This PDF file contains the front matter associated with SPIE Proceedings Volume 11132, including the Title Page, Copyright Information, Table of Contents, Author and Conference Committee lists.

The method for mapping linear polarization imaging variables to the color channels of hue, saturation, and value in the HSV color space is a common technique for the visualization of polarization imaging data. This method utilizes the structural similarities between polarization vision and color vision so that the full linear polarization information is depicted in a single image. Recent developments have attempted to address issues, arising from the fact that the HSV color space is not an accurate model of human color vision, by mapping the polarization channels of intensity, degree, and angle to the color channels of lightness, colorfulness, and hue defined in the perceptually uniform color space CAM02-UCS. While the theoretical benefits of this method have been demonstrated using metrics of perceptual uniformity and channel independence, the practical benefits to human observers has not been studied. In this user study, the two methods are compared using a series of forced-choice questions on the perceived magnitude differences in DoLP value to determine 1) which method produces fewer errors, 2) which method produces a more linear scale in degree of polarization perception, 3) whether the perception of degree of polarization is independent of intensity and angle of polarization.

An important application for remote sensing is the detection and discrimination of targets of interest. Polarimetry can be used by remote sensing systems to identify the materials from which targets are made. If an imaging polarimeter is used, the target can also be resolved spatially. A fundamental material property is its complex index of refraction, which can be calculated from polarimetric measurements of the material. Previous work has shown the feasibility of estimating a material’s complex index of refraction from measurements of the polarized reflected radiance in the visible and nearinfrared spectral regions. A new technique is being developed for estimation of the complex index of refraction using measurements of the polarized radiance from a material’s self-emission. Measurements are made in the mid-wave infrared and spectral regions and are used to calculate the Stokes vector, which is then used to calculate the degree of linear polarization (DoLP). An equation is derived for the DoLP as a function of the Fresnel coefficients, which are themselves a function of the complex index of refraction and the angle of emission. Complex index of refraction values calculated from measured material DoLP values are presented. An initial goal of this work is to use the technique to discriminate between metals and dielectrics.

Laser remote sensing represents a powerful tool that enables the accurate measurement of the speed of moving targets. Crucially, most sensing techniques are 2-Dimensional in nature and do not enable direct determination of the full velocity vector of objects moving in 3D. A disadvantage that is very often compensated with two-dimensional techniques that in many cases are hard to implement and in others, require complicated postprocessing analysis. Here we demonstrate a novel technique that enables the direct and simultaneous measurement of both velocity components using a single interrogating beam. This technique is based on the use of complex light beams, whose polarization and spatial degree of freedom are coupled in a non-separable way. We present experimental results of a proof-of-principle experiment by applying our technique to the specific case of helical motion, of great relevance in a wide of research areas.

The Photochemical Reflectance Index (PRI) provides insight remote sensing into plant physiological processes occurring at leaf to canopy scales. We have found that PRI displays greater sensitivity to these processes if redefined to exclude the leaf surface reflectance. Here we suggest our published method for estimating leaf surface reflectance using linear polarizers underestimates the actual leaf surface reflectance. We suggest part of the leaf volume reflectance obtained using our published method represents light diffusely scattered by the leaf surface. We propose here a modification to our published method in order to obtain estimates of vPRI that are presumably more sensitive to leaf photochemistry.

Determining whether a cloud is composed of spherical water droplets of polyhedral ice crystals (i.e., the thermodynamic phase) from a passive remote sensing instrument is very difficult because of the immense variety of clouds and their highly variable microphysical properties. To improve upon the popular method of radiance ratios, we enhance the classification ability by adding polarimetric sensitivity to an instrument that measures radiance in three short-wave infrared bands. Clouds typically induce a polarization signature on the order of a percent, and so sensitive optics are required for accurate classification. In this paper, we present the combination of spectral and polarimetric sensitivity for cloud thermodynamic phase classification using data from a ground-based, 3-band, short-wave infrared polarimeter and cloud-phase validation from a dual-polarization lidar. We then analyze the classification quality of various methods using surface-fitting techniques to show that the addition of polarimetry is advantageous for cloud classification.

A compact long wave infrared (LWIR) channeled spectro-polarimeter (IRCSP) has been developed for integration into the ESTO-funded Submm-Wave and LWIR Polarimeters (SWIRP) project to measure the microphysical properties of cloud ice. The IRCSP rotates incident linearly polarized light using the combination of a quarter waveplate with a fast axis at 45◦ and a thick birefringent crystal; the output polarization state’s orientation is then a function of wavelength. To modulate and then measure the rotated light, a subsequent wiregrid linear polarizer tilted at 20◦ generates two output paths with opposite polarities in reflection and transmission to enable joint radiometric and polarimetric measurement and correct for atmospheric attenuation. The two symmetric optical paths following the linear polarizer each consist of a diffraction grating and uncooled microbolometer to simultaneously measure the resulting intensity fringes. Angle and degree of linear polarization (AOLP, DOLP) are retrieved across 8.5-12.5 µm with 1 µm resolution using Fourier decomposition of the modulated spectrum. The IRCSP will not only measure H-V variance but will produce the first full linear Stokes measurements (I, Q, and U) of upper-tropospheric cirrus clouds in the LWIR. Following thermal and polarimetric calibration, the polarimeter is expected to achieve 0.5% DOLP accuracy over 90% of the spectral band.

SPEXone is a compact five–angle spectropolarimeter that is being developed as a contributed payload for the NASA Plankton, Aerosol, Cloud and ocean Ecosystem (PACE) observatory, to be launched in 2022. SPEXone will provide accurate atmospheric aerosol characterization from space for climate research, as well as for light path correction in support of the main Ocean Color Instrument. SPEXone employs dual beam spectral polarization modulation, in which the state of linear polarization is encoded in a spectrum as a periodic variation of the intensity. This technique enables high polarimetric accuracies in operational environments, since it provides snapshot acquisition of both radiance and polarization without moving parts. This paper presents the polarimetric error analysis and budget for SPEXone in terms of polarimetric precision and polarimetric accuracy. We consider factors that contribute to instrumental polarization and modulation efficiency, which will be calibrated on-ground with high, but finite accuracy. The sensitivity to dynamic systematic effects in a space environment, such as degradation and ageing of components and small variations in the temperature and thermal gradients is addressed and quantified. Finally, the impact of scene dependent error sources, mainly resulting from stray light, are assessed and the total polarimetric error budget is presented. We show that SPEXone complies with the radiometric SNR requirement of 300, yielding a minimum polarimetric precision of 200 (fully polarized light) to 300 (unpolarized light) over the full spectral range for dark ocean scenes at high solar zenith angle. Assuming a stray light correction factor of 5 and considering a moderate contrast scene, the expected in-flight polarimetric accuracy of SPEXone is 1.5 · 10⁻³ for unpolarized scenes and 2.9 · 10⁻³ for highly polarized scenes, compliant with the polarimetric accuracy requirement. This performance should enable SPEXone to deliver the data quality that enables unprecedented aerosol characterization from space on the NASA PACE mission.

WIRC+Pol is a near-infrared low-resolution spectropolarimeter on the 200-inch Telescope at Palomar Observatory. The instrument utilizes a polarization grating to perform polarimetric beam splitting and spectral dispersion simultaneously. It can operate either with a focal plane slit to reduce sky background or in a slitless mode. Four different spectra sampling four linear polarization angles are recorded in the focal plane, allowing the instrument to measure all linear polarization states in one exposure. The instrument has been on-sky since February 2017 and we found that the systematic errors, likely arising from flat fielding and gravity effects on the instrument, limit our accuracy to ~1%. These systematic effects were slowly varying, and hence could be removed with a polarimetric modulator. A half-wave plate modulator and a linear polarizer were installed in front of WIRC+Pol in March 2019. The modulator worked as expected, allowing us to measure and remove all instrumental polarization we previously observed. The deepest integration on a bright point source (J = 7.689, unpolarized star HD65970) demonstrated uncertainties in q and u of 0.03% per spectral channel, consistent with the photon noise limit. Observations of fainter sources showed that the instrument could reach the photon noise limit for observations in the slitless mode. For observations in slit, the uncertainties were still a factor of few above the photon noise limit, likely due to slit loss.

We present the design of a point-and-shoot non-imaging full-Stokes spectropolarimeter dedicated to detecting life on Earth from an orbiting platform like the ISS. We specifically aim to map circular polarization in the spectral features of chorophyll and other biopigments for our planet as a whole. These non-zero circular polarization signatures are caused by homochirality of the molecular and supramolecular configurations of organic matter, and are considered the most unambiguous biomarker. To achieve a fully solid-state snapshot design, we implement a novel spatial modulation that completely separates the circular and linear polarization channels. The polarization modulator consists of a patterned liquid-crystal quarter-wave plate inside the spectrograph slit, which also constitutes the first optical element of the instrument. This configuration eliminates cross-talk between linear and circular polarization, which is crucial because linear polarization signals are generally much stronger than the circular polarization signals. This leads to a quite unorthodox optical concept for the spectrograph, in which the object and the pupil are switched. We discuss the general design requirements and trade-offs of LSDpol (Life Signature Detection polarimeter), a prototype instrument that is currently under development.

The NEOPol project’s goal is to build and validate in a laboratory setting a prototype polarimeter for Near Earth Objects (NEOs) observations, together with a dedicated automated pipeline for polarimetric data processing and a web service for data storage and visualization. The outcome of the project will be 1) a polarimeter dedicated to NEO observations, 2) one adapter to a prospective telescope interface where the instrument will be mounted, 3) data processing chain to reduce and analyze the data from the polarimeter, 4) a web service for data storage, reduction, visualization and results browsing, 5) desktop UI for polarimeter’s CCD camera and polarimeter sensory data.

The sky polarization pattern during solar eclipse totality shifts from the usual daytime clear-sky pattern, with maximum polarization in an arc located 90° from the Sun, to one with maximum polarization slightly above the horizon in a ring nominally concentric about the zenith. A sequence of 9 visible-wavelength all-sky images are shown throughout totality for the 21 August 2017 solar eclipse from a site near Rexburg, ID USA (43.8294°N, 111.8849°W). A neutral region appeared in the southwest quadrant of the all-sky images, directly opposite the eclipsed Sun, and evolved in size and radial position throughout the 2 min 17 s of totality.

Beetles of the families Scarabaeidae and Hybosoridae display left-handed circular polarization due to the Bouligand arrangement of chitin fibers in their cuticle. We intend to verify and understand, or disprove, the apparent and hitherto unexplained universality of left-handed polarization in beetles that exhibit circular polarization. We here report the first results of our ongoing massive survey of one of the largest beetle collections in the world, covering ±10.000 beetle genera. To facilitate the scanning of museum drawers full of beetles, drawers were placed in a purpose-built setup and automatically photographed in RGB colors through polarization filters mounted on a motorized wheel. A total of 6 photographs were taken, through left- and right-handed circular polarization filters, and four linear polarization filters mounted at 0, 90, 45, and -45 degrees. From these, the full Stokes parameters were calculated across the drawer. Images were segmented to obtain polarization parameters representing individual insects. Taxonomic information was obtained for each drawer, by automatically reading the database accession number. Specimens showing circular polarization in taxa for which this has hitherto not been studied are selected to be studied in more detail later, using a custom designed spectropolarimetric integral-field unit. Polarization can then be analyzed as a function of wavelength, resulting in both detailed hyperspectral imaging data and fully resolved Stokes parameters per spectral bin. Our two-stage high-throughput optical screening approach allows for bioprospecting for biophysical properties of valuable and potentially irreplaceable museum specimens, such as type specimens, or specimens of rare or even extinct species.

We show an experiment for the direct visualization of two subtle optical phenomena: optical rotation in a chiral medium and the angular profile of point dipole scattering. By passing a narrowband linear-polarized light beam into a tank filled with a sucrose solution, we see dark and light bands that exhibit the change in polarization state with propagation. This change in polarization state is made visible by the presence of point scattering particles in the liquid which scatter light in the angular profile of elemental dipoles. Using a white light beam for input, this effect generates a wonderful rainbow-like pattern of colors resulting from the medium's optical rotatory dispersion.

We have recently extended the concepts of generalized channeled polarimetry to keep proper account of all the multi-carrier harmonics generated by Photoelastic Modulators (PEMs). In order to build a Mueller matrix polarimeter out of such devices, the system needs to include at least four PEMs, each modulating at a different frequency. In our previous treatment, we have deliberately deferred the concept of multi-carrier harmonics of different PEMs mixing within the same channel. Despite the choice being a reasonable one due to the difficulty of precisely controlling PEMs' mechanical resonance properties due to manufacturing tolerances and temperature dependence, there are instances where having mixed channels enables a significantly better reconstruction SNR. Here, we revisit the omission by quantifying the additional performance that can be achieved with mixed channels, and explore the bounds on the level of frequency shift control required to ensure the predicted performance. We demonstrate that deliberate design of mixed channels is particularly beneficial when reconstructing with a low number of channels. Conversely, the level of control required to ensure an accurate enough alignment of higher harmonics leads to diminishing returns when reconstructing with a high number of channels.

Polarization effects and phenomena arise due to the vectorial nature of light. Many modern optical techniques rely on such effects; while sometimes polarization effects appear in a detrimental way. It is of great concern to take such effects into optical system modeling and design. Instead of adding polarization onto rays, we follow the field tracing concept and it is a natural choice for polarization modeling. In field tracing, light is represented in the form of electromagnetic field with all vectorial information, and various electromagnetic field solvers are used to modeling light interaction with different optical components. We present simulation examples on several polarization phenomena, for example, focusing light into birefringent crystal, using polarizer in non-paraxial situation, vectorial effect in tightly focused light, polarization conversion at sub-wavelength gratings, and so on.

We discuss practical design constraints for snapshot Mueller matrix spectropolarimeters, and reveal a robustness problem with existing designs. By carefully choosing the ratios of thicknesses between the four thick retarders used in these systems, we can avoid requiring extremely tight tolerances, though at a cost in overall bandwidth. We provide example designs and quantify the robustness-resolution tradeoff.

Recently we have presented theoretical predictions and numerical modeling that show that a more advanced processing scheme can significantly improve the performance of photoelastic modulator (PEM)-based Mueller polarimeters. Of note, by simply including all of the multi-carrier harmonics rather than a hand-selected subset thereof, the sensitivity of the system can be enhanced by up to a factor of six in certain elements of the Mueller matrix. This paper extends our work on PEM-based Mueller polarimeters to PEM-based partial Mueller systems with 2 PEMs, one PEM each in the generator and analyser. Our findings clearly demonstrates significant performance improvement through the use of a substantially large set of multi-carrier harmonics rather than a hand-selected subset. We also present results from our experimental PEM testbed system that verifies the numerical findings.

We present a method to measure the polarization of light scattered on structured surfaces, through the implementation of a Mueller-matrix polarimeter, using focused illumination. Typically the scattered light has been measured using an incident beam with a diameter on the order of a few cm for surfaces with scales of the order of microns, mainly to avoid problems with the speckle pattern of light, however in this way it is not possible to obtain information on local variations in the polarization effects presented on the surface. Therefore, we use an incident spot size of a few microns to illuminate and analyze the local variations in the polarization state produced by the sample. First, we will begin by describing the instrumentation of the polarimeter, which uses Liquid Crystal Variable Retarders (LCVRs) to control the incident and detected polarization states. Our device implements a calibration and data extraction method, which allows us to reduce the experimental error in the instrument to obtain efficient measurements. We use as a sample, a reflective structured surface with dimensions of 15 microns and we use an incident beam size of 5 microns to perform a preliminary qualitative interpretation and comparison of results of experimental cases with results of numerical calculation based on the Kirchhoff approximation of light scattering, including polarization effects, the simulations has been previously verified with other methods. We conclude about the advantages of measuring the polarization effect in the scattering pattern from one point to another in the studied sample.

Recent advancements in channeled spatio-temporal polarization sensor systems have shown potential for improved imaging performance. Lithographic processes now allow for the manufacture of pixelated focal plane arrays with both color and polarization filters applied at the per pixel level. Both Sony and Pau’s group at the University of Arizona have demonstrated the manufacture of these hybrid sensors. These new sensors produce spatially channeled hybrid color/polarization systems and crowd the available channel bandwidth space in the Nyquist square. We present a new system design which utilises polarization elements to generate additional temporal carriers, allowing for the separation of color and polarization channels. This separation has the potential to improve the hybrid system performance for certain classes of scene statistics and is analogous to a kind of super-resolution effect similar to a vibrating sensor or using motion for subsampling. The separation can be achieved by varying the polarization sensitive pixels in time, e.g. a rotating half waveplate or an electro-optic polarization element. We show the system design for an existing COTS Sony sensor as well as a design with improved performance over the Sony focal plane array, along with preliminary results on possible system performance.

Polymer and liquid crystal devices have long been used for displays but are also useful for polarization control in precision optics. They have performance and cost advantages over historically important optical materials like quartz, calcite, mica and other crystal materials. These advantages include larger apertures much lower sensitivity to angle of incidence and temperature. The polymer films are an essential building block for multifilm achromatic retarders and wide angular field retarders. The liquid crystals enable low voltage electrical rather than mechanical control of polarization.

We compare the theoretical properties of microgrid polarization cameras and show that the 0-45-90-135 and the 0-60-120 configurations for the micropolarizer orientations have the same noise performance. However, from the standpoint of spatial sampling efficiency, we show that the 0-45-90-135 is clearly more efficient. From the calibrated micropolarizer diattenuation and orientation properties of a commercially available microgrid polarization camera, we also derive formulas for the as-built performance of this camera. By correcting for the imperfect diattenuation, we show that one can achieve high-performance polarimetry using these low-performance micropolarizers through the use of a high-precision calibration. The tradeoff in doing so is a surprisingly small 25% increase in the noise.

Channeled spectropolarimetry measures the spectral dependence of the polarization states of light. This technique is marked by its snapshot feature, in that the complete polarization states can be determined simultaneously from a single intensity spectrum. However, without athermalization, it suffers from high sensitivity to temperature, which in turn, degrades the polarimetric reconstruction accuracy. In this paper, we present a calibration technique for a fiber-based channeled spectropolarimetry that leverages phase-shifting interferometry to accurately demodulate the retarders' phase, thereby improving the accuracy of the acquired Stokes parameters. Additionally, it enables robust spectropolarimetric performance that is insensitive to environmental perturbations. Experimental results demonstrate that calibrations using phase-shifting interferometry improve the Stokes reconstruction results by approximately a factor of 3 when compared to the reference beam calibration method.

We present a scatterometer to estimate the correlation distance (CD) of a one-dimensional random rough surface from polarization sensitive bistatic measurements. The system, which constitutes our first effort to implement the variable coherence polarimetry (VCPol) technique, combines a source with controllable spatial coherence and polarization properties and a Stokes polarimeter. The working principle of the source is given by the generalized van Cittert–Zernike theorem for quasi-homogeneous, planar electromagnetic sources, which describes the propagation of the second-order correlation properties of the beam-like field generated by the source, allowing us to control the spatial coherence and polarization of the beam through the manipulation of the spectral density and polarization distributions of the source. Our results show that the CD can be correctly estimated for onedimensional random rough surfaces with peak-to-valley distances comparable with the CD. However, if the peak-to-valley distance is small in comparison with the CD, the estimation obtained with our system is far from the actual value. Due to technical limitations, in the first stage of this project we were not able to build our system in a monostatic configuration, which is an appealing feature of VCPol particularly important in remote sensing applications. However, our future efforts will aim at building a scatterometer working in a monostatic configuration.

Channeled Spectropolarimeters (CHSP) are compact optical instruments that have potential for making precise polarization measurements without any moving parts. While most spectropolarimeters use rotating elements to make measurements, CHSPs use mechanically fixed thick retarders to modulate the Stokes vector onto the spectrum of light. In realistic applications, CHSPs must have calibration algorithms that give stable measurements in a variety of environmental conditions. Previous researchers developed a self-calibration algorithm that uses redundant channel information to compensate temperature-induced phase fluctuations in real-time without any additional reference measurements. In this paper we discuss the stability of the self-calibration technique. We identify a mathematical ambiguity in the algorithm that limits the range of temperatures over which the algorithm is stable. For a 60𝜆:120𝜆 channeled spectropolarimeter with quartz retarders, the stable temperature range is only 27°C and is not suitable for many applications outside of the laboratory. We propose and demonstrate a modified algorithm that uses the slope of the phase to remove the mathematical ambiguity and extend the temperature range of the system. The demonstration shows stable operation over a 41°C temperature range and shows promise for increasing stability over a temperature range suitable for extreme terrestrial conditions.

We present numerical results of the simulation of the polarimetric response of microscopic, semitransparent specimens immersed in water. The polarimetric response observed in our simulations comes from the shape and structure of the observed specimens, rather than from intrinsic polarization properties of the material out of which they are made. We discuss the computational methods used to perform the simulations, which consist of four stages (scattering, propagation from the specimen to the microscope objective, propagation through a polarimeter, and focusing onto the detector), as well as the feasibility of measuring the simulated polarimetric response of the specimens using a well-calibrated polarimetric microscope. As part of our analysis, we discuss some technical limitations of the equipment available in our group to build a polarimetric microscope and some limitations of the calibration method that we use, namely: the eigenvalue calibration method.

Metasurfaces, nanophotonic arrays of subwavelength phase shifting elements, hold promise for the miniaturization of a variety of bulk optical elements. Owing to the flexibility with which their constituent elements may be engineered, metasurfaces allow for point-to-point polarization control on a subwavelength scale. Metasurfaces, then, represent an exciting new platform for polarization optics. A single metasurface may combine many different polarization-dependent functionalities that would ordinarily be spread out over many optical elements. We describe how, through relatively simple optimization methods, a metasurface producing arbitrarily specified polarization states can be designed. This functionality is equivalent to a traditional diffraction grating with individual waveplate optics on each order; here, all the necessary polarization optics can be integrated into a flat, efficient, and ultrathin metasurface optical element. Moreover, such a metasurface can be used in a reverse configuration as a parallel snapshot polarimeter with no need for additional polarization optics. We present a detailed experimental characterization of this device in the visible spectral region and a comparison of the performance of the metasurface to a commercially available rotating waveplate polarimeter. Metasurfaces can enable compact, miniaturized sensors for polarimetry and polarization imaging. We will conclude with a perspective on these possibilities and their implications for remote sensing. Metasurface polarization optics can overcome limitations of previous diffractive/grating based polarimetry schemes are potentially of significant interest to the imaging polarimetry community.

Retarders or waveplates are tools for polarization modification in bulk optical systems. These devices usually have a strong wavelength dependence in their performance, making them suitable for use over a wavelength band on the order of a few percent of the center wavelength for which they are made. Display and tunable laser applications are examples that can require consistent polarization modification over a much broader wavelength range. We discuss new methods and designs for dramatically increasing range of performance over wavelength and angle of incidence and review older methods as well. We show examples of achievable performance using modern polymer and liquid crystal materials.

Measuring a target’s radial velocity is usually achieved using high-resolution spectroscopy; however, higher signal to noise ratios can be obtained using direct correlation spectrometers (DCSs). In our system, a liquid crystal spatial light modulator serves as the mask against which the incident spectrum is correlated, and the polarization is controlled to enable both in- and out-of-band light to be captured simultaneously. This offers enhanced performance against atmospheric scintillation and may also enable single-shot radial velocity measurements. In this paper, we describe the design and implementation of our polarization-DCS and experimental validation is performed by acquiring radial velocity measurements of Venus.

Channeled polarimeters modulate the Stokes parameters onto harmonic carriers of a particular independent domain such as time, space, wavenumber, or angle of incidence. Because the modulation creates many channels within the frequency sampling space of the detector array, channel bandwidth is crucial for this type of device. Much researches has been conducted to exploit more bandwidth in polarimeters that modulate in space, time, or wavenumber along. Our group and others have provided previous theoretical designs for hybrid-domain modulation strategies in order to extend the distance between channels in the Fourier domain through a bandwidth tradeoff approachin order to provide a wider channel bandwidth than systems utilize only one of the corresponding domains. This paper will present results from a a spatio-temporally modulated Stokes polarimeter. The system trades off the bandwidth between space and time to obtain further channel separations. In this work, we demonstrate the system implementation and the experiment results. The experiment compared the spatio-temporal hybrid domain modulated Stokes polarimeter with the spatial and temporal domain only modulated Stokes polarimeter to verify the prediction from the theoretical work. The experimental results indicated that comparing to the spatial and temporal domain only modulated Stokes polarimeters the hybrid-domain modulated polarimeter provides a better image reconstruction and contrast on signals with moderate bandwidth extension. We also consider adaptive reconstruction methods that allow the reconstruction filters to be tailored to the input data. This strategy will allow the bandwidth of the system to be optimally exploited for any particular task.

Diffractive optical elements (DOEs), with attractive features such as excellent performance and compact configuration, are now becoming increasingly important to a wide range of optical system applications. In this paper, we have used the patterned photoalignment method to produce switchable gratings. It is found that these gratings combine good optical quality with very fast dynamical response at very low driving voltage. A sub-millisecond steering with active FLC as a polarization selector and passive polarization grating (PG) as a diffractive element. A systematic analysis is conducted from the device fabrication to the element working mechanism with their potential problems and corresponding solutions included. The polymerizable liquid crystal PG shows compact size, light weight, robustness, and low cost. Switching time of 82μs is realized by binary switching between two circular polarizations before incident on PG utilizing FLC driven by two electrical polarities. Overall efficiency of 95.7% is achieved with steering angle of 17.66° by 1064nm laser.

The fully polarimetric SAR (PolSAR) data offers four polarimetric modes (i.e., HH, HV, VH, VV) and have shown the ability to provide better interpretation than single polarization case, which led to high classification accuracy. In this study, an efficient classification method for PolSAR data based on a subspace projection segmentation (SPS) approach is proposed to improve the classification accuracy. Instead of performing the comparison of multi-dimensional (MD) polarimetric feature vectors, the SPS first transforms the MD polarization feature vectors into one-dimensional (1D) projection lengths by projecting the feature vectors onto one reference subspace which is chosen to maximize the separation of two types of data. After the transformation, any 1D thresholding technique, such as the Otsu’s thresholding, can be applied to perform segmentation efficiently, which results in the reduction of computation complexity in segmentation. The proposed SPS can divide the data into proper homogeneous regions, that is, PolSAR data with similar polarization features being grouped together into regions. In the study, the polarimetric feature vectors are extracted from the coherent/covariance matrices obtained by the polarimetric scattering information. In addition, the referenced projection subspace is selected based on the coherent/covariance matrices of PolSAR data. Finally, the performance of the proposed SPS method is validated by simulations on PolSAR data obtained by NASA Airborne Synthetic Aperture Radar System (AIRSAR) during the PacRim II project and Advanced Land Observing Satellite (ALOS). Simulation results show that the proposed approach can reduce the computational complexity more effectively than other existing methods, and also achieve good classification accuracy.

The fully polarimetric synthetic aperture radar (PolSAR) with high resolution and quad-polarization data has shown the ability to provide better interpretation and high classification accuracy. But PolSAR image quality is critical disturbed due to speckle noise not only in the three intensities (HH, HV, VV) of PolSAR but also in the three complex correlation terms (HH-VV, VV-HV and HV-HH). Thus, reducing speckle noise level while preserving polarization scattering mechanisms and spatial resolution of PolSAR becomes a challenging task. Several filters widely used in SAR images can achieve effective speckle reduction, but can also lead to edge blurring and strong reflective scatter depressing. To mitigate these deficiencies, in the study, we proposed an improved speckle filtering approach by combining existing filters (such as Lee or Sigma filters) with edge/strong target detectors. Before performing filtering, strong targets and edges are detected and preserved by the proposed detectors. By the detection preprocessing, the improved filtering approach can not only reduce speckle noise but also preserve the target signature. The effectiveness of the proposed improved speckle filters is validated by two kinds of PolSAR data, one obtained by NASA Airborne Synthetic Aperture Radar System (AIRSAR) and the other data obtained by Advanced Land Observing Satellite(ALOS). From experimental results, the proposed improved filter provides promising results for suppressing speckle noise and preserving the potential targets.

In this work, we proposed the usage of a rotating polarizer-analyzer polarimeter to retrieve retardance parameters of a sample by treating it as an elliptical retarder that can be characterized by three parameters: total retardance, fast axis orientation and an ellipticity related parameter. By employing the Mueller matrix approach, we developed the demodulation algorithm to retrieve each parameter with the association of the Fourier series analysis. We present experimental results considering dextrose concentrations diluted in distilled water scaling in a range from 30mg/dl to 45mg/dl. For comparison purposes, we employed the method of rotating an analyzer and compare the optical activity variation for both methods.

Mueller polarimetry imaging is gaining acceptance in diagnostic imaging as a potential tool for identifying tissue pathology by the integrated analysis of tissue response to polarized light. The Mueller matrix derived parameters have been related to the structural changes occurring in the tissues during pathogenesis of a disease. An in-house developed Mueller polarimetric imaging system has been explored in this study to differentiate between the normal and sclerodermic regions of unstained skin biopsy samples with varying collagen densities in the dermis. The optical response of excessive collagen deposition in scleroderma gets reflected in the depolarization, diattenuation, and retardance parameters obtained through polar decomposition and singular value analysis. In this study, higher depolarization, retardance and diattenuation values were observed in the scleroderma region as compared to their normal counterpart, suggesting an increased level of collagen deposition, which was further correlated with the histopathological findings. The developed system aims at its deployment in pathology labs to provide stain-free examination procedures in the long run.

Study of the lidar measurement is very significant in a variety of applications including forest remote sensing. Among them, polarimetric lidar is a relatively new but important active remote sensing tool. This study covers a comprehensive description of the system performance of both the polarimetric lidar and non-polarimetric lidar. Noticeably, relative performances of both lidar systems can be estimated exploiting several classifiers such as artificial neural network, k-NN (k-nearest neighbor) classifier and the discriminant function. In each of these attitudes, the principal aspect is to compare the classification results obtained by different classifiers to obtain improved lidar performance. In this case, utility of polarimetric and non-polarimetric waveform features for classification was tested using a group of randomly selected trees such as pines, elm, blue spruce, maple, choke cherry, and green ash. The k-NN classifier obtained 92% accuracy using non-polarimetric data. However, for k-NN classifier the value of k is provided by the user. Strikingly, same k-NN classifier achieved 96 % accuracy using polarimetric data. Again, artificial neural network classifier achieved 96% classification accuracy using polarimetric lidar data whereas the classification accuracy it received was around 89 % using non-polarimetric lidar data. Most poor performance was received by discriminant analysis. In case of nonpolarimetric data, discriminant analysis results in only 59 % efficiency. In contrast, about 75 % classification accuracy was observed using polarimetric data for discriminant analysis. Though the listed classifiers can perform better using polarimetric data than non-polarimetric data, artificial neural network can be employed for better performance.