Available online at www.sciencedirect.com Physica E 17 (2003) 418–419 www.elsevier.com/locate/physe Linear optical properties and photonic mode dispersion in GaAs/AlGaAs photonic crystal slabs M. Patrini a ; * , M. Galli a , M. Agio a , L.C. Andreani a , D. Bajoni a , G. Guizzetti a , L. Businaro b; c , E. Di Fabrizio b; c , F. Romanato b; c , A. Passaseo c a INFM and Dipartimento di Fisica “A. Volta”, Universit a di Pavia, Via Bassi 6, 27100 Pavia, Italy b TASC-INFM Nanolithography Beamline, Synchrothron Light Source, 34012 Basovizza-Trieste, Italy c NNL-INFM, Universit a di Lecce, via per Arnesano, 73100 Lecce, Italy Abstract GaAs/AlGaAs photonic crystal waveguides with unconventional tilted-square lattices and dierent lling factors are fully investigated by means of variable angle reectance spectroscopy, which yields the photonic band dispersion, and theoretical calculation of both reectance spectra and photonic band structure. ? 2002 Elsevier Science B.V. All rights reserved. PACS: 42.70.Qs; 81.07.-b Keywords: Photonic crystals; Optical spectroscopy; Patterned waveguides In the last few years there has been considerable interest in two-dimensional (2D) photonic crystal waveguides, also known as photonic crystal slabs, as they can be used to control the propagation of light in the visible and near-infrared spectral range [1]. Recently, it was shown [2] that a complete 2D photonic gap can be achieved in a square lattice of rotated square rods in a range of lling factors near to the close-packing condition. In this work, we present the experimental and theoretical investigation of 2D tilted-square lattice photonic crystals patterned in a GaAs/AlGaAs waveguide. The waveguide, grown in a horizontal LP-MOCVD system, was characterized by near-normal incidence reectance and spectroscopic ellipsometry: as a * Corresponding author. Tel.: +39-0382-507-709; fax: +39- 0382-507-563. E-mail address: patrini@sicavolta.unipv.it (M. Patrini). result the values of 576 nm for the GaAs core and of 1:63 m for the Al 0:25 Ga 0:75 As cladding thick- nesses were obtained. The waveguide was patterned using X-ray lithography with a gold mask previously prepared by electron-beam lithography, obtaining samples with the same lattice (tilted-square, lattice constant a = 500 nm), but dierent basis. In order to keep the guiding properties of the structure, both the core and part of the cladding were etched. Here we present the spectroscopic characterization of two samples: RUN3, whose basis is a dielectric pillar (side 0:51a, lling factor f =0:26) and L2, whose more complicated basis is a square air ring in dielectric (internal side 0:32a, external side 047a, lling factor f =0:88). The photonic band structure was derived analyzing the variable angle-reectance spectra of the samples, a method rstly developed by Astratov and coworkers [3]. The spectra were taken in the 0.5–1:5 eV region 1386-9477/03/$ - see front matter ? 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S1386-9477(02)00900-1