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LD pumped erbium glass passively Q-switched 1.5μm microchip laser is a research hotspot in laser ranging and imaging application. The high repetition rate microchip laser has serious thermal effect problem, so it is difficult to work stably for a long time. This paper reports a passively Q-switched 1535nm laser with erbium-ytterbium co-doped phosphate glass using double-ended adhesive-free bonding technology. The laser combines YAG crystal, Er3+/Yb3+: glass and Co2+[/sup : MgAl2O4 by bonding to improve the thermal effect of the laser. At the same time, by optimizing the size of the pump light spot, the initial transmittance T0 of the saturable absorber and the reflectivity R of the output mirror, the utilization efficiency of the pump light is improved and the influence of thermal effect is further reduced. The results show that the laser output with the repetition rate of 1kHz, the single pulse energy of 40μJ, pulse width of 8ns, peak power of 5kW, beam quality of 1.4, can output stably for a long time.

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.

This Conference Presentation, “Bioresorbable phosphate glass microstructured optical fiber for simultaneous light and drug delivery,” was recorded for the SPIE Photonics Europe 2020 Digital Forum.

Er3+ doped tellurite-based glasses were prepared using standard melting process and their physical, optical, thermal, optical and luminescence properties were measured and compared. We found that the addition of Na2O in the TeO2-ZnO system leads to higher emission at 1.5μm as compared to the addition of TeO2, Bi2O3, BaO, Nb2O5. We found that Bi2O3 should be used in order to increase the intensity of the upconversion under 976 nm excitation. The glasses were heat treated in order to grow crystals in these glasses. Surface crystallization occurred upon heat treatment with the precipitation of multiple crystals, the composition of which depends on the glass composition. The heat treatment was found to have no impact on the intensity of the emission at 1.5 μm. However, it increases the intensity of the red upconversion, especially for Bi2O3 containing glass.

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.

Publisher’s Note: This conference presentation, originally published on 23 May 2018, was withdrawn on 18 July 2019 per author request

For avoiding the defect of introducing contamination for doped phosphate glass in conventional polishing technology, this paper proposes the machining method of Ion Beam Figuring(IBF). Material removal mechanism is also presented from a microscopic view. Surface roughness was analyzed by changing the incidence angle of normally and 20°. The results show that both surface roughness RMS are increased a little, and the PSD(power spectral density) of surface roughness RMS is shown, too.

Phosphate glass is an attractive material for rare-earth-doped fiber manufacturing because high doping levels are possible without introducing negative effects such as up-conversion or increased non-radiative recombination. In this paper we present a novel PM heavily Yb-doped polarization maintaining large mode area phosphate fiber and a < 100 W power level amplifier based on this fiber. The fiber was fabricated by a rod-in-tube technique. An 18 cm long piece of the fiber was used to build a high-power all-fiber amplifier. 106 W of output power at 1030 nm was achieved with 55 % slope efficiency with respect to the launched pump power. To the best of our knowledge, this is the highest average power ever demonstrated for short phosphate fiber lasers.

In order to study the mist phenomenon on phosphate glass, the chemical composition of the hydrolysis layer on the glass surface of phosphate glass was investigated. The solid and liquid components of the used slurry and the surface composition of polished phosphate glass were tested. The experimental results show that the SIMS test results show that the content of K does not change with depth, and the content of Mg, Al, Nd firstly increases with depth and then tends to be gentle; K element does not participate in chemical reactions during polishing, just simply mechanical removed; but Mg, Al, and Nd elements are not only mechanically removed but also participate in chemical reactions and are precipitated as ions, which is consistent with the XRF test results. It is proposed a new substance generated on the surface of phosphate glass during polishing process, a hydrolysis layer formation model was proposed. The mist phenomenon is related to the hydrolysis layer, which is different from the substrate material and properties (density, light reflectance, etc.). So different scattered light is seen and the thicker the hydrolyzed layer, the stronger the scattered light. Moreover, the severity of mist is related to the thickness of the mist layer, and the thicker the thickness, the more severe the mist.

Optical fibers have been employed for several years in biomedicine and mainly used for light delivery and collection with high efficiency and selectivity. So far most of the research effort has been devoted to the optical configurations and the functions of the fibers rather than on the materials employed. Indeed, this aspect has been mainly considered to assure biocompatibility with tissues and non-toxic behavior limiting the choice mostly to silicate fibers. We report on the recent advances in engineering inorganic glass optical and hollow fibers fabricated with optical glasses which are also resorbable in body fluids. Suitable phosphate glass compositions were designed to combine resorbability and optical transparency. Glasses were fabricated by melt-quenching inside a chamber furnace under a flux of dried air and cast into preheated brass molds. The fibers were obtained by preform drawing, with the core rod fabricated by melt quenching whilst the cladding tube by rotational casting. Extrusion techniques were also applied to obtain more complex cross sections with increased functionalities. Glasses and fibers were characterized in their physical and optical properties. The materials showed high stability toward crystallization and a wide optical transmission window, ranging from the ultraviolet to the near infrared wavelength regions. Hollow fibers were employed to demonstrate multifunctional fiber probes, able to provide drug delivery and light excitation in the prospect of developing resorbable endoscopes for intravital monitoring and therapy, such as photodynamic therapy. Optimization of drug delivery was carried out using functionalization procedures on the surface of both bulk glasses and hollow fibers, aiming to modify the release kinetics: a silanization protocol was developed and successfully tested using different organic compounds. The modification of the surface roughness was monitored using atomic force microscopy, while surface energy changes verified using contact angle measurements. The possibility of performing drug excitation was assessed by guiding light through the capillary using optical beams produced by different wavelength sources covering the visible spectrum. Finally, mechanical characterization of the prepared optical fibers and hollow fibers was carried out to measure the elastic moduli, the tensile strength and the minimum radius of curvature attainable. The overall results allowed to demonstrate the reliability of the proposed optical fibers and hollow fibers for biomedical applications.

In this paper we present on-chip mode-locked waveguide lasers fabricated in Yb-doped phosphate glass and Er, Ybdoped phosphate glass. At 1 micron wavelength, pulse repetition rates of up to 15 GHz with pulses ~800 fs were demonstrated and at 1.5 micron, picosecond pulses with a repetition rate up to 7 GHz were demonstrated. Dispersion was controlled in the cavity by varying the spacing between the waveguide and the SESAM, while the repetition rate could be controlled by varying the optical power. The average power can also be scaled using an integrated optical amplifier and on-chip gain of up to 10 dB was demonstrated. All these individual components can be integrated in a single platform to achieve a high-power on-chip multi-GHz optical frequency comb. Furthermore, we discuss an application of such laser sources in high-capacity telecommunications applications.

High repetition rate slab amplifier (HRRSA) is extraordinarily indispensable for the future fusion power plant, ultra-short laser, laser weapon, and so on. Thermal controlling is the decisive factor for the repetition rate and the output energy of the slab amplifier. For larger clear aperture HRRSA, flash-lamp pumped slab amplifier based on neodymium phosphate glass (Nd:glass) is chosen with the liquid cooling. The liquid coolant circulates across the Nd:glass and takes off the thermal induced in the pumping process. A novel liquid coolant (Series A) whose refractive index is the same with Nd:glass is proposed to alleviate the wavefront distortion induced by thermal. The chemical stability of the liquid coolant under high energy flash-lamp irradiation with 200 shots and under the irradiation of a 1053nm laser with 19 hours and 37 hours are experimented. The results show that the chemical stability of the liquid coolant is stable under irradiation.

Neodymium phosphate glass (Nd:glass) is the typical gain medium in the large clear aperture slab amplifiers, and provide more than 99% energy of a high power laser facility. Cladding structure is employed for decreasing the amplified spontaneous emission (ASE) and parasitic oscillation (PO) which are the key limits for the gain of large clear aperture slab amplifier. Polymer cladding is generally used since it was proposed. Polymer is an organic glue which has risk to decompose and fracture under high flash-lamp irradiation while the irradiation is a common condition in the operation of a high power laser facility. Once the polymer glue falls off, the suppression of ASE and PO of cladding structure would be damaged. In addition, the impurities existing in the glue may form the counteractive scattering sources and reduce the suppression of the cladding structure. Moreover, the decomposer of the organic glue may affect the cleanliness of the slab cavity. Thus, an inorganic edge cladding structure based on hydroxide-catalysis bonding (HCB) was proposed which can match the requirements of the cladding structure and evade the organic glue in the high flash-lamp irradiation slab cavity. An antireflective film was used as the medial material whose refractive index was matched with the cladding structure. Bonded samples were prepared based on HCB and confirmatory experiment under high flash-lamp irradiation was finished.

Multifunctional fibers are developed worldwide for enabling many new advanced applications. Among the multiple new functionalities that such fibers can offer according to their design, chemical composition and materials combination, the co-transmission of light and electrical signals is of first interest for sensing applications, in particular for optogenetics and electrophysiology. Multifunctional fibers offer an all-solid approach relying on new ionic conducting glasses for the design and manufacturing of next generation optrodes, which represents a tremendous upgrade compared to conventional techniques that requires the utilization of liquid electrolytes to carry the electrical signal generated by genetically encoded neuronal gated ion channels after optical excitation. After a systematic study conducted on different ion-conductive glass systems, silver phosphate-based glasses belonging to the AgI-AgPO3-WO3 and AgI−AgPO3−Ag2WO4 systems were found to be very promising materials for the target application. Several types of fibers, including single-core step-index fibers, multimaterial fibers made of inorganic and optical polymeric glasses have been then fabricated and characterized. Light transmission ranging from 400 to 1000 nm and electrical conductivity ranging from 10−3 and 10−1 S·cm−1 at room temperature (AC frequencies from 1 Hz to 1 MHz) were demonstrated with these fibers. Very sharp fiber tapers were then produced with high repeatability by using a CO2 laser optical setup, allowing a significant shrinking from the fiber (300 μm diameter) to the taper tip (25-30 μm diameter).

40P 2 O 5 -20Al 2 O 3 -(30-x)Na 2 O-10BaO-xEr 2 O 3 (PANB) glasses with different Er 3+ concentrations were fabricated by the traditional melt quenching method and their spectroscopic properties were investigated. Glass thermal stability is investigated by differential scanning calorimetry (DSC) (T x -T g =138°C) which indicates a better recrystallization performance than that of fluorophosphates glass and fluorotellurite glass. The derived Judd-Ofelt intensity parameters of Er 3+ doped PANB glass (Ω 2 =18.8, Ω 4 =15.9, Ω 6 =5.38(×10 -20 cm 2 )) indicate higher asymmetry and stronger covalent environment when compared with Er 3+ doped tellurite, fluoride and fluorotellurite glasses. Compared with Er 3+ transitions in other glass hosts, large stimulated emission cross-section and broad full wave at half maximum (FWHM) were found to be 4.58×10 -20 cm 2 and 60 nm centered at ∼1550 nm, respectively. It implies a potential material for infrared lasers and amplifiers.

Glass matrix doped with rare-earth ions is a promising laser active medium for high power laser systems. Due to amorphous structure of glasses the absorption and emission spectra lines are broader in comparison with crystalline materials thus pumping radiation can be absorbed efficiently, moreover much broader gain bandwidth is suitable for generation of ultra-short pulses. Another advantage of the glass matrix is the possibility to fabricate large volume ingots and simultaneously preservation of sufficient optical quality. The lower thermal conductivity of glasses can be compensated by geometry of the active medium for instance shaped into fibres or discs. We present temperature dependence of spectroscopic and laser properties of newly developed Er, Yb - doped potassium-lanthanum phosphate glass, which is appropriate for generation of radiation at 1.53 μm. The sample of Er,Yb:KLaP glassy mixture was cut into disc shape with dimensions of 2.5 mm (thickness) and 5 mm (diameter) and its faces were polished plan-parallelly without being anti-reflection coated. The temperature dependence of the transmission and emission spectra Er,Yb:KLaP together with the fluorescence decay time were measured the temperature range from 80 to 400 K. The fluorescence lifetime of manifold 4I13/2 (upper laser level) prolonged and the intensity of up-conversion radiation decreased with decreasing temperature. The longitudinal excitation of Er,Yb:KLaP was carried out by a fibre-coupled laser diode (pulse duration 2 ms, repetition rate 10 Hz, pump wavelength 969 nm). Laser resonator was hemispherical, with flat pumping mirror (HR @ 1.5 μm) and spherical output coupler (R = 98 % @ 1.5 - 1.6 μm). The Er,Yb:KLaP glass laser properties were investigated in the temperature range 80 - 300 K. The highest slope efficiency with respect to absorbed pumped power was 6.1 % at 80 K. The maximum output of peak amplitude power was 0.71 W at 80 K, i.e. 1.2 times higher than at 300 K. Tunability of laser wavelength at 80 K in range 1528 - 1552 nm was obtained using MgF2 birefringent filter. From our measurement it can be concluded, that spectroscopic and laser properties of newly developed Er,Yb:KLaP glass are slightly temperature dependent.

Micro spherical resonators have attracted significant attention in recent years due to their interesting optical properties and the range of applications for which they can be used. Most of the publications dedicated to micro spherical Laser are devoted to lasing effects in different materials where the spectral properties of the emission depends on (i) the choice of dopant (e.g. Er3+, Yb3+, Tm3+) and (ii) the host matrix (e.g. silica, fluoride, phosphate or telluride glass) in which the dopant is embedded. Yet, the dynamics of theses Lasers are still to be studied. This paper shows experimental results on the amplitude fluctuations of a Whispering Gallery Mode Laser, also known as relative intensity noise (RIN). It gives information about the dynamics inside the cavity, such as photon lifetime, effective pumping rate and noise sources. We use as active medium Er3+ doped fluoride ZBLALiP glass and also industrial IOG-1 Yb3+- Er3+ co-doped phosphate glass. Theses glasses are well adapted to the development of micro spherical Laser operating in the infrared region, in particular with emission wavelengths falling respectively in the C-band and C+L band. We have observed that the RIN can provide insurance about the emission of the Laser. Moreover, we have shown that a single-mode emission comes with the presence of multiple harmonics of the relaxation frequency, which is the signature of a Laser with high noise levels. In this particular case, the second and higher orders of intensity fluctuations cannot be neglected any longer in the small-signal analysis.

The spectroscopic properties of rare earth ions in many different hosts have been investigated, including surveys of Nd 3+ in silicate, phosphate, fluorophosphates and fluoride glasses. Some of the thermal-optical properties of materials are influenced by temperature change, such as thermal diffusivity, specific heat and luminescence quantum efficiency. In this work the luminescence quantum efficiency of PANK: Nd 3+ , as a function of temperature (80- 480 K), was investigated using the normalized lifetime thermal lens technique. This system presents high quantum efficiency at low Nd 3+ concentration and at ambient temperature, ~100%, which decrease as temperature increase. Below room temperature the effects are not in accord with the maximum value of η, which must be unity.

In this work, we have used a Ti 3+ :Safira laser tuned at 803nm to performed time-resolved measurements using the Z-scan technique to characterize the nonlinear optical properties of phosphate glasses. The glass matrices, labeled PAN (P 2 O 5 -Al 2 O 3 -Na 2 CO 3 ) and PANK (P 2 O 5 -Al 2 O 3 - Na 2 O-K 2 O), were doped with increasing Nd 3+ concentration, ranging from 0.5 to 5 wt%. For both systems, we have seen that the optical nonlinearity has a linear dependence with the doping ion concentration. Therefore, we propose a new approach to obtain the parameters Δα and Δσ. All results obtained are in good agreement with others found in the literature.

In this work optical spectroscopic characterization was performed in a Er-doped phosphate glass matrix PAN (P2O5-Al2O3-Na2CO3). Due to its high phonon energy, only the 1550 nm emission band was observed. Therefore, we have applied the normalized lifetime thermal lens technique in order to determine the luminescence quantum efficiency of this emission. These results were compared with that obtained with the standard Judd-Ofelt calculations. Besides absorption spectra, emission spectra as also obtained. Therefore, the gain coefficient spectra could be evaluated for different population inversions. Finally, figures of merit for the optical amplifiers were estimated and compared with others Er-doped materials.

The development and validation of small size laser sources for space based range finding is of crucial importance to the development of miniature LIDAR devices for European space missions, particularly for planet lander probes. In this context, CENTRA-SIM is developing a passively q-switched microchip laser in the 1.5μm wavelength range. Pulses in the order of 2 ns and 100μJ were found to be suitable for range finding for small landing platforms. Both glass and crystalline Yb-Er doped active media are commonly available. Crystalline media present higher thermal conductivity and hardness, which allows for higher pumping intensities. However, glass laser media present longer laser upper-state lifetime and 99% Yb-Er transfer efficiency make phosphate glasses the typically preferred host for this type of application. In addition to this, passively q-switched microchip lasers with Yb-Er doped phosphate glass have been reported to output >100μJ pulses while their crystalline host counterparts achieve a few tens of μJ at best. Two different types of rate equation models have been found: microscopic quantities based models and macroscopic quantities based models. Based on the works of Zolotovskaya et al. and Spuhler et al, we have developed a computer model that further exploits the equivalence between the two types of approaches. The simulation studies, using commercial available components allowed us to design a compact laser emitting 80μJ pulses with up to 30kW peak power and 1 to 2 ns pulse width. We considered EAT14 Yb-Er doped glass as active medium and Co2+:MgAl2O4 as saturable absorber. The active medium is pumped by a 975nm semiconductor laser focused into a 200μm spot. Measurements on an experimental test bench to validate the numerical model were carried out. Several different combinations of, saturable absorber length and output coupling were experimented.

Nd doped phosphate glass is widely used as gain media in high power laser system. It is traditionally polished with the annular polishing technology. The edge effect is inevitable in annular polishing process and it results in the low manufacturing efficiency. Ion Beam Figuring (IBF) is a highly deterministic, non-contact method for the ultra-precision optics fabrication. So the edge effect is avoided. Nanometer and sub-nanometer precision is realizable in IBF. In this paper, Nd doped phosphate glass was polished with IBF, and the evolvement of surface roughness was emphasized. The roughness of surface polished with ion beam at normal and oblique incidence was researched. The oblique incident angle was 45°. The surface roughness was measured with the white light interferometer. No evident change was observed. This means that the pre-finish roughness can be preserved in IBF. The results denote that IBF is a feasible method to correct the contour errors of Nd doped phosphate glass, and the roughness will not be coarsened.

The optimized geometry based on high-order active microring resonators (MRR) geometry is proposed. The solution possesses both the filtering and amplifying functions for the signal at around 1534nm (pump 976 nm). The cross-grid resonator with laterally, series-coupled triple-microrings, having 15.35μm radius, in a co-propagation topology between signal and pump, is the structure under analysis (commonly termed an add-drop filter).

Phosphate glasses are known to produce high gain for the Er 3+ emission into 1540nm , especially when sensitized with Yb. Unfortunately, the phosphate glass matrix tends to be weaker than other available amorphous materials. Unlike crystalline materials, glass chemical structure around the active ion can be optimized for both mat erial strength and laser output. Reported here is the result from a design of experiment that was completed in order to strengthen the glass structure of a commercially available phosphate laser glass without impacting its laser output efficiencies . Laser output per formance results for the glass that met the targeted thermal and mechanical limits are presented. This effort concludes with a scalable material that is ultimately released to the commercial market. Keywords: Eye -safe, laser g lass, phosphate laser glasses, erbium laser spectroscopy, erbium laser gain 1. INTRODUCTION Retina -safe operation in open -air is of high interest to the next generation of lasers that are being utilized for many industrial, defense and medical applications. Those wavelength s that are considered to be the best for retina safe operations (also called eye -safe ) fall in the range between 1400nm and1800nm . For laser s in medicine, the targeted wavelength regimes coincide with the absorption features of hemoglobin, melanin, and hydroxyl groups in the tissues [1] . Wavelengths ab ove 1400nm are easily absorbed by tissues, making it possible for rapid thermal heating below the skin which is useful for aesthetic and surgical lasers. The trivalent Er ion can produce direct emission into the 1540 nm wavelength, thus, it is the rare -ear th emitter of choice for many eye -safe applications. In recent years, the need for high beam quality under passive operation in open air applications have renewed interest in Er -doped bulk glasses as the gain material o f choice for solid -state eye -safe las ers . The increasing need for higher energy outputs and improved repetition rates is the motivation for seeking a new material in the phosphate glass space. Thus, a study was initiated in order to strengthen a commercially available laser glass (SCHOTT LG940) by adding modifiers that increase the short -range order in the starting phosphate glass structure . However, it is well known that the addition of the elements that drive the glass stability will decrease the laser gain obtained . It is also known that Er

Phosphate glasses are known to produce high gain for the Er3 + emission into 1540nm, especially when sensitized with Yb. Unfortunately, the phosphate glass matrix tends to be weaker than other available amorphous materials. Being that glasses are engineerable, a study was initiated in order to strengthen the glass structure of a commercially available phosphate laser glass without impacting its laser output efficiencies. Secondly, we seek to understand the impact of the various glass modifiers that drive thermal shock resistance of phosphate glasses on the Er emission manifolds. This report details a number of compositions that were designed, melted and analyzed for properties. Laser output performance results for the glasses that met the targeted parameters are presented.

The permanent refractive index change induced by ultrashort laser pulses in zinc phosphate glasses has been investigated both at the surface and in bulk. At the sample surface, irradiations have been performed by using loosely focused single fs-laser pulses at different energies. Optical microscopy images of the irradiations illustrate an interferometric pattern in form of concentric Newton rings due to the laser induced multilayer system (unmodified glass, thin laser-modified layer, air). This experimental reflectivity modulation along with simulations based on Abeles theory for multilayer optical systems allows retrieving laser-induced refractive index changes on the order of Δns= -10 -3 . In bulk, fs-laser written waveguides have been generated by translating the sample with respect to a tightly focused laser beam. The so-produced waveguides have been characterized by studying the optical near field of the TEM 00 guided mode at 660 nm and using white light microscopy. The optical changes linked to the inscribed waveguides have been characterized by measuring the far field output profiles yielding values of approximately Δn b = +3·10 -4 . The laser-modified optical properties in bulk and at the surface will be linked to the glass structural changes as well as discussed in terms of the role of the incubation effects for multi-pulse processing.

Femtosecond laser-induced modification of Au-doped phosphate glass at different pulse repetition rates using an Yb femtosecond amplifier emitting pulses of up to 120 μJ energy at 1030 nm with adjustable repetition rate up to 100 kHz is presented. At the repetition rate as low as 1 kHz, only refractive index modification and formation of red color centers are observed. Increasing the average output laser power resulted in increase of color intensity, but this color could be easily erased by the heat treatment at 300˚C for 20 min indicating athermal nature of these laser-induced effects. By contrast, at the repetition rate from 25 kHz to 100 kHz, cumulative heating effect was demonstrated and allowed to realize for the first time one-stage laser-induced growth of Au nanoparticles in the solid glass accompanied by the appearance of a thermally stable red color. Z-scan analysis of nonlinear properties of the studied glass samples is carried out. Details of Au nanoparticles growth and phosphate glass modification by the tightly focused femtosecond laser beam are discussed.

An analytic model of the scattering response of a highly Yb 3+ /Er 3+ -codoped phosphate glass microring resonator matrix is considered to obtain the transfer functions of an M x N cross-grid microring resonator structure. Then a detailed model is used to calculate the pump and signal propagation, including a microscopic statistical formalism to describe the high-concentration induced energy-transfer mechanisms and passive and active features are combined to realistically simulate the performance as a wavelength-selective amplifier or laser. This analysis allows the optimization of these structures for telecom or sensing applications.

In this work the analytical model of the scattering response of a highly Yb 3+/ Er 3+- codoped phosphate glass microring resonator array is developed. The microscopic statistical formalism is used to simulate its performance as a wavelengthselective amplifier. The performance of the integrated add-drop filter was investigated based on the signal transfer functions for Through and Drop ports, correlated the with gain coefficient and its dependence on pump power, signal power and Yb 3+/ Er 3+- dopants concentration. In consequence, microring arrays with gain operating in the near infrared spectral range and, in particular, in the 1.5-mm wavelength band (emission band of Er-doped fiber amplifiers and lasers, already used in several bio/chemical sensing tasks) are highly attractive.

Strong ion migration in shown to enable the production of high refractive index contrast waveguides by fs-laser writing in a commercial (Er,Yb)-doped phosphate based glass. Waveguide writing was performed using a high repetition rate fslaser fibre amplifier operated at 500 kHz and the slit shaping technique. Based on measurements of the NA of waveguides, the positive refractive index change (∆n) of the guiding region has been estimated to be ∼1-2 x10 -2 . The compositional maps of the waveguides cross-sections performed by X-ray microanalysis evidenced a large increase of the La local concentration in the guiding region up to ~25% (relative to the non-irradiated material). This large enrichment in La was accompanied by the cross migration of K to a neighbouring low refractive index zone. The refractive index of the La-phosphate glass increases linearly with the La2O3 content (∆n per mole fraction increase of La2O3 ≈ 5x10 -3 ) mainly because of the relative mass of the La 3+ ions. The density increase without substantial modification of the glass network was confirmed by space-resolved micro-Raman spectroscopy measurements showing minor variations in the (PO2)sym vibration Raman band. These results provide evidence for the feasibility of adapting the glass composition for enabling laser-writing of high refractive index contrast structures via spatially selective modification of the glass composition.

Silver (Ag + ) doped phosphate glass exhibits an intense photoluminescence (PL) when the non-irradiated Ag + -doped phosphate glass is excited with about 230 nm ultra-violet light. In x-ray irradiated glass, intense radiophotoluminescense (RPL) is observed when the irradiated glass is excited with about 340 nm ultra-violet light. It is found that the RPL spectrum includes two emission bands such as blue emission band peaked at about 460 nm (lifetime: about 6.6 ns) and yellow RPL emission band peaked at about 560 nm (lifetime : about 2.2μs). The PL intensity is decreased with increasing x-ray irradiation dose, while the RPL intensity is increased with x-ray absorbed dose. For the annealing of x-ray irradiated glass at 523 K, the RPL intensity is decreased with annealing, while the PL intensity is increased with annealing. The RPL is vanished and the PL is recovered at original intensity by annealing at 523 K for 40 min. This means that there is a complementary relationship between the PL and RPL on irradiation and heat-treatment processes. The RPL intensity is increased with increasing the x-ray absorbed dose in the range from 0.01 mGy to about 20 Gy, showing that the Ag + -doped phosphate glass can be useful for individual radiation monitoring and environmental radiation monitoring. On the basis of such potentiality of glass as the dosimeter, the application of Ag + -doped phosphate glass on environmental radiation monitoring is discussed and the RPL response of the glass for α- particle and heavy-particle (He, C, Fe particle) irradiation is demonstrated.

New Yb 3+ , Er 3+ and Tm 3+ triply doped fluoro-phosphate glasses belonging to the system NaPO 3 -YF 3 -BaF 2 -CaF 2 have been prepared by the classical melt-casting technique. Glasses containing up to 10 wt.% of rare-earth ions fluorides have been obtained and characterized by using differential scanning calorimetry (DSC), UV-visible-near-infrared spectroscopy and up-conversion emission spectroscopy under excitation with a 975 nm laser diode. Transparent and optically homogeneous glass-ceramics have been reproducibly obtained by appropriate heat treatment in view to manage the red, green and blue emissions upon 975 nm laser excitation. According to the applied thermal heat-treatment, a large enhancement of intensity of the up-conversion emission – from 10 to 160 times higher – has been achieved in the glassceramics compared to that of glasses, suggesting incorporation of the rare-earth ions into the crystalline phase. Furthermore, a large range of color rendering has been observed in these materials by controlling the laser excitation power and material crystallization rate. Time-resolved luminescence experiments as well as X-ray diffractometry and scanning electron microscopy techniques have been employed in order to understand and correlate the multicolor emission changes to the crystallization behavior of this material. A progressive phase transformation of the fluorite-type CaF 2 -based nanocrystals initially generated was observed along with increasing heat-treatment time, thus modifying the rare earth ions spectroscopic features.

First step of Er-Yb laser based on PTR glass creation was made. Complex study of luminescent characteristics of PTR glass doped with Er-Yb with recorded holograms was made. Direct measurements of population inversion of main Erbium level 4 I13/2 for different Erbium concentrations and pumping power was made. Was shown that spectral and luminescent characteristics of poly-functional PTR glass doped with Er-Yb and recorded holograms are comparable to the traditional laser barium phosphate glass.

The peculiarities of the outside influences on the all-optical poling process and on the formed nonlinear optical structures of second-order polarizability are studied. The basic attention is given to considering the outside influences of the laser radiations with different powers and also the variations of temperature. The observed kinetics during the outside influence in the studied phosphate glass materials was investigated and it was shown the possibility of the sufficiently increase of the photo-integrated grating structures in the all-optical poling process by means of the outside thermal influence.

In the article analysis of UV abso rption and visible fluorescence of Sm 3+ and Tb 3+ ions doped phosphate glass with molar composition: 65P 2 O 5 + 8Al 2 O 3 + 10BaO + 17(Na 2 O + MgO + ZnO) have been investigated. As a result of optical pumping fabricated glass with radiation from a deuterium lamp four luminescence bands were observed near to the wavelength of 600 nm for Sm 3+ ions and 550 nm for Tb ions. It was found that larger energy gap between laser and ground levels leads to the strongest emission in the visible range in terbium doped glasses than in glasses doped with samarium ions. Both fabricated glasses are characterized by the ability to selectively detect the radiation in the UV range. Keywords : phosphate glass, Sm 3+ , Tb 3+ , UV excitation, visible emission, down-conversion 1. INTRODUCTION The needs of modern photonics impose on technologists and designers of optical fibers to search new glassy materials capable of propagation of electromagnetic radiation in a wide spectrum range. A choice of a matrix and optimization of its chemical, electrooptical and magnetooptical properties determines the range of applications [1-3]. Phosphate glasses are characterized by uniqu e properties, which are: high transmission in the range of UV-VIS-NIR, low refractive index (n = 1.5), dispersion, thermal stability, mechanical resistance and the ability to adopt high concentration of RE ions [4, 5]. It is high solubility of rare earth ions in multicomponent phosphate glasses that enables the construction of fiber amplifiers and fiber lasers [6-8]. On the other hand, the absorption edge in the range of short wavelengths of 200 nm enables to use them as active materials for the detection of UV radiation [9]. When considering the fabrication of such a sensor based on phosphate glasses the maximum phonon energy of the matrix, which is approx. 1000 cm

A 10-mm-long cylindrical shell was written in neodymium doped phosphate glass by a femtosecond laser delivering pulses with a pulse repetition of 1 kHz, energies of 90 uJ and duration of 120 fs. The pulses were focused below the glass surface by an objective producing ablation filaments about 200 um in length. During processing, the sample was placed on a three-dimensional (3-D) translation stage, which moved along an enclosed pattern in the horizontal plane followed by a minor descent less than the filament length in the vertical direction. As this procedure continued, a cylinder, which demonstrated optical waveguiding, was fabricated with a rarified periphery and densified center region due to plasmonic expansion and outward shockwave upon laser ablation. The refractive-index contrast, propagation loss, near- and farfield mode distribution, and microscopic fluorescence micrograph of the waveguides were measured. 1-to-N splitters with adjustable splitting ratio were also fabricated using current approach indicating its 3-D processing flexibility. Compared with previous femtosecond laser fabrication methods, waveguides prepared in this approach exploit both depressed cladding and stress-induced refractive index increase in core region and show controllable mode conduction, strong field confinement, large numerical aperture, low propagation loss, acceptable thermal stability and intact core region.

We present an all-solid tellurite-phosphate photonic bandgap fiber (PBGF) with high-index rods in the cladding. The low-index background material is phosphate glass (PZNK) and the high-index rods are made of tellurite glass (TZLB). The all-solid tellurite-phosphate PBGF has three bandgaps and the first one is wide in frequency. It is easier to draw than the silicon PBGF due to the phosphate glass has lower fiber-drawing temperature. It can be widely used in the photoelectron field, compact nonlinear devices and devices which work in the mid-infrared range, such as wavelength filter, phase-locked high-power lasers, fiber sensors in the mid-infrared for gases detecting, etc.

Thermal-Lens (TL) for fluorescence quantum efficiency (η) characterizations in a new phosphate glass matrix doped with Nd 3+ were performed. η studies were accomplish in function of Nd 3+ concentrations (0.5-3 x 10 20 ions/cm 3 ). In addition, fluorescence quenching was studied by measuring the concentration dependence of the fluorescence lifetime. The results obtained by TL and fluorescence lifetime techniques are in good agreement, and corroborate with the theory for an energy transfer process involving a pair of ions, in which the main process occurring is cross-relaxation (CR).

The compositional dependences of glass formation, thermal properties and optical properties are investigated for TeO 2 -ZnO-Na 2 O-P 2 O 5 system for hybrid microstructured optical fibers. The refractive indexes at 1.55 μm and glass transition temperature vary in a wide range from 1.513 to 2.036 and from 265°C to 376°C by controlling of the TeO 2 /P 2 O 5 and ZnO/Na 2 O content, respectively. These properties endow tellurite-phosphate glasses with large freedom in the hybrid microstructured optical fiber design. The structures of glasses are investigated by Raman spectra to understand the structural dependence on composition. Using the present glasses, some microstructured optical hybrid fibers with particular dispersion profiles are designed and demonstrated.

Phosphate glasses can dissolve high concentrations of rare earths and have excellent spectroscopic properties making them useful solid-state laser materials. Solid-state lasers doped with different rare-earth ions find applications in a wide range of LIDAR (Light Detection and Ranging) and sensing applications; phosphate glasses are useful host materials for many applications in the visible and near-infrared spectral regions. For example, trivalent erbium (Er 3+ ) doped phosphate glasses operate at the eye-safe wavelength of 1.54 μm and are used for range finding and sensing applications. Tm 3+ doped solid-state lasers operating at ~ 2 μm can be used for wind-shear and turbulence monitoring. Similarly, Nd-doped metaphosphate glasses are the preferred gain medium for high-peak-power lasers used for fusion energy research because they can store optical energy at greater densities than other glass-types and can be fabricated in large sizes with high rare-earth ion concentration. This paper discusses issues affecting glass quality, with particular focus on defect formation, especially crystallisation. Avoiding crystallisation during processing is essential to form high quality laser cavities. The work presented explores some of the factors controlling these defects including contamination during melting. The crystallisation behaviour of the glass was investigated for several different phosphate glass compositions and different melting conditions, including melting duration, temperature and crucible material.

Focused femtosecond laser pulses from a 1 MHz fiber laser were used to create modifications in Er- Yb doped zinc phosphate glass. Two glasses with similar phosphate glass networks but different network modifiers were investigated. To understand the resulting changes caused by the femtosecond laser pulses various characterization techniques were employed: glass structural changes were investigated with confocal Raman spectroscopy, defect generation as well as local Er and Yb environment were investigated with confocal fluorescence spectroscopy, and elemental segregation resulting from heat accumulation effects was ascertained by scanning electron microscopy.

Bulk Erbium-doped lasers are widely used for long-distance telemetry and ranging. In some applications such as coherent Doppler radars, laser outputs with a relatively long pulse width, good beam profile and pulse shape are required. High energy Q-switched Er:glass lasers were demonstrated by use of electro-optic (E/O) Q-switching or frustrated total internal reflection (FTIR) Q-switching. However, the output pulse durations in these lasers were fixed to relatively small values and extremely hard to tune. We report here on developing a novel and compact Q-switched Er:Yb co-doped phosphate glass laser at an eye-safe wavelength of 1.5 μm. A rotating mirror was used as a Q-switch. Co-linear pump scheme was used to maintain a good output beam profile. Near-perfect Gaussian temporal shape was obtained in our experiment. By changing motor rotation speed, pulse duration was tunable and up to 240 ns was achieved. In our preliminary experiment, output pulse energies of 44 mJ and 4.5 mJ were obtained in free-running and Q-switched operation modes respectively.

Two samples of Er-Yb doped phosphate glass were tested as a gain medium of longitudinally diode pumped laser. One sample was a simple Er:Yb:glass rod (length 2.8 mm), second sample was composite rod consisting of 2.8mm long Er:Yb:glass and 6mm long YAG crystal. Diameter of both samples was 6 mm. Dopant concentration for Er:Yb:glass was 0.75 × 10 20 cm −3 Er and 1.7 × 10 21 cm −3 Yb. The goal of the experiment was to investigate an effect of the undoped YAG cap on the Er:Yb:glass laser operation. The active medium, fixed in cupreous heatsink, was placed inside the 150mm long resonator consisted of a flat pumping mirror (HR @ 1.52−1.65 μm, HT @ 0.97 μm) and curved output coupler (r = 150 mm, R = 97% @ 1.52−1.61 μm). For Er:Yb:glass pumping a fiber coupled laser diode, operating in pulsed regime, was used. The pumping pulse width, energy, and wavelength were 1 ms, 10 mJ, and 975 nm, respectively. The decrease of Er:Yb:glass laser output pulse energy with increasing pumping repetition rate was observed for both samples. In case of simple Er:Yb:glass the energy dropped from 1.4mJ to 0.6mJ after pumping duty cycle increase from 0.5% to 6 %. In case of composite YAG/Er:Yb:glass active medium the relative output energy decrease was only 20% for pumping duty cycle increase from 0.5% to 10%. This result showed that the slope of the output energy decrease with increasing duty cycle was approximately four times slower for composite active media in comparison with simple Er:Yb:glass.

Four wave mixing and supercontinuum from tellurite photonic crystal fibers have been widely researched. Their efficiencies depend largely on fiber nonlinearity and chromatic dispersion. We have shown that the composite microstructured optical fibers (CMOFs) can have high flexibility on chromatic dispersion control when refractive index difference between core and cladding becomes larger. Cladding materials with much lower refractive index than tellurite glass are required. We report here a novel tellurite core-phosphate cladding CMOF. Phosphate glasses which thermal expansion coefficient, viscosity, glass transition temperature, deformation and crystallization temperature are close to those of tellurite 78TeO 2 - 5ZnO - 12Li 2 O - 5Bi 2 O 3 (mol%) (TZLB) glass are systematically investigated. The phosphate glass we developed has high transparency and a broad transmission region up to 3 μm as well as a notably low refractive index. Using the phosphate glass doped with mixed alkali oxides obtained in this work, the refractive index difference between core and cladding becomes as high as 0.5 which is sufficiently high to control the chromatic dispersion with high freedom. Our work shows that tellurite-phosphate CMOFs are promising candidates as highly nonlinear fibers with freely controlled chromatic dispersion for nonlinear applications.