Linear Polarization Modulation Research Articles

High-dimensional anticounterfeiting nanodiamonds authenticated with deep metric learning

Physical unclonable function labels have emerged as a promising candidate for achieving unbreakable anticounterfeiting. Despite their significant progress, two challenges for developing practical physical unclonable function systems remain, namely 1) fairly few high-dimensional encoded labels with excellent material properties, and 2) existing authentication methods with poor noise tolerance or inapplicability to unseen labels. Herein, we employ the linear polarization modulation of randomly distributed fluorescent nanodiamonds to demonstrate, for the first time, three-dimensional encoding for diamond-based labels. Briefly, our three-dimensional encoding scheme provides digitized images with an encoding capacity of 109771 and high distinguishability under a short readout time of 7.5 s. The high photostability and inertness of fluorescent nanodiamonds endow our labels with high reproducibility and long-term stability. To address the second challenge, we employ a deep metric learning algorithm to develop an authentication methodology that computes the similarity of deep features of digitized images, exhibiting a better noise tolerance than the classical point-by-point comparison method. Meanwhile, it overcomes the key limitation of existing artificial intelligence-driven classification-based methods, i.e., inapplicability to unseen labels. Considering the high performance of both fluorescent nanodiamonds labels and deep metric learning authentication, our work provides the basis for developing practical physical unclonable function anticounterfeiting systems.

Deep learning and genetic algorithm driven accelerated design for frequency-multiplexed complex-amplitude coding meta-hologram.

Frequency-multiplexed metasurfaces represent a significant innovation in breaking the functional limitations of traditional metasurfaces, showing immense potential in multi-channel communication. However, existing frequency-multiplexed metasurfaces primarily focus on pure phase and linear polarization modulation, neglecting the modulation for complex amplitude and circularly polarized waves. Additionally, crosstalk suppression between dual-frequency channels often requires meticulous tuning of the meta-atom structure. Therefore, manually designing a set of meta-atoms that satisfies both complex amplitude modulation and low crosstalk at dual frequencies is extremely challenging and time-consuming. Here, we utilize the method of deep learning and genetic algorithm to design a kind of meta-atom capable of bi-spectral 2-bit amplitude and arbitrary phase modulation, which greatly reduces the design difficulty and achieves excellent low-crosstalk performance. This method can be easily generalized to the design of other complex meta-atoms to improve the design efficiency. Furthermore, we propose a frequency-multiplexed complex-amplitude coding meta-hologram for modulating left-handed circularly polarized (LCP) waves. When illuminated with LCP light, it can reconstruct two distinct holographic images at two different frequencies in the near field with high quality. The independent modulation capability of the metasurface for multiple degrees of freedom of frequency, amplitude and phase gives it broad application prospects in multi-channel communication, data storage and perfect holography.

Introduction of non-symmetric inserts into a symmetric split-ring resonator: design of a bifunctional metasurface for linear polarization conversion and circular dichroism

Metasurfaces have shown their versatile capabilities in light-field shaping. To further pursue dense integration and miniaturization in photonics, a combination of multiple diversified functionalities into a metasurface is a promising solution. Recent bifunctional metasurfaces have relied on meta-atom superposition and tunable material introduction. The former supports simultaneous multi-functions, while the latter provides flexible adjustment. To achieve simultaneous and tunable multi-functions using a simple structure, based on a split-ring resonator metasurface with the linear polarization modulation function, here, we additionally introduced resonance to induce anti-symmetric polarization absorption for circular polarization modulation. As a proof-of-concept, we propose a bifunctional THz metasurface that combines linear polarization conversion and circular dichroism for polarization control and detection applications. Moreover, by changing the Fermi levels of graphene, both the frequency ranges of linear polarization conversion and circular dichroism can be adjusted. This work provides a reference to photonics integration related to polarization engineering and other distinct functionalities.

Saturated confocal fluorescence microscopy with linear polarization modulation

Saturated confocal fluorescence microscopy with linear polarization modulation

All-Optical Modulation of Single Defects in Nanodiamonds: Revealing Rotational and Translational Motions in Cell Traction Force Fields.

Measuring the mechanical interplay between cells and their surrounding microenvironment is vital in cell biology and disease diagnosis. Most current methods can only capture the translational motion of fiduciary markers in the deformed matrix, but their rotational motions are normally ignored. Here, by utilizing single nitrogen-vacancy (NV) centers in nanodiamonds (NDs) as fluorescent markers, we propose a linear polarization modulation (LPM) method to monitor in-plane rotational and translational motions of the substrate caused by cell traction forces. Specifically, precise orientation measurement and localization with background suppression were achieved via optical polarization selective excitation of single NV centers with precisions of ∼0.5°/7.5 s and 2 nm/min, respectively. Additionally, we successfully applied this method to monitor the multidimensional movements of NDs attached to the vicinity of cell focal adhesions. The experimental results agreed well with our theoretical calculations, demonstrating the practicability of the NV-based LPM method in studying mechanobiology and cell-material interactions.

Structured illumination microscopy based on asymmetric three-beam interference

Structured illumination microscopy (SIM) is a rapidly developing super-resolution technology. It has been widely used in various application fields of biomedicine due to its excellent two- and three-dimensional imaging capabilities. Furthermore, faster three-dimensional imaging methods are required to help enable more research-oriented living cell imaging. In this paper, a fast and sensitive three-dimensional structured illumination microscopy based on asymmetric three-beam interference is proposed. An innovative time-series acquisition method is employed to halve the time required to obtain each raw image. A segmented half-wave plate as a substantial linear polarization modulation method is applied to the three-dimensional SIM system for the first time. Although it needs to acquire 21 raw images instead of 15 to reconstruct one super-resolution image, the SIM setup proposed in this paper is 30% faster than the traditional spatial light modulator-SIM (SLM-SIM) in imaging each super-resolution image. The related theoretical derivation, hardware system, and verification experiment are elaborated in this paper. The stable and fast 3D super-resolution imaging method proposed in this paper is of great significance to the research of organelle interaction, intercellular communication, and other biomedical fields.

Modelling and Simulation for the Electro-optic Characteristics of BaTiO3 Crystal Film Waveguide with Complementary Push-pull Polarization Modulations

BaTiO3 crystal films, possessing the advanced electro-optic (EO) properties, have been activating a broad interest in research and development of EO modulators for optic-fibre communications. However, the accurate measurements for the key physical parameter, the EO coefficient, is still at unoriented state. In this work, a BaTiO3 crystal film is grown on a magnesium oxide (MgO) crystal substrate and a device structure having an ultrahigh two-dimensional (2D) optic-electric field interaction is designed to conduct the synchronous measurements for the EO coefficient r 51 and the birefringence b eo of the BaTiO3 crystal film with an intra-guide push-pull modulation of linear polarization. As a result, the average values of 570±2pm/V and -0.0135±0.0007 of r 51 and b eo are obtained, respectively. Furthermore, a theoretical model for analysing the measurement accuracies of r 51 and b eo, and the accuracy dependences on the drive voltage and optic-electric interaction efficiency are studied, leading to an efficient way to developing the high-speed BaTiO3 crystal film EO modulators.

Circularly Polarized States Spawning from Bound States in the Continuum.

Bound states in the continuum in periodic photonic systems like photonic crystal slabs are proved to be accompanied by vortex polarization singularities on the photonic bands in the momentum space. The winding structures of polarization states not only widen the field of topological physics but also show great potential that such systems could be applied in polarization manipulating. In this Letter, we report the phenomenon that by in-plane inversion (C_{2}) symmetry breaking, pairs of circularly polarized states could spawn from the eliminated bound states in the continuum. Along with the appearance of the circularly polarized states as the two poles of the Poincaré sphere together with linearly polarized states covering the equator, full coverage on the Poincaré sphere could be realized. As an application, ellipticity modulation of linear polarization is demonstrated in the visible frequency range. This phenomenon provides a new degree of freedom in modulating polarization. The C points could also find applications in light-matter interactions. Further studying and manipulating the reported polarization singularities may lead to novel phenomena and physics in radiation modulating and topological photonics.

Multi-octave metamaterial reflective half-wave plate for millimeter and sub-millimeter wave applications.

The quasi-optical modulation of linear polarization at millimeter and sub-millimeter wavelengths can be achieved by using rotating half-wave plates (HWPs) in front of polarization-sensitive detectors. Large operational bandwidths are required when the same device is meant to work simultaneously across different frequency bands. Previous realizations of half-wave plates, ranging from birefringent multi-plates to mesh-based devices, have achieved bandwidths of the order of 100%. Here we present the design and experimental characterization of a reflective HWP able to work across bandwidths of the order of 150%. The working principle of the novel device is completely different from any previous realization, and it is based on the different phase-shift experienced by two orthogonal polarizations reflecting, respectively, off an electric conductor and an artificial magnetic conductor.

SIMULTANEOUS LINEAR AND CIRCULAR OPTICAL POLARIMETRY OF ASTEROID (4) VESTA

From a single, 3.8-hour observation of asteroid (4) Vesta at $13.7^\circ$ phase angle with the POLISH2 polarimeter at the Lick Observatory Shane 3-m telescope, we confirm rotational modulation of linear polarization in $B$ and $V$ bands. We measure the peak-to-peak modulation in degree of linear polarization to be $\Delta P = (294 \pm 35) \times 10^{-6}$ (ppm) and time-averaged $\Delta P / P = 0.0577 \pm 0.0069$. After rotating the plane of linear polarization to the scattering plane, asteroidal rotational modulation is detected with $12 \sigma$ confidence and observed solely in Stokes $Q/I$. POLISH2 simultaneously measures Stokes $I$, $Q$, $U$ (linear polarization), and $V$ (circular polarization), but we detect no significant circular polarization with a $1 \sigma$ upper limit of 140 ppm in $B$ band. Circular polarization is expected to arise from multiple scattering of sunlight by rough surfaces, and it has previously been detected in nearly all other classes of Solar System bodies save asteroids. Subsequent observations may be compared with surface albedo maps from the Dawn Mission, which may allow identification of compositional variation across the asteroidal surface. These results demonstrate the high accuracy achieved by POLISH2 at the Lick 3-m telescope, which is designed to directly detect scattered light from spatially unresolvable exoplanets.

Phase-shifting interferometry with four interferograms using linear polarization modulation and a Ronchi grating displaced by only a small unknown amount

A method to reduce the number of captures needed in phase-shifting interferometry is proposed on the basis of grating interferometry and modulation of linear polarization. The case of four interferograms is considered. A common-path interferometer is used with two windows in the object plane and a Ronchi grating as the pupil, thus forming several replicated images of each window over the image plane. The replicated images, under proper matching conditions, superpose in such a way so that they produce interference patterns. Orders 0 and +1 and −1 and 0 form useful patterns to extract the optical phase differences associated to the windows. A phase of π is introduced between these orders using linear polarizing filters placed in the windows and also in the replicated windows, so two π-shifted patterns can be captured in one shot. An unknown translation is then applied to the grating in order to produce another shift in the each pattern. A second and final shot captures these last patterns. The actual grating displacement and the phase shift can be determined according to the method proposed by Kreis before applying proper phase-shifting techniques to finally calculate the phase difference distribution between windows. Related simulations and experimental results are given.

Object separation by polarimetric and spectral imagery fusion

When light is reflected from object surface, its spectral characteristics will be affected by the surface’s elemental composition, and its polarimetric characteristics will be governed by the surface’s roughness and conductance. Polarimetric and multispectral imaging can provide complementary discriminative information in applications such as object separation. However, few methods have been proposed to fuse the information provided by polarimetric and multispectral imagery for better object separation results. Considering that the metal and dielectric materials, and the manmade objects and natural background have different polarimetric and multispectral features, in this paper we propose a simple yet powerful method for object separation by using the polarimetric and spectral characteristics of specular and diffuse reflected light. A polarimetric imagery fusion algorithm is first proposed based on the degree of linear polarization modulation to distinguish different objects. Then the spectral and polarimetric information, which can be extracted from the specular and diffuse reflected light, is fused by using the HSI color space mapping for more robust object separation. Experiments on real outdoor and indoor images are performed to evaluate the efficiency of the proposed scheme.

Heterodyne Linear Polarization Modulation Ellipsometer

In this study, a novel heterodyne linear polarization modulation ellipsometer (LPME) is developed. It is based on a linear polarization rotator and is integrated with a common path heterodyne interferometer for ellipsometric parameter measurement. LPME is an amplitude-sensitive interferometric ellipsometer that can not only provide a wider range for its polarization modulation frequency than that of a conventional photometric ellipsometer but also be used for measurement in real time. LPME is also insensitive to laser intensity fluctuations. The independence of the elliptical polarization to the incident laser beam induced by imperfections in the quarter-wave plate in LPME is analyzed.