Real-time Polarization Research Articles

Analysis and Correction of Polarization Response Calibration Error of Limb Atmosphere Ultraviolet Hyperspectral Detector.

A UV hyperspectral instrument was designed with a polarization measurement channel for real-time in-orbit polarization correction to reduce the influence of polarization on the detection accuracy of atmospheric radiation. One of the prerequisites for in-orbit polarization calibration is accurately calibrating the instrument's polarization properties in the laboratory. This study first introduces the calibration method and measuring device of the polarization characteristics of the ultraviolet (UV) hyperspectral detector and conducts a polarization calibration test of the instrument. The two main error sources introduced by the calibration device were emphatically analyzed, and the correction method of the error sources was deduced theoretically. Finally, the polarization calibration results of the UV hyperspectral detector were corrected, and the uncertainty analysis of the corrected calibration results was about 1.4%, which provides effective ground polarization calibration data for the on-orbit polarization correction of the instrument.

Robustness enhancement of dynamic spectroscopic ellipsometry by compensating temperature dependency of the monolithic polarizing interferometer.

This paper describes a robust dynamic spectroscopic ellipsometer that can provide a highly accurate and reliable real-time spectroscopic polarization measurement capability for various in-line nanoscale measurement applications. The robustness of dynamic spectroscopic ellipsometry is enhanced significantly by employing a compensation channel that removes the temperature dependency of the monolithic polarizing interferometric module, and it results in highly accurate dynamic spectral ellipsometric measurements. We present how the monolithic interferometer is affected by external disturbances and show experimentally that the proposed scheme can provide a few hundreds of times long-term stability enhancement compared with a single-channel-based dynamic spectroscopic ellipsometer scheme.

Multiple quasi-perfect vector vortex beams with arbitrary 3D position on focus.

We show a method for creating multiple independent quasi-perfect vector vortex beams with real-time programmable radii, topological charges, polarization orders, and position in three dimensions using a device based on a phase-only liquid-crystal-on-silicon display. We achieved the simultaneous generation of up to seven independent beams, with topological charges from -3 to 3, and found great agreement between the simulated and the measured phases and polarization structures. Additionally, we used the same scheme for enhancing the depth of focus of a single beam, resulting in a "tube" beam that preserves its properties during propagation.

Polarization-selective absorptive and transmissive metamaterials.

A polarization sorting metamaterial with polarization filtering and absorption is proposed. When unpolarized incident light strikes the metamaterial, one polarization component is completely absorbed, and the other polarization component is completely transmitted. We achieved an absorption extinction ratio of up to 350 and a transmission extinction ratio of 425 simultaneously in the LWIR. Unlike the 50% energy utilization limit of other polarization absorbers due to the complete reflection of another polarization component, our proposed metamaterial can be composed of layered polarization selective absorption devices to achieve more than 90% energy utilization. Therefore our design can provide a new solution for real-time polarization detection.

Integrated Real-Time Polarization Image Sensor Based on UV-NIL and Calibration Method

Polarization image could reveal detailed information that is submerged in conventional intensity images. In order to obtain the polarization image of the target immediately, an integrated polarization sensor with real-time processing capability was constructed. The integrated polarization sensor composed of polarization-dependent module and processing unit. For modulate intensity, a kind of fabrication process based on ultraviolet nanoimprint lithography (UV-NIL) was proposed to integrate micro-polarizer arrays on packaged CMOS sensor. FPGA was used as processing unit to demodulate, reconstruct and display polarization image in real time. Considering the actual fabrication process, a calibration method based on discrete Fourier transform and relative entropy was proposed to improve the reliability of the sensor. The proposed calibration model has well versatility on various polarization devices. This article provided a cost-effective and compatible integration process for polarization image sensors.

Strategy to Achieve Augmented Photoelectrochemical Water Oxidation via Heteroband Structure Engineering and In Situ Interface Activation.

A simple strategy to achieve remarkable activity of photoelectrochemical (PEC) water oxidation is both a critical requirement prior to accelerating the deployment of hydrogen and an important pursuit for renewable solar energy utilization. Despite various ways to improve the PEC performance, laborious fabrication and a statically driven process for water oxidation are still the most challenging tasks. We, herein, demonstrated an extremely simple but extraordinary effective strategy to boost PEC water splitting in a three-dimensional (3D) network structure (Ni foam, i.e., NF)-supported ZnO nanowire (NW)/CdS nanoparticle (NP) (NF/ZnO/CdS) photoelectrode. On the one hand, the establishment and optimization of a heteroband junction between ZnO NWs and CdS NPs substantially reduce the solar energy loss and increase the photocarrier utilization rate at the interface of two phases. On the other hand, the solution flow rotation in the unique macroporous 3D network structure gives rise to obvious piezoelectric (PE) polarization of ZnO located on the skeleton of Ni foam, which can dynamically enforce directional charge transfer. This real-time self-built PE polarization, assisted by the heteroband junction, enables the NF/ZnO/CdS photoanode system to obtain an improved photocurrent density by 12.2-fold compared with pure ZnO (at 1.23 V vs RHE). This work sheds light on an ingenious design strategy for fabricating photoelectrodes that combines a simplified structure and an effectively enhanced water oxidation performance.

Algorithms for calculating polarization direction based on spatial modulation of vector optical field

Polarization is an important property of electromagnetic waves, and measuring their polarization properties fast and precisely is a very important issue in many applications, such as skylight polarization navigation, optical activity measurement, imaging polarimetry, spectroscopic ellipsometry, and fluorescence polarization immunoassay . The polarization measurement method based on vector optical field modulation and image processing is a new type of spatial modulation polarization detection technology. The key step of this technique moving to practical application is determined by effective polarization measuring algorithms with high speed and accuracy. In order to find out the method of fast and precisely calculating polarization direction, the principle of polarization direction measurement based on vector optical field and spatial modulation is introduced briefly, and the basic characteristics of the spatially modulated intensity distribution images are analyzed. According to the properties of spatially modulated image, we propose and implement four different polarization direction calculation methods, which are the Radon transform, intensity modulation curve detection, radial integration, and image correlation detection, and also introduce their working principles and physical thoughts elaborately. To compare the detailed performances of these four algorithms, an experimental setup is constructed to collect the images and perform the algorithm verification, and the stabilities, speeds and accuracies of the four algorithms are compared. The research results indicate that all the four methods can achieve their stable and reliable polarization direction detections. The three methods, intensity modulation curve detection, radial integration and image correlation detection, can achieve the polarization direction measuring accuracy better than 0.01° . The intensity modulation curve detection and radial integration have relatively fast calculation speed and the best comprehensive performances , and are the most promising methods to realize real-time and high-precision polarization measurement.

Research on Algorithms for Calculating Polarization Direction Based on Spatial Modulation of Vector Optical Field

Polarization is an important property of electromagnetic waves, and measuring their polarization properties fast and precisely is a very important issue in many applications, such as skylight polarization navigation, optical activity measurement, imaging polarimetry, spectroscopic ellipsometry, fluorescence polarization immunoassay and so on. The polarization measurement method based on vector optical field modulation and image processing is a new type of spatial modulation polarization detection technology. The key step of this technique moving to practical application is determined by the effective polarization measuring algorithms with high speed and accuracy. In order to find out the fast and high precision polarization direction calculation methods, the principle of polarization direction measurement based on vector optical field and spatial modulation is introduced briefly, and the basic characteristics of the spatially modulated intensity distribution images are analyzed. According to the properties of spatially modulated image, we have designed and implemented four different polarization direction calculation methods, which are the Radon transform, intensity modulation curve detection, radial integration and image correlation detection, and their working principles and physical thoughts are introduced elaborately. To compare the detailed performance of these four algorithms, an experimental setup has been constructed to collect the images and perform the algorithm verification, and the stability, speed and accuracy of the four algorithms are compared respectively. The research results indicate that all the four methods can achieve stable and reliable polarization direction detection. The three methods of intensity modulation curve detection, radial integration and image correlation detection, can obtain the measurement accuracy of polarization direction better than 0.01 degrees. The intensity modulation curve detection and radial integration own the fast calculation speed relatively, and their overall performances are the best, and they are the most promising methods for realizing real-time and high-precision polarization measurement.

Polarization-based research on a priori defogging of dark channel

The image enhancement method based on dark channel priori defogging performs well in target detection, but it takes the light intensity information as the carrier and the single optical dimension leads the target characterization efficiency to decline. Based on the sensitivity of polarization to physical properties, in this paper a proposal is made that polarization information is introduced into the traditional dark channel priori defogging method to enhance the recognition degree between different objects. The theory of backscattering and polarization detection in dark channel priori defogging method is studied, and the mechanical polarization filtering imaging equipment is built to verify the target characterization function of the proposed method in foggy environment. The research shows that the dark channel priori defogging method based on polarization can obtain the light intensity and polarization information of the object at the same time. Compared with the traditional dark channel priori defogging method, using the polarization difference between the target and the background can significantly improve their contrast. This research result can be applied to the existing polarization imaging instrument system to realize real-time backscattering and polarization information extraction, and further improve the efficiency of target detection and characterization in fog.

Real-Time Polarization Measurement Based on Spatially Modulated Polarimeter and Deep Learning

Real-Time Polarization Measurement Based on Spatially Modulated Polarimeter and Deep Learning

Real-time polarization compensation system for wavelength division multiplexing in low noise fiber channel based on single photon counting feedback

The physical effects such as random birefringence of fiber optic channels due to environmental influences make the optical signals transmitted in them have sensitive polarization variations, which seriously affects the performance of polarization biased code quantum key distribution systems. In this paper, a low-noise fiber channel wavelength division multiplexing real-time polarization compensation system is presented, where single photon counting is used as a feedback signal. The system can acquire the fiber channel polarization change information by detecting the photon counting of the conjugate reference light. In the system, the compensation algorithm is designed to control the electric polarization controller to calibrate the polarization state of the quantum signal light under the corresponding polarization base in real time, and the stable fiber channel polarization compensation is successfully achieved. In order to verify the effectiveness of the compensation system, a quantum key distribution test based on BB84 protocol with a transmission distance of 25.2 km is conducted, and stable test results of up to 8 hours are obtained in the laboratory environment and the simulated metropolitan area network buried fiber environment, with the average quantum bit error rate being 0.52% and 1.25%, respectively. The experimental results show that this system can guarantee the stable operation of polarization-encoded quantum key distribution in the buried fiber environment in urban areas.

4-domain twisted liquid crystal micropolarizer array for visible linear polarization imaging

In this paper, a 4-domain twisted liquid crystal micropolarizer (twisted-LCMP) array was designed and fabricated enabling linear polarization imaging in the visible band. It contains a pixelized twisted-LC layer and a polarizer. The optimized twist angles were designed as ±22.5° and ±67.5° for best extinction ratio. A large birefringence LC material was used to fulfill the Mauguin condition in a wider visible band. Using a digital micromirror device (DMD) lithography system, the twisted-LCMP array was fabricated precisely using the photoalignment technique. It exhibited excellent optical performance, which could meet the requirements for polarization imaging. The measurement error for degree of linear polarization (DoLP) and angle of polarization (AoP) were less than 1.15% and 0.65°. The proposed twisted-LCMP array has great potential to be integrated directly into a camera for real-time linear polarization imaging.

Real-time polarization microscopy of fibrillar collagen in histopathology

Over the past two decades, fibrillar collagen reorganization parameters such as the amount of collagen deposition, fiber angle and alignment have been widely explored in numerous studies. These parameters are now widely accepted as stromal biomarkers and linked to disease progression and survival time in several cancer types. Despite all these advances, there has not been a significant effort to make it possible for clinicians to explore these biomarkers without adding steps to the clinical workflow or by requiring high-cost imaging systems. In this paper, we evaluate previously described polychromatic polarization microscope (PPM) to visualize collagen fibers with an optically generated color representation of fiber orientation and alignment when inspecting the sample by a regular microscope with minor modifications. This system does not require stained slides, but is compatible with histological stains such as H&E. Consequently, it can be easily accommodated as part of regular pathology review of tissue slides, while providing clinically useful insight into stromal composition.

Research on a real-time polarization compensation method for dynamic quantum communication terminals

In the experiment of quantum key distribution in free space, the polarization degradation and the propagation directions of the four polarization-encoded quantum light beams vary relative to each other and reduce the service life of the terminals, which severely limits their practical application. In order to solve the above problems, we report research on real-time polarization compensation methods for dynamic quantum communication terminals. The difference from Micius is that our proposed system emits quantum lights through the same optical fiber to ensure high-precision coaxiality, and uses a set of wave plates to compensate for both the polarization degradation caused by single-mode fiber and the polarization change caused by optical elements. We introduce our polarization compensation methods in detail and present a design for a dynamic polarization compensation scheme and experimental device. The final experimental polarization extinction ratio of our dynamic optical system is greater than 30 dB after real-time polarization compensation, which meets quantum communication requirements. The successful implementation of this method can effectively improve terminal service life and provide a foundation for the practical applications of quantum communication.

Adaptive linear reconstruction with regularizer for channeled spectropolarimeter

A channeled spectropolarimeter (CSP) measures spectrally resolved Stokes parameters from a snapshot. However, the reconstruction of Stokes parameters may suffer from noise and systemic errors, lowering the measurement accuracy. To accurately reconstruct Stokes parameters from the experimental data with random noise and residual systematic errors after calibration, we propose an adaptive linear reconstruction with regularizer (ALRR) for CSP. By modeling an l1-norm optimization problem with a 1-norm regularizer consisting of coefficients from the Legendre polynomials basis, together with an adaptive residual threshold considering the systematic errors and noise, Stokes parameters are reconstructed accurately in the presence of noise and systemic errors. Simulation results demonstrate the efficiency and noise-robustness of ALRR with a signal-to-noise ratio of 12 dB, while its self-adaption and accuracy are validated experimentally with a root-mean-square error of < 0.04. The proposed method can have important potential in real-time polarization measurement and processing for modulated polarimeters (i.e., Stokes CSP and Mueller CSP).

Real-time polarization imaging integrated technology for solid-state low-light imaging

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed

Recent Progress on Ultrathin Metalenses for Flat Optics.

SummaryAs technology advances, electrical devices such as smartphones have become more and more compact, leading to a demand for the continuous miniaturization of optical components. Metalenses, ultrathin flat optical elements composed of metasurfaces consisting of arrays of subwavelength optical antennas, provide a method of meeting those requirements. Moreover, metalenses have many other distinctive advantages including aberration correction, active tunability, and semi-transparency, compared to their conventional refractive and diffractive counterparts. Therefore, over the last decade, great effort has been focused on developing metalenses to investigate and broaden the capabilities of metalenses for integration into future applications. Here, we discuss recent progress on metalenses including their basic design principles and notable characteristics such as aberration correction, tunability, and multifunctionality.

CONSTRUCTION AND TEST OF BIO-INSPIRED IMAGING POLARIZATION NAVIGATION PROTOTYPE

Abstract. Bio-inspired polarization navigation is a promising navigation method inspired by insects’ autonomous foraging and homing behaviour. Many insects acquire their spatial orientation by sensing the polarization pattern of the skylight. We propose utilization of solar meridian in the polarized skylight as an orientation cue because of its significant features. Using its features, we then design and construct an imaging polarization navigation prototype. The prototype consists of a field-division polarization imaging sensor, the corresponding software, an interface, and the solar-meridian recognizing and measurement algorithm. The field-division polarization imaging sensor is the core component of the prototype and acquires polarized intensity images. To adapt to the demand of real-time on navigation system, we then propose an optimized real-time polarization image processing and pattern recognition algorithm based on Hough transform. The azimuth measurement accuracy of the sensor is then calibrated using a facility that is able to get higher azimuth accuracy by measurement of the star light. To verify the navigation capability of the developed system, we use a dynamic experiment, where the prototype is installed on the top of a vehicle and its navigation performance is compared with GNSS.

Reconstructing Stokes parameters from non-uniform division-of-focal-plane modulation

Division-of-focal-plane modulation is a powerful technique for real-time polarization imaging. This technique, however, suffers from the non-uniformity of the performance of linear polarization filters and photodetectors. We study the Stokes parameters reconstruction from the division-of-focal-plane modulation in the presence of the non-uniformity. Two reconstruction methods, named as ordinary least-squares and smoothing regularization methods, are proposed. The performance of the proposed methods are evaluated through Fourier analysis, numerical simulations, and experiments. The results indicate that the proposed methods can effectively mitigate the reconstruction errors and artifacts caused by the non-uniformity, and therefore may further facilitate the practical application of the division-of-focal-plane technique.

280-km experimental demonstration of a quantum digital signature with one decoy state.

A quantum digital signature (QDS) guarantees the unforgeability, nonrepudiation, and transferability of signature messages with information-theoretic security, and hence has attracted much attention recently. However, most previous implementations of QDS showed relatively low signature rates and/or short transmission distance. In this Letter, we report a proof-of-principle phase-encoding QDS demonstration using only one decoy state. First, such a method avoids the modulation of the vacuum state, thus reducing experimental complexity and random number consumption. Moreover, incorporated with low-loss asymmetric Mach-Zehnder interferometers and a real-time polarization calibration technique, we have successfully achieved a higher signature rate, e.g., 0.98 bit/s at 103 km, and to date, a record-breaking, to the best of our knowledge, transmission distance of over 280-km installed fibers. Our work represents a significant step towards real-world applications of QDS.