Quality Factor Assessment of a Laser speckle pattern for Stress sensing in a Statistical Modal Sensors

The most commonly used Q.Fs (quality factors) such as MIG (mean intensity gradient), MIOSD (mean intensity of the second derivative) etc. are not useful quality assessment metrics for laser speckle due to uniform intensity distribution of individual speckles in a laser speckle pattern. For this reason, MFFI (Multi-Factor Fusion Index) was introduced which incorporates both the gray-level intensity distribution and morphological information of speckles. Q.Fs assessment was intended for DIC (digital image correlation) purpose but have never been looked into, for perturbation sensing (e.g. Stress etc.) purposes. In this paper, the MFFI for different angles of polarization and the optimum value of this quality assessment metric for particular angle was considered and has been demonstrated for stress sensing by applying varying loads on a particular region along the length of a fibre by calculating statistical “normalized” radial first and second moments for specified region of interests (ROIs).