Real-time Polarization Measurement Research Articles

Spatially Resolved, Real-Time Polarization Measurement Using Artificial Birefringent Metallic Elements

Polarization states define a fundamental property in optics. Consequently, polarization state characterization is essential in many areas of both field industrial applications and scientific research. However, a full identification of space-variant Stokes parameters faces great challenges, like multiple power measurements. In this contribution, we present a spatially resolved polarization measurement using artificial birefringent metallic elements, the so-called hollow waveguides. Differently oriented and space-variant hollow waveguide arrays, a stationary analyzer and a CMOS camera form the basis of the experimental setup for one single spatially resolved power measurement. From this power measurement, the Stokes parameters can be calculated in quasi-real-time, with a spatial resolution down to 50 μm in square. The dimensions of the individual hollow waveguides, which are less than or equal to the employed wavelength, determine the spectral range, here in the near infrared around λ = 1550 nm. This method allows for the rapid and compact determination of spatially resolved Stokes parameters, which is experimentally confirmed using defined wave plates, as well as an undefined injection-molded polymer substrate.

Performance of Disposable Cu/CuSO4 Reference Electrode in Reinforced Concrete Corrosion Analysis

The investigation of reference electrode performance for corrosion analysis has been widely conducted over the last decade. The need for a disposable and reliable reference electrode is a specific need for corrosion investigation. This research investigated the effectiveness of liquid-based and solid-state reference electrodes, which are disposable and provide reliable performance. The electrode was prepared with low-cost material preparation (disposable usage) within a Copper-Copper Sulphate (CCS) liquid-based and solid-state electrodes. The potential stability was already tested for dependability by measuring the Open Circuit Potential (OCP) on the rebar concrete specimen. The behaviour of solid-state reference and liquid-based reference electrodes in terms of polarization was studied in a corroded environment. Real-time potential data was also obtained for the corrosion rate investigation. The result shows the consistency performance of (OCP) value during corrosion measurement. The deviation of the maximum to a minimum potential value less than 0.02 V, verifies that the liquid-based copper (Cu) electrode and solid-state copper (Cu) electrodes are reliable, adaptable, and disposable for reinforced concrete corrosion measurement. In terms of corroded rebar potential measurement, the real-time polarization measurement result shows that the high-risk corroding occurred on the embedded rebar and was validated by directly visualizing the rebar concrete specimen. Therefore, the results obtained allow us to conclude that the disposable of both reference electrodes shows their stability and significantly reduces the reinforced concrete corrosion research cost.

Real-time polarization measurement based on spatially modulated polarimeter and deep learning

Spatially modulated polarimeter (SMP) can be employed to obtain the polarization states of light by a single shot of intensity image, and it is stable, robust and easy to use. In order to simplify the calculation procedures and improve the measurement speed, we introduce the deep learning (DL) method into SMP. In this work, a convolutional neural network (CNN) based on VGGNet architecture has been trained by simulated samples that are generated by a theoretical model of a spatially modulated system. Then the trained CNN is utilized to evaluate the Stokes parameters of the input light beam according to its spatially modulated image obtained in the real experiment. The mean absolute error between the evaluated values and the true values of the normalized Stokes parameters can be less than 0.02, and the evaluation of each image takes only 0.03–0.04 s. Compared with the traditional Fourier analysis method, the DL method is close in accuracy while greatly enhanced in speed, making real-time polarization measurement achievable.

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

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

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).

Geometric calibration algorithm of polarization camera using planar patterns

Polarization pattern provides additional information besides spectral signatures. It can be used in many applications, such as navigation, defect detection and object identification. A novel polarization camera composed of four synchronized cameras is proposed, and it can realize real-time polarization measurement. This study particularly concentrates on the geometric calibration of the system. The projection model is analyzed and the multi-camera calibration algorithm is proposed. Firstly, each camera is calibrated separately using planar patterns, and then the geometric calibration algorithms are performed. Due to the geometrical constraint, a global optimization method results in smaller estimation uncertainties. A mean rotation error of 0.025° and a mean translation error of 0.26mm are achieved after geometric calibration. The images are rectified to establish a correspondence among cameras and are combined to acquire the polarization measurement. The polarization pattern of the skylight is measured by the system and the results are consistent with the previous studies.

A LabVIEW-based real-time measurement system for polarization detection and calibration

A rapid real-time polarization measurement system was designed and implemented in this paper. The system is centered round a computer running application developed for the purpose. The paper illustrates how to build such an excellent application with National Instruments’ graphical programming language LabVIEW, a synchronized high speed multi-channels data acquisition card and some photoelectric conversion module in detail. With simple and friendly user interface, the experimental result shows that the measurement system has high computational efficiency, high precision calibration matrix, which can be efficiently utilized in experiments relating to the measurement of polarization.

Design and Implementation of Real-Time Polarization Measurement System Based on LabVIEW

A rapid real-time polarization measurement system was designed and implemented in this paper. The system is centered round a laptop running application developed for the purpose. The paper illustrates how to build such an excellent application with National Instruments graphical programming language LabVIEW, a synchronized high speed multi-channels data acquisition card and some photoelectric conversion module in detail. With simple and friendly user interface, the experimental result shows that the measurement system has high computational efficiency, high precision calibration matrix, which can be efficiently utilized in experiments relating to the measurement of polarization.

Precise real-time polarization measurement of terahertz electromagnetic waves by a spinning electro-optic sensor

We propose and develop a method to quickly and precisely determine the polarization direction of coherent terahertz electromagnetic waves generated by femtosecond laser pulses. The measurement system consists of a conventional terahertz time-domain spectroscopy system with the electro-optic (EO) sampling method, but we add a new functionality in the EO crystal which is continuously rotating with the angular frequency ω. We find a simple yet useful formulation of the EO signal as a function of the crystal orientation, which enables a lock-in-like detection of both the electric-field amplitude and the absolute polarization direction of the terahertz waves with respect to the probe laser pulse polarization direction at the same time. The single measurement finishes around two periods of the crystal rotations (∼21 ms), and we experimentally prove that the accuracy of the polarization measurement does not suffer from the long-term amplitude fluctuation of the terahertz pulses. Distribution of the measured polarization directions by repeating the measurements is excellently fitted by a gaussian distribution function with a standard deviation of σ = 0.56°. The developed technique is useful for the fast direct determination of the polarization state of the terahertz electromagnetic waves for polarization imaging applications as well as the precise terahertz Faraday or Kerr rotation spectroscopy.

Near-field Fourier transform polarimetry by use of a discrete space-variant subwavelength grating

We present a unique method for real-time polarization measurement by use of a discrete space-variant subwavelength grating. The formation of the grating is done by discrete orientation of the local subwavelength grooves. The complete polarization analysis of the incident beam is determined by spatial Fourier transform of the near-field intensity distribution transmitted through the discrete subwavelength dielectric grating followed by a subwavelength metal polarizer. We discuss a theoretical analysis based on Stokes-Mueller formalism, as well as on Jones calculus, and experimentally demonstrate our approach with polarization measurements of infrared radiation at a wavelength of 10.6 microm.

Real-time analysis of partially polarized light with a space-variant subwavelength dielectric grating

A novel method for real-time polarization measurement is presented. The method is based on a space-variant wave plate that we realized as a computer-generated space-variant subwavelength dielectric grating. The Stokes parameters of the incident beam are determined by Fourier analysis of the space-variant intensity transmitted through the grating and an analyzer. We discuss the design and realization of such wave plates and demonstrate our technique with polarization measurements of both polarized and partially polarized CO(2)-laser radiation at a wavelength of 10.6 mum.

Space-Variant Polarization-State Manipulation with Computer-Generated Subwavelength Gratings

Novel methods for space-variant polarization-state manipulation using subwavelength metal and dielectric gratings are presented. By locally controlling the period and direction of the grating, we show that any desired polarization can be achieved. The methods presented in this paper are generic to any portion of the spectrum, and we present experimental demonstrations of our theory using CO2 laser radiation at a wavelength of 10.6 m. Moreover, we exploited our computer-generated subwavelength gratings to demonstrate a polarization Talbot self-imaging, as well as nondiffracting periodically space-variant polarization beams, and a unique method for real-time polarization measurement. We also present novel optical phase elements based on the space-domain Pancharatnam-Berry phase. Unlike diffractive and refractive elements, the phase is not introduced through optical path differences, but results from the geometrical phase that accompanies space-variant polarization manipulation. We intoduce and experimentally demonstrate PancharatnamBerry phase optical elements (PBOEs) based on computer-generated subwavelength gratings such as polarization beamsplitters, optical switches and spiral phase.

Spatial Fourier-transform polarimetry using space-variant subwavelength metal-stripe polarizers

A novel method for rapid polarization measurement is suggested. The method is based on a periodic space-variant polarizer that can be realized by use of subwavelength metal-stripe gratings. The Stokes parameters of the incident beam are determined by Fourier analysis of the space-variant intensity transmitted through the grating, thus permitting real-time polarization measurement. We discuss the design and realization of such polarizers and demonstrate our technique with polarization measurements of CO(2)-laser radiation at a wavelength of 10.6mum.