Glass-ceramic optical fiber containing Ba2TiSi2O8 nanocrystals for frequency conversion of lasers

Recent Advances in Fabrication and Applications of Yttrium Aluminum Garnet-Based Optical Fiber: A Review

Yttrium aluminum garnet (YAG)-based optical fiber is one of the research hotspots in the field of fiber lasers due to its combined advantages of a wide doping range of rare earth ions and the high mechanical strength of YAG material, as well as the flexibility and small size of the fiber structure. YAG-based optical fibers and related laser devices can be used in communication, sensing, medicine, etc. A comprehensive review of YAG-based optical fibers is provided in this paper. Firstly, the fabrication processes of YAG-based optical fibers are summarized and the structure and properties of fibers are classified and compared. Secondly, according to the optical wavelength regions, rare earth-doped YAG-based optical fibers for the applications of single-frequency and mode-locked fiber lasers are summarized. Lastly, the development challenges in both the fabrication and applications of YAG-based optical fibers are discussed.

Glass Ceramic Fibers Containing PbS Quantum Dots for Fluorescent Temperature Sensing

Glass ceramics (GCs) containing PbS quantum dots (QDs) are prepared for temperature sensing. Broadband emissions are detected in the GCs when PbS QDs are precipitated from the glasses, and emissions centers are modulated from 1250 nm to 1960 nm via heat treatments. The emission centers of GCs exhibit blue-shifts when environment temperatures increase from room temperature to 210 °C. Importantly, the shift values of emission centers increase linearly with the test temperature, which is beneficial for applications in temperature sensing. A temperature sensor based on PbS QDs GC is heat-treated at 500 °C for 10 h, possesses the highest sensitivity of 0.378 nm/°C, and exhibits excellent stability and repeatability at high temperatures (up to 210 °C). Moreover, GC fibers are fabricated by using the GCs as the fiber core. The sensitivity of the temperature-sensing sensor of the GC fibers is also demonstrated and the sensitivity is as high as 0.558 nm/°C. The designed PbS QDs GCs provide a significant materials base for the manufacturing of fluorescent temperature sensors and the GC fibers offer significant opportunities for temperature detection in complex, integrated and compact devices.

Boosted Second Harmonic Generation and Cascaded Sum Frequency Generation from a Surface Crystallized Glass Ceramic Microcavity

The development of novel materials and structures for efficient second-order nonlinear micro/nano devices remains a significant challenge. In this study, the remarkable enhancement of second-harmonic generation (SHG) and cascaded sum frequency generation in whispering gallery mode microspheres made of surface-crystallized glass with a 6-µm Ba2TiSi2O8 crystal layer are demonstrated. Attributed to the core-shell design, the Ba2TiSi2O8 located on the surface can be efficiently coupled with whispering gallery modes, resulting in a highly efficient micron-scale cavity-enhanced second-order optical nonlinearity. Greatly enhanced SHG of the microcavity is observed, which is up to 80 times stronger than that of a non-resonant sample. Furthermore, owing to the wavelength non-selectivity of random quasi-phase matching, ultra-wideband SHG with a strong response ranging from 860 to 1600 nm and high-contrast polarization characteristics is demonstrated. The glass-ceramic-based microsphere cavity also boosts the cascading optical nonlinearity, manifested by a two-magnitude enhancement of cascaded sum frequency generation. This work delineates an efficient strategy for boosting nonlinear optical response in glass ceramics, which will open up new opportunities for applications in photonics and optical communications.

Low-Temperature Fluoro-Borosilicate Glass for Controllable Nano-Crystallization in Glass Ceramic Fibers

A fluorosilicate (FS) nano-crystallized glass ceramic (NGC) is one of the most commonly used gain materials for applications in optical devices due to its excellent thermal stability as well as high-efficiency luminescence. However, FS glass can hardly be used to prepare NGC fibers due to its high preparation temperature. Here, a series of low-temperature fluoro-borosilicate (FBS) glasses were designed for the fabrication of active NGC fibers. By modulating B₂O₃, the preparation temperature of FBS glass was reduced to 1050 °C, and the crystallization in FBS NGCs was more controllable than in FS NGC. The crystallization of the impure phase was inhibited, and single-phase rare earth (RE)-fluoride nanocrystals were controllably precipitated in the FBS NGCs. The 40Si-20B FBS NGC not only exhibited a higher optical transmittance, but the luminescence efficiency was also much higher than traditional FS NGCs. More importantly, NGC fibers were successfully fabricated by using the designed FBS glass as core glass. Nanocrystals were controllably precipitated and greatly enhanced, and upconversion luminescence was observed in NGC fibers. The designed FBS NGCs provided high-quality optical gain materials and offered opportunities for fabricating a wide range of NGC fibers for multiple future applications, including fiber lasers and sensors.

Space-Selective Control of Functional Crystals by Femtosecond Laser: A Comparison between SrO-TiO2-SiO2 and Li2O-Nb2O5-SiO2 Glasses

We report on space-selective crystallization of congruent and polar Sr2TiSi2O8 crystals in a stoichiometric SrO-TiO2-SiO2 glass induced by (1030 nm, 300 fs) femtosecond laser irradiation. This allows us to compare with non-congruent laser-induced crystallization of polar LiNbO3 in non-stoichiometric Li2O-Nb2O5-SiO2 glass and gain information on the mechanism of nanocrystals orientation with the laser polarization that we pointed out previously. Using scanning electron microscopy (SEM), second harmonic generation (SHG), and electron backscattered diffraction (EBSD), we studied the laser-induced crystallization according to the laser processing parameters (pulse energy, pulse repetition rate, scanning speed). We found (1) a domain where the laser track is filled with crystals not perfectly textured (low energy), (2) a domain where an amorphous volume remains surrounded by a crystallized shell (high energy). This arises from Sr out-diffusion and may give rise to the crystallization of both SrTiO3 and Sr2TiSi2O8 phases at low speed. In the one-phase domain (at higher speed), the possibility to elaborate a tube with a perfect Fresnoite texture is found. A significant difference in size and morphology whereas the crystallization threshold remains similar is discussed based on glass thermal properties. Contrarily to Li2O-Nb2O5-SiO2 (LNS) glass, no domain of oriented nanocrystallization controlled by the laser polarization has been found in SrO-TiO2-SiO2 (STS) glass, which is attributed to the larger crystallization speed in STS glass. No nanogratings have also been found that is likely due to the congruency of the glass.

Influence of substrate on ultrafast water transport property of multilayer graphene coatings

The ultrafast water transport in graphene nanoplatelets (GNPs) coating is attributed to the low friction passages formed by pristine graphene and the hydrophilic functional groups which provide a strong interaction force to the water molecules. Here, we examine the influence of the supporting substrate on the ultrafast water transport property of multilayer graphene coatings experimentally and by computational modelling. Thermally cured GNPs manifesting ultrafast water permeation are coated on different substrate materials, namely aluminium, copper, iron and glass. The physical and chemical structures of the GNPs coatings which are affected by the substrate materials are characterized using various spectroscopy techniques. Experimentally, the water permeation and absorption tests evidence the significant influence of the substrate on the rapid water permeation property of GNPs-coating. The water transport rates of the GNPs coatings correspond to the wettability and the free surface energy of their substrates where the most hydrophilic substrate induces the highest water transport rate. In addition, we conduct molecular dynamics (MD) simulations to investigate the transport rate of water molecules through multilayer GNPs adjacent to different substrate materials. The MD simulations results agree well with the experimental results inferring the strong influence of the substrate materials on the fast water transport of GNPs. Therefore, selection of substrate has to be taken into consideration when the GNPs-coating is placed into applications.

Powder-in-Tube Reactive Molten-Core Fabrication of Glass-Clad BaO-TiO2-SiO2 Glass-Ceramic Fibers

In this paper we report the fabrication of glass-clad BaO-TiO₂-SiO₂ (BTS) glass-ceramic fibers by powder-in-tube reactive molten-core drawing and successive isothermal heat treatment. Upon drawing, the inserted raw powder materials in the fused silica tubing melt and react with the fused silica tubing (housing tubing) via dissolution and diffusion interactions. During the drawing process, the fused silica tubing not only serves as a reactive crucible, but also as a fiber cladding layer. The formation of the BTS glass-ceramic structure in the core was verified by micro-Raman spectroscopy after the successive isothermal heat treatment. Second-harmonic generation and blue-white photoluminescence were observed in the fiber using 1064 nm and 266 nm picosecond laser irradiation, respectively. Therefore, the BTS glass-ceramic fiber is a promising candidate for all fiber based second-order nonlinear and photoluminescence applications. Moreover, the powder-in-tube reactive molten core method offers a more efficient and intrinsic contamination-free approach to fabricate glass-ceramic fibers.

Nano-Structured Optical Fibers Made of Glass-Ceramics, and Phase Separated and Metallic Particle-Containing Glasses

For years, scientists have been looking for different techniques to make glasses perfect: fully amorphous and ideally homogeneous. Meanwhile, recent advances in the development of particle-containing glasses (PCG), defined in this paper as glass-ceramics, glasses doped with metallic nanoparticles, and phase-separated glasses show that these “imperfect” glasses can result in better optical materials if particles of desired chemistry, size, and shape are present in the glass. It has been shown that PCGs can be used for the fabrication of nanostructured fibers—a novel class of media for fiber optics. These unique optical fibers are able to outperform their traditional glass counterparts in terms of available emission spectral range, quantum efficiency, non-linear properties, fabricated sensors sensitivity, and other parameters. Being rather special, nanostructured fibers require new, unconventional solutions on the materials used, fabrication, and characterization techniques, limiting the use of these novel materials. This work overviews practical aspects and progress in the fabrication and characterization methods of the particle-containing glasses with particular attention to nanostructured fibers made of these materials. A review of the recent achievements shows that current technologies allow producing high-optical quality PCG-fibers of different types, and the unique optical properties of these nanostructured fibers make them prospective for applications in lasers, optical communications, medicine, lighting, and other areas of science and industry.

Transformation of molecular compounds with Ba(Sr)/Al/Si and Ca(Sr, Ba)/Ti(Zr, Hf)/Si heteroelements as new efficient route to metal silicate materials

Silicon-based moieties were anchored in heterometallic alkoxide platforms to obtain molecular clusters based on the M-O-M'-O-Si motif for the generation of mixed-metal silicate materials. Single-source molecular precursors with structures [M{(μ-ddbfo)2Al(OSiPh3)2}2], where dbbfoH = 2,3-dihydro-2,2-dimethylbenzofuran-7-ol and M = Ba (1), Sr (2), [Sr4Ti2(μ6-O)(μ3,η2-OCH2CH2OMe)8(η-OCH2CH2OMe)2(OSiPh3)4] (3), [Sr4M'2(μ4-OH)(μ3,η2-OCH2CH2OMe)4(μ,η2-OCH2CH2OMe)6(μ-X)(OSiPh3)4] (4, with M' = Zr and X = Cl; 5 with M' = Hf and X = OH), [Sr3Hf2(μ5-O)(μ3,η2-OCH2CH2OMe)4(OCH2CH2OMe)4(OSiPh3)4] (6), and [Ca2M'2(μ3-OH)2(μ,η2-OCH2CH2OMe)4(η2-HOCH2CH2OMe)2(η-OCH2CH2OMe)2(OSiPh3)4] for M' = Zr (7), Hf (8), were prepared by substitution of methyl groups, using Ph3SiOH or chloride atoms with KOSiPh3, in [M{(μ-ddbfo)2AlMe2}2] (M = Sr, Ba) or [M4M'2(μ6-O)(μ3,η2-OCH2CH2OMe)8(OCH2CH2OMe)2(HOCH2CH2OMe)xCl4] (M = Ca, Sr, Ba, M' = Ti, Zr, Hf and x = 0, 4). The precursors were characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray structural analysis. Thermal decomposition of compounds 1-8 at 1000 °C led to formation of ceramic materials that consisted of mixed-metal oxide nanocrystallites embedded in an amorphous SiO2 matrix. Compounds 1 and 2 decomposed to BaAl2Si2O8 and SrAl2Si2O8 aluminosilicates, 4 gave a mixture of SrSiO3, ZrO2, SrZrO3 and Sr7ZrSi6O21, 5 and 6 gave mixtures of various compounds, including SrHfO3, Hf0.96Si0.04O2, and SiO2, 7 lead to CaZrO3, ZrO2 and Ca3ZrSi2O9 and 8 gave a HfO2, Ca2HfSi4O12 and SiO2 phase. The thermolysis of compound 3 gave SiO2 particles of average size 40-90 nm, which contained spherical SrTiO3, SrSiO3 and Sr2TiSi2O8 nanocrystallites of diameter 5-16 nm.