As an increased demand in high resolution display, the pixel size in the image sensor is reduced to increase the resolution. Although there have been recent studies on metasurface color routers to overcome the limitation of the conventional image sensor, there are still limitations in that the designed devices do not show the advantages of router or are difficult to fabricate. In this study, the fabricable metasurface that distribute three visible wavelengths to each targeted color sensor is proposed numerically. For the distribution like the Bayer pattern, a dual focal phase profile is utilized for green color. The designed metasurface size is 2 μm by 2 μm, and the routing efficiencies are 12 %, 25 %, and 30 % for 473 nm, 532 nm, and 660 nm, respectively, where the performance in red light exceed the fundamental limit of efficiency of the conventional Bayer color filter array.
Recently, nanostructures composed of tapered apertures have been researched for electromagnetic field enhancement. Tapered plasmonic aperture antenna can concentrate transverse electric dipoles and longitudinal magnetic dipoles in tiny volume of plasmonic waveguide or metasurface. It is an important element for efficient nonlinear optics, modification of spontaneous decay rates, and sensitive nanophotonic sensors to simultaneously intensify both of electric and magnetic fields. However, even though their advantages include apparent theory based on constructive interference of surface plasmons and relatively simple fabrication, the enhancement performances are not strong as much as those of conventional bridged bowtie aperture antenna. Here, we propose a novel design with reflection type metasurface patterned by a funnel-shaped waveguide cavity array. This supports longitudinal cavity mode along the direction of incident light in addition to perimeter cavity mode or transverse cavity mode of conventional tapered apertures. Longitudinal cavity mode contributes to electric and magnetic fields on transverse plane and transverse cavity mode with funnel shape induces strong circulating currents around tiny volume that generate magnetic dipoles on longitudinal plane. To demonstrate our proposed design, we carry out three-dimensional finite element method for numerical calculation. It shows resonant average (maximum) enhancements of electric and magnetic intensities reach about 177 (1484) and 91 (274), respectively, at the wavelength of 1120 nm. Furthermore, the enhancement of spontaneous decay rates and Purcell effect are verified numerically. Our design can offer a new approach of various nano-optical applications such as biochemical sensor, nonlinear optics, and photoluminescence application.
We proposed a refractive index sensor using a phase-compensated cavity whose resonant wavelength can be tuned by the alignment between layers. The structures are composed of double-layered nanoslit array, which has total thickness of 100 nm while the cavity length is 30 nm thick. Using nanoslit array as a reflector has made it possible to design the phase shift carefully so that the subwavelength Fabry-Pérot cavity can be obtained. When the cavity is filled with sensing medium, where the field enhancement is achieved by Fabry-Pérot (FP) resonance, the proposed structure is found to achieve sensitivity ranging from 337 nm/RIU to 1250 nm/RIU at each different alignment. The resonant wavelength ranges from 1100 nm to 2500 nm, which contains biological windows and telecommunication wavelength range, so the structure is expected to be used in various purposes.
Surface plasmon polaritons (SPPs) are surface-bounded electromagnetic waves, propagating along a metal-dielectric interface. Due to larger wavenumber of SPPs compared with propagating light in free-space, additional couplers are required to excite SPPs. Dielectric prisms, gratings, apertures, and optical antennas are widely used. Recently, controlling excitation property of SPPs with coherent characteristics of incident lights, such as polarization and interference has been demonstrated. In this work, we propose a coherent plasmon cavity whose energy density can be tuned by polarization of the incident light. With polarization-sensitive aperture array, it is possible to launch counter-propagating SPPs with phase difference controlled by an angle of polarization. By rotating the polarization angle by 90 degrees, the energy density inside the cavity is enhanced 45 times larger compared with the minimum case.
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