Subwavelength gratings and applications

This Ph. D thesis investigates the fabrication and applications of subwavelength gratings.; The first objective of this study is aimed at finding low-cost, high throughput fabrication techniques that are capable of producing high-quality nano-scale gratings over a relatively large scale.; The second objective is to explore the applications of nano-scale gratings in subwavelength optical elements (SOE), a new type of compact, highly efficient optical devices that are compatible with semiconductor device fabrication technologies and have the potential to be suitable for integration.; This thesis is divided into 5 chapters. Chapter 1 is an introduction to the subject of gratings. A brief review of the evolution of different grating fabrication methods and applications is included in this chapter.; Chapters 2, 3, and Chapter 4 of the thesis are devoted to the question of nano-scale grating fabrication. Technologies concerning the generation of high spatial-frequency periodic patterns over a large scale using interference lithography (IL) are covered in Chapter 2. The role of nanoimprint lithography (NIL) as a low-cost replication tool for the production of nano-gratings is discussed in detail in Chapters 3 and 4. More specifically: Chapter 3 presents several NIL-based technologies that are used to overcome some of the limitations inherent with the interference lithography fabrication process; Chapter 4 presents a novel mask technology promising for the large-scale production of gratings by NIL.; Finally, several applications of nano-scale gratings in subwavelength optical elements (SOE) are discussed in Chapter 5.; Most of the SOE devices investigated in this study are based on the birefringence and the index-averaging effects of nano-gratings in the long-wavelength domain. A brief summary of the general theory 103–104 proposed by P.Yeh et al. concerning the optical properties of subwavelength gratings can be found in Appendix A.; Since the orientation-dependent wet chemical etching of silicon was used extensively in this research, a relatively detailed discussion of this technique is also included in Appendix B of this dissertation.