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.
We propose a highly sensitive hybrid-plasmonic sensor based on thin-gold nanoslit arrays. The transmission characteristics of gold nanoslit arrays are analyzed as changing the thickness of gold layer. The surface plasmon polariton mode excited on the sensing medium, which is sensitive to refractive index change of the sensing medium, is strengthened by reducing the thickness of the gold layer. A design rule is suggested that steeper dispersion curve of the surface plasmon polariton mode leads to higher sensitivity. For the dispersion engineering, hybrid-plasmonic structure, which consists of thin-gold nanoslit arrays, sensing region and high refractive index dielectric space is introduced. The proposed sensor structure with period of 700 nm shows the improved sensitivity up to 1080 nm/RIU (refractive index unit), and the surface sensitivity is extremely enhanced.
In this paper, we propose a bilayer metasurface which is capable of launching helicity-inverted wave only in the forward direction. In order to obtain directional scattering characteristics of individual cells, we employed two layers of thin metasurfaces that are separated by a dielectric spacer. Multiple scattering analysis is used to derive design conditions for single metasurface reflectances for each polarization and it was shown that such target reflectances are realizable with split-ring aperture. The unit cell structure optimized for forward-only scattering of cross-polarization component is shown to have power extinction ratio as high as 32. The proposed structure can potentially form a supercell with reflective cells so that geometric phases of transmitted light and reflected light can be independently controlled. The proposed scheme is expected to pave a way to new types of metasurfaces with multiplexed optical functions.
Metasurfaces refer to periodic arrays of thin nano-antennas which are separated by subwavelength length. Due to the strong capability of nano-antenna distributions in phase profile generation, hologram generation using metasurfaces has attracted attention of many researchers. We propose a reflective type hologram by a metasurface composed of Z-shaped nano-antennas. The proposed metasurface renders precise phase modulation with spatially varying orientation, which attributes to the increase of the level of phase distribution. It has different plasmonic resonance mode for the orthogonal linear polarized incidence that makes different phase delay effect for orthogonal input. The metasurface we propose shows phase modulation characteristics over a wide wavelength range between 800 nm and 1,500 nm. Also it achieves high polarization conversion efficiency above 80% in a broad bandwidth. Meta-hologram using the metasurface has opened the possibility of variety of structures and expanded to near-infrared region. We expect our proposal could be applied to the more complicated meta-holograms.
We suggest a linear polarization sensor, which has been developed for the Shack-Hartmann wave-front sensor. Our system is classified into three parts. First, polarization filter using wire-grid-plate structure selects only one polarized wave between two linear orthogonal polarization states. Second, graded index layer refracts the wave passed and gives the wave-front distortion. Third, a lens array, one part of the Shack-Hartmann wave-front sensor, focuses the wave on focal plane. We can detect linear polarization state through measuring displacement of the spot centroid. This study on polarization sensor can offer help on vector field sensing, which is crucial to obtain a complete description of light in nanoscale device.
In this invited paper, we glance at the history of plasmonic sensors and provide the optimization study of representative
plasmonic sensors such as surface plasmon resonance (SPR) sensors, localized SPR sensors, and fiber grating SPR
sensors. The key variables of specific plasmonic sensors are numerically examined and compared. Furthermore, we
discuss the recent developments and prospect on various plasmonic sensors.