Suchergebnisse

We report on the direct low-repetition rate femtosecond pulse laser microfabrication of optical waveguides in KTP crystals and the characterization of refractive index changes after the thermal annealing of the sample, with the focus on studying the potential for direct laser fabricating Mach-Zehnder optical modulators. We have fabricated square cladding waveguides by means of stacking damage tracks, and found that the refractive index decrease is large for vertically polarized light (c-axis; TM polarized) but rather weak for horizontally polarized light (a-axis; TE polarized), this leading to good near-infrared light confinement for TM modes but poor for TE modes. However, after performing a sample thermal annealing we have found that the thermal process enables a refractive index increment of around 1.5x10−3 for TE polarized light, while maintaining the negative index change of around −1x10−2 for TM polarized light. In order to evaluate the local refractive index changes we have followed a multistep procedure: We have first characterized the waveguide cross-sections by means of Raman micro-mapping to access the lattice micro-modifications and their spatial extent. Secondly we have modeled the waveguides following the modified region sizes obtained by micro-Raman with finite element method software to obtain a best match between the experimental propagation modes and the simulated ones. Furthermore we also report the fabrication of Mach-Zehnder structures and the evaluation of propagation losses. ; This work was partially supported by the Ministerio de Economía y Competitividad, under Project FIS2013-44174-P, by the Spanish Government under project MAT2013-47395-C4-4-R and TEC2014-55948-R and by the Generalitat de Catalunya under project 2014SGR1358. F.D. acknowledges additional support through the ICREA academia award 2010ICREA-02 for excellence in research.

3 pages, 3 figures. ; We report on the mechanisms responsible for the formation of optical waveguides upon femtosecond laser irradiation of an alkaline lead-oxide silicate glass. MicroRaman spectroscopy and nonlinear fluorescence were employed to probe the local glass network structure and the formation of optically active defects respectively. At low laser pulse energies, the laser modified region is formed by a single light guiding region, whereas for pulses above 14 µJ the modified region is formed by a central dark zone, which does not guide light, accompanied by light guiding zones located in the surrounding of the dark one. This behavior is different from that observed in common silica glass systems but agrees with recent results obtained in phosphate and heavy metal oxide glasses. However, our results show that, unlike the latter glass, local densification of the glass occurs in the whole laser modified region, i.e., in the dark and the guiding zones. The suppression of light guiding in the dark region is explained by a high density of absorbing color centers. ; This work was partially supported by CICYT (Spain) under Project No. DPI2002-00151. One of the authors (V.D.B.) acknowledges the financial support of the CSIC and the European Social Fund through an I3P Ph.D. fellowship. Another author (P.L.-A. acknowledges funding from the Spanish Government ( the Ramón y Cajal program and Grant No. TIC2003-07485). ; Peer reviewed

Depressed-index channel waveguides with a circular and photonic crystal cladding structures are prepared in a bulk monoclinic Tm:KLu(WO4)2 crystal by 3D direct femtosecond laser writing. The channel waveguide structures are characterized and laser operation is achieved using external mirrors. In the continuous-wave mode, the maximum output power of 46 mW is achieved at 1912 nm corresponding to a slope efficiency of 15.2% and a laser threshold of only 21 mW. Passive 𝑄-switching of a waveguide with a circular cladding is realized using single-walled carbon nanotubes. Stable 7 nJ/50 ns pulses are achieved at a repetition rate of 1.48 MHz. This first demonstration of ∼2 μm fs-laser-written waveguide lasers based on monoclinic double tungstates is promising for further lasers of this type doped with Tm3+and Ho3+ ions . ; Ministerio de Economía y Competitividad (MINECO) (FIS2013-44174-P, FIS2015-71933-REDT, MAT2013-47395-C4-4-R, MAT2016-75716-C2-1-R, TEC 2014-55948-R); Departament d'Innovació, Universitats i Empresa, Generalitat de Catalunya (DIUE) (2014SGR1358); Junta de Castilla y León (UIC016, SA046U16); Institució Catalana de Recerca i Estudis Avançats (ICREA) Academia (2010ICREA-02); H2020 Marie Skłodowska-Curie Actions (MSCA) (657630); Government of the Russian Federation (074-U01); National Research Foundation of Korea (NRF) Korea of MSIP (2016R1A2A1A05005381).

We report on efficient laser operation of the first holmium monoclinic double tungstate waveguide laser fabricated by femtosecond direct laser writing. A depressed-index buried channel waveguide with a 60 μm diameter circular cladding was inscribed in 5 at.% Ho3+:KGd(WO4)2. It was characterized by confocal microscopy and μ-Raman and μ-luminescence spectroscopy, indicating well-preserved crystallinity of its core. Pumped by a thulium bulk laser, the holmium waveguide laser generated 212 mW at 2055 nm with a slope efficiency of 67.2%. The waveguide propagation losses were 0.94±0.2 dB/cm. ; Agència de Gestió d'Ajuts Universitaris i de Recerca (AGAUR) (2017SGR755); Horizon 2020 Framework Programme (H2020) (747055); Consejería de Educación, Junta de Castilla y León (SA046U16, UIC016); Ministerio de Economía y Competitividad (MINECO) [FIS2017-87970-R, MAT2016-75716-C2-1-R (AEI/FEDER, UE), TEC 2014-55948-R]; Generalitat de Catalunya (2016FI_B00844, 2017FI_B100158, 2018FI_B200123); ICREA academia (2010ICREA-02); Government of the Russian Federation (074-U01); European Community's Horizon 2020 Research (654148); Laserlab- EUROPE (MBI MBI002365).

We report on the fabrication, µ-Raman characterization, and continuous-wave laser operation of a channel waveguide with a hexagonal optical-lattice-like cladding fabricated in monoclinic Tm:KLu(WO4)2 crystal by femtosecond direct laser writing. µ-Raman spectroscopy indicates preservation of the crystalline quality in the core region and an anisotropic residual stress field. When pumped by a Ti:Sapphire laser at 802 nm, the Tm:KLu(WO4)2 buried channel waveguide laser generated 136 mW at 1843.7 nm with a slope efficiency of 34.2% and a threshold as low as 21 mW, which are the record characteristics for femtosecond-laser-written Tm crystalline waveguide lasers. The variation of the output coupling resulted in discrete wavelength tuning of the laser emission from 1785 to 1862 nm. The propagation losses in the waveguide are ~1.2 ± 0.3 dB/cm. ; E. K. acknowledges financial support from the Generalitat de Catalunya under grants 2016FI_B00844 and 2017FI_B100158. F.D. acknowledges additional support through the ICREA academia award 2010ICREA-02 for excellence in research. X. M. acknowledges support from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 657630. A. R. acknowledges funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Individual Fellowship Grant Agreement No. 747055. P. L. acknowledges financial support from the Government of the Russian Federation (Grant 074-U01) through ITMO Post-Doctoral Fellowship scheme.

4 págs,; 5 figs. ; Ridge waveguide lasers have been fabricated on Nd doped LiNbO crystals. The fs-laser writing technique was used to define ridge structures on a gradient-index planar waveguide fabricated by Zn-diffusion. This planar waveguide was formed in a z-cut LiNbO substrate homogeneously doped with a 0.23% of Nd ions. To obtain lateral light confinement, the surface was then micromachined using a multiplexed femtosecond laser writing beam, forming the ridge structures. By butting two mirrors at the channel waveguide end-facets, forming a waveguide laser cavity, TM-polarized laser action at 1085 nm was achieved by end-fire TM-pumping at 815 nm. The waveguide laser shows a threshold of 31 mW, with a 7% of slope efficiency. © 2016 Elsevier B.V. All rights reserved ; This work was supported by the Spanish Government under projects TEC2014-52642-C2-1-R and MAT2013-47395-C4. ; Peer Reviewed

M.A. Butt, M.C. Pujol, R. Solé, A. Ródenas, G. Lifante, M. Aguiló, F. Díaz, S. N. Khonina, R. V. Skidanov and Payal Verma, "Fabrication of optical waveguides in RbTiOPO4 single crystals by using different techniques", XIII International Scientific and Technical Conference on Optical Technologies in Telecommunications,SPIE 9807 (26 March, 2016): doi:10.1117/12.2231368. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited ; Proceedings of XIII International Scientific and Technical Conference on Optical Technologies in Telecommunications Conference (Ufa, Russian Federation) ; In this work, we have demonstrated the use of different technologies to fabricate straight channel waveguides, S-bend waveguides, Y-splitter and Mach -Zehnder (MZ) structures on RbTiOPO 4 crystals and its isomorphs. We used reactive ion etching (RIE), inductively coupled plasma-RIE (ICP-RIE), femtosecond pulse laser micro-fabrication and ion diffusion techniques to structure these crystals. Computer simulations have been carried out and compared with the optical characterization of the waveguides which are in agreement with each other. ; This work is supported by the Ministry of Education and Science of the Russian Federation, Russian Science Foundation (grant No. 14-19-00114), Spanish Government under Projects MAT2011-29255-C02-02, TEC2014-55948-R, MAT2013-47395, C4-4-R/1-R and by the Catalan Authority under Project 2014SGR1358

Novel methods for production of nanomaterials are urgently needed for various applications, especially in defence. In this work, we propose a direct method to produce silver nanoneedles using the femtosecond laser direct writing (LDW) technique. Femtosecond pulses were focused by a microscope objective on to a metal sheet to produce the nanoneedles. Nanoneedles of required dimensions were fabricated with a simple replacement of microscope objective of different numerical aperture. Further, we have investigated the effect of confinement. Finally, the application of nanoneedles is demonstrated for trace level detection of picric acid using surface enhanced Raman spectroscopy and a field deployable portable Raman spectrometer.

We report on the diverse pulsed operation regimes of a femtosecond-laser-written Yb:KLuW channel waveguide laser emitting near 1040 nm. By the precise position tuning of a carbon-nanotube-coated saturable absorber (SA) mirror, the transition of the pulsed operation from Q-switching, Q-switched mode-locking and finally sub-GHz continuous-wave mode-locking are obtained based on the interplay of dispersion and mode area control. The Q-switched pulses exhibit typical fast SA Q-switched pulse characteristics depending on absorbed pump powers. In the Q-switched mode-locking, amplitude modulations of the mode-locked pulses on the Q-switched envelope are observed. The radio-frequency spectrum represents the coexistence of Q-switching and mode-locking signals. In the purely mode-locked operation, the waveguide laser generates 2.05-ps pulses at 0.5 GHz. ; National Research Foundation of Korea (2018H1A2AA1061480, 2019R1A2C3003504, 2020R1A4A2002828); Spanish Government (FIS2017-87970-R, MAT2016-75716-C2-1-R (AEI/FEDER,UE)); Junta de Castilla y León (SA287P18); Generalitat de Catalunya (2017SGR755).

A channel waveguide (WG) buried immediately below the surface of a Yb:KLuW crystal is used as a laser gain medium for passive 𝑄-switching by both evanescent- and direct-field interactions with single-walled carbon nanotubes (SWCNTs) near 1040 nm. The SWCNTs used as saturable absorbers (SAs) are deposited on top of the half-ring-type channel WG fabricated via femtosecond direct laser writing. The 𝑄 -switched WG laser delivers 88.5 ns pulses at a 1.16 MHz repetition rate with a maximum average output power of 680 mW. For the two different interaction schemes with SWCNT-SAs, the pulse characteristics, depending on the output coupling ratio and absorbed pump power, are experimentally investigated and compared to the results of theoretical analyses of the SA 𝑄-switched operation. ; National Research Foundation of Korea (2017R1A4A1015426, 2018H1A2A1061480); Spanish Government (FIS2017-87970-R, MAT2016-75716-C2-1-R (AEI/FEDER, UE)); Junta de Castilla y León (SA287P18); Generalitat de Catalunya (2017SGR755).

Ultra-short pulsed laser ablation may be used for high-precision machining with very low thermal influence on the processed materials. Due to this reason, lasers are increasingly used for processing of advanced materials, such as titanium alloys, nickel-based alloys or steel, every year. In this study, four advanced technical materials were analysed and compared under femtosecond laser irradiation with three different wavelengths. The main laser-material interaction parameters were identified, namely the ablation threshold and removal efficiency parameters. Higher removal rates were found for Ti6Al4V alloy with all three harmonic wavelengths. To increase process productivity, a method of increasing the repetition rate and scanning speed was presented. With the maximum repetition rate, the productivity increased five-fold with a similar removed depth and surface quality. Finally, the suitability of the identified parameters with regard to quality and productivity was demonstrated for fabrication of two complex structures – honeycomb and dot – which has the potential to improve friction properties of advanced materials.

In this work, the potential of femtosecond laser for optical fiber end-face inscription is highlighted by presenting a reliable setup for optical fiber longitudinal writing. This set-up has been used to write 1 dimension diffraction grating at the fiber end-face. Its far field intensity distribution has been measured and compared with simulations assuming rectangular air hole structure of same width and period. By comparing diffraction efficiencies, a first attempt of measuring hole deep is achieved. ; This work has been supported by the projects TEC2013-47264-C2-1-R, TEC2016-76021-C2-2-R (AEI/FEDER, UE) financed with FEDER funds, and grant BES-2014-069736 of the Spanish government and by the Parliament of Cantabria postdoc grant.

We report here the results obtained in surface ablation of RbTiOPO4 single crystals by femtosecond laser. We fabricated and characterized one-dimensional (1D) diffraction gratings with different lattice spacings of 15 and 20 μm, and with a sub-modulation of the period introduced in the later. The optical and electronic microscopy characterization and filling factor analysis of these diffraction gratings are reported. We also show that the roughness generated on the grooves by the ablation process can be improved by chemical etching. ; This work was partially funded by the European Commission under the Seventh Framework Program under Project Cleanspace FP7-SPACE-2010-1-GA-263044, supported by the Spanish Government under Projects PI09/90527, TEC2009-09551, AECID A/024560/09, FIS2009-09522, HOPE CSD2007-00007 and SAUUL CSD2007-00013 (Consolider-Ingenio 2010), by Catalan Government under Projects 2009SGR235 and 2009SGR549, by Junta de Castilla y León under Project GR27, and by the Research Center on Engineering of Materials and Systems (EMaS) of the URV. J.J.C. is supported by the Education and Science Ministry of Spain and European Social Fund under the Ramón y Cajal program, RYC2006-858. We also acknowledge support from the Centro de Laseres Pulsados, CLPU, Salamanca, Spain.

AbstractPhotonic chips have been recognized as a promising platform for information technology. On‐chip optical interferometers as fundamental building blocks of photonic chips are under extensive research with both conventional and novel fabrication techniques. Among them, recently, femtosecond laser has been attracting a great deal of attention as a powerful tool for directly writing micro‐optical devices in various materials due to its flexibility and three‐dimensional fabrication capability. This article gives a review on the working principles and recent achievements of on‐chip waveguides and interferometers fabricated by femtosecond laser, showing their potential applications in various scenarios.