Polarization-Related Coherence Losses In Phased Optical Arrays

Abstract

Coherent superposition (phasing) in optical arrays can only be achieved when the individual beams maintain their initial coherence throughout the system. Reflections on metallic surfaces cause phase shifts of less than 180 degrees resulting in elliptical polarization which depends both on the plane and angle of incidence. Since the use of relay mirrors is essential in phased optical arrays , these phase shifts have an effect on the mutual coherence of the beams associated with the individual array elements. This paper presents the results of an investigation to estimate polarization effects for optical phased array systems, and the resulting loss of mutual coherence. Of specific interest were cases where sets of relay mirrors define different planes of incidence within the optical array. It was found that the resulting losses in coherence are a strong function of the angle of incidence at each mirror in the relay systems. The resulting implications for the design of optical array systems are discussed. It is also shown how the results can be applied to broadband, partially coherent radiation.