Laser-writing of ring-shaped waveguides in BGO crystal for telecommunication band

We report on the fabrication of ring-shaped waveguides operating at the telecommunication band in a cubic Bi4Ge3O12 (BGO) crystal by using technique of femtosecond laser writing. In the regions of laser written tracks in BGO crystal, positive refractive index is induced, resulting in so-called Type I configuration. The modal profiles are within the designed track cladding with ring-shaped geometries, which are analogous to circular optical lattices. The homogenous guidance along both TE and TM polarizations has been obtained at telecommunication wavelength of 1.55 μm. Both straight and S-curved waveguiding structures have been produced with ring-shaped configurations. This work paves the way to fabricate complex photonic networks for telecommunications by using ring-shaped waveguides in compact chips.National Natural Science Foundation of China (NSFC) (61775120); Junta de Castilla y León (Project SA046U16); Spanish Ministerio de Economía y Competitividad (MINECO, FIS2013-44174-P, FIS2015-71933-REDT)

Ultrafast direct laser writing of cladding waveguides in the 0.8CaSiO3-0.2Ca3(PO4)2 eutectic glass doped with Nd3+ ions

We report on tubular cladding optical waveguides fabricated in Neodymium doped Wollastonite-Tricalcium Phosphate glass in the eutectic composition. The glass samples were prepared by melting the eutectic powder mixture in a Pt-Rh crucible at 1600 °C and pouring it in a preheated brass mould. Afterwards, the glass was annealed to relieve the inner stresses. Cladding waveguides were fabricated by focusing beneath the sample surface using a pulsed Ti:sapphire laser with a pulsewidth of 120 fs working at 1 kHz. The optical properties of these waveguides have been assessed in terms of near-field intensity distribution and transmitted power, and these results have been compared to previously reported waveguides with double-line configuration. Optical properties have also been studied as function of the temperature. Heat treatments up to 700 °C were carried out to diminish colour centre losses where waveguide's modes and transmitted power were compared in order to establish the annealing temperature at which the optimal optical properties were reached. Laser experiments are in progress to evaluate the ability of the waveguides for 1064 nm laser light generation under 800 nm optical pumpingThis work has been partially supported by the projects MAT2013-48426-C2-1-R, DISFOTINT (MECC, TEC2010-21574-C02-01/02) and MICROSERES (Comunidad de Madrid, P2009/TIC-1476). Dr. Daniel Sola thanks the Bosch and Siemens Home Appliances Group, the 7th Framework Programme EU No 314630-UV Marking and MAT2013-41045-R for the financial support of his contrac

Signalling through the yeast MAPK Cell Wall Integrity pathway controls P-body assembly upon cell wall stress.

Post-transcriptional control of mRNA is a key event in the regulation of gene expression. From yeast to human cells, P-bodies are cytoplasmic RNA-protein aggregates that play an essential role in this process, particularly under stress conditions. In this work, we show that in the model yeast Saccharomyces cerevisiae cell wall stress induces the formation of these structures. This effect is dependent on multiple elements in the Cell Wall Integrity (CWI) MAPK signalling pathway, a signal transduction cascade responsible for the maintenance of cell integrity under adverse environmental conditions. Remarkably, P-body assembly requires the catalytic activity of the MAPK of the pathway, Slt2/Mpk1. In accordance with the control exerted by this signalling pathway, the timing of P-body formation is similar to that of the activation of the CWI pathway. Noticeably, mRNAs whose expression is regulated by this pathway localize in P-bodies after the cell is exposed to stress following a temporal pattern coincident with CWI pathway activation. Moreover, when these mRNAs are overexpressed in a mutant background unable to form visible P-bodies, the cells show hypersensitivity to agents that interfere with cell wall integrity, supporting that they play a role in the mRNA lifecycle under stress conditions

Implementación de nuevas metodologías docentes en asignaturas del Área de Óptica: aula invertida y aprendizaje colaborativo

Memoria ID-036. Ayudas de la Universidad de Salamanca para la innovación docente, curso 2021-2022

Thermal and Optical Characterization of Undoped and Neodymium-Doped Y3ScAl4O12 Ceramics

Y3–3xNd3xSc1Al4O12 (x = 0, 0.01, and 0.02) ceramics were fabricated by sintering at high temperature under vacuum. Unit cell parameter refinement and chemical analysis have been performed. The morphological characterization shows micrograins with no visible defects. The thermal analysis of these ceramics is presented, by measuring the specific heat in the temperature range from 300 to 500 K. Their values at room temperature are in the range 0.81–0.90 J g1–K–1. The thermal conductivity has been determined by two methods: by the experimental measurement of the thermal diffusivity by the photopyroelectric method, and by spectroscopy, evaluating the thermal load. The thermal conductivities are in the range 9.7–6.5 W K–1 m–1 in the temperature interval from 300 to 500 K. The thermooptic coefficients were measured at 632 nm by the dark mode method using a prism coupler, and the obtained values are in the range 12.8–13.3 × 10–6 K–1. The nonlinear refractive index values at 795 nm have been evaluated to calibrate the nonlinear optical response of these materials.This work is supported by the Spanish Government under projects MAT2011-29255-C02-01-02, MAT2013-47395-C4-4-R, and the Catalan Government under project 2014SGR1358. It was also funded by the European Commission under the Seventh Framework Programme, project Cleanspace, FP7-SPACE-2010-1-GA No. 263044

Watt-level ultrafast laser inscribed thulium waveguide lasers

International audienceWe report on the first watt-level ultrafast laser inscribed Thulium waveguide (WG) lasers. Depressed-index buried channel WGs with a circular cladding (type III) are produced in monoclinic Tm3+:KLu(WO4)2 crystals. Laser operation is achieved under conventional (3H6 → 3H4) and in-band (3H6 → 3F4) pumping. In the former case, employing a Raman fiber laser emitting at 1679 ​nm as pump, the continuous-wave Tm channel WG laser generated 1.37 ​W ​at 1915–1923 ​nm with a record-high slope efficiency of 82.7% (with respect to the absorbed pump power), a threshold of only 17 ​mW and a spatially single-mode output with linear polarization. The WG propagation losses were 0.2 ​± ​0.3 ​dB/cm. Passive Q-switching of Tm channel WG lasers is achieved using Cr2+:ZnS and Cr2+:ZnSe saturable absorbers. With Cr2+:ZnS, record-short pulses of 2.6 ns/6.9 ​μJ ​at a repetition rate of 8.0 ​kHz were generated. The developed WGs are promising for compact GHz mode-locked lasers at ~2 ​μm

Tm 3+ and Ho 3+ colasing in in-band pumped waveguides fabricated by femtosecond laser writing

International audienc