Specklegram in a multiple-mode fiber and its dependence on longitudinal modes of the laser source.
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.
Li
Jun
J
Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai, China. ljsiom@yahoo.com.cn
Cai
Haiwen
H
Geng
Jianxin
J
Qu
Ronghui
R
Fang
Zujie
Z