Fluoride Glass Fibers Research Articles

Mechanical durability of ZBLAN and aluminum fluoride-based optical fiber

Zero stress aging and static fatigue experiments were performed on fluoride glass fibers of ZBLAN and aluminum fluoride-based compositions to examine the mechanical durability in aqueous solutions. ZBLAN fiber, which has the higher initial strength, becomes weaker than initially lower strength aluminum fluoride-based fiber in less than one hour in pH 7 buffer solution at 30/spl deg/C. This is shown to be due to dissolution of the glass and precipitation of crystals at the glass/coating interface. In 1N NaOH the solubility is higher, resulting in less precipitation and hence less strength degradation. Although ZBLAN fiber degrades more quickly when a high strain is applied, at low applied strain the residual strength is higher than is observed when do strain is applied. These results indicate that future work on fluoride glass fibers for use in aqueous environments should focus on optimization of the as-drawn strength of durable glass, such as aluminum fluoride-based material, rather than on making small strength improvements to already strong but less durable glass, since such improvements will be quickly lost in aggressive environments.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Antimony-based strained-layer 2-2.5 mu m quantum well lasers

The authors present calculations which show that compressive or tensile strain introduced into the well material of InGaAsSb/AlGaSb quantum well lasers reduces the threshold current density compared with double heterostructure and lattice-matched lasers. The operating wavelength can be close to 2.55 mu m, the region of lowest attenuation in fluoride glass fibres.

Formation of scattering centres in fluoride glass preforms and fibres

The fluorozirconate family of glasses has been identified as suitable candidate material for trivalent rare-earth ion doped fibre laser amplifier devices. Their unsuitability however for passive application in the telecommunication network has been recognised due to the formation of scattering centres in the vitreous phase. These are predominantly crystals that form as a result of the tendency for glass devitrification. In the present work, the origin of these scattering centres, particularly crystals, has been identified by considering the thermodynamic aspects of the melting behaviour of crystals. The classical nucleation and crystal growth models have been taken into consideration to explain the origin of crystals as scattering centres in glass preforms and in fibres.

Characterization of fluoride glasses for single-mode optical fibers with large refractive index difference

Abstract In order to obtain fluoride glass optical fibers with large refractive index difference between the core and the cladding, refractive indices and viscosities of PbF2-doped core glasses and HfF4-incorporated cladding glasses were systematically investigated. From the point of view of viscosity matching, it was found that the 9 mol% PbF2-doped core glass containing 14 mol% NaF was the most adequate choice in combination with the 43 mol% HfF4-incorporated cladding glass containing 22 mol% NaF. Using a casting method, single-mode fluoride glass fibers with relative refractive index difference of 2.9% were successfully fabricated.

Derniers dÉveloppements concernant les amplificateurs optiques

State of the art optical amplifier technologies are reviewed focusing on research at ntt. The following developments will be described : an erbium-doped silica fiber with a very high gain coefficient of 11.0 dB/mW, a very small (volume : 36 cc) fiber amplifier module pumped by a 980 nm InGaAs laser diode, an Er-doped fiber amplifier pumped by an AlGalnP visible laser diode, praseodymium-doped fluoride glass fiber amplifiers operating in 1300 nm band, silica-based erbiumdoped planar lightwave circuit amplifiers, and their applications in various optical transmission and measurement systems. The future trends in the optical amplifier research are also described.

Gain saturation characteristics of Raman amplification in silica and fluoride glass optical fibers

Raman amplification in silica and fluoride glass fibers is studied experimentally and theoretically. Two tunable dye lasers are employed to provide pump and signal light. In an 80 m long silica glass fiber, a small-signal gain of 39 dB has been achieved at a pump wavelength of 580 nm. The gain bandwidth is 127 cm -1 in small-signal amplification and 250 cm -1 in saturated amplification. In an 18 m long fluoride glass fiber, a small-signal gain of 9.3 dB has been obtained. The measured Raman-gain coefficient at 580 nm is (2±0.5) × 10 -11 cm/W in the fluoride glass fiber.

Spectral optimization of a pulsed HF chemical laser for efficient energy delivery through a low-loss fluoride glass optical fiber

Pulsed HF chemical lasers oscillating in the midinfrared region of the spectrum where water can strongly absorb are suitable for the organic tissue ablation. For such a medical application, a flexible energy delivery system using an optical fiber is indispensable. The fluoride glass optical fiber may be used for low-loss optical energy delivery of the pulsed HF laser. Using an intracavity CO2 absorption cell, we have optimized pulsed multiline HF chemical laser spectrum for low-loss energy delivery through a fluoride glass optical fiber whose transmission loss is theoretically estimated to be minimum around 2.5 μm. The fractional output energy of P1-0(3) and P1-0(4) lines, which are sitting in the lowest loss spectral region of the practical fluoride glass fiber, exceeded half the multiline output energy using a line selective intracavity CO2 gas cell. The P1-0(4) line extracted from the resonator with a diffraction grating was successfully delivered through a 3-m-long commercial fluoride glass fiber (core/cladding diameter=450/500 μm). The delivered energy of 11.9 mJ was achieved with the corresponding energy fluence of 12 J/cm2 and peak intensity of 22 MW/cm2 at the exit core surface without optical damage.

Current status of infrared fiber optics for medical laser power delivery.

There are a host of fiber-optic delivery devices available for use with the Er:YAG, HF, CO, and CO2 lasers at 2.9, 2.8, 5.3, and 10.6 microns wavelengths, respectively. While many of these fibers are not as convenient to use as conventional silica fibers, they offer the ability to deliver infrared laser energy for a wide variety of medical applications. The fundamental attributes of fluoride glass, chalcogenide glass, single-crystal sapphire, and polycrystalline silver halide optical fibers are reviewed and their practical properties tabulated.

Optical damage thresholds at 294 μm in fluoride glass fibers

Optical damage thresholds at lambda = 2.94 microm have been investigated in one single-mode (11-microm core, 125-microm cladding) and five multimode fluoride glass fibers. (These five fibers consist of three conventional ones, 70-microm core, 140-microm cladding, 150-microm core, 200-microm cladding, and 200-microm core, 250-microm cladding, and two low-attenuation ones, 200-microm core, 250-microm cladding, and 350-microm core, 400-microm cladding.) The induced surface damage is discussed by means of electron microscopic analysis. Power limits for safe transmission are presented.

Optical fibre delivery and tissue ablation studies using a pulsed hydrogen fluoride laser

We describe an experimental study of the transmission of pulsed, multiline (2.67–2.95 μm) hydrogen fluoride (HF) laser radiation in a fluoride glass fibre. For a 400 ns full-width at half-maximum (fwhm) duration laser pulse transmission measurements and photoacoustic techniques show that non-linear loss at the fibre input surface appears to set a maximum useful input fluence of ∼15 J cm−2 for the 500 μm core diameter fibre used. However, with modest length fibres, exit fluence levels adequate for the ablation of soft tissue can be obtained with the fibre operating well below this limiting value. Removal rate measurements and scanning electron microscope evaluation of the irradiated site for bovine cornea ablated using the fibre-delivered HF laser pulses are reported.

Rare-earth doped fluoride glass fibres

Fluoride glass optical fibres are characterized by a large optical window covering the range 0.4–5 μm which permits excitation and fluorescence spectroscopy in a much more extended domain than with silica-based fibres. The local ligand field acting on the rareearth ions affects the radiative lifetime, phonon relaxation, excited state absorption, and emission peak broadening. Finally, the fibre structure provides excellent optical confinement for observing laser emission in the visible and mid-IR regions at very low threshold power, permitting laser diode pumping. Multiphonon processes are also observed leading to the up-conversion of IR into the visible or UV and making possible the development of new laser sources for optical recording laser printing, optical amplification, medical and optical sensor applications.

Effects of thermal history on crystal size distributions and scattering in fluoride glass fibres

The rates of nucleation and growth of crystals in ZBLAN glass have been analysed and differences have been found between previously reported models. These differences are most acute in the case of crystal nucleation rates. It is shown that, depending on which model is selected, the predicted stability of the glass is dramatically altered. The lowest stability predictions appear to have been based upon the most reliable data. The more reliable nucleation and growth models are used in a computer simulation which predicts crystal size distributions for any chosen thermal cycle. The thermal cycles arising from preform casting and fibre drawing are considered, and the resulting distributions are presented. Signal losses due to scattering of between 0.1 and 10 dB/km at wavelength 2.55 μm are predicted for long optical fibres, assuming that the nucleation and growth models are accurate. The predicted loss is sensitive to the time and temperature of the fibre drawing process, and is shown to be lower for a fast hot draw than for a slower cooler draw.

Radiation thermometry for low temperatures using an infrared hollow waveguide

Various optical fibers were compared theoretically for application to remote radiation thermometry. The highest optical transmission efficiency is attained with a fluoride glass fiber for the temperature range of > 700°C, with a halide crystalline fiber for 120 to 700°C, and with a dielectric-coated metal hollow waveguide for < 120°C. To realize remote sensing of lower temperatures, i.e., from room temperature to ~300°C, a radiometric experiment was carried out using a Ge-coated Ag hollow waveguide. When ambient temperature changed from 22 to 50°C, a serious error arose in the measured temperature, which is attributed to the increase of thermal radiation from the heated waveguide. Since the effect of such noise radiation is inevitable in thermometry using infrared fibers, we propose a measurement method to compensate for the noise level. With the compensation, the effect of ambient temperature was reduced successfully and reliable thermometry was established.

Er:YAGレーザー医用システム

The wavelength of Er: YAG laser is 2.94μm and this ability of incising biotissues is much stronger than CO2 laser (10.6μm). Furthermore, Er: YAG lasers cause much less thermal damage to biotissues than CO2 lasers, because Er: YAG lasers are more easily absorbed by water than CO2 lasers are. For studying possibilities of applying Er: YAG lasers to endoscopy, we tested fluoride glass fiber (ZrF4),chalcogenide glass fiber (As2S3) and hollow light guide all of which may be used in Er: YAG laser delivery system. The transmittance of the fluoride and the chalcogenide fibers we measured was 90% and 75% at 1m long, respectively. The test shows that these fibers are applicable to Er: YAG laser endoscopes, although the fibers have a fragile mechanism and some other problems yet to be solved. On the other hand, the transmittance of the Al hollow light guide measured 75% per meter. This hollow light guide may be too large to be used for endoscopy but it will be applied to surgical laser scalpels. We proposed the solid state laser of new type. This laser have the two kinds of GSAG host crystals which are doped with Cr and Nd, or Cr and Er. The wavelength of this laser are 1.06μm and 2.74μm, also this have photocoagulation and incision capability for biotissues.

Challenges in obtaining low loss fluoride glass fibers

The contribution from the different mechanisms to the total loss at 2.55 μ m is reviewed. The observations suggest that extrinsic scattering induced by the different fiberizing techniques is the biggest limitation to achieving low loss in fluoride fibers. Extrinsic scattering is mainly due to microcrystals which grow on heterogeneities which can be subsequently eliminated and bubbles which are frequently present in all fiberizing techniques. A new fiberizing technique called the core injection technique (CIT) is discussed which potentially eliminates the presence of bubbles.

CW room temperature upconversion lasing in Er 3+-doped fluoride glass fiber

Continuous-wave, room temperature laser oscillation at 548 nm in Er3+-doped fluorozirconate fiber pumped at 800 nm is reported. The threshold was 410 mW of the 800 nm pump power. An output power of 10 mW was obtained at 548 nm with a slope efficiency of 7%. Other compositions and geometries of fluoride glasses are proposed to produce upconversion laser glasses with higher efficiencies.

1.55 µm Gain in a Short Er3+-doped Zirconium Fluoride Glass Fiber

1.55 µm gain was measured in a 28 mm long zirconium fluoride glass single-mode fiber which was pumped with a 514.5 nm argon ion laser.

Upconversion in fluoride glass fibers

Research News: Compact visible (blue) lasers are required for applications such as barcode reading, laser printing, and high‐definition optical recording. An alternative method to frequency doubling to obtain blue laser light is the up‐conversion of infrared light. In this process photons are converted to higher energies by generating high‐energy excited states in the energy level scheme of a rare‐earth ion which then emit at a higher frequency than that of the infrared excitation source.

Influence of Processing Parameters on the Strength of Fluoride Glass Fibers

The different factors affecting the tensile strength of heavy‐metal fluoride glasses are presented. Surface crystals were found to be responsible for the lower fiber strength. The tensile strength of fluoride glass fibers can be increased by controlling the preform surface and drawing in a dry atmosphere. Using lower draw temperature and dual polymeric coatings increases the strength. Finally, phosphate glass overclad on fluoride glass fiber can be used to prevent surface hydrolysis during the drawing process and increases the tensile strength of fibers due to formation of compressive stress on the outside of the glass fiber.

Amplification and lasing at 1.3 μm in praseodymium-doped fluorozirconate fibres

Light emission from the 1G4 → 3H5 transition around 1.3 μm of Pr3+ has been studied in fluoride glass (ZBLAN) fibres. Pumping at 1064 nm yields extracted laser power of a few mW at 1.294 μm. Gain curves centred at 1.295 μm have been obtained, with gross gains of more than 15dB at 1.319 μm. Changes of the output ASE with pumping conditions are explained by excited state absorption or energy transfer from the 1G4 upper level of the transition.