Strong correlations between incoherent vortices

Measuring the topological charge of coherence vortices through the geometry of the far-field cross-correlation function

Determination of orbital angular momentum of optical vortex beams has attracted the attention of many researchers over the last few years. For some applications, it is convenient to use a partially coherent vortex beam because of its robustness. In this work, we developed a method to measure the topological charge of a partially coherent vortex beam. Our method relies simply in the measurement of the minimum radius of a zero contour of the modulus of the cross-correlation function and in the measurement of the full width at half maximum of its central spot.

Sorting of spatially incoherent optical vortex modes

Coherent optical vortices have promising applications in quantum and classical optical communication. They add new degrees of freedom to code information. In this context, to implement a tool enabling sorting of spatially multiplexed vortex states is fundamental. By other hand, spatially incoherent vortices can be more robust in propagation through noise media, such as turbulent atmosphere or obstacles that block part of the light. Therefore, in this work we propose directly applying a high-resolution sorting scheme to spatially incoherent vortex states.

Discrimination of incoherent vortex states of light

Coherence vortex (CV) states provide a new way for optical manipulation and communication. As a promising option for increasing the data-transmission capacity, CV multiplexing warrants investigation. However, few studies have focused on discriminating and sorting CV states with different topological charges. In this work, we examine the cross-spectral density (CSD) of a CV state embedded in an incoherent light field and so-called incoherent vortex (ICV). Given a multiplexed ICV, we propose a method to recognize the constituting single ICVs therein. Our analytical results, which are derived according to the coherence theory and the paraxial propagation law and are given in analytical forms, show that the CSD can reveal the topological charge spectrum of a multiplexed incoherent Laguerre-Gaussian mode. This proposal can be used for free-space communication and remote sensing where light fields with low coherence are preferable to completely coherent beams.

Topological structures in vector speckle fields

We here demonstrate on both theoretical and experimental bases a method to recover the topological structure of a monochromatic optical field that has suffered diffuse transmission. This method consists of two steps: first, a linearly polarized sample beam is mixed with a coaxial Gaussian beam in orthogonal polarization states resulting in a Poincaré beam; second, a polarization-related spatial correlation function is considered and measured for the overall speckle field arising by optical diffusion. The singularities of the sample beam turn out to be imaged into the correlation function of the vector speckle field.

Robustness of a coherence vortex

We study, experimentally and theoretically, the behavior of a coherence vortex after its transmission through obstacles. Notably, we find that such a vortex survives and preserves its effective topological charge. Despite suffering changes on the modulus of the coherence function, these changes disappear during propagation.

Characterizing coherence vortices through geometry

We produce coherence vortices experimentally and numerically due to the orbital angular momentum of light beams and study the dependence of their bright ring area and dark region on their different orders. This is a linear dependence with a slope proportional to the bright ring area or dark area. We show that it is possible to estimate any order of coherence vortices, including fractional orders, just by calculating the bright ring area or dark area of the vortices for some specific parameters of the incident beam.