Modulation Devices Research Articles

Electrically Tunable Strong Optical Nonlinearity in Near‐Infrared by Coupled Metallic Quantum Wells

AbstractAn electrically tunable nonlinear optical device working at near‐infrared wavelength is theoretically and experimentally demonstrated. Ultrahigh optical second‐order nonlinearity from titanium‐nitride‐based coupled metallic quantum wells can be electrically tuned by external electric field. Tunability of second‐order susceptibility χ(2) reaches a 63% modulation depth with an average tunability of 10.5% per volt. In addition, electro‐optic modulation of second‐harmonic signal is presented by continuous tuning of χ(2) over a long period of time with high stability. These results provide a new material platform with actively controllable strong nonlinearity for future nonlinear photonic systems, such as ultra‐compact opto‐electronic modulation devices and reconfigurable nonlinear metamaterials and metasurfaces.

High-performance semi-transparent organic solar cells driven by the dipole-controlled optoelectrical response of bilateral self-assembled monolayer strategy

A bilateral self-assembled monolayer (SAM) strategy is proposed to improve the performance of both opaque/translucent and rigid/flexible organic solar cells (OSCs), which have great potential for various high-value applications such as portable, building-integrated and vehicle-integrated photovoltaics. By applying the dipole-controlled SAMs to both ITO/ZnO and ZnO/active layer interfaces, the work function of the ZnO electron transport layer was reduced, which improved charge transport and reduced carrier recombination at the interface. The opaque OSCs with the bilateral SAM demonstrated significant performance improvement with power conversion efficiencies (PCEs) reaching 17.20% and 16.96% for rigid and flexible OSCs. When used in semi-transparent OSCs together with MoO3/Ag/MoO3 electrode, in semi-transparent (ST) OSCs, PCE and average visible transmittance (AVT) can be improved simultaneously, and 10.37% PCE and 36.27% AVT demonstrate a remarkable light utilization efficiency (LUE) of 3.85%. Finally, the large area (10 × 10 cm2) ST-OSC module was fabricated and demonstrated a PCE of 8.17% and LUE of 2.5%, among the best-reported values for inverted module devices. The developed bilateral SAM strategy can be useful in developing high-performance OSCs of both opaque/translucent and rigid/flexible types for various practical applications.

Aluminum-based plasmonic metasurface for computational spectrometry with full coverage of visible light.

Reconstructive spectrometers/spectral cameras have immense potential for portable applications in various fields, including environmental monitoring, biomedical research and diagnostics, and agriculture and food safety. However, the performance of these spectrometers/spectral cameras is severely limited by the operational bandwidth, spectral diversity, and angle sensitivity of the spectral modulation devices. In this work, we propose a compact spectrometer based on plasmonic metasurfaces that operate across the entire visible wavelength range, covering wavelengths from 400 to 750 nm. We experimentally demonstrate the effective spectral reconstruction achieved by the designed metasurface spectrometer, exhibiting angle tolerance to the incident light within the range of ± 12°. Our results highlight the potential for constructing broadband, large field-of-view hyperspectral cameras.

Multicenter study of the safety and effectiveness of intracranial aneurysm treatment with the p64MW-HPC flow modulation device

Background and purpose The new p64 flow diverter with hydrophilic polymer coating (HPC) was designed to reduce thrombogenicity. To date, it is unclear how antithrombogenic surface modifications affect neoendothelialization and thrombus formation in patients with unruptured intracranial aneurysms. The purpose of this study was to evaluate the safety and effectiveness of the p64MW-HPC in the treatment of unruptured aneurysms of small to giant size and of both the anterior and posterior circulation. Materials and methods Between March 2020 and October 2022 all patients with unruptured intracranial aneurysms treated with the p64MW-HPC were included at five neurovascular centers. Demographic data, aneurysm characteristics, antiplatelet therapy, procedural complications, and clinical and angiographic outcomes were recorded. Results A total of 100 patients with 100 unruptured intracranial aneurysms met the inclusion criteria. Eighty-three aneurysms were classified as saccular, 12 aneurysms were fusiform, 4 aneurysms dissecting, and 1 aneurysm was blister-like. Dual antiplatelet therapy with Clopidogrel and Aspirin was given in 68 cases, and with Ticagrelor and Aspirin in 24 cases. Technical issues with deployment were encountered in 14 cases (torsion ( n = 3), foreshortening ( n = 8), and incomplete opening ( n = 3)). Ischemic stroke occurred in a total of seven cases. In one patient a wire perforation and subsequent severe ICH occurred. Complete aneurysm occlusion at angiographic follow-up (mean time = 7 months) was seen in 73% and adequate occlusion in 93%. Conclusion This study is the largest multicenter study to date documenting the safety and effectiveness of the new antithrombogenic p64MW-HPC in the treatment of unruptured intracranial aneurysms of the anterior and posterior circulation.

Terahertz rewritable wavefront modulator based on indium oxide and DMSO-doped PEDOT:PSS.

An optically rewritable and electrically erasable terahertz (THz) wavefront modulator based on indium oxide (In2O3) and DMSO-doped PEDOT:PSS is proposed. The modulator has a three-layer structure of In2O3/PEDOT:PSS/quartz, which can weaken the THz transmission under the action of light excitation. Optically written THz Fresnel plates, which can focus the input Gaussian beam into a point, were realized. After optical excitation, the function of the device reduces slowly if it is stored in the room environment. However, the function can be stored for a long time if it is encapsulated in the nitrogen environment. If a bias voltage of 22 V is applied on the device, the function of the device can be erased in 10 seconds. The new function can be written into the device after wiping. Experiments on THz rewritable holographic devices are carried out to show the validity of this approach. This method can provide new devices for THz wavefront modulation and develop tunable optical imaging elements.

Zn2+-Enhanced Lithium Magnesium Molybdate Ultralow Temperature Cofired Ceramics for Terahertz Wavefront Modulation Applications.

High efficiency, high frequency, low error, and low latency of wavefront modulation are challenges that must be addressed simultaneously in 5G/6G communication systems. In order to cope with these challenges, novel Li2Mg2-xZnxMo3O12 (x = 0.00-0.08) ceramics are prepared by a solid-state reaction method. The microwave dielectric properties (εr = 8.7, Q × f = 61,312 GHz, τf = -59.1 ppm/°C) and terahertz transmission properties (εr1 = 8.3, tanδ1 = 0.00908, Tamplitude = 0.673, Δphase = 27.65°) of this ceramic (x = 0.06, 625 °C) are effectively enhanced by Zn2+. The chemical compatibility between this ceramic and the Al electrode is demonstrated. The reflection amplitude of this ceramic combined with the Al electrode at 0.5 THz is revealed, and the error between simulation and experiment is only 0.06. A terahertz reflective device for wavefront modulation is designed and demonstrated by using this ceramic and Al electrode. This device can deflect the wavefront of cross-polarized waves and has a certain isolation effect on co-polarized waves. This work accelerates the development of dielectric ceramics and ultralow temperature cofired ceramics technology in the terahertz field.

High-Quality Acousto-Optic Modulators with High Diffraction Efficiency, Polarization Extinction Ratio, and Small Insertion Loss Based on a Novel BaO-TeO2 -WO3 Glass.

The Q-switched material and device have attracted extensive attention due to their irreplaceable role in pulsed lasers. In this paper, BaO-TeO2 -WO3 glass (BTW glass) with sound velocity and sound attenuation coefficient of 3422 m-1 s and 0.653dB cm-1 is successfully selected and fabricated as acousto-optic material. Both free-spaced and fiber-coupled acousto-optic modulation devices based on BTW glass are designed and fabricated. The primary parameters such as diffraction efficiency, polarization extinction ratio, and insertion loss are comparable to or even surpassed that of commercial devices. A 1064nm pulsed laser is successfully realized with a BTW glass free-spaced acousto-optic modulator. The maximum optical conversion efficiency, the narrowest pulse width, and the maximum single pulse energy of the 1064nm pulsed laser are 32%, 54ns, and 242.6 µJ, respectively. Both the device and laser performance indicate that the BTW glass is a remarkable acousto-optic material.

Frontier in two-dimensional materials with nonlinearity: A big data analysis of saturable absorbers for pulse lasers applications

The peculiar nonlinear optical responses of two-dimensional (2D) materials endow them highly attractive for photonics applications. This review systematically discusses the performance of pulsed lasers employing 2D materials as their modulation device. First, it is crucial to categorize 2D materials that can act as saturable absorbers, encompassing a range of substances such as Graphene, Black Phosphorus, Topological Insulators, MXene, and even heterojunction. Furthermore, a thorough investigation is conducted to analyze the performance indexes to study the nonlinear characteristics of 2D materials in the pulse generation. Especially, the focus is on the 1.5 [Formula: see text]m band ultrafast lasers utilizing 2D materials. This paper also provides a comprehensive analysis of the obstacles and prospects in 2D materials preparation, and their utilization in the pulse laser systems.

Multi-frequency modulator of dual plasma-induced transparency in graphene-based metasurface

Graphene-based metamaterials can generate plasma-induced transparency (PIT), offering a new approach for achieving modulators with optimal modulation performance. This study presents a multi-frequency modulator based on novel monolayer graphene structure. We utilize Coupled Mode Theory (CMT) for thorough theoretical investigations, yielding theoretical values that agree well with simulation results. Moreover, we discuss the implications of the Fermi level on PIT and the influence of graphene carrier mobility on switch modulation. The research findings illustrate the successful realization of a high-performance multi-frequency modulator by indirectly controlling the phase of the dual PIT transmission spectra through an adjustable bias voltage. Notably, at a frequency of 3.93 THz, the increasing of carrier mobility enhances the modulation depth of the modulator from 89.22 % to 97.88 % and reduces the insertion loss from 0.34 dB to 0.12 dB. Hence, our research has substantial implications for designing excellent tunable terahertz optical modulator devices and contributing to the advancement of optical communication systems and optoelectronic applications.

Research on near-infrared ultrafast excited carrier dynamics of a pyrene-based derivative and its application in femtosecond laser

Femtosecond laser, compared to continuous wave (c.w.) or nanosecond laser, has shown great promise in diversities of frontier applications because of its extremely short pulse width, high peak power and low thermal effect. In order to obtain femtosecond laser output, the design of suitable saturable absorber (SA) materials as a nonlinear modulation device is a key issue for a given laser system. However, the previous SA materials are limited in inorganic semiconductors, which have some constraints such as narrow working wavelength ranges, complex preparation process and high cost. By contrast, organic semiconductors have high molecular design freedom, good flexibility, simple preparation process, and low cost, and would act as an ideal SA material. Here, we report a novel strategy to tune and realize the femtosecond laser out by employing an organic small molecule SA of (Z)-2-(4-(pyrene-1-yl) phenyl)-3-(4-(1,2,2-triphenylvinyl) phenyl) acrylonitrile (Py-TPE). We show that Py-TPE has an ultrafast excited carrier relaxation time less than 20 ps, shorter than most of inorganic semiconductor materials. More importantly, by depositing such Py-TPE on the surface of tapered fiber as an SA device in Er-doped fiber laser system, an ultrafast fiber laser output with a pulse width as narrow as 447 fs and good stability was realized. This is the first report, to the best of our knowledge, to achieve femtosecond laser by taking advantage of the Py-TPE with ultrafast excited carrier relaxation time. These results demonstrate that Py-TPE is a novel organic saturable absorption material with great potential application in ultrafast laser and photonics.

Electro-optic effects of lithium borate crystals studied by first-principles method

In respect to the electro-optic (EO) effect, LiB3O5 (LBO) and Li2B4O7 (LB4) contain the same elements but represent two extremes in the family of nonlinear optical (NLO) borate crystals: one with large second harmonic generation (SHG) coefficients but very small reported EO coefficients, the latter has extremely small SHG coefficients yet EO coefficients were found even larger than the practical EO modulator crystal β-BaB2O4 (BBO). The puzzle was unraveled through first-principles studies of the two crystals and it is found that the vibrational and electronic contributions to the EO effect were canceled in LBO and the major contributions are from piezoelectric induced effect for LB4 with electronic contributions negligible. In addition to the EO and NLO coefficients, dielectric, elastic, piezoelectric and elasto-optic constants are all obtained simultaneously. More importantly, fully determining the elastic, elasto-optic constants, all 4th rank tensors, can be adopted to calibrate the experimental uncertainties and help to design practical surface acoustic wave (SAW) or acoustic optic modulator (AOM) devices.

Durable effects of deep brain ultrasonic neuromodulation on major depression: a case report

BackgroundSevere forms of depression have been linked to hyperactivity of the subcallosal cingulate cortex. The ability to stimulate the subcallosal cingulate cortex or associated circuits noninvasively and directly would maximize the number of patients who could receive treatment. To this end, we have developed an ultrasound-based device for effective noninvasive modulation of deep brain circuits. Here we describe an application of this tool to an individual with treatment-resistant depression.Case presentationA 30-year-old Caucasian woman with severe treatment-resistant non-psychotic depression was recruited into a clinical study approved by the Institutional Review Board of the University of Utah. The patient had a history of electroconvulsive therapy with full remission but without sustained benefit. Magnetic resonance imaging was used to coregister the ultrasound device to the subject’s brain anatomy and to evaluate neural responses to stimulation. Brief, 30-millisecond pulses of low-intensity ultrasound delivered into the subcallosal cingulate cortex target every 4 seconds caused a robust decrease in functional magnetic resonance imaging blood-oxygen-level-dependent activity within the target. Following repeated stimulation of three anterior cingulate targets, the patient’s depressive symptoms resolved within 24 hours of the stimulation. The patient remained in remission for at least 44 days afterwards.ConclusionsThis case illustrates the potential for ultrasonic neuromodulation to precisely engage deep neural circuits and to trigger a durable therapeutic reset of those circuits.Trial registration ClinicalTrials.gov, NCT05301036. Registered 29 March 2022, https://clinicaltrials.gov/ct2/show/NCT05301036

Column coded scanning aperture hyperspectral imaging system.

The line scanning hyperspectral imaging system (LS-HIS), which relies on a mechanical slit or spatial light modulation device for single channel spatial scanning, is widely used in various fields such as biomedical imaging and remote sensing. However, in scenes that require low light illumination, a decrease in luminous flux will increase exposure time, leading to a significant decrease in scanning efficiency and signal-to-noise ratio (SNR). To address this issue, we present a flexible column coded scanning aperture hyperspectral imaging system (CCSA-HIS) using a spatial light modulator digital micromirror device (DMD). By introducing the concept of multiplex and constructing a multiplexing encoding matrix, we form a one-dimensional multi-column coded scanning aperture, which greatly improves scanning efficiency. Experimental comparisons demonstrate that this approach achieves higher SNR and equivalent spatial and spectral resolution in significantly less sampling time compared to LS-HIS. In short, our scheme provides a new imaging technology for the field of hyperspectral imaging with good theoretical value and engineering significance.

A Sub-Terahertz High-Speed Traveling-Wave Switch Modulator Based on Dynamically Tunable Double-Resonant Coupling Units

High-speed direct modulation devices are of great significance for the development of high-speed communication systems with large bandwidth, miniaturization, and low complexity. However, an increase in the carrier frequency in the sub-terahertz band and above will negatively impact high-performance direct modulation devices due to the large insertion loss and low on–off ratio. Based on the traveling-wave modulation mechanism, this article adopts the zero-phase-difference amplitude modulator design method. More specifically, a 1- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m small anode Schottky diode is combined with a Z-type matching structure to form a dual-resonant coupling dynamic tunable unit. Interunit coupling is found to further improve the on–off ratio. In this way, high-speed dynamic modulation is performed for the transmission traveling-wave amplitude with low insertion loss and a high on–off ratio. On this basis, a 0.14-THz on–off keying (OOK) high-speed traveling-wave modulator is proposed, and our results showed that a on–off ratio of 25.4 dB could be achieved at the zero-phase-difference point by only using two dynamic structural units. Meanwhile, the control voltage could be adjusted to achieve high-speed modulation with a phase difference of only 3.66 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^\circ$</tex-math> </inline-formula> during the entire control voltage transition, a data rate of 24 Gb/s, and 33.99% sidebands occupation.

Design of programmable beam splitting metasurface

Metasurface has been applied as one critical platform for electromagnetic modulation devices. Here, a programmable metasurface loaded with positive-intrinsic negative (PIN) diodes is proposed to realize dynamic switching of arbitrary multi-beam. Furthermore, the multi-beam coding sequence is optimized by a genetic algorithm (GA) to achieve dual- to nine-beam with different scattering directions. As a proof of concept, a programmable metasurface prototype that operates around 8 GHz is designed and fabricated to be tested in far-field measurements. The beam splitter has been verified by theoretical analysis and numerical simulation to have a power efficiency of over 70%. In the measurement system, multi-beam splitting phenomena are obtained using DC control of the PIN diodes “on” and “off”, which is consistent with the simulation results. The proposed beam splitter can be designed with real-time multi-beam switching and intelligently provides coding sequences with multiple directive angles, thus providing potential benefits for next-generation antennas.

Plexcitonic optical chirality in the chiral plasmonic structure-microcavity-exciton strong coupling system.

Chiral plexcitonic systems exhibit a novel chiroptical phenomenon, which can provide a new route to design chiroptical devices. Reported works focused on the two-mode strong coupling between chiral molecules and nanoparticles, while multiple-mode coupling can provide richer modulation. In this paper, we proposed a three-mode coupling system consisting of a chiral Au helices array, a Fabry-Pérot cavity, and monolayer WSe2, which can provide an extra chiral channel, a more widely tunable region, and more tunable methods compared to two-mode coupled systems. The optical response of this hybrid system was investigated based on the finite element method. Mode splitting observed in the circular dichroism (CD) spectrum demonstrated that the chiroptical response successfully shifted from the resonant position of the chiral structure to three plexcitons through strong coupling, which provided a new route for chiral transfer. Furthermore, we used the coupled oscillator model to obtain the energy and Hopfield coefficients of the plexciton branches to explain the chiroptical phenomenon of the hybrid system. Moreover, the tunability of the hybrid system can be achieved by tuning the temperature and period of the helices array. Our work provides a feasible strategy for chiral sensing and modulation devices.

Vortex beam generator based on exceptional topological phase in terahertz all-dielectric metasurface

In this study, an all-dielectric metasurface with an F-shaped chiral structure in the terahertz region has been proposed. The coupling between the electric and magnetic dipole modes supported by the metasurface can be adjusted by varying the structural parameters. In the parameter space composed of l l and s, any closed path around exceptional point in the circular polarization conversion channel t rl generates a topologically protected exceptional topological phase. A vortex beam generator with a unit topological charge was proposed to provide a novel concept for designing terahertz metasurface wavefront modulation devices.

High-speed electro-optic modulation in topological interface states of a one-dimensional lattice

Electro-optic modulators are key components in data communication, microwave photonics, and quantum photonics. Modulation bandwidth, energy efficiency, and device dimension are crucial metrics of modulators. Here, we provide an important direction for the miniaturization of electro-optic modulators by reporting on ultracompact topological modulators. A topological interface state in a one-dimensional lattice is implemented on a thin-film lithium-niobate integrated platform. Due to the strong optical confinement of the interface state and the peaking enhancement of the electro-optic response, a topological cavity with a size of 1.6 × 140 μm2 enables a large modulation bandwidth of 104 GHz. The first topological modulator exhibits the most compact device size compared to reported LN modulators with bandwidths above 28 GHz, to the best of our knowledge. 100 Gb/s non-return-to-zero and 100 Gb/s four-level pulse amplitude modulation signals are generated. The switching energy is 5.4 fJ/bit, owing to the small electro-optic mode volume and low capacitance. The topological modulator accelerates the response time of topological photonic devices from the microsecond order to the picosecond order and provides an essential foundation for the implementation of large-scale lithium-niobate photonic integrated circuits.

Nanometer resolution of 2D single-shot low-coherence & comb-based profilometry based on the effect of discrete height of spatial phase modulator surface

A 2D single-shot comb-based interferometer is well known as a powerful tool for inline inspection owing to its high speed, extensive measurement range, and anti-vibration. However, nanometer resolution is still a milestone that has not been achieved in comb-based interferometers owing to the precision limitation caused by the discrete profile of the spatial phase modulator (SPM) device, typically in the range of several micrometers. Therefore, this study confirms 2D single-shot comb-based profilometry at sub-micron and nanometer-scale resolutions. The system first investigates the effect of the discrete limitation of the SPM surface profile and then verifies the submicron detection ability of the optical frequency comb-based setup. It was quantitatively shown that the highest resolution can be obtained by properly setting the step size of the spatial phase modulator and the SPM surface resolution of the imaging optics. The highest profilometry resolution was recorded at 26.4 nm in a short measurement range, while the setup using the optical comb source with millimeters measurement range for industrial application also can achieve a resolution of approximately 259.2 nm. The results demonstrate the system feasibility in overcoming the discrete limitations of the SPM profile. It also demonstrates for the first time that the so-called 2D single-shot comb-based interferometer can achieve nanometer-scale profilometry resolution covering the measurement range from tens of millimeters to sub-micrometer detection.

A switchable terahertz metamaterial absorber between ultra-broadband and dual bands

Based on the phase change properties of vanadium dioxide (VO2), we propose a terahertz metamaterial absorber that can be switched flexibly between ultra-broadband and dual bands. The absorber consists of a resonator array above a conductive ground layer separated with a dielectric spacer, which includes four square-loop VO2 resonators and a crossed gold resonator in each unit cell. By changing the conductivity of VO2 through thermal control, the absorber can achieve the switching between ultra-broadband absorption and dual-band absorption. Simulation results show that at high temperature, the absorber realizes more than 90% absorption bandwidth in the range of 3.98 to 9.06 THz, which can be elucidated by the wave-interference theory and impedance matching theory. At low temperature, up to 95% of the dual-band absorption occurs at 5.95 and 6.95 THz, which originates the dipole mode and nonlocal surface-Bloch mode of metal resonators. In addition, the absorber has the advantages of polarization-independence and wide-angle absorption. Compared with previous studies, our design can switch between two absorption modes and its absorption performance is greatly improved. The proposed absorber design scheme is expected to expand terahertz devices and enable a variety of applications in the terahertz range, such as modulation, sensing, stealth, and switching devices.