Ultrafast heterodyne mode imaging and refractive index mapping of a femtosecond laser written multimode waveguide

We demonstrate imaging of individual modes in a femto-second laser written multimode waveguide by spatialheterodyne interferometry and decomposition in data post-processing. Despite the spatial and temporal overlap between multiple waveguide modes, we show the extraction of amplitude for each individual mode and their corresponding temporal dynamics. The mode imaging scheme is effective with the presence of intermodal interference and can be prospective for sensing of ultrafast phase and refractive index fluctuations. We also reconstruct the two-dimensional transverse refractive index map of the multimode waveguide leveraging all the imaged modes and substantiate the reconstructed index map by simulation. (C) 2021 Optica Publishing Group

Automated summary

In this study, we demonstrate the imaging of individual modes in a femto-second laser written multimode waveguide using spatial heterodyne interferometry and data post-processing decomposition. Despite the overlap between multiple waveguide modes, we are able to extract the amplitude and temporal dynamics of each individual mode. This mode imaging scheme shows promise for sensing ultrafast phase and refractive index fluctuations.