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We proposed a new method for designing graded index lens using liquid crystal infiltration into annular photonic crystals. Applying an external nonuniform voltage in the transverse direction perpendicular to the direction of light propagation yields different orientation of liquid crystal molecules inside the photonic crystal unit cells. As a result, a gradient refractive index was modulated. We numerically investigate focusing properties of the designed graded index structure using plane-wave expansion and finite-difference time-domain methods. The gradient refractive index profile was adjusted by varying the nonuniform voltage excitations, which consequently altered the focal distance of the graded index structure. A wide tuning range of 1856 nm was achieved for focal distance by the proposed graded index structure. This feature can be implemented for planning a flat lens with tunable focal distance based on electro-optic effect. These achievements may have future applications in some optical devices such as near-field imaging and scanning.

An aryl triazene (3-hydroxy-3-phenyl triaz-1-en-1-benzoic acid) was synthesized and first utilized as a highly selective ligand for the preparation of a novel optical sensor for nickel ion determination in aqueous solutions. The ligand was chemically bonded to a transparent agarose membrane after its epoxy activation for this purpose. Study of the complex formation between the ligand and some metal ions including Ni2+, Cu2+, UO22+, Cr3+, Fe3+, Mg2+, Co2+, Pb2+, Ca2+, and Ag+, in aqueous media, indicated a high selectivity towards Ni2+and Cu2+for it. After immobilization of the ligand on the agarose membrane, its selectivity for Ni2+was substantially increased and a more distinct isosbestic point was observed. In addition, a sharp color change from yellow to green was detected upon contact with a solution of nickel ion at pH 9. The effects of pH, ligand concentration, response time, and interfering ions were carefully studied for the optical sensor. No significant interference from the above metal ions was observed. The absorbance of the membrane at 420 nm was linear for Ni2+concentrations up to 9 × 10−4mol L−1with an R2of 0.991. A detection limit of 2.74 × 10−6mol L−1, repeatability of 2.2%, and reproducibility of 4.2% were obtained for the Ni2+quantitation. The optical sensor was used for the analysis of nickel ion in some river water samples with satisfactory results.

Using the Dirichlet-to-Neumann map method, we have calculated the photonic band structure of two-dimensional metallodielectric photonic crystals having the square and triangular lattices of circular metal rods in a dielectric background. We have selected the transverse electric mode of electromagnetic waves, and the resulting band structures showed the existence of photonic bandgap in these structures. We theoretically study the effect of background dielectric on the photonic bandgap.

In this paper, we theoretically study the electromagnetic surface waves localized at the interface between a homogeneous dielectric medium and a semi-infinite, one-dimensional photonic crystal (1D PC). The semi-infinite 1D PC is made of alternative layers of right-handed (RH) and dispersive left-handed (LH) materials in the presence of a liquid crystal (LC) cap layer. In this structure, we derive the surface waves dispersion relation with tunable switching and localization by using an analytical direct matching procedure within the Kronig–Penny model. It is shown that, for both of layer arrangements, the variation of molecules orientation of the LC cap layer acts as an effective tool to tune the type (tuned switching) and localization of the surface waves and it also can create a surface mode with maximum localization in the first frequency bandgap.