Distributed Analysis on the Spatial Mode Structure in a PANDA-Type Few-Mode Fiber By Brillouin Dynamic Gratings

We present the experimental analysis on the spatial mode structure in a PANDA-type few-mode fiber (PANDA-FMF) by the intermodal operation of Brillouin dynamic grating (BDG). Polarization-maintaining mode selective couplers are newly developed to selectively launch different optical modes for the pump and probe waves, and the characterization of the intra- and intermodal Brillouin scatterings in the PANDA-FMF is demonstrated. Distributions of effective refractive index (ERI) differences between six guided modes (LP01x, LP01y, LP11(o)x, LP11(o)y, LP11(e)x, and LP11(e)y) are measured by optical time-domain analysis of the intermodal BDG reflection spectra, and a unique ERI hierarchy among LP11 modes with different lobe orientations and polarization directions is reported for the first time in the PANDA-FMF. The analysis on the origin of measured ERI hierarchy is also presented by numerical simulations on the effect of core ellipticity.

Automated summary

The experimental analysis focused on the spatial mode structure in a PANDA-type few-mode fiber (PANDA-FMF) and the impact of different factors, such as intermodal operation of Brillouin dynamic grating (BDG) and core ellipticity. New polarization-maintaining mode selective couplers were developed to selectively launch various optical modes for pump and probe waves. It was found that the LP11 modes in PANDA-FMF exhibit a unique hierarchy in effective refractive index (ERI) related to lobe orientations and polarization directions.