Photonic molecules for improving the optical response of macroporous silicon photonic crystals for gas sensing purposes

Abstract

In this paper, we report the benefits of working with photonic molecules in macroporous silicon photonic crystals. In particular, we theoretically and experimentally demonstrate that the optical properties of a resonant peak produced by a single photonic atom of 2.6 µm wide can be sequentially improved if a second and a third cavity of the same length are introduced in the structure. As a consequence of that, the base of the peak is reduced from 500 nm to 100 nm, while its amplitude remains constant, increasing its Q-factor from its initial value of 25 up to 175. In addition, the bandgap is enlarged almost twice and the noise within it is mostly eliminated. In this study we also provide a way of reducing the amplitude of one or two peaks, depending whether we are in the two- or three-cavity case, by modifying the length of the involved photonic molecules so that the remainder can be used to measure gas by spectroscopic methods.

Macroporous Silicon Filters, a Versatile Platform for NDIR Spectroscopic Gas Sensing in the MIR

“…Fabrication of macroporous silicon narrow filters.-Before photoelectrochemical etching, several pre-processes -i.e. implantation, oxidation, lithography, etc.-had to be carried out in order to prepare the samples -details can be consulted elsewhere [17][18][19][20][21][22] -. As a result of this initial step, the front surface of the samples was pre-structured with a square array of inverted pyramids separated by a pitch of 700 nm.…”

“…Recent studies reported proofs of concept showing that macroporous silicon PhCs with a cavity in the middle can be used as narrow filters for the selective and sensitive detection of gases. 17,18 The aim of this paper is to experimentally verify this point and to validate the technology in the entire mid-infrared band. The study begins by describing the optical response of several filters along the MIR -see Figure 1-.…”