LP01 to LP0m mode converters using all-fiber two-stage tapers

• We propose an all-fiber mode converter between LP01 and LP0m modes using two stages of tapers.
• Three converters between LP01 and LP0m, m=2, 3, and 4, are designed for C-band.
• We analyze the tolerance of the dimensions of the structures to drifts from their optimal values.
• We discuss fabrication issues and challenges.

A mode converter between LP01 and LP0m modes is proposed using two stages of tapers. The first stage is formed by an adiabatically tapering a circular fiber to excite the desirable LP0m mode. The second stage is formed by inserting an inner core (tapered from both sides) with a refractive index smaller than the original core. This second stage is used to obtain low insertion loss and high extinction ratio of the desired LP0m mode. Three converters between LP01 and LP0m, m=2, 3, and 4, are designed for C-band, and simulation results show that less than 0.24, 0.54 and 0.7 dB insertion loss and higher than 15, 16, and 17.5 dB extinction ratio over the entire band were obtained for the three converters, respectively.