Showing papers on "Polarization rotator published in 1982"

Phased array antenna employing linear scan for wide-angle arc coverage with polarization matching

Abstract: The present invention relates to an antenna arrangement which includes a polarization diplexer capable of bidirectionally directing two orthogonally polarized signals along one path in the far field of the antenna arrangement and along two separate paths in the near field for interception along at least one of the paths by an array of feed elements. The array is arranged to provide a fixed linear phase taper along one axis across the array to produce or intercept a beam squinted at an angle 90 degrees-α to the face of the array and including a signal polarized in a first direction. Phase shifting means selectively produce a linear phase taper along a second axis across the face of the array orthogonal to the first axis to cause the beam to traverse a predetermined arc in the far field of view. Polarization mismatch at the array from the diplexer is overcome by providing a single properly inclined 90 degree polarization rotator or by two properly inclined 90 degree polarization rotators depending on the direction of polarization and whether the array is a linear or a two-dimensional array.

Observation of rotational polarization produced in molecule-surface collisions

Abstract: The rotational polarization produced by scattering a rotationally cold beam of NO from Ag(111) has been measured by laser-induced fluorescence. A strong rotational polarization perpendicular to the surface normal is observed. The degree of polarization depends strongly on final rotational state, incident energy, incident angle, and surface temperature.

Birefringence and polarization effects in fiber gyroscopes

Abstract: A formalism is presented for treating birefringence and polarization in fiber optic sensors. This formalism is applied to study theoretical characteristics of fiber gyroscopes which are operated with various states of polarization of the input light including nonpolarized and partially polarized light, which have potentially useful characteristics. Measurements supporting the theoretical predictions are described.

Electro optic switch

Abstract: An optical switch utilizes a birefringent device to cause orthogonally polarized components of an arbitrarily polarized incident light beam to propagate along separate paths. A polarization rotator is positioned in one path to rotate the polarization of the light beam propagating therealong to that of the light beam in the other path. The two paths are simultaneously deflected to selected parallel paths in accordance with the switching desired. A second polarization rotator reestablishes the initial polarization and the beams are recombined by a second birefringent device to emerge from the selected output terminal as an arbitrarily polarized light.

Degree of polarization in anisotropic single-mode optical fibers: Theory

Abstract: The degree of polarization for propagation waves in anisotropic single-mode fibers is formulated in terms of light source spectrum, incident polarization condition, and fiber parameters. The polarization degree deterioration is based on the incident wave split into two eigenpolarization modes inherent in the fiber. Since the two eigenpolarization modes have different group velocities from each other, the degree of polarization is degraded when both of the modes are excited. Polarization degree is preserved when only one of the eigen-polarization modes is excited. The degradation is determined by the mutual correlation function γ, between the two modes, which depends on the light source spectra, fiber polarization dispersion, and fiber length.

Birefringence caused by thermal stress in elliptically deformed core optical fibers

Abstract: Birefringence and polarization dispersion introduced by thermal stress in single-mode fibers with elliptical core are formulated here in terms of fiber structure parameters, thermal expansion coefficients, and thermoelastic constants. Thermal stress distribution and birefringence characteristics are estimated within first-order perturbation with respect to fiber core ellipticity. Normalized frequency dependence of birefringence and polarization dispersion is also derived in this paper. Birefringence and polarization dispersion in elliptical core fiber are seen to depend on thermal stress rather than geometrical anisotropy for relatively small relative index differences. Numerical examples are presented for germanosilicate, borosilicate, and phosphosilicate glass fibers.

Birefringence measurement in optical fibers by polarization-optical time-domain reflectometry.

Abstract: The technique of polarization-optical time-domain reflectometry is analyzed to see how the polarization properties of an optical fiber may be deduced from the backscattered light. It is shown that, subject to certain assumptions, the polarization is modified as it would be by a linear retarder. The results of measurements on a fiber showing both linear and circular retardation are given and compared with a theoretical model. The experiments show that the accuracy of measurement is limited by changes in the polarization, due to the scattering process, which vary randomly along the fiber.

Linearly single polarization fibers with zero polarization mode dispersion

Abstract: The optimum waveguide structure for linearly single polarization fibers, which satisfies the large modal birefringence and the zero polarization mode dispersion simultaneously, has been investigated. The basic waveguide structure is the single-mode optical fiber that has an elliptical core and stress-applying parts with a different expansion coefficient from that of the cladding. Waveguide parameters, such as index difference, core ellipticity, and cutoff wavelength, are first determined to obtain highly birefringent fibers with B = 1 \times 10^{-5} or B = 5 \times 10^{-5} . The structure of the stress-applying parts that provides zero polarization mode dispersion is then determined.

Gravitational effects on the polarization plane

Abstract: We study the rotation of the polarization plane of an electromagnetic wave due to a gravitational field. An evolution law for the polarization plane is derived in the geometric optics approximation. For the particular case of a Kerr space-time, we obtain the polarization plane rotation for an incident light ray parallel to the Z axis at z = -∞ and for a radially outgoing one. The results are compared with others which have already appeared in the literature.

Method and apparatus for determining the polarization state of a light wave field

Abstract: The local state of polarization of a light wave field is determined by measuring the radiation transmitted by one or several polarizers with three different azimuth angles A modified TV camera is used having its usually provided tri-color filters replaced by polarization filters whose azimuth angles differ from each other by 60° respectively On a connected color monitor, the local polarization state can be concluded from the local brightness, the hue, and the saturation The polarization camera can preferably be used for ellipsometric measurings, in an interferometric system for surface topography, and in interferometric holography The display of the polarization state of the color monitor can be supplemented by electronic means, eg emphasizing points having the same state of polarization

Polarization holding in elliptical-core birefringent fibers

Abstract: Polarization holding in high-birefringence elliptical-core fibers is evaluated for the fiber birefringence spatial frequency range 1.5 cm-1 cm-1, corresponding to beat lengths from 1.6 mm to 4.2 cm. This range of spatial frequencies is spanned by making measurements with a broad-band light source on four fibers with different degrees of birefringence. In this way, the strength of the internal birefringence perturbations is mapped to give the first experimental measure of their power spectrum. It is shown that commonly available fiber jackets can significantly degrade the polarization holding. For low spatial frequencies, the strength of the perturbations decreases rapidly with increasing frequency, but this rate decreases by more than half over a one-and-a-half order of magnitude increase in spatial frequency. A possible origin of the perturbations is suggested and it is shown that the strength of these perturbations must be reduced if polarization holding to a very high degree is to be realized in elliptical-core fibers. Presently, internal perturbations limit the polarization holding to ≤ 14.4 dB over 1 km.

Observation of bistable behavior in the polarization of a laser.

Abstract: The output of a single-mode He–Ne laser with internal mirrors is usually linearly polarized in one of two orthogonal directions. This polarization state may be selected by a tunable injected signal or by feedback from a tunable secondary optical resonator. The laser will remain in the selected polarization even after the injected signal or the feedback from the secondary resonator is removed. This effect has potential applications as a fast switch or as an optical memory. An explanation based on intracavity birefringence is given for this bistable behavior in the polarization.

Use of circularly polarized optical beams to suppress self-focusing instability in a nonlinear cubic medium with repeaters

Abstract: A theoretical and experimental investigation is made of the suppression of small-scale self-focusing in high-power solid-state laser systems with repeaters by using circular polarization. The improvement in the output focused energy obtained experimentally for circular polarization as compared to that for linear polarization (~ 1.5 times higher) shows good agreement with the calculated value.

Polarization Holding in Ellipitical-Core Birefringent Fibers

Abstract: Polarization holding in high-birefringence elliptical-core fibers is evaluated for the fiber birefringence spatial frequency range 1.5 cm/sup -1/ < Beta/sub i/ < 40 cm/sup -1/, corresponding to beat lengths from 1.6 mm to 4.2 cm. This range of spatial frequencies is spanned by making measurements with a broad-band light source on four fibers with different degrees of birefringence. In this way, the strength of the internal birefringence perturbations is mapped to give the first experimental measure of their power spectrum. It is shown that commonly available fiber jackets can significantly degrade the polarization holding. For low spatial frequencies, the strength of the perturbations decreases rapidly with increasing frequency, but this rate decreases by more than half over a one-and-a-half order of magnitude increase in spatial frequency. A possible origin of the perturbations is suggested and it is shown that the strength of these perturbations must be reduced if polarization holding to a very high degree is to be realized in elliptical-core fibers. Presently, internal perturbations limit the polarization holding to /spl les/14.4 dB over 1 km.

Polarization demodulation: A new approach to the reduction of polarization artifacts from vibrational circular dichroism spectra

Abstract: In vibrational circular dichroism (VCD) measurements and other polarization modulation techniques, artifact signals often arise due to polarization sensitivity of the optical components located subsequent to the sample. In this paper, we describe a method for demodulating the light beam after passage through the sample in such a manner that only one linearly polarized state is allowed to reach the detector, thus eliminating these artifacts. The method is a beam reversal technique in which the light subsequent to the sample is redirected through the photoelastic modulator in such a way that the retardation produced on the first traversal through the modulator is removed. The light is returned to its original state of linear polarization prior to detection. The method is applicable to Fourier transform as well as to dispersive spectrometers since demodulation is effected for all wavelengths simultaneously. The results of preliminary demodulation experiments are presented and found to be more than 90% efficient in removing circular dichroism intensity of a birefringent origin.

Rapidly turnable laser system

Abstract: A rapidly tunable laser system which is operative to tune the laser beam emission to a predetermined wavelength in accordance with the polarization state thereof is disclosed. The laser beam emission may be tuned between predetermined wavelengths as rapidly as it can be altered between polarization states. More specifically, the laser system includes a polarization modulator for modulating the radiation beam emitted from a laser cell between at least two polarization states, and at least two diffraction gratings which are uniquely and fixedly aligned to specularly reflect and retroreflect radiation incident thereupon. The retroreflected radiation is of a wavelength uniquely identified with the angle of incidence of the corresponding diffraction grating. One diffraction grating retroreflects radiation at one wavelength and response to one polarization state of the radiation beam, and the other diffraction grating retroreflects radiation at another wavelength in response to radiation at another polarization state. Hence, the laser system may be tuned between the one and another wavelengths by modulating the radiation beam between the one and another polarization states by the polarization modulator. The laser beam emission may be tuned between the predetermined wavelengths as rapidly as it can be altered between the polarization states.

Linearly Single Polarization Fibers with Zero Polarization Mode Dispersion

Abstract: The optimum waveguide structure for linearly single polarization fibers, which satisfies the large modal birefringence and the zero polarization mode dispersion simultaneously, has been investigated. The basic waveguide structure is the single-mode optical fiber that has an elliptical core and stress-applying parts with a different expansion coefficient from that of the cladding. Waveguide parameters, such as index difference, core ellipticity, and cutoff wavelength, are first determined to obtain highly birefringent fibers with B = 1 X 10/sup -5/ or B = 5 X 10/sup -5/. The structure of the stress-applying parts that provides zero polarization mode dispersion is then determined.

Polarization control element for phased array antennas

Abstract: Each antenna of the phased array is supplied a lineal polarized wave which has been shifted in phase and rotated in polarization in accordance with a cascade connection of a NRCP, Faraday rotator and a RNRCP. The control windings of the Faraday rotator and the rotating polarizer determine the amount of phase shift and rotation of the polarization of the propagating wave.

Circularly polarized modal skew rays in graded-index optical fibers

Abstract: For a given modal skew ray in a graded-index optical fiber, the intrinsic angular momentum associated with the direction of circular polarization in space can, as we know, have two different orientations, and the states of the polarization or the directions of the polarization have been considered so far to be invariant. This paper shows that this is valid only for high frequencies but fails for low frequencies and in certain special optical fibers. A critical frequency is calculated at which the direction of rotation of its circular polarization changes. It is pointed out that the feature of this anomalous polarization critically depends on the inhomogeneity of the medium. Some profiles of refractive index are examined.

Polarization properties of few-mode glass fiber waveguides with noncircular cores

Abstract: An investigation was made of the dependences of the degree of polarization P of the output radiation on the wavelength of directional radiation and the length of a fiber waveguide with an oval core and a birefringence of δn = 2×10−5. In a few-mode (V≈6) regime such fibers ensure the high value of P over distances amounting to few tens of meters. An increase in the number of modes and in the length of a fiber reduced P; the first two cutoffs were accompanied by a step-like change in P. The polarization properties of birefringent fiber waveguides were explained by a difference between the polarization characteristics of the higher modes and by intermode conversion. A new polarization method was proposed for determining the cutoff wavelengths of the higher modes. The method is suitable for any type of fiber waveguide, but it is particularly convenient in the case of the waveguides with a complex refractive index profile.

Laser-induced polarization anisotropy in In three-level system

Abstract: We observed a polarization change induced by laser radiation in the Raman-type three-level atom In in the presence of Ar. The observed two components in the polarization change spectrum of the probe beam correspond to the resonant Raman scattering and the luminescence processes in the spontaneous emission. The dependence of their intensities on the collision with Ar atoms agrees with the theory.

Onthemeritsofbicircular polarization forstereocolortv

Abstract: A 3-Dviewingsystembased monochrome3-DTV usingcolor on bicircular polarization for differencesto generatetwodis