Showing papers on "Polarization rotator published in 1988"

Piezoelectric effects in strained-layer superlattices

Abstract: Because zinc‐blende structure semiconductors are piezoelectric, polarization fields can be generated in the constituent materials of strained‐layer superlattices by lattice‐mismatch‐induced strain. The orientation of the polarization fields depends on the superlattice growth axis. Because one of the constituent layers of the superlattice is in biaxial tension and the other is in biaxial compression, the sign of the polarization field is opposite in the two constituent layers making up the superlattice period. Thus, sheets of divergence of polarization occur at the interface for a longitudinal induced polarization and sheets of curl of polarization occur at the interface for a transverse induced polarization. For a [111] growth axis, the induced polarization is purely longitudinal; for a [110] growth axis, the induced polarization is purely transverse. For a general growth axis the induced polarization has both longitudinal and transverse components. The sheets of divergence of polarization generate intern...

Neutron polarization with polarized 3He

Abstract: An effective polarizer for thermal and epithermal neutrons is possible with polarized, high density, gaseous 3 He. We describe the technique of 3 He polarization by spin exchange with laser optically pumped Rb vapor which can provide 6 cm 3 of > 70% polarized 3 He at a density of 3×10 20 atoms cm −3 (10 atm at STP). The 3 He polarization can be rapidly reversed, a requirement for sensitive symmetry tests.

Electric current sensor using the faraday effect

Abstract: An electric current detector has a light source for generating light having substantially linear polarization and a predetermined polarization direction, a material substantially transparent to the light, the material having at least one characteristic direction, and the material exhibiting the Faraday effect in response to a magnetic field generated by the electric current. Also the light is launched into the material, and a predetermined angle established between the polarization direction and the characteristic direction, the predetermined angle chosen to permit separation of a rotation of the polarization of the light by the Faraday effect from polarization effects on the light by a birefringence of the material. A value of 22.5° for the magnitude of the predetermined angle permits a separation of the rotation of the polarization due to the Faraday effect from polarization effects due to a birefringence of the material.

Dynamic Responses of Ferroelectric Liquid Crystals in the Surface-Stabilized Geometry I

Abstract: The dynamic response of surface-stabilized ferroelectric liquid crystals was studied on the basis of a continuum theory. In this work, polarization electric field was consistently introduced through Poisson's equation, including the polarization charge accompanied by an elastic deformation. An improved anchoring energy consistent with inclined smectic layers relative to the bounding plates is put forward. From numerically calculated results, the polarization current and the hysteresis curves are found to be crucially affected by the inherent chirality and the polarization electric field. Remarkably, it is shown that an increase of the inherent chirality or the negative dielectric anisotropy results in a doubly or a triply peaked polarization switching current under an alternating external field.

Light blocking and vision restoration apparatus with glint control

Abstract: According to one aspect of the invention, a system for controlling light, includes (1) apparatus for responding to incident electromagnetic radiation, including a first medium through which incident electromagnetic radiation may be transmitted; liquid crystal means positioned with respect to said first medium for responding to a characteristic of the incident electromagnetic radiation to cooperate with such first medium to effect refraction of such electromagnetic radiation at an interface of said first medium and said liquid crystal means; and (2) apparatus for filtering a wavelength of light, including a variable polarization rotator means for supplying input light at a prescribed angle of polarization, variable dispersion means for rotating the plane of polarization of such input light an amount that is a function of the wavelength of such input light, and analyzer means for blocking transmission of that light which is output by said variable dispersion means and has a plane of polarization which is crossed relative to the axis of polarization of said analyzer means. The invention also may include a glint reducing device.

Optical systems with thin film polarization rotators and method for fabricating such rotators

Abstract: A method for fabricating a polarization rotator which includes a thin film waveguide exhibiting essentially zero linear birefringence in the absence of an externally applied stress, as well as an optical system incorporating said rotator, is disclosed.

Antenna system having azimuth rotating directive beam with selectable polarization

Abstract: A rotating reflector is used to provide a beam scan throughout a predetermined angle such as 360°. A circular polarizer is coupled with the reflector and converts received linearly polarized energy into circularly polarized energy. A fixed feed is configured to receive the reflected circularly polarized energy and converts such energy to linearly polarized energy. The antenna system can receive the same linear polarization of energy throughout its 360° scan angle without polarization mismatch or orthogonal polarization losses. The relative orientation of the two polarizers may be adjusted to receive any orientation of linear polarization of energy throughout the scan angle. For example, they may be oriented so that the antenna system receives vertically polarized energy, slant 45° linearly polarized energy, or horizontally polarized energy.

Determination of the absolute magnetic moment direction in Cr2O3 using generalized polarization analysis

Abstract: Generalized polarization analysis, in which all three components of polarization of both incident and scattered neutron beams are determined, can be used to probe fine details of magnetic structure. For instance, in certain antiferromagnetic crystals such as Cr2O3 neutrons scattered from reflections containing both nuclear and magnetic components have the direction of their polarization rotated in the plane containing the scattering vector as was demonstrated by Alperin [International Conference on Magnetism (Moscow, 1973)]. The sense of the rotation depends on whether the moments point towards the center of symmetry or away from it. The two corresponding configurations are distinguishable because the coordinating octahedra of oxygen ions are not centrosymmetric and should therefore have different energies. We have used a new technique which exploits the Meissner effect to obtain magnetic isolation to measure the rotation of the neutron polarization by the 102 and 104 (hexagonal) reflections of Cr2O3 between 7 and 320 K. The results show that the lower‐energy configuration is the one in which the chromium moments point towards the smaller of the two equilateral triangles of oxygen neighbors. The measured depolarizations were found not to be consistent with a simple domain model.

Optical time delay apparatus

Abstract: An optical time delay unit for use in an optical phased array beam-steering system includes a switchable polarization rotator in conjunction with Brewster plates and mirrors to form electrically-selectable optical paths of different lengths. The switchable polarization rotator is aligned with the optical beam and is responsive to a control signal for varying the polarization of light passing therethrough. The Brewster plates receive the light passing through the first polarization rotator and are transmissive to a first polarization and reflective of a second. The transmissive and reflective paths are of different lengths, and are recombined at a second Brewster plate. The original polarization may be restored by a second polarization rotator. A plurality of time delay units may be cascaded to permit selection from among many paths of various lengths. In a preferred embodiment, the polarization rotators include liquid crystal cells having nematic phase molecules. Optically-transparent electrodes are formed on the cell windows by an ion implantation process. A planar phased array beam-forming system comprises a plurality of time delay units, illustratively arranged in a 2-by-2 configuration, wherein each unit is illuminated by a corresponding sector of a single light beam.

Stress-optic effects, birefringence, and reduction of birefringence by annealing in fiber Fabry-Perot interferometers

Abstract: The effects of inherent fiber birefringence, packaging stresses, and stress tuning on the behavior of a fiber Fabry-Perot interferometer are examined. A polarization doublet due to birefringence is observed. For birefringence of 1 ps/km, the doublet spacing is 40 MHz, at 1.5- mu m wavelength, independent of the FFP finesse or free spectral range, and is due mainly to the inherent fiber birefringence. It was found that annealing depressed-cladding single-mode fiber reduced the fiber birefringence, for example, from 40-80 MHz to 15-25 MHz. Where the bandpass of the FFP is greater than the birefringence doublet, this device should be polarization insensitive for most applications. >

Liquid crystal cell window

Abstract: An optical time delay unit for use in an optical phased array beam-steering system includes a switchable polarization rotator in conjunction with Brewster plates and mirrors to form electrically-selectable optical paths of different lengths. The switchable polarization rotator is aligned with the optical beam and is responsive to a control signal for varying the polarization of light passing therethrough. The Brewster plates receive the light passing through the first polarization rotator and are transmissive to a first polarization and reflective of a second. The transmissive and reflective paths are of different lengths, and are recombined at a second Brewster plate. The original polarization may be restored by a second polarization rotator. A plurality of time delay units may be cascaded to permit selection from among many paths of various lengths. In a preferred embodiment, the polarization rotators include liquid crystal cells having nematic phase molecules. Optically-transparent electrodes are formed on the cell windows by an ion implantation process. A planar phased array beamforming system comprises a plurality of time delay units, illustratively arranged in a 2-by-2 configuration, wherein each unit is illuminated by a corresponding sector of a single light beam.

In-line holographic lens arrangement

Abstract: An optical system for an in-line holographic lens or lens array which is designed to produce and pass a symmetrical focused beam of light while or blocking or attenuating the zero order in-line collimated beam illuminating and passed by the lens. Each holographic lens is designed to produce a symmetrical focused beam of light, and has particular applicability to high quality, low f-number holographic lenses. In the optical system, the in-line holographic lens is illuminated by a reconstruction beam of light such that it produces a focused beam of light along the optical axis of the lens, and also passes the zero order in-line reconstruction beam. A polarization rotator is positioned along the optical axis to receive the focused beam of light and also the zero order reconstruction beam, with the focused beam of light being incident thereon and traversing through the polarization rotator at different angles from the zero order reconstruction beam. This results in the zero order reconstruction beam being rotated in polarization differently from the focused beam of light. A polarization filter is positioned along the optical axis to receive the light output of the polarization rotator, and has the polarization angle thereof positioned substantially at the polarization angles of the focused beam, such that it substantially passes the focused beam of radiation and substantially attenuates the zero order reconstruction beam.

Direct pulse technique for spontaneous polarization dynamics and molecular reorientation processes in ferroelectric liquid crystals

Abstract: A method has been devised for studying the spontaneous polarization, dynamics of polarization reversal, and the molecular reorientation processes that occur in the bulk and surfaces of ferroelectric liquid crystals. These studies have been carried out by analyzing the current response to triangular‐ and square‐wave forms. The current response to a triangular wave yields the spontaneous polarization by conveniently subtracting the background contribution due to the conductive and capacitive currents. Molecular reorientation processes which take place within the bulk and the boundary surface layer can be studied by the appearance of polarization current peaks on the triangular‐wave response. The dynamics of polarization reversal between bistable states and of the polarization change between the zero‐field relaxed state and either of the saturation remanent polarization states have been studied by applying ‘‘symmetric’’ and ‘‘asymmetric’’ square waves. The technique can also be successfully applied to solid ...

The ferroelectric polarization of liquid crystals and its measurements

Abstract: In liquid crystals, the chiral tilted smectic phases only present, a spontaneous (ferroelectric) polarisation, which is due to the molecular rotations cramped by the structure in these phases. The amplitude of the polarisation given by a polar group on the molecule varies with the distance of this group from the chiral part. This spontaneous polarization is a very important parameter because its linear coupling with an applied electrical field is the basis of all applications of these compounds. The measurement of the polarization is obtained from the current induced when it is reversed. I comment on different methods to obtain a good measurement by polarization reversal in the whole sample and separation of the reversal current from the ionic and displacement currents.

Overcoming Polarization Aberrations In Microscopy

Abstract: A long-standing problem in polarized light microscopy has been the inability, due to polarization aberrations, to achieve simultaneously high spatial resolution and high contrast. The rotation of the plane of polarization at oblique interfaces between crossed polars causes the pupil function to resemble a dark cross rather than being uniformly dark. Likewise, the point spread function has the visual appearance of a four-leaf clover rather than the ideal Airy disk, and is also space-variant. Images formed with these systems are severely degraded. In this paper the theory of polarization aberrations is applied to the analysis of three solutions to this problem: Reducing the system aperture to block troublesome high-aperture rays; the AVEC-POL method, in which high bias compensation introduces counterbalancing aberrations; and the polarization rectifier, an optical element designed to introduce equal and opposite rotations of the electric vector.

A quasi-optical polarization rotator

Abstract: We present the theory and first measurements concerning a quasi-optical polarization rotator capable of operating over a broad frequency band.

Automatic endless polarization control with integrated-optical Ti:LiNbO(3) polarization transformers.

Abstract: In coherent-optical transmission systems continuous or endless polarization matching between the superposed beams must be ensured. We describe a practical closed-loop polarization-control system with two integrated-optical retarders acting as polarization transformers. They have variable retardations and variable eigenmodes, i.e., adjustable birefringence magnitude and orientation as in a Babinet–Soleil compensator. In theory, one retarder would be sufficient. However, a second device is added to correct nonideal behavior of the first. The intensity losses during polarization control are less than 0.15 dB.

Optical feedback isolator

Abstract: Method and apparatus for isolating optical feedback in a laser interferometer having a laser light source from which a linear polarized outgoing laser beam of certain polarization orientation is derived. The interferometer also redirects the outgoing laser beam to form a return laser beam directed to a receiver. The outgoing laser beam and the return laser beam are physically close and are substantially parallel. The linearly polarized outgoing laser beam is converted to circular polarization. A portion of the circularly polarized return laser beam directed toward the laser light source is converted back to linear polarization with polarization orientation orthogonal to the polarization orientation of the outgoing laser beam. A portion of the circularly polarized return laser beam directed toward the receiver is converted back to linear polarization with polarization orientation being substantially the same as the polarization orientation of the outgoing laser beam. The portion of the return laser beam with polarization orientation orthogonal to the polarization orientation of the outgoing laser beam is directed away from the laser light source, and the portion of the return laser beam with polarization orientation substantially the same as the polarization orientation of the outgoing laser beam is directed toward the receiver.

Optical amplifier and method for amplifying optical polarization state change effects

Abstract: An optical amplifier for amplifying optical polarization state change effects comprises an arrangement for passing polarized light through a material a plurality of times such that changes in the polarization state of the polarized light from the respective passes of the light through the material are cumulative. The amplifier can be used in a method for detecting optical polarization state change effects wherein polarized light which is passed through the material is detected. The material may be a liquid sample from a high performance liquid chromatography system.

Reflective device for polarization rotation

Abstract: It is shown that a three-mirror device with ideal mirror reflectivities may be used in place of a halfwave plate to rotate the plane of polarization of a plane polarized beam by any angle with no loss of polarization purity. For coated mirrors, with more general reflectivities, specifications are set on the allowed reflectivity ratio and phase shift difference for the s and p components in order that polarization purity be preserved to a specified amount.

Optical directional coupler

Abstract: PURPOSE:To increase the dependency of a coupling ratio upon the polarization direction to miniaturize a coupler by providing an area where a material different in modulus of elasticity from an optical waveguide film is packed on the optical waveguide film which is made transparent by heating. CONSTITUTION:Grooves 10-1 and 10-2 are formed on cores 4-1 and 4-2 of a clad layer 3 made transparent by heating with the same width as cores by the reactive ion etching method, and air is packed in these grooves as gas different in modulus of elasticity from the quartz glass of core layers. As the result, the compressive stress applied to the optical waveguide film from a substrate 1 produced through the process where it is made transparent by heating is made uneven to increase the difference of refractive index distribution between polarized light beams, which are propagated in the lengthwise direction of an optical coupling part, in the vicinity of cores. Thus, since the dependency of the coupling ratio upon the polarization direction is increased, a miniaturized coupler having separating and branching functions in a short distance is obtained.

Transformation of neutron polarization in polarized media and tests of T invariance.

Abstract: A general analysis is given for the modification of neutron polarization resulting from passage through a polarized medium. The previously proposed search for precession (properly defined) of neutron spin about k\ifmmode\times\else\texttimes\fi{}S remains a valid test of T invariance in the presence of other spin-dependent interactions which cause further changes. However, as noted by Bunakov and Gudkov, the development of transverse polarization along this direction is not an absolute test, but, if such polarization is found, the measurement of corresponding asymmetry in the transmission of polarized neutrons is shown to furnish an unambiguous test. A complete set of such tests is given.

Semiconductor laser with external resonator

Abstract: PURPOSE: To make the width of an oscillation spectral line of an LD narrow stably by making an optical fiber into a single polarization fiber and by letting a polarization face of the light output from a semiconductor laser be in accord with a proper polarization face of the single polarization fiber. CONSTITUTION: A polarization face of the light 3 emitted from a semiconductor laser 1 is usually parallel with a junction face of the semiconductor laser 1 (x direction). When the polarization face of the emitted light 3 is in accord with a polarization face of the reflected feedback light 4 from an external resonator, both lights interfere with each other with the maximum interference efficiency. When the polarization face of the reflected feedback light is vertical (y direction) with the polarization face of the emitted light 3, both lights do not interfere at all. This is the reason why the polarization face of the light emitted from the semiconductor laser gets in accord with the proper polarization face of the single polarization fiber. Therefore, the polarization face of the emitted light gets always in accord with the polarization face of the reflected feedback light; thereby, both lights interfere with each other with the maximum interference efficiency stably with the passage of time. As a result, the width of a spectral line can be made narrow stably. COPYRIGHT: (C)1989,JPO&Japio

Scatter symmetrization in multi-mode ring laser gyros

Abstract: SCATTER SYMMETRIZATION IN MULTI-MODE RING LASER GYROS Abstract Disclosed herein is a method and apparatus for achieving scatter symmetrization in a multi-mode non-planar ring laser gyro The retro scatter effect which results in scatter coupling in each of the left and right circular polarized sets of beams is equalized, so that the scatter coupling may be common-mode rejected during the analysis phase of the ring laser gyro operation This equalization is achieved by unique orientation of the mirrors and the non-reciprocal polarization rotator The non-reciprocal rotator which may be a Faraday rotator, is rotated in such a manner that its angle of rotation relative to an angle fixed at the plane of incidence of one of the mirrors of the leg is proportional to the positioning of the rotator along the axis between the mirrors of this leg In this manner equal scatter coupling will occur in the left and right circularly polarized light and this scatter coupling may be common-mode rejected for purposes of deriving accurate rotational information Scatter symmetrization is also achieved by con-figuring the mirrors in legs of equal length so the amount of image rotation attributed to each leg is proportional to the leg length

Dynamics of polarization growth and polarization reversal in PVDF films

Abstract: The authors present measurements of the maximum displacement at the end of a rectangular high-voltage pulse together with the remanent polarization after the pulse under short-circuit condition as a function of the polarizing pulse end length. The pulse length varied from 10 mu s to 100 s, and the field strength ranged from 0.8 MV/cm to 2 MV/cm. The original samples were reversely polarized or unpolarized 12- mu m-thick films containing 37% beta -material. It is concluded that the cooperative model combined with six-site potential alone cannot explain the observed switching back of the remanent polarization, its delayed development, and the long times necessary for polarization reversal. The results are qualitatively consistent with a model of charge injection and charge trapping at polarized crystallites. >

Externally pumped polarization-preserving phase conjugator

Abstract: We demonstrate an externally pumped phase conjugator that preserves polarization on reflection and does not exhibit the frequency shift present in self-pumped phase conjugators. Our results show that for linearly polarized incident light the phase-conjugate reflection reproduces the angle of polarization to within the experimental error of 1%. For circularly polarized incident light, our results show that the helicity of polarization is preserved on reflection.

Polarization of λ=1.55 μm InGaAsP Ridge-Waveguide Lasers

Abstract: The influence of waveguide parameters on the polarization of the lasing mode is investigated for λ=1.55 µm InGaAsP-InP ridge-waveguide lasers. It is found experimentally that for weak index guiding the lasers are polarized TM, whereas for gain guided or strongly index guided devices the polarization is TE. This behaviour is in excellent agreement with calculations based on a recently developed ridge-waveguide laser model. It is demonstrated that stable TE or TM polarization can arbitrarily be established by means of an appropriate choice of the laser parameters.

Integrated Optical Polarization Controller Chip In LiNbO3 Using A Near Z Axis Propagation Direction

Abstract: We assess the design and fabrication of an optically wideband four element polarization controller chip in LiNb03 for use in the 1.55 µm wavelength low loss window of silica fibres. The design allows for mixing of the local oscillator (LO) and signal by the integration of a 3 dB coupler which should provide suitable outputs for a balanced detector pair. In addition, we attempt to optimise mode converter performance in the device by using near Z axis propagation. The results inidicate that there are some unforseen problems that arise when couplers and off axis waveguide structures are fabricated on this particular crystal orientation.

Single-Mode Fiber Pseudo-Depolarizer

Abstract: A technique for the pseudo-depolarization of a long-coherence length source is described, which is based on a simple polarization modulation scheme. Using a length of high birefringence fiber wound on a piezoelectric transducer, a simple all-fiber polarization scrambler can be constructed. Details of an electro-optic scrambler are also reported. The depolarization technique is shown to eliminate the effects of input-lead-birefringence induced polarization fading in interferometric sensors.