Design and fabrication of two-dimensional hexagonal photonic crystals with a linear waveguide in erbium doped GeO2-Bi2O3-PbO-TiO2 glasses

In this work, we designed and recorded two-dimensional Hexagonal Photonic Crystals (2D-HPC) layers, with a linear waveguide, in erbium doped GeO 2 -Bi 2 O 3 -PbO-TiO 2 glassy films, by combining the techniques of holographic recording and femtosecond (fs) laser micromachining. The 2D-HPC is recorded holographically in a photoresist film coated on a glass substrate by exposing the sample to the same interference pattern twice and rotating the sample of 60° between the exposures. After the development a two dimensional hexagonal array of photoresist columns remain on the glass substrate. The recording of the waveguide is made by a fs laser micromachining system focused at sample surface. The laser spot produces the ablation of the photoresist columns generating a defect line in the periodic hexagonal array. After the recording of the photoresist template, the erbium doped GeO 2 -Bi 2 O 3 -PbO-TiO 2 film is evaporated on the photoresist and finally the photoresist template is removed using acetone. The design of the geometrical parameters of the 2D-HPC is performed by calculation of the dispersion mode curves of the photonic crystal using a 2D finite element method. The proper geometrical parameters depend on both the refractive index of the glass film and thickness. Such parameters as well as the period of the 2D-HPC have been defined in order to obtain a photonic band gap in the region of erbium luminescence band. In such condition the erbium luminescence will propagate only through the waveguide.