Speckle reduction in multimode fiber with a piezoelectric transducer in radial vibration for fiber laser marking and display applications

We propose and experimentally demonstrate an effective method to reduce far-field speckle noise in multimode fiber with a short cylindrical piezoelectric transducer (PZT) vibrating in radial direction. In this study, the fiber was coiled as tightly as possible around the mandrel of the PZT and periodic stretching effect was caused by the radial oscillations of the actuator. This technique can be adapted at a high modulation frequency, so the speckle patterns can be time-averaged. The output of the optical fiber was intensively observed by a CCD camera. By counting all the pixels corresponding to relative intensity graded 256 levels in selected area and by calculating the mean value and standard deviation of the intensity, we can measure the speckle contrast and vibration effect in quantitative measurands. It was clearly observed that the characteristics of the speckle pattern in vibration-ON-state were significantly reduced than that of vibration-OFF-state by comparing the proposed measurands as well as direct CCD images. We expect that the proposed speckle reduction technology would find viable applications in realization of fiber laser, laser marking, optical trapping and projection display systems.