Design of elliptical-core five-mode group selective photonic lantern over the C-band

We report the design of an elliptical-core five-mode group selective photonic lantern (EC-F-MGS-PL) supporting ten spatial modes over the C-band, whose output fiber is an elliptical-core few mode fiber (EC-FMF). Initially, we fix the cladding diameters of all input fibers to form an elliptical structure. With the help of beam propagation methods (BPM), we carry out comprehensive geometrical optimization of various input fiber bundle, and identify the optimal setting of input fiber bundle in order to achieve the maximum mode selectivity, low insertion loss (IL), and high mode conversion efficiency (MCE) for all five mode groups. Next, we optimize each fiber core diameter and propose a two-step tapering process, for the ease of performance enhancement for the EC-F-MGS-PL. Finally, the mode field evolution and the wavelength dependent operation of the proposed EC-F-MGS-PL is numerically investigated. A mode selectivity of 9∼17 dB and IL of 0.1∼0.38 dB for all five mode groups can be achieved over the C-band, while MCE keeps between 83.3%-95.8%. By taking into account of the fabrication process, we believe that both the design strategy and optimization procedure of the EC-F-MGS-PL are helpful for the implementation of multi-input-multi-output (MIMO)-less mode division multiplexing (MDM) transmission.