Polarization Characteristics Of Light Research Articles

Research on polarization characteristics of background light by modified polarization difference imaging method

<sec>The random scattering event of light by water medium is the primary reason for the degradation in underwater imaging. Underwater polarization imaging technology can enhance the signal-to-noise ratio of imaging effectively by utilizing the polarization information difference between background scattered light and target light. However, as scattering events increase in the water body, it is difficult to maintain the polarization characteristics of light, which reduces the effect of removing scattering based on polarization characteristics. In addition, the polarization rule of background scattered light in water is unclear, and there is a lack of quantitative description of the polarization characteristics of scattered light. Therefore, the study of polarization transmission characteristics of underwater scattered light is of great significance in reducing the scattering light of underwater polarization imaging.</sec><sec>In order to clarify the polarization characteristics of underwater background scattered light, especially the polarization angle information, this paper proposes a method for ascertaining polarization angle of background light based on modified polarization difference imaging method. In this method, the coupling relationship between optimal weight coefficient and enhancement measure evaluation (EME) value of the Stokes vector difference result is analyzed, and the background light polarization angle is calculated based on the optimal weight coefficient. Combined with the experimental results, the EME distribution trend of the optimal weight coefficient and the modified polarization difference imaging method results in different turbidity water bodies are determined, the scattering suppression limit is explored, and the trend of background scattered light polarization direction with turbidity of water is analyzed. The results show that the proposed method can obtain the exact polarization angle of background scattered light in different water environments, revealing a trend that the polarization direction of background scattered light becomes orthogonal to the incident light direction as the turbidity of the water increases. This research provides a methodological basis for determining the polarization direction of the background scattered light in underwater imaging.</sec>

Image quality improvements of diffuse optical tomography by using multiple polarization components

The inverse process of diffuse optical tomography (DOT) is ill-posed, which has a significant effect on the quality of the reconstructed results. In this paper, the polarization characteristics of light are introduced into the inverse solution model of DOT to increase the solution constraints and improve the imaging quality. The spectral element method is used to numerically solve the vector radiative transfer equation, which is used to simulate the propagation of polarized light in a scattering medium. The DOT reverse solution algorithm based on the polarization component is constructed so that the Stokes vector can be used for absorption coefficient and scattering coefficient reconstruction. The simulation and experimental results show that when polarized light is used for incidence, using the intensity component and the multi-polarization component to solve the DOT inverse model can improve the reconstruction accuracy of the medium absorption coefficient distribution and the DOT image quality.

Progressive polarization based reflection removal via realistic training data generation

The reflection effect is unavoidable when taking photos through glasses or other transparent materials, which introduces undesired information into pictures. Hence, removing the influence of reflection becomes a key problem in computer vision. One of the main obstacles of recent learning based approaches is the lacking of realistic training data. To address this issue, we introduce a new dataset synthesis method as well as a novel neural network architecture for single image reflection removal. First, we make use of the polarization characteristics of light into the synthesis of datasets, so as to obtain more realistic and diversified training dataset POL. Then, we design a novel Progressive Polarization based Reflection Removal Network (P2R2Net), which preliminary estimates the coarse background layer to guide the final reflection removal. We demonstrate that our method performs better than the state-of-the-art single image reflection removal methods through quantitative and qualitative experimental comparisons. Specifically, the average PSNR of our restored images selected from three representative benchmark datesets: “Real20”, “SIR2” and “Nature” is improved at least 0.49 compared with existing methods and reaches to 24.52.

Cholesteric layers with tangential-conical surface anchoring for an electrically controlled polarization rotator

The voltage dependences of polarization characteristics of light passed through the cholesteric layers with tangential-conical boundary conditions have been investigated. It has been shown that such layers allow turning the polarization azimuth more than 70 ∘ because of the unique untwisting effect of the cholesteric helix, due to free azimuthal rotation of the director on the substrate with conical anchoring. Optical cells under study have some advantages (low control voltage, smooth variation of polarization azimuth, simplicity of design) and can be used as an electrically controlled polarization rotator of white light.

Indium gallium nitride quantum dots: consequence of random alloy fluctuations for polarization entangled photon emission

We analyze the potential of the c-plane InGaN/GaN quantum dots for polarization entangled photon emission by means of an atomistic many-body framework. Special attention is paid to the impact of random alloy fluctuations on the excitonic fine structure and the excitonic binding energy. Our calculations show that c-plane InGaN/GaN quantum dots are ideal candidates for high temperature entangled photon emission as long as the underlying C 3v -symmetry is preserved. However, when assuming random alloy fluctuations in the dot, our atomistic calculations reveal that while the large excitonic binding energies are only slightly affected, the C 3v symmetry is basically lost due to the alloy fluctuations. We find that this loss in symmetry significantly impacts the excitonic fine structure. The observed changes in fine structure and the accompanied light polarization characteristics have a detrimental effect for polarization entangled photon pair emission via the biexciton–exciton cascade. Here, we also discuss possible alternative schemes that benefit from the large excitonic binding energies, to enable non-classical light emission from c-plane InGaN/GaN quantum dots at elevated temperatures.

Study on the Mechanism of Magneto-optical Modulation Temperature

In recent years, magneto-optical modulation has a wide range of applications and good performance in the fields of azimuth transfer, magnetic field measurement, metal surface damage detection, etc. The core technology is to achieve accurate measurement of the angle by applying the polarization characteristics of light. The magneto-optical modulation system based on this principle belongs to a kind of electrical components. When working, it needs to load a certain current excitation, which causes the temperature of the system to rise, which in turn has a certain influence on the electrical characteristics of the device, and even causes the working state of the system to occur. Change, so in practical applications, temperature factors must be considered. On the basis of fully understanding the structure and working principle of the components, the paper makes a reasonable simplification of the overall structure of the equipment, and obtains the research physical model and numerical heat transfer model. The results show that one of the main heat sources of the system when the solenoid coil and the stainless steel bracket are used, the system temperature is getting higher with the increase of working time.

Sensitivity study on the contribution of scattering by randomly oriented nonspherical hydrosols to linear polarization in clear to semi-turbid shallow waters.

The influence of hydrosol nonsphericity on the polarization characteristics of light under water is investigated by combining accurate single-scattering models for randomly oriented spheroidal scatterers with a radiative transfer model that employs Stokes formalism and considers refraction of direct unpolarized solar radiation and 100% linearly polarized radiation at the air-water interface followed by single scattering. Variations in what we call the "linear polarization phase function" (the degree of linear polarization as a function of scattering angle and the angle of linear polarization as a function of scattering angle) are examined for a wide range of spheroid aspect ratios and complex refractive indices of hydrosols. Implications for polarization-sensitive marine organisms and for remote sensing of the marine environment are discussed.

Sensitivity study on the effect of the optical and physical properties of coated spherical particles on linear polarization in clear to semi-turbid waters

The influence of internal inhomogeneities within hydrosol particles on the polarization characteristics of light is investigated by combining an accurate coated sphere (core-shell) single-scattering model with a radiative transfer model that employs Stokes formalism and considers refraction of direct solar radiation at the air-water interface followed by single scattering. A Junge particle size distribution is assumed. Variations in what we call the "linear polarization phase function" (the degree of linear polarization as a function of scattering angle and the E-vector orientation as a function of scattering angle) are examined as a function of variations in the characteristics of the hydrosol particles. An extensive sensitivity study on the influence of variations in the real and imaginary parts of the refractive index of both the core and shell of the hydrosol particles and on the influences of variations in the ratio between the core radius and shell radius is conducted, varying the values of these parameters over the entire parameter space documented in the literature for actual hydrosol particles. In addition, calculations are conducted for specific parameter combinations in order to demonstrate the influence of some of the most important groups of hydrosols, namely, phytoplankton, gas bubbles, carbonaceous hydrosols, and mineral hydrosols, on the polarization field under water. Variations as a function of solar zenith angle are also investigated. Due to the assumption of single scattering, the results presented are relevant to conditions of low wind speed and a low scattering optical depth and/or low single-scattering albedo within the water body (clear to semi-turbid waters at shallow geometric depths and/or moderate to strong absorption within the water body) outside of Snell's window. Possible implications for aquatic animal polarization vision, for light polarization pollution, and for remote sensing are discussed.

Linear Polarization Characteristics Within the Rosh HaNikra Mid-Littoral Cave, Israel

Light polarization characteristics, i.e., degree of linear polarization (DoLP) and angle of linear polarization (AoLP)E- vector angle, including annual and daily patterns, were documented in the depth of the littoral cave system of Rosh HaNikra on the northern Mediterranean shore of Israel (33° 5′ 35.24″ N, 35° 6′ 17.16″ E), based on light intensity sampled through polarizing filters at different hours of the day on different days of the year. . This is the first study to investigate the state of light polarization in such a unique habitat in which photosynthetic organisms, such as cyanobacteria, microalgae and macroalgae thrive. Such organisms play an essential ecological role as the energy base for the cave’s fauna. .Using these two methods, we found unique winter polarization characteristics within the cave, including high values of DoLP in the morning and at noon, reaching 50%, and nearly constant AoLP throughout the day. Given the low levels of light intensity that typically exist within the cave in the winter months, the relatively high DoLP and the nearly constant AoLP throughout the day may play a significant role in improving the ability of photosynthetic organisms within the cave to harvest light by orienting their light-harvesting receptors with respect to the AoLP. Using the polarization photograph analysis method, we were able to determine the polarization characteristics originating from the sky, reflection off of the far sea surface, and reflection off of (including refraction into followed by refraction out of) the cave wall separately. The maximum DoLP values originating from the sky, far ocean, and cave walls were found to be 27%, 50%, and 35%, respectively. The lowest daily variation in AoLP was that of light reflecting off the cave walls. The present pioneering study lays the foundation for any subsequent study of the role of light polarization in the distribution of the algal flora on the cave walls in and out of the water in the Rosh HanNikra cave and in sea caves in general.

Passive underwater polarization imaging detection method in neritic area

Underwater imaging is widely applied to mariculture, archaeology, and hydrocarbon exploration, because it can provide the information about visualized target. Among various underwater imaging techniques, polarization imaging is of particular interest to us, due to its simple system structure and low cost. It images the waterbody through using the polarization characteristics of light, specifically, the background light and target light. Active polarization imaging method illuminates a target scene with an artificial polarized light source to provide polarization information for imaging. But in neritic area, active imaging leads to complex light scattering conditions when artificial light and natural light are superimposed together, which further leads to poor image quality. Passive underwater polarization imaging attempts to recover a clear image by utilizing the polarization characteristics of background light and target light. However, serious color cast always appears in the final image, resulting from light absorbed by water, which may further result in target distortion. In this manuscript, we present a passive underwater polarization imaging method for detecting a target in neritic area. A depth-information-based underwater Lambertian reflection model is established by incorporating the depth information into the traditional Lambertian reflection model. First, we attribute the light changes in color and brightness of a Lambertian surface to the spatial variation of the light. According to Lambertian reflection model, the appearance of a target on a detector depends on the light source, the surface reflectance, and the camera sensitivity function. But in underwater imaging, light attenuation at different wavelengths also varies with depth. By analyzing the transmission characteristics of background light in water, we build a physical relationship between the depth information of the scene and the background light. After that, we take the depth information as the weight of light intensity distribution. Then we calculate the product of the light intensity and the camera sensitivity function in the underwater scene according to gray world algorithm, and the real color information of the target can be obtained. Finally, the clear image of an underwater target scene can be obtained, where color cast is calibrated and background light is removed. Underwater experiments are conducted to demonstrate the validity of the proposed method. Besides, the quantitative analyses also verify the improvement of the quality in final target image. Compared with conventional passive underwater polarization imaging methods, the proposed method is capable of detecting targets in various conditions, with the color cast problem solved. It can provide underwater images with better quality and valid detailed information. Furthermore, the proposed method is easy to conduct with no need to change the conventional polarization imaging system and is promising in various practical applications.

Generalized Kubelka-Munk approximation for multiple scattering of polarized light.

We introduce a new model for multiple scattering of polarized light by statistically isotropic and mirror-symmetric particles, which we call the generalized Kubelka-Munk (gKM) approximation. It is obtained through a linear transformation of the system of equations resulting from applying the double spherical harmonics approximation of order one to the vector radiative transfer equation (vRTE). The result is a 32×32 system of differential equations that is much simpler than the vRTE. We compare numerical solutions of the vRTE with the gKM approximation for the problem in which a plane wave is normally incident on a plane-parallel slab composed of a uniform absorbing and scattering medium. These comparisons show that the gKM approximation accurately captures the key features of the polarization state of multiply scattered light. In particular, the gKM approximation accurately captures the complicated polarization characteristics of light backscattered by an optically thick medium composed of a monodisperse distribution of dielectric spheres over a broad range of sphere sizes.

Discrimination between spheres and spheroids in a detection system for single particles based on polarization characteristics

The polarization characteristics of light scattered by particles are sensitive to the morphology of the scatterers. In this study, we employed the finite element method (FEM) with a finite element software (COMSOL multiphysics) to retain the potentiality to extend the theoretical study of scattering in this work to single particles with more complex morphology and arbitrary orientation. The angular distribution profiles of the scattering field components perpendicular and parallel to the incident polarization direction are obtained for spherical and spheroidal particles. By comparison with the spheres’ preservation of the polarization, cross-polarization effects for differently oriented spheroidal particles are revealed. The question how to experimentally discriminate the particles with smooth surface moving freely in the detected area at single-particle level according to polarization is addressed. To this end, polarizing devices are inserted into an interference particle imaging (IPI) system. By detecting the orthogonally polarized components of the light, the preservation of the polarization state after scattering by spheres and the occurrence of cross-polarization effects after scattering by spheroids are verified experimentally with the fringes in the IPI system as a reference. A feasible method for distinguishing a spheroidal from a spherical shape at the single-particle level based on the existence of a cross-polarized component of the scattered light is proposed.

Analyzing combinations of circular birefringence, linear birefringence, and elliptical dichroism in magneto-optical rotators

We derive analytic expressions for the polarization characteristics of light emerging from a magneto-optical medium possessing arbitrary contributions from linear and circular birefringence as well as magnetic circular dichroism. The medium is placed inside a static magnetic field. The rotation of the plane of polarization and the ellipticity of the resultant light exhibit interesting characteristics that can be a useful guide in the design and analysis of new photonic devices. Furthermore, the Jones matrices are derived in all cases, including for elliptical dichroism, indicating the role of hyperbolic trigonometric functions in modeling the effects of dichroism. Finally, implications for experimental detection of the polarization state and the limits on the performance of optical isolators are discussed.

Highly stable blue-emission in semipolar (11-22) InGaN/GaN multi-quantum well light-emitting diode

We demonstrate highly stable blue-emission on the semipolar (11-22) InGaN/GaN multi-quantum well light-emitting diode (LED) that has been prepared by the direct lateral-overgrowth method. The LED clearly displays bright blue-emission (λ ∼ 441 nm) with the reduced quantum-confined Stark effect. The variation of the emission-wavelength takes place only at the small injection-current range (<10 mA), and the net variation is less than 1.3 nm for wide driving-current ranges (5–100 mA). After the stabilization of light emission, the optical power is linearly increased with increasing the driving-current (1–1.8 mW). Additionally, the LED exhibits the stable light-polarization characteristics.

Second-harmonic generation in a laterally azo-bridged trimer ferroelectric liquid crystal: Phase matching in the presence of a helicoidal structure

Optical second-harmonic generation (SHG) has been studied in a trimer smectic C* liquid crystal especially designed for nonlinear optical applications. The molecule has a long conjugated donor-acceptor unit that transversally links three parallel rod-shaped moieties. A strong SHG signal has been observed at a fundamental wavelength of 1369 nm even in the presence of the spontaneous helicoidal structure of the smectic C* phase. This unusual behavior has been interpreted as due to the existence of phase matching, in which the wave vector mismatch is compensated by the wave vector of the helix. This point has been confirmed by the study of the SHG intensity versus sample thickness and light polarization characteristics. The main coefficient of the second-order susceptibility tensor of the material has been estimated to be d(22) = 28 pm/V.

Optical polarization properties of m-plane AlxGa_1-xN epitaxial films grown on m-plane freestanding GaN substrates toward nonpolar ultraviolet LEDs

Light polarization characteristics of the near-band-edge optical transitions in m-plane AlxGa1-xN epilayers suffering from anisotropic stresses are quantitatively explained. The epilayers were grown on an m-plane freestanding GaN substrate by both ammonia-source molecular beam epitaxy and metalorganic vapor phase epitaxy methods. The light polarization direction altered from E [symbol see text]c to E//c at the AlN mole fraction, x, between 0.25 and 0.32, where E is the electric field component of the light and [symbol see text] and // represent perpendicular and parallel, respectively. To give a quantitative explanation for the result, energies and oscillator strengths of the exciton transitions involving three separate valence bands are calculated as functions of strains using the Bir-Pikus Hamiltonian. The calculation predicts that the lowest energy transition (E1) is polarized to the m-axis normal to the surface (X3) for 0< x ≤ 1, meaning that E1 emission is principally undetectable from the surface normal for any in-plane tensile strained AlxGa1-xN. The polarization direction of observable surface emission is predicted to alter from c-axis normal (X1) to c-axis parallel (X2) for the middle energy transition (E2) and X2 to X1 for the highest energy transition (E3) between x = 0.25 and 0.32. The experimental results are consistently reproduced by the calculation.

Why are nitride lasers limited to the spectral range from ∼340 to 530 nm?

AbstractWe recently suggested that careful optimization of residual strain in nitride laser structures could be used to extend the operating wavelength into the red and infrared spectral region (Sharma and Towe, J. Appl. Phys. 106, 104509 (2009) and Appl. Phys. Lett. 96, 191105 (2010) [1, 2]). At the other wavelength extreme, in the ultraviolet, non‐optimal residual strain in nitride emitters with AlGaN layers and large crystal‐field splitting energies can cause a switching in emitted light polarization characteristics, leading to less efficient devices. Although Al‐rich AlGaN quantum wells favour shorter emission wavelengths, these structures also exhibit poor carrier confinement. These factors suggest that even in the ultra‐violet, the key limiting constraint for the development of lasers is the amount of residual strain in the structures. To properly resolve these issues, a critical analysis of strain, quantum confinement, and the polarization properties of nitride quantum well structures is warranted (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Measurement of light polarization characteristics from an oil-polluted soil surface in near-infrared bands

Oil pollution can be monitored by infrared remote sensing technology. In this work, the degree of polarization (DOP) was established as a quantitative index of oil pollution. The crude oil and the local typical surface soil from the Songyuan oil field in Jilin province were collected. Some soil samples with four levels of oil content and three levels of water content were prepared and measured. The DOP of the polluted soil and the clean soil in the field was also measured at 180° relative viewing azimuth angle, and 10°, 30° and 50° viewing zenith angles. It was found that with rising soil oil content, the DOP of the reflected light on the soil surface increased when the soil water content was low, and decreased when the soil water content was high.

Polarization characteristics of photonic quantum ring laser with three-dimensional whispering gallery resonances

We report polarization characteristics of light from a photonic quantum ring (PQR) laser of three-dimensional (3D) whispering gallery modes. The 3D polarization states of light from the PQR laser were studied with a home-built solid-angle scanner capable of detecting the spatial intensity distribution in a wide range of solid angles. The analysis shows that the dominant polarization vectors of the PQR laser emitting in the surface normal direction lie always tangential to the PQR perimeter, which means there is a strong carrier-photon coupling.

Light-polarization characteristics of electroluminescence from InGaN∕GaN light-emitting diodes prepared on (112¯2)-plane GaN

Light polarization and emission spectra from InGaN∕GaN quantum-well light-emitting diodes (LEDs) were investigated. The LEDs were prepared on the (112¯2) plane of wurtzite GaN. Polarization and spectrum measurement was performed at different observation angles with respect to the LED surface. Partially polarized electroluminescence was confirmed at any angle of observation, where the emission intensity tended to be greater when a polarizer was aligned along the c axis of the InGaN∕GaN LED structure. The results clearly indicated the inclination of the c axis relative to the LED surface. As a result, two light polarizations were identified and they were assigned to two different electronic transitions in relation to emission peak energies. Possible alteration of the valence-band structure was suggested due to the induced strain.