Abstract-We have designed and fabricated waveguides that incorporate two-dimensional (2-D) photonic crystal geometry for lateral confinement of light, and total internal reflection for vertical confinement. Both square and triangular photonic crystal lattices were analyzed. A three-dimensional (3-D) finite-difference timedomain (FDTD) analysis was used to find design parameters of the photonic crystal and to calculate dispersion relations for the guided modes in the waveguide structure. We have developed a new fabrication technique to define these waveguides into silicon-on-insulator material. The waveguides are suspended in air in order to improve confinement in the vertical direction and symmetry properties of the structure. High-resolution fabrication allowed us to include different types of bends and optical cavities within the waveguides.Index Terms-Finite-difference time-domain (FDTD) methods, nanooptics, optical device fabrication, photonic bandgap (PBG) materials, photonic crystals (PCS), photonic crystal waveguides.

Photonic crystal planar circuits designed and fabricated in silicon on silicon dioxide are demonstrated. Our structures are based on two-dimensional confinement by photonic crystals in the plane of propagation, and total internal reflection to achieve confinement in the third dimension. These circuits are shown to guide light at 1550 nm around sharp corners where the radius of curvature is similar to the wavelength of light. © 2000 American Institute of Physics. ͓S0003-6951͑00͒04038-9͔The planar photonic crystal ͑PC͒ concept is a recent innovation 1 that can permit the miniaturization of integrated optical circuits to a scale comparable to the wavelength of light. In principle, this technology makes it possible to fabricate planar optical circuits with a packing density four to five orders of magnitude higher than the present state of the art, thus realizing the original objective of integrated optics.Waveguiding in a planar circuit requires confinement of the light in three dimensions. This can be achieved by making a three-dimensional ͑3D͒ PC. [2][3][4] However, fabrication of good quality 3D PC structures is a difficult process, and, in terms of fabrication, a more appealing approach is based on the use of the lower-dimensional PCs to achieve confinement of light in all three dimensions. That idea is employed in the case of the thin dielectric slab perforated with twodimensional ͑2D͒ PC. [5][6][7][8][9][10][11][12][13] In the vertical direction, light is confined to the slab due to total internal reflection ͑TIR͒, and in the lateral direction, light is controlled by the means of distributed Bragg reflection due to the presence of the 2D PC. The PC structure that we consider here consists of a periodic arrangement of holes etched into a planar Si slab suspended so that it is surrounded by air on both sides. We have studied the propagation of light in this structure using methods based on plane-wave expansion and the 3D finitedifference time-domain algorithm 9 to analyze Maxwell's equations. Kuchinsky et al. 12 have shown that a Si guide imbedded in a PC slab having a thickness equal to 0.5•pitch of the PC lattice supports two modes: one diffractive, from the periodic PC lattice, and one refractive from the contrast in the index of refraction between the core and the cladding. Johnson et al. 13 have shown in the case of a Si slab perforated with a triangular lattice of holes that there is a thickness limit for the PC waveguide above which the bandgap width significantly decreases. In agreement with that work we find that conditions for waveguiding are more restrictive in a waveguide with a finite third dimension than in a 2D PC of infinite extent in the third dimension. 14,15 The demonstration of waveguiding by photonic band gap ͑PBG͒ confinement is a difficult challenge, but a necessary achievement in order to realize the goal of planar optical circuits with higher levels of integration. A recent letter by Tokushima et al. 16 reports experiments on light propagation in a structure that lies well outside the p...

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Micromachined thermal heater platforms offer low electrical power consumption and high modulation speed, i.e. properties which are advantageous for realizing nondispersive infrared (NDIR) gas-and liquid monitoring systems. In this paper, we report on investigations on silicon-on-insulator (SOI) based infrared (IR) emitter devices heated by employing different kinds of metallic and semiconductor heater materials. Our results clearly reveal the superior high-temperature performance of semiconductor over metallic heater materials. Long-term stable emitter operation in the vicinity of 1300 K could be attained using heavily antimony-doped tin dioxide (SnO 2 :Sb) heater elements.

The prognosis in lung cancer depends largely on early stage detection, and thus new screening methods are attracting increasing attention. Canine scent detection has shown promising results in lung cancer detection, but there has only been one previous study that reproduces a screening-like situation. Here breath samples were collected from 122 patients at risk for lung cancer (smokers and ex-smokers); 29 of the subjects had confirmed diagnosis of lung cancer but had not yet been treated and 93 subjects had no signs or symptoms of lung cancer at the time of inclusion. The breath samples were presented to a trained sniffer dog squadron in a double-blind manner. A rigid scientific protocol was used with respect to earlier canine scent detection studies, with one difference: instead of offering one in five positive samples to the dogs, we offered a random number of positive samples (zero to five). The final positive and negative predictive values of 30.9% and 84.0%, respectively, were rather low compared to other studies. The results differed from those of previous studies, indicating that canine scent detection might not be as powerful as is looked for in real screening situations. One main reason for the rather poor performance in our setting might be the higher stress from the lack of positive responses for dogs and handlers.

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