  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. Practical implementations of multimode fiber in such
applications, however, 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 5pm.

Optics;Applied Physics