Circular polarization

About: Circular polarization is a research topic. Over the lifetime, 15201 publications have been published within this topic receiving 234418 citations.

Resolving Light Handedness with an on-Chip Silicon Microdisk

Abstract: The efficient manipulation of circularly polarized light with the proper handedness is key in many photonic applications. Chiral structures are capable of distinguishing photon handedness, but while photons with the right polarization are captured, those of opposite handedness are rejected. In this work, we demonstrate a planar photonic nanostructure with no chirality consisting of a silicon microdisk coupled to two waveguides. The device distinguishes the handedness of an incoming circularly polarized light beam by driving photons with opposite spins toward different waveguides. Experimental results are in close agreement with numerical results, which predict extinction ratios over 18 dB in a 20 nm bandwidth. Owing to reciprocity, the device can also emit right or left circular polarization depending on the chosen feeding waveguide. Although implemented here on a CMOS-compatible platform working at telecom wavelengths, the fundamental approach is general and can be extended to any frequency regime and te...

The Spectrum and Variability of Circular Polarization in Sagittarius A* from 1.4 to 15 GHz

Abstract: We report here multiepoch, multifrequency observations of the circular polarization in Sagittarius A*, the compact radio source in the Galactic center. Data taken from the Very Large Array (VLA) archive indicate that the fractional circular polarization at 4.8 GHz was -0.31%, with an rms scatter of 0.13%, from 1981 to 1998, in spite of a factor of 2 change in the total intensity. The sign remained negative over the entire time range, indicating a stable magnetic field polarity. In the summer of 1999, we obtained 13 epochs of VLA A-configuration observations at 1.4, 4.8, 8.4, and 15 GHz. These observations employ a new technique that produces an error of 0.05% at 1.4, 4.8, and 8.4 GHz and 0.1% at 14.9 GHz. In 1999 May, September, and October, we obtained 11 epochs of Australia Telescope Compact Array (ATCA) observations at 4.8 and 8.5 GHz. In all three data sets, we find no evidence of linear polarization greater than 0.1%, in spite of strong circular polarization detections. Both VLA and ATCA data sets support three conclusions regarding the fractional circular polarization: (1) the average spectrum is inverted, with a spectral index α ≈ 0.5 ± 0.2; (2) the degree of variability is roughly constant on timescales of days to years; and (3) the degree of variability increases with frequency. We also observed that the largest increase in fractional circular polarization was coincident with the brightest flare in total intensity. Significant variability in the total intensity and fractional circular polarization on a timescale of 1 hr was observed during this flare, indicating an upper limit to the intrinsic size during outburst of 70 AU at 15 GHz. The fractional circular polarization at 15 GHz reached -1.1%, and the spectral index was strongly inverted (α ~ 1.5) during this flare. We tentatively conclude that the spectrum has two components that match the high- and low-frequency total intensity components.

Multi-Frequency, Linear and Circular Polarized, Metamaterial-Inspired, Near-Field Resonant Parasitic Antennas

Abstract: Several metamaterial-inspired, electrically small, near-field resonant parasitic antennas are presented. Both electric and magnetic couplings to the parasitic are compared and contrasted. The electric-coupled versions are shown to be more efficient and to have more bandwidth. The evolution of circular polarized designs from their linear counterparts by introducing multiple parasitics having different resonant frequencies is demonstrated. Single L1 and dual band L1/L2 GPS systems are emphasized for practical illustrations of the resulting performance characteristics. Preliminary experimental results for a dual band, circularly polarized GPS L1/L2 antenna are provided and underscore several practical aspects of these designs.

Spatially engineered polarization states and optical vortices in uniaxial crystals

Abstract: We describe how the propagation of light through uniaxial crystals can be used as a versatile tool towards the spatial engineering of polarization and phase, thereby providing an all-optical technique for vectorial and scalar singular beam shaping in optics. Besides the prominent role played by the linear birefringence, the influence of circular birefringence (the optical activity) is discussed as well and both the monochromatic and polychromatic singular beam shaping strategies are addressed. Under cylindrically symmetric light-matter interaction, the radially, azimuthally, and spirally polarized eigen-modes for the light field are revealed to be of a fundamental interest to describe the physical mechanisms at work when dealing with scalar and vectorial optical singularities. In addition, we also report on nontrivial effects arising from cylindrical symmetry breaking, e.g. tilting the incident beam with respect to the crystal optical axis.

Photon Vector Polarization and Coherence Parameters in an Electron-Photon Coincidence Experiment on Helium

Abstract: We present linear and circular polarization measurements of 31P-- 21S (501.6 nm) photons detected in delayed coincidence with electrons inelastically scattered from the 31P level of helium. Vector polarization and coherence parameters of the coincident radiation provide direct experimental evidence of the coherent nature of the excitation process. Atomic orientation is obtained directly from the circular polarization measurements. Analysis of the data also yields lambda and chi parameters for 31P excitations, which are compared with previous data and theory.