Fiber lasers have become very popular in the recent two decades due to numerous advantages compared to other solid-state lasers, e.g. their robustness, efficient cooling, high power compatibility, flexibility, large gain bandwidth and comfortable handling. Visible fiber lasers are increasingly becoming a new research focus, since they can be pumped very efficiently with new powerful, commercially available high-power GaN diodes in the UV wavelength range. Potential and important applications, especially in the biomedical field, are spectroscopy, microscopy and microsurgery. So far, fluoride glasses, e.g. ZBLAN, InF and AlF, are the most promising host glasses to realize stable visible fiber lasers. Most of them are originally designed for the MIR spectral range, but they also have the potential to cover the VIS. Pr3+ in ZBLAN glass is very attractive as it offers many possible laser transitions in the VIS and NIR range. In [1] a wide tunability in the VIS and NIR is demonstrated by core-pumping of a very short Pr3+-doped ZBLAN fiber. Regarding the visible spectral range, laser output powers up to 2.3 W around 635 nm were reported recently in a monolithic ZBLAN fiber laser with a Fiber- Bragg grating, but with reduced slope efficiency of 14% [2]. An alternative approach, where authors demonstrated up to 5 W laser power and 25.7% efficiency around 635 nm, is the direct and spliceless connection of pump and laser fiber using an end-facet coating mirror as input coupler [3]. Using this approach emission wavelength is power dependent and not locked.
We have investigated the laser performance and tunability of a highly Pr3+ doped fluoride glass fiber. Absorption and emission properties as well as laser characteristics in different resonator configurations have been studied. We have achieved 1.3 W output power @ 635nm wavelength with a slope efficiency of 30.6% with respect to the incident pump power. Furthermore, to the best of our knowledge, we present results on wavelength tunability with cladding-pumping on a several meter long Pr3+-doped ZBLAN fiber for the first time.
We present new designs of optical silica fibers tailored for sensing applications. Highly versatile MCVD technology allows co-doping of fused silica in a large variety of elements and the deposition of differently doped layer structures. Co-doping of Ge/B- or Ge/Al enables tuning the refractive index and thus adapting the mode field of the fibers. Ge/Ce co-doping allows tuning the photosensitive properties for Fiber Bragg grating inscription. Combining Ge- and Al-doping modifies the fiber properties for improved distributed sensing applications. We report realization of the designs and present first results of fiber properties.
Work is supported by German BMBF contract 03RU1U071J.
Applying the highly versatile and flexible MCVD technology at Leibniz-IPHT two new designs for optical sensing fibers were realized by co-doping of fused silica. For FBG sensing a Ge/B co-doped fiber with a mode field diameter adapted to standard single mode telecom fibers was prepared. The influence of boron on the attenuation at the inscription wavelength 1550 nm is visible. For distributed Brillouin sensing applications a preform with lateral separated germanium and aluminum doped regions and nearly step-index characteristic was fabricated by the MCVD in combination with the solution doping technique. Theoretical analysis of the acoustic properties and Brillouin spectrum have been shown, that this design is a potential candidate for strain and temperature discrimination. Because of the high temperatures during the preparation processes the radial refractive index and dopant concentration profiles of both fiber designs are influenced by diffusion.
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