Planar long period gratings for photonic applications

This work presents long period grating (LPG) devices based on a silica-on-silicon planar waveguide platform. All-silica and hybrid polymer / silica device architectures are demonstrated for potential applications in wavelength filtering, power distribution, and various types of sensors. The grating structure was realized through a periodic corrugation on a thermally oxidized silicon layer that also serves as the waveguide lower cladding. For the hybrid architecture, waveguide ridges were photo-patterned in a layer of low-loss fluorinated poly(arylether ketone), and covered with a similar polymer cladding having lower refractive index. For all-silica LPGs, GeO2-doped silica waveguides were fabricated over the grating by PECVD and reactive ion etching, and embedded in a layer of borophosphosilicate glass (BPSG) with a refractive-index matched to that of the lower cladding material. In these structures, the corrugated silica layer allows a stable grating structure, while the fluorinated polymer or silica waveguides offer low propagation loss and versatile processability. Strong rejection bands have been observed in the C+L wavelength region, in good agreement with theoretical calculations. Based on these designs, an array of waveguides incorporating long period gratings has also been fabricated. Distribution of light at the resonance wavelength across all channels, from a single input, has been demonstrated. These results are promising for power distribution in photonic network applications or on-chip sensors. The sensitivities of the fabricated LPGs to temperature and to the refractive index of the surrounding medium have been investigated and are discussed.