Showing papers on "Polarization rotator published in 1995"

Light-polarization dynamics in surface-emitting semiconductor lasers.

Abstract: A four-level model which takes account of the polarization of the laser field by including the spin sublevels of the conduction and valence bands of a semiconductor allows us to introduce vector rate equations which account for the polarization degree of freedom of the laser emission. Analysis of these rate equations and their extension to include transverse degrees of freedom provides important physical insight into the nature of polarization instabilities in surface-emitting semiconductor lasers. In the absence of transverse effects the model predicts a marginally stable linearly polarized state. The type of dynamical response of the polarization degrees of freedom is linked to the relative time scale of spontaneous-emission and spin-relaxation processes. With transverse effects included, we predict the existence of stable transverse spatially homogeneous intensity outputs with arbitrary direction of linear polarization in the transverse plane. The stability of the off-axis emission solutions to long-wavelength perturbations is investigated and, in addition to an Eckhaus instability associated with a global phase, we predict a polarization instability associated with a relative phase of the complex field vector. The role of phase anisotropy in the laser cavity is explored close to threshold and we predict that it stabilizes two preferred orthogonal directions of polarization, which, however, are discriminated in their stability properties by transverse effects.

Illumination system and display device

Abstract: An illumination system includes a polarization selective holographic element, which includes at least one optically anisotropic material, arranged to separate light of a first polarization type from light of a second polarization type, and converting section for converting light of at least one of the first and second polarization types to light of a common polarization type Where the polarization selective holographic element separates two orthogonal components of plane polarized light from one another, the converting section can include a polarization rotator, for example a half wave plate, or alternatively a quarter wave plate and a reflector arranged to reflect light back through the quarter wave plate Where the polarization selective holographic element separates opposite handed components of circularly polarized light, the converting section can include a reflector

Polarization control of vertical-cavity surface emitting lasers using a birefringent metal/dielectric polarizer loaded on top distributed Bragg reflector

Abstract: A novel polarization control method using a birefringent metal/dielectric (semiconductor) polarizer has been proposed for the purpose of controlling the polarization state of vertical-cavity surface-emitting lasers (VCSEL's). The proposed structure provides a phase difference for two orthogonal polarization states, resulting in reasonably large reflectivity difference in two polarizations. We have experimentally demonstrated the polarization control InGaAs-GaAs VCSEL's while maintaining a low threshold current density of 660 A/cm/sup 2/. A predominant polarization state along the designed orientation is obtained up to two times the threshold. >

Polarization scattering by soliton-soliton collisions.

Abstract: We have discovered experimentally that soliton–soliton collisions in wavelength division multiplexing significantly alter the polarization states of the colliding solitons. Analysis shows that the change in polarization is according to the cross product of the Stokes vectors of the colliding solitons. Birefringence of the fiber spans can turn this polarization scattering into a significant source of timing jitter.

Polarization mode dispersion minimization in fiber-wound piezoelectric cylinders.

Abstract: We describe a technique for minimizing polarization mode dispersion (PMD) in broadband interferometry for use with phase modulators of the type formed by coiling nominally circular-core single-mode optical fiber onto piezoelectric cylinders. The technique involves using two piezoelectric elements, arranged to be optically orthogonal. We show that in the general case the two cylinders give rise to four distinct interferograms, but by careful alignment of the elements we reduce these to two coincident interferograms. Hence the large PMD of a single-element modulator is reduced to a negligible level.

Theoretical analysis of birefringence and form‐induced polarization mode dispersion in birefringent optical fibers: A full‐vectorial approach

Abstract: A new numerical method for analyzing birefringence and dispersion characteristics of birefringent optical fibers is presented. A major advantage of the method, based on the solution of full‐vectorial Maxwell equations, is its high accuracy no matter how great the geometrical anisotropy of the optical fiber. To verify the reliability of our numerical procedure, the modal birefringence and the form‐induced polarization mode dispersion in elliptical core fibers with different eccentricities are investigated and their values compared with some theoretical and experimental results.

Synchronous polarization and phase modulation for improved performance of optical transmission systems

Abstract: A method and apparatus is provided for modulating the polarization of an optical signal. A polarization modulator receives an optical signal onto which data has been modulated at a predetermined frequency. The polarization modulator modulates the state of polarization of the optical signal at a frequency phase locked and equal to the same predetermined frequency at which the data is modulated onto the optical signal. The polarization modulation is performed so that the average value of the state of polarization over each modulation cycle is substantially equal to zero.

Coupled mode analysis of polarization volume hologram

Abstract: We theoretically analyze polarization holographic recording based on photoinduced dichroism and birefringence. Such vectorial recording is achieved by preferentially transforming dye molecules aligned with the incident polarization in dynamic photoanisotropic organic materials. Orthogonal linear and orthogonal circular recording geometries, which produce only pure polarization modulations, are considered. The analytic solutions of the intensity and phase of the recording beams at steady state are derived. The theoretical results indicate the dependence of diffraction efficiency on the photoinduced dichroism and birefringence and on the polarization state of the probe beam. Results of numerical simulation are provided and compared with the analytic solutions. >

Oscillation polarization selective semiconductor laser and optical communication system using the same

Abstract: An oscillation polarization selective semiconductor laser that switches oscillation polarization modes between two different polarization modes includes a laser structure on a substrate. An active layer of the laser structure includes plural sets of quantum wells and barriers. The structure of at least one set of quantum wells and the barriers is different from the other sets so that the gain spectra generated in the active layer for induced mutually perpendicular propagation modes are selectively controlled by controlling the carrier density injected into the active layer. The oscillation polarization selective semiconductor laser may be used as a light source in optical communication systems.

Linearly polarized fiber-optic laser

Abstract: A fiber-optic laser comprising a birefringent optic fiber possessing a Bragg grating at each of its ends,. A light source emits a light beam having two modes of polarization in the fiber. The birefringence of the fiber makes it possible to keep the two polarization modes separate. The two Bragg gratings are photo-recorded in the fiber and are made in such a way that their resonance wavelength is matched for one polarization. The wave emitted by the fiber is then polarized linearly along P1. Applications to linearly polarized lasers for optical transmission, instrumentation, spectroscopy, medicine, the detection of chemical species and telemetry.

Apparatus and method for driving oscillation polarisation selective light source, and optical communication system using the same

Abstract: In a light source apparatus, the polarization mode of oscillation light from a semiconductor laser is switchable between two different polarization modes when a modulation current is injected into a portion of a light waveguide of the semiconductor laser. Light in one polarization mode and light in the other polarization mode are separately obtained from the oscillation light from the semiconductor laser. At least the light in one of the two different polarization modes is converted to an electric signal. Current injected into the semiconductor laser is controlled based on the electric signal such that a modulation state of light from the semiconductor laser is stabilized. The light in the other polarization mode, or light in one polarization mode emitted from the other emission side of the semiconductor laser may be used for optical transmission.

Oscillation polarization mode selective semiconductor laser, modulation method therefor and optical communication system using the same

Abstract: A semiconductor laser includes a semiconductor laser structure having an active layer. The laser structure is designed such that light in both of two polarization modes can be excited therein. First and second reflectors are provided, and at least one of them is a distributed reflector which determines first and second reflection wavelengths for the two polarization modes. A coupling unit is provided for coupling the laser structure and the first and second reflectors for either of the light of the two polarization modes at first and second coupling wavelengths, which respectively coincide with the first and second reflection wavelengths. One of the light of the two polarization modes at the first and second reflection wavelengths is selectively propagated along a cavity comprised of the laser structure and the first and second reflectors by a control unit. Thus, light oscillates in one of the two polarization modes at the first and second reflection wavelengths.

Plane-wave reflection from uniaxial chiral interface and its application to polarization transformation

Abstract: Plane-wave reflection and transmission in a planar interface between air and an axially chiral uniaxial medium whose axis is parallel to the interface is considered in the present study. By finding the reflection dyadic and its eigensolutions, we demonstrate that by dimensioning the uniaxial medium in a proper way, it is possible to make a reflection-transforming reflecting surface. The surface is able to transform the incident linear polarization into any other polarization with chosen axial ratio and handedness, and the reflected polarization can be continuously adjusted by rotating the surface around its normal direction. The reflected power is seen to be independent of the polarization of the reflected wave.

Compensation of polarization mode dispersion by means of the Kerr effect for nonreturn-to-zero signals.

Abstract: We demonstrate numerically that a compensation of the polarization mode dispersion can be observed for nonreturn-to-zero signals as a result of a trapping effect, in analogy to the well-known soliton behavior. Conditions for such compensation are shown, and a comparison with the soliton case is reported.

Infrared polarization signatures for targets

Abstract: Based upon known surface optical properties, we develop a model to calculate and analyze the linear and circular polarization signatures for targets of known geometric shapes. The linear and circular polarization radiation (emission and reflection) generated from the target surfaces are studied in two model surface structures: metallic and non-metallic substrates with/without dielectric coating. Infrared I, Q, U, and V images of a model cylindrical target with these surfaces are calculated. This paper shows that dielectric coating enhances the power of generating circular polarization radiation. In addition to the linear polarization, circular polarization imaging attributable to target surface reflection is also shown to be feasible for practical application.

Compact programmable photonic variable delay devices

Abstract: Optical variable delay devices for providing variable true time delay to multiple optical beams simultaneously. A ladder-structured variable delay device comprises multiple basic building blocks stacked on top of each other resembling a ladder. Each basic building block has two polarization beamsplitters and a polarization rotator array arranged to form a trihedron; Controlling an array element of the polarization rotator array causes a beam passing through the array element either going up to a basic building block above it or reflect back towards a block below it. The beams going higher on the "ladder" experience longer optical path delay. An index-switched optical variable delay device comprises of many birefringent crystal segments connected with one another, with a polarization rotator array sandwiched between any two adjacent crystal segments. An array element in the polarization rotator array controls the polarization state of a beam passing through the element, causing the beam experience different refractive indices or path delays in the following crystal segment. By independently control each element in each polarization rotator array, variable optical path delays of each beam can be achieved. Finally, an index-switched variable delay device and a ladder-structured variable device are cascaded to form a new device which combines the advantages of the two individual devices. This programmable optic device has the properties of high packing density, low loss, easy fabrication, and virtually infinite bandwidth. The device is inherently two dimensional and has a packing density exceeding 25 lines/cm2. The delay resolution of the device is on the order of a femtosecond (one micron in space) and the total delay exceeds 10 nanosecond. In addition, the delay is reversible so that the same delay device can be used for both antenna transmitting and receiving.

Dispersion compensator and optical amplifier

Abstract: A dispersion compensator of the present invention includes a dispersion compensation fiber and a polarization conversion mirror. The dispersion compensation fiber has color dispersion of a sign opposite to the sign of the color dispersion of the optical fiber transmission line, and the length thereof is set so as to conform to the value of the color dispersion of the optical fiber transmission line. Light propagating in the optical fiber transmission line then propagates in the dispersion compensation fiber from a first end toward a second end of it and is supplied to the polarization conversion mirror. The light supplied to the polarization conversion mirror is converted into light of a polarization condition orthogonal and time-reversed to the polarization condition of the light supplied to the polarization conversion mirror, and propagates in the dispersion compensation fiber from the second end toward the first end of it. This enables compensation not only for color dispersion but also for polarization mode dispersion.

Demonstration of amplification of a polarized soft-x-ray laser beam in a neonlike germanium plasma.

Abstract: We report results of polarization experiments on the collisionally excited Ne-like Ge soft-x-ray laser where we have used an injector-amplifier multistage geometry. The polarization state of the x-ray beam was analyzed by two crossed 45{degree} angle of incidence multilayer mirrors which act as linear polarizers. Results were evaluated by comparing intensities of time-integrated beam patterns behind each polarizer. The polarization state of the amplified spontaneous emission (ASE) output at 23.2 and 23.6 nm from the injector plasma alone was systematically studied and, as expected, revealed no macroscopic degree of polarization observable within the precision of the experiment. When the injector output beam was linearly polarized by using a third 45{degree} angle of incidence multilayer mirror and coupled into the amplifier plasma, the degree of polarization of the amplifier output was {similar_to}0.98, the total gain-length product attained for the polarized beam was {approx}12, and the final beam energy was {approx}20 nJ. The results obtained are discussed with relevance to processes determining the polarization properties of unsaturated ASE systems.

Optical isolator, circulator, switch or the like, including a faraday rotator

Abstract: Optical isolator, circulator, switch or the like, including a Faraday rotator to which a magnetic field is applied which is oriented along the direction of propagation of light and which is arranged between a preceding polarization filter and a succeeding polarization filter whose planes of polarization enclose an angle with respect to each other such that light can only traverse in one direction, the Faraday rotator having different propagation constants βTE and βTM in a TE plane and a TM plane, respectively. The elaborate technique for adapting the propagation constants of the TE wave and the TM wave is mitigated in that the TE plane of the Faraday rotator is aligned in such a way that it extends between the planes of polarization of the polarization filters.

Polarization measurement of SR from a helical undulator using a quarter‐wave plate for a wavelength of 12.8 nm

Abstract: At a wavelength of 12.8 nm, polarization states of nominally circularly polarized light emitted from a helical undulator and monochromatized by a grating monochromator were measured (KEK‐PF BL‐28A). With a transmission‐type multilayer quarter‐wave plate and a multilayer mirror polarization analyzer mounted on a beamline ellipsometer, all polarization parameters of the circularly polarized SR at various conditions were determined. The best degree of circular polarization after the grating monochromator was found to be as high as 0.95.

Polarization properties of a twisted fiber laser.

Abstract: The characteristics of the output polarization angle and the polarization-mode beat frequency of a twisted fiber laser are investigated. A theoretical model is used to describe successfully the polarization properties.

Method for reducing birefringence in optical gratings

Abstract: A method is provided for reducing the polarization shift between different modes of an optical signal propagating in an optical grating (55) having a plurality of waveguides (39,...39M) extending in a common plane. The method includes the step of imparting curvature to the optical grating along a line that traverses the plurality of waveguides in a direction that is substantially perpendicular to the direction in which the optical signal propagates. The curvature varies in a nonuniform manner along the line (A-B) to which it is imparted. The curvature may vary in a substantially linear manner along this line, which in some cases may define a symmetry axis of the grating. Sufficient curvature may be imparted to substantially eliminate the polarization shift. The curvature may be imparted by flexing the optical grating at two contact points respectively located near a longest and shortest of the plurality of waveguides.

Polarization state changing apparatus and polarization degree measuring apparatus using the same

Abstract: A polarization state changing apparatus which can change the polarization state of an incident polarized light entering to an optical fiber to any direction and can output is provided. This polarization state changing apparatus, in an embodiment, comprises three polarization plane maintaining optical fibers 10, 20 and 300 which are serially connected at two polarization plane changing parts 30 and 30'. Those three polarization plane maintaining optical fibers are connected at the polarization plane changing parts 30 and 30'so that the optical axes X and Y of the adjacent optical fibers are mutually rotated at an angle of 45 degrees in terms of the fiber axis. Stress application parts for applying stress to each of the polarization plane maintaining optical fibers are provided. In a specific example, each optical fiber is wound around each piezoelectric element cylinder and predetermined stress is applied to each optical fiber by driving those piezoelectric element cylinders by power supplies each of which oscillating frequency and generated voltage are both variable. Also, a polarization degree measuring apparatus using the polarization state changing apparatus is provided to measure degree of polarization accurately and quickly.

Optical apparatus with combined polarization functions

Abstract: Apparatus performs polarization dependent functions although the apparatus is polarization independent with respect to the outside world. The apparatus produces parallel beams with like polarization, and the parallel beams are then subject to polarization dependent processing.

Polarization-based fiber optic delay lines

Abstract: Multichannel fiber-optic delay line architectures using optical polarization switching are proposed that use nonpolarization maintaining single-mode fibers while still maintaining high extinction polarization properties of the switched optical beams. Critical birefringence compensation and noise reduction techniques are introduced and demonstrated for these delay lines showing high optical polarization extinction (> 39 dB) and electrical signal-to-noise ratio (> 92 dB) results.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Anisotropic diffusion of the state of polarization in optical fibers with randomly varying birefringence.

Abstract: Polarization diffusion in communication fibers is studied Diffusion of the states of polarization in an optical fiber is found to be anisotropic on the surface of the Poincare sphere The predicted anisotropy has significant implications for nonlinear evolution in long-distance communication systems

Polarization chaos in an optically pumped laser.

Abstract: We study the steady-state and dynamic behavior of an optically pumped J = 0 → J = 1 → J = 0 laser operating with an isotropic ring cavity and an axial magnetic field. The gain anisotropy induced by a linearly polarized pump-laser field leads, in the steady state, to locking of the two circularly polarized components of the laser field, which acquires a linear polarization parallel to that of the pump field. In the presence of laser intensity instabilities, however, locking does not occur, and polarization instabilities appear. For the first time to our knowledge, polarization chaos has been found in a laser system.