Phase Retardation Research Articles

Super electro-optic modulation in bulk KTN:Cu based on electric-field-enhanced permittivity

The electric-field-enhanced effect of permittivity can improve the performance of electro-optic modulators and deflectors. A theoretical model of super electro-optic modulation based on the field-enhanced effect of the permittivity was proposed. Results showed that a strong field-enhanced effect can greatly reduce the half-wave voltage and increase the modulation depth as a result of increased relative dielectric permittivity and permittivity gradient to the electric field. For bulk paraelectric KTN:Cu near the Curie temperature, we found a novel phenomenon that the response of relative dielectric permittivity to the bias electric field was closely related to the frequency, including attenuation, invariance, and enhancement. We effectively selected the frequencies corresponding to the strong field-enhanced effect by measuring the dielectric-frequency spectrum under the bias voltage. At these frequencies, a phase retardation of π was achieved through 2Vpp AC modulation voltage, indicating that the half-wave voltage was reduced by one order of magnitude.

Design of reflective phase retarders in the extreme ultraviolet based on chirped Mo/Si multilayer mirrors.

The extreme ultraviolet (EUV) phase retarder is an important optical element for polarization analysis and conversion of EUV synchrotron radiation. In this paper, a linearly chirped Mo/Si multilayer mirror is used to design an EUV phase retarder. With increasing thickness variation of the chirped multilayer, the reflective phase retardation between s- and p-polarized light increases at first and then reaches its maximum value. When the bilayer number increases from 2 to 20, the maximum phase retardation for an EUV source with a photon energy of 90 eV increases from 5.97° to 245.10° for a linearly chirped Mo/Si multilayer with 14.7 nm central thickness. In addition, the phase retardations of chirped mirrors at different photon energies (80 eV, 85 eV and 90 eV) are also investigated and compared. Furthermore, the physical mechanism of reflective phase retardation improvement is also studied by investigating the field intensity distributions inside chirped mirrors.

33.3: Adaptive Modulation System of the Liquid Crystal Phase Modulators

An adaptive modulation system for a liquid crystal (LC) phase modulator is demonstrated. In order to achieve the highresolution phase distribution, the information of the transmittance distribution transformed by phase retardation is applied. By the adjustment algorithm and adaptive algorithm, the phase distribution of the LC phase modulator can perfectly match the designed phase profile in a short modulation time. The adaptive modulation system shows potential application in optical communication, wearable device and display.

Composite achromatic quartz wave plate with adjustable retardation and temperature insensitivity.

In order to obtain a composite achromatic wave plate with adjustable retardation, temperature insensitivity, and achromatic bandwidth of 500 nm, a five-element composite achromatic quartz wave plate is designed based on particle swarm optimization. The total phase retardation can be adjusted by rotating the azimuth angle of the central wave plate. The results show that the total phase retardation is adjustable with the range of 90°-180° when the range of temperature and the achromatic wavelength is -20-80∘C and 750-1250 nm, respectively. The absolute value of the relative deviation of the maximum phase retardation is less than 3.6%, which meets the design requirements of the wave plate. The temperature insensitivity of the five-element wave plate is better than the three- and four-element wave plates. This method is of great reference value for designing this kind of composite achromatic wave plate.

Identification of thermo optical parameters of 8ocb pure and nano dispersed liquid crystalline compound using image processing based IME method

In the present paper synthesis, characterization and image enhancement studies have been carried out on 8ocb LC with dispersed ZnO nanoparticles in conjunction with identification of thermo optical parameters at various concentrations. The microscopic textures are analyzed with MATLAB tool to obtain optical parameters. Image processing methods are used to identify the behavior of optical transmittance, absorption coefficient and phase retardation calculated using proposed Illumination Map Estimation (IME) technique and compared with the available literature. The proposed image processing-based method is a simple experimentation procedure to identify the thermo optical parameters of liquid crystal compounds for various electro optic applications.

Spin-decoupled metasurface for broadband and pixel-saving polarization rotation and wavefront control.

In this paper, a strategy to achieve a simultaneous wavefront shaping and polarization rotation, without compromising the number of pixels and energy efficiency as well as having broadband operation range, is proposed. This strategy is based on the application of a spin-decoupled phase metasurface composed by only one set of metal-insulator-metal (MIM) umbrella-shaped chiral unit cells. Quasi-non-dispersive and spin-decoupled phase shift can be achieved simply by changing single structural parameter of the structure. By further merging the Pancharatnam-Berry (PB) geometric phase, conversion of an incident LP light beam into right- and left-handed circularly polarized reflected beams with similar amplitudes, desired phase profiles and controlled phase retardation on a nanoscale is enabled with high efficiency. Based on the proposed strategy, a polarization-insensitive hologram generator with control optical activity, and a multiple ring vortex beam generator are realized. The results obtained in this work provide a simple and pixel-saving approach to the design of integratable and multitasking devices combining polarization manipulation and wavefront shaping functions, such as vectorial holographic generators, multifocal metalenses, and multichannel vector beam generators.

Inch-scale graphene-based LC tunable phase retarders: Experimental study of surface interaction between liquid crystal-polyimide-graphene layers

Recently Liquid Crystal (LC) devices open new route for the next generation optical elements revealing on novel materials that come to a scene, among which graphene endorse amazing capabilities. Herein, we perform detailed study of the surface interaction between LC molecules, graphene (single and multilayer) and alignment layer during assembling tunable LC phase retarders on arbitrary substrates. By considering the surface free energy of graphene a proper selection of polyimide (PI) as a polar layer for non-contact planar alignment of LC molecules is presented. Surface anchoring energy and pre-tilt angle value have been determined to characterize the interfaces at the boundary and their impact on the dynamic performances of assembled LC devices. Besides the excellent phase modulation repeatability over the large-scale area of retrofitted LC structures, an electrically tunable LC phase retarder supported by graphene on PDMS substrate that exhibits great potential for future ITO-free integrated photonic devices and bio-oriented technologies is demonstrated.

Parallel‐to‐orthogonal polarisation‐state converter for dual‐mode Nd:YVO 4 microchip laser

Polarisation-state conversion from parallel linear polarisation to orthogonal linear polarisation was successfully demonstrated using a birefringence crystal for the two longitudinal oscillation modes of a dual-mode Nd:YVO4 microchip laser. The laser emitted two longitudinal oscillation modes simultaneously in the vertical linear polarisation state with a frequency difference of 101 GHz. In the experiment, it was shown that by using a 17-mm-long LiNbO3 birefringence crystal, it was possible to almost perfectly convert the polarisation state of the two oscillation modes by providing a π-rad difference in phase retardations between the two oscillation modes. The residual elliptic component was eliminated using a pair of waveplates.

Identification of thermo optical parameters in 4l-hexyloxy-4-cyanobyphenyl with dispersed ZnO nano particles

Abstract In this present article, synthesis, characterization, and study of optical parameters through image enhancement methods have been carried out on 4l-hexyloxy-4-cyanobyphenyl (6OCB) pure liquid crystal (LC) and 6OCB with dispersion of 0.5 wt% ZnO nanoparticles. Textural determinations of the synthesized compounds are recorded by using SDTECHS POM connected with a hot stage and camera. differential scanning calorimetry (DSC) is used to measure enthalpy and transition temperature values. The results show that the dispersion of ZnO in 6OCB exhibits nematic phase as same as the pure 6OCB with slightly reduced clearing temperature as expected. Further characterization is carried out by various spectroscopic techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet visible (UV–Vis) spectroscopy. To evaluate and identify the behavior of optical parameters viz optical transmittance (OT), absorption coefficient (AC), and phase retardation (PR) as a function of temperature, an image processing method has been proposed, i.e. illumination enhancement algorithm (IEA) using MATLAB software. The proposed enhancement algorithm is one of the simplest and efficient algorithms to evaluate the thermo optical parameters for various electro optical applications. The results are compared with the body of the data available.

A modified method for calibration of polarimetric components using polarizing interferometry

Polarization interferometer technique has been developed for calibration of phase retardation elements such as quarter/half wave plate with known tolerance in each one. In addition, this technique is used to measure unknown retardation elements to identify its phase retardation. A polarizing beam splitter is placed after Sagnac interferometer to split the produced fringes into p and s polarization interferograms to be analyzed. The phase retardation measurements depend on two states, the reference state which includes recording the reference p and s interferogram images without placing the sample then measuring state at which the p and s interferogram images are recorded after placing the sample inside Sagnac interferometer. Six images are recorded for each interferogram under a controlled environment to calculate the repeatability of measurements and for uncertainty estimation. The detected images are mathematically processed to determine the phase retardation of the polarimetric components. The results are found to be in a good consequent with the data measured by Senarmont compensator method.

Pathognomonic macular ripples are revealed by polarized infrared retinal imaging.

A pathognomonic macular ripple sign has been reported with scanning laser ophthalmoscopy images in patients with foveal hypoplasia, though the optical basis of this sign is presently unknown. Here we present a case series of seven individuals with foveal hypoplasia (based on spectral domain optical coherence tomography). Each patient underwent infrared scanning laser ophthalmoscopy retinal imaging in both eyes, acquired with and without a polarization filter and assessment for a ripple-like effect in the fovea. On imaging, macular ripples were present in all eyes with foveal hypoplasia when using a polarization filter, but not when imaged without the filter. We conclude that the macular ripple sign is an imaging artifact attributable to the unique pattern of phase retardation of the Henle fiber layer in the setting of foveal hypoplasia. By utilizing a polarization filter with retinal photography, this feature can be exploited to promptly identify foveal hypoplasia in settings where OCT is not possible due to nystagmus.

Spatial characteristics of rotating magnetic field (RMF) plasma acceleration method in open magnetic field configuration under partial RMF penetration

In typical electrodeless radio frequency plasma thrusters, application of a rotating magnetic field (RMF) is expected to drive an azimuthal electron current via the non-linear Hall-term effect, resulting in an additional electromagnetic acceleration effect in the presence of a diverging magnetic field. Large increases in ion Mach number and electron density were found, comparing cases with and without the RMF, under a partial RMF penetration into a plasma. Spatial characteristics of the RMF acceleration were investigated to clarify the causes of these increments: 2D profiles of plasma parameters and time-varying RMF components were measured. Partial penetration of the RMF into plasma with a phase retardation was found, but the RMF azimuthal current was driven. Large diamagnetic current derived from the large density gradient also increased by the RMF application. Synergistic acceleration effect derived from the driven RMF current and the density gradient results in the plasma acceleration effect even under the partial penetration.

Curved-Mechanical Characteristic Measurements of Transparent Conductive Film-Coated Polymer Substrates Using Common-Path Optical Interferometry

This study proposes a method for measuring curved-mechanical characteristics based on a whole-folding test for transparent conductive film-coated polymer substrates using common-path optical interferometry. Accordingly, 80-, 160-, and 230-nm indium tin oxide films coated on 40 × 40 mm 125-μm-thick polyethylene terephthalate (PET) substrates, and monolayer graphene films coated on 40 × 40 mm 250-μm-thick PET substrates are inspected and analyzed under the curving conditions of 50-, 30-, 20-, and 10-mm radii before and after an 11,000 whole-folding cycle test based on a 10-mm folding radius. This study utilizes the changes in the phase retardations of transparent conductive film-coated polymer substrates under different curving conditions before and after 11,000 whole-folding cycles to analyze the substrates’ residual stress characteristics that were the direct result of manufacturing process parameters. The results from this study of curved-mechanical characteristic measurements of flexible transparent conductive substrates can provide designers with improved product development and can assist manufacturers in improving the manufacturing design of enhanced coating processes.

Polarization properties of retinal blood vessel walls measured with polarization sensitive optical coherence tomography.

A new method based on polarization-sensitive optical coherence tomography (PS-OCT) is introduced to determine the polarization properties of human retinal vessel walls, in vivo. Measurements were obtained near the optic nerve head of three healthy human subjects. The double pass phase retardation per unit depth (DPPR/UD), which is proportional to the birefringence, is higher in artery walls, presumably because of the presence of muscle tissue. Measurements in surrounding retinal nerve fiber layer tissue yielded lower DPPR/UD values, suggesting that the retinal vessel wall tissue near the optic nerve is not covered by retinal nerve fiber layer tissue (0.43°/µm vs. 0.77°/µm, respectively). Measurements were obtained from multiple artery-vein pairs, to quantify the different polarization properties. Measurements were taken along a section of the vessel wall, with changes in DPPR/UD up to 15%, while the vessel wall thickness remained relatively constant. A stationary scan pattern was applied to determine the influence of involuntary eye motion on the measurement, which was significant. Measurements were also analyzed by two examiners, with high inter-observer agreement. The measurement repeatability was determined with measurements that were acquired during multiple visits. An improvement in accuracy can be achieved with an ultra-broad-bandwidth PS-OCT system since it will provide more data points in-depth, which reduces the influence of discretization and helps to facilitate better fitting of the birefringence data.

Quadrature phase detection based on phase shift of self-mixing interferometer for real-time displacement measurement

A real-time displacement reconstruction technique based on a phase retardation method is proposed. By introducing a waveplate and a polarization beam splitter into the external cavity, two self-mixing signals with a phase shift of π∕2 can be obtained. Then the displacement of the external object can be reconstructed by a quadrature demodulation algorithm, which significantly simplifies the data processing and meets the requirements of real-time displacement reconstruction techniques. The results show that the absolute errors of the reconstructed displacements are less than 75 nm.

A phase differential heterodyne interferometer for simultaneous measurement of straightness error and displacement

A phase differential heterodyne interferometer for simultaneous measurement of straightness error and displacement is proposed. In this interferometer, a modified mobile sensor composed of a Wollaston prism and a semi-reflective plane mirror is adopted to obtain the straightness error and displacement information simultaneously. A phase differential measurement is utilized to obtain phase differential signals for straightness error and displacement measurement, respectively, by using phase retarder and polarizing beam-splitter. Based on the relationship of π phase difference between the nonlinear errors of phase differential signals, the periodic nonlinear error of measurement results can be compensated. Benefiting from this design, the proposed interferometer can not only obtain the straightness error and displacement simultaneously, but also reduce the nonlinearity of measurement and the influence of the measured object’s rotation. The optical configuration and measurement principle are described in detail. The influence of Wollaston prism’s roll error is also discussed. And three verification experiments are presented at last.

Optical coherence tomography imaging of evoked neural activity in sciatic nerve of rat

We investigate changes in optical coherence tomography (OCT) images in response to evoked neural activity in the sciatic nerve of rats in vitro. M-scans were obtained on peripheral nerves of rats using a swept source polarisation sensitive OCT system, while a nerve cuff acquired electrical neural recordings. From a total of 10 subjects: three had no stimulation (controls), three had paw stimulation, and four had nerve stimulation. Changes in the OCT signal intensity, phase retardation, phase, and frequency spectra were calculated for each subject and reference samples of a mirror and microspheres in solution. Observed changes in intensity in three paw stimulation and two nerve stimulation subjects and changes in frequency spectra amplitude in two paw stimulation subjects were above the reference noise level and were temporally consistent with osmotic swelling from ion currents during neural activity. Light scattering changes produced by osmotic swelling, which have previously been characterised in squid and crab nerves, are also thought to occur in myelinated fibres on a scale which is detectable using OCT. Imaging neural activity in myelinated tissue using OCT creates new possibilities for functional imaging in the peripheral and central nervous systems.

Optical absorption tunability and local electric field distribution of gold-dielectric-silver three-layered cylindrical nanotube* *Project supportedby the Programs for Anhui Provincial Natural Science Foundation, China (Grant Nos. 1808085MA20 and 1808085MA05), Excellent Young Talents in University of Anhui Province, China (Grant No. gxyq2017027), the Key Scientific Research Foundation of Anhui Provincial Education Department, China (Grant Nos. KJ2019A0564 and KJ2018A0366), the Key Research

The effects of inner nanowire radius, shell thickness, the dielectric functions of middle layer and surrounding medium on localized surface plasmon resonance (LSPR) of gold-dielectric-silver nanotube are studied based on the quasi-staticapproximation. Theoretical calculation results show that LSPR of gold-dielectric-silver nanotube and LSPR numbers can bewell optimized by adjusting its geometrical parameters. The longer wavelength of mode takes place a distinct red-shift with increasing the inner nanowire radius and the thickness of middle dielectric layer,while a blue-shift with increasing outer nanotube thickness. The physical mechanisms are explained based on the plasmon hybridization theory, induced charges and phase retardation. In addition, the effects of middle dielectric function and surrounding medium on LSPR, and the local electric field factor are also reported. Our study provides the potential appications of gold-dielectric-silver nanotube in biological tissues, sensor and related regions.

A scattering similarity based calculation model for oil film identification

To identify oil spill at sea, a method of characterizing the scattering of the detected oil spill target is proposed, based on its polarization characteristics. Due to the unique feature that Mueller matrix is able to comprehensively describe polarization characteristics and has a close relation to the target itself, we propose to use a Mueller matrix polarimeter to calculate Mueller matrix. Combined with the conditions for physical realizability, the Mueller matrix is filtered to achieve a higher level of accuracy. Based on Pauli basis decomposition, the scattering similarity parameters (SSP) between the target and the typical scattering are studied. The formulas of SSP expressed by amplitude ratio and phase retardation in Fresnel reflection are derived, which help us discover the relationship among SSPs. A new concept of scattering similarity parameter difference (SSPD) is proposed and the relationship between SSPD and degree and polarization (DOP) is derived. The difference of SSPD curves between water and oil film is used to distinguish them, which can effectively detect oil spill.

Impact of deposition conditions on nanostructured anisotropic silica thin films in multilayer interference coatings

Recent developments of nanostructured coatings have reached a point where extensive investigations within multi-layer systems are necessary for further implementation in novel photonic systems. Although sculptured thin films are explored for decades, no optical and structural measurements have been performed for anisotropic nanostructured multi-layer coatings with different deposition conditions of the dense layer. In this paper, we present extensive morphological analysis on silica nanostructured anisotropic films. Changing the deposition angle from 66° to 84°, indicate the changes in surface filling from 84% to 57%, respectively, while phase retardance has a maximal value of 0.032°/nm at 70° and 72° angles. We also present the investigation of covering such structures with the dense layer at different conditions. As a result, the technology for maintaining initial anisotropic properties is developed for extending spectral difference 1.6 times and phase retardation by 5% in anisotropic multi-layer coatings. Furthermore, we present simulations of growing silica layer using experimental conditions in the Virtual Coater framework resulting in virtual anisotropic films for comparison with measurements. The minimal impact on the anisotropy of porous layer is reached with the deposition of dense layer at 30° angle during constant substrate rotation.