Emission cross-section synthesis in rare earth doped optical fiber

Novel techniques to control the effective emission cross section of a rare earth doped optical fiber with a functional cladding structure are reviewed for applications in active fiber devices. Firstly we discuss evanescent wave filtering technique based on the overlap in the radiative transition cross sections between the emitting ion in the core and the absorbing ion in the inner cladding. Secondly a W-type three layered fiber structure is analyzed in terms of modal guidance and location of the LP01 mode cut-off, by which the emission at the longer wavelength is selectively attenuated. The design concepts, fabrication process, and device performances are discussed for each application.