Thermal effects on double clad octagonal Yb:glass fiber laser

Thermally-induced change of refractive index in fiber lasers due to high power pumping can modify propagation mode characteristics. The modes guiding in the core and cladding for different heat loads in an octagonal double clad ytterbium doped glass (Yb:glass) fiber laser were simulated. The variations of the core confinement factor for core modes at signal wavelength and for cladding modes at pump wavelength, as a function of heat loads were calculated. The cladding modes are bounded to the core region by increasing the heat load. This effect is due to thermal lensing; that is a lens-like behavior of the glass medium induced by temperature distribution.