A new platform for integrated photonic sensing with nanostructured thin films

A new platform for optical sensing based on evanescent field interferometric devices and the application of dielectric nanostructured thin films as sensing environment is developed. Validation of this new platform is achieved through a complete cycle of design, fabrication and optical characterization. During the course of fabrication work, an integrated circuit compatible process for Si3N4 low temperature plasma etching is established. Optical characterization of Al2O3 structured thin films deposited on tilted substrates addressed two main aspects of film optical properties: the refractive index as related to deposition parameters and film birefringence. The dielectric films analyzed induce significant asymmetry with refractive index values that enable a retarder-like behavior. Quantitative analysis of the effect under normal incidence light demonstrated a strong orientation dependent transmittance with a large polarization rotation angle of 4.76°/mum. The enhanced rotation angle achieved presents an attractive and quite inexpensive technique for fabricating optical retardation plates of different dimensions.;The application of modal analysis on highly birefringent deposited TiO 2 films allowed determination of film anisotropy via refractive index evaluation. It is concluded that the refractive indices for TE and TM modes propagating along the film are different, with a Deltan=0.044 obtained. Light propagating parallel to the substrate, as opposed to the normal propagation occurring in conventional applications, demonstrates a strong modal interaction, with transmitted light highly affected by the column orientation. Limited interaction of the evanescent field with the birefringent cladding is compensated by the long propagating distance.;Optical loss analysis on fabricated waveguides shows that as the wavelength approaches lambda=1.62 mum, attenuation due to intrinsic material absorption and scattering are reduced substantially, reaching 0.62 dB/cm. Finally, the optical characterization of interferometer-based fabricated devices with ZrO2 or TiO2 films deposited on the sensing area has demonstrated optical sensing capability of this platform. A maximum phase shift of pi/10 on the MZI transmission spectra permitted the refractive index measurement of a known gas. In addition, device sensitivity is confirmed by measuring the output time response, where devices with TiO2 film in sensing layer demonstrated higher sensitivity.