Wave Plate Research Articles

Research progress on terahertz achromatic broadband polarization wave plates

The electromagnetic wave in the terahertz region shows many promising characteristics, such as non-ionization, “fingerprint” spectrum, sensitivity to weak resonance, strong penetration to non-polar substances, and so on. This study reviews the recent achievements of terahertz achromatic broadband polarization wave plates. The key parameters to evaluate the performance of terahertz polarized wave plates are described briefly. The relevant works, and benefits and drawbacks of terahertz wave plates based on diverse materials and designs, notably metamaterial wave plates, are summarized based on unique material attributes and design methodologies. Additionally, the current state of the terahertz achromatic broadband wave plate is generalized, along with the role of metamaterial in the design of terahertz wave plate, the innovative interdisciplinary path of terahertz metamaterial polarization is explained, and future research prospects are explored.

Dynamically tunable broadband output coupling of optical oscillators based on non-cyclic geometric phase mirror

We present a uniquely versatile and efficient mirror system capable of real-time fine-tuning in reflection and transmission properties across a broad wavelength range and at a high optical power. Leveraging the principles of the non-cyclic geometric phase (GP) acquired by the clockwise and counterclockwise beams of the Sagnac interferometer satisfying the anti-resonant condition on propagation through the quarter-wave plate, half-wave plate, and quarter-wave plate combination having fast axes oriented at 45° (fixed), θ (variable), and −45° (fixed) with respect to the vertical, respectively, our mirror system offers dynamic transmission control across 0–100% without the need for realignment. Notably, the GP-based mirror (GP-mirror) preserves the polarization state of the reflected beam, making it ideal for polarization-sensitive applications. The wavelength insensitivity of the GP enables seamless operation of the mirror across a wide wavelength range. As a proof-of-principle, we use the GP-mirror as the output coupler of a continuous-wave, green-pumped, doubly resonant optical parametric oscillator (DRO) based on a 30-mm-long MgO:sPPLT crystal and obtain stable operation at high powers over a wide wavelength tuning range. For a pump power of 5 W, the DRO provides an output power of 2.45 W at an extraction efficiency as high as 49% when operated at optimum output coupling. The DRO shows a maximum pump depletion of 89% and delivers an optimum output power across a tuning range ≥90 nm. The demonstrated concept offers a promising approach for advancing the capabilities and control of coherent optical sources tunable across different spectral regions and in all time scales from continuous-wave to ultrafast femtosecond domain.

Non-Hermitian wave dynamics of odd plates: Microstructure design and theoretical modelling

The concept of odd elasticity was recently introduced to characterize the elastic behavior of solids that consist of active components, exhibiting an asymmetric elastic modulus tensor. In this paper, we propose, for the first time, the microstructure design of an odd plate, which is composed of a lattice plate with a piezoelectric-patch-based sensor–actuator feed-forward system. By leveraging the nonreciprocal coupling between shear forces and bending curvatures, the odd plate constitutive relation is formulated in the low frequency region, which features as four asymmetric coupling parameters known as “odd parameters”. We reveal that the two-dimensional (2D) odd plates can perform directional wave energy amplification and the amplification angle can be determined analytically through the rotation of coordinate system. We also numerically demonstrate the directional wave amplification phenomena that arise from the optimal combination of odd parameters. In addition, we analytically uncover the presence of Stoneley-like interfacial waves between two plates with two odd parameters in opposite signs, which is further characterized by the numerical simulation. Unlike interfacial waves between topological structures, the interfacial waves between odd plates can exist for any working frequency, enabling the design of some novel waveguides. This research on the control of flexural waves in odd plates could shed lights on 2D non-Hermitian systems in elasticity.

Tunable Harmonics Generation from Low Average Power Mode-Locked Er-Fiber Laser Using Periodic Poled Nonlinear Crystals

Abstract: Sufficient second, third, and fourth harmonic generation of mode-locked Er-doped fiber laser (ML - EDFL) was experimentally demonstrated. This was achieved by using periodically poled KTiOPO4 (PPKTP) and PP LiNbO3 (PPLN) PPLN nonlinear crystals. Harmonic generation in both crystals depended on the direction of polarization. The highest conversion efficiency was obtained by using a half-wave plate to rotate the polarization before the crystals. When using the PPKTP nonlinear crystal, conversion efficiencies of 4.88%, 0.02%, and 0.002% were obtained for second, third, and fourth harmonics generation at wavelengths of 980, 520, and 390 nm, respectively. For the PPLN nonlinear crystal, temperature and polarization direction were optimized for each harmonic generation wavelength. As a result, conversion efficiencies of 8.6%, 0.1%, and 0.007% were obtained for second, third, and fourth harmonic generation at the same respective wavelengths. Tunable wavelength ranges and their SHGs, as well as the multi-wavelength output and their corresponding SHG wavelengths, were also reported. Keywords: Er-fiber laser, Passive mode-locked fiber laser, Nonlinear polarization rotation, PPKTP, PPLN, SHG, THG, FHG. PACS: Fiber lasers, 42.55.Wd, Mode locking, 42.60.Fc.

Form birefringent polymeric structures realized by 3D laser printing.

The 3D laser printing of form birefringent structures promises fast prototyping of polarization-sensitive photonic elements. However, achieving the quarter- and half-wave phase retardation levels needed in applications still remains a challenge, especially at visible wavelengths. Thickness of the birefringent region, usually consisting of simple 1D gratings, must be sufficiently large to ensure the required retardance, making the 3D laser-printed gratings prone to mechanical collapse. Here we demonstrate 3D laser-printed mechanically robust form birefringent 3D structures whose thickness and phase retardation can be increased without loss of mechanical stability, and report on the realization of compact self-supporting structures exhibiting quarter- and half-wave phase retardation at visible wavelengths.

Guided wave propagation in a double-layer plate with a nonlinear spring-interface

This article derives the solution to the guided wave fields in a double-layer plate consisting of two sublayers. It is assumed that the two sublayers are linearly elastic. They are bonded together at their interface by a nonlinear adhesive layer of infinitesimal thickness. This allows us to propose a nonlinear spring-interface model. Based on such an idealized model for the double-layer plate, guided wave fields in the plate are solved using the modified normal mode expansion method. It is found that the nonlinearity of the spring-interface can generate resonant guided waves in the double-layer plate. Specifically, when certain conditions are met, mixing of two primary guided waves will generate resonant guided waves whose frequencies are either the sum or difference of those of the two primary waves. Amplitudes of such resonant mixed waves are proportional to the compliance of the nonlinear spring-interface. As a special case, if the two primary waves have the same frequency, a resonant second harmonic guided wave may be generated. In addition, the conditions that generate resonant mixed waves are identified. We believe that the results of this work provide the theoretical foundation on which nondestructive evaluation techniques using nonlinear guided waves can be developed to nondestructively evaluate, for example, the bond strength of thin coating on a substrate.

Accurate and robust calibration method for simultaneous Stokes polarimetry

The simultaneous Stokes polarimetry (SSP) plays a crucial role in various fields, including the characterization of suspended particles in air and water, as well as the measurement of the Mueller matrix of samples. System calibration is a critical step for improving the accuracy of the Stokes polarimetry. However, there is a lack of commercially available SSP, and the corresponding calibration method is not yet fully developed. In this paper, an accurate and robust calibration method for SSP based on division-of-amplitude is proposed, which includes intensity monitoring and geometric optimization. The optimal calibration method significantly can reduce measurement time while maintaining high calibration accuracy and robustness. The maximum root-mean-square error of the measured Stokes vector can be minimized to less than 0.0061, which represents approximately a tenfold improvement in accuracy compared to the traditional calibration method using a rotating quarter-wave plate. Additionally, the measurement errors of Stokes vectors are minimized globally to ensure robust measurement. Based on this foundation, the calibrated SSP is capable of tracking the changes in random Stokes vectors with fast speed. These results demonstrate the importance of selecting appropriate calibration polarization states and the significance of incorporating light intensity monitoring to enhance the accuracy and robustness of polarization calibration.

Transient Loss-Induced Non-Hermitian Degeneracies for Ultrafast Terahertz Metadevices.

Non-Hermitian degeneracies, also known as exceptional points (EPs), have attracted considerable attention due to their unique physical properties. In particular, metasurfaces related to EPs can open the way to unprecedented devices with functionalities such as unidirectional transmission and ultra-sensitive sensing. Herein, an active non-Hermitian metasurface with a loss-induced parity-time symmetry phase transition for ultrafast terahertz metadevices is demonstrated. Specifically, the eigenvalues of the non-Hermitian transmission matrix undergo a phase transition under optical excitation and are degenerate at EPs in parameter space, which is accompanied by the collapse of chiral transmission. Ultrafast EP modulation on a picosecond time scale can be realized through variations in the transient loss at a non-Hermitian metasurface pumped by pulsed excitation. Furthermore, by exploiting the physical characteristics of chiral transmission EPs, a switchable quarter-wave plate based on the photoactive metasurface is designed and experimentally verified and realized the corresponding function of polarization manipulation. This work opens promising possibilities for designing functional terahertz metadevices and fuses EP physics with active metasurfaces.

Numerical solution of the cavity scattering problem for flexural waves on thin plates: Linear finite element methods

Flexural wave scattering plays a crucial role in optimizing and designing structures for various engineering applications. Mathematically, the flexural wave scattering problem on an infinite thin plate is described by a fourth-order plate wave equation on an unbounded domain, making it challenging to solve directly using the regular linear finite element method (FEM). In this paper, we propose two numerical methods, the interior penalty FEM (IP-FEM) and the boundary penalty FEM (BP-FEM) with a transparent boundary condition (TBC), to study flexural wave scattering by an arbitrary-shaped cavity on an infinite thin plate. Both methods decompose the fourth-order plate wave equation into the Helmholtz and modified Helmholtz equations with coupled conditions on the cavity boundary. A TBC is then constructed based on the analytical solutions of the Helmholtz and modified Helmholtz equations in the exterior domain, effectively truncating the unbounded domain into a bounded one. Using linear triangular elements, the IP-FEM and BP-FEM successfully suppress the oscillation of the bending moment of the solution on the cavity boundary, demonstrating superior stability and accuracy compared to the regular linear FEM when applied to this problem.

Multiple Reflections and the Near-Field Effects on a Metamaterial Quarter-Wave Plate

Metamaterial-based quarter-wave plates (QWPs) have emerged as promising candidates for advanced polarization control in a variety of optical applications, owing to their unique properties, such as ultra-thin profiles and tailored spectral responses. We design an ultra-thin, high-efficiency, and broadband QWP in transmission mode based on a TiO2/Au grating structure. We show that multiple reflections and the near-field effects associated with the integration of these devices pose challenges that must be considered when combining multiple metamaterials. We present insights that facilitate improved design methodology and the optimization of integrated metamaterial QWPs and other metadevices. Our results contribute to the development of miniaturized and high-density advanced lightwave and polarization control devices in optical systems.

Omnidirectional broadband phase modulation by total internal reflection.

Phase modulation plays a crucial role in shaping optical fields and physical optics. However, traditional phase modulation techniques are highly dependent on angles and wavelengths, limiting their applicability in smart optical systems. Here, we propose a first-principle theory for achieving constant phase modulation independent of incident angle and wavelength. By utilizing a hyperbolic metamaterial and engineering-specific optical parameters, different reflective phase jumps are achieved and tailored for both transverse electric (TE) and transverse magnetic (TM) waves. The aimed reflection phase difference between TE and TM waves can be thus achieved omnidirectionally and achromatically. As an example, we propose a perfect omnidirectional broadband reflection quarter wave plate. This work provides fundamental insights into manipulating optical phases through optical parameter engineering.

High power single-frequency 1112 nm laser by an insertable Nd:YAG/YAG bonded monolithic planar ring oscillator.

A high power single-frequency operation at 1112 nm with novel insertable monolithic planar ring oscillator based on a Nd:YAG/YAG bonded crystal is proposed. In a proof-of-principle experiment, a finely designed coating on the output surface is carried out to ensure single-wavelength oscillation at 1112 nm, together with a half-wave plate and a Tb3Ga5O12 crystal inserted in the open space of the bonded block to realize the unidirectional operation with power scalability. Consequently, the single-frequency laser delivers an output power of 3.9W at 1112.3 nm with a slope efficiency of 58.6% and an optical-to-optical efficiency of 17.7%. The power fluctuation is measured to be within ± 0.26% over 20 min, and the laser linewidth is estimated to be 4.15 MHz (Δλ = 0.017 pm).

Numerical simulation study of wave dissipation performance of step‐type breakwaters

AbstractTo improve the force endurance capacity of plate breakwaters, a step‐type plate breakwater was proposed. The performance of the step‐type breakwater was investigated by numerical simulation method. First, a two‐dimensional numerical regular wave tank was constructed using FLUENT software, and the effectiveness of the tank application was verified by comparing with theoretical value and test data. Then, the numerical tank was used to simulate various working conditions, and the variation rules of the breakwater transmission coefficient with wave height, period, perforation rate, relative plate width, wave steepness, and number of layers were obtained. Finally, the difference in the wave dissipation mechanism between the step‐type breakwater and the “”‐type breakwater was discussed. The results indicated that the transmission coefficient of the step‐type breakwater was small, which also proved to be good at dissipating long‐period waves. In general, the wave dissipation performance of the step‐type breakwater was better than that of the “”‐type breakwater. The research can provide some clues for the research and design of corresponding breakwaters.

Mueller matrix analysis of spun wave plate for arbitrary SOP conversion.

The developments in polarized light have spawned a multitude of novel applications in optical fiber systems, but the design and fabrication of practical fiber wave plates with high degree of integration still remain a challenging issue. To address this problem, an all-fiber spun wave plate (SWP) for arbitrary state of polarization (SOP) conversion is proposed in this work, and its principle is analyzed with Mueller matrix. Simulations are conducted to exhibit the arbitrary SOP conversion capability of the proposed SWP, and two key parameters, including the maximum spinning rate (ξmax) and linear birefringence (δ), are investigated for efficient conversion of desired SOP. Different functions to increase the spinning rate ξ from 0 to ξmax, computational efficiency and accuracy related to N are discussed in detail. Furthermore, the depolarization effect caused by retardation of SWP is also considered. The results of this research suggest that the proposed SWP exhibits promising performance in arbitrary SOP conversion, and the meticulous analysis of the numerical computation, design, and implementation of SWP presented in this work can provide novel insights for devloping fiber wave plates.

A highly birefringent photonic crystal fiber based on a central trielliptic structure: FEM analysis

In this study, a highly birefringent photonic crystal fiber (PCF) with a simple center trielliptic is presented. The finite element method is applied in this study to analyze PCF. By adjusting the ellipticity and other parameters, the fiber performances can be optimized. As the parameters of the PCF are finalized, i.e., the number of cladding N = 4, lattice constant Λ = 1.6 μm, and ellipticity η = 2, a high birefringence of 3.56 × 10−2 can be obtained at the wavelength λ = 1.55 μm . Moreover, the dispersions of the X- and Y-polarized modes are relatively flat in the range of 1 μm to 1.55 μm along with a confinement loss as low as 9.63 × 10−6 dB m−1. Besides, this structure has demonstrated remarkable robustness, maintaining its superior performance even when subjected to significant displacements or rotations. Due to the characteristics of the high birefringence and low confinement loss, this PCF can be used for long distance optical fiber communication, fiber sensing, dispersion compensation, and supercontinuum generation.

One-step jones matrix polarization holography for polarization-sensitive materials using angular-multiplexing

A polarization digital holography (DH) using angular multiplexing was developed for extracting the Jones matrix of anisotropy materials in one step. This technique is implemented by adopting an off-axis interferometric configuration connecting two identical CCD cameras. The combined orthogonal 45° beams is split using a nonpolarizing beam splitter to produce the sample and reference beams. Our method yields two angular-multiplexing polarization interferograms simultaneously, in which the orthogonal fringe directions for each interferogram are modulated by two self-installed retro-reflector mirrors. In this case, the spatially resolved Jones matrix parameters of the polarization-sensitive materials can be determined in one step. The basic feasibility of the scheme is verified by measuring the Jones matrices of polarizing optics, a transmitted spatial light modulator, and synthetic mica plates.

Amplitude noise suppression in Yb:doped NALM oscillators utilizing saturable absorber settings.

Optical frequency combs based on fiber lasers mode-locked (ML) with a nonlinear amplifying loop mirror (NALM) have become the backbone of many cutting-edge applications, ranging from precision spectroscopy to quantum physics. Being extremely precise measurement tools, understanding their passive stability and low-noise operation regimes is vital. While several influences on the laser noise have been studied, many parameters remain poorly understood. Here, we systematically analyze under which preconditions the artificial saturable absorber settings of the laser can be modified during operation without losing mode-locking and the effects on laser noise, the spectrum and the output power. Our results show that it is possible to decrease the amplitude noise (AM noise) of the laser by more than 50 % by simply rotating a wave plate within the laser cavity. Additionally, we discuss differences to a similar effect observed in a NALM-alike laser amplifier and of changing the output coupling. These findings deepen our understanding and capabilities of optimizing the noise performance of ML fiber lasers, enable us to investigate new parameter spaces, and can be used to further optimize the noise performance of the NALM laser design, making it an ideal light source for advanced setups both in research and industry.

Design of optical compensation film for improving the optical performance of organic light emitting diodes

The organic light emitting diode (OLED) display is one of the most promising devices among next-generation information displays because of the advantage of optically clear self-emitting characteristics. Nevertheless, in the conventional OLED display device, the luminous efficiency is increased by using a metal electrode having a high reflectance in the cell, but due to the reflection characteristic in the cell from the incident of external light, the dark characteristic is deteriorated and the contrast characteristic is dramatically reduced. In order to overcome this disadvantage, we propose an optical configuration consisting of a polarizer, quarter-wave plate (QWP), and C-plate for wide-band and wide-view performance, which mean high contrast in visual wavelength range and viewing angle in terms of polar and azimuthal angles while maintaining the transmittance characteristics of OLED when external light is incident. To designing an optimized optical configuration, the phase differences of light were calculated with trigonometric method and polarization characteristics were analyzed using a Poincaré sphere when passing through each optical film. To verify the optical performance of the proposed optical configuration, we applied it to OLED devices through experiments, as a result we confirmed that optical performance could be improved in terms of wide-band and wide-view without disturbing with the transmittance of OLED device.

Active anisotropic polarization conversion meta-surface for 6G communication bandgap in the reflection mode

This paper investigates a single-layered active anisotropic meta-surface design capable of achieving high polarization conversion efficiency in the 6 G communication band gap. Additionally, the designed structure can convert the linear polarization of the incoming wave fronts to its cross-polarization and linear polarization to circular polarization in the reflection mode. The polarization conversion characteristic is achieved due to the strong anisotropic behavior of the meta-surface. Such a simple design can achieve a 90% to 100% cross-polarization conversion efficiency over a frequency region of [0.28–0.36] THz. The linear to circular polarization conversion is performed near 0.26 THz and 0.40 THz. Between these two frequencies, band linear to cross-polarization conversion is more prominent. The proposed design can be tuned from a half-wave plate (HWP) or linear polarization converter to a quarter-wave plate (QWP) or circular polarization converter using the chemical potential of graphene. The optical response of the meta-surface behaves differently from different incident angles. The proposed polarization converter can contribute to the development of active polarization device.

Electro-optic solution to overcome the transient regime of a cavity dumped UV laser source?

Laser marking is one of the main industrial applications of lasers. To mark many materials or to obtain patterns of small dimensions, triggered pulsed solid laser sources are increasingly used emitting in the fundamental in the infrared and to which two nonlinear (NL) stages are added to obtain an emission in the UV. The conversion efficiency as well as that of the marking then depends mainly on the peak power of the UV pulses generated. One of the solutions for obtaining a higher peak power is to reduce the duration of the laser pulses. To do this, it is possible to change the architecture of the laser cavity by switching from a Q-Switch operating mode (QS) to a cavity dumped mode (CD). With this architecture it is thus possible to reduce the duration of the pulses by an order of magnitude. This peak power gain is unfortunately achieved at the cost of a very long transient regime, up to a few tens of milliseconds, compared to the classic QS which generally only occurs for the first laser pulse. Unfortunately, laser marking is by nature based on chopped operation for the laser, which corresponds to working permanently in a transient state. Marking with a CD architecture laser is then often full of defects and therefore unacceptable in terms of quality. After a study of the problem specific to the use of a UV source with CD architecture in the context of marking, we propose an original solution to dissociate the chopped regime, specific to marking, from the transient regime of the laser. This solution is based on the use of an RTP (Rubidium Titanyle Phosphate RTiOPO4) electro-optical crystal placed between the laser output and the NL stages. This crystal is driven like a half-wave plate by high voltage square pulses of a duration corresponding to the duration of the marking laser pulse trains. This thus makes it possible to obtain laser operation in a stabilized regime, therefore outside the transient regime, and simultaneously chopped operation characteristic of laser marking. The new operating mode obtained is characterized in detail with the new marking performances which prove to be optimal and compatible with the requirements of a quality marking. In addition to making the CD architecture compatible with laser marking, this solution also makes it possible to adjust the average power, and therefore the energy of the laser pulses to adapt it according to the materials and this without changing the thermal behavior of the laser. Last advantage, by adjusting the extinction voltage applied to the RTP outside the cavity, it is also possible to keep a few milliwatts of the marking laser beam as the aiming beam, with the certainty of perfect alignment with the full power beam.