Far-Field to Near-Field Coupling for Enhancing Light-Matter Interaction

This thesis reports on theoretical, modeling, and experimental research within the framework of a key scientific question, which is enhancing the coupling between diffraction-limited far-field and sub-wavelength quantum emitter/absorber. A typical optoelectronic device delivers an optical process such as light detection (e.g. photodetector) or light intensity modulation (e.g. electro-absorptive modulator). In conventional devices, optical process is in the form of far-field or guided wave modes. The main aim of this thesis is to show that converting these modes into near-field domain can enhance the performance of the optoelectronic device. Light in the form of far-field can be converted into near-field domain by the optical antenna. Among different optoelectronic devices, this thesis focuses mainly on integrating the optical antenna with infrared photodetectors. The available semiconductors have weak infrared absorption that reduces light detection efficiency. Integration of the optical antenna with infrared absorber (such as quantum wells in quantum well infrared photodetector (QWIP)) increases the infrared absorption. Particularly this integration is favorable as the optical antenna has low metallic loss in infrared region.;The author of this thesis believes that optical antenna has unique properties in confining light on the scale of deep sub-wavelength, enhancing electric field intensity and delivering optical energy to semiconductor absorbers. These properties are reaching into practical applications only if overall optical performance is low loss, parameter free (independent of optical parameters such a polarization and angle of incident) and broadband. In this thesis, the integration of optical antenna with infrared photodetectors and thermophotovoltaic are researched and developed which satisfy the aforementioned criteria.;In addition, several different optical antennas have been designed, fabricated and characterized in order to analyze and demonstrate the improvement of infrared absorption. In terms of design, novel optical antennas were simulated and proposed for a variety of infrared photodetectors such as a quantum well infrared photodetector, metal-insulator-metal detector, Schottky infrared photodetector, and two-photon absorption infrared detector. Antenna analyzes are not limited to light detection as a chapter of this thesis devoted on design and develop of a low power and ultrafast all-optical/optomechanical switchable antenna. The rest of the manuscript contains the novel lithography method in order to fabricate optical antennas with low cost and in cm-scale area. The method is based on the microsphere photolithography that expose photoresist underneath each microsphere with a focused intensive light -so called photonic nanojet. The developed lithography method takes advantage of microscopic range of optical path (micro-optics) in microsphere lenses that allows to push the exposure wavelength beyond deep UV region, where the refractive optics becomes impractical due to severe material absorption. The author believes that micro-optics lithography is an excellent candidate for large area and high throughput fabrication of sub-100-nm feature sizes in periodic array. In particular, this method facilitates the feasibility of metasurfaces and metamaterials, optical coating with efficient photon extraction/trapping, and highly sensitive bio-sensors in near IR and visible ranges of spectrum.