Showing papers on "Optical polarization published in 1989"

Solar radiative transfer in cirrus clouds. I - Single-scattering and optical properties of hexagonal ice crystals. II - Theory and computations of multiple scattering in an anisotropic medium

Abstract: The light scattering and absorption programs of Cai and Liou (1982) and Takano and Jaweera (1985) are extended to include hexagonal ice crystals randomly and horizontally oriented in space. The scattering and polarization results for the ice crystals are calculated. The results are compared with measurement data. The single-scattering properties for horizontally oriented columns and plates are presented and used to explain halos and arcs observed in the atmopshere. In the second section, the theory and computations for multiple scattering in cirrus clouds containing oriented ice crystals are presented. The radiative transfer in clouds composed of horizontally oriented ice crystals is formulated. Also, reflected and transmitted intensities, planetary albedo, and polarization in multiple scattering by ice crystals are discussed.

Polarization memory of multiply scattered light.

Abstract: Light backscattered from an optically dense random medium is shown to exhibit a pronounced polarization dependence. An unexpected memory of the incident circular polarization of multiply scattering light arises because the wave's helicity is randomized less rapidly than is its direction. A simple model is developed to account for the observed polarization dependence of the intensity and temporal correlations of the intensity fluctuations of backscattered light.

Polarization analysis of optical systems

Abstract: For most optical systems it is typically assumed that the transmitted wavefront has uniform for Gaussian) amplitude and constant polarization state. This is the default assumption of geometrical optics. This paper considers methods suitable for analyzing systems for which this assumption is not valid. Such methods of polarization analysis include polarization ray tracing and polarization aberration theory. Definitions of the basic classes of polarization phenomena and a review of the Jones calculus are included to form a basis for the discussion.

Adaptive polarisation diversity receiver configuration for coherent optical fibre communications

Abstract: We describe an implementation of the polarisation diversity detection technique for coherent heterodyne communications which maintains the total IF amplitude at a constant level, irrespective of fluctuations in the state of polarisation of either the signal or local oscillator optical fields at the output polarisation beam-splitter.

The FN method for radiative transfer models that include polarization effects

Abstract: The F N method is used to construct an accurate solution for all components ( m ⩾ 0) in a Fourier representation of the Stokes vector basic to the scattering of polarized light. Computational aspects of the solution are reported in detail, and the established solution is used to obtain numerical results, accurate to six significant figures, for the four Stokes parameters for each of two considered test problems.

Integrated optical, acoustically tunable wavelength filter

Abstract: A TM/TE convenor is combined with a TE-pass polariser on a common LiNbO3 chip to obtain an integrated optical, acoustically tunable wavelength filter Its tuning range is 145–157 μm wavelength with a filter half-width of 28 nm Owing to the combined acoustical/optical strip guide structure used in the mode convenor, a very low acoustic drive power of only 9 mW is required

Optical phonon modes in a double heterostructure of polar crystals

Abstract: The equation of motion for the polarization vector for a double heterostructure of polar crystals is solved exactly within the framework of the continuum model. There exist only two types of phonon modes, the interface modes and the confined bulk modes, whose eigenvectors are obtained explicitly. Dispersion relations are derived analytically for the interface modes, while the confined bulk modes are dispersionless, a fact consistent with the model. It is also found that in Raman scattering experiments the symmetric interface modes are predominantly longitudinal optical (LO) and the antisymmetric interface modes transverse optical (TO). In the central region of the Brillouin zone, however, they both split into two branches oscillating at LO and TO frequencies, respectively. Possible reinterpretation of various experiments is briefly discussed.

Ultrashort pulse train generation through induced modulational polarization instability in a birefringent Kerr-like medium

Abstract: The nonlinear evolution of the polarization in a birefringent nonlinear dispersive medium is subject to two competing instabilities: degenerate steady-state polarization instability and nondegenerate three-wave mixing parametric instability. We predict that, by inducing modulational polarization instabilities, one may generate a train of ultrashort pulses from continuous-wave (cw) radiation propagating in a birefringent optical fiber, even in the normal dispersion regime. The input signal and the generated train of pulses are polarized along a principal axis of the fiber that is perpendicular to the pump polarization. Varying the choice of the fiber axis for the pump polarization and the sign of dispersion leads to substantially different shapes and bandwidths of the modulational instability gain curves. In turn, this may greatly affect the temporal characteristics of the generated pulses. The pulse width (on a picosecond or subpicosecond time scale), the repetition rate (up to a few terahertz), and the compression factor of the train can be adjusted by varying the initial sideband detuning or by tuning the fiber birefringence.

Polarization fluctuation measurements on installed single-mode optical fiber cables

Abstract: Measurements are reported of the polarization fluctuation observed at 1550 nm on samples of cable that Telecom Australia has installed in its interexchange network. The rate of polarization fluctuations is found to be slow, on the order of hours. The fluctuation in the polarization angle is typically in the range of 2-10 degrees each day, with some changes up to about 25 degrees . The results indicate there are no significant limitations on implementing polarization control in a coherent system receiver. >

High hydrostatic pressure effects in highly birefringent optical fibers

Abstract: The effect of high hydrostatic pressure on polarization properties in highly birefringent (HB) optical fibers is experimentally evaluated up to 200 MPa. The results are discussed in terms of beat-length changes under high pressure. It is found that oscillatory behavior of the output signal exiting from the HB bow-tie fiber and monitored in the plane parallel to one of its own two principal axes can be attributed to a pressure-induced increase of beat-length parameter. This effect can be applied to sense high hydrostatic pressure using appropriately configured HB fiber, but it could be a disadvantage in underwater communication systems using HB fibers if these are not adequately protected. >

Polarization-encoded optical shadow-casting: direct implementation of a carry-free adder.

Abstract: Carry-free addition based on the redundant binary number system is adopted for the lensless polarization-encoded optical shadow-casting (POSC) system. A carry-free POSC adder is designed by determining the codings of (1) the redundant input bits for generating the intermediate sum and intermediate carry and (2) the intermediate sum and intermediate carry for generating the carry-free sum.

Polarization Ray Trace

Abstract: A ray representing a vector wave is traced through an optical system. The electric field perpendicular to the (ray) direction of propagation is represented by a Jones vector. At each surface the results of a thin-film calculation are used to form a "surface" Jones matrix. For a given ray, a product of surface Jones matrices forms an "instrumental" ray matrix. Coordinate frames and sign conventions are emphasized.

Nonlinear fiber couplers: switches and polarization beam splitters.

Abstract: Propagation in a nonlinear coupler at a specified input power is like that in a linear coupler with a specified but nonsinusoidal periodic refractive index. This suggests novel schemes for reducing the switching power and leads to simple analytical expressions for ideal switches and for power-sensitive polarization beam splitters. Most importantly, we show that the critical power is reduced significantly by "freezing" a nonsinusoidal refractive index into the basic linear structure that mimics the nonlinear index above the critical power, thus biasing the nonlinear coupler.

Stability of polarized modes in a quasi-isotropic laser

Abstract: The polarization states of quasi-isotropic lasers are highly sensitive to residual cavity anisotropics and to weak (parasitic) anisotropic feedback. Internal anisotropics are usually constant, whereas the effective mirror anisotropy produced by feedback is strongly frequency (phase) dependent. In this paper we develop a model for such a laser and obtain analytic steady-state solutions for the case when both anisotropics are parallel. The linear stability analysis is also analytic. For the 3.39-μm He–Ne laser the theory explains the previously observed variations with frequency of the intensity of the laser, the regions of monostable linear polarization, and in the bistable region the inverse dependence of the width of the hysteresis loop on the low-signal net gain. In contrast to Lamb’s theory the calculations show that the polarization flip arises from an instability in the relative phase between the vector components of a mode.

A liquid-crystal phase modulator for large-screen projection

Abstract: The substitution of a liquid-crystal phase modulator for the electrically deformable oil film used for image generation in some large-screen projectors is studied. The liquid crystal causes a voltage-dependent phase shift to the incident light, which is converted into amplitude-modulated light by means of a schlieren optical system. A cell configuration in which the phase shift is about equal for both polarization directions, so that no polarizers are necessary and therefore optical efficiency can be increased, was found. The diffraction properties of the resulting rectangular phase grid were investigated. When used with a thin-film transistor array or a wafer-scale MOS transistor array as drivers, a gray scale projection is possible. >

Polarization of far-infrared radiation from molecular clouds

Abstract: The paper reports measurements of the polarization of far-infrared emission from dust in nine molecular clouds. Detections were obtained in Mon R2, in the Kleinmann-Low (KL) nebula in Orion, and in Sgr A. Upper limits were set for six other clouds. A comparison of the 100 micron polarization of KL with that previously measured at 270 microns provides new evidence that the polarization is due to emission from magnetically aligned dust grains. Comparing the results for Orion with measurements at optical wavelengths, it is inferred that the magnetic field direction in the outer parts of the Orion cloud is the same as that in the dense core. This direction is nearly perpendicular to the ridge of molecular emission and is parallel to both the molecular outflow in KL and the axis of rotation of the cloud core. In Mon R2, the field direction which the measurements imply does not agree withthat derived from 0.9-2.2 micron polarimetry. The discrepancy is attributed to scattering in the near-infrared. In Orion and Sgr A, where comparisons are possible, the measurements are in good agreement with 10 micron polarization measurements.

Broad-band optical directional couplers and polarization splitters

Abstract: A method is described for designing broadband optical directional couplers. The basic idea is to determine an optimum distance between the waveguides where wavelength dependence of the coupling coefficient vanishes at a given wavelength. The method is applied to design directional coupler polarization splitters. As an example the computer design of a polarization splitter made of single-mode twin-core optical fiber is presented. The extinction ratio obtained for waves with undesired direction of polarization is better than -20 dB within a wavelength range of 80 nm. The sensitivity of the design to variations of the main parameters caused by the production process is discussed for characteristic examples. >

Polarization Aberration Diagrams

Abstract: Polarization aberrations are variations of the polarization associated with different ray paths through an optical system. This paper presents particular polarization aberration expansion that is second order in the object and pupil coordinates and describes polarization effects that are functionally equivalent to the wavefront aberration terms: piston, tilt, and defocus. This polarization aberration expansion is applicable to weakly polarizing systems, such as radially symmetric systems of lenses and coatings, as well as to strongly polarizing systems incorporating polarizers and retarders. A computer simulation of this expansion has been performed, and graphical results are presented displaying the effect of 24 of these polarization aberrations acting on linearly and circularly polarized light.

The miniblazar in 3C 273

Abstract: The compact core of 3C 273 has been studied for over two years using optical photometry and accurate polarimetry. A wealth of polarization behavior, including variable polarization, observed at a level of under 1 percent is described. The results indicate that 3C 273 harbors a weak continuum component having all the characteristic properties of blazars. It is predicted that other compact radio sources with low optical polarization will also be found to harbor miniblazars. The detection of variable polarization in 3C 273 strengthens the link between superluminal motion at radio wavelengths and blazar activity at optical wavelengths.

Brillouin gain variation due to a polarization-state change of the pump or Stokes fields in standard single-mode fibers.

Abstract: The effect of pump or Stokes field polarization-state changes on Brillouin gain is investigated in standard (non-polarization-maintaining) single-mode fibers with a modal birefringence of ~10−7. The Brillouin gain change due to polarization azimuth variation of the input pump or Stokes field reaches ±31% of the average gain expected for a completely scrambled polarization state. This polarization effect on the Brillouin gain may lead to cross-talk fluctuation in bidirectional coherent transmission systems and to degradation of Brillouin amplifier performance.

A very wide-band frequency response measurement system using optical heterodyne detection

Abstract: A very-wide band frequency response measurement system for optical devices has been established using the optical heterodyne detection method utilizing two distributed feedback-laser diodes (DFB-LDs). By controlling the laser diode (LD) temperature, the beat frequency is swept from DC to beyond several tens of gigahertz and the measurable bandwidth can be extended to that frequency without any additional calibration. In this system, the spectral linewidth of each LD is stabilized by the two-stage optical isolator and the lightwaves are mixed with the same polarization by a polarization-maintaining optical coupler. The optical frequency fluctuation of the LD is detected by the change of the transmitted optical power through Fabry-Perot etalon and the frequency is controlled by the negative feedback to the LD temperature. Included are a comparison of measurement methods, features of the developed measurement system, and the measurement results. >

BER evaluation for phase and polarization diversity optical homodyne receivers using noncoherent ASK and DPSK demodulation

Abstract: An analysis of the performance of phase diversity receivers using amplitude-shift keying (ASK) and differential phase-shift keying (DPSK) is presented. Both (2*2) and (3*3) multiport receivers are investigated. Asymptotic methods are used to estimate the bit error rate (BER) and signal-to-noise power ratio (SNR) dependence for each type of the receiver. The analysis favors the squarers as the demodulators for ASK whose performance approaches that of the ideal heterodyne detector in the limit of large SNR. A modification of the ASK ((3*3)) receiver which cancels the local oscillator intensity noise is proposed. Receivers which comprise polarization and phase diversity techniques are also investigated for both ASK and DPSK. Their performance is independent of the polarization state of the received signal, and the value of SNR required to obtain the BER of 10/sup -9/ is only a few tenths of a decibel greater than that needed by the phase diversity receivers. >

The optical and near-infrared continuum polarization of five magnetic white dwarf stars - new observations and considerations regarding its origin

Abstract: Linear and circular broadband continuum polarization measurements throughout the 0.35-1.65-micron spectral region were obtained for GrW +70 deg 8247, GD 229, G240-72, G227-35, and LP 790-29. The continuum is found to be characterized by significant Coulomb modification of the Landau-type autoionization thresholds. The spectral characteristics of continuum polarization originating from a centered dipole field distribution are predicted. The magnetobremsstrahlung model can describe several characteristics of the polarization of Grw + 70 deg 8247, suggesting that plasma eigenmodes draw the resultant continuum polarization away from a photoionization edge. 86 refs.

Single droplet size, velocity, and optical characteristics by the polarization properties of scattered light.

Abstract: A method is described for obtaining size, velocity, and optical properties of transparent spherical droplets employing the polarization characteristics of scattered light. A preliminary analysis of the Lorenz-Mie solution, in comparison with geometrical optics, points out the importance of surface waves in the side scattering region between θ = 85° and θ = 120°. Here the horizontal component of scattered light due to surface waves prevails over that due to external reflection for droplets smaller than 100 μm and the polarization ratio γ = CHH/CVV can be employed for determining the particle size. A dual-beam system is made of two equal intensity circularly counterotating polarized laser beams which generate a polarized fringe pattern in the interference volume. The polarization ratio of scattered light, at a fixed scattering angle θ, and velocity is obtained by analysis of the bursts produced by individual droplets. The method was tested by determining the size and velocity distribution functions of droplet arrays produced by a Berglund-Liu atomizer operated either in monodisperse or in bidisperse regimes. The angular pattern of the polarization ratio was determined on calibrated streams of transparent droplets with different refractive indices, and the influence of this parameter on the role of surface waves in different angular scattering regions is discussed.

Polarization properties of phase conjugation by degenerate four-wave mixing in a medium of rigidly held dye molecules

Abstract: The saturation properties of dye molecules that are rigidly held in a solid host are qualitatively different from those of molecules that are free to rotate. We have found that these unique saturation characteristics can be exploited to achieve nearly perfect vector phase conjugation for field strengths near the saturation intensity. We have studied these properties experimentally by using fluorescein-doped boric acid glass as the nonlinear-optical material.