Numerical simulation of reduction of scattering clutters in an underwater lidar system by using an axicon as spatial filter

The performance of underwater LIDAR is deteriorated by scattering. Scattering contributes to worsens ranging and even cause the signal light to be buried in “clutter” in turbid water. We proposed an underwater laser ranging model applying an axicon as spatial filter to separate the scattering clutter from the target-reflected signal. This approach exploits the difference in spatial coherence between target-reflected signal and scattered clutter. An axicon was placed in front of the detector to convert the spatially coherent target reflected Gaussian beam to zero-order Bessel beam, while the scattered clutter cannot be converted and only be focused. A pinhole aperture that matched the Bessel beam was used to block the scattering light distributed outside. Therefore, a spatial filter composed of an axicon and a pinhole aperture provides an effective way to partially blocked undesired scattered light without affecting the target-reflected light. The effect of the filter was simulated by Zemax simulation software, which shows that the filter can reduce the scattering clutter received by the detector to suppress scattering, especially in turbid water.