Phase-disturbing speckle-suppressing by contact fiber scrambler
To measure the focal ratio degradation of astronomical fibers,we use laser as the light source which can do with bringing the light to a focal point and we can control the injection position.The laser has a high coherency and there are a number of modes in the large-core fiber.Consequently,the output spot will be a speckle.The presence of speckle makes the energy distribution of optical field uneven,so that its hard to calculate the spot radius.To reduce the influence of the speckle,the contact-type mode scrambler is developed in our research.Its used to make the fiber vibrate at a suitable frequency of 0-80 Hz,and the vibration amplitude is 0.5 cm.The phase of different propagation modes is changed randomly in order to vibrate the modes and reduce the influence of the speckle.Different vibration result is observed by setting different vibration frequency and different CCD exposure time.The estimate of the vibration result can be given by using the method of contrast and Fourier Transform.Three different core diameters (10μm,125μm,320μm) are contrast with each other for convenience.The result shows that the vibration frequency between 65-70 Hz is best,and the optimum exposure time is 30 ms for all three diameters.The vibration of fiber using mode scrambler can reduce the speckle obviously under coherent illumination.
large diameter fiber: laser speckle mode disturbing
Wang Jing Yan Yunxiang Wang Henan Tian He Liu Yongjun Zhang Xiaowei Sun Weimin
Key Lab of In-fiber Integrated Optics, Ministry Education of China, Harbin Engineering University, Harbin 150001, P.R. China
国际会议
秦皇岛
英文
1485-1488
2015-09-18（万方平台首次上网日期，不代表论文的发表时间）