Microchip lasers emitting at 1535nm are a valued tool for laser range-finding owing to their compactness, increased eye-safety, and ability to generate short laser pulses. We present the development of a longitudinally diode-pumped, passively Q-switched eye-safe laser utilizing an Er³⁺ and Yb³⁺ doped phosphate laser glass and a Co²⁺:MgAl₂O₄ crystal acting as a saturable absorber. The laser and its solid-state components are designed to produce 5 ns short laser pulses at 1535 nm. The design process is aided by analytical expressions derived from the coupled laser rate equations, which are also solved numerically. For verification, an experimental setup of the passively Q-switched laser emitting at 1535nm is built and several measurements will be presented, including the laser pulse duration, the pulse energy statistics, and the transverse intensity profile of the passively Q-switched laser. Very good agreement is achieved between the predicted and measured laser pulse duration with a lowest obtained value of 7.3 ns. The maximum laser pulse energy is 15.7 μJ in lowest-order transverse mode operation of the laser.

The generation of short pulses in fiber lasers using saturable absorbers made of graphene oxide (GO), focusing on film thickness, was studied and optimized. The saturable absorber comprised a GO thin film deposited onto a single-mode fiber using the spray coating technique. Water-dispersed GO with a concentration of 4 mg/mL, characterized by a high proportion of monolayer flakes, was employed. This thin film was integrated into a cavity ring laser featuring an erbiumdoped fiber amplifier (EDFA), resulting in a fiber laser emitting at a central emission wavelength of approximately 1564 nm and having a total cavity length of approximately 120 m. By controlling intracavity polarization, short-pulsed light was generated through mode-locking, Q switching, or a combination of both regimes.

This work presents a comprehensive characterization of the cavity ring laser operating under the mode-locking regime. It encompasses an analysis of the spectral behavior, focusing on the evolution of the Kelly’s sidebands with increasing pump power, as well as an assessment of its temporal stability. Moreover, the effects of the aging of the saturable absorber material were studied after a time period of 6 months after the fabrication. It was observed that the general characteristics of spectral signal of the laser were maintained, with long-term stability.

In the paper, the possibility of obtaining broadband NIR luminescence in germanate glasses and fibers doped with transition metals (Cr, Ni), bismuth (Bi), and rare-earths (RE) has been investigated. In bismuth-doped GGB glasses, the influence of Sb2O3 content on luminescence properties has been studied, and the possibility of drawing glass into fiber. Luminescence at 1.3 μm with FWHM=209 nm was observed for the glass doped with 3 mol% Sb2O3 and 1.5 mol% Bi2O3. In the next step, the spectroscopic properties of Cr³⁺ doped GGB glass and optical fiber were investigated. After drawing glass into fiber FWHM (full with at half maximum) at 1.0 μm increased from 202 nm to 234 nm compared to bulk glass. Obtained luminescence at 1.0 μm can be attributed to the ⁴T₂ → ⁴A₂ transition of Cr³⁺ ions. For multicore glass-ceramic optical fiber, broadband near-infrared emission in the range of 1.1 to 2.1 μm was obtained under 940 and 980 nm pump excitation as a superposition of luminescence bands of Ni²⁺, Er³⁺, Tm³⁺ and Ho³⁺ ions.

This contribution presents a combined experimental and theoretical study on solid state random lasers in the visible (VIS) and near-infrared (NIR) domains operating in the diffusive regime under ultrafast pumping. NIR random lasers are based on Nd-doped crystal powders, while the VIS random laser is a ground powder of a Rhodamine B-doped hybrid compound incorporated into a di-ureasil host. A precise time-resolved analysis performed by using spatial filtering allows us to study the time evolution of local and spatially integrated random laser emissions. The study shows that the dynamics of both types of systems can be described by a similar rate equation model based on a statistical distribution of photon trajectories in an amplifying medium.

We investigate a new phenomenon, where a reciprocal fiber ring laser switches from bidirectional to unidirectional operation above a certain pump power threshold. We present significant simplifications regarding earlier experiments, which for the first time allow the identification of individual nonlinear effects. We highlight the unique role of stimulated Raman scattering in triggering unidirectional operation.

In this paper, we numerically simulate the population of levels of an Yb:Er:Tm:Ho co-doped germanate glass pumped at 980 nm, that could be able to generate broad emission in a wavelength range from 1500 nm to 2100 nm. The aim of this work is to study the possibility of reaching a homogeneous inversion of Er, Tm and Ho, in order to further develop ultra-broadband active devices. We study the influence of a variation in the concentration of the dopants in such a complex system, which exhibits many energy transfer phenomena between different rare earth ions. Furthermore, we computed the transfer function of the system to evaluate the pump noise influence.

In this paper, a fiber amplifier based on ZBLAN fiber doped with dysprosium is designed and optimized considering an in-band pumping scheme. The model is validated by comparing the simulated amplified spontaneous emission with the experimental curves reported in the literature. It allows to investigate the amplification of the signal of a continuous-wave fiber laser emitting in the wavelength range from 2.9 μm to 3.25 μm. The numerical analysis is carried out via home-made code that accurately takes into account the rate equations and the power propagation equations for the signal, pump, and amplified spontaneous emission. The finite element method (FEM) is used to calculate the modal overlap in the designed pump fiber combiner with the Dy³⁺-doped core. By employing an input pump power P_p = 5 W at the wavelength λ = 2.82 μm, a signal power P_s = 2 mW at the wavelength λ = 2.95 μm, a fiber length L = 3 m an amplifier output power of 0.5 W and an optical gain of about 24 dB are achieved. The obtained results are attractive for feasible innovative applications, e.g. the development of all-in-fiber systems. For instance, the pump and signal beams can be obtained via an Er:ZBLAN fiber laser and coupled with the dysprosium fiber through a single-mode fluoride coupler.

In this work, we study the potential of Eu-doped 2D α-MoO3 nanocrystal films for their implementation in nanophotonic luminescent devices. The films have been fabricated by pulsed laser deposition by alternate deposition of MoO3 and Eu targets. The result was a multilayer nano-film of MoO3 layers and Eu3+ doping ions between them. The resulting films are amorphous with of Eu concentrations up to 0.3%. Upon, thermal treatment the formation of the crystals occurs. When this MoO3 crystals are excited by a 355 nm laser, a clear luminousness emission peak appears in the red around 611 nm correspond to the 5D0→7F2 transition of Eu3+. This work is promising towards the development of integrated nano-emitting devices based in 2D α-MoO3.

We report on a Holmium-doped femtosecond polarization-maintaining (PM) all-fiber amplifier system at a central wavelength of 2050nm that is designed as a seed source for a Holmium:YLF-based amplifier. The amplifier system employs a three-stage amplification process for power scaling while reducing the repetition rate. The first two Holmium-fiber amplifiers are core-pumped at a wavelength of 1940 nm. The final amplification stage is based on a double-clad Thulium-fiber, whose gain spectrum allows for the simultaneous amplification of the remaining pump light from the second amplifier stage and the Holmium-signal. Temporal pulse-stretching to a pulse duration of 190 ps using a chirped fiber Bragg grating (CFBG) prevents nonlinearities. We obtained pulse energies up to 300 nJ at 50 kHz.

Our work demonstrated a tunable Polarization Maintaining (PM) thulium-doped fiber two stages amplifier system spanning the 1820–1880nm range with a fiber-coupled output power as high as 30W CW. In addition, the high-power booster stage is made using double clad fibers pumped with 793nm laser diodes wich contrasts with the usual core-pumping using Erbium-Ytterbium laser sources emitting around 1570nm. To the best of our knowledge, this marks the first reported demonstration of a 30W level all-fiber PM TDFA Master Oscillator Power Amplifier (MOPA) operating within the 1820–1880nm wavelength regime. The significance of this achievement extends to a wide array of applications, including but not limited to quantum computing.

We present a single-oscillator Tm-doped fiber laser emitting 184 W at 1.95 μm with 49.4% slope-efficiency, 0.6 nm FWHM at 1949.6 nm. An M² factor is 1.3 at 30% of the maximum output power. We used commercially available fiber components and developed splice optimization technique based on beam diameter monitoring. Compact and efficient polymer-based cooling solution is implemented to aim for industry-friendly application.

We overview recent advances in visible single- and double-clad fluoride fiber lasers pumped by blue GaN laser diodes. The spectroscopic properties of ZBLAN glasses doped with Pr³⁺, Ho³⁺ and Dy³⁺ ions are revised. Power scalable efficient continuous-wave visible fluoride fiber lasers emitting in the green, yellow, red and deep-red spectral ranges are presented. Pumped by a single-emitter 6-W 443-nm GaN laser diode, a continuous-wave red double-clad Pr:ZBLAN fiber laser delivered 1.51 W at 634.5 nm with a slope efficiency of 31.0%, a laser threshold of 0.63 W and a spatially single-mode output (M² ~1.02). Employing a high-power fiber-coupled laser module, power scalability up to 4.61 W was achieved at the expense of a lower slope efficiency of 22.8% and an increased laser threshold of 1.74 W. Green Ho:ZBLAN (543 nm) and yellow Dy:ZBLAN (575 nm) fiber lasers with high-brightness core pumping at 450 nm are also reported delivering 100 mW-level output with slope efficiencies of 31.2% and 19.6%, respectively, operating on the fundamental mode. A numerical model to predict the visible laser performance is presented and guidelines for further engineering of visible fiber laser sources are given.

MIR cascade lasing is a solution to mitigate the negative impact of excited state absorption on the performance of yellow lasers made of ZBLAN fibers doped with Dysprosium. A low-loss cavity with nearly ideal mirror reflectivity in both yellow and MIR wavelength ranges yields optimal results, but fabricating FBGs with extremely high reflectivity remains challenging in fluoride glasses. In this work, we use our matrix-based model to provide insights into the influence of FBGs quality on the performance of yellow Dy-doped ZBLAN FLs with MIR cascade lasing. Results reveal that reducing the front mirror reflectivity at the yellow wavelength lowers the laser slope efficiency, whereas decreasing the reflectivity of the mirrors constituting the cavity for the MIR emission leads to an increase in the threshold.

Fiber lasers have become very popular in the recent two decades due to numerous advantages compared to other solid-state lasers, e.g. their robustness, efficient cooling, high power compatibility, flexibility, large gain bandwidth and comfortable handling. Visible fiber lasers are increasingly becoming a new research focus, since they can be pumped very efficiently with new powerful, commercially available high-power GaN diodes in the UV wavelength range. Potential and important applications, especially in the biomedical field, are spectroscopy, microscopy and microsurgery. So far, fluoride glasses, e.g. ZBLAN, InF and AlF, are the most promising host glasses to realize stable visible fiber lasers. Most of them are originally designed for the MIR spectral range, but they also have the potential to cover the VIS. Pr³⁺ in ZBLAN glass is very attractive as it offers many possible laser transitions in the VIS and NIR range. In [1] a wide tunability in the VIS and NIR is demonstrated by core-pumping of a very short Pr³⁺-doped ZBLAN fiber. Regarding the visible spectral range, laser output powers up to 2.3 W around 635 nm were reported recently in a monolithic ZBLAN fiber laser with a Fiber- Bragg grating, but with reduced slope efficiency of 14% [2]. An alternative approach, where authors demonstrated up to 5 W laser power and 25.7% efficiency around 635 nm, is the direct and spliceless connection of pump and laser fiber using an end-facet coating mirror as input coupler [3]. Using this approach emission wavelength is power dependent and not locked.

Recent advances in low-loss fluoride glasses have enabled the development of Dy-doped ZBLAN fibers for yellow lasers, either tunable or not, pumped by blue GaN laser diodes. Recently, the impact of excited state absorption on Dy-doped tunable FLs has been investigated, showing potential enhancements enabled by MIR cascade lasing. In this study, the optimal fiber length for MIR and yellow emission was analyzed as a function of pump power and mirror reflectivity. Results reveal a mismatch between the optimal lengths for yellow and MIR emission. This suggests the possibility of minimizing the cascade lasing threshold through cavity optimizations aimed at reducing the length mismatch, thus enhancing performance at low pump power levels too.

The field of mid-infrared fiber photonics has seen significant progress in recent years [1]. In virtually all molecules, transitions involving changes in both vibrational and rotational states can be excited by illumination with light at midinfrared wavelengths from ~ 2 – 15 Μm, giving rise to a plethora of application in environmental sensing, defense, and medicine, to only name a few. However, for most applications, compact and monolithic laser sources without bulky and sensitive free-space optical components are needed. While in-fiber components in mid-infrared compatible soft-glass fibers [2,3] as well as fiber endcaps [4] for long-term stable operation have both been demonstrated, little work to date has focused on the fabrication of fiber-pigtailed optical chips that could offer additional functionalities. The femtosecond laser direct-write technique is a highly versatile method that enables the inscription of tailored three-dimensional photonic circuits into bulk glasses [5]. Here we summaries our recent progress into the fabrication of linear and nonlinear waveguide chips for the realization of all fiber mid-infrared sources.

Fluoride glasses exhibit two majors features of great interest for medical use. Transparent from UV to mid-IR, fluoride glass fibers are the most transparent ones in the 2µm-5.5µm spectral . Their low phonon energy and the large solubility of rare earth in fluoride glass matrix allows many (> 60) rare earth transitions of interest for laser generation and amplification. 2.9µm wavelength corresponds to the water absorption peak. As human body is made of 70% of water, 2.9µm fiber lasers are ideal for surface treatment of living tissues. A new generation of 2.9µm fiber lasers is becoming the game changer of dermatology lasers, and will be key in the next generation of robotic surgery. Single mode visible lasers are of great interest for medical imaging and DNA sequencing. However their power is limited with respect to future requirements. A new generation of multiwatts visible fiber lasers is emerging and will be able to answer many needs for medcial imaging.

An optical fiber amplifier based on a fluoroindate fiber doped with praseodymium (Pr³⁺:InF₃) has been designed. The chosen fiber has a double-cladding and a 2-D shape. The electromagnetic behavior of the fiber has been simulated via a Finite Element Method (FEM) software, and the design of the fiber amplifier has been performed via a computer code, solving the rate-equations and power propagation equations. The gain G and the Amplified Spontaneous Emission (ASE) noise have been investigated as a function of different input parameters as the input signal power P_s0, the fiber length L_fiber , and the signal wavelength λ_s. The simulated fiber amplifier exhibits a bandwidth B_G close to B_G = 100 nm around the central signal wavelength λ_g = 4 μm, and a gain G close to G = 30.7 dB, when an input signal power P_S = 10 μW and a pump power P_P = 75 mW are considered. This pump value seems particularly low and further investigation will be performed to better understand this unexpected promising value.

In this paper, a 2×2 single-mode coupler based on indium fluoride optical fibers from Le Verre Fluoré (Bruz, France) is designed and characterized in the mid-infrared wavelength range. Coupled mode theory and finite element method are employed for its design. The 2×2 optical fiber coupler is fabricated via fused biconical tapering technique, employing a Vytran® GPX-2400 glass processing system. The primary constraint associated with the limited temperature range for processing indium fluoride optical fibers has been successfully addressed. Two identical fluoroindate (InF3) step-index optical fibers having a core diameter d_co = 7.5 μm, cladding diameter d_co = 125 μm, and numerical aperture NA = 0.30 are inserted into a fluoroindate capillary with a lower refractive index. The whole structure is tapered down ~ 2.4 times the initial diameter for a waist length L_w = 21.6 mm to achieve power coupling between the two optical fibers. The device is characterized at the wavelength λ = 3.34 μm, employing an interband cascade laser pigtailed with a single-mode fluoroindate optical fiber. The 2×2 optical fiber coupler is characterized in terms of through port and cross port powers, showing perfect agreement with the numerical results. A coupling ratio CR = 48.1:51.9 is measured at the wavelength λ = 3.34 μm, with a reduced excess loss E_L < 1.2 dB. These results pave the way for reliable fabrication of highperformance fused optical fiber components that can boost research toward the development of all-in-fiber mid-infrared systems, such as in-band pumped mid-infrared amplifiers.

Power scaling of fiber lasers has always been pursued, being limited by nonlinear effects and heat generation in the active fiber and various components. Among the most critical components are cladding light strippers (CLS) between amplifier chains, removing light from leaked higher order modes, the unabsorbed pump or losses from splices and components. Polymer-based CLS work sufficiently well for the near-IR including the pump wavelength at 793 nm but suffer from high absorption at the signal wavelength near 2 μm and have not been evaluated in detail in this regime. Therefore, it is necessary to examine different acrylates and siloxanes at both the pump and signal wavelengths individually concerning their performance as CLS and test their limits. We present a CLS with an improved design which can withstand 7.5 W at 2039 nm while stripping >46 dB. For higher powers to >800 W, we examine CO₂-laser inscribed CLS at the pump wavelength, reaching 21 dB stripping efficiency within only 15 mm of length.

In contrast to conventional optical systems, which are optimized for wavelength-independent imaging, hyperchromats aim for strongly wavelength-dependent focal lengths. In this contribution, the design parameters of hyperchromatic two-lens optical systems were derived that provide strong axial color splitting expressed by extremely low equivalent Abbe numbers. These systems have been investigated for compositions of either pure refractive or all diffractive lenses, as well as hybrid configurations thereof. First, lens doublets made of cemented elements are considered and the variables affecting the equivalent Abbe number of the system are investigated. In particular, the influence of the focal lengths of the individual lenses and the Abbe numbers of the selected lens materials are taken into account. The best parameter-sets were determined by paraxial numerical simulations for different cemented configurations. To ensure a simple implementation, especially to avoid exotic or potentially harmful materials, only readily available inorganic standard glasses were considered. In the next phase of this investigation an air gap was inserted between the two lenses, which is an additional influence parameter on the equivalent Abbe number. Following the paraxial considerations, selected two-lens configurations were transferred to the non-paraxial domain and refined using optical design software, also taking aberrations into account. To further reduce achievable equivalent Abbe numbers, an aspherical surface was introduced to compensate for spherical aberrations. Finally, for the refractive doublets an equivalent Abbe number of 2.4 was achieved, which corresponds to only 12% of the smallest Abbe number of the selected materials. This result was even surpassed by the hybrid hyperchromat, resulting in an extraordinary minimum equivalent Abbe number of -0.6 that is more than five times smaller than the Abbe number of diffractive lenses.

A high sensitivity temperature sensor exploiting indium fluoride optical fibers is designed and characterized. It is based on a non-adiabatic tapered optical fiber, acting as a Mach-Zender interferometer. The sensitivity of the sensor is predicted via mode analysis, performed with Finite Element Method, and then computing the phase delay between the LP01 mode and the LP02 mode. By considering the effect of the thermal expansion and of the thermo-optical properties of the glass, respectively on the waist length and on the core and the cladding refractive indices, the sensing mechanism is explained. The non-adiabatic tapered optical fiber (Le Verre Fluoré IFG SM [2.95] 7.5/125) sensor is fabricated with Vytran GPX-2400 glass processing system, addressing the difficulties of indium fluoride glass, including its inclination to crystallize, its limited temperature range for fabrication, and its low glass transition temperature. The sensor is characterized in the mid-infrared spectral range with an interband cascade laser, emitting at the wavelength λ = 3.34 µm.

We report on a detailed spectroscopic study of heavily Er³⁺-doped LiYF₄ epitaxial layers with the goal of developing mid-infrared waveguide lasers. Layers with a doping level up to 11 at.% Er³⁺ were grown on (001) oriented undoped bulk LiYF4 substrates using LiF as a solvent. The absorption spectrum of Er³⁺ ions was measured. Under excitation at 973 nm, the layers exhibited intense and strongly polarized mid-infrared luminescence spanning from 2.65 to 2.90 μm related to the ⁴I_11/2 → ⁴I_13/2 Er³⁺ transition. The peak stimulated-emission cross-section at the expected laser wavelength was calculated to be 0.88×10^-20 cm² at 2809 nm for π-polarization. By means of low-temperature (12 K) spectroscopy, the experimental crystal-field splitting of Er³⁺ multiplets was determined. The luminescence dynamics from Er³⁺ excited states were studied. For the 11 at.% Er³⁺ doping, the luminescence lifetimes of the ⁴I_13/2 and ⁴I_11/2 manifolds amounted to 5.54 ms and 2.66 ms, respectively.

The intent of this brief discussion is to provoke consideration that silica remains the best choice for all fiber optics applications, including those operating in the visible, near-IR, and even IR spectral region, exhibiting high or low optical nonlinearities, power-scalability, and even some newer and important effects such as internal laser cooling. Silica's superiority will be compared to those for fluoride, chalcogenide, and hollow core fibers.

This presentation will show the history of fluoride glass fibers, in particular with the description of current applications and future applications.

The benefits obtained in terms of costs and applicability by the development of flexible and stretchable electronics, compared to its rigid counterpart, have fostered the quest for flexible photonic technologies and integrated platforms on suitable material systems. By adding mechanical flexibility to photonic structures, novel functionalities would be added to their already broad range of applications. In case of oxides, their typical qualifying properties in terms of transparency, high thermal and chemical resistance could be exploited in suitable material systems. Here it is presented two flexible SiO2/HfO2 1D photonic crystals, fabricated by radio frequency sputtering. As expected, the systems show a strong dependence of the optical features on the light incident angle. Nevertheless, the most interesting result is the experimental evidence that, even after the sample breakage, where the flexible glass shows naked-eye visible cracks, the multilayer structures generally maintain their integrity, resulting to be promising systems for flexible photonic applications thanks to their optical, thermal and mechanical stability.

We present a novel, simple and low-cost protocol for fabricating pure Si, or Si1−xGex or Ge-based, sub-micrometric dielectric antennas with ensuing hybrid integration into different plastic supports. The dielectric antennas are realized exploiting the natural instability of thin solid films to form regular patterns of monocrystalline atomically smooth SiGe nanostructures that cannot be realized with conventional methods. By adjusting the annealing treatment and the semiconductor film thicknesses, different classes of nanoarchitectures can be formed, from elongated and periodic structures to disordered structures with a footprint of just a few tens of nm. This latter disordered case presents a significant suppression of the large-scale fluctuations that are conventionally observed in ordered systems and shows an almost hyperuniform behavior character.

In the present study, oxyfluoride glass-ceramics (GCs) containing NdF₃-doped LaF₃ nanocrystals were prepared with different amounts of Ag as a co-dopant. The structural and optical properties of the GCs were characterized to identify the presence of the metallic nanoparticles, as well as their role in Nd³⁺ photoluminescence. Site-selective emission spectra show that Ag co-doped samples, thermally treated in an N₂ atmosphere, exhibit increased luminescence of Nd³⁺ ions in the crystalline phase compared to Ag-free analogues. This effect can be attributed to the local field enhancement at the LaF₃ nanocrystals due to the presence of Ag⁰ nanoparticles.

Upconversion nanoparticles are appealing to various applications due to their energy conversion capabilities. However, their potential is limited by low efficiency, reproducibility, and poor morphology control. In this work, the synthesis of NaYF₄ co-doped with Yb³⁺ and Tm³⁺ ions using both thermal decomposition (TD) and microwave irradiation heating (MW) using non-polar solvent were explored. Finding that the samples obtained by MW irradiation not only reduced reaction time but also decreased particle size from micrometers to nanometers. Also, their particle size distribution and shape control improved. The upconverted emission obtained in both cases is in consistency with the characteristic emission band of thulium located at 360, 451, 476, 645, and 802 nm corresponding with ¹D₂→³H₆, ¹D₂→³F₄, ¹G₄→³H₆, ¹G₄→³F₄, and ³H₄→³H₆ transitions, respectively.

Co-doped laser materials with two active ions coupled by energy transfer is an interesting case where both ions can take part in the laser output intensity. Depending on the concentration of both co-dopants, the strength of the energy transfer coupling them or even the pumping rate, a competition between the two ions can take place which will affect the laser characteristics such as the laser wavelength. This competition between two emitting ions is illustrated here in the case of CaF₂ co-doped with neodymium and ytterbium ions. The advantage of Nd³⁺ is that its absorption cross-section around 791nm is higher than that of Yb³⁺ at ~980nm, enabling an efficient excitation of Yb³⁺ by pumping Nd³⁺ with a subsequent Nd³⁺-to-Yb³⁺ energy transfer (ET). Combining Nd³⁺ and Yb³⁺ with Gd³⁺ buffer ions further enables breaking up opticallyquenched Nd3+ clusters. Nd³⁺,Yb³⁺,Gd³⁺:CaF₂ crystals exhibit broadband emission, extending the Yb³⁺ spectrum via the Nd³⁺ contribution at longer wavelengths. Before addressing the laser gain competition between Nd³⁺ and Yb³⁺ ions, the Nd³⁺⟶Yb³⁺ ET efficiency was estimated using two approaches based on luminescence intensity and lifetimes, showing its dependency on Yb³⁺ doping. We achieved an ET efficiency of 80% in 0.5%Nd,3%Yb,2%Gd:CaF₂. CW laser action using different Nd,Yb,Gd:CaF₂ crystals resulted in a 17% slope efficiency versus absorbed pump power and a 200mW laser threshold. The expected laser gain competition between Nd³⁺ and Yb³⁺ ions leads to a change of the laser wavelength within the 1045-1067nm range depending on the Yb³⁺ concentration and output coupler transmission. These results are clearly explained by investigating the respective contribution of Nd³⁺ and Yb³⁺ to the gain cross-section and its dependence on Yb³⁺ doping concentration and Nd3+ population inversion. The gain cross-section profile is either dominated by one of the Nd³⁺ emission peaks (1065nm, 1048nm), or flat across 1045-1067nm, in which case the laser oscillates randomly within this spectral range. We show how a large Nd3+ inversion ratio leads to depletion of the Yb³⁺ 2F7/2 ground state through ET, resulting in two main effects: the saturation of the ET, as the ground-state Yb³⁺ acceptor concentration diminishes, and a shift of the laser line towards shorter wavelengths, due to weaker Yb³⁺ reabsorption.

We report on fully polarization-maintaining Er-doped fiber laser mode-locked by SESAM. After adjusting the mode spot area on the SESAM the laser demonstrates the harmonic mode-locking in the whole pump range up to ~355mW with the maximum pulse repetition rate (PRR) ~1145MHz while the supermode suppression level (SSL) does not exceed 25 dB. It is shown that optical injection of an external continuous wave (CW) into the laser cavity results in an increase of the SSL by two-three orders of magnitude. Moreover, it is shown that the CW injection makes it possible to increase the critical pump power and, accordingly, to raise the maximum laser PRR up to the value of ~2195 MHz. This operation does not degrade the quality of laser polarization. Performed numerical simulations allow explaining the observed effects qualitatively.

A compact optical delay line optoelectronic oscillator is designed to fit in a volume of less than 1 liter consists in a 1.55 μm wavelength laser, a modulator, an optical fiber acting as a delay line, a photodetector, a X-band microwave amplifier and a driving coupler. This oscillator is stable in terms of nominal delivered frequency. In addition, its elements are less sensitive to environmental and mechanical disturbances. Compactness is evaluated in terms of efficiency and the signal is characterized in terms of power delivered and stability of the nominal frequency. We rely on the measurement of phase noise carried out using a bench developed in the laboratory and we give an approximation of the specifications with an uncertainty of 1,5 dB at 2 σ for an output microwave signal calculated according a modern approach, by enriching the work done on the radio frequency or microwave signals.

This study investigates the feasibility of inducing crystallization in tellurite-phosphate glass within the TeO₂-P₂O₅-BaF₂- ZnF₂-Na₂O-Er₂O₃ system by direct laser writing (DLW) technique using a femtosecond laser beam operating at 1030 nm with a pulse duration of 230 fs. Two irradiation modes were examined: stationary-mode (1 MHz repetition rate, 160 nJ pulse energy, 120 s exposure time, for dot patterning) and translational-mode (200 kHz repetition rate, 10 μm/s translation speed, 470 nJ pulse energy, for line patterning) of laser irradiation. Our results, validated by Raman spectroscopy and scanning electron microscopy, revealed the formation of barium fluoride and zinc barium phosphate crystals in the areas irradiated employing stationary-mode. However, only barium fluoride nanocrystals were detected in the lines induced by the fs-laser employing the translational-mode. SEM analysis of the morphology and size of the laser-induced crystals showcased intriguing findings. In stationary-mode, barium fluoride crystals were distributed across the entire dot pattern area (30 μm), while zinc barium phosphate crystals were predominantly located at the edges of the dot spheres (with a size of 10 μm). Interestingly, barium fluoride nanocrystals with a size below 100 nm were detected in the area of laser irradiation in translational mode. Further structural analysis revealed alterations in the tellurite (TeO₄) and phosphate (Q⁰) structural units within the glass matrix of the fs-laser crystallized tellurite-phosphate system. Moreover, we discussed the changes in erbium emission across the UV-NIR region in both laser-induced crystals and the parent glass. Notably, a stronger emission of erbium ions was observed in the glass compared to the crystalline phases, which needs further investigations. These preliminary findings underscore the potential of fs-laser writing for the development of telluritephosphate glass-ceramics.