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A highly efficient spatial beam splitter based on coupled cavity waveguide with surface taper modification structure is proposed. The beam splitter is analyzed with the finite difference time domain numerical method. By modifying the number of the coupled multi-channel taper cylinders along horizontal direction and the number of waveguides along vertical direction, the spatial profile of the electric field can be varied and the direction of Poynting vector can be changed.

Graphene derivatives, possessing strong Raman scattering and near-infrared absorption intrinsically, have boosted many exciting biosensing applications. The tunability of the absorption characteristics, however, remains largely unexplored to date. Here, we proposed a multilayer configuration constructed by a graphene monolayer sandwiched between a buffer layer and one-dimensional photonic crystal (1DPC) to achieve tunable graphene absorption under total internal reflection (TIR). It is interesting that the unique optical properties of the buffer-graphene-1DPC multilayer structure, the electromagnetically induced transparency (EIT)-like and Fano-like absorptions, can be achieved with pre-determined resonance wavelengths, and furtherly be tuned by adjusting either the structure parameters or the incident angle of light. Theoretical analyses demonstrate that such EIT- and Fano-like absorptions are due to the interference of light in the multilayer structure and the complete transmission produced by the evanescent wave resonance in the configuration. The enhanced absorptions and the huge electrical field enhancement effect exhibit potentials for broad applications, such as photoacoustic imaging and Raman imaging.

At present, it is very important to create new types of mirrors, nonlinear light frequency transformers and optical filters with controlled optical properties. In this connection, it is of great interest to study photonic crystals. Their dielectric permittivity varies periodically in space with a period permitting Bragg diffraction of light. In this paper, we have investigated the optical properties of mesoporous three-dimensional (3D) opal-type and one-dimensional (1D) anodic alumina photonic crystals, filled with different dielectrics, ferroelectrics and piezoelectrics. We have compared the optical properties of initial mesoporous photonic crystals and filled with different substances. The possibility of mesoporous photonic crystals using selective narrow-band light filters in Raman scattering experiments and nonlinear mirrors has been analyzed. The electromagnetic field enhancing in the case of exciting light frequency close to the stop band edges has been established. The optical harmonics and subharmonics generation in mesoporous crystals, filled with ferroelectrics and piezoelectrics was proposed.

Sol–gel technology was applied to fabricate Eu-doped BaTiO₃/SiO₂ multilayer structures by spinning on silicon and fused silica substrates. Eu photoluminescence (PL) was investigated depending on the annealing temperature of these structures. The samples demonstrate the room temperature luminescence corresponding to ⁵${\text{D}}_0\to {}^7$F_J ($J=1$, 2, 3, 4) transitions of trivalent europium with the most intensive band at 615 nm. For the structure on fused silica with Eu in the BaTiO₃ cavity, increase of the annealing temperature from $450^{\circ }$C to $700^{\circ }$C results in modification of the luminescence indicatrix and lowering of the luminescence intensity in the direction along the surface normal. For BaTiO₃/SiO₂ multilayer structure generated on silicon, scanning electron microscopy (SEM) analyses reveal disordering after annealing at $1000^{\circ }$C. This heat treatment provides also an increase of the Eu luminescence intensity.

This paper describes the theoretical investigation of enhancement in temperature sensitivity using one-dimensional (1D) symmetric defective photonic crystal (PC) containing Si (Silicon) and Bi₄Ge₃O${}_{12}$ (Bismuth Germanate, BGO) material. The proposed sensor consists of a defect layer (air defect) sandwiched between two 1D-PCs with a symmetrical and asymmetrical structure composed of Si and BGO, respectively. Sensor performance has been evaluated by calculating the transmittance spectra of the proposed structure. In order to obtain the transmittance spectra, a transfer matrix method (TMM) is employed. The principle of temperature sensing is based on the shift in the resonant wavelength (or peak) of the transmission mode with a change in temperature. This is due to the temperature-dependent refractive index of the Si and BGO layers. Analysis of the transmittance spectra shows that temperature sensitivity of 1D-PC structure can be enhanced by using a symmetric defective PC with and without an external defect layer over asymmetric defective PC. It is found that symmetric defective PC with and without defect shows sensitivity equal to 0.173nm/^∘C and 0.140nm/^∘C, whereas asymmetric defective PC shows 0.125nm/^∘C, for the same parameters. Further, the results show that symmetric defective 1D-PC (without the presence of any external defect layer) gives a higher Q-factor than a symmetric and asymmetric defective 1D-PC with an external defect layer. The proposed structure is cost-effective, easy to fabricate and compact in size.