We present an infrared perfect absorber model composed of gold nanobars and a photonic microcavity. The inevitable losses in metamaterials are taken as an advantage for high absorbance efficiency. By adjusting the structural geometry, the device can be used for refractive index sensing. In our calculation with a spacer thickness H = 90 nm it can yield more than 99% absorbance in the near-infrared frequency region. The full-width at half-maximum can be realized up to an extremely narrow value of 40.8 nm and the figure of merit can be obtained as high as 357. For sensing applications with a perfect absorber, our work can serve as a model of coupling between the localized surface plasmon within nanoparticles and the propagating surface plasmon along the planar metal layer. The novel concept has great potential to maintain its performance of localized surface plasmon in practical applications.

Based on complementary fractal geometry structures, we design a novel infrared quasi-three-dimensional (3D) nanocavity with a localized enhanced field with multiband resonant frequencies. The fractals offer the nanostructure two important characteristics, multiband functionality and a subwavelength effect. The electric field, power flow, and the field intensity distributions are given to indicate the internal mechanism of the localized enhanced field in the nanocavity. Additionally, the effective medium method is established to retrieve the permittivity and impedance of the structure. It is shown that a strongly enhanced localized field is achieved in the nanocavity at two different resonant frequencies by using the finite difference time domain method. The field intensity in the nanocavity is enhanced by a factor of up to 60 times over that of the incident light because of the important contribution of the loss factor in the permittivity. The surface plasmon hybridization is thought to play an important role in the strong localized field enhancement. The multiband property and high localized intensity offer the nanocavity great potential for applications in surface enhanced Raman scattering and other nanoscale novel devices.

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Abstract6G is believed to go beyond communication and provide integrated sensing and computing capabilities for a vision of Connected Intelligence with everything connected, everything sensed, and everything intelligent. Integrated sensing and communication will play a vital role for the fusion of physical and cyber worlds. The exploration of higher frequency bands, larger bandwidth, and more advanced large antenna technologies is paving the way towards the goal. In particular, the study of THz opens the possibility to have high resolution sensing and imaging capability on a communication mobile device. In this paper, we take a step along this direction and justify such possibility by building a THz sensing prototype with millimeter level imaging resolution while considering the physical aperture constraint of typical mobile device.