Berlin 2008 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 24: Photonic crystals II

HL 24.5: Talk

Tuesday, February 26, 2008, 10:30–10:45, EW 202

Silicon on insulator photonic crystal nanostructures for label free optical biosensing — •Thomas Zabel, Dominic F. Dorfner, Uli Rant, Gerhard Abstreiter, and Jonathan J. Finley — Walter Schottky Institut, TU Muenchen, Am Coulombwall 3, 85748 Garching

Silicon based photonic crystal (PC) nanostructures are of widespread interest for realizing optical waveguides, low-loss bends and nanoscale cavities. The mode frequencies of such cavities is highly sensitive to their local dielectric environment, making them interesting for sensitive label free optical bio-sensing. We have designed and realized 2D PC nanocavity sensors based on the biocompatible SOI material system by defining a triangular lattice of air-holes in a 300nm thick freestanding Si membrane. The 400nm lattice pitch results in a 2D PBG extending from ∼1.4−1.6µ m. A W1 waveguide is used to guide light into the structures and evanescently couple to point defect nanocavities defined in their immediate vicinity. Light from a tunable laser source allows measurements of cavity Q-factors and resonant frequencies by detecting radiation from the surface. Operating such structures in air and a micro-fluidic cell allow us to measure the cut-off wavelength of the PC waveguide and the cavity modes as a function of the local dielectric environment. We have optimized the cavity design and achieved Q-factors up to ∼ 46000 in air and observed mode shifts up to Δ λ=50nm upon immersing in various solvents. These structures allow local refractive index changes of Δ n/n < 0.001 to be detected. Perspectives for sensing non-specifically adsorbed proteins such as BSA will be discussed. Supported financially by the Nanosystems Initiative Munich