.A straightforward way is to reduce the size of a single pixels in a conventional LCoS device.At present,mainstream manufacturers has reduced the size of LCoS to 3.74pm.It requires the corresponding reduction of LCD cell thickness with the reduction of Pixel size,otherwise the edge field effect between pixels will affect phase modulation.Therefore,it is possible to continue to reduce the cell thickness,for example to less than microns(also known as micro-phase modulator).Another way is to further increase the birefringence of the liquid crystal to achieve 2? modulation,which in turn poses a challenge to liquid crystal materials.At the moment,it seems that there are still great difficulties to its realization.Due to the highly localized and sub-wavelength characteristics of surface plasmas,metal nanostructures can be used to manipulate and regulate the optical field effectively.Therefore,a novel phase modulation device model is studied by combining metal nanostructures that utilizing FP resonance excited by interface SPP between metals and changing the dielectric environment of the structure by the electronic controlled tunability of LC.The thesis mainly includes the following research contents and results:(1)In this thesis,the top electrode of LCoS is replaced by the deep sub-wavelength metal grating of F-P resonance to form a metal-insulator-metal structure.The phase of reflected light is modulated by the interaction of surface plasma and F-P in grating slit.Although the structure of the Liquid Crystal Cell looks similar to the traditional LCoS,the working physics of the two are completely different.In the device model,the Liquid Crystal Birefringence is used to modulate the reflective boundary of the deep subwavelength metal grating,which is different from the traditional LCoS that uses the Birefringence of the liquid crystal in the Liquid Crystal Cell to get the phase modulation.In turn,the phase of reflected light in the slit is affected.(2)This thesis builds a simulation experiment platform based on CST Microwave Studio and TechWiz software.The effects of the Pixel pitch and grating structure parameters on the phase modulation and the intensity of reflected light are studied.The reflection intensity and phase modulation ability of visible light are investigated by changing the Pixel pitch and grating parameters in the visible light range and the dynamic range of dielectric constant of liquid crystal material.The results show that the phase modulation between 260nm and 340nm is close and the reflectivity is high.By changing the height and width of the grating,close modulation and strong reflection intensity can also be achieved.It is concluded that the distribution of liquid crystal director and electric field does not change obviously in the range of different pixel pitch by studying the distribution of liquid crystal director and electric field.indicating the performance is robust.(3)In the fabrication process of phase modulation devices,because the parameters of the device model are quite different from those of traditional devices,the key factors such as uniformity and cell thickness are studied.Through the repeated experiments on the process flow and parameters of device fabrication,the traditional experimental cleaning and sealing steps are further studied to perfect the technology of preparing small-size and low-cell-thickness phase modulation devices under laboratory conditions.Software-controlled chip-level packaging equipment is introduced to improve the technology of making small-size,thin-box-thick phase modulation devices under laboratory conditions.Finally,the parameters of the liquid crystal cell such as the thickness of the liquid crystal cell and the grating structure are tested.