Multi-channel mode converter based on a modal interferometer in a two-mode fiber

Mode converter is one of the key devices in mode-division multiplexing optical communication systems for overcoming current limitation of the transmission capacity in a single mode fiber. In this paper, we proposed a multi-channel mode converter with the concept of modal interferometer in two mode fiber. Two lateral stress points in two mode fiber function as in-line fiber mode couplers to construct the modal interferometer, and both transmission spectra and near-field patterns confirmed that the LP01 mode was successfully converted into LP11 mode at the multiple channels. The measured mode conversion efficiency almost completely follows the theoretical tendency. Finally, the mode conversion was realized at 20-channels in the C+L wavelength band with conversion efficiency up to 99.5% and insertion loss as low as 0.6 dB. Furthermore, the channel spacing can be freely tailored by selecting different distance between two stress points.