Mode Polarization Research Articles

Modulating stacking mode and molecular polarization in CTF/molecule heterojunction for meliorating photocatalytic CO2 conversion with nearly 100% CO selectivity

Herein, two conjugated molecules, i.e., D-π-A TAPT and non-D-A TAPB, are finely designed to incorporate with covalent triazine framework (CTF) in A-A and A-B stacking mode via π-π interaction, respectively. The transient photocurrent response of the generated AA-CTF/TAPT Z-Scheme heterostructure is 1.14 × 10-7 A, significantly higher than that of the other two metal-free heterostructures (AA-CTF/TAPB and AB-CTF/TAPT). The promoted photocarrier transportation is attributed to strong polarization (dipole moment = 2.634 D) imposed by the D-π-A effect in TAPT that motivates the interfacial charge separation, and the coexisting charge transfer channel built by the ordered A-A stacking mode in AA-CTF that expedites the charge delivery. The photocatalytic CO2 conversion conducted by AA-CTF/TAPT gives the optimal CO conversion rate as 7.47 μmol·g−1·h−1, and with nearly 100 % product selectivity obtained, which is attributable to the lower energy barrier of CO desorption barrier (−1.07 eV) rather than that of CHO* formation (1.52 eV) for generating CH4.

Amplitudes and polarizations of quadratic quasi-normal modes for a Schwarzschild black hole

General Relativity predicts the existence of quadratic quasi-normal modes at second order in perturbation theory. Building on our recent work, we compute the amplitudes and polarizations of these modes for non-rotating black holes, showing that they are completely determined by the amplitudes and polarizations of linear modes. We obtain the ratio of quadratic to linear amplitudes, which still depends on the initial conditions of the merger through the polarization of linear modes. However, we demonstrate that this dependence is captured by four fundamental numbers, independent of initial conditions, representing four different combinations of linear modes parities. Additionally, we prove two selection rules regarding the vanishing of classes of quadratic modes. Our results are available online as a package which provides the ratio of amplitudes across a broad spectrum of angular momenta.

Behavior of the Position and Ellipticity Angles at Polarization Mode Transitions in Pulsar Radio Emission

Polarization observations of radio pulsars show that abrupt transitions in the polarization vector’s position angle can be accompanied by large excursions in the vector’s ellipticity angle, suggesting the vector passes near the right or left circular pole of the Poincaré sphere. The behavior of the angles can be explained by a transition in dominance of the orthogonal polarization modes or a vector rotation caused by a change in the phase difference between the modes. Four polarization models are examined to quantify and understand the behavior of the angles at a mode transition: coherent polarization modes, partially coherent modes, incoherent modes with nonorthogonal polarization vectors, and incoherent orthogonal modes with an elliptically polarized emission component. In all four models, the trajectory of the mode transition on the Poincaré sphere follows the geodesic that connects the orientations of the mode polarization vectors. The results from the models can be similar, indicating that the interpretation of an observed transition within the context of a particular model is not necessarily unique. The polarization fraction of the emission and the average ellipticity angle depend upon the statistical character of the mode intensity fluctuations. The polarization fraction increases as the fluctuations increase. The excursion in ellipticity angle can be large when the mode intensities are quasi-stable and is suppressed when the intensity fluctuations are large.

Cascaded partitioned phase modulation for cross-connection of orbital angular momentum mode and polarization multiplexing channels.

Multi-dimensional orbital angular momentum (OAM) mode multiplexing provides a promising route for enlarging communication capacity and establishing comprehensive networks. While multi-dimensional multiplexing has gained advancements, the cross-connection of these multiplexed channels, especially involving modes and polarizations, remains challenging due to the needs for multi-mode interconversion and on-demand polarization control. Herein, we propose an OAM mode-polarization cross-transformation solution via cascaded partitioned phase modulation, which enables the divergently separated OAM modes to be independently phase-imposed within distinct spatial regions, leading to the synergistic conversion operation of mode and polarization channels. In demonstrations, we implemented the cross-connection of three OAM modes and two polarization multiplexed channels, achieving the mode purity that exceeds 0.951 and polarization contrast up to 0.947. The measured mode insertion losses and polarization conversion losses are below 3.42 and 3.54 dB, respectively. Consequently, 1.2 Tbit/s quadrature phase shift keying signals were successfully exchanged, yielding the bit-error-rates close to 10-6. Incorporating with increased partitioned phase treatments, this approach shows promise in accommodating massive mode-polarization multiplexed channels, which hold the potential to augment networking capability of large-scale OAM mode multiplexing communication networks.

The orientation dependence of cavity-modified chemistry.

Recent theoretical studies have explored how ultra-strong light-matter coupling can be used as a handle to control chemical transformations. Ab initio cavity quantum electrodynamics calculations demonstrate that large changes to reaction energies or barrier heights can be realized by coupling electronic degrees of freedom to vacuum fluctuations associated with an optical cavity mode, provided that large enough coupling strengths can be achieved. In many cases, the cavity effects display a pronounced orientational dependence. Here, we highlight the critical role that geometry relaxation can play in such studies. As an example, we consider a recent work [Pavošević et al., Nat. Commun. 14, 2766 (2023)] that explored the influence of an optical cavity on Diels-Alder cycloaddition reactions and reported large changes to reaction enthalpies and barrier heights, as well as the observation that changes in orientation can inhibit the reaction or select for one reaction product or another. Those calculations used fixed molecular geometries optimized in the absence of the cavity and fixed relative orientations of the molecules and the cavity mode polarization axis. Here, we show that when given a chance to relax in the presence of the cavity, the molecular species reorient in a way that eliminates the orientational dependence. Moreover, in this case, we find that qualitatively different conclusions regarding the impact of the cavity on the thermodynamics of the reaction can be drawn from calculations that consider relaxed vs unrelaxed molecular structures.

Power spectra and circular polarization of primordial gravitational waves with parity and Lorentz violations

The violations of parity and Lorentz symmetries in gravity can change the propagating properties of gravitational waves (GWs) in the cosmological background, which can arise from a large number of parity- and Lorentz-violating theories. In this paper, through a systematic parametrization for characterizing possible derivations from the standard GW propagation in general relativity, we study both the parity- and Lorentz-violating effects on the power spectra and the polarization of the primordial gravitational waves (PGWs) during the slow-roll inflation. To this end, we calculate explicitly the power spectrum and the corresponding circular polarization of the PGWs analytically by using the uniform asymptotic approximation. It is shown that the new contributions to power spectra contain two parts, one from the parity-violating terms and the other from the Lorentz-violating terms. While the Lorentz-violating terms can only affect the overall amplitudes of PGWs, the parity-violating terms induce nonzero circular polarization of PGWs, i.e., the left-hand and right-hand polarization modes of GWs have different amplitudes.

Reconfigurable OAM Antenna With Flexibility on Mode Numbers, Polarization, and Frequency

Reconfigurable OAM Antenna With Flexibility on Mode Numbers, Polarization, and Frequency

Single wavelength MDM-PDM 800-Gb/s net data rate transmission over a standard multimode fiber employing a Kramers-Kronig receiver.

We propose a high-speed multimode fiber short-reach optical interconnect system based on a Kramers-Kronig (KK) field reconstruction with the mode division multiplexing (MDM) and polarization division multiplexing (PDM) technology. In this work, the LP01, LP21a, LP21b, and LP02 modes are selected as independent channels to carry information. The demonstration achieved the 800 Gb/s net data rate per wavelength with a bit-rate-distance-product (BDP) of 8 Tb/s·km. To the best of our knowledge, this is the highest experimental record of a single wavelength BDP over the SMMF with KK detection. In addition, we discuss the system performance after all multiple-input multiple-output (MIMO) and partial MIMO processing and give guidance on the trade-off between system performance and computational resource.

Empowering high-dimensional optical fiber communications with integrated photonic processors

Mode-division multiplexing (MDM) in optical fibers enables multichannel capabilities for various applications, including data transmission, quantum networks, imaging, and sensing. However, high-dimensional optical fiber systems, usually necessity bulk-optics approaches for launching different orthogonal fiber modes into the optical fiber, and multiple-input multiple-output digital electronic signal processing at the receiver to undo the arbitrary mode scrambling introduced by coupling and transmission in a multi-mode fiber. Here we show that a high-dimensional optical fiber communication system can be implemented by a reconfigurable integrated photonic processor, featuring kernels of multichannel mode multiplexing transmitter and all-optical descrambling receiver. Effective mode management can be achieved through the configuration of the integrated optical mesh. Inter-chip MDM optical communications involving six spatial- and polarization modes was realized, despite the presence of unknown mode mixing and polarization rotation in the circular-core optical fiber. The proposed photonic integration approach holds promising prospects for future space-division multiplexing applications.

Nearly Perfect Routing of Chiral Light by Plasmonic Grating on Slab Waveguide

AbstractGrating couplers are widely used to couple waveguide modes with the far field. Their usefulness is determined not only by energy efficiency but also by additional supported functionality. In this paper, a plasmonic is demonstrated grating on a silicon nitride slab waveguide that couples both transverse electric (TE) and transverse magnetic (TM) waveguide modes with circularly polarized light in the far field. Specifically, it is experimentally confirmed that circularly polarized light excites TE and TM modes propagating in opposite directions, and the direction is controlled by the handedness. The routing efficiency for normally incident light reaches up to 95%. The same structure operates in the outcoupling regime as well, demonstrating up to 97% degree of circular polarization, where the handedness is determined by the polarization and propagation direction of outcoupled modes. The results pave the way for the realization of polarization‐division multiplexers and demultiplexers, integrated circular polarization emitters, as well as detectors of the polarization state of the incident optical field.

Ultra-sensitive pressure sensor with low-temperature crosstalk based on the Vernier effect and helical structure

What we believe to be a novel high-sensitivity fiber-optic pressure sensor based on the vernier effect and helical structure is proposed and experimentally verified. The sensor utilizes the superposition of higher-order mode Mach-Zehnder interference and Sagnac fundamental mode polarization interference in a single fiber ring to achieve the vernier effect. In addition, a non-invasive encapsulation structure was fabricated to convert the rise and fall of the pressure value into the change in the twist angle of the optical fiber. This approach reduces the interference of the detecting medium on the sensor signal while simultaneously increasing the sensitivity of the pressure sensor. According to experimental data, the detection sensitivity of the sensor can reach −67277 nm/MPa, which is 65 times higher than the sensitivity of the conventional vernier effect pressure sensor. It also solves the issue of temperature interference with the Vernier-effect structured fiber optic sensor. The sensor has a measured temperature cross-sensitivity of 0.000065 kPa/°C, which is significantly lower than that of comparable sensors. This makes the sensor highly sensitive and ideal for low crosstalk pressure measurement.

B-mode polarization forecasts for GreenPol

We present tensor-to-scalar ratio forecasts for GreenPol, a hypothetical ground-based B-mode experiment aiming to survey the cleanest regions of the Northern Galactic Hemisphere at five frequencies between 10 and 44 GHz. Its primary science goal would be to measure large-scale cosmic microwave background (CMB) polarization fluctuations at multipoles ℓ ≲ 500, and thereby constrain the primordial tensor-to-scalar ratio r. The observations for the suggested experiment would take place at the Summit Station (72 ° 34N, 38 ° 27W) on Greenland, at an altitude of 3216 m above sea level. For this paper we simulated various experimental setups, and derived limits on the tensor-to-scalar ratio after CMB component separation using a Bayesian component separation implementation called Commander. When combining the proposed experiment with Planck HFI observations for constraining polarized thermal dust emission, we found a projected limit of r < 0.02 at 95% confidence for the baseline configuration. This limit is very robust with respect to a range of important experimental parameters, including sky coverage, detector weighting, foreground priors, among others. Overall, GreenPol would have the possibility to provide deep CMB polarization measurements of the Northern Galactic Hemisphere at low frequencies.

Inverse design of a silicon-based ultra-compact four-channel mode splitter with dual polarizations

We adopt the inverse-designed method and demonstrate an ultra-compact four-channel mode splitter with dual polarizations, which enables mode division multiplexing and polarization division multiplexing simultaneously without changing the mode orders and suitable for fabrication and integration based on silicon-on-insulator platform. The four TE0, TM0, TE1 and TM1 modes at the central wavelength of 1550 nm can be efficiently split with low insertion loss (<1.9 dB), low channel crosstalk (<−17 dB), low reflection loss (<−18 dB). Moreover, the proposed mode splitter has the potential of incorporating the wavelength division multiplexing for mass data transmission and high computing parallelism.

A dual‐band dual‐polarized omnidirectional patch antenna for on‐body application

AbstractAiming at the 3.5 GHz world interoperability for microwave access band and 5.8 GHz industrial scientific medical band, a dual‐band antenna operating in omnidirectional mode is proposed. The antenna uses a single‐layer dielectric substrate made of FR‐4, which is cheap and easy to process. It uses circular patches and metal branches to generate orthogonal electric fields to achieve circular polarization. At the same time, the upper patch is symmetrically slotted in a T shape, so that the patch produces two resonance frequencies. The measured impedance bandwidth of the antenna in circular polarization on‐body mode and linear polarization on‐body mode is 110 MHz (3.41–3.52 GHz) and 460 MHz (5.42–5.88 GHz), respectively. In addition, the antenna shows good performance under bending conditions and close to human tissue. At the same time, the low specific absorption rate value proves that the antenna is safe to wear on the human body.

Engineering the plasmon modes of a confined electron gas

Abstract The volume plasmon modes of a confined electron gas are engineered in a step-like semiconductor potential, which induces the formation of adjacent regions of different charge density. Each region supports spatially localized collective modes. Adjacent modes are theoretically demonstrated to couple, forming delocalized modes, which are well-described with a hybridization picture. Exploiting the thin-film Berreman effect, the engineered plasmon modes are directly observed in optical measurements. Using a quantum microscopic theory, the asymmetry of the single-particle electronic states is shown to be directly imprinted on the nonuniform polarization of the collective modes.

Deep learning-based approach for high spatial resolution fibre shape sensing

Fiber optic shape sensing is an innovative technology that has enabled remarkable advances in various navigation and tracking applications. Although the state-of-the-art fiber optic shape sensing mechanisms can provide sub-millimeter spatial resolution for off-axis strain measurement and reconstruct the sensor’s shape with high tip accuracy, their overall cost is very high. The major challenge in more cost-effective fiber sensor alternatives for providing accurate shape measurement is the limited sensing resolution in detecting shape deformations. Here, we present a data-driven technique to overcome this limitation by removing strain measurement, curvature estimation, and shape reconstruction steps. We designed an end-to-end convolutional neural network that is trained to directly predict the sensor’s shape based on its spectrum. Our fiber sensor is based on easy-to-fabricate eccentric fiber Bragg gratings and can be interrogated with a simple and cost-effective readout unit in the spectral domain. We demonstrate that our deep-learning model benefits from undesired bending-induced effects (e.g., cladding mode coupling and polarization), which contain high-resolution shape deformation information. These findings are the preliminary steps toward a low-cost yet accurate fiber shape sensing solution for detecting complex multi-bend deformations.

Non-orthogonal cavity modes near exceptional points in the far field

Non-orthogonal eigenstates are a fundamental feature of non-Hermitian systems and are accompanied by the emergence of nontrivial features. However, the platforms to explore non-Hermitian mode couplings mainly measure near-field effects, and the far-field behaviours remain mostly unexplored. Here, we study how a microcavity with non-Hermitian mode coupling exhibits eigenstate non-orthogonality by investigating the spatial field and the far-field polarization of cavity modes. The non-Hermiticity arises from asymmetric backscattering, which is controlled by integrating two scatterers of different size and location into a microdisk. We observe that the spatial field overlap of two modes increases abruptly to its maximum value, whilst different far-field elliptical polarizations of two modes coalesce when approaching an exceptional point. We demonstrate such features experimentally by measuring the far-field polarization from the fabricated microdisks. Our work reveals the non-orthogonality in the far-field degree of freedom, and the integrability of the microdisks paves a way to integrate more non-Hermitian optical properties into nanophotonic systems.

Proton- and Alpha-driven Instabilities in an Ion Cyclotron Wave Event

Ion-scale wave events or wave storms in the solar wind are characterized by enhancements in magnetic field fluctuations as well as coherent magnetic field polarization signatures at or around the local ion cyclotron frequencies. In this paper, we study in detail one such wave event from Parker Solar Probe's (PSP) fourth encounter, consisting of an initial period of left-handed (LH) polarization abruptly transitioning to a strong period of right-handed (RH) polarization, accompanied by a clear core beam structure in both the alpha and proton velocity distribution functions. A linear stability analysis shows that the LH-polarized waves are anti-sunward propagating Alfvén/ion cyclotron waves primarily driven by a proton cyclotron instability in the proton core population, and the RH polarized waves are anti-sunward propagating fast magnetosonic/whistler waves driven by a firehose-like instability in the secondary alpha beam population. The abrupt transition from LH to RH is caused by a drop in the proton core temperature anisotropy. We find very good agreement between the frequencies and polarizations of the unstable wave modes as predicted by linear theory and those observed in the magnetic field spectra. Given the ubiquity of ion-scale wave signatures observed by PSP, this work gives insight into which exact instabilities may be active and mediating energy transfer in wave–particle interactions in the inner heliosphere, as well as highlighting the role a secondary alpha population may play as a rarely considered source of free energy available for producing wave activity.

Sub-wavelength focused light and optical trapping application based on two-mode interference from an optical micro-/nanofiber

The ability to focus light on a subwavelength scale is essential in modern photonics. Optical microfiber-based sub-wavelength focusing will allow a miniaturized, flexible and versatile tool for many applications such as biomedical imaging and optomechanics. For a separate mode exited from an optical micro-/nanofiber endface, the photons will experience significant diffraction into the free space. This situation can be changed by incorporating two-mode interference along with the specific spatial distributions of both &lt;i&gt; &lt;b&gt;E&lt;/b&gt; &lt;/i&gt;-field amplitude and phase. Herein we report a novel approach to realizing sub-wavelength focusing based on the two-mode interference exited from an optical microfiber endface. By utilizing specific distributions of &lt;b&gt;&lt;i&gt;E&lt;/i&gt;&lt;/b&gt; -field amplitude and phase of two interacting optical modes, interference field patterns with a single focus (e.g., via a two-mode set of HE&lt;sub&gt;11&lt;/sub&gt; and HE&lt;sub&gt;12&lt;/sub&gt;) or multiple foci (e.g., via a two-mode set of HE&lt;sub&gt;11&lt;/sub&gt; and HE&lt;sub&gt;31&lt;/sub&gt;) can be obtained. Then, it is proved that the constructed foci will readily facilitate and selective trapping of nanoparticles. Circular polarization of optical mode is utilized in order to bring in angular symmetry of sub-wavelength focusing patterns compared with linear polarized optical modes. Our simulation results show that the smallest focal spot produced from the EH&lt;sub&gt;11&lt;/sub&gt; and HE&lt;sub&gt;12&lt;/sub&gt; mode interference has a full width at half-maximum (FWHM) of ~ 348 nm (i.e. 0.65&lt;i&gt;λ&lt;/i&gt;). Such a subwavelength focusing field is applied to the optical trapping of an 85 nm-diameter polystyrene nanosphere. Further calculation reveals that the stable trapping can be fulfilled with axial and transverse trap stiffness of 11.48 pN/(μm·W) and 64.98 pN/(μm·W), as well as axial and transverse potential well of 101 &lt;i&gt;k&lt;/i&gt;&lt;sub&gt;B&lt;/sub&gt;T/W and 641 &lt;i&gt;k&lt;/i&gt;&lt;sub&gt;B&lt;/sub&gt;T/W via two-mode interference of HE&lt;sub&gt;11&lt;/sub&gt; and HE&lt;sub&gt;12&lt;/sub&gt;. These values demonstrate the great improvement over conventional tapered fibers. Further investigations show that different foci, via a two-mode set of HE&lt;sub&gt;11&lt;/sub&gt; and HE&lt;sub&gt;31&lt;/sub&gt;, exhibit unlike trap stiffness and potential wells, justifying the potential for nanoparticle size sorting. Based on the flexible all-fiber device, this subwavelength focusing strategy by two-mode interference may find promising applications in optical manipulation, superresolution optical imaging, data storage and nanolithography.

Asymmetric transmission of cascaded acousto-optic device and whispering gallery mode microcavity

In this paper, an asymmetric transmission scheme is proposed by cascading an acousto-optic device and a coupled whispering gallery mode (WGM) microsphere cavity, and it is demonstrated theoretically and experimentally. With the acousto-optic interaction in a fiber, the vector modes of the fundamental core mode can be converted into the different vector modes of a cladding (linear polarization, LP) mode, and because of the optical path difference between the cladding vector modes, the polarization of the cladding mode will be changed. The cladding mode can be converted back into the core fundamental mode by coupling a WGM microcavity. By calculating the overlapping of the mode fields in the tapered fiber and the microcavity at the resonance wavelength, the coupling coefficients between different LP modes and WGM will be solved. And, the transmitivities and conversion coefficients of the two fiber modes can be obtained on condition that the polarization of the incident light does not coincide with the polarization orientation of the WGM. The transmission spectra of the coupled WGM microcavity are calculated by using Matlab program for eight states, including the states at different incident directions, different incident polarizations of input, whether the acoustic wave is on or off. The results show that the conversion coefficient from the cladding mode to the core mode is completely different from that of the contrary process when the acoustic wave is working. And the forward incident light and backward incident light have completely different transmission characteristics, thus resulting in the asymmetric transmission. The transmittances of forward incidence and reverse incidence at different polarizations are also studied, both of them change periodically with the polarization angle, and their phase difference is equal to the polarization change caused by acousto-optic interaction in the fiber. In the experiment, a two-stage tapered fiber is used to realize the acousto-optic interaction and the coupling of whispering gallery mode at the same time. By controlling the working states of the system, the same 8 states as in the calculation are studied experimentally. The results show that due to the polarization-selection effect of the WGM, the light energy incident from the opposite directions will show different transmission characteristics. While the forward transmittance reaches a maximum value of about 0.505, the reverse transmittance reaches a minimum value of about 0.010, and the transmission isolation reaches about 17 dB. The transmittances in two directions are measured at different incident polarization angles, the transmission isolation is analyzed, and the polarization change of cladding mode in the fiber is verified to be about &lt;inline-formula&gt;&lt;tex-math id="M1"&gt;\begin{document}${80^ \circ }$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20230653_M1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20230653_M1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;. The measured results coincide with the calculations from the developed theory well. Finally, the shortcomings and optimization method of the scheme are discussed. The asymmetric transmission scheme in this paper inherits the advantages of rapid response and good tuning of acousto-optic device, and has an all-fiber structure, which has important application potential in optical switch and isolator.