Orthogonal Polarization Research Articles

A New Emission Mode of PSR B1859+07

Previous studies have identified two emission modes in PSR B1859+07: a normal mode that has three prominent components in the average profile, with the trailing one being the brightest, and an anomalous mode (i.e., the A mode) where emissions seem to be shifted to an earlier phase. Within the normal mode, further analysis has revealed the presence of two submodes, i.e., the cW mode and cB mode, where the central component can appear either weak or bright. As for the anomalous mode, a new bright component emerges in the advanced phase while the bright trailing component in the normal mode disappears. New observations of PSR B1859+07 using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) have revealed the existence of a previously unknown emission mode, dubbed the Af mode. In this mode, all emission components seen in the normal and anomalous modes are detected. Notably, the mean polarization profiles of both the A and Af modes exhibit a jump in the orthogonal polarization angle modes in the bright leading component. The polarization angles for the central component in the original normal mode follow two distinct orthogonal polarization modes in the A and Af modes respectively. The polarization angles for the trailing component show almost the same but a small systematic shift in the A and Af modes, roughly following the values for the cW and cB modes. Those polarization features of this newly detected emission mode imply that the anomalous mode A of PSR B1859+07 is not a result of “phase shift” or “swooshes” of normal components, but simply a result of the varying intensities of different profile components. Additionally, subpulse drifting has been detected in the leading component of the Af mode.

Bi-channel compressive hyperspectral imager based on polarization conversion metasurface

Metasurfaces have demonstrated remarkable capabilities in manipulating light fields and reducing the size of conventional optical elements to ultrathin devices, and compressive hyperspectral imaging systems can effectively utilize the spectral modulations of metasurfaces through spectral transmission tuning. In this paper, a bi-channel compressive hyperspectral imager based on polarization conversion metasurfaces is proposed. The metasurface layer of this device is able to modulate and convert the polarized incidence into two outputs of different transmission spectra with orthogonal polarizations, providing two channels of hyperspectral information that can be detected by a polarization image sensor in one snapshot. Additionally, this design offers a compact size, high speed, and accurate reconstruction through the utilization of a macro-pixel segmentation method for compressive sensing algorithms, and it is firmly demonstrated that the proposed hyperspectral imaging technology surpasses other traditional compressive hyperspectral image recovery methods in terms of improved reconstruction quality. Therefore, it is envisioned that this technology will find significant applications in various fields, including food safety, biomedical imaging, precision agriculture, object detection and so on.

Optical computation of Laplace operator using Pancharatnam-Berry lens of large focal length

We propose an optical Laplace operator consisting of a large-focal-length Pancharatnam-Berry lens placed on the Fourier plane of an optical imaging system and sandwiched with two orthogonal linear polarizers. Theoretical analysis reveals that the isotropic second-order differentiation derives from the quadratic phase attached to the left-handed and right-handed circularly polarized light. The Pancharatnam-Berry lens made of liquid crystal with high transmittance and diffraction efficiency is integrated into different imaging systems to realize edge detection for both amplitude and phase objects, and the results conform to the theory well. This work paves the way to implement Laplace operator in practical applications such as image processing and high-contrast microscopy.

PDM-SHD NFDM transmission with envelope-detection feedback polarization tracking and optical injection locking.

Nonlinear frequency division multiplexing (NFDM) systems, especially the eigenvalue communications have the potential to overcome the nonlinear Shannon capacity limit. However, the baud rate of eigenvalue communications is typically restricted to a few GBaud, making it challenging to mitigate laser frequency impairments such as the phase noise and frequency offset (FO) using digital signal processing (DSP) algorithms in intradyne detections (IDs). Therefore, we introduce the polarization division multiplexing-self-homodyne detection (PDM-SHD) into the NFDM link, which could overcome the impact of phase noise and FO by transmitting a pilot carrier originating from the transmitter laser to the receiver through the orthogonal polarization state of signal. To separate the signal from the carrier at the receiver, a carrier to signal power ratio (CSPR) unrestricted adaptive polarization controlling strategy is proposed and implemented by exploiting the optical intensity fluctuation of the light in a particular polarization rather than its direct optical power as the feedback. Optical injection locking (OIL) is used subsequently to amplify optical power of pilot carrier and mitigate the impact of signal-signal beat interference (SSBI). Additionally, the effects of cross-polarization modulation (XPolM) and modulation instability (MI) in long haul transmission are explored and inhibited. The results show that the tolerable FO range is about 3.5 GHz, which is 17 times larger than the ID one. When 16-amplitude phase shift keying (APSK) or 64-APSK constellations are used, identical Q-factor performance can be obtained by using distributed feedback (DFB, ∼10 MHz) laser, external cavity laser (ECL, ∼100kHz), or fiber laser (FL, ∼100 Hz), respectively, which demonstrates that our proposed PDM-SHD eigenvalue communication structure is insensitive to the laser linewidth. Under the impact of cycle slip, the Q-factor difference of 16-APSK signal between the ECL-ID system and ECL-SHD system can be up to 8.73 dB after 1500 km transmission.

Spectral interference ellipsometry for film thickness measurement on transparent substrate

Measuring film thickness on transparent substrate is crucial and universal for semiconductor chips. This paper proposes an orthogonal polarization common-path film thickness measurement system without the frustration of back-surface reflection based on spectral interference ellipsometry. The proposed system demonstrates that the phase stability of spectral interference reached 5×10-4 rad under common path. Combined with ellipsometry, the back-surface reflection issues were theoretically deduced and solved by the proposed system. The measured thicknesses of three kinds of film specimens on transparent substrates agreed well with those determined using a commercial ellipsometer. The measurement precision was greater than 1 nm.

Dual-parameter femtosecond mode-locking pulse generation in partially shared all-polarization-maintaining fiber Y-shaped oscillator with a single saturable absorber

We present a design of a mode-locked fiber laser based on a polarization-maintaining (PM) Y-shaped fiber structure, which employs a single semiconductor saturable absorber mirror (SESAM) and a common polarization beam combiner (PBC) to achieve dual- parameter mode-locking femtosecond pulse in two orthogonal polarization states. The two output pulses have different characteristics, such as repetition frequency (87.3 MHz and 91.3 MHz), average output powers (2.1 mW and 1.9 mW), pulse durations (299 fs and 377 fs) and spectral profiles (centered at 1565.6 nm and 1563.6 nm with spectral width of 9.96 nm and 9.93 nm). The properties of the two pulses are experimentally characterized and their potential applications in areas such as bistable frequency lasers and dual femtosecond optical frequency comb is discussed.

Optical Tunable Frequency-Doubling OEO Using a Chirped FBG Based on Orthogonally Polarized Double Sideband Modulation

We propose and experimentally demonstrate a tunable frequency-doubling optoelectronic oscillator (FD-OEO) based on a single-bandpass dispersion-induced microwave photonic filter (MPF) consisting of a Mach–Zehnder modulator (MZM), a linearly chirped fiber Bragg grating and polarization-multiplexed dual-loop. Thanks to the polarization dependence of the MZM, a special double sideband modulation is implemented where the optical carrier (OC) and subcarriers are orthogonally polarized. By simply tuning the PC in the OEO loop, the phase difference between the orthogonal polarization carrier and two sidebands can be controlled, and thus the center frequency of the fundamental OEO can be tuned. Furthermore, a PC and a polarizer are placed outside the OEO to achieve optical carrier suppression (OCS) modulation, which ensures that a frequency-tunable microwave signal at the second-harmonic frequency is generated. In the experiment, a fundamental frequency signal with tunable frequency from 3.6 to 6.85 GHz and FD-OEO with a tunable frequency range from 7.2 to 13.7 GHz are generated.

Climatology of aerosol types and their vertical distribution over Iran using CALIOP dataset during 2007–2021

The present study uses a Lidar-based aerosol type's extinction coefficient (EC) of the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) on the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission to investigate the spatio-temporal changes in the vertical cross section of aerosols from 2007 to 2021 in Iran. Aerosol characteristics i.e., the EC values (levels) and frequency are presented in a seasonal time scale. The trend of aerosol types EC in the vertical profile was estimated using Sen's slope estimator. Moreover a Pearson's correlation was employed to assess the link between climatic factors (temperature, pressure and relative humidity) and aerosol types EC. It is found that smoke followed by polluted continental have the largest EC levels than dust and polluted dust. The highest level and frequency of dust EC were observed in summer at an average altitude of 0.7 and 4.5 km, respectively in southern Iran. The highest level and greatest frequency of polluted continental were detected in summer and winter respectively at an altitude of below 2 km in the southern and northern polluted cities of Iran. The highest level and the greatest frequency of polluted dust EC were recorded in summer in the south of Iran at an average altitude of 4.5 km. Both the maximum smoke EC level and frequency were detected in winter and in the south of Iran at an average altitude of 4 km. A significant decreasing (increasing) trend of dust (polluted continental) EC was observed in spring and summer (summer) at an altitude below 5 (3) km in most regions (northern part) of Iran. Polluted dust showed an increasing trend in spring in most regions at an altitude below 5 km. The correlation between climatic factors and aerosol EC varied according to seasons, altitudes, and aerosol type. The common feature was the positive correlation between aerosol types EC and relative humidity in most regions, seasons and altitudes. In the final step, six polluted cities were analyzed for aerosol's trend and the correlations.

A Switchable A-T-A Rasorber With Polarization Selectivity and High Roll-Off Characteristics

Switchable rasorber has attracted a great deal of interest in recent years due to its in-band shielding ability. In this work, a methodology for designing a switchable rasorber with high roll-off and polarization selection characteristics is proposed. The device can be switched between rasorber, polarization selection and absorber modes, and composes of two resistive layers (a passive and an active resistive layer) and a frequency selective surface (FSS). Transmission zeros (TZs) are introduced in the FSS design to improve the roll-off characteristic of its transmission band. The PIN diodes on the active resistive layer and FSS can be independently controlled in the orthogonal polarizations to realize the polarization selectivity. The simulation results indicate that the device exhibits a 27.5% fractional transmission bandwidth (3.42 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 4.51 GHz) under rasorber mode. In addition, the fractional absorption bandwidth is as large as 142.9% (1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 6 GHz) under absorber mode. A prototype is fabricated and measured to validate the proposed design methodology. This work is promising for designing metamaterials (MMs) with excellent flexibility and high performance.

Propellant Influence on Electromagnetic Environment Generated by Stationary Plasma Thrusters

Possible aspects of violation of the functional safety of spacecraft in terms of electromagnetic compatibility with electric rocket thrusters in their work on alternative working substances are considered. The procedure of experimental determination of spectral–time characteristics of own electromagnetic radiation of laboratory model of stationary plasma thruster SPT-70 developed by the Research Institute of Applied Mechanics and Electrodynamics of the Moscow Aviation Institute is described. Measurements of noise emissions were carried out on a vacuum installation with a “radiotransparent” compartment and a shielded echo-free camera in the frequency range of 1–12 GHz for typical discharge capacities (600, 800, and 1000 W), vertical and horizontal polarization, and various working substances used (krypton and xenon). The conducted studies have allowed obtaining new comparative results of the assessment of spectral characteristics of SPT-70 radiation for standard modes and prospective working bodies within the orthogonal polarization bases. The new results should include information about the radiation characteristics of SPT-70 in the time area. It is shown that the transition from xenon to krypton retains the pulsed nature of the radiation of a stationary plasma thruster, leading not only to an increase in the amplitude of pulses, but also to an increase in the frequency of repetition of “bursts” and an increase in their duration, which requires additional measures to ensure electromagnetic compatibility in order to preserve the functional safety of the spacecraft.

A polarization-dependent near-infrared metamaterial absorber based on the hybrid halide perovskite in two orthogonal directions

A wide-angle and polarization-sensitive metamaterial absorber is highly desired for near-infrared optical applications, such as stealth coatings, photovoltaic materials, and detectors. Although current near-infrared metamaterial absorbers achieve high absorption rates, they are typically either polarization-independent or only sensitive to one direction. Herein, a (CH3NH3)PbBr3-based perfect absorber with high absorption in both orthogonal directions and polarization sensitivity has been designed. The maximum absorption in the transverse magnetic (TM)-polarized light exceeds 99.6% at 800–1000 nm. The maximum absorption in the transverse electric (TE)-polarized light exceeds 98.9% at 1500–1800 nm, and the peak absorption is more than 84.3% at 1800–2200 nm using finite-difference time-domain methods. By modifying various structural parameters, the absorption of the absorber could be separately shifted in a wide wavelength region. In addition, the designed absorber maintains good performance at large angles of incidence. This structure can be applied to other hybrid perovskite materials by simply changing the structural parameters. These results present a huge potential for applications based on metamaterial absorbers, such as infrared polarization imaging, selective spectral detection, near-infrared sensing, and polarization multiplexing.

Generation of a radially polarized beam in a polycrystalline ceramic Yb:Lu2O3 thin-disk laser

We report on the generation of a continuous-wave (CW) radially polarized beam with an Yb:Lu2O3 polycrystalline ceramic disk in a thin-disk laser (TDL) oscillator. A circular grating-waveguide mirror (CGWM) with a high polarization discrimination given by a reflectivity difference between the two orthogonal polarization states of 44.6% was used as a polarization-selective cavity end-mirror. An output power of 175 W was achieved with an optical efficiency of 39.6%. A high degree of radial polarization of 96.2% and a beam propagation factor of M2hor. = 2.05 and M2ver. = 2.32 were measured at the maximum output power.

Dielectric diatomic metasurface-assisted versatile bifunctional polarization conversions and incidence-polarization-secured meta-image.

Dielectric metasurface empowering efficient light polarization control at the nanoscale, has recently garnered tremendous research interests in the field of high-resolution image encryption and display, particularly at low-loss wavelengths in the visible band. Nevertheless, due to the single fixed polarization conversion function, the image (either positive or negative image) can always be decrypted in a host-uncontrollable manner as long as the user applies an analyzer to select the polarization component of the output light. Here, we resort to half-waveplate- and quarter-waveplate-like silicon nanopillars to form a metamolecule of a dielectric diatomic metasurface, which can yield versatile linearly polarized (LP) and circularly polarized (CP) light upon orthogonally linear-polarized incidences, providing new degrees of freedom for image display and encryption. We show both theoretically and numerically that versatile different paired LP and CP combinations could be achieved by simply adjusting the orientation angles of the two nanopillars. The bifunctional polarization conversion functions make possible that a meta-image can only be seen when incident light is linearly polarized at a specific polarization angle, whereas no image can be discerned for the orthogonal polarization incidence case, indicating the realization of incidence-polarization secured meta-image. This salient feature holds for all individual metamolecules, reaching a remarkable image resolution of 52,916 dots per inch. By fully exploiting all polarization conversions of four designed metamolecules, three-level incidence polarization-secured meta-image can also be expected.

Global 3-D distribution of aerosol composition by synergistic use of CALIOP and MODIS observations

Abstract. For the observation of the global three-dimensional distribution of aerosol composition and the evaluation of the shortwave direct radiative effect (SDRE) by aerosols, we developed a retrieval algorithm that uses observation data from the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the Cloud–Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) satellite and the Moderate Resolution Imaging Spectroradiometer (MODIS) on board Aqua. The CALIOP–MODIS retrieval optimizes the aerosol composition to both the CALIOP and MODIS observations in the daytime. Aerosols were assumed to be composed of four aerosol components: water-soluble (WS), light-absorbing (LA), dust (DS), and sea salt (SS) particles. The outputs of the CALIOP–MODIS retrieval are the vertical profiles of the extinction coefficient (αa), single-scattering albedo (ω0), asymmetry factor (g) of total aerosols (WS+LA+DS+SS), and αa of WS, LA, DS, and SS. Daytime observations of CALIOP and MODIS in 2010 were analyzed by the CALIOP–MODIS retrieval. The global means of the aerosol optical depth (τa) at 532 nm were 0.147±0.148 for total aerosols, 0.072±0.085 for WS, 0.027±0.035 for LA, 0.025±0.054 for DS, and 0.023±0.020 for SS. τa of the CALIOP–MODIS retrieval was between those of the CALIPSO and MODIS standard products and was close to the MODIS standard product. The global means of ω0 and g were 0.940±0.038 and 0.718±0.037; these values are in the range of those reported by previous studies. The horizontal distribution of each aerosol component was reasonable; for example, DS was large in desert regions, and LA was large in the major regions of biomass burning and anthropogenic aerosol emissions. The values of τa, ω0, g, and fine and coarse median radii of the CALIOP–MODIS retrieval were compared with those of the AERONET products. τa at 532 and 1064 nm of the CALIOP–MODIS retrieval agreed well with the AERONET products. The ω0, g, and fine and coarse median radii of the CALIOP–MODIS retrieval were not far from those of the AERONET products, but the variations were large, and the coefficients of determination for linear regression between them were small. In the retrieval results for 2010, the clear-sky SDRE values for total aerosols at the top and bottom of the atmosphere were -4.99±3.42 and -13.10±9.93 W m−2, respectively, and the impact of total aerosols on the heating rate was from 0.0 to 0.5 K d−1. These results are generally similar to those of previous studies, but the SDRE at the bottom of the atmosphere is larger than that reported previously. Consequently, comparison with previous studies showed that the CALIOP–MODIS retrieval results were reasonable with respect to aerosol composition, optical properties, and the SDRE.

Dipole-Dependent Waveguiding in an Anisotropic Metal-Organic Framework.

The interaction between excitons and photons underlies a range of emergent technologies, such as directional light emission, molecular lasers, photonic circuits, and polaritonic devices. Two of the key parameters that impact exciton-photon coupling are the binding energy of excitons and the relative orientations between the exciton dipole and photon field. Tightly bound excitons are typically found in molecular crystals, where nevertheless the angular relationship of excitons with photon fields is difficult to control. Here, we demonstrate directional exciton dipoles and photon fields, anchored by metal-ligand coordination. In a pyrene-porphyrin bichromophoric metal-organic framework (MOF), we observe that the perpendicular arrangement of the pyrene- and porphyrin-based exciton dipoles engenders orthogonal polarizations of their respective emissions. The alignment of the directional exciton and photon fields gives rise to an anisotropic waveguide effect, where the pyrene- and the porphyrin-based emissions show distinct spatial distribution within microplate-shaped MOF crystals. This capability to simultaneously host heterogenous excitonic states and anisotropic photon fields points toward MOFs' yet-to-be-realized potential as a platform for advancing the frontier in the field of exciton-photonics, which centers around engineering emergent properties from the interplay between excitons and photons.

Inverse design of a polarization demultiplexer for on-chip path-entangled photon-pair sources based on single quantum dots.

Epitaxial quantum dots can emit polarization-entangled photon pairs. If orthogonal polarizations are coupled to independent paths, then the photons will be path-entangled. Through inverse design with adjoint method optimization, we design a quantum dot polarization demultiplexer, a nanophotonic geometry that efficiently couples orthogonally polarized transition dipole moments of a single quantum dot to two independent waveguides. We predict 95% coupling efficiency, cross talk less than 0.1%, and Purcell radiative rate enhancement factors over 11.5 for both dipoles, with sensitivity to dipole misalignment and orientation comparable to that of conventional nanophotonic geometries. We anticipate our design will be valuable for the implementation of triggered, high-rate sources of path-entangled photon-pairs on chip.

Underwater polarization de-scattering imaging based on orthogonal polarization decomposition with low-pass filtering

Previous polarization imaging methods tend to assume that the degree of polarization of the target reflected light is a constant, while the targets with nonuniform polarization characteristics are less considered. The required background area or prior knowledge hinders the practical application of underwater polarization imaging technology. In this paper, we analyzed the basic physical model of underwater imaging, and proposed a new underwater polarization de-scattering method by considering orthogonal polarization decomposition of both the target reflected and backscattered light. The polarized-difference intensity of the backscattered light can be directly calculated from the polarization orientation angle of the two horizontal decomposition components. Meanwhile, a low-pass filter was used to suppress noise and globally evaluate the degree of polarization of the backscattered light. The proposed method can automatically distinguish the underwater targets polarization characteristics, and no background area or any prior information is required. The laboratory simulation experimental results demonstrate that this method can effectively improve the quality of underwater images under different conditions.

Multi-stage spontaneous symmetry breaking of light in Kerr ring resonators

Symmetry breaking of light states is of interest for the understanding of nonlinear optics, photonic circuits, telecom applications and optical pulse generation. Here we demonstrate multi-stage symmetry breaking of the resonances of ring resonators with Kerr nonlinearity. This multi-stage symmetry breaking naturally occurs in a resonator with bidirectionally propagating light with orthogonal polarization components. The derived model used to theoretically describe the system shows that the four circulating field components can display full symmetry, full asymmetry, and multiple versions of partial symmetry, and are later shown to result in complex oscillatory dynamics - such as four-field self-switching, and unusual pulsing with extended delays between subsequent peaks. To highlight a few examples, our work has application in the development of photonic devices like isolators and circulators, logic gates, and random numbers generators, and could also be used for optical-sensors, e.g. by further enhancing the Sagnac effect.

Arbitrarily structured quantum emission with a multifunctional metalens

Structuring light emission from single-photon emitters (SPEs) in multiple degrees of freedom is of great importance for quantum information processing towards higher dimensions. However, traditional control of emission from quantum light sources relies on the use of multiple bulky optical elements or nanostructured resonators with limited functionalities, constraining the potential of multi-dimensional tailoring. Here we introduce the use of an ultrathin polarisation-beam-splitting metalens for the arbitrary structuring of quantum emission at room temperature. Owing to the complete and independent polarisation and phase control at the single meta-atom level, the designed metalens enables simultaneous mapping of quantum emission from ultra-bright defects in hexagonal boron nitride and imprinting of an arbitrary wavefront onto orthogonal polarisation states of the sources. The hybrid quantum metalens enables simultaneous manipulation of multiple degrees of freedom of a quantum light source, including directionality, polarisation, and orbital angular momentum. This could unleash the full potential of solid-state SPEs for their use as high-dimensional quantum sources for advanced quantum photonic applications.

A Broadband Double-Layer Transmitarray Antenna Based on Polarization Conversion Elements

A broadband double-layer transmitarray antenna (TA) is proposed in this letter. In order to obtain broadband performance in a double-layer structure, we use a “receiving-transmitting” (RX-TX) structure instead of a double-layer frequency selective surface. The elements of the new TA are composed with metal layers and dielectric substrate. Both the metal layer are connected by a metallized via and etched with orthogonal slots. The RX and TX layers work without interfering while converting the linearly polarized incident wave into orthogonal polarization. Phase compensation can be achieved by changing the direction and length of the microstrip meander ling. Then, a broadband TA is designed. Considering the simplicity of the design, we sequentially selected eight phase states at 45° intervals for phase modulation. The measured maximum antenna gain is 24.5 dBi. The center frequency is 10 GHz. The measured 1-dB and 3-dB gain bandwidth(BW) are 18.7% and 29.4%, respectively. The maximum aperture efficiency (AE) is 51%.