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Rotating elliptical nanowire arrays as two-dimensional photonic crystals has been proposed and studied in this Letter. The analysis of the four lowest energy bands and the first bandgap width of some examples illustrates that the rotation and configuration of the primitive cell can have effects on the reducibility of the Brillouin zone. As the central element’s orientation changes, the irreducible Brillouin zone could be expanded to the whole first Brillouin zone. Special attention has been paid to the nanowire arrays with adjacent elements perpendicular to each other, and the irreducible Brillouin zone unexpectedly retracted back to the 1/8 of the first Brillouin zone though the symmetry of elements is lower than that of the square lattice. Meanwhile, the first bandgap width of the perpendicular array can be adjusted by the rotation of each primitive element.

Dual-grating structure thin-film silicon solar cells with different front and back grating periodicities are designed The geometrical parameters of both gratings are investigated. The reflection is greatly reduced by the front grating, whereas the absorption in the long wavelength is increased because of the back grating. The short circuit current of the combined structure is enhanced by 16.8% for a 1-\mu m thick c-Si layer compared with that of the conformal grating structure. The short circuit current can be further increased by creating a relative lateral displacement between the front and back gratings. The displacement results in a more remarkably enhanced absorption when the thickness of the active layer is reduced, indicating its importance in the design of ultra-thin high-efficiency solar cells.

Band structures of one-dimensional (1D) photonic crystals (PCs) containing dispersive left-handed metamaterials are studied theoretically. The results show that the structure possesses a type of photonic band gap originating from total internal reflection (TIR). In contrast to photonic band gaps corresponding to zero average refractive index and zero phase, the TIR gap exhibits sharp angular effect and has no polarization effect. It should also be noted that band structures of transverse electric (TE) and transverse magnetic (TM) mode waves are exactly the same in the PCs we studied.

Light scattering properties of back grating structures that composed of one-dimensional ZnO gratings and a flat 300-nm Al reflectors are investigated. Results show that grating structures cause an 8% reduction of the total reflectivity, as grating periods increasing from 620 to 1 435 nm, both the diffuse reflectivity and the haze parameter enhance drastically between 400 and 1 000 nm, whereas the diffraction angle at normal incidence reduce greatly, which agree with the values calculated from grating equation. It is concluded that rear gratings have the potential of scattering a substantial amount of incident light to specific angles and enlarging the optical path.

In this letter, a design with both metal nanoparticles and back diffraction gratings is put forward for enhancing the efficiency of thin film silicon solar cells. The coupling mechanism between the metal nanoparticles and silicon absorber layer, and that between the incident light and the modes of the silicon absorption layer through the grating layer are both analyzed. The interaction between the front metal nanoparticles and back gratings is analyzed, which substantially increases the light trapping by 58% compared to flat solar cell.

A bandpass filter with twin wideband channels in a single-layer guided-mode resonance grating is presented. Strong refractive-index modulation is used to support the excitation of multimode resonances TE1,0, TE1,1, TE2,0, TE1,2, and TE2,1, which are excited by the first and second diffraction orders, relate asymmetrical line shapes and broad low-transmission bands, where TE is the transverse electric. Taking advantage of narrow linewidth and sharp edge line shape in the spectra of TE2,v (v is the mode), a bandpass filter with form factors of 0.61 and 0.7 for long- and short-wave channels is presented to demonstrate this concept.

Reflection filters have various applications in optical communication and other systems. In this letter, we propose a narrowband high-reflection filter composed of dielectric and metallic layers, in which an optimized filter combined with an admittance-matching layer with broad stop band is achieved. The structure can be expressed as Sub | (HL)13H2L(HL)313Cr0.84H | air, with full-width at half-maximum (FWHM) bandwidth of 2.5 nm. Based on this structure, reflection filters with multi-peaks are presented, and the law of distribution of peak positions is drawn.