Showing papers on "Waveplate published in 2010"

Guided-mode resonant wave plates.

Abstract: We introduce half-wave and quarter-wave retarders based on the dispersion properties of guided-mode resonance elements. We design the wave plates using numerical electromagnetic models joined with the particle swarm optimization method. The wave plates operate in reflection. We provide computed results for reflectance and phase in the telecommunication spectral region near 1.55 microm wavelength. A surface-relief grating etched in glass and overcoated with silicon yields a half-wave plate with nearly equal amplitudes of the TE and TM polarization components and pi phase difference across a bandwidth exceeding 50 nm. Wider operational bandwidths are obtainable with more complex designs involving glass substrates and mixed silicon/hafnium dioxide resonant gratings. The results indicate a potential new approach to fashion optical retarders.

Broadband one-dimensional photonic crystal wave plate containing single-negative materials.

Abstract: The properties of the phase shift of wave reflected from one-dimensional photonic crystals consisting of periodic layers of single-negative (permittivity- or permeability-negative) materials are demonstrated. As the incident angle increases, the reflection phase shift of TE wave decreases, while that of TM wave increases. The phase shifts of both polarized waves vary smoothly as the frequency changes across the photonic crystal stop band. Consequently, the difference between the phase shift of TE and that of TM wave could remain constant in a rather wide frequency range inside the stop band. These properties are useful to design wave plate or retarder which can be used in wide spectral band. In addition, a broadband photonic crystal quarter-wave plate is proposed.

Polarization converters based on axially symmetric twisted nematic liquid crystal

Abstract: An axially symmetric twisted nematic liquid crystal (ASTNLC) device, based on axially symmetric photoalignment, was demonstrated. Such an ASTNLC device can convert axial (azimuthal) to azimuthal (axial) polarization. The optical properties of the ASTNLC device are analyzed and found to agree with simulation results. The ASTNLC device with a specific device can be adopted as an arbitrary axial symmetric polarization converter or waveplate for axially, azimuthally or vertically polarized light. A design for converting linear polarized light to axially symmetric circular polarized light is also demonstrated.

Optical displacement meter

Abstract: An optical displacement meter includes: a spatial filter configured to extract light under measurement of a wavelength focused on a measurement target and to specify the wavelength of the light under measurement; a polarizer configured to divide the light collimated and caused to propagate in one direction into linearly polarized beams in two directions orthogonal to a propagating direction; a wavelength plate that allows passage of the linearly polarized beams to produce elliptically polarized light having a phase difference commensurate with a light wavelength; a polarized light separator configured to divide the elliptically polarized light into polarized light components in the two directions; and a computing circuit configured to perform computation of (A−B)/(A+B) by use of light quantity signals A and B, which respectively correspond to the two polarized light components.

Improvement of linewidth in laser beam lithographed computer generated hologram.

Abstract: We propose a new laser lithographic technique with enhanced resolution. A calcite wave plate is introduced in our system to separate an input lithographic beam into two orthogonally polarized beams. After going through an imaging lens, these two beams meet again on the focal point, and generate a small interferogram that sharpens the shape of the focused beam spot. Using this phenomenon, we can overcome the diffraction limit of the imaging lens and achieve a 486-nm-linewidth.

Small-sized Terahertz time-domain spectrograph

Abstract: The utility model discloses a small-sized Terahertz time-domain spectrograph, which is characterized in that the spectrograph comprises a femtosecond pulse optical laser device, a 1/2 wave plate and a polarization beam splitter, wherein the 1/2 wave plate and the polarization beam splitter are arranged at the output end of the femtosecond pulse optical laser device, and the polarization beam splitter divides a beam of laser into a beam of pump light and a beam of detection light; the pump light is gathered on a Terahertz emitter based on a photoconductive antenna through a pump light path, and the photoconductive antenna is used for radiating Hertzian wave; generated Hertzian radiation wave is gathered on a Terahertz detector through passing through a transmission measurement module or a reflection measurement module; and the generated Hertzian radiation wave and detection light are in collinear coupling on the Terahertz detector, electro-optic sampling of the time-domain electric field of the Hertzian wave is performed by utilizing the electrooptical effect, and Hertzian time-domain signals are sent to a data acquisition and processing system for signal transformation and processing. Therefore, the utility model has the characteristics of small volume, tightness, convenient movement, high distinguishing precision of time-domain of the spectrograph, quick measurement speed and easy popularization and application, can ensure the measurement precision.

Stokes polarimetry of a hybrid vector beam from a spun elliptical core optical fiber

Abstract: A hybrid vector polarization beam with a donut like intensity profile is produced at the output of a spun elliptical core optical fiber by coupling an off-axis TEM 00 laser mode at the input. The local polarization states of the fiber output are analyzed using Stokes polarimetry. The Stokes parameters are measured using a combination of quarter wave plate and linear polarizer. A detailed polarization map of the hybrid beam's cylindrically symmetric and varying elliptical polarization state around the beam axis is also numerically discussed.

THz generation by a two-color pulse in prealigned molecules

Abstract: We demonstrate that the THz generation in air from a two-color pulse, composed of the fundamental and second-harmonic waves, can be coherently controlled by field-free molecular alignment. By tuning its time delay to properly match various molecular alignment revivals, the THz generation from the two-color pulse can be promoted or decreased due to the spatial cross-(de)focusing effect and the alignment-dependent ionization probabilities of the prealigned diatomic molecules in air. For the two-color pulse of orthogonally polarized fundamental and second-harmonic waves, the polarization of the generated THz radiation can be controlled by the field-free molecular alignment, which functions as a transient dynamic wave plate for the two-color pulse with different phase velocities for the orthogonally polarized field components. The plasma effect on the THz generation of the two-color pulse is also observed, leading to additional amplitude and polarization control of the THz radiation.

Depth illumination and detection optics

Abstract: A depth image capture device uses a circular polarization structure positioned at the output of an illumination radiation source, such as a diode laser. A linear polarization element receives the collimated illumination radiation and provides polarized radiation to a quarter wave plate. Radiation exits the quarter wave plate as circularly polarized radiation and is provided to a diffractive optical element outputting a pattern to illuminate a target. A detector receives a reflection of the output pattern from the target.

Polarization-Insensitive Variable Optical Attenuator and Wavelength Blocker Using Liquid Crystal Polarization Gratings

Abstract: We demonstrate a variable optical attenuator (VOA) based on liquid crystal polarization gratings (LCPGs), which eliminates the need for complex polarization management found in competing LC technologies. We then configure the VOA as a multi-channel wavelength blocker resulting in a simple, compact architecture with high performance and low cost. Together with a dual fiber collimator, relay lenses, a diffraction grating, a quarter wave plate, and a mirror we achieve optical attenuation of ~50 dB with minimal polarization dependent loss (≤ 0.3 dB) and insertion loss ( ≤ 2.5 dB). The device also manifests competitive wavelength flatness (≤ 0.35 dB variation), response times ( ~ 40 ms), and temperature dependent loss (≥ 47 dB maximum attenuation up to 85°C). We describe the principle of operation, explain the fabrication process and optimization challenges, and finally present the system design and experimental results for a four-channel, 100 GHz wavelength blocker in the C-band.

Tuneable sagnac comb filter including two wave retarders

Abstract: In this paper we study theoretically and experimentally a wavelength-tuneable Sagnac birefringence filter. The device is a Sagnac interferometer including a symmetric fibre coupler and a length of high-birefringence fibre in the loop. A wave retarder is inserted at each end of the birefringent fibre for absolute wavelength tuning. We show theoretically that wavelength tuning through wave plate orientation ensuring constant amplitude of the filtering function is possible only if a minimum of two wave retarders are included in the setup. The position of the transmission peaks then varies linearly with the angle of one of the retarders and can be adjusted over one entire channel spacing. This happens only when a quarter-wave retarder and a half-wave retarder are used, if the former is oriented at 45° with respect to the fibre birefringence axes, while the orientation of the latter serves as the adjustment parameter. The theoretical predictions are confirmed by the experimental results.

A cryogenic waveplate rotator for polarimetry at mm and sub-mm wavelengths

Abstract: Mm and sub-mm waves polarimetry is the new frontier of research in Cosmic Microwave Background and Interstellar Dust studies. Polarimeters working in the IR to MM range need to be operated at cryogenic temperatures, to limit the systematic effects related to the emission of the polarization analyzer. In this paper we study the effect of the temperature of the different components of a waveplate polarimeter, and describe a system able to rotate, in a completely automated way, a birefringent crystal at 4K. We simulate the main systematic effects related to the temperature and non-ideality of the optical components in a Stokes polarimeter. To limit these effects, a cryogenic implementation of the polarimeter is mandatory. In our system, the rotation produced by a step motor, running at room temperature, is transmitted down to cryogenic temperatures by means of a long shaft and gears running on custom cryogenic bearings. Our system is able to rotate, in a completely automated way, a birefringent crystal at 4K, dissipating only a few mW in the cold environment. A readout system based on optical fibers allows to control the rotation of the crystal to better than 0.1{\deg}. This device fulfills the stringent requirements for operation in cryogenic space experiments, like the forthcoming PILOT, BOOMERanG and LSPE.

Displacement measurement device, exposure apparatus, and working device

Abstract: A device has a scale on which a grating pattern is formed, a light source to irradiate light on the scale, a wavelength plate to transform multiple diffracted lights from the light source into circular polarized light, respectively, an optical element to superposition and cause interference of the multiple diffracted lights, and a photodetector to receive the interfered light. Also, a generating unit to generate linearly polarized light by the light from the light source, so that the multiple diffracted lights input to the wavelength plate become linearly polarized light with a same mutual polarization direction.

Wave-Plate Structures, Power Selective Optical Filter Devices, and Optical Systems Using Same

Abstract: In an embodiment, an optical filter device includes an input polarizer for selectively transmitting an input signal. The device includes a wave-plate structure positioned to receive the input signal, which includes first and second substantially zero-order, zero-wave plates arranged in series with and oriented at an angle relative to each other. The first and second zero-wave plates are configured to alter a polarization state of the input signal passing in a manner that depends on the power of the input signal. Each zero-wave plate includes an entry and exit wave plate each having a fast axis, with the fast axes oriented substantially perpendicular to each other. Each entry wave plate is oriented relative to a transmission axis of the input polarizer at a respective angle. An output polarizer is positioned to receive a signal output from the wave-plate structure and selectively transmits the signal based on the polarization state.

Polarization conversion device, polarized illumination optical device, and liquid crystal projector

Abstract: Polarizing split layers 26 and reflection layers 27 are provided on bonding surfaces between prism rods 24 a and 24 b . Polarization conversion devices 25 are bonded to an emission surface from which linearly polarized light being reflected by the polarizing split layers 26 and reflected by the reflection layer 27 are emitted. The polarization conversion devices 25 are formed by bonding plural prism rods 30 with side surfaces being inclined by 45° with respect to an incidence surface. Retardation films formed of dielectric multilayers are provided between the bonding surfaces to give a phase difference of a ½ wavelength to transmitted light. The retardation films and bonding borderlines 31 are inclined by 45° within a plane perpendicular to an optical axis of linearly polarized light so that an optical axis of the retardation film has an angle of 45° with respect to a polarization direction of the linearly polarized light.

A two-color pump probe atomic magnetometer for magnetoencephalography

Abstract: In recent years, atomic magnetometers (AMs) have demonstrated sub-femtotesla sensitivities and have emerged as potential replacements for superconducting quantum interference devices (SQUIDs). In an AM, a circularly polarized pump laser aligns the electron spins in a cloud of alkali metal vapor. Changes occur in the optical properties of the vapor when its collective moment interacts with an external magnetic field, resulting in a measurable polarization rotation of a linearly polarized probe beam. We present a unique pump/probe scheme in which a pump beam tuned to the 87Rb D1 line (795 nm) and a probe beam tuned to the D2 line (780 nm) share a single optical axis. A dichroic waveplate is used to circularly polarize the pump beam while leaving the probe beam linearly polarized. Based upon this scheme, we have developed a small profile, fiber-coupled AM. By independently optimizing pump/probe power and detuning, we are able to achieve intrinsic single-channel sensitivity of < 5 fT/√Hz, which is suitable for demanding applications such as magnetoencephalography (MEG). Furthermore, through straightforward adaptations of the current design, it should be possible to create dense, reconfigurable arrays of AMs for whole-head MEG.

Multifunctional reflection-type magneto-optic spectrum measuring system

Abstract: The invention discloses a multifunctional reflection-type magneto-optic spectrum measuring system which uses a super-continuous white light source, a grating monochromator, a plurality of polarized lenses, a photoelastic modulator, a broad band 1/4 and 1/2 wave plate, a non-polarization beam splitter (NPBS), a single-ended differential detector and an OXFORD low-temperature superconducting magnet system to form a spectrum detection system with a flexible and variable structure. The invention can realize the measurement of reflection-type magnetic circular dichroism (MCD), polar magneto-optical Kerr effect, polarized reflection spectrum and magnetic wire magnetic linear dichroism (MLD) on the same light path. The system has high sensitivity and can be used for fields, such as basic physics research, material characteristic analysis, light polarization modulation communication and the like.

Outage Statistics in a Waveplate Hinge Model of Polarization-Mode Dispersion

Abstract: The properties of the waveplate hinge model of polarization-mode dispersion (PMD) are studied in detail, and its statistics are compared to those of the traditional hinge model based on the assumption of an isotropic output after each hinge. In particular, the probability density function of the differential group delay for each individual frequency band is computed using a combination of importance sampling and the cross-entropy method. The outage probability is then obtained combining these results with the outage map method, allowing the fraction of bands with unacceptable outage probabilities to be quantified by the noncompliant capacity ratio (NCR). The results show that the traditional hinge model significantly overestimates the NCR compared to the waveplate hinge model.

Despeckling Apparatus and Method

Abstract: An apparatus and method that reduces laser speckle by using stimulated Raman scattering in an optical fiber (710, 718). The fiber core diameter and length are selected to achieve a desired output color. An adjustable despeckler is formed by combining two optical fibers (710, 718) in parallel and adjusting the amount of light in each path with the help of a rotatable waveplate (704) and a pola7rizer (706) as a beam splitter. A homogenizing device (722) illuminates a projector (724).

Super-precision surface measuring system based on polarization phase-shifting microscopy interference technology

Abstract: The invention provides a super-precision surface measuring system based on a polarization phase-shifting microscopy interference technology, belonging to the field of an optical precision measurement technology. The system comprises a light source (1), a collimating mirror (2), a linear polarizer (3), a depolarization amici prism (4), a microscope (5), a polarization amici prism (6), a reference plane mirror (8), 1/4 wave plate (9), an analyzer (10), an imaging device (11) and a data processing system (12). The invention combines the polarization phase-shifting technology and the Michelson interference microscopy, overcomes a series of problems of the PZT phase-shifting method in a general phase-shifting microscopy interference system and has the advantages of simple structure, simple and accurate phase-shifting, high measuring precision, fast measuring speed and the like.

Circularly polarized localized near-field radiation at the nanoscale

Abstract: Diffraction-limited circularly polarized electromagnetic radiation has been widely used in the literature for various applications at both optical and microwave frequencies. With advances in nanotechnology, emerging plasmonic nano-optical applications, such as all-optical magnetic recording, require circularly polarized electromagnetic radiation beyond the diffraction limit. In this study, a plasmonic cross-dipole nano-antenna is investigated to obtain a circularly polarized near-field optical spot with a size smaller than the diffraction limit of light. A cross-dipole nano-antenna is composed of four metallic nano-rods placed at a perpendicular orientation with respect to each other. The performance of the nano-antenna is investigated through numerical simulations. In the first part of this study, the nano-antenna is illuminated with a diffraction-limited circularly polarized radiation. An optimal antenna geometry is specified to obtain an intense optical spot that satisfies two necessary conditions for circular polarization: a phase difference of 90° and a unit amplitude ratio between the electric field components in the vicinity of the antenna gap. In the second part of this study, the nano-antenna is illuminated with diffraction-limited linearly polarized radiation. It is shown that the phase difference between the electric field components can be adjusted by selecting either different antenna lengths or different gap distances in the vertical and horizontal directions. Due to the relatively short wavelength of surface plasma waves on the antenna, it is demonstrated that the phase difference can be sufficient to obtain circularly polarized light. An optimal physical configuration for the nano-antenna and the polarization angle of the incident light is identified to obtain a circularly polarized optical spot beyond the diffraction limit from diffraction-limited linearly polarized radiation.

Analysis of throughput for multilayer infrared meanderline waveplates

Abstract: A meanderline wave retarder is a unique type of frequency-selective-surface (FSS) that enables a change in the state of optical polarization. The principles of operation are very similar to a typical crystalline waveplate, such that the artificially structured meanderline array has both 'slow' and 'fast' axes that provide a phase offset between two orthogonal wave components. In this paper, we study the behavior and response of multilayered meanderline quarter-wave retarders designed for operation at 10.6 mum wavelength (28.28 THz). It will be shown that meanderline quarter-wave plates with more than a single layer exhibit improved transmission throughput at infrared frequencies due to impedance matching, similar to a multilayer optical film coating. Numerical data, both from simulations and measurements, are presented to validate this claim.

Quarter-wave plate polariser based on frequency selective surface

Abstract: A quarter-wave plate polariser based on frequency selective surface is presented for 75 GHz applications. The FSS consists of a cross dipole on a low loss substrate having different arm lengths in x- and y- directions. This is done to achieve a quarter-wave plate effect at the desired frequency. Theoretically, about 98% circular polarisation is achieved at the centre frequency. Preliminary theoretical results are presented.

On Stokes polarimeters for high precision CMB measurements and mm Astronomy measurements

Abstract: Several on-going and future experiments use a Stokes polarimeter (i.e. a rotating wave plate followed by a steady polarizer and by an unpolarized detector) to measure the small polarized component of the Cosmic Microwave Background. The expected signal is typically evaluated using the Mueller formalism. In this work we carry-out the signal evaluation taking into account the temperatures of the different optical devices present in the instrument, their non- idealities, multiple internal reflections, and reflections between different optical components. This analysis, which exploits a new description of the radiation transmitted by a half wave plate, can be used to optimize the experimental setup as well as each of its optical components. We conclude with an example of application of our analysis, studying a cryogenic polarization modulator developed for detecting the interstellar dust polarization.

Full-field optical coherence tomography by achromatic phase shifting with a rotating half-wave plate

Abstract: An achromatic phase shifter with a rotating half-wave plate (HWP) and a full-field optical coherence tomography (FF-OCT) system based on it are presented. The novel configuration of this phase shifter in the FF-OCT system can achromatically provide a phase shift of eight times the rotation angle of the HWP. The theoretical calculation of the phase shift and numerical analysis of the phase shift error, as well as the amplitude ratio, are conducted by means of Jones matrices. The actual phase shift has also been measured to confirm the validity of the '8θ phase shift—HWP rotation angle θ' relation. The coherent image of a mirror has been obtained by using the Hariharan algorithm to verify the phase shifter's feasibility. Using traditional phase shifting algorithms, en-face images of a coin have been measured at different depths to illustrate the tomographic capability of this FF-OCT system. In comparison with other current systems, our design has several advantages, and high-resolution high-speed FF-OCT imaging can be envisioned. The phase shifter can be used for common path setups and is very suitable for implementing the phase shifting of a broad-spectrum light source.

Non-contact laser detection method of guide rail rolling angle

Abstract: The invention discloses a non-contact laser detection method of a roll angle of a lead rail, which is carried out according to the following steps: a detection device is adopted and linear polarization laser sent by a laser is used as detecting light which irradiates into a 1/2 wave plate of a sensitive element and irradiates towards a right angle prism after passing through the 1/2 wave plate; the detecting light is reflected through the right angle prism to obtain a converse light beam which is parallel to an incident light beam, and the converse light beam irradiates in to a polarization beam splitter after passing through the 1/2 wave plate again, then two beams of emergent light of the polarization beam splitter respectively enter two photodetectors to generate an electric current signal reflecting the intensity of the light; the electric current signal passes through a signal processing circuit to obtain a voltage signal reflecting the difference of the light intensity of the twobeams of the light, finally the voltage signal is processed by a computer for obtaining the reflection of the size and the direction of the roll angle of the lead rail to be detected. The method of the invention can be used by processing or measuring equipment which adopts the linear lead rail for realizing the dynamic and static detection of the roll angle of the linear lead rail thereof. The detection method of the invention has comparatively high detection precision.

Surface plasmon resonance and bio-sensing-based water chip

Abstract: The invention discloses a surface plasmon resonance and bio-sensing-based water chip. A light source, a beam expanding lens, a polarizer, an isosceles right-angle prism, a quarter wave plate, a polarization analyzer, an imaging lens and a planar array CCD are arranged in turn along the light direction, wherein the hypotenuse surface of the isosceles right-angle prism is plated with a gold film; biological modification is performed on the gold film so as to form a bio-sensitive film subjected to specific adsorption with impurities in aqueous solution to be detected; the refractive index change of the impurities to the aqueous solution to be detected is converted into light intensity change of reflected light; and the refractive index change is detected by using the SPR effect on the interface between the gold film and the isosceles right-angle prism so as to detect the concentration of substances in the solution. When the water chip is used, the concentration of various substances in the water can be detected at one time, a light path and a mechanical structure are simplified and the water detection efficiency is improved.

Fiber magnetic optical probe device and its usage system

Abstract: A magnetic-optic probe of optical fiber consists of light being guided by optical fiber and Faraday magneto-optic rotator It is featured as setting wave plate at back of Faraday magneto-optic rotator to use said wave plate to make rotation of polarization surface on two beams of output lights form said rotator and carrying out magneto-optic induction and polarization detection on two orthogonal polarization components simultaneously in equivalent way

Multi-wavelength selection switch

Abstract: The utility model relates to the fields of optics and optical fiber communication, in particular to an optical switch capable of selecting wavelength. A multi-wavelength selection switch of the utility model is arranged on the back of a collimator array, and comprises a dispersion optical grating, a wavelength selection switch module and a plane reflecting mirror, and further consists of a dispersion compensation optical grating which is arranged on the outgoing optical path of the dispersion optical grating for converting DWDM signals emitted by the dispersion optical grating into collimated lights, wherein the wavelength selection switch module is composed of a 1/2 wave plate, a Work-off crystal or PBS prism, a liquid crystal wave plate pair, a Faraday spinner, a 1/4 wave plate and a planet reflecting mirror, and the wave selection switch module is arranged on the outgoing optical path of the dispersion compensation optical grating for transmitting each wavelength to the appointed channel. The utility model adopts the technical scheme, is a novel simple multi-wavelength selection switch structure, and has much lower insertion loss.