Showing papers on "Waveplate published in 2006"

Terahertz achromatic quarter-wave plate

Abstract: Phase retarders usually present a strong frequency dependence. We discuss the design and characterization of a terahertz achromatic quarter-wave plate. This wave plate is made from six birefringent quartz plates precisely designed and stacked together. Phase retardation has been measured over the whole terahertz range by terahertz polarimetry. This achromatic wave plate demonstrates a huge frequency bandwidth (upsilonmax/upsilonmin approximately 7), and therefore can be applied to terahertz time domain spectroscopy and polarimetry.

Voltage-controlled liquid-crystal terahertz phase shifter and quarter-wave plate

Abstract: Phase shift exceeding π/2 at 1 THz is demonstrated by using electrically controlled birefringence in a homeotropically aligned nematic liquid crystal (E7) cell, 570 μm in thickness. The driving voltage required for a phase shift of 90° is 125 V (rms). We demonstrate that the phase shifter works as an electrically switchable quarter-wave plate at 1 THz. The device can also be used as an electrically tuned phase compensator around the quarter-wave point near 1 THz.

High resolution autostereoscopic display

Abstract: A high-resolution autostereoscopic display is provided. The autostereoscopic display includes a controller (131); a display panel (121) receiving an image signal from the controller (131), forming an image, and including pixels and an inactive area between the pixels; a polarizer (124) polarizing light emitted from the display panel (121) to have a first polarization; a polarization switching controller (130); a polarization switch (125) selectively converting the light with the first polarization into light with a second polarization in response to the electrical control of the polarization switching controller (130); a selection controller (129); a first electro-optical birefringent layer (126) having an optical axis that direction is changed by an electrical control of the selection controller (129) and including a plurality of first lenticular lenses (126a) separated by a predetermined pitch; and a second electro-optical birefringent layer (127) having an optical axis that direction is changed by the electrical control of the selection controller (129), includes a plurality of second lenticular lenses that are arranged with the same pitch as the first lenticular lenses (126a) are and shifted by half the pitch from the first lenticular lenses (126a).

Confocal self-interference microscopy from which side lobe has been removed

Abstract: The present invention relates to confocal self-interference microscopy. The confocal self-interference microscopy further includes a first polarizer for polarizing reflected or fluorescent light from a specimen, a first birefringence wave plate for separating the light from the first polarizer into two beams along a polarizing direction, a second polarizer for polarizing the two beams from the first birefringence wave plate, a second birefringence wave plate for separating the two beams from the second polarizer into four beams along the polarizing direction, and a third polarizer for polarizing the four beams from the second birefringence wave plate, in the existing confocal microscopy. Optic-axes of the first and second birefringence wave plates exist on the same plane, optic-axes of the first and second birefringence wave plates are inclined from an optical axis of the entire optical system at a predetermined angle, and self-interference spatial periods of the first and second birefringence wave plates are different from each other.

Snapshot complete imaging polarimeter using Savart plates

Abstract: An interferometric method for measuring the two-dimensional distribution of the state of polarization (SOP) of light is presented. A pair of Savart plates, a half-wave plate, and an analyzer are inserted between the lenses of a double-diffraction imaging system, so that multiple interference fringes are generated over the video camera. The Fourier analysis of the image obtained from the video camera allows us to determine the two-dimensional distributions of the four Stokes parameters over the object plane. No mechanical or active components for polarization control are required and two dimensional distributions of any parameters related to SOP can be determined from the single image. Principle of this method is experimentally demonstrated by measuring the SOP distribution of the light transmitted by a liquid crystal cell.

Achromatic half-wave plate for submillimeter instruments in cosmic microwave background astronomy: modeling and simulation

Abstract: We adopted an existing formalism and modified it to simulate, with high precision, the transmission, reflection, and absorption of multiple-plate birefringent devices as a function of frequency. To validate the model, we use it to compare the measured properties of an achromatic five-plate device with a broadband antireflection coating to expectations derived from the material optical constants and its geometric configuration. The half-wave plate presented here is observed to perform well with a phase shift variation of <2° from the ideal 180° over a bandwidth of Δv/v∼1 at millimeter wavelengths. This formalism represents a powerful design tool for birefringent polarization modulators and enables its optical properties to be specified with high accuracy.

Space-variant waveplate for polarization conversion, methods and applications

Abstract: Embodiments of the invention are directed to apparatus and methods for converting spatially homogeneously polarized light into spatially inhomogeneously polarized light having a fast axis orientation that varies in a smooth and continuous manner over a pupil aperture. A space-variant waveplate referred to herein as a polarization converter includes an optically transmissive window characterized by a symmetric stress birefringence that provides at least λ/4 retardance and, more particularly, λ/2 retardance over an annular region centered about the optical axis of the window. Structural embodiments of the polarization converter include a mechanical compression housing and a thermal compression housing. Radially and azimuthally polarized vortex beams including cylindrical vector beams and counter-rotating beams can be generated from uniformly plane polarized input beams propagating through the polarization converter. Low-order polarization vortex beams can be optically combined to produce higher-order scalar vortex beams. Embodiments of the invention are also directed to various optical illumination and imaging systems utilizing the apparatus and methods described herein.

Linear to axial or radial polarization conversion using a liquid crystal gel

Abstract: Two types of liquid crystal (LC) gels with radial or twisted-radial molecular orientation are fabricated using a radial electric field generated by an indium-tin-oxide hole electrode in the bottom substrate. If the top substrate is not buffed, the radial-type LC gel is formed which can convert linearly polarized light into axially polarized light. On the other hand, if the top substrate is homogeneously buffed, then a twisted-radial LC gel is produced which can convert linearly polarized light into radially polarized light. These polarization converters are useful for diffractive optics and optical imaging systems.

Achromatic half-wave plate for submillimeter instruments in cosmic microwave background astronomy: experimental characterization

Abstract: An achromatic half-wave plate (HWP) to be used in millimeter cosmic microwave background (CMB) polarization experiments has been designed, manufactured, and tested. The design is based on the 5-plates Pancharatnam recipe and it works in the frequency range 85-185 GHz. A model has been used to predict the transmission, reflection, absorption, and phase shift as a function of frequency. The HWP has been tested by using coherent radiation from a back-wave oscillator to investigate its modulation efficiency and with incoherent radiation from a polarizing Fourier transform spectrometer (FTS) to explore its frequency behavior. The FTS measurements have been fitted with an optical performance model which is in excellent agreement with the data. A detailed analysis of the data also allows a precise determination of the HWP fast and slow axes in the frequency band of operation. A list of the HWP performance characteristics is reported including estimates of its cross polarization.

Optical filter and optical device provided with this optical filter

Abstract: Light emitted from a taking lens 20 enters a first birefringent plate 1 a to be spatially divided along a first direction extending perpendicular to the direction in which the light advances to achieve two separate rays L 10 and L 20. The vibrational planes of the two light fluxes L 10 and L 20 emitted from the first birefringent plate 1 a are converted to a circularly polarized light by a phase plate 1 c. The two light fluxes L 10 ′ and L 20 ′ emitted from the phase plate 1 c are each spatially divided into two by a second birefringent plate 1 d along a second direction extending perpendicular to the first direction to achieve four separate rays L 11, L 12. L 21 and L 22, to be guided to an imaging plane 15 a of an imaging device 15. At least either the first birefringent plate or the second birefringent plate is constituted of lithium niobate, rutile, Chilean nitrate, or the like.

Reduced wavelength-dependent quarter-wave plate fabricated by a multilayered subwavelength structure

Abstract: We developed a novel fabrication method of a reduced wavelength-dependent quarter-wave plate (QWP) based on form birefringence of a multilayered subwavelength structure. The multilayered structure was constructed by depositing a high-refractive-index thin film on a subwavelength-structured substrate with a low refractive index. The surface structure of the substrate was shallow enough to be formed by a mass replication technology. A high-refractive-index subwavelength grating was formed on ridges of the substrate by sputtering Zn2SnO4 (refractive index of 2.03 at a wavelength of 633 nm). Moreover, since the grooves of the high-refractive-index grating were very deep and narrow, the dispersion of form birefringence suppressed the dependency of phase retardance on the wavelength of light in a limited spectral region. The phase retardance of the fabricated QWP was 89° at a 633 nm wavelength and 79° at a 785 nm wavelength.

Broadband two-dimensional photonic crystal wave plate

Abstract: It is demonstrated in this work that the phase shift of reflected wave as a function of frequency changes smoothly within the stop band of two-dimensional photonic crystal, while it changes sharply within the passband. In the stop band, the difference between the phase shift of TE and that of TM reflected wave could remain constant in a rather wide frequency region. By using the difference of phase shift, the authors obtain a kind of half-wave plate that can be used in broad spectral bandwidth. Such photonic crystal wave plates have predominance in optical and optoelectronic integration.

Equivalent retarder-rotator approach to on-state twisted nematic liquid crystal displays

Abstract: Polarization properties of a twisted nematic liquid crystal cell are fully characterized by an equivalent optical system that consists of a retarder wave plate and a rotator. In this paper we show that this result is of interest to optimize the light-modulation capabilities of a voltage-addressed liquid crystal display (LCD). We provide two examples. First, we demonstrate a calibration method that can be carried out by a standard polarimetric technique with a high degree of precision. Second, we propose an optical device to generate a family of equiazimuth polarization states by adding a quarter-wave plate to the LCD. We find that the design procedure is best described in geometrical terms on the Poincare sphere by use of the equivalent model. Finally, laboratory results corresponding to a commercial LCD are presented.

Optimization of the contrast ratio of a ferroelectric liquid crystal optical modulator

Abstract: In this work we present a simple method for the characterization of a ferroelectric liquid crystal (FLC) optical modulator and the optimization of its contrast ratio. This device acts as switchable wave-plate, where the orientations of the principal axes rotate under the action of a bipolar applied voltage. It is designed to produce a binary intensity modulation when the phase shift introduced between the principal axes is equal to π radians. We present a simple technique to optimize its response when the phase shift differs from this ideal value, in order to produce a highly contrasted intensity modulation. The technique uses elliptically polarized light and requires the use of an additional quarter-wave-plate. This situation is experimentally demonstrated using a commercially available ferroelectric liquid crystal cell and two He–Ne lasers with wavelengths of 543 and 633 nm, respectively.

Two-wave-plate compensator method for full-field retardation measurements.

Abstract: The two-wave-plate compensator (TWC) method is expanded for full-field retardation measurements by use of a polarization microscope. The sample image is projected onto a CCD camera connected to a computer, allowing the retardation to be measured at all pixels. The retardation accuracy of this implementation of the TWC is evaluated to be 0.06 nm. The method is applied to polarization-maintaining fibers and long-period fiber gratings. The measured retardation is in good agreement with the crossed-polarizer images of the fibers. The method achieves a spatial resolution of 0.45 µm and a retardation resolution of 0.07 nm. The full-field TWC method can thus be a useful tool for characterizing and monitoring the fabrication of optical devices.

Pulse polarization splitting in a transient wave plate

Abstract: We demonstrate propagation of ultrafast laser pulses through a molecular gas acting as a transient wave plate under conditions of strong phase modulation. The resulting decomposition of a linearly polarized laser pulse into two nearly distinct, orthogonally polarized laser pulses is demonstrated with transiently aligned, linear molecules.

Polarization rotator and a crystalline-quartz plate for use in an optical imaging system

Abstract: A polarization rotator and crystalline quartz plate for use with an optical imaging system. The system has 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.

High-efficiency integrated polarized backlight system for liquid crystal display

Abstract: We propose a multiwavelength polarized backlight system (BLS) that is based on the stress-induced birefringence and the multilayer subwavelength grating. The polarized BLS requires no prism sheets and no quarter wave plate. Moreover, because of the high extinction ratio, the rear absorbing polarizer of the liquid crystal display panel is not required anymore. The proposed backlight can fully utilize the light, and the intensity at near normal angles is 2.3 times higher than that of a conventional unpolarized light emitting backlight.

Polarimeter with two ferroelectric liquid-crystal modulators attached to the Yunnan solar tower.

Abstract: A polarimeter to be mounted on the Yunnan solar tower is described. It features the ability to simultaneously measure the magnetic fields of the solar photosphere and chromosphere by analyzing the Stokes spectra of those magnetosensitive lines forming in the two regions with very high efficiency of polarization measurement. The polarimeter consists of two ferroelectric liquid crystals and one lambda/4 wave plate before a polarizing beam splitter. The achromatism of the design is emphasized to get the maximum combination efficiency over a spectral range from 5000 to 6000 angstrom. For the used solar absorption lines MgI517.27, FeI525.06, FeI630.15, and FeI630.25 nm, the design gives theoretical efficiencies of polarization measurements, which are 0.999, 1.0, 0.943, and 0.943, respectively. A comparison with other reference polarimeters, such as the Synoptic Optical Long-term Investigation of the Sun, the Tenerife infrared polarimeter, and the La Palma Stokes Polarimeter, is carried out. (c) 2006 Optical Society of America.

Calibration strategies for instrumental polarization at the 10 −5 level

Abstract: Many current instrumental developments for both solar and nighttime telescopes are directed at measuring the polarization state of the incoming light in addition to determining its spatial, temporal and/or spectral properties. Such polarimeters need to be sensitive down to a polarization degree of the order of 10-5 e.g. to employ the full range of diagnostics to accurately measure solar magnetic fields or to enable direct imaging of extrasolar planetary systems. At the low polarization degree of these observations, it is crucial to accurately know the polarization properties of the instrument itself. Since instrumental polarization is inevitable for any telescopic configuration with oblique reflections or refractions, it is always necessary to cope with it by means of calibration in combination with (limited) forward modeling. I present general strategies based on discrete Fourier analysis for the calibration of instrumental polarization to enable astronomical (spectro-)polarimetry at the 10-5 level. The technique only assumes the presence of a freely rotatable polarizer and (quarter) wave plate to create known input polarization states. The Fourier components of the observed output polarization contain information about the full instrumental polarization, as well as about non-ideal effects in the calibration elements, polarized input to the calibration unit and non-linear response of the detector.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A spectroscopic method for determining thickness of quartz wave plate

Abstract: A spectroscopic method to determine thickness of quartz wave plate is presented. The method is based on chromatic polarization interferometry. With the polarization-resolved transmission spectrum (PRTS) curve, the phase retardation of quartz wave plate can be determined at a wide spectral range from 200 to 2000 nm obviously. Through accurate judgment of extreme points of PRTS curve at long-wave band, the physical thickness of quartz wave plates can be obtained exactly. We give a measuring example and the error analysis. It is found that the measuring precision of thickness is mainly determined by the spectral resolution of spectrometer.

Polarization-dependent reflective dispersion relations of photonic crystals for waveplate mirror construction

Abstract: We have measured the polarization-dependent phase shift imparted to the radiation reflected by a two-dimensional photonic crystal within the band gap spectral region. We show that the relative phase between retroreflected basis polarizations can be large, reaching and exceeding a quarter of a wave in spectral regions of extremely high reflectivity for certain crystals. Using this property, we have directly experimentally demonstrated the operation of a reflective quarter-waveplate. All-dielectric, reflective waveplates could generate new applications involving polarization control

Analysis of polarization state by digital holography with polarization modulation

Abstract: The digital holographic technique is applied to analyze the spatial distribution of polarization state of light transmitted through anisotropic objects using an orthogonal linearly polarized reference beam. The polarization orientation of reference beam is switched by an optical fiber Faraday rotator for successive hologram recording. To confirm the principle of polarization analysis, a quarter wave plate (QWP) is used and the distribution of polarization state over the object surface is analyzed for various orientations of the QWP. By providing an area of a known polarization for a part of the object wave as a reference, a phase drift of the reference waves can be evaluated and compensated for using the reference area. The principal axis and ellipticity of polarization ellipse are calculated and compared with their theoretical values. A good agreement between the experimental and theoretical values is observed.

Phase shifts in frustrated total internal reflection and optical tunneling by an embedded low-index thin film

Abstract: Simple and explicit expressions for the phase shifts that p- and s-polarized light experience in frustrated total internal reflection (FTIR) and optical tunneling by an embedded low-index thin film are obtained. The differential phase shifts in reflection and transmission Δr,Δt are found to be identical, and the associated ellipsometric parameters ψr,ψt are governed by a simple relation, independent of film thickness. When the Fresnel interface reflection phase shifts for the p and s polarizations or their average are quarter-wave, the corresponding overall reflection phase shifts introduced by the embedded layer are also quarter-wave for all values of film thickness. In the limit of zero film thickness (i.e., for an ultrathin embedded layer), the reflection phase shifts are also quarter-wave independent of polarization (p or s) or angle of incidence (except at grazing incidence). Finally, variable-angle FTIR ellipsometry is shown to be a sensitive technique for measuring the thickness of thin uniform air gaps between transparent bulk media.

System and method for laser speckle reduction

Abstract: A system (100) and method for reducing or eliminating speckle when using a coherent light source (112, 114, 116) is provided. A refracting device (125), comprising a birefringent material, is positioned such that the refracting device intercepts the coherent light. The refracting device rotates, thereby causing the ordinary and/or extraordinary beams to move. The human eye integrates the movement of the beams, reducing or eliminating laser speckle. The refracting device may include one or more optical devices formed of a birefringent material. Wave plates, such as a one-half wave plate, may be inserted between optical devices to cause specific patterns to be generated. Multiple optical devices having a different orientation of the horizontal component of the optical axis may also be used to generate other patterns. Furthermore, the refracting device may include an optical device having multiple sections of differing honrizontal components of the optical axis.

Measurement of retardations of arbitrary wave plates by laser frequency splitting

Abstract: A measurement system utilizing laser frequency splitting is presented for the precise measurement of retardations of arbitrary wave plates. The wave plate to be measured is inserted into a laser resonance cavity, and its retardation can be determined by measuring the difference of split frequencies and longitudinal mode spacing of the laser. In the system, mode spacing measurement is performed under multimode oscillation according to the relation between polarization directions of modes. To solve the problem of strong mode competition in measuring half-wave plates, a transverse magnetic field is applied to weaken the competition so as to make the system applicable even when the frequency difference is less than the threshold for strong mode competition. The error of the system is less than 5 arcmin, and standard deviations of about 1 arcmin are obtained from repeated experiments samples of quarter- and half-wave plates. No element rotation is required during measurement, and no mechanical quantity, such as angle, needs to be measured.

Investigation into chiral active waveplates

Abstract: An examination into a chiral liquid crystal active waveplate device using a one-dimensional model, giving numerical results, is presented. The model calculates the director and flow configuration by minimizing the free energy of the chiral nematic modeled with fixed boundary conditions. The static case of varying the flexoclectric coefficients, electric field magnitude, and dielectric anisotropy is examined and it is shown that both flexoelectricity and dielectric effects alter the birefringence of the device in the presence of an electric field. The dynamic reaction to a rotating electric field is then examined.