Statistical analysis of electromagnetic fields modulated by depolarizers through complex ABCD optical systems

Abstract

A polarization-dependent modulation device, the rough-surfaced retardation plate is proposed as a depolarizer in this thesis. It realizes the decorrelation to the incident field like the traditional diffuser, and scrambles the polarization state simultaneously like a depolarizer. For various surface-roughness plate models, the comprehensive and rigorous analysis of its modulation behaviour is achieved. On the basis of the 2×2 beam coherence-polarization matrix, the statistical properties of the modulated field are examined to reveal the dependence on the surface structure of the rough-surfaced retardation plate. Within the framework of the Complex ABCD matrix theory for general optical propagation systems under the paraxial approximation, the propagated polarization speckle on observation plane over a distance is studied. The analytical expression of its beam coherence-polarization matrix illustrating the change of degree of coherence and polarization on propagation is obtained too. It is approved that the depolarizer provides a flexible and simple method to generate the randomly de-correlated and depolarized speckle with spatially varying polarization states. In addition, the dynamic properties of polarization speckle are analysed to reveal the shape and the motion features of the polarization speckles on the observation plane. At last, a depolarizer consisting of random polarizer cells is introduced to generate polarization speckle as an attempt for a potential method different from the common phase modulation screens.