Grating assisted optical waveguide couplers for mode division multiplexing

In optical telecommunication technology the capacity of the transmission bandwidth will soon be achieved [1]. In addition to the wavelength, polarization and phase of the light, one can increase the spatial dimension of the optical fiber core as a fourth degree of freedom to enhance the transmission capacity. This can be done by increasing the diameter of the fiber core itself and, hence, applying multi-mode fibers or even by using a fiber with multiple cores. These approaches are summarized as spatial division multiplexing (SDM) [1]. One form of SDM is the mode division multiplexing (MDM) [2]. In MDM, different field modes are used as individual transmission channels. Besides the use of few mode fibers (fm-fibers) a key challenge to enable MDM lies in the development of mode selective coupler structures.