Spectral shaping in a multimode fiber by all-fiber modulation

In the past few years, there is a renewed interest in using multimode fibers for a wide range of technologies such as communication, imaging, and spectroscopy. However, practical implementations of multimode fibers in such applications are held back due to the challenges in dealing with modal dispersion, mode coupling, and the fiber's sensitivity to mechanical perturbations. Here, we utilize these features of multimode fibers to generate all-fiber reconfigurable spectral filters. By applying computer-controlled mechanical deformations to the fiber along with an optimization algorithm, we manipulate the light propagation in the fiber and control its output field. Using this approach, we demonstrate tunable bandpass filters and dual-band filters with spectral resolutions as low as 5 pm.