Optical retardance measurement with constant sensitivity using vector vortex beams

The measurement of optical retardance is the cornerstone of important imaging and sensing systems, such as differential interference contrast (DIC) microscopy and chiral analysis. Conventional approaches employ Gaussian beams and infer the retardance from polarization changes, resulting in phase-estimation sensitivities that depend on the unknown phase. In a proof-of-principle experiment, we demonstrate here a type of optical retardance detector. It makes use of a vector vortex beam, a type of structured light endowed with optical modes that carry opposite orbital angular momentum (OAM). Using quantum estimation theory tools, we demonstrate that the sensitivity of phase estimation is independent of the value of the unknown phase and can be even better than the conventional approach. We experimentally validate the proposed scheme, demonstrating the potential of structured light for robust and uniform optical retardance sensing.