Wave Plate Research Articles

Line-field dispersive interference ellipsometry based on an anisotropic crystal

We propose an anisotropic crystal-based line-field dispersive interference ellipsometry, capable of both transmission and reflection measurements. This technique is adept at characterizing the optical polarization properties of transparent materials and is applicable for real-time film thickness monitoring in industrial line-field configurations. Experimental demonstrations include the dynamic line-field birefringent phase of the quarter-wave plate and the Soleil-Babinet compensator in the near-infrared band. The developed method also accurately measured the thickness distribution of a conveyor-based film specimen with thicknesses of 250 nm and 510 nm. A phase stability of 9.5 × 10−4 rad under 200 Hz update rate was demonstrated.

Snapshot Multi-Wavelength Birefringence Imaging.

A snapshot multi-wavelength birefringence imaging measurement method was proposed in this study. The RGB-LEDs at wavelengths 463 nm, 533 nm, and 629 nm were illuminated with circularly polarized light after passing through a circular polarizer. The transmitted light through the birefringent sample was captured by a color polarization camera. A single imaging process captured light intensity in four polarization directions (0°, 45°, 90°, and 135°) for each of the three RGB spectral wavelength channels, and subsequently measured the first three elements of Stokes vectors (S0, S1, and S2) after the sample. The birefringence retardance and fast-axis azimuthal angle were determined simultaneously. An experimental setup was constructed, and polarization response matrices were calibrated for each spectral wavelength channel to ensure the accurate detection of Stokes vectors. A polymer true zero-order quarter-wave plate was employed to validate measurement accuracy and repeatability. Additionally, stress-induced birefringence in a PMMA arch-shaped workpiece was measured both before and after the application of force. Experimental results revealed that the repeatability of birefringence retardance and fast-axis azimuthal angle was better than 0.67 nm and 0.08°, respectively. This approach enables multispectral wavelength, high-speed, high-precision, and high-repeatability birefringence imaging measurements through a single imaging session.

Dynamic analysis and manipulation of self-starting single-pulse mode-locking in a Yb-doped fiber laser with Figure-9 all-normal-dispersion

The self-starting single-pulse mode-locked mechanisms in an all-normal-dispersion (ANDi) Figure-9 fiber laser are portrayed via an integrated simulation approach, which combines rate equations with the General Nonlinear Schrödinger Equation (GNLSE). The simulation results indicate that the mode-locking performances and pulse characteristics are significantly influenced by the splitting ratio, linear phase shift, gain, and asymmetric placement of gain fiber positions within the loop directly, providing effective quantified guidance for self-starting high-quality pulse generation. An experimental oscillation based on a nonlinear amplifying loop mirror (NALM) was established, operating under different widths of bandpass filters. Combining simulation for parameter optimization, the introduced linear phase shift and the coupling ratio were adjusted by changing the rotation angle of the combination wave plate to determine the optimal mode-locked operating point. A spectral bandwidth of 10.4 nm and a pulse duration of 17.5 ps, delivering 0.67 nJ of pulse energy, have been achieved in a modified mode-locked Yb-doped fiber laser.

Directional Phase and Polarization Manipulation Using Janus Metasurfaces.

Janus metasurfaces, exemplifying two-faced 2D metamaterials, have shown unprecedented capabilities in asymmetrically manipulating the wavefront of electromagnetic waves in both forward and backward propagating directions, enabling novel applications in asymmetric information processing, security, and signal multiplexing. However, current Janus metasurfaces only allow for directional phase manipulation, hindering their broader application potential. Here, the study proposes a versatile Janus metasurface platform that can directionally control the phase and polarization of terahertz waves by integrating functionalities of half-wave plates, quarter-wave plates, and metallic gratings within a cascaded metasurface structure. As a proof-of-principle, the study experimentally demonstrates Janus metasurfaces capable of independent and simultaneous control over phase and polarization, showcasing propagation direction-encoded focusing and polarization conversion. Moreover, the directionally focused points are utilized with distinct polarization states for advanced applications in direction- and polarization-sensitive detection and imaging. This unique strategy for simultaneous phase and polarization control with direction-dependent versatility opens new avenues for designing ultra-compact devices with significant implications in imaging, encryption, and data storage.

Spectropolarimetric properties of vortex retarders.

Vortex retarders are optical retarders with a uniform retardance, but with a fast axis that varies azimuthally over the area of the optic. This affects the radial and azimuthal polarization components of the incoming beam. The vortex retarders discussed here generate TEM10 and TEM20 Laguerre-Gaussian beams. While several varieties of these vortex retarders exist, designed to function at specific wavelengths, and a few studies have reported their use at those wavelengths, almost no data exists detailing their polarimetric properties outside those wavelengths. Using a Mueller matrix spectropolarimeter with dual-rotating retarders, the polarization properties of four zero-order half-wave vortex retarders have been measured across a broad wavelength range of 300-1100nm. This data contributes to a more complete description of the spectral properties of these popular retarders.

Real, imaginary and complex branches of Lamb waves in p-type piezoelectric semiconductor GaAs plate: Numerical and experimental investigation

First, we experimentally measure the concentration of holes of the piezoelectric semiconductor (PSC) Gallium arsenide (GaAs) material based on the Hall effect measurement. We then numerically calculate the Lamb wave characteristics in a p-type PSC GaAs plate using this measured value of the concentration of holes (estimated at approximately p0=3.5431×1025m−3). To guarantee the coupling effect that makes the Lamb wave a piezo-active wave, the GaAs crystal is oriented in a specific orientation of (110) plane. Ordinary differential equation (ODE) method is employed to calculate the dispersion curves, 3D view of the mechanical displacements, 3D view of the electric potential and 3D view of the concentrations of holes. Results show that the appearance of the complex branches of the Lamb modes coincides with the vanishing of the imaginary part of the wavevector (Im(k1)) to zero, which is a very remarkable finding that has not been discussed in previous studies. Meanwhile, these complex branches start exactly at the point of Zero-group-velocity (ZGV). Moreover, the present work highlights the hole drift characteristics of PSC GaAs and provides a critical comparative discussion with those published by (Zhu et al., 2018) for the PSC ZnO plate. Accordingly, the “Screening effect” phenomenon that is based on the positive holes in the negative electric potential region is discussed. The present results provide a theoretical and fundamental guidance on the development of smart devices based on the PSC GaAs material.

Tunable bandgaps of guided waves by periodic shunting circuits in multilayered piezoelectric plates

The multi-mode and dispersion characteristics of guided waves in plate bring great challenges to the manipulation of guided waves and controlling vibration and noise. In this study, the Stroh formalism is developed to establish a theoretical model for deriving the dispersion relations of guided waves in a multilayered piezoelectric plate. The dispersion characteristics under different electrical boundary conditions introduced by periodic shunting circuits are discussed to reveal the influences of external circuits on guided wave propagation. The proper shunting circuit is not only the key point to obtain the specific frequency of bandgap, but also the effective method to control the bandwidth. Furthermore, for the separation of symmetric and anti-symmetric modes of guided waves, the multilayered piezoelectric plate with a mirror plane is studied by using an equivalent model. Results indicate that the propagation behaviors of guided waves in multilayered piezoelectric plates can be interpreted by developed Stroh formalism, and their bandgaps can be effectively manipulated by periodically external circuits. The tunable bandgaps in this work could be helpful for designing smart devices of wave isolation based on multilayered piezoelectric plate.

Circularly polarized plane terahertz waves radiated from a resonant tunneling diode integrated with a collimating metalens and quarter-wave plate

Terahertz flat optics based on metasurfaces can replace massive optical components with optically thin components. However, metasurfaces with unprecedented material properties frequently produce a specified function, and terahertz flat optics has yet to be commonly adopted in terahertz devices that require multiple functions. Here, we present a two-layer component composed of a collimating metalens and a quarter-wave plate that convert linearly polarized terahertz wide-angle radiation waves from a resonant tunneling diode to circularly polarized plane waves. Our findings would be applied to laminate structures with optical vortices, ultrahigh directivity and arbitrary wavefront control in 6 G wireless communications.

A Q-switched Ho:YAG spatial ring cavity laser with three corner cube prisms pumped by a 1908 nm fiber laser

We demonstrate a tri-corner cube Q-switched Ho:YAG spatial ring cavity laser, which was resonantly pumped by a 1908 nm fiber laser. The polarization state of the intracavity oscillating laser was adjusted by a half-wave plate, and a continuous s-polarized laser of 2.57 W at 2090.9 nm was obtained at a pump power of 18.5 W, corresponding to an optical-to-optical conversion efficiency of 13.9 % and a slope efficiency of 33.3 %. When the corner cube prism, which has the weakest anti-misalignment capability, was tilted vertically by 1° or horizontally by 0.92°, the laser could still output the laser. For Q-switched operation, the tri-corner cube Ho:YAG laser has a pulse energy of 9.86mJ and a pulse width of 178.8 ns at a repetition rate of 100 Hz. At the maximum output energy, the beam quality was Mx2 = 1.3, My2 = 1.2.

Deep-learning-assisted sidewall profiling white light interferometry system for accurately measuring 3D profiles and surface roughness on the groove sidewalls of precision components.

The accurate measurement of surface three-dimensional (3D) profile and roughness on the groove sidewalls of components is of great significance to diverse fields such as precision manufacturing, machining processes, energy transportation, medical equipment, and semiconductor industry. However, conventional optical measurement methods struggle to measure surface profiles on the sidewall of a small groove. Here, we present a deep-learning-assisted sidewall profiling white light interferometry system, which consists of a microprism-based interferometer, an optical path compensation device, and a convolutional neural network (CNN), for the accurate measurement of surface 3D profile and roughness on the sidewall of a small groove. We have demonstrated that the sidewall profiling white light interferometry system can achieve a measurement accuracy of 2.64 nm for the 3D profile on a groove sidewall. Moreover, we have demonstrated that the CNN-based single-image super-resolution (SISR) technique could improve the measurement accuracy of surface roughness by over 30%. Our system can be utilized in cases where the width of the groove is only 1 mm and beyond, limited only by the size of the microprism and the working distance of the objective used in our system.

A Highly Efficient Plasmonic Polarization Conversion Metasurface Supporting a Large Angle of Incidence

The angle of incidence of the compact polarization conversion device is crucial for practical use in integrated miniaturized optical systems. However, this index is often ignored in the design of quarter-wave plate based on metasurface. Herein, it is shown that a thick metallic cross-shaped hole array supports extraordinary optical transmission peaks controlled by a Fabry–Pérot (FP) resonator mode. The positions of these peaks have been proven to be independent over a large range of incidence angles. We numerically design a miniatured quarter-wave plate (QWP) with an 80 nm bandwidth (840~920 nm) and approximately 80% average efficiency capable of effectively functioning as a linear-to-circular (LTC) polarization converter at an incidence inclination angle of less than 30°. This angle-insensitive compact polarization conversion device may be significant in a new generation of integrated metasurface-based photonics devices.

Investigation of the Zero-Frequency Component of Nonlinear Lamb Waves in a Symmetrical Undulated Plate.

When an ultrasonic pulse propagates in a thin plate, nonlinear Lamb waves with higher harmonics and a zero-frequency component (ZFC) will be generated because of the nonlinearity of materials. The ZFC, also known as the static displacement or static component, has its unique application on the evaluation of early-stage damages in the elastic symmetrical undulated plate. In this study, analysis of the excitation mechanism of the ZFC and the second harmonic component (SHC) was theoretically and numerically investigated, and the material early-stage damage of a symmetrical undulated was characterized by studying the propagation of nonlinear Lamb waves. Both the ZFC and SHC can be effectively employed in monitoring the material damages of the undulated plate in its early stage. However, several factors must be considered for the propagation of the SHC in an undulated plate because of the geometric curvature and interference between the second harmonics during propagation, preventing efficient application of this technique. If the fundamental wave can propagate in the plate regardless of the plate boundary conditions, an accumulative effect always exists for the ZFC in a thin plate, indicating that the ZFC is independent of the structural geometry. This study reveals that the ZFC-based inspection technique is more efficient and powerful in characterizing the damages of a symmetrical undulated plate in the early stage of service compared to the second harmonic method.

Intensity modulation of orthogonally polarized laser with two weak light reinjection beams of the bifurcated sub-cavity

This paper proposes a specially designed laser cavity with two reinjected beams to achieve coupled self-mixing interference. Based on the orthogonally polarized laser, a wave plate is employed to construct the bifurcated sub-cavity, and the oscillating laser mode splits into two. Under the domination of the sub-cavity, both the intensity and frequency of the orthogonally polarized beams exhibit near-sinusoidal modulation with a certain phase difference. The modulated intensity also has a long period envelope if the sub-cavity is tuned with pitch angle. Thus, it has potential to acquire the extension and bending displacement of such key components in a space-borne instrument.

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.