Surface plasmons, as a local electromagnetic field mode generated or stimulated at the interface between common metal and dielectric, can be used to greatly break through the optical diffraction limit and also localize the electric-field and then light energy in a sub-wavelength scale. It is already a research hotspot in recent years. As shown, several patterned metal nano-array can be utilized to produce relatively strong surface plasmon resonance, so as to achieve a nano-scaled localized light field on the surface of the functioned metal structure. In this paper, silicon dioxide materials are used as the substrate, and the common gold materials are fabricated into a metal film, and then the sub-wavelength metal nano-tip arrays with several morphology such as the cone-shaped, the triangular-pyramid-shaped, and the quadrangular-pyramid-shaped, are designed respectively. The functioned metal nano-structures are symmetric and asymmetric coating mode. The electric field distribution characteristics of the structure under the internal excitation mode of the incident light with vertical incidence are analyzed. The simulations show that the local field enhancement can be clearly observed at the nano-tip of the cone-shaped in the asymmetric case, but the symmetry is not. Analysis shows that the destructive interference occurs when the surface plasmons are excited by a linearly polarized light on both sides of a conical structure propagate to its top, so failure to produce focusing effect. Therefore, to the case of symmetrical film through adjusting the incident angle of light, different incident angles will affect the enhancement of the local field at the tip of the cone.
The Fabry-Perot interferometer (FP) can be used as a kind of filter for obtaining spectral information of targets in several wavelength ranges such as in the visible or infrared regions. So far, the spectral imaging devices based on FP effect mainly include the electrically controlled liquid-crystal filtering structures and the micro-electro-mechanical filtering architectures (MEMS). MEMS are generally micro-structures that integrate micro-sensors for converting incident microbeams into arrayed electronic signals and micro-actuators. The MEMS-FP filter constructed by combining the MEMS and FP functions, can be further integrated into a chip-level imaging spectrometer to achieve spectral imaging operation. The design of distributed Bragg reflectors (DBRs) is an important part to obtain a high transmittance for MEMS-FP structure. Different number of layers of optical film is calculated and compared in this paper and the transmittance can reach 82% and the FWHM is ~ 1nm in the infrared region of 3-5um. Angle of incidence is also considered and the simulation result shows poor robustness. We propose that two liquid-crystal microlens arrays can be mounted on FP arrays to get a high filling-factor and a more flexible range of incident angles.
Metallic micro-nano-structure arrays can be used to induce a collective oscillation of free electrons on the surface of metal films, so as to generate relatively strong surface plasmons (SPs) at the metal and medium interface and further localized light field under the excitation of incident lightwaves. As the oscillating light field propagating along the interface, the field strength can be increased reasonably at the functioned metal surface such as the incident light energy being localized in the sub-wavelength region defined by the functioned micro-nano-structures. The common beam diffraction limit formed during lightwave transmission or process can be broken effectively. Through constructing SPs over the special micro-nano-structures, the infrared reflection characteristics can be changed and then the local light field originated from incident infrared radiation also be enhanced significantly so as to efficiently perform infrared detection. Generally, the reflectivity and light field distribution behaviors of the functioned metal surface can be modulated by changing featured parameters of the metallic micro-nano-structural arrays. In this paper, a metal micro-nano-patterned structures with an arrayed tip is established for compressing the incident light field and then reducing the reflectivity of the metal surface and thus sensing incident light energy. A finite integral method for simulating and analyzing the structural characters such as the distance between tips, the tip sharpness, the thickness of the metal film, is utilized to acquire the reflectivity and field enhancement characteristics. The infrared reflection spectrum and the near-field intensity distribution of the metallic micro-nano-structure are compared and analyzed. The results show that the response frequency and excitation intensity of SPs over the nano-tip array, the intensity and distribution region of the strong light field, can be controlled by matching the structural parameters and layout. The optimization of the metallic micro-nanostructure arrays is conducted so as to lay a solid foundation for further development of the similar technologies.
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