We show how to construct and calibrate a full-Stokes imaging polarimeter system by combining the video data from two separate polarization cameras with a nonpolarizing beamsplitter and a waveplate. As a result, this system can capture the full Stokes vector at each pixel for 3 megapixel images at up to 60 Hz. To demonstrate some of the advantages of measuring the s 3 Stokes vector component that is normally not measured in polarization cameras, we show three experiments: viewing three-dimensional glasses, detecting a scarab beetle in a natural environment via the circular dichroism of its shell, and mixing an optically active liquid with a neutral liquid.

Video-rate full-Stokes imaging polarimeter using two polarization cameras

On-chip polarization-sensitive photodetectors offer unique opportunities for next-generation ultra-compact polarimeters So far, mainstream approaches have relied on the anisotropic absorption of natural materials or artificial structures However, such a model is inherently restricted by correlation between the polarization ratio (PR) and diattenuation, leading to small PR values (1 < PR < 10) Here, we report nanoantenna-mediated semimetal photodetectors, which enable configurable polarity transition by exploiting the vectorial and non-local photoresponse in semimetals By tuning the orientation of nanoantennas, PR values vary from positive (unipolar regime) to negative (bipolar regime), covering all possible numbers (1 → ∞/−∞ → −1) In particular, the PR values at the polarity-transition point could approach infinity Such a polarity transition hereby transcends the conventional PR–diattenuation relationship Furthermore, our device allows the subtle measurement of polarization-angle perturbation down to 002° Hz−1/2 in the mid-infrared range Our findings highlight the potential of semimetals as a promising material platform for miniaturized polarimetry Mid-infrared polarization detectors based on nanoantenna-mediated few-layer graphene are demonstrated By tuning the orientation of nanoantennas, the polarization ratios vary from positive to negative, and cover values from 1 to ∞/−∞ then to −1

Mid-infrared semimetal polarization detectors with configurable polarity transition

Snapshot polarization imaging has gained interest in the last few decades. Recent research and technology achievements defined the polarization Filter Array (PFA). It is dedicated to division-of-focal plane polarimeters, which permits to analyze the direction of light electric field oscillation. Its filters form a mosaicked pattern, in which each pixel only senses a fraction of the total polarization states, so the other missing polarization states have to be interpolated. As for Color or Spectral Filter Arrays (CFA or SFA), several dedicated demosaicking methods exist in the PFA literature. Such methods are mainly based on spatial correlation disregarding inter-channel correlation. We show that polarization channels are strongly correlated in images. We therefore propose to extend some demosaicking methods from CFA/SFA to PFA, and compare them with those that are PFA-oriented. Objective and subjective analysis show that the pseudo panchromatic image difference method provides the best results and can be used as benchmark for PFA demosaicking.

https://hal.archives-ouvertes.fr/hal-01908503/document

Survey of Demosaicking Methods for Polarization Filter Array Images.

A demand for division of focal plane (DoFP) polarization imaging technology grows rapidly as nanofabrication technologies become mature. For real-time polarization imaging, a DoFP polarimeter often trades off its spatial resolution, which may cause instantaneous field of view (IFoV) errors. To deal with such problems, interpolation methods are often used to fill the missing polarization information. This paper presents an interpolation technique using Newton's polynomial for DoFP polarimeter demosaicking. The interpolation is performed in the polarization difference domain with the interpolation error taken into consideration. The proposed method uses an edge classifier based on polarization difference and a fusion scheme to recover more accurate boundary features. Experiments using both synthetic and real DoFP images in visible and long-wave infrared spectrum demonstrate that the proposed interpolation method outperforms the state-of-the-art techniques quantitatively as well as visually to reduce nonconformities caused by high-frequency energy.

Demosaicking DoFP images using Newton’s polynomial interpolation and polarization difference model

Polarization is one of the three fundamental properties of light, along with color and intensity, yet most vertebrate species, including humans, are blind with respect to this light modality. In contrast, many invertebrates, including insects, spiders, cephalopods, and stomatopods, have evolved to detect polarization information with high-dynamic-range photosensitive cells and utilize this information in visually guided behavior. In this paper, we present a high-dynamic-range polarization imaging sensor inspired by the visual system of the mantis shrimp. Our bioinspired imager achieves 140 dB dynamic range and 61 dB maximum signal-to-noise ratio across 384×288 pixels equipped with logarithmic photodiodes. Contrary to state-of-the-art active pixel sensors, where photodiodes in individual pixels operate in reverse bias mode and yield up to ∼60  dB dynamic range, our pixel has a logarithmic response by operating individual photodiodes in forward bias mode. This novel pixel circuitry is monolithically integrated with pixelated polarization filters composed of 250-nm-tall × 75-nm-wide aluminum nanowires to enable snapshot polarization imaging at 30 frames per second. This sensor can enable many automotive and remote sensing applications, where high-dynamic-range imaging augmented with polarization information can provide critical information during hazy or rainy conditions.

Bioinspired polarization imager with high dynamic range

A 3.2-MP four-directional polarization image sensor with air-gap wire-grid polarizer is described. The image sensor was fabricated using a wafer process and incorporates back-illumination and an antireflection layer to minimize optical flaring and ghosting problems. In testing, the sensor achieved a polarization transmittance of 63.3% and an extinction ratio of 85 at 550 nm, thereby outperforming conventional polarization sensors. The proposed sensor also exhibited good oblique-incidence characteristics, even with small polarization pixels of $2.5~\mu \text{m}$ . Based on these results, the proposed image sensor is suitable for various megapixel fusion-imaging applications, such as reducing surface reflections, highly accurate depth mapping, and condition-robust surveillance.

3.2-MP Back-Illuminated Polarization Image Sensor With Four-Directional Air-Gap Wire Grid and 2.5- $\mu$ m Pixels

Polarization information is useful in highly functional imaging. This paper presents a four-directional pixel-wise polarization CMOS image sensor using an air-gap wire grid on 2.5-μm back-illuminated pixels. The fabricated air-gap wire grid polarizer achieved a transmittance of 63.3 % and an extinction ratio of 85 at 550 nm, outperforming conventional polarization sensors. The pixel-wise polarizers fabricated with the wafer process on back-illuminated image sensors exhibit good oblique-incidence characteristics, even with small polarization pixels of 2.5 μm. The proposed image sensor realizes mega-pixel various fusion-imaging applications, such as surface reflection reduction, highly accurate depth mapping, and condition-robust surveillance.

Yusuke Uesaka

Papers

3.2-MP Back-Illuminated Polarization Image Sensor With Four-Directional Air-Gap Wire Grid and 2.5- $\mu$ m Pixels

Four-directional pixel-wise polarization CMOS image sensor using air-gap wire grid on 2.5-μm back-illuminated pixels