Showing papers on "Circular polarization published in 2007"
TL;DR: It is experimentally demonstrate that the magnetization can be reversed in a reproducible manner by a single 40 femtosecond circularly polarized laser pulse, without any applied magnetic field, revealing an ultrafast and efficient pathway for writing magnetic bits at record-breaking speeds.
Abstract: We experimentally demonstrate that the magnetization can be reversed in a reproducible manner by a single 40 femtosecond circularly polarized laser pulse, without any applied magnetic field. This optically induced ultrafast magnetization reversal previously believed impossible is the combined result of femtosecond laser heating of the magnetic system to just below the Curie point and circularly polarized light simultaneously acting as a magnetic field. The direction of this opto-magnetic switching is determined only by the helicity of light. This finding reveals an ultrafast and efficient pathway for writing magnetic bits at record-breaking speeds.
1,208 citations
TL;DR: In this article, the authors report on the generation of radially and azimuthally polarized Q-switched laser radiation and its application in material processing and show that depending on the optical properties of the metal, either radial or azIMuthal polarization shows the best efficiency and the effect is attributed to waveguiding.
Abstract: We report on the generation of radially and azimuthally polarized Q-switched laser radiation and its application in material processing. The power levels were sufficiently high to study micro-hole drilling in different metals. Depending on the optical properties of the metal, either radial or azimuthal polarization shows the best efficiency and the effect is attributed to waveguiding. For steel, a comparison to linearly or circularly polarized laser radiation indicates that the doughnut-shaped beam with azimuthal polarization is the most energy-efficient in producing holes of the same diameter and depth.
466 citations
TL;DR: Bomzon et al. as discussed by the authors presented a Pancharatnam-Berry phase optical element for wavefront shaping in the visible spectral domain, based on patterned liquid crystal technology, with the possibility of electro-optically switching between opposite helicities by controlling the handedness of the input circular polarization.
Abstract: We report the realization of a Pancharatnam-Berry phase optical element [Z. Bomzon, G. Biener, V. Kleiner, and E. Hasman, Opt. Lett. \textbf{27}, 1141 (2002)] for wavefront shaping working in the visible spectral domain, based on patterned liquid crystal technology. This device generates helical modes of visible light with the possibility of electro-optically switching between opposite helicities by controlling the handedness of the input circular polarization. By cascading this approach, fast switching among multiple wavefront helicities can be achieved, with potential applications to multi-state optical information encoding. The approach demonstrated here can be generalized to other polarization-controlled devices for wavefront shaping, such as switchable lenses, beam-splitters, and holographic elements.
272 citations
TL;DR: A comprehensive review of spin-polarized light-emitting diodes and surface emitting lasers is provided in this paper, concluding with a discussion of future prospects and operation principles and design of spinpolarised light sources.
Abstract: Spin-polarized light sources are a new class of devices in which the radiative recombination of spin-polarized carriers results in luminescence exhibiting a net circular polarization. The operation principles and design of spin-polarized light sources are discussed. A comprehensive review of experimental work on spin-polarized light-emitting diodes and surface-emitting lasers is provided, concluding with a discussion of future prospects.
190 citations
TL;DR: Adding an actively-controlled liquid crystal retarder provides the capability to identify depolarizing particles by alternately transmitting linearly and circularly polarized light, a departure from established techniques.
Abstract: Polarization-sensitive detection of elastic backscattered light is useful for detection of cloud phase and depolarizing aerosols. The U.S. Department of Energy’s Atmospheric Radiation Measurement Program has deployed micropulse lidar (MPL) for over a decade, but without polarized detection. Adding an actively-controlled liquid crystal retarder provides the capability to identify depolarizing particles by alternately transmitting linearly and circularly polarized light. This represents a departure from established techniques, which transmit exclusively linear polarization or exclusively circular polarization. Mueller matrix calculations yield simple relationships between the well-known linear depolarization ratio δlinear, the circular depolarization ratio δcirc, and this MPL depolarization ratio δMPL.
149 citations
TL;DR: In this article, the authors used direct laser writing to fabricate high-quality polymeric 3D spiral photonic crystals using a 2D network of bars at or close to the top of the 3D crystal.
Abstract: Chiral 3D photonic crystals are an interesting subclass of 3D photonic crystals. For example, large complete 3D photonic bandgaps have been predicted for high-index-contrast silicon square-spiral structures; corresponding experiments using glancing-incidence deposition, interference lithography, or direct laser writing have been published. In addition to complete gaps or stop bands, theory also predicts polarization stop bands, i.e., stop bands for just one of the two circular polarizations. Such polarization stop bands can give rise to strong circular dichroism, which can potentially be used for constructing compact “thin-film” optical diodes. In this report, we fabricate high-quality polymeric 3D spiral photonic crystals via direct laser writing. The measured transmittance spectra of these low-index-contrast structures reveal spectral regions where the transmittance is below 5 % for one circular incident polarization and above 95 % for the other—for just eight lattice constants along the propagation direction. The experimental data are compared with scattering-matrix calculations for the actual finite structures, leading to good agreement. For what conditions do we expect strong circular dichroism? For circular polarization of light, the tip of the electricfield vector simply follows a spiral. The pitch of this spiral is just the material wavelength k. Thus, intuitively, we expect a chiral resonance from spiral photonic crystals if the pitch of circularly polarized light matches the pitch of the dielectric spirals, i.e., the lattice constant az. This condition, k/az = 1, corresponds to the edge of the second Brillouin zone, i.e., to a wave number kz = 2p/k= 2p/az. Recall that the edge of the first Brillouin zone is at kz = p/az. Thus, one does not anticipate a strong chiral response around and below the fundamental stop band (or bandgap), but rather at higher frequencies. Theory for high-index silicon-based structures confirms this intuitive reasoning. We have repeated similar calculations for low-index-contrast polymeric structures, revealing essentially the same trends. The parameters of the 3D spiral photonic crystals to be discussed below are the result of an optimization with respect to circular dichroism. The samples in our experiments are made by direct laser writing, which essentially allows for the fabrication of almost arbitrarily shaped 3D photoresist structures. Details of our process based on the commercial thick-film resist SU-8 can be found in the Experimental section and in earlier work. Our structures are mechanically supported by a 2D network of bars at, or close to, the top of the 3D crystal. As the spirals are not at all mechanically connected to their neighbors, very unstable low-quality structures would result without this grid. Furthermore, all the structures for optical experiments are surrounded by a thick massive wall (see Fig. 1a), which aims at reducing the effects of strain on the 2D grid caused by photoresist shrinkage during development. Here, we use a round (rather than a rectangular) wall in order to evenly distribute strain inside the wall. Through numerical calculations (see below), we have confirmed that the distortion of the optical properties by the 2D network is only marginal. Most importantly, the network does not introduce any chirality. A small gallery of selected electron microscopy images is shown in Figure 1, which gives first evidence that the sample quality is very good. Figure 1a gives an overview of the sample to be optically characterized below. The sample parameters are: in-plane lattice constant axy = 1.3 lm, pitch az = 1.3 lm, spiral diameter d = 0.78 lm, volume filling fraction 34.7 %, lateral diameter of the spiral arms darm = 380 nm, ratio between the axial and the lateral diameter 2.7, and N = 8 lattice constants along the z-direction. These parameters were extracted from the close-up cross-sectional view in Figure 1a. To demonstrate the versatility of our approach, Figure 1b exhibits a cut of a structure with axy = 1.5 lm, az = 1.5 lm, and N = 4. Because the focused-ion-beam cut was stopped in between two rows of spirals, the stabilizing network mentioned C O M M U N IC A IO N
143 citations
TL;DR: In this paper, a reconfigurable microstrip antenna with switchable circular polarization using a piezoelectric transducer (PET) is presented, where two dielectric perturbers attached to the PETs are used to create perturbations for the desired circular polarizations.
Abstract: This letter presents a novel reconfigurable microstrip antenna with switchable circular polarization using a piezoelectric transducer (PET). Two dielectric perturbers attached to the PETs are used to create perturbations for the desired circular polarizations. Right-hand circular polarization (RHCP) or left-hand circular polarization (LHCP) can be produced by pulling down one of the PETs and lifting up the other one. The full-wave simulation and measured results show good agreement. An axial ratio of less than 1 dB is observed
137 citations
TL;DR: In this article, the polarization signature of primordial gravitational waves imprinted in cosmic microwave background (CMB) anisotropies is discussed and the current constraints on the circularly polarized GWB from large angular scales (l < 16) of the three year WMAP data are discussed.
Abstract: We discuss the polarization signature of primordial gravitational waves imprinted in cosmic microwave background (CMB) anisotropies. The high-energy physics motivated by superstring theory or M-theory generically yield parity violating terms, which may produce a circularly polarized gravitational wave background (GWB) during inflation. In contrast to the standard prediction of inflation with un-polarized GWB, circularly polarized GWB generates non-vanishing TB and EB-mode power spectra of CMB anisotropies. We evaluate the TB and EB-mode power spectra taking into account the secondary effects and investigate the dependence of cosmological parameters. We then discuss current constraints on the circularly polarized GWB from large angular scales (l < 16) of the three year WMAP data. Prospects for future CMB experiments are also investigated based on a Monte Carlo analysis of parameter estimation, showing that the circular polarization degree, varepsilon, which is the asymmetry of the tensor power spectra between right- and left-handed modes normalized by the total amplitude, can be measured down to |varepsilon| 0.35(r/0.05)^{-0.6}.
120 citations
TL;DR: A novel reconfigurable quadri-polarization diversity aperture-coupled patch antenna which can provide four polarization states is presented which provides potential polarization diversity features for wireless local area networks and multiple-input multiple-output systems.
Abstract: We present a novel reconfigurable quadri-polarization diversity aperture-coupled patch antenna which can provide four polarization states. By controlling the dc bias voltage of the pin-diodes on the feeding network, we can reconfigure the proposed antenna to provide a pair of orthogonal linear polarizations and a pair of orthogonal circular polarizations. Numerical and experimental results validate our design. This novel antenna provides potential polarization diversity features for wireless local area networks and multiple-input multiple-output systems
118 citations
TL;DR: Computer simulation results show that the estimation accuracy generally improves with an increasing number of source position measurements and laboratory results indicate that the proposed method is effective for recovering the reflection angle and that the estimated index of refraction provides a feature vector that is robust to the reflection angles.
Abstract: A passive-polarization-based imaging system records the polarization state of light reflected by objects that are illuminated with an unpolarized and generally uncontrolled source. Such systems can be useful in many remote sensing applications including target detection, object segmentation, and material classification. We present a method to jointly estimate the complex index of refraction and the reflection angle (reflected zenith angle) of a target from multiple measurements collected by a passive polarimeter. An expression for the degree of polarization is derived from the microfacet polarimetric bidirectional reflectance model for the case of scattering in the plane of incidence. Using this expression, we develop a nonlinear least-squares estimation algorithm for extracting an apparent index of refraction and the reflection angle from a set of polarization measurements collected from multiple source positions. Computer simulation results show that the estimation accuracy generally improves with an increasing number of source position measurements. Laboratory results indicate that the proposed method is effective for recovering the reflection angle and that the estimated index of refraction provides a feature vector that is robust to the reflection angle.
109 citations
TL;DR: In this article, the polarization signature of primordial gravitational waves imprinted in cosmic microwave background (CMB) anisotropies was discussed and the current constraints on the circularly polarized GWB from large angular scales were discussed.
Abstract: We discuss the polarization signature of primordial gravitational waves imprinted in cosmic microwave background (CMB) anisotropies. The high-energy physics motivated by superstring theory or M-theory generically yields parity violating terms, which may produce a circularly polarized gravitational wave background (GWB) during inflation. In contrast to the standard prediction of inflation with unpolarized GWB, circularly polarized GWB generates non-vanishing TB- and EB-mode power spectra of CMB anisotropies. We evaluate the TB- and EB-mode power spectra taking into account the secondary anisotropies induced by the reionization and investigate the dependence of cosmological parameters. We then discuss current constraints on the circularly polarized GWB from large angular scales () of the three year WMAP data. Prospects for future CMB experiments are also investigated based on a Monte Carlo analysis of parameter estimation, showing that the circular polarization degree, e, which is the asymmetry of the tensor power spectra between right- and left-handed modes normalized by the total amplitude, can be measured down to .
TL;DR: Vacuum-stimulated Raman transitions are driven between two magnetic substates of a 87Rb atom strongly coupled to an optical cavity, which produces a stream of single photons with alternating circular polarization in a predetermined spatiotemporal mode.
Abstract: Vacuum-stimulated Raman transitions are driven between two magnetic substates of a 87Rb atom strongly coupled to an optical cavity. A magnetic field lifts the degeneracy of these states, and the atom is alternately exposed to laser pulses of two different frequencies. This produces a stream of single photons with alternating circular polarization in a predetermined spatiotemporal mode. MHz repetition rates are possible as no recycling of the atom between photon generations is required. Photon indistinguishability is tested by time-resolved two-photon interference.
TL;DR: In this article, photoexcitations in helical aggregates of a functionalized, chiral oligophenylenevinylene (MOPV) are described in the form of dressed (polaronic) Frenkel excitons.
Abstract: Photoexcitations in helical aggregates of a functionalized, chiral oligophenylenevinylene (MOPV) are described going beyond the Born−Oppenheimer approximation, in the form of dressed (polaronic) Frenkel excitons. This allows for accurate modeling of the experimentally observed wavelength dependence of the circular polarization in fluorescence, which directly probes the non-adiabatic nature of the electron-vibration (EV) coupling in this system. The fluorescence photon is emitted from a nuclear geometry in which one MOPV and its two nearest neighbors have a nuclear equilibrium that differs appreciably from the ground state due to the presence of the excited state. The absorption and emission band shape and the circular dichroism are consistent with a coherence range of the emitting excitation of approximately two neighboring molecules. Random fluctuations in the zero-order excited-state energy of the MOPVs (disorder) limit the exciton delocalization and can be described by a Gaussian distribution of energi...
TL;DR: Surprisingly, it is found that the alignment of the ripple structure turned left or right by 45 degrees with respect to the incident plane when using right and left circularly polarized light, respectively.
Abstract: The evolution of surface morphology of tungsten irradiated by single-beam femtosecond laser pulses is investigated. Ripplelike periodic structures have been observed. The period of these ripples does not show a simple relation to the wavelength and angle of incidence. The orientation of ripples is aligned perpendicularly to the direction of polarization for linearly polarized light. Surprisingly, we find that the alignment of the ripple structure turned left or right by 45° with respect to the incident plane when using right and left circularly polarized light, respectively. The period of the ripple can be controlled by the pulse energy, the number of pulses, and the incident angle. We find a clear threshold for the formation as a function of pulse energy and number of pulses. The mechanism for the ripple formation is discussed, as well as potential applications in large-area structuring of metals.
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TL;DR: In this paper, it is shown that radial polarization leads to the best light beam focalisation in terms of spot size, whereas circular polarization induces best light confinements in air, whereas for numerical apertures beyond 8, radial polarization seems the right solution.
TL;DR: In this paper, a laser beam with circular polarization can be converted into either radial or azimuthal polarization by a microfabricated spiral phase plate and a radial (or azimauthal)-type linear analyzer.
Abstract: A laser beam with circular polarization can be converted into either radial or azimuthal polarization by a microfabricated spiral phase plate and a radial (or azimuthal)-type linear analyzer. The resulting polarization is axially symmetric and is able to produce tightly focused light fields beyond the diffraction limit. We describe in detail the theory behind the technique and the experimental verification of the polarization both in the far field and at the focus of a high numerical aperture lens. Vector properties of the beam under strong focusing conditions were observed by comparing the fluorescence images corresponding to the focal intensity distribution for both radial and azimuthal polarizations. The technique discussed here may easily be implemented to a wide range of optical instruments and devices that require the use of tightly focused light beams.
TL;DR: It is shown that by illuminating an InGaAs/GaAs self-assembled quantum dot with circularly polarized light, the nuclei of atoms constituting the dot can be driven into a bistable regime, in which either a thresholdlike enhancement or reduction of the local nuclear field by up to 3 T can be generated by varying the pumping intensity.
Abstract: We show that by illuminating an InGaAs/GaAs self-assembled quantum dot with circularly polarized light, the nuclei of atoms constituting the dot can be driven into a bistable regime, in which either a thresholdlike enhancement or reduction of the local nuclear field by up to 3 T can be generated by varying the pumping intensity. The excitation power threshold for such a nuclear spin “switch” is found to depend on both the external magnetic and electric fields. The switch is shown to arise from the strong feedback of the nuclear spin polarization on the dynamics of the spin transfer from electrons to the nuclei of the dot.
TL;DR: In this article, photochromic diarylethene, 1,2-bis[2-methyl-5-(3-fluorophenyl)-3-thienyl] perfluorocylcopentene ( 1a ), was synthesized.
TL;DR: In this paper, the radio emitting magnetar AXPJ1810-197 was observed to be nearly 80-95 per cent polarized, often with a low but significant degree of circular polarization at all frequencies.
Abstract: We present polarization observations of the radio emitting magnetar AXPJ1810-197. Using simultaneous multifrequency observations performed at 1.4, 4.9 and 8.4 GHz, we obtained polarization information for single pulses and the average pulse profile at several epochs. We find that in several respects this magnetar source shows similarities to the emission properties of normal radio pulsars while simultaneously showing striking differences. The emission is nearly 80-95 per cent polarized, often with a low but significant degree of circular polarization at all frequencies which can be much greater in selected single pulses. The position angle swing has a low average slope of only 1 deg deg-1, deviating significantly from an S-like swing as often seen in radio pulsars which is usually interpreted in terms of a rotating vector model and a dipolar magnetic field. The observed position angle is consistent at all frequencies while showing significant secular variations. On average, the interpulse is less linearly polarized but shows a higher degree of circular polarization. Some epochs reveal the existence of non-orthogonal emission modes in the main pulse and systematic wiggles in the PA swing, while the interpulse shows a large variety of position angle values. We interpret many of the emission properties as propagation effects in a non-dipolar magnetic field configuration where emission from different multipole components is observed.
TL;DR: A novel method for the electric polarization reversal in TbMnO3 without the application of an electric field or heat is reported.
Abstract: For the memory application of magnetoelectric multiferroics, not only bistability (i.e., ferroelectricity) but also the switching of the polarization direction with some noneverlasting stimulus is necessary. Here, we report a novel method for the electric polarization reversal in TbMnO 3 without the application of an electric field or heat. The direction of the magnetic-field-induced polarization along the a axis (P a ) is memorized even in the zero field where P a is absent. The polarization direction can be reversed by rotating the magnetic-field direction in the ab plane.
TL;DR: A design of a polarization converter between linear, circular, and elliptic accomplished with an on-chip high-Q dielectric microring resonator is presented with an optical bistability effect making the polarization of the transmitted light dependent on its spectral or intensity history.
Abstract: We present a design of a polarization converter between linear, circular, and elliptic accomplished with an on-chip high-Q dielectric microring resonator. Nonlinear polarization switching can be accomplished at modest input intensities because of the high-intensity compression in the ring. We predict an optical bistability effect making the polarization of the transmitted light dependent on its spectral or intensity history. © 2007
TL;DR: In this article, the authors examined the partial polarization of focused light and demonstrated that the focusing of unpolarized light results in rings of full polarization in the focal plane of the focusing optics.
Abstract: The polarization of light is important in a great variety of optical phenomena, ranging from transmission, reflection and scattering to polarimetric imaging of scenes and quantum-mechanical selection rules of atomic and molecular transitions. Among some less-well-known phenomena that illustrate the vectorial nature of light are the Pancharatnam1 (or geometric2) phase, singularities in the polarization pattern of clear sky3 and polarization of microwave background radiation4. Here, we examine the partial polarization of focused light. We experimentally demonstrate a rather surprising phenomenon, where the focusing of unpolarized light results in rings of full polarization in the focal plane of the focusing optics. The polarization rings are imaged with a resolution of <100 nm by probing the focal region using a gold nanoparticle.
TL;DR: In this paper, the authors investigated the influence of defect layer thickness variation and its location in the chiral photonic crystal (CPC) and also its optical axes orientation, as well as of CPC thickness variation on defect mode properties.
Abstract: In the present paper we consider some properties of defect modes in chiral photonic crystals with an anisotropic defect layer. We solved the problem by Ambartsumian's layer addition method. We investigated the influence of the defect layer thickness variation and its location in the chiral photonic crystal (CPC) and also its optical axes orientation, as well as of CPC thickness variation on defect mode properties. Variations of the optical thickness of the defect layer have its impact on the defect mode linewidth and the light accumulation in the defect. We obtain that CPCs lose their base property at certain defect layer thicknesses; namely, they lose their diffraction reflection dependence on light polarization. We also show that the circular polarization handedness changes from right-handed to left-handed if the defect layer location is changed, and therefore, such systems can be used to create sources of elliptically polarized light with tunable ellipticity. Some nonreciprocity properties of such systems are investigated, too. In particular, it is also shown that such a system can work as a practically ideal wide band optical diode for circularly polarized incident light provided the defect layer thickness is properly chosen, and it can work as a narrow band diode at small defect layer thicknesses.
TL;DR: In this article, a double-bent microstripline was proposed to feed the antenna at two different positions to achieve a circularly polarized annular-ring slot antenna, which achieved 10.5% axial-ratio bandwidth (ARBW) for the former and 10.0% for the latter.
Abstract: A novel design of a circularly polarized annular-ring slot antenna is discussed. The circular polarization is attained through a newly proposed double-bent microstripline that feeds the antenna at two different positions. Several structural parameters were experimentally studied with care to establish a design procedure, which was subsequently drawn into a design flow chart. Validation was carried out using the antennas designed at 3.5 and 1.59 GHz. The measured 3-dB axial-ratio bandwidth (ARBW) for the former is 10.5% and for the latter, 10.0%, which is larger than the 8.5% 3-dB ARBW required by an Inmarsat application.
TL;DR: In this article, the authors fabricate and characterize polymeric three-dimensional layer-by-layer chiral photonic crystals and obtain a circular dichroism from polarization stop bands.
Abstract: We fabricate and characterize polymeric three-dimensional layer-by-layer chiral photonic crystals. The obtained circular dichroism from polarization stop bands is comparable with that of recently demonstrated circular-spiral photonic crystals. Moreover, telecommunication wavelengths are easily accessible with the layer-by-layer approach; even visible wavelengths are in reach.
TL;DR: In this article, an elaboration procedure and properties of a cholesteric liquid crystal (CLC) gel whose optical characteristics go beyond the 50% reflectance limit are reported.
Abstract: Cholesteric liquid crystals (CLCs) selectively reflect light when the wavelength matches the helical pitch. The reflectance is limited to 50% of ambient, unpolarized light because only circularly polarized light of the same handedness as the helix is reflected. Here the elaboration procedure and the properties of a CLC gel whose optical characteristics go beyond the 50% reflectance limit are reported. Photopolymerizable monomers are introduced into the volume of a CLC exhibiting a thermally induced helicity inversion and the blend is then cured with UV light when the helix is right‐handed. The reflectance exceeds 50% when measured at the temperature assigned at a cholesteric helix with the same pitch but a left‐handed sense before reaction. The reflection properties are investigated in the infrared region. From scanning electron microscopy investigations, it is shown that the organization of the mesophase is transferred onto the structure of the network. The gel structure is discussed as consisting of a p...
TL;DR: The use of stress birefringence in the creation of vortex illumination is described and a finite element plane-stress model is used to analyze the space-variant anisotropy.
Abstract: We describe the use of stress birefringence in the creation of vortex illumination. A trifold symmetric stress pattern will provide an annular region that exhibits polarization vortices when illuminated with linearly polarized light and scalar vortices when illuminated with circularly polarized light. A finite element plane-stress model is used to analyze the space-variant anisotropy.
TL;DR: In this article, a low threshold and high efficiency laser based on dye-doped cholesteric liquid crystals (CLCs) is demonstrated using an input excitation with the same handedness of circular polarization as the helical structure of the sample at the shorter wavelength band edge of the reflection band.
Abstract: A low threshold and high efficiency laser based on dye-doped cholesteric liquid crystals (CLCs) is demonstrated using an input excitation with the same handedness of circular polarization as the helical structure of the sample at the shorter wavelength band edge of the reflection band. The responsible mechanism originates from the dramatic increase of the optical density of state (DOS) at the band edges. The calculated DOS of the CLC system confirms the authors’ experimental results.
TL;DR: Two-dimensional gratings made up of an array of differently twisted nematic structures are obtained by crossed assembling of 1D polarization holograms recorded at the photoaligning substrates that diffract light in different directions with different polarization states that can be optically controlled.
Abstract: Two-dimensional (2D) gratings made up of an array of differently twisted nematic structures are obtained by crossed assembling of 1D polarization holograms recorded at the photoaligning substrates. The rotating linear polarization pattern, produced by the interference of two opposite circularly polarized beams, is recorded on the azo-dye doped polyimide aligning layers. The 2D gratings diffract light in different directions with different polarization states, that can be optically controlled. Orthogonal circularly and linearly polarized diffraction orders are simultaneously obtained irradiating the grating with a linearly polarized beam. An external ac voltage allows to completely control the diffracted energy distribution.
TL;DR: This work reports on a software-based corneal birefringence compensation that uses the polarization state of the light backscattered at the retinal surface to measure the cornean bireFringence.
Abstract: In previous publications we have reported on polarization-sensitive optical coherence tomography (PS-OCT) systems that measure and image retardation and axis orientation of birefringent samples with only a single input polarization state. This method requires that the sample is illuminated by circularly polarized light. In the case of retinal imaging, the retina is measured through the birefringent cornea, which causes a deviation of the sampling beam from the circular polarization state. To obtain undistorted birefringence patterns of the retina by PS-OCT, the corneal birefringence has to be compensated. We report on a software-based corneal birefringence compensation that uses the polarization state of the light backscattered at the retinal surface to measure the corneal birefringence. This information is used to numerically compensate the corneal birefringence. Contrary to hardware-based solutions, our method accounts for local variations of the corneal birefringence. We implemented the method in a state of the art spectral domain PS-OCT system and demonstrate it in a test sample and human retina in vivo.