High concentration Yb-Er co-doped multi-component phosphate glasses for compact eye-safe optical amplifiers

In recent years, the increasing need of airborne LIght Detection And Ranging (LIDAR) systems for environmental monitoring and surveillance has noticeably boosted the development of compact eye-safe optical amplifiers. In this scenario, multi-component phosphate glasses can be regarded as ideal candidate materials as they can be doped with a large amount of rare-earth (RE) ions without clustering, thus enabling the realization of few-cm long optical amplifier sections featured by high optical gain per unit length. In this work we will report the ongoing activities and the recent results obtained by our research group on the design, processing and characterization of a series of Yb-Er co-doped phosphate glasses to be used as active materials for the core of a waveguide amplifier. The physical, thermo-mechanical, optical and spectroscopic properties of the prepared glasses have been thoroughly investigated

TeO2-ZnO-La2O3 glass composition for mid infrared wavelengths generation and transmission in optical fibers

Numerous applications in the Mid InfraRed (Mid IR) wavelength region still require basic optical components such as sources and optical fibers as transmission medium. Thanks to its mid IR transparency and nonlinearity, tellurite glass allows for developing both these types of components. However, practical applications require materials able to handle high optical intensity through enhanced material damage threshold. We report on the synthesis of a tellurite glass in the TeO2-ZnO-La2O3 (TZL) system which presents enhanced thermo mechanical properties with respect to typical tellurite glass compositions. We measured for the TZL composition a glass transition of 626 K, hence 70 K higher than the glass transition temperature of “standard” TZN compositions. The coefficient of thermal expansion was measured to be 138.10-6/K as compared to typical value of 180.10-6/K for TZN glass. We manufactured two types of fibers to assess the prospect for achieving high average power SC sources and Mid IR transmission in TZL glass fibers. First, a high Numerical Aperture (NA) aperture fiber was developed through standard rod in tube technique, where the cladding glass tube was manufactured by extrusion. The 50 μm core fiber presents an optical attenuation value of 0.26 dB/m at 1.55 μm. As an intermediate step towards the fabrication of an antiresonant hollow core fiber for high power transmission, we manufactured a preform and drew it into a cane. A TZL glass tube, 120 mm long and 9 mm/12 mm of inner/outer diameters (ID/OD) was manufactured via rotational casting technique. This latter tube was drawn into a tube of 2 mm in diameter which was cut into sections 130 mm long. Seven of those were stacked in another tellurite glass tube 6.5 mm/12 mm of ID/OD diameters, respectively. This preform was then drawn into a microstructured cane 1.6 mm in diameter which features tubular structures periodically arranged and of uniform thickness

Multifunctional bioresorbable phosphate glass optical fibers for theranostics

We report on the design and development of microstructured phosphate glass optical fibers for minimally invasive diagnosis and therapy. We discuss preliminary results of fiber drawing and characterization

Toward the fabrication of directly extruded microstructured bioresorbable phosphate glass optical fibre preforms

The steps toward the fabrication of directly-extruded microstructured fibre preforms made of a bioresorbable phosphate glass are herein presented. Microstructured fibres show a wide range of applications, i.e. photonic crystal fibres, large mode area fibres, hollow gas/liquid sensors, etc. Nevertheless, the fabrication of bioresorbable microstructured fibres has not been feasible so far due to a lack of bioresorbable transparent glass and more flexible fibre preform fabrication techniques. A custom developed calcium-phosphate glass has been designed and carefully prepared in our laboratory to be dissolvable in a biological fluid while being optically transparent and suitable for both preform extrusion and fibre drawing. This glass has been characterised both in terms of mechanical and optical properties as well as for dissolution in aqueous medium. Furthermore, the proposed glass is thermally stable, i.e. can be processed both in the extruder and in the drawing tower. Several extrusion experiments have been carried out with different glass preforms’ shapes. Analyses of these preforms by means of Optical Profilometry and Atomic Force Microscopy have been carried out to assess the roughness of the surface of the extrudate. To support the production of an optimized die for the preform extrusion, a simplified laminar flow model simulation has been employed. This model is intended as a tool for a fast and reliable way to catch the complex behaviour of glass flow during each extrusion and can be regarded as an effective design guide for the dies to fulfil specific needs for preform fabrication. After die optimisation, extrusion of a capillary was realised, and a stacking of extruded tubes was drawn to produce a microstructured optical fibre made of bioresorbable phosphate glass. The combination of bioresorbability and fibre microstructure, show a promising pathway toward a new generation of implantable biomedical devices

Phosphate glass optical fibers for applications in sensing and biomedicine

Remote sensing and biomedicine require specifications and performance that are met by phosphate glass optical fibers. We report on our main achievements to date and provide insight into new functionalities

Rare earth doped phosphate fibre amplifier at 1.5 μm for LIDAR

The research work reports on the design and fabrication of a compact optical fibre amplifier operating at 1.5 μm. A novel Yb/Er co-doped phosphate glass was developed and the optical fibre preform fabricated by rod-in-tube technique

High-power laser testing of calcium-phosphate-based bioresorbable optical fibers

Silica optical fibers are employed in endoscopy and related minimally invasive medical methods thanks to their good transparency and flexibility. Although silicon oxide is a biocompatible material, its use involves a serious health risk due to its fragility and the fact that potential fiber fragments can freely move inside the body without the possibility of being detected by conventional methods such as X-ray imaging. A possible solution to this issue can be the development of optical fibers based on bioresorbable (i.e., biodegradable and biocompatible) materials, which exhibit the important benefit of not having to be explanted after their functionality has expired. The optical power transmission tests of recently developed single-mode (SM) and multi-mode (MM) bioresorbable optical fibers based on calcium-phosphate glasses (CPGs) are here reported. A continuous-wave (CW) fiber laser at 1080 nm with output power up to 13 W and picosecond laser sources at 515 and 1030 nm with MW pulse peak power were used to test the transmission capabilities of the CPG fibers. No degradation of the CPG fibers transmission under long-term illumination by CW laser was observed. A laser-induced damage threshold (LIDT) at a fluence higher than 0.17 J/cm2 was assessed with the picosecond laser sources

Characterization of sub-nanosecond pulsed laser amplification with Er:Yb co-doped phosphate glass fibers

We present an experimental characterization of the amplification of sub-nanosecond duration laser pulses at a wavelength of 1538 nm in short custom-made Er:Yb phosphate glass fibers with different core diameters. The fibers vary in their diameter from 100 µm (highly multi-mode) down to 12 µm (single-mode). The peak power, energy per pulse, and spectral shape of the amplified signal are presented. With our input pulses, the measurements show that the large core diameter fibers do not increase the amplification of the 1538 nm signal. We believe this is due to the high re-absorption of the Er3+ ions in the phosphate fiber. The optimal fiber geometry was found to have a core diameter of 20 µm with a length of 14 cm. The maximum peak power is 8.25 kW, corresponding to a net gain of 10.9 dB, with a pulse duration of 0.7 ns and a repetition rate of 40 kHz