Measuring optical vortices in a speckle pattern by means of dual shearing-type Sagnac interferometers

Measuring the positions of the singularities of the optical vortices is an essential part in the research of speckles and adaptive optics. The measurement accuracy is restricted by the performance of optical devices and the properties of optical vortices, such as density and size. In order to achieve highly accuracy and wide range of application, the dual shearing-type Sagnac interferometers were proposed using two shearing plates to adjust the precision of optical vortices measurement. The shearing displacements are able to balance the measuring precision and the value of the intensity ratio point to provide optimal measurement performance. And the optimal shearing displacement is about a tenth of the speckle size. This method realizes measuring the positions of the singularities of the optical vortices in a speckle pattern in one measurement. And it is useful for the observation of optical vortices with different sizes and densities in a speckle pattern, especially for the high density condition.