Effects of the speckle size on non-holographic fiber specklegram sensors

• Fiber Specklegram Sensors for measuring high frequency mechanical perturbations are presented.
• Performance of high frequency mechanical detection systems is improved by the control of the fiber speckle size.
• As the grain size of the fiber speckle increases the reproducibility of the sensor increases too.

In this work, a technique to improve the dynamical behavior of a non holographic fiber specklegram sensor for measuring high frequency mechanical perturbations is experimentally demonstrated. In these arrangements, the speckle pattern produced by a multimode optical fiber is coupled to an optical fiber of low numerical aperture, which produces a filtering effect that can be used as optical transduction mechanism. In our proposal, the influence of the speckle size on the sensor performance is evaluated by changes in the numerical aperture of the multimode fiber. A strong effect of the near field fiber speckle size on the reproducibility of the mechanical perturbation is found. The behavior of the reproducibility is evaluated by the calculation of the mean of the variance and the correlation between the mechanical and optical normalized signals.