Efficient and compact photonic lanterns through cascaded tapering

With the number of modes in photonic lantern (PL) increasing, a longer adiabatic taper is required, which is not feasible for fabrication. A cascaded-taper-based PL is proposed as a type of efficient and compact multiplexer/demultiplexer. It has many advantages to design and draw the PL through multi-taper cascade. For the double-taper PL with its longitudinal profile optimized, the coupling efficiency of mode group LP01 and LP11 reaches its optimal value of 90.8% and 90.0% when the length is 5.15 cm, while the corresponding efficiency of the single-taper PL is only 74.6% and 85.6%, respectively. Besides, the triple-taper PL optimized with the same material has a length of 4.65 cm. The optimal coupling efficiency of mode group LP01 and LP11 is 89.5% and 89.1%, while the single-taper PL with the same length is only 72.6% and 84.4%, respectively. Without loss of generality, the optimal adiabatic taper profiles of the two-modegroup PLs are obtained by beam propagation method. As a comparison, only when the length of the single-taper twomode- group PLs is 9 cm, the coupling efficiency of mode group LP01 and LP11 reaches the optimal values of 92.4% and 94.1% respectively. Although the optimal coupling efficiency of the double-taper and triple-taper PLs is slightly lower than that of the optimal single-taper ones, they will exhibit better performance when the length must be shorter.