Photonic band gap materials, also known as photonic crystals, are very promising optical materials because of their particular properties to interact with light. They consist of materials with a periodical variation of their refractive index in one, two or three spatial dimensions and can be seen as a generalization of the well-known multilayer coatings. The most relevant result of this periodic variation is that the propagating photons must obey special dispersion relations, very different from those found in common materials. Since these dispersion relations are analogous to the bands in electronic materials, they are known as photonic bands. Photonic crystals are manufactured by several methods, depending on their dimensionality and on the used base materials. In this work we will focus on two-dimensional photonic crystals based on macroporous silicon made by electrochemical etching of silicon wafers previously patterned with a standard photolithography method.

In order to characterize these materials, it is important to be able to measure their photonic bands. We have developed a characterization procedure for these photonic crystals based on angle-resolved spectroscopic reflectometry and on the comparison of the measurement with the corresponding model simulation. The specific lattice constants of the studied photonic crystals range from 4 to 11 microns, which results in photonic bands in the spectral range of the Mid-IR. We have adapted the existing photonic band measurement techniques to this spectral range using a FTIR spectrometer equipped with a reflection attachment. Furthermore, we have implemented numerically the model for the interaction of the incident light with the photonic structures and we will show the results of the comparison between measurement and simulation. Finally, we will demonstrate that the same technique can be extended to polarimetric measurements to improve the recognition of the photonic bands.

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1. Fabrication of Silicon Oxide Microneedles from Macroporous Silicon