Investigation of an image processing method of step-index multimode fiber specklegram and its application on lateral displacement sensing

An image processing algorithm named gray level co-occurrence matrix (GLCM) is introduced to improve the fiber specklegram sensors applied to displacement sensing. The GLCM algorithm is used to analyze the Fourier phase spectra of step-index multimode fiber (MMF) specklegrams. Approximately linear relations between the GLCM features and the lateral displacement between the launching SMF and the MMF have been obtained, which indicate the capability of lateral displacement sensing by GLCM analysis of the specklegrams. Experimental results show that lateral displacement detection can be realized by MMFs with a wide range of parameters and the method exhibits better performance than the conventional NIPC (normalized intensity inner product coefficient) method.