Speckle Reduction in Near-field Image of Multimode Fiber with a Piezoelectric Transducer

Abstract

We propose and experimentally demonstrate an effective method to reduce near-field speckle noise at the output of a 50 μm graded index multimode fiber using a short cylindrical piezoelectric transducer (PZT) vibrating in the radial direction. The fiber was coiled as tightly as possible around the mandrel of the PZT and a periodic stretching effect was caused by the radial oscillations of the actuator. The output of the optical fiber using the He-Ne laser source was intensively observed by a CCD camera. By counting all the pixels corresponding to relative intensity graded into 256 levels in the selected area and by calculating standard deviation and mean value of the intensity, we could measure the speckle contrast and vibration effect quantitatively with reduction ratio of pixels and line profile of the illuminated region. It was clearly observed that the characteristics of the speckle pattern in the vibration-on state were significantly improved over that of the vibration-off state due to time-averaged smoothing.

Energy calibration of integrated path differential absorption lidars

“…For continuous-wave (cw) lasers, many techniques rely on creating some variation in the speckle pattern and averaging it over time. This may be done by vibrating the fiber (e.g., by attaching the fiber to loudspeakers [48], or PZT elements [49] by using rotating diffusors [50] or light pipes [51]. However, most speckle reduction techniques are aiming to reduce the speckle contrast only for slow detectors such as the human eye (∼30 ms).…”

Absolute Distance Metrology Using Diode Pumped Nd:YVO4/KTP Green Laser

“…This high vibration mixes the modes and then the modes cannot be discriminated by the detector or the human eye and consequently the image appears smooth. 14 The signal is sent to the interferometer input to measure the distances (0.5 mm, 10 mm, 50 mm, 80 mm and 100 mm) made by the mirror.…”

Record-High Efficiency Speckle Suppression in Multimode Fibers Using Cascaded Cylindrical Piezoelectric Ceramics

“…So far, a variety of dynamic techniques for mitigating laser speckle have been introduced. These methods include oscillating the projection screen [9], swiftly altering the lens focus [10], rotating a ball-mirror diffuser system [11], applying angle diversity to the beam by quickly vibrating piezoelectric benders [12], or vibrating multimode fibers [13][14][15][16][17][18][19][20][21].…”