Polarization Control Research Articles

Experimental investigation of SRS polarization pulling in depleted pump regime for various pump SOPs

This article presents an experimental investigation of polarization pulling based on stimulated Raman scattering induced by a continuous, fully polarized pump wave in an optical fibre. By means of probe wave states of polarization aggregation, degree of polarization and gain analysis, an assessment of all-optical polarization control, repolarization and amplification in a standard single mode fibre in depleted pump regime is presented. Polarization pulling is proved to be dependent on fibre length, pump power, and pump state of polarization, with respect to pump depletion effect, acting oppositely to the polarization pulling effect. Authors evaluate results aiming to obtain a configuration of stimulated Raman scattering parameters, which allows for the most effective polarization pulling, with respect to statistical stability of the process measured by standard deviation of polarization degree and polarization-dependent gain of the probe wave. The highest polarization attraction efficiency was obtained for 15 km, 0.97 W and the horizontal polarization state of the pump wave.

Wavelength continuously tunable and wavelength spacing variable comb filter based on a High-Birefringence fiber loop mirror

We demonstrated an all-fiber comb filter that can continuously tune the wavelength for four switchable wavelength spacings. The comb filter consists of a fiber loop mirror (FLM) that is inserted with three polarization maintaining fibers (PMFs) and three polarization controllers (PCs). The transmission characteristics of the comb filter was theoretically analyzed. The output characteristics of the comb filters shows a dependence of the orientation angles of the PCs. With the angles being optimally set, the comb filter with four different wavelength spacings can be achieved. The wavelength continuously tunable and wavelength spacing variable mechanisms are elaborated. The three PCs are employed to enable the tunable and switchable functions. The two PCs between the PMFs serve as a polarization rotator to align the birefringent axes of the PMFs for varying the wavelength spacing while the PC adjacent to the optical coupler can be used for wavelength tuning function. When the two quarter-waveplates (QWPs) of the PC are optimally set at π/4 and - π/4, the half-waveplate (HWP) acts as a wavelength tuning element, and when the QWPs are set at zero degrees, the HWP serves as an amplitude tuning element. The center wavelength of the comb filter could be linearly tuned with the rotation angle of the HWP, and a π/2 change in the rotation angle leads to a wavelength change in one free-spectral-range (FSR). A π/4 change in the rotation angle could bring the normalized peak transmission from its maximum at 1 to minimum at 0. The proposed tunable technique has been verified by our experimental results. We experimentally demonstrated the comb filters can switch among FSRs of 0.75 nm, 1.01 nm, 1.51 nm, and 3.1 nm with tunable functions.

Interfacial Polarization Control Engineering and Ferroelectric PZT/Graphene Heterostructure Integrated Application.

Integration and miniaturization are the inevitable trends in the development of electronic devices. PZT and graphene are typical ferroelectric and carbon-based materials, respectively, which have been widely used in various fields. Achieving high-quality PZT/graphene heterogeneous integration and systematically studying its electrical properties is of great significance. In this work, we reported the characterization of a PZT film based on the sol-gel method. Additionally, the thickness of the PZT film was pushed to the limit size (~100 nm) by optimizing the process. The test results, including the remnant and leakage current, show that the PZT film is a reliable and suitable platform for further graphene-integrated applications. The non-destructive regulation of the electrical properties of graphene has been studied based on a domain-polarized substrate and strain-polarized substrate. The domain structures in the PZT film exhibit different geometric structures with ~0.3 V surface potential. The I-V output curves of graphene integrated on the surface of the PZT film exhibited obvious rectification characteristics because of p/n-doping tuned by an interfacial polarized electric field. In contrast, a ~100 nm thick PZT film makes it easy to acquire a larger strain gradient for flexural potential. The tested results also show a rectification phenomenon, which is similar to domain polarization substrate regulation. Considering the difficulty of measuring the flexural potential, the work might provide a new approach to assessing the flexural polarized regulation effect. A thinner ferroelectric film/graphene heterojunction and the polarized regulation of graphene will provide a platform for promoting low-dimension film-integrated applications.

Coherence-tailorable vector fiber source

Apart from the polarization and spatial mode, the degree of coherence (DoC), as a new degree of freedom (DoF), has actuated the control of structured optical fields beyond into a higher dimension. However, the control of DoC mainly focuses on the spatial coherence, and so far, there are no reports on the modulation of temporal coherence of the structured light. Here, a temporal coherence-tailorable vector fiber source is proposed and experimentally demonstrated. With a two-mode long-period fiber grating and polarization control, switchable transverse-mode outputs including azimuthally polarized mode TE01 and radially polarized mode TM01 are performed in an all-fiber compact regime. Benefitting from a tunable superfluorescent fiber source as the illumination of spatial mode control, the temporal coherence and the operating wavelength of vector beams can be simultaneously modulated. This work may not only advance a considerable protocol for creating and manipulating high-dimensional vectorial optical field, but also open up a promising avenue for potential applications in optical communication, high-resolution imaging, and particle trapping.

A compact single‐layer reflective metasurface for high‐efficiency polarisation conversion applications in C and X bands

AbstractThe authors design and experimentally analyse an anisotropic metasurface for the simultaneous conversions of linear cross and circular polarisations in the C and partial X bands. The proposed compact structure utilises a dual‐cut square‐ring resonator and a square patch on an FR4 substrate above a ground plane. The full‐wave simulations exhibit over 92% efficiency in cross‐conversion over a fractional bandwidth (BW) of 52.3%. The proposed metasurface efficiently converts linear to circular polarisation in two different bands, achieving left‐hand circularly polarised and right‐hand circularly polarised efficiencies exceeding 93% and 89%, respectively. The compact unit‐cell with dimension 0.22λ × 0.22λ attains stable polarisation transformation efficiency rates exceeding 80% up to 40° incident angles. The design is adaptable for efficient wide BW across both lower and higher (millimetre‐wave) frequencies through scaling. A prototype of the proposed polarisation converter (PC) was realised and validated effectively in measurements, aligning well with simulations. This PC features a novel and simple structure with multifunctional wideband operation, stable incident angle output, polarisation insensitivity, and scalability, making it an efficient front‐end for various radio frequency applications, including polarisation control and polarisation transformers.

Ferrocene-functionalized polydopamine film timely mediates M1-to-M2 macrophage polarization through adaptive wettability

Dynamical control of macrophage polarization from M1 (pro-inflammatory) to M2 (anti-inflammatory) at implant surfaces is essential for balancing innate immunity and tissue repair. In this aspect, the design of orthopedic implant that can response to inflammation microenvironment with transformation in surface properties has shown promising in timely driving M1-to-M2 macrophage transition. Considering excessive reactive oxygen species (ROS) contribute to macrophage M1 polarization and progression of inflammation, in this study, ferrocene modified polydopamine (PDA-Fc) films were deposited on plasma sprayed Ti coatings to endow the implants with ROS-responsive and -scavenging abilities. Plasma sprayed Ti (PST) coating and PDA modified PST coating (PST/PDA) served as control. The presence of PDA endowed PST/PDA and PST/PDA-Fc with free-radical scavenging abilities. Moreover, PST/PDA-Fc showed adaptive wettability as evidenced by increased hydrophilicity under H2O2 treatment. With respect to PST/PDA, PST/PDA-Fc exerted greater effects on inducing lipopolysaccharides-induced M1 macrophages to adopt M2-type macrophage phenotype, characterized by higher percentage of CD206-positive cells, increased cell elongation rate and higher expression level of anti-inflammatory cytokine arginase type 1. The results obtained in our study may provide a prospective approach for manipulating an appropriate immune response at implant surfaces.

Polarity-Mediated Antisolvent Control Enables Efficient Lanthanide-Based near-Infrared Perovskite LEDs.

Alloying lanthanide ions (Yb3+) into perovskite quantum dots (Yb3+:CsPb(Cl1-xBrx)3) is an effective method to achieve efficient near-infrared (NIR) luminescence (>950 nm). Increasing the Yb3+ alloying ratio in the perovskite matrix enhances the luminescence intensity of Yb3+ emission at 990 nm. However, high Yb3+ alloying (>15%) results in vacancy-induced inferior material stability. In this work, we developed a polarity-mediated antisolvent manipulation strategy to resolve the incompatibility between a high Yb3+ alloying ratio and inferior stability of Yb3+:CsPb(Cl1-xBrx)3. Precise control of solution polarity enables increased uniformity of the perovskite matrix with fewer trap densities. Employing this strategy, we obtain Yb3+:CsPb(Cl1-xBrx)3 with the highest Yb3+ alloying ratio of 30.2% and a 2-fold higher electroluminescence intensity at 990 nm. We lever the engineered Yb3+:CsPb(Cl1-xBrx)3 to fabricate NIR-LEDs, achieving a peak external quantum efficiency (EQE) of 8.5% at 990 nm: this represents the highest among perovskite NIR-LEDs with an emission wavelength above 950 nm.

Generation of spatiotemporal dark pulse or polarization domain wall solitons in a partial multimode mode-locked fiber laser

In this paper, we have experimentally investigated different operational states of a partial multimode Er-doped spatiotemporal mode-locked (STML) fiber laser. The STML is enabled by nonlinear multimode interference (NL-MMI) effect from the partial multimode cavity structure. It is found that by adjusting the multimode polarization controller (PC) and the pump power, the STML dark pulses, bright pulses, as well as the polarization domain wall solitons can all be obtained, alternatively. The fused-tapered multimode coupler is responsible for the dark pulses generation via the enhanced modal cross-phase coupling. It is believed that the present findings can offer an important insight into the spatiotemporal dynamics of the STML solitons.

Design and implementation of the logic gates using electrically doped configurable polarity control double gate tunnel FET

This paper designs and implements the basic logic and universal gates based on the proposed electrically doped, configurable polarity control double gate tunnel FET (ED-CPC-DGTFET). In contrast to the CMOS and MOSFET, the primary concern of the proposed device is to overcome the transistor count needed to design logic gates. A few compact realizations of logic gates have been reported earlier using conventional double-gate TFETs. The main key to designing and implementing logic gates with the proposed structure is controlling the channel’s tunneling barrier height by altering the gate electrode work function. Additionally, abrupt interband tunneling of TFET by varying gate bias makes the device appropriate for implementing logic gates. The proposed device has a dynamic configuration that can change from n-type to p-type DGTFET by varying the bias at PG-1 and PG-2. Since lightly doped TFETs have a low ON-state current therefore, a high-k material (HfO 2 ) is employed in place of SiO 2 on top of the source side to enhance the ON-state current. Using two-dimensional simulations, the device is designed to implement logic gates with gate lengths of 50 nm and silicon body thicknesses of 10 nm (t si ). OR and AND logic gates are implemented using the n-type ED-CPC-DGTFET structure, and universal gates are implemented using the p-type variant of the proposed ED-CPC-DGTFET structure by independently biasing the top and bottom gates against various inputs.

Frequency response of the non-polarization-maintaining depolarized sagnac interferometer based on maximum fringe contrast

The Sagnac Interferometer offers a promising solution to the speckle problem in interferometric detection due to its insensitivity to environmental low-frequency interference, making it well-suited for applications such as laser ultrasonic detection. Control of the polarization state of light is imperative for achieving high sensitivity in optical fiber interferometer and ensuring optimal quiescent operating conditions. This study employed the coherence matrix method to analyze the theory of optimal polarization control in a non-polarization-maintaining depolarized Sagnac Interferometer, encompassing the deduction of the stable π/2 initial phase bias and the maximum fringe contrast of 50% in theory. In experimental observations during PZT simulated large amplitude ultrasound experiments, the fringe contrast reached 48.4%. Furthermore, the system's amplitude-frequency response was evaluated using an electro-optics phase modulator, demonstrating its capability to detect high-frequency signals within 100 MHz These findings provide essential insights into optimizing the Sagnac Interferometer's performance for laser ultrasonic detection and its potential applications in high-frequency signal detection and ultrasonic amplitude measurement.

Numerical study of valence band states evolution in AlxGa1-xAs [111] QDs systems

Quantum dots (QDs) are very attractive nanostructures from an application point of view due to their unique optical properties. Optical properties and valence band (VB) state character was numerically investigated with respect to the effects of nanostructure geometry and composition. Numerical simulation was carried out using the Luttinger–Kohn model adapted to the particular case of QDs in inverted pyramids. We present the source code of the 4-band Luttinger–Kohn model that can be used to model AlGaAs or InGaAs nanostructures. The work focuses on the optical properties of GaAs/AlGaAs [111] QDs and quantum dot molecules (QDMs). We examine the dependence of Ground State (GS) optical properties on the structural parameters and predict optimal parameters of the QD/QDM systems to achieve dynamic control of GS polarization by an applied electric field.

Deeply subwavelength mid-infrared phase retardation with α-MoO3 flakes

Phase retardation is a cornerstone of modern optics, yet, at mid-infrared (mid-IR) frequencies, it remains a major challenge due to the scarcity of simultaneously transparent and birefringent crystals. Most materials resonantly absorb due to lattice vibrations occurring at mid-IR frequencies, and natural birefringence is weak, calling for hundreds of microns to millimeters-thick phase retarders for sufficient polarization rotation. Here, we demonstrate mid-IR phase retardation with flakes of α-MoO3 that are more than ten times thinner than the operational wavelength, achieving 90 degrees polarization rotation within one micrometer of material. We report conversion ratios above 50% in reflection or transmission mode, and wavelength tunability by several micrometers. Our results showcase that exfoliated flakes of low-dimensional crystals can serve as a platform for mid-IR miniaturized integrated low-loss polarization control.

Wavelength-tunable quasi-unidirectional spatiotemporal mode-locked solitons in an isolator-free Er-doped fiber laser

In this letter, we have demonstrated the realization of the wavelength-tunable spatiotemporal mode-locked (STML) operation in an Er-doped partial multimode fiber laser without the intracavity isolator. The laser adopts an all-fiber structure and the saturable absorption effect is attributed to nonlinear multimode interference (NL-MMI) from the single mode fiber-graded index multimode fiber-single mode fiber (SMF-GIMF-SMF) design. The STML laser can operate in the quasi-unidirectional regime with an emission strength difference of larger than 30 dB for the two counter-propagating lasers. And the switching between the dominating operating directions in the clockwise (CW) or counter-clockwise (CCW) directions can be easily achieved by adjusting the MM polarization controller (PC). Both STML conventional solitons (CSs) and the STML soliton molecules are obtained with a similar tunable wavelength from ∼1.56 μm to ∼1.58 μm for the opposite operating directions. Furthermore, the spatial dynamics of the STML soliton are also investigated in detail. The experimental results are of great help for us to explore nonlinear spatiotemporal dynamics and provide potential applications in fields of all-optical signal processing, fiber sensing and information coding.

Solvent-Free Organic Liquids: An Efficient Fluid Matrix for Unexplored Functional Hybrid Materials.

ConspectusThe invention of solvent-free organic liquids (SOLs) was serendipitous. However, the curiosity-driven research in the later stage delivered new soft materials with exciting optical, and optoelectronic properties along with appealing physical characteristics suitable for the futuristic applications. A slight change in the molecular design resulted in a drastic change in the physical state of molecules demonstrating monomer-like features in the bulk. The basic idea of core isolation has been successful in delivering new SOLs with attractive functional properties. The unique fluid matrix associated with SOLs offers a tremendous opportunity for making hybrid materials by simple mixing. The chance to study the fundamentally important electron transfer, energy transfer, charge transfer interactions, triplet-state emissions, and even detailed NMR experiments in the solvent-free neat state is the major attraction of SOLs. Usually, solvents and their polarity control such molecular properties, and in the case of SOLs, it avoids the use of solvents to study such fundamentally important properties. Besides, SOLs protect the triplet emitters and excited state processes involving triplet states from quenchers and make the analysis possible under ambient conditions.Our effort in this direction was focused on tuning the ground and excited state properties by transforming conventional organic molecules to SOLs and further value addition by preparing the hybrid SOLs. We developed a series of hybrid SOLs, exploring room-temperature phosphorescence, thermally activated delayed fluorescence, charge or energy transfer between donor and acceptor SOLs, selective explosive sensing, etc. A slight variation in the chemical structure or optoelectronic properties of the individual components imparted exciting optical features for the hybrid SOLs. It includes nonemissive charge transfer, tunable emission exciplex, room temperature phosphorescence, and thermally activated delayed fluorescence SOLs. The liquid matrix of donor SOLs accommodated varying amounts of acceptor SOLs to tune the ground and excited state features. In all examples of donor-acceptor-based hybrid SOLs, even a low amount of acceptor, such as a donor-acceptor ratio of 1000:1, can cause pronounced optical properties. Hence, the evaluation of the optical properties of SOLs, especially, in the absence of solvents is so special that it avoids the interference of solvent molecules. Still, the major drawback of SOLs remains unsolved until we report polymerizable SOLs. Although a large variety of SOLs have been reported in the literature, the long-lasting problem of surface stickiness of SOLs was resolved by polymerizable SOLs. It enabled the development of flexible, foldable, and stretchable large-area luminescent films suitable for lighting and display devices. In this Account, we summarize our work on SOLs, hybrid SOLs, polymerizable SOLs, and the application of SOLs in selective sensing of explosives. Finally, an outlook on the feasibility of luminescent polymerizable SOLs in futuristic applications is provided.

Quantum field theory for coherent photons: isomorphism between Stokes parameters and spin expectation values

Stokes parameters (S) on the Poincaré sphere are very useful values to describe the polarisation state of photons. However, the fundamental principle on the nature of polarisation is not completely understood, yet, because we have no concrete consensus on how to describe spin of photons, quantum-mechanically. Here, we have considered a monochromatic coherent ray of photons, described by a many-body coherent state, and established a fundamental basis to describe the spin state of photons, in connection with a classical description based on Stokes parameters. We show that a spinor description of the coherent state is equivalent to Jones vector for polarisation states, and obtain the spin operators (Ŝ) of all components based on rotators in an SU(2) group theory. Polarisation controllers such as phase-shifters and rotators are also obtained as quantum-mechanical field operators to change the phase of the wavefunction for polarisation states. We show that the Stokes parameters are quantum-mechanical average of the spin operators, S=⟨Ŝ⟩.

Control-gate-free reconfigurable transistor based on 2D MoTe2 with asymmetric gating

As transistor footprint scales down to the sub-10 nm regime, the process development for advancing to further technology nodes has encountered slowdowns. Achieving greater functionality within a single chip requires concurrent development at the device, circuit, and system levels. Reconfigurable transistors possess the capability to transform into both n-type and p-type transistors dynamically during operation. This transistor-level reconfigurability enables field-programmable logic circuits with fewer components compared to conventional circuits. However, the reconfigurability requires additional polarity control gates in the transistor and potentially impairs the gain from a smaller footprint. In this paper, we demonstrate a 2D control-gate-free reconfigurable transistor based on direct modulation of out-of-plane conduction in an ambipolar MoTe2 channel. Asymmetric electrostatic gating at the source and drain contacts is employed in the MoTe2 transistor resulting in different Schottky barrier widths at the two contacts. Consequently, the ambipolar conduction is reduced to unipolar conduction, where the current flow direction determines the preferred carrier type and the transistor polarity. Temperature dependence of the transfer characteristics reveals the Schottky barrier-controlled conduction and confirms that the Schottky barrier widths at the top contact are effectively tuned by electrostatic gating. Without the complexity overhead from polarity control gates, control-gate-free reconfigurable transistors promise higher logic density and lower cost in future integrated circuits.

Multiwavelength fiber laser based on enhanced bidirectional SOA utilizing Lyot filter

We demonstrated a multiwavelength fiber laser (MWFL) based on two bidirectional semiconductor optical amplifiers (SOAs) and a Lyot filter. The structure is enhanced by placing two -SOAs in a bidirectional region to improve the lasing performance. This resulted in a higher extinction ratio (ER) of 36.05 dB, as earlier work only achieved a maximum extinction ratio (ER) of 17 dB utilizing an SOA based on bidirectional configuration. The performance of the MWFL in unidirectional and bidirectional configurations, as well as different parameter settings of SOA current and polarization controller (PC) angle is examined. Using a unidirectional configuration decreases the amplification on one side of the SOA, hence reducing the wavelength bandwidth by 2 nm, which is equivalent to six lasing lines. According to the wavelength bandwidth of 13 nm and channel spacing of 0.22 nm, the optimal performance of MWFL employing bidirectional configuration is 56 lasing lines within 3 dB bandwidth. Consequently, we decreased each SOA's operating current, resulting in lower lasing lines. Changing the PC angle modifies the polarization degree and state, hence impacting multiwavelength flatness and wavelength bandwidth performance. When the polarizer is removed, the ER and lasing lines are decreased to 42 dB and 9 nm, respectively. The MWFL has high stability with a peak power fluctuation of 0.25 dB in 120 min.

Induced Circularly Polarized Luminescence and Exciton Fine Structure Splitting in Magnetic-Doped Chiral Perovskites.

Magnetic impurity doping in semiconductors has emerged as an important strategy to endow exotic photophysical and magnetic properties. While most reported hosts are centrosymmetric semiconductors, doping magnetic ions into a noncentrosymmetric chiral semiconductor can offer additional control of photonic and spin polarization. In this work, we synthesized a Mn2+-doped chiral two-dimensional (2D) perovskite, Mn2+:(R-MPA)2PbBr4 (R-MPA+ = R-methyl phenethylammonium). We found that the optical activity of chiral 2D perovskites is enhanced with an increased concentration of Mn2+ ions. Additionally, efficient energy transfer from the chiral host to the Mn2+ dopants is observed. This energy transfer process gives rise to circularly polarized luminescence from the excited state of Mn2+ (4T1 → 6A1), exhibiting a photoluminescence quantum yield up to 24% and a dissymmetry factor of 11%. The exciton fine structures of undoped and Mn2+-doped (R-MPA)2PbBr4 are further studied through magnetic circular dichroism (MCD) spectroscopy. Our analysis shows that chiral organic cations lead to an exciton fine structure splitting energy as large as 5.0 meV, and the splitting is further increased upon Mn2+ doping. Our results reveal the strong impacts of molecular chirality and magnetic dopants on the exciton structures of halide perovskites.

Large and active circular dichroism in a photosensitive silicon based metasurface

Active circular dichroism (CD) is highly required for flexible polarization control in modern terahertz (THz) systems. In this work, we numerically achieve large and active CD in THz region by optically controlling photosensitive silicon in a gold/silicon hybrid cross-shape metasurface. At the incident angle of 75°, the proposed metasurface exhibits large CD. By tuning the conductivity of photosensitive silicon with an optical pump, the large CD (0.89) can be dynamically switched to 0.06 and the peak frequency is blue shifted around 0.09 THz. The simultaneous switching of CD strength and peak frequency is attributed to the variation of resonance modes between electric and magnetic dipole resonances. Our proposed active metasurface with dynamic CD has profound potential in the fields of reconfigurable THz devices.

Nonlocal Metasurface with Chiral Exceptional Points in the Telecom-Band.

The exceptional point (EP) is the critical phase transition point in parity-time (PT) symmetry systems, offering many unique physical phenomena, such as a chiral response. Achieving chiral EP in practical applications has been challenging due to the delicate balance required between gain and loss and complicated fabrication, limiting both working band and device miniaturization. Here, we proposed a nonlocal metasurface featuring orthogonal gold nanorods, where loss modulation is achieved through rod size and lattice pitch. By tuning the coupling strength, we experimentally observed the PT symmetry phase transition and chiral EP in the telecom-band. The experimental and simulated circular conversion dichroism at EP reach 0.79 and 0.99, respectively. We also demonstrated an abrupt phase flip of a specific component near EP theoretically. This work provides a feasible scheme for exploring EP in polarized space within the telecom-band, which may find applications in polarization control, wavelength division multiplexing, ultrasensitive sensing, imaging, etc.