Fabricaiton and Characterization of Waveguide Structures in Transparent Optical Materials

Tesis Doctoral inédita cotutelada por la Shandong University de China y la Universidad Autónoma de Madrid. Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura: 31-03-201

Passively Q-switched Nd:YVO4 waveguide laser using graphene as a saturable absorber

We report on passively Q-switched lasers in femtosecond laser written waveguide in Nd:YVO4 crystal. Using graphene as a saturable absorber, passively Q-switched waveguide laser operations are achieved along both TE and TM polarizations with single modal profiles. Furthermore, all-angle linear light pump was utilized to investigate the thorough information of the polarization effects of the laser, showing that the optimum polarization for laser generation is TE. The maximum average output power is estimated to be 129 mW with 12.2% slope efficiency, corresponding to single-pulse energy of 8.1 nJ, pulse duration of 25.0 ns and repetition rate of 16.3 MHz.This work was supported by the National Natural Science Foundation of China (No. 11274203) and Ministerio de Economía y Competitividad under Project FIS2013-44174-P, Spain

Spontaneous micro-modification of single-layer graphene induced by femtosecond laser irradiation

Permanent micro-modifications in single-layer graphene with a spontaneous periodic structural change have been induced by femtosecond (fs) laser irradiation. These modifications present a regular variation along the radial direction from a central ablated region. Based on the obtained micro-Raman spectrum and the reflective micro-spectrum of laser-irradiated graphene, structural modification with periodic variations containing several spectral regimes has been observed, which was in good agreement with periodic topography of the structure observed using an atomic force microscope. It has also been found that several regions of the laser induced structures were with different optical properties, which were identified to be correlated with different modification mechanisms. In addition, after fs laser processing, graphene still maintains crystallinity. This work may be helpful for the development of graphene-based microstructures or devices by fs laser pulsesThis work was supported by the National Natural Science Foundation of China (No. 11535008), Junta de Castilla y León (Project SA046U16), and MINECO (FIS2013-44174-P, FIS2015-71933-REDT)

Femtosecond laser direct writing of few-mode depressed-cladding waveguide lasers

We report on mirrorless laser operation of Nd:YVO4 single- and double-cladding waveguides fabricated by femtosecond laser direct writing. Fundamental- (LP01) and high-order-mode (LP03, LP05) guiding and lasing have been observed in waveguides with different geometries and sizes. Double-cladding waveguides exhibit good guiding and lasing performance via inheriting advantages respectively from individual single cladding. As a result, continuous-wave lasing with a threshold as low as 59 mW is obtained, depending on the optical feedback provided only by Fresnel reflections at the waveguide end faces. By using few-layer graphene as saturable absorber, passively Q-switched operation in fabricated waveguides is also achieved.National Natural Science Foundation of China (11704201, 61775120); Consejería de Educación, Junta de Castilla y León (SA287P18); Ministerio de Economía y Competitividad (FIS2017-87970R); Natural Science Foundation of Tianjin City (17JCQNJC01600)

Three-dimensional dielectric crystalline waveguide beam splitters in mid-infrared band by direct femtosecond laser writing

We report on the fabrication of three-dimensional waveguide beam splitters in a dielectric Bi4Ge3O12 (BGO) crystal by direct femtosecond laser writing. In the laser written tracks of BGO crystal, positive refractive index is induced, resulting in so-called Type I configuration waveguiding cores. The “multiscan” technique is utilized to shape cores with designed cross-sectional geometry in order to achieve guidance at mid-infrared wavelength of 4 μm. The fundamental mode guidance along both TE and TM polarizations has been obtained in the waveguide structures. With this feature, we implement beam splitters from 2D to 3D geometries, and realize 1 × 2, 1 × 3, and 1 × 4 power splitting at 4μm.This work was supported by the National Natural Science Foundation of China (No. 11274203), Junta de Castilla y León under project (SA086A12-2), and Ministerio de Economía y Competitividad under project (FIS2013-44174-P), Spain

Two-photon luminescence thermometry: towards 3D high-resolution thermal imaging of waveguides

We report on the use of the Erbium-based luminescence thermometry to realize high resolution, three dimensional thermal imaging of optical waveguides. Proof of concept is demonstrated in a 980-nm laser pumped ultrafast laser inscribed waveguide in Er:Yb phosphate glass. Multi-photon microscopy images revealed the existence of well confined intra-waveguide temperature increments as large as 200 °C for moderate 980-nm pump powers of 120 mW. Numerical simulations and experimental data reveal that thermal loading can be substantially reduced if pump events are separated more than the characteristic thermal time that for the waveguides investigated is in the ms time scale.Ministerio de Economía y Competitividad of Spain (MINECO) (FIS2013-44174-P, MAT2013-47395-C4-1-R); National Natural Science Foundation of China (NSFC) (11274203)

Optical waveguides in LiTaO3 crystals fabricated by swift C5+ ion irradiation

We report on the optical waveguides, in both planar and ridge configurations, fabricated in LiTaO3 crystal by using carbon (C5+) ions irradiation at energy of 15 MeV. The planar waveguide was produced by direct irradiation of swift C5+ ions, whilst the ridge waveguides were manufactured by using femtosecond laser ablation of the planar layer. The reconstructed refractive index profile of the planar waveguide has showed a barrier-shaped distribution, and the near-field waveguide mode intensity distribution was in good agreement with the calculated modal profile. After thermal annealing at 260 °C in air, the propagation losses of both the planar and ridge waveguides were reduced to 10 dB/cm.This work is supported by the National Natural Science Foundation of China (No. U1332121) and the 973 Project (No. 2010CB832906) of China. S.Z. acknowledges the funding by the Helmholtz-Gemeinschaft Deutscher Forschungszentren (HGF-VHNG-713). J.R.V. thanks supports from Junta de Castilla y León under project SA086A12-2 and the Centro de Láseres Pulsados (CLPU)

Optical lattice-like cladding waveguides by direct laser writing: fabrication, luminescence, and lasing

We report on the fabrication of optical lattice-like waveguide structures in an Nd:YAP laser crystal by using direct femtosecond laser writing. With periodically arrayed laser-induced tracks, the waveguiding cores can be located in either the regions between the neighbored tracks or the central zone surrounded by a number of tracks as outer cladding. The polarization of the femtosecond laser pulses for the inscription has been found to play a critical role in the anisotropic guiding behaviors of the structures. The confocal photoluminescence investigations reveal different stress-induced modifications of the structures inscribed by different polarization of the femtosecond laser beam, which are considered to be responsible for the refractive index changes of the structures. Under optical pump at 808 nm, efficient waveguide lasing at ∼1 μm wavelength has been realized from the optical lattice-like structure, which exhibits potential applications as novel miniature light sources.National Natural Science Foundation of China (NSFC) (11274203); Ministerio de Economia y Competitividad (MINECO) (FIS2013-44174-P, MAT2010-21270-C04-01)

Optical ridge waveguides in Er3+/Yb3+ co-doped phosphate glass produced by ion irradiation combined with femtosecond laser ablation for guided-wave green and red upconversion emissions

This work reports on the fabrication of ridge waveguides in Er3+/Yb3+ co-doped phosphate glass by the combination of femtosecond laser ablation and following swift carbon ion irradiation. The guiding properties of waveguides have been investigated at 633 and 1064 nm through end face coupling arrangement. The refractive index profile on the cross section of the waveguide has been constructed. The propagation losses can be reduced considerably after annealing treatment. Under the optical pump laser at 980 nm, the upconversion emission of both green and red fluorescence has been realized through the ridge waveguide structures.This work was supported by the National Natural Science Foundation of China (No. 11305094). S.Z. acknowledges the funding by the Helmholtz-Gemeinschaft Deutscher Forschungszentren (HGF-VH-NG-713). J.R. Vázquez de Aldana thanks the support from Junta de Castilla y León (Project SA086A12-2)

Cooperative Stabilization of the [Pyridinium-CO2-Co] Adduct on a Metal-Organic Layer Enhances Electrocatalytic CO2 Reduction.

Pyridinium has been shown to be a cocatalyst for the electrochemical reduction of CO2 on metal and semiconductor electrodes, but its exact role has been difficult to elucidate. In this work, we create cooperative cobalt-protoporphyrin (CoPP) and pyridine/pyridinium (py/pyH+) catalytic sites on metal-organic layers (MOLs) for an electrocatalytic CO2 reduction reaction (CO2RR). Constructed from [Hf6(μ3-O)4(μ3-OH)4(HCO2)6] secondary building units (SBUs) and terpyridine-based tricarboxylate ligands, the MOL was postsynthetically functionalized with CoPP via carboxylate exchange with formate capping groups. The CoPP group and the pyridinium (pyH+) moiety on the MOL coactivate CO2 by forming the [pyH+--O2C-CoPP] adduct, which enhances the CO2RR and suppresses hydrogen evolution to afford a high CO/H2 selectivity of 11.8. Cooperative stabilization of the [pyH+--O2C-CoPP] intermediate led to a catalytic current density of 1314 mA/mgCo for CO production at -0.86 VRHE, which corresponds to a turnover frequency of 0.4 s-1