Abstract: The present invention provides a method for fast switching of optical properties in photonic crystals using pulsed/modulated free-carrier injection. The results disclosed herein indicate that several types of photonic crystal devices can be designed in which free carriers are used to vary dispersion curves, stop gaps in materials with photonic bandgaps to vary the bandgaps, reflection, transmission, absorption, gain, or phase. The use of pulsed free carrier injection to control the properties of photonic crystals on fast timescales forms the basis for all-optical switching using photonic crystals. Ultrafast switching of the band edge of a two-dimensional silicon photonic crystal is demonstrated near a wavelength of 1.9 ?m. Changes in the refractive index are optically induced by injecting free carriers with 800 nm, 300 fs pulses. Band-edge shifts have been induced in silicon photonic crystals of up to 29 nm that occurs on the time-scale of the pump pulse.

Abstract: The invention relates to a method for the analysis of the qualitative and/or quantitative composition of fluids with at least one light source, one interaction space area in which the light interacts with the fluid, and one detection device for detecting the interaction between the fluid and the light. The device and the method are characterised in that a photonic the gap structure is provided creating a greater reduced group velocity in the interaction space area and thus an increased dwell time for the light in the interaction space area. This means that the interaction space area can be considerably reduced in size, which allows a compact design of the device.

Abstract: The present invention provides a method for fast switching of optical properties in photonic crystals using pulsed/modulated free-carrier injection. The results disclosed herein indicate that several types of photonic crystal devices can be designed in which free carriers are used to vary dispersion curves, stop gaps in materials with photonic bandgaps to vary the bandgaps, reflection, transmission, absorption, gain, or phase. The use of pulsed free carrier injection to control the properties of photonic crystals on fast timescales forms the basis for all-optical switching using photonic crystals. Ultrafast switching of the band edge of a two-dimensional silicon photonic crystal is demonstrated near a wavelength of 1.9 &mgr;m. Changes in the refractive index are optically induced by injecting free carriers with 800 nm, 300 fs pulses. Band-edge shifts have been induced in silicon photonic crystals of up to 29 nm that occurs on the time-scale of the pump pulse.