Photonic crystal cavity based gas sensor

We have studied the response of a photonic crystal cavity to changes of the ambient refractive index. Transmission measurements of the cavity under different gaseous environments and pressures showed a linear dependence of the resonance wavelength on the refractive index of the ambient gas. A change of the refractive index by 10(-4) leads to a shift of the resonance by 8 pm, which is readily detectable due to the high quality factor of the cavity. The observed wavelength shifts agree well with finite-difference time domain simulations of the cavity. (c) 2008 American Institute of Physics.