Showing papers on "Polarization rotator published in 2000"

Laser beams with axially symmetric polarization

Abstract: An analysis of the vector wave equation was conducted. A class of self-similar solutions with inhomogeneous polarization corresponding to the resonator modes is deduced. The modes with inhomogeneous polarization can be selected by a diffraction element with polarization selectivity used as one of the resonator mirrors. Diffraction elements with high polarization selectivity of about 100% are necessary for generating `pure' radially polarized modes. The radially polarized beam provides a higher energy efficiency (the product of the depth of the cut by the cutting velocity) for laser cutting metals than the circularly polarized main mode does under the same conditions. The two limiting cases of resonance absorption on the spherical plasma target could be realized using axially polarized beams: the resonance absorption is maximum in the case of radial polarization and does not occur in the case of azimuthal polarization.

Two-dimensional polarization encoding with a phase-only liquid-crystal spatial light modulator

Abstract: We show how to two dimensionally encode the polarization state of an incident light beam using a parallel-aligned liquid-crystal spatial light modulator (LCSLM). Each pixel of the LCSLM acts as a voltage-controlled wave plate and can be programmed over a 2pi phase range at a wavelength of 514.5 nm. Techniques are reviewed for either rotating the major axis of elliptically polarized light or for converting an input linearly polarized beam into an arbitrary elliptically polarized beam. Experimental results are demonstrated in which we generate various two-dimensional spatial patterns of polarized light. Several potential applications are suggested. We also report an unexpected edge-enhancement effect that might be useful in image processing applications.

Dual polarization modulation: A real-time, spectral-multiplex separation of circular dichroism from linear birefringence spectral intensities

Abstract: A real-time, spectral-multiplex method for the complete separation of circular dichroism (CD) spectra from linear birefringence (LB) spectra is presented. The method, called dual polarization modulation (DPM), involves the introduction of a second source of polarization modulation after the CD sample. The first source of polarization modulation, as in conventional CD spectrometers, is located before the sample. Intensity signals at the detector in phase with each of the two polarization modulation frequencies are demodulated simultaneously in parallel and combined electronically in opposition to eliminate the LB spectrum by real-time cancellation. The accuracy of the cancellation can be adjusted electronically without the need to change the optical alignment of the instrument. The DPM method permits baseline-corrected CD spectra to be measured without the need for a subsequent CD background measurement.

Polarization luminaire and projection display

Abstract: A polarization luminaire is disclosed having a light source, a system of the optical integrator, a polarized light splitting device for splitting a light emitted from the light source into two kinds of polarized lights whose polarization directions are perpendicular to each other and whose traveling directions are apart from each other by an angle of less than 90 degrees, and a polarization conversion device for causing the two kinds of polarized lights to have the same polarization direction. The polarized light splitting device is placed on one of the entrance side and the outputting side of the first lens plate of the system of the optical integrator or is placed within the second lens plate. A prism beam splitter having a polarized light splitting film constituted by a thermally stable dielectric multi-layer film is suitable for the polarized light splitting device. Most of the polarized lights can be utilized by causing the polarized lights to have the same polarization direction. Further, the polarized lights, which have uniform brightness, can be emitted. Consequently, the polarization luminaire is suited to be a luminaire for use in a projection display that has liquid crystal light valves.

Propagation-induced polarization changes in partially coherent optical beams

Abstract: Propagation of a partially coherent optical beam inside a linear, nondispersive, dielectric medium is studied, taking into account the vector nature of the electromagnetic field. Propagation-induced polarization changes are studied by using the Gaussian-Schell model for the cross-spectral-density tensor. The degree of polarization changes with propagation and also becomes nonuniform across the beam cross section. The extent of these changes depends on the coherence radius associated with the cross-correlation function. For optical beams with symmetric spectra, the bandwidth of the source spectra is found to play a relatively minor role.

Probability densities of second-order polarization mode dispersion including polarization dependent chromatic fiber dispersion

Abstract: We describe experiments and simulation of second-order polarization mode dispersion (PMD) components in optical fibers with emphasis on polarization-dependent chromatic dispersion (PCD). Excellent agreement is found in comparisons of experimental, simulated, and theoretical probability densities. To our knowledge, these are the first such comparisons for the second-order PMD magnitude and the PCD.

Variable delay device for an optical component such as a polarization mode dispersion compensator

Abstract: A variable delay device of the type used to correct for polarization mode dispersion in a signal transmitted over an optical communications system. In an exemplary embodiment, the variable delay device uses a plurality of polarization rotators and delay elements aligned in series and alternating with one another. The polarization rotators map the fast polarization mode component of the incoming optical signal to the slow axes of one or more delay elements, to achieve a desired pattern of relative incremental delays which total the initial differential delay being compensated. The delay elements may have uniform or non-uniform incremental delay values, and the polarization rotators may be selectively actuated to achieve the desired pattern of delay values corresponding to the intended total delay. Examples of suitable delay devices include waveguides having relatively high differential group delay characteristics associated with two orthogonal axes compared with conventional single-mode transmission fiber, and examples of suitable polarization rotators include twisted nematic liquid crystal (TNLC) or ferroelectric liquid crystal (FLC) cells which rotate the polarization mode components of the optical signal by 90° when actuated.

Polarization of Thermal X-Rays from Isolated Neutron Stars

Abstract: Since the opacity of a magnetized plasma depends on polarization of radiation, the radiation emergent from atmospheres of neutron stars with strong magnetic fields is expected to be strongly polarized. The degree of linear polarization, typically ~10%-30%, depends on photon energy, effective temperature, and magnetic field. The spectrum of polarization is more sensitive to the magnetic field than the spectrum of intensity. Both the degree of polarization and the position angle vary with the neutron star rotation period so that the shape of polarization pulse profiles depends on the orientation of the rotational and magnetic axes. Moreover, as the polarization is substantially modified by the general relativistic effects, observations of polarization of X-ray radiation from isolated neutron stars provide a new method for evaluating the mass-to-radius ratio of these objects, which is particularly important for elucidating the properties of the superdense matter in the neutron star interiors.

Polarization properties of light backscattered from a two layer scattering medium.

Abstract: The polarization properties of light backscattered from a two layer scattering medium are investigated. Linear, circular and elliptical polarization states are considered and it is demonstrated that the degree of polarization of the backscattered light is sensitive to the optical properties of both layers and to layer thickness. Furthermore, it is shown that the polarization memory of circularly polarized light enables deeper layers to be probed whereas linearly polarized light is more sensitive to surface layers. This has applications for characterizing burns and melanoma.

Mean-square magnitude of all orders of polarization mode dispersion and the relation with the bandwidth of the principal states

Abstract: Using the retarded plate model, we derive the correlations and the mean-square values of all orders of polarization mode dispersion (PMD) as well as the autocorrelation function of the PMD vector. Our results provide the signal bandwidth below which the first-order approximation of the principal states of polarization is valid. We show that this bandwidth depends only on the mean value of the differential group delay. Our theoretical results are supported by simulations and experiments.

Theory of polarization rotation and conversion in vertically coupled microresonators

Abstract: Two orthogonally polarized waveguide modes can exchange power through an intermediate level, if the polarization state of that level is tilted with respect to the polarization states of the waveguide. Microrings with modest sidewall angles support such tilted modes. Ultracompact, wavelength selective polarization rotators might be achieved. Simple analytic expressions are derived for polarization rotation by vertically-coupled resonators in terms of geometrical factors.

Jones matrix for second-order polarization mode dispersion.

Abstract: A Jones matrix is constructed for a fiber that exhibits first- and second-order polarization mode dispersion (PMD). It permits the modeling of pulse transmission for fibers whose PMD vectors have been measured or whose statistics have been determined by established PMD theory. The central portion of our model is a correction to the Bruyere model.

Study of the frequency autocorrelation of the differential group delay in fibers with polarization mode dispersion.

Abstract: We study the frequency autocorrelation of the differential group delay (DGD) in fibers with polarization mode dispersion (PMD). We show that the correlation bandwidth of the DGD is comparable with that of the orientation of the PMD vector. Furthermore, we show that all the most general statistical properties of polarization mode dispersion in long fibers are uniquely determined by the mean DGD. An estimate of the accuracy of measurements in which the mean DGD is extracted by frequency averaging in a single fiber is obtained as a function of the measured bandwidth.

Analytical theory for PMD-compensation

Abstract: We derive exact analytical expressions for the expected pulse broadening in a fiber-optic transmission system suffering from both first- and higher order polarization mode dispersion (PMD). Furthermore, we quantify the influence of two simple PMD-compensation techniques.

Interferometers utilizing polarization preserving optical systems

Abstract: Interferometers (510) utilizing polarization-preserving optical systems (511, 512) by plane polarized beams are deviated through preselected angles without changing their linear state of polarization. The interferometers (510) utilizing such optical systems have a variety of applications and are particularly suitable for use in the field of distance measuring interferometry to enhance measurement accuracy by reducing undesirable polarization effects that can introduce errors associated with an otherwise present undesirable polarization rotation found in classical retroreflectors. Prismatic optical elements are preferably used to construct assemblies (511, 512) which can include polarization beam splitting coating arrangements and/or birefringent materials to enhance the extinction ratio between orthogonally polarized beams propagating through such systems.

Achromatic linear polarization rotator using twisted nematic liquid crystals

Abstract: In this letter, we propose a simple configuration that is capable of rotating a linear polarization state of light by a certain angle for a wide range of wavelengths. The device consists of three liquid-crystal cells: two homogeneous cells and one twisted nematic (TN) cell. It is well known that a thick TN cell can rotate the linear polarization state of light by following the twisted structure. However, for a thin TN cell, achromatic polarization rotation is not possible. By the use of the Poincare sphere model of the TN structure, we demonstrate that if one thin homogeneous cell is placed before and another one is placed after a thin TN structure, then a linear polarization state can be transformed close to the eigenmodes of TN. Therefore, this structure can be used to achieve the achromatic polarization rotation. This letter provides a detailed discussion of the theoretical analysis and a demonstration of the achromatic linear polarization rotator by the use of a 1.9 μm TN cell for the wavelength range 450–700 nm.

Static-electric-field-induced polarization effects in harmonic generation

Abstract: Two static-electric-field-induced effects on harmonic generation are demonstrated analytically and numerically: elliptic dichroism (in which the harmonic yield is different for right and left elliptically polarized laser fields) and elliptical polarization of harmonics produced by linearly polarized driving laser fields. Both effects stem from interference of real and imaginary parts of the nonlinear atomic susceptibilities. Possibilities for experimentally measuring these effects are discussed.

An inverse compton scattering model of pulsar emission. III. Polarization

Abstract: Qiao and his collaborators recently proposed an inverse Compton scattering model to explain radio emission from pulsars. In this paper, we investigate the polarization properties of pulsar emission in the model. First of all, using the lower frequency approximation, we derived the analytical amplitude of the inverse Compton scattered wave of a single electron in a strong magnetic field. We found that the outgoing radio emission of a single relativistic electron scattering off the "low-frequency waves" produced by gap sparking should be linearly polarized and have no circular polarization at all. However, considering the coherency of the emission from a bunch of electrons, we found that the outgoing radiation from the inner part of the emission beam, i.e., that from the lower emission altitudes, preferentially has to have circular polarization. Computer simulations show that the polarization properties, such as the sense reversal of circular polarization near the pulse center, the S-shape of position angle swing of the linear polarization, and a strong linear polarization in conal components, can be reproduced in the ICS model.

Rear projection screen using birefringent optical film for asymmetric light scattering

Abstract: A dispersing element for a rear projection screen assembly is sensitive to the polarization of the light passing through the element. In particular, the element disperses light having a first polarization differently from light having a second polarization orthogonal to the first polarization. The dispersing element may be aligned with a polarization axis neither parallel nor perpendicular to the polarization of the light passing through the element. The dispersing element may also be employed with a polarizer to remove unwanted light that propagates through the dispersing element. The dispersing element may also be rotatably mounted relative to a polarized light source so as to vary the angle between the polarization axis of the element and the polarization direction of the light.

Polarization mode dispersion compensating apparatus

Abstract: A signal light from an optical transmission line propagates on a first optical fiber and enters a polarization converter. The polarization converter converts the input light with the given polarization into a linear polarization with a desired angle using two Faraday rotators and a quarter wave plate between them. The output light of the polarization converter propagates on a second optical fiber and enters a polarization beam splitter. The polarization beam splitter splits the light from the second optical fiber into two mutually orthogonal polarization components (e.g. TE and TM components) and outputs either of them (e.g. the TE component) toward a third optical fiber. A portion of the light propagating on the third optical fiber is split by an optical coupler and enters a photodetector. A bandpass filter (BPF) extracts a clock component of the signal from an output of the photodetector. A controller controls the polarization converter to adjust the polarization angle of the output light so as to maximize the output of the BPF according to the output of the BPF.

Polarization studies in multiply scattering chiral media

Abstract: The interactions of polarized light with an optically active (chi- ral), multiply scattering medium are investigated using a relatively simple experimental system incorporating polarization modulation and synchro- nous detection techniques. The polarization properties of diffusely scat- tered light are studied as a function of scatterer particle concentration, chiral molecule concentration, and detection direction. A newly derived method for simultaneous extraction of the total degree of polarization, and optical rotation of the linearly polarized fraction, is theoretically dis- cussed and experimentally implemented, using optically thick turbid me- dia with the presence of one chiral component. The method requires measurements at several orientations of the analyzing linear polarizer, followed by data fitting to yield the unknown sample polarization proper- ties. The accuracy and robustness of this method in the cases of weak signals and noisy data are superior to previous two-point approaches of data analysis. The measurable polarization preservation on multiple scattering, affected by the chirality and turbidity of the medium and by the detection geometry as described, provides a useful tool with which to probe the properties of multiply scattering media. © 2000 Society of Photo- Optical Instrumentation Engineers. (S0091-3286(00)03602-3)

High efficiency flat illuminator for liquid crystal micro-display

Abstract: An illumination system for a flat panel micro-display device includes a flat panel edge lit lightguide having a polarizing layer on a major surface and a polarization rotator and reflector proximate to an edge face of the lightguide. The polarization rotator changes the polarization state of light that is initially reflected from the polarization layer to a desired polarization state from an undesired polarization state and the reflector reflects the light back to the polarization layer. The rotated and reflected light propagating within the lightguide passes though the polarizing layer and illuminates a LCD panel of the micro-display. The combination of the polarization rotator and the reflector provide a controlled system in which most of the initially reflected light is utilized to illuminate the LCD panel. In an embodiment, the polarizing layer is a polarizing film that passes P polarized incoming light and reflects S polarized incoming light, the polarization rotator is a quarter wave plate that rotates light by a quarter wave, and the reflector is a mirror that reflects light without changing the polarization state of the light.

Polarization separation device and projection-type display apparatus

Abstract: A polarization separation device has a grating having a recurring blaze-shaped grating pattern formed on one surface of a transparent base plate and an optically anisotropic material layer arranged adjacent to the grating and having different refractive indices in the direction in which the grating pattern recurs and in the direction perpendicular to that direction. The polarization separation device separates light incident thereon into two linearly polarized light components that have polarization planes perpendicular to each other in accordance with the polarization directions thereof by refracting one and simply transmitting the other of those two linearly polarized light components. Here, the refractive index N0 of the grating and the refractive indices Ne and Np of the optically anisotropic material layer with respect to one and the other, respectively, of the linearly polarized light components are defined as follows: | Ne−N 0|≧0.2, and | Np−N 0|≦0.03.

Optical all-pass filters for polarization mode dispersion compensation.

Abstract: Polarization mode dispersion (PMD) compensation is addressed by decomposition of a fiber’s Jones matrix into amplitude and phase responses, which are then compensated for separately. Cubic and higher-order phase compensation substantially reduce the cumulative probability at a given system penalty over first-order PMD compensation, as demonstrated for a 40‐Gbit/s non-return-to-zero signal and a fiber PMD with a differential group delay of 20 ps (rms). Single-stage all-pass filters provide tunable compensation that is comparable to that obtained with a variable-delay line, and multistage all-pass filters are well suited for higher-order phase compensation.

A two-panel projection system employing complementary illumination

Abstract: An imaging system, comprising a broadband unpolarized white light source (81), a polarization converter system for converting polarization axes of unpolarized white light into a substantially single polarization axis, to produce a beam of polarized light, a selective polarization filter (82), adapted to selectively rotate a polarization axis of a selected spectral band of light of the with respect to remaining polarized light based on a control signal (119), a polarized beam splitter (84), for separating light having a the substantially single polarization axis from light having a rotated polarization axis, a pair of electro-optic spatial light modulators (86, 89), disposed along a path of light within the spectral band and a path of remaining light outside the spectral band, respectively, and being adapted to modulate an image therein, and a polarized beam splitter (88), for recombining modulated light from the pair of light modulators. In a preferred embodiment, the selective polarization filter (82, 72) is divided into a plurality of regions (70, 71), each adapted to independently and selectively rotate a polarization axis of a selected spectral band of light of the with respect to remaining polarized light.

Measurement of polarization mode dispersion vectors using the polarization-dependent signal delay method

Abstract: We describe a new time-domain method for determining the vector components of polarization-mode dispersion from measurements of the mean signal delays for four polarization launches. Using sinusoidal amplitude modulation and sensitive phase detection, we demonstrate that the PMD vector components measured with the new method agree with results obtained from the more traditional Muller Matrix Method.

On the second-order approximation of PMD

Abstract: A second-order polarization mode dispersion (PMD) approximation based upon the pulse-width distortion has been studied. It shows that a complete second-order approximation should include the second derivative of the PR-ID vector as well as the first derivative of the PMD vector. Second-order pulse distortions are explicitly expressed including a 'first-order' term involving principal states of polarization (PSP) of the pulse and a second-order term involving the beating between fiber chromatic dispersion and effective PMD chromatic dispersion. An analytical result is derived for the probability of second-order PR-ID power penalty. It shows that the mean PMD of the fiber should be restricted to 26 ps and 18 ps, respectively for an optical link with zero and 850 ps/nm chromatic dispersion, in order to maintain a one dB second-order PMD power penalty with a probability below 10/sup -6/ at a data rate of 10 Gb/s. The analysis also indicates that a second-order PMD compensator can be used as a dynamic chromatic dispersion compensator.

Depolarizing polarization mode combiner

Abstract: A pump source for a fiber Raman amplifier uses multiple lasers to generate high pump power or to generate a pump beam having a tailored spectrum for producing a desired Raman gain spectral profile. Light from two lasers, in mutually orthogonal polarization states directed to a polarization combiner that produces an output having light mixed at the two orthogonal polarization states. A depolarizer depolarizes the output. The depolarizer defines first and second orthogonal polarization modes oriented so that the light output from the polarization combiner in one polarization state excites the first and second polarization modes of the depolarizer equally and the light output from the polarization combiner in the other polarization state also excites the first and second polarization modes of the depolarizer equally.

A study of polarization decay as applied to improved imaging in scattering media

Abstract: Polarization decay of linearly polarized light propagating in a multiply scattering isotropic medium with embedded model inhomogeneity (absorbing half-plane) is studied experimentally and by means of Monte Carlo simulation. Possibilities of polarization visualization and the location of inhomogeneities masked by scattering media are discussed on the basis of results obtained after comparison with direct measurements of the spatial distribution of the intensity of the scattered light.

Generalized formulation and symmetry properties of reciprocal nonabsorbing polarization devices: application to liquid-crystal displays

Abstract: We present a general formulation based on the Jones-matrix theory for reciprocal nonabsorbing polarization devices, including polarization interference filters and liquid-crystal displays. The development of this formulation is based on general symmetry conditions that relate the Jones matrix when the device is illuminated from the front side and from the back side. The application to liquid-crystal displays results in a constraint of the Jones-matrix elements, which represents a generalization of the existing models that explain their modulation properties.