Airan Rodenas

Three-dimensional mid-infrared photonic circuits in chalcogenide glass

We report the fabrication of single-mode buried channel waveguides for the whole mid-IR transparency range of chalcogenide sulphide glasses (λ ≤ 11 μm), by means of direct laser writing. We have explored the potential of this technology by fabricating a prototype three-dimensional three-beam combiner for future application in stellar interferometry that delivers a monochromatic interference visibility of 99.89% at 10.6 μm and an ultrahigh bandwidth (3-11 μm) interference visibility of 21.3%. These results demonstrate that it is possible to harness the whole transparency range offered by chalcogenide glasses on a single on-chip instrument by means of direct laser writing, a finding that may be of key significance in future technologies such as astrophotonics and biochemical sensing.

70% slope efficiency from an ultrafast laser-written Nd:GdVO4 channel waveguide laser.

We report high efficiency continuous wave laser oscillations at 1063.6 nm from an ultrafast laser written Nd(3+):GdVO4 channel waveguide under the 808 nm optical excitation. A record 17 mm·s(-1) writing speed was used while the low propagation loss of the waveguide (~0.5 dB·cm(-1)) enabled laser performance with a threshold pump power as low as 52 mW and a near to quantum defect limited laser slope efficiency of 70%.

Mid-infrared waveguide lasers in rare-earth-doped YAG

We report near-infrared (IR) to mid-IR (up to 3.4 μm wavelength) multimode waveguiding in deep buried channel waveguides fabricated inside rare-earth ion-doped ceramic YAG for the first time to our knowledge. Waveguide laser operation at around 2 μm wavelength with multi- or single-transverse modes is also preliminarily demonstrated from these waveguides.

Femtosecond laser written surface waveguides fabricated in Nd:YAG ceramics

Near surface channel waveguides have been fabricated in Neodymium doped YAG ceramics by using IR femtosecond laser irradiation at the low frequency regime. Single mode guidance has been demonstrated with propagation losses of ~1 dB/cm. Time resolved confocal micro-luminescence experiments have been used to determine the spectroscopic properties of the Nd(3+) laser ions in the channel waveguide as well as to elucidate the waveguide formation processes.

High-contrast step-index waveguides in borate nonlinear laser crystals by 3D laser writing.

We report the ultrafast fabrication of high-contrast step-index channel waveguides in Nd(3+):YCa(4)O(BO(3))(3) borate laser crystals by means of 3D direct laser writing. Guiding up to 3.4 μm wavelength is demonstrated for the first time in a laser written crystalline waveguide. Modeling the measured fundamental modes at the wavelengths of 1.9 µm and 3.4 µm allowed us to estimate the high laser-induced refractive index increments (index contrasts) to be 0.010 (0.59%), and 0.005 (0.29%), respectively. Confocal µ-Raman spectral imaging of the waveguides cross-sections confirmed that the cores have very well defined step profiles, and that the increase in the refractive index can be linked to the localized creation of permanent intrinsic defects. These results indicate that this crystalline waveguides are a potential candidate for the development of 3D active waveguide circuits, due to the laser and electro-optic properties of rare earth doped borate crystals.

Confocal Raman imaging of optical waveguides in LiNbO3 fabricated by ultrafast high-repetition rate laser-writing

We report on the confocal Raman characterization of the micro-structural lattice changes induced during the high-repetition rate ultrafast laser writing of buried optical waveguides in lithium niobate (LiNbO(3)) crystals. While the laser beam focal volume is characterized by a significant lattice expansion together with a high defect concentration, the adjacent waveguide zone is largely free of defects, undergoing only slight rearrangement of the oxygen octahedron in the LiNbO(3) lattice. The close proximity of these two zones has been found responsible for the propagation losses of the guided light. Subjacent laser-induced periodic micro-structures have been also observed inside the laser focal volume, and identified with a strong periodic distribution of lattice defects.

Anisotropic lattice changes in femtosecond laser inscribed Nd3+:MgO:LiNbO3 optical waveguides

We report on the fabrication and microspectroscopy imaging of femtosecond laser written double-filament based Nd3+:MgO:LiNbO3 optical waveguides. The waveguiding high refractive-index regions are identified by blueshifts of the Nd3+ ion fluorescence lines with no deterioration in the fluorescence efficiency, whereas filamentary low-index regions are identified by both a Nd3+ line redshift and a fluorescence efficiency reduction. The lattice structural micromodifications at the origin of both waveguide formation and Nd3+ fluorescence changes have been investigated by means of confocal micro-Raman experiments. We have found that the direct laser written filaments are mainly constituted by a large density of defects, together with a marked axial compression perpendicular to the filaments (along the optical c-axis). Conversely, the high-index waveguiding regions are characterized by a pronounced anisotropic dilatation of the LiNbO3 lattice xy-planes.

Direct laser writing of near-IR step-index buried channel waveguides in rare earth doped YAG

A new (to our knowledge) ultrashort laser pulse irradiation regime that allows us to directly modify and increase the refractive index of rare earth doped YAG polycrystalline ceramics has been identified. Single-mode buried channel waveguides in both Ho:YAG and Er:YAG ceramics at the near-IR wavelengths of 1.55 μm and 1.95 μm are demonstrated by fabricating positive square step-index cores. Minimum propagation losses of 1.5 dB cm(-1) at a 1.51 μm wavelength have been preliminarily obtained. Confocal microluminescence mapping reveals that the increased refractive index regions retain the near-IR spectral properties of Er3+ ions in the YAG crystalline matrix.

Quantum dot enabled thermal imaging of optofluidic devices

Quantum dot thermal imaging has been used to analyse the chromatic dependence of laser-induced thermal effects inside optofluidic devices with monolithically integrated near-infrared waveguides. We demonstrate how microchannel optical local heating plays an important role, which cannot be disregarded within the context of on-chip optical cell manipulation. We also report on the thermal imaging of locally illuminated microchannels when filled with nano-heating particles such as carbon nanotubes.

Direct laser writing of three-dimensional photonic structures in Nd:yttrium aluminum garnet laser ceramics

We report on the direct laser writing of a three-dimensional photonic structure in a neodymium doped yttrium aluminum garnet laser ceramic. The fabricated structure consists of a voxel-based face centered cubic lattice showing a stop band centered at 2.4 μm. Confocal luminescence imaging was used to study the submicron low refractive-index voxels constituting the photonic structure, as well as to elucidate how the luminescence properties of the neodymium laser ions are modified by the writing process.