Optical study of 2D photonic crystals in an InP/GaInAsP slab waveguide structure
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Optical study of 2D photonic crystals in an InP/GaInAsP slab waveguide structure Rolando Ferrini1, David Leuenberger1, Mikaël Mulot2, Min Qiu2, Jürgen Moosburger3, Martin Kamp3, Alfred Forchel3, Srinivasan Anand2, and Romuald Houdré1 1 Institut de Micro et Opto-électronique, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland. 2 Department of Microelectronics and Information Technology, Royal Institute of Technology , Electrum 229, S-16440 Kista, Sweden. 3 Technische Physik, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany. ABSTRACT We report on the optical properties of two dimensional (2D) photonic crystals (PCs) deeply etched in an InP/GaInAsP step-index waveguide. Transmission (T) measurements through simple PC slabs and through one-dimensional (1D) Fabry-Pérot (FP) cavities between PC mirrors are reported and compared to theory. A 2D finite difference time-domain (FDTD) method combined to a phenomenological out-of-plane loss model is used to assess different loss contributions. The PC optical properties are deduced from the FP peak analysis. The origin of the high T level observed inside the stopgap is investigated.
INTRODUCTION In photonic crystal (PC) structures the periodic arrangement of different elements with strong dielectric contrast affects the properties of photons forbidding light propagation along specific directions within relatively large energy bands known as photonic band-gaps (PBGs) [1,2]. In the last few years it has been proved that, although an omnidirectional PBG is only possible in a three-dimensional (3D) PC, a two-dimensional (2D) PC combined to a vertical stepindex waveguide offers enough light control for integrated optics applications [3]. The potentials of this approach have been successfully demonstrated both in GaAs-based structures (λ ≈ 1.0 µm) [3] and in InP-based systems at telecommunication application wavelengths (λ ≈ 1.5 µm) [4]. In this paper we describe the optical characterization of quasi-2D PCs deeply etched into an InP/GaInAsP slab waveguide. The internal light source (ILS) technique is used to measure the transmission (T) spectra through simple PC slabs and one-dimensional (1D) Fabry-Pérot (FP) cavities formed between two PC mirrors. A 2D finite difference time-domain (FDTD) method is used to best fit the experimental data. The exact amount of out-of-plane losses is assessed and the hole depth/shape contributions are analyzed. The optical properties of the PC structures are determined and the origin of the high T level detected inside the stopgap is discussed.
EXPERIMENT Quasi-2D PCs consisting of a triangular lattice of air holes were fabricated on nominally undoped GaInAsP/InP heterostructures grown by metal organic vapor phase epitaxy (MOVPE) on n-InP substrates (see figure 1(a)). Moderate filling factor values (f ≈ 0.30) were chosen in order to minimize out-of-plane losses [3,4]. Such low f values result in a full gap only in the K6.3.1
200 nm
transverse electric (TE) polarization direction. The PC structures were etched normal
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