Modal analysis of semiconductor cylinder fibers

Semiconductor cylinder fibers (SCFs) are novel amplifying waveguide structures in which a semiconducting film is interlaid between conventional core and cladding fiber layers. We investigate the modal properties of SCFs by way of a comprehensive model which takes into account the wavelength-dependent refractive indexes of both the core and cladding glass layers and the semiconductor. Our semiconductor model also includes both thin-film effects and carrier-induced changes in the complex refractive index. We show that annular modes which are highly confined to the semiconductor are supported, and we calculate the corresponding modal effective indexes. Finally, we demonstrate that, depending on the pump-induced carrier concentration, a large gain is possible across a broad spectral region.