Publications de Georgios Violakis

Monitoring of Torque Induced Strain in Composite Shafts with Embedded and Surface-Mounted Optical Fiber Bragg Gratings

John Botsis, Georgios Violakis, Georgios Pappas

In this study, silica glass, optical fiber Bragg gratings (FBGs) are used for torque-induced strain monitoring in carbon fiber reinforced polymer (CFRP) hollow shafts toward the development of a methodology for structural load monitoring. Optical fibers wi ...

2021

Microfabrication of curved sidewall grooves using scanning nanosecond excimer laser ablation

Patrik Willi Hoffmann, André Gabriel Kostro, Josef Andreas Schuler, Georgios Violakis, Jing Gong

Novel glazing with embedded micro-mirrors can significantly reduce the energy consumption due to cooling and lighting in buildings. Especially promising are large arrays of periodic micro compound-parabolic-concentrators (CPCs) with angular-selected transm ...

SPIE2018

An experimental-numerical investigation of hydrothermal response in adhesively bonded composite structures

Hans Georg Limberger, John Botsis, Véronique Michaud, Roohollah Sarfaraz Khabbaz, Georgios Violakis, Luis Pablo Canal Casado

Water absorption and thermal response of adhesive composite joints were investigated by measurements and numerical simulations. Water diffusivity, saturation, swelling, and thermal expansion of the constituent materials and the joint were obtained from gra ...

Elsevier2015

Monitoring strain gradients in adhesive composite joints by embedded fiber Bragg grating sensors

Hans Georg Limberger, John Botsis, Véronique Michaud, Roohollah Sarfaraz Khabbaz, Georgios Violakis, Luis Pablo Canal Casado

The adhesive bonding of composite materials can be applied to assemble light-weight structures for aeronautical applications. However, the application of adhesive bonds in primary load-bearing structures is limited by the lack of adequate techniques to mon ...

Elsevier2014

Annealing of UV Ar+ and ArF excimer laser fabricated Bragg gratings: SMF-28e fiber

Hans Georg Limberger, Georgios Violakis

Fiber Bragg gratings fabricated in pristine SMF-28e fibers using pulsed ArF-excimer and cw 244-nm Ar+ laser were annealed using tempering rates from 0.0038 to 0.25 K/s. Demarcation energy mapping allowed for the determination of the frequency factors and t ...

Optical Society of America2014

Stability of Fiber Bragg Gratings Fabricated Using UV Ar+ and ArF Excimer in Bismuth-Aluminum-co-Doped Silica Fibers

Hans Georg Limberger, Georgios Violakis

Continuous annealing of fiber Bragg gratings fabricated using cw and pulsed laser irradiation in Bi-Al-co-doped fibers of different concentrations show activation energy spectra linked to Bi-Al. Thermal stability maps were obtained by their analytical repr ...

2014

Monitoring strain gradients in adhesive composite joints by embedding fibre Bragg grating sensors

Hans Georg Limberger, John Botsis, Véronique Michaud, Behzad Dehghan Manshadi, Georgios Violakis, Luis Pablo Canal Casado

2013

Dose dependence of luminescence increase in H2-loaded Bi-Al co-doped optical fibers by cw 244-nm and pulsed 193-nm laser irradiation

Hans Georg Limberger, Georgios Violakis

The near infrared luminescence is increased in H2-loaded Bi-Al co-doped optical fibers by irradiation of cw 244-nm or pulsed 193-nm laser light. The dose dependence is different for the two lasers. ...

Ieee2013

UV-induced luminescence and photosensitivity in bismuth-aluminum doped optical fibers

Georgios Violakis

EPFL2013

Photosensitivity and Luminescence Induced by ArF-Irradiation of Hydrogen Loaded Bi-SiO2 Fiber

Hans Georg Limberger, Georgios Violakis

Bi:SiO2 fiber drawn under oxidizing conditions shows ultra-low photosensitivity and no NIR luminescence under 1064 nm pumping. Hydrogen loading followed by ArF irradiation induced both. The increase of photosensitivity and the creation of luminescence cent ...

2013

Thermal decay of UV Ar+ and ArF excimer laser fabricated Bragg gratings in SMF-28e and Bi-Al-doped optical fiber

Hans Georg Limberger, Georgios Violakis, Pouneh Saffari

Fiber Bragg Gratings were fabricated using a 193-nm-ArF-excimer laser with ac index changes of 0.6×10E-4 and 2.2×10E-4 in pristine and H2-loaded Bi-Al-SiO2 fibers. Thermal annealing of the FBGs was investigated using continuous isochronal annealing. ...

2012

Thermal decay of ArF-excimer-laser fabricated fiber Bragg gratings in Bi-Al-doped optical fibers

Hans Georg Limberger, Georgios Violakis, Pouneh Saffari

Fiber Bragg Gratings were fabricated using a 193-nm-ArF-excimer laser with ac index changes of 0.6×10E-4 and 2.2×10E-4 in pristine and H2-loaded Bi-Al-SiO2 fibers. Thermal annealing of the FBGs was investigated using continuous isochronal annealing. ...

2012

Fabrication of Bragg Gratings in Microstructured Bi:SiO2 Optical Fiber Using an ArF Laser

Hans Georg Limberger, Georgios Violakis

An ArF excimer laser was used to fabricate Bragg gratings in Bi:SiO2 core - microstructured cladding optical fiber. Average and modulated refractive index changes of 2.7 × 10E-4 and 1.0 × 10E-4 were induced in pristine fiber. Fiber luminescence was also me ...

IEEE2012

Stress changes in H2-loaded SMF optical fibers induced by cw-Ar+ 244 nm irradiation

Hans Georg Limberger, Nandita Aggarwal, Georgios Violakis

Bragg gratings were inscribed in H2-loaded SMF-28e optical fibers and measured for axial stress changes for various exposure doses. Mean refractive index changes as high as 7.5 × 10-3 were observed under cw-244 nm irradiation of 143 W/cm2. Bragg grating re ...

Optical Soc Amer2012

Fabrication of Bragg gratings in microstructured and step index Bi-SiO2 optical fibers using an ArF laser

Hans Georg Limberger, Georgios Violakis

An ArF excimer laser was used to fabricate Bragg gratings in fibers with Bi-SiO2 core and microstructured or F-doped claddings without fiber presensitization. Average and modulated refractive index changes of 2.7 x 10(-4) and 1.0 x 10(-4) were induced in p ...

Optical Society of America2012

Strong fiber Bragg gratings in Bi-Al co-doped H2-loaded optical fibers using CW-Ar+ laser

Hans Georg Limberger, Georgios Violakis

Bragg gratings with reflectivity > 93% were fabricated in Bi-Al co-doped H-2-loaded optical fibers. Average index changes as high as +2.5x10(-3) were obtained. Positive core stress changes indicate a compaction contribution to the total index change. ...

Optical Soc America, 2010 Massachusetts Ave Nw, Washington, Dc 20036 Usa2011

Fabrication and thermal decay of fiber Bragg gratings in pristine and H-2-loaded Bi-Al co-doped optical fibers

Hans Georg Limberger, Georgios Violakis

A cw-244-nm-Ar+ laser was used to fabricate Bragg gratings in pristine and H-2-loaded Bi-Al-SiO2 optical fibers with index changes as high as 3.6 x 10(-4) and 19.3 x 10(-4), respectively. For comparison, fiber Bragg gratings in pristine and H-2-loaded SMF- ...

Optical Society of America2011

Fabrication of mode field converter in H2-loaded SMF-28e using CW-Ar+ laser

Hans Georg Limberger, Nandita Aggarwal, Georgios Violakis

We report on mode field diameter changes of -31% due to UV-induced core refractive index changes of

Optical Soc America, 2010 Massachusetts Ave Nw, Washington, Dc 20036 Usa2011

Fabrication of fiber Bragg gratings in 40 mm diameter low GeO2 silica fiber using cw-Ar+-laser

Hans Georg Limberger, Georgios Violakis

Mean index changes >10-3 were obtained in non-hydrogen-loaded 3% GeO2-doped silica fibers with a 9/40 micrometer core/cladding diameter using a cw 244-nm-Ar+-laser. Core stress changes are positive indicating a compaction contribution to the index change. ...

Optical Society of America2010

Formation of Bragg gratings in pristine SMF-28e fibre using cw 244-nm Ar+-laser

Hans Georg Limberger, Georgios Violakis

The formation of short Bragg gratings in SMF-28e non-hydrogen loaded pristine fibre using a cw Ar+ laser operating at 244 nm is reported. Mean refractive index changes >10-3 were obtained for a laser intensity of about 513 W/cm2 and a total dose of 5.9 MJ/ ...

Institution of Engineering and Technology2010