Hierarchical micro/-nanostructures were produced on polycarbonate polymer surfaces by employing a two-step UV-laser processing strategy based on the combination of Direct Laser Interference Patterning (DLIP) of gratings and pillars on the microscale (3 ns, 266 nm, 2 kHz) and subsequently superimposing Laser-induced Periodic Surface Structures (LIPSS; 7–10 ps, 350 nm, 100 kHz) which adds nanoscale surface features. Particular emphasis was laid on the influence of the direction of the laser beam polarization on the morphology of resulting hierarchical surfaces. Scanning electron and atomic force microscopy methods were used for the characterization of the hybrid surface structures. Finite-difference time-domain (FDTD) calculations of the laser intensity distribution on the DLIP structures allowed to address the specific polarization dependence of the LIPSS formation observed in the second processing step. Complementary chemical analyzes by micro-Raman spectroscopy and attenuated total reflection Fourier-transform infrared spectroscopy provided in-depth information on the chemical and structural material modifications and material degradation imposed by the laser processing. It was found that when the linear laser polarization was set perpendicular to the DLIP ridges, LIPSS could be formed on top of various DLIP structures. FDTD calculations showed enhanced optical intensity at the topographic maxima, which can explain the dependency of the morphology of LIPSS on the polarization with respect to the orientation of the DLIP structures. It was also found that the degradation of the polymer was enhanced for increasing accumulated fluence levels.

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Amorphous Al2O3 is an attractive material for integrated photonics. Its low losses from the UV till the mid-IR together with the possibility of doping with different rare-earth ions permits the realization of active and passive functionalities in the same chip at the wafer level. In this work, the influence of reactive gas flow during deposition on the optical (i.e., refractive index and propagation losses) and material (i.e., structure of the layer) characteristics of the RF reactive sputtered Al2O3 layers is investigated and a method based on the oxidation state of the sputtering target is proposed to reproducibly achieve low loss optical guiding layers despite the continuous variation of the condition of the target along its lifetime.

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Luminescence quenching due to ion cluster formation in erbium ion doped amorphous aluminium oxide, limits the maximum doping concentration that can be incorporated into the material and, consequently, the maximum achievable optical gain. By controlling the reactive sputtering deposition parameters, layers with different morphologies can be deposited. In this work, we investigate low propagation loss poly-crystalline aluminium oxide thin films and the effect of erbium doping on the crystallinity. We have developed a reactive sputter process to reproducibly obtain high refractive index (n~1.72 at 633 nm) poly-crystalline thin films with very low slab waveguide losses from the near-UV to the midinfrared wavelength range. Slab waveguide losses as low as 1.8 dB/cm at 407 nm and less than 0.1 dB/cm at 1550 nm of wavelength have been experimentally characterized. Both the undoped and erbium doped layers were deposited by reactive sputter coating with, a set substrate temperature of 700 °C. Preliminary TEM analyses show no discernible change in the crystallinity of the doped layers with respect to their undoped counterparts. The high optical quality of this material, in combination with a potentially increased rare-earth ion doping concentration, could pave the way towards high-gain on-chip amplifiers in different wavelength ranges and efficient on-chip lasers.

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The accurate analysis of propagation losses is key as optimization tool for the development of new integrated optical waveguides. Channel waveguide propagation losses can be determined by studying the resonances of microring resonators. In this work, we study the propagation losses of TiO 2 channel waveguide by analyzing the transmission of microring resonators in the wavelength range from 1460 to 1640 nm. Propagation losses as low as 1.0 dB/cm at 1550 nm of wavelength have been experimentally demonstrated.