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This paper gives an overview of the 3-µm silicon-oninsulator (SOI) platform that is openly available from VTT and suitable for the realization of photonic integrated circuits (PICs) for near and mid-infrared applications. Specific benefits of this thick-SOI PIC platform include low optical losses (∼0.1 dB/cm), ultradense integration (µm-scale bends), small polarization dependency (down-to-zero birefringence), and ability to tolerate relatively high optical powers (>1 W). Fabrication technology is based on an i-line stepper and 150-mm wafer size. Open access to the waveguide platform is supported by design kits, wafer-level testing, multi-project wafer runs, dedicated R&D runs, and small-to-medium volume manufacturing.

A novel guided-wave optical power coupler is presented, based on two 2x2 50/50 multimode interference splitters connected with tapered waveguides that play the role of a phase shifter. By simply changing the length of this phase shifter, these double-MMI couplers can be easily designed to get any desired splitting ratio. Results of simulations are discussed and compared with the characterizations of devices fabricated on micron-scale SOI wafers, to highlight pros and cons of the proposed solution. The fabricated splitters have been found to have average losses about 0.4 ± 0.5 dB and splitting ratios ranging from 56/44 to 96/4.

Water containing suspended nanobubbles is utilized in various applications. The observed lifetime of suspended nanobubbles is several weeks, whereas, according to the classical theory of bubble stability, a nanosized bubble should dissolve within microseconds. Explanations for the longevity of nanosized bubbles have been proposed but none of them has gained general acceptance. In this study, we derive an explanation for the existence of metastable nanobubbles solely from the thermodynamic principles. According to our analysis, the dissolution of nanosized aqueous bulk bubbles is nonspontaneous below 180 nm diameter due to the energy requirement of gas dissolution. Hydrophobic surfaces have a further stabilizing effect, and the dissolution becomes nonspontaneous in surface nanobubbles having a diameter below 600 nm.

Early-age hydration of ordinary Portland cement is now acknowledged to originate from nucleation and crystal growth of calcium–silicate–hydrates. The acceleration mechanism of water-soluble inorganic substances, such as calcium chloride, is still unclear. In the present study, the acceleration mechanism was approached in two independent ways. First, the acceleration effect of filler materials (limestone and quartz powder) and calcium chloride (CaCl2) were studied experimentally with a conduction calorimeter. Second, the calcium chloride effect was studied with thermodynamic modelling. The experimental test results showed that the filler materials accelerated the acceleration period of ordinary Portland cement hydration, whereas calcium chloride accelerated hydration throughout the 24 h measuring period. A synergistic effect was observed with fillers and calcium chloride. Thermodynamic modelling indicated that calcium chloride provides a supersaturation with respect to pure calcium–silicate–hydrate. It was concluded that the supersaturation provides a qualitative explanation for both calcium chloride-induced acceleration and the synergistic effect observed with fillers.