A photonic-crystal waveguide sensor is presented for biosensing. The sensor is applied for refractive index measurements and detection of protein-concentrations. Concentrations around 10 mug/ml (0.15muMolar) are measured with excellent signal to noise ratio, and a broad, dynamic refractive index sensing range extending from air to high viscous fluids is presented.

Both quasi-TE and TM polarisation spectra for a silicon-on-insulator (SOI) waveguide are recorded over (1100-1700)nm using a broadband supercontinuum source. By studying both the input and output polarisation eigenstates we observe narrowband resonant cross coupling near the lowest quasi-TE mode cut-off. We also observe relatively broadband mixing between the two eigenstates to generate a complete photonic bandgap. By careful analysis of the output polarisation state we report on an inherent non-reciprocity between quasi TE and TM fundamental mode cross coupling. The nature of polarisation distinction in such bandgap structures is discussed in the context of polarisation scattering at an interface.

Several planar photonic crystal components topology-optimized for TE-polarized light, including 60 masculine bends, Y-splitters, and 90 masculine bends, have been characterized for the TM polarization. The experimental results are confirmed by finite-difference time-domain calculations. The surprising efficiency for TM-polarized light is found and paves the way for photonic crystal components suitable for both polarizations.

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