Showing papers by "Angel Rodríguez published in 2017"

Enhanced geometries of macroporous silicon photonic crystals for optical gas sensing applications

Abstract: A macroporous silicon photonic crystal is designed and optimized theoretically for its use in gas sensing applications and IR optical filters. Light impinges perpendicularly onto the sample surface (vertical propagation) so a three-dimensional (3d) structure is used. For gas sensing, a sharp resonance is desired in order to isolate an absorption line of the gas of interest. The high Q-factors needed mandate the use of a plane defect inside the PhC to give rise to a resonant mode inside the bandgap tuned to the gas absorption line. Furthermore to allow gas passage through the device, an open membrane is required. This can affect the mechanical resilience. To improve the strength of the photonic crystal the pores are extended after the “active” 3d part. The number of modulations, and the extension length have been optimized to obtain the largest Q-factor with reasonable transmitted power. These proposed structures have been experimentally performed, probing an enhancement of almost an order of magnitude in the Q-factor in respect with the basic case. Simulations considering CO2 have been performed showing that the proposed structures are promising as precise optical gas sensors.

Effect of fabrication tolerances in macroporous silicon photonic crystals

Abstract: Macroporous silicon photonic crystals show a great potential for a range of applications such as optical sensing or signal processing. These applications require tight fabrication tolerances. In particular, the effect of process variability in 3-d photonic crystals and out of plane propagation has been seldom studied in literature. In this paper we report the effect fabrication imperfections on the spectral response of macroporous silicon photonic crystals. To quantify fabrication disorder and its influence, several 3-d macroporous silicon structures were fabricated consisting of modulated pores arranged in a square lattice. The pore modulation is similar to a stretched sinusoidal waveform. Lattice pitch is 700 nm, pore diameter is in the range from 250 nm to 520 nm, and modulation period is 1.2 μm. The samples were characterized by SEM inspection and the actual etched pore profiles extracted. The statistical analysis of the profiles reveals two main sources of randomness: radius variability and modulation period irregularity. Surface roughness and asymmetry do not seem to play a major role. Several FDTD simulations have been performed based on the statistical parameters extracted, and the results are compared to actual FT-IR measurements of the fabricated samples. The obtained results show that, in general, the dispersion in z period has the most severe effect in the structure’s optical response.

Improved transmission and thermal emission in macroporous silicon photonic crystals with 700 nm pitch

Abstract: In this paper we study the transmittance and the emission response of two different macroporous silicon structures with cavities. The aim is to evaluate the viability of these structures to be employed in a future gas sensor device.

Development of gas sensors based in photonic crystal slabs

Abstract: This work describes an innovative application of structures of photonic crystal slabs for gas sensors. Structures consisting in double ring have been studied by simulation. Their working mechanism is based in the effect of a given target gas in the pores of the slab. The effect pursued is to translate the variation of refraction index of the gas inside the pores into a shift in the position of peaks of transmission associated to resonances in the device.