Structural and optical studies of porous silicon buried waveguides: Effects of oxidation and pore filling using DR1 dyes J. Charrier a, * , M. Kloul b , P. Pirasteh a , J.-F. Bardeau b , M. Guendouz a , A. Bulou b , L. Haji a a Laboratoire d’optronique, CNRS-UMR 6082 – FOTON, BP 80518, ENSSAT 6 rue de Kerampont, 22305 Lannion Cedex, France b Laboratoire de Physique de l’Etat Condense ´, CNRS-UMR 6087, Universite ´ du Maine, 72085 Le Mans Cedex 09, France Received 18 July 2006; received in revised form 16 November 2006; accepted 1 December 2006 Available online 15 February 2007 Abstract This paper deals with the structural and optical properties of buried waveguides manufactured from mesoporous silicon films (as-formed porous silicon layers, after oxidation, after filling with active DR1 dyes). It is shown that the oxidation process only induced a weak morphology transformation. The 2D profiles of cross-sections of the waveguides by micro-Raman mapping were done in order to check the oxidation rate and to probe the DR1 filling of the layers. This latter appeared homogeneous but surprisingly is greater in the weaker porosity layer. The light propagation through these different waveguides was observed and losses were measured and analyzed. The losses decreased after oxidation but they increased after filling. Ó 2006 Elsevier B.V. All rights reserved. 1. Introduction Optical waveguides are one of the most elementary com- ponents in photonic integrated circuits. They play a role in the propagation of light and in the connection of optoelec- tronic components (lasers, detectors, ...). Buried wave- guides or rib/ridge waveguides are used in practical applications. Silicon is a material of great interest for the manufacture of photonic devices because it is obviously compatible with silicon-based microelectronics. Therefore, silicon has already been investigated in combination with SiO 2 to produce waveguides [1,2]. Another way to produce optical waveguides is to use porous silicon layers. The elec- trochemical etching of bulk silicon substrate allows a broad range of porosities and refractive indices to be obtained. Porosity is modulated by changing current density during the anodisation process [3]. The thickness of the obtained porous silicon (PS) layer is defined by the anodisation time. Using this principle, different types of PS waveguides have been manufactured. The guiding layer is composed of a PS layer with a low porosity (high refractive index) and the cladding layer is also a PS layer but with a higher porosity (low refractive index) [4–10]. Once obtained, the waveguides were oxidized to extend the operating wave- length range into the visible wavelength spectrum. Such an approach was used to form either rib or buried wave- guides. Propagation losses of 0.3–5 dB cm À1 in the visible and NIR spectra were demonstrated for oxidized porous silicon waveguides (OPSW) [4–10] whereas losses were higher for porous silicon waveguides (PSW) (5– 10 dB cm À1 ). But among these values, the lowest losses were often obtained after a densification step of oxidized porous silicon waveguides. Nevertheless, another inherent feature of porous silicon material is its open pore network. In principle, this can be used to modify the waveguide property in situ, by filling the pores with other materials. Depending on the properties of the materials, they impart active functions that could be used in optical components [11,12] or in sensors [13,14]. In this study, we used buried oxidized porous silicon 0925-3467/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2006.12.003 * Corresponding author. Tel.: +33 2 96 46 91 14; fax: +33 2 96 46 90 76. E-mail address: joel.charrier@univ-rennes1.fr (J. Charrier). www.elsevier.com/locate/optmat Optical Materials 30 (2007) 431–437