Polarization Mode Research Articles

Stably polarized 795 nm vertical-cavity surface-emitting lasers with anti-phase SiNx surface gratings

795 nm vertical-cavity surface-emitting lasers (VCSELs) with dielectric surface gratings to control the output polarization are designed and fabricated. The calculated results demonstrate that a well-designed SiNx surface grating positioned on the surface of an anti-phase VCSEL structure enhances the reflectivity difference between the two polarization modes compared to a conventional GaAs surface grating, consequently resulting in a larger gain anisotropy in VCSELs and a high orthogonal polarization suppression ratio (OPSR). Characterization shows that a peak-to-peak OPSR of 30.3 dB is achieved at 85°C for 795 nm VCSELs with a SiNx surface grating of 5 µm in diameter and an oxide aperture of ∼4µm, demonstrating the effectiveness of the SiNx surface grating in polarization control for 795 nm VCSELs.

Quantum fluctuations lead to glassy electron dynamics in the good metal regime of electron doped KTaO3

One of the central challenges in condensed matter physics is to comprehend systems that have strong disorder and strong interactions. In the strongly localized regime, their subtle competition leads to glassy electron dynamics which ceases to exist well before the insulator-to-metal transition is approached as a function of doping. Here, we report on the discovery of glassy electron dynamics deep inside the good metal regime of an electron-doped quantum paraelectric system: KTaO3. We reveal that upon excitation of electrons from defect states to the conduction band, the excess injected carriers in the conduction band relax in a stretched exponential manner with a large relaxation time, and the system evinces simple aging phenomena—a telltale sign of glassy dynamics. Most significantly, we observe a critical slowing down of carrier dynamics below 35 K, concomitant with the onset of quantum paraelectricity in the undoped KTaO3. Our combined investigation using second harmonic generation technique, density functional theory and phenomenological modeling demonstrates quantum fluctuation-stabilized soft polar modes as the impetus for the glassy behavior. This study addresses one of the most fundamental questions regarding the potential promotion of glassiness by quantum fluctuations and opens a route for exploring glassy dynamics of electrons in a well-delocalized regime.

Broadband dispersion compensation and high birefringence photonic crystal fiber for CWDM/DWDM networks

In this study, we propose a new design based on photonic crystal fibers (PCFs) for broadband dispersion compensation in telecommunication networks. The proposed design has a hexagonal structure arrangement of air-holes rings of different diameters between the silica core and the cladding. The PCF properties like effective area, nonlinearity, dispersion slope, confinement loss, and birefringence are reported and discussed. For the best performance we present three designs A, B and C. Simulation results show that the three designs cover the six-telecommunication optical bands O-, E-, S-, C-, L- and U- bands (wavelengths ranging from 1260 to 1675 nm). Design A achieves a large negative dispersion value of about − 1716 ps/(nm.km) with relative dispersion slope equals to that of conventional single-mode optical fibers (SMFs) of about 0.0036 nm−1, which makes it very suitable for long-haul DWDM transmission systems. With a little modification in the core, designs B and C achieve much higher confinement ability and achieve a very large birefringence value for polarization mode dispersion and sensing applications. Design C is engineered to have exact opposite dispersion of SMF with zero dispersion at the wavelength 1310 nm, which makes it a promising design in CWDM transmission system. The numerical values have been investigated using the full vector finite element method.

Influence of Photonics and Plasmonics Effect on Ultrathin Amorphous Silicon Thin Film Solar Cell

Abstract Our recent surge in silicon derived materials has major demand in thin film photovoltaic (PV) modules and enhancing the significant numbers. The rigorous coupled wave analysis method is a simple and fast method also known as developed to determine the light absorption and cell efficiency. The optics of thin film solar cells (amorphous silicon) garnering crucial role in the photovoltaic market. In this work, an ultrathin thin film amorphous silicon solar cell PV performance investigated by periodically textured surfaces at the nanoscale level. This analysis of periodic textured substrate was deriving optimal surface textures. The nanogratings lead to light scattering mechanism with the higher order diffraction angle and enhanced the light absorption of the incidence spectrum. The influence of grating period and height, the collection of the charge carriers increased at various wavelengths from ultraviolet, visible and infrared spectral regions are discussed with the assistance of photonic and plasmonic modes. Finally, nanoscale engineering mechanism the optimized thin film amorphous silicon solar cell yielded the highest current densities (22.6 and 23.8 mA/cm2) in both polarization modes.

Dominance of polarization modes and absorption on self-focusing of laser beams in collisionless magnetized plasma

This work investigates the polarization modes i.e., Extraordinary (E-mode) and Ordinary (O-mode) on self-focusing of higher-order mode of elegant Hermite-cosh-Gaussian (EHChG) laser beams within collisionless magnetized plasma medium. In this study, the authors have taken transverse electromagnetic ([Formula: see text]) mode with mode indices (0, 4) and explored. The ponderomotive force is primarily responsible for the dielectric constant’s nonlinearity in this context. Also, WKB and paraxial approximations via the parabolic wave equation approach are used to establish the general form of differential equations for beam-width parameters in both transverse dimensions of the beam. In this paper, the authors have theoretically investigated the dominance of polarization modes and absorption coefficient on self-focusing. The final results show good enhancement of laser propagation through collisionless plasma medium.

A multi-band elastic metamaterial for low-frequency multi-polarization vibration absorption

The vibration of engineering structures in actual practice occurs across numerous frequency ranges and includes diverse polarization modes such as bending, torsion, and expansion. Nevertheless, most reported elastic metamaterials are designed for a single frequency range or a single elastic wave mode, thereby making it challenging to simultaneously suppress the propagation of vibrational energy across multiple frequency ranges and polarization modes. To address this limitation, we propose a two-degree-of-freedom elastic metamaterial exhibiting a multi-frequency range elastic band gap and multi-polarization mode elastic wave band gap. By incorporating periodic vibration-absorbing units, gradient parameter vibration-absorbing units, and different polarization mode vibration-absorbing units to the actual equipment support structure, we achieve respective vibration attenuation enhancement, broadband vibration absorption, and multi-polarization mode vibration absorption. We systematically verify the effectiveness of our design through kinetic theoretical analysis, full-wave field simulations, and experimental tests. This metamaterial vibration absorption device can effectively meet the application requirements of complex vibration reduction involving multi-frequency ranges and modes in practical engineering, providing novel insights into equipment vibration and noise reduction design that holds significant reference value for engineering applications.

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.

Polarization‐directed nanophotonic routers based on two‐dimensional inorganic molecular crystals

AbstractPhotonic and plasmonic hybrid nanostructures are the key solution for integrated nanophotonic circuits with ultracompact size but relative low loss. However, the poor tunability and modulability of conventional waveguides makes them cumbersome for optical multiplexing. Here we make use of two‐dimensional molecular crystal, α‐Sb2O3 as a dielectric waveguide via total internal reflection, which shows polarization‐sensitive modulation of the propagating beams due to its large polarization mode dispersion. Both experiments and simulations are performed to verify such concept. These Sb2O3 nanoflakes can be coupled with plasmonic nanowires to form nanophotonic beam splitters and routers which can be easily modulated by changing the polarization of the incidence. It thus provides a robust, exploitable and tunable platform for on‐chip nanophotonics.image

Modulation Format Identification Based on Multi-Dimensional Amplitude Features for Elastic Optical Networks

A modulation format identification (MFI) scheme based on multi-dimensional amplitude features is proposed for elastic optical networks. According to the multi-dimensional amplitude features, incoming polarization division multiplexed (PDM) signals can be identified as QPSK, 8QAM, 16QAM, 32QAM, 64QAM and 128QAM signals using the k-nearest neighbors (KNNs) algorithm in the digital coherent receivers. The proposed scheme does not require any prior training or optical signal-to-noise ratio (OSNR) information. The performance of the proposed MFI scheme is verified based on numerical simulations with 28GBaud PDM-QPSK/-8QAM/-16QAM/-32QAM/-64QAM/-128QAM signals. The results show that the proposed scheme can achieve 100% of the correct MFI rate for all six modulation formats when the OSNR values are greater than their thresholds corresponding to the 20% forward error correction (FEC) related to a BER of 2.4 × 10−2. Meanwhile, the effects of residual chromatic dispersion, polarization mode dispersion and fiber nonlinearities on the proposed scheme are also explored. Finally, the computational complexity of the proposed scheme is analyzed, which is compared with relevant MFI schemes. The work indicates that the proposed technique could be regarded as a good candidate for identifying modulation formats up to 128QAM.

High-Q two-dimensional photonic crystal nanocavity on glass with an upper glass thin film.

We numerically analyze two-dimensional photonic crystal (PhC) nanocavities on glass with a thin glass film on top of the structure. We investigated a multistep heterostructure GaAs PhC nanocavity located on glass. We found that covering the structure even with a very thin glass film efficiently suppresses unwanted polarization mode conversion occurring due to the asymmetric refractive index environment around the PhC. We also uncovered that the glass-covered structure can exhibit a higher Q factor than that observed in the structure symmetrically cladded with thick glass. We point out that the mode mismatch between the PhC nanocavity and modes in the upper glass film largely contributed to the observed Q-factor enhancement. These observations were further analyzed through the comparison among different types of on-glass PhC nanocavities covered with thin glass films. We also discuss that the in-plane structure of the upper glass film is important for additionally enhancing the Q factor of the nanocavity.

Interaction of a quantum particle with gravitational wave in modified gravity theory

We present the formal solution for a quantum mechanical particle responding to gravitational wave (GW) in the framework of modified theories of gravity (MTG) where, apart from the two standard tensorial modes of polarization of GW, we have considered an additional scalar mode. The presence of this longitudinal scalar mode makes it necessary to extend the usual two-dimensional description of matter-GW interaction to a three-dimensional one. Naturally this requires non-trivial changes in the quantum mechanical treatment which we elaborate in this paper.

Effect of surface anchoring energy on a liquid crystal optical waveguide-based polarization rotator

This study reports the effect of the surface anchoring energy of a liquid crystal (LC) cell on the performance of the liquid crystal optical waveguide polarization rotator (LCOW-PR) for the purpose of providing a theoretical reference for practical preparation of the LCOW-PR. First, the expression for the deflection angle of the director at the boundary of the LC cell is derived so that the distributions of the director and dielectric tensor of the LC can be accurately solved under any anchoring energy. On this basis, the correlation between the crucial indicators such as the polarization conversion length (PCL) together with the polarization conversion efficiency (PCE) of the LCOW-PR and the anchoring effect strength is constructed by combining with the existing numerical algorithms. The numerical results show that the maximum variation of the PCL is lower than 0.1 µm as the anchoring effect strength increases from 1×10−6J/m2 to 1×10−3J/m2, while the PCE decreases from 99.72% to 78.33%. This implies that the PCL of the LCOW-PR does not depend on the surface anchoring energy, but the anchoring effect strength of the orientational layer must be controlled to the order of 10−6J/m2 or even lower to achieve high-performance conversion between the polarization modes. Simultaneously, the effectiveness of the calculations in this work is verified with the help of the coupled mode theory as well as a comparison to previous reports.

Plasmonic couplings in Ag-Au heterodimers.

The plasmonic coupling between silver (Ag) and gold (Au) nanoparticles (NPs) under four polarization modes was examined: a longitudinal mode (L-mode), where the electric field of a linearly polarized incident light parallels the dimer axis, and three transverse modes (T-modes), where the electric field of the light is perpendicular to the dimer axis. The coupling was studied using the discrete dipole approximation followed by an in-house postprocessing code that determines the extinction (Qext), absorption (Qabs), and near-field (Qnf) spectra from the individual NPs as well as the whole system. In agreement with the literature results, the extinction/absorption spectra of the whole dimer have two peaks, one near the Ag localized surface plasmon resonance (LSPR) region and the other at the Au LSPR region, with the peak at Ag LSPR being reduced in all modes and the peak at Au LSPR being red-shifted and increased in the L-mode but not in the T-modes. It is further shown that the scattering at the Ag LSPR region is reduced and becomes less than the isolated Ag NPs, but the absorption at the Ag LSPR is increased and becomes greater than the isolated Ag NPs for the 50nm Ag-Au heterodimer. This suggests that the scattering from Ag NPs is being reabsorbed by the neighboring Au NPs due to the interband electronic transition in Au at that wavelength range. The Qext from the individual NP in the heterodimer shows the presence of the Fano profile on the Au NP but not on the Ag NP. This phenomenon was further investigated by using a dielectric particle (DP) placed near the Ag or Au NPs. The Fano profile appears in the absorbing DP spectra placed near either Ag or Au NPs. However, the Fano profile is masked upon further increases in the refractive index value of the DP particle. This explains the absence of a Fano profile on the Ag NPs in the Ag-Au heterodimer. The large near-field enhancement on both Ag and Au NPs at the Au plasmonic wavelength in the L-mode for large NPs was investigated through a DP-Au system. The large enhancement was shown to arise from a large imaginary component of the DP refractive index and a small real component. Through examination of both the near- and far-field properties of the individual NPs as well as the whole system and examinations of DP-Ag and DP-Au systems, our study provides a new understanding of the couplings between Ag and Au NPs.

RESEARCH OF THE FEATURES OF DIGITAL SIGNAL FORMATION IN SATELLITE COMMUNICATION LINES

Context. Remote sensing of the Earth is now widely used in various fields. One of the challenges of remote sensing is the creation of inexpensive satellite systems operating in polar circular orbits. These systems require the development of a receptiontransmission system that allows tens of gigabits of video information to be transmitted to an earth receiving station within ten minutes. That is, there is a need to create a communication system that provides high speed data transmission from small satellites weighing up to 50 kg.
 Objective. The aim of the work is to study the features of digital signal formation in modern satellite communication lines and to develop a communication system with a high data transfer rate (usually 300 Mbit/s), which can be applied to small Earth Observation satellites.
 Method. Proposed concept for building a high-speed data transmitter from a remote sensing earth satellite using commercially available off-the-shelf technology. Calculations of the power flow density created at the input of the receiving earth station were performed to find out the possible power of the on-board transmitter.
 Results. A diagram of a communication system based on the DVB-S standard using the technology of commercially available off-the-shelf products has been developed. The high-speed data transmitter is implemented on a Xilinx® Zynq Ultrascale+ ™ MPSoC FPGA microchip, which is located on an Enclustra Mercury XU8 module with a high-performance dual 16-bit AD9174 DAC. The on-board transmitter with a power of up to 2 W meets the requirements of the ITU Radio Regulations for the power flux density on the surface of the Earth, which is created by the radiation of the space station EESS in the range 8025–8400 MHz. It is shown that the energy reserve of the communication line of 3 dB is achieved for various commands for coding and modulation changes with an increase in the elevation angle, which allows to increase the speed of information transmission.
 Conclusions. An original receiving-transmitting system was developed for use in small satellites for remote sensing of the Earth. It is shown that the function of adaptive modeling of ACM of the DVB-S standard allows you to automatically change the transmission parameters in real time depending on the changing conditions of the channel, providing opportunities for more flexible and effective data transmission in various conditions, which will allow to increase the volumes of information transmitted by communication session. The proposed system operates in the X-band and is built using commercially available off-the-shelf products. An antenna with double circular polarization is used as the emitter. Two physical channels represent two polarization modes: right circular polarization and left circular polarization, each of which has three frequency channels.

A novel bifunctional metasurface based on independent control of transmission and reflection amplitudes and phases

ABSTRACT A novel bifunctional metasurface (MS) operating at two frequencies is proposed to manipulate reflected and transmitted waves independently. The element is composed of a slot sandwiched by two C-shape spilt rings (CSRRs). The middle layer is the metal sheet etched the slots, and it is used to select polarization mode of reflection and transmission. Also, it isolates the reflection and transmission elements and eliminates the coupling between them. Therefore, the reflection or transmission amplitude and phase of the proposed MS can be regulated by the corresponding single metal layer compared with the current bifunctional elements. This is helpful to shorten design time. Also, a higher transmission amplitude is achieved with fewer substrate layers and lower profile. The reflection and transmission mode operate at 17.6 GHz and 12.6 GHz, respectively. As a proof of concept, a full-space multibeam generator is validated both numerically and experimentally and a full-space bifocal metalens is demonstrated numerically. The proposed MS provides a new kind of low cost, lightweight, and easily modularized planar devices for microwave applications.

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.

Effective Realization of Higher Order Circular Polarized OAM Mode Circular Patch Antenna

Effective Realization of Higher Order Circular Polarized OAM Mode Circular Patch Antenna

Dwarf Pulses of 10 Pulsars Detected by FAST

How pulsars radiate is a long-standing problem. Detailed polarization measurements of individual pulses shed light on currently unknown emission processes. Recently, based on supersensitive observations, dwarf pulses have been recognized as weak narrow pulses often appearing during the nulling state. In this study, we report the detection of dwarf pulses from 10 pulsars, PSRs B0525+21, B1237+25, J1538+2345, J1824−0127, J1851−0053, B1901+10, J1939+10, B1944+17, B2000+40, and J2112+4058, based on observations conducted with the Five-hundred-meter Aperture Spherical radio Telescope. Dwarf pulses of five pulsars are clearly discernible in the two-dimensional distribution of pulse intensity and pulse width. For the other five pulsars, PSRs J1538+2345, J1824−0127, J1939+10, B2000+40, and J2112+4058, only a few dwarf pulses are detected from pulse stacks. The dwarf pulses can emerge in both cone and core emission components for PSR B1237+25, and the polarization angles of these dwarf pulses are mostly in the orthogonal polarization mode of normal pulses for PSR B1944+17. In general, pulsars with detected dwarf pulses tend to be located within the “death valley” region of the distribution of pulsar periods and period derivatives.

Circularly Polarized and Linear Polarized Mode Multiplexing OAM Antenna Using Sequentially Rotated Technique

Circularly Polarized and Linear Polarized Mode Multiplexing OAM Antenna Using Sequentially Rotated Technique

Wave-optics limit of the stochastic gravitational wave background

The stochastic gravitational wave background (SGWB) is a rich resource of cosmological information, encoded both in its source statistics and anisotropies induced by propagation effects. We provide a theoretical description of it, without employing tools which rely on the geometric optics assumption. Our formalism is based on the so-called classical matter approximation and it is able to capture wave-optics effects, such as interference and diffraction. We show that the interaction between the gravitational waves and the cosmic structures along the line-of-sight produce observable scalar and vector polarization modes, on top of modulating the tensorial ones. We build the two point correlation function describing the statistics of the SGWB, and introduce the intensity and gravitational Stokes parameters for all its components. In the case of an unpolarized, Gaussian and statistically homogeneous SGWB, we show that the interaction with matter modulates its intensity and does not generate a net difference between left- and right-helicity tensor and vector modes, as expected. We demonstrate that, in order to produce QT- and UT-tensor polarization modes the background must possess a hexadecapole anisotropy, while a quadrupole anisotropy can source the vector QV- and UV-Stokes parameters.