The DBR filters comprised 20 porous layers with alternating low and high refractive indices. The MM-102 concentration rugate filters were fabricated by sinusoidal modulation of refractive index with 16 and 32 periods. The time-dependent current profiles for anodization were calculated based on experimentally determined

dependencies on current density of the effective refractive index (calculated using the Bruggeman model [8] from porosity values) and of porous silicon formation rate. The power supply for the anodization process was provided with NI LabView™ controlled Gossen Metrawatt PSP-1500 power source (Gossen Metrawatt, Nürnberg, MK-0457 chemical structure Germany). The current density for all filters fabricated in this work was set between 20 and 70 mA/cm2. All photonic crystals were designed and fabricated to have a central wavelength λ 0 in the visible spectrum. An optical setup was constructed in order to measure the tunability induced by tilting and pore-filling of a photonic crystal (Figure 1). The setup consisted of a halogen lamp (12 V, 50 W) emitting light in the visible and near-infrared region, an Avantes FC-UV400-1-ME (Avantes, Apeldoorn, the Netherlands) optical patch cable guiding the light from the halogen lamp towards the porous silicon photonic crystal, a plano-convex GSK1120212 datasheet lens to collimate the diverging light beam from the optical fiber patch cable, a manual rotation mount with 360° angle of rotation with minimum

precision of 2° angle of rotation, and finally an AvaSpec-2048 spectrometer (Avantes). Light reflected from the photonic crystal was guided to the spectrometer by a fiber. The entire setup was assembled on an optical breadboard with all components being firmly fixed to avoid vibrations. The photonic crystal was attached to a holder which was fixed on the rotational mount. Normal incidence of the collimated light on the photonic crystal was chosen. The AvaSpec-2048 spectrometer input fiber was fixed on another optical sliding rail with its position synchronized with the

angle of rotation mount. To measure the influence of tilting the photonic MRIP crystal on the shift of the central wavelength to λ θ , the rotational mount was rotated manually from 0° (normal incidence) to 50° in steps of 10°. Figure 1 Optical setup for measurements of the spectrum of a photonic crystal at various tilting angles. In order to measure the dual tunability with the pore-filling and the tilting, a closed chamber with dedicated inlet and outlet orifices for vapor or liquid, an anti-reflection glass window, and a holder for the porous Si photonic crystal was constructed. Ethanol vapor was pumped into the closed chamber by a self-designed circulating system through the inlet orifice and left through the outlet orifice. The spectrometer detector fiber was synchronized to the rotation in such a way that this detector fiber was always aligned to the light reflected from the crystal.