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An Athermal Slot-Waveguide Mach-Zehnder Interferometer for Lab-on-Chip Applications
KTH, School of Electrical Engineering (EES), Microsystem Technology.
2011 (English)Student paper other, 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Label-free optical biosensors are interesting for their compact size, capability for quantitative real-time measurements, and detection of very low analyte quantities. However, these sensors are highly temperature sensitive. Consequently, active temperature control is usually employed in such sensors, but for low cost, mobile, lab-on-chip applications, active temperature control is often not feasible, due to the additional size and cost it entails. This thesis presents methods to minimize the temperature sensitivity of optical silicon slot-waveguides for biosensing applications. By taking advantage of the opposite polarity of the thermo-optic coefficients (TOCs) of silicon and water, and choosing a suitable geometrical design, an athermal slot-waveguide can be created. Three waveguides were designed close to the athermal operating point. The design was based on finite element simulations. The studied waveguides are trough-etched on a silicon-on-insulator (SOI) substrate and designed to operate in water. For the characterization of the temperature sensitivity of the slot-waveguides, an asymmetric Mach-Zehnder interferometer was designed. This design includes surface grating couplers, single-mode waveguides, multimode-interference couplers, strip-slot converters and directional couplers. Three Mach-Zehnder interferometers with different asymmetries were designed. The devices were patterned in a single electron beam lithography step and micro-fabricated by plasma etching of an SOI wafer with a 220 nm device layer and a 2 m buried oxide. For the first characterization measurements, a refractive index matching oil (Cargille 50350) suitable for the grating couplers, was used as top cladding. The quality of all the devices allowed us to make a group index evaluation in the the wavelength range from 1460-1580 nm, and determine the temperature sensitivities of the slot-waveguides. The group index evaluation confirms the validity of the design and fabrication methods. The thermal compensation works as expected. To allow characterization of the slot-waveguides operating in water, a microfludic cartridge was molded in off-stoichiometry thiol-ene polymer.

Place, publisher, year, edition, pages
EES Examensarbete / Master Thesis, XR-EE-MST 2011:008
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-91811OAI: diva2:511269
Available from: 2012-03-20 Created: 2012-03-20 Last updated: 2012-03-20Bibliographically approved

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