Showing papers on "Waveplate published in 2004"

Time-resolved backscattering of circularly and linearly polarized light in a turbid medium

Abstract: Time-resolved backscattering profiles of circularly and linearly polarized light were measured from a turbid medium composed of small and large polystyrene sphere particles in water. It is shown that, based on the measurements of the time-resolved backscattered copolarized and cross-polarized components of the incident polarized light, either linearly or circularly polarized light can be used to effectively image an object that is deep inside a turbid medium composed of small particles, depending on the depolarization properties of the object itself. For large particles such as in tissue, fog, and clouds, the experimentally observed polarization memory effect on the backscattering temporal profiles suggests that a significant improvement in the image contrast can be achieved by use of circularly polarized light.

Suppression of polarization switching in vertical-cavity surface-emitting lasers by use of optical feedback

Abstract: The polarization properties of vertical-cavity surface-emitting lasers (VCSELs) subject to optical feedback are studied experimentally. It is thereby demonstrated that polarization-selective optical feedback can be utilized to entirely eliminate VCSEL polarization switching over the entire device operating range.

Mechanisms of optical angular momentum transfer to nematic liquid crystalline droplets.

Abstract: A detailed study is presented that evaluates the relative importance of wave plate behavior, scattering processes and absorption phenomena in transferring optical torque from circularly polarized light to optically trapped nematic droplets. A wide range of parameters is considered: droplet diameters between 1 and 15 μm, birefringence values from 0.15 to 0.26 and trapping beam powers from 50 mW to 400 mW. Wave plate behavior is verified through the dependence of torque on droplet diameter and material birefringence. The dependence of the magnitude of the torque on material birefringence confirms the additional importance of the scattering mechanism. Absorption processes are found to be negligible.

Two-wave-plate compensator method for single-point retardation measurements

Abstract: The two-wave-plate compensator (TWC) technique is introduced for single-point retardation measurements. The TWC method uses a known wave plate together with a wave plate of unknown retardation and produces a linearly polarized output that allows a null of intensity to be detected. The TWC method is compared both theoretically and experimentally with the existing Brace–Kohler and Senarmont methods. The resolution of the TWC is shown to be 0.02 nm. TWC enables the measurement of a sample retardation with as little as 0.13% error and thus is more accurate than either the Brace–Kohler or the Senarmont method.

Depolarization of light in a multiply scattering medium: effect of the refractive index of a scatterer.

Abstract: We report the results of a study carried out to investigate the influence of the refractive index and size parameter of a scatterer on the depolarization of linearly and circularly polarized light in a turbid medium. The results show that for a given refractive index of the surrounding medium, the influence of the refractive index of the scatterer on the depolarization of both linearly and circularly polarized light is rather weak for samples with smaller-sized scatterers (Rayleigh scatterers, radius $a⪡\ensuremath{\lambda}$, anisotropy parameter $g\ensuremath{\leqslant}0.2$). For a given value of optical thickness ($\ensuremath{\tau}={\ensuremath{\mu}}_{\mathrm{s}}\ifmmode\times\else\texttimes\fi{}d$, ${\ensuremath{\mu}}_{\mathrm{s}}$ being the scattering coefficient, $d$ the physical thickness), the depolarization of circularly polarized light was observed to be higher than that of linearly polarized light for these samples. In contrast, for samples prepared using larger-sized scatterers (Mie scatterers, $a\ensuremath{\geqslant}\ensuremath{\lambda}$, $g\ensuremath{\geqslant}0.7$), linearly polarized light was observed to depolarize much faster than circularly polarized light when the refractive index of scatterers was large $(n=1.59)$ but no appreciable difference in depolarization of linearly and circularly polarized light was observed when the refractive index of scatterers had a lower value $(n=1.37)$. Further, for scattering samples having Mie scatterers, for comparable values of $\ensuremath{\tau}$ and $g$, depolarization of polarized light was much higher for samples with scatterers of lower refractive index.

Achromatic and super-achromatic zero-order waveplates

Abstract: We discuss a brief classification of waveplates including achromatic and super-achromatic ones. Anizotropic properties of polymethylmethacrylat (PMMA) subjected to one-axis stretching are analyzed. The parameters controlling the value of the PMMA birefringence are identified and their typical spectral dependence is discussed. The technology for manufacturing achromatic and super-achromatic, one-axis-stretched PMMA waveplates is described, which excludes any mechanical processing of waveplate component surfaces. Technical characteristics of achromatic and super-achromatic waveplates manufactured of the same material (anisotropic PMMA) are discussed. It is shown that the use of the same material eliminates the appearance of interference ripple in transmission, which is a typical characteristic of quartz–MgF2 super-achromatic waveplates. Examples of using super-achromatic waveplates in astronomical observations are described.

Switchable broadband achromatic half-wave plate with nematic liquid crystals.

Abstract: We describe a broadband achromatic half-wave retarder for normally incident light of arbitrary polarization. The device consists of a stack of one nematic liquid-crystal cell with uniform alignment sandwiched between two twisted nematic layers that have identical twist angles (135°) but different orientations of their surface alignment. As a specific application, for light with linear polarization at 45° to the optic axis of the homogeneous cell the stack functions efficiently as an optical switch. The switch rotates the incident linear polarization by 90° in the absence of an electric field. When sufficiently high voltage is applied to all three layers, the device produces a near-zero effect on the incident polarization. An achromatic response in the spectral range 400–700 nm is achieved for both activated and quiescent states.

Switchable display apparatus

Abstract: In one aspect, a display apparatus comprises: an emissive spatial light modulator comprising an array of pixels of organic electroluminescent material each arranged to output substantially polarised light; a switchable polariser being switchable between a first and a second polarisation mode in which the polariser passes light of respective polarisation components; and a birefringent lens positioned to receive light from the spatial light modulator. The birefringent lens is arranged to direct light of a first polarisation component into a first directional distribution and to direct light of a second polarisation component into a second directional distribution different from the first directional distribution, the birefringent lens and the switchable polariser being positioned in series. In another aspect, a display apparatus comprises: an emissive spatial light modulator comprising an array of pixels each arranged to output randomly polarised light; a birefringent lens positioned to receive light from the spatial light modulator arranged in a first mode of operation of the display apparatus to direct light of a first polarisation component into a first directional distribution and in a second mode of operation of the display apparatus to direct light of a second polarisation component into a second directional distribution different from the first directional distribution; a quarter waveplate; and a linear polariser. The quarter waveplate is arranged between the spatial light modulator and the birefringent lens and the linear polariser is arranged on the opposite side of the birefringent lens from the quarter waveplate.

Simultaneous absolute measurements of principal angle and phase retardation with a new common-path heterodyne interferometer.

Abstract: This study demonstrates a new method for simultaneously measuring both the angle of the principal axis and the phase retardation of the linear birefringence in optical materials We used a circular common-path interferometer (polariscope) as the basic structure modulated by an electro-optic (EO) modulator An algorithm was developed to simultaneously measure the principal axis and the phase retardation of a λ/4 or λ/8 plate as a sample In the case of a λ/4 plate, the average absolute error of the principal axis is approximately 377°, and that of the phase retardation is approximately 103° (109%) The retardation error is within the 5% uncertainty range of a commercial wave plate Fortunately, the nonlinear error caused by the reflection phase retardation of the beam splitter dose not appear in the new system Therefore the error could be attributed to misalignment and defects in the EO modulator or the other optical components As for the repeatability of this new common-path heterodyne interferometer, the average deviation for the principal axis is 0186° and the phase retardation is 0356° For the stability, the average deviation for the principal axis is 0405° and the phase retardation is 0635° The resolution of this new system is estimated to be ∼05°, and the principal axis and phase retardation could be measured up to π and 2π, respectively, without ambiguity

Multispectral, multifusion, laser-polarimetric optical imaging system

Abstract: A multi-energy polarization imaging method consisting of a multi-fusion, dual-rotating retarder / multiple-energy complete Mueller matrix-based polarimeter and dual-energy capabilities The system includes a light source (14) for illuminating a target (18) with a first quantity of light having a first wavelength and a second quantity of light having a second wavelength, the first and second wavelength being different. A polarization-state generator (22) generates a polarization state for each of the first and second quantities of light, and includes a first polarizer (26) through which the first and second quantities of light are transmitted before entering a first waveplate (32). A polarization-state receiver (44) evaluates a resulting polarization state of the first and second quantities of light following illumination of the target (18), the polarization-state receiver (44) including a second waveplate (48) through which the first and second quantities of light are transmitted before entering a second polarizer (51). An optical image-capture device captures a first image of the target illuminated by the first quantity of light and a second image of the target illuminated by the second quantity of light. A processing unit assigns a weighting factor to at least one of the first and second images and evaluates a weighted difference between the first and second images to generate a multi-energy image of the target (18).

Photonic crystal based polarization control devices

Abstract: It has recently been shown that the polarization of electromagnetic radiation can be completely controlled using devices constructed entirely from photonic crystals. We will review these important developments, focusing on effects that occur for propagation in the periodic plane of two-dimensional, dielectric structures. Specifically, we survey the recent experimental results demonstrating waveplates and polarizers based on two-dimensional photonic crystals.

Polariscope for simultaneous measurement of the principal axis and the phase retardation by use of two phase-locked extractions

Abstract: A novel polariscope with electro-optic modulation that is capable of simultaneous measurement of the principal axis and the phase retardation of an optical linear birefringent medium by means of two phase-locked extractions is described. A phase compensator is used to suppress the transmission phase-retardation effect of the beam splitter, thereby enhancing the precision of the measuring performance. The validity of the proposed design is demonstrated by measurement of the principal axis and phase retardation of a quarter-wave plate sample. There are absolute errors of 0.25° on average and 0.58° at maximum in the principal-axis measurement and of 0.75° (0.83%) on average and 3.11° at maximum in the phase-retardation measurement. Meanwhile, the retardation error lies within a 5% uncertainty range of a commercial wave plate. The root-mean-square resolutions for the principal-axis angle and phase-retardation measurements are 0.042° and 0.081°, respectively. Finally, the dynamic ranges of the principal-axis angle measurement and the phase-retardation measurement extend as far as 180°.

Optical pickup, optical information recording/reproducing apparatus using the same, and phase variable wave plate used in the pickup and the apparatus

Abstract: Laser beams respectively emitted from a SHG blue laser unit and a red semiconductor laser unit that have photo detectors respectively are turned into parallel lights by a collimator lens and then coupled by a dielectric multi-layer film mirror so as to be propagated on the same optical axis. The dielectric multi-layer film mirror is configured so as to transmit light with a wavelength of 500 nm or shorter and reflect light with a wavelength of 500 nm or longer for both P wave and S wave. The lights that are transmitted and reflected by the dielectric multi-layer film mirror pass through a polarizing hologram and a phase variable wave plate and are focused on an optical disk by an objective lens. In this manner, a simple configuration can realize a compatibility with many types of optical disks and a stable signal detection even when using a polarizing optical detection system.

Interference effects in single wave plates

Abstract: Although the presence of interference effects related to wave plate retarders has been known for some time, their overall polarimetric properties are generally not fully appreciated. The effects of interference within a simple wave plate is explored by extension of the Airy formulation describing multiple-beam interference within a parallel plate. It is first demonstrated that phase delay does not grow linearly with plate thickness as expected from the standard simple formula appearing in optical texts. The wavelength dependences of the phase delay, polarizance and transmittance of simple quarter- and half-wave plates are presented to highlight the effects that internal interference has on the operation of these devices.

Circularly polarized plate, vertically-oriented liquid crystal display panel and production methods for them

Abstract: A circularly polarized plate comprising a λ/4 phase difference plate (1) and a linearly polarized plate (2) laminate on the main surface of the λ/4 phase difference plate (1) so that its absorption axis forms an angle of about 45˚ with respect to the delay phase axis of the λ/4 phase difference plate (1). The λ/4 phase difference plate (1) has characteristics of reverse wavelength dispersion and an Nz coefficient of at least 1.6. The circularly polarized plate comprises the λ/4 phase difference plate having characteristics of reverse wavelength dispersion and an Nz coefficient of at least 1.6, and the linearly polarized plate laminate on the main surface of the λ/4 phase difference plate. When a reference direction is set as a direction parallel to one side of a rectangular flat shape, the circularly polarized plate is formed so that the delay-axis direction of the λ/4 phase difference plate forms an angle of about +90˚ with respect to the reference direction, and the absorption-axis direction of the linearly polarized plate forms an angle of about +45˚ with respect to the reference direction. When any of these configurations is used, a circularly polarized plate excellent in viewing angle characteristics and a vertically-oriented liquid crystal display panel provided with this are provided.

Manipulation and growth of birefringent protein crystals in optical tweezers.

Abstract: We report on the trapping, rotation, and in-situ growth of birefringent tetragonal lysozyme crystals in optical tweezers operating at a wavelength of 1070 nm. Variation of the pH and lysozyme concentration of the solution during growth was used to alter the length to width ratio of the crystals, and hence their orientation in the tweezers. Crystals with the optical axis skewed or perpendicular to the trapping-beam axis could be rotated by changing the orientation of linearly polarized light. We observed spontaneous spinning of some asymmetric crystals in the presence of linearly polarized light, due to radiation pressure effects. Addition of protein to the solution in the tweezers permitted real-time observation of crystal growth.

Optical module, and optical transmission device

Abstract: To provide optical modules and optical transmission devices that are suitable for communication forms using multimode optical fibers, an optical module includes a surface-emitting type semiconductor laser that emits polarized light oscillating in a multimode which is preferentially oriented in two given polarization axes, and an optical member that demonstrates at least one function among a transmission function, a reflection function, a refraction function, and a diffraction function alternatively to a predetermined polarization. The optical member is disposed such that a principal plane thereof intersects with a traveling direction of emission light of the surface-emitting type semiconductor laser and a polarization axis of the polarization plane does not overlap with the polarization axes of the emission light of the surface-emitting type semiconductor laser.

Endless fiber-to-fiber polarization controller based on ceramic programmable waveplates

Abstract: In this letter, we report a fast and endless polarization controller based on lead lanthanum zirconate titanate (PLZT) ceramic programmable waveplates. A set of four volume electrodes placed in a cylindrical arrangement are drilled in an electrooptic ceramic plate. By using the Kerr effect, and taking advantage of the high electrooptic coefficient and fast response time of the PLZT, we thus, obtain a fast rotatable and variable waveplate. Then, cascading two of these waveplates produces an endless polarization controller.

Interference effects in compound and achromatic wave plates

Abstract: Compound and achromatic wave plates are investigated with respect to multiple-beam interference within their elements. The phase delay, transmittance and polarizance are all shown to display fringes through the spectrum. In the past, achromatic devices have had apparent success in instruments with spectral pass-bands which are sufficiently broad to average out the effects of the fringe structures. According to the accuracy of any prospective measurement, it is now shown that their intended properties require detailed scrutiny when they are employed in optical systems involving medium to high spectral resolution.

Non-linear and quantum optics of a type II OPO containing a birefringent element 2. Bright entangled beams generation

Abstract: We describe theoretically the quantum properties of a type-II Optical Parametric Oscillator containing a birefringent plate which induces a linear coupling between the orthogonally polarized signal and idler beams and results in phase locking between these two beams. As in a standard OPO, the signal and idler waves show large quantum correlations which can be measured experimentally due to the phase locking between the two beams. We study the influence of the waveplate on the various criteria characterizing quantum correlations. We show in particular that the quantum correlations can be maximized by using optimized quadratures.

Integrated micro-optic architecture for combining and depolarizing plural polarized laser beams

Abstract: A multimode laser beam depolarization and combining architecture integrates a combiner for polarized multimode light beams with a multimode beam depolarizer, that produces a composite depolarized output beam optimized for application to a Raman optical amplifier A high-order depolarizing 45° waveplate is used to effectively depolarize multimode laser beams produced by a Fabry-Perot (FP) laser The high-order 45° waveplate has a length that achieves multi mode dispersion-dependent depolarization of the beam over its travel path through the crystal, and may comprise a birefringent material such as YVO4 having a large difference between its extraordinary and ordinary indices of refraction

Stability calculations for the ytterbium-doped fibre laser passively mode-locked through nonlinear polarization rotation

Abstract: We investigate theoretically a fibre laser passively mode-locked with nonlinear polarization rotation. A unidirectional ring cavity is considered with a polarizer placed between two sets of a halfwave plate and a quarterwave plate. A master equation is derived and the stability of the continuous and mode-locked solutions is studied. In particular, the effect of the orientation of the four phase plates and of the polarizer on the mode-locking regime is investigated.

Calibration of the instrumental polarization of the Domeless Solar Telescope at the Hida Observatory

Abstract: A new spectropolarimeter is developed at the Domeless Solar Telescope (DST) in Hida Observatory. It consists of a rotating waveplate, Wollaston prisms, and a high-dispersion spectrograph which is vertically installed at the focus of the DST. In order to realize a high-precision measurement, it is inevitable to compensate the instrumental polarization due to the DST. We observed the quiet region of the Sun, which is considered to be highly unpolarized, with and without a sheet linear polarizer or circular polarizer set at the entrance window of the telescope. The theoretical model which represents the total instrumental polarization of the DST with some characteristic parameters was calculated and compared with the observation. The model that two flat mirrors have different properties can explain the observation in 0.5% accuracy for the unpolarized light, and in 7% for the polarized light.

Non-linear and quantum optics of a type II OPO containing a birefringent element - 1. Classical operation

Abstract: We describe theoretically the quantum properties of a type-II Optical Parametric Oscillator containing a birefringent plate which induces a linear coupling between the orthogonally polarized signal and idler beams and results in phase locking between these two beams. As in a standard OPO, the signal and idler waves show large quantum correlations which can be measured experimentally due to the phase locking between the two beams. We study the influence of the waveplate on the various criteria characterizing quantum correlations. We show in particular that the quantum correlations can be maximized by using optimized quadratures.