Showing papers on "Polarization rotator published in 1983"

Origins and control of polarization effects in single-mode fibers

Abstract: The polarization state of light in single-mode fibers is very sensitive to any perturbation which is not symmetric about the fiber axis. While this is a source of noise, drift, or signal fading in some applications, it can also be exploited in novel guided-wave devices. The basic birefringences that couple the two modes and change the polarization state along the fiber are reviewed. The three cases of uniform, phase-matched, and random coupling are considered. Polarization preservation in both low- and high-birefringence fibers is achieved by reducing this coupling. In addition to polarization-state changes, bireftingent fibers can quickly reduce the polarization degree of nonmonochromatic light if both modes are excited, a characteristic that greatly simplifies evaluation of the degree of polarization preservation in these fibers. Current evaluations of the birefringence and the polarization-holding ability of state-of-the-art fibers are discussed, and it is concluded that fibers with good polarization-holding properties are becoming available.

Degree of polarization in the Lyot depolarizer

Abstract: Analytic output equations for the degree of polarization of light exiting a Lyot depolarizer are derived from a coherency matrix representation. Design criteria are obtained for sources of different spectral shape.

Electro-optical switch for unpolarized optical signals

Abstract: An optical 1×N switch uses a polarizing beam splitter cube and a reflector to separate an arbitrarily polarized incident light beam into polarized components which propagate along parallel paths. A polarization rotator is positioned in the path of the reflected component to rotate the plane of polarization of the light beam component propagating therealong to be coplanar with that of the undeviated light beam in the parallel path. The two beams are simultaneously or individually deflected by selectively activating the electrodes of a liquid crystal nematic reflector/transmitter array confined between prismatic bodies to emerge at one or more of a plurality of desired outputs. In a second embodiment, a second polarization rotator and polarizing beam combiner assembly re-establishes the initial polarization and the beams are thereby combined to emerge from one or more selected output terminals as an arbitrarily polarized light beam. The switch exhibits extremely low crosstalk and insertion loss by utilizing the energy of both parallel and normal incidence polarization components and avoiding propagation of undesired stray polarization components as occurs with a liquid crystal polarizer.

Circular polarization antenna

Abstract: A circular polarization antenna having wide-band circular polarization characteristics and impedance characteristics is accomplished by feedng N-antenna elements which are shifted at an interval of π/N rad. with respect to the boresight direction with differential phase shift of an interval of π/N rad. corresponding to the angular orientation of the antenna elements so as to obtain perfect circular polarization with respect to the boresight direction. This antenna construction can be applied to circular polarization antennas of various types, thereby allowing a wide-band circular polarization array antenna or an array antenna for dual orthogonal circular polarizations having high polarization discrimination to be achieved.

Measurement of fiber birefringence by wavelength scanning: effect of dispersion

Abstract: Scanning the wavelength in high-birefringence fibers inherently measures the group delay difference, and not the phase delay difference, between the two polarization modes. Dispersion of the birefringence will result in a 10–20% error in fiber beat lengths interpolated from such measurements, even if only stress birefringence is present. Geometrical dispersion can introduce even larger errors in some fibers.

Polarization independent beam splitter

Abstract: A new type of beam splitter is described, which is capable of producing a division of light in a polarization independent manner. Typical beam splitters (used off-axis) have a pronounced polarization dependence. The device is a thin plate of suitably oriented, birefringent material having a thickness chosen to interchange the characteristic polarizations of the beam between the faces of the plate. The reflection/refraction ratio at the two boundaries are then complementary and the combined effect is insensitive to the polarization of the incident beam.

Polarization rotation compensator and optical isolator using the same

Abstract: A polarization rotation compensator and an optical isolator using the same are described. The optical isolator comprises a first birefringent wedge plate; a polarization rotation compensator composed of a combination of a half-wave plate whose principal axis is inclined at an angle of θ/2 with respect to the plane of polarization of the incident light and a quarter-wave plate whose principal axis is inclined at an angle of θ with respect to the plane of polarization of the incident light; a Faraday rotator; and a second birefringent wedge plate; wherein the Faraday rotator, quarter wavelength plate, and half-wavelength plate are respectively arranged in the order of propagation of the backward light or of the forward light.

Broad-band wide-angle quasi-optical polarization rotators

Abstract: A quasi-optical and wide-angle (of incidence) polarization rotator is described and analyzed. It consists of three or more parallel, equispaced wire-grid polarizers whose wires are oriented in different directions. With the proper choice of the number of grids, their spacings, and their relative orientations, such a polarization rotator is capable of operating over a broad frequency band and a wide range of angles of incidence. A seven-grid 90\deg polarization rotator was designed to operate over a 42 percent relative bandwidth for a \pm 60\deg range of angles of incidence with less than 0.1 dB transmission loss. Various designs based upon our analysis are given. The impetus for this work is the specific application of this polarizer in a dually polarized multibeam satellite ground station antenna employing a linear array feed. The design of a seven-grid polarization rotator for the ground station antenna is presented.

Experimental Study on Higher Order Reflection by Monodomain Cholesteric Liquid Crystals

Abstract: Reflection spectra have been measured in the spectral region of the second and the third order selective reflections for monodomain cholesterics of various cell thicknesses at various angles of incidence. Thicker cells give rise to higher reflectance at larger angles of incidence. The second order reflection region consists of three bands which show characteristic polarization correlation: The central band is a total reflection band, where incident light of any polarization is reflected. The reflected light is a polarized when it polarized light is incident and vice versa. Contrary to the central band, two side bands are selectively reflected; σ(π) polarized light is reflected in the longer (shorter) wavelength band retaining its polarization. The third order reflection bands observed for the first time have been found to give the same polarization characteristics as that of the second order reflection bands.

Technique for Measuring the Amount of Pressure-Induced Polarization Scrambling by Optical Windows in High Pressure Light Scattering Cells

Abstract: A simple method for estimating the amount of pressure-induced polarization scrambling by optical windows in the high pressure Raman scattering cells is proposed. This method is based on the measurement of the depolarization ratio ρ for a polarized band (ρ = 0) for which a nonzero value of ρ is produced by the leakage of the Ivv component due to stress-induced birefringence of the window material. As an illustrative example the measurement of ρ for the polarized ν3(A1) band in liquid tetramethyltin is presented.

Use of modulation of elliptic light polarization for the study of electric birefringence of polymer solutions in pulse fields

Abstract: A compensation method was developed for measuring electric birefringence in the pulse field of constant and sinusoidal voltage which is based on the use of modulation of elliptic light polarization. The method enables the equilibrium Kerr effect and kinetics of electric birefringence of conductive polymer solutions to be examined.

Propagation characteristics of single polarization fibers.

Abstract: Detailed studies have been carried out for various dopants on the coupling length (L) of the two fundamental modes of orthogonal polarization to preserve a state of linear polarization over long lengths. Theoretical calculations indicate that L < 2.3 mm is essential to maintain good polarization. Two fundamental single polarization fibers, the elliptical-core and elliptical-clad fibers, have been prepared by CVD. Experimental results show that a B2O3 dopant yields a substantially large anisotropic birefringence than does GeO2 and P2O5. The effects of noncircularity and normalized frequency of the fiber on L have been experimentally considered.

Birefringence Measurements In Single Mode Optical Fiber

Abstract: Because their cores are not perfectly circular or because of stress, inherent to the structure or externally applied, practical single mode fibers are birefringent. These sources of birefringence are reviewed briefly. A simple model for the fiber consists of a combination of one linearly birefringent element and one circularly birefringent element. Depending on the magnitude of the birefringence, different techniques of evaluating the parameters of the model may be suitable. Several methods appropriate for low and high birefringence fiber are described and some of their advantages and disadvantages outlined. In an idealized single mode optical fiber, in which none of the structural or optical parameters varies with the azimuthal coordinate, all polarization states within the fundamental mode are degenerate; that is, neither the phase nor group velocity depends on polarization. In practice, however, this degeneracy is usually lifted by non-circularity of the core, by inherent stress in the guiding structure, or by stress resulting from bending, pressure, or twisting. Light entering the fiber with an arbitrary polarization state will then be resolved into a pair of orthogonal polarization states that propagate with different velocities. As a phase shift develops between them, the state of polarization will vary periodically along the fiber. The orthogonal states may be linear, circular, or in general elliptical, depending on the specific mechanisms involved.

Circular polarization of impact radiation produced by polarized electrons in mercury

Abstract: Polarization measurements of nonresonant radiation produced by impact excitation of mercury atoms by polarized electrons are reported. In particular, the circular polarization of the transition 7/sup 3/S/sub 1/..-->..6/sup 3/P/sub 0/ (404.7 nm) is presented as a function of electron energy. At excitation threshold, the polarization predicted by theory has been confirmed while above threshold the polarization is strongly affected by resonances. Connections with the role of the atomic interactions in the excitation process and with electron polarimetry are discussed.

Polarization dispersion measurement on twisted single-mode optical fibers

Abstract: A new method for measuring polarization dispersion between two eigen polarization modes is presented. It utilizes the measured phase shift corresponding to birefringence difference between two adjacent wavelengths. This method makes it possible to measure small polarization dispersion by using a short test piece even when eigen polarization modes are elliptically polarized. A polarization dispersion of 0.4 ps/km in twisted single-mode fibers can be measured in an approximately 4-m-long fiber by using 1.152- and 1.161-μm lines in a He-Ne laser. Experimental data that polarization dispersion decreases with an increase in fiber twist ate in very close agreement with theoretical results.

A Tunable 90° Rotator Using a Total Reflection by a Monodomain Cholesteric Liquid Crystal Cell

Abstract: A tunable 90° rotator using a cholesteric liquid crystal cell is presented. The idea is based on a unique optical feature of cholesterics, a total reflection. In the total reflection region, linearly polarized incident light is totally reflected and the incident polarization is rotated by about 70°. In other words, 80% of the incident light intensity can be converted to the perpendicular component to the incident polarization over a relatively wide spectral range, 485 nm–670 nm. The cell of another tuning range is also easily obtained by choosing the helical pitch of cholesterics.

Polarization distribution in ferroelectrics calculated by regularization method from pyroelectric measurements

Abstract: The present paper deals with the polarization distribution along the polar axis in ferroelectrics. We derived the integral equation connecting the frequency dependence of the pyroelectric response with the polarization distribution in ferroelectrics. The polarization distribution is obtained from the integral equation by regularization method using electronic computer. Frequency dependences of the amplitude and the phase of the dynamic pyroelectric response were taken as the initial data.As the example, polarization distribution was determined for Ba0.4Sr0.6Nb2O6 crystal at room temperature. Polarization is shown to become one order of the magnitude lower as compared to the volume polarization near the electrode surface, which served as a cathode during monodomainization. In the process of heating near the phase transition one observes the polarization reversal of the surface region on the cathode.

Linear birefringence and optical activity in the far-infrared propagation in a Tokamak

Abstract: A simple theory is developed to study the polarization of high-frequency electromagnetic waves in plasmas. The elliptical birefringence is separated into the effects of linear birefringence and optical activity for frequencies much above the plasma frequency. It is shown that linear birefringence and optical activity are essentially independent phenomena related respectively to the transversal and longitudinal magnetic fields. The theory is applied to study experimental results on the measurement of electron density and plasma current in Tokamaks. The conditions for pure linear birefringence or pure optical activity are derived. An equation is obtained for the polarization evolution on the Poincare sphere including collisional attenuation to first order.

A free electron laser with versatile polarization capability

Abstract: A novel configuration of free electron laser system is proposed that is capable of generating coherent radiation whose polarization is arbitrary and rapidly adjustable. The magnet configuration is similar to that of the optical klystron except that the undulators are placed perpendicular rather than parallel to each other. The gain of the system is analyzed in the small signal regime, and is found to be similar to that of the optical klystron. The polarization of the laser radiation at maximum gain is found to be different from the polarization of the spontaneous radiation.

New concept in optical information storage: Thermal relaxation of strain birefringence

Abstract: Theoretical and preliminary experimental results are presented to demonstrate a new concept in optical information storage. The recording medium is a birefringent sheet of stretched polymer; the recording event is a modification of the birefringence by the action of heat, for instance, that generated by an absorbed laser pulse, or derived from contact with a heat source; the readout is based on the detection of changes in the state of polarization of a reading beam.