A perfect ultra-narrow band infrared metamaterial absorber based on the all-metal-grating structure is proposed. The absorber presents a perfect absorption efficiency of over 98% with an ultra-narrow bandwidth of 0.66 nm at normal incidence. This high efficient absorption is contributed to the surface plasmon resonance. Moreover, the surface plasmon resonance-induced strong surface electric field enhancement is favorable for application in biosensing system. When operated as a plasmonic refractive index sensor, the ultra-narrow band absorber has a wavelength sensitivity 2400 nm/RIU and an ultra-high figure of merit 3640, which are much better than those of most reported similar plasmonic sensors. Besides, we also comprehensively investigate the influences of structural parameters on the sensing properties. Due to the simplicity of its geometry structure and its easiness to be fabricated, the proposed high figure of merit and sensitivity sensor indicates a competitive candidate for applications in sensing or detecting fields.

A surface plasmon polaritons (SPPs) refractive index sensor which consists of two metal-insulator-metal (MIM) waveguides coupled to each other by a ring resonator is proposed. The transmission properties are numerically simulated by finite element method. The sensing characteristics of such structure are systematically analyzed by investigating the transmission spectrum. The results indicate that there exist three resonance peaks in the transmission spectrum, and all of which have a linear relationship with the refractive index of the material under sensing. Through the optimization of structural parameters, we achieve a theoretical value of the refractive index sensitivity as high as 3460nmRIU⁻¹. Furthermore, this structure can also be used as a temperature sensor with temperature sensitivity of 1.36nm/°C. This work paves the way toward sensitive nanometer scale refractive index sensor and temperature sensor for design and application.

We propose and numerically investigate a novel ultra-broadband solar absorber by applying iron in a 2D simple metamaterial structure. The proposed structure can achieve the perfect absorption above 95% covering the wavelength range from 400 to 1500 nm. The average absorption reaches 97.8% over this wavelength range. The broadband perfect absorption is caused by the excitation of localized surface plasmon resonance and propagating surface plasmon resonance. We first propose and demonstrate that the iron is obviously beneficial to achieve impedance matching between the metamaterial structure and the free space over an ultra-broad frequency band in the visible and near-infrared region, which play an extremely important role to generate an ultra-broadband perfect absorption. In order to further broaden the absorption band, we also demonstrate the perfect absorption exceeding 92% for the 400–2000 nm range by adding the number of metal-dielectric pairs and using both gold and iron simultaneously in the proposed structure. The average absorption of the improved absorber reaches 96.4% over the range of 400–2000 nm. The metamaterial absorbers using iron are very promising for many applications, which can greatly broaden the perfect absorption band in the solar spectrum and, meanwhile, can enormously reduce the cost in the actual production.

We propose and numerically demonstrate an ultra-broadband graphene-based metamaterial absorber, which consists of multi-layer graphene/dielectric on the SiO2 layer supported by a metal substrate. The simulated result shows that the proposed absorber can achieve a near-perfect absorption above 90% with a bandwidth of 4.8 Thz. Owing to the flexible tunability of graphene sheet, the state of the absorber can be switched from on (absorption > 90%) to off (reflection > 90%) in the frequencies range of 3–7.8 Thz by controlling the Fermi energy of graphene. Moreover, the absorber is insensitive to the incident angles. The broadband absorption can be maintained over 90% up to 50°. Importantly, the design is scalable to develop broader tunable terahertz absorbers by adding more graphene layers which may have wide applications in imaging, sensors, photodetectors, and modulators.

We propose and numerically investigate a perfect ultra-narrowband absorber with an absorption bandwidth of only 1.82 nm and an absorption efficiency exceeding 95% in the visible region. We demonstrate that the perfect ultra-narrowband absorption is ascribed to the coupling effect induced by localized surface plasmon resonance. The influence of structural dimensions on the optical performance is also investigated, and the optimal structure is obtained with the extremely low reflectivity (0.001) of the resonance dip. The perfect absorber can be operated as a refractive index sensor with a sensitivity of around 425 nm/RIU and the figure of merit (FOM) reaching 233.5, which greatly improves the accuracy of the plasmonic sensors in visible region. Moreover, the corresponding figure of merit (FOM*) for this sensor is also calculated to describe the performance of the intensity change detection at a fixed frequency, which can be up to 1.4 × 105. Due to the high sensing performance, the metamaterial structure has great potential in the biological binding, integrated photodetectors, chemical applications and so on.

A near-infrared plasmonic refractive index (RI) sensor with figure of merit (FOM) as high as 124.6 is proposed and investigated numerically. The RI sensing is realized by employing the linear relation between resonant wavelength and RI of the material under detecting. Based on the fillet cavity coupled with two metal-insulator-metal waveguides, transmission efficiency (T) and optical resolution (FWHM) of the RI sensor are both improved to a great extent with T = 95% and FWHM = 12nm, keeping acceptable wavelength sensitivity of 1496nm/RIU within the near-infrared region. In addition, a sensitivity as high as 3476nm/RIU is obtained by optimizing the shape and size of fillet cavity. In general, the high FOM, transmittance and sensitivity achieved by our design may get further applications in biomedical science and nanophotonic circuits.