Light Polarization Modulation Research Articles

A terahertz chiral metamaterial with tunable dual-band to broadband circular dichroism based on Dirac semimetals

Chiral metamaterials play a crucial role in manipulating the electromagnetic waves. This paper intoduces a three-dimensional Dirac semimetal materials (3D DSM) metamaterial structure tailored for tunable and broadband circular dichroism (CD) effects at terahertz (THz) frequencies. Using the Jones matrix, electromagnetic multipole resonance theory, and the atomic orbital hybridization model, the resonant performance for the DSM based metamaterials in reflection and transmission design is systematically analysed, in terms of the resonant peak and bandwidth. Simulation results show that the bilayer DSM metamaterial supports the chiral response with dual-band resonance in transmitted spectra, and its CD and working frequency could be tuned by adjusting the rotation angle between the upper and lower DSM metamaterial layers and Fermi level of DSM. Therefore, the tunable CD from 0 to 0.51 could be achieved across a wide THz frequency from 3.56 THz to 4.02 THz. Additionlly, the resonant frequency is highly sensitive to the surrounding refractive index (RI), yielding a RI sensing sensitivity up to 308.6 GHz/RIU. The proposed DSM based chiral metamaterial features a tunable and broadband design, offering a universal design method and potential applications for the modulation of light polarization, chiral sensing and imaging, and communications.

Spin–orbit torque reconfigurable diffraction gratings

Spin–orbit torque (SOT) provides a convenient, fast, and efficient way to switch the magnetization and has been applied in memory, logic, and microwave devices. Here, we report the application of SOT in the spatial modulation of the optical field. We construct a diffraction grating composed of perpendicularly magnetized current channels that can be switched using the SOT current pulses, and the resulting periodic magnetization patterns are transferred into the polarization modulation of light through the magneto-optical effect. We demonstrate that the periodic structures and diffraction peaks of the grating can be reconfigured electrically. These results would open up an avenue to the application of the state-of-the-art spintronic technologies in fast tunable diffractive optics.

Ultrafast All‐Optical Control of Light Chirality with Nanostructured Graphene

AbstractUltrafast nanophotonics is a rapidly growing area of study focused on creating nanodevices that can modulate the properties of light at, to this date, unparalleled speed. To facilitate the growth of this field, there is a growing need for compact metamaterial designs for the manipulation of the amplitude, phase, and polarization of light. One promising strategy involves leveraging the optical nonlinearity of nanostructured materials to alter their permittivity by interacting with high‐intensity ultrashort laser pulses. This study showcases how such requirements can be met through the utilization of 2D materials, particularly graphene. The nonlinear optical response of a graphene nanorectangle array is theoretically modeled to achieve all‐optical, fully reversible, broadband, and ultrafast dynamic control of light chirality. This is achieved by taking advantage of the energy relaxation dynamics of coherently excited localized plasmons supported by the metasurface, and the transient increase in electron temperature in graphene. Using finite‐difference time‐domain simulations, ultrafast dynamic tuning between circular and linearly polarized light is demonstrated. The proposed platform gives promise for ultrathin, CMOS‐compatible nanophotonic systems that can provide high‐speed, room‐temperature modulation of light polarization.

Designing a Hybrid Perovskite with Enlarged Birefringence and Bandgap for Modulation of Light Polarization.

Birefringent crystals have important applications in optoelectronics areas due to their ability to modulate and polarize light. Despite increasing discovery of the birefringence potential of new crystals, it remains a great challenge to optimize both birefringence and bandgap simultaneously. Herein, a 1D chain-like hybrid perovskite birefringent crystal designed by 3D-to-1D dimensional tailoring, (GAM)2 PbI7 ·H2 O (GAM=C5 N10 H10 ), is presented, showing enlarged birefringence of 0.49@550nm and enlarged optical bandgap (2.48eV). Consequently, the birefringent quality factor of (GAM)2 PbI7 ·H2 O is up to 2.8 times that of the template MAPbI3 . In particular, the birefringence is much larger than those of commercial birefringent crystals and surpasses that of the vast majority of hybrid perovskite known to date. Theoretical calculations reveal that the strongly anisotropic arrangement of (GAM)2.5+ π-conjugated cations and ordered PbI6 octahedra contributes to the large birefringence and wide bandgap of (GAM)2 PbI7 ·H2 O. It is believed that this work will provide a new pathway toward the rational design and synthesis of hybrid perovskite birefringent crystals for compact wide-bandgap polarization dependent devices.

Multi-point optical fiber hydrogen detection system based on light polarization modulation

A hydrogen sensing system including 8 sensors based on light polarization modulation is developed and demonstrated for simultaneous multi-point hydrogen sensing with high sensitivity. Each sensor is composed of a polarizer, a polarization control, and a short segment of polarization maintaining fiber (PMF) coated with Pt-loaded WO3. Due to the exothermic reaction between hydrogen and WO3 with the help of catalyst Pt, the local temperature of PMF increases and the reflective spectrum of the sensor shift accordingly. The self-developed control system software achieves the sequential scanning and recording of the reflection spectra of each sensor by programable controlling a light switch, and then gives the measured hydrogen concentration of each channel in real-time according to the spectrum shift by using an automatic dip finding algorithm with Gaussian fitting. The experimental results show that the proposed type of sensor has ultra-high hydrogen sensitivity, with a maximum value of −20.22 nm/% (vol %); packaging with foam substrate helps to reduce the response time of the device; the hydrogen sensor is almost unaffected by environmental relative humidity. Moreover, the hydrogen sensing system is experimentally proved having good stability and repeatability.

Anisotropic optical and magnetic response in self-assembled TiN–CoFe2 nanocomposites

Transition metal nitrides (e.g., TiN) have shown tremendous promise in optical metamaterials for nanophotonic devices due to their plasmonic properties comparable to noble metals and superior high temperature stability. Vertically aligned nanocomposites (VANs) offer a great platform for combining two dissimilar functional materials with a one-step deposition technique toward multifunctionality integration and strong structural/property anisotropy. Here, we report a two-phase nanocomposite design combining ferromagnetic CoFe2 nanosheets in the plasmonic TiN matrix as a new hybrid plasmonic metamaterial. The hybrid metamaterials exhibit anisotropic optical and magnetic responses, as well as a pronounced magneto-optical coupling response evidenced by Magneto-optic Kerr Effect measurement, owing to the novel vertically aligned structure. This work demonstrates a new TiN-based metamaterial with anisotropic properties and multifunctionality toward light polarization modulation, optical switching, and integrated optics.

Finding a Deep-UV Borate BaZnB4 O8 with Edge-sharing [BO4 ] Tetrahedra and Strong Optical Anisotropy.

The polarization modulation of deep-UV light is an important process that incorporates functionality to selectively respond to light-mater interaction. Typically, optical anisotropy is foremost to the use efficiency of deep-UV birefringent crystals. Herein, a new congruently melting polyborate with extremely large birefringence (Δn(001) =0.14@589.3 nm) and band gap (6.89 eV) is discovered as a high performance birefringent crystal, which breaks the current deadlock of deep-UV polyborates that usually show small birefringence. The rigid tetrahedra, including [ZnO4 ] and edge-sharing [BO4 ] tetrahedra, make all the planar [BO3 ] triangles in the lattice adopt preferential arrangement and thereby lead to an extraordinary large birefringence that is larger than all the deep-UV borates with experimentally measured values. Structural analyses with the additional theoretical calculations were used to study the origin of strong optical anisotropy in BaZnB4 O8 .

Observation of antiferromagnetic domains in Cr2O3 using nonreciprocal optical effects

The archetypal magnetoelectric (ME) antiferromagnet ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$, which has the diagonal components of linear ME tensor, exhibits several different types of nonreciprocal optical effects: the electric field-induced $(E\text{\ensuremath{-}}\mathrm{induced})$ Faraday effect, the electric field-induced magnetic circular dichroism ($E\text{\ensuremath{-}}\mathrm{induced}$ MCD), and the spontaneous nonreciprocal rotation of reflected light (NRR). In principle, antiferromagnetic (AFM) domains of ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ are expected to be distinguished by using these effects. However, such domain observations have never been reported mainly due to the smallness of the effects studied to date. In this study, we demonstrate that all these nonreciprocal optical effects allow the observation of AFM domains in ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$. We first measured spectra of the $E\text{\ensuremath{-}}\mathrm{induced}$ Faraday effect and $E\text{\ensuremath{-}}\mathrm{induced}$ MCD, and found that relatively large effects appear in the visible light region. Then, by imaging spatial distributions of the three nonreciprocal effects via field and light-polarization modulation imaging techniques, we succeeded in visualizing AFM domains. Intriguingly, the domain patterns obtained via the bulk sensitive $E\text{\ensuremath{-}}\mathrm{induced}$ Faraday effect and MCD and those via the surface-sensitive NRR are identical to each other, revealing that the AFM domains in ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ are uniform in the thickness direction. The domain observation methods provided here will be widely applied to various ME antiferromagnets, not only insulators but also metals, with the diagonal components of linear ME tensor.

Double‐Modification Oriented Design of a Deep‐UV Birefringent Crystal Functionalized by [B12O16F4(OH)4] Clusters

Polarization modulation of deep-UV light is of great significance to the current technologies, and to this end, birefringent crystal has emerged as an invaluable material as it allows for the effective light modulation. Herein, double-modification strategy driven by F and OH anions that makes double effects towards the critical property enhancement of deep-UV birefringent crystals is proposed. This leads to the discovery of a new hydroxyborate (NH 4 ) 4 [B 12 O 16 F 4 (OH) 4 ] with unprecedented giant cluster as a deep-UV birefringent crystal with large birefringence (Δ n exp. = 0.12@546 nm). Such a birefringence sets a record among inorganic hydroxyborates with experimentally measured birefringence. The [B 12 O 16 F 4 (OH) 4 ] cluster in near-plane arrangement is enabled by the hydrogen-bonding interactions; and it is theoretically confirmed to be optical-active for large birefringence and band gap, in which the π-conjugated modules, [BO 3 ] and [BO 2 (OH)], are the main sources of large optical anisotropy.

Factors Affecting Surface Plasmon Coupling of Quantum Wells in Nitride-Based LEDs: A Review of the Recent Advances.

Surface plasmon (SP)-enhanced quantum-well (QW) LEDs have proved their potential in replacing conventional lighting devices for their high-performance capabilities in ultraviolet (UV), blue and green spectral ranges. The SP-enhanced QW-LEDs have applications in light emission enhancement, light polarization, color conversion, and speed modulation. The electric field of the plasmonic mode of a metal couples with the exciton energy of QWs in resonance results in efficiency enhancement to several folds. The strength of the SP–QW coupling is mainly influenced by the type of metal used for SP enhancement, the metal nanostructure geometry, and the penetration depth of the SP fringing field in the p-GaN. The use of an appropriate dielectric interlayer between the metal and the p-GaN allows further control over SP resonance with QW emission wavelength. The penetration depth defines the p-GaN thickness and the QW period number for effective SP–QW coupling. The optimization of these parameters is key to achieve high efficiencies in SP-enhanced QW-LEDs for various applications. This review explains the SP enhancement mechanism and the key challenges facing the SP enhancement of QW-LEDs. The main factors that affect the SP–QW coupling have been explained in detail based on recent reports devoted to this field.

Active Suppression of Piezoelectric Ringing in Pockels Cells for Laser Cavity Application

Pockels cells used as electro-optical modulators in high-power high-repetition lasers suffer from piezoelectric ringing phenomenon due to piezoelectric properties of the crystals. A new method for active suppression of the piezoelectric ringing in Pockels cells is proposed in this work. It is based on symmetric control of Pockels cell using burst of short positive and negative voltage pulses with the same amplitude instead of a single long pulse for light polarization modulation. Rising and falling edges of pulses of the burst induce symmetrical acoustic waves of the opposite phase and cancel the piezoelectric ringing of the crystal. A new high voltage driver capable of generating positive and negative pulses of tens of nanoseconds of 3 kV magnitude was developed for this purpose. The amplitude of laser beam intensity pulsations caused by the piezoelectric ringing can be reduced up to five times when active suppression method is used for the deuterated potassium dihydrogen phosphate (DKDP) Pockels cell. Such crystals like DKDP, LiNbO3, and LiTaO3 may benefit from the proposed method and find new use in lasers of high repetition rate where piezoelectric ringing is a major limiting factor.

Transient optical symmetry breaking for ultrafast broadband dichroism in plasmonic metasurfaces

Ultrafast nanophotonics is an emerging research field aimed at the development of nanodevices capable of light modulation with unprecedented speed. A promising approach exploits the optical nonlinearity of nanostructured materials (either metallic or dielectric) to modulate their effective permittivity via interaction with intense ultrashort laser pulses. While the ultrafast temporal dynamics of such nanostructures following photoexcitation has been studied in depth, sub-ps transient spatial inhomogeneities taking place at the nanoscale have been so far almost ignored. Here we theoretically predict and experimentally demonstrate that the inhomogeneous space-time distribution of photogenerated hot carriers induces a transient symmetry breaking in a plasmonic metasurface made of highly symmetric metaatoms. The process is fully reversible, and results in a broadband transient dichroic optical response with a recovery of the initial isotropic state in less than 1 picosecond, overcoming the speed bottleneck caused by slower relaxation processes, such as electron-phonon and phonon-phonon scattering. Our results pave the way to the development of ultrafast dichroic devices, capable of Tera bit/s modulation of light polarization.

Dynamic characterization of polarization property in liquid-crystal-on-silicon spatial light modulator using dual-comb spectroscopic polarimetry.

Spectroscopic polarimetry (SP) is a powerful tool for characterization of thin film, polarization optics, semiconductor, and others. However, mechanical polarization modulation of broadband light hampers its application for dynamic monitoring of a sample. In this article, we demonstrate the dynamic SP with features of polarization-modulation-free polarimetry and spectrometer-free spectroscopy benefiting from dual-comb spectroscopy (DCS) using a pair of optical frequency combs (OFCs). DCS enables the direct determination of polarization without the need for polarization modulation by using mode-resolved OFC spectra of amplitude and phase for two orthogonally linear-polarized lights while securing rapid, high-precision, broadband spectroscopy without the need for spectrometer. Effectiveness of the proposed system is highlighted by visualizing the hysteresis property of dynamic response in a liquid-crystal-on-silicon spatial light modulator at a sampling rate of 105 Hz.

Enhanced magnetic modulation of light polarization exploiting hybridization with multipolar dark plasmons in magnetoplasmonic nanocavities

Enhancing magneto-optical effects is crucial for reducing the size of key photonic devices based on the non-reciprocal propagation of light and to enable active nanophotonics. Here, we disclose a currently unexplored approach that exploits hybridization with multipolar dark modes in specially designed magnetoplasmonic nanocavities to achieve a large enhancement of the magneto-optically induced modulation of light polarization. The broken geometrical symmetry of the design enables coupling with free-space light and hybridization of the multipolar dark modes of a plasmonic ring nanoresonator with the dipolar localized plasmon resonance of the ferromagnetic disk placed inside the ring. This hybridization results in a low-radiant multipolar Fano resonance that drives a strongly enhanced magneto-optically induced localized plasmon. The large amplification of the magneto-optical response of the nanocavity is the result of the large magneto-optically induced change in light polarization produced by the strongly enhanced radiant magneto-optical dipole, which is achieved by avoiding the simultaneous enhancement of re-emitted light with incident polarization by the multipolar Fano resonance. The partial compensation of the magneto-optically induced polarization change caused by the large re-emission of light with the original polarization is a critical limitation of the magnetoplasmonic designs explored thus far and that is overcome by the approach proposed here.

Polarization in D-shaped fiber modulated by magneto-optical dichroism of magnetic fluid

The polarization of a D-shaped fiber is modulated after immersing it in magnetic fluid (MF) and applying a magnetic field. Theoretical analysis predicts that magneto-optical dichroism of MF plays a key role in light polarization modulation. During light polarization modulation, the evanescent wave polarized parallel to the magnetic field has greater loss than its orthogonal component. Light polarization of a D-shaped fiber with a wide polished surface can be modulated easily. High concentration MF and a large magnetic field all have great ability to modulate light polarization.

Mercury geochemistry of deep-sea sediment cores from the Kuril area, northwest Pacific

In the present study we report mercury data in the sediment cores obtained during a Germany-Russian and Russian-Germany cruises onboard the Vessels Sonne and Akademik M.A. Lavrentyev in Kuril area. This region cover an extensive area of the Northwest Pacific included the trench system and adjacent abyssal plain, ranging zone off the Kuril Islands. Kuril area is characterized by high water biological productivity, intensive volcanic activity, and hydrological features. Mercury concentrations in sediment cores were analyzed using a Zeeman atomic absorption spectrometer with high frequency modulation of light polarization and a pyrolysis attachment to determine its occurrence, distribution, and deposition flux. Mercury concentrations in the sediments ranged between 8 and 170 ppb; its minimal concentrations (8–15 ppb) were detected in sandy turbidites. For the pre-industrial period, Hg flux ranged between 33 and 36 µg/m2 year. The maximum Hg flux (44 µg/m2 year) corresponded to the 1980, with decreases of up to 30 µg/m2 year in modern sediments (top-core sediment samples). The Hg outlet temperature in the bottom sediments corresponded to a physically sorbed form of Hg and depends on the Hg content of diatoms (siliceous residues). Hg concentrations were significantly positivly correlated with total organic carbon content but negativly correlated with Al, Fe, Zr, and Sr contents. Thus, two main factors affected Hg burial in bottom sediments; atmospheric deposition of Hg and biological productivity. The effect volcanic activity has not been clearly established in this study.

Reflective optical fiber sensor based on light polarization modulation for hydrogen sensing

A simple reflective hydrogen-sensing system based on polarization modulation is proposed and experimentally demonstrated. The sensing unit consists of a polarizer, a polarization control, and a sensing head composed of a short segment of polarization-maintaining fiber (PMF) with a Pt-loaded ${{\rm WO}_3}$WO3 coating. When the sensing head is exposed to a hydrogen environment, heat is generated due to the interaction between hydrogen and ${{\rm WO}_3}$WO3 with the help of catalyst Pt in air; then, the local temperature of the PMF increases, which results in the reflection spectrum shift because the light polarization state changes due to the variation of the birefringence coefficient of the PMF. Experimental results show that the system is capable of producing a rapid response to hydrogen with a high sensitivity of $\sim{18.04}\;{\rm nm/}\% $∼18.04nm/% (vol%) within the concentration range of 0–4% (vol%). Additionally, the sensing head has a probe structure with reflective measurement and immunity to humidity. Such features make the sensing system promising in the fields of hydrogen transportation or storage.

Ultrafast tunable modulation of light polarization at terahertz frequencies

Controlling light polarization is one of the most essential routines in modern optical technology. Since the demonstration of optical pulse shaping by spatial light modulators and its potential in controlling the quantum reaction pathways, it paved the way for many applications as a coherent control of the photoionization process or as polarization shaping of terahertz (THz) pulses. Here, we evidenced efficient nonresonant and noncollinear χ(2)-type light-matter interaction in femtosecond polarization-sensitive time-resolved optical measurements. Such nonlinear optical interaction of visible light and ultrashort THz pulses leads to THz modulation of visible light polarization in bulk LiNbO3 crystal. Theoretical simulations based on the wave propagation equation capture the physical processes underlying this nonlinear effect. Apart from the observed tunable polarization modulation of visible pulses at ultrahigh frequencies, this physical phenomenon can be envisaged in THz depth-profiling of materials.

Transverse relaxation determination based on light polarization modulation for spin-exchange relaxation free atomic magnetometer**Project supported by the National Natural Science Foundation of China (Grant No. 61227902), the National Key R&D Program of China (Grant No. 2017YFB0503100), and the Natural Science Foundation of Beijing Municipality, China (Grant No. 4162038).

A transverse relaxation determination of spin-exchange relaxation free (SERF) magnetometer based on polarization modulation technique is proposed. Compared with the radio-frequency (RF) excitation and light intensity excitation methods used in SERF magnetometer, the light polarization modulation method has a high stability in low-frequency range, which indicates a more accurate transverse relaxation measurement.

Magnetic Field Sensor Exploiting Light Polarization Modulation of Microfiber With Magnetic Fluid

We demonstrate an optical fiber magnetic field sensor that can measure both magnetic field intensity and directions. It is designed by immersing a microfiber into magnetic fluid (MF) and based on the light polarization detection. When there is external magnetic field, the magnetic nanoparticles of MF generate a noncircular symmetric distribution around the microfiber, and MF exerts magneto-optical dichroism. Light will be polarized after passing through the microfiber. The time response of the fiber magnetic field sensor is studied. It is found that the intensity of the magnetic field can be measured directly only when it satisfies the detectable threshold condition. Furthermore, the magnetic field sensor possesses good orientation response to the magnetic field directions. The signal analysis system consists of a polarization beam splitter and two photodetectors. The sensor designed has the advantages of both simple structure and low cost, without needing any precise spectral analyzer.