Showing papers on "Polarization rotator published in 2002"

Focus shaping using cylindrical vector beams

Abstract: We report a focus shaping technique using generalized cylindrical vector beams. A generalized cylindrical vector beam can be decomposed into radially polarized and azimuthally polarized components. Such a generalized cylindrical beam can be generated from a radially polarized or an azimuthally polarized light using a two-half-wave-plate polarization rotator. The intensity pattern at the focus can be tailored by appropriately adjusting the rotation angle. Peak-centered, donut and flattop focal shapes can be obtained using this technique.

Degree of polarization for optical near fields.

Abstract: We investigate an extension to the concept of degree of polarization that applies to arbitrary electromagnetic fields, i.e., fields whose wave fronts are not necessarily planar. The approach makes use of generalized spectral Stokes parameters that appear as coefficients, when the full 3 x 3 spectral coherence matrix is expanded in terms of the Gell-Mann matrices. By defining the degree of polarization in terms of these parameters in a manner analogous to the conventional planar-field case, we are led to a formula that consists of scalar invariants of the spectral coherence matrix only. We show that attractive physical insight is gained by expressing the three-dimensional degree of polarization explicitly with the help of the correlations between the three orthogonal spectral components of the electric field. Furthermore, we discuss the fundamental differences in characterizing the polarization state of a field by employing either the two- or the three-dimensional coherence-matrix formalism. The extension of the concept of the degree of polarization to include electromagnetic fields having structures of arbitrary form is expected to be particularly useful, for example, in near-field optics.

Polarization spectroscopy of a closed atomic transition: applications to laser frequency locking

Abstract: We study polarization spectroscopy of Rb vapour. A weak probe beam analyses the birefringence induced in a room temperature vapour by a strong counterpropagating circularly polarized pump beam. In contrast to most other work on polarization spectroscopy, we use a polarization beam splitting cube and two detectors (rather than a polarizer and one detector) to analyse the probe beam. The signal is in the form of a derivative of a Lorentzian. For theoretical analysis we study the closed atomic transition 5 2S1/2 (F = 3) → 5 2P3/2 (F' = 4) in the D2 line of 85Rb. We study the time needed to redistribute population among the mF states, derive an expression for the expected lineshape and present experimental data in excellent agreement with theory. The polarization spectrum provides an ideal error signal for frequency stabilization of a laser. We describe the geometry and parameters for optimizing the error signal.

Communication with dynamically fluctuating states of light polarization.

Abstract: The fast, irregular, fluctuations of the state of polarization of light output from an erbium doper fiber ring laser are used to communicate digital information. The experiments illustrate the application of a dynamical encoding and information recovery scheme that is robust to perturbations of the communication channel, a standard single mode fiber. A fiber-optic polarization analyzer was used to measure and visualize the polarization dynamics at nanosecond time scales on the Poincare sphere.

QED and the high polarization of the thermal radiation from neutron stars

Abstract: The thermal emission of strongly magnetized neutron-star atmospheres is thought to be highly polarized. However, because of the different orientations of the magnetic field over the surface of the neutron star (NS), it is commonly assumed that the net observed polarization will be significantly reduced as the polarization from different regions will cancel each other. We show that the birefringence of the magnetized QED vacuum decouples the polarization modes in the magnetosphere; therefore, the direction of the polarization follows the direction of the magnetic field up to a large distance from the stellar surface. At this distance, the rays that leave the surface and are destined for our detectors pass through only a small solid angle; consequently, the polarization direction of the emission originating in different regions will tend to align together. The net observed polarization of the thermal radiation of NSs should therefore be very large. Measurement of this polarization will be the first direct evidence of the birefringence of the magnetized vacuum due to QED and a direct probe of behavior of the vacuum at magnetic fields of order of and above the critical QED field of $4.4\ifmmode\times\else\texttimes\fi{}{10}^{13} \mathrm{G}.$ The large observable polarization will also help us learn more about the atmospheric properties of NSs.

Projection display using a wire grid polarization beamsplitter with compensator

Abstract: A display apparatus ( 10 ) including a light source ( 15 ) for forming a beam of light ( 130 ). A pre-polarizer ( 45 ) polarizes the beam of light ( 130 ) to provide a polarized beam of light. A wire grid polarization beamsplitter ( 50 ) receives the polarized beam of light and transmits the polarized beam of light which has a first polarization, and reflects the polarized beam of light which has a second polarization. A reflective spatial light modulator ( 55 ) selectively modulates the polarized beam of light that has a first polarization to encode image data thereon in order to form a modulated beam ( 360 ) and reflects the modulated beam back to the wire grid polarization beamsplitter ( 50 ). A compensator ( 260 ) is located between the wire grid polarization beamsplitter ( 50 ) and the reflective spatial light modulator ( 55 ) for conditioning oblique and skew rays of the modulated beam ( 360 ). The wire grid polarization beamsplitter ( 50 ) reflects the compensated modulated beam ( 360 ) and the wire gird polarization beamsplitter ( 50 ) is rotated in plane to optimize the contrast. A polarization analyzer ( 60 ) removes residual light of the opposite polarization state from the compensated modulated beam ( 360 ). Image-forming optics ( 20 ) form an image from the compensated modulated beam ( 360 ).

Elimination of polarization degeneracy in round waveguides.

Abstract: We show how to design a round optical fiber so that it is effectively single moded, with no polarization degeneracy. Such fibers would be free from the consequences of polarization degeneracy or near degeneracy – phenomena such as polarization fading in interferometry, and polarization mode dispersion – and so may offer an alternative to polarization maintaining fibers for the avoidance of these phenomena. The design presented builds on an earlier observation of polarization selective refection in Bragg fibers.

Simple technique for measuring the Goos–Hänchen effect with polarization modulation and a position-sensitive detector

Abstract: An original approach to directly measuring the Goos-Hanchen longitudinal shift between TE and TM polarization states during a total internal reflection is introduced. The technique is based on the modulation of the polarization state of a laser by an electro-optic modulator combined with a precise measurement of the resulting spatial displacement with a position-sensitive detector. This method presents many advantages over other techniques and allows measurements at different wavelengths over a broad range for the incident angle.

Measure of twist-induced circular birefringence in long single-mode fibers: theory and experiments

Abstract: Production defects and external perturbations cause standard telecommunication fibers to be randomly birefringent. Fiber birefringence is the origin of the well-known polarization mode dispersion (PMD), which degrades system performances. The knowledge of birefringence properties may be crucial, especially when problems like development of low-PMD fibers or PMD interaction with optical nonlinearities in very high-capacity systems are faced. Some techniques are known to measure birefringence, and useful results have been obtained for both installed and wound-on-drum fibers. However, measurement of the circular component of birefringence still presents difficulties. In this paper, a new method for circular birefringence measurement is proposed that applies to long single-mode twisted fibers. The technique is based on polarization-sensitive optical time-domain reflectometry. Experimental results are in good agreement with the theoretical analysis.

Dispersion of birefringence and differential group delay in polarization-maintaining fiber

Abstract: We present an interferometric technique for measurement of the dispersion of birefringence in polarization-maintaining fibers. The approach yields measurements over a broad spectral range from analysis of single interferograms obtained in a tandem inteferometer. The technique is demonstrated to measure first-, second-, and third-order dispersion of the differential propagation constant, corresponding to differential group delay (DGD) and its dispersion to second order; measurements are immune to asymmetry in the interferomgram that is being processed. The technique is further applied to measurement of the temperature dependence of DGD and its first-order dispersion.

Micro-electro-mechanical system-based digitally controlled optical beam profiler.

Abstract: An optical beam profiler is introduced that uses a two-dimensional (2-D) small-tilt micromirror device. Its key features include fast speed, digital control, low polarization sensitivity, and wavelength independence. The use of this 2-D multipixel device opens up the important possibility of realizing several beam profile measurement concepts, such as a moving knife edge, a scanning slit, a moving pinhole, a variable aperture, and a 2-D photodiode array. The experimental proof of the optical beam profiler concept using a 2-D digital micromirror device to simulate the 2-D moving knife edge indicates a small measurement error of 0.19% compared with the expected number based on a Gaussian beam-propagation analysis. Other 2-D pixel arrays such as a liquid-crystal-based 90° polarization rotator sandwiched between crossed polarizers can also be exploited for the optical beam whose polarization direction is known.

Wavelength selective optical switch

Abstract: A wavelength selective switch, in which an input optical signal is wavelength-dispersed and polarization-split in two angularly oriented planes. A polarization rotation device, such as a liquid crystal polarization modulator, pixelated along the wave-length dispersive direction such that each pixel operates on a separate wavelength channel, rotates the polarization of the light signal passing through the pixel, according to the control voltage applied to that pixel. The polarization modulated signals are then wave-length-recombined and polarization-recombined by means of similar dispersion and polarization combining components as were used to respectively disperse and split the input signals. The direction of the output signal is determined by whether the polarization of a particular wavelength channel was rotated by the polarization modulator pixel, or not. In this way, a fast, wavelength dependent, optical switch is provided, capable of use in WDM switching applications.

Analysis of the spatial distribution of polarized light backscattered from layered scattering media.

Abstract: The scattering of polarized light from a two layer scattering medium is investigated using Monte Carlo simulations. First order and normalized second order moments are used to analyze the spatial properties of the emerging light in different polarization states. Linearly and circularly polarized illumination is used to probe different depths. Absorption and layer thickness are varied and it is demonstrated that the determination of these values is aided by the inclusion of polarization information. The lateral and depth localization of light by polarization subtraction is also quantified. Potential applications of these techniques are burn depth and melanoma thickness measurements.

Two-mode emission and polarization dynamics at lasing threshold in a vertical-cavity surface-emitting laser

Abstract: Summary form only given. VCSELs are well known to show polarization instabilities or polarization switching (PS) if the current is changed as well as fluctuations of their state of polarization at fixed current. Nevertheless, in most devices only one of two possible orthogonal linear polarized fundamental transverse modes, which are frequency split by birefringence, is emitted at the threshold to laser emission. In this contribution, we present the results of experimental investigations on the situation when both of the fundamental transverse modes are excited at threshold.

Structures and methods for reducing aberration in integrated circuit fabrication systems

Abstract: An optical system includes multiple cubic crystalline optical elements and one or more polarization rotators in which the crystal lattices of the cubic crystalline optical elements are oriented with respect to each other to reduce the effects of intrinsic birefringence and produce a system with reduced retardance. The optical system may be a refractive or catadioptric system having a high numerical aperture and using light with a wavelength at or below 248 nanometers. The net retardance of the system is less than the sum of the retardance contributions of the respective optical elements. In one embodiment, all cubic crystalline optical elements are oriented with identical three dimensional cubic crystalline lattice directions, a 90° polarization rotator divides the system into front and rear groups such that the net retardance of the front group is balanced by the net retardance of the rear group. The optical system may be used in a photolithography tool to pattern substrates such as semiconductor substrates and thereby produce semiconductor devices.

Method for compensating polarization mode dispersion occurring in optical transmission fiber and apparatus therefor

Abstract: Method for compensating polarization mode dispersion, The method includes: transforming states and directions of polarization components of an optical signal received from the optical transmission line, rotating the polarization components of the optical signal output from the polarization controller, separating two orthogonal polarization components of the output from the polarization rotator so that a first polarization component is transmitted to an output path and a second polarization component is transmitted to a monitoring path, controlling the PC using a feedback control to minimize an electrical power filtered at a specified frequency so that the two orthogonal polarization components of the optical input signal to the polarization beam splitter are aligned to two axes of the PBS, and controlling the polarization rotator by comparing an optical power of the first polarization component transmitted to the output path with an optical power of the second polarization component transmitted to the monitoring path.

Structures and methods for reducing aberration in optical systems

Abstract: An optical system includes multiple cubic crystalline optical element (162) and one or more polarization rotator (180) in which the crystal lattices of the cubic crystalline optical elements are oriented with respect to each other to reduce the effects of intrinsic birefringence and produce a system with reduced retardance. The optical system may be a refractive or catadioptric system having a high numerical aperture and using light with a wavelength at or below 248 nanometers. The net retardance of the system is less than the sum of the retardance contributions of the respective optical elements.

All fiber polarization mode dispersion compensator

Abstract: A polarization mode dispersion compensator corrects polarization mode dispersion in an optical signal having a fast polarization mode component, a slow polarization mode component and a time differential between the components. The compensator includes a phase shifter and a variable delay section. An input of the phase shifter is coupled to an optical device that provides an optical signal that exhibits polarization mode dispersion. The phase shifter functions to rotate the optical signal principal states of polarization to a desired orientation. The variable delay section includes an input, an output and at least one optical fiber delay line. The input of the variable delay section is coupled to the output of the phase shifter and the desired orientation of the optical signal principal states of polarization are substantially rotated to be in alignment with one of a fast axis and a slow axis of each of the one or more fiber delay lines. In this manner, the variable delay section functions to delay the principal states of polarization of the optical signal with respect to one another as a function of whether the principal states of polarization traverse said one of a fast axis and a slow axis of the at least one optical fiber delay line, thus reducing the time differential between the components.

Polarization holographic grating based on azo-dye-doped polymer-ball-type polymer-dispersed liquid crystals

Abstract: A polarization grating (PG) written in an azo-dye-doped film of polymer-ball-type polymer-dispersed liquid crystals was investigated. The writing beams were two mutually orthogonal (s- and p-polarized) polarized beams. The PG resulted from molecular reorientation of the liquid crystals as a result of their interaction with the dye molecules adsorbed on the surface of the polymer balls. Polarization characteristics of the diffracted beams and the grating pattern were studied under a polarizing optical microscope with a crossed analyzer. The results indicate that the PG diffracts the linearly polarized incident light into beams with various polarizations. Accordingly, the grating can be used as an unpolarized or a polarized beam splitter, depending on the polarization of the incident light. A model based on the Jones matrix approach was developed, and it closely fits the experimental results.

Polarization-switching influence on the intensity noise of vertical-cavity surface-emitting lasers

Abstract: We experimentally investigate the influence of polarization switching on the intensity noise of transverse single-mode vertical-cavity surface-emitting lasers. We show that a polarization switch always leads to strong noise in the two individual orthogonal polarization modes over a large range of pump current in the vicinity of the switch, whereas the effect on the total emission noise strongly depends on the strength of the coupling between total intensity noise and polarization fluctuations, which is mainly determined by the amount of birefringence. Thus our results demonstrate that the occurrence of a polarization switch can have a strong deteriorating effect on the noise behavior, not only if polarization selection is present, but also on the total emission noise, and therefore has to be considered in future investigations and low-noise applications.

Influence of polarization mode dispersion value in dispersion-compensating fibers on the polarization dependence of Raman gain

Abstract: Polarization mode dispersion (PMD) of amplifying or transmitting fibers may significantly change the polarization dependence of Raman gain. Experimental results are presented that show low polarization dependence of the Raman gain in dispersion-compensating fibers with high PMD values for both copropagating and counterpropagating pumping configurations. The measured data demonstrate that it is possible to avoid the need for depolarization of a pump source in Raman amplifiers.

Reducing aberration in optical systems comprising cubic crystalline optical elements

Abstract: An optical system includes multiple cubic crystalline optical elements and one or more polarization rotators in which the crystal lattices of the cubic crystalline optical elements are oriented with respect to each other to reduce the effects of intrinsic birefringence and produce a system with reduced retardance. The optical system may be a refractive or catadioptric system having a high numerical aperture and using light with a wavelength at or below 248 nanometers. The net retardance of the system is less than the sum of the retardance contributions of the respective optical elements. In one embodiment, all cubic crystalline optical elements are oriented with identical three dimensional cubic crystalline lattice directions, a 90° polarization rotator divides the system into front and rear groups such that the net retardance of the front group is balanced by the net retardance of the rear group. The optical system may be used in a photolithography tool to pattern substrates such as semiconductor substrates and thereby produce semiconductor devices.

Polarization mode dispersion of spun fibers: an analytical solution.

Abstract: A simple analytical solution is derived from coupled-mode theory to describe the evolution of polarization mode dispersion (PMD) in spun fibers. For practical fibers with a beat length greater than a few meters, the solution is valid for a whole category of periodic spin profiles. We find that the PMD change factor is independent of the intrinsic birefringence of the fiber and the fiber PMD scales linearly with the fiber length in the short length regime. This solution allows us to determine phase-matching conditions for spun fibers, in which the PMD evolves periodically along the fiber. An example of determining the phase-matching conditions of sinusoidal-type spin profiles is given.

Polarization and wavelength stable superfluorescent sources

Abstract: The instability of the mean wavelength of a superfluorescent fiber source (SFS) is reduced by randomizing the polarization of light from a pump source or by using polarization maintaining components. In one embodiment, the polarization of a pump source is made more random, leading to greater stability of the mean wavelength of the SFS, with an output mean wavelength that is stable to better than 3 ppm for full rotation of the pump polarization state. In another embodiment, the polarization of optical radiation throughout the device is kept substantially constant by using polarization maintaining fiber and components, thereby leading to enhanced mean wavelength stability of the SFS.

Method and apparatus for compensating for polarization mode dispersion (PMD) using a Mach-Zender interferometer

Abstract: Polarization Mode Dispersion (PMD) causes an optical pulse to be split into two arbitrarily oriented orthogonally polarized PMD pulses with a differential group delay therebetween in an optical transmission line. To compensate for the PMD induced distortion, a polarization controller in a PMD compensator selectively adjusts the aligning of the received arbitrarily oriented first and second principal states of polarization of the PMD pulses to match fixed orientations of predetermined first and second principal states of polarization of a beam splitter. First and second output paths of the beam splitter are coupled to first and second paths of a Mach-Zender interferometer arrangement. The Mach-Zender interferometer arrangement measures the PMD differential delay between the first and second principal states of polarization of the respective first and second PMD optical pulses, and selectively compensates for the measured differential delay. An optical combiner combines output signals from first and second paths of the interferometer arrangement to generate a combined output signal. A control arrangement selectively controls both the compensation for a measured differential delay in the interferometer arrangement in response to at least a portion of the combined output signal from the optical combiner, and selectively controls the adjustment of the aligning of the received arbitrarily oriented first and second polarizations in the polarization controller.

Variable linear polarization from an X-ray undulator

Abstract: A new X-ray undulator has been designed and constructed which produces linearly polarized X-rays in which the plane of polarization can be oriented to a user selectable angle, from horizontal to vertical. Based on the Apple-II elliptically polarizing undulator (EPU), the undulator rotates the angle of the linear polarization by a simple longitudinal motion of the undulator magnets. Combined with the circular and elliptical polarization capabilities of the EPU operating in the standard mode, this new undulator produces soft X-ray radiation with versatile polarization control. This paper describes the magnetic structure of the device and presents an analysis of the magnetic field with varying undulator parameters. The variable linear polarization capability is then exhibited by measuring the X-ray absorption spectrum of an oriented polytetrafluoroethylene thin film. This experiment, which measures the linear dichroism of the sample at two peaks near the C 1s absorption edge, demonstrates the continuous polarization rotation capabilities of the undulator.

Nonlinear guided propagation of few-optical-cycle laser pulses with arbitrary polarization states

Abstract: The physics of guided nonlinear propagation of ultrashort pulses with an arbitrary polarization state is investigated down to the few-cycle regime. The electric field of the pulse is described in terms of monochromatic circularly polarized waves; numerical simulations for the propagation of ultrashort pulses with elliptical and circular polarization are presented and discussed. The theoretical results can be applied to the compression of high-energy laser pulses with an arbitrary polarization state. An experimental demonstration of the compression of circularly polarized pulses is presented.

Optical imaging system with polarizer and a crystalline-quartz plate for use therewith

Abstract: An optical imaging system having several imaging optical components (L 1 -L 16 ) sequentially arranged along an optical axis ( 16 ), a means for creating radially polarized light arranged at a given location in that region extending up to the last of said imaging optical components, and a crystalline-quartz plate employable in such a system. A polarization rotator ( 14 ) for rotating the planes of polarization of radially polarized light and transforming same into tangentially polarized light, particularly in the form of a crystalline-quartz plate as noted above, is provided at a given location within a region commencing where those imaging optical components that follow said means for creating radially polarized light in the optical train are arranged. The optical imaging system is particularly advantageous when embodied as a microlithographic projection exposure system.

Polarized excimer laser-induced birefringence in silica

Abstract: We have used linearly polarized 193-nm-excimer laser irradiation to create polarization-induced birefringence in silica. We have observed the polarization-induced birefringence irrespective of whether the sample undergoes net compaction or expansion. The sign of the birefringence is dependent on whether the glass is expanding or compacting. It is suggested that the birefringence derives from an anisotropic density change effected by the linearly polarized exposure. This effect can be expressed formally as an optical frequency-induced dc electrostriction.