This PDF file contains the front matter associated with SPIE Proceedings Volume 12142, including the Title Page, Copyright information, Table of Contents and Conference Committee list.

Incorporating new optical materials as nanocrystals into glass fibres for new functionalities has recently become a hot research topic. Our team (funded by the European FET Open project NCLAS) investigates the introduction of nanoscale laser crystallites into the core of optical fibres using the glass powder doping method. Active Y₂O₃:Pr³⁺ nanocrystals (NCs) were prepared via different synthesis methods, and structurally and spectroscopically characterized. After modification of technological parameters, the optimised NCs have been proposed as a luminescence centres to embed into germanate and silicate glass hosts. Glasses were analysed in terms of optical (transmission, refractive index matching to NCs) and thermal (thermal stability, viscosity, thermal expansion coefficient) parameters. Crystallisation issues during fibre drawing were particularly investigated. In a first step, glass powder-NCs mixing techniques and fibre preform preparation were developed. It was shown that temperature cycle profiles including dwell time and heating/cooling ramp rates influenced the glass-NCs properties and can lead to glass crystallisation or NCs dissolution. The sintering investigations pointed out the melting temperature limits to preserve active NCs in the glasses. In germanate glasses, Y₂O₃:Pr³⁺ dissolution was noticed at 800°C. In the case of the silicate glass compositions these regions vary from 700°C to 1050°C. The results allowed to select optical fibre drawing conditions performed by the powder-in-tube method. Their distribution uniformity is not yet sufficient, requiring further optimisation of the drawing kinetics.

Planar polycrystalline laser waveguides with the structure YAG/Yb:YAG/YAG were produced by ceramic processing. Transparent ceramics represent a valid alternative to single crystals as the flexibility of the ceramic process paves the way to new application opportunities. The implementation of different ceramic shaping techniques allows the production of complex or multicomponent (composite) structures that are generally difficult or about impossible to obtain with single crystals. A practical example are the planar structures presented here, characterized by a strict control of the dopant distribution obtained already during the shaping process, without further machining or bonding. The waveguides are composed of a laser active Yb:YAG layer obtained by tape casting with a thickness between 100 and 250 μm placed between dopant-free YAG cladding obtained by oxide powder mixing. The refractive index of Yb:YAG is higher than YAG thus realizing a multimode waveguide. Two types of geometries were tested: 1. simple planar waveguide with a sandwich structure (confinement in one direction); 2. waveguide with a rectangular cross section (confinement in two directions). The waveguides were tested for laser emission in a cavity end pumped by a fiber coupled diode laser, under quasi-CW pumping conditions (rectangular pump pulses with 10 ms duration, 10 Hz), delivering up to 60W at 936 nm. The planar waveguide has shown a maximum output power of 14.4 W (slope efficiency 39.1%, optical efficiency 27.4%) whereas the 2D waveguide had a maximum output power of 11.6 W (slope efficiency 38.4%, optical efficiency 22.4%). Lasing wavelength was 1030 nm.

Noble metal colloids in a dielectric matrix material exhibit surface plasmon resonance at visible wavelengths, which is well known to lead to intense coloration effects. The absorption peak at the resonance frequency is linked to a change of the refractive index even at wavelengths only marginally affected by the absorption. We explore the potential of using this refractive index change for creating dielectric waveguides by means of a versatile photocatalytic silver deposition process. The specific planar waveguide structure consists of a thin high refractive index layer comprising the photocatalyst and the silver colloids, topped by a cladding layer, on a low refractive index glass substrate. Using grating coupling, waveguide modes guided predominantly in the cladding could be demonstrated using red light with acceptable losses down to the 10 dB/cm range. However, the change of the effective refractive index that can be achieved with silver colloids at this low attenuation is below 10-4 , only sufficient for very weak lateral guiding. The fundamental mode centered on the high refractive index layer would be more sensitive to the amount of silver colloids, but this applies to both the effective refractive index and the attenuation. A significant reduction of the bandwidth of the surface plasmon resonance peak would be required to improve this trade-off. So far, the greater potential seems to be in the integration of areas containing silver colloids for sensors or nonlinear devices with plasmonic waveguides defined by fully metallized areas.

The research interest for tungsten oxide (WO₃) as a photonic material is prompted by its extraordinarily broad range of applications, deriving from its polymorphism and variety of substoichiometric WO_3-x phases. WO₃ contributes compact and smooth electrochromic layers for smart windows, UV optical detectors and nanoporous photo-electro-catalytic membranes. Full-optical chemical sensors can also be provided, by optically read-out of its chemically modified dielectric response. Radio-Frequency (RF) sputtering is a versatile method to synthesize WO_3-x. It provides films of different stoichiometric ratios, either glassy or crystalline, either porous or compact. In this work we report about an ongoing experimental activity on optical-grade WO_3-x thin films, fabricated by non-reactive magnetron RF-sputtering in Ar atmosphere. Stoichiometry and structure are tailored by post-growth thermal annealing in dry air. Annealed films are quite transparent in the near infrared NIR and short-wave infrared SWIR optical range. Their quality was assessed by morphological, structural and compositional characterizations. Dielectric properties were evaluated by optical spectroscopy and ellipsometry, also rating the amount of optical anisotropy of thin films in its crystalline phase. To boost the sensitivity of RF-sputtered WO_3-x layers as spectroscopic opto-chemical sensors, their direct integration at top of 1D Photonic bandgap structures can be conceived. We summarize the results on the design of a photonic chip structure, formed by a silica-titania multilayer and capped with a 450 nm-thick WO_3-x film, that effectively confines near-IR optical field in the topmost layer, as suitable for sensing of environmental contaminants in gas and vapor phase.

Integration of photonic systems on deformable substrates has given rise to flexible photonics, a research field that has rapidly emerged in recent years. By adding mechanical flexibility to planar photonic structures, the spectrum of applications gains an incredible expansion. Flexible glassy photonic structures require a careful design and suitable fabrication protocols, in order to keep the optical and spectroscopic properties similar to their traditional rigid counterparts, even under mechanical deformation. Here, a radio frequency (RF) sputtering deposition protocol is developed for fabricating glass-based 1D photonic crystals on ultrathin flexible glass as well as on rigid substrates for comparison. Three different 1D multilayer structures, constituted by SiO₂ and HfO₂ layers, were first designed and modelled by Transfer Matrix Method to tailor targeted optical features (transmission windows, stopband ranges) and then fabricated by RF-sputtering technique. The structural, morphological, and optical features of the samples were investigated. In particular, the transmission spectra of the glass-based 1D photonic crystals, deposited on both flexible and rigid substrates, were acquired to highlight up to which extent the different nature of the substrates and the mechanical deformations (bending tests on the flexible structures) are not influencing the key spectral properties of the photonic crystals.

To efficiently sense small gas concentrations using a whispering gallery mode resonator a xerogel coating can be applied onto the surface of the resonator. In this way, gas molecules can enter into the xerogel layer where they can interact with the electric filed of the whispering gallery modes. Here we present some results on ammonia gas detection using a silica microsphere coated with a sol-gel porous silica xerogel. The frequency shift of an isolated whispering gallery mode was measured in dependence on the ammonia gas concentration in the testing chamber and efficient gas sensing was observed. We discuss the observed results and elaborate how the proposed systems sensitivity can be tailored in respect to the geometrical parameters of the system including the sphere radius and the coating thickness.

For the development of flexible photonic devices, polymeric substrates are of capital importance due to their low cost and mechanical flexibility. However, they are sensitive to the environment’s influence on their durability. To overcome problems of polymeric substrates’ stability, we developed organically modified hybrid silica-titania coated PET (polyethylene terephthalate) films. The focus was put on the determination of the optical properties’ changes in dependence on the synthesis and materials processing parameters. Thanks to the application of the coatings, a protection effect on substrate and improvement in the transparency in comparison to the uncoated heat-treated polymeric material, was obtained.

The luminescence properties of Dy³⁺ and Tb3+ single- as well as Dy³⁺ / Tb³⁺ double-doped barium borate glasses are investigated for their potential as light-converter. In double-doped barium borate glass an energy transfer from Dy³⁺ to Tb₃₊ is observed, i.e., an intense green luminescence from the doped Tb³⁺ ions results upon excitation at Dy³⁺-related absorption bands. Ray-tracing simulations allow for an evaluation of singleand double-doped light guides in different length. Here, the luminous flux and luminance values at the rough output face of a luminescent light guide are determined.

In this work, we present preliminary results of the fabrication and characterization of 1D Fabry–Perot microcavity realized on Yb3+ activated SiO2-SnO2 glass-ceramic (SiO2-SnO2:Yb3+). A radiofrequency-sputtering/sol-gel hybrid deposition process was developed for the microcavity fabrication. The fabrication included (i) radiofrequency-sputtering (rf-sputtering) of SiO2/HfO2 Bragg reflectors and (ii) sol-gel deposition of the active SiO2-SnO2:Yb3+ defect layer. A good control and enhancement of the spontaneous emission for Yb3+ luminescence sensitized by SnO2 nanocrystals was achieved exploiting microcavity properties. Such results are valuable for development of low-threshold rare-earth-based coherent light sources, pumped by broadband UV diodes.

This work is devoted to investigation of the spectral and luminescent properties of lithium-germanate, lithium-sodium germanate and lithium-zinc-germanate glass ceramics obtained by high-temperature heat treatment of the initial glass doped with manganese and chromium ions. It is shown that when sodium is added to Mn-doped lithium germanate glass-ceramics, the luminescence intensity of Mn4+ ions increases from 5 to 37% of the quantum yield. In lithium-zinc-germanate glass-ceramics, the simultaneous presence of Mn4+ ions in an octahedral environment with red luminescence near 670 nm and Mn2+ ions in a tetragonal environment with long persistent green luminescence at 540 nm is found. The maximum quantum yield for red luminescence was 47%, for green luminescence – 23%. The intensity ratio of different luminescence bands depends on the ratio of lithium / zinc ions in the glass composition. In all studied glass-ceramics, Cr3+ ions demonstrate weak luminescence with a maximum in the region of 690–698 nm. The possibility of using the materials under study as a luminescent red radiation source material is considered.

The aim of this work is to investigate temperature effect on spectral properties CsPbI3 perovskite nanocrystals nucleated in borogermanate glass by isothermal heat treatment at different temperatures. The temperature dependence of the first exciton absorption intensity in the heating-cooling cycle has a form of hysteresis loop, which helps determine crystallization and melting temperatures. Considering anomalies on heat curves, a phase transition from a non-perovskite to a cubic crystal structure is found in the range of 420-460℃. The increase of initial nucleation temperature from 470 to 550℃ results in a change of phase transitions temperatures: melting, crystallization, and transition from a non-perovskite to a cubic crystal structure increase in the regions 454-475, 281-301 and 421-459℃ respectively due to quantum-sized effect. Results demonstrate that the cesium lead halide perovskite properties can be stabilized up to 440℃, which greatly exceeds the chemical resistance of perovskites in organic matrix.

Nanoparticles in optical fibers have gained tremendous interest over the last three years, in particular as optical fiber sensors. The performance of such fibers is based on the analysis of Rayleigh backscattered light with Optical Backscatter Reflectometry. To customize the shape of nanoparticles, i.e. light scattering, we will discuss on two different thermal treatments: (i) thermal engineering operating during the drawing of the preform containing nanoparticles, (ii) by heating the fibers with a conventional furnace. These approaches demonstrate the ability to tune the shape of the nanoparticles thanks to appropriate heat treatment.

Eu³⁺ - doped oxyfluoride tellurite-germanate glass-ceramics were fabricated by the controlled crystallization method. The microstructure and structure of samples were analysed using x-ray diffraction (XRD), transmission electron microscopy (TEM), and infrared spectroscopy (IR). The EuF₃ introduction caused the rise of the non-bridging oxygens/fluorides in glass network in a consequence of the [TeO,F₄] and [GeO,F₄] structural units transformation into the [TeO,F₃]/[TeO,F₃₊₁], and [GeO,F₆], respectively. These changes were caused by Eu³⁺ ions, which played the role as a network modifier and led to the new non-bridging oxygens/fluorides Te–O,F− Eu³⁺O,F−–Te, and Ge– O,F−Eu³⁺O,F−–Ge, linkages formation and the ZnTe crystalline phase. The structure changes caused by the Eu3 + ions incorporation in the crystalline phase have been discussed in accordance to analysed the photoluminescence (PL) spectra and decay curves. It was showed a significant increase of the 5D0 → 7F1 magnetic-dipole transition intensity and decay times for transparent glass-ceramics sample. It confirmed the migration of Eu3+ ions from the amorphous network into ZnTe nanocrystals.

Nowadays, continuous wave (cw) lasers have conquered a broad spectrum of applications in industrial laser processing and can be considered as the dominant tools in many manufacturing floors. This is reflected by the enormous average annual growth rates of 25-30 % and the continuous research efforts dedicated to this laser type leading to ever increasing output power and beam quality. This development imposes ever increasing demands on the quality of the optical laser components, that have to withstand the usually harsh industrial environment and high power levels. In fact, the corresponding of the laser components is a key factor for the efficiency and economic success of an employed laser material process. This in turn requires a thorough assessment of the quality parameters ruling the stability of such components. Among many other quality parameters, the Laser Induced Damage Threshold (LIDT) is one of the leading parameters that has to be investigated in detail. The corresponding measurement facilities and protocols as well as the evaluation of the data have to be performed with high reproducibility and comparability among different testing laboratories. As a consequence, such qualifications can only be achieved on the basis of well-defined international standards defining the complete procedure for the determination of LIDT values. We investigated the laser induced damage threshold of different types of optics using a cw laser with a wavelength of 1030 nm and power up to 6 kW, applying beam diameters of approximately 200-300 µm on the surface. The samples were irradiated for at least 30s or until damage occurred. First, it was necessary to review the existing DIN EN ISO 21254 regarding cw-irradiation of mirrors with a 25 mm diameter. An important aspect is the number of possible irradiation spots on each optic with respect to the damage size as well as the emitted debris. Both effects limit the statistical accuracy, the ISO procedure needs to be adapted to the measurement conditions. Additionally, we investigated the influence of substrate materials and coating processes on the LIDT of high reflective coatings and their damage behavior, especially regarding their thermal conductivity. The results were then compared with simulations concerning the maximum temperature within the optical component.

Fluoroindate glasses co-dopped with Er³⁺ at different concentrations were synthesized using the melting quenching technique, where it was observed that the emission peak located at 1.53 μm associated with 4I_13/2→4I15/2 transition of Er₃₊ increases up to 11.5 times with increasing ErF₃ content up to 1.4 mol. %. Such increase is significant due to their proximity with one of the most important telecommunication windows (1.55 μm) which the spite of all the studies around it, some challenges like its efficiency need to be optimized. The effect of sensitization of the Er³⁺ by Yb³⁺ ions was also evaluated. The increase in luminescence intensity (~19%) was obtained by co-doping of 1.4ErF₃ glass by 0.8YbF₃. This effect is related to the efficient Yb³⁺→ Er³⁺ energy transfer.

The laser transition at 1.05μm of Nd³⁺:CaF₂, known to be quenched because of cross-relaxation energy transfers among Nd³⁺ ions, can lead to laser operation by codoping Nd3+ with optically inactive buffer ions, such as gadolinium and yttrium. This codoping enables a fine tailoring of the laser crystal spectroscopic properties depending on the nature and the concentrations of the co-dopants. We present in this work the investigation of laser gain measurements and its detailed characterization using a CaF2:0.5%Nd, 2.5%Gd,2.5%Y crystal, obtaining a laser amplification of 25% in small signal conditions with 800mW of pump power. Continuous wave (CW) laser action is also achieved with the same crystal leading to a 46% slope efficiency with respect to the absorbed pump power using an 8% output coupler transmission. The tunability of this laser crystal is also investigated from 1048 to 1072 nm for different pump wavelengths showing a flat spectral profile around 1052 nm. All these results show that this type of crystal is appealing for high peak power diode-pumped amplifiers and ultrashort pulse generation.

Holmium ions (Ho³⁺) are attractive for generation of green emission according to the ⁵F₄+ ⁵S₂ → ⁵ I₈ transition. We report on the assessment of the potential of Ho³⁺ -doped fluoride glasses for green fiber lasers exploiting the double-clad fiber geometry. ZBLAN glasses doped with HoF3 (0.1 – 0.9 mol%) were studied. The absorption cross-section for the ⁵ I₈ → ⁵F₁+ ⁵G₆ transition is 1.75×10^-20 cm² at 448.5 nm. Under excitation in the blue, the glasses exhibit intense green luminescence. The stimulated-emission cross-section for the ⁵F₄+ ⁵S₂ → ⁵ I₈ transition is 0.67×10^-20 cm² at 549 nm. With increasing the HoF₃ doping level, the luminescence lifetime of the ⁵F₄+ ⁵S₂ states slowly decreases in the range of 291 – 180 μs. The output performance of a diode-pumped green Ho fiber laser was simulated for a fiber geometry with a double D-shaped inner cladding. The variable parameters were the HoF3 doping level, the fiber length, and the output coupling. It is shown that the generation of watt-level green output from such a laser is possible when using relatively short (<1 m) fibers with low doping levels (about 0.5 mol% HoF₃), as well as high transmissions of the output coupler (<60%, depending on the passive losses in the fiber).

We report on the synthesis and a detailed spectroscopic study of an Er³⁺ -doped “mixed” (Lu,Y,La)2O3 transparent sesquioxide ceramic. Nanopowders of the composition (Lu_0.63Y_0.25La_0.05Er_0.07)2O3 were obtained by a glycine-nitrate self-propagating high-temperature synthesis. The ceramics were obtained by vacuum sintering at 1750 °C for 3 hours. La₂O₃ acted as a sintering additive and increased the disorder of the sesquioxide lattice. The ceramic had a cubic (C-type) structure. At 1.05 μm, its transmission was 78.9%. The ceramic exhibited intense mid-infrared emission owing to the ⁴ I_11/2 → ⁴ I_13/2 Er ³⁺ transition. The corresponding peak stimulated-emission cross-section σSE is 1.12×10-20 cm² at 2717 nm. The luminescence spectrum exhibited a considerable inhomogeneous broadening as compared to the parent compounds, Er:Lu₂O₃ and Er:Y₂O₃. The luminescence lifetimes of the ⁴ I_11/2 and ⁴ I_13/2 manifolds were measured (1.99 ms and 3.35 ms, respectively), representing a favorable ratio for mid-IR laser operation. The crystal-field splitting of Er³⁺ multiplets in C₂ sites was determined at low temperature.

Femtosecond mid-IR and long wave IR lasers provide tremendous opportunities for imaging and sensing because they combine high spatial coherence of the laser beams (crucial for remote sensing), high temporal coherence of mode-locked oscillators (enabling dual comb spectroscopy in important molecular fingerprint region), and few-optical-cycle pulses (enabling IR sensing with high dynamic range via electric field sampling with low cost room temperature near-IR photodetectors). The development of such a sources (especially compact and field-deployable sources) is a challenging task that relies on the most advanced bulk laser technologies, new gain and nonlinear materials for a wide range of laser wavelengths. We present a viable route to the generation of power and energy scalable few-cycle pulse trains in the IR and describe the application of the developed sources for dual comb spectroscopy. The laser architecture is based on a combination of laser and nonlinear interactions in polycrystalline Cr:ZnS media that enables simultaneous amplification of ultrashort pulses, nonlinear pulse compression to 2-optical-cycle, and nonlinear broadening of pulses’ spectrum to an optical octave. Importantly, all of the necessary optical signals for stabilization of the frequency comb with the large lever arm are generated directly inside polycrystalline Cr:ZnS. This, in turn, has allowed us to implement robust and reliable shoe-box sized middle-IR frequency combs with ultra-low timing jitter of the pulse trains, broad instantaneous spectra, and Watt-level average power.

We report on the growth, structure and spectroscopy of an Er³⁺ -doped Na₅Y₉F₃₂ (5NaF∙9YF₃) crystal featuring significant inhomogeneous spectral broadening. Single-crystals of Na₅Y₉F₃₂ doped with 0.22 – 9.63 at.% Er3+ were grown by the Czochralski method. Er:Na5Y9F32 exhibits a cubic fluorite-type structure (a = 5.4881(2) Å for 5.59 at.% Er³⁺ doping). The most intense Raman band of this material is found at ~404 cm^-1 . Er³⁺ ions in Na₅Y₉F₃₂ exhibit a broad and smooth emission band owing to the ⁴ I_11/2 → ⁴ I_13/2 transition with a maximum stimulated-emission cross-section of 0.42×10^-20 cm₂ at 2708 nm. According to the Judd-Ofelt analysis, the radiative lifetime of the ⁴ I_11/2 multiplet is 10.0 ms and the luminescence branching ratio β( ⁴ I_11/2 → ⁴ I_13/2) is 17.6%. The luminescence lifetimes of the ⁴ I_11/2 and ⁴ I_13/2 Er³⁺ states were studied as a function of the doping concentration. For 5.59 at.% Er doping, they are 7.72 ms and 6.69 ms, respectively, representing a favorable ratio for mid-infrared laser operation.

The Large Mode Area (LMA) fibers are attractive in the field of new components in optical fiber technology in the field of sensing and novel radiation sources. The numerical analysis of multi-ring (multi trench) fiber construction is investigated for eye-safe transmission spectral range (1400-2100 nm). The optical fiber refractive profile construction of ∆n (0.001- 0.004) for different radial step ∆r (1.0-1.6 µm) is used for the investigation of linearly polarized modes (LP01 and LP11) propagation. The maximum mode field diameter (MFD) of LP01 was calculated. The results confirm the LMA propagation possibility in the presented fiber construction. The single-mode guiding was confirmed for different ∆n and ∆r parameters in the investigated spectral range. The cutoff wavelength <1400 nm and single-mode operation are possible for ∆n=0.001 and ∆r=1 µm.

We demonstrate operation of a tunable mode-locked thulium-doped fiber laser, based on a wavelength-selective chirped fiber Bragg grating (CFBG). By applying strain to the CFBG, we shift its reflection band and can thereby tune the emission-wavelength of the fiber laser between 2022 nm and 2042 nm. We obtain a pulse train at 9.4 MHz repetition rate and a pulse duration between 9.0 and 12.8 ps. To the best of our knowledge, we report the first tunable mode-locked thulium-doped fiber laser using a tunable CFBG as wavelength-selective element.

Here, we present a high pulse energy Raman laser at 1946 nm wavelength pumped with a 1533 nm linearly polarized fiber laser, with ∼92 μJ pulse energy, ∼60 pm linewidth, 8 kHz repetition rate, and 7 ns pulse duration. The Raman laser is based on the stimulated Raman scattering (SRS) effect in an 8-meter carbon dioxide (CO2) filled nested anti-resonant hollow-core fiber (ARHCF). The nested structure contributes to the significant reduction of the fiber loss caused by light leakage, surface scattering and bend, therefore allowing coiling the gas-filled ARHCF with a relatively small bend radius of just ~5 cm. When the pressure in the CO2-filled ARHCF increases from 1 to 17 bar, the pulse energy first reaches the maximum pulse energy level of 16.3 μJ (corresponding to 28 % quantum efficiency) at only 1.2 bar, and then rapidly decreases due to the pressure-dependent overlap of the Raman laser line with the absorption band of CO₂ at 2 μm spectral range. The relative intensity noise (RIN) of the Raman laser reaches a minimum level (4%) when the pulse energy exceeds ∼8 µJ. Due to the low amount of heat release during the SRS process, the laser has a good long-term stability without significant drift. Our results constitute a novel and promising technology towards high-energy 2 μm lasers.

We propose here to study experimentally and numerically periodic amplitude fluctuations of a pulse train emitted by a 1030 nm all-PM fiber mode-locked laser. Nonlinear Polarization Evolution (NPE) permits to achieve the mode-locking operation. NPE only occurs along a long span of standard PM fiber located between an off-axis polarizer and a Faraday Mirror. In the rest of the cavity composed of an Ytterbium doped fiber and a chirped Fiber Bragg Grating, NPE does not occur because the light propagates only according to the slow axis of the fiber. When the mode-lock regime is established, the laser delivers a stable pulse train at a repetition rate of 1.01 MHz. Beyond a given pump power, a periodic amplitude fluctuation of the pulse train appears. This fluctuation has a period two times longer than the pulse train period: a pulse with high amplitude is always followed at the next round-trip by a pulse with smaller amplitude and this latter is followed by a high amplitude pulse and so on. It forms a so-called period doubling. The amplitude modulation increases with the pump power. If the pump power is further increased, then period quadrupling and then octupling are observed and an experimental bifurcation diagram is reported. A significant increasing of pump power leads to a route to chaotic amplitude variation.

We numerically consider the system of coupled Raman fiber lasers which depending on the phase shifts between coupled cavities can be operated either in PT-symmetric or PT-broken generation regime. Within the full dynamical model of coupled NLSE we plot the generation properties map over phase shifts and pump powers. We found different types of the generated radiation in both PT-symmetric and PT-broken phase: quasi-CW stochastic generation, generation of noise-like pulses, and stable pulsed generation of narrow pulses of 100-200 ps width. We also reveal transitions between different generation states and types of the radiation over pump power and/or phase shifts between coupled cavities. In addition, we determined the optimal parameters of a system of coupled Raman fiber lasers to achieve pulsed lasing depending on the lasing regime with respect to PT symmetry.

We study multiphoton absorption-induced damages to standard silica multimode optical fibers, induced by means of femtosecond infrared laser beams. During the damaging process, the dynamics of beam propagation turns out to non-trivially evolve over a time scale of several hours. Such a long term evolution produces an irreversible drop of the optical transmission, which is accompanied by a drastic change of the output supercontinuum spectrum. A microscopic analysis of the damages was carried out by means of both optical microscopy and absorption-contrast computed X-ray tomography. This has permitted us to obtain information about the sign of the refractive index variation which is induced by the optical breakdown. Our results will find application in a wide array of emerging technologies employing high-power fiber optic beams, such as fiber lasers and micromachining.

A tapered Er-doped fiber amplifier for high peak power pulses amplification has been developed and tested. The core diameter changed from 15.8 µm (mode field diameter (MFD) 14.5 µm) to 93 µm (MFD 40 µm) along 3.7 meters maintaining single-mode performance at 1555 nm (according to the S2-method, the part of the power of high-order modes does not exceed 1.5 %). The amplification of 0.9 ns pulses with spectral width below 0.04 nm up to a peak power above 200 kW (limited by self-phase modulation) with a slope pump-to-signal conversion efficiency of 15.6% was demonstrated.

Optical Whispering Gallery Mode (WGM) microresonators are an ideal platform for miniature and high sensitive sensors. They exhibit very small mode volumes and extremely high Q factors of the order of 10⁶ - 10⁹ providing a platform with low nonlinearity thresholds and low detection limits to environmental changes. Here we present and discuss some of the WGM-based applications we have been developing in our lab. Specifically, we present a WGM strain sensor based on a silica stretchable microsphere, with a Q factor of 108 . Tension stress is applied along a microsphere with two fiber tails by pulling on one tail. Consequently, the microsphere's WGMs are shifted and the measurement may serve as a strain sensor. Based on this strain sensor, a WGM magnetic sensor is suggested where the mechanical response of a magnetostrictive material to a varying magnetic field applies the tension stress. In addition, a narrow linewidth laser source for these sensors is described here as well, where a multimode diode laser is locked to a single WGM of the microsphere via self-injection feedback from the microsphere. This optical locking is accompanied with a substantial spectral narrowing of the multimode diode laser.

Enhancing the efficiency of solar energy harvesting schemes, particularly photocatalytic processes, by means of spectral converting materials stands up as an emerging route not yet fully explored. In this context, there is a growing interest in harvesting energy from the large near-infrared (NIR) range of solar radiation (approx. 60% in terms of the photon number or 40% of the energy from the sun’s total incoming radiation) for various energy and environmental applications. The immediate goal is to bridge the gaps of photocatalysts by shifting NIR photons into UV-VIS ones through up-conversion photonic mechanisms. Here we present different photonic materials (glasses, crystals and solvothermal core-shell nanocrystals) showing high intense NIR-to-UV-VIS upconversion luminescence. Photocatalytic degradation of organic dye methylene blue as a pollutant model has been successfully attained under NIR radiation. We have also successfully achieved hydrogen and oxygen evolution via water-splitting using Al-doped SrTiO3 (STO:Al) photocatalyst, loaded with rhodium-chromium oxide (RhCrOx) as a hydrogen evolution cocatalyst in order to enable the overall water-splitting reaction. Both experiments have been carried out under low-power commercial 980 nm laser irradiation. Up-conversion driven photocatalysis is proved, as a solely photonic effect, converting incident NIR radiation before reaching the contaminated solution. We also explore the implementation of rare-earth doped upconversion materials with the performance of luminescent solar concentrators (LSC), as a promising option for enhancing the efficiency of optical devices

A new method of laser energy delivery in turbid media has been created. It can greatly reduce light power transmission loss by using multibeam interference. The feasibility of the method has been proved by theoretical calculation. The apparatuses have also been designed and show excellent performance. The method uses a mode-locked fiber laser to emit a short laser pulse into a mirrored negative dispersion device. The light pulse spectral components form multiple beams with different frequencies. As dispersion occurs, the width of the laser pulse is broadened in the device, and so the combined intensity of the multiple beams is greatly decreased. When these beams enter the turbid medium, the medium absorption and scattering will also be greatly reduced because of their greatly decreased combined intensity. Meanwhile, the positive dispersion of the turbid medium starts to compress the broadened laser pulse. If the mirrored negative dispersion device is designed to produce ideal mirrored dispersion compensations, the broadened laser pulse can be compressed well in the turbid medium and create a combined intensity maximum, which becomes an internal light layer with extremely high intensity. In this way, the laser energy delivery distance can be largely increased. For example, the calculations show that wireless optical communication distances can be increased to more than 1000m in clean ocean water, and no incision laser surgery operating depths can be increased to more than 5cm with the possibility of even up to 10cm in the human body with a high precision of ~1μm and no X-ray radiation injury.

Enhanced Rayleigh backscattering optical fibers, interrogated by an optical frequency domain reflectometer, are used to perform remote real-time measurements of X-ray irradiation profiles, with possible application as dosimeters in radiotherapy treatments. The enhanced Rayleigh backscattering is obtained by proper engineering of the composition of fiber core, either by introduction of Aluminum or Magnesium silicate nanoparticles as radiation-sensitive dopants. A detectable radiation-induced refractive index change can be spatially resolved through the measurement of the frequency shift of the Rayleigh backscattering along the fiber. It is experimentally demonstrated that two mechanisms of radiation-induced refractive index change take place. At doses nearly compatible with those delivered in radiotherapy, a negative refractive index is induced, whereas at high doses the change is positive. This behavior is also confirmed by the shift of Bragg wavelength of a fiber Bragg grating inscribed in the nanoparticles-doped fiber and used as a reference.

In the paper, 1.4 – 2.2 μm broadband emission under 796, 808, 980 nm laser diode excitation in low phonon energy germanate glass system co-doped with 0.7Er₂O₃/0.35Tmo₂O₃ (1st core) and 0.7Tm₂O₃/0.15Ho₂O₃ (2nd core) were investigated. Next, double-core, double-clad optical fiber has been developed by the modified rod-in-tube technique. Amplified spontaneous emission (ASE) in double-clad optical fiber with 3dB bandwidth was measured to be 346 nm and 677 nm for - 10 dB. ASE spectrum is a result of the partial donor-acceptor energy transfer and superposition of Er³⁺: 4I_13/2 → 4I_13/2, Tm³⁺: ³F₄ → ³H₆, 1.8 μm and (Ho^3+:5I₇ → ⁵I₈) 2 μm emission bands. Excellent spectroscopic properties indicate that the developed germanate optical fiber is a promising active element for construction compact, broadband ASE sources.

Rare-earth-doped solid-state lasers utilize distributed-feedback (DFB) resonators to generate ultra-narrow-linewidth emission down to a few kHz. The longitudinal modes of a single Fabry-Pérot and a DFB resonator are influenced by the structure, the optical excitation configuration, and external feedback, as has been observed experimentally. Here we investigate the influence of bi-directional launching of light and external feedback on the longitudinal modes of single Fabry-Pérot, double Fabry-Pérot, and DFB resonators. These results can be exploited for the technological advancement of DFB lasers.

A novel fiber laser based on a fluoroindate glass doped with erbium ions and cladding pumped with red light is designed. In the simulation, the pump beam at 635 nm wavelength is injected in a commercially available double D-shaped, fewmode, optical fiber fabricated by Le Verre Fluoré in order to excite the 4F9/2 energy level. A strong population inversion between ⁴F_9/2 and ⁴I_9/2 energy levels is obtained, thus allowing emission in the 3400-3600 nm band. The electromagnetic analysis of the fiber, performed by the finite element method, shows that up to six signal modes at 3500 nm are supported. An exhaustive mathematical model based on five rate equations for the erbium ion populations, coupled with the power propagation equations for the pump and all the signal modes, is developed. Both cases of forward and bidirectional pumping are considered. All the spectroscopic parameters employed in the model, including the absorption/emission cross sections, the lifetimes and the branching ratios, are taken from the literature. The numerical code allows for evaluating the output signal power, the threshold pump power, and the slope efficiency. The behavior of the laser is studied by varying several parameters, such as the cavity length, the erbium concentration and the output mirror reflectivity. Preliminary simulations show that, with pump powers of a few hundred mW, lasing can be obtained. These results will be improved by using an evolutionary optimization technique, like the particle swarm optimization approach, and promise interesting low-cost applications.

Fiber lasers emitting in the 3-5 μm wavelength range have attracted much interest during the last years, thanks to their wide potential employment in different fields, such as remote sensing, air pollution detection, communication applications, and medical diagnostics. Fluoroindate fibers allow transmission in this range and can be doped with different rare-earth ions, including erbium, holmium, dysprosium, and neodymium. Recent experiments have shown the feasibility of emission at λ = 3.92 μm wavelength employing Ho:Nd co-doped fluoroindate glass, encouraging the investigation on continuous-wave (CW) emission lasers. In this work, a complete model of Ho:Nd co-doped fluoroindate fiber pumped at λp = 808 nm and emitting at λ = 3920 nm is developed, in order to find the unknown energy transfer parameters, thus allowing a correct design. The energy transfer parameter recovering is performed by simulating the fluoroindate fiber via a finite element method (FEM) code, by solving the rate equations with a homemade code and by matching simulations with experimental values reported in literature. The results pave the way for the accurate design of a CW laser emitting at λ = 3920 nm, potentially with better efficiency than lasers based on Ho³⁺ -heavily-doped fluoroindate fibers. Preliminary fiber laser design has been based on commercially available fluoroindate fibers, including double cladding fibers, in order to choose the best geometry for the fiber laser and investigate its feasibility.

In this work we investigated the possibility of generating subpicosecond pulses as a result of a modulation instability of continuous wave signals with a large modulation depth. In our case a large modulation depth of a continuous wave is achieved by using a cylindrical waveguides with a running refractive index wave (RRIW). Here, the entire cascade fiber system is a cylindrical waveguides RRIW connected in series with a section of passive fiber with anomalous dispersion. To achieve high peak power values in the generated pulse train, it is necessary to add a section of active fiber with normal dispersion to the stage. It is shown that, as a result of the regime of a induce modulation instability, pulses with a peak power that are orders of magnitude higher than the power of the incoming pump wave can be formed.

In this paper it was investigated the dynamics of frequency-modulated pulses in fiber cascades, consisting of a fibers with sequentially formed refractive index gratings with different periods. It is shown that the proposed scheme can be used to generate picosecond and subpicosecond pulses with peak powers of the order of ~1 MW. In the considered cascade structures, it is shown that it is possible to form stable sequences of pico- and subpicosecond pulses with a subterahertz repetition rate directly from continuous wave signals as a result of a modulation instability regime.

Zinc-silicate glass-ceramic materials based on ZnO and Zn₂SiO₄ nanoparticles distributed in amorphous silica matrix represent one of the most perspective options to improve the photoluminescence properties of E^r3+ ions, thanks to their low phonon energy and the possibility of energy transfer between the ZnO/Zn₂SiO₄ nanoparticles and Er³⁺ ions. In this paper, we focus on the investigation of crystallization in the sodium- and potassium-zinc-silicate system and the photoluminescence properties of Er₃₊ -doped glass-ceramic materials. It was found that the presence of Na2O promotes the crystallization of Zn2SiO4 resulting in non-transparent glass-ceramic material at 750 °C, whereas the K₂O-ZnO-SiO₂ material remained transparent in the entire heat treatment range. Nevertheless, the crystallization of ZnO and Zn2SiO₄ leads to an increase of photoluminescence intensity of Er³⁺ ions by up to 300 % compared to the pre-cursor glass. The Stark-splitting of the Er³⁺ emission spectra at 1.5 μm after 978 nm excitation as well as shortening of the fluorescence lifetime suggest the incorporation of Er³⁺ ions inside the highly symmetric environment of ZnO and Zn₂SiO₄.

We report on suppression of supermode noise in harmonically mode-locked fiber laser achieved through the injection of continuous wave (CW) into the laser cavity. Implementing this method, we have shown experimentally that supermode suppression level of harmonically mode-locked laser could be increased by 20-30 dB depending on the pulse energy of the mode-locked laser. Experiments have refined the requirements to the positions inside the laser spectrum assigned to the injected CW component, a Kelly soliton sideband, and the transparency peaks of the birefringent filter formed in the ring fiber cavity. The effect takes places at proximity of the injected CW to the Kelly sideband leading to phase-locking between the CW and the solitons.

Fiber ring laser harmonically mode-locked through nonlinear polarization evolution with the pulse repetition rate up to 6.75 GHz is demonstrated. We report on a new method of fine repetition rate tuning with the use of external continuous wave injected into the ring laser cavity. With this method, we have shown experimentally that the pulse repetition rate of the harmonically mode-locked laser can be tuned over a few GHz range with the minimal possible step equal to the fundamental frequency of the ring cavity.

We study the properties of glasses and crystals after an ultraviolet (UV) laser ablation process using 300 fs duration pulses, centered at 206 nm wavelength at the repetition rate of 50 kHz. We show that linear light absorption allows fabricating grooves with a surface roughness in the order of tens of nanometers and even sub-10 nm with low heat affected zones (HAZ) without any post-processing. We produced a single scan laser ablated microchannels’ depth, surface roughness and full width at half maximum maps based on the experimental results. These maps show relations with an overlap of laser pulses and a pulse energy and are useful when considering the working regime for specific applications. Our results depict the minimum channel bottom roughness of 8 nm in Sapphire after one scan. This value represents several times smaller roughness when compared to the nanosecond UV laser ablation. We have also studied a multi shot ablation and by evaluating our results using a scanning electron microscope (SEM) we noticed nanogratings on the walls of the craters of soda-lime and BK7 glasses with a period of 300 nm, that is bigger than the laser wavelength (206 nm). We also show that a precise surface micro patterning can be achieved with our experimental setup. Finally, our theoretical fluence distribution optimization provides a precise fabrication parameters estimate for a small surface roughness condition.

In this paper, we give an estimate of the uncertainty associated with the phase noise measured for an optoelectronic oscillator. This uncertainty is better than 2 dB at 2 sigma

In this paper, we discuss the principle of coupling an optical signal to an optical resonator. We give the broad outlines of the principle and the experimental parameters then we look at how to optimize this coupling using finite element simulations on COMSOL software. Simulation of the coupling is based on straight and ring waveguides placed very close to each other so the waveguide can be transmitted from one to other.

Surface roughness is an important parameter that has a great influence on various material properties. It determines the rate of corrosion, wettability, as well as optical properties of different materials. Low roughness (< 100 nm Ra) surfaces are difficult to achieve even with fs pulses, therefore investigation of the theoretical intricacies is of major interest when engraving transparent materials. In our study, we numerically investigate the evolution of the surface roughness when it is scanned with a UV femtosecond laser beam and compare the numerical results to the experimentally acquired values. The study contains a single scan as well as multiple scans (up to 10 scans) on the surface. We found that in the case of a single scan the dominant surface roughness determining factor is the overlap of the pulses in x and y directions. It was found, that parameters such as pulse overlap, laser-scanner synchronization, and initial beam profile strongly influence the resulting surface roughness in a nonlinear manner. In the case of a multi-scanned surface, we determined that the resulting surface roughness can be minimized by introducing rotation of every following layer at a certain angle with respect to the previous one. The angle for minimized surface roughness highly depended on system configuration. The investigated theoretical model is in good relation to the experimentally acquired results and provides valuable information when optimizing the process for minimal-roughness micromachining.

We describe the method that allows us to give an estimation of the uncertainty on the frequency peak by Brillouin Light Scattering. It isthe speed of phonons in a material excited by a visible green 532 nm wavelength laser. We follow the Guide to the Expression of Uncertainty in Measurement to obtain a first estimation of the speed of the phonons at 5 % at 2 sigma.

In this study, we present results on direct fiber surface ablation using UV femtosecond laser pulses (206 nm, 50 kHz, 210 fs). The research is carried out experimentally and simulatively. The simulative experiment demonstrates that fringe visibility is best when half of the fiber core is removed. The fringe free spectral range (FSR) decreases as the trench length increases. The experimental study contains the investigation on parameter optimization for trench-like surface formation on the fiber via direct laser ablation, suitable for Mach – Zehnder interferometer (MZI) formation. Linear light absorption allows to fabricate deep, regular structures on the fibers with small (148 ± 12 nm) bottom surface roughness.

Fluoroindate glass is characterized by low phonon energy (500 cm^-1 ), which enables most of the radiative transitions in the lanthanides to occur in the range VIS-NIR. It allows considering this matrix as a potential host glass for NIR emission and light sources. This work reports the fabrication and analysis of luminescence properties, and structure of the fluoroindate glasses and glass-ceramics (GC) co-doped with Eu³⁺ ions. The materials' microstructure and structure were analysed using X-ray diffraction (XRD) and Raman measurement techniques, respectively. It has been shown that the basic structural units in the glass network are [InF₆] octahedrons tetrahedrons. The luminescence analysis was performed in the glass and glass-ceramics samples doped with EuF₃ showing the excitation and emission properties and changes in the lifetimes. The excitation at 395 nm resulted in different emissions in blue, green, and red which correspond to the transitions from ⁵D_J (J=0 to 3) multiples to the ⁷F_J (J= 0 to 6), which is the effect of the low phonon energy of the matrix and is comparable with other low phonon materials. In the glass-ceramics, the effect of network ordering around the Eu³⁺ ions was noticed. The fluorescence intensity ratio R/O related to ⁵D₀→⁷F₂ and ⁵D₀→⁷F₁ transitions in Eu³⁺ decreased from 0.74 to 0.56 value. Obtained results allowed to consider this GC material as a potential host for luminescent material and possibly glass fiber sources.

Ultimate generation of luminescent security inks have been used to detect counterfeiting including applications in banknotes, quick response codes (QR codes), barcodes, security documents, drug packaging and food security. Anti counterfeiting strategies are competitively developed against fast-growing counterfeit markets. So far, most security inks are based on the down-conversion effect, that is transforming UV incident radiation into visible light. But the substrates are sensitive to this UV “reading light”, which leads to a reduction of the contrast between the substrate and the printed sample. Therefore, rare-earth doped upconversion luminescent materials present significant advantages compared to standard fluorescent dyes, such as invisibility in ambient light, excitation by low cost commercial NIR irradiation and a lack in background noise, due to negligible auto-fluorescence from the surface. However, more attention needs to be paid on the codification of overall emitted luminescence, so it will be more difficult to mimic by ever increasing sophisticated counterfeiters. Thus, we present upconversion emissions in rare-earth doped nano-glass-ceramics (nGCs) under NIR excitation at 980 nm. Intensity ratios among UV and VIS upconversion emission bands can be tailored by modifying doping concentration level. Specific doping level, excitation wavelength and focusing conditions give rise to additional security features based on light-responsive encryption security patterns. A multi-digit code based on these intensity ratios can be set from resulting spectra, providing a proof-of-concept test for light-responsive encryption security patterns.

NaYbF₄:Tm³⁺ based-nanostructured materials have been synthesized by solvothermal method and sol-gel technique. Observed high intense UV-blue up-conversion luminescence, under low-power commercial 980 nm laser irradiation, have been applied to enhance photocatalytic activity. Thus, photocatalytic degradation of methylene blue, as an organic pollutant model, was proved as a unique photonic effect, converting incident NIR radiation before reaching the contaminated solution

We report on the structure and spectral-luminescent properties of a composite ZnO-Er₂O₃-Yb₂O₃ optical ceramic. The ZnO ceramic codoped with 1 wt% Er³⁺ and 4 wt% Yb³⁺ was prepared by uniaxial hot pressing of oxide powders at 1180 °C in vacuum. The maximum total transmittance of the ceramic is ~40%. The ceramic is a composite material comprised of hexagonal ZnO microcrystals (mean size: 10-15 μm, a = 3.251 Å and c = 5.201 Å) and cubic sesquioxide Er₂O₃ and Yb2O3 nanocrystals (mean size: ~130 nm, a = 10.450 Å and 10.555 Å, respectively). Its texture is dominated by the ZnO prism planes (100). The absorption spectrum of the ceramic demonstrates bands characteristic of Er³⁺ and Yb³⁺ ions in the Er₂O₃ and Yb₂O₃ crystals, respectively. The ceramic exhibits intense red upconversion luminescence. The X-ray induced luminescence spectrum contains two intense emission bands. The more intense one with a maximum at ~390 nm is due to the near-band-edge transitions and its decay time is ~1 ns. The broad band in the green represents defect emission. Its decay deviates from the single-exponential law revealing several characteristic times of ~6, 60 and 250 ns. The free carrier concentration of the composite ceramic is ~7.65×10¹⁸ cm^-3, which is significantly higher than that for the undoped ZnO one.

Trivalent titanium ions (Ti³⁺) are known for their broadband emission in the visible and near-IR. Zinc aluminate spinel, or gahnite (ZnAl₂O₄) is known as a host matrix for transition-metal ions. We report on the structure and spectroscopic properties of transparent zinc aluminosilicate glass-ceramics (GCs) nucleated by TiO2 and based on Ti³⁺-doped ZnAl₂O₄ nanocrystals. The initial glasses were melted under different redox conditions. After heat-treatments at the temperatures in the range of 720 to 1100 °C, transparent GCs were obtained. The materials were studied by the DSC method, XRD analysis, Raman, absorption and luminescence spectroscopy. The main crystalline phase in GCs is ZnAl₂O₄ with a cubic structure. The crystals are 5 - 21 nm in size. Their unit cell parameters vary with the heat-treatment temperature due to the titanium ions entering the gahnite nanocrystals. The volume fraction of gahnite nanophase increases with the heat treatment temperature. At 1000 – 1100 °C, TiO₂ (rutile) crystals with a size of 11 - 37 nm also appear. In GCs obtained from glasses melted under reducing conditions, broadband absorption is observed in the visible and near IR due to the Ti³⁺ ions in Oh positions in ZnAl₂O₄ crystals, the absorption of Ti³⁺ - Ti⁴⁺ pairs and the appearance of Ti³⁺ self-doped rutile. By changing the redox conditions of the glass synthesis, one can control the content of titanium ions in various oxidation states and the spectral properties of GCs.

This work focuses on the fabrication process of SiO₂–CaO and SiO₂–CaO–ZnO glasses. To obtain glass powders, modified Stöber sol–gel synthesis was used. The X-ray diffraction patterns and infrared absorption spectra were used to investigate the structure of materials showing that the binary system was fully amorphous while the ternary one showed partial crystallization of dicalcium silicate. The scanning electron microscopy imagining allowed to determine the morphology of glass particles as well as their composition and distribution of Si, Ca, and Zn elements in the tested samples. The final glass composition was slightly different from the assumed and was equal to 85SiO₂–15CaO and 85SiO₂–6.5CaO–8.5ZnO (in wt.%). The particles of both glasses were spherical, but the ones of the SiO₂–CaO–ZnO sample were smaller (diameter around 100 nm) and had a narrow range of size distribution. Considering the photocatalytic properties of zinc oxide, the photocatalytic degradation of methylene blue was shown in an aqueous solution in the presence of SiO₂–CaO–ZnO glass.

We demonstrate a highly-Yb-doped fiber with pedestal and triple-cladding stretching fiber for utilizing in chirped pulses amplification systems with high ratio of stretching/compression and low level of stimulated Raman scattering. The stretching triple-cladding fiber consisting of high-index Ge-doped core, low-index F-doped depression concentric layer and high-index Ge-doped concentric layer. By varying the fiber structure parameters (refractive indexes and geometrical size) we were able to tailor its dispersion parameter and its slope values in order to match these with a grating-pair compressor ones to obtain better pulse compression quality (shortest possible duration and pedestal-free structure). Realized fiber has dispersion parameter of -140 ps/nm/km at 1026 nm and slope of 12 um^-1. The highly-Yb-doped fiber for the final amplification stage of the CPA has aluminophosphorosilicate glass core with a germanium-doped pedestal around it; core/pedestal diameters were 14/50 um, outer cladding has square shape with edge size of 130 um. Despite of high Yb ions content (cladding absorption of 40 dB/m at 976 nm) the core NA was only 0.09 due to the creation of the pedestal. We utilized a 23 cm piece of the fiber to amplify 22ps chirped pulses with 1.432 MHz repetition rate up to 10.2W of average power, when the first stokes of Raman starts to evolve, corresponding to 320 kW of peak power. The pump-to-signal conversion efficiency was 64%. M2 factor was 1.15/1.12. Experiments on amplification of the 500 ps chirped pulses and its compression will be presented at the conference.

The demand for transparent conductive films (TCFs) is dramatically increasing. In this work tungsten oxide (WO_3-x) is studied as a possible option additional to the existed TCFs. We introduce WO_3-x thin films fabricated by a non-reactive magnetron RF-sputtering process at room temperature, followed by thermal annealing in dry air. Films are characterized morphologically, structurally, electrically, optically, and dielectrically. Amorphous WO_3-x thin films are shown to be n-type conductive while the transparency extends to the near-IR. By evaluating a figure of merit for transparent-conductive performance and comparing to some most-widely used TCFs, WO_3-x turns out to outperform in the near-IR optical range

Femtosecond laser pulses are more and more spread for the micro/nano-machining of various materials. Bragg gratings are known to be good written within optical fibers using the point-by-point or line-by-line technique. The objective of our work is to produce Bragg grating sensors within planar glass substrates. To this aim, the synthesis of an optical waveguide in a glass substrate is a key parameter. Among the physical techniques that are available one of them is the utilization of a femtosecond laser. In this paper, we report our achievements obtained with the so-called Femtoprint machine, a commercial device created to engineer materials. We show the parameters that were used to produce waveguides in planar substrates. We show the characterization set-up that was implemented and report the first experimental results that were obtained.