We demonstrate the potential of applying hollow core and negative curvature optical fibers (HC-NCF) as efficient sensors to monitor the concentration of three high-toxicity gases: methane (CH4), carbon monoxide (CO), and nitrogen monoxide (NO). Numerical simulations demonstrate that the insertion of holes in such fibers guarantees the entry of these gases into their hollow core and allows strong interaction of these gases with the low-loss mode propagating in the HC-NCF. This interaction between light and gas in spectral regions with high gas absorption allows one to monitor reduced concentrations of these gases present in the environment simply by monitoring the optical power at the fiber output. The results show a linear behavior of propagation losses as a function of concentrations of 0% to 100% of CO and NO gas, and for concentrations of 0% to 5% of CH4 gas. This linearity between the propagation losses and the variation of the concentrations of gases in the environment can promote its application in healthcare and environment, to monitor low concentrations of gases ensuring high speed and accuracy.
In this work we present a comparative study of two processes for the fabrication of an array of microchannels for microfluidics applications, based on integrated-circuit technology process steps, such as lithography and dry etching. Two different methods were investigated in order to study the resulting microstructures: wet and dry deep etching of silicon substrate. The typical etching depth necessary to the target application is 50 μm.
Optical sensors based on integrated photonics have experienced impressive advancements in the past few decades and represent one of the main sensing solutions in many areas including environmental sensing and medical diagnostics. In this context, optical microcavities are extensively employed as refractive index (RI) sensors, providing sharp optical resonances that allow the detection of very small variations in the surrounding RI. With increased sensitivity, however, the device is subjected to environmental perturbations that can also change the RI, such as temperature variations, and therefore compromise their reliability. In this work, we present the concept and experimental realization of a photonic sensor based on coupled microcavities or Photonic Molecules (PM) in which only one cavity is exposed to the sensing solution, allowing a differential measurement of the RI change. The device consists of an exposed 5-μm radius microdisk resonator coupled to an external clad microring resonator fabricated on silicon-on-insulator (SOI) platform. This design allows good sensitivity (26 nm/RIU) for transverse electrical mode (TE-mode) in a compact footprint (40 × 40 μm2), representing a good solution for real-life applications in which measurement conditions are not easily controllable.
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