Showing papers on "Optical polarization published in 1990"

Artificially soft and hard surfaces in electromagnetics

Abstract: A transversely corrugated surface as used in corrugated horn antennas represents a soft boundary. A hard boundary is made by using longitudinal corrugations filled with dielectric material. The concept of soft and hard surfaces is treated in detail, considering different geometries. It is shown that both the hard and soft boundaries have the advantage of a polarization-independent reflection coefficient for geometrical optics ray fields, so that a circularly polarized wave is circularly polarized in the same sense after reflection. The hard boundary can be used to obtain strong radiation fields along a surface for any polarization, whereas the soft boundary makes the fields radiated along the surface zero. >

Generating radially polarized beams interferometrically.

Abstract: Two interferometric techniques for converting a linearly polarized laser beam into a radially polarized beam with uniform azimuthal intensity are described. The techniques are based on the linear combination of orthogonally polarized beams, which have tailored intensity and phase profiles. Linearly polarized beams with intensity profiles tailored using a modified laser or an apodization filter are combined in separate experiments to produce radially polarized light. A beam with an extinction ratio of −21.7 dB and azimuthal intensity variations of less than ±12% is produced using the modified laser output. The second technique uses circularly polarized light and a unique spiral phase delay plate to produce the required phase profile. When focused, a radially polarized beam has a net longitudinal field useful for particle acceleration and, perhaps, other unique applications.

Polarization control for coherent communications

Abstract: Two practical implementations of endless polarization control are described. The first approach uses polarization maintaining fiber transducer, while the second uses an integrated optic lithium niobate device. In order to characterize the lithium niobate device in detail, a technique for analyzing the birefringence as a function of the applied voltages was developed, and the measured performance of the devices is presented. Fractional-wave controllers for both static and endless control applications are considered, and design rules for maximum wavelength-window and minimum loss fiber-loop polarization adjusters are given. Endless control using various configurations of the three types of transducers is discussed, and it is shown how apparently different schemes are closely related. >

Determination of the electrooptic coefficient of a poled polymer film.

Abstract: The use of the rate of change of the relative phase shift of p- and s-polarized light with voltage to determine the electrooptic coefficient of a poled polymer film is discussed.

Optical polarization maps of star-forming regions in Perseus, Taurus, and Ophiuchus

Abstract: New optical linear polarization maps are presented of the star-forming regions near L1506 in Taurus, L1755 in Ophiuchus, and the complex of dark cloud which extends from L1448 in B5 in Perseus. The former two show a well-defined peak magnetic field direction in the plane of the sky with a finite dispersion about that peak which is smaller than would be expected for a random distribution of field distributions. The dispersion in the position angle of filamentary clouds within these complexes implies that clouds which appear elongated on the plane of the sky are not all associated with a pattern of polarization vectors particularly parallel or perpendicular to their geometry. Instead, clouds tend to be oriented at the angle formed by their axis and the mean direction of the local large-scale field. For the dark cloud complex, a bimodal distribution of the polarization vector angle is taken to result from at least two distributions of gas along the line of sight which appear as a complex in projection. 55 refs.

Wavelength-tunable single-frequency and single-polarisation Er-doped fibre ring-laser with 1.4 kHz linewidth

Abstract: A narrow linewidth of 1.4 kHz with single frequency operation is demonstrated in an Er-doped fibre ring-laser. A stable lasing spectrum can be achieved using a single polarisation fibre-cavity. An optical bandpass filter incorporated in the ring-cavity makes the lasing wavelength tunable, and a 2.8 nm tuning range is demonstrated.

The optical polarization properties of quasars

Abstract: Optical polarimetry is presented for 163 radio-selected quasars, including a complete sample of 90 sources stronger than 2 Jy at 5 GHz. Synchrotron components are detected in over 30 percent of these flat spectrum quasars, with an optical polarization threshold of p greater than 3 percent. The fraction of polarized quasars is a strong function of the compactness of the radio emission, as measured on VLBI scales. Including the duty cycle correction, essentially every quasar with S(core) greater than S(ext) at radio wavelengths has a prominent blazar component at optical wavelengths. Virtually all of the radio sources with weak emission lines (or BL Lac objects) are highly polarized. Optical and radio polarization are not correlated, and there is no difference in the alpha(ro) distributions of high- and low-polarization quasars, or sources with strong and weak emission lines. Redshift information is incomplete, but BL Lac objects appear to have lower redshifts than strong-lined quasars. 76 refs.

Strongly directional emission from AlGaAs/GaAs light emitting diodes

Abstract: We show for the first time that strongly directional emission of defined polarization can be achieved from conventional AlGaAs/GaAs double heterostructure surface emitting LEDs via coupling to surface plasmons. By microstructuring the surface, we have fabricated LEDs with a beam divergence of less than 40 and a drastically increased quantum efficiency. We prove that surface plasmon excitation aid emission mechanism has the potential to overcome basic external quantum efficiency losses and to improve the performance of LEDs.

An Optical Polarization Survey of the Palomar-Green Bright Quasar Sample

Abstract: Les observations polarimetriques optiques d'un ensemble, complet jusqu'a la magnitude B = 16.2, de 114 quasars du Palomar-Green Bright Quasar Survey sont presentees. La distribution et la variabilite de la polarisation sont analysees.

Surface plasmon polaritons in thin metal films and their role in fiber optic polarizing devices

Abstract: The polarization-selective evanescent field coupling of an optical wave in a 1.3- mu m, fiber to surface, plasmon polaritons supported by a thin aluminium film was investigated theoretically and experimentally. Good agreement was observed between the theoretically predicted conditions for efficient coupling and the experimentally determined conditions for high TM/TE extinction ratio of the optical field. The use of silver and chrome in place of aluminum was investigated experimentally at 1.3 mu m, and 0.63- mu m devices using aluminium were also studied. The results led to the realization of readily manufacturable, high-extinction-ratio (>50 dB) low-loss ( >

New Liquid Crystal Polarized Color Projection Principle

Abstract: A wide-aperture, color projection principle is presented whose functional parts, namely, polarizers, bandpass filters and electrooptical modulators, consist entirely of liquid crystal elements. The concept ideally enables one hundred percent input-output light conversion. The angular and wavelength dependences of planar cholesteric layers and layer combinations are shown. From them optical filter/polarizer elements result with adjustable center wavelengths and tunable bandwidths. The filters comprise novel cholesteric liquid crystals with a temperature dependence of their center wavelengths as low as 0.06 nm/°C. New, circularly polarized operating modes for twisted nematic (TN-LCDs) and other field effects exhibit not only low threshold voltages, but also voltage-transmission (reflection) characteristics whose slope is adjustable over a wide range. Thus, the new modes are applicable in high-information-content, actively addressed television TN-LCDs requiring gray scale, as well as in displays requiring large time multiplexing rates approaching those of supertwist LCDs.

Quantum beats of light hole and heavy hole excitons in quantum wells

Abstract: We report the first observation of quantum beats due to the interference of the polarization decay of heavy hole and light hole excitons in semiconductor quantum wells.

Polarization properties of substrate-mode holographic interconnects

Abstract: The polarization properties of cascaded substrate-mode holographic optical elements are analyzed and demonstrated The design criteria for polarization selective and nonselective elements are given and verified with experimental volume holograms formed in dichromated gelatin emulsions Using the experimental grating parameters, it is estimated that a reconfigurable optical bus with eight nodes can be made Improved control of hologram construction parameters can increase this to more than 500 nodes Use of this device with a reconfigurable interchange coupler and a multistage optical bus is also examined

Scattering from slightly rough random surfaces: a detailed study on the validity of the small perturbation method

Abstract: A perturbative expression up to fourth order in k0σ (k0 = 2π/λ; σ being the rms of the surface height and λ the wavelength) has been obtained for the mean diffuse intensity from a one-dimensional random rough surface that has normal statistics and a Gaussian correlation function for s polarization. For p polarization it is not possible to obtain this expression because of the existence of certain resonances; thus the calculations must be restricted to second order in k0σ. Perturbative calculations were derived from the Rayleigh hypothesis and also from the extinction theorem. The expression for the diffuse component of the mean scattered intensity was the same for p waves in both cases up to second order in k0σ. For s waves the equality was obtained up to fourth order in k0σ. Comparisons with exact numerical results and with those obtained by using the Kirchhoff approximation are made. This comparison allows us to establish assessments on the validity of the perturbative solution and to obtain some new interesting facts. In addition, the behavior of the diffuse halo at small σ/λ as a function of the correlation length T, the angle of incidence θ0, and the polarization is discussed. The validity of the Rayleigh hypothesis is also studied.

Analysis of input-polarization-induced phase noise in interferometric fiber-optic sensors and its reduction using polarization scrambling

Abstract: The dependence of the phase shift of an interferometric fiber sensor on the input state of polarization is analyzed, and it is shown that fluctuations in the input polarization to a fiber interferometer can lead to the generation of excess phase noise. The relationship between this effect and the variation in visibility with input polarization is described and theoretically confirmed. The use of depolarized source light to eliminate input-polarization-induced excess phase noise is theoretically and experimentally demonstrated. >

Polarization effects of seawater and underwater targets.

Abstract: In underwater optical imaging using pulsed laser radiation the vector nature of the electromagnetic wave can be used to produce polarization contrast. We have analyzed different polarimetric transformations of light pulses through seawater on immersed targets and defined optimum conditions for using polarization parameters.

Ray tracing with polarization parameters

Abstract: Incorporating polarization parameters into the lighting model can enhance the physical realism of images rendered with a ray tracer. Polarization effects can be important in certain scenes, and the difference in rendering even simple scenes with and without proper treatment of polarization can be striking. All light waves possess a state of polarization, which changes almost every time light reflects off a material surface. A single reflection partially polarizes and may even completely polarize previously unpolarized light. Polarization influences the rendering of a scene because the reflected radiant intensity depends largely on the incident light waves's polarization state. E. Wolf's (1959) coherence matrix formalism of polarization has been incorporated into the Torrance-Sparrow reflectance model. This combination allows elegant quantitative derivations of the altered polarization state of light upon reflection in a ray tracer. Comparisons of identical scenes rendered with a conventional ray tracer and the ray tracer presented incorporating a polarization model show that the present method renders specular interobject reflections more accurately with respect to reflected radiance and color. >

Optical interaction between a dielectric tip and a nanometric lattice: implications for near-field microscopy

Abstract: We make a theoretical analysis of the interaction of the field transmitted by a subwavelength tip and a two-dimensional subwavelength lattice. Such a model provides a new insight into the resolution achievable by near-field microscopy and confirms the experimental results obtained recently. In the present model the probe, characterized by its electric dipolar susceptibility, is assumed to be locally spherical, and the representation of the sample is based on a discrete description of the matter. This permits separation of the electric field detected by the probe after reflection into two different parts that describe both the continuum character and the corrugation of the surface. Numerical results performed on a two-dimensional lattice are similar to those obtained by atomic force microscopy and exhibit specific behavior such as a strong dependence on the polarization of the incident field.

Multilevel coherent optical system based on Stokes parameters modulation

Abstract: A multilevel transmission system that allows efficient exploitation of a single-channel bandwidth in coherent optical communication systems is proposed. It is based on Stokes parameter modulation and a decision on the Poincare sphere. The block scheme of the transmitter, which is able to provide a generic output state of polarization (SOP) starting from a linearly polarized optical field, is shown and described. The propagation along the fiber is described in order to derive the expression of the optical field at the receiver input. The spectral characteristics of the transmitted and the received optical signals are analyzed. >

Multiprocessor design using polarization-encoded optical shadow-casting.

Abstract: An efficient algorithm for designing a multiprocessor logic unit using a polarization-encoded optical shadow casting system is presented. Both efficient minterm pairing and associative memory mapping with dual addresses are exploited for the design For illustration, the algorithm is used to design a parallel adder–subtracter unit.

Diffraction image formation in optical systems with polarization aberrations. I - Formulation and example

Abstract: This paper is the first in a series that will examine image formation in optical systems with polarization aberrations. The present paper derives the point-spread function (PSF) and the optical transfer function for optical systems with polarization aberration and explores how image formation depends on the coherence and polarization state of the source. It is shown that the scalar PSF of Fourier optics can be generalized in the presence of polarization aberration to a 4 x 4 point-spread matrix (PSM) in Mueller matrix notation. A similar 4 x 4 optical transfer matrix (OTM) is shown to be an appropriate generalization of the optical transfer function. The PSM and the OTM are associated with the optical system and are independent of the incident polarization state but dependent on the coherence of the illumination. Since an optical system with polarization aberrations will have a different PSF and optical transfer function for different incident polarization states, the PSM and the OTM act as filters with regard to the incident polarization state. Example calculations are performed for a circularly retarding lens.

An optical and near-infrared polarization survey of Seyfert and broad-line radio galaxies. I, Statistical properties

Abstract: Copyright Royal Astronomical Society. [Full text of this article is not available in the UHRA]

Soliton stability in birefringent optical fibers: analytical approach

Abstract: Propagation of short pulses in birefringent optical fibers is considered in the framework of two coupled nonlinear Schrodinger equations. When the amplitudes of the pulses belonging to different polarizations are equal, we propose a simple analytical explanation of the amplitude threshold for the capture of two partial pulses into a coupled two-component pulse. Our approach is based on a soliton phenomenology. The analytical dependence of the amplitude threshold on linear birefringence is in good agreement with numerical results of Menyuk [ J. Opt. Soc. Am. B5, 392 ( 1988)]. The influence of small dissipative losses on the effect is also discussed.

Large Aperture Polarized Light Source and Novel Liquid Crystal Display Operating Modes

Abstract: A wide aperture liquid crystal polarized light source (LC-PLS) is presented which converts unpolarized-into circular- and/or linearly polarized light with an efficiency better than 80% Moreover, new operating modes for electro-optical field-effects on which liquid crystal displays (LCDs) are based are shown to increase the transmission of twisted nematic (TN)-LCDs by a factor of two Besides, a 25% shift of the TN-LCD transmission-voltage characteristics towards lower voltages is achieved One of the new, reflective LCD-operating modes is shown to avoid light absorption by thin film transistor structures in actively addressed LCD-projection systems Within the bandpass region of the cholesteric liquid crystal filters the combination of LC-PLS with appropriate LCD-operating mode is shown to increase the transmission of LCD-projection systems three to five times compared with conventional LCD-projectors

High‐frequency polarization self‐modulation and chaotic phenomena in external cavity semiconductor lasers

Abstract: Optical pulses with repetition rates up to several hundred MHz have been generated through a polarization self‐modulation effect in an external cavity semiconductor laser modified by the insertion of a quarter‐wave retardation plate. These pulses are generated without the need for any high‐speed electronics. At higher bias, period doubling and chaotic phenomena are also observed.

Graded-index plastic optical fiber composed of methyl methacrylate and vinyl phenylacetate copolymers

Abstract: Graded-index plastic optical fiber whose transmission attenuation is 143 dB/km at 651-nm wavelength was fabricated by heat-drawing the corresponding GI preform rod. This rod is prepared by the interfacial-gel copolymerization technique of methyl methacrylate (MMA) and vinyl phenylacetate (VPAc). The total scattering loss of the GI preform rod is ~60 dB/km at 633 nm. The graded-index profiles of the optical fibers are almost the same as those of the corresponding preforms with cladding sheaths. The index distributions of their core regions are quadratic against the distance from the center axis. The numerical aperture estimated from the index difference is ~0.20.

Polarization control for coherent fiber-optic systems using nematic liquid crystals

Abstract: One of the obstacles to coherent fiber-optic communications is the unpredictable polarization drift which necessitates the use of an active polarization controlling system to match the polarizations of the signal and local oscillator. The polarization match must be maintained during the reset of any of the finite range components to prevent loss of data. A novel and practical system which uses three liquid-crystal devices for the polarization matching process is presented, and the required reset control algorithm and its derivation are described in detail. >

Analysis of spatial pseudodepolarizers in imaging systems

Abstract: The objective of a number of optical instruments is to measure the intensity accurately without bias as to the incident polarization state. One method to overcome polarization bias in optical systems is the insertion of a spatial pseudodepolarizer. Both the degree of depolarization and image degradation (from the polarization aberrations of the pseudodepolarizer) are analyzed for two depolarizer designs: (1) the Cornu pseudodepolarizer, effective for linearly polarized light, and (2) the dual Babinet compensator pseudodepolarizer, effective for all incident polarization states. The image analysis uses a matrix formalism to describe the polarization dependence of the diffraction patterns and optical transfer function.