Light-matter interaction at the nanoscale : optical emitters, antennas and sensors

Abstract

The research presented in this thesis addresses four devices based on light-matter interactions at the nanoscale. These devices include 1) an optical emitter hosted in bulk diamond, 2) an optical antenna used to extract emission from emitters in bulk diamond, 3) a novel lab-on-fiber optical sensor with nanoimprinted nanostructures on the fiber sidewall and 4) a large-scale optical sensor with spatially varying plasmonic nanostructures. First, the distribution of nitrogen-vacancy (NV) color centers in diamond created by means of helium ion beam irradiation is experimentally characterized via stimulated emission depletion (STED) microscopy and ground state depletion (GSD) microscopy. Then, a numerical model is developed to study the distribution and quantity of NV centers created by single-pixel irradiation of helium ion beam. The dependence of the distribution on the helium ion dose and the nitrogen concentration in the diamond is also investigated using this model. The conversion ratio from separated nitrogen-vacancy pairs to NV centers is also experimentally studied and explained by the simulation results. Second, a nanoparticle-based optical antenna is designed and fabricated for extracting emission from NV centers in diamond. This optical antenna has a relatively weak effect on the intrinsic optcal properties of the emitters. The material and size of the optical antenna are carefully selected based on their simulated extraction enhancement performance. Then, the extraction performance of nanodiamonds of the optimal size is experimentally characterized. The experimental results are well explained by the simulation. Third, a new type of lab-on-fiber sensor termed a “sidewall-imprinted fiber” (SIF), which is fabricated by directly imprinting nanostructures on the sidewall of a fiber, is proposed. The newly developed nanoimprint lithography method offers various advantages, such as low cost, high throughput, and time efficiency. A model that combines ray optics and physical optics is developed to study the light scattering behavior in the imprinted region of an SIF. The application of an SIF for sensing the ambient refractive index is then demonstrated using both peak-tracing and intensity-reading methods. Finally, another optical sensor with spatially varying plasmonic structures is fabricated by means of interference lithography and nanoimprint lithography. The interference lithography system used is an upgraded version of a two-beam interference lithography for writing uniform patterns. This gradient pattern device exhibits gradient structural colors. Then, the fabricated device is applied to sense the ambient refractive index using a method based on image recognition, which is a highly sensitive and spectrometer-free approach.