Small-scale metal-dielectric-metal circular polarization analyzer integrated with semiconductor

Abstract

Detection, analysis, and generation of circular polarized light (CPL) is important for various applications in optics and photonics. However, it typically involves complex and/or multiple optical components forming a barrier for achieving miniaturized integrated photonic systems. Considerable amount of research have been performed to design compact yet efficient structures that can clearly discriminate the two states of circular polarization. Especially, spiral plasmonic lenses (SPLs) are recently suggested as a candidate for miniature circular polarization analyzers. Depending on the input polarization state of CPL, the SPL’s focal shape changes dramatically (spot or annular shape), and thus can be easily discriminated. Although the integrated implementation of the CPL analyzer based on the conventional SPLs has been reported before, the chip-scale polarimeter has an overall area of 70μm×70μm, making miniaturized photonic integration involving CPL still challenging. In this study, we demonstrate a super compact chip-scale CPL analyzer $(footprint of ~ 17 X 17 \mu m^2)$ based on the metal-dielectric-metal (MDM) structure. By placing the submicron-scale semiconductor right below the SPL, we integrate a conventional or double-aperture-based SPL with the semiconductor photoconductor embedded in the MDM structure. According to our numerical simulations, the absorption ratio of two circular polarized states differ by orders of magnitude, indicating that efficient discrimination of two handedness of circular polarization can be achieved even with smaller device size. Moreover, an improved SPL structure with two columns of aperture arrays following a spiral curve can also be incorporated. The enhanced discrimination at the focal spot can be observed due to unidirectional coupling of SPPs, indicating efficient discrimination of two circular polarization states. Actual experimental demonstration of MDM CPL analyzer is performed, and its interference patterns and resonant behavior are also investigated.