Energy level decay processes in Ho3+-doped tellurite glass relevant to the 3-µm transition

The primary excited state decay processes relating to the 5I6 --> 5I7 at 2.9 um laser transition in singly Ho3+-doped tellurite (TZBG) glass have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the 5I6 energy level at 1151 nm and 5I7 energy level at 1958 nm has established that the rate of energy transfer up-conversion between holmium ions excited to the 5I7 level is negligible for Ho3+ concentrations up to 4 mol. %. Excited state absorption was not observed from either the 5I7 or 5I6 levels and the luminescence from the 5I7 and 5I6 energy levels was measured to peak at 2050 nm and 2930 nm, respectively. The 5I6 level has a low luminescence efficiency of 8.9% due to strong nonradiative multiphonon relaxation. In contrast, decay from the 5I7 level is essentially fully radiative. A linear decrease in the decay time of the 5I6 level with Ho3+ concentration augmentation results from energy transfer to OH ions in the glass (with NOH=8.2x10^17 ions cm^-3) and reduces the luminescence efficiency of the 5I6 level to 8% for [Ho3+]=4 mol. %. Numerical simulation of a fiber laser incorporating 4 mol. % Ho3þ showed that a population inversion of 7.8% is reached for square pulses of 100 us duration and a repetition frequency of 20 Hz at a moderate pump intensity of 418 kW cm^-2 if energy transfer to OH- radicals is neglected

Toward a high concentration Yb-Er phosphate glass optical amplifier for eye-safe compact LIDAR

LIDAR systems offer a powerful remote sensing technique that has been successfully employed for several applications. The key component of a LIDAR system is the laser source whose main parameters contributes to overall system performance. An advantageous approach to realize a high power LIDAR source is the MOPA configuration, in which a master oscillator produces a highly coherent beam and an optical amplifier is used to boost the beam output power while preserving its main spectral properties. The NATO SPS project “CALIBER” (CompAct eye safe Lidar source for AirBorne lasER scanning) aims to develop a compact, lightweight and low cost version of a LIDAR source that can be placed on small UAVs or in specific locations of premises where a small footprint equipment is required. Following the requests of a high degree of compactness while maintaining high performance and low cost, the choice for the optical amplifier fell on an Yb/Er co doped phosphate glass based waveguide. Phosphates are recognized to be an ideal host material for engineering the amplification stage of a pulsed MOPA thanks to their ability to maximize energy extraction and minimize the nonlinearities. They enable extremely high doping levels of rare--earth ions to be incorporated in the glass matrix without clustering, thus allowing the fabrication of compact active devices with high gain per unit length (> 5 dB/cm). In this work we report on the design and fabrication of a series of Yb/Er--doped phosphate glasses to be used as active materials for the core of a fiber amplifier. The fabricated glasses were thoroughly characterized and the best composition selected for the fabrication of the first amplifier prototype. Suitable cladding compositions were explored and the final core/cladding glass pair was used to realize a multi--mode optical fiber. Preliminary results of optical amplification are presented using a CW source as seed laser

Yb-doped phosphate double-cladding optical fiber laser for high-power applications

A Yb-doped phosphate glass double cladding optical fiber was prepared using a custom designed glass composition (P2O5 - Al2O3 - Li2O - B2O3 - BaO - PbO - La2O3) for high-power amplifier and laser applications. The preform drawing method was followed, with the preform being fabricated using the rotational casting technique. This technique, previously developed for tellurite, fluoride or chalcogenide glass preforms is reported for the first time using rare earth doped phosphate glasses. The main challenge was to design an adequate numerical aperture between first and second cladding while maintaining similar thermo-mechanical properties in view of the fiber drawing process. The preform used for the fiber drawing was produced by rod-in-tube technique at a rotation speed of 3000 rpm. The rotational casting technique allowed the manufacturing of an optical fiber featuring high quality interfaces between core and internal cladding and between the internal and external cladding, respectively. Loss attenuation was measured using the cut-back method and lasing was demonstrated at 1022 nm by core pumping with a fiber pigtailed laser diode at the wavelength of 976 n

Nonsilica Oxide Glass Fiber Laser Sources: Part I

Nonsilica oxide glasses have been developed and studied for many years as promising alternatives to the most used silica glass for the development of optical fiber lasers with unique features and properties. Depending on the glass former of choice, these glasses can offer very distinctive physical properties if compared to silica-based glasses. With regard to the development of photonic fiber devices, these key properties include low phonon energy, high rare-earth ion solubility, high optical nonlinearity and easy handling procedures. This chapter, part I of a detailed study concerning nonsilica oxide glass–based optical fiber laser sources, reviews the main properties of three different nonsilica oxide glass families, namely phosphate, germanate and tellurite. The manufacturing process of an optical fiber using these glass materials is also discussed in Section 3 of this chapter

Fibra ottica bioriassorbibile microstrutturata per il rilascio di fluidi, in particolare farmaci, e la trasmissione di luce

La presente invenzione si riferisce ad una fibra ottica microstrutturata bioriassorbibile per condurre segnali luminosi e consentire, allo stesso tempo, il rilascio e/o prelievo di farmaci o altre sostanze chimiche. La funzione di condurre segnali luminosi, in particolare da e verso il paziente, consente di applicare protocolli diagnostici; la funzione di rilascio di farmaci o il prelievo di campioni in forma fluida, ad esempio in soluzione, consente di applicare protocolli terapeutici e diagnostici. Entrambi i protocolli sono pertanto applicabili sullo stesso dispositivo dell’invenzione, i.e. la fibra ottica microstrutturata. Inoltre, la bioriassorbibilità è definita come la capacità di un materiale di dissolversi all’interno di un organismo vivente (in particolare del corpo umano) senza provocare effetti dannosi e/o alterazioni metaboliche significative

Bioresorbable phosphate glass microstructured optical fiber for simultaneous light and drug delivery

Biomedical needs have recently boosted the development of brand-new multifunctional and bioresorbable optical fibers, especially in the field of theranostics. Biocompatible fibers represent great tools for in-body monitoring, diagnostics, and photo-dynamic therapy, thanks to their ability to carry light and act as a drug delivery system in capillary form. Optical fibers are also convenient because of their production scalability since they can be drawn into kilometers starting from a single preform, thus limiting production costs. Furthermore, biocompatible optical fibers can be easily adapted to different applications since they can be well integrated into catheters and other medical instrumentations. In this scenario, calcium-phosphate glass (CPG) optical fibers are promising candidates, thanks to their enhanced thermo-mechanical features and biocompatibility. Moreover, their resorbability, as well as mechanical and optical properties, can be finely tuned by tailoring the specific glass composition. In the present work, we report on our latest results in this field starting from the full characterization of CPG optical fibers by means of in-vitro dissolution tests and in-vivo experiments. Dissolution tests in simulated body fluid revealed that a high amount of MgO can effectively decrease the dissolution time, while in-vivo experiments showed no inflammatory response in the tested animals. The possibility of tailoring the resorption time of the CPG fiber is a key factor in several applications where different operational times are needed, e.g. from few days to few months. In addition, we will show the application of a CPG-based multifunctional fiber to deliver a photosensitive drug and its activation by light carried with the same fiber. Finally, we will report on the design and fabrication of a bioresorbable microstructured CPG fiber by properly combining rotational casting and extrusion techniques

High concentration Er-doped phosphate glass optical fibers for single-frequency fiber amplifiers

The continuous improvement of interferometric gravitational-wave detectors (GWDs) and the preparations for next generation of GWDs set highly demanding requirements on their laser sources. A promising candidate to fulfill the challenging requirements of GWD laser sources is the hybrid master-oscillator power fiber amplifier (MOPFA) configuration. The implementation of a MOPFA relies principally on commercial silica glass-based optical fiber technology, which has been key in the successful development of high-power fiber amplifiers but that poses also a limitation to power scaling of these devices. It is well known that erbium (Er) ions tend to cluster in silica glass leading to ion-ion interactions and degradation of performance. The limited concentration of RE ions per unit length implies a limited optical gain per unit length and thus the requirement for long amplifying fiber lengths that enforce deleterious nonlinear effects, foremost stimulated Brillouin scattering (SBS). Numerous SBS suppression techniques have been proposed, alongside investigation of specialty optical fibers. One of the most promising solutions is the use of highly doped optical fibers based on multicomponent phosphate glass that allows the fabrication of ultra-compact active devices with minimized nonlinearities. To realize compact optical fiber amplifiers operating at 1.5 µm, a series of highly Er3+-doped custom phosphate glass compositions was designed and fabricated to be used as active materials for the core of the fiber amplifiers. Suitable cladding compositions were explored. Core and cladding glasses were synthesized by melt-quenching method. The core glass was cast into a cylindrical mold to form a rod, whereas the cladding tube was fabricated by extrusion technique. Phosphate fibers were then manufactured by drawing the preform assembled by rod-in-tube technique. Preliminary results of the application of the Er3+-doped phosphate fiber as laser active medium in a fully monolithic single-mode single-frequency core-pumped MOPFA setup resonantly pumped at around 1480 nm are presented

Highly doped multicomponent phosphate glass fibers for compact pulsed optical amplifiers

In recent years, there has been a growing interest towards compact high peak-power pulsed laser sources for applications such as LIDAR, range findings, remote sensing, communications and material processing. A common laser architecture used to realize these sources is the Master Oscillator Power Amplifier (MOPA), in which a master oscillator produces a highly coherent beam and a fiber amplifier boosts the output power, while preserving its main spectral properties. Phosphate glasses are recognized to be an ideal host material for engineering the amplification stage of a pulsed MOPA since they enable extremely high doping levels of rare-earth ions to be incorporated in the glass matrix without clustering, thus allowing the fabrication of compact active devices with high gain per unit length. With the aim of realizing compact optical fiber amplifiers operating at 1 and 1.5 µm, a series of highly Yb3+- and Yb3+/Er3+-doped custom phosphate glass compositions were designed and fabricated to be used as active materials for the core of the amplifiers. Suitable cladding glass compositions were explored and final core/cladding glass pairs were selected to realize single-mode and multi-mode optical fibers. Core and cladding glasses were synthesized by melt-quenching technique. The core glass was then cast into a cylindrical mold to form a rod, while the cladding glass was shaped into a tube by rotational casting method or extrusion technique. The latter has been extensively employed for the manufacturing of tellurite and germanate glass preforms, but only recently the first example of active phosphate fiber preform fabricated by this method has been reported by our research team. Phosphate fibers were then manufactured by preform drawing, with the preform being obtained by the rod-in-tube technique. Preliminary results of pulsed optical amplification at 1 and 1.5 µm are presented for a single-stage MOPA