Abstract
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.
Highlights
Optical sensors are attracting attention for a variety of applications including medical diagnostics, environmental monitoring, security and manufacturing
Many optical waveguide sensors rely on a small refractive index change that occurs when a target analyte binds to or otherwise interacts with an optical surface
One of the most studied refractive index sensor designs is the solid core evanescent wave sensor, which relies on the small overlap between the evanescent tail of an optical mode with a surface-bound analyte [1,2,3,4] – typically a weak effect that requires a long interaction length to produce a measurable signal
Summary
Optical sensors are attracting attention for a variety of applications including medical diagnostics, environmental monitoring, security and manufacturing. One of the most studied refractive index sensor designs is the solid core evanescent wave sensor, which relies on the small overlap between the evanescent tail of an optical mode with a surface-bound analyte [1,2,3,4] – typically a weak effect that requires a long interaction length to produce a measurable signal. A solution to this issue is to employ a waveguide structure that confines light in two dimensions and guides parallel to substrate This design allows relatively long interaction length by extending the length of sensing area. We describe the fabrication and characterization of a single-mode porous silicon integrated MZI waveguide, with a polymer passivation layer used to confine the analyte to a prescribed region. We compare the performance of the integrated MZI to a comparable fiber-based MZI, and show greatly improved stability
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