Polarization Filter Research Articles

Negative curvature fiber (NCF) polarization filter with large polarization loss ratio and ultralow loss in the terahertz range

A high-performance polarization filter based on the negative curvature fiber (NCF) with an asymmetric cladding structure is proposed and analyzed. The resonant effects of the x-polarization fundamental mode (XPFM) of the NCF are enhanced by the single-layer semi-elliptical tubes with a gradient wall thickness in the x-axis direction, while the anti-resonant effects of the y-polarization fundamental mode (YPFM) are strengthened by the nested double-layer elliptical tubes in the y-axis direction. The optimized structure shows a polarization loss ratio of greater than 100 in the range of 0.98–1.02 THz in addition to propagation losses of 0.94 dB/m and 7.43 × 10−4 dB/m at 1 THz for XPFM and YPFM, respectively. A polarization loss ratio of 1,276 is achieved and the polarization loss ratio is 6,321 at 0.98 THz. Our results show that the NCF polarization filter delivers better performance than recently reported filters in the terahertz band and the results reveal a new strategy to design high-performance polarization filters.

Resin infiltration versus fluoride varnish for visual improvement of white spot lesions during multibracket treatment. A randomized-controlled clinical trial

AimsThis study aimed to evaluate the visual improvement of resin infiltration of white spot lesions (WSL) during orthodontic treatment with the multibracket appliance (MBA) compared to fluoride varnish.MethodsPatients aged 12–17 years with at least one WSL with an International Caries Detection and Assessment System (ICDAS) score of 1–2 during an active MBA treatment were included and randomized to receive either resin infiltration (Icon) or fluoride application (Flairesse). Standardized digital images were obtained before, one-day, one-week, one-month, three-months and six-months after treatment using a DSLR camera and a matching polarization filter. A grey reference card was used for color standardization. A Matlab routine was used to measure the color difference between adjacent healthy enamel and treated WSL. The independent-samples t-test was used for intergroup and paired-samples t-test for intragroup comparison.ResultsImages of 116 teeth from 36 patients were analyzed. The ΔE for the “Icon” treated WSL was smaller (T1ICON = 5.0 ± 1.4) than in the fluoride group (T1Fluoride = 8.4 ± 3.2). Caries infiltration significantly improved the aesthetic appearance of WSL (p < 0.001), which remained satisfactory at six months (T5ICON = 5.2 ± 1.6).ConclusionWSL infiltration management during orthodontic treatment was superior to topical fluoridation in not only arresting the enamel lesions but also significantly improving the aesthetic appearance of demineralized regions around the brackets.Clinical relevanceWSL treatment in orthodontic patients is usually initiated after debonding. Research has shown that the earlier WSL is treated, the better the aesthetic outcome. There is limited data on the efficacy of resin infiltration of WSL during orthodontic treatment.

Controlling the broadband enhanced light chirality with L-shaped dielectric metamaterials

The inherently weak chiroptical responses of natural materials limit their usage for controlling and enhancing chiral light-matter interactions. Recently, several nanostructures with subwavelength scale dimensions were demonstrated, mainly due to the advent of nanofabrication technologies, as a potential alternative to efficiently enhance chirality. However, the intrinsic lossy nature of metals and the inherent narrowband response of dielectric planar thin films or metasurface structures pose severe limitations toward the practical realization of broadband and tailorable chiral systems. Here, we tackle these problems by designing all-dielectric silicon-based L-shaped optical metamaterials based on tilted nanopillars that exhibit broadband and enhanced chiroptical response in transmission operation. We use an emerging bottom-up fabrication approach, named glancing angle deposition, to assemble these dielectric metamaterials on a wafer scale. The reported strong chirality and optical anisotropic properties are controllable in terms of both amplitude and operating frequency by simply varying the shape and dimensions of the nanopillars. The presented nanostructures can be used in a plethora of emerging nanophotonic applications, such as chiral sensors, polarization filters, and spin-locked nanowaveguides.

Measurement technology based on a Stokes parametric polarization system

Structured light measurement systems often use polarization filters to reduce image interference from highly reflective areas. This method can be effective, but it may also reduce the brightness of specific areas, particularly overly dark portions, which can affect the accuracy of the measurement results. This paper proposes a measurement method for a polarization system based on Stokes parameters to solve the problem. After adjusting the polarization filter to angles of 0°, 45°, and 90°, the camera captures an image of the object and calculates the corresponding Stokes parameters to generate the expected polarization angle histogram. Then, based on the detailed information on the angle distribution, the accurate mathematical model is used to screen the interval, and the optimal polarization angle is determined by orthogonal processing while ensuring the signal-to-noise ratio and image quality. Finally, an image fusion technology synthesizes a set of fringe projection images with the preferred polarization angles. Experiments have shown that this new method effectively addresses the issue of interference in the highlighted region when using conventional polarization filters. Additionally, it significantly improves the quality of the fringe pattern. The polarization angle selection in the experimental process is made more rapid and accurate through the quantitative mathematical model calculation of the polarization angle, significantly improving the system’s measurement efficiency.

Ultra-low loss, single polarization hollow-core anti-resonant fiber

In this paper we present a new hollow-core anti-resonant fiber (HC-ARF). The structural asymmetry is constructed by the introduction of elliptical quartz tubes in the core region, which can greatly improve the birefringence and enhance the polarization extinction ratio. Meanwhile, the semicircular and circular nested quartz tubes in the cladding region also contribute to the decrease of the confinement loss of the fundamental mode. A finite element algorithm is used to analyze the effects of each parameter on the performance of the designed HC-ARF. The final simulation results illustrate that the designed structure achieves the values of birefringence and polarization extinction ratio of 2.4×10−5 and 257 in the common wavelength band of 1550 nm, and polarization filtering with a bandwidth of 4 nm. It is worth mentioning that the loss of the y-polarized fundamental mode in the 1550 nm wavelength band reaches an ultra-low value of 0.014 dB/m. The corresponding fundamental mode loss has remained extremely low in the wavelength range considered. Our proposed device still has good bending resistance, where the loss of the y-polarized mode is about 0.04 dB/m and decreases gradually when the bending radius is 5 cm. We believe that the proposed HC-ARF can be used in polarization-sensitive fiber devices and can be widely applied in polarization-sensitive fiber communication systems such as fiber lasers and fiber gyroscopes.

Long-Range Imaging LiDAR with Multiple Denoising Technologies

The ability to capture and record high-resolution images over long distances is essential for a wide range of applications, including connected and autonomous vehicles, defense and security operations, as well as agriculture and mining industries. Here, we demonstrate a self-assembled bistatic long-range imaging LiDAR system. Importantly, to achieve high signal-to-noise ratio (SNR) data, we employed a comprehensive suite of denoising methods including temporal, spatial, spectral, and polarization filtering. With the aid of these denoising technologies, our system has been validated to possess the capability of imaging under various complex usage conditions. In terms of distance performance, the test results achieved ranges of over 4000 m during daylight with clear weather, 19,200 m at night, 6700 m during daylight with haze, and 2000 m during daylight with rain. Additionally, it offers an angular resolution of 0.01 mrad. These findings demonstrate the potential to offer comprehensive construction strategies and operational methodologies to individuals seeking long-range LiDAR data.

Reliability of non-polarized versus polarized digital photographs for evaluation of gingival redness

Introduction: The reported prevalence of gingivitis in various developed countries is considered high. This rate escalates with the increase in age, especially around puberty which affects their oral health related quality of life. The consequences of periodontal diseases observed in adults mostly had their inception earlier in life. Gingival conditions were found to be worse than caries among adolescents and were not taken seriously compared to caries. Aim: Comparison between the gingival redness in group of Egyptian children as evaluated using analyzed polarized versus non-polarized digital photographs. Subjects and methods: 47 Egyptian participants aged 11-14 years-old from Newgiza University outpatients’ clinic agreed to participate were recruited and agreed to participate in the study. Gingival redness was evaluated using analyzed digital photographs with and without cross polarizing filter then analyzed via Adobe Photoshop Creative Cloud (CC) 2021 software. Comparison between non-polarized and polarized photos was performed using independent t-test. Results: The study showed that non-polarized photos were significantly higher in number of red pixels than polarized photos as P &lt;0.05. Reliability between two different digital photographic techniques was performed using Cronbach alpha (α), which revealed strong agreement between polarized and non-polarized digital photographic evaluation. Conclusion: Digital photography can be used in evaluation of gingival redness with or without cross polarizing filter.

Living jewels: iterative evolution of iridescent blue leaves from helicoidal cell walls.

Structural colour is responsible for the remarkable metallic blue colour seen in the leaves of several plants. Species belonging to only ten genera have been investigated to date, revealing four photonic structures responsible for blue leaves. One of these is the helicoidal cell wall, known to create structural colour in the leaf cells of five taxa. Here we investigate a broad selection of land plants to understand the phylogenetic distribution of this photonic structure in leaves. We identified helicoidal structures in the leaf epidermal cells of 19 species using transmission electron microscopy. Pitch measurements of the helicoids were compared to the reflectance spectra of circularly polarised light from the cells to confirm the structure-colour relationship. By incorporating species examined with a polarising filter, our results increase the number of taxa with photonic helicoidal cell walls to species belonging to at least 35 genera. These include 23 monocot genera, from the orders Asparagales (Orchidaceae) and Poales (Cyperaceae, Eriocaulaceae, Rapateaceae) and 17 fern genera, from the orders Marattiales (Marattiaceae), Schizaeales (Anemiaceae) and Polypodiales (Blechnaceae, Dryopteridaceae, Lomariopsidaceae, Polypodiaceae, Pteridaceae, Tectariaceae). Our investigation adds considerably to the recorded diversity of plants with structurally coloured leaves. The iterative evolution of photonic helicoidal walls has resulted in a broad phylogenetic distribution, centred on ferns and monocots. We speculate that the primary function of the helicoidal wall is to provide strength and support, so structural colour could have evolved as a potentially beneficial chance function of this structure.

High-crosstalk polarization filter based on double-D photonic crystal fiber with amethyst and gold

Polarization filters based on surface plasmon resonance (SPR) have undergone rapid development in recent years. In this work, a dual D-type PCF polarization filter based on SPR is designed and analyzed. The filter improves the limiting loss of the core mode by gilding the semi-circular split ring and inlaying amethyst. The influence of the structural parameters of the filter on the filtering characteristics is analyzed by the finite element method. The results show that the core mode losses of the x and y polarized light are 32[Formula: see text]dB/cm and 910.56[Formula: see text]dB/cm at 1.55[Formula: see text][Formula: see text]m, respectively. For a fiber length of 1000[Formula: see text][Formula: see text]m, the crosstalk and bandwidth are 763.11[Formula: see text]dB and 700[Formula: see text]nm, respectively. In addition, the impact of manufacturing errors in the structural parameters on the filter performance is discussed. The filter has excellent filtering characteristics and large potential in optical communication and optical sensing.

Cascaded momentum-space polarization filters enabled label-free black-field microscopy for single nanoparticles analysis

Label-free optical imaging of single-nanometer-scale matter is extremely important for a variety of biomedical, physical, and chemical investigations. One central challenge is that the background intensity is much stronger than the intensity of the scattering light from single nano-objects. Here, we propose an optical module comprising cascaded momentum-space polarization filters that can perform vector field modulation to block most of the background field and result in an almost black background; in contrast, only a small proportion of the scattering field is blocked, leading to obvious imaging contrast enhancement. This module can be installed in various optical microscopies to realize a black-field microscopy. Various single nano-objects with dimensions smaller than 20 nm appear distinctly in the black-field images. The chemical reactions occurring on single nanocrystals with edge lengths of approximately 10 nm are in situ real-time monitored by using the black-field microscopy. This label-free black-field microscopy is highly promising for a wide range of future multidisciplinary science applications.

Mechanically gated data display via synergizing the mechanochromism of chiral photonic elastomers and optically responsive molecules

Mechanochromic fluorophores and elastomers gain great potential in dynamic data encryption and anti-counterfeiting due to their instant responses, excellent handleability, high-throughput data-verification, and multi-dimensional security features. However, the reported mechanochromic fluorophores generally require solvent fuming or thermal annealing to revert their responses, sacrificing the handleability and lengthening the authentication time. For the mechanochromic elastomers, the data input requires precisely control the dose of the crosslinkers or phase tuning agents, making the high-throughput data-processing rather challenging. Here we developed a mechanically gated data display by synergizing the mechanochromism of chiral photonic elastomers and optically responsive molecules. Specifically, the reflectance or emission of the dyes/fluorophores could be selectively reflected or transmitted by the elastomers with desired photonic bandgaps, leading to data displays of given color/fluorescence. Mechanically stretching the elastomers can readily tuning their photonic bandgaps over a wide range, thereby notably alternating the corresponding reflection and emission wavelength, and the outcome of displayed data. Relaxing the elastomers rapidly restores the initial data. Moreover, the displayed data varies notably under L- and R-circular polarizer filter, respectively, offering good programmability and multi-dimensional security features. This work represents a unique data protection approach and enables properties unattainable by conventional mechanochromic fluorophores and elastomers.

A grating-modified broadband D-type photonic crystal fiber polarization filter

In this paper, a D-type grating-modified broadband photonic crystal fiber polarization filter based on surface plasmon resonance is proposed. The asymmetric design of D-type photonic crystal fiber is helpful to achieve single-mode polarization filtering, and grating can increase the coupling between the core mode and the SPP mode and thus increase the constraint loss. From our simulation results, it can be seen that the applicable bandwidth range can easily reach 1 μm. At the communication wavelength of 1750 nm, the calculated constraint losses of x-polarized and y-polarized core modes are 4.2526 dB cm−1 and 1491.8 dB cm−1, respectively, and the crosstalk is up to 1292 dB. The proposed grating-modified of photonic crystal fiber has achieved good filtering effect in the near-infrared band, and even extended to the mid-infrared band.

Pulse buildup dynamics in a self-starting Mamyshev oscillator.

The Mamyshev oscillator (MO) can generate high-performance pulses. However, due to their non-resonant cavities, they usually are not self-starting, and there is almost no effort to reveal the pulse buildup dynamics of the MO. This paper investigates the dynamic of single pulse (SP) and multi-pulse formation in a self-starting MO. It indicated that both SP self-starting and multi-pulse self-starting can be obtained by adjusting the oscillator parameters. More importantly, increasing pump power could only result in bound state pulses (BSPs) if SP self-starting was formed. With the increase of the pump power, the pulse number in BSPs would increase. However, multiple pulses could not be formed only by increasing the pump power, and the BSPs obtained here underwent SP generated from noise, amplified, and then bounded, which is different from conventional passive mode-locked fiber lasers (CPMLFLs). On the other hand, if multiple pulses were self-initiated, BSPs, pulse bunch, and harmonic mode-locked pulses (HMLPs) could be obtained by adjusting the polarization state and pump power in the cavity. Furthermore, once any of the above states are formed, if the oscillator polarization state and filter interval are unchanged, only increasing the pump power from zero, the original state can still be obtained, which is consistent with the characteristics of the CPMLFLs. These findings will provide new insights into the pulse dynamics of self-starting MO, which will be significant for studying ultrafast laser technology and nonlinear optics.

Single-double-band switchable optical circular polarizers based on surface plasmon resonance.

A single-double-band switchable circular polarization filter based on surface plasmon resonance exhibits significant potential for applications in fields such as communication and sensing due to its adjustable, low-cost, and easy integration features. In this study, we propose a bi-layer rod nanostructure and use FEM simulation to study the transmission spectra of the structure. The results demonstrate that the structure exhibits both single- and double-band circular polarization filtering effects, which can be switched by varying geometric parameters such as the distance between the two layers and the width of nanorods. Furthermore, the filtering effects of both single- and double-band are highly dependent on the length of the nanorods, with average extinction rates reaching 486 and 2020/129, respectively; the operating bandwidths (defined as extinction ratio >10) can reach 170nm and 35nm/70nm, respectively. The underlying physical mechanisms are clarified by analyzing the electric dipole, magnetic dipole resonance modes, and induced chiral fields on nanostructures.

Dual-Side Polished Surface Plasmon Resonance–Based Photonic Crystal Fiber for Refractive Index Sensing and Polarization Filtering

Dual-Side Polished Surface Plasmon Resonance–Based Photonic Crystal Fiber for Refractive Index Sensing and Polarization Filtering

Rapid detection of per- and polyfluoroalkyl substances (PFAS) using paper spray-based mass spectrometry

Traditional PFAS analysis by mass spectrometry (MS) is time-consuming, as laborious sample preparation (e.g., extraction and desalting) is necessary. Herein, we report fast detection of PFAS by paper spray (PS)-based MS techniques, which employs a triangular-shaped filter paper for sample loading and ionization (≤ 3 min per sample). In this study, PS-MS was first used for direct PFAS analysis of drinking water, tap water, and wastewater. Interestingly, food package paper materials can be directly cut and examined with PS-MS for possible PFAS contamination. For samples containing salt matrices which would suppress PFAS ion signal, desalting paper spray mass spectrometry (DPS-MS), was shown to be capable of rapidly desalting, ionizing and detecting PFAS species such as per-fluorooctanoic acid (PFOA) and per-fluorosulphonic acid (PFOS). The retention of PFAS on paper substrate while salts being washed away by water is likely due to hydrophilic interaction between the PFAS polar head (e.g., carboxylic acid, sulfonic acid) with the polar filter paper cellulose surface. The DPS-MS method is highly sensitive (limits of detection:1.2–4.5 ppt) and can be applicable for directly analyzing soil extract and soil samples. These results suggest the high potential of PS-MS and the related DPS-MS technique in real-world environmental analysis of PFAS.

Influence of a gray background and the illuminant on tooth shade selection

Statement of problemVisual shade selection in dentistry may be influenced by factors that include the background color and the illuminant. PurposeThe purpose of this clinical study was to evaluate the influence of using a gray background and a light-correcting device on visual shade selection. Material and methodsTwo experienced clinicians assessed the incisor color of 30 volunteers using the VITA 3D-MASTER shade guide. Visual analyses were carried out using or not (control) a gray background, with and without (control) a light-correcting device (Smile Lite). Furthermore, the use of a polarizing filter was evaluated. Data from a clinical spectrophotometer were defined as the standard instrumental analysis. The agreement and the similarity (based on the whitening indexes of tabs) were evaluated between instrumental and visual analyses. Statistical testing was conducted through ordinal logistic regression and repeated-measures ANOVA. The Shapiro-Wilk test was used to confirm the data distribution, and homogeneity of variance was assessed with the Levene test (α=.05) ResultsThe use of Smile Lite resulted in lighter tabs than indicated by the instrumental analysis, and the opposite was observed in its absence. The polarizing filter did not affect the results (P>.05). For similarity, the illuminant improved the results (P<.001). The gray background reduced the differences between visual and instrumental analysis only in the absence of the Smile Lite (P<.001). ConclusionsThe color similarity between visual and instrumental analysis improved with the use of a light-correcting device with or without a polarization filter. A gray background was useful only without the light-correcting device. CLINICAL IMPLICATIONSUsing a light-correcting device improved the reliability of visual shade selection with no beneficial effect by adding a polarizing filter. In addition, the use of a gray background can be useful only in the absence of a light-correcting device.

Development of microstrip reflectors antenna arrays for focus and polarization filtering on microwave

Focusing microwave systems design is considered. All researching antennas are manufactured as microstrip reflectarrays. Results numerical and experimental researches are given. The printed polarizing filter of a ship radar antenna is developed and experimentally tested. It is shown, that the proposed filter has the improved characteristics.

Random pinhole attenuator for high-power laser beams

Abstract The intensity attenuation of a high-power laser is a frequent task in the measurements of optical science. Laser intensity can be attenuated by inserting an optical element, such as a partial reflector, polarizer or absorption filter. These devices are, however, not always easily applicable, especially in the case of ultra-high-power lasers, because they can alter the characteristics of a laser beam or become easily damaged. In this study, we demonstrated that the intensity of a laser beam could be effectively attenuated using a random pinhole attenuator (RPA), a device with randomly distributed pinholes, without changing the beam properties. With this device, a multi-PW laser beam was successfully attenuated and the focused beam profile was measured without any alterations of its characteristics. In addition, it was confirmed that the temporal profile of a laser pulse, including the spectral phase, was preserved. Consequently, the RPA possesses significant potential for a wide range of applications.

Reverse-designed photonic crystal fiber-based polarization filter with optimal performance

Reverse-designed photonic crystal fiber-based polarization filter with optimal performance