Fast Axis Angle Research Articles

Multispectral polarization microscopy of different stages of human oral tissue: A polarization study.

Many optical techniques have been used in various diagnostics and biomedical applications since a decade and polarization imaging is one of the non-invasive and label free optical technique to investigate biological samples making it an important tool in diagnostics, biomedical applications. We report a multispectral polarization-based imaging of oral tissue by utilizing a polarization microscope system with a broadband-light source. Experiments were performed on oral tissue samples and multispectral Stokes mapping was done by recording a set of intensity images. Polarization-based parameters like degree of polarization, angle of fast axis, retardation and linear birefringence have been retrieved. The statistical moments of these polarization components have also been reported at multiples wavelengths. The polarimetric properties of oral tissue at different stages of cancer have been analyzed and significant changes from normal to pre-cancerous lesions to the cancerous are observed in linear birefringence quantification as (1.7 ± 0.1) × 10-3 , (2.5 ± 0.2) × 10-3 and (3.3 ± 0.2) × 10-3 respectively.

Effects of graphene layer addition on sensitivity of surface plasmon resonance sensor for immunoglobulin M detection

A novel technique is proposed for detecting immunoglobulin M (IgM) using differential Mueller matrix polarimetry and a surface plasmon resonance (SPR) sensor enhanced through the addition of multiple (1–10) thin layers of graphene on the sensing surface. Simulations are first performed to optimize the structure of the SPR device. The feasibility of the proposed sensor is then demonstrated by measuring the principal fast axis angle (α) of linear birefringence (LB) of human IgM serum aqueous solution samples with known concentrations in the range of 0–250 ng/ml. The results shows that α increases linearly over the considered concentration range. However, α reduces with an increasing number of graphene layers. The finest resolution of 7.8 ng/ml is obtained from the sensor incorporating three graphene layers.

Single-Layer-Graphene-Coated and Gold-Film-Based Surface Plasmon Resonance Prism Coupler Sensor for Immunoglobulin G Detection.

A graphene-based surface plasmon resonance (SPR) prism coupler sensor is proposed for the rapid detection of immunoglobulin G (IgG) antibodies. The feasibility of the proposed sensor is demonstrated by measuring the IgG concentration in phantom mouse and human serum solutions over the range of 0–250 ng/mL. The results show that the circular dichroism and principal fast axis angle of linear birefringence increase in line with increases in IgG concentration over the considered range. Moreover, the proposed device has a resolution of 5–10 ng/mL and a response time of less than three minutes. In general, the sensor provides a promising approach for IgG detection and has significant potential for rapid infectious viral disease testing applications.

Four-dimensional compressed spectropolarimetric imaging

Polarized hyperspectral images contain rich information representing both surface texture and spectral signature of target scene. However, it is difficult to obtain the full-Stokes parameters of hyperspectral images directly. A compressive imaging system is proposed in this paper to recover the four-dimensional polarized hyperspectral images with full-Stokes parameters using quarter-wave plate (QWP) and liquid crystal tunable filter (LCTF). Changing the fast axis angle of QWP provides the degrees of freedom to modulate the polarization states. The LCTF serves as the broad-band spectral filter to modulate the spectral signatures. The output of LCTF is modulated by a coded aperture in spatial domain, and then the modulated polarized hyperspectral images are projected and multiplexed on a two-dimensional detector. Based on the compressive sensing theory, the full-Stokes polarized hyperspectral images can be reconstructed from several compressive measurements by solving the convex optimization problems with sparsity prior. The feasibility of proposed system is verified by simulations and experiments. Compared to the traditional compressive spectropolarimetric imaging methods, the proposed method is beneficial to reduce the compression rate, and thus shorten the data acquisition time. This work also paves a new way for the full-Stokes polarized hyperspectral imaging system with simple and compact structure.

Direct Stress Birefringence Distribution Measurement in Lens Using Refractive Index Matching Liquid

Stress birefringence (SBR) of optical components is significant in polarization-dependent and fine optical applications, such as optical lithography. However, the methods generally used for high-resolution birefringence distribution detection are unsuitable for measuring samples with nonplanar surfaces, such as lenses, owing to refraction and aberration. In this work, we propose and verify a method for directly measuring SBR distributions in a lens. An aqueous glycerol solution is used as the refractive index matching liquid to rectify the measuring light path. The retardation level of the matching liquid is confirmed to be considerably smaller than that of the window, thus simplifying the measurement error. The retardation levels of the optical plate and wave plate obtained using this method are consistent with that measured in air (Δ <; 0.025 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> and 0.212°, respectively), as well as with the fast axis angle of the wave plate (Δ <; 0.15 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> ). Additionally, the SBR distribution of the lens sample coincides with its physical state and is repeatable with a coefficient of variation of less than 2.585%. This method provides a convenient tool for SBR distribution measurements in a lens, which could be extended to the measurement of optical components exhibiting any surface shape.

Hyperspectral polarization-compressed imaging and reconstruction with sparse basis optimized by particle swarm optimization

Hyperspectral polarized images are widely used in target detection, and compressive sensing has been developed to shorten the acquisition time and reduce the memory usage. However, the current systems have defects in measuring the polarization information, and current sparse bases meet problems in reconstructing process. This paper combines compressive sensing and machine learning to obtain polarized images. Both the simpler system and the sparse basis optimizing method are developed. Liquid crystal tunable filter (LCTF) serves as both hyperspectral filter and linear polarizer. The LCTF compresses the first three Stokes parameters by changing the transmission axis angle of its incident surface. The LCTF and quarter-wave plate (QWP) compress all four Stokes parameters by changing the fast axis angle of QWP. Then, the Stokes parameters can be reconstructed based on the sparse basis optimized by particle swarm optimization (PSO) algorithm. The sparse basis optimized through the spatially local images of a target in one spectral band also works for both global images of this target in many other spectral bands and images of other targets.

An interferometric method for simultaneously determination the phase retardation and fast-axis azimuth angle of a wave plate

In this study, an interferometric method was proposed for the simultaneous measurement of phase retardation and fast-axis azimuth angle of a wave plate by using a Mach–Zehnder interferometer. The wave plate to be tested is placed in one of the light passages in the interferometer, and two analyzers with transmission axes at horizontal and vertical orientations are arranged at the two output regions. When a linearly polarized laser light beam is passed through the interferometer, two interference light beams are simultaneously generated. Through an analysis of the intensities of the two light beams, the phase retardation and fast-axis azimuth angle of the tested wave plate can be simultaneously determined using specially derived equations. The feasibility of the proposed method was demonstrated using measurements of zero-order half-wave and zero-order quarter-wave plates. The proposed method is easy to operate, enables rapid measurement, and has high stability and accuracy.

Nonideal optical response of liquid crystal variable retarders and its impact on their performance as polarization modulators

Liquid crystal variable retarders (LCVRs) will be used for the first time in a space instrument, the Solar Orbiter mission of the European Space Agency, as polarization states analyzers (PSAs). These devices will determine the Stokes parameters of the light coming from the Sun by temporal polarization modulation, using the so-called modulation matrix O. This is a matrix constituted by the first rows of properly selected PSA Mueller matrices. Calibrating a space instrument, in particular, finding O, is a critical point because in a spacecraft there is no possibility of physical access. Due to the huge difficulty in calibrating the complete instruments in all possible scenarios, a more complete calibration of the individual components has been done in ground in order to make extrapolations to obtain O in-flight. Nevertheless, apart from the individual calibrations, the experimental errors and nonideal effects that inhibit the system to reach the designed and theoretical values must be known. In this work, description and study of these effects have been done, focusing on the nonideal effects of the LCVRs and the azimuthal misalignments between the optical components of the PSA during the mechanical assembly. The Mueller matrix of a representative LCVR has been measured and mathematically decomposed by logarithm decomposition, looking for values of circular birefringence and fast axis angle variations as a function of voltage. These effects, in the absence of other nonidealities, affect the polarimetric performance, reducing the polarimetric efficiencies in some cases until 11%. Nevertheless, in this case, they are negligible if compared to the other nonideality studied, which are the azimuthal misalignments between the PSA optical components. The study presented in this work is key to extrapolate the PSA O matrix if the expected instrumental set-point temperatures are not reached in flight and can be used for the design and implementation of other polarimetric instruments.

Alternative method for measuring the phase retardation and fast axis of a wave plate

An alternative method is proposed for simultaneously measuring the phase retardation and fast axis angle of a wave plate by utilizing a radially polarized symmetric light beam. A horizontal polarized laser is passed through a spatial filter, a zero-order vortex half-wave retarder, for measuring the light beam. An analyzer and a charge-coupled device are used for the measurement. The charge-coupled device captures two intensity variation patterns before and after a wave plate to be tested is rotated by 45° in any initial fast axis angle direction. Through analysis of the intensity values, the phase retardation and fast axis angle of the wave plate to be tested can be accurately determined using mean calculation. To validate the proposed method, half-wave and quarter-wave plates were measured experimentally. The measurement errors of phase retardation and fast axis angle were approximately 0.087° and 0.094°, respectively.

45° double-drive photoelastic modulation.

In this report, a new type of double-drive photoelastic modulation effect is studied. Two piezoelectric actuators are connected to a symmetric photoelastic crystal at an angle of 45°. The actuators and crystal have the same resonant frequency. By adjusting the amplitude and phase difference between the driving voltages of the two piezoelectric actuators, two special forms of photoelastic modulation can be realized, namely, a pure standing wave form and a pure traveling wave form. The retardation magnitude and the azimuth angle of the modulation fast axis can be regulated in the pure standing wave, and the modulation axis moves circumferentially in the pure traveling wave. We have experimentally observed the two special photoelastic modulation modes, and the test and calibration methods are also reported.

A Research on Improving the Precision of Rotating-Wave Plate Polarization Measurement

The device errors of a rotating-wave-plate-based polarization measurement system can be mainly categorized as the angle error of the polarization prism, the fast axis angle error of wave-plate and the retardation error. By applying Fourier analysis to solve Stokes vectors, we obtain the formulas to calculate the three errors mentioned above, using linear 0° and 45° polarized light to illuminate the system for the error solving. We analyze the measurement errors of the degree of polarization, the polarization purity and the intensity of polarization state, under certain simulation conditions. The results show that after the calibration, the measurement accuracy is improved. Finally, we analyze the effects of the angle error of the linear polarized light used for calibration to the measurement of the three parameters.

All fiber optics circular-state swept source polarization-sensitive optical coherence tomography

A swept source (SS)-based circular-state (CS) polarization-sensitive optical coherence tomography (PS-OCT) constructed entirely with polarization-maintaining fiber optics components is proposed with the experimental verification. By means of the proposed calibration scheme, bulk quarter-wave plates can be replaced by fiber optics polarization controllers to, therefore, realize an all-fiber optics CS SSPS-OCT. We also present a numerical dispersion compensation method, which can not only enhance the axial resolution, but also improve the signal-to-noise ratio of the images. We demonstrate that this compact and portable CS SSPS-OCT system with an accuracy comparable to bulk optics systems requires less stringent lens alignment and can possibly serve as a technology to realize PS-OCT instrument for clinical applications (e.g., endoscopy). The largest deviations in the phase retardation (PR) and fast-axis (FA) angle due to sample probe in the linear scanning and a rotation angle smaller than 65 deg were of the same order as those in stationary probe setups. The influence of fiber bending on the measured PR and FA is also investigated. The largest deviations of the PR were 3.5 deg and the measured FA change by ~12 to 21 deg. Finally, in vivo imaging of the human fingertip and nail was successfully demonstrated with a linear scanning probe.

A novel CW yellow light generated by a diode-end-pumped intra-cavity frequency mixed Nd:YVO4 laser

We report an efficient continuous-wave (CW) yellow beam based on a Nd:YVO4 laser with a dual-wavelength wave plate, which is a full-wave plate at 1342 nm and a quarter-wave plate at 1064 nm. By inserting the dual-wavelength wave plate into the laser cavity and tuning the fast axis angle, based on the polarized property emission of Nd:YVO4, two simultaneous wavelengths of 1064 nm and 1342 nm were achieved. A LiB3O5 (LBO) crystal that is cut for critical type I phase matching at room temperature is used for summing frequency generation (SFG) of the laser. At an incident pump power of 5 W, a maximum CW output of 224 mW was obtained for a yellow laser with a wavelength of 593.5 nm and an optical-to-optical efficiency of 4.48%. To the best of our knowledge, this is the first time that a dual-wavelength wave plate has been used to realize a Nd:YVO4 yellow laser output.

Real-time Measurement of Full Field Retardation Near Quarter Wavelength

A real-time method to measure full field retardation near quarter wavelength is proposed. The circularly polarized beam passes through a sample with a large aperture. The measuring beam then goes through a quarter-wave plate and is then split by a Wollaston prism. An image with two sub-images is then detected by a high-speed image sensor. The full field retardation near quarter wavelength can be obtained in real time by processing the image. The measured retardation is independent of the fast axis angle of the sample and the fluctuation of the initial intensity. In experiments, a wedge waveplate is measured with different fast axis angle and initial intensity, and the full field retardations are acquired. The maximum and standard deviation of the full field retardation is 1.5° and 0.4°. The validity of the method is verified.

POLARIZATION-SENSITIVE OPTICAL COHERENCE TOMOGRAPHY USING A MODIFIED BALANCE DETECTOR

In conventional polarization-sensitive optical coherence tomography (PS-OCT), phase retardation is obtained by the amplitude of P and S polarization only, and the fast axis angle is obtained by the phase difference in P and S polarizations via Hilbert transformation. In this paper, we proposed a modified PS-OCT setup in which the phase retardation and fast axis angle are simply expressed as the function of the amplitude of P and S polarization and their differential signal. Due to the common-path feature between the two channels of P and S polarization, the fluctuation in the measurement of phase retardation and fast axis angle caused by excess noise and phase noise from the laser source can be reduced by the differential signal of P and S polarization via a modified balance detector. Thus, the signal of phase retardation and fast angle axis in the deep layer of a porcine sample can be improved.

Simultaneous measurement of retardation and fast axis angle of eighth-wave plate in real time

A simultaneous measurement method for the retardation and the fast axis angle of the eighth-wave plate in real time is proposed. The beam emitted from the laser passes through the circular polarizer and the eighth-wave plate to be measured successively, and then is split by the Dammann grating to form three sub-beams. They are analyzed by an analyzer array and detected by a detector array. Three detection signals are obtained simultaneously to calculate the retardation and the fast axis angle in real time. In experiments, a crystal quartz sample is measured at different fast axis angles. The average and standard deviation of its retardation respectively are 40.9°and 0.5°. The maximum measurement deviation of the fast axis angle is 2.1°. The usefulness of the method is verified.

S054024 球背後の界面活性剤水溶液流れの複屈折分布

Axisymmetric flow of surfactant solutions past a sphere moving at constant velocity is experimentally investigated. Test fluids used are entangled wormlike micelle solutions of 30mM cetyletrimethylammonium bromide and sodium salicylate at various molar ratios. To obtain full-field flow birefringence image of transient flows behind an impulsively started sphere, a division of focal plane type polarization image sensor is utilized. Left circularly polarized light is used as incident light and the degree of linear polarization (DOLP) and the angle of polarization (AOP) of transmitted light are measured, from which distributions of spatially averaged values of the retardation and the angle of fast axis of the fluid are obtained. Distributions of the retardation along the centerline of the sphere are investigated at various Deborah numbers. At a critical Deborah number, the retardation distributions become propagate at a constant speed away from the sphere. The measurements also show the abrupt change in the wake accompanied by the necking of the cross section when Deborah number exceeds a critical value.

Simultaneous measurement of retardance and fast axis angle of a quarter-wave plate using one photoelastic modulator

A method for simultaneous measurement of the retardance and the fast axis angle of quarter-wave plate using one photoelastic modulator is presented. A laser beam passes through a polarizer, a photoelastic modulator, the quarter-wave plate to be measured, and an analyzer to be detected. Before and after the quarter-wave plate is rotated 45° at any initial fast axis direction, two detection signals are obtained to resolve simultaneously the retardance and the fast axis angle. In experiments, a quarter-wave plate was measured with fast axis angles from -89° to 90°. The average and the standard deviation of the retardances at different fast axis directions are respectively 89.50° and 0.17°. The maximum measurement deviation of the fast axis angle is 0.5°. The usefulness of the method is verified.

Analog-Based Detection Method in Optical Low-Coherence Reflectometer for Measurement of Retardation and Fast-Axis Angle

This study presents a novel detection method in optical low-coherence reflectometer for the simultaneous measurement of the reflectivity and birefringence characteristics of a sample. By implementing analog electronics in a standard two-channel time domain low-coherence reflectometer, the ratio of the envelope amplitude between two orthogonal interferometric signals, which is used for calculating the retardation angle, can then be analog-decoded using a differential detection scheme based on the quotient rule of a logarithmic function. The proposed method for direct retardation measurement benefits from common-mode noise suppression advantages that support efforts to improve the accuracy of phase retardation measurement. Furthermore, a full interferometric signal to extract the phase information is not needed for calculating fast-axis angle. Reductions in data acquisition rates and processing time are expected. The results from a calibrated test plate were correspondingly presented.

Assessment of arterial characteristics in human atherosclerosis by extracting optical properties from polarization-sensitive optical coherence tomography

In this research, we assessed arterial characteristics in human atherosclerosis by determining both scattering and birefringence properties of vessel tissue from polarization-sensitive optical coherence tomography (PS-OCT) images. We demonstrated that optical characteristics including scattering coefficient (mu(s)), effective anisotropy factor (g(eff)), birefringence coefficient (Delta n), and fast-axis angle (beta) of normal and different kinds of atherosclerotic lesions in human vessels can be quantitatively described. Based on our findings, a quantitative PS-OCT image criterion for plaque characterization was constructed.