Polarization State Analyzer Research Articles

Snapshot Imaging of Stokes Vector Polarization Speckle in Turbid Optical Phantoms and In Vivo Tissues

Significance: We present a system to measure and analyze the complete polarization state distribution of speckle patterns generated from in vivo tissue. Accurate measurement of polarization speckle requires both precise spatial registration and rapid polarization state acquisition. A unique measurement system must be designed to achieve accurate images of polarization speckle patterns for detailed investigation of the scattering properties of biological tissues in vivo. Aim and approach: This system features a polarization state analyzer with no moving parts. Two pixel-polarizer cameras allow for the instantaneous acquisition of the spatial Stokes vector distribution of polarization speckle patterns. System design and calibration methods are presented, and representative images from measurements on liquid phantoms (microsphere suspensions) and in vivo healthy and tumor murine models are demonstrated and discussed. Results and Conclusions: Quantitative measurements of polarization speckle from microsphere suspensions with controlled scattering coefficients demonstrate differences in speckle contrast, speckle size, and the degree of polarization. Measurements on in vivo murine skin and xenograft tumor tissue demonstrate the ability of the system to acquire snapshot polarization speckle images in living systems. The developed system can thus rapidly and accurately acquire polarization speckle images from different media in dynamic conditions such as in vivo tissue. This capability opens the potential for future detailed investigation of polarization speckle for in vivo biomedical applications.

Holistic and in situ calibration method for a spectral-temporally modulated Mueller spectropolarimeter

The spectral-temporally modulated Mueller spectropolarimeter (STMSP) offers advantages of broader band limitation, better resolution, and faster detection speed. However, the current STMSP calibration method separates the polarization state generator and analyzer, necessitating subsequent recombination, which is inefficient and unstable. In this paper, a holistic and in situ calibration method for STMSP is proposed. It only requires insertion of a polarizer as a reference sample, eliminating the need for separate calibration and recombination. The STMSP is calibrated in situ as a whole, addressing the misalignment error of the spectral modulation module, the total polarimetric errors of the temporal modulation module, and the spectral modulation transfer function of the spectrometer. Experimental results demonstrate high accuracy, with a root mean square error (RMSE) of 0.0004, which is an order of magnitude lower than that of the dual-rotating retarder spectropolarimeter (DRRSP) after eigenvalue calibration. This demonstrates its potential for enabling faster and more accurate acquisition of the Mueller spectra.

Distributed vibration and temperature sensing system by multiplexed fiber scattering spectra

A new, to the best of our knowledge, distributed optical fiber vibration and temperature hybrid sensing system is proposed and experimentally demonstrated. The proposed system only employs two signal channels, which is more compact and practical. Based on the structure of the optical time domain reflectometer (OTDR), the Rayleigh scattering light and the Raman anti-Stokes scattering light is extracted for vibration and temperature sensing, respectively. For vibration sensing, a new differential location algorithm based on polarization state analysis of the Rayleigh scattering light is proposed to locate the vibration events. It first rectifies the original OTDR traces by fiber attenuation compensation to make each position in it with the same pulse power level. And then, by difference of adjacent traces and threshold discrimination, the vibration positions are identified and located. For temperature sensing, a temperature calibration unit and algorithm are adopted to dynamically correct the trace data and reduce the temperature measurement error caused by the instability of the pulse laser source. The experiment is conducted with a fiber range of about 12 km and laser pulse width of 60 ns, and the experimental results show that the maximum error range for temperature measurement is −0.7∘C to 1.3°C, with a root mean square (RMS) error of 0.85°C in the entire temperature measurement range. Additionally, the spatial resolution (SR) for both vibration and temperature sensing is 6 m.

Metasurface‐Based Mueller Matrix Microscope

AbstractIn conventional optical microscopes, image contrast of objects mainly results from the differences in light intensity and/or color. Muller matrix optical microscopes (MMMs), on the other hand, can provide significantly enhanced image contrast and rich information about objects by analyzing their interactions with polarized light. However, state‐of‐the‐art MMMs are fundamentally limited by bulky and slow polarization state generators and analyzers. Here, the study demonstrates a metasurface‐based MMM, i.e., Meta‐MMM, which is equipped with a chip‐integrated, single‐shot metasurface polarization state analyzer (Meta‐PSA). The Meta‐MMM is featured with high‐speed measurement (≈2s per Muller matrix (MM) image), superior operation stability, dual‐color operation, and high measurement accuracy (measurement error 1–2%) for MM imaging. The Meta‐MMM is applied to nanostructure characterization, surface morphology analysis, and discovering birefringent structures in honeybee wings. The Meta‐MMMs hold the promise to revolutionize various applications from biological imaging, medical diagnosis, and material characterization to industry inspection and space exploration.

Multivariable Optimization Method for Improving the Self-Calibration and Accuracy of a Binary Polarization State Analyzer

Multivariable Optimization Method for Improving the Self-Calibration and Accuracy of a Binary Polarization State Analyzer

Development and Calibration of a Vertical High-Speed Mueller Matrix Ellipsometer

In order to meet the requirements of dynamic monitoring from a bird’s eye view for typical rapidly changing processes such as mechanical rotation and photoresist exposure reaction, we propose a vertical high-speed Mueller matrix ellipsometer that consists of a polarization state generator (PSG) based on the time-domain polarization modulation and a polarization state analyzer (PSA) based on division-of-amplitude polarization demodulation. The PSG is realized using two cascaded photoelastic modulators, while the PSA is realized using a six-channel Stokes polarimeter. On this basis, the polarization effect introduced by switching the optical-path layout of the instrument from the horizontal transmission to the vertical transmission is fully considered, which is caused by changing the incidence plane. An in situ calibration method based on the correct definition of the polarization modulation and demodulation reference plane has been proposed, enabling the precise calibration of the instrument by combining it with a time-domain light intensity fitting algorithm. The measurement experiments of SiO2 films and an air medium prove the accuracy and feasibility of the proposed calibration method. After the precise calibration, the instrument can exhibit excellent measurement performance in the range of incident angles from 45° to 90°, in which the measurement time resolution is maintained at the order of 10 μs, the measurement accuracy of Mueller matrix elements is better than 0.007, and the measurement precision is better than 0.005.

Bayesian inference approach for Full Poincaré Mueller polarimetry

Full Poincaré Mueller Polarimetry is a new technique for characterizing samples by means of their Mueller matrix. The method is based on the use of a full Poincaré beam as a generator of polarization states. These beams present different polarization states, covering the entire Poincaré sphere surface, at different points in the beam cross section. To obtain the Mueller matrix, Stokes parameters are collected at both the entrance and the output of the sample. They are calculated from irradiance measurements at each pixel of a CCD camera for different configurations of the polarization state analyzer. These measurements can be processed in several ways. In this work, we propose to use Bayesian inference, in particular, Markov chain Monte Carlo methods, to obtain, without any prior knowledge of the sample, its Mueller matrix together with its uncertainties. The new approach is tested with experimental measurements of different samples and compared with the real theoretical Mueller matrices. Excellent agreement is observed between the experimental results and the theoretical ones for all the samples tested.

Design of polarization direction detection circuit

In the polarized light angle measurement system, it is important to detect the polarization direction of linearly polarized light. First, the principle of polarized light angle measurement is introduced, and then the polarization direction detection circuit is designed. This circuit receives the light intensity output signal from the Polarization State Analysis and converts it to an electrical signal. The electrical signal is filtered, amplified, sampled, and integrated to obtain a stable and useful electrical signal waveform. The polarization direction is judged by the waveform, which plays a role in the field of polarized light angle measurement and realizes accurate angle measurement. The simulation results show that the circuit can detect weak light signals and achieve 71.45 dB–97.95 dB adjustable gain. A stable and clear signal waveform can be obtained. The polarization direction can be determined by using the waveform. The circuit has a simple structure, good stability, and easy realization.

Solar Light Radiometry Calibration Unit for a ScanPol Polarimeter of the Aerosol-UA Space Mission

The Aerosol-UA space mission will study aerosol microphysical characteristics in the Earth’s atmosphere based on the multispectral scanning polarimeter (ScanPol) and imaging polarimeter (MSIP). Both polarimeters must be precisely calibrated on the ground and in orbit to provide correct measurements. This paper considers the results of developing an experimental device for the radiometric calibration of the ScanPol. We consider the calibration unit design and operation principle to form a luminous flux with unchanged or well-predicted characteristics in a specified direction. The construction of the radiometric calibration unit is based on a sun-illuminated reflective diffuser made from the white opal glass MS20. We evaluated the scattering and polarization characteristics of the diffuser in laboratory experiments at a wide range of wavelengths. The results suggest that the polarization properties of the diffuser are negligible. The diffuser scattering parameters are close to Lambertian for illuminance conditions, which is necessary for radiometric calibration. The calibration unit was manufactured and tested during field observations of solar radiation. The results will be used for its improvement, mainly to reduce the observed stray scattered radiation entering the telescopes of the ScanPol polarization state analyzer.

Scene-adaptive spatially channeled imaging Mueller polarimeter.

A spatially adaptive Mueller matrix imaging polarimeter is described, simulated, and demonstrated with preliminary experiments. The system uses a spatial light modulator (SLM) in the polarization state generator (PSG) to create spatial carriers that controlled by the pattern written to the SLM. The polarization state analyzer (PSA) is a commercial division of focal plane imaging polarimeter. The PSG/PSA pair form a 9-channeled partial Mueller matrix polarimeter that measures a 3 × 3 sub-matrix of the Mueller matrix. We demonstrate that adapting the PSG modulation to the spatial frequency structure of the scene can reduce channel crosstalk and improve reconstruction accuracy. Initial experiments are performed that demonstrate the SLM's ability to produce sufficient modulation diversity to create the desired channel structure. Though there are several experimental challenges to obtain accurate Mueller matrix imagery, we demonstrate a system that adapts to the particular scene spatial frequency structure.

Mueller matrix imaging polarimeter at the wavelength of 265 nm.

Mueller matrix imaging polarimeters (MMIPs) have been developed in the wavelength region of >400n m with great potential in many fields yet leaving a void of instrumentation and application in the ultraviolet (UV) region. For the first time to our knowledge, an UV-MMIP is developed for high resolution, sensitivity, and accuracy at the wavelength of 265nm. A modified polarization state analyzer is designed and applied to suppress stray light for nice polarization images, and the errors of the measured Mueller matrices are calibrated to lower than 0.007 in pixel level. The finer performance of the UV-MMIP is demonstrated by the measurements of unstained cervical intraepithelial neoplasia (CIN) specimens. The contrasts of depolarization images obtained by the UV-MMIP are dramatically improved over those obtained by our previous VIS-MMIP at the wavelength of 650nm. A distinct evolution of depolarization in normal cervical epithelium tissue, CIN-I, CIN-II, and CIN-III specimens can be observed by the UV-MMIP with mean depolarization promotion by up to 20 times. This evolution could provide important evidence for CIN staging but can hardly be distinguished by the VIS-MMIP. The results prove that the UV-MMIP could be an effective tool in polarimetric applications with higher sensitivity.

Liquid-crystal based drift-free polarization modulators: Part II. Ultra-stable Stokes and Mueller polarimeters.

We have previously reported a new design for drift-free liquid-crystal polarization modulators (LCMs) based on liquid-crystal variable retarders (LCVRs). Here, we study their performance on Stokes and Mueller polarimeters. LCMs have polarimetric responses similar to LCVRs and can be used as temperature-stable alternatives to many LCVR-based polarimeters. We have built an LCM-based polarization state analyzer (PSA) and compared its performance to an equivalent LCVR-based PSA. Our system parameters remained stable over a wide range of temperature, precisely from 25°C to 50°C. Accurate Stokes and Mueller measurements have been conducted, paving the way to calibration-free polarimeters for demanding applications.

Hybrid calibration method for Mueller matrix microscopy

System calibration is a crucial step for improving the accuracy of the Mueller matrix microscope, many calibration methods have been proposed and widely used in practice. Most existing calibration methods adopt modeled or un-modeled strategy for the entire system. In this paper, we propose a hybrid calibration method to reduce systematic errors of the Mueller matrix microscope. By considering the characteristics of polarization state generator (PSG) and polarization state analyzer (PSA), we adopt modeled strategy for PSG and un-modeled strategy for PSA, therefore combines the advantages of both modeled and un-modeled calibration methods. By measuring only two reference samples to solve the error model of the PSG and then reconstructing the instrument matrix of PSA. Hybrid calibration method is validated on different Mueller matrix microscopes established in our previous studies, the results show that this method can perform satisfactorily on Mueller matrix microscope with different PSG & PSA schemes, numerical apertures, wavelengths, and optical geometries.

Silicon-based decoder for polarization-encoding quantum key distribution

Silicon-based polarization-encoding quantum key distribution (QKD) has been widely studied, owing to its low cost and robustness. However, prior studies have utilized off-chip devices to demodulate the quantum states or perform polarization compensation, given the difficulty of fabricating polarized independent components on the chip. In this paper we propose a fully chip-based decoder for polarization-encoding QKD. The chip realizes a polarization state analyzer and compensates for the BB84 protocol without requiring additional hardware. It is based on a polarization-to-path conversion method that uses a polarization splitter-rotator. The chip was fabricated using a standard silicon photonics foundry; it has a compact design and is suitable for mass production. In the experimental stability test, an average quantum bit error rate of 0.59% was achieved through continuous operation for 10 h without any polarization feedback. Furthermore, using the developed feedback algorithm, the chip enabled the automatic compensation of the fiber polarization drift, which was emulated by a random fiber polarization scrambler. In the case of the QKD demonstration, we obtained a finite-key secret rate of 240 bps over a fiber spool of 100 km. This study represents an important step toward the integrated, practical, and large-scale deployment of QKD systems.

Full Poincaré Mueller Polarimetry Using a CCD Camera

A new method is proposed to perform Mueller matrix polarimetry using a Full Poincaré beam (i.e., a non-uniformly polarized beam presenting all polarization states across its section) as a parallel polarization state generator and a charge-coupled device (CCD) camera as a detector of the polarization state analyzer. In this way, the polarization change is measured for all possible input states simultaneously. To obtain the Mueller matrix of the sample, the overdetermined system of equations that relates the input and output states of polarization is solved by means of the Moore–Penrose pseudo-inverse. Preliminary numerical simulations are performed to identify and exhaustively analyze the main sources of error. In order to test the method, experimental measurements are presented for several known samples, showing an excellent agreement between the experimentally obtained Mueller matrices and the theoretically expected ones.

The single-cell landscape of kidney immune cells reveals transcriptional heterogeneity in early diabetic kidney disease

The pathogenesis of diabetic kidney disease (DKD) involves multifactorial processes that converge to initiate and advance the disease. Although DKD is not typically classified as an inflammatory glomerular disease, mounting evidence supports the involvement of kidney inflammation as a key contributor in DKD pathogenesis, particularly through macrophages. However, detailed identification and corresponding phenotypic changes of macrophages in DKD remain poorly understood. To capture the gene expression changes in specific macrophage cell subsets in early DKD, we performed single-cell transcriptomic analysis of CD45-enriched kidney immune cells from type 1 diabetic OVE26 mice at two time points during the disease development. We also undertook a focused analysis of mononuclear phagocytes (macrophages and dendritic cells). Our results show increased resident and infiltrating macrophage subsets in the kidneys of mice with diabetes over time, with heightened expression of pro-inflammatory or anti-inflammatory genes in a subset-specific manner. Further analysis of macrophage polarization states in each subset in the kidneys showed changes consistent with the continuum of activation and differentiation states, with gene expression tending to shift toward undifferentiated phenotypes but with increased M1-like inflammatory phenotypes over time. By deconvolution analysis of RNAseq samples and by immunostaining of biopsies from patients with DKD, we further confirmed a differential expression of select genes in specific macrophage subsets essentially recapitulating the studies in mice. Thus, our study provides a comprehensive analysis of macrophage transcriptomic profiles in early DKD that underscores the dynamic macrophage phenotypes in disease progression.

Optimal Configurations of Mueller Polarimeter for Gaussian–Poisson Mixed Noise

The accuracy of the Mueller polarimeter is usually affected by Gaussian–Poisson mixed noise, and by optimizing the instrument matrices of polarization state generator and polarization state analyzer in the measurement system, the estimation variance caused by Gaussian noise can be suppressed, and the estimation variance caused by Poisson noise can be made independent of the sample. However, the optimization procedure usually targets only the numerical value of the instrument matrix without considering how to configure the measurement system to achieve the optimal instrument matrix. In this paper, we investigate how to make the measurement system optimal for different measurement systems by combining geometric optimization on the Poincaré sphere and finally propose a series of measurement configurations for different applications.

Reconstruction and calibration methods for a Mueller channeled spectropolarimeter.

Channeled spectropolarimeter (CSP) measures spectrally resolved Stokes vector of light and Mueller matrix of sample from a snapshot. While reconstruction and calibration methods for Stokes CSP have been well established, their Mueller CSP counterparts are lacking. In this paper, we propose methods for Mueller spectrum reconstruction and Mueller CSP calibration. Mueller CSP is modeled as a modulation matrix, linking the Mueller spectrum to be measured and the modulated spectrum from the spectrometer. We describe an optimization problem to solve the Mueller spectrum, where both the regularizer and the residual threshold constrain the result, making our reconstruction accurate, efficient, and noise-robust. The Stokes spectrum generated by polarization state generator and the analyzing vector of polarization state analyzer are measured in situ, the convolution of which construct the calibrated modulation matrix of Mueller CSP. Total polarimetric errors and spectroscopic errors are treated as a whole and represented by the calibrated modulation matrix. Both imaging and non-imaging Mueller CSP are experimentally calibrated. Reconstruction results show high accuracy with a root-mean-square error (RMSE) of 0.0371. The proposed methods help make Mueller CSP practical and have the potential to be general reconstruction and calibration methods for imaging and non-imaging Stokes-Mueller CSP.

Optimizing Mueller polarimetry in noisy systems through over-determination.

Mueller polarimetry measurements are increasingly being used to image highly dynamic and short-lived phenomena such as plasma discharges. For phenomena such as these, exposure times below 1 µs must be used. Unfortunately, these low exposure times significantly reduce the signal-to-noise ratio, making accurate and consistent measurements difficult. To overcome this limitation, we investigated increasing the number of Stokes vectors produced from a polarization state analyzer and polarization state generator, a process known as over-determination. To conduct our analysis, we used results from physical experiments using Stokes vectors generated by liquid crystal variable retarders. These results were then verified using data from simulations. First, we conclude that increasing the degree of over-determination is a simple and effective way of dealing with this noise; however, we also convey that choosing the best scheme is not an entirely trivial process. Second, we demonstrate that over-determination gives rise to hitherto inaccessible information that allows for the quantification of statistical noise and, crucially, the pinpointing of the origin of systematic error, a highly beneficial process that has been lacking until now.

Snapshot spectroscopic Mueller matrix polarimetry based on spectral modulation with increased channel bandwidth.

This paper presents a snapshot spectroscopic Mueller matrix polarimetry based on spectral modulation. The polarization state generator consists of a linear polarizer in front of two high-order retarders, and the polarization state analyzer is formed by two non-polarization beam splitters incorporated with three high-order retarder/linear analyzer pairs. It can simultaneously generate three modulated spectra used for reconstructing the 16 spectroscopic Mueller elements of the sample. Since each of the modulated spectra produces seven separate channels equally spaced in the Fourier domain, the channel bandwidth can be enhanced efficiently compared with the conventional spectrally modulated spectroscopic Mueller matrix polarimetry. The feasibility of the proposed spectroscopic Mueller matrix polarimetry is demonstrated by the experimental measurement of an achromatic quarter-wave plate.