We propose plasmonic metal-insulator-metal (MIM) metamaterial designs for the sensing of two infrared wavelength bands, the mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) band by using a photon sorting technique. The proposed structures can capture light effectively on the metasurfaces based on coupling of free space energy to a subwavelength plasmonic mode. Photon sorting can be performed such that the incident light with a broad spectrum upon the metasurfaces can be "split" according to wavelength, channeling different spectral bands to different physical regions of the array on the surface where it is then absorbed by the insulator. Two different structures described in this work are (1) Square-type structure which consists of MIM resonators being periodically arranged to form a polarization independent sensor and (2) Meander-type structure which consists of MIM resonators being connected to form the meander shaped sensor. Mercury Cadmium Telluride (HgCdTe) posts are used as absorbing material within the MIM structure to generate free carriers and allow for collection of carrier charges. The proposed structures have compact designs and exhibit efficient light splitting and absorption for the IR spectral band. Structural and material properties, the electric field distribution and Poynting vector fields at the resonance frequencies are provided. Applications include thermal imaging, night vision systems, rifle sights, missile detection and discrimination, dual bandwidth optical filters, light trapping, and electromagnetically induced transparency.
Two-dimensional compound gratings (2dCGs) are capable of π-radian difference phase resonances (PRs). Circulation and concentration of s- and p-polarized light incident on 2dCG metal structures are studied. In prior work, it has been shown that PRs can occur for s- and p-polarized light in one-dimensional compound gratings (ldCGs). In contrast, the structure studied in this work has two asymmetric holes in the unit cell, each filled with a material of high dielectric permittivity (Epsilon=l0.84) and can support PRs in 2dCGs in the spectral range from 8 to 12 GHz. Due to asymmetry within the system, the two apertures react differently to the incident light and support polarization dependent PRs that are resonantly excited within the apertures. It is shown that PRs occur in 2dCGs with similar characteristics of ldCGs, such as having narrow bandwidths, high Q values, and high concentrations of electromagnetic fields. However, PRs occurring on 2dCGs have a benefit of manipulating in more numerous ways as compared with ldCGs. As the incident light excites waveguide cavity modes, the fields in the corresponding neighboring cavities in 2dCGs are coupled by circulations of counter-propagating modes and the π-radian phase differences produce a concentration and narrowband inversion of the transmissivity/opacity. The dependencies of bandwidth and wavelength of the PRs on structural and material properties, polarization of the incident beam, as well as the Poynting vector fields are described. Applications include narrow bandwidth optical filters, light trapping, antireflection coatings, waveguiding structures, and electromagnetically induced transparency.
Optical metasurfaces demonstrate outstanding capabilities of optical parameters modifications by changes in the structural architecture at the nano-scale level. We demonstrate results of electrophoretic experiments that modify the structure of a metasurface by using diamond nanoparticles with sizes much smaller than the wavelength of light; the nanoparticles are suspended in an aqueous solution and a uniform electric field is applied. The electric field controls the concentration of nanoparticles inside the sub-wavelength apertures and on the top plane of the metasurface. The higher concentration of diamond nanoparticles increases the refractive index of the suspension as well as increasing scattering and absorption. Results of optical material parameter characterization for a wavelength of 512 nm are provided for different concentrations of the diamond nanoparticles dispersions.