Research Of Optical Focusing Device Based On Surface Plasmonics

With the development of modern science and technology, the requirement fromlife, industrial, defense and other fields are calling the improving of the performanceand the decreasing of the size of components. The size of the Large Scale Integratedcircuit and some parts of the micro and nano devices has reached the nanometerscale, and the size of the devices is still developing towards a constantly downsizingtrend. With the increasing demands on the size of the device, the difficulty ofprocessing and manufacturing cost is also rising. An optical focusing device ispurposed to design for subwavelength focusing, balancing the focal performanceand the difficulty of processing.In this paper, a subwavelength focusing device is designed to facilitateindustrial production. This design uses the delay the phase of the surface plasmonresonance effects in a subwavelength metal slit and the extraordinary opticaltransmission effect of the metal film for light. The design of multilayer aperiodicmetal grating can achieve any position of quasi-far field focusing，and the maximumdepth-to-width-ratio is acceptable.With use of the finite difference time domain method (FDTD) for numericalsimulation, it is demonstrated that the transverse magnetic mode650nm incidentlight focused a hot spot in subwavelength scale through the device. In the design ofthis device, the maximum depth-to-width ratio requirement of the device is smallerthan10:1, and the minimum line width of slits is20nm. In this paper, of layers ofmetal grating is simulated when processing the grating, obtaining that this structurenot only has the characteristics of low aspect ratio requirements, but also is notsensitive to the errors of the alignment. The requirement of processing can be met by the main stream processing technology level.In this paper, a Grating-Fresnel hybrid lens with band-pass function is alsointroduced. It achieves a long focal depth, super-resolution focusing point forincident light with wavelength of500nm at the same time. Meanwhile, it scatters thelight that is not in the work band. The subwavelength focusing devices designed inthis paper has great application prospects in laser direct writing, data storage, andoptical probe.