Fast Fourier Transform

Quad-band plasmonic perfect absorber using all-metal nanostructure metasurface for refractive index sensing

Metamaterials (MMs) offer great potential for achieving optical absorption due to their novel electromagnetic properties. MM absorbers can overcome the thickness limitation and provide excellent absorption performance over the wide frequency range, thereby enable the swift emergence of some promising applications. Moreover, the optical sensors based on MM absorbers have shown great potential in several fields. This review concentrates on the recent progresses in MM-based optical absorbers and spectral sensing. We present four aspects of MM-based optical absorption: the metal-insulation-metal arrangements, the optical coherence, the functional materials, and some novel approaches. Also, we present three aspects of MM-based optical sensing: the refractive index sensing, gas and molecule sensing, and surface-enhanced Raman scattering. Finally, the current challenges and prospects in device designs, fabrications have been discussed. This review is with the purpose to give a generalized knowledge of MMs for optical absorption and sensing, thus inspiring the investigations on MMs for other devices and their practical applications.

https://iopscience.iop.org/article/10.1088/1361-6463/abccf0/pdf

Recent progresses on metamaterials for optical absorption and sensing: A review

This paper reports on high-accuracy simulation of a grating structure based fiber optic plasmonic sensor for salivary cortisol sensing. Gratings of SiO2 and SiC (one at a time) in combination with a thin Ag layer are considered to be in direct contact with analyte medium (solutions containing different concentrations of cortisol) considering that the groove regions are also filled with analyte. The optimization of Ag layer thickness is carried out to achieve maximum power loss (PL) corresponding to cortisol concentration variation. The variation of PL (in dB) spectra with the angle of incidence (α) is the sensing mechanism of the proposed scheme. Sensing performance is extensively analyzed in terms of sensitivity, limit-of-detection (LOD) and figure-of-merit (FOM) that incorporates both the sensitivity and the width of the corresponding PL curves. While the sensitivity and FOM values are significantly large, the results also reveal that in angular interrogation mode (AIM), an average LOD of 9.9 pg/mL and 9.8 pg/mL is obtained for SiO2 and SiC-based sensor designs, respectively. When the intensity interrogation method (IIM) in place of AIM is considered, an average LOD of 22.6 fg/mL and 68.17 fg/mL is obtained for SiO2 and SiC-based sensor designs, respectively. LOD (with IIM, in particular) is considerably better than the present-state-of-art related to cortisol monitoring. Pragmatic model for possible practical implementation of sensor scheme is also discussed. The involvement of optical fiber in the proposed sensor design makes it possible to implement it as a flexible sensor or for wearable solution for cortisol detection via sweat monitoring as well as for measuring cortisol level in aquaculture tanks where concentration levels are much lower than 10 ng/mL.

On The Application of SiO2/SiC Grating on Ag for High-Performance Fiber Optic Plasmonic Sensing of Cortisol Concentration.

We derive generic phase and amplitude coupling relations for beam splitters-combiners that couple a single port with three output ports or input ports, respectively. We apply the coupling relations to a reflection grating that serves as a coupler to a single-ended Fabry-Perot ring cavity. In the impedance-matched case such an interferometer can act as an all-reflective ring mode cleaner. It is further shown that in the highly undercoupled case almost complete separation of carrier power and phase signal from a cavity strain can be achieved.

/pdf/three-port-beam-splitters-combiners-for-interferometer-2px8kjwse0.pdf

Three-port beam splitters-combiners for interferometer applications

In this paper, we propose a refractive index sensor with self-reference performance based on a two-dimensional grating structure, mainly consisting of periodic arrays of triple layer dielectric nanodisks and a continuous substrate separated by a thin gold film. Three reflection dips are observed and manipulated to realize self-reference and high sensing performance due to the excitation of magnetic dipole mode resonance, substrate mode resonance and metal layer assisted guide mode resonance. These hybrid modes have been explained by the distributions of the electric and magnetic fields in the nanostructure. A detailed analysis of the influences of material thickness on the optical properties of the proposed refractive index sensor is also investigated. Moreover, the proposed refractive index sensor demonstrates a high sensing performance, an important application for future biomedical applications, with a bulk refractive index sensitivity of 672 nm RIU−1 (RIU: refractive index unit) and figure of merit of 1050 RIU−1. Importantly, the function of self-reference is realized simultaneously. Finally, it also shows excellent sensing performance, with the maximum value exceeding 168 000 by measuring the light intensity change in the reflected light at a certain wavelength. This makes it much more suitable for applications in the field of portable detection.

Self-referenced refractive index sensor based on hybrid mode resonances in 2D metal-dielectric grating

Narrowband absorber based on magnetic dipole resonances in two-dimensional metal–dielectric grating for sensing

Better performances of two-dimensional (2D) grating are required recently, such as polarization independence, high efficiency, wide bandwidth and so forth. In this paper, we propose a 2×2 2D silver cylindrical array grating with excellent polarization-independent high diffraction efficiency (DE) over communication band for beam splitting. The grating was calculated by rigorous coupled wave analysis (RCWA) and can achieve over 24% DE of four first diffraction orders at 1550 nm with nonuniformity of 1.43% in both transverse electric (TE) and transverse magnetic (TM) polarizations, which is a significant improvement over previous reports. The holographic exposure technology, wet chemical development process and electron beam evaporation were used to fabricate the 2D grating. The correctness and accuracy of the calculation are fully verified with the measurement result of fabricated grating. Excellent performances of the 2D splitter we proposed will have great potential for applications in optical communication, semiconductor manufacturing and displacement measurement.

Polarization-independent 2×2 high diffraction efficiency beam splitter based on two-dimensional grating

High-efficiency polarization-independent gold-coated crossed grating under normal incidence

We proposed a slanted grating suitable for RGB bands which is polarization-independent and has a high diffraction efficiency of −1st order under normal incidence. We used Rigorous Coupled Wave Analysis (RCWA)and simulated annealing (SA) algorithm to optimize grating parameters and the simulation results showed that the -1st order diffraction efficiency of TE and TM polarizations in the RGB band under normal incidence both exceed 83%, which can be used for three-dimensional (3D) display. Then, by using rigorous modal theory, simplified modal method (SMM), and mode coupling theory, we analyzed the reason for the high-efficiency of −1st order diffracted light. Moreover, the numerical simulation of the simplified modal method is consistent with the rigorous coupled wave analysis of the small slanted angle grating. Therefore, the simplified modal method can be used for small slanted angle gratings as its physical analysis proved that small slanted angle gratings and rectangular gratings have equivalence to a certain extent. This work not only presents numerical solutions of slanted grating with high efficiencies over a wide range of RGB wavelength, but also enables us to have a deeper understanding of the diffraction of slanted gratings.

/pdf/high-efficiency-polarization-independent-slanted-grating-for-1mydj21av1.pdf

Yongfang Xie

Papers

Self-referenced refractive index sensor based on hybrid mode resonances in 2D metal-dielectric grating

Narrowband absorber based on magnetic dipole resonances in two-dimensional metal–dielectric grating for sensing

Polarization-independent 2×2 high diffraction efficiency beam splitter based on two-dimensional grating

High-efficiency polarization-independent gold-coated crossed grating under normal incidence

High Efficiency Polarization-Independent Slanted Grating for RGB Bands