A novel technique for splicing a small core Ge-doped photonic crystal fiber (PCF) was demonstrated using a commercial fusion splicer with default discharge parameters for the splicing of two standard single mode fibers (SMFs). Additional discharge parameter adjustments are not required to splice the PCF to several different SMFs. A low splice loss of 1.0 approximately 1.4 dB is achieved. Low or no light reflection is expected at the splice joint due to the complete fusion of the two fiber ends. The splice joint has a high bending strength and does not break when the bending radius is decreased to 4 mm.

No abstract

In the last years rare earth doped double-clad fibers have been developed to high-power laser sources. Important progress was possible by increasing numerical aperture of the pump cladding and decreasing numerical aperture of the laser core. The high NA of the pump cladding enables the acceptance of large pump intensities whereas the low NA of the laser core makes possible to increase the core diameter and to decrease the laser power density retaining high beam quality. Here, actual challanges are discussed and possibilities are demonstrated to use microstructures for improved fiber designs which are realized by stacking and drawing of capillaries and rods. The rare earth doped parts are prepared by modified chemical vapor deposition and solution doping, but other routes of powder technology are also studied. Concerning the currently most important laser and amplifier types -Yb doped at 1.1 : m wavelength and Er/Yb doped at 1.55 : m wavelength -, the question of a high pump aperture is similar, but the limitations concerning a low core aperture are fairly different, because an efficient Er/Yb laser demands high phosphorus co-doping which naturally increases the core NA. The applied microstructures comprise "holey" fiber cross sections in form of "air clads" for the pump light and multiple hole ring structures for laser core and inner cladding. Moreover, microstructured cores made from solid parts yield new possibilities and parameters to compensate the high refractive index of the active material and to optimize the large mode area design. key words: fiber laser, rare-earth doping, microstructured fiber

The concept of microstructured and photonic band gap fibres opens a wide range of flexibility to introduce specific functionality in fibre light guiding properties and to adapt optical fibres to specific applications. In addition to flexible structural parameters, the use of specific material properties further increases the design freedom in optical fibres. In order to demonstrate the wide functional capabilities of such fibres, we have investigated different index guiding and photonic band gap fibres made from pure and modified silica and from non‐silica materials. The main interest in the use of different materials than the well‐known high‐purity silica is to utilize special optical properties such as high nonlinearity, specific dispersion or extended infrared transmission windows. A main challenge for such unconventional materials is to transfer the excellent properties of silica‐based photonic crystal fibres, like low spectral loss or good durability, to the modified or non‐silica materials. The preparation of modified silica‐based photonic crystal fibres was implemented by the MCVD doping process or by the use of high‐melting lanthanium or lead silicate special glasses. Highly germanium‐doped silica rods were used for the preparation of index guiding and for band gap guiding fibres. The prepared fibres were investigated in their mode propagation properties and compared to model calculations. Application examples are presented for spectral fibre sensing and for supercontinuum generation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on generation of blue light exploiting high-order mode propagation in a microstructured fiber pumped by a Ti:Sapphire close to the zero-dispersion wavelength of the first high-order mode. An new interesting regime was observed with axial offset pump. With 230 mW of incident pump power we generated over 3 mW in the 450-510 nm window achieving 50 μW/nm power density. In a final round of measurements we were able to show generation of a peak at 350 nm. This complex regime has still to be fully investigated but we believe an optimized fiber design will allow to efficiently extend the operation of Ti:Sapphire laser to UV/blue wavelength region