Wave Plate Research Articles

Highly efficient multifunctional metasurface integrating lens, prism, and wave plate

The miniaturization of optical systems is crucial for various applications, including compact augmented reality/virtual reality devices, microelectromechanical system sensors, ranging technologies, and microfabricated atomic clocks. However, reliance on bulky discrete optical elements has been a significant obstacle to achieving this miniaturization. This work introduces a highly efficient multifunctional metasurface (MFMS) that seamlessly integrates a lens, prism, and quarter-wave plate (QWP). This innovation allows simultaneous collimation, beam deflection, and polarization conversion within a singular thin element. Specifically, for the prism-QWP bifunctional integration, we achieved a high diffraction efficiency of 72.8% and a degree of circular polarization of −0.955 under exposure to linearly polarized light at a wavelength of 795 nm, proving its potential for ultracompact atomic clock applications. Moreover, the lens-prism-QWP trifunctional integration successfully showed diffraction-limited focusing performance with a numerical aperture of 0.4, which was sufficient to collimate a beam with a divergence angle of 20∘, corresponding to the light emitted from a standard vertical-cavity surface-emitting laser.

Non-linear dynamics and bandgap control in magneto-rheological elastomers metamaterials with inertial amplification

Sandwich plate structures are extensively utilized in engineering due to their favorable stiffness-to-weight ratio. Nonetheless, these lightweight thin-walled structures frequently encounter challenges related to inadequate low-frequency vibration performance, which significantly restricts their applications, particularly in the realm of precision instruments which is sensitive to vibration. This study introduces an innovative design of an active nonlinear metamaterial, to achieve tunable broadband low-frequency bandgaps for sandwich plates. The nonlinear oscillator incorporates an inertia amplification mechanism (IAM), Euler-buckled beams, mass elements, and magneto-rheological elastomers (MREs), which are modulated via external magnetic fields to adjust the material's stiffness dynamically. Employing Hamilton's principles and the plate wave expansion method (PWE), the dispersion relations for the metamaterial plate are derived, elucidating the dispersion surfaces and the band structures within its sandwich-like plates.The dynamical equations of the metamaterial plate are formulated and validated through numerical simulations using the Galerkin method, confirming the theoretical predictions. The results demonstrate effective control over low-frequency and broadband bandgaps under low mass ratio conditions through strategic manipulation of the inertia amplification factor and magnetic flux. The study extensively explores the nonlinear dynamic responses of the metamaterial, highlighting the significant impact of excitation amplitudes on the amplitude-dependent bandgaps.

Vanadium dioxide-assisted switching of a half-wave and quarter-wave plate to a dual-band absorber for the terahertz wave

In this study, we present a broadband, multi-functional, and switchable metamaterial for terahertz (THz) waves. The metamaterial design achieves high polarization conversion efficiency and can seamlessly transition between a polarization converter (PC) and a dual-band absorber through the phase transition behavior of vanadium dioxide (VO2). Our design facilitates linear to-cross (Half-wave plate) and linear to-circular (Quarter-wave plate) polarization conversion across a bandwidth extending from 0.58 THz to 0.88 THz, and 0.35 THz to 0.50 THz respectively. Near-perfect absorption at 0.35 THz and 0.99 THz was observed when VO2 changed its phase from an insulator to a conductor. These broadband features are realized through a straightforward metamaterial design incorporating only a reflector, a dielectric spacer, and an antenna (meta-atom resonator). Our designed structure demonstrates impressive angular stability for incident angles ranging from 0° to 45°. The proposed switchable metamaterial holds promise for advancing the development of tunable polarization rotating devices and on/off switching LPC devices, offering broad applications in THz detection, sensing, and communications.

Combining Optical and Digital Compensation: Neural Network-Based Channel Equalisers in Dispersion-Managed Communications Systems

Combining Optical and Digital Compensation: Neural Network-Based Channel Equalisers in Dispersion-Managed Communications Systems

Electro-optic Q-switched Yb:YAG thin disk laser with widely continuously tunable pulse width at a stable output of over 80 W

We report an electro-optic Q-switched Yb:YAG thin disk laser with widely continuously tunable pulse width ranging from 16.4 to 432.2 ns. The tunability was achieved through a simple and convenient method by rotating both the Pockels cell and the quarter-wave plate at either identical or slightly different angles. Based on the 72-pass pump module and 224.4 W laser diode pumping source, a pulsed output of over 80 W was attained at a repetition rate of 100 kHz. The output power and output pulse train remained stable in the whole tuning range. The corresponding output power was 82.7 W and 84.4 W for the minimum and maximum pulse width, respectively. A model which was exceedingly more accurate than previous models describing the tunability of the pulse width were proposed and the simulation results of this model exhibited strong agreement with the experimental measurements.

Optimization of retarder parameters for switchable privacy mode automotive displays under asymmetric viewing conditions

A switchable privacy mode (SPM) display should not be seen by a driver during driving (privacy mode), but it needs to be seen by the driver and a co-driver when a car is stopped (share mode). In this work, a SPM display was designed using a bottom twisted-nematic (TN) liquid crystal display (LCD) and a top in-plane switching (IPS) LCD where a half-wave plate (HWP) is located between the two LCD panels. The SPM display in front of the co-driver was considered, which is seen under asymmetric viewing conditions. The orientation of the slow axis, retardation dispersion, and biaxiality of the retarder were varied to maximize the SPM’s optical performance in the driver’s and co-driver’s viewing directions. Transmittance at the driver’s viewing direction can be reduced from 4.22 to 0.03% in privacy mode by replacing the positive dispersion retarder with a negative dispersion retarder.

CMB polarization signal demodulation with a rotating half-wave plate

ABSTRACT Several forthcoming Cosmic Microwave Background polarization experiments will employ a Continuously Rotating Half-Wave Plate (CRHWP), the primary purpose of which is to mitigate instrumental systematic effects. The use of a CRHWP necessitates demodulating the time-ordered data during the early stages of data processing. The standard approach is to “lock in” on the polarization signal using the known polarization modulation frequency and use Fourier techniques to filter out the remaining unwanted components. However, an alternative, less well-studied option is to incorporate the demodulation directly into the map-making step. Using simulations, we compare the performance of these two approaches to determine which is most effective for B-mode signal recovery. Testing the two techniques in multiple experimental scenarios, we find that the lock-in technique performs best over the full multipole range explored. However, for the recovery of the largest angular scales (multipoles, $\ell \lt 100$) we find essentially no difference in the recovery of the signal between the lock-in and map-making approaches, suggesting that a parallel analysis based on the latter approach could represent a powerful consistency check for primordial B-mode experiments employing a CRHWP. We also investigate the impact of a detector-differencing step, implemented prior to demodulation, finding that, in most scenarios, it makes no difference whether differencing is used or not. However, analysing detectors individually allows the point at which information from multiple detectors is combined to be moved to later stages in the analysis pipeline. This presents alternative options for dealing with additional instrumental systematic effects that are not mitigated by the CRHWP.

Design of an aperiodic Cr/C reflective multilayer quarter-wave plate at the carbon K-edge

An aperiodic Cr/C reflective multilayer quarter-wave plate is designed and optimized at the carbon K-edge, by implementing both the genetic algorithm (GA) and the non-dominated sorting genetic algorithm II (NSGA-II). The performance is demonstrated using test free electron laser (FEL) pulses simulated by GENESIS to convert the imperfect linearly polarized light to circular polarization; the characteristics are verified by a numerical analysis of the Stokes parameter of the FEL pulses before and after penetration through the multilayer.

On Klein tunneling of low-frequency elastic waves in hexagonal topological plates

Incident particles in the Klein tunnel phenomenon in quantum mechanics can pass a very high potential barrier. Introducing the concept of tunneling into the analysis of phononic crystals can broaden the application prospects. In this study, the structure of the unit cell is designed, and the low frequency (< 1 kHz) valley locked waveguide is realized through the creation of a phononic crystal plate with a topological phase transition interface. The defect immunity of the topological waveguide is verified, that is, the wave can propagate along the original path in the cases of impurities and disorder. Then, the tunneling phenomenon is introduced into the topological valley-locked waveguide to analyze the wave propagation, and its potential applications (such as signal separators and logic gates) are further explored by designing phononic crystal plates. This research has broad application prospects in information processing and vibration control, and potential applications in other directions are also worth exploring.

3.2 GHz first shear horizontal-mode plate wave resonator on a 175°YX LiNbO3 thin plate showing 24.6% bandwidth

In this study, a first shear horizontal (SH1) mode plate wave resonator for HF and wide-band filters was investigated. From FEM simulation, the SH1 mode plate wave exhibited a high phase velocity of 23 km s−1 and a high electro-mechanical coupling factor (k 2) of 37% on (0°, 85°, 0°) LiNbO3 (LN) with a thickness of 0.1λ (λ: wavelength). The SH1 mode resonator was fabricated on a 0.5–0.57 μm thick LN film. An 80 nm Al IDT electrode was formed with λ varied from 4–16 μm. Finally, 50 nm thick Al was deposited to form an electrically short bottom plane, which was required to generate a SH1 mode wave. The fabricated device exhibited a resonance frequency (f r) of 2.24 GHz, an anti-resonance frequency (f a) of 2.8 GHz, a wide fractional bandwidth (FBW) of 20%, an impedance (Z) ratio of 35.4 dB, and TCF of −90.8 ppm/°C at f r and −74.8 ppm/°C at f a.

SH waves in orthotropic piezomaterials considered surface effects

Nowadays, orthotropic piezomaterials have enormous potential in producing electronic devices owing to their inherent merits, e.g., intrinsically robust piezoelectricity. Nevertheless, the previous theoretical studies merely report surface effects on the physical properties of SH waves in a layered transversely isotropic piezoelectric structure. Filling such a blank is a special necessity for optimizing Surface Acoustic Wave (SAW) sensors. Thus, the present paper aims to determine how surface effects and interfacial imperfection affect the attributes of SH waves in a layered orthotropic piezoelectric semi-space by means of surface piezoelectricity theory and a linear spring model. The structure mainly consists of the piezoelectric film's bottom and top surface layers and the imperfect bonding between the piezoelectric film and elastic half-space. To explicitly figure out surface and imperfect interface effects on the mechanical behavior of SH waves in a layered piezoelectric half-space, we extensively derive the phase velocity equations of SH waves in an orthotropic piezoelectric plate and an orthotropic piezoelectric half-space. Then, a comparison study among SH waves in a layered piezoelectric semi-space, a piezoelectric plate, and a piezoelectric half-space is conducted. As a result, it is revealed that the attributes of SH waves dramatically vary as the piezoelectric films’ thickness changes from microscale to nanoscale. In addition, phase velocity increases or decreases with an increasing surface elastic constant or surface density due to the enhancement of stiffness or density of the whole structure. When the ratio of piezoelectric film thickness to wavelength is small, imperfect parameters substantially reduce the phase velocity owing to a decreasing interface elastic stiffness. The comparison study shows that the imperfect parameter does not influence the waves’ velocity, while the ratio of film thickness to wavelength is relatively considerable. Anisotropic piezoelectric constant essentially weakens surface effects on the waves’ velocity. Intriguingly, a linear function is acquired and is used to measure surface density via the slope of the linear function. The summaries supply unique guidelines and instructions to open an avenue for designing and manipulating surface acoustic wave nanosensors in the future.

Sagnac interferometer current transformer based on pulse multiplexing network structure

The monitoring of current plays an important role in accurately grasping the working status of the power system. In this paper, a Sagnac interferometer (SI) current transformer (CT) based on pulse multiplexing network structure is proposed. The network multiplexing structure can multiplex a pulsed light into multiple sensing signals, eliminating interference from light source power jitter and sudden changes in optical path loss. SI consists of a uniaxial working coupler, a 45° Faraday rotator, two quarter wave plates (QWPs), and spun fiber. The uniaxial working coupler used can achieve slow axis operation and fast axis cutoff, and convert light into linear polarization light. After passing QWPs, the forward and backward light changes from linear polarization to circular polarization, which can be used for current sensing. Experiments have shown that it has good linearity and repeatability. The proposed sensor has the advantages of low cost and simple structure, which has broad prospects in applications with not very high precision requirements.

Enhancing unilateral EMAT performance through topological optimization of Halbach permanent Magnet arrays

A novel unilaterally excited electromagnetic acoustic transducer (EMAT) is proposed as a solution to address the challenge of weak electromagnetic ultrasonic detection signals being susceptible to interference from clutter noise signals. EMAT employs Halbach permanent magnet array (HPMA) structure and a coil designed based on Huygens superposition principle. This design enables the generation and reception of highly directive Rayleigh surface waves in aluminum plates. To enhance the operational efficiency of EMAT while maintaining a high level of directivity for surface waves, a penalty function is implemented in COMSOL Multiphysics for the topological optimization of EMAT. The objective function in this optimization process is based on covariance (COV) of the magnetic induction intensity. The research results suggest that the homogeneity of the magnetic induction intensity within the coil region is enhanced by 50 % following topological optimization compared to the original design. The energy conversion efficiency of EMAT is enhanced by 5 times compared to traditional designs. The surface wave speed was determined to be 2631 m/s when measured at a frequency of 400 kHz. The value indicates a relative error of 6.37 % in comparison to the theoretical speed. The results indicate that EMAT has the capability to generate high-directional and pure Rayleigh waves.

Selective topological valley transport of elastic waves in a Bragg-type phononic crystal plate

Based on the quantum valley Hall effect analogy, this work proposes a phononic crystal plate with ligament-type beams to obtain the topological valley transmission of elastic waves. A pure Bragg degenerate state appears in the high-frequency region with a resonator introduced. By rotating the central scatterer and the beams, the mirror symmetry is broken to form a topological bandgap. Subsequently, this work finds that two selective edge states also appear beside the commonly non-trivial crossing edge states in the topological bandgap by calculating the projected band and eigenvalue spectrum of the supercell with different valley Hall phases phononic crystals. Their appearance is due to band separation of the topological edge states caused by an increase in the rotation angle. Both selective edge states can transmit topologically in specific paths. They will help further to broaden the width of the frequency band of topological transmission. Besides, an elastic wave splitter is designed and demonstrated numerically, which can form two channels and three channels in different frequency bands. With the topological selective edge state disappearing, a topological corner state exists in the edge bandgap. This work provides a theoretical reference for practical applications of broadband elastic wave topological transmission and elastic energy trapping.

Design of guided wave magnetostrictive patch transducer with vertical static bias magnetic field for pipe inspection

Compared with electromagnetic acoustic transducer (EMAT), magnetostrictive patch transducer (MPT) has higher energy conversion efficiency. MPT is often used to excite and receive long-distance ultrasonic guided waves for defect detection or structural health monitoring of large industrial equipment. In this work, a new design method of permanent magnet MPT using the vertical static bias magnetic field to excite shear horizontal (SH) guided waves is proposed. First, the mathematical model of exciting ultrasonic guided waves by a vertical static bias magnetic field MPT is established, and the equivalent surface stress in the magnetostrictive patch is calculated. It is shown that the vertical static bias magnetic field MPT can excite SH guided waves in plates. Then, the influence of static bias magnetic field intensity on the amplitude of guided wave signal is analyzed. Compared with other traditional MPTs, the amplitude of SH guided wave signal excited by the vertical static bias magnetic field MPT is increased. Finally, a periodic permanent magnet (PPM)-MPT with a central frequency of 120 kHz is designed. The proposed PPM-MPT improves the energy conversion efficiency compared to the circumferential alternating permanent magnet array type MPT. The PPM-MPT can detect defects in a steel pipe with a wall thickness of 3.5 mm and an inner diameter of 100 mm. The results show that the PPM-MPT designed in this paper successfully detects the through hole with a diameter of 2 mm, and the cross-section loss rate of the defect is about 0.6 %.

Optical Frequency Transfer on the Order of 10−19 Fractional Frequency Instability over a 64 m Free-Space Link

High-precision time–frequency is widely used in time measurement, satellite navigation, scientific research, and other fields. With the rapid development of optical clock technology, the fractional frequency instability and uncertainty of optical clock have reached 10−18 orders of magnitude, which is expected to contribute to generating the International Atomic Time and may even be used to redefine the “second” in the future. Therefore, the long-distance transfer of time–frequency signals between optical atomic clocks is of great significance. Free-space optical frequency transfer technology is one of the important technologies for solving the space-based optical clock comparison because of its high transfer precision and easy networking characteristics. In order to solve the long-distance space-based optical clock comparison, this paper investigates a free-space active phase noise compensation method using an Acousto-Optic Modulator (AOM), based on the traditional optical fiber phase noise compensation scheme. This new method is more flexible and scalable than the optical fiber time–frequency transfer technology. The optical frequency transfer over a 64 m free-space link is demonstrated. The fractional frequency transfer instability during free running is 9.50 × 10−16 at 1 s, and 4.44 × 10−16 at 2000 s, and the fractional frequency instability after compensation is 7.10 × 10−17 at 1 s, 3.07 × 10−19 at 2000 s, which is about 1–3 orders of magnitude better than that in free running, and provides a feasible scheme for space-based optical clock comparison.

Single-beam low-frequency loss modulation technique for two-photon absorption measurement

We present a straightforward and reliable single-beam configuration designed for the assessment of two-photon absorption (2PA) through the utilization of the loss modulation technique. Mechanical rotation of a half-wave plate induces a sinusoidal modulation in the envelope of the probe pulse train. The elimination of spurious signals is achieved by determining the difference of the lock-in amplifier output at the focused and defocused positions of the sample. Our findings, based on measurements with dye solutions and crystalline silicon, demonstrate the feasibility of determining the 2PA coefficient, subject to preliminary calibration of the setup with reference samples. Remarkably, the acquisition of the 2PA signal in silicon at 1030 nm is accomplished with less than 200 pJ energy of the laser pulse, overcoming the challenge posed by concurrent linear absorption. Additionally, a signal of 3PA is revealed despite the presence of 2PA and linear absorption.

Integrated 800 Gb/s O-band WDM optical transceiver enabled by hybrid InP-polymer photonic integration

We propose and demonstrate a novel O-band wavelength division multiplexing (WDM) optical transceiver enabled by the hybrid photonic integration of indium phosphide (InP) components into a polymer-based photonic motherboard called PolyBoard. The optical engine hosts an eight-fold InP electro-absorption modulated laser (EML) array at the transmitter part exhibiting &gt;35GHz electro-optical bandwidth and an eight-fold InP photodiode (PD) array at the receiver part with 50 GHz bandwidth, butt-end coupled to the PolyBoard motherboard, which accommodates passive arrayed waveguide gratings (AWGs) at the transmitter and receiver sides, responsible for performing the wavelength multiplexing and demultiplexing functionalities, respectively. What we believe to be a novel thin-film-based O-band half-wave plate is placed at the receiver side AWG, ensuring the polarization insensitivity of the prototype. The optical engine’s design is discussed in the manuscript, demonstrating experimental results from its static and dynamic evaluation. Individual characterization of the transmitter and receiver sides of the optical engine is presented before evaluating the optical engine as a whole in a loopback configuration. The obtained results underscore the potential of the proposed hybrid photonic integrated transceiver for supporting 800 Gb/s capacity in intra-datacenter optical interconnects for transmission distances up to 2 km.

Tunable broadband polarization retarders.

We theoretically propose a type of tunable polarization retarder, which is composed of sequences of half-wave and quarter-wave polarization retarders, allowing operation at broad spectral bandwidth. The constituent retarders are composed of stacked standard half-wave retarders and quarter-wave retarders rotated at designated angles relative to their fast polarization axes. The proposed composite retarder (CR) can be tuned to an arbitrary value of the retardance by varying the middle retarder alone while maintaining its broadband spectral bandwidth intact.

Topological rainbow trapping of shear horizontal waves in a phononic crystal plate with tapered surface

Topological interface states have localized field enhancement characteristics. Integrating them with the concept of rainbow trapping undoubtedly be a more effective method for elastic energy localization and collection. In this paper, the tunable interface state of shear horizontal (SH) waves is realized in a one-dimensional (1D) phononic crystal (PC) plate by modifying the structural parameters of unit cells with tapered surfaces, where the interface state emerges in the overlapping band gaps of two types of unit cells with different Zak phases. Furthermore, we assembled seven types of unit cells with gradient variations, achieving topological rainbow trapping. Meanwhile, the robustness of the rainbow state has been demonstrated, and more separated frequencies are obtained by changing the order of these unit cells. The results of the study demonstrate that the highly localized, compact, and broadband tunable topological rainbow system we designed holds promise for applications in areas such as elastic energy harvesting, filtering, and multi-frequency signal processing.