Violation of Bell's inequality for phase singular beams
  We have considered optical beams with phase singularity and experimentally verified that these beams, although being classical, have properties of two mode entanglement in quantum states. We have observed the violation of Bell's inequality for continuous variables using the Wigner distribution function (WDF) proposed by Chowdhury et al. [Phys. Rev. A \textbf{88}, 013830 (2013)]. Our experiment establishes a new form of Bell's inequality in terms of the WDF which can be used for classical as well as quantum systems. 
Shashi Prabhakar, Salla Gangi Reddy, A. Aadhi, Chithrabhanu   Perumangatt., G. K. Samanta, and R. P. Singh
quant-ph physics.optics