Methods and applications for filtering, selecting a mode in a multi-mode waveguide

摘要

PURPOSE: A mode filtering and selecting method at a multiple mode waveguide and a waveguide amplifier, a semiconductor laser and vcsel using the same are provided to enable a single mode to be guided with respect to a single direction by a filtering or selection rule obtained by changing a periodic refractive index at a clad portion of a waveguide. CONSTITUTION: A waveguide amplifier using mode filtering at a multiple mode waveguide is provided to enlarge a core size of a multiple waveguide consisting of a core(20) and a clad, and to enlarge a size of a mode field even at a single mode, in which light is passed at the single mode, by making a refractive index of a clad by a refractive index structure of the clad have a higher refractive index(22) only at the single mode.