Designer vector beams maintaining a robust intensity profile on propagation through turbulence

We report experiments on propagation of scalar and vector optical beams through random phase screens mimicking turbulence and show that the intensity profile of the beam containing a C-point polarization singularity shows maximally robust behavior. This observation is explained in terms of the polarization and orbital angular momentum (OAM) diversity in the beam. The $l=0$ and $l=1$ OAM states whose vector superposition leads to the C-point singularity are seen to produce complementary speckle intensity patterns with significant negative correlation on propagation through a random phase screen. This unique property of C-point singularity makes it superior to other inhomogeneous polarization states as demonstrated in our simulations and experiments. The results provide an important generic guideline for designing beams that can maintain superior beam intensity profile on passing through random phase fluctuations and are expected to have a number of applications.

Figure 1

Schematic setup for studying propagation of a polarization singular beam through random phase screen.

Figure 2

Simulation results of beams with different polarization structure and their corresponding far-field intensity on passing through a random phase screen. The intensities for individual RCP and LCP components are also shown. The correlation coefficient between the RCP and LCP intensities is calculated over 50 random phase screen realizations.

Figure 3

Experimental setup for polarization singular beam generation.

Figure 4

(a) Phase of a sample random screen. (b) Plot of $ln(S(f_x,f_y=0))$ and $ln\left(f_x\right)$.

Figure 5

The experimentally observed intensities for beams carrying V-point polarization singularity, namely azimuthal and radial polarization, and beams containing C-point polarization singularities, namely lemon and star, are shown in panels (a) and (b) and panels (c) and (d) respectively. The decomposition of the beams in RCP-LCP basis is also illustrated. Row I shows the Fraunhoffer diffraction intensities for no-phase screen case while row II shows the intensities when the beam has passed through a random phase screen.

Figure 6

Simulated and experimentally observed SNR curves for the total beam and its RCP-LCP components is shown for V-point and C-point beam in panels (a) and (c) and panels (b) and (d) respectively. Panel (e) shows SNR curves for beam containing C-point dipole structure. Panel (f) shows a summary SNR comparison for C-point carrying beams, V-point carrying beams, C-point dipole beam, and homogeneously polarized Gaussian and a charge-1 vortex beam. The parameter $r$ on the $x$ axis denotes the diffraction limited spot size.