Theoretical And Experimental Investigation On Optical Absorption And Light Propagation Based On Micro- And Nano-Structures

The control of the light propagation and optical absorption has always been important topicsin the field of optics and optical engineering.High performace,compact and integratable optical devices based on micro-and nanostructures have attracted much attention in recent years.In this thesis,investigations on broadband optical absorption(perfect absorbers)and manipulation of light propagation(angular filters)based on microand nano-structures will be focused,in which systematic theoretical design,numerical simulation and experimental verification and measurement will be conducted and presented.The main contents and novelity of the thesis are as follows:(1)A large-area,ultrathin metasurface perfect absorber(MSPA)based on coupled Mie resonances from integrated arrays of silicon and metallic pillarsis proposed and demonstrated theoretically and experimentally.In contrast to previous structures and mechanisms,coupled Mie resonances are generated from two pillars of dissimilar materials(dielectric and metallic)of the same dimensions within an ultrathin structure such that the Mie resonances of dielectric and metallic patterns occur complementarily at different wavelengths to realize broadband absorption over the entire visible wavelength band.Double-beam interference lithography,reactive ion etching,and sputter coated depositions are utilized to fabricate the proposed MSPA.Experimental results show that with an appropriate arrangement of the patterned geometry,an average polarization independent absorption of 0.958 in the entire visible band(wavelength range from 400 to 760 nm)is achieved and remains high at 0.912 when the incident angle increases to 70?.The proposed MSPA is thus an effective way to realize a large-area,ultrathin metasurface absorber with a relatively simple and easy to fabricate structure.(2)A hot-electron photodetector enhanced by the absorption based on Mie resonanceshas been proposed.Perfect absorption is firstly realized by the Mie resonances from silver nano-pillar,and then an electrical current is generated in the titanium dioxide due to internal photoelectric effect,a hot-electron photodetector is,therefore,realized.Double-beam interference lithography and reactive ion etching is utilized to fabricatethe absorber and hot-electron photodetector.Experimental results show that the average absorption at the wavelength range from 400 nm to 800 nm is 0.818.Calculated photoelectric conversion efficiency is higher than 4% at this wavelength range and reaches 9.371% at the wavelength of 482 nm.In contrast,the photoelectric conversion efficiency of conventional silver-titanium dioxide plate structure in this band islower than 2%.This photodetector based on absorption from silver nano-pillar array will have important applications and development prospects in the field of photodetection.(3)A monolithic,all-metallic and flexible metasurface perfect absorber(black nickel)based on coupled Mie resonances originated from vertically stepped Ni nanopillars homoepitaxially grown on Ni substrate is proposed and demonstrated theoretically and experimentally.Coupled Mie resonances are generated from Ni nanopillars with different sizes such that Mie resonances of the stepped two sets of Ni nanopillars occur complementarily at different wavelengths to realize polarization-independent broadband absorption over the entire visible band(wavelength range from 400 nm to 760 nm)within an ultra-thin surface layer of totally 162 nm thick only.Two-step double-beam interference lithography and electroplating are utilized to fabricate the proposed monolithic metasurface that can be arbitrarily bent and pressed.A black nickel metasurface is experimentally demonstrated in which an average polarization independent absorption of 0.961 in the visible band is achieved and remains 0.815 when the incident angle increases to 70?.(4)An all-dielectric double-layer linear grating to realize angular filtering for polarized incident light is proposed and demonstrated theoretically and experimentally.Theorical result shows that,under the condition of TM incidence and at the designed resonant wavelength,the transmission of the double-layer grating drops sensitively as the incident angle increases.The transmission is zero(the entire incident light is reflected)when the incident angle increases to 12?,which exihibits excellent angulat filtering behavior.Double-beam interference lithography and sputter coated depositions are utilized to fabricate the proposed angular filter.Experimental results show thatthe divergence angle of the transmitted beam through the angular filtering sample at the wavelength of 632 nm is 7.76?,and the transmission is as high as 0.961 at normal incidence.The ultra-thin all-dielectric angular filter is very easy to fabricate in large area,which has important applications in directional lighting and image processing.(5)An all-dielectric,polarization-independent angular filter with photonic crystal composed of semiconductor compatible silicon/silica pairs is proposed and demonstrated theoretically and experimentally.The near-symmetric directional band gap of p-and s-polarized components and Fabry-Pérot resonances are utilized to realize efficient polarization-independent angular filtering for normal incidence.The proposed angular filter is designed and experimentally demonstrated in a large area(5cm×5cm)with multilayer sputtering depositions.Experimental measurements show that a divergence angle of the polarization-independently transmitted beam through the angular filtering sample at 1550 nm is 2.2? only and the transmission is as high as 0.8 at normal incidence.The proposed and demonstrated angular filter suggests an effective way to design and implement semiconductor compatible,all-dielectric and polarization-independent angular filters in a fashion of simple structure and easy-fabrication,which is expected to have great applications in lighting,beam manipulation,optical coupling and optical communications.