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A 60° photonic crystal waveguide bend with improved transmission characteristics

Moghaddam M. K., Mirsalehi M. M., Attari A. R.

Optica Applicata

2009

Vol. 39, nr 2

307-317

In this paper, a 60° waveguide bend is designed in a two-dimensional (2D) photonic crystal (PC) slab to provide high transmission over a large bandwidth. We apply geometrical modification in the bend region to improve the transmission characteristics. This modification results in increasing the relative bandwidth from 6.5% to 25.7% of photonic band gap width. Using the effective refractive index, the structures designed are simulated by the 2D finite-difference time-domain (FDTD) method. As a specific application, we use the improved bend structure in a PC waveguide directional coupler and show that the drop output increases significantly.

Optimization of two- dimensional photonic crystal waveguides for TE and TM polarizations

Danaie M., Attari A. R., Mirsalehi M. M., Naseh S.

Optica Applicata

2008

Vol. 38, nr 4

643-655

In this paper, we optimize the geometries of some 2D photonic crystal waveguides to increase their single-mode bandwidths for TE and TM polarizations. Using the Plane Wave Expansion (PWE) method combined with optimization algorithm, we find the local maxima as well as the global maximum. A photonic crystal waveguide geometry is proposed which has a single-mode normalized bandwidth of 41% for TM polarization. This value is about 7% greater than the corresponding value for the commonly used square lattice of dielectric rods in which a row is removed. Also, some waveguide geometries are proposed for TE polarization and it is shown that one of these geometries can provide a single-mode bandwidth of 39%, while the widest bandwidth reported so far for the TE case is 21%. The dielectric material used for both cases is GaAs with a dielectric constant of 11.4.