Polarization Filter Research Articles

Comparison of High-Speed Polarization Imaging Methods for Biological Tissues.

We applied a polarization filter array and high-speed camera to the imaging of biological tissues during large, dynamic deformations at 7000 frames per second. The results are compared to previous measurements of similar specimens using a rotating polarizer imaging system. The polarization filter eliminates motion blur and temporal bias from the reconstructed collagen fiber alignment angle and retardation images. The polarization imaging configuration dose pose additional challenges due to the need for calibration of the polarization filter array for a given sample in the same lighting conditions as during the measurement.

54.1: Invited Paper: Highly efficient Quantum Rods LEDs for LCD backlights

Efficient white LEDs with efficacy of > 200 lm/W are much desirable for lighting and displays. LCDs is the market leader with an approximate 70% market share, particularly in the medium‐ to large‐size display segment. The largest portion of power consumption for LCDs belongs to LCD backlight, accounting for 70%–80% of the total power consumption, which strongly depends on the content and resolution of display panels. [1–8] The polarizer and color filters are the two main components responsible for high‐power consumption. Although the phosphor‐based LED backlights are much more efficient than the CCFL backlight, the efficiency of display backlight LEDs varies in the range of 70–85 lm/W. A large portion of the phosphor‐based LED light is lost in color filters [1–5]. The LED efficacy further decreases at the high brightness required for outdoor applications [4]. Intensive efforts have been made to replace the phosphor with quantum dots‐based downconverters, but the efficiency and stability of these devices are still in their infancy. Quantum rods (QRs), the elongated shape nanoparticles, show superior properties such as relatively larger Stokes shifts, polarized emission, and high light out‐coupling efficiency in the solid‐state. The challenges are as follows: 1. high quantum yield of QRs in the thin solid films covering the whole visible range; 2. good in‐plane alignment of the QRs on the LEDs; and 3. high photo‐stability and low‐temperature quenching. In this talk, we will try to discuss all these challenges. We will also discuss the merits of gradient alloyed CdSe/ZnXCd1‐XS/ZnS and CdSe/CdS/ZnS core/shell/shell QRs downconverters showing high efficacy LEDs covering a wide color gamut. These QRs‐based LEDs attain the luminous efficacy (LE) of 149 lm/W (@10mA), wide color gamut (118% NTSC), which is exceedingly higher than the state‐of‐the‐art quantum dot and phosphor‐based on‐chip LED, which paves the way for the future display backlight with the efficacy of > 200 lm/W.

Fast data-driven computation and intuitive visualization of fiber orientation uncertainty in 3D-polarized light imaging

In recent years, the microscopy technology referred to as Polarized Light Imaging (3D-PLI) has successfully been established to study the brain’s nerve fiber architecture at the micrometer scale. The myelinated axons of the nervous tissue introduce optical birefringence that can be used to contrast nerve fibers and their tracts from each other. Beyond the generation of contrast, 3D-PLI renders the estimation of local fiber orientations possible. To do so, unstained histological brain sections of 70 μm thickness cut at a cryo-microtome were scanned in a polarimetric setup using rotating polarizing filter elements while keeping the sample unmoved. To address the fundamental question of brain connectivity, i. e., revealing the detailed organizational principles of the brain’s intricate neural networks, the tracing of fiber structures across volumes has to be performed at the microscale. This requires a sound basis for describing the in-plane and out-of-plane orientations of each potential fiber (axis) in each voxel, including information about the confidence level (uncertainty) of the orientation estimates. By this means, complex fiber constellations, e. g., at the white matter to gray matter transition zones or brain regions with low myelination (i. e., low birefringence signal), as can be found in the cerebral cortex, become quantifiable in a reliable manner. Unfortunately, this uncertainty information comes with the high computational price of their underlying Monte-Carlo sampling methods and the lack of a proper visualization. In the presented work, we propose a supervised machine learning approach to estimate the uncertainty of the inferred model parameters. It is shown that the parameter uncertainties strongly correlate with simple, physically explainable features derived from the signal strength. After fitting these correlations using a small sub-sample of the data, the uncertainties can be predicted for the remaining data set with high precision. This reduces the required computation time by more than two orders of magnitude. Additionally, a new visualization of the derived three-dimensional nerve fiber information, including the orientation uncertainty based on ellipsoids, is introduced. This technique makes the derived orientation uncertainty information visually interpretable.

Polarization Image Laser Line Extraction Methods for Reflective Metal Surfaces

In this work, we propose a novel pipeline method for laser line extraction from images with a polarization image sensor. The proposed method is specifically developed for strong laser beam reflections from metal surfaces. For the preprocessing stage, we propose a demosaicing algorithm for color polarizer filter array (CPFA) sensors. This can be implemented by using either one-quarter or full resolution of the sensor. In addition, we propose two methods for optimizing the information available in a 12-channel color polarization image. The first method is based on the minimum linearly polarized irradiance, and the second method is based on the linear polarization intensity. These preprocessing and optimization methods are combined with laser line extraction methods. The laser line extraction is done with either the polarized finite impulse response (FIR) center of gravity (COG), where the laser line coordinates are computed from the filtered laser intensity distribution, or with the polarized FIR-Peak, where the laser line coordinates are calculated from the first derivative of the filtered laser signal. The performance of the proposed algorithms is studied experimentally using a laser line scanner assembly, made of a polarization camera, and a laser line projector operating in the blue wavelength range.

Specular Reflection Suppression through the Adjustment of Linear Polarization for Tumor Diagnosis Using Fluorescein Sodium.

In tumor surgery, the edges of the tumor can be visually observed using a fluorescent contrast agent and a fluorescent imaging device. By distinguishing it from normal tissues and blood vessels, it is possible to objectively judge the extent of resection while visually observing it during surgery, and it guarantees safe tumor resection based on more information. However, the main problem of such an imaging device is the specular reflection phenomenon. If specular reflection overlaps with important lesion locations, they are a major factor leading to diagnostic errors. Here, we propose a method to reduce specular reflection that occurs during tumor diagnosis using a linear polarization filter and fluorescent contrast agent. To confirm the effect of removing specular reflection, a self-made fluorescein sodium vial phantom was used, and the reliability of the results was increased using a large animal (pig) test. As a result of the experiment, it was possible to obtain an image in which specular reflection was removed by controlling the rotation angle of the filter by 90° and 270°, and the same results were confirmed in the phantom experiment and the animal experiment.

Molecular Orientation‐Induced Polarization Filtering based on Organic Heterostructures

AbstractDemonstration of efficient polarization‐signal filtering induced by molecular orientation in organic heterostructures remains elusive. Herein, an epitaxial growth technology is developed for blue‐emissive horizontal p‐distyrylbenzene (DSB) nanosheet (NS) arrays on 9,10‐dicyanoanthracene (DCA)‐dominated (DCA)1‐x(DSB)x doped nanowire (NW) backbone via a facile stepwise solution‐processed method. It is shown that the DSB NS arrays generate blue amplified spontaneous emission (ASE), whereas the backbone of the (DCA)1‐x(DSB)x displays intense yellow emission. Surprisingly, the blue ASE can effectively propagate in (DCA)1‐x(DSB)x backbone immunity to DCA absorption and realize polarization filtering of output ASE. The mechanism of the orthogonal polarization between blue‐ASE from branches and absorption of DCA molecules in the backbone is responsible for the efficient transport of higher‐energy photons in narrow‐gap emitters. This molecular orientation‐induced polarized‐light transport can serve to control light propagation and function as polarization filter in a single heterostructure. The research provides an interesting example for the exploration of novel all‐optical switch devices in photonic circuits.

Modified Newton-residual interpolation for division of focal plane polarization image demosaicking.

With the improvement of semiconductor processing technology, polarization sensors using division of focal plane have gradually become the mainstream method of polarization imaging. Similar to the color restoration method of the Bayer array sensor, the spatial information of polarized image is also recovered through the polarization demosaicking algorithm. In this paper, we propose a new modified Newton-residual interpolation polarization image demosaicking algorithm based on residual interpolation, which is suitable for a monochrome or color polarization filter array. First, we use the modified Newton interpolation method to generate edge-sensitive guiding images. Then, we carry out the improvement of the guide process during the residual interpolation by performing variance statistics on the local window image in the guiding process, so that the edges and flat image blocks have different guiding weights. Finally, we obtain edge-preserving results by applying these two improvements, which reduces the zipper effect and edge confusion. We compare the results of various algorithms on experimental data, demonstrating that our algorithm has impactful improvements in the evaluation metrics based on the ground-truth images.

Twin-tube terahertz fiber for a polarization filter.

A simple polymer twin-tube terahertz (THz) fiber that can be used as a polarization filter is proposed and investigated using the finite element method in this paper. The twin-tube THz fiber consists of two closely spaced identical tubes located symmetrically inside the protecting jacket. The simulation results show that the y-polarization fundamental mode (YPFM) can be well confined between the two tube walls near the fiber center, while the x-polarization fundamental mode (XPFM) has a huge confinement loss due to the coupling with the tube mode. For the fundamental mode (FM), a polarization extinction ratio (PER) of 30 dB can be realized after a 1.3 cm length of the fiber, and the insertion loss of the YPFM is less than 0.5 dB at 1 THz. In addition, higher order modes (HOMs) can be effectively suppressed by further increasing the fiber length. Simulation results indicate that all HOMs have powers being 30 dB lower than that of the supported YPFM after a 7.44 cm length of the fiber, and the insertion loss of the YPFM is less than 2.7 dB at 1 THz. Furthermore, the effects of fiber structure parameters on the loss properties are investigated, proving that the proposed fiber has a good fabrication tolerance. Owing to the simple structure, the proposed fiber polarization filter is easy to be fabricated and low-cost, which makes it a potential application in commercial THz systems.

Laser Fabrication of Highly Ordered Nanocomposite Subwavelength Gratings.

Optical nanogratings are widely used for different optical, photovoltaic, and sensing devices. However, fabrication methods of highly ordered gratings with the period around optical wavelength range are usually rather expensive and time consuming. In this article, we present high speed single-step approach for fabrication of highly ordered nanocomposite gratings with a period of less than 355 nm. For the purpose, we used commercially available nanosecond-pulsed fiber laser system operating at the wavelength of 355 nm. One-dimensional and two-dimensional nanostructures can be formed by direct laser treatment with different scan speed and intensity. These structures exhibit not only dispersing, but also anisotropic properties. The obtained results open perspectives for easier mass production of polarization splitters and filters, planar optics, and also for security labeling.

Scalable and highly efficient approach for an on-chip single-photon source

Integrated photonic circuits with quantum dots provide a promising route for scalable quantum chips with highly efficient photonic sources. However, unpolarized emission photons in general sacrifice half efficiency when coupling to the waveguide fundamental mode by a cross polarization technique for suppressing the excitation laser, while suspended waveguide photonics sources without polarization filters have poor scalability due to their mechanical fragility. Here, we propose a strategy for overcoming the challenge by coupling an elliptical Bragg resonator with waveguides on a solid-state base, featuring near-unity polarization efficiency and enabling on-chip pulsed resonant excitation without any polarization filters. We theoretically demonstrate that the proposed devices have outstanding performance of a single-photon source with 80% coupling efficiency into on-chip planar waveguides and an ultra-small extinction ratio of 10 − 11 , as well as robustness against quantum dot position deviation. Our design provides a promising method for scalable quantum chips with a filter-free high-efficiency single-photon source.

ПРИМЕНЕНИЕ ПЕЧАТНЫХ ДИФРАКЦИОННЫХ РЕШЕТОК ДЛЯ УПРАВЛЕНИЯ ПОЛЯРИЗАЦИЕЙ ЭЛЕКТРОМАГНИТНЫХ ВОЛН МИКРОВОЛНОВОГО ДИАПАЗОНА

The paper is devoted to consideration of variants of solution to some problems of diffractionfor printed arrays with anisotropic inhomogeneities. The rotation of the plane of polarization isrealized by means of a twist-reflector. On the basis of computational and full-scale experiments itwas shown that twist reflectors based on microstrip reflective type antenna arrays (RAA) can bequite broadband. The obvious advantage of such twist-reflectors is simplicity of the technology oftheir manufacture, small thickness and weight. In addition, in twist-reflectors based on printedRAA, it is possible to constructively realize the necessary phase distributions of the field on theirsurfaces. Thus, it becomes possible to use such twist-reflectors to create phase-correcting twistreflectors.It is shown that introduction of impedance loads in the construction of the re-radiatingelements of the printed RAA opens additional possibilities for controlling the field scattered by it.Thus, twist reflectors with improved characteristics can be realized on the basis of microstrip-pinRAA. The results of numerical studies based on the author algorithms and computational programsare presented. Besides, spatial polarizing filters and a controllable twist-reflectors basedon microstrip RAA are considered. If microstrip elements of a twist-reflector contain controllableloads, then qualitatively new type of the microwave device is formed. This device enables to controlpolarization of the scattered field. Such devices can be named by polarizing modulators ormanipulators. By means of printed RAA with elements of complex topology the spatial polarizers,which can transform electromagnetic waves with linear polarization in waves with rotating polarizationand, in particular, in waves with circular polarization, are realized.

Modified D-type surface plasmon resonance (SPR)-based photonic crystal fiber (PCF) for application as a polarization filter and refractive index sensor

A surface-modified D-type photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) is reported for application as a polarization filter and refractive index sensor. The gold film is deposited on the surface of the designed fiber structure to stimulate the SPR effect. Through etching, the upper surface of the designed structure forms an angle of 170°. The etching angle changes the distance between the fiber core and the surface of gold film to enhance the local field SPR effect. The designed optical device is numerically simulated using the finite element method (FEM), the mode distribution is studied, and the coupling phenomenon is analyzed. At a wavelength of 1.31 µm, the y-polarization loss is 1307.90 dB/cm, while the loss of x-polarization is 1.13 dB/cm; at 1.55 µm, the y-polarization loss is 1755.19 dB/cm, while the x-polarization loss is only 1.24 dB/cm. In the case of the same structure parameters as the proposed polarization filter, of which communication window is 1.55 µm, the designed structure also serves as a refractive index sensor from 1.330 to 1.365. The average sensitivity of the refractive index sensor is up to 4857 nm/RIU, and the highest sensitivity is 7588 nm/RIU when the refractive index is 1.365. The results show that the reported SPR-based PCF simultaneously implements dual communication window polarization filtering and refractive index sensing. Hence, the designed device has promising applications with good filtering and sensing performance.

High Extinction Ratio and Large Bandwidth PCF Polarization Filter With Gold-Wires Coated by Monocrystalline Silicon

A kind of high extinction ratio (ER) and large bandwidth photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance is proposed. The SPP modes can be inspired by two gold-wires to improve the filter characteristics and the effect of surface plasmon resonance is further enhanced by cladding monocrystalline silicon surrounding gold-wires. An asymmetric structure of leakage channel is introduced in y-pol direction axis which intensifies the energy leakage to external cladding, high polarization extinction ratio is occurred. By using the finite element method (FEM), the structural parameters and optical properties are quantitatively analyzed. Numerical analysis shows that two main adjacent resonance peaks appear in y-pol direction, confinement losses of y-pol core mode at the resonance wavelength of 1519 and 1664 nm are 573.33 and 543.21 dB/cm, while the losses of x-pol core mode are 16.97 and 0.98 dB/cm. When the fiber length L=3 mm, the maximum ER reaches 1449 dB at the wavelength of 1519 nm, and the bandwidth with ER better than 20 dB reaches 405 nm. Hence the proposed PCF with gold-wires coated by monocrystalline silicon would have a widely application in optical fiber communication, optical information processing and other fields.

The design of polarization-maintaining and polarization-filtering hollow core with nested anti-resonance nodeless fiber for THz guidance

A polarization-maintaining and polarization-filtering hollow core fiber with nested anti-resonant nodeless tubes for the THz regime is proposed. The model is designed by the finite element method to operate at 1.0 THz using TOPAS copolymer as the fiber material. The proposed structure consists of four outer tubes with one inner tube each in the orthogonal arrangement. The fiber was optimized to obtain the lowest loss by varying the tube thickness. The simulation results show that the thickness of 0.09 mm was suitable for a low loss of 0.2 dB m−1 operating at 1.0 THz. The fiber property of high birefringence @ 1.5 × 10−4 was made by introducing unequal radial distances between the outer and inner tubes of the orthogonal arrangement. In addition, at a particular difference of the radial distance, it was found that the proposed fiber can act as a polarization filter indicating by having a high crosstalk.

Painting in polarization

The array of colors and patterns seen when birefringent materials are inserted between polarizers is a source of amusement, popular science demonstrations, and art. This phenomenon of polarization-filtered coloration is commonly but misleadingly referred to as “interference colors,” despite not arising from the effects of interference. In this work, I clarify the link between polarization filtering and the observed colors and demonstrate how various aspects of birefringence in common household films provide opportunities and challenges for their use in art.

METHOD FOR SPATIAL POLARIZATION COMPENSATION OF JAMMING

Context. To protect radars from active noise interference (jamming) acting along the side lobes of the antenna pattern, spatial signal filtering is used, which is realized by using diversity reception of the useful signal and interference. In this case, the difference in the directions of interference and signal makes it possible to compensate for interference and detect a useful signal. However, in the case where the source of interference is in the main lobe, the differences between the desired signal and the interference are reduced. This leads to significant distortion of the antenna main lobe pattern. As a result, the accuracy of angular coordinates measurement deteriorates, as well as the sensitivity of the receiving radar device. The article proposes a new method for spatial polarization processing of radar signals, which provides compensation for active noise interference both as from the directions of the side lobes and from the direction of the main beam of the antenna pattern. Objective. The goal is to develop a method for spatial polarization processing of radar signals under the influence of active noise interference both along the side lobes of the antenna pattern and along the main lobe. Method. The method is implemented by using structural adaptation of the noise protection device, depending on the direction of the interference. In this case, the control signal for structural adaptation is formed according to the magnitude of the current spatial filter weighting coefficient value. Results. A block diagram of a spatial polarizing filter which provides compensation for active noise interference acting both on the side lobes and on the main lobe of the radar antenna pattern. The mathematical model of the compensation unit that implements the structural adaptation of the spatial polarization filter has been developed. Under the conditions of the first special polarization basis, the efficiency of noise suppression acting along the main lobe of the antenna pattern is estimated. Conclusions. The scientific novelty of the research is the development of a new method of spatial polarization processing of radar signals under difficult conditions of radar operation under massive active noise interference. The practical significance of the research is in the development of a block diagram of a spatial polarizing filter that provides compensation for interference both from the direction of the side lobes and from the direction of the main lobe of the antenna pattern. The mathematical model of the filter has been developed. The efficiency of noise suppression under the conditions of the first special polarization basis is estimated.

Dark stereo

It is often desirable or unavoidable to display Virtual Reality (VR) or stereoscopic content at low brightness. For example, a dimmer display reduces the flicker artefacts that are introduced by low-persistence VR headsets. It also saves power, prolongs battery life, and reduces the cost of a display or projection system. Additionally, stereo movies are usually displayed at relatively low luminance due to polarization filters or other optical elements necessary to separate two views. However, the binocular depth cues become less reliable at low luminance. In this paper, we propose a model of stereo constancy that predicts the precision of binocular depth cues for a given contrast and luminance. We use the model to design a novel contrast enhancement algorithm that compensates for the deteriorated depth perception to deliver good-quality stereoscopic images even for displays of very low brightness.

Fabrication of a reflective polarization wavelength filter via anodization of a Ti grating film.

A reflective-type polarization wavelength filter was fabricated by anodizing a Ti grating film. This polarization filter consisted of a Ti film, an anodized titanium oxide film (thickness ∼25nm), and a photoresist grating with a pitch of 410 nm. The reflectance was less than 10% for both polarizations at 490-675 nm at an incident angle of 9°. In addition, the transverse electric (TE) reflectance of the fabricated element was over 40%, whereas the transverse magnetic (TM) reflectance was 25.8% at 375 nm. Upon increasing the incident angle to 75°, the TE reflectance increased to 77.8% at 375 nm, whereas the TM reflectance decreased to 5.9%.

Dual‐interference filtering method for the main lobe based on polarimetric monopulse radar

In the field of target tracking, monopulse radar is widely used to obtain the positions of radar targets. The achieved angle measurement performance is greatly weakened when barrage interference is contained in the main lobe of the receiving antenna. Interference signals can be easily filtered by the conventional polarization filtering (PF) method. However, the conventional PF method is unable to address situations in which two barrage interferences with different polarization states are contained in the main lobe, because the polarizations of both interferences become complex. To filter dual-interference sources in the main lobe, a novel polarimetric filtering method is proposed in this letter. This novel method is based on polarization selection, which is implemented to suppress one of the dual-interference sources. The appropriate polarimetric parameters are first selected by a monopulse ratio constraint condition. Then, the spatial location of the other interference source can be measured. After searching the whole polarimetric domain, the spatial parameters of the two interference sources can be acquired by the polarimetric monopulse system. Finally, the waveforms of the interference signals can also be estimated during the filtering process. The results of a microwave chamber experiment demonstrate that this novel filtering method is effective.

A Reconfigurable Surface-Plasmon-Based Filter/Sensor Using D-Shaped Photonic Crystal Fiber.

A reconfigurable surface-plasmon-based filter/sensor using D-shaped photonic crystal fiber is proposed. Initially a D-shaped PCF is designed and optimized to realize the highly birefringence and by ensuring the single polarization filter. A tiny layer of silver is placed on the flat surface of the D-shaped fiber with a small half-circular opening to activate the plasmon modes. By the surface plasmon effect a maximum confinement loss of about 713 dB/cm is realized at the operating wavelength of 1.98 µm in X-polarized mode. At this wavelength the proposed fiber only allows Y-polarization and filters the X-polarization using surface plasmon resonance. It is also exhibiting maximum confinement loss of about 426 dB/cm at wavelength 1.92 µm wavelength for Y-polarization. At this 1.92 µm wavelength the proposed structure attenuated the Y-polarization completely and allowed X-polarization alone. The proposed PCF polarization filter can be extended as a sensor by adding an analyte outside this filter structure. The proposed sensor can detect even a small refractive index (RI) variation of analytes ranging from 1.34–1.37. This sensor provides the maximum sensitivity of about 5000 nm/RIU; it enables this sensor to be ideally suited for various biosensing and industrial applications.