Optical waveguides comprised of nanoporous materials are uniquely suited for on-chip sensing applications, because they allow for a target chemical or analyte to directly infiltrate the optical material that comprises the core of the waveguide. We describe here the fabrication and characterization of nanoporous waveguides, and demonstrate their usefulness in measuring small changes in refractive index when exposed to a test analyte. We use a process of electrochemical etching and laser oxidation to produce channel waveguides and integrated on-chip Mach-Zehnder structures, and we compare the responsivity and interferometric stability of the integrated sensor to that of a fiber-based interferometer. We quantify the detection capability by selectively applying isopropanol to a 200 μm length waveguide segment in one arm of the interferometer, which produces a phase shift of 9.7 π. The integrated interferometer is shown to provide a more stable response in comparison to a comparable fiber-based implementation.
Nanoporous silicon is known to have a thermal conductivity that is orders of magnitude smaller than the bulk crystalline silicon from which it is formed. Even though the strong columnar microscopic structure of porous silicon indicates the possibility of highly anisotropic thermal properties, there have been no measurements. We report here an experimental investigation of this anisotropy. An analytical heat spreading model with 3x thermal conductivity measurement method was used to derive both in-plane and cross-plane conductivities. Additionally, we describe a finite element analysis that supports the experimental measurements. Our measurements reveal that because of the nanoscale columnar nature of the material, the in-plane thermal conductivity of nanoporous silicon is 1-2 orders of magnitude smaller than the cross-plane thermal conductivity and 2-3 orders of magnitude smaller than that of crystalline silicon, making it comparable to the best thermal insulators available. V C 2015 AIP Publishing LLC.
The nonlinear response of nanoporous silicon optical waveguides is investigated using a novel pump-probe method. In this approach we use a two-frequency heterodyne technique to measure the pump-induced transient change in phase and intensity in a single measurement. We measure a 100 picosecond material response time and report behavior matching a physical model dominated by free-carrier effects significantly stronger than those observed in traditional silicon-based waveguides.
Based on the Microshutter Array (MSA) subsystems developed at NASA Goddard Space Flight Center (GSFC) for the James Webb Space Telescope (JWST), Next Generation Microshutter Array (NGMSA) has been developed to be used as multi-object selectors for future telescopes in space applications. Microshutter arrays function as transmission devices. Selected shutters fully open at 90 degrees permitting income light going through, while the rest of shutters keep closed. The programmable microshutter open and close make the device perform as a multi object selector that can be used on space telescopes. Utilizing a multi object selector, the telescope efficiency can be increased to 100 times or more. Like JWST MSAs, NGMSA features torsion hinges, light shields, front and back electrodes for shutter actuation, latch, and closing. The difference is that JWST MSA utilized the magnetic actuation while NGMSA the electrostatic actuation.
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