Polarization Camera Research Articles

Quantitative magnetooptical analysis using indicator films for the detection of magnetic field distributions, temperature, and electrical currents

The accurate characterization of local magnetic fields and temperature is vital for the design of electronic systems. To meet this imperative, we present a novel non-contact approach for simultaneous quantitative magnetic field imaging and temperature sensing using magnetooptics and a bismuth-doped yttrium iron garnet film with out-of-plane anisotropy. For the direct signal quantification, a Stokes polarization camera is employed in a conventional magnetooptical microscope. The magnetization in the garnet is modulated with an external magnetic field to continuously image the Faraday rotation at four distinct points along the saturating magnetization loop. The method enables sensing of the magnetooptical signal in saturation, the magnetooptical susceptibility, the temperature, and self-calibrated driftfree imaging of the out-of-plane magnetic field component. A spatial resolution of magnetic field in the micrometer range with millisecond exposure time is demonstrated. The method is verified by analyzing the stray magnetic field distribution of electrical current in a wire simultaneously to the Joule heating induced by the applied current.

Single-Shot Fringe Projection Profilometry Based on LC-SLM Modulation and Polarization Multiplexing

Fringe projection profilometry (FPP) is extensively utilized for the 3D measurement of various specimens. However, traditional FPP typically requires at least three phase-shifted fringe patterns to achieve a high-quality phase map. In this study, we introduce a single-shot FPP method based on common path polarization interferometry. In our method, the projected fringe pattern is created through the interference of two orthogonal circularly polarized light beams modulated by a liquid crystal spatial light modulator (LC-SLM). A polarization camera is employed to capture the reflected fringe pattern, enabling the simultaneous acquisition of four-step phase-shifting fringe patterns. The system benefits from advanced anti-vibration capabilities attributable to the common path self-interference optical path design. Furthermore, the utilization of a low-coherence LED light source results in reduced noise levels compared to a laser light source. The experimental results demonstrate that our proposed method can yield 3D measurement outcomes with high accuracy and efficiency.

Single shot radial constant shearing interferometry with axicon using Polarization camera

Single shot radial constant shearing interferometry with axicon using Polarization camera

Quantitative analysis of human blood glucose by dynamic optical rotation angle of multiple wavelengths based on the polarization camera

Measurement of blood glucose concentration is important in the prevention and treatment of diabetes. To improve the measurement signal-to-noise ratio and accuracy, using a polarization camera as the sensor, this paper proposes a multi-wavelength dynamic optical rotation angle method to quantitatively analyze human blood glucose. First, this paper utilizes a split-time approach to drive nine different wavelengths of light sources to work separately to achieve the collection of multiple different wavelengths of data and increase the amount of information. Second, to capture images with an array sensor such as a camera, using space-for-accuracy, this paper uses the cumulative value of the gray values of all pixel points in the image at each angle as the light intensity value to improve the amplitude (light intensity) resolution. Third, the extraction method of the dynamic optical rotation angle in this paper is to extract the difference between the maximum and minimum values of the optical rotation angle from each cycle of the signal of the continuous cyclic change of the length of the optical path, and the accumulated value of the difference of multiple cycles is recorded as the dynamic optical rotation angle, which not only reduces the errors caused by the individual differences, the external environment and the measuring instrument, but also has the effect of averaging and improves the signal-to-noise ratio of the optical rotation angle. To prove the effectiveness of the proposed methods, human finger real and simulation experiments are carried out, respectively. Firstly, the polarization camera is used to collect the image data of elliptically polarized light of nine different wavelengths of linearly polarized light after passing through the human body’s finger, and obtains the optical rotation angle under each wavelength that changes with the photoplethysmography (PPG) through data processing, and extracts the dynamic optical rotation angles of the nine wavelengths by the extraction method, and the human body’s blood glucose can be quantitatively analyzed. Secondly, this paper builds a simulation model to simulate the blood volume conversion of the human finger, and uses the simulation experimental system to collect the dynamic optical rotation angles of nine wavelengths of a total of 137 human serum samples, and uses partial least squares regression to establish a model between the dynamic optical rotation angles and blood glucose concentration. In the results of predicting all samples using the model, the correlation coefficient and root mean square error were 0.7960 and 2.16 mmol/L, respectively, both of which improved by 137.26 % and decreased by 35.33 %, respectively, compared to the existing method. The experimental results show that the method in this paper has high accuracy in detecting the blood glucose concentration in human beings, which is of great significance in realizing the noninvasive quantitative analysis of human blood glucose components by the polarized light method.

POLCAM: instant molecular orientation microscopy for the life sciences

Current methods for single-molecule orientation localization microscopy (SMOLM) require optical setups and algorithms that can be prohibitively slow and complex, limiting widespread adoption for biological applications. We present POLCAM, a simplified SMOLM method based on polarized detection using a polarization camera, which can be easily implemented on any wide-field fluorescence microscope. To make polarization cameras compatible with single-molecule detection, we developed theory to minimize field-of-view errors, used simulations to optimize experimental design and developed a fast algorithm based on Stokes parameter estimation that can operate over 1,000-fold faster than the state of the art, enabling near-instant determination of molecular anisotropy. To aid in the adoption of POLCAM, we developed open-source image analysis software and a website detailing hardware installation and software use. To illustrate the potential of POLCAM in the life sciences, we applied our method to study α-synuclein fibrils, the actin cytoskeleton of mammalian cells, fibroblast-like cells and the plasma membrane of live human T cells.

A Lightweight, Polarization-Camera Equipped Sensor Rig for the Development of Autonomous Surface Vehicles

Abstract Situational Awareness (SITAW) of Autonomous Surface Vessels (ASV) is critical for safe and efficient maritime operations, enabling these vehicles to understand their environment better and make informed decisions. High-quality data sets from relevant maritime environments are needed to advance the development of SITAW, as it is both the backbone of any learning-based method and the development and validation of classical methods. Research vessels such as the full-scale ferry milliAmpere2 provide such data, but there tends to be a considerable labor cost associated with their operation. With this in mind, we have developed a portable sensor rig that makes collecting sensor data significantly easier. The sensor rig is designed for easy transport and operation by a single individual. It can also be temporarily attached to an existing vessel, making it versatile for a wide range of data collection scenarios. The sensor rig is equipped with a Jetson Orin AGX computer, two dual-band GNSS receivers, a high-quality IMU, and two color polarization cameras. Accurate synchronization of all sensors and the computer to UTC is achieved using a microcontroller for triggering and a custom Pulse Per Second (PPS)-enabled Linux kernel on the Jetson. The sensor rig is controlled and monitored by connecting a smartphone to its hosted web app, which provides a live stream from the cameras and information about the sensors. We present a new dataset from the river Nidelva in Trondheim, Norway, to demonstrate the sensor rig’s potential and the benefit of color polarization cameras in the maritime domain. We show how the data from color polarization cameras can be used directly to make the water surface more visibly distinct and remove reflections and sun glare. This new data set consists of synchronized stereo color polarization video, raw IMU data, and raw GNSS data, and it is made publically available to the research community.

Examination of flow birefringence induced by the shear components along the optical axis using a parallel-plate-type rheometer

In this study, the concept of rheo-optics was applied to explore the flow birefringence induced by the stress components along the camera’s optical axis since it is often overlooked in the traditional theories of photoelastic flow measurement. A novel aspect of this research is that it involved conducting polarization measurements on simple shear flows, specifically from a perspective in which a shear-velocity gradient exists along the camera’s optical axis. A parallel-plate-type rheometer and a polarization camera are employed for these systematic measurements. The experimental findings for dilute aqueous cellulose nanocrystal suspensions demonstrate that the flow birefringence can be expressed as a power law based on the power of the second invariant of the deformation-rate tensor. This suggests that flow birefringence can be universally characterized by the coordinate-independent invariants and a pre-factor determined by the direction of polarization measurement. By adjusting the nonlinear term in the stress-optic law, its applicability could be expanded to include three-dimensional fluid stress fields in which the stress is distributed along the camera’s optical axis.

Real-time full Stokes quantitative imaging with a pixelated polarization camera

Real-time full Stokes quantitative imaging with a pixelated polarization camera

U²PNet: An Unsupervised Underwater Image-Restoration Network Using Polarization.

This article presents U 2PNet, a novel unsupervised underwater image restoration network using polarization for improving signal-to-noise ratio and image quality in underwater imaging environments. Traditional methods for underwater image restoration using polarization require specific cues or pairs of underwater polarization datasets, which limit their practical applications. Our proposed method requires only one mosaicked polarized image of the scene and does not require datasets for pretraining or specific cues. We design two subnetworks (T-net and B textsubscript ∞ -net) to accurately estimate the transmission map and background light, and unique nonreference loss functions to ensure effective restoration. Our experiments are based on an indoor polarization simulated dataset and a real polarization image dataset constructed from our underwater robotic platform equipped with polarization cameras. Experiment results demonstrate that our proposed method achieves state-of-the-art performance on both simulated and real underwater polarization images. The code and datasets will be available at https://github.com/polwork/U-2Pnet.

Reliable measurement selection mechanism-based tightly coupled inertial/bionic polarization integration with position correction

Tightly coupled SINS/BPNS (strapdown inertial navigation system/bionic polarization navigation system) integration has been proven to be a promising navigation tactic to substitute SINS/GNSS (global navigation satellite system) integration in GNSS-denied environments. However, the existing tightly coupled SINS/BPNS integrations lack SINS position correction and the reliable screening of BPNS measurements, leading to difficulty to complete navigation tasks. This paper presents an enhanced tightly coupled SINS/BPNS integration to correct both SINS position and attitude and conduct reliable measurement screening for BPNS. This method establishes a new measurement model by formulating the relationship between the SINS position error and angle of E-vector to effectively correct the SINS position. Based on the corrected SINS position, the solar position is calculated and further plugged in the measurement model, leading to improved accuracy. Further, based on the focal plane polarization camera, a mechanism of reliable measurement selection with two-level processing is developed and combined with the extended Kalman filter to improve the filtering robustness for tightly coupled SINS/BPNS integration. Results of simulations and experiments show that the proposed method not only can effectively correct SINS navigation information, but also can possess a strong robustness to exclude unreliable BPNS measurements, leading to enhanced navigation performance for tightly coupled SINS/BPNS integration.

Snapshot Multi-Wavelength Birefringence Imaging.

A snapshot multi-wavelength birefringence imaging measurement method was proposed in this study. The RGB-LEDs at wavelengths 463 nm, 533 nm, and 629 nm were illuminated with circularly polarized light after passing through a circular polarizer. The transmitted light through the birefringent sample was captured by a color polarization camera. A single imaging process captured light intensity in four polarization directions (0°, 45°, 90°, and 135°) for each of the three RGB spectral wavelength channels, and subsequently measured the first three elements of Stokes vectors (S0, S1, and S2) after the sample. The birefringence retardance and fast-axis azimuthal angle were determined simultaneously. An experimental setup was constructed, and polarization response matrices were calibrated for each spectral wavelength channel to ensure the accurate detection of Stokes vectors. A polymer true zero-order quarter-wave plate was employed to validate measurement accuracy and repeatability. Additionally, stress-induced birefringence in a PMMA arch-shaped workpiece was measured both before and after the application of force. Experimental results revealed that the repeatability of birefringence retardance and fast-axis azimuthal angle was better than 0.67 nm and 0.08°, respectively. This approach enables multispectral wavelength, high-speed, high-precision, and high-repeatability birefringence imaging measurements through a single imaging session.

Demonstration of chirped pulse phase-shifting digital holography for capturing the sequence of ultrafast optical wavefronts

We experimentally demonstrate chirped pulse phase-shifting digital holography. This method, recently proposed, allows for capturing the sequence of ultrafast optical wavefronts with picosecond time resolution in a single-shot manner. In our experiment, we recorded two object pulses with a time separation of 1.67 ps using 35-fs-width optical pulses, employing a diffractive optical element and a bandpass filter, on a single polarization camera simultaneously. We reconstructed both the intensity and phase images of these object pulses using modified calculations that account for corrections in the polarization states of the reference waves, thereby improving the quality of the reconstructed images.

High-Speed Stress Field Measurement In A Soft Substrate During Droplet Impact

In this study, we utilized high-speed photoelastic tomography to quantify dynamic stress fields within a soft substrate during droplet impact. This manuscript details the measurement technique, which employs a high-speed polarization camera and the principles of photoelastic tomography. Our method successfully enabled the quantitative measurement of dynamic stress fields in a soft substrate during droplet impact. Additionally, we conducted an analysis of the impact force derived through the spatial integration of the measured stress field. The discussion explored the interplay between the maximum impact force, droplet viscosity, and substrate elasticity. Our findings indicate that the maximum impact force 𝐹max can be expressed as a function with a self-similar variable of 𝑅𝑒 / 𝐶𝑎^2 , where 𝑅𝑒 is Reynolds number representing the droplet inertial force and droplet viscous force and 𝐶𝑎 is Cauchy number representing the ratio of the droplet inertial force and substrate elastic force. This combination, 𝑅𝑒 / 𝐶𝑎^2 , represents the relationship between the relaxation time of droplet and substrate deformation ( 𝜂/ 𝐸), the contact time of the droplet (𝑅 / 𝑉), and the ratio of substrate elastic force to droplet inertial force. Consequently, the maximum impact force 𝑅𝑒 / 𝐶𝑎^2 is determined by the balance between the relaxation and contact times. We believe that our developed method will significantly enhance the understanding of droplet impact phenomena. Furthermore, it holds potential for broader applications in various engineering processes, such as analyzing stress distribution in materials caused by liquid jet impact and studying cavitation bubbles in viscoelastic materials. This method's ability to provide detailed quantitative measurements of dynamic stress fields offers a valuable tool for future research and technological advancements in related fields.

Single-frame fringe pattern analysis with synchronous phase-shifting based on polarization interferometry phase measuring deflectometry (PIPMD)

In the domain of phase measuring deflectometry (or fringe projection profilometry), utilizing only a single-frame fringe pattern to achieve high-precision three-dimensional reconstruction has emerged as a focal point of ongoing research. To achieve four-step phase-shifting demodulation from a single-frame fringe pattern, this paper proposes a Polarization Interferometry Phase Measuring Deflectometry (PIPMD). This method primarily relies on a Michelson polarization interferometry structure to produce projected polarization interference fringes, which are then captured by a polarization camera as modulated single-frame deformed fringe patterns. These single-frame fringe patterns enable pixelated four-step phase shifting with adjacent 2 × 2 pixel units. To validate the proposed method, a series of experiments has been conducted, including surface shape detection of a concave spherical mirror and an off-axis parabolic mirror, as well as dynamic deformation measurements of a deformable mirror. All experimental results consistently indicate that the polarization interference-based fringe projection technique can achieve synchronized phase-shifting demodulation of single-frame fringe patterns, thereby facilitating high-precision reconstruction of the fringe patterns captured in a single frame. This synchronous phase-shifting technique can overcome the influence of air disturbances in traditional four-step phase-shifting methods, thereby enhancing the accuracy of phase demodulation. Additionally, this polarization interference-based Phase Measuring Deflectometry exhibits promising application prospects in dynamic measurements.

Photon discerner: adaptive quantum optical sensing near the shot noise limit

Photon statistics of an optical field can be used for quantum optical sensing in low light level scenarios free of bulky optical components. However, photon-number-resolving detection to unravel the photon statistics is challenging. Here, we propose a novel detection approach, that we call ‘photon discerning’, which uses adaptive photon thresholding for photon statistical estimation without recording exact photon numbers. Our photon discerner is motivated by the field of neural networks where tunable thresholds have proven efficient for information extraction in machine learning tasks. The photon discerner maximizes Fisher information per photon by iteratively choosing the optimal threshold in real-time to approach the shot noise limit. Our proposed scheme of adaptive photon thresholding leads to unique remote-sensing applications of quantum degree of linear polarization camera and quantum LiDAR. We investigate optimal thresholds and show that the optimal photon threshold can be counter-intuitive (not equal to 1) even for weak signals (mean photon number much less than 1), due to the photon bunching effect. We also put forth a superconducting nanowire realization of the photon discerner which can be experimentally implemented in the near-term. We show that the adaptivity of our photon discerner enables it to beat realistic photon-number-resolving detectors with limited photon-number resolution in certain applications. Our work suggests a new class of detectors for information-theory driven, compact, and learning-based quantum optical sensing.

Using polarization cameras for snapshot imaging of phase, depth, and spectrum

Using polarization cameras for snapshot imaging of phase, depth, and spectrum

Wide-field full-Stokes polarimetry for conical light based on all-dielectric metasurface

Polarization camera based on CMOS sensor and nano wire-grid technology have found widespread applications in medical diagnostics, remote sensing and industrial inspection. However, the limited filtering properties of wire-grid polarizers and the small field-of-view provided by conventional microlens restrict the energy efficiency of these systems while also increasing their cost, size and weight. In this study, we propose an innovative approach that integrates focusing and splitting of polarization states into a single-layer all-dielectric metasurface. This metasurface enables full-Stokes polarization imaging for a wide field-of-view conical light. The design of the metasurface utilizes a phase compensation method to effectively focus orthogonal polarized conical light onto the central pixel of the CMOS sensor. Theoretical analysis demonstrates that this metasurface can accurately detect full-Stokes parameters within ±20° incident cone angles with an average efficiency reaching 83.0%. The angle can be extended to ±90° with an average efficiency exceeding 80%. We fabricated a three super-pixel metasurface prototype, and experimental measurements reveal its ability to efficiently focus and split three pairs of orthogonal polarization states under ±11° conical angle incidence with an average focusing efficiency of 68.1%. This study presents a promising solution for achieving wide field-of-view and high-efficiency polarization detection in integrated CMOS systems.

Compact Single-Shot Dual-Wavelength Interferometry for Large Object Measurement with Rough Surfaces

Single-shot dual-wavelength interferometry offers a promising avenue for surface profile measurement of dynamic objects. However, current techniques employing pixel multiplexing or color cameras encounter challenges such as complex optical alignment, limited measurement range, and difficulty in measuring rough surfaces. To address these issues, this study presents a novel approach to single-shot dual-wavelength interferometry. By utilizing separated polarization illumination and detection, along with a monochromatic polarization camera and two slightly different wavelengths, this method enables the simultaneous recording of two frames of separated interferometric patterns. This approach facilitates straightforward optical alignment, expands measurement ranges, accelerates data acquisition, and simplifies data processing for dual-wavelength interferometry. Consequently, it enables online shape measurement of large dynamic samples with rough surfaces.

Towards multi-views cloud retrieval accounting for the 3-D structure collected by directional polarization camera

The structure of a cloud is three-dimensional (3-D). Nevertheless, cloud research is predominantly developed in one-dimensional (1-D) hypothesis from passive optical satellite measurements. Cloud retrieval algorithms typically do not consider the parallax displacement of clouds in multi-view images. Inversion of cloud properties based on two-dimensional (2-D) coordinates cannot solve multi-view radiation changes which are caused by macro-structure of a cloud in 3-D space. In this study, we included the 3-D structure of clouds by repositioning cloud pixels within a 3-D coordinate system utilizing the directional polarization camera (DPC) data before conducting cloud property retrieval. It is followed by identification of location of cloud in each observational view’s image plane. Observational paths of clouds are rebuilt at each observational view. Furthermore, computer graphics methods are employed to establish spatial relationship among different cloud observational paths. The radiational and geometrical information are relocated in unified 3-D sub-pixel space. Finally, 3-D cloud radiation information could be applied to retrieve cloud properties. The case results demonstrate that our method can effectively reduce mixed pixels of clouds and clear sky by 5.79% while decrease indistinguishable pixels in cloud phase classification by 2.11%. It leads to an enhancement in the classification accuracy of water clouds and ice clouds by 3.30% and 4.03%, respectively. Therefore, it is concluded that considering the impact of cloud structure before retrieval would significantly improve accuracy.

Polarization-multiplexed snapshot lateral shearing interferometric sensor for surface roughness measurements

A compact optical roughness measurement sensor based on lateral shearing interferometry is theoretically described and experimentally verified. By adopting the advanced surface roughness parameter extraction methods based on statistical machine learning technique and the partial integration approach, the sensor using a polarization grating and a polarization camera can instantaneously obtain a surface gradient map and provide reliable surface roughness parameters. To verify the operation and the performance of the sensor, a flat mirror and roughness standard specimens were measured, and the results were compared with those of a white light scanning interferometer as the reference values. As a result, the roughness parameters were very close to the reference values with <5 nm accuracy and <0.1 nm repeatability.