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Particulate density currents, such as pyroclastic flows and turbidity currents, are prone to flow in a supercritical state, due to their small density difference in relation to the ambient fluid. Facies deposited in supercritical-flow conditions are therefore likely to be common, yet their recognition and analysis remain difficult in the stratigraphic record. This is commonly ascribed to the poor preservation potential of deposits from high-energy supercritical flows. However, the number of documented flume datasets on supercritical-flow dynamics and sedimentary structures is very limited compared to available experiments on subcritical flows, and our inability to identify and interpret such deposits might also be due to insufficient knowledge. This work presents the results of systematic experiments spanning the full range of supercritical-flow bedforms (antidunes, chutes-and-pools, cyclic steps) developed over mobile sand beds of variable grain sizes. Flow character and related bedform patterns are constrained through time-series measurements of bed configurations, flow depths, flow velocities and Froude numbers. The results allow the refinement and extension of current bedform stability diagrams in the supercritical-flow domain. Sedimentary structures associated with the development of supercritical bedforms under variable aggradation rates are revealed by means of a synthetic aggradation technique and compared with examples from field and flume studies. Image sequences show the direct coupling of flow processes, bed configurations and resultant sedimentary structures for selected supercritical bedforms. Aggradation rate, which is highly variable in pyroclastic events, is observed to bear an important influence on the geometry of supercritical-flow structures, and it should be held in consideration for the identification and mutual distinction of supercritical bedforms in the volcaniclastic record.

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A compact, mass producible Silicon On Insulator (SOI) based pressure sensor consisting of a folded Micro Ring Resonator (MRR) on a circular diaphragm is successfully designed, fabricated and characterized. An application of pressure deflects the diaphragm, causing stress in the MRR, which elongates the waveguide length and changes the effective refractive index of the guided mode. This results in a shift in its resonant wavelengths, which represents the applied pressure. This integrated device is successfully fabricated and a linear dependence between the resonance wavelength shift and the applied pressure at a constant temperature is measured. Such a pressure sensor finds applications in environments in which only minimal invasion is tolerated.

A compact, mass producible Silicon On Insulator (SOI) based pressure sensor consisting of a folded Micro Ring Resonator (MRR) on a circular diaphragm is successfully designed, fabricated and characterized [1-3]. The MRR is designed to be single mode for TE polarized light at 1550 nm. The folded MRR has a total length of 1500 μm which is folded to cover an area of 50X400 μm2 and has a guide-width of 450 nm. The circular diaphragm having a diameter of 1350 μm and a thickness of 15 μm is fabricated by reactive ion etching from the substrate side. Light is coupled into the MRR through the “in” port and measured at the “through” port using grating couplers. An application of pressure deflects the membrane, causing stress in the MRR, which in turn changes the effective refractive index the waveguide [4]. This results in a shift in its resonant wavelengths, which represent the applied pressure. Figure 1A shows the measured linear dependence between the resonance wavelength shift and the applied pressure at a constant temperature. Figure 1 B shows a SEM image of part of the membrane with MRR and Figure 1 C shows a schematic of the folded MRR. Such a pressure sensor finds applications in environments in which only minimal invasion is tolerated, such as in medical instrumentation.

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One of the important issues of System-on-a-package integration is the interconnection between independent Photonic Integrated Circuits (PICs). In this work, this issue is addressed by the use of Vertical Grating Couplers (VGCs) as the element for the interconnection between two Silicon-on-Insulator (SOI) PICs. Theoretical simulations using the finite-difference time-domain (FDTD) computational technique have shown that the coupling efficiency can be at least as good as 41%. In order to prove the principle, two SOI-PICs fabricated in ePIXfab have been stacked vertically via the foundry's standard VGCs.

Silicon based SOI PICs are finding new applications in the field of sensing. Since Silicon does not produce light, to deploy these sensors in real-world applications a fiber-chip connection is required. In this work we detail the fabrication of V-grooves for fiber attachment to the chip, including the design, (hard) masking and the etching process. Our results show that V-groove attached fibre is an optimized solution for SOI based sensor PICs.

Integrated Nano Photonic (INP) sensors will be used in medical and space applications in the near future. Therefore, these devices must also be able to withstand harsh environments without failure. For space and medical applications radiation hardness is a very important issue. At TNO we have investigated the radiation hardness of nano photonic devices using electro-magnetic radiation and high energy particles. We have bombarded various ring resonators and couplers with gamma rays, protons and electrons. After the tests the device operation is verified and compared to non-radiated devices.

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A detailed survey was carried out on a mesotidal shoal and intershoal channel complex near the mouth of the Eastern Scheldt in the southwestern part of The Netherlands during the summers of 1976 and 1977. The objectives were to establish a relationship between the morphological changes through time and its influence on the development of the preserved sedimentary sequence. The investigated area is divided into four zones, each one characterized by specific depositional processes and their related bedforms: (a) the outer channel bend and margin, which is mainly covered by flood-oriented large-scale catenary ripples and sand waves; (b) the channel thalweg and inner bend, which is dominated by ebb-oriented mega-ripples; (c) the inner channel margin, which is characterized by a levee wall; (d) the adjacent shoal areas, which generally are flat but may be covered by patches of flood- or ebb-oriented large-scale ripples. The preserved vertical sequence of sedimentary structures in each zone is more or less in accordance with the presence of the dominant bedforms within the respective zones. Sequential analysis shows that the net sedimentation within the outer channel margin is much less when compared to the sediment accumulation within the inner channel margin. This means that the lateral accretional units of the inner channel margin are a dominant feature within the preserved sequence of such a shoal and intershoal channel complex, and also that the preservation potential of sedimentary structures in the inner margin sequence is considerable higher as that compared to the outer margin sequence. Consequently, preservation of the megaripples, a major bedform in a large part of the investigated area, will be limited and will form only a minor part within an ancient analoguous sequence.