Fabrication and application of geometric phase optical devices using pixelated nanograting array

Abstract

Next-generation optical technologies, such as AR/VR glasses and digital 3D signage, are now considered essential components in various fields. To implement these optical technologies, miniaturization and high-efficiency optical devices are required. However, traditional refractive and diffractive optical devices face technical challenges due to their physical limitations. Consequently, a new type of optical device is needed to satisfy these conditions. Extensive research is being conducted on geometric phase (GP) based devices as next-generation optical devices that meet these criteria. Conventional optical devices control the phase through the optical path difference. However, the geometric phase optical device (GPOD) is a novel type of optical device that utilizes the GP, which is the phase generated depending on the polarization state of light and the orientation of anisotropic materials. By locally controlling the orientation of anisotropic materials to form a desired phase distribution, there is no scattering due to discontinuities in the surface height, resulting in minimal noise and energy loss. Moreover, being only a few micrometers thick, GPODs offer advantages in the integration of optical systems. In this study, various types of GPODs were fabricated using a pixelated nano-grating (PNG) array with arbitrary angles and periods as a rubbing substrate for orienting reactive mesogen (RM) in arbitrary directions. We integrated GPOD with existing optical components, leading to the application of innovative multi-focal lenses and intraocular lenses (IOL). Additionally, a multi-direction screen was designed using another application of the PNG array. Through the control of localized light directions, the formation of images from multiple viewpoints was achieved. In Chapter 1, a brief overview of GPOD and the primary focus of this study is provided. In Chapter 2, the principles and key components of the photolithography system used for fabricating the PNG array are elucidated. Utilizing this system, the PNG arrays pertinent to the study were produced. In Chapter 3, the grating equation for an arbitrary obliquely incident beam interacting with a nonparaxial diffraction grating model will be discussed. Based on this, passive and active types of multi-direction screens were implemented that locally control the direction of light to generate multi-perspective images. In Chapter 4, the fabrication of various GPODs is explored by leveraging the PNG array as a rubbing substrate for aligning the RM. Subsequently, these are integrated with refractive optical components to derive novel optical devices. In Chapter 5, utilizing the GP, a new form of Multi-focal intraocular lens (MF IOL) has been developed, and its performance was evaluated using standardized IOL measurement techniques. Moreover, not only a single GP layer but also multiple GP layers were utilized to implement a range of IOL designs. In conclusion, this study introduces the photolithography system capable of fabricating the PNG array and presents GPODs and multi-direction screens based on this PNG array. Despite their slim profile and lightweight nature, these optical devices exhibit high efficiency. Their suitability for mass and large-area production via the nanoimprint process suggests promising applications in various industrial sectors.