Nanoimprinted distributed feedback lasers comprising TiO₂ thin films: Design guidelines for high performance sensing

Design guidelines for optimizing the sensing performance of nanoimprinted second order distributed feedback dye lasers are presented. The guidelines are verified by experiments and simulations. The lasers, fabricated by UV-nanoimprint lithography into Pyrromethene doped Ormocomp thin films on glass, have their sensor sensitivity enhanced by a factor of up to five via the evaporation of a titanium dioxide (TiO₂) waveguiding layer. The influence of the TiO₂ layer thickness on the device sensitivity is analyzed with a simple model that accurately predicts experimentally measured wavelength shifts induced by varied superstrate refractive indices. The superstrate refractive index is additionally shown to determine which of the possible waveguiding modes dominates for lasing, indicating a method
to flexibly select the polarization of the laser. The detection limit of the sensor system is further discussed, finding an optimum at 7.5·10⁻⁶ RIU. Wavelength changes caused by dye bleaching must be taken into account for long-term measurements.