Rare-earth elements doped novel photonics sources
Abstract
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.