Optical polarization

About: Optical polarization is a research topic. Over the lifetime, 13992 publications have been published within this topic receiving 244284 citations.

Robust Multilevel Coherent Optical Systems With Linear Processing at the Receiver

Abstract: This paper investigates optical coherent systems based on polarization multiplexing and high-order modulations such as phase-shift keying (PSK) signals and quadrature amplitude modulations (QAM). It is shown that a simple linear receiver processing is sufficient to perfectly demultiplex the two transmitted streams and to perfectly compensate for group velocity dispersion (GVD) and polarization mode dispersion (PMD). In addition, in the presence of a strong phase noise of the lasers at the transmitter and receiver, a symbol-by-symbol detector with decision feedback is able to considerably improve the receiver robustness with a limited complexity increase. We will also discuss the channel estimation and the receiver adaptivity to time-varying channel conditions as well as the problem of the frequency acquisition and tracking. Finally, a new two-dimensional (polarization/time) differential encoding rule is proposed to overcome a polarization-ambiguity problem. In the numerical results, the receiver performance will be assessed versus the receiver complexity.

The Australia Telescope 20 GHz (AT20G) Survey: analysis of the extragalactic source sample

Abstract: The Australia Telescope 20 GHz (AT20G) survey is a blind survey of the whole Southern sky at 20 GHz with follow-up observations at 4.8, 8.6 and 20 GHz carried out with the Australia Telescope Compact Array (ATCA) from 2004 to 2008. In this paper we present an analysis of radio spectral properties in total intensity and polarization, sizes, optical identifications and redshifts of the sample of the 5808 extragalactic sources in the survey catalogue of confirmed sources over 6.1 sr in the Southern sky (i.e. the whole Southern sky excluding the strip at Galactic latitude |b| < $1\buildrel{\circ}\over{.}5$ ).The sample has a flux density limit of 40 mJy. Completeness has been measured as a function of scan region and flux density. Averaging over the whole survey area the follow-up survey is 78 per cent complete above 50 mJy and 93 per cent complete above 100 mJy. 3332 sources with declination δ < −15° have good quality almost simultaneous observations at 4.8, 8.6 and 20 GHz. The spectral analysis shows that the sample is dominated by flat-spectrum sources, with 69 per cent having spectral index α 20 8.6 > − 0.5 (S∝ν α ). The fraction of flat-spectrum sources decreases from 81 per cent for S 20 GHz > 500 mJy to 60 per cent for S 20 GHz < 100 mJy. There is also a clear spectral steepening at higher frequencies with the median α decreasing from −0.16 between 4.8 and 8.6 GHz to −0.28 between 8.6 and 20 GHz.Simultaneous observations in polarization are available for all the sources at all the frequencies. 768 sources have a good-quality detection of polarized flux density at 20 GHz; 467 of them were also detected in polarization at 4.8 and/or at 8.6 GHz so that it has been possible to compare the spectral behaviour in total intensity and polarization. We have found that the polarized fraction increases slightly with frequency and decreases with flux density. The spectral indices in total intensity and in polarization are, on average, close to each other, but we also found several sources for which the spectral shape of the polarized emission is substantially different from the spectral shape in total intensity. The correlation between the spectral indices in total intensity and in polarization is weaker for flat-spectrum sources.Cross-matches and comparisons have been made with other catalogues at lower radio frequencies, and in the optical, X-ray and γ-ray bands. Redshift estimates are available for 825 sources.

Photoinduced anisotropy in rigid dye solutions for transient polarization holography

Abstract: The characteristics of rigid solutions of organic dyes suitable for holographic recording-fluorescein/orthoboric acid, methyl red/polymethylmetacrylate, and methyl orange/polyvinylalcohol-are investigated. All of the three systems allow real-time recording and do not exhibit fatigue up to more than 104cycles of recording erasure. The system fluorescein/orthoboric acid possesses a faster response time than the other two systems-around 0.1 s. The phase character of the recording in the system methyl orange/polyvinylalcohol explains the high diffraction efficiency-up to 35 percent-in polarization holographic recording. New experimental results on the kinetics of the photoinduced anisotropy are presented and the mechanisms which could possibly speed up the processes, repeated periodically, are discussed.

Polarimetric fiber laser sensors

Abstract: Apparatus for measuring a physical quantity such as pressure, temperature, strain etc., by using a beat frequency of a longitudinal mode, a transverse mode or two polarization modes of the optical fiber laser. In the rare-earth optical fiber laser as a resonator, there are two different polarization modes normal to each other. Since the optical path lengths of the optical fiber laser for the two polarization modes are different, longitudinal mode frequencies of each polarization mode are different depending on the birefringence of resonator which is varied as an external physical quantity such as pressure, temperature, strain etc. Due to the variation in the birefringence of the resonator, the longitudinal mode frequency difference between two polarization modes becomes varied. This variation is linearly proportional to the physical quantity externally applied. The difference in longitudinal mode frequency between polarization modes can be measured from a beat signal of the polarization modes. Accordingly, it is possible to measure the physical quantity by measuring the variation in polarization mode beat frequency.