Polarization Filter Research Articles

Comparative Evaluation of Hue Value Chroma using Cross Polarised Photography

Introduction: Digital photographs offer a wide range of colour options. They aid in increasing communication between a dentist and a technician by making the morphology, colour, and texture of the teeth easier to visualise. A polarising filter reduces reflections and glare while boosting colour saturation in an image. The aim of the study was to analyse images with and without polarised photography. Methodology: A total of 125 images of shade guidelines were collected for this study, 5 each shade tab for 5 shades (A1 to A4). We looked at the following shade guidance systems: VITA Classical (VITA Zahnfabrik) (control), IPS e. max Ceram (Ivoclar Vivadent) were photographed with a Canon EOS 60D digital camera and a 100-mm Canon Macro Lens. Ambient light, exposure (1/125, f16), ISO (100), flash (ETTL), distance, focusing (1:1), and backdrop were all standardized in the photographs. The Adobe RGB colour system was utilised since it covers nearly half of the Lab colour space. Results: Mean and standard deviation values of images with and without cross polarised photography were compared. Hue, value, chroma of the images were assessed showing no statistical difference among the images with and without cross polarised photography. Conclusion: Compared to visual and digital photographic approaches for choosing shades, the application of polarising filters had negligible effect on shade choice. When routinely practised, shade matching can improve a clinician's ability to choose the appropriate shade. Thus, knowledge and training may help someone become better at shade matching. Keywords: Hue, value, chroma, cross polarised photography, Camera, Ring flash, Micro lens.

GST-based polarization approach to picking P-and S-waves arrival time for high-speed rail early warning system

The first arrival time of seismic P- and S- waves affects the determination of the beginning of an earthquake by the Earthquake Early Warning System for High-speed Rail (HSREEWs). Accordingly, we propose an approach to picking P- and S-waves arrival time for HSREEWs. This approach can treat the continuous seismic signals in real-time without prior knowledge of whether an earthquake occurs. Firstly, we replace the fixed time window of the S transform (ST) with the dynamic window of the generalized S transform (GST) to make the necessary time of signal processing more flexible. Meanwhile, the GST extends the sequential signal to the time-frequency domain (TF), and combines the TF polarization to construct four three-component polarization filters. Accordingly, the P-wave and S-wave can be separated from the seismic waveform by those filters, which effectively avoids the phenomenon that the S-wave phase is difficult to determine because of the interference of S-wave overlapping in the coda region. Secondly, based on the instantaneous frequency of seismic signal, we construct a new STA/LTA (GSPA-STA/LTA) with the characteristic function (CF) of constrained TF spectrum to pick the first arrivals of the P- and S-waves, and provide the corresponding automatic picking algorithm. Finally, we analyze 504 seismic events larger than Ms40 near the Japanese Tohoku Shinkansen to comprehensively verify the effectiveness of our approach. Since the P-wave and S-wave are first separated, the subsequent process just has to identify the first arrival times of their respective components. The approach has a good practical value in maintaining the safe operation of high-speed rail under earthquake, which meets the industry demands for speed, scale and accuracy in HSREEWs.

Incoherent digital holography with two polarization-sensitive phase-only spatial light modulators and reduced number of exposures.

I propose methods for reducing the number of exposures in incoherent digital holography with two polarization-sensitive phase-only spatial light modulators (IDH with TPP-SLMs). In IDH with TPP-SLMs, no polarization filters are required, and not only three-dimensional (3D), but polarization information is also obtained. However, seven exposures are required to conduct filter-free polarimetric incoherent holography. In this article, the optical designs and modified phase-shifting interferometry to reduce the number of recordings are described. IDH with TPP-SLMs has the potential for filter-free single-shot multidimensional incoherent holographic imaging.

Utility of Spectral Filtering to Improve the Reliability of Marine Fauna Detections from Drone-Based Monitoring.

Monitoring marine fauna is essential for mitigating the effects of disturbances in the marine environment, as well as reducing the risk of negative interactions between humans and marine life. Drone-based aerial surveys have become popular for detecting and estimating the abundance of large marine fauna. However, sightability errors, which affect detection reliability, are still apparent. This study tested the utility of spectral filtering for improving the reliability of marine fauna detections from drone-based monitoring. A series of drone-based survey flights were conducted using three identical RGB (red-green-blue channel) cameras with treatments: (i) control (RGB), (ii) spectrally filtered with a narrow 'green' bandpass filter (transmission between 525 and 550 nm), and, (iii) spectrally filtered with a polarising filter. Video data from nine flights comprising dolphin groups were analysed using a machine learning approach, whereby ground-truth detections were manually created and compared to AI-generated detections. The results showed that spectral filtering decreased the reliability of detecting submerged fauna compared to standard unfiltered RGB cameras. Although the majority of visible contrast between a submerged marine animal and surrounding seawater (in our study, sites along coastal beaches in eastern Australia) is known to occur between 515-554 nm, isolating the colour input to an RGB sensor does not improve detection reliability due to a decrease in the signal to noise ratio, which affects the reliability of detections.

Enhancement of Seismic Phase Identification Using Polarization Filtering and Array Analysis

ABSTRACT Seismic arrays play a crucial role in identifying weak signals in the seismic wavefield based on their expected slowness and backazimuth values. However, their resolution power is limited when studying phases with similar horizontal slownesses and arrival times, such as receiver-side or source-side reverberations and converted phases. Therefore, we investigate the benefit of applying polarization filtering to three-component seismograms before stacking to remove undesired signals and increase the signal-to-noise ratio of the array. Customized polarization filters enable more sophisticated wavefield separation and robust phase identification on vespagrams. However, selecting the suitable polarization filter requires a balance between noise reduction and the preservation of desired signals. We find that degree-of-polarization filters generally excel in suppressing incoherent noise. On the other hand, some filters, for example, based solely on ellipticity, do not yield notable enhancements for body waves and may even produce adverse effects, specifically for phases that arrive late in the seismogram. We demonstrate these findings using data recorded by AlpArray and surrounding permanent stations.

Large-area ultracompact pixelated aluminum-wire-grid-based metamaterials for Vis-NIR full-Stokes polarization imaging

The study of pixelated metamaterials that integrate both the functions of linear and circular polarization filters is rapidly growing due to the need for full-Stokes polarization imaging. However, there is a lack of large-area, ultracompact pixelated full-Stokes metamaterials with excellent performance, especially circular polarization filters with a high extinction ratio, a broad operating bandwidth, and a low-cost, high-quality, efficient manufacturing process, which limits the practical applications of pixelated full-Stokes metamaterials. In this study, we propose a universal design and fabrication scheme for large-area, ultracompact pixelated aluminum wire-grid-based metamaterials used in Vis-NIR full-Stokes polarization imaging. The aluminum wire-grid was designed as a linear polarization filter with an average linear polarization extinction ratio of 36,000 and a circular polarization filter with an average circular polarization extinction ratio of 110 in Vis-NIR. A large-area, ultracompact 320×320 pixelated aluminum wire-grid-based full-Stokes metamaterial was fabricated using nanoimprint lithography and nano transfer printing with the advantages of low cost and high efficiency. This metamaterial was used to achieve full-Stokes polarization imaging with errors within 8.77%, 12.58%, 14.04%, and 25.96% for Stokes parameters S0, S1, S2, and S3, respectively. The inversion errors of the compensated Stokes parameters can be reduced to 0.21%, 0.21%, 0.42%, and 1.96%, respectively.

Applications of Time‐Frequency Domain Polarization Filtering to InSight Seismic Data

AbstractThe seismometer Seismic Experiment for Interior Structure (SEIS) onboard the InSight lander was used to continuously record the seismicity on Mars from February 2019 to December 2022. To maximize the information that can be extracted from the seismic data, it is critical to identify and to suppress undesired features (e.g., environmental noise, scattered waves, seismic imprint of lander vibrations) and non‐seismic noise (e.g., instrument related artifacts). We present an advanced polarization filtering workflow in the time‐frequency domain to suppress undesired features and to enhance the signal‐to‐noise ratio of the SEIS recordings. We estimate time‐frequency‐dependent polarization attributes such as the ellipticity, directionality of the particle motion, and the degree of polarization to identify and filter out undesired data parts. After filtering in the time‐frequency domain, the seismic data are transformed back to the time domain, yielding broadband waveform data that can be used for further seismological analysis. We illustrate the benefits of our filtering approach with three use cases. Firstly, we show how polarization filtered data can help to constrain the source mechanism of the sol 1,222 event, the largest marsquake detected so far. Using the proposed polarization filtering techniques, we are able to enhance the S‐wave arrival by suppressing interfering randomly polarized scattered waves to successfully infer on the moment tensor of this event. Secondly, we show that polarization filters can be used to suppress instrument‐related glitches and, thirdly, to remove the seismic imprint left by the vibrating lander (mechanical resonances of the lander).

Three-component high-resolution seismic time–frequency polarization filter

SUMMARY The analysis of earthquake recordings from three-component instruments can be challenging due to overlapping events. Time–frequency (TF) polarization methods are efficient tools for this purpose, which can discriminate these events. Previous polarization methods did not consider all three components simultaneously while transferring data to TF domain, which can cause inaccuracies in the reconstruction of wave amplitudes. Therefore, the three-component sparse adaptive S transform (3C-SAST) algorithm is preferred to other TF decompositions since it is mainly developed for polarization analysis purposes, and outperforms other TF methods. In this paper, we developed the 3C-SAST by adding a parameter to adjust the sparseness of the solution and make the resolution flexible. The developed TF decomposition is then used to extend the Morozov & Smithson method to TF domain, and devise a new TF polarization filter whose invertibility and resolution flexibility make it a promising tool for wavefield separation. This filter can eliminate the out-of-plane arrival energies and extract the Rayleigh waves for multicomponent data, which has application in Rayleigh wave tomography and seismological studies. We demonstrated the efficiency of the proposed method for seismic surface waves separation using synthetic signals and three-component teleseismic earthquake recording.

Tunable all-fiber polarization filter based on graphene-assisted metal gratings for the O- and C-bands

All-fiber polarization filters have important applications in optical communication, sensing, and fiber lasing. However, the incompatibility between high extinction ratio and short interaction length is a problem for miniaturization. In addition, current passive designs make polarization filters work in a fixed wavelength band, which limits the dynamic polarization control. Here, we integrate subwavelength metal gratings on graphene-covered D-shaped single-mode fibers to achieve tunable polarization filters, whose operating bandwidth has a significant improvement over previous works. In the simulation, the x-polarized mode couples effectively with the surface plasmon polariton mode and suffers extremely high transmission loss (up to ∼38dB/mm). At the same time, the y-polarized mode remains low insertion loss of ∼0.58dB/mm. By changing the chemical potential of graphene, the loss peak of the x-polarized mode can be adjusted in the range covering the wavelength bands from 1.272 to 1.353 µm or from 1.54 to 1.612 µm, which results in an adjustable broadband filter with a high extinction ratio over 20 dB. The proposed filter provides a promising polarization control scheme for integrated devices in the fields of communication, sensing, and lasing.

Forgotten treasures in the HST/FOC UV imaging polarimetric archives of active galactic nuclei

Context. Over its 13 yr of operation (1990–2002), the Faint Object Camera (FOC) on board the Hubble Space Telescope (HST) observed 26 individual active galactic nuclei (AGNs) in ultraviolet (UV) imaging polarimetry. However, not all of the observations have been reduced and analyzed or set within a standardized framework. Aims. We plan to reduce and analyze the AGN observations that have been neglected in the FOC archives using a consistent, novel, and open-access reduction pipeline of our own. We then extend the method to the full AGN sample, thus leading to potential discoveries in the near future. Methods. We developed a new pipeline in Python that will be able to reduce all the FOC observations in imaging polarimetry in a homogeneous way. Most of the previously published reduced observations are dispersed throughout the literature, with the range of different analyses and approaches making it difficult to fully interpret the FOC AGN sample. By standardizing the method, we have enabled a coherent comparison among the different observational sets. Results. In this first paper of a series exploring the full HST/FOC AGN sample, we present an exhaustively detailed account of how to properly reduce the observational data. Current progress in cross-correlation functions, convolution kernels, and a sophisticated merging and smoothing of the various polarization filter images, together with precise propagation of errors, has provided state-of-the-art UV polarimetric maps. We compare our new maps to the benchmark AGN case of NGC 1068 and successfully reproduce the main results previously published, while pushing the polarimetric exploration of this AGN futher, thanks to a finer resolution and a higher signal-to-noise ratio (S/N) than previously reported. We also present, for the first time, an optical polarimetric map of the radio-loud AGN IC 5063 and we examine the complex interactions between the AGN outflows and the surrounding interstellar medium (ISM). Conclusions. Thanks to our newly and standardized reduction pipeline, we were able to explore the full HST/FOC AGN sample, starting with observations that had not been previously published (e.g., IC 5063 here). This pipeline will allow us to make a complete atlas of UV polarimetric images of the 26 unique AGNs observed by the FOC, highlighting the importance and necessity of (imaging) polarimeters for the upcoming new generation of 30-m class telescopes.

An Efficient Multi-AUV Cooperative Navigation Method Based on Hierarchical Reinforcement Learning

Positioning errors introduced by low-precision navigation devices can affect the overall accuracy of a positioning system. To address this issue, this paper proposes a master-slave multi-AUV collaborative navigation method based on hierarchical reinforcement learning. First, a collaborative navigation system is modeled as a discrete semi-Markov process with defined state and action sets and reward functions. Second, trajectory planning is performed using a hierarchical reinforcement learning-based approach combined with the polar Kalman filter to reduce the positioning error of slave AUVs, realizing collaborative navigation in multi-slave AUV scenarios. The proposed collaborative navigation method is analyzed and validated by simulation experiments in terms of the relative distance between the master and slave AUVs and the positioning error of a slave AUV. The research results show that the proposed method can not only successfully reduce the observation and positioning errors of slave AUVs in the collaborative navigation process but can also effectively maintain the relative measurement distance between the master and slave AUVs within an appropriate range.

Pixelated Filter Array for On-Chip Polarized Spectral Detection.

On-chip multi-dimensional detection systems integrating pixelated polarization and spectral filter arrays are the latest trend in optical detection instruments, showing broad application potential for diagnostic medical imaging and remote sensing. However, thin-film or microstructure-based filter arrays typically have a trade-off between the detection dimension, optical efficiency, and spectral resolution. Here, we demonstrate novel on-chip integrated polarization spectral detection filter arrays consisting of metasurfaces and multilayer films. The metasurfaces with two nanopillars in one supercell are designed to modulate the Jones matrix for polarization selection. The angle of diffraction of the metasurfaces and the optical Fabry-Perot (FP) cavities determine the spectrum's center wavelength. The polarization spectral filter arrays are placed on top of the CMOS sensor; each array corresponds to one pixel, resulting in high spectral resolution and optical efficiency in the selected polarization state. To verify the methodology, we designed nine-channel polarized spectral filter arrays in a wavelength range of 1350 nm to 1550 nm for transverse electric (TE) linear polarization. The array has a 10 nm balanced spectral resolution and average peak transmission efficiency of over 75%, which is maintained by utilizing lossless dielectric material. The proposed array can be fabricated using overlay e-beam lithography, and the process is CMOS-compatible. The proposed array enables broader applications of in situ on-chip polarization spectral detection with high efficiency and spectral resolution, as well as in vivo imaging systems.

Unsupervised design for broadband multispectral and polarization filter array patterns.

Imaging multiple wavelength and polarization components is problematic due to the complexity of equipment and the increase in the number of imaging shots, so imaging using filter arrays with various patterns has been widely reported from elemental research to practical applications. Most of them use bandpass filters with different center wavelengths for each pixel. Recently, however, filter arrays with multimodal transmission characteristics have been proposed using photonic crystals or Fabry-Perot filters. In any of these methods, the design of the filter array arrangement pattern is important to improve the quality of the captured image, as well as the improvement of the demosaicking algorithm. One way to design a filter array pattern is to minimize the mean squared error (MSE) between the ideal image and the demosaicked image. However, the more multidimensional the imaging components, the more difficult it becomes to collect training data. In such cases, it is necessary to empirically determine candidate transmission characteristics and patterns of filter arrays. In this study, we propose a method for evaluating filter array patterns without using any training data in the design of filter arrays for multispectral and polarization imaging. The proposed method estimates the MSE by approximating the autocorrelation matrix without using image data by expressing the imaging model as a linear forward problem and the demosaicking as a linear inverse problem. Since this method can be applied not only to ideal bandpass filter arrangements, but also to multispectral filter arrays with multimodal spectral transmission characteristics and even multispectral polarization filter arrays with different extinction ratios at different wavelengths, we will show that image quality can be improved over empirical arrangements by evaluating these patterns and by testing examples of optimal designs using genetic algorithms.

Chip-integrated metasurface full-Stokes polarimetric imaging sensor

Polarimetric imaging has a wide range of applications for uncovering features invisible to human eyes and conventional imaging sensors. Chip-integrated, fast, cost-effective, and accurate full-Stokes polarimetric imaging sensors are highly desirable in many applications, which, however, remain elusive due to fundamental material limitations. Here we present a chip-integrated Metasurface-based Full-Stokes Polarimetric Imaging sensor (MetaPolarIm) realized by integrating an ultrathin (~600 nm) metasurface polarization filter array (MPFA) onto a visible imaging sensor with CMOS compatible fabrication processes. The MPFA is featured with broadband dielectric-metal hybrid chiral metasurfaces and double-layer nanograting polarizers. This chip-integrated polarimetric imaging sensor enables single-shot full-Stokes imaging (speed limited by the CMOS imager) with the most compact form factor, records high measurement accuracy, dual-color operation (green and red) and a field of view up to 40 degrees. MetaPolarIm holds great promise to enable transformative applications in autonomous vision, industry inspection, space exploration, medical imaging and diagnosis.

Detection of preexisting quantum entanglements between dipole–photon discrete observables

We performed measurements of laser beam power polarized in different angles as 0^circ , 45^circ and 90^circ passing close to a symmetric shielded capacitor with parallel plates and through a polaroid filter configured with angles as 0^circ , 45^circ and 90^circ . An unusual light power variation was detected during the charging and discharging of the high voltage capacitor even considering the suppression of known electromagnetic interaction between laser beam and capacitor. The light power variation curves also indicated a typical pattern of charge and discharge of capacitors. The combination of the angles of the laser beam polarization and polaroid filter surprisingly indicated the measurement of correlations between the polarizations of photons and electric dipoles of the capacitor dielectric. These novel results can only be explained supposing the preexisting condition of quantum entanglements between discrete observables of electric dipoles and photons.

Dual-function plasmonic device on photonic crystal fiber for near to mid-infrared regions

Broadband multifunction optical devices can play an important role in the field of integrated photonics but achieving high tunability and versatility on a fabricated device by implementing external control or structural modification is still challenging. In this article, what we believe to be a new dual-function optical device based on photonic crystal fiber, having an ultra-broad bandwidth that partially covers near-infrared (IR) to mid-IR regions, is proposed and analyzed. This device is designed on a fabrication friendly geometry such a way that it can be used as a polarization filter as well as refractive index sensor without any external tuning or structural modification. In this case, plasmonic material plays a crucial role for achieving simultaneous operation of the device both in communication and sensing applications. Our proposed device, with a fiber length of 100 µm, can effectively suppress the y-polarized light within the wavelength range of 1.29 µm to 1.60 µm, while the x-polarized light is maintained properly in the core, and vice-versa for the region of 1.69 µm to 4.39 µm. The maximum confinement losses of 840.8 dB/cm, 1013.2 dB/cm, 659.65 dB/cm, and 792.68 dB/cm are obtained at wavelengths of 1.37 µm, 1.56 µm, 1.72 µm, and 2.65 µm, respectively. By maintaining a crosstalk level of better than 20 dB, this device achieves broad bandwidths of 310 nm over the 1.29 µm to 1.60 µm wavelength range and 2700 nm over the 1.69 µm to 4.39 µm wavelength range. In addition to the filtering performance, our device possesses sensing capabilities, which is also well discussed as an example of refractive index sensor. Considering the analyte refractive index of 1.10-1.40, this device shows an average wavelength sensitivity of 1000 nm/RIU. Therefore, the above exceptional characteristics of our proposed device make it suitable for both optical communication and sensing systems.

Examining polarizing and non-polarizing filters for road sports.

The use of sunglasses and polarized sunglasses is common in all aspects of life and is very popular in outdoor athletic activities. However, the choice of athletes regarding their sunglasses is often not dictated by the performance ensured by one model rather than another but by other factors such as look or wearability due also to the lack of technical data on cataloguess. A conscious choice of filters to use, also according to road and weather conditions, supported by quantitative data, would instead allow athletes to improve their visual comfort and sport experience. The transmission spectra of 10 pairs of sports sunglasses (five polarized and five not polarized) were measured and related to the road luminance for different sun positions in both horizontal and vertical polarizations. The luminous transmission factor was calculated, and the luminance quantities while wearing the glasses were defined and calculated for all cases. A survey was submitted to a group of athletes to collect their impressions and relate them to the measurement results. The pairs of polarized and non-polarized sports sunglasses showed similar transmission factors, so their ability to mitigate outdoor light is almost the same-the main difference lies in the polarized light transmitted. Outdoor measurements showed that the light reflected by the road has a substantial polarized horizontal component. Polarized sunglasses block much of the light reflected by the road, resulting in a darker appearance of the road and reducing the glare of the scene in bright sunlight. The decrease in road luminance increases the contrast discrimination of other objects in the scene, which reflect sunlight in a non-polarized way (e.g., non-flat surfaces). The survey demonstrates that interviewed athletes prefer polarized sunglasses for these aformentioned reasons. This study highlights the advantages of polarizing sunglasses for athletic activities on roads because the road surface often reflects polarized light depending on the position of the sun.

Quantitative interocular suppression in children with intermittent exotropia.

We have demonstrated that the depth of unbalanced interocular suppression can be quantified by balancing the interocular luminance differences required when both eyes are viewing simultaneously. In this study, we aimed to investigate the applicability of this method in children with intermittent exotropia (IXT), offering a quantitative assessment of interocular suppression in individuals with binocular imbalance. Additionally, we evaluated its association with the clinical characteristics of IXT. Interocular suppression in IXT was quantitatively measured using a polarizer and neutral-density (ND) filters. The density of the ND filter was adjusted incrementally from 0.3ND to 3ND, with a step size of 0.3ND (a total of 10 levels). Our prospective study involved 46 patients with IXT (mean age: 10.12 ± 4.89 years; mean ± SD) and 24 normal observers (mean age: 7.88 ± 1.83 years). The suppression test exhibited good test-retest reliability, supported by statistical analysis. We observed more pronounced interocular suppression in individuals with IXT compared to controls. Notably, the magnitude of suppression during distant and near viewing significantly differed in IXT (1.55 ± 0.93 vs. 0.57 ± 0.64; Z = 4.764, p < 0.001). Furthermore, we identified a positive correlation between interocular suppression and data obtained from the Worth-4-Dot test. Additionally, interocular suppression showed a significant association with distance control scores. Our novel test offers a convenient and reliable means to quantify interocular suppression in patients with IXT. The quantitative assessment of interocular suppression provides a sensitive tool to evaluate the clinical characteristics of IXT.

High-performance terahertz polarization filter based on the anti-resonant fiber

A novel terahertz polarization filter based on the anti-resonant fiber is designed and analyzed. The polarization extinction ratio (PER) is improved by using high-resistivity silicon (HRS) as the bulk material in conjunction with a double conjoined tube cladding structure. The effects of the structure and material of the anti-resonant fiber on the polarization filtering characteristics are analyzed by the finite element method. The PER of the anti-resonant fiber reaches 100 dB and the insertion loss of y-polarization fundamental mode (YPFM) is less than 0.66 dB at 1 THz when the anti-resonant fiber length is 5.58 cm. The bandwidth can be expanded by changing the fiber length and for a fiber length of 8 cm, the frequency bandwidth is 0.92–1.14 THz and the insertion loss is less than 3 dB. The polarization filter is demonstrated to deliver excellent performance in the terahertz frequency range and has large commercial potential in terahertz communication and biomedical spectroscopy.

Six high-performance photonic crystal fiber polarization filters based on surface plasmon resonance

Six high-performance photonic crystal fiber polarization filters based on surface plasmon resonance