Fiber Lasers and Glass Photonics: Materials through Applications IV

I will explore various facets of photonic quantum systems and their application in photonic quantum technologies. Firstly, I will focus into quantum foundations and by discuss quantum interference, a key element in photonic quantum technologies. I will highlight how the distinguishability and mixedness of quantum states influence the interference of multiple single photons – and demonstrate novel schemes for generating multipartite entangled quantum states. I will then address photonic quantum computing, specifically focusing on the building blocks of photonic quantum computers. This includes the generation of resource states essential for photonic quantum computing. I will then shift to photonic quantum networks, covering both their hardware aspects and showcasing quantum-network applications that extend beyond bi-partite quantum communication. Lastly, I will outline how photonic integration facilitates the scalability of these systems and discuss the associated challenges.

Joining the rich photophysics of organic light-emitting materials with the exquisite sensitivity of optical resonances to geometry and refractive index enables a plethora of devices with unusual and exciting properties. Examples from my team include biointegrated microlasers for real time sensing of cellular activity and long-term cell tracking, as well as the development of photonic implants with extreme form factors and wireless power supply that support thousands of individually addressable organic LEDs and thus allow optogenetic targeting of neurons deep in the brain with unprecedented spatial control. Very recently, by driving the interaction between excited states in organic materials and resonances in thin optical cavities into the strong coupling regime, we unlocked new tuning parameters which may play a crucial role in the next generation of TVs and computer displays to achieve even more saturated colour while retaining angle-independent emission characteristics.

The development of a passively Q-switched eye-safe solid-state laser for laser range-finding is presented. Utilizing an erbium and ytterbium co-doped phosphate glass and cobalt-doped spinel, the laser is designed for the generation of 5 ns laser pulses at 1535 nm. The design of the laser, including the doping concentrations, dimensions and mirror reflectivities of the laser components is laid out. Following the design procedure, a laboratory setup of a passively Q-switched laser emitting at 1535 nm is built and initial experimental results 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 single transverse mode operation of the laser.

Frequency-Shifted-Feedback Mode-Locked Fibre Lasers are not as common as SESAM-based or figure 8/9 mode-locked ultrafast fiber lasers. It is mainly because that type of lasers requires a frequency-shifter like Acousto-Optics Modulator (AOM) which increases the complexity of the system for similar operation. Here, we took benefit of the optical transmission modulation and wavelength shifting effects of the AOM to build a fiber laser that can operate at different repetition rates. Pulsed operation (100ps) at the fundamental repetition rate (3.5MHz) of the laser cavity as well as first and second harmonics regimes have been obtained and show stable behaviour over hours.

The generation of short pulses in fiber lasers using graphene oxide (GO) and how adjusting the thickness of the material influenced the laser's performance is presented in this work. A GO thin film was spray-coated onto a single-mode fiber. Then, it was integrated into a ring laser with an erbium-doped fiber amplifier, resulting in a fiber laser with a central wavelength of approximately 1550 nm. By controlling the intracavity polarization, the generation of short pulses was achieved under the mode-locking regime. The study includes a detailed examination of the laser’s behavior, such as the spectral variations and the evolution of Kelly’s sidebands with increased pump power and its stability over time.

Solid state dewetting (SSD) is a natural shape instability occurring in thin solid films when heated at high temperature: it transforms a flat layer in isolated islands. SSD can be efficiently exploited in several fields, including flexible photonics, photocatalysis or dielectric Mie resonator, to form perfectly ordered and complex nano-architectures over large scales, as well as randomly organized, isolated islands. Among the dewetting systems reported in literature, in our group SiGe dewetting, i.e. SiGe structures directly formed on an electrically insulating and optically transparent substrate, has been efficiently exploited to realize arrays of nanostructures with footprint ranging from few nm up to several μm. Additionally, dewetting of Ge, which is of particular interest for photonic devices working at near and mid-infrared frequency, has recently started to be investigated. This work purpose is to study dewetted SiGe and Ge islands and to exploit them to produce flexible films for photonic sensing applications. In particular, also an innovative approach to transfer SiGe and Ge dewetted islands into a flexible substrate such as polydimethylsiloxane (PDMS) will be presented.

Broadband emission from 1.0 to 2.1 μm is essential in various fields such as medicine, metrology, and sensing systems. Available optical fiber ASE sources operate in the 1.5 µm (Er3+), 1.8 m (Tm3+), 2.1 m (Ho3+) bands. A challenge persists in the 1-1.4 µm band. Research on active glasses and glass-ceramics optical fibers emitting in this band revolves around d-block metals: nickel, bismuth, and chromium. Novel concepts are connected with combining luminescence from d-block metals and rare-earth ions (Tm3+, Er3+, Ho3+). Such materials can be used as cores of multicore optical fibers. This work presents the broadband luminescence properties in the 1.4 - 2.1 um spectral range Er3+/Tm3+/Ho3+ germanium-based glasses and their multicore (up to 11 cores), double-clad optical fibers under NIR laser-diode excitation. Moreover, the fabrication and luminescent properties of Ni2+/Cr3+/Bi3+, rare-earth co-doped glasses, and multicore optical fibers will also be analyzed.

This contribution presents a combined experimental and theoretical study on the solid-state random lasers operating in the VIS and NIR domains. A precise time-resolved analysis performed by using spatial filtering of the random laser emissions allows us to study the dynamics of individual random laser modes. The study shows that the dynamics of both types of systems can be described by a similar rate-equation model based on an statistical distribution of photon paths 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, and that additional events have to happen in the active fiber.

Multi-scale 3D architecture with highly localized fluorescence contrast in photosensitive silver-containing glasses by means of femtosecond laser writing can be obtained. We will present results obtained on electron-irradiated glass samples by EPR spectroscopy and in-situ cathodoluminescence. This allowed for understanding the initial phenomena of electron deposition and charge trapping by identifying the nature of point defects and Ag species. In addition, a careful point defects analysis of fs-laser written silica glass as a function of the laser deposited energy for [50-500 fs] pulse durations was leaded highlighted the role of certain defects in the chemical etching of fused silica glass

We obtained 51 W of UV laser light at 343nm for 8 ns temporally square-shape pulse at 400 kHz repetition rate which corresponds to a peak power of 42.5kW and a conversion rate of 38% from a 133W linearly polarized signal at 1030nm. This high UV power is achieved by third harmonic generation of infrared beam which is generated thanks to a newly developed Ytterbium-doped rod-type high-power amplifier effectively singlemode fiber with a hybrid hexagonal and aperiodic cladding design. Two fibers with MFD at 47µm and 67µm were tested. The 47µm MFD fiber allow to reach up to 200W of singlemode signal before the TMI appearance. This fiber can deliver 150 W of 1030 nm signal with a 250 W pump light, for different nanosecond pulse durations and repetition rates with excellent beam quality (M²<1.1).

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 Pp = 5 W at the wavelength λ = 2.82 μm, a signal power Ps = 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.

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 all-fiber amplifier system at a central wavelength of 2050nm that will be used as seed source for a Ho:YLF-based amplifier. The amplifier system employs a three-stage amplification process for power scaling while reducing the repetition rate. The first two Holmium-doped fiber amplifiers are core-pumped at a wavelength of 1940nm. 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 via reabsorption. Temporal pulse-stretching to a pulse duration of 190ps using a CFBG prevents nonlinearities. We obtained pulse energies up to 300nJ at 50kHz.

The development of high-power 2-µm fiber laser source is a growing concern for both civil and military sectors. Nevertheless, the splices between active and passive fibers needed in a monolithic design are still an issue. The geometry mismatch between the fibers and particularly the presence of a pedestal around the core of active fibers creates a light coupling from this pedestal to the cladding of the passive fiber when spliced together. This signal light propagating in the cladding results in a beam degradation that reduces the laser performances. In this communication, we present the development of an all-pedestal fiber laser source, in which all the components have been manufactured on a first generation of passive fiber with a pedestal around its core, perfectly matched to its associated active fiber, in order to maintain the coupling light in a quasi-singlemode pedestal area that will not degrade the output beam.

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.

In this conference, we show the realization of a high power 2.12 μm Ho3+-doped fiber (HDF) laser integrating for the first time to our knowledge a 1.94 μm triple clad fiber (3CF) combiner. This 3CF combiner, specifically developed for the above mentioned HDF laser, presents low losses properties thanks to a low-index glass capillary implemented in the component. Moreover, in this contribution we will discuss the power scalability of such a HDF laser monolithic architecture based on a triple clad fiber combiner pumped at 1.94 μm using Tm3+-doped fiber lasers.

Thulium-doped fiber lasers (TDFL) emitting around 2 µm receive growing attention. The Tm3+ ions may be pumped around 0.8 µm into the 3H4 level, but the maximum achievable efficiency in theory reaches only 40 %. Much higher efficiencies are achievable in practice thanks to the cross-relaxation (CR) effect, also called „2-for-1“ process. To trigger the CR effect, very high contents of Tm3+ ions are required, which places significant requirements on the material design; high concentrations of Al2O3 are typically needed to prevent concentration quenching in highly-doped fibers. MCVD method combined with nanoparticle doping is one of the most perspective methods for the preparation of highly doped alumino-silicate fibers. In this contribution, a large set of thulium-doped fibers was prepared by various methods. The fibers were analyzed with emphasis on the fluorescence lifetime and laser performance, and the nanoparticle doping method was evaluated in comparison with conventional fabrication methods.

An analytical model of holmium-doped fiber laser is proposed and verified experimentally. The model is based on a two-level model, assumes only transitions between levels 5I8 and 5I7 of the Ho3+ ion in silica, and enables to express the threshold pump power and laser slope efficiency in a closed form. The effect of intrinsic losses is modeled by a physically motivated semi-empirical formula. The model is compared with a numerical one and its application limits are discussed.

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 the 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 single-mode output. 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 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.

Mid-InfraRed (MIR) cascade lasing is a solution to mitigate the negative impact of Excited State Absorption (ESA) on the performance of yellow lasers made of ZBLAN fibers doped with Dysprosium (Dy). A low-loss cavity with nearly ideal mirror reflectivities in both yellow and MIR ranges yields optimal results, but fabricating Fiber Bragg Gratings (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 FBG 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 slope efficiency, whereas decreasing the reflectivity of the mirrors constituting the MIR cavity leads to an increase in the MIR threshold. Consequently, enhancements in the fabrication process for fluoride fibers and devices are crucial to unlock the potentially achievable performance of these yellow FLs.

The laser performance and tunability of a highly Pr3+-doped fluoride glass fiber will be presented. Absorption and emission properties as well as laser characteristics in different resonator configurations have been studied. We have achieved 3 W output power at 635nm wavelength with a slope efficiency of 33% with respect to the incident pump power. Furthermore, we present results on wavelength tunability with cladding-pumping on a several meter long Pr3+-doped ZBLAN fiber.

Lately, yellow lasers have been showing promising results for the treatment of diabetic retinopathy. In this study, a numerical model for Dy-doped yellow fiber lasers has been developed to analyze the impact of the most significant input parameters. The impact of input pump power, cavity length, and reflectivities of the mirrors on the output signal power has been studied, by evaluating the impact of the lifetime of Dy-energy levels. Additionally, an investigation of excited state absorption has been conducted. Simulation results provide valuable insights into both the qualitative and quantitative influence of these input parameters on the performance and efficiency of Dy-doped fiber lasers for yellow emission.

Recent advances in low-loss fluoride glasses have enabled the development of Dysprosium-doped ZBLAN fibers for yellow lasers, either tunable or not, pumped by blue GaN laser diodes. In previous work, our matrix-based simulation model based on the rate equations has been applied to investigate the impact of Excited State Absorption (ESA) on Dy-doped tunable FLs, showing potential enhancements enabled by MIR cascade lasing. In this study, the optimal fiber length for MIR and yellow emission has been analyzed as a function of pump power, cavity length, and mirror reflectivity. Results reveal a mismatch between the optimal lengths for yellow emission and MIR cascade lasing, with the latter being shorter in all considered cavity designs so far. This suggests the possibility of reducing the MIR threshold through tailored cavity optimizations aimed at minimizing fiber length without compromising yellow emission, thus enhancing performance even at lower pump power levels.

The mid-infrared region of the electromagnetic spectrum (2-20 μm) has attracted significant scientific and technological interest as all molecules have their ro-vibrational absorption lines in this wavelength range. Therefore, the mid-IR is usually referred to as the ‘molecular fingerprint’ region. Owing to the high-impact applications that result from the strong molecule-photon interaction, such as trace molecular detection for airport security screening and non-invasive breath analysis, research in mid-IR lasers and photonics has become one of the hottest topics in modern optics research over the last few years. In this talk I will summarise our recent advancements towards the development of all-fibre mid-infrared laser sources based on fluoride-glass optical fibres. In particular I will focus on the direct femtosecond laser-inscription of wavelength-selective couplers in mid-infrared compatible glasses, the fabrication of nonlinearly coupled waveguide arrays for use as artificial saturable absorbers, as well as on femtosecond laser direct-writing of in-fibre components like Bragg gratings and polarisers.

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_s=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.

Currently, the development of lasers operating in the mid-infrared (MIR), is of greater interest for a wide range of applications. All pump diodes are supplied with silica fibres. Together with the high water absorption of fluoride fibers catalyzed by high pump power density, this makes it impossible to use external butt-coupling techniques to inject pump source radiation into a fluoride fiber. We proposed and implemented the idea of the side-polished (D-shaped) fiber-based pump combiner. The pump combiner with 75% efficiency has been developed. The TEC system of cooling and heating with temperature feedback allowed for a reduction in losses in the system from 1.32 dB to 1.02 dB.

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 dco = 7.5 μm, cladding diameter dco = 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 Lw = 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 EL < 1.2 dB.

Optical cavities with nonlinear elements and delayed self-coupling are widely explored candidates for photonic reservoir computing (RC). For time series prediction applications that appear in many real-world problems, energy efficiency, robustness and performance are key indicators. With this contribution I want to clarify the role of internal dynamic coupling and timescales on the performance of a photonic RC system and discuss routes for optimization. By numerically comparing various delay-based RC systems e.g., quantum-dot lasers, spin-VCSEL (vertically emitting semiconductor lasers), and semiconductor amplifiers regarding their performance on different time series prediction tasks, to messages are emphasized: First, a concise understanding of the nonlinear dynamic response (bifurcation structure) of the chosen dynamical system is necessary in order to use its full potential for RC and prevent operation with unsuitable parameters. Second, the input scheme (optical injection, current modulation etc.) crucially changes the outcome as it changes the direction of the perturbation and therewith the nonlinearity. The input can be further utilized to externally add a memory timescale that is needed for the chosen task and thus offers an easy tunability of RC systems.

Programmable photonic circuits manipulate the flow of light on a chip by electrically controlling a set of tunable analog gates connected by optical waveguides. Light is distributed and spatially rerouted to implement various linear functions by interfering signals along different paths. A general-purpose photonic processor can be built by integrating this flexible hardware in a technology stack comprising an electronic monitoring and controlling layer and a software layer for resource control and programming. This processor can leverage the unique properties of photonics in terms of ultra-high bandwidth, high-speed operation, and low power consumption while operating in a complementary and synergistic way with electronic processors. This talk will review the recent advances in the field and it will also delve into the potential application fields for this technology including, communications, 6G systems, interconnections, switching for data centers and computing.

We first carry out a stability analysis on the standard two-wave STRS process in frequency-detuned two-mode fiber amplifiers, in the presence of pump/signal quantum defect thermal load. We show that the standard two-wave STRS process is stable against small modal perturbations, and as such it does not describe adequately the widely observed thermally-induced TMI process. We further show that inclusion of FWM effects and three-wave interaction, through the addition of an anti-Stokes LP11 wave, is required to describe modal instabilities above a power threshold, and a previously derived TMI power threshold formula is recovered. This work sheds new light on the standard STRS process and adds new insight into its connection with TMI effects in high power fiber amplifiers.

Fiber lasers are reliable and flexible sources of high laser power with excellent beam quality. However, limitations due to nonlinear and thermal effects, hamper further power scaling. We will give an overview over relevant influencing factors for these limitations, on the component side as well as regarding system design. Experimental examples in the 1µm and 2µm spectral region will be shown for the proposed techniques to tackle several of these obstructions, with a focus on ways to suppress transverse mode instabilities. Remaining limitations for single fiber systems can be overcome by parallelization of amplification, using multiple actively doped cores running below the critically power threshold each. Such fiber cores can be housed separately or in a single multi-core fiber. We will address coherent and spectral methods to (re-)combine multiple fiber laser output beams while maintaining beam quality and discuss scaling aspects and potential limitations to these architectures.

In the era of high-power laser systems, there is a constant demand for compact and efficient short-pulsed amplifiers delivering high power with an excellent beam profile and high polarization stability. In this presentation, I will review the advantages of active tapered double-clad fiber amplifier technology and different geometrical concepts. The special geometrical architecture of tapered fibers enables the direct amplification of picosecond pulses from tens of milliwatts to hundreds of watt levels in a single amplification stage. The recent technological progress in tapered fibers led to a doubling of the average power level, preserving excellent output spatial and polarization characteristics. The spun tapered fiber features low birefringence resulting in improved polarization stability at high power levels. Moreover, this geometrical architecture is exploited for the amplification of structured light, maintaining complex polarization profiles and spatial intensity distribution.

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.

We will report on recent advances in fabrication of large volume silica based, doped fiber preform materials synthesized via powder-based processes. Recently, there has been increased interest for power scaling in fiber based laser applications that requires large core volumes with excellent homogeneity in refractive indices, but also chemical variety (in terms of high dopant concentrations, different dopants). A structural fiber variety requires dedicated large volume core material of reproducible and tailorable chemical composition. Established technologies such as modified chemical vapor deposition (MCVD) or crucible melting rely on complex thermal processing, and are limited in accessible chemistries, dopant concentration, achievable functionalities, and in case of MCVD in achievable core sizes. The current process development thus targets to overcome such draw-backs by including novel approaches to enable extreme material combinations, enhanced reactivity, or novel functions.

Thulium-doped fiber lasers working in the 2-μm wavelength range are particularly important because they belong to the group of so-called eye-safe lasers. Although their efficiencies are getting closer to the efficiencies of the matured ytterbium fiber lasers, the record output power of thulium fiber lasers is still orders of magnitude below its potential, looking for technology breakthroughs that would overcome the current limitations. Novel fiber designs, e.g., using structured core of the active fiber, and new ways of mitigating thermal and temperature effects may enable further increase of the output power. In the paper, we will review our proof-of-concept experiment of the pedestal-free thulium doped silica fiber with a large nanostructured core, where the initial preforms of the active medium were made by the nanoparticle-doping and MCVD methods. Next, measurement of temperature-dependent thulium cross sections will be reviewed as well as application of these cross-section spectra for prediction of thulium fiber laser operation using recently derived closed form expressions for the laser threshold and slope efficiency under pumping at 790 nm by the two-for-one process.

Experimental results on optical properties of Tm-doped oxide glass fibres based on different technologies and host materials are presented. Silica fibres and crystal-derived fibres (CDF) are compared. Crystal-derived fibres offer potentially higher doping levels than those made by Modified Chemical Vapor Deposition technology providing the ability to tune optical properties towards new applications. A detailed analysis of absorption and fluorescence properties of the 3F4 and 3H4 levels within a concentration range from 0.08 up to 1.52 mol% Tm2O3 is provided resulting in an extensive and specific energy level scheme for 789nm core-pumping.

In the world of optics, hyperchromats occupy a unique position due to their ability to amplify dispersion effects, making them very interesting for applications such as surface profiling or spectroscopic measurements. This contribution provides a comprehensive study of the factors influencing two-element hyperchromats with cemented and air-spaced lenses. The systems investigated include purely refractive, diffractive and hybrid systems containing both refractive and diffractive elements. To find the optimum parameters for these configurations, numerical calculations and subsequent optimizations were performed using optical design software. To further reduce the achievable equivalent Abbe numbers, an aspherical surface was introduced. This provided the opportunity to develop hyperchromatic systems with extremely low equivalent Abbe numbers and large axial chromatic splittings. The strongest cemented system achieved an equivalent Abbe number that was only 12 percent of the Abbe number of the single lenses used. Even more powerful were the air-spaced hyperchromats, which reduced the equivalent Abbe number by more than five times compared to their components.

Light sources in the mid-infrared (m-IR) between 2 and 20 µm are of great interest for molecular sensing, medical, security and defense applications. The availability of broadband, coherent and high-brightness fibered sources has many advantages compared to thermal IR sources or quantum cascade lasers, and the generation of supercontinuum (SC) in engineered optical fibers pumped by femtosecond lasers is one way to reach this goal. We propose here to give a state of the art of the field related with the different types of glasses and optical fibers that can be used for that purpose. Since the infrared glasses of interest for nonlinear optical applications are generally low Tg glasses, new paradigms have emerged in terms of materials combinations and design of new multimaterial optical fibers and we propose to give here some new insights in the field.

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.

Chalcogenide glasses are appropriate hosts to deliver high power in fibre in the mid-infrared region (abbreviated MIR, defined as 3 to 50 microns wavelength in the British Standard, International Standard for Organization [1]) since they offer a transparency window in this spectral domain. Our work aims to study the relation between the optical glass fibre properties and fibre transmission of mid-infrared optical power. [1] British Standards Institution, BS ISO 20473:2007 Optics and Photonics. Spectral Bands. 2007, BSI. p. 10.

We report on a detailed spectroscopic study of Er3+-doped LiYF4 epitaxial layers with the goal of de-veloping mid-infrared waveguide lasers. 11 at.% Er:LiYF4 single-crystalline layers were grown by Liquid Phase Epitaxy on undoped oriented substrates under Ar atmosphere. The layers exhibited intense and strongly polarized mid-infrared luminescence at 2.65-2.90 µm owing to the 4I11/2→4I13/2 Er3+ transition. The maximum stimulated-emission cross-section was 1.61×10-20 cm2 at 2720 nm for π-polarization. The crystal-field splitting of Er3+ multiplets was determined. The luminescence dynam-ics from Er3+ excited states were systematically studied yielding the rates of non-radiative relaxation and the parameters of energy-transfer upconversion and cross-relaxation.

Fluoride-based fibres have attracted notable attention for their thermal properties, such as a thermal expansion coefficient that is 30 times larger than that of silica fibres. In this work, we discuss the thermal behaviour of FBGs inscribed in different fluoride-based fibres, such as ZBLAN and InF3, for application as thermal sensors for cryogenic temperatures. The FBGs were inscribed utilizing the Talbot interferometer with a Ti:Sapphire fs-laser combined with frequency-doubling crystal.

This round table panel discussion will focus on the limits of different types of fiber. The intent of this presentation 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.

Since the 1970s, optical fibers have undergone considerable development and are now used in a very wide range of applications, covering telecommunications, environment, medical applications, etc., thanks to the development of amplifiers, lasers and sensors. Such progress has been made possible by the considerable work carried out to improve the transparency of optical fibers. In recent years, a new family of optical fibers has been developed incorporating nanoparticles. Such fibers were first envisaged as a means of locally modifying the chemical environment of luminescent ions (rare-earth and transition metal ions) in order to offer new lasers. However, the light scattering induced by nanoparticles limits this application. More recently, light scattering has instead been exploited to develop sensors (temperature, stress, chemistry, biology, etc.). This presentation will review these fibers, presenting the fabrication processes, the fundamental issues involved in nanoparticles formation and their different applications.

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

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.

We examined the potential of amorphous Ge-Bi-Se chalcogenide films prepared from RF magnetron co-sputtering.(Co)-sputtered films’ compositions were analysed using EDX spectroscopy. Pre-deposition calculations were used to find the expected composition, and a good agreement with experimentally determined compositions were observed. The amorphous to crystalline phase change in films were closely examined by XRD analysis and Raman spectroscopy in terms of atomic % of Ge by slowly increasing the GeSe2 contribution during co-sputtering. The influence of the composition on the optical band gap energy, refractive index and transmission spectra were also analysed using variable angle spectroscopic ellipsometry(VASE) and spectrophotometry analysis from visible to mid-IR. Third-order nonlinear optical parameters of the co-sputtered films were estimated using Sheik-Bahae formalism. The ridge waveguides were fabricated from RF magnetron co-sputtered Ge-Bi-Se films on Si/SiO2 substrate to obtain single-mode waveguides at 1.55 µm. Financial support from Czech Science Foundation and European Union’s Horizon Europe Framework Programme under grant agreement No 101092723 is greatly acknowledged.

We report the first demonstration of excitability in all-fiber lasers with 1550 nm. We present clear numerical evidence in this passive Q-switched device with gain and absorption sections to determine excitability properties, including a threshold-based stimulus response and not much response delay between the input pulse and the excitable response with increasing noise amplitude. Our numerical results are consistent with the excitability basis as demonstrated by a study of Yamada’s model; they pave the way for new and reliable all-fiber architectures for photonic memory and neural-inspired computing applications

This work aims to provide the comparative study of luminescent features of thulium-doped low phonon materials – ZBLAN glasses and YF3 nanocrystals, investigated over an extremely broad spectral range extending from UV to mid-IR. Measurements and analysis of absorption, excitation, and emission characteristics recorded under direct and up-converted excitation, together with fluorescence dynamics of metastable levels, enabled determining the comprehensive spectroscopic picture of Tm3+ and Tm3++Yb3+ doped low phonon systems giving a good starting point for numerical modelling of lasing properties and efficiency of different excitation schemes.

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 appproach, by enriching the work done on the radio frequency or microwave signals.

In this work, we summarize the research results on the short wavelength emission properties of PMMA-based nanocomposites doped with oxide and fluoride nanocrystals activated with erbium ions (and sensitized with ytterbium ions), which are intended for use in polymer fiber amplifiers, lasers and incoherent light sources. We have investigated the structural and luminescence properties of a series of oxide and fluoride nanopowders with varying dopant concentrations, which enabled the optimization of dopant concentration and, in turn, manufacturing and testing the PMMA-based composites. These have been characterized with respect to the luminescent features and compared with the original nanopowders. All those results will be presented and discussed in the context of application potential and technological challenges.

Utilizing a femtosecond laser (wavelength: 1030 nm, pulse duration: 230 fs) we induced crystallization within a glass matrix composed of TeO2-P2O5-BaF2-ZnF2-Na2O-ErF3. The laser-induced glass-ceramics were analysed for microstructural and structural modifications using scanning electron microscopy (SEM) and Raman spectroscopy, respectively. Our analysis revealed an increase in nanoscale barium fluoride crystals within the laser-modified area as the repetition rate decreased from 500 kHz to 200 kHz and energy levels escalated from 200 nJ to 600 nJ (illustrated by darker lines in fluorescence images). Moreover, zinc barium phosphate crystallized into microcrystals following laser irradiation at 1 MHz and energy levels ranging from 170 to 200 nJ (indicated by dots). Raman spectra confirmed alterations in the tellurite (TeO4, TeO3) and phosphate structural units within the glass network of glass-ceramics compared to the parent glass, characterized by three Q3, two Q2, and one Q1 bridging oxygens. Additionally, we discuss the changes in erbium emission across the UV-NIR region within both laser-induced crystals and the parent glass.

In this paper, we report on a high-energy, high-power quasi-continuous wave (QCW) operation of a double-clad thulium (Tm) fiber laser. We constructed an efficient high-power Tm fiber laser which produced rectangular-shaped pulses at 1940 nm with a > 6 J pulse energy and a 10 ms pulse duration at a 10 Hz repetition rate, corresponding to an average power of > 60 W and a peak power of > 600 W for ~ 110 W of incident pump power at 793 nm. The detailed laser characteristics and the ablation of stones with a constructed laser are discussed.

Various applications in the medical, defence and industrial fields exist for thulium-doped fibre lasers (TDFL) emitting in the 2 µm spectral region. All-fibre laser architectures represent optimized designs especially for applications that require high reliability in harsh environments. These architectures can be further improved by reducing the amount of fibre components and therefore reducing the failure probability. We investigate mode field adaption techniques between an active and passive fibre by changing the refractive index profiles of both fibres. The findings of this investigation are used to optimize a core-pumped TDFL with up to 75% slope efficiency.

3D laser nanoprinting based on multi-photon absorption (or multi-step absorption) has become an established commercially available and widespread technology. Here, we focus on recent progress concerning increasing print speed, improving the accessible spatial resolution beyond the diffraction limit, increasing the palette of available materials, and reducing instrument cost.

Biological discovery is a driving force of biomedical progress. With rapidly advancing technology to collect and analyze information from cells and tissues, we generate biomedical knowledge at rates never before attainable to science. Nevertheless, conversion of this knowledge to patient benefits remains a slow process. To accelerate the process of reaching solutions for healthcare, it would be important to complement this culture of discovery with a culture of problem-solving in healthcare. The talk focuses on recent progress with optical and optoacoustic technologies, as well as computational methods, which open new paths for solutions in biology and medicine. Particular attention is given on the use of these technologies for early detection and monitoring of disease evolution. The talk further shows new classes of imaging systems and sensors for assessing biochemical and pathophysiological parameters of systemic diseases, complement knowledge from –omic analytics and drive integrated solutions for improving healthcare.

The integration of flexible photonics into high value composite structures, such as those made of Carbon Fibre Reinforced Polymer (CFRP) offers new intelligent sensing capability for sustainable manufacture and through-life structural monitoring. Through utilisation of the planar functionality offered by flexible photonics, within these composite matrices, enables the creation of new intelligent structures for a host of sectors including aerospace, clean energy infrastructure and automotive. This presentation highlights the design considerations needed when integrating flexible photonics into fibre reinforced polymers (FRPs) and highlights some promising opportunities that showcase specific demonstrations achieved for flexible planar doped silica. Notable applications, such as scalable tri-axial strain sensing and the implementation of a branching optical network architecture within an FRP composite, will be presented to illustrate the new functionality offered.

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 Si1−xGex-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 SiGe 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 behaviour character.

This presentation explores the interdisciplinary realm of nanocomposite material design, integrating materials engineering, chemistry, and photonics. Focusing on the innovative use of nanocomposite glasses containing noble metal nanoparticles, the discussion delves into the novel opportunities these materials present for developing sensing structures based on LSPR (Localized Surface Plasmon Resonance). Additionally, transparent glass-ceramics are spotlighted as high-performing materials in functional photonic applications for optical fiber technology.

In the present study, oxyfluoride glass-ceramics (GCs) containing LaF3 nanocrystals doped with NdF3 were prepared with different amounts of Ag added as a co-dopant. Different Ag-containing precursors were employed being AgNO3 the most suitable for obtaining Ag nanoparticles segregated in the glass matrix. The GCs thermal, structural and optical properties were characterized in order to identify the presence of the metallic nanoparticles as well as its role on the photoluminescence enhancement. The site-selective emission and excitation spectra show that samples co-doped with Ag exhibit an increase of the luminescence of Nd3+ ions in the crystalline phase compared with Ag-free analogues. This effect can be attributed to the enhancement of the local field 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.

Scattering optical fibers containing nanoparticles have recently gained a strong interest. Their development remains limited due to the lack of reliable processes to control the nanoparticles properties. We report here a femtosecond-laser-based approach to modify on-demand the characteristics of the NPs and thus the scattering properties of the optical fiber. A highly scattering core of a lanthanum silicate NP-doped optical fiber has been irradiated by a high repetition rate femtosecond laser. The measurements performed with an optical backscatter reflectometer show that the affected zone clearly presents reduced optical losses. This can be attributed to the alteration of the NPs which is confirmed by the SEM images of the fiber core before and after laser irradiation. These results open up a new manufacturing avenue that has never been explored before and will offer an innovative solution for real control of the scattering properties of optical fibers.

We show an in-depth spectroscopic characterization of CaF2 co-doped with neodymium and ytter-bium ions. The Nd3+ absorption around 791nm enables efficient excitation of Yb3+ ions through Nd3+⟶Yb3+ energy transfer (ET). Combining Nd3+ and Yb3+ along with Gd3+ buffer ions enables broad emission bands around 1µm in Nd3+,Yb3+,Gd3+:CaF2 crystals. The Nd3+⟶Yb3+ high ET effi-ciency within Nd3+-Yb3+ clusters was estimated. Laser action using different Nd,Yb,Gd:CaF2 crys-tals resulted in a 17% laser slope efficiency versus absorbed pump power and a200mW laser threshold. The laser wavelength changes are explained in detail by investigating the respective contributions of Nd3+ and Yb3+ to the gain cross-section. The laser gain is either dominated by one of the Nd3+ emission peaks (1065nm, 1048nm), or exhibits a flat profile (1045-1067nm range). A large Nd3+ inversion ratio depletes the Yb3+ ground state through ET, saturating the energy trans-fer, and shifting the laser emission line towards shorter wavelengths.

Femtosecond laser offers a means to confine energy beyond the diffraction limit. Applied to glass, this high energy confinement leads to intriguing modification of the glass structure, inducing a variety of events such as nano-crystallization, amorphization or phase separation. Here, we review these structural modifications, their observations as well as means to control it and one can achieve nanoscale confinement along the laser propagation axis. Furthermore, we discuss how they can be used in the context of functional micro-devices through selected applications, taken from research conducted in our research group, including nano-scale positioning, single-material photoconductive devices and information storage.

Numerous innovations in photonics were realized on the base of nonlinear optical properties and notably in information technologies. To take advantage of nonlinear optical properties of glass, multi-disciplinary research efforts were necessary combining optics, glass chemistry, material science as well as development of optical or electrical polarizations processes. This presentation addresses fundamental aspects of the second order optical properties in glasses, but will also give more details on recent progresses demonstrating that amorphous inorganic material can now compete with lithium niobate single crystal. By using a thermo-electrical imprinting process, the possibility to manage at the micrometer scale geometry and location of efficient second order optical responses. (χ(2)= 29 pm.V−1 at 1.06 µm) is demonstrated on amorphous niobate optical thin films. This paves the way for the future design of integrated nonlinear photonic circuits based on amorphous inorganic materials enabled by the spatially selective and efficient second order optical susceptibility of these promising and novel optical materials.

The development of stable coherent light sources at the nanoscale is of key significance for novel applications in nanophotonics and nanotechnology. Here we demonstrate the generation of stable self-Q-switched laser pulse trains in the ns and µs temporal domains while featuring subwavelength nanolasing spatial confinement [1]. The approach combines a Nd3+ doped Lithium Niobate crystal which provides laser gain in the NIR spectral region, plasmonic chains of Ag nanoparticles that enable subwavelength spatial confinement of laser radiation, and a 2D-monolayer (MoS2) acting as saturable absorber to achieve the temporal confinement of laser radiation. The results pave the way for the integration of ultra-fast lasers at the nanoscale, in which the synergetic hybridization of the materials involved could benefit applications such as high-speed communications, advanced manufacturing, ultra-sensitive sensing or quantum computing, providing a wealth of opportunities for light manipulation and control at subwavelength scales. References [1] M. O Ramírez, P. Molina, D. Hernández-Pinilla, et al., Laser Photonics Rev. (in press), 2023. DOI:10.1002/lpor.202300817.

Fibre Bragg gratings (FBGs) transform a conventional multi-mode optical fibres into side-emmitting light sources with controllable emission angles, which find applications in endoscopy, (bio-)photoreactors and spectroscopy. The FBGs were inscribed in of soft-glass indium fluoride-based optical fibres with a two-beam phase-mask interferometer and a 266-nm femtosecond laser. The scattering pattern was imaged in Fourier space accessed by inserting a Bertrand lens in the beam path. Fibre rotation during the imaging yields a 360-deg all-around view. The FBGs far-field scattering pattern demonstrated discrete broken bands, or scattering cones with different opening angles, for the different laser colours. Furthermore, multiple cones could be observed for the case of complicated, higher harmonics grating refractive index profiles, which provides additional tool to design tailored fibre light emitters or guided light analyser gratings.