20 Décembre – Thesis defense - Miguel Diez

10 h Amphi 3 - building A9 (University of Bordeaux / Talence campus)

Patterning and characterization of polymer nanostructures for optical biosensing.

Optical waveguides, ring resonators and grating couplers based on polymer nanostructures are now considered as promising technologies for integrated biophotonic sensing systems. Commonly, the patterning of polymers at the sub-micron scale requires the use of time and cost-consuming equipments such as electron beam lithography. Direct patterning of high refractive index polymer devices on CYTOP is now achievable and provides symmetric waveguides with top water-like claddings. In addition, transparency of polymers makes them suitable for operation in the visible range, being of major interest for biophotonic applications. In this thesis, we report on two main topics: the fabrication process of sub-wavelength polymer nanostructures on CYTOP and the potential sensing capabilities of these structures as visible microspectrometers. The optical nanostructures consist in an optical microring resonator with sub-wavelength gratings to efficiently couple the light inside the photonic circuit. Periods shorter than 300nm are patterned to efficiently couple the input light into 350nm x 350nm waveguides allowing single-mode operation. The whole device is imprinted in a single step using soft imprint lithography called NanoImprint Lithography. We obtain a minimal residual layer (<50nm) which is achieved with a dedicated design of the master stamp to enhance the polymer flow during the pressure step. The different characterizations performed on both polymer layer and the imprinted device show good agreement with the predicted values by simulation. However, rigorous ellipsometry characterization of the thermo-optic coefficient suggest different instability mechanism of these devices under thermal cycling. The performance of these devices as absorption micro-spectrometers is demonstrated analytically regardless the platform or wavelength. Finally, in addition to the fabrication process we provide a set of design rules based on the theoretical optimization of the ring resonator for absorption sensing.

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