Research On Radiation Properties Of Subwavelength Structures In Optical Frequency

With the development of modern information technology, miniaturization andhighly integration of optical devices become a trend. In this thesis, we designed andstudied two different types of subwavelength structures aiming to generate a collimatedbeam and a focused beam, respectively. In essence, the structures are both based onsurface plasmon polaritons which are excited from the corrugated metal surface. Mainworks and conclusions are listed as follow:1. A subwavelength structure based on Ag/Al/Ag multilayer, consisting of a narrowslit and periodically patterned metallic grooves, with property of high directionalradiation, is proposed and an experimental platform used for direct optical far-fieldmeasurement is designed and built. In our simulations, we analyzed the influences ofbeaming effect on structure parameters, and optimized the values by finite elementmethod. Moreover, we performed a series of experiments to test the far-field radiationperformances of the proposed sample. The results show that the structure can radiatelight with small divergence angle in far field by TM light and the experimental data arein good accordance with simulation results, which confirms that the subwavelengthstructure does have the ability to emitting light with beaming effect in far field.2. A plasmonic lens of long depth of focus (DOF) by radially polarized light ispresented. The lens is composed of an annular aperture and concentric grooves. Underradially polarized illumination, a subwavelength focal spot is obtained in opticalmeso-field. The influence of depth-tuned annular grooves on focusing properties,including focal length, DOF and full-width half-maximum (FWHM), are investigated.Furthermore, the focusing efficiency can be greatly enhanced by introducing a circularmetallic grating which surrounds the annular slit.