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We have developed a new technique to produce a Yb-doped fused silica bulk glass which is very well suited for fiber laser applications. The starting point is a liquid suspension of SiO2 particles which is doped by a solution of rare earth ions. After dehydration, purification and vitrification we achieve a bubble-free homogeneous Yb-doped fused bulk silica, which is further processed by the plasma outside deposition (POD) technique into preforms for active laser fibers with a large active fiber core. The laser function of our Yb-doped silica was successfully proved in a side-pumped fiber laser setup. We present the results of the laser experiments.

Diffusion of Ge and F was studied during drawing of silica optical fibres. Preforms were drawn using various draw conditions and fibres analysed using the etching and Atomic Force Microscope (AFM) technique. The results were confirmed by comparison with fibre Refractive Index Profiles (RIP). Both Ge and F were found to diffuse at high temperature, 2100°C, and low draw speed, 10m/min. Diffusion simulations showed that most diffusion occurred in the neck-down region. The draw temperature and preform feed rate had a comparable effect on diffusion, whereas preform diameter did not significantly affect the diffusion.

As a key supplier of synthetic fused silica to the fiber optics industry, Heraeus is committed to innovative and up-and-coming technologies such as microstructured or photonic crystal fibers (PCF).

Heraeus has long produced fused silica materials with optimized optical properties for a broad range of specialty fiber applications and is offering Fluosil® rods with a unique high fluorine concentration up to 7% in the fused silica network.

Fluosil® tubes are characterized by the unique high fluorine concentration up to 7 % in their fused silica network, which leads to a depressed index of refraction up to -26 x10-3.

Deep UV application of optical fibers has been restricted due to the strong photodegradation in silica fibers transmitting deep UV light. We have developed an improved all silica preform for the production of multimode fibers with drastically improved resistance to UV-light. Two key experiments have been performed in order to characterize the solarization behavior of such fibers: (1) ArF-excimer laser and deuterium lamp photodegradation spectroscopy enables the in situ observation of defect center creation. (2) Long time photodegradation excimer laser experiments (ArF and KrF) are a good tool to predict the fiber's lifetime for applications with such lasers. Compared to standard high OH all silica fibers the optimized fibers show an exceptionally low creation of E'-centers (215 nm). Hydrogen doping of such fibers further increases the UV-resistance: Even after prolonged excimer laser irradiation (ArF: 20 X 106 pulses, 5 mJ/cm2, 400 Hz; KrF: 20 X 106 pulses, 50 mJ/cm2, 500 Hz) these fibers maintained their very high initial transmission, neither E'-center nor NBOH-center (265 nm) absorption could be observed.

Optical fibers with broadband transmission from the UV through the IR have not been available because the silica core material either has OH absorption bands in the IR or UV absorption due to intrinsic structural defects or chlorine. We have developed a new silica core material which can be fabricated into an optical fiber with very good transmission characteristics from 350 nm to 2000 nm. The transmission performance is stable with time because the fiber is not doped with hydrogen.

Optical fibers with broadband transmission from the UV through the IR have not been available because the silica core material either has OH absorption bands in the IR or UV absorption due to intrinsic structural defects or chlorine. We have developed a new silica core material which can be fabricated into an optical fiber with very good transmission characteristics from 350 nm to 2000 nm. The transmission performance is stable with time because the fiber is not doped with hydrogen.

Power transmission of xenon chloride excimer lasers through optical fibers is necessary for medical applications where tissue removal is performed within the human body. The most important application at present is excimer laser coronary angioplasty. Typical levels of energy densities applied by optical fibers for this application cause color center generation in fused silica leading to transmission decrease called photodegradation. This effect depends essentially on the grade of the fused silica. Important parameters are fiber length, pulse duration, energy density, and the irradiated cross sectional area of the optical fiber endface. For a new grade of core material the influence of these parameters on the transmission performance is described. The obtained material improvement leads to a significant reduction of the observable transmission decrease as a function of the number of laser pulses applied. Thus continuous operation of the laser in the region of the typical transmission plateaus at considerably higher and constant energy levels at the distal fiber end becomes feasible. This offers a new option for more reliable dosimetry in medical applications.

Standard Fluosil® preforms are made using our Plasma Outside Deposition (POD) process. This process can also be readily utilized for depositing highly fluorine doped layers onto substrate materials, both solid and tubular.

Heraeus has long produced fused silica materials with opti-mized optical properties for a broad range of specialty fiber applications.

Power transmission of excimer laser radiation at 308 nm through waveguides is of growing importance in medical applications. The maximum energy densities achievable at distal fused silica optical fiber ends are limited by the surface damage threshold of fused silica and by photodegradation of the optical fiber material. Limitations due to the surface damage threshold at the front surface can be avoided by applying tapered fiber geometries. In order to minimize photodegradation effects color center formation caused by high energy UV radiation has to be reduced. This involves optimization of the fused silica material properties and the necessity of modifying the manufacturing processes. Measurements on all silica fibers at 308 nm wavelength (XeCl excimer laser) show different influences of core material manufacturing. Not only the overall decrease of transmission but also the dependence of transmission changes on the number of laser pulses and defect annealing are strongly affected. Consequences for improved performance of all silica optical fibers in angioplasty are demonstrated by measurements on specially produced samples.

Fluosil® preforms are fused silica core step index multimode preforms made using the Plasma Outside Deposition (POD) process. This process facilitates the creation of a highly fluorine doped cladding with a depressed index compared to fused silica.

The transmission properties of a glass fiber are predominantly determined by its content of hydroxide ions. Fibres with a high OH-content feature very good transmission in the UV range, wheras the IR-transmission is limited by OH-absorption bands. In contrast, fibers with low OH-content transmit infrared light well, but often have undesirable absorption bands in the UV. This article illustrates how the properties of the core material influence potential applications of a glass fiber in different wavelength ranges.