This PDF file contains the front matter associated with SPIE Proceedings Volume 11357, including the Title Page, Copyright Information, Table of Contents, Author and Conference Committee lists.

Opening Remarks for Volume 11357: Fiber Lasers and Glass Photonics: Materials through Applications II

We present the radio frequency sputtering fabrication protocols for the fabrication on flexible polymeric substrates of glass-based 1D photonic crystals and erbium activated planar waveguides. Various characterization techniques, such as atomic force microscopy and optical microscopy, are employed to put in evidence the good adhesion of the glass coating on the polymeric substrates. Transmittance measurements are performed on the multilayer structure and indicate that there are no differences between the samples deposited on the polymeric and SiO₂ substrates, even after bending. Prism coupling technique is used to measure the optical parameter of the planar waveguide fabricated on flexible substrates. The ⁴I_13/2 → ⁴I_15/2 emission band, detected upon TE₀ mode excitation at 514.5 nm, exhibits the spectral shape characteristic of Er³⁺ ions embedded in a crystalline environment.

One of the current forefront in the field of photonic are flexible photonic research and development. The desired deliverable is to adjust the mechanical properties of materials to fabricate flexible photonic systems with various applications, e.g. gratings, channel waveguides, solar cells, protective coatings. It is well known that sol-gel metal oxide coatings may find applications as flexible coatings in photonics. Moreover, these materials can be easily functionalized to obtain materials with additional special, desired, properties like easy-to-clean, anti-fingerprint, anti-fogging and others, what is attractive for the potential of future commercialization of flexible photonic materials. In this work, we present the first step of research aimed to obtain silica-based coatings with appropriate adhesion on flexible substrates as poorly wettable surface – polymer PET and Ti-6Al-4V and 316L metallic thin foil as active oxide surface. The use of various types of substrates was aimed at presenting diversity in the possibilities of using the proposed coating materials. Nanoindentation, tensile test and scratch test of the investigated samples were studied. Measuring the mechanical properties of thin oxide films is difficult because it is usually impossible to detach of coating, not destroying its, from substrates. The thickness of coatings can range from a dozen to a few hundred nanometres, so complete methodology to determine a full set of mechanical properties is still lacking. In literature, the surface of samples is measured without a clear indication on coating properties, but on features which are the results of substrate-coating combinations.

Flexible photonics is an emerging technology in photonics applications. The availability of ultra thin glasses with thicknesses raging from tens to hundreds of microns is an appealing opportunity to be considered for flexible photonics applications substrates. The increase in mechanical characteristics, specifically strength, for such glasses is achieved by specific chemical compositions and ion exchange processes. The main physical effects to be considered are the introduction of residual stress profiles and refractive index modifications. Both aspects may interfere with flexible photonics applications of these glass substrates. There will be discussed the underpinning physics of stress build up and relaxation and how these effects may affect refractive index. The discussion will be mainly focused to the most promising glass chemical compositions already widely used in consumer electronics applications that is sodium aluminosilicates.

Er³⁺ doped tellurite-based glasses were prepared using standard melting process and their physical, optical, thermal, optical and luminescence properties were measured and compared. We found that the addition of Na₂O in the TeO₂-ZnO system leads to higher emission at 1.5μm as compared to the addition of TeO₂, Bi₂O₃, BaO, Nb₂O₅. We found that Bi₂O₃ should be used in order to increase the intensity of the upconversion under 976 nm excitation. The glasses were heat treated in order to grow crystals in these glasses. Surface crystallization occurred upon heat treatment with the precipitation of multiple crystals, the composition of which depends on the glass composition. The heat treatment was found to have no impact on the intensity of the emission at 1.5 μm. However, it increases the intensity of the red upconversion, especially for Bi₂O₃ containing glass.

The accurate knowledge of the rare-earth spectroscopic parameters is fundamental for the design of both fiber and integrated active devices. The lifetimes, the branching ratios, the up-conversion, the cross-relaxation, the energy transfer coefficients of the rare-earths must be preliminarily identified before the design. The particle swarm optimization (PSO) is an efficient global search approach; when applied to rare-earth-doped host materials and devices, it permits the rare-earth spectroscopic characterization starting from optical gain measurements. The model for the peculiar case of a SiO₂ - SnO₂ : Er³⁺ glass ceramic system is illustrated. Two different, direct and indirect, pumping schemes are considered for the rare-earth spectroscopic characterization. In the direct pumping scheme, a pump at 378 nm wavelength is used to excite the erbium ions. The SnO₂ does not take part in the excitation process. On the contrary, in the indirect pumping scheme the SnO₂ is involved by exploiting the absorption band around 307 nm wavelength via a proper pump. In this case, the energy transfer between the SnO₂ and the Er³⁺ ions occurs during the amplification process. The fabricated SiO₂ - SnO₂ : Er³⁺ glass ceramic slab waveguide is simulated via a finite element method (FEM) code and a homemade code is used to solve the rate equations. In order to identify the value of the SnO₂-Er³⁺ energy transfer coefficient, the ratio between the two simulated optical gains at 1533 nm wavelength, with the direct and indirect pumping schemes, is compared with the ratio between the two emission intensity measurements.

Mixed-alkali-alumina-borate glasses doped with different Cr₂O₃ content are prepared by conventional melt-quenching technique. Luminescent glass-ceramics is derived by volume crystallization of the precursor glass via two-stage heat treatment. The structural, spectral, and luminescent properties of the glass-ceramics are determined by X-ray diffraction, optical absorption, and photoluminescent spectroscopy. The XRD studies reveal the LiAl₇B₄O₁₇: Cr³⁺ nanocrystals nucleation during the heat treatment. The photoluminescence spectra consist of three intense bands in the 685 – 715 nm region. The features and background of the complex concentration dependence of the luminescence lifetime are discussed. The maximum quantum yield value under 532 nm excitation is 41%.

In this work, we report the influence of the excitation power density on the upconversion emission of Er³⁺ ions in novel glass-ceramic optical fibers containing NaLuF₄ nanocrystals codoped with 0.5ErF₃ and 2YbF₃ (mol%) prepared by the rod-in-tube method and controlled crystallization. Intense upconverted green and red emissions due to (²H_11/2,⁴S_3/2)→⁴I_15/2 and 4F_9/2→⁴I_15/2 transitions, respectively, together with a blue emission due to ²H_9/2→⁴I_15/2 transition has been observed under excitation at 980 nm. The upconversion emission color changes from yellow to green by increasing the excitation power density which allows to manipulate the color output of the Er³⁺ emission in the glass ceramic fibers. The tunable emission color is easily detected with the naked eye. This interesting characteristic makes these glass-ceramic fibers promising materials for photonic applications.

Controlling and manipulating light-matter interaction phenomena at the nanoscale leads to a variety of fascinating effects that are currently the focus of an intense research from both a fundamental and technological perspectives. In this talk, I will summarize the most recent advances on the fabrication and performance features of coherent light sources operating at the nanoscale, which are attained by the interaction of localized surface plasmons with optical gain nonlinear dielectric media [1]. The optical gain is provided by functional ferroelectric platforms, either by stimulated emission [2] or by nonlinear frequency conversion processes [3]. The mechanisms responsible for the intensification of the radiation–matter interaction processes are discussed in each case.

Transparent ceramics of cobalt-doped zinc aluminium spinel (gahnite), Co²⁺:ZnA₂O₄, are synthesized by hot pressing at 1520 °C for 4 h in the presence of zinc fluoride, ZnF₂, as a sintering additive. The effect of the ZnF₂ content (3–10 wt%) on the microstructure, Raman spectra, optical absorption and luminescence of ceramics is studied. The ceramics feature clean grain boundaries, the absence of pores and a narrow grain size distribution (mean grain size: 70-100 μm) resulting in high in-line transparency close to the theoretical limit. The obtained ceramics are suitable for fabrication of saturable absorbers of erbium lasers.

Random distributed feedback fibre lasers are well known type of fiber lasers where the optical feedback is organized via amplified Rayleigh scattering on random in space sub-micron refractive index inhomogenities¹. Random distributed feedback fiber lasers found their applications in telecommunications and distributed sensing systems, as well as attracted considerable amount of interest from researches². It is well-known that the generation spectrum of random distributed feedback fiber laser is a wide spectrum of typical width of 1 nm. It can be specifically tailored to demonstrate multiwavelength, tunable operation etc. However, the main features of the generation spectrum should be defined by the nature of the feedback itself. Usually the smooth bell-shaped spectrum is attributed to the incoherent nature of the feedback³. It is well known however that the Rayleigh scattering is an elastic scattering and should be resulted in the coherent feedback, which in turn leads to narrow features in the generation spectrum. Recently, narrow modes have been observed in the generation of the random distributed feedback fiber laser by means of scanning Fabry-Perot interferometer⁴. The spectral width of modes was about tens of picometers and was limited by the spectral resolution of the scanning interferometer. Those modes were attributed to the stimulated Brillouin scattering.

Yttrium orthoaluminate (YAlO₃) is an attractive laser host crystal for doping with thulium (Tm³⁺) ions. We report on the absorption and stimulated-emission (SE) cross-sections of this orthorhombic (sp. gr. Pnma) Tm:YAlO₃ crystal for the principal light polarizations, E || a, b and c. Polarized absorption data lead to the Judd-Ofelt parameters Ω₂ = 1.46, Ω₄ = 2.82 and Ω₆ = 1.09 [10^-20 cm²]. In particular, for the ³H₄ → ³H₅ transition, it is found a stimulated emission cross section of 0.86×10^-20 cm² at 2278 nm corresponding to an emission bandwidth of ~12 nm (for E || b). Continuous-wave laser operation on this ³H₄ → ³H₅ transition is achieved with an 1.8 at.% Tm:YAlO₃ crystal under laser-pumping at 776 nm. The mid-infrared Tm:YAlO₃ laser generated 0.96 W at ~2274 nm with a slope efficiency of 61.8% and a linear laser polarization (E || b). Tm:YAlO₃ is promising for mode-locked lasers at ~2.3 μm.

In this work spectroscopic and laser characteristic of photo-thermo-refractive (PTR) glasses doped with different concentrations of rare-earth ions (ytterbium-erbium and Neodymium) were comprehensively carried out. Spectroscopic parameters were obtained using some theoretical techniques like Judd-Ofelt theory and Fuchtbauer-Landenburg (F-L) theory. Results show that the optimal concentration of neodymium oxide in PTR is 0.5 mol%, at which the glass demonstrates the best spectral characteristics. It was found that PTR glass doped with 0.1 mol% of erbium oxide and codoped with 2 mol% of ytterbium oxide also shows good spectral-luminescent properties. Laser action on those two samples was demonstrated. optical losses were found to be 0.34 % for neodymium- doped PTR active element and 0.28 % in the case of erbium and ytterbium co-doped active element. These values are quite low and compared to that obtained in commercial laser glasses. It was concluded that the rare-earth ions doped PTR glass isIn this work spectroscopic and laser characteristic of photo-thermo-refractive (PTR) glasses doped with different concentrations of rare-earth ions (ytterbium-erbium and Neodymium) were comprehensively carried out. Spectroscopic parameters were obtained using some theoretical techniques like Judd-Ofelt theory and Fuchtbauer-Landenburg (F-L) theory. Results show that the optimal concentration of neodymium oxide in PTR is 0.5 mol%, at which the glass demonstrates the best spectral characteristics. It was found that PTR glass doped with 0.1 mol% of erbium oxide and codoped with 2 mol% of ytterbium oxide also shows good spectral-luminescent properties. Laser action on those two samples was demonstrated. optical losses were found to be 0.34 % for neodymium- doped PTR active element and 0.28 % in the case of erbium and ytterbium co-doped active element. These values are quite low and compared to that obtained in commercial laser glasses. It was concluded that the rare-earth ions doped PTR glass is a promising material that can be a good candidate for producing the DFB lasers. a promising material that can be a good candidate for producing the DFB lasers.

A scheme of a passively mode-locked fiber laser that deploys a Bismuth-doped germano-phosphosilicate fiber as an active medium is introduced. It operates at Bismuth amplification maximum of 1320 nm if suitably pumped at 1220 nm. We also introduce a model to describe the nonlinear light propagation in this laser in the regime of normal and anomalous group-velocity dispersion. The model is developed for two polarizations states accounting for a broad range of dynamical regimes connected to the state of cavity polarization. It also includes a low level of amplification in Bismuth. Depending on the level of the gain saturation energy, we observe the formation of stable dissipative solitons or incoherent pulses in the normal cavity group-velocity dispersion regime or the formation of single or two solitons per roundtrip in the anomalous dispersion regime. The results coincide well with already published experimental observations of dynamics in Bismuth lasers at 1320 nm which validates our model. As for the application potential, the introduced laser scheme can be used to effectively treat skin acne and various other medical applications.

Sub-surface femtosecond laser waveguide writing in ZnS is being investigated using both experimental and numerical simulations. We show that non-linear absorption and self-focusing play a critical role in the creation of the sub-surface modifications. The wavelength- and intensity dependence of the non-linear optical parameters change the strength of the sub-surface modifications when using lasers operating at different wavelengths. We investigate several wavelength ranges of interest, covering the wavelength peaks of the different non-linear processes. Furthermore, we compare the results of the numerical simulations to several different experiments and show a close correlation between the experimentally obtained results and the numerically obtained results. Finally, we also show that in the investigated wavelength range between 800nm and 1000nm there is no significant difference between the commonly used wavelengths for femtosecond laser processing, provided the other processing parameters are the same.

In this work, the existence of different crystal field sites for the rare-earth-doped tin dioxide nanopowder and RE-doped SiO2-SnO2 glass-ceramics is investigated. The slightly different crystal field symmetries have been resolved by using site-selective fluorescence line-narrowing spectroscopy. The obtained results show that a variety of optically non equivalent sites exist for the europium ion in the tin dioxide oxide structure associated to different allowed positions of the oxygen vacancies, whereas additional spectral disorder is found in the case of the glass-ceramic matrix. Ultrafast spectroscopy performed on Eu³⁺-doped tin dioxide nanocrystals shows that host-rare earth energy transfer occurs at a transfer rate of about 1.5×10⁶ s^-1. Similar experiments carried out for the Er³⁺-doped glass-ceramic system also validate the hypothesis that both host and matrix-excited RE emissions are decoupled due to the different origins of the involved physical mechanisms.

We systematically study cross-relaxation (CR) and ion clustering in Tm³⁺:CaF₂ crystals using a spectroscopic approach. For this, the luminescence from the ³H₄ and ³F₄ states was monitored for a broad range of Tm³⁺ doping concentrations, from 0.01 at.% to 7 at.%. The decay curves were fitted using a model of two ions classes, namely isolated ions showing no energy-transfer processes and ions with neighbors exhibiting both CR and energy-transfer upconversion (ETU), and accounting for energy-migration. The fraction of ions with neighbors and the microscopic concentration-independent CR and ETU parameters are deduced. The critical Tm³⁺ doping level for which at least half of the active ions are clustered is only 0.7 at.%. The obtained results are relevant for achieving efficient laser operation of Tm³⁺:CaF₂ crystals at the ³F₄ → ³H₆ (at ~1.9 μm) and the ³H₄ → ³H₅ (at ~2.3 μm) transitions.

In this paper, we performed numerical and experimental study of the stability of bismuth-doped high-GeO₂ glass core fiber used as an active medium in lasers operating in the wavelength region 1600 - 1800 nm. Mainly, we focus on the investigation of the joint effects of temperature and pumping radiation on the spectroscopic and laser characteristics of the fibers. Temporal evolution of the degradation of bismuth-related active centers (BACs) under pumping at 1550 nm, as well as the annealing of the fibers at temperature ranging from 300 to 550 °C was experimentally revealed and studied. A model describing the photochemical processes of the transformation of the BACs at different ambient conditions was proposed and used to make a long-term prediction of the dynamics of the process. The ability to simulate the long-term behavior of the medium might be instrumental since direct measurements are time consuming and therefore impractical. In addition, we performed numerical simulation to find out how the effect of photoinduced degradation of BACs affects the performance of a laser based on this type of fibers.

We have carried out measurements of Brillouin Scattering Stimulation on an optical resonator fabricated in Magnesium Fluoride. This technique allow obtaining various peaks corresponding to transverse and longitudinal frequencies inside the material. It correspond to slow transverse frequencies, fast transverse frequencies and longitudinal frequencies even if the precise determination is still to be improved.

Optical frequency combs (OFC's) are extremely important for optoelectronics to date. They have found a great variety of practical applications. Some of proposed OFCs generation methods apply acousto-optic (AO) devices. The AO devices in such schemes are used either as the element devoted to the OFC phase stabilization or, much less often, they play the role of the key element responsible for optical radiation frequency shifting in the frequency-shifting loop (FSL). In this paper we continue the theoretical examination of new OFC generation method based on joint application of collinear AO diffraction geometry and FSL. This method gives two novel OFC generation schemes. In the first one collinear AO cell is fed by radio-frequency (RF) generator and FSL connects AO cell optical output and input. The second scheme includes not only FSL but also the optoelectronic feedback connecting the optical output of the system with the piezoelectric transducer of the AO cell. In this case the system operates like optoelectronic generator and external RF generator is not needed. The theoretical model is presented for both cases. Each of the systems gives the possibility to generate OFCs in several ways with varying characteristics. The influence of collinear AO diffraction parameters on the generated OFC characteristics such as spectral width, number of spectral components and envelope shape is examined.

In the present work, we fabricated Yb-doped hybrid fiber, where unwanted mode suppression was achieved due to selective mode amplification technique. An asymptotically single-mode propagation regime of the realized hybrid fiber was observed in the amplifier scheme even for the case when significant amount of undesirable modes was excited at the fiber input. Measured dispersion of the hybrid fiber at wavelength of 1030 nm was about 70 psec/(nmkm). The realized hybrid fiber was used as nonlinear compressor in all-fiber amplifier scheme. As a seed source we used a commercially available chirped pulse laser (λ~ 1030 nm, a spectrum width was 11 nm and a pulse repetition rate was 42 MHz, pulse duration was adjusted to be of 1 psec by diffraction gratings established on the output of the seed laser). In our experiment to guarantee shorter optimal active fiber length we chose wavelength stabilized pump source at 976 nm. Thus the record high peak power (~10 kW) for all-fiber femtosecond Yb-doped laser schemes was achieved.

The development and the emergence of fully integrated all-fiber optical systems is very interesting from a technical point of view in photonics. Indeed, the development of mutimaterials fibers combining both optical waveguide properties and simultaneous in-fiber electrical excitation could provide plenty of innovative signal-processing, sensing or imaging functionalities. Here, we report the engineering of a new glass/metal composite fiber. For the glass, we have chosen tellurite glasses for their excellent thermo-viscous abilities (low T_g) and linear/nonlinear optical properties. This low T_g allows to have a larger panel of potential metals to be co-drawn with. The synthesis is firstly realized by build-in-casting at room atmosphere which allows to get a large-core. Then, the rod-in-tube technique and the insertion of metallic wires allow to get a step-index fiber with a small-core (7μm) and two continuous metallic electrodes running along the fiber axis (Øelectrodes = 30μm). Thus, we obtain a tellurite-based core-clad dual-electrode composite fiber made by direct, homothetic preform-to-fiber thermal co-drawing. The rheological and optical properties of the selected glasses allow both to regulate the metallic melting flow and to manage the refractive index core/clad waveguide profile. We will discuss the engineering of these multimaterials optical fibers and their characterization: thermal and viscosity properties, linear optical properties (loss), electrical properties with a continuity of the electrodes over meters of fiber.

We will discuss the use of some of the standard methods of computational materials science to predict the optical properties of glasses. Given the accuracy of state-of-the-art ab initio methods to simulate the dielectric properties of solids, some of these methods turn out to be a viable alternative to experimental studies, and they also allow for the prediction of dielectric properties in frequency ranges, which might not be easily accessible in a real experiment. Density functional based linear response theory for example allows for the simulation of dielectric properties over a wide frequency range, related to the many-electron system of a solid. We will summarize the corresponding theoretical background, and discuss the predictions made by applying some of these theoretical and numerical approaches to a variety of glasses. Beyond the modelling of one-particle excitations that contribute to the dielectric properties of a solid, we also point out the possibility to include contributions from particle-hole excitations based on the Bethe-Salpeter equation. We will summarize the corresponding theoretical background and show some numerical examples. Additional contributions to the dielectric properties, which stem from the vibrational motion of ions in a solid, are less straightforward to implement. Therefore, our principal focus will be on a critical assessment of various theoretical and numerical approaches discussed in the literature. With respect to novel types of technological applications based on thin glass films, we will focus on the implementation of up/down-conversion process in conventional types of solar cells as mediated by the deposition of glass layers containing rare earth ions. We will point out several possibilities, where numerical rather than experimental data may become the basis of a typical solar cell device simulation. Finally, we will suggest possible methodological improvements, which also take advantage of the accuracy and the numerical efficiency of first principles approaches.

Multi-core fibers (MCFs) are promising solutions for high power fiber based devices as they reduce nonlinearity and other unwanted detrimental effects, like transverse mode instability, by transporting, instead of a single high power beam, several low-powered ones to be coherently combined at the fiber output. This method relies on accurate evaluation of the phase differences between signals in different cores, which are significantly impacted by changes in the effective index of the propagating modes. For this to be effective, spatial heat generation must be accounted for. In particular, the heat flux from the doped cores to the external boundary causes a temperature gradient across the fiber, which affects the refractive index distribution, creating the chance for effective index change and thus dephasing of the output beams, which is harmful for beam combining. The results of in-depth numerical analysis on the performance of 9-core and 16-core MCFs under thermal effects are presented by studying the mode phase sensitivity to heat load and by introducing a coupled-mode theory model to study possible optical coupling effects. The effectively single-mode condition is also investigated by calculating the core modal overlap differences between fundamental and higher-order modes.

Some materials present difficulties for the fabrication of channel waveguides with standard technologies. They may suffer incompatibilities with the physical or chemical processes required in one or more steps involved in the fabrication technology itself or in the standard patterning techniques. An experimental Er3+ doped tungsten-tellurite glass, which gets damaged by standard lithographic techniques is one of such cases. However, this glass is of great interest thanks to its excellent optical and spectroscopic properties, high refractive index (nbulk < 2.0 at 635 nm), low cut-off phonon energy and broad emission bandwidth for the erbium (< 60 nm) within the C band of optical telecommunications. We have therefore successfully demonstrated a novel method of fabrication, namely by focussed C4+ ion beam implantation (FIB). Relatively heavy and swift ions like the ones used in this experiment allow to change the material properties with fluencies even 10 times lower than those required when using light ions. The use of a focussed beam has also allowed us to directly write the channel waveguides on the sample, without the use of any lithographic procedure, which renders the whole process flexible and simpler. The Er3+ doped tellurite glass with 60TeO2–25WO3–15Na2O-0.5Er2O3 (mol. %) composition was prepared by melt-quenching technique. The FIB irradiations were carried out at the 3 MV Tandetron 4130 MC (High Voltage Engineering Europa B.V.) of the Nuclear Physics Institute AV CR, Řež, with 4–6 nA beam current, 1·1014-5·1016 ions/cm2 fluence and the size of the scanning beam was 8 μm × 12 μm. The as-implanted waveguides showed very high propagation losses, about 14-20 dB/cm at 1400 nm, outside the absorption band of Er3+. A stepwise (each step 30 minutes long) thermal annealing allowed to reduce losses. At 150 °C, propagation losses decreased to 1.5 dB/cm. At higher temperatures propagation losses rose again, but at 200 °C coupling losses decreased, so that the best insertion loss, about 5 dB, was measured at this stage. The near-field images showed that the waveguide was monomode up to 1540 nm and that the mode width does not vary significantly with increasing temperature, whereas the estimated depth of the waveguides shows a slight increase. In order to obtain more information about the structural changes caused by the ion beam irradiation, profilometry and Raman characterisation has been carried out on the channel waveguides and also these results will be presented at the conference.

The output power of fiber-based single-frequency amplifiers, e.g. for gravitational wave detectors, is typically limited by nonlinear effects (e.g. stimulated Brillouin scattering). In addition to a high output power, long-term stable and less complex laser systems are required. It has been shown that all-fiber amplifier systems can be a suitable option to avoid power scaling problems of single-frequency solid-state lasers with injection locking. Chirally-coupled-core (3C®) fibers have been specifically designed to enable single-mode operation with a large mode area core to overcome these limitations. 3C®-fibers consist of a step-index fiber structure, whose signal core is additionally chirally surrounded by one or more satellite cores. For this purpose, the all-solid design of 3C®-fibers allows a manufacturing process of fiber-based components. We present various optical components based on 3C®-fibers for the realization of a single-frequency all-fiber amplifier. These amplifiers typically consist of a mode field adapter (MFA), cladding light stripper (CLS) and pump combiner (PC) to minimize the excitation of higher order modes, remove residual pump light and optimize the coupling efficiency of the pump light in the 3C®-fibers. The components have been specifically designed for the first time with 3C®-fibers and tested according to their performance. As a first prototype, a robust and monolithic fiber amplifier with an ytterbiumdoped 3C®-fiber in combination with commercially available standard fibers was developed. Overall, the fiber amplifier achieves an optical output power of 165W in a linearly polarized TEM00-mode. This work emphasizes the high potential of amplifiers based on 3C®-fibers as laser sources for the next generation of gravitational wave detectors and demonstrates that compact and robust amplifiers can be realized using 3C®-fibers.

Optical fibers mid-infrared (mid-IR) supercontinuum (SC) generation for sources covering the 1–20 μm range are of great interest for many applications in optics, spectroscopy, sensing for environmental monitoring or medical diagnosis and treatment. We present here our work regarding two low phonon energy glasses families, leading to highly nonlinear optical fibers for SC generation: tellurites and seleno-telluride glasses. Tellurite fibers are suitable for working in the 1-5 μm range, when seleno-telluride ones are intended to the 2-16 μm range. For tellurites, we focus on the definition of glass pairs suitable for the drawing of step index fibers with a controlled chromatic dispersion for a femto-second (fs) pumping around 2 μm. In the case of chalcogenide glasses, we focus on the Ge-Se-Te ternary system, which offers the advantage of allowing the drawing of step index or micro-structured fibers avoiding the usage of toxic arsenic. Depending on the fiber geometry the management of the chromatic dispersion is quite different. Suspended core fibers allow to shift deeply the unique zero dispersion wavelength (ZDW) towards short wavelengths for fs pumping around 2- 3 μm. For step index fibers, it is possible to design waveguides with no, one or two ZDW. Various pumping schemes are available between 3 and 9 μm, with a fs tunable source. As a result, SC generation experiments in these different fibers allows to reach wide spanning spectra, between 1 and more than 5 μm for tellurite fibers, and between 2 and more than 14 μm in the case of chalcogenides ones.

Many important molecules show strong characteristic vibrational transitions in the mid-infrared (MIR) part of the electromagnetic spectrum. This leads to applications in spectroscopy, chemical and bio-molecular sensing, security and industry, especially over the mid- and long- wave infrared atmospheric transmission windows of 3-5 μm and 8-13 μm. In this paper, we review some of our more recent experimental and simulation work aimed at developing new light sources based on chalcogenide glass optical fibres that can help us utilize this spectral region for biomedical applications. This includes the development of supercontinuum and bright luminescent sources and our progress towards fibre-based lasers. We place these developments in the context of MIR imaging and spectroscopy in order to show how they bring the promise a new era in healthcare and clinical diagnostics.

In this paper, we have developed Yb-doped fiber suitable for creation of all-fiber seed laser schemes operating near 977 nm. The fiber was based on a ring-doping design (cladding was partially doped with Yb-ions), which allowed us to fabricate a relatively small core and provide mode field diameter (MFD) of the active fiber comparable with standard fibers (to achieve small splicing losses with commercially available optical fibers) and, simultaneously, increase absorption from the cladding to keep a reasonably high lasing efficiency. So MFD_x of the fiber was 12 μm, MFD_y was 14 μm. Outer silica cladding of the active fiber was decreased to diameter of 80 μm and a special pump and signal combiner was used to inject pump and signal into the active fiber. Based on the developed Yb-doped fiber an all-fiber polarization maintaining mode-locked laser with central wavelength around 977 nm was demonstrated for the first time. SESAM was used as a saturable absorber. The laser was self-starting for pump powers above 4.6 W, with the output power of 3 mW. The autocorrelation was the best fitted with sech² profile and pulse duration was estimated to be as long as 9.5 ps. The fundamental cavity frequency corresponded to the pulse repetition rate of 33.532 MHz. Signal-to-noise ratio measured in the radio frequency range was more than 50 dB, the line width was below 1 kHz, which indicate ultimate stability of the fabricated mode-lock laser.

This paper reviews our latest achievements in the field of 2.1 um ultrafast Ho:fiber-based laser sources, including tunable all-fiber oscillators, diode-pumped optical preamplifier (booster), and high power fiber-based amplifiers. Pulse energy up to 1 mJ at the wavelength around 2.1 um was demonstrated out of picosecond ultrashort-pulse oscillator-amplifier system. On the application side, we report the volume modification of silicon using picosecond 2.1 μm laser system. We present both modelling and experimental results for the 2.1 μm ultrashort laser pulse interaction with silicon.

Fiber lasers are a great source for tunable lasers due to the wide and relatively flat gain spectra of rare earth transitions in a glassy host (as compared to crystals). Thulium (Tm)-doped fibers, in particular, offer an extremely wide tunability of up to 330 nm in the 2μm wavelength region in a dual gain module configuration¹. More recently, new concepts have emerged, which allow the synchronized emission of two or even more wavelengths². These sources are particularly useful for nonlinear frequency conversion via four-wave mixing (FWM) or difference frequency generation (DFG). We will present a very versatile fiber-integrated approach based on Fiber-Bragg-Grating (FBG) arrays implemented in a theta-shaped cavity. The Tm-doped fiber source emits typical average powers of 0.5W and is tunable from 1931nm to 2040nm. The emission linewidth follows the spectral characteristic of the FBG and is typically 30GHz in our case. This concept allows a constant wavelength-independent repetition rate as well as a synchronous emission of two or even three independently tunable wavelengths. The tuning is performed purely electronically by optical gating, and in addition the pulse duration can be tuned between 4ns and 25ns. The switching speed is very fast and was measured to be less than 10μs. These experiments will be contrasted with a different approach based on a VLMA fiber associated to a set of two volume Bragg gratings (VBG), one of them being angle-tunable. This concept allows pulsed (Q-switched) as well as CW operation and features a continuous and wider tunability of up to 144nm especially and also the dual wavelength mode. The output power was > 4.5W in CW mode and pulse peak power of 12kW have been obtained in the Q-switched mode with pulse durations of 25ns.

Nowadays, the request for femtosecond lasers operating between 1.7 μm and 2 μm is continuously growing for many applications. Mode-locked Holmium- or Thulium-doped fiber lasers based on Saturable Absorber Mirror (SAM) are typically the first approach to generate pulses in this spectral range but this technique suffers from a lack of tunability. Indeed, the operating wavelength is fixed by the SAM and the gain fiber. Another way to reach the 2 μm-spectral range consists to exploit the nonlinear phenomena appearing in optical fibers and in particular the Soliton-Self Frequency Shift (SSFS) effect from an Erbium-fiber laser. Several systems based on this phenomenon allowed the generation of ultrashort pulses at different wavelengths and in different type of fibers (step-index, PCF, …). In this paper, we report on the design of a compact and robust all-Polarization-Maintaining (PM) fiber system entirely based on commercial PM components. This system allows to generate a single femtosecond pulse continuously tunable from 1700 nm to 2050 nm. We also demonstrate that the sub-150 fs pulses are transform-limited over all the spectral range and thanks to an optimized rate conversion close to 50 %, the pulse energy and the peak power can reach the nJclass and the kW-class respectively, which represents a gain a of factor 2 compared to the previous works.

Optical fibre sensors based on long period gratings (LPG) modified with functional coatings that can change their optical properties in response to the presence of the particular analyte have attracted much research attention. Ultimately such sensors have the capability to become highly sensitive and selective bio- and chemical sensors. In addition to the advantages of all optical fibre sensors such as miniature size, immunity to electromagnetic interference and low power consumption, LPGs offer wavelengths encoded information which eliminates the need for a reference and are mechanically robust which makes them attractive for practical application. One of the key components in LPG bio- and chemical optical fibre sensors is a capture layer that provides chemical selectivity to the target analyte. In this work, an overview of the different LPG bio- and chemical optical fibre sensors functionalised with various capture layers such as mesoporous thin films, molecularly imprinted polymers (MIPs) and metal-organic frameworks (MOFs) will be presented. Particular focus will be given to potential applications of the novel optical fibre LPG sensors in healthcare with examples of measuring biomarkers (protein M-immunoglobulin) and drug delivery (anaesthetics) in intensive care.

Optical Backscatter Reflectometry (OBR) can transform a single mode fiber (SMF) in a distributed sensor. The operation principle is based on Rayleigh scattering occurring in optical fibers. Rayleigh scattering is a fiber deterministic property and its spectral signature is affected by temperature and strain changes in terms of wavelength shift. The OBR operation is limited to a single sensing fiber, while a parallel of multiple fibers results problematic for detection, since the parallel backscattered power cannot be discriminated. Critical applications, mainly in medical field, require both distributing sensing and high spatial sensor density. The current implemented solutions, exploiting optical switches, present a large temporal offset, not suitable for real-time operation. Here, an innovative paradigm of simultaneous spatial distributed multiplexing based on Scattering Level (SLMux) is presented. To achieve this operation, it is possible to exploit the properties of a high scattering MgO nanoparticles doped fiber (NPDF). This fiber is characterized by a random pattern of nanoparticles in the core. Its high backscattering, more than 40 dB larger than a SMF, can be used to discriminate the sensing point in the NPDF when inserted in a fiber parallel with other SMFs. This novel paradigm is suitable for critical applications of biomedical engineering, some of them successfully demonstrated in our laboratories. One of them consists in 2D/3D thermal mapping during hyperthermia tumor treatment, which is obtained by applying a radiofrequencies (RF) in the tumoral area to raise the temperature over 60 °C, thus inducing cellular mortality. The local temperature monitoring is fundamental to stop the RF dosing and avoid tissue carbonization. A second application consists of 3D shape sensing of medical tools, like needles. The shape reconstruction of needles during penetration in human body is fundamental in high precision applications. The shape of a needle equipped with optical fibers, can be reconstructed by sensing the strain along the fiber. A parallel of four fibers can reconstruct both 3D shape and compensate temperature.

Development of efficient, non-destructive, time-saving and innovative instruments for material identification surveying is urgently requested in several fields, including solid-state physics, industrial processing, waste recycling and environmental contamination detection. In this respect, coupling laser-induced breakdown spectroscopy (LIBS) and (near-infrared unit) NIR reflectometry with hyperspectral imaging spectroscopy (HIS), owing to its power and versatility, is key to more efficient and time-saving diagnostic of chemical and physical properties of rocks and unconsolidated materials. Here we present the FLY-SPEC instrument conceived to combine these three relevant techniques for space exploration surveying. The recent assemblage of its LIBS unit has allowed us to conduct our first pilot experiments.

This work describes a procedure based on a set of thermally stimulated luminescence measurements coupled to an original theoretical analysis which allows estimating the distribution in energy of carrier-trapped states developing in the bandgap of silica-based optical fiber glasses under ionizing irradiation. This procedure is applied to undoped, aluminum-, phosphorus- and rare-earth-doped silica samples from tailormade optical fiber preforms, after irradiations in two very different conditions. The extracted Densities Of Trapped States (DOTS) always relate to distributions of trapped holes. Within a 1-1.5 eV energy range above the valence band, these DOTS contain the energy levels of well-known intrinsic or dopant-related color centers recognized as major contributors to the radiation-induced attenuation in silica fibers. Long irradiation times strongly impact the DOTS by depleting shallow states and favoring the “condensation” of holes in deep levels. This enhances the density of color centers (deeper than 1 eV) and explains part of the RIA increase with the dose.

SrAl₂O₄ that is optically activated by Eu²⁺, often additionally co-doped with Dy³⁺, is a non-radioactive persistent phosphor which is known for its excellent afterglow properties. It has found various applications, e.g. in the watch industry, for security signs, in medical diagnostics, and in photovoltaics. The monoclinic SrAl₂O₄ was synthesized in polycrystalline form and structurally characterized. Its luminescence and afterglow properties were studied. Wavelength-dependent thermoluminescence experiments were performed on SrAl₂O₄:Eu and SrAl₂O₄:Eu,Dy polycrystalline samples. Substitution of Sr²⁺ by Eu²⁺ on two different Sr sites in the crystal is associated with blue and green Eu²⁺ emission. Excitation at 445 nm allows to selectively excite one of the two different Eu²⁺ ions, whereas excitation at 375 nm excites both Eu²⁺ ions. Incorporation of dysprosium increases significantly (by a factor of about 4 to 8) the total number of traps involved in the afterglow of this persistent phosphor. Increasing the temperature at which the samples are irradiated (loaded) from 173 K to 248 K reveals that many new traps can only be occupied or activated at higher temperatures, leading to a strong increase of the integrated thermoluminescence intensity, in particular for the Dy-codoped samples. The results of this study reveal that the diversity of traps leading to the long afterglow is much larger than previously reported in the literature. We propose that the presence of dysprosium induces an excitation-induced charge-transfer reaction Eu²⁺ + Dy³⁺ → Eu³⁺ + Dy²⁺. However, the principal traps responsible for the efficient afterglow are temperature-activated and appear to be associated with the green-emitting Eu²⁺ ion on the Sr2 site coupled to a nearby dysprosium ion.

Multiphasic optical fibers are promising systems to develop new optical devices. The main issue for their optimization is the control of the structure of the phases. To improve the structuring capabilities, fiber drawing has been evidenced to modify the size and shape of the multiphasic structure of optical fibers. This possibility comes from the occurence of capillary effects during the flow of the material during the fiber drawing. To use the fiber drawing as a structure tailoring step, the main hindrance is the lack of information on the physical properties of the systems of interest. To that aim, this article presents the work done to measure these properties. Based on experimental results, the characterization of the flow of the fiber drawing of silica-based optical fibers containing nanoparticles is presented. A numerical model for the simulation of the flow of particles and its validation are detailed. Preliminary results of the deformation of particles of various properties in the flow of the fiber drawing are finally presented, indicating a possible non-newtonian behaviour of the particles.

Hybrid plasmonic photonic structures combine the plasmonic response with the photonic band gap, holding promise for utilization as optical switches and sensors. Here, we demonstrate the active modulation of the optical response in such structures with two different external stimuli, e.g. laser pulses and bacteria. First, we report the fabrication of a miniaturized (5 x 5 mm) indium tin oxide (ITO) grating employing femtosecond laser micromachining, and we show the possibility to modulate the photonic band gap in the visible via ultrafast photoexcitation in the infrared part of the spectrum. Note that the demonstrated time response in the picosecond range of the spectral modulation have an industrial relevance. Moreover, we manufacture one-dimensional photonic crystals consisting of a solution-processed dielectric Bragg stack exposing a top-layer of bio-active silver. We assign the bacterial responsivity of the system to polarization charges at the Ag/bacterium interface, giving rise to an overall blue shift of the photonic band gap.

A series of 2-(1-benzyl-2-(styryl)-6-methylpyridin-4(1H)-ylidene) fragment containing glassy organic compounds have been synthesized from relevant luminescent 4H-pyran-4-ylidene derivatives and investigated as potential solution processable emitters. Glass transition temperatures of synthesized 1H-pyridine compounds are above 100°C with thermal stabilities higher than 260°C. In the solutions of dichloromethane their absorption bands are in the range from 350 nm to 500 nm with photoluminescence from 500 nm to 650 nm. In a contrary to the 4H-pyran-4-ylidene derivatives, the incorporation of various electron acceptor fragments within the 1H-pyridine fragment containing molecules only slightly influenced absorption and photoluminescence band shifts. Based on these compounds, neat spin-cast films were obtained and investigated as light-emitting mediums which show amplified spontaneous emission (ASE) with λ_max in the range from 603 nm to 615 nm with ASE threshold values as low as 46 μJ/cm². Synthesized 1H-pyridine derivatives show perspective to be applied as solution-processable components for light-amplification studies.

We report on a novel approach to fabricate channel (ridge) waveguides (WGs) in bulk crystals using precision diamond saw dicing. The channels feature a high depth-to-width aspect ratio (deep dicing). The proof-of-the-concept is shown for a Tm:LiYF₄ fluoride crystal. Channels with a depth of 200 μm and widths of 10–50 μm are diced and characterized with a confocal laser microscopy revealing a r.m.s. roughness of the walls of about 1 μm. The passive waveguiding properties of the channels are proven at ~815 nm showing almost no leakage of the guided mode into the bulk crystal volume. The laser operation is achieved in quasi-CW regime. The maximum peak output power reaches 0.68 W at ~1.91 μm with a slope efficiency of 53.3% (in σ-polarization). The laser mode has a vertical stripe intensity profile. The proposed concept is applicable to a variety of laser crystals with different rare-earth dopants and it is promising for sensing applications.

A simple recursive method based on the circulating field approach to obtain the exact electric-field and intensity distributions in an arbitrary multi-resonator structure is presented. Reflectivity curves obtained via this method and the coupled-mode theory are compared.

The steps toward the fabrication of directly-extruded microstructured fibre preforms made of a bioresorbable phosphate glass are herein presented. Microstructured fibres show a wide range of applications, i.e. photonic crystal fibres, large mode area fibres, hollow gas/liquid sensors, etc. Nevertheless, the fabrication of bioresorbable microstructured fibres has not been feasible so far due to a lack of bioresorbable transparent glass and more flexible fibre preform fabrication techniques. A custom developed calcium-phosphate glass has been designed and carefully prepared in our laboratory to be dissolvable in a biological fluid while being optically transparent and suitable for both preform extrusion and fibre drawing. This glass has been characterised both in terms of mechanical and optical properties as well as for dissolution in aqueous medium. Furthermore, the proposed glass is thermally stable, i.e. can be processed both in the extruder and in the drawing tower. Several extrusion experiments have been carried out with different glass preforms’ shapes. Analyses of these preforms by means of Optical Profilometry and Atomic Force Microscopy have been carried out to assess the roughness of the surface of the extrudate. To support the production of an optimized die for the preform extrusion, a simplified laminar flow model simulation has been employed. This model is intended as a tool for a fast and reliable way to catch the complex behaviour of glass flow during each extrusion and can be regarded as an effective design guide for the dies to fulfil specific needs for preform fabrication. After die optimisation, extrusion of a capillary was realised, and a stacking of extruded tubes was drawn to produce a microstructured optical fibre made of bioresorbable phosphate glass. The combination of bioresorbability and fibre microstructure, show a promising pathway toward a new generation of implantable biomedical devices.

In this poster we are interested in knowing how multi-physic optimization can simulate and be helpful to find an optimal design for resonator coupling. It is based on COMSOL multi-physics software.

We report on random lasing observed with 5-m-long Er-doped fiber comprising an array of weak fiber Bragg gratings (FBGs) inscribed in the fiber core and uniformly distributed over the whole fiber length. The laser design ensures domination of dynamical population inversion grating over the FBGs in total distributed feedback enabling laser stabilization and nonlinear laser line filtering of the natural laser Lorentzian linewidth down to sub-300-Hz range, both observed in the experiment.

Multilayer structures are commonly used components in optics and photonics due to their unique properties to manipulate the spectral response of light. Multilayer-driven components for sensing purposes can bring some advantages such as high sensitivity, fast signal response, electromagnetic interference immunity, and low power consumption. Thus, a mechanically coupled optical system can be the right candidate for force and vibration detection. In this work, we propose and demonstrate an optomechanical sensing system for pressure and vibration detection using two multilayer structures, a circular membrane, a light source, and a photodiode. The design of this proposed system consists of two parts, which are optical design and mechanical design. In the optical design, we modeled the optical response of the multilayer structures in the visible spectra using the Transfer Matrix Method. The mechanical response, on the other hand, is calculated using finite element simulations via the COMSOL Multiphysics software. The multilayer structures are fabricated by RF-Sputtering technique and then integrated through a 3D printed mechanical housing. The sensor characteristics (sensitivity and resonance frequency) are experimentally investigated by a static loading test and a transient response analysis. Results are shown that the sensor frequency around 510 Hz and the sensitivity of the sensor about 50 Pa.

We report on the first laser operation of a novel double molybdate compound, Yb:KY(MoO₄)₂. Single-crystals were grown by the Low Temperature Gradient (LTG) Czochralski method. The crystal structure (orthorhombic, sp. gr. Pbna – D¹⁴_2h) was refined with the Rietveld method. Yb:KY(MoO₄)₂ exhibits a layered structure leading to a strong optical anisotropy and a perfect cleavage along the (100) plane. The stimulated-emission cross-section for Yb³⁺ ions is 3.70×10^-20 cm² at 1008.0 nm and the emission bandwidth is 37 nm (for light polarization E || b). Continuous-wave laser operation is achieved in a 3 at.% Yb:KY(MoO₄)₂ crystal plate (thickness: 286 μm) under diode pumping. The microchip laser generated a maximum output power of 0.81 W at 1021-1044 nm with a slope efficiency of 76.4% and linear polarization. Yb:KY(MoO₄)₂ crystal films / plates are attractive for sub-ns passively Q-switched microchip lasers and thin-disk lasers.

The influence of phosphate content on the formation and luminescent properties of Nd³⁺-doped fluorophosphate glass has been studied. Using the Judd-Ofelt theory the phenomenological intensity parameters Ωt (t= 2; 4; 6) were obtained. Absorption and emission measurements are performed in order to evaluate the spontaneous emission probability, absorption cross-section, emission cross-section, fluorescence lifetime and quantum efficiency. The stimulated emission cross-sections ⁴F_3/2→4I_11/2 and transitions were determined according to J-O theory by the modified reciprocity method (MR) for all phosphate concentrations and theoretical gain cross sections have been calculated. The effects of the glass rigidity and phosphate presence in glass composition on radiative properties have been estimated. In order to evaluate the amplification properties of studied samples at 1.06 μm, gain/loss spectra for glass with 5 mol.% of Ba(PO₃)₂ and commercial Nd³⁺-doped glass were experimentally obtained. Comparison with commercial Nd³⁺ doped glass showed that fluorophosphate glass has a higher gain of 1.8 dB/cm.

We report on fabrication, structure, spectroscopic and nonlinear properties of a new functional optical material – transparent glass-ceramics (GCs) based on Co²⁺,Ga³⁺-codoped ZnO (Co²⁺:GZO) nanocrystals. The introduction of Ga³⁺ cations that are smaller than Zn²⁺ ones and have a different valence state, is expected to modify the crystal field around the Co²⁺ ions leading to broadband absorption at the ⁴A₂(⁴F) → ⁴T₁(⁴F) transition. The glass of the ZnO – K₂O – Al₂O₃ – SiO₂ system was doped with 3 mol% Ga₂O₃ and 0.05 mol% CoO. Transparent GCs were produced by secondary heattreatments at 680 – 860 °C. They contained one crystalline phase - nanosized (8 – 26 nm) hexagonal GZO crystals, Ga³⁺ ions being distributed between the ZnO nanocrystals and the residual glass. The absorption spectra of GCs contained an intense band at 1.3-1.65 μm related to the ⁴A₂(⁴F) → ⁴T₁(⁴F) Co²⁺ transition in T_d sites. A rise of IR losses due to the free charge carrier scattering in GZO was observed. Absorption saturation of transparent GCs was studied at ~1.54 μm. They exhibited low saturation fluence, 0.7–1.3 ± 0.2 J/cm², and high laser-induced damage threshold, ~25 J/cm². Co²⁺,Ga³⁺- codoped ZnO-based transparent GCs are promising for passive Q-switching of eye-safe erbium lasers emitting at ~1.5- 1.7 μm.

We propose to estimate the error on the frequencies obtained when using the method of Brillouin Light Scattering (BLS). This method of characterization makes it possible to determine a frequency shift in the microwave domain. This shift corresponds to the speed of propagation of the phononic waves inside or on the surface of the material that one wants to characterize. The question arises as to how precisely the microwave frequency will be given. We feel that this will depend on several factors such as the direction and dispersion of the laser signal, but also the characteristics of the instruments used. We therefore refer to the Guide of Uncertainties Measurements (GUM). This guide edited by the ‘Bureau International de Poids et Mesures’ (BIPM) makes it possible to have a tool in the estimate of the error that one seeks to determine. In this poster, it is shown that the accuracy of the determination of the propagation speed can be of a few percent.