Showing papers on "Waveplate published in 2005"

Simple high efficiency optical coherence domain reflectometer design

Abstract: The present invention discloses simple and yet highly efficient configurations of optical coherence domain reflectometry systems. The combined use of a polarizing beam splitter (614a) with one or two polarization manipulator(s) (634a and 646) (e.g. a Faraday rotator or a quarter wave plate) that rotate the returned light wave polarization to an orthogonal direction, enables one to achieve high optical power delivery efficiency as well as fixed or predetermined output polarization state of the interfering light waves reaching a detector (652a) or detector array, which is especially beneficial for spectral domain optical coherence tomography. In addition, the system can be made insensitive to polarization fading resulting from the birefringence change in the sample (620a) and reference (622a) arms. Dispersion matching can also be easily achieved between the sample and the reference arm for high resolution longitudinal scanning.

Effects of sample arm motion in endoscopic polarization-sensitive optical coherence tomography

Abstract: Motion of the sample arm fiber in optical coherence tomography (OCT) systems can dynamically alter the polarization state of light incident on tissue during imaging, with consequences for both conventional and polarization-sensitive (PS-)OCT. Endoscopic OCT is particularly susceptible to polarization-related effects, since in most cases, the transverse scanning mechanism involves motion of the sample arm optical fiber to create an image. We investigated the effects of a scanning sample arm fiber on the polarization state of light in an OCT system, and demonstrate that by referencing the state backscattered from within a sample to the measured state at the surface, changes in polarization state due to sample fiber motion can be isolated. The technique is demonstrated by high-speed PS-OCT imaging at 1 frame per second, with both linear and rotary scanning fiber-optic probes. Measurements were made on a calibrated wave plate, and endoscopic PS-OCT images of ex-vivo human tissues are also presented, allowing comparison with features in histologic sections.

Polarization patterns hide and display using photoinduced anisotropy of photochromic fulgide

Abstract: Photoinduced anisotropy of a photochromic pyrrylfulgide/PMMA film was investigated by using two linearly polarized beams. Excitation by linearly polarized light induces into the film an optical axis that has the same polarization as the excitation beam. This causes a change of the transmittance and of the polarization state of the detection beam. With a microscope a matrix of 4×4 light spots with different polarizations were recorded in the pyrrylfulgide/PMMA film. If readout with non-polarized light, the matrix of light spots show no information pattern. However, when readout with differently polarized lights, different patterns can be displayed. The experiment demonstrates that pyrrylfulgide/PMMA films can be used to hide two differently polarized patterns, which may be applied in camouflage technology.

Monitor for showing high-resolution and three-dimensional images and method

Abstract: A display system in which images from two displays that have the same optical polarization that is not affected by reflection by a beam splitter which combines images from the displays, and half wave plate optical retarders to rotate plane of polarization and to null out optical dispersion effects to provide for stereo viewing of images via plane polarizers that have the same polarization direction.

Backscattering target detection in a turbid medium by use of circularly and linearly polarized light

Abstract: The polarization properties of the backscattered light from a turbid medium containing large-diameter (10.143-microm) and small-diameter (0.202-microm) spherical polystyrene particles are studied. It is shown that the difference in the polarization properties of the emerging light that originates at the target and that is backscattered from the medium allows for improvement of image contrast by use of polarized light. Based on the images obtained by the CCD camera, the polarization memory effect with circularly polarized light is demonstrated to have an advantage over the linear polarization technique in imaging a highly reflective target inside a turbid medium containing large particles.

Generation of terahertz pulses with arbitrary elliptical polarization

Abstract: We employ two different methods to generate controllable elliptical polarization of teraherz (THz) pulses. First, THz pulses are generated via optical rectification in nonlinear crystals using a pair of temporally separated and perpendicularly polarized optical pulses. The THz ellipticity is controlled by adjusting the relative time delay and polarization of the two optical pulses. We generate mixed polarization states of single-cycle THz pulses using ZnTe, and elliptically polarized multicycle THz pulses in periodically poled lithium niobate crystals. Second, we generate elliptically polarized THz pulses by making a THz “wave plate” using a combination of a wire-grid THz polarizer and a mirror to transform linearly polarized multicycle THz pulses into elliptical polarization.

Cell parameter determination of a twisted-nematic liquid crystal display by single-wavelength polarimetry

Abstract: Optical transmittance of a 90-twisted nematic liquid crystal cell inserted between crossed or parallel polarizers is neither sensitive to the molecular twist sense nor to the exchange between the extraordinary and the ordinary birefringence axis at the input face of the cell. In this article, the equivalence between a twisted-nematic liquid crystal cell and the combination of a retardation wave plate and a polarization rotator is fully exploited to understand the physical origin of these ambiguities. We determine, in a simple way, cell parameters by means of standard cell transmittance measurements when both crossed and parallel polarizers are rotated simultaneously. We show that this procedure, which is subjected to the aforementioned ambiguities, can be completed by additional polarimetric measurements. In particular, we demonstrate that the twist angle, twist sense, retardation, and the rubbing direction can be univocally determined by experimental measurement of the Stokes parameters of the light tran...

Nonlinear polarization rotation of elliptical light in cubic crystals, with application to cross-polarized wave generation

Abstract: We have investigated theoretically and experimentally the nonlinear propagation of intense elliptically polarized light pulses along a fourfold axis of the cubic crystal BaF2. Third-order nonlinear optical processes generate a cross-polarized wave, an effect that presents significant possibilities for application in femtosecond pulse contrast enhancement. The experimental setup consists of an input linear polarized light that passes through a cubic crystal sandwiched between two crossed quarter-wave plates. The exit orthogonal polarization-state production amount is measured at the output of an analyzer. When the light impinging on the sample is elliptically polarized with a quarter-wave plate at 22.5 deg, the achieved efficiency reaches 15%. It is more than twice that of a conventional polarization filter based on nonlinear ellipse rotation in an isotropic medium. This device is compared with previously reported polarization filtering [J. Opt. Soc. Am. B21, 1659 (2004)], in which a linearly polarized light produced a perpendicular field component. The theoretical model describes in detail the obtained dependencies and allows the different nonlinear processes that contribute to the generation of a cross-polarized wave to be distinguished. Possible applications are discussed.

Polarization conversion and "focusing" of light propagating through a small chiral hole in a metallic screen

Abstract: Propagation of light through a thin flat metallic screen containing a hole of twisted shape is sensitive to whether the incident wave is left or right circularly polarized. The transmitted light accrues a component with handedness opposite to the incident wave. The efficiency of polarization conversion depends on the mutual direction of the hole’s twist and the incident light’s wave polarization handedness and peaks at a wavelength close to the hole overall size. We also observed a strong transmitted field concentration at the center of the chiral hole when the handedness of the chiral hole and the wave’s polarization state are the same.

Millimeter-wave achromatic half-wave plate.

Abstract: We have constructed an achromatic half-wave plate (AHWP) suitable for the millimeter wavelength band. The AHWP was made from a stack of three sapphire a-cut birefringent plates with the optical axes of the middle plate rotated by 50.5 deg with respect to the aligned axes of the other plates. The measured modulation efficiency of the AHWP at 110 GHz was 96 ± 1.5%. In contrast, the modulation efficiency of a single sapphire plate of the same thickness was 43 ± 4%. Both results are in close agreement with theoretical predictions. The modulation efficiency of the AHWP was constant as a function of incidence angles between 0 and 15 deg. We discuss design parameters of an AHWP in the context of astrophysical broadband polarimetry at the millimeter wavelength band.

Optical receiver and optical reception method compatible with differential quadrature phase shift keying

Abstract: In an optical receiver according to the present invention, an input signal light subjected to the differential quadrature phase shift keying (DQPSK) is incident on a PANDA type fiber in a linearly polarized state by 45°, so that a delay time difference corresponding to one symbol is generated between orthogonal polarization components in the DQPSK signal light, and then, the signal light is branched by a half mirror into two, to be sent to first and second paths respectively, thereby giving, by a ¼ wave plate disposed on one of the paths, a relative birefringent amount difference of π/2 between the lights propagated through the respective paths. Then, each of the lights propagated through the first and second paths is separated into two orthogonal polarization components by a polarization beam splitter, and the respective polarization components are received by a differential reception circuit so that in-phase components and quadrature components in the DQPSK signal are demodulated. Thus, a small sized and low cost optical receiver capable of stably demodulating the DQPSK signal is provided.

Method for manufacturing divided waveplate filter

Abstract: An adhesive layer is formed on a substrate by printing such that the adhesive layer has a predetermined pattern. A film having a phase-difference characteristic is bonded thereon to form a divided waveplate material layer. The divided waveplate material layer is divided all at once with cutter blades disposed in a row such that the divided waveplate material layer has the predetermined pattern. Then the divided waveplate material layer remaining on portions to be removed is removed, thereby forming divided waveplates on the substrate such that the divided waveplates have the predetermined pattern.

Polarization conversion element, lighting optical device, exposure system, and exposure method

Abstract: A polarization conversion element capable of converting, with a limited light quantity loss, a linearly polarized incident light having a polarization direction in an almost single direction into a circumferentially polarized light having a polarization direction in an almost circumferential direction. A polarization conversion element (10) for converting the polarization state of an incident light into a specified polarization state. It is formed of an optical material having optical rotation, for example, quartz, and has a thickness distribution changing in a circumferential direction. The thickness distribution is so set that a linearly polarized light having a polarization direction in an almost single direction is converted into a circumferentially polarized light having a polarization direction in an almost circumferential direction. It has a plurality of circumferentially divided areas (10A-10D), and two arbitrary adjacent areas in the plurality of areas are different in thickness from each other. Also, two arbitrary facing areas in the plurality of areas have optical rotation angles almost equal to each other.

Optimal design of achromatic true zero-order waveplates using twisted nematic liquid crystal.

Abstract: Phase retarders usually show strong wavelength dependence. A novel and simple configuration with the combination of two twisted nematic liquid-crystal cells is proposed for the design of a true zero-order achromatic quarter-wave plate. The present optimization method considers the material dispersion. Simulation computations show a good achromatic behavior of the optimized waveplate. Compared with other types of broadband quarter-wave plates, the present device is compatible with classical liquid-crystal displays and can be expected to be used in precision polarimeters with low cost and enhanced light efficiency.

Compensation of polarization-dependent loss in transmission fiber gratings by use of a Sagnac loop interferometer.

Abstract: We analyze the transmission characteristics of a Sagnac loop interferometer containing a polarization-dependent loss element and lossless polarization-converting elements by use of Jones matrices. We show that polarization independence in the transmission mode can be achieved in such a configuration and that maximum transmittance occurs when a half-wave plate is used for the polarization-converting element. The result is verified experimentally for a fiber acousto-optic tunable filter and cascaded long-period fiber gratings with either intrinsic or process-induced polarization-dependent filtering characteristics.

Achromatic wave plates for optical pickup units fabricated by use of imprint lithography.

Abstract: We report achromatic form-birefringence wave plates for optical pickup units. Material dispersion and structure dispersion are balanced in a rigorous multilayer design. A trilayer grating using SiNx?SiOyNz?SiO2 provides easily accessible process control points and relaxed fabrication tolerance. We demonstrate precise patterning by using nanoimprint lithography on UV-curable polymers, alleviating a major fabrication challenge. The achromatic wave plates exhibit 90±3° retardance and >95% transmittance as measured by a Mueller matrix method at wavelengths of 640–800?nm.

Reset-free integrated polarization controller using phase shifters

Abstract: An endless, reset-free polarization controller implemented with planar lightwave circuits using phase shifters for tuning is proposed and demonstrated. By avoiding the need for tunable polarization mode converters, simple fabrication processes and a large range of material systems can be used, since neither the electrooptic effect nor a rotatable birefringence axis are necessary for device operation. The proof of concept is demonstrated by implementing the equivalent of a rotating waveplate using Ge-doped silica-on-silicon waveguides and thermooptic phase shifters. The polarization controller is shown to have excellent tolerance to fabrication variations. Fast thermooptic control (on the order of 10 kHz) is achieved using high-index-contrast (4%) waveguides.

Polarized light transmission screen and stereoscopic image displaying apparatus using the polarized light transmission screen

Abstract: A polarized light transmission screen and a stereoscopic image displaying apparatus capable to display a clear stereoscopic image with few little cross talks over a wide wavelength range. In a polarized light transmission screen 30, a 90-degree rotation regions 32 b include in piles a plurality of retarders of which the directions of the optical axes differ with one another, and when the linearly polarized light having a polarization axis of a specific direction is made to be transmitted, they rotates the polarization axis by 90 degrees in total by each of the plurality of retarders rotating the polarization axis less than 90 degrees in steps. A 0-degree rotation regions 32 a include in piles a plurality of retarders of which the directions of the optical axes differ with one another, and when the linearly polarized light having a polarization axis of a specific direction is made to be transmitted, the polarization axes of incidence and emission are the same direction.

Illuminating apparatus and projector

Abstract: An illuminating apparatus includes a polarized light beam splitter, a first polarized light source device, and a second polarized light source device. The first polarized light source device has a first light source device, a first polarized light separation prism, and a first polarization element. The second polarized light source device has a second light source device, a second polarized light separation prism, and a second polarization element. The illuminating light flux having the first polarized light component emitted from the first polarized light source device and illuminating light flux having the second polarized light component emitted from the second polarized light source device are both linear polarized light components and have different polled light axis from each other. The polarized light beam splitter synthesizes the illuminating light flux having the first polarized light component emitted from the first polarized light source device and the illuminating light flux having the second polarized light component emitted from the second polarized light source device to emit.

Monolithically integrated circular polarizers with two-layer nano-gratings fabricated by imprint lithography

Abstract: We developed an integrated circular polarizer based on stacking an aluminum nano-wire grid polarizer with a dielectric nano-grating-based quarter waveplate. The polarizer consists of 65 nm wide and 130 nm tall aluminum wires with a period of 148 nm. For integration, the aluminum nanowires were buried into a silicon dioxide matrix by a trench filling and planarization technology. The buried nanowire polarizer achieved excellent optical performance in a broad wavelength range from 400 nm to >900nm. On top of the buried and planarized nanowire polarizer, a visible quarter waveplate based on a 200 nm period silicon nitride nano-grating was fabricated. Both the 148 nm period aluminum grating and the 200 nm period silicon nitride grating were fabricated by an ultraviolet (UV)-nanoimprint lithography. The ability to integrate multiple nanostructure-based optical layers opens a path for novel integrated optical devices, as well as a new strategy for driving both miniaturization and cost.

Display system using two displays and polarization direction rotation for showing high-resolution and three-dimensional images and method and use of a dbef beam splitter

Abstract: A display system in which images from two displays that have the same optical polarization that is not affected by reflection by a beam splitter which combines images from the displays, and a half wave plate optical retarder to rotate plane of polarization of light from one display prior to impingement on the beam splitter, and a polarizer filter to block transmission to the beam splitter of leakage light caused by optical dispersion by the half wave plate. A display system in which images represented by polarized light from two displays are incident on a DBEF beam splitter, the direction of plane of polarization of one of the images relative to the DBEF is such that the DBEF preferentially transmits that direction and the direction of plane of polarization of the other of the images, which is directed to the other surface of the beam splitter, is such that the DBEF preferentially reflects that light.

Wide bandwidth light source

Abstract: PROBLEM TO BE SOLVED: to realize a wide bandwidth light source capable of a stable operation providing a less spectrum variation. SOLUTION: Optical pulses 202 outputted by this optical pulse-generating device 201 are split by optical coupler 210 . The one of split optical pulses is inputted in white light-emitting device 204 to emit the white light having the wide bandwidth. The other split is inputted in optical band pass filter 212 in operation-stabilizing circuit 207 . Optical detector 213 detects a signal level of a specific wavelength and input in feedback circuit 215 to generate first and second feedback signals 205 and 206 . Ring resonator fiber laser 208 uses any one of them and controls a rotation angle of the waveplate to realize stabilization of the output.

A Millimeter-Wave Achromatic Half Wave Plate

Abstract: We have constructed an achromatic half wave plate (AHWP) suitable for the millimeter wavelength band. The AHWP was made from a stack of three sapphire a-cut birefringent plates with the optical axes of the middle plate rotated by 50.5 degrees with respect to the aligned axes of the other plates. The measured modulation efficiency of the AHWP at 110 GHz was $96 \pm 1.5$%. In contrast, the modulation efficiency of a single sapphire plate of the same thickness was $43 \pm 4$%. Both results are in close agreement with theoretical predictions. The modulation efficiency of the AHWP was constant as a function of incidence angles between 0 and 15 degrees. We discuss design parameters of an AHWP in the context of astrophysical broad band polarimetry at the millimeter wavelength band.

Beam profile complex reflectance system and method for thin film and critical dimension measurements

Abstract: Device and method for measuring complex reflectance using a light source for generating a light beam with known polarization state, a lens for focusing the beam onto a sample surface such that various rays within the focused beam create a spread of angles of incidence θ, a waveplate for retarding one polarization state of the beam, a polarizer for generating interference between beam polarization states, and a detector with a two dimensional array of detector elements for generating intensity signals in response to the beam, wherein each detector element corresponds to a unique angle of incidence θ and azimuthal angle o of the reflected beam A processor calculates magnitude and phase values for the reflected beam by using the intensity signals corresponding to at least one incident angle θ and a plurality of azimuthal angles o within the at least one incident angle θ sufficient to enable a meaningful Fourier analysis thereof

Optical voltage sensor using a pulse-controlled electrooptic quarter waveplate

Abstract: An optical voltage sensor is presented which can be used for the measurement of dc voltage by use of a Pockels crystal associated with a pulse-controlled electrooptic quarter waveplate. The measurand dc voltage signal is converted into the amplitude of an ac pulse-modulated voltage-sensing signal. Therefore, the output sensing signal is immune to electromagnetic interference owing to the applications of pulse modulation and lock-in amplifying techniques. In addition, the voltage-sensing signal is obtained from a single light path and free from light intensity fluctuations. The dc voltage of /spl plusmn/0.4 to /spl plusmn/180 V has been measured with 1.8% nonlinear error.

Polarisation-sensitive optical coherence tomography for material characterisation and testing

Abstract: Optical Coherence Tomography (OCT) is an emerging technology for high-resolution non-contact imaging of semitransparent structures. Originally developed for medical diagnostics, we extend the OCT-technique to problems posed in material testing and characterization. Layer thickness and refractive indices as well as internal structures of polymer parts have been determined within this study. An extension of OCT, namely polarisation-sensitive OCT (PSOCT) has been used to identify regions of increased anisotropy within injection-moulded plastic parts and to determine quantitatively internal strain within translucent materials in a nondestructive way. Introduction and experimental: Optical Coherence Tomography (OCT) is an emerging technology for high-resolution non-contact imaging of semitransparent structures. The measurement principle of OCT is based on an interferometric detection of path-length distributions of low-coherence light back-reflected from interfaces within the sample [1-3]. The original application of OCT is the imaging of the human retina [1] and has been extended to the characterisation of a variety of biological tissues [3]. Anyhow, the applications of OCT outside the biomedical sector, especially for material characterisation and testing are so far only marginally touched: e.g. OCT imaging of glass fibre composites and the detection of subsurface defects and cracks in other non-biological materials, like in ceramics [4,5]. Polarisation-Sensitive OCT (PS-OCT) is an extension to the classical OCT method and maps in addition to the light intensity distribution the polarisation state of light within the sample [6-8]. Thus, additional physical parameters (like birefringence) and enhanced structural information, that is difficult to resolve with other imaging techniques, can be obtained. Recently, we extended for the first time classical OCT measurements to PS-OCT to characterise and non-destructively test injection-moulded polymer parts for a qualitative determination of internal strain fields and regions of material anisotropy [9]. In the current study we present new applications of classical OCT, like non-destructive thickness measurements of lacquer-layers and discrimination between individual layers, even when of same consistence and composition. Furthermore, we performed, simultaneously to PS-OCT, tensile stress-strain experiments on different polymeric materials to measure the stress-optical coefficient in the perspective of a quantitative and non-destructive determination of residual and induced internal stress in samples. For the presented study we used a PS-OCT set-up as schematically depicted in Fig. 1. The beam of a low coherent light source is linearly polarised (vertically) and divided equally into two arms of a Michelson interferometer. In the reference arm a scanning mirror varies the optical path length. The quarter wave plate in the reference arm provides after back-reflection from the mirror linearly polarized light rotated by 45° to its original polarisation direction. The sample under investigation is placed in the other arm and is illuminated by circularly polarized light with the help of a second quarter wave plate.

Integrated optical multiplexer and demultiplexer

Abstract: Optical multiplexers ( 100, 300 ) and demultiplexers ( 500, 600 ) are provided. In one implementation, an apparatus is provided. Th apparatus includes a first laser diode pair ( 101, 102 ), a second laser diode pair ( 103, 104 ), a polarization rotator ( 110 ) coupled between the first and second laser diode pairs, and an output port ( 105 ). The first and second laser diode pairs include a first laser diode ( 101 103 ), a polarization beam splitter ( 106, 111 ), a first quarter waveplate ( 107, 112 ), a filter ( 108, 113 ), a second quarter waveplate ( 109, 114 ), and a second laser diode ( 102, 104 ). The first and second laser diode pairs are coupled to the polarization rotator at the polarization beam splitter of each laser diode pair. In one implementation, the apparatus is operable to multiplex distinct light signals emitted from the first and second laser diodes. In another implementation, an apparatus is provided th is operable to demultiplex an input light beam having a plurality of distinct channels.

Broad spectral range polarization rotator

Abstract: A switchable apochromatic polarization rotator is provided. A first fixed waveplate has a first principal axis fixed in a first orientation. A second fixed waveplate has a second principal axis fixed in a second orientation. First and second switchable waveplates have principal axes oriented such that broad spectral range electromagnetic radiation transmitted through all of the waveplates has a first rotated polarization, wherein, in response to one or more control signals applied to the switchable waveplates, the principal axes of the switchable waveplates rotate such that the electromagnetic radiation transmitted through all of the waveplates has a second rotated polarization. The switchable waveplates utilize ferroelectric liquid crystal material, nematic liquid crystal material, or be mechanically rotated to adjust for orientation of their principal axes. Utilizing waveplates as described may be used to tune for a desired spectral range and/or compensate for temperature dependencies.

Color-sequential lcos projector using single beam splitter

Abstract: A reflective drum color-sequential projection system using a single electro-optic modulator (LCOS) and a single polarizing beam splitter (PBS). Unpolarized light passes through an polarization conversion system and pre-polarizer as linearly S-polarized light to a polarizing beam splitter, which diverts it by reflection to a rotating reflective color drum RD to make sequential primary sub-beams of red, green and blue. These sub-beams pass through a quarter wave plate (QWP) on the way back and forth to the reflective drum and becoming oppositely polarized to P-polarized light, allowing the sub-beams reflected from the drum to pass through the beam splitter to a reflective device, an electro-optic modulator (LCOS). The electro-optic modulator selectively changes the polarization of light intended for projection back to S-polarized light, which upon reflection back to the beam splitter, is reflected and diverted for projection, preferably passing through an analyzer and into a projection lens.