Wave Plate Research Articles

Rydberg-atom-based system for benchmarking millimeter-wave automotive radar chips

Rydberg atomic sensors and receivers have enabled sensitive and traceable measurements of rf fields at a wide range of frequencies. Here, we demonstrate the detection of electric field amplitude in the extremely-high-frequency (EHF) band, at 131GHz. In our approach, we propagate the EHF field in a beam, with control over its direction and polarization at the detector using photonic wave plates. This way, we take advantage of the highest detection sensitivity, registered for collinear propagation and circular polarization. To exhibit the potential for applications in this kind of Rydberg-atom-based detection, we perform test measurements on the EHF field emitted from an on-chip radar, which is designed to be used in the automotive industry as a vital sign detector. Our work elucidates practical applications of Rydberg-atom media and photonic metamaterial elements. Published by the American Physical Society 2024

Parametric study of traveling wave motion in energy absorption mode

There are two modes of traveling wave motion, traveling wave propulsion and traveling wave energy absorption. In this paper, a two-dimensional flexible traveling wave plate is taken as the research object. The characteristic length and characteristic parameter of traveling wave motion are determined by numerical simulation, and the parametric study of the traveling wave motion in energy absorption mode is conducted. The effects of dimensionless amplitude and dimensionless wave velocity on the energy absorption characteristics of flexible traveling wave plate are analyzed, and the mechanism of traveling wave energy absorption is revealed. The results show that the larger the dimensionless amplitude is, the stronger the work capacity of the traveling wave plate becomes, while the absolute amplitude or absolute wavelength has little effect on the work capacity of the traveling wave plate. Under different waveforms, the work capacity of the traveling wave plate increases first and then decreases as the dimensionless wave velocity increases. Within the parameter range studied in this article, when the dimensionless amplitude is 0.2 and the dimensionless wave velocity is 0.5, the traveling wave plate can achieve an energy absorption efficiency of about 40 %.

The Simons Observatory: Design, Integration, and Testing of the Small Aperture Telescopes

The Simons Observatory (SO) is a cosmic microwave background survey experiment that includes small-aperture telescopes (SATs) observing from an altitude of 5200 m in the Atacama Desert in Chile. The SO SATs will cover six spectral bands between 27 and 280 GHz to search for primordial B-modes to a sensitivity of σ(r) = 0.002, with quantified systematic errors well below this value. Each SAT is a self-contained cryogenic telescope with a 35° field of view, 42 cm diameter optical aperture, 40 K half-wave plate, 1 K refractive optics, and <0.1 K focal plane that holds >12,000 transition edge sensor detectors. We describe the nominal design of the SATs and present details about the integration and testing for one operating at 93 and 145 GHz.

Practical considerations for the amplification of electro-optically detected THz signals

Advances in THz methods and applications require the detection of weak THz pulsed signals. One solution to this problem is to amplify weak signals using optically biased electro-optical (EO) techniques. Several different EO amplification schemes are compared. The simplest of these involves using a non-polarizing beam splitter followed by two quarter-wave plates set to small positive and negative angles, respectively. The signals are then passed through polarizers perpendicular to the polarization of the 800 nm EO detector crystal gating beam. As long as sufficient intensity is present in the gate pulse for linear photodiode detection, amplification of up to 10 times with dynamic ranges for single sweep scans of &gt;104 is obtained.

Generation of vectorial vortex beams by a coherently combined laser array.

With the superpositions of spin and orbital angular momentum, vectorial vortex beams (VVBs) have attracted great attention in recent years. Many approaches have been developed to generate such beams, but high-power output is not supported. Here, we report the coherent beam combining (CBC) for generating VVBs that are compatible with high-power fiber amplifiers. The laser array is composed of two discrete vortex arrays with left-handed and right-handed circular polarization states. The phase and polarization of each beamlet are manipulated simultaneously. Experimentally, the phase noise in the amplifiers is compensated by the all-fiber internal phase control feedback structure. Quarter-wave plates are employed as polarization state converters. When the system is in the closed loop, a distinct and stable VVB can be obtained in the far-field. This work could provide a significant reference for the future implementation of high-power structured beams.

Terahertz phase imaging of large-aperture liquid crystal modulator with ITO interdigitated electrode

Abstract We have fabricated and characterized a large-aperture electrooptic phase modulation device operating in the terahertz (THz) frequency range. The device consists of a 1.6 mm thick nematic liquid crystal placed between glass plates with a novel interdigitated electrode design. Using THz time-domain spectroscopy (THz-TDS) coupled with raster scanning imaging, we evaluated phase modulation across a 25 mm diameter LC device and mapped the spatial uniformity of phase shift. Our results confirm the functionality of the LC cell as a controllable quarter-wave plate at 0.26 THz and half-wave plate at 0.52 THz. This work contributes to the development of large-aperture and transmissive LC devices as low-cost phase plates for THz waves and paves the way for future applications in THz modulators.

Dynamic tailoring large-area surface plasmon polariton excitation

Abstract We propose and demonstrate a method for dynamically changing the patterning of the surface plasmon polariton (SPP) excitation over a large area under spatially inhomogeneous polarized illumination. By illuminating a 1D gold grating with shallow rectangular grooves with a spatially structured polarization beam of near-infrared light (780 nm), we selectively excited SPPs on an extended area. The parameters used to fabricate the grating coupler, matched the wave vector of the incident light with that of the SPP to achieve an efficient coupling. The incident wave illuminating the grating is a spatially inhomogeneous polarized beam. We designed local polarization states to control the local excitation of the SPP in order to pattern large areas. For real-time local control of the polarization state of the extended incident beam, we used a setup with a spatial light modulator and quarter-wave plate.

Design and fabrication of polarization independent LCoS phase modulators with polymer waveplate and analog driving

Abstract Phase-only liquid crystal on silicon (LCoS) spatial light modulators are used in a variety of applications. Despite their wide use, current phase-only LCoS devices are hindered by their single-polarization modulation. We propose a polarization independent LCoS device which uses a polymer quarter-wave plate for polarization conversion. We designed a custom pixel circuit which enables high driving voltage and high pixel grayscale by utilizing an analog driving frame buffer pixel circuit. Our pixel circuit is optimized for small pixel size and the silicon backplanes can be fabricated at a traditional foundry. We demonstrate polarization independent phase modulation through optical beam steering tests for various input polarizations. Our fabricated device lays the foundation for commercial LCoS devices highly suitable for wavelength selective switches, holographic display, wavefront correction, and optical beam shaping.

Analytical prediction of temperature effects on Lamb wave response in smart plates and its experimental verification

Abstract This article examines the effectiveness of a recently developed theoretical model for the generation and sensing of Lamb waves in thin plates with surface-bonded piezoelectric transducers in predicting temperature effects on Lamb waves and their time reversibility. In particular, the analytical model provides a closed-form solution, which incorporates both the shear-lag effect of the bonding layer and the system inertia in transducer-plate interaction modeling. Temperature-dependent material properties and thermal expansion of the system constituents are considered to predict the Lamb wave signal under a thermal environment. The accuracy of the theoretical prediction is assessed in comparison with experimental results obtained using an aluminum plate with adhesively bonded lead zirconate titanate transducers to its surface at different system temperatures ranging from 20°C to 75°C. Comparison is also made with experimental data and analytical solutions presented earlier without considering the inertia effect. The study reveals that the current solution accurately predicts the change in Lamb wave signal due to temperature variation, including the frequency dependency of the peak amplitude change with temperature rise. However, the theoretical model fails to predict the experimental trends when the inertia terms are neglected. The current model is also used to study the contributions of individual system parameters to the overall temperature effect on the time reversibility of Lamb waves and its dependence on the excitation frequency.

Frequency and voltage-modulation multistable wave plate based on liquid crystals doped with silica nanoparticles

In this study, we demonstrate an all-range multistable liquid crystal (LC) wave plate. Its multistability arises from the formation of silica nanoparticle networks within the LC cell on the substrates, which stabilize LC molecules and induce varying phase retardation. Modulating the phase retardation of the LC wave plate can be achieved through the application of a DC pulse or by adjusting the frequency of the pulse. This multistable characteristic not only conserves energy but also enhances its versatility across diverse domains.

Generating controllable optical trap arrays with a polarization-based metalense

Metalenses have been widely used in various optical systems due to their compact size, lightweight nature and high efficiency. This paper presents a novel metalense for generating multiple optical trap arrays. The proposed metalense is composed of many unit cells of half-wave plate. By changing the polarization state of the incident light, the optical trap array generated by the metalense can be controlled. To evaluate its performance, we simulate the metalense with total trap numbers of 4 and 6 respectively. The results show that the produced optical trap arrays exhibit precise positioning, uniform size, and intensity distribution. Furthermore, the arrays maintain excellent uniformity and shape integrity even when the number of optical traps is increased. Compared with the previous metalenses only produce a specific optical trap array, the designed metalense offers higher flexibility and better meets the experimental requirements of multi-trap optical tweezers. Our metalense exhibits significant potential for the integration and miniaturization of optical trap arrays, as well as other focusing optical systems.

Generation and modulation of soliton molecules in an all-polarization-maintaining fiber laser mode-locked by NPE

In this paper, we report the experimental observation of multiple soliton molecule forms and modulation results in an all-polarization-maintaining (PM) linear fiber laser mode-locked by nonlinear polarization evolution (NPE). The relationship between the waveplate angle and the reflectivity profile of the structure is analyzed numerically. Experimentally, it was found that the soliton number inside the bound states decreases from 4 solitons to 1 soliton by reducing the pump power. The soliton separation and the spectral shape could be evolved by slightly rotating the angle of the half-wave plate or λ/8-wave plate respectively. In addition to the above soliton molecules with regular triangular autocorrelation envelopes, (2+1)-type and (1+2+1)-type compound bound states are also obtained, and the fine temporal structure inside these soliton complexes are obtained by numerical simulation. The investigated results enrich the nonlinear dynamics of femtosecond mode-locked fiber lasers and lay the foundation for the application of all-PM fiber lasers mode-locked by NPE.

Reconfigurable terahertz multifunctional wave plates with VO2/Ge hybrid metasurfaces.

Active control of polarization using metasurfaces is crucial in terahertz optics, offering promising advancements in sensing, imaging, and telecommunications. Here, we developed reconfigurable terahertz multifunctional wave plates by leveraging vanadium dioxide/germanium hybrid metasurfaces. This approach allows for mutual role changing of metasurface among quarter-wave plate, half-wave plate, and full-wave plate, facilitated by the introduction of continuous-wave and pulse lasers. The photoinduced phase change of vanadium dioxide, along with the bridging control of germanium, plays a key role in the transition of multifunctional wave plates. Also, the analysis of polarization conversion ratio, ellipticity, and underlying physics demonstrates the ability of multifunctional wave plates. These discoveries deliver valuable insight into advanced polarization control and demonstrate the potential for innovative active-control devices.

Atypical second harmonic A0 mode Lamb waves in non-uniform plates for local incipient damage monitoring

Plates with non-uniform thickness, such as stiffened and notched plates, are commonly seen in engineering applications. Monitoring incipient damage in these structures is crucial to ensure their safety during service. Second harmonic Lamb waves hold great promise for structural health monitoring applications. However, the mechanisms underpinning the generation of the second harmonic Lamb waves in non-uniform plates are still not well understood due to the complex wave field. To tackle this issue, a theoretical analysis is first conducted to highlight the so-called atypical second harmonic A0 mode waves (2nd A0 waves) generated at the structural non-uniform section. Their existence, as well as their potential for local incipient damage monitoring applications, is then confirmed by finite element simulations. Experiments are carried out on a notched aluminum plate to monitor the incipient plastic damage induced by bending. Three mechanisms contributing to the generation of the atypical 2nd A0 waves in the non-uniform plate are identified: mode conversion from the second harmonic S0 mode waves, asymmetric nonlinear driving forces at the non-uniform section, and the mutual interaction between the mode-converted fundamental A0 and S0 waves. This study shows that the reported atypical 2nd A0 waves provide an effective means for monitoring local incipient damage in non-uniform structures.

Modeling optical systematics for the Taurus CMB experiment

We simulate a variety of optical systematics for Taurus, a balloon-borne cosmic microwave background (CMB) polarisation experiment, to assess their impact on large-scale E-mode polarisation measurements and constraints of the optical depth to reionisation τ.We model a one-month flight of Taurus from Wanaka, New Zealand aboard a super-pressure balloon (SPB).We simulate night-time scans of both the CMB and dust foregrounds in the 150 GHz band, one of Taurus's four observing bands.We consider a variety of possible systematics that may affect Taurus's observations, including non-gaussian beams, pointing reconstruction error, and half-wave plate (HWP) non-idealities.For each of these, we evaluate the residual power in the difference between maps simulated with and without the systematic, and compare this to the expected signal level corresponding to Taurus's science goals.Our results indicate that most of the HWP-related systematics can be mitigated to be smaller than sample variance by calibrating with Planck's TT spectrum and using an achromatic HWP model, with a preference for five layers of sapphire to ensure good systematic control.However, additional beam characterization will be required to mitigate far-sidelobe pickup from dust on larger scales.

Elastic birefringent metamaterials and quarter-wave plate

The elastic matrices of extremal metamaterials have one or more zero eigenvalues, allowing energy-free deformation modes. These elastic metamaterials can be well approximated by manufactured microstructures. They can exhibit an unprecedented capacity to manipulate bulk and surface waves, which are unavailable with conventional solids due to the easy deformation modes, as already exemplified by pentamode materials (PMs). In this paper, we theoretically investigate a direct one-to-one correspondence of birefringent metamaterial and quarter-wave plate between optical and elastic waves based on a carefully designed quadramode material (QM). This QM metamaterial allows only two transverse wave modes, eliminating mode conversion due to the presence of the longitudinal mode. The characteristics of the elastic birefringent metamaterial and elastic quarter-wave plate are demonstrated by both homogenized and corresponding discrete models. A free space elastic wave isolator, analogous to a diode in electronics, is also proposed, which can effectively protect upstream sources or systems from back-reflected noise or interference. An additional benefit of the discrete model is also revealed for its working frequency tunability through deformation. This work provides the first study on elastic birefringent metamaterials and tunable elastic quarter-wave plate, which may stimulate applications of extremal elastic metamaterials for controlling elastic wave polarization.

Best reconstruction frequency for time-reversal process of Lamb waves and its determination from a single measurement

This article presents a theoretical framework for the concept of the best reconstruction frequency (BRF) of Lamb waves in elastic plates and its significance in the context of structural health monitoring (SHM). The time-reversal process (TRP) of Lamb waves has been widely explored for baseline-free damage detection in thin-walled structures. Previous studies have indicated that the accuracy of damage detection can be significantly improved by exciting Lamb waves at a frequency where the time-reversibility in the undamaged state is maximum within a desired frequency range. This frequency, termed the BRF, has been determined phenomenologically in prior research but lacked a rigorous theoretical foundation. In this study, the BRF is derived as the frequency at which the amplitude dispersion of the main mode of the reconstructed signal after the TRP is minimized. Accordingly, a method is put forth to determine this frequency from a single measurement using a broadband excitation eliminating the need to compute the similarity between the reconstructed and input waveforms at different excitation frequencies. The developed theory is validated with experiments conducted on an aluminium plate with Lamb waves generated and sensed by surface-bonded piezoelectric patch transducers. Notably, the study establishes that the BRF is a system property specific to a given transducer-plate-adhesive system and is independent of the distance between transducers. This characteristic makes it suitable for identifying damage locations when employing multiple sensing paths. The findings constitute an important milestone in understanding the TRP of Lamb waves and developing robust SHM technologies based on it.

Reflective multi-layer metasurface based on half-wave plate structure for polarization control in the visible-near-infrared region

The precise control of the polarization of the electromagnetic field in the optical range is studied. A numerical simulation was performed, which corresponds to the optical devices operating in the 650–800 nm range and does not present any obstacles for fabrication. According to this, the three-layer system based on metasurfaces was developed, which operates as a half-wave plate consisting of a metal-dielectric-metal structure and takes very small dimensions, more than 3 times smaller than the observed wavelength. This half-wave plate is reflective and exhibits almost ideal behavior with a spectral width of about 10 nm within 735–745 nm. The losses are negligible, and the amplitude ratio of the directly reflected components in almost the entire studied spectrum exceeds 90%. With a spectrum of about 100 nm within 650–800 nm, it is 99%. Also, the system has an advantage characteristic of metasurfaces: regardless of the angle of the incident wave with the normal, it shows high efficiency, and even when the incident wave is below 45°, the polarization conversion ratio (PCR) remains greater than 80%. The system has optimal geometric dimensions, which works especially well, but even if the dimensions change (due to fabrication defects), its effectiveness does not weaken. The proposed system can become a very promising optical device and be used to control the state of electromagnetic waves in the optical range.

Perfect vortex beams generation based on reflective geometric phase metasurfaces

Perfect vortex beam (PVB) is a propagating light field with radial intensity distribution independent of topological charge and carrying orbital angular momentum (OAM). PVBs can be generated through the Fourier transformation of a Bessel-Gaussian (BG) beam, which traditionally requires a precisely aligned optical setup consisting of a spiral phase plate, a conical lens, and a Fourier lens. However, such traditional schemes are usually bulky and unstable. Here, we have utilized a method that differs from conventional approaches, employing metasurfaces designed as planar Pancharatnam-Berry (PB) phase elements to substitute for all the required components. Unlike traditional methods based on reflective or refractive elements, metasurface elements can significantly reduce the system's footprint. Because the use of metallic metasurfaces allows for a more flattened design plane, in this paper, we have demonstrated the generation of PVB within the 8 GHz microwave frequency band based on a single-layer metallic metasurface. The metasurface is composed of a square ring metal structure, which can serve as a half wave plate to provide the required geometric phase distribution for incident circularly polarized light to generate PVB. By rigorously optimizing the parameters of the square-ring structures, we have generated vortex beams carrying OAM with different topological charges. These vortex beams exhibit a constant radial intensity distribution, which validates their "perfect" characteristics. In addition, we also extracted the mode purity of different vortex beams, so that the mode states of different vortex beams can be distinguished. These results provide broader value for the application of perfect vortex beams in communication.

Analysis of a THz unit-structured grating metasurface wave plate

Analysis of a THz unit-structured grating metasurface wave plate