title: Specklegram in a multiple-mode fiber and its dependence on longitudinal modes of the laser source.
abstract: A specklegram in a multimode fiber (MMF) has successfully been used as a sensor for detecting external disturbance. Our experiments showed that the sensitivity in the sensor with a multiple longitudinal-mode laser as its source was much higher than that with a single longitudinal-mode laser. In addition, the near-field pattern observations indicated that the coupling between different transverse modes in the MMF is quite weak. Based on the experimental results, a theoretical model for the speckle formation is proposed, taking a bend-caused phase factor into consideration. It is shown in the theoretical analysis that the interferences between different longitudinal modes make a larger contribution to the specklegram signals.
authors.affiliation: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai, China. ljsiom@yahoo.com.cn
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.forename: Haiwen
authors.initials: H
authors.lastname: Cai
authors.forename: Jianxin
authors.initials: J
authors.lastname: Geng
authors.forename: Ronghui
authors.initials: R
authors.lastname: Qu
authors.forename: Zujie
authors.initials: Z
authors.lastname: Fang