Lab-in-a-Needle – Überlagerte Fasersensoren für Bio-Medizinische Anwendungen
Optik, Quantenoptik und Physik der Atome, Moleküle und Plasmen
Zusammenfassung der Projektergebnisse
Due to their small size, high sensitivity and applicability at high temperatures and in harsh environments, fiber-optic sensors play an important role e.g. in monitoring environmental and industrial processes, in chemistry, biology and medicine. Common applications are the measurement of the refractive index (RI) of gases and liquids, often combined with the requirement for suitable temperature compensation. Various measurement principles are available for fiber sensors, such as fiber Bragg and long-period gratings, evanescent field sensors, or the use of surface plasmons. A particularly simple and efficient method is the use of open cavities like Fabry-Pérot (FP) resonators. In this project, we explored the possibility to multiplex several such sensors on a single optical fiber. For this purpose, FP resonators were realized by cutting grooves into a standard stepindex silica fiber using a precision diamond-blade wafer saw. The depth of these cuts was slightly larger than the fiber cladding radius and resulted in optical-grade surfaces with typical roughness in the range of a few nanometres. The typical lengths of fabricated resonators are determined by the blade thickness used and was in the range of 40 to 100 microns. For the measurements of the reflection spectra, light from a broadband fiber-coupled superluminescent diode was coupled to the FP cavities and reflected spectra around 1550 nm wavelength were recorded. In order to extract the RI and temperature-induced changes of these spectra, phase tracking of the essential fast FT components has proven to be a wellsuited method. RI measurements showed the principal capability of such sensors to reliably measure as low as 10^−5 RI steps. We showed that multiplexing of up to four highly sensitive FP micro-resonators at the tip of a single-mode optical fiber is possible. Additional dielectric coatings of some of the sensor elements allowed for a high sensitivity of 1100 to 1200 nm/RIU for all the sensor elements. In order to compensate for inherent temperature changes during measurements, we followed two different strategies. In a first approach, the solid-core fiber elements in-between two adjacent FP sensors were used, based on the thermal expansion and thermo-optic coefficient of silica. This resulted in a sensitivity of 20 pm/°C for temperature, fully sufficient for most applications. In a second approach, we developed a method to insert and glue a small piece of Si into one of the diced cavities. By using such an inlay, the relatively high thermo-optic coefficient of Si can be used to increase the sensitivity to temperature changes when compared to solid-core silica cavities. As a result, with this alternative concept the temperature sensitivity was increased by a factor of four. The low cost, compact all-fiber design, high sensitivity and resolution, and the ability to fill open fiber cavities with functional materials or coatings make the developed fiber-integrated FP sensors promising candidates for numerous sensing applications. The additional possibility of multiplexing by fabricating several adjacent FP cavities using precise diamond saw cutting allows precise measurements of refractive index distributions even in small volumes, which is of particular interest for biomedical applications.
Projektbezogene Publikationen (Auswahl)
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Dual parameter fiber-integrated sensor for refractive index and temperature measurement based on Fabry–Perot micro-resonators. Applied Optics, 58(8), 2076.
Suntsov, Sergiy; Rüter, Christian E. & Kip, Detlef
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Design of Fiber-Tip Refractive Index Sensor Based on Resonant Waveguide Grating with Enhanced Peak Intensity. Applied Sciences, 11(15), 6737.
Yao, Yicun; Xie, Yanru; Chen, Nan-Kuang; Pfalzgraf, Ivonne; Suntsov, Sergiy; Kip, Detlef & Ren, Yingying
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Fiber-optic sensor measuring spatial distributions of refractive index and temperature. Applied Optics, 60(5), 1428.
Pfalzgraf, Ivonne; Suntsov, Sergiy & Kip, Detlef
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Multiplexed fiber-optic Fabry-Pérot cavities for refractive index and temperature sensing fabricated using diamond-blade dicing. EPJ Web of Conferences, 255, 08001.
Pfalzgraf, Ivonne; Suntsov, Sergiy; Hasse, Kore & Kip, Detlef
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Multiplexing temperature-compensated open-cavity Fabry–Perot sensors at a fiber tip. Applied Optics, 60(33), 10402.
Pfalzgraf, Ivonne; Suntsov, Sergiy & Kip, Detlef
