Holographic photopolymer structures and applications
MetadataShow full item record
Nanoscale optical technology is a breathtaking field. The interest in using nanostructure stems in different fields like mechanical, electrical, biochemical and optical is because of their potential superior properties. Our goal is to find new techniques to design and fabricate novel micro and nano structures that are cost efficient and easy to fabricate. Particularly, this thesis concentrates on the design, fabrication and characterization of holographic writing of reflection gratings for different purposes and applications. The development of periodic nanostructured materials with precise optical assets can extensively impact the growth of optical based sensors. Furthermore, the fabrication of these structures in low-cost polymer systems can decrease the price of these methods which are associated with spectral analysis and color filtering. For instance, reflective Bragg filters can be generated by fabricating a multilayered polymer based structure with a modulated refractive index profile. One technique to generate this kind of periodic structure is the holographic lithography method. During past decades, there has been major study through laser based holography technique to control the size and location of nanoscale droplets of liquid crystals in a polymer based structure . The development of holographic gratings from polymer dispersed liquid crystals (H-PDLCs) enables the generation of transmission and reflection gratings. These patterns are created by the interference of a coherent laser beam inside a polymer syrup that contains a liquid crystal, a photoreactive monomer and a photoinitiator. In chapter one, we introduce the holographic lithography technique and present the properties of the chemical components of the pre-polymer syrup that is used in this dissertation. In chapter two, we describe the fabrication set-up for transmission and reflection gratings. Also, the standard H-PDLC material systems are modified and optimized to meet precise specifications like high resolution and high reflection intensity in the spectrum. A variety of solvent concentrations and fabrication conditions are compared to verify their effects on the resulting optical performance. Particularly, we characterize and study the morphologies of the fabricated polymeric gratings in terms of optical reflection and transmission, surface and cross-section morphologies and thickness variations. Chapter three presents a single beam one-step holographic interferometry technique to create porous polymer structures with controllable pore dimension and position to produce compact graded photonic bandgap structures for linear variable optical filters. By presenting a forced internal reflection patterning, we enhance the blue region reflection peaks to over 80% and achieve a high, stable and uniform optical reflection for the visible wavelength region. Additionally by optimizing the power density, we improve the resolution. A new method of fabricating low cost spectrometers which not only detect the visible optical wavelengths but can also detect ultraviolet (UV) and near infrared light (NIR) is presented in chapter four. In this chapter, we extend this visible graded grating into a double-band rainbow-colored structure based on the second-order Bragg diffraction. We demonstrate a method which can achieve a uniformly high performance rainbow grating that can cover a spectrum wavelength range from 350 nm to 900 nm. Chapter five demonstrates a technique of fabricating a 3D PBG structures in a large scale area by combining holographic lithography and pinholes. Different patterns are illustrated and the morphologies of the samples are presented. The closing chapter, chapter six, provides a summary of the work accomplished in this thesis and presents some ideas for the future direction of studies. We demonstrate a technique to fabricate an array of a dye-doped H-PDLC graded reflection grating which is useful for biosensing applications. Another major research goal that we work on is designing and presenting a fabrication method for 1D and 2D metamaterial structures in a large scale area by using the holographic lithography method.