MDM transmission using air-clad photonic lanterns

MIMO less few mode transmission is performed using two spatial channels transmitted through 1 km of two mode graded index fiber at 10 Gb/s modulation rate. The multiplexing and de-multiplexing of the spatial channels are done using air clad photonic lanterns. The power in the two degenerate LP11 modes are added electrically and counted as a single channel. The Q values calculated for the LP01 and LP11 channels are 5.4 and 4.7 respectively. We also show that, the signal degradation due to modal interference can be mitigated by using different laser sources for different spatial channels with some wavelength spacing. The wavelength separation increases the modal beat frequency beyond the detector bandwidth, thus improving the transmission performance. Using two laser sources with a wavelength spacing of 0.2 nm between the spatial modes could improve the Q compared to the case where a single laser source is split between the spatial channels with some extra length of fiber in one of the paths for optical decorrelation.