Synchrotron x-ray μ-tomography to model the thermal radiative properties of an opaque ceramic coating at T = 1000 K

Synchrotron x-ray μ-tomography has been used to reconstruct the three-dimensional view of a rough surface extracted from a heterogeneous ceramic coating composed of Pr2NiO4+δ. Radiographs with a resolution of 0.7 μm have been recorded at T = 300, 600, and 900 K. The analysis of surface geometry makes use of the geometrical optic approximation up to T = 900 K possible. Subsequently, a large number of rays (105) are impinged onto the numerical surface, as revealed by x-ray tomography, to reproduce the normal emissivity of the coating. This normal emissivity was obtained beforehand by infrared emittance spectroscopy at T = 1000 K. Comparison of the two approaches suggests that the optical contribution of the coating micropores can be integrated into the ray tracing code. The effective medium approximation is used for this purpose. Finally, the applicability of this hybrid approach is discussed.

Coupling. Theory of Coupling Loss of an Ion Exchanged Multimode Channel Waveguide to Optical Fibers

SummaryThe potential applicability of multimode integrated optical branching waveguides and couplers is limited primarily by their coupling loss to optical fibers. To get a reasonably detailed theoretical insight, the fiber-to- fiber coupling loss of a section of a multimode channel waveguide fabricated, e.g., by ion exchange in a glass substrate is calculated using a ray-optic approximation. An approach of the length-averaged coupling loss results in a simple and efficient calculation procedure which enables one to optimize the parameters of a channel waveguide for minimum coupling loss. Coupling losses as low as 2 dB and 0.25 dB can be obtained for single channel and sandwich structures, respectively, coupled to standard graded-index fibers.