Polarization Position Research Articles

Numerical Simulations of Single-Step Holographic Interferometry for Split-Ring Metamaterial Fabrication.

Artificial microstructures, especially metamaterials, have garnered increasing attention in numerous applications due to their rich and distinctive properties. Starting from the principle of multi-beam interference, we have theoretically devised a beam configuration consisting of six symmetrically distributed coherent beams to generate two-dimensional microstructures with diverse shapes of unitcells under different polarization combinations. In particular, a split-ring metamaterial template is achieved with two adjacent circularly and four linearly polarized beams with such single-step holographic interferometry. Furthermore, simulation results show that the orientation and shape of the split-ring unitcell can be accurately adjusted by controlling the polarization position, polarization degree, or power ratio of the coherent beams. The optimal parameters to produce a high-quality split-ring metamaterial with a contrast higher than 0.97 are obtained. These results provide useful guidance for the effective and low-cost fabrication of metamaterials with diverse unitcells.

Spatial, temporal and numerical regulation of polar flagella assembly in Pseudomonas putida.

The Gram-negative bacterium Pseudomonas putida bears a tuft of flagella at a single cell pole. New flagella must be assembled de novo every cell cycle to secure motility of both daughter cells. Here we show that the coordinated action of FimV, FlhF and FleN sets the location, timing and number of flagella assembled. The polar landmark proteins FimV and FlhF are independently targeted to the nascent new pole during or shortly after cell division, but FimV stabilizes FlhF association with the cell poles. FlhF determines the polar position of the flagella by targeting early flagellar components to the cell pole and preventing their nucleation at non-polar sites. FlhF also promotes efficient flagellar assembly and indirectly stimulates Class III flagellar promoter activation by promoting secretion of the anti-FliA anti-σ factor FlgM. The MinD-like ATPase FleN partitions between the cell poles and the cytoplasm. Cytoplasmic FleN regulates flagellar number by preventing excessive accumulation of FlhF at the cell poles that may otherwise lead to hyperflagellation, likely by antagonizing FleQ-dependent transcriptional activation. FimV is essential to FleN polar location. FimV and FleN temporally regulate the onset of flagellar assembly by preventing premature polar targeting of FlhF and the ensuing premature targeting of additional flagellar components. Our results shed new light on the mechanisms that ensure the timely assembly of the appropriate number of flagella at the correct polar location in polarly flagellated bacteria.

Investigating Kozai-Lidov oscillations and disc tearing in Be star discs

Abstract Recent simulations of Be stars in misaligned binary systems have revealed that misalignment between the disc and binary orbit can cause the disc to undergo Kozai-Lidov (KL) oscillations or disc-tearing. We build on our previous suite of three-dimensional smoothed particle hydrodynamics simulations of equal-mass systems by simulating eight new misaligned Be star binary systems, with mass-ratios of 0.1 and 0.5, or equal-mass systems with varying viscosity. We find the same phenomena occur as previously for mass ratios of 0.5, while the mass ratio of 0.1 does not cause KL oscillations or disc-tearing for the parameters examined. With increased viscosity in our equal-mass simulations, we show that these phenomena and other oscillations are damped out and do not occur. We also briefly compare two viscosity prescriptions and find they can produce the same qualitative disc evolution. Next, we use the radiative transfer code hdust to predict observable trends of a KL oscillation, and show how the observables oscillate in sync with disc inclination and cause large changes in the polarization position angle. Our models generate highly complex line profiles, including triple-peak profiles that are known to occur in Be stars. The mapping between the SPH simulations and these triple-peak features gives us hints as to where they originate. Finally, we construct interferometric predictions of how a gap in the disc, produced by KL oscillations or disc-tearing, perturbs the visibility versus baseline curve at multiple wavelengths, and can cause large changes to the differential phase profile across an emission line.

Triple trouble with PSR J1618−3921: Mass measurements and orbital dynamics of an eccentric millisecond pulsar

Context. PSR J1618−3921 is one of five known millisecond pulsars (MSPs) in eccentric orbits (eMPSs) located in the Galactic plane, whose formation is poorly understood. Earlier studies of these objects revealed significant discrepancies between observations and predictions from standard binary evolution scenarios of pulsar-helium white dwarf (HeWD) binaries, especially in the case of PSR J0955−6150, for which mass measurements ruled out most eMSP formation models. Aims. We aim to measure the masses of the pulsar and its companion, and constrain the orbital configuration of PSR J1618−3921. This facilitates understanding similarities among eMSPs and could offer hints as to their formation mechanism. Methods. We conducted observations with the L-band receiver of the MeerKAT radio telescope and the UWL receiver of the Parkes Murriyang radio telescope between 2019 and 2021. These data were added to archival Parkes and Nançay observations. We performed a full analysis on this joint data set with a timing baseline of 23 years. We also used the data from recent observations to give a brief account of the emission properties of J1618−3921, including a rotating vector model (RVM) fit of the linear polarisation position angle of the pulsar. Results. From the timing analysis, we measure a small but significant proper motion of the pulsar. The long timing baseline allowed for a highly significant measurement of the rate of advance of periastron of ω̇ = (0.00145±0.00010)°yr−1. Despite the tenfold improvement in timing precision from MeerKAT observations, we can only report a low-significance detection of the orthometric Shapiro delay parameters, h3 = 2.70−1.47+2.07 μs and ς = 0.68−0.09+0.13. Under the assumption of the validity of general relativity (GR), the self-consistent combination of these three parameters leads to mass estimates of the total and individual masses in the binary of Mtot = 1.42−0.19+0.20 M⊙, Mc = 0.20−0.03+0.11 M⊙, and Mp = 1.20−0.20+0.19 M⊙. We detect an unexpected change in the orbital period of Ṗb = −2.26−0.33+0.35 × 10−12, that is an order of magnitude larger and carries an opposite sign to what is expected from the Galactic acceleration and the Shklovskii effect, which are a priori the only non-negligible contributions expected for Ṗb. We also detect a significant second derivative of the spin frequency, f̈. The RVM fit reveals a viewing angle of ζ = (111 ± 1)°. Furthermore, we report an unexpected, abrupt change in the mean pulse profile in June 2021 of unknown origin. Conclusions. We propose that the anomalous Ṗb and f̈ we measure for J1618−3921 indicate an additional varying acceleration due to a nearby mass. The J1618−3921 binary system is likely part of a hierarchical triple, but with the third component much farther away than the outer component of the MSP in a triple star system, PSR J0337+1715. This finding suggests that at least some eMSPs might have formed in triple star systems. Although the uncertainties are large, the binary companion mass is consistent with the Pb − MWD relation, which has been verified for circular HeWD binaries and also for the two HeWDs in the PSR J0337+1715 system. Future regular observations with the MeerKAT telescope will, due to the further extension of the timing baseline, improve the measurement of Ṗb and f̈. This will help us further understand the nature of this system, and perhaps improve our understanding of eMSPs in general.

Polarization position angle standard stars: a reassessment of θ and its variability for seventeen stars based on a decade of observations

ABSTRACT Observations of polarization position angle ($\theta$) standards made from 2014 to 2023 with the High Precision Polarimetric Instrument (HIPPI) and other HIPPI-class polarimeters in both hemispheres are used to investigate their variability. Multiband data were first used to thoroughly recalibrate the instrument performance by bench-marking against carefully selected literature data. A novel co-ordinate difference matrix (CDM) approach – which combines pairs of points – was then used to amalgamate monochromatic ($g^\prime$ band) observations from many observing runs and re-determine $\theta$ for 17 standard stars. The CDM algorithm was then integrated into a fitting routine and used to establish the impact of stellar variability on the measured position angle scatter. The approach yields variability detections for stars on long time-scales that appear stable over short runs. The best position angle standards are $\ell$ Car, o Sco, HD 154445, HD 161056, and $\iota ^1$ Sco, which are stable to $\le$0.123$^\circ$. Position angle variability of 0.27–0.82$^\circ$, significant at the 3$\sigma$ level, is found for 5 standards, including the Luminous Blue Variable HD 160529 and all but one of the other B/A-type supergiants (HD 80558, HD 111613, HD 183143, and 55 Cyg), most of which also appear likely to be variable in polarization magnitude (p) – there is no preferred orientation for the polarization in these objects, which are all classified as $\alpha$ Cygni variables. Despite this we make six key recommendations for observers – relating to data acquisition, processing and reporting – that will allow them to use these standards to achieve $\lt $ 0.1$^\circ$ precision in the telescope position angle with similar instrumentation, and allow data sets to be combined more accurately.

MeerKAT observations of pair-plasma induced birefringence in the double pulsar eclipses

ABSTRACT PSR J0737−3039A/B is unique among double neutron star systems. Its near-perfect edge-on orbit causes the fast spinning pulsar A to be eclipsed by the magnetic field of the slow spinning pulsar B. Using high-sensitivity MeerKAT radio observations combined with updated constraints on the system geometry, we studied the impact of these eclipses on the incident polarization properties of pulsar A. Averaging light curves together after correcting for the rotation of pulsar B revealed enormous amounts of circular polarization and rapid changes in the linear polarization position angle, which occur at phases where emission from pulsar A is partially transmitted through the magnetosphere of pulsar B. These behaviours confirm that the eclipse mechanism is the result of synchrotron absorption in a relativistic pair-plasma confined to the closed-field region of pulsar B’s truncated dipolar magnetic field. We demonstrate that changes in circular polarization handedness throughout the eclipses are directly tied to the average line of sight magnetic field direction of pulsar B, from which we unambiguously determine the complete magnetic and viewing geometry of the pulsar.

On the Flux Density Spectral Property of High Linearly Polarized Signal from Pulsar J0332+5434

The polarization position angles (PPA) of time samples with high linear polarization often show two parallel tracks across the pulsar profile that follow the rotating vector model (RVM). This feature supports coherent curvature radiation (CCR) as the underlying mechanism of radio emission from pulsars, where the parallel tracks of the PPA represent the orthogonal extraordinary (X) and ordinary (O) eigenmodes of strongly magnetized pair plasma. However, the frequency evolution of these high linearly polarized signals remains unexplored. In this work, we explore the flux density spectral nature of high linearly polarized signals by studying the emission from PSR J0332+5434 over a frequency range between 300 and 750 MHz, using the Giant Metrewave Radio Telescope. The pulsar average profile comprises a central core and a pair of conal components. We find the high linearly polarized time samples to be broadband in nature, and in many cases, they resemble a narrow spiky feature in the conal regions. These spiky features are localized within a narrow pulse longitude over the entire frequency range, and their spectral shapes sometimes resemble an inverted parabolic shape. In all such cases, the PPA is exclusively along one of the orthogonal RVM tracks, likely corresponding to the X-mode. The inverted spectral shape can, in principle, be explained if the high linearly polarized emission in these time samples is formed due to the incoherent addition of CCR from a large number of charged solitons (charge bunches) exciting the X-mode.

Robust optical singularity detection enabled by spin-synchronized shearing interference

Singular beams carrying phase and polarization singularities have been extensively studied for applications in optical communication, quantum information processing, optical imaging, and other fields. However, developing a robust method to detect optical singularity that is insensitive to wavelength, polarization, and illumination position remains a significant challenge. In this study, we propose and demonstrate a robust optical singularity detection scheme based on spin-synchronized shearing interference (SSSI) using spin-dependent gradient phase modulation of a quarter-wave liquid–crystal polarization grating. Since the spin-dependent gradient phase modulation of the polarization grating is wavelength-independent, and the two circular bases of the incident field can be measured simultaneously, the proposed method is robust to wavelength and polarization. Additionally, we have verified that SSSI performs well in detecting multi-singularity cylindrical vector beam. This work provides a practical and straightforward scheme for robust optical singularity detection.

Unifying Building Instance Extraction and Recognition in UAV Images

Building instance extraction and recognition (BEAR) extracts and further recognizes building instances in unmanned aerial vehicle (UAV) images, holds with paramount importance in urban understanding applications. To address this challenge, we propose a unified network, BEAR-Former. Given the difficulty of building instance recognition due to the small area and multiple instances in UAV images, we developed a novel multi-view learning method, Cross-Mixer. This method constructs a cross-regional branch and an intra-regional branch to, respectively, extract the global context dependencies and local spatial structural details of buildings. In the cross-regional branch, we cleverly employed cross-attention and polar coordinate relative position encoding to learn more discriminative features. To solve the BEAR problem end to end, we designed a channel group and fusion module (CGFM) as a shared encoder. The CGFM includes a channel group encoder layer to independently extract features and a channel fusion module to dig out the complementary information for multiple tasks. Additionally, an RoI enhancement strategy was designed to improve model performance. Finally, we introduced a new metric, Recall@(K, iou), to evaluate the performance of the BEAR task. Experimental results demonstrate the effectiveness of our method.

Current state of development, adoption, implementation of legislation on mobilization issues and its effectiveness

Public relations that arise in connection with mobilization as an important military component of repelling armed aggression by Russia and protecting the borders and territories of Ukraine from a large-scale invasion of Russian troops are currently a priority and urgent issue in the state and concern all layers of society. But such an important issue requires effective, high-quality, optimal and effective legislative regulation. And in part, these efforts have already been implemented in the adopted Law No. 3633-IX dated April 11, 2024 «On Amendments to Certain Legislative Acts of Ukraine Regarding Certain Issues of Military Service, Mobilization, and Military Registration». At the same time, the state of development, adoption, implementation of legislation on mobilization and its effectiveness require professional discussion by legal scholars and are an actual scientific topic with different points of view (and sometimes polar approaches or positions to one or another aspect of mobilization, which is normal). The purpose of the article is to provide a definition of the concept of «mobilization», referring to legislative and open sources and explaining the main components, problems of this phenomenon (at the same time military, military, legal and legal), improving the effectiveness of legislation in this area. Also, on the basis of the scientific opinions of scientists, highlight approaches to the essence of the main manifestations and components of mobilization. This issue is considered in the article and it is established that the current state of development, adoption, implementation of legislation on mobilization and its effectiveness (as a certain process, which involves mandatory and specific components and successive stages, as well as the result, which must necessarily be received) is a response to today’s challenges and requests for the purpose of defending the country in the conditions of a large-scale military invasion of the Russian Federation and repelling armed aggression (with the de-occupation of territories). The very fact that on April 11, 2024 the deputies adopted Law No. 3633-IX «On Amendments to Certain Legislative Acts of Ukraine Regarding Certain Issues of Military Service, Mobilization, and Military Registration» shows that work in this direction is ongoing and will be carried out in the future through appropriate legislative changes. but at the same time, it is necessary to take into account not only the expediency of the quantitative and qualitative filling of the army, but also the need to ensure the rights and freedoms of citizens during mobilization. In addition, in the process of law-making in this direction, it is necessary to take into account the opinion of professional lawyers, the conclusions of experts, the doctrinal approaches of legal scholars in order to ensure the effectiveness of legislation on mobilization issues. Key words: mobilization, mobilization preparation, mobilization measures, legal regulation, armed aggression, war, legislation, law on mobilization, draft Law No. 10449 dated 30.01.2024, Law No. 3633-IX dated 11.04.2014, effectiveness of legislation.

PSR B0943+10: Mode Switch, Polar Cap Geometry, and Orthogonally Polarized Radiation

As one of the paradigm examples to probe into pulsar magnetospheric dynamics, PSR B0943+10 (J0946+0951) manifests representatively, showing a mode switch, orthogonal polarization, and subpulse drifting, frequently studied below 600 MHz. Here, both integrated and single pulses are studied at a high frequency (1.25 GHz) with FAST. The mode switch is studied using a profile decomposition method. A phase space evolution for the pulsar’s mode switch shows a strange-attractor-like pattern. The radiative geometry is proposed by fitting polarization position angles with the rotating vector model. The pulsar pulse profile is then mapped to the sparking locations on the pulsar surface, and the differences between the main pulse’s and the precursor component’s radiative processes may explain the X-ray’s synchronization with radio mode switch. Detailed single pulse studies on B0943+10's orthogonally polarized radiation are presented, which may support certain models of radiative transfer of polarized emission. In particular, the difference in orthogonal polarization modes’ circular polarization might reflect the cyclotron absorption in pulsar magnetospheres. B0943+10's B and Q modes evolve differently with frequency and have different proportions of orthogonal modes, which indicates possible magnetospheric changes during mode switch. For Q mode pulse profile, the precursor and the main pulse components are orthogonally polarized, and are probably originated from different depths in the magnetosphere. The findings could impact significantly on the pulsar electrodynamics and the radiative mechanism related.

Spindle Detection Based on Elastic Time Window and Spatial Pyramid Pooling.

Sleep spindles have emerged as valuable biomarkers for assessing cognitive abilities and related disorders, underscoring the importance of their detection in clinical research. However, template matching-based algorithms using fixed templates may not be able to fully adapt to spindles of different durations. Moreover, inspired by the multiscale feature extraction of images, the use of multiscale feature extraction methods can be used to better adapt to spindles of different frequencies and durations. Therefore, this study proposes a novel automatic spindle detection algorithm based on elastic time windows and spatial pyramid pooling (SPP) for extracting multiscale features. The algorithm utilizes elastic time windows to segment electroencephalogram (EEG) signals, enabling the extraction of features across multiple scales. This approach accommodates significant variations in spindle duration and polarization positioning during different EEG epochs. Additionally, spatial pyramid pooling is integrated into a depthwise separable convolutional (DSC) network to perform multiscale pooling on the segmented spindle signal features at different scales. Compared with existing template matching algorithms, this algorithm's spindle wave polarization positioning is more consistent with the real situation. Experimental results conducted on the public dataset DREAMS show that the average accuracy of this algorithm reaches 95.75%, with an average negative predictive value (NPV) of 96.55%, indicating its advanced performance. The effectiveness of each module was verified through thorough ablation experiments. More importantly, the algorithm shows strong robustness when faced with changes in different experimental subjects. This feature makes the algorithm more accurate at identifying sleep spindles and is expected to help experts automatically detect spindles in sleep EEG signals, reduce the workload and time of manual detection, and improve efficiency.

Decoding the Nature of Coherent Radio Emission in Pulsars I: Observational Constraints

Radio observations from normal pulsars indicate that the coherent radio emission is excited by curvature radiation from charge bunches. In this review, we provide a systematic description of the various observational constraints on the radio emission mechanism. We have discussed the presence of highly polarized time samples where the polarization position angle follow two orthogonal well-defined tracks across the profile that closely match the rotating vector model in an identical manner. The observations also show the presence of circular polarization, with both the right and left handed circular polarization seen across the profile. Other constraints on the emission mechanism are provided by the detailed measurements of the spectral index variation across the profile window, where the central part of the profile, corresponding to the core component, has a steeper spectrum than the surrounding cones. Finally, the detailed measurements of the subpulse drifting behaviour can be explained by considering the presence of non-dipolar field on the stellar surface and the formation of the partially screened gap (PSG) above the polar cap region. The PSG gives rise to a non-stationary plasma flow that has a multi-component nature, consisting of highly energetic primary particles, secondary pair plasma, and iron ions discharged from the surface, with large fragmentation resulting in dense plasma clouds and lower-density inter-cloud regions. The physical properties of the outflowing plasma and the observational constraints lead us to consider coherent curvature radiation as the most viable explanation for the emission mechanism in normal pulsars, where propagation effects due to adiabatic walking and refraction are largely inconsequential.

The Method of Searching for Rotations of the Polarization Position Angle of Quasars

The Method of Searching for Rotations of the Polarization Position Angle of Quasars

Evolved and Cultural Intuitions. Highly Speculative Remarks on the Origins of our Sense of Fairness

The question of whether the sense of fairness constitutes an exclusively human trait has been answered mostly from two polar positions: the first one unambiguously affirms such exclusivity, thus denying the relevance of cognitive ethology to understand our evaluations of justice; the second one, on the contrary, postulates the existence of a (proto) sense of fairness in non-human animals, strongly related to ours, which would make cognitive ethology highly relevant to understand the mechanisms on which our evaluative practices are based. From a position of extreme caution in relation to the possibility of (eventually) offering concrete evidence in favor of innatist theses such as the one I will defend here, I will suggest that i) in line with the rupturist positions, it is possible to preserve the human exclusivity of the sense of justice, ii) in line with the continuist positions, the relevance of studies coming from cognitive ethology is guaranteed, insofar as (ex hypotesi) our evaluative practices often take as input innate psychological dispositions shared with other species. Finally, I will suggest that the concept of rationalization is central to determine in each case the possible articulation between innate dispositions and explicit justifications.

Investigating Zonal Asymmetries in Stratospheric Ozone Trends From Satellite Limb Observations and a Chemical Transport Model

AbstractThis study investigates the origin of a zonal asymmetry in stratospheric ozone trends at northern high latitudes, identified in satellite limb observations over the past two decades. We use a merged data set consisting of ozone profiles retrieved at the University of Bremen from SCIAMACHY and OMPS‐LP measurements to derive ozone trends. We also use TOMCAT chemical transport model (CTM) simulations, forced by ERA5 reanalyses, to investigate the factors that drive the asymmetry observed in the long‐term changes. By studying seasonally and longitudinally resolved observation‐based ozone trends, we find, especially during spring, a well‐pronounced asymmetry at polar latitudes with values up to +6 % per decade over Greenland and −5 % per decade over western Russia. The control CTM simulation agrees well with these observed trends, whereas sensitivity simulations indicate that chemical mechanisms involved in the production and removal of ozone, or their changes, are unlikely to explain the observed behavior. The decomposition of TOMCAT ozone time series and ERA5 geopotential height into the first two wavenumber components shows a clear correlation between the two variables in the middle stratosphere and demonstrates a weakening and a shift in the wavenumber‐1 planetary wave activity over the past two decades. Finally, the analysis of the polar vortex position and strength points to a decadal oscillation with a reversal pattern at the beginning of the century. The same is found in the ozone trend asymmetry. This further stresses the link between changes in the polar vortex position and the identified ozone trend pattern.

The Thousand-Pulsar-Array programme on MeerKAT – XIV. On the high linearly polarized pulsar signals

ABSTRACT The S-shaped swing of the linear polarization position angle (PPA) observed in many pulsars can be interpreted by the rotating vector model (RVM). However, efforts to fit the RVM for a large sample of pulsars observed with the MeerKAT telescope as a part of the Thousand-Pulsar-Array (TPA) programme, only succeeded for about half the cases. High time-resolution studies suggest that the failed cases arise due to the presence of orthogonal polarization modes, or highly disordered distribution of PPA points. One such example is PSR J1645−0317. Recently it has been shown that the RVM can be recovered in this pulsar by using only time samples which are greater than 80 per cent linearly polarized. In this work, we test this novel approach on the brightest 249 pulsars from the TPA sample, of which 177 yield sufficient highly polarized samples to be amenable to our method. Remarkably, only nine of these pulsars (5 per cent) now fail to fit the RVM as opposed to 59 per cent from the original analysis. This result favours the paradigm that the underlying mechanism is coherent curvature radiation.

Investigation of Profile Shifting and Subpulse Movement in PSR J0344-0901 with FAST

We report two phenomena detected in PSR J0344−0901 from two observations conducted at frequencies centered at 1.25 GHz using the Five-hundred-meter Aperture Spherical Radio Telescope. The first phenomenon manifests as the pulse emission shifting to later longitudinal phases and then gradually returning to its original location. The event lasts for about 216 pulse periods, with an average shift of about 0.°7 measured at the peak of the integrated profile. Changes in the polarization position angle (PPA) are detected around the trailing edge of the profile, together with an increase in the profile width. The second phenomenon is characterized by the apparent movement of subpulses, which results in different subpulse track patterns across the profile window. For the first time in this pulsar, we identify four emission modes, each with unique subpulse movement, and determine the pattern periods for three of them. Pulse nulling was not detected. Modeling of the changes in the PPA using the rotating vector model gives an inclination angle of 75.°12 ± 3.°80 and an impact parameter of −3.°17 ± 5.°32 for this pulsar. We speculate that the subpulse movement may be related to the shifting of the pulse emission.

Radio Pulsar B0950+08: Radiation in the Magnetosphere and Sparks above the Surface

We observed the nearby radio pulsar B0950+08, which has a 100% duty cycle, using the Five-hundred-meter Aperture Spherical Radio Telescope. We obtained the polarization profile for its entire rotation, which enabled us to investigate its magnetospheric radiation geometry and the sparking pattern of the polar cap. After we excluded part of the profile in which the linear polarization factor is low (≲30%) and potentially contaminated by jumps in position angle, the rest of the swing in polarization position angle fits a classical rotating vector model (RVM) well. The best-fit RVM indicates that the inclination angle, α, and the impact angle, β, of this pulsar, are 100.°5 and −33.°2, respectively, suggesting that the radio emission comes from two poles. We find that, in such RVM geometry, either the annular vacuum gap model or the core vacuum gap model would require that the radio emissions come from a high-altitude magnetosphere with heights from ∼0.25 R LC to ∼0.56 R LC, with R LC being the light cylinder radius. Both the main and interpulses’ sparking points are located away from the magnetic pole, which could relate to the physical conditions on the pulsar surface.

Non-orthogonal optical multiplexing empowered by deep learning

Orthogonality among channels is a canonical basis for optical multiplexing featured with division multiplexing, which substantially reduce the complexity of signal post-processing in demultiplexing. However, it inevitably imposes an upper limit of capacity for multiplexing. Herein, we report on non-orthogonal optical multiplexing over a multimode fiber (MMF) leveraged by a deep neural network, termed speckle light field retrieval network (SLRnet), where it can learn the complicated mapping relation between multiple non-orthogonal input light field encoded with information and their corresponding single intensity output. As a proof-of-principle experimental demonstration, it is shown that the SLRnet can effectively solve the ill-posed problem of non-orthogonal optical multiplexing over an MMF, where multiple non-orthogonal input signals mediated by the same polarization, wavelength and spatial position can be explicitly retrieved utilizing a single-shot speckle output with fidelity as high as ~ 98%. Our results resemble an important step for harnessing non-orthogonal channels for high capacity optical multiplexing.