We have excited both LP<sub>01</sub> and LP<sub>11</sub> modes using a high magnification objective lens (60×) in a nonlinear photonic
crystal fibre (PCF) of core diameter 2.2μm and simultaneously detected the modes using low coherence interferometry.
We placed the nonlinear PCF of length ~11cm in one arm of an interferometer, and then interfered the output with light
in the reference arm onto a photodetector via a single mode collection fibre positioned at a point in a near-field image of
the fibre endface. More than one fringe packet was observed in the interferogram, indicating the presence of two modes
propagating in the fibre core. To uniquely identify the dispersion curves we need to know which mode corresponds to
each fringe packet in the interferogram. In the same experimental setup we replaced the photodetector with a digital
CCD camera to record the 2-D interference pattern across the image as function of group delay. A Fourier analysis
technique was used to compute the intensity and phase of the mode field patterns corresponding to the various
interferograms. Using this technique we can simultaneously measure the group velocity dispersion and the mode profile
with phase information of the modes excited in a multimode PCF.
Ytterbium doped sodium phosphotellurite glasses are made with different Yb<sup>3+</sup> concentrations. Physical properties of the new glasses are reported. The glasses show high absorption and emission cross-sections and higher lifetime of [equation] transition. Laser performance parameter <i>σ<sub>e</sub></i> × <i>τ<sub>f</sub></i>, with a value as high as 2.14×10<sup>-20</sup> cm<sup>2</sup>-ms and the laser threshold intensity as low as 1.79 KW/cm<sup>2</sup> are reported. The laser parameters of these Yb<sup>3+</sup> doped glasses show that they are potential to fabricate high power laser and broadband optical amplifiers.