Morphological properties of thermochromic VO2—porous silicon based hybrids reveal the growth of well-crystalized nanometer-scale features of VO2 as compared with typical submicron granular structure obtained in thin films deposited on flat substrates. Structural characterization performed as a function of temperature via grazing incidence X-ray diffraction and micro-Raman demonstrate reversible semiconductor-metal transition of the hybrid, changing from a low-temperature monoclinic VO2(M) to a high-temperature tetragonal rutile VO2(R) crystalline structure, coupled with a decrease in phase transition temperature. Effective optical response studied in terms of red/blue shift of the reflectance spectra results in a wavelength-dependent optical switching with temperature. As compared to VO2 film over crystalline silicon substrate, the hybrid structure is found to demonstrate up to 3-fold increase in the change of reflectivity with temperature, an enlarged hysteresis loop and a wider operational window for its potential application as an optical temperature sensor. Such silicon based hybrids represent an exciting class of functional materials to display thermally triggered optical switching culminated by the characteristics of each of the constituent blocks as well as device compatibility with standard integrated circuit technology.

We report experimental results on an optical fiber pressure sensor based on multimode interference effects (MMIs). The key component is a small multimode fiber (MMF) section without cladding, which is placed on a direct contact with a polydimethilsiloxane polymer layer previously attached to a pressure-sensitive membrane. When the applied pressure is increased, both the polymer contact area and the induced stress on the MMF increase directly proportional with the applied pressure. Both effects contribute to losses of the propagating modes, and since the MMI spectrum is formed by the interference of the propagating modes, the net effect is that the intensity of the spectral response of the MMI is reduced as the pressure is increased. Therefore, by tracking a single wavelength, the intensity changes are correlated to the applied pressure values. The response of the sensor is highly linear within a pressure range of 0-960 kPa with a sensitivity of - 0.145 ×10 ^-3 mW/kPa. The key features of the MMI pressure sensor are its low-cost and high repeatability.