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Abstract We report noble metal doped optical fiber which is suitable for laser and helps enhancing fluorescence when it is doped with active elements. Silver nano-clusters (average diameter 1.5 nm) in the core of a standard step index fiber are doped using standard fiber fabrication method. These fibers show broad visible fluorescence in the wavelength range 420–700 nm under 405 nm excitation. This appears to occur due to long interaction length of pump light with the metal nano-clusters and quantum confinement effect. We observe enhanced fluorescence from rare earth ions (i.e. Tm3+ and Yb3+) in presence of silver nano-clusters when the optimized length of the fiber is pumped by using 980 nm fiber-pig-tailed laser diode. The experimental results are explained with the help of analytical and quantum mechanical models. These fibers would be helpful to make efficient optical fiber based light sources mostly in the visible range.

1 Introduction Conventional fiber based light source is made with the help of rare earth (RE) doped optical fiber where the core glass is doped with RE ions such as Tm3+, Yb3+, Er3+ etc. with limited fluorescence emission efficiency. The absorption and emission cross-sections of the RE ions in silica glass are insufficient to produce large optical emission band with available commercial pumping sources. Since R. Chattopadhyay
A. Haldar
M.C. Paul
S.K. Bhadra Fiber Optics and Photonics Division, CSIR-Central Glass and Ceramic Research Institute, 196 Raja S. C. Mullick Road, Kolkata 700032, India A. Haldar Optoelectronics Research Centre, University of Southampton, B53, Southampton, SO17 1BJ, UK R. Chattopadhyay
S.K. Bhadra (&) Raman Centre for Atomic, Molecular and Optical Sciences, Indian Association for the Cultivation of Science (IACS), Kolkata 700032, India e-mail: [email protected] © Springer Nature Singapore Pte Ltd. 2017 I. Bhattacharya et al. (eds.), Advances in Optical Science and Engineering, Springer Proceedings in Physics 194, DOI 10.1007/978-981-10-3908-9_12

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noble metal-nano-clusters (MNCs) have interesting optical properties when they are doped in dielectric materials, we tried to dope some noble metals, especially Silver (Ag) nanoclusters (NCs) in the fiber core to fabricate a new family of fluorescent fiber which are capable of producing fluorescence emission without RE ions. On the other hand the characteristics fluorescence emission of RE doped fiber is enhanced in presence of MNCs. The main challenge in synthesis of MNCs in dielectric host is to maintain the desired structural stability. Without any scaffold the clusters tend to aggregate to larger particle, which is an irreversible process as it happens in fluid. It would be an added advantage if these Ag-NCs are synthesized in the core glass of an optical fiber to get niche properties. The immobility of the clusters will prevent aggregation of the NCs. Furthermore enhanced fluorescent output could be possible in the visible regime due to the long interaction length of propagating optical field with M