Highly reflective visible color filter based on a double layer TiO2 subwavelength structure

Color filters based on all-dielectric subwavelength structures (SWSs) allow precise control of the coloration during production. However, SWS manufacturing typically requires complex processes, such as lift-off or etching. Here, highly reflective color filters manufactured without lift-off and etching techniques were experimentally demonstrated using a double-layer high-contrast all-dielectric SWS. The SWSs were fabricated on optical glass substrates using electron beam lithography and evaporation. Visible reflection spectra were controlled by adjusting structural parameters. Red, green, and blue colorations were experimentally demonstrated with 57%, 63%, and 72% reflectivities, respectively. High reflectivity, manufacturing throughput and level of control of the manufactured filter color make them suitable for imaging, display, and sensing applications

GaN-Based High-Contrast Grating for Refractive Index Sensor Operating Blue-Violet Wavelength Region

Owing to its versatility, optical refractive index (RI) sensors with compact size and high chemical stability are very suitable for a wide range of the applications in the internet of things (IoT), such as immunosensor, disease detection, and blood mapping. In this study, a RI sensor with very simple system and high chemical stability was developed using GaN-based high-contrast grating (HCG). The designed HCG pattern was fabricated on GaN-film grown on c-plane sapphire substrate. The fabricated GaN-HCG sensor can detect minuscule RI change of 1.71 × 10–3 with extreme simple surface normal irradiation system. The light behavior inside the GaN-HCG was discussed using numerical electromagnetic field calculation, and the deep understand of the sensing mechanism was provided. The simple system and very high chemical stability of our sensor exploit RI sensing applications in IoT society

Highly sensitive magnetic field sensor with normal-incidence geometry using Ni-based bilayer subwavelength periodic structure operating in visible-wavelength region

We successfully demonstrate a highly sensitive optical sensor for detecting magnetic fields with normal-incidence geometry that uses a Ni-based bilayer subwavelength periodic structure (SWS) operating in the visible-wavelength region. The electromagnetic field distribution within the SWS as calculated by the finite-difference time-domain method indicates that the bilayer SWS has the potential to detect minuscule magnetic fields without the need for a complex incidence system. Our bilayer Ni-SWS system with its very simple normal incidence geometry is experimentally able to detect magnetic field changes of the order of a few millitesla

High-sensitivity refractive index sensor with normal incident geometry using a subwavelength grating operating near the ultraviolet wavelength

A high-sensitivity refractive index sensor is demonstrated for the first time, near the ultraviolet (UV) wavelength region using a Si3N4-subwavelength grating (SWG) with a normal incident optical geometry. Using the eigenmode within the Si3N4-SWG, a high sensitivity for the refractive index is expected by finite-difference time-domain calculation, without an oblique incident geometry. The proposed SWG is fabricated and the high-sensitivity refractive index sensor operating near the UV wavelength is experimentally and successfully developed. The normal transmitted intensity through the fabricated SWG varies considerably with slight changes in the refractive index. The experimental sensitivity of the SWG attained 1240 % per refractive index unit (RIU) and the sensitivity shows good agreement with the calculation. These experimental results suggest that our refractive index sensor with a normal incident geometry can measure a refractive index change of 8.06 x 10-4 RIU, if the optical detection system can measure an intensity change of 1%

Dual-wavelengths filter operating at visible wavelength region using subwavelength grating on waveguide structure

A dual-wavelength filter was experimentally demonstrated using subwavelength grating (SWG)/waveguide structure. We designed the structural parameters of the SWG and the waveguide to find the reflection peaks in the visible wavelength region. To investigate the optical response of the designed SWG/waveguide structure, finite-difference time-domain (FDTD) numerical calculations were performed for electromagnetic field distribution. The dual reflection peaks from our proposed structure were predicted in visible wavelength regions by the FDTD calculation. The calculated electromagnetic field distribution also revealed that the reflection peaks were associated with resonances in the SWG and waveguides. We fabricated the SWG/waveguide with typical electron-beam lithography techniques, and two reflection peaks were observed at wavelengths of 486 nm and 590 nm with bandwidths of 45 nm and 58 nm, respectively. These experimental results indicate that dual-wavelength filters can be successfully realized without complex fabrication processes

Magnetically tunable visible reflectivity utilizing the electron accumulation in indium-tin-oxide waveguide layer with subwavelength grating

Magnetic field detection was experimentally demonstrated utilizing the optical spectral change of Al-subwavelength grating (SWG) on indium-tin-oxide (ITO) layer. The Al-SWG was fabricated on the ITO layer by electron-beam lithography technique. The fabricated sample shows the peak in the reflection spectrum resulting from the excitation of guided-mode in ITO layer. Electron accumulation layer in ITO was induced by applying magnetic field and flowing current, and the accumulation layer decreased the reflection peak intensity. As the magnetic field of 172 mT was applied, the intensity decreasing reached to 3 % of that without magnetic field. The intensity returned to the original value before measurement when the magnetic field and the current disappeared. These results indicate that our structure can detect tens of mT magnetic field without degaussing

Ultra-thin deep ultraviolet perfect absorber using an Al/TiO2/AlN system

An ultra-thin perfect absorber for deep ultraviolet light was realized using an Al/TiO2/AlN system. The TiO2 thickness was optimized using the Fresnel phasor diagram in complex space to achieve perfect light absorption. As a result of the calculation almost perfect absorption into the TiO2 film was found, despite the film being much thinner than the wavelength. An optimized Al/TiO2/AlN system was fabricated, and an average absorption greater than 97% was experimentally demonstrated at wavelengths of approximately 255–280 nm at normal light incidence. Our structure does not require nanopatterning processes, and this is advantageous for low-cost and large-area manufacturing

Optical detection for magnetic field using Ni-subwavelength grating on SiO2/thin-film Ag/glass structure

An optical sensor for magnetic field detection using Ni-subwavelength grating (SWG) on SiO2/Ag-thin-film/glass substrates was experimentally developed on the basis of the re-radiation condition of surface-plasmon-polaritons (SPPs) at Ag surfaces. The fabricated sample showed two dips in the reflection spectra associated with SPP excitation, and the optical response exhibited good agreement with that simulated by the finite-difference time-domain method. The reflectivity at one of the dip wavelengths varied minimally with the application of the magnetic field, whereas that at the other dip wavelength significantly decreased owing to the large electric field overlap of SPP with the magnetized Ni-SWG. As a result, a magnetic field on the order of a few mT could be detected with a simple normal-incidence optical system

Highly Sensitive Refractive Index Sensor using Dual Resonance in Subwavelength Grating/Waveguide with Normally Incident Optical Geometry

A highly sensitive refractive index sensor with normally incident optical geometry was experimentally demonstrated using dual resonance in a subwavelength grating (SWG) on a waveguide. Two eignemodes within the SWG and waveguide were utilized for refractive index sensing with the reduction of noise such as background noise. The finite-difference time-domain numerical method was used to estimate the refractive index sensing performance of our sensor. The calculated electric field clarified that the incident light could excite modes in the SWG and waveguide with normally incident optical geometry, and the modes formed two resonance reflection peaks. The calculation showed that these dual resonance peaks depended differently on the refractive index of the ambient around the sensor, and the intensity difference between both resonance peaks varied with the slight change in refractive index of the ambient. The sensor was fabricated using traditional electron-beam lithography techniques, and two reflection resonant peaks were experimentally obtained. The difference between the dual resonance peak intensities varied significantly with the minuscule change in refractive index of the ambient around the sensor, and the resolution of the refractive index reached 7.65 × 10–4, assuming a spectrometer intensity sensitivity of 1%