Berlin 2008 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 6: Photonic crystals I
HL 6.4: Vortrag
Montag, 25. Februar 2008, 10:15–10:30, EW 201
Gas sensing using photonic crystal cavities — •Thomas Stichel, Thomas Sünner, Thomas Schlereth, Sven Höfling, Soon-Hong Kwon, Martin Kamp, and Alfred Forchel — Technische Physik, Universität Würzburg, Am Hubland, 97074 Würzburg
Cavities in two-dimensional photonic crystals (PhC) can localize light in mode volumes on the order of a cubic wavelength. Due to the high quality factor of the cavities, which can be as high as 106, the spectral position of the resonance can be a very sensitive probe for local changes of the refractive index.
We have studied the dependence of the resonance wavelength of PhC cavities on the type and pressure of the ambient gas. The cavities are based on photonic crystals etched into GaAs membranes. A small change of the lattice constant or the width of a W1 PhC waveguide over a few lattice constants is used to provide the optical confinement. The transmission measurements were performed in a box that can be evacuated or filled with different gases. Light from a tunable laser source at 1.55 µ m is used to probe the resonance of the cavities. Measurements of the cavity resonance in different gaseous environments (N2, SF6, He) show a a clear dependence of the resonance on the refractive index and the pressure of the gas. Changes of the refractive index on the order of 2*10−4 can be readily detected and are in good agreement with three dimensional finite difference time domain calculations.