Reduction of speckle contrast in multimode fibers using piezoelectric vibrator

We experimentally investigate a technique to reduce speckle contrast in multimode fibers by using a piezoelectric vibrator. The speckle patterns in multimode fiber are attributed to the interference between the propagation modes of the fiber. If the optical fiber is externally vibrated, the output pattern is modulated due to mode couplings of the propagation modes. In this experiment, a part of fiber was fixed on the piezoelectric plate and applied high frequency oscillations. It was clearly observed that the speckle contrast of the output pattern was dramatically reduced by applying vibration. We investigated the factors which affect the speckle contrast, such as core diameter, fiber bending radius, shape of fiber core, exposure time of camera, etc. We found that non-circular shaped core fiber might be more effective to reduce speckle contrast in multimode fibers.