Polarization Control Research Articles

Polarization division multiplexing link using a high-speed lithium niobate automatic polarization demultiplexer

We propose and experimentally demonstrate a polarization division multiplexing (PDM) link employing an integrated dual-polarization thin-film lithium niobate (TFLN) modulator and an on-chip automatic polarization demultiplexer. The tracking speed of an 80-Gb/s PDM link achieves a maximum of 600 rad/s with a bit error rate (BER) below 2.4 × 10−2. Furthermore, at a polarization scrambling rate (SR) of 100 rad/s, BERs maintain around 1.7 × 10−3 over a period of half an hour. This configuration takes advantage of the TFLN platform, which includes high-speed modulation, fast polarization control, and a compact footprint, effectively doubling capacity per wavelength using simple direct detection. The demonstration highlights the effectiveness of on-chip polarization multiplexing and demultiplexing, particularly in scenarios involving polarization fluctuations, offering promising prospects for applications in commercial short-reach data centers.

Influence of polarization on demodulation methods for determining the SRI value for a single TFBG and an orthogonal grating system

This paper presents a comparison of the spectra of single and cascade of two tilted fiber Bragg grating (TFBG) sensors. These sensors are characterized by high sensitivity to the refractive index. The disadvantage of a single TFBG is cross-sensitivity to changes in the polarization of the light introduced to the sensor, which is visible both when analyzing individual modes and when analyzing a wide spectral range with global demodulation algorithms. In response, a cascade structure was created consisting of a set of two TFBGs connected in series with 90 degrees of mutual rotation between them. This work presents a comparison of the polarization cross-sensitivity of sensor spectral demodulation algorithms for measuring the surrounding refractive index (SRI). While maintaining the high accuracy of the SRI measurement typical of TFBG gratings, a cascade of two such gratings properly oriented toward each other allows for a significant reduction in the sensitivity of the SRI measurement to polarization changes. Importantly, the reduction in the polarization cross-sensitivity is significantly greater for the demodulation methods that determine the cutoff wavelength shift; owing to this, a perpendicular TFBG(P-TFBG) measurement system without polarization control remains highly reliable. The application of the proposed P-TFBG system also allows greater SRI sensitivity to be obtained for a single tilted grating with the same tilt angle.

Intelligent multi-parameter control of a rectangular pulse in a passively mode-locked fiber laser

Rectangular pulses with tunable width and intensity in fiber lasers are critical for the study of nonlinear pulse dynamics and applications of nanosecond laser sources. However, due to the complex nonlinear dynamics within the laser cavity, precisely controlling multiple parameters of the rectangular pulses in fiber lasers remains challenging. Here, we propose an approach for intelligently controlling the intensity and width of rectangular pulse using an improved particle swarm optimization (PSO) algorithm in a passively mode-locked fiber laser with a nonlinear polarization rotation (NPR) technique. By automatically adjusting the electronic polarization controller (EPC) and pump power, multiple parameters of the output rectangular pulse can be effectively tailored, and thus, to desirable ones. This enables the flexible setting of the intensity and width of the rectangular pulse within the permissible range in a passively mode-locked fiber laser. Our approach provides a promising way to meet the diverse demands of seed laser source in scientific and engineering fields.

Bi-functional and tri-channel image displays based on a single-size nanostructured metasurface enabled by dual-orientation-degeneracy

Benefiting from the extraordinary ability of manipulating lightwaves at the subwavelength scale, nanostructured metasurfaces are expected to achieve multifunctional and multichannel integration to expand functionality and increase information capacity. However, multifunctional and multichannel metasurfaces always consist of various anisotropic nanostructures, inevitably bringing challenges to design and fabrication. In this study, we propose a concept of dual-orientation-degeneracy containing twofold orientation degeneracy. The first-level degeneracy is a one-to-four mapping scheme between the intensity of Channel 1 and orientation angle and the second-level degeneracy refers to a one-to-two mapping between the intensity of Channel 2 and orientation angle. Additionally, we provide a minimalist design of bi-functional and tri-channel image displays based on a single-size nanostructured metasurface. The designed metasurface integrates two functionalities of nanoprinting and holography, which can generate a continuous grayscale meta-image, a binary meta-image and a phase-only holographic image. Three channel displays can be readily switched by polarization controls. More importantly, the metasurface is achieved merely by reconfiguring the orientation angles of the nanostructures with fixed geometries, relieving the structure design and fabrication burden. The presented minimalist design strategy is universal and applicable, which can contribute to advanced research and applications in ultra-compact image displays, high-dense optical storage, multi-folded optical anti-counterfeiting, etc.

Impact of light polarization on laser speckle contrast imaging with a custom phantom for microvascular flow

Laser speckle contrast imaging (LSCI) is a non-invasive, powerful, and cost-effective imaging technique that has seen widespread adoption across various medical fields, particularly for blood flow imaging. While LSCI provides physicians with valuable insights into changes or occlusions in blood flow, the technique is susceptible to various factors and parameters that can impact measurement sensitivity and signal-to-noise ratio (SNR). These include the scattering of light, which can affect the quality and reliability of the LSCI data. The polarization of light holds significant promise to enhance the performance of LSCI. In this study, we employed polarization manipulation of light to investigate its impact on the performance of LSCI for measuring flow. Focusing on the application of LSCI in microcirculation within capillaries, we examined the effect of polarization control on the technique's flow measurement capabilities using a custom-designed phantom system. This phantom consisted of three tubes with inner diameters of 1.1 mm, 1.6 mm, and 2.8 mm, embedded in a polydimethylsiloxane (PDMS) matrix with optical properties similar to biological tissue. By manipulating the polarization of both the incident and reflected light, alternating between parallel and perpendicular states, we compared the performance of our LSCI system in detecting flow for different tube diameters and depths within the phantom. Our study revealed that while depth is a critical parameter influencing flow detection using LSCI, employing perpendicular polarization (between incident and reflected light) resulted in the lowest measurement error and highest SNR compared to parallel polarization and the absence of polarization control.

Diverse and controllable soliton molecules in a fiber laser based on PbBi4Te7 saturable absorber

With the advancement of optical communication, optical encoding, and optical storage technologies, the demand for tunable mode-locked fiber lasers (MLFL) with soliton molecules is continuously increasing. The novel ternary two-dimensional topological insulator PbBi4Te7 provides an effective pathway for realizing tunable soliton molecules in MLFL. This study employs a combined liquid phase exfoliation (LPE) and optical deposition methods (ODMs) to prepare PbBi4Te7 saturable absorbers (SAs). In the same MLFL, conventional soliton (CS), controllable soliton molecules with adjustable soliton numbers and intervals, as well as multi-soliton complexes are obtained. Among them, a fundamental frequency CS pulse at 22.778 MHz with a signal-to-noise ratio (SNR) of up to 71 dB is achieved. By adjusting the pump power, 2nd-, 3rd-, 4th-, 9th-, and 11th-order soliton molecules were obtained. By tuning the polarization controller (PC), switching of the soliton interval for 2nd-, 3rd-, and 4th-order soliton molecules was achieved. Additionally, we obtained three unequally spaced multi-soliton complexes: 2 + 1 soliton molecule, 2 + 2 soliton molecule complex and 2 + 2 + 1 soliton molecule complex. The results indicate that PbBi4Te7-SA exhibits outstanding nonlinear optical performance.

Intermittent polarity inversion of stainless-steel paired electrodes for efficient and durable water electrolysis

Designing robust and cost-effective catalysts through straightforward and replicable techniques is crucial for advancing water electrolysis. In this study, we introduce a dynamic polarization control method for the continuous activation of stainless steel (SS) substrates to achieve high water-splitting performance and durability. By applying periodic inverted current density during high-current–density operation (0.5 or 1 A cm−2) on bare SS adopted as both cathode and anode substrates, a NiFe-based oxide structure favorable for the hydrogen evolution reaction is formed at the cathode, while a Fe-incorporated NiOOH structure with high efficacy for the oxygen evolution reaction develops at the anode. Implemented in an anion exchange membrane water electrolysis system, this inverted polarization approach applied for the SS paired electrolyzer system successfully maintains a cell voltage of approximately 1.9 V for 500 h at a current density of 1 A cm−2 using bare SS for both electrodes.

Real-time fully digital control scheme for pulse coherent beam combining.

A fully digital control scheme for non-polarization-maintaining (non-PM) nanosecond pulse coherent beam combining (CBC) is proposed, where digital locking of optical coherence by single-detector electronic-frequency tagging (LOCSET) for active phase control and stochastic parallel gradient descent (SPGD) for active polarization control is proposed. The fully digital control scheme is integrated on a real-time field-programmable gate array (FPGA) empowered hardware platform and then experimentally validated in a four-channel all-fiber non-fully polarization-maintaining nanosecond pulse CBC system. Consequently, the system can be fully locked in 9.5 ms, and the polarization extinction ratio (PER) of the combined beam is 21.5 dB with a CBC efficiency of 95.3%. The fully digital control scheme integrates the advantages of digital LOCSET and multi-channel active polarization control, enhancing the channel scalability and the potential output power of the non-PM pulse CBC system.

Study of complex instability in a Thulium-doped figure-eight fiber laser including a polarization-imbalanced NOLM with no polarization control.

This study proposes a Thulium-doped figure-eight (F8) fiber laser design to be used as a platform to explore complex dynamics in passively mode-locked fiber laser systems. The proposed scheme incorporates a polarization-imbalanced nonlinear optical loop mirror (PI-NOLM) without a polarizer in the ring section. The absence of a polarizer prevents controlling the polarization state at the PI-NOLM input, which in turn allows the PI-NOLM switching power to vary dynamically during the laser operation. This leads to an intermittent noise-like pulse (NLP) operation, which is affected by complex instability in the form of non-periodic Q-switched-like behavior. Using real-time time-domain mapping techniques, we get a deep insight into the laser intricate dynamics, which involves not only NLPs, but also solitons and quasi-continuous-wave components with their subtle interactions. This study highlights the importance of the PI-NOLM in F8 laser schemes for the study and understanding of complex dynamics in Thulium-doped fiber lasers, which have been less extensively studied compared to other rare-earth-doped lasers. Our findings will contribute to the optimization and design of advanced laser systems for various scientific and industrial applications.

High efficient bi-functional metasurface with linear polarization conversion and asymmetric transmission for terahertz region

Abstract Polarization control is crucial in contemporary photonics, but achieving broad bandwidths and high efficiencies remains a significant challenge. Here, we propose a wideband and high-efficiency metasurface designed for linear polarization conversion and asymmetric transmission (AT) in the terahertz region based on a three-layer chiral structure. By integrating a double-split ring and strip resonator, the design can improve both wide bandwidth and high-efficiency cross-polarization conversion and AT capabilities for a linearly polarized wave. The operating band for AT is 0.73-3.01 THz with an efficiency above 0.8, while the polarization conversion ratio exceeds 0.99 across the 0.56-3.94 THz range. The underlying physical mechanism behind wideband transmission polarization conversion was fully elucidated through theoretical analysis and the characterization of surface current distribution. This designed structure can be used in terahertz imaging, sensing, and communication.

Compact polarization splitter-rotator based on lithium niobate-on-insulator platform

We propose a compact mode-coupled polarization splitter-rotator (PSR) based on the lithium niobate-on-insulator platform. The PSR is composed of an asymmetric directional coupler, a taper, and an S-bend. Cross-polarization mode coupling is achieved using a ridge waveguide and air cladding to break the symmetry of the waveguide cross section with a length of only 61 μm. Simulation results show that the insertion losses of this device in the 1500–1600 nm range are less than 1.85 and 0.31 dB for TM0 and TE0 modes, respectively, and the extinction ratios are more than 22.5 and 22.7 dB, respectively. In addition, the PSR exhibits a polarization conversion efficiency of 99.97% at 1550 nm. The proposed PSR has great potential for applications in polarization-division multiplexing transmitters and on-chip polarization controllers.

Theoretical Analysis on Active Polarization Control of Fiber Laser Based on Root Mean Square Propagation Algorithm

High-power linearly polarized fiber lasers are widely used in coherent beam combination, nonlinear frequency conversion, and gravitational wave detection. With the increase in output power, it is challenging for fiber lasers to maintain a high polarization extinction ratio (PER). Combined with intelligent techniques, active polarization control is a prospective method to obtain the laser output with high PER and high stability. We demonstrate a comprehensive model of an active polarization control system. The root mean square propagation (RMS-Prop) algorithm is used to control the non-polarization-maintaining (non-PM) fiber laser to generate linearly polarized laser. The parameters of the RMS-Prop algorithm are theoretically analyzed, including cost function, perturbation amplitude, and global learning rate. The simulation results show that PER is the optimal cost function. When the perturbation amplitude is 0.06 and the global learning rate is 0.6, the system can achieve the optimal control speed and accuracy. By comparison with the stochastic parallel gradient descent (SPGD) algorithm, the RMS-Prop algorithm has an advantage in obtaining higher PER.

Electrical Control of Valley Polarized Charged Exciton Species in Monolayer WS2.

Excitons are key to the optoelectronic applications of van der Waals semiconductors, with the potential for versatile on-demand tuning of properties. Yet, their electrical manipulation remains challenging due to inherent charge neutrality and the additional loss channels induced by electrical doping. We demonstrate the dynamic electrical control of valley polarization in charged excitonic states of monolayer tungsten disulfide, achieving up to a 6-fold increase in the degree of circular polarization under off-resonant excitation. In contrast to the weak direct tuning of excitons typically observed using electrical gating, the charged exciton photoluminescence remains stable, even with increased scattering from electron doping. By exciting at the exciton resonances, we observed the reproducible nonmonotonic switching of the charged state population as the electron doping is varied under gate bias, indicating a resonant interplay between neutral and charged exciton states.

Rational Control of Maximum EMI/CPL Intensity and Wavelength of Bora[6]helicene via Polarity and Vibronic Effects.

Solvent polarity control as an efficient methodology to regulate the chiroptical properties, including spectral shape, width, intensity, wavelength, etc., has emerged as a novel frontier in optical materials design. However, the underling relationship connecting polarity to the optical property remains unclear. Herein, using state-of-the-art computations and the FC|VG model, the solvent effect on the chiroptical properties of bora[6]helicene was accurately and systematically computed to shed light on this issue. It is found that the vibronic coupling is crucial in explaining the spectral shape, width, and relative intensity of different peaks. Moreover, the intensity and position of the emission (EMI) and circularly polarized luminescence (CPL) are closely related to the polarity of the solvent. Intriguingly, we got a series of good linear relationships between polarity and EMI|CPL (|r| ≥ 0.95). Thus, this parameter can be used as a potential descriptor to estimate the intensity and position of EMI|CPL, leading to new strategies for designing fully colored fluorescent materials.

Single layer vanadium oxide assisted switchable metasurfaces for transmissive and reflective polarization conversion

Polarization control using metasurfaces is highly advantageous; however, most metasurfaces operate exclusively in either transmission or reflection mode. Additionally, achieving both wide bandwidth and high efficiency simultaneously in their design remains a significant challenge. Here, we design a high-efficiency and wideband switchable metasurface that can switch between transmissive and reflective polarization conversion modes by utilizing a single layer of I-shaped resonators and gold-vanadium dioxide (VO2) alternating gratings printed on a quartz substrate. When VO2 transitions to its metallic phase, the continuous metal layers of gold-VO2 eliminate transmission and the designed metasurface operates as a reflective cross-polarization converter with a polarization conversion ratio (PCR) exceeding 0.9 over a broad frequency range of 1.4–3.3 THz. Conversely, when VO2 is in its insulator phase, the THz incoming wave can transmit through the gratings, and the design behaves as a transmissive cross-polarization converter with a PCR above 0.99 in the 0.75-4.0 THz range for a forward y- polarized wave. The working mechanism for both transmissive and reflective polarization conversion modes is explained through theoretical analysis and surface current distributions. With the advantages of facile design, high performance, and dual functionality, our design is expected to be applied in the fields of imaging, sensing, and communication.

Valley-Hybridized Gate-Tunable 1D Exciton Confinement in MoSe2.

Controlling excitons at the nanoscale in semiconductor materials represents a formidable challenge in the quantum photonics and optoelectronics fields. Monolayers of transition metal dichalcogenides (TMDs) offer inherent 2D confinement and possess significant exciton binding energies, making them promising candidates for achieving electric-field-based confinement of excitons without dissociation. Exploiting the valley degree of freedom associated with these confined states further broadens the prospects for exciton engineering. Here, we show electric control of light polarization emitted from one-dimensional (1D) quantum-confined states in MoSe2. Building on previous reports of tunable trapping potentials and linearly polarized emission, we extend this understanding by demonstrating how nonuniform in-plane electric fields enable in situ control of these effects and highlight the role of gate-tunable valley hybridization in these localized states. Their polarization is entirely engineered through either the 1D confinement potential's geometry or an out-of-plane magnetic field. Controlling nonuniform in-plane electric fields in TMDs enables control of the energy (up to five times its line width), polarization state (from circular to linear), and position of 1D confined excitonic states (5 nm V-1).

A novel multifunctional chiral metasurface with asymmetric transmission

The multiband, multifunctional chiral metasurface with asymmetric transmission exhibits significant potential for diverse applications in modern communication systems, ranging from enhanced signal modulation and polarization control to advanced beam steering and compact antenna design. This research presents a versatile and advanced chiral metasurface operating at multiple bands with diverse functionalities, including asymmetric transmission. The proposed metasurface effectively transforms an incoming Linearly Polarized (LP) wave into a Circularly Polarized (CP) wave. Additionally, it functions as a 90° polarization rotator for the incident LP wave. The design starts with an element of a 2 × 2 supercell comprising a Square Split Ring Resonator (SSRR) and an I-shaped resonator. The right diagonal elements of a supercell undergo scaling down, giving rise to a rotational asymmetry. Chirality is introduced into the design, and cross polarization conversion is enhanced by rotating all four elements by 90° relative to each other. On the back side of the substrate, each element undergoes a 90° rotation compared to its counterpart on the front side, realizing the asymmetric transmission feature. The incorporation of multiband and multifunctional features within a single supercell equips the subject chiral metasurface to be utilized in various engineering applications.

Control of spin-wave polarity and velocity using a ferrimagnetic domain wall

We present a theoretical study of the scattering of spin waves by a domain wall (DW) in a ferrimagnetic (FiM) spin chain in which two sublattices carry spins of unequal magnitudes. We find that a narrow but atomically smooth FiM DW exhibits a different behavior in comparison with similarly smooth ferromagnetic and antiferromagnetic DWs due to the inequivalence of the two sublattices. Specifically, for sufficiently weak anisotropy, the smaller spin at the center of the DW is found to become precisely normal to the easy axis, selecting an arbitrary direction in the xy plane and thereby breaking the U(1) spin-rotational symmetry spontaneously. This particular form of a FiM DW does not occur in antiferromagnetic systems and is shown to lead to a strong dependence of spin-wave scattering pattern on the state of polarization of the spin wave, which can be either right-handed or left-handed, suggesting the utilization of such a narrow DW as a spin-wave filter. Moreover, we find that in the case of an atomically sharp DW, where all the spins point either up or down due to strong easy-axis anisotropy and therefore the polarization of the spin wave is conserved upon transmission, the wave vector of the spin-wave changes after passing through the DW leading to a change in the group velocity of the spin wave. This change of the wave vector indicates the acceleration or deceleration of the spin waves and thus a sharp FiM DW could serve as a spin-wave accelerator or decelerator in spintronics devices, offering a functionality absent in a ferromagnetic and an antiferromagnetic counterpart. Our results indicate that FiM spin textures can interact with spin waves distinctly from ferromagnetic and antiferromagnetic counterparts, suggesting that they may offer spin-wave functionalities that are absent in more conventional magnets. Published by the American Physical Society 2024

Surface polarization profile of ferroelectric thin films probed by X-ray standing waves and photoelectron spectroscopy

Understanding the mechanisms underlying a stable polarization at the surface of ferroelectric thin films is of particular importance both from a fundamental point of view and to achieve control of the surface polarization itself. In this study, we demonstrate that the X-ray standing wave technique allows the surface polarization profile of a ferroelectric thin film, as opposed to the average film polarity, to be probed directly. The X-ray standing wave technique provides the average Ti and Ba atomic positions, along the out-of-plane direction, near the surface of three differently strained \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm {BaTiO_3}$$\\end{document} thin films. This technique gives direct access to the local ferroelectric polarization at and below the surface. By employing X-ray photoelectron spectroscopy, a detailed overview of the oxygen-containing species adsorbed on the surface is obtained. The different amplitude and orientation of the local ferroelectric polarizations are associated with surface charges attributed to different type, amount and spatial distribution of the oxygen-containing adsorbates.

Control of the light polarization in ferromagnetic diode structures InGaAs/GaAs/δ-Mn

Electric-field influence on the polarization of the quantum well photoluminescence is studied in the diode structures InGaAs/GaAs/δ-Mn with narrow GaAs spacer dS = 2–5 nm at small magnetic field. Weakening of the circular polarization degree with increasing electric-field evidence about significant contribution of the stationary mechanism of the carriers’ polarization due to their exchange coupling with a nearby ferromagnetic δ-Mn-layer.