Rare-earth elements doped novel photonics sources
Jha, Nitin Saurabh
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This thesis presents the work carried out on the development of novel photonic sources based in rare-earth doped ions. It discusses in detail the properties of rare earth ions and its applications. The three major components of this work, namely, rare-earth doped solid state hosts, rare-earth doped speciality fibres, and rare-earth doped waveguide lasers have been presented in different chapters. The host glasses for the rare-earth doped gain mediums have been prepared by the traditional melt-quenching technique and spectroscopic studies have been carried out on them. Experiments to realise multi-wavelength lasers operating in the visible range have been carried out on the samarium doped phosphate glasses, owing to samarium‟s unique multiple emission peaks at 561 nm, 596 nm, and 643 nm with violet-blue excitation. Due to the relatively low emission cross section value of trivalent samarium ions (3.911 X 10-22 cm2 at 596 nm), it requires a much higher pump power. Due to the lack of high pump power diodes in the violet wavelength range, laser action could not be demonstrated. Further spectroscopic investigations on the samarium doped glasses and crystals revealed that the presence of excited state absorption could be a factor as well which discourages the realisation of laser emission in the sample. Rare-earth doped multicore optical fibres have been designed and fabricated for the realisation of active multiplexer elements and multi-wavelength lasers. Optical fibres with six cores and two cores respectively have been fabricated. Each of the six cores of the fibre were doped with erbium with the aim to develop active multiplexer elements which could incorporate multiplexing and amplification together. The cores showed considerable gains, with the maximum gain of around 30 dB – 40 dB in the wavelength range of 1500 nm – 1600 nm. The cores of the two core fibre were doped with ytterbium and erbium/ytterbium with the aim to demonstrate simultaneous laser action at 1 μm and 1.5 μm. The fibre, upon cladding pumping at 976 nm, demonstrated simultaneous laser emissions at 1061 nm and 1536 nm from the ytterbium and erbium/ytterbium doped cores, respectively. The laser action was observed with Fresnel reflection from the parallel cleaved facets of the fibre. The slope efficiency of the emission for both the cores were ~1%, which is quite low, considering the Fresnel reflection lasing. CW modelocked waveguide laser has been demonstrated in ytterbium doped bismuthate glasses. The waveguides were inscribed by the ultrafast laser inscription technique. The waveguide laser operated at the repetition rate of around 1.94 GHz with the pulse duration of about 1.1 ps at the wavelength of 1029 nm.