Fe-Doped Polycrystalline CeO2 as Terahertz Optical Material

Fe-doped CeO2 is synthesized by ceramic method and the effects of Fe doping on the structure and properties are characterized by ordinary methods and terahertz-time domain spectrometer （THz-TDS） technique. Our results show that pure CeO2 only has a small dielectric constant ε of 4, while a smell amount of Fe （0.9 at.%） doping into CeO2 promotes densification and induces a large e of 23. From the THz spectroscopy, it is found that for undoped CeO2 both the power absorption and the index of refraction increase with frequency, while for Fe-doped CeO2 we measure a remarkable transparency together with a fiat index curve. The absorption coefficient of Fe-doped CeO2 at frequency ranging from 0.2 to 1.8 THz is less than 0.35 cm-1, implying that Fe-doped CeO2 is a potential THz optical material.     

Bend-Induced Distortion in Large Mode Area Holey Fibre

A simplified scheme of bend-induced mode distortion is introduced into bent holey fibres, the distorted mode distribution and mode effective area reduction are investigated using the finite difference method. Numerical results show that the modes of bent holey fibres with small bend radius shift away from the core and are deformed greatly, and the mode areas drop significantly as the bend radius decreases, which severely affects the fibre laser performance. The propagation characteristics of bent holey fibres at given wavelength are determined by fill factor and normalized bend radius. Finally, the transition normalized bend radius that represents the location of the mode area beginning to fall off is obtained.