Nano-optical devices are gaining rapid finding applications in many areas, from sensors to biomolecular devices based on thin films. The precise atomic scale film thickness control and uniformity is a backbone for maintaining propagating optical modes through the waveguide nanostructures fabricated by lithography. Lithography is the key technology that has driven the dynamic growth in the microelectronics and nanophotonics industries over the past three decades. Lithography together with Atomic Layer Deposition (ALD) is a powerful tool for the size reduction of accurately fabricated nanostructures and devices. Replicated Nanophotonic structures in different optical polymer materials are achieved by Nanoimprinting Lithography technology which are employed to augment cost-effective methods and aid for rapidly growing Nanoencapsulation technologies. The design and fabrication of such Resonant Waveguide Gratings (RWGs) for different applications are presented herein. The book also describes the thermo-optic coefficients of various organic and inorganic materials for athermal operation of RWGs over a wide range of temperatures and Polarization-independent subwavelength RWGs.