The ex-situ doping approach provides a straightforward method of adding optically active nano-to-micron scale crystal (OANMC) particles into glass. The primary problem preventing widescale adoption of this method is dissolution of the particles into the glass during fabrication. A quantitative understanding of the dissolution dynamics of OANMC particles in molten glass is therefore essential. Here, we study the dissolution characteristics of macroscopically-sized optical materials in a tellurite (75TeO2–15ZnO–10Na2O, TZN) glass melt. Using YAlO3 (YAP) as a model crystal, we quantified the dissolution kinetics at 600 and 800 oC by fitting the experimental data using the modified Weibull function and the shrinking core models. We establish that YAP dissolution is predominantly diffusion-controlled and well described by the diffusion distance-controlled dissolution (DDD) model. We show the strong correlation between the dissolved fraction and the mean cation–anion bond length for PrF3, YAP, Y3Al5O12 (YAG), sapphire, quartz, and silica at 600 oC, where shorter (stronger) bonds were associated with less dissolution. In contrast, at 800 oC the correlation was not observed, which we attribute to the temperature-dependent solubility and dissolution rate coefficient. These findings offer practical guidance for the incorporation of ex-situ-made OANMC particles into glass matrices.

This study characterizes, for one value of the Tm3+ concentration, the populating and de-populating mechanisms of the 1G4 level of the Tm3+ ion in an aluminosilicate glass host under standard 790 nm pumping conditions. The 3H4, 3H4 -> 1G4, 3F4 energy transfer upconversion (ETU) microscopic rate parameter is determined to be 5 +/-0.5 s-1, which was obtained using the fluorescence rise time after pulsed excitation of the 3H4 level. We also provide evidence that the 1G4 level is initially populated by pump excited state absorption at lower pump power, however this process makes a minor relative contribution to populating the 1G4 level compared to ETU, in the limit of high power and for the Tm3+ concentration considered in this study. Quantification of the de-populating energy transfer processes of the 1G4 level was achieved after direct excitation at 465 nm, resulting in the total microscopic rate parameters for all cross relaxation and ETU processes relevant to this level being 4,000 +/- 250 s-1 and 2,500 +/- 500 s-1 , respectively. The energy migration rate of this level was determined to be 1550 +/- 150 s-1. This report also provides a more general form of the intrinsic decay time calculation for each energy level of Tm3+-doped aluminosilicate glass as a function of Al2O3 content, which is based upon the modification of the non-radiative decay rate of Tm3+-doped silica from adding Al2O3.

This study focuses on quantification of the well-known cross-relaxation, energy transfer upconversion and energy migration processes in Tm3+-doped aluminosilicate glass fibers. A detailed energy transfer model has been applied to fluorescence decay measurements of the H-3(4) and F-3(4) energy levels of Tm3+-doped aluminosilicate fibers over a range of incident pump power. These fibers spanned a range of Tm3+-doping concentrations, enabling the relationships between these energy transfer processes and Tm3+-doping concentration to be measured. We find that the functional dependence with the Tm-3 vertical bar concentration is markedly different for each energy transfer process. In addition, our findings are suggestive that the host composition of aluminosilicate glass presents unique energy transfer properties for Tm-3 vertical bar-doped fibers, compared with other common host materials.

A high slope efficiency of 12%, a stabilized output power of 250 mW at a wavelength of 581.8 nm, and what we believe to be a record peak output power of 450 mW have been achieved from a diode-pumped high concentration Dy3+:BaF2 nanoparticle (NP)-doped silicate fiber laser. The performance is primarily attributed to a reduction in the overall background loss within the cavity and a higher Dy3+ concentration in the pre-synthesized NPs. Almost 60% of the initial laser power remains in the steady state after several hours of the fiber being pumped by high-power 450 nm radiation, suggesting a modified local rare-earth ion environment. Such an environment likely leads to moderate photodarkening resistance, which results from the reduced energization of nearby precursor defects in the aluminosilicate glass, typically forming strongly absorbing defect centers. The result opens the door to a new class of lasers that exploits the remarkable material properties of silicate glass for the efficient generation of visible light.

Numerical simulations of Dy 3+ -doped aluminosilicate fiber lasers for yellow light emission are presented. The 4 F 9/2 → 6 H 13/2 laser transition emitting at approximately 580 nm has been developed experimentally with 445 nm diode pumping and shows promise for higher output power in both silicate and in particular fluoride glass hosts. In this report, we focus on accumulating the published spectroscopic data in order to quantify cross relaxation (CR) in each of these hosts and use it to estimate its role in the laser dynamics. The model involves calculation of the branching ratios, and radiative and nonradiative decay rates and compares well with reported experimental results. We show the important role of the background losses on previous laser performance and the relatively strong increase in the laser threshold as a result of CR despite the moderately low Dy 3+ concentrations that have been experimentally tested.

We experimentally demonstrate a yellow laser based on Dy:BaF2 nanoparticle (NP) doped aluminosilicate fiber. We obtain an output laser with a center wavelength of ~581.5 nm and a maximum output power of ~21 mW.

A silica fiber laser based on Dy 3+ -doped nanoparticles (NPs) and operating at a wavelength of ∼581.5 nm is reported. Specifically, Dy-doped BaF 2 nanoparticles were synthesized, and suspension doped into an aluminosilicate preform fabricated using conventional MCVD methods. Though the precursor BaF 2 reacts partially with the SiO 2 host, a presumed barium rich environment and localized doping persists. Spectroscopic characterization included visible emission spectrum, fluorescence decay, and loss of spectrum measurements and, where applicable, comparisons are made to previously reported Dy 3+ -doped silica visible fiber lasers. To the best of the author’s knowledge, this is the first report on a dysprosium NP-doped silica fiber and visible fiber laser made using this approach. This work paves the way for the development of visible silica fiber lasers with engineered local environments surrounding the rare earth ions.

A silica fiber laser based on Dy3+-doped 3 +-doped nanoparticles (NPs) and operating at a wavelength of similar to 581.5 nm is reported. Specifically, Dy-doped BaF2 2 nanoparticles were synthesized, and suspension doped into an aluminosilicate preform fabricated using conventional MCVD methods. Though the precursor BaF2 2 reacts partially with the SiO2 2 host, a presumed barium rich environment and localized doping persists. Spectroscopic characterization included visible emission spectrum, fluorescence decay, and loss of spectrum measurements and, where applicable, comparisons are made to previously reported Dy3+-doped 3 +-doped silica visible fiber lasers. To the best of the author's knowledge, this is the first report on a dysprosium NP-doped silica fiber and visible fiber laser made using this approach. This work paves the way for the development of visible silica fiber lasers with engineered local environments surrounding the rare earth ions.

We present initial measurements of the basic spectroscopic parameters and photodarkening characteristics for a Sm 3+ -doped aluminophosphosilicate (APS) glass fibre with a large phosphorous-to-aluminium ratio that is pumped at 400 nm using an InGaN diode laser. The spectroscopic parameters are compared with previous studies. We demonstrate that the presence of a P:Al ratio ∼9 leads to the formation of P-related colour centres only, causing absorption in the visible part of the spectrum that directly overlaps with the strongest Sm 3+ transitions at 600 nm and 650 nm. We propose an explanation for the photoionization of the P-related defect precursors in high P:Al ratio APS glass based on excited state absorption from the upper state of Sm 3+ that is followed by subsequent high-energy UV photons emission. We also establish that large P:Al ratios in APS fiber can effectively inhibit the reduction of Sm 3+ to Sm 2+ . These findings lay the groundwork for further development of visible fibre lasers based on Sm 3+ -doped silicate glass.

We demonstrate a new design for active fluoride glass fibres in which a metal coating instead of a polymer coating is applied. A 2- μ m-thick silver layer is fabricated chemically to the periphery of the fiber, that in this case is doped with Dy 3+ ions, and coating lengths of up to 20 cm were produced. The temperature rise in the core of the fiber was accurately measured using a sensitive fiber Mach-Zenhder interferometer (MZI) employing a stabilised He-Ne laser. We use this setup to show that the metal coating can achieve a reduction in the fibre core temperature by up to 22% for low launched pump power levels. A basic two-dimensional model shows reasonable agreement with the experiment. This work paves the way for the development of active fluoride fiber applications in which reducing and stabilising the temperature of the fibre is critical.

We report the high-efficiency operation of a 3.05 µm dysprosium-doped fluoroindate glass fiber laser that is in-band pumped at 2.83 µm using an erbium-doped fluorozirconate glass fiber laser. The demonstrated slope efficiency of the free-running laser of 82% represents approximately 90% of the Stokes efficiency limit; a maximum output power of 0.36 W, the highest for a fluoroindate glass fiber laser, was recorded. Narrow-linewidth wavelength stabilization at 3.2 µm was achieved by utilizing a first-reported, to the best of our knowledge, high-reflectivity fiber Bragg grating inscribed in the Dy3+-doped fluoroindate glass. These results lay the foundation for future power-scaling of mid-infrared fiber lasers using fluoroindate glass.

In the creation of nano- and macro-sized solid-state laser sources that emit light from pump light absorption, the main light-emitting component typically consists of rare earth or transition metal ions (optical centres) doped into an optically transparent solids in the form of a crystal or glass. This has led to countless demonstrations of laser systems and basic wavelength converters emitting over many octaves from the ultraviolet to the mid-infrared. Energy exchange from pump to laser via energy storage in the metal ion drives the process but, as the concentration of the ions increases, energy can transfer between the ions leading to a redistribution of the excited electronic states. Recently there has been very strong interest in exploiting energy transfer within nano-sized particles that are highly doped with rare earth ions. In this context and others, this paper sets out a basic review of the fundamental concepts related to energy transfer between excited and ground state ions with a view to assist in the basic understanding of energy transfer. With this understanding it is hoped that these important processes can be even further developed leading to higher efficiencies, higher output power and a wider range of emitted wavelengths.

Recent studies suggest fluoroindate (InF3 glass fibers to be better suited for the development of mid-infrared fiber lasers systems as compared to the commonly used fluorozirconate (ZBLAN) fibers [1]. The extended transparency window up to 5.5 $\upmu \mathrm{m}$ and the increased resistance to water ingress [2] allowed the demonstration of laser emission in 3 - 4 $\upmu \mathrm{m}$ region using a variety of dopants as well as record output powers in the 4 $\upmu \mathrm{m}$ region [3]. However, the reported efficiencies to date are all well below the Stokes limit, suggesting background loss (BL) to be a limiting factor for power scaling of fluoroindate fiber lasers [4].

A mode-locked, dual-wavelength pumped 3.5 $\mu$ m fiber laser using frequency shifted feedback utilizing an acousto-optic modulator is reported. Pulses of 3.8 ps with 9.7 nJ were obtained at a repetition rate of 37.75 MHz. The resulting peak power is 2.55 kW. An electronically wavelength swept, mid-IR interrogator is built to characterize a mid-IR fiber Bragg grating.

In the development of fiber sources emitting in the mid-infrared, the primary light emitter is typically a rare-earth ion that is doped into an optical fiber composed of soft glass. For a number of transitions, the most important to date being the 3 μm transitions of Er 3+ and Ho 3+ , it has been found necessary to either codope with another rare-earth ion to quench the lower laser level, or involve high rare-earth ion concentrations so that favorable energy transfer processes can increase the optical gain. For these cases, the transfer of energy between the rare-earth ions takes place resulting in a redistribution of the populated electronic states of the ions. In this chapter, we will introduce the basic concepts and theory of energy transfer between excited and ground states of the rare-earth ions. In the modeling of mid-infrared photonic systems, a rate equation approach is typically used. The understanding of energy transfer and the quantization of the energy transfer parameters is needed so that the transfer parameters (e.g., in units of s −1 ) can be used in numerical modeling of mid-infrared fiber light source systems. Numerical modeling of fiber lasers employing codoping is particularly important and in conjunction with spectroscopic measurements, understanding and optimization of the overall system can result. Since the concentration of rare-earth ions used for mid-infrared fiber photonics is never greater than 10 mol%, we will not be discussing the exchange interaction. We also examine the temporal behavior derived from experimental measurements from a number of rare-earth ions that exhibit mid-infrared emission and demonstrate the essential characteristics of the various types of energy transfer.

The generation of high-power coherent radiation extending beyond the so-called near-infrared region of the electromagnetic spectrum has been a challenging task for the scientific community over the last decades. To that purpose, although fiber lasers are featuring several advantages namely in terms of their ruggedness and beam quality, their initial development has been mainly relying on fused silica possessing a wavelength operation window restricted to the near-IR. The advent of fluoride glass fibers allowing for significant doping levels of lanthanides along with superior optical and physical properties has, however, changed the deal. Nowadays, doped double-clad fluoride glass fibers with minimum background losses on the order or even below 10 dB/km near 2.6 μm are commercially produced, which has fueled the development of watt-level monolithic fiber lasers covering the wavelength range between 2.7 and 3.9 μm thanks to three trivalent lanthanide ions, Er3+, Ho3+, and more recently Dy3+. In this chapter, we first review from an historical perspective of the main developments that have led to such achievement. A special attention is also paid to the various strategies that have been deployed to alleviate the so-called bottleneck issue that is plaguing several mid-infrared (MIR) emission bands from those ions. Then the main engineering challenges that are specific to the power scaling issues related to MIR generation from fluoride glass fibers are addressed. Finally, future perspective for these sources along with their most promising application fields are discussed.

The importance of spectroscopy to the development of rare-earth-doped fiber systems cannot be overstated. Parameters such as the energy level lifetimes, absorption and emission cross sections, and the energy transfer parameters in more concentrated systems determine the viability of any laser transition. The parameters form the input-to-numerical models that are developed to optimize and understand the performance of the mid-infrared light source. In this chapter, the essential spectroscopic parameters are presented, discussed, and compared. This chapter is concerned with laser transitions that emit light with wavelengths shorter than 4 μm and the host for the rare-earth ions is confined to fluoride glass, the glass host that has underpinned the development of light sources in the mid-infrared.

We report a comprehensive characterization of tunable continuous-wave (CW) and passive Q-switching laser performance of Dy-doped zirconium fluoride fiber emitting around 3 µm. The in-band pumped CW laser operation is investigated for pump wavelengths varying from 2.7 µm to 2.825 µm, for fiber lengths ranging from 0.4 m to 2 m, and for output coupling efficiency from 10% to 50%, leading to a maximum laser slope efficiency of 44% and a tuning range larger than 300 nm. With Findlay-Clay analysis and Rigrod analyses, optimal cavity parameters are retrieved, paving the way for further optimizations in performance. The passively Q-switched laser operation of Dy-doped fluoride fiber is achieved employing a semiconductor saturable absorber mirror for the first time, demonstrating a stable operation with a minimum pulse duration of 580 ns, a highest repetition frequency of 103 kHz and a pulse energy up to 300 nJ.

A mode-locked, dual-wavelength pumped 3.5 µm fiber laser using frequency-shifted feedback is reported. Pulses of 3.8 ps with 8.7 nJ were obtained. An electronically wavelength swept, mid-IR interrogator is built to characterize a mid-IR fiber Bragg grating.