Showing papers by "Martin Kristensen published in 2011"

Direct slow-light excitation in photonic crystal waveguides forming ultra-compact splitters.

Abstract: Based on a series of 1x2 beam splitters, novel direct excitation of slow-light from input- to output-region in photonic crystal waveguides is investigated theoretically and experimentally. The study shows that the slow-light excitation provides over 50 nm bandwidth for TE-polarized light splitting between two output ports, and co-exists together with self-imaging leading to ~20 nm extra bandwidth. The intensity of the direct excitation is qualitatively explained by the overlap integral of the magnetic fields between the ground input- and excited output-modes. The direct excitation of slow light is practically lossless compared with transmission in a W1 photonic crystal waveguides, which broadens the application-field for slow-light and further minimizes the size of a 1x2 splitter.

Photonic Crystal Biosensor Chip for Label-Free Detection of Bacteria

Abstract: Narrow polarization-mixing resonances in planar photonic crystals are studied as candidate components for label-free refractive index sensors for detecting bacteria causing sepsis through the identification of DNA strands

Relaxed fabrication tolerance for self-imaging photonic crystal waveguide splitters using a tapered multimode interference region.

Abstract: The power imbalance between different waveguide outputs is compensated by manipulating the dispersion of the guided propagation in the multimode interference (MMI) region. This is attainable using a tapered region at the beginning of the MMI region that has been verified through simulation and experiment. From this, the fabrication tolerance for the diameters of holes in a tapered 1×3 photonic crystal waveguide (PhCW) splitter is relaxed up to a range of at least 27 nm. The output power is well-balanced to within 1 dB. The effective bandwidth of the splitters shifts only around 13 nm, for a reduction of 10 nm in the diameter of the PhCW holes. The optimized component is an outstanding ultracompact 1×3 splitter for the photonic integrated circuit (PIC).

CHARGED PARTICLE BEAM PROFILE DETECTOR BASED ON Yb-DOPED OPTICAL FIBERS ∗

Abstract: A radiation robust, high dynamic range beam profile detector based on scintillating fibers will be presented. The beam profile detector has been developed for particle therapy type ion beams of multiple hundreds MeV/n in the intensity range from 10 5 to 10 9 ions/s as a simple and less expensive replacement for MWPC based detectors. Scintillating fibers are typically based on doped polymers, which are sensitive to radiation damage. Here we report on the advantage of using silica optical fibers doped with rare-earth elements for the purpose of detecting ionizing radiation. Specifically, we find that ytterbium doped fibers generate a strong emission signal in the near-infrared from the Yb 3+ state when penetrated by ionizing radiation, and that the fiber emission has a high radiation resistance. We demonstrate the use of such fibers in a beam profile detector for charged particle beams in medical applications (radionuclide production and hadron therapy); more generally they are a promising alternative for prolonged use in ionizing radiation, such as accelerator diagnostics equipment or space applications.