Showing papers on "Polarization rotator published in 1986"

Polarization instabilities in birefringent nonlinear media: application to fiber-optic devices

Abstract: The intensity-dependent refractive index leads to an instability in the polarization state of an intense light beam oriented along the fast axis of a birefringent nonlinear medium. Depending on initial conditions, the spatial evolution of the polarization state can be oscillatory or rotatory, in a manner analogous to the motion of a nonlinear pendulum.

Eigenstate of polarization in a fiber ring resonator and its effect in an optical passive ring-resonator gyro

Abstract: Resonance characteristics of an optical fiber ring resonator are derived taking the effect of birefringence into account. We introduce the concept of the eigenstate of polarization to discuss the resonance characteristics resulting from the polarization fluctuation. Using this concept, the polarization problem in an optical passive ring-resonator gyro (OPRG) is discussed to reveal that this causes gyro drift. A way to reduce the drift is to use not polarizers but two polarization controllers. The precision required for polarization control is estimated; it is found difficult to do in practice. We discuss another configuration to solve the polarization problem in an OPRG without polarization controllers.

Polarization in antennas and radar

Abstract: An Introduction to Antennas. Representation of Wave Polarization. Polarization Matching of Antennas. Polarization Characteristics of Some Antennas. Generation of General Polarizations. Polarization Changes by Reflection and Transmission. Partial Polarization. Polarization Measurements. Appendixes.

Effect of Polarization Field on Elastic Deformation in a 180° Twisted Sample of Chiral Smectic C Liquid Crystal

Abstract: The effect of the polarization field on the elastic deformation in chiral smectic C liquid crystals is presented. In this work, a 180° twisted sample of chiral smectic C liquid crystal is concerned and the polarization field induced by the spontaneous polarization is consistently taken into account as well as an externally applied electric field. It is found that the effect of the polarization field must not be neglected to study such deformation of chiral smectic C liquid crystals when there exists the polarization charge induced by the spontaneous polarization.

Polarization controlling device comprising a beam splitter for controllably bifurcating an input polarized beam to two polarization controlling elements

Abstract: For first and second polarization controlling elements (181, 182) driven by first and second driving voltages in a polarization controlling device, a beam splitter (15) has a dividing ratio controllable between 1:0 and 0:1 and divides an input polarized beam having an input polarization state. An output polarized beam is derived from first and second polarization controlled beams to have an output polarization state. While the dividing ratio is kept at 1:0 so that the second polarization controlled beam is null, the first driving voltage may approach either of a positive and a negative limit. In this event, a control unit (25) changes the dividing ratio to 0:1. Even while the second polarization controlled beam is null, the control unit controls the second driving voltage so that the both driving voltages are congruent modulo a unit voltage difference which makes each element carry out equivalent polarization control. The first driving voltage is likewise controlled. When the input polarization state optionally varies, the output polarization state can be defined by a mode filter, a laser diode, or two parameters descriptive of a coherent polarized beam. Irrespective of the input polarization state, the output polarization state can be defined by a signal beam which reaches the device with an optionally varying polarization state.

Polarizing apparatus and method utilizing an optical fiber

Abstract: An apparatus selectively transmits light in one of two orthogonal polarizations in an optical fiber. The apparatus has a facing surface formed at one location on the fiber to expose the evanescent field of an optical signal in the fiber. A nematic liquid crystal is placed in contact with the facing surface so that it is in communication with the evanescent field of the optical signal. The nematic crystals have a first orientation state which presents a first refractive index to light traveling in one polarization and a second refractive index to light traveling in the other polarization. The light traveling in one polarization is well guided while the light traveling in the other polarization is radiated at the facing surface. Thus, only light of one polarization continues to propagate through the fiber. The nematic crystals have a second orientation state in which the relative refractive indices for the two polarizations of light are changed so that the polarization which was originally well guided is radiated at the facing surface and the polarization which was originally radiated is well guided. The change in the orientation states of the nematic crystals is accomplished by applying an electric field between two electrodes so that the nematic crystals align themselves with the electric field.

Optical systems with antireciprocal polarization rotators.

Abstract: An optical system, e.g., an optical fiber communication system or an optical mass storage device, which includes a linearly birefringent polarization rotator useful in an optical isolator or optical circulator. The rotator, which compensates for the effects oflinear birefringence and is substantially antireciprocal, includes two or more material regions which are capable of subjecting incident light to elliptic birefringences. However, the sign and/or magnitude of the linear, or the sign and/or magnitude of the circular, components of the elliptic birefringences differ from region to region. Moreover, the length of each region, except the first or last region, is substantially equal to one-half the birefringent period of the region. The length of the first or last region, by contrast, is substantially equal to one-quarter the birefringent period of the region.

Effects of circular birefringence on light propagation and reflection

Abstract: A gyrotropic (i.e., circularly birefringent) medium gives rise to a variety of interesting optical effects in addition to the well‐known one of optical activity, the rotation of a plane of linear polarization. This article considers manifestations of gyrotropy associated principally with light reflection from a transparent chiral medium. Such effects include the possible inequality of the angles of reflection and incidence, the generation of elliptically polarized light from incident linearly polarized light, and the differential reflection of right and left circularly polarized light. Reflection from a transparent gyrotropic medium is similar in some ways to, although distinct from, reflection from a conductor or absorbing medium.

The polarization of decimetric pulsations

Abstract: A sample of 10 decimetric broadband pulsations were observed in 1980–1983 and analyzed in polarization. Half of the data set was 85–100% circularly polarized, the other half showed a mild polarization of 15–55%. The polarization is constant in time and frequency for the strongly polarized group. All the mildly polarized bursts originate from near the limb; the lower degree of circular polarization is likely to be caused by depolarization due to propagation effects. The degree of polarization is constant throughout the event, but varies in frequency for the mild polarized group. Following the leading spot hypothesis, the magneto-ionic mode of the emission was found to be extraordinary. The high circular polarization of the pulsations was interpreted to be determined by the emission mechanism itself, not by propagation effects or cut-offs (contrary to the metric type I noise storms). Implications for pulsation models are discussed.

Polarization matching mixer

Abstract: A method of mixing light from a signal source with light from a local oscillator for heterodyne or homodyne detection using differential detection techniques is described. In the method and apparatus of the invention, incoming light is matched to the polarization of the local oscillator no matter what the polarization of the incoming light is. A sequence of three polarization beamsplitters is utilized to achieve this match. The local oscillator signal and the incoming signal are incident on separate faces of a first polarization beamsplitter. Each is divided into two beams by that beamsplitter and paired with the orthogonally polarized component of the other, each signal/local oscillator pair exiting from one exit face of the first polarization beamsplitter. The second polarization beamsplitter resolves one of these pairs into sum and difference pairs of matched polarization which interfere and are detected by square law detectors, forming currents which are subtracted in a differential amplifier. The third polarization beamsplitter repeats this process with the other pair of beams from the first polarization beamsplitter. The result is two net output currents which between them contain all the phase and amplitude information needed to define and control the polarization of the incoming signal. In addition to reducing sensitivity to the polarization state of the incoming signal, the use of polarization beamsplitters substantially improves optical efficiency, in comparison to prior art using amplitude beamsplitters.

Polarization rotation in meteor burst communication systems

Abstract: The problems of polarization rotation losses, in meteor burst communication systems, are examined using a theoretical model developed for the purpose. The paper takes into account both the polarization changes due to ionospheric Faraday rotation and the rotation of the wave polarization that takes place as a result of scattering from underdense meteor trails. Linearly polarized systems, employing copolar transmitting and receiving antennas, and hybrid systems, employing a linearly polarized transmitting antenna and a circularly polarized receiving antenna, are studied. It is shown that, particularly in linearly polarized systems, polarization rotation may introduce unexpected diurnal performance variations in systems operating at frequencies ∼40 MHz. For the two 40-MHz linearly polarized links investigated in detail the model predicts that, for noon summer solstice conditions during periods with a high solar sunspot number, these losses cause a reduction in data throughput to between 15 and 70% of the value expected had no polarization rotation occurred. By using a cross polarization approach, qualitative experimental confirmation of the predictions is also given.

Optical coupler utilizing low or zero birefringence optical fibers and a method of making same

Abstract: Polarization beam splitters/combiners or polarization insensitive beam splitters/combiners are manufactured from low or zero birefringence single mode optical fibre, rather than high birefringence fibre, by using a differential pulling technique to induce the appropriate amount of form birefringence, the fibres being stretched further than hitherto.

Method and apparatus for uniform microwave bulk heating of thick viscous materials in a cavity

Abstract: A method and apparatus for uniform bulk heating of thick viscous materials in a cavity (5) not specifically designed for microwave heating. Microwaves are passed through a first waveguide (2) to a polarization rotator (3). The direction of polarization of the incoming waves is rotated slowly and continuously and subsequently the rotated waves are passed through a second waveguide (4) to the cavity (5) to be heated.

Optical branching device using a liquid crystal

Abstract: The invention relates to an optical branching device which may be used as an optical isolator, circulator or switch. The device comprises two polarization-sensitive beam splitters. Each beam splitter comprises a prism and a rhombohedral plate between which a liquid crystal film is interposed. An optical device for rotating the plane of polarization of linearly polarized light is arranged between the two beam splitters. The polarization rotation device may comprise a Faraday rotator with a constant or a switchable direction of magnetization and a half-wave plate. Alternatively, the polarization rotation device may comprise a liquid crystal film interposed between two electrodes.

Reflection optical activity of uniaxial media

Abstract: The possibility to investigate optical activity of uniaxial media by measuring the difference between the intensities of reflected electromagnetic waves (emw) of different circular polarization (reflection optical activity—ROA) is discussed. The components of the gyration tensor and the polarization of the normal emw in uniaxial media are found. The reflection of emw is studied in two cases: (a) optical axis normal to the boundary; (b) optical axis normal to the plane of incidence. Three modifications of differential spectroscopy are proposed: (1) left and right circularly polarized waves—usual reflection; (2) total reflection–circular polarization (TROA); (3) total reflection of linearly polarized waves with different azimuths of vibration. The specific features of the proposed methods (ROA and TROA) are discussed as well as the possibility of studying the optical activity induced by nondegenerate and degenerate excitations (vibrations).

Birefringence measurements of single-mode fibers using the polarization shuttle pulse technique

Abstract: A novel and practical polarization shuttle pulse (PSP) technique has been developed to measure the intrinsic birefringence in short lengths of nominally circular-core low-birefringence single-mode fibers. By adding a linear polarizer, a Soleil-Babinet compensator, and a linear analyzer to the conventional shuttle-pulse arrangement, the length dependence of the phase delay (and hence the birefringence) can be measured nondestructively. An order-of-magnitude improvement in measurement repeatability over the conventional cut-back method has been achieved.

Polarization Aberrations Of Lenses

Abstract: Polarization aberrations are variations of intensity and polarization of an optical beam in the exit pupil of an optical system, and the dependence of these variations on the position of the object in the field. A set of functions has been derived to describe the low-order polarization aberrations of a symmetric optical system. A method is given for calculating polarization aberration coefficients for a refracting system from a paraxial raytrace. A model of these aberrations as weak polarizers that vary across the pupil will be discussed.

Signal polarization rotator

Abstract: The signal polarization rotator utilizes a rotatable signal transition structure having one section (15-1) which acts as a coaxial transmission line center con­ductor, a section (15-2) suspended over a first ground plane (11-1), a section (15-3) above a second ground plane (11-2), the latter section varying in distance from the ground plane in an ex­ponential, exponential like or linear taper (15-3), and optionally an extended section which in the preferred embodiment is used because of waveguide dimensions and acts as approximately a one quarter wavelenth gap radiator (15-4) and a section (15-5) coupled to the coaxial center conductor and the gap radiator.

An investigation of the linear polarization in emission features of active regions

Abstract: A study has been made of linear polarization in ‘moustaches’ using the Hα and Hβ lines. A Wollaston prism and an achromatic λ/2-plate were employed in the study. In the course of the observations, the major axis of the plate was placed at 0° and 22°.5 with respect to the horizontal axis of the installation. The Stokes parameters J, Q, and U were recorded, thus enabling the degree of polarization and the field azimuth to be determined. During the first three minutes of the existence of the moustaches, the two lines revealed a linear polarization of about 7% located at the center of the lines. No polarization was found during the later stage of the moustaches' lifetimes. Whenever the linear polarization is present, there is a tendency for the polarization to decrease rapidly, in accompaniment of a turning of the azimuth. Several mechanisms for interpreting the polarization observed in the moustaches are examined. Some suggestions are made in support of the excitation of hydrogen atoms in the moustaches initiated by a high-energy electron flux or vertical heat conduction.

Impact Excitation of 4 2 P-Potassium by Polarized Electrons

Abstract: The present work investigates the 42 P impact excitation of potassium by longitudinally polarized electrons. Exchange scattering causes a polarization transfer from the primary electron beam to the ensemble of excited atoms which results in a non zero circular polarization of the fluorescence light emitted in foreward direction. The experimental values of light polarization agree well with values calculated using close coupling data of Moores.

Spectral polarization method for the determination of birefringence and polarization dispersion in strongly birefringent single-mode waveguides

Abstract: It is shown that a spectral polarization method can be used to determine directly the spectral dependence of the polarization dispersion of radiation propagating along a single-mode fiber waveguide, and of the "group" birefringence proportional to this dispersion. The interpretation of the results is confirmed experimentally by a study of a model sample of a birefringent crystal and of a single-mode fiber waveguide using other methods. It is also shown that this method can be used to determine highly accurately the cutoff wavelength of a single-mode fiber waveguide.

Optical nuclear polarization in the gas phase

Abstract: Optical nuclear polarization (absorption) has been detected experimentally for the first time in benzaldehyde under UV irradiation in a magnetic field of 4.7 T. The phenomenon has been interpreted theoretically under the assumption of a non-equilibrium electron (optical) polarization transfer to the nuclear subsystem by a scalar cross relaxation mechanism of the second kind.

Polarization Retaining Single-Mode Fiber With Improved Coil Performance

Abstract: High birefringence, polarization retaining single-mode optical waveguides have been developed for applications requiring stable performance when the fiber is coiled. Recent designs employing high-expansion aluminum-doped stress rods have demonstrated polarization holding parameters better than 6.0 x 10-6m-1 with little degradation of h-parameter or attenuation down to 2 cm diameter coil configurations.

Recovering polarization of light of arbitrary polarization propagating through distoring medium by phase conjugation reflection back through said medium

Abstract: The tensorial nature of the nonlinear constant or the electro-optic coefficient of the phase conjugate material makes it impossible to perform true phase conjugation of fields with arbitrary polarization states, i.e., to recover the polarization state of the incident light of arbitrary polarization after the phase conjugation. It is demonstrated here that an optical wave propagating through a polarization and mode scrambling medium can regain its original polarization state after phase conjugation followed by reverse propagation through the polarization and mode scrambling medium. Such polarization recovery is achieved even while a magnetic field is applied to the medium, but with power loss proportional to the magnitude of the magnetic field.

Polarization Maintaining Single Mode Couplers

Abstract: Advanced single mode fiber sensors have been the subject of continued research over the past few years. Of particular importance has been the trend toward the use of highly bi-refringent single mode fibers. High birefringence fiber, while simplifying sensor design, complicates the design of system components such as couplers. In this paper the development of single mode polarization maintaining couplers is presented.

Ka‐band circular polarization analyzer

Abstract: A simple device is described to test the circular polarization of microwave radiation. It employs two matched apertures, opposite 45° twists, and a hybrid coupler to separate and measure the two circularly polarized components of an incident wave.

Variable laser beam attenuation

Abstract: A laser with a single internally or externally established polarization plane is passed first through a liquid crystal attenuation control and thence to a linear polarization filter whose polarization plane is orthogonal to the plane of the laser. The polarization of the beam is rotated an amount determined by the voltage applied to the electrodes of the liquid crystal device. The degree of such rotation determines the amplitude of the component parallel to and hence passed by the linear polarization filter.

Polarization effects in production and decay of Z 0

Abstract: In the standard model, the polarization of ${Z}^{0}$, singly produced by arbitrarily polarized incident electron and positron beams, is obtained in a manifestly covariant way. It is shown that the vector polarization of ${Z}^{0}$ depends on the longitudinal polarization of the incident beams while the tensor polarization of ${Z}^{0}$ depends on both the transverse polarization and longitudinal polarization of the incident beams. We also obtain the polarization effects on the forward-backward asymmetry, the longitudinal asymmetry, and the final polarization of an outgoing fermion in the decay process ${Z}^{0}$\ensuremath{\rightarrow}ff\ifmmode\bar\else\textasciimacron\fi{}.