Optical Modulation Research Articles

Ultralong Bistable, Electrolytic MnO2-Based, Electrochromic Battery Enabled by Porous, Low-Barrier, Hydroxylated TiO2 Interface.

Electrochromic (EC)battery technology shows great potential in future "zero-energy building" by controlling outdoor solar transmission to tune heat gain as well as storing the consumed energy to reuse across other building systems. However, challenges still exist in exploring an electrochemical system to satisfy requirements on both ultra-long optical memory (also called bistability) without continuous power supply and high energy density. Herein, an ECbattery is proposed to demonstrate ultra-long bistability (>760h) based on the reversible deposition and dissolution of manganese oxide (MnO2) without the addition of any mediators. A porous low-barrier hydroxylated titanium dioxide (TiO2) interface is incorporated to synergistically enrich Mn2+-affinity active sites for deposition and effectively reduce the electron transport barrier of MnO2 for dissolution, thereby significantly improving the reversibility, high optical modulation (60.2% at 400nm), and energy density (352mAhm-2). The modification strategy is also verified on the cathode-less button cells with a much higher average coulombic efficiency (99.9%) compared to the batteries without the porous hydroxylated TiO2 interface (74.6%). These achievements lay a foundation for advancements in both electrochromism and Zn-Mn aqueous batteries.

Manipulating photonic spin Hall split based on nonlinear effect and surface plasmon resonance

In this work, we present a surface plasmon resonance (SPR) structure containing AuAl2 and a nonlinear Kerr medium. Based on the modulation of the refractive index of the Kerr medium by pumped light, we analyze the effects of the SPR structure and pumped light on the photonic spin Hall effect (PSHE). The numerical results indicate that the thickness of the AuAl2 exerts a profound impact on the SPR, while the intensity of the pump light (Ip) exerts a significant influence on the resonance angle. The transverse shift (TS) is very sensitive to the refractive index (RI) of the sensing layer after increasing through the SPR. Furthermore, it is observed that the sign of the TS of the PSHE can be modulated according to Ip within a specific angle of incidence. In light of these findings, we put forth a novel optical signal modulation and RI sensing scheme based on PSHE. Our study provides a new mechanism for practical applications of PSHE in optical communication and precision measurement.

An optical measurement method of DC total electric field with space charges based on probe self-rotation modulation

Researching the measurement of DC total electric field with space charges (Poisson field) can help establish a monitoring system for the electromagnetic environment of UHVDC transmission lines and protect the health of the ecological environment. This paper proposes a DC total electric field optical measurement method based on the Pockels effect and probe self-rotation modulation. It can address the issues of internal charge drift and external charge accumulation in traditional optical probes when measuring DC electric fields with space charges. Theoretical analysis was conducted on measurement under probe rotation, and the optical modulation system was integrated into a probe with dimensions of 60 mm × 30 mm × 20 mm. A self-rotating platform for the probe was designed, and the influence of rotation mode on the results was analyzed. It was found that the sensitivity was higher when using the horizontal-horizontal mode. The signal processing system was tested, showing that the probe retained around 50 % of its original output when rotating at low speeds (frequency 1–3 Hz), fully meeting the measurement requirements. The test platform has been constructed, and the probe’s sensitivity was assessed under an AC electric field and validated under a DC electric field. Finally, the optical method proposed in this paper was used to measure the DC total electric field with space charges under a small model of a unipolar HVDC transmission line. Five locations under the line were selected as measurement points, and the results were compared with those obtained from a field mill probe and numerical simulation. This comparison indicates that the proposed method agrees with experimental and simulation results. The average sensitivity of the self-rotating optical probe was 3.71 mV/(kV/m). The error did not exceed 5 % in high-field strength areas (above 20 kV/m) and was also controlled within 15 % in low-field strength areas (below 20 kV/m).

Bio-inspired Mechanically Responsive Smart Windows for Visible and Near-Infrared Multiwavelength Spectral Modulation.

Mechanochromic light control technology that can dynamically regulate solar irradiation is recognized as one of the leading candidates for energy-saving windows. However, the lack of spectrally selective modulation ability still hinders its application for different scenarios or individual needs. Here, inspired by the generation of structure color and color change of living organisms, a simple layer-by-layer assembly approach toward large-area fabricating mechanically responsive film for visible and near-infrared multiwavelength spectral modulation smart windows is reported here. The assembled SiO2 nanoparticlesand W18O49 nanowires enable the film with an optical modulation rate of up to 42.4% at the wavelength of 550nm and 18.4% for the near-infrared region, separately, and the typical composite film under 50% stretching shows ≈41.6% modulation rate at the wavelength of 550nm with NIR modulation rate less than 2.7%. More importantly, the introduction of the multilayer assembly structure not only optimizes the film's optical modulation but also enables the film with high stability during 100000 stretching cycles. A cooling effect of 21.3 and 6.9 °C for the blackbody and air inside a model house in the real environmental application is achieved. This approach provides theoretical and technical support for the new mechanochromic energy-saving windows.

Amorphous Hydrated Tungsten Oxides with Enhanced Pseudocapacitive Contribution for Aqueous Zinc‐Ion Electrochromic Energy Storage

AbstractTungsten oxides suffer from sluggish ion diffusion kinetics, limited ion storage capacity, and inadequate stability within the aqueous zinc ion electrolyte, thereby constraining their applicability in electrochromic energy storage devices (EESDs). Here, the amorphous hydrated tungsten oxide films with large optical modulation, fast response speed, large capacity, and high cycling stability are reported, enabled by tuning the contents of structural water and adjusting the pH value of aqueous zinc ion electrolyte. The enhancement of the electrochromic and ion storage performance is mainly due to the introduction of structural water which triggers pseudocapacitive behavior dominated by surface redox reaction, resulting in high electrochemical activity and fast electrochemical kinetics. Meanwhile, the relatively low pH value ensures the chemical stability of the hydrated tungsten oxide film, in synergy with surface redox that avoids ion trapping, leading to extraordinary cycling stability of up to 13000 cycles, marking the state‐of‐the‐art stability for tungsten oxide‐based materials in aqueous electrolyte. Based on the hydrated tungsten oxide films, high‐capacity and stable large‐size EESDs are constructed with the capability of visually monitoring energy status, recovering energy, and regulating light. This work provides a simple yet effective strategy for enhancing the performance of tungsten oxide‐based aqueous zinc ion EESDs.

The preparation of low-cost tungsten oxide films by solution-coating technique and NIR annealing for high-performance complementary electrochromic devices

Electrochromic devices can adjust their transparency by applying an electrical voltage and serve as intelligent window systems for managing incoming sunlight. In this study, we employed an environmentally friendly, large-area solution coating method to form tungsten oxide (WO3) thin films for the fabrication of electrochromic devices. We applied a WO3 precursor solution, with water as the primary solvent, onto ITO glass through blade coating and utilized near-infrared (NIR) light annealing for drying in order to rapidly optimize the film characteristics. The resulting WO3 film, combined with an ion storage layer – either sputtered NiO or blade-coated Prussian Blue (PB) - and injected with a UV-curable electrolyte, resulted in a complementary electrochromic device that exhibited good performance characteristics. For the device with NiO as the ion storage layer, the optical transmittance modulation (ΔT) can achieve 50 % at a wavelength of 680 nm, maintaining a ΔT of 45 % after 3000 coloration-bleaching cycles. For the device with PB as the ion storage layer, the ΔT achieved 64 % at 630 nm, maintaining a ΔT of 60 % after 3000 coloration-bleaching cycles. Therefore, we believe this WO3 solution coating technique combined with rapid NIR annealing technology holds promise as a low-cost and efficient method for the future production of electrochromic devices.

Q-factor and wavelength adjustable ultra-perfect absorption under critical coupling through epsilon-near-zero-based absorbers

Perfect absorption with adjustable Q factor and wavelength is essential in both theory and application. To address this issue, a structure composed of an epsilon-near-zero (ENZ)- SiO2 grating and a multilayer dielectric structure was designed. In the structure, the intrinsic loss is related to the ENZ thickness, while the external leakage depends on the grating parameters. By adjusting the ENZ film thickness, the intrinsic loss rate was tuned to match the external leakage rate corresponding to different grating parameters, realizing the critical couplings with different Q factors and wavelengths. Under critical coupling, the absorption rate reached a maximum of 99.999%, demonstrating ultra-perfect absorption. The Q factor was adjusted from 4350 to 35800, and the absorption wavelength was modified from 1050 to 1282 nm. The design work may provide new ideas for developing wavelength- and Q-selective absorbers, optical modulators, dielectric sensors, and photodetectors.

Magneto-optical metasurfaces for high-Q perfect absorption with quasi-bound states in the continuum.

We present a novel, to the best of our knowledge, magneto-optical (MO) metasurface composed of a bismuth iron garnet (BIG) nanocube array, designed to achieve near-perfect absorption through quasi-bound states in the continuum (QBICs). This metasurface supports a stable QBIC mode induced by MO-induced permittivity terms that break the symmetry of the permittivity tensors, corresponding to a longitudinal electric dipole (ED) mode. By integrating graphene to introduce material loss, the absorption reaches 99.6% at a wavelength of 1512.3 nm with a Q factor of 9440, despite monolayer graphene's inherent absorption being only 2.3%. The inherent transverse ED background mode, with high reflection and low Q, helps decrease the radiative loss of the QBIC mode, allowing the structure to surpass the 50% absorption limit. This approach offers a simplified pathway for designing high-Q metasurface perfect absorbers, with potential applications in optical switches and modulators.

Novel Optical Modulator Photonic Device Based on TiN/Ti3C2 Heterojunction.

Due to the ability of optical modulators to achieve rapid modulation of optical signals, meeting the demands of high-speed data transmission, modulators based on different novel nanomaterials have become one of the research hotspots over the past dacade. Recently, TiN/Ti3C2 heterojunction exhibits highly efficient thermo-optic performance and extremely strong stability. Therefore, we have demonstrated an all-optical modulator based on the principle of Michelson interference and the thermo-optic effect in this paper. The modulator employs a TiN/Ti3C2 heterojunction-coated microfiber (THM) and further demonstrates its ability to generate phase shifts through an ASE light source. The modulator, with a phase shift slope of 0.025π/mW, can also convert the phase shifts of signal light into amplitude modulation through Michelson interference. The fixed signal light wavelength is 1552.09 nm, and the modulation depth is stable at about 26.4 dB within a wavelength detuning range of -10 to 6 nm; The waveforms of signal light at modulation rates of 500 Hz, 1000 Hz, 2000 Hz, and 3000 Hz were tested, and a 3 dB modulation bandwidth of 2 kHz was measured. The all-optical modulator based on THM has the advantages of high efficiency and stability and has broad application prospects in the fields of all-optical signal processing and high-speed optical communication.

Novel Functional Organic Chromophores

Porphyrins and other tetrapyrroles are highly suitable for sensing operations based on their synthetic flexibility and chromophore structures where an analyte might interact to stimulate some variation in directly observable optical colour or fluorescence emission modulation. Their chromophore structures also allow access to electronic triplet states, which can be harnessed for the generation of singlet oxygen – a highly reactive species useful for photodynamic action against tumours or microorganisms. Here we discuss the sensing activity of several β-substituted porphyrins1 including not only by the introduction of suitable interacting units but also by the adaptation of non-planar porphyrins for the synthesis of porous structures. The latter are applied for film formation and sensing involving nanomechanical sensors. Selectivity and mechanisms of sensing activity are discussed. We will also introduce new efficient singlet oxygen generating materials based on agglomeration of an oxidized porphyrin chromophore as metal-organic frameworks,2 electron deficient porous polymers, or using resorcinarenes.3 The use of these materials for selective oxidation of organic substrates is demonstrated. Overall, the results demonstrate the efficacy of the chromophore approach to functional materials. The self-assembly properties of porphyrins and nitrogen rich acene compounds, the pyrazinacenes, will also be considered based on contrasting cases of on-surface mobility and immobility, and the introduction of particular functionality influencing the resulting supramolecular structures.

Performance study of an optical modulator based on a funnel-shaped waveguide with tip-plasma effect

Electro-optical modulators play a crucial role in the field of optical communications; high modulation depth and low loss are used to qualify optical modulators. In this study, the tip-plasmon effect was utilized to improve the optical mode confinement and achieve a significant enhancement of the optical-graphene coupling. The evaluated modulator demonstrates robust performance characteristics, exhibiting a modulation depth of up to 8.5 dB/µm while sustaining a transmission loss of 2.3 dB/µm. Furthermore, the modulator operates with an energy efficiency of 4.36 fJ/bit and achieves a modulation bandwidth of 293 GHz, assuming a modulation length of 20 µm.

Vibration-Induced Sweeping Operation in Fiber Lasers

A new vibration-based mechanism of optical frequency/wavelength sweeping in fiber lasers induced by optical path length modulation of a laser cavity section is proposed. The mechanism is implemented for an erbium-doped fiber ring laser with a saturable absorber. Without the vibrations, the laser generates a single longitudinal mode (SLM) radiation. We show experimentally for the first time that mechanical vibrations of the laser cavity section can lead to mode dynamics in both frequency and time domains. The possibility of obtaining various mode dynamics, such as vibration-induced sweeping in a wavelength range of up to 2.2 nm or SLM generation with periodic mode hopping between two fixed longitudinal modes depending on the pump wavelength, is experimentally shown. In this vibration-based approach, the interval between changes in the laser cavity modes has good stability, because it directly relates to the vibration period.

Multiple Chirality Switching of a Dye‐Grafted Helical Polymer Film Driven by Acid & Base

AbstractA stimuli‐responsive multiple chirality switching material, which can regulate opposed chiral absorption characteristics, has great application value in the fields of optical modulation, information storage and encryption, etc. However, due to the rareness of effective functional systems and the complexity of material structures, developing this type of material remains an insurmountable challenge. Herein, a smart polymer film with multiple chirality inversion properties was fabricated efficiently based on a newly‐designed acid & base‐sensitive dye‐grafted helical polymer. Benefited from the cooperative effects of various weak interactions (hydrogen bonds, electrostatic interaction, etc.) under the aggregated state, this polymer film exhibited a promising acid & base‐driven multiple chirality inversion property containing record switchable chiral states (up to five while the solution showed three‐state switching) and good reversibility. The creative exploration of such a multiple chirality switching material can not only promote the application progress of current chiroptical regulation technology, but also provide a significant guidance for the design and synthesis of future smart chiroptical switching materials and devices.

Retina‐Like Chlorophyll Heterojunction‐Based Optoelectronic Memristor with All‐Optically Modulated Synaptic Plasticity Enabling Neuromorphic Edge Detection

AbstractOptoelectronic memristors, which possess the potential capacities of in‐sensor computing, promote the development of highly efficient neuromorphic vision. In this work, a novel optoelectronic memristor based on chlorophyll (Chl) heterojunction is proposed, which consists of two types of Chl derivatives (zinc methyl 3‐devinyl‐3‐hydroxymethyl‐pyropheophorbide‐a and methyl 131‐deoxo‐131‐dicyanomethylene‐pyropheophorbide‐a). Chl heterojunction improves the optoelectronic performance of the device due to its ability to efficiently separate photogenerated electron‐hole pairs. The device exhibits the synaptic potentiation and inhibition behaviors under light stimulations of 430 and 730 nm, respectively, thus demonstrating the all‐optically modulated synaptic plasticity. The switching mechanism can be attributed to the photo‐ionization/deionization of oxygen vacancies at the zinc oxide (ZnO)/Chl interface. In addition, the image pre‐processing functions of contrast enhancement and noise reduction are implemented in a memristive array. In particular, the edge detection function has been implemented by utilizing reversible optical modulation, which highlights the object outline. The optoelectronic memristor based on the Chl heterojunction proposed here provides a promising foundation for advancing neuromorphic vision.

Multiple Chirality Switching of a Dye-Grafted Helical Polymer Film Driven by Acid & Base.

A stimuli-responsive multiple chirality switching material, which can regulate opposed chiral absorption characteristics, has great application value in the fields of optical modulation, information storage and encryption, etc. However, due to the rareness of effective functional systems and the complexity of material structures, developing this type of material remains an insurmountable challenge. Herein, a smart polymer film with multiple chirality inversion properties was fabricated efficiently based on a newly-designed acid & base-sensitive dye-grafted helical polymer. Benefited from the cooperative effects of various weak interactions (hydrogen bonds, electrostatic interaction, etc.) under the aggregated state, this polymer film exhibited a promising acid & base-driven multiple chirality inversion property containing record switchable chiral states (up to five while the solution showed three-state switching) and good reversibility. The creative exploration of such a multiple chirality switching material can not only promote the application progress of current chiroptical regulation technology, but also provide a significant guidance for the design and synthesis of future smart chiroptical switching materials and devices.

Performance testing of a novel short axis photomultiplier tube for the HUNT project

Photomultiplier tubes (PMTs) with large-area cathodes are increasingly being used in cosmic-ray experiments to enhance detection efficiency. The optical modules (OMs) of the High-Energy Underwater Neutrino Telescope (HUNT) have employed a brand new N6205 20-inch microchannel plate photomultiplier tube (MCP-PMT) developed by the North Night Vision Science & Technology (Nanjing) Research Institute Co. Ltd. (NNVT). In order to make the 20-inch PMT fit into the 23-inch diameter pressure-resistant glass sphere, NNVT improved the internal structure of PMT and shortened the height of PMT by more than 10 cm. The first batch of these PMTs has been delivered for preliminary research work. This paper describes a specific PMT testing platform built for the first batch of 15 MCP-PMTs, and some performance parameters of PMT, such as peak-to-valley ratio, TTS and nonliniearity, are measured. The measurement results show that the new PMT still has good performance and can meet the requirements of HUNT project.

Electric tuning of plasmonic resonances in ultrathin gold nanoribbon arrays

Ultrathin plasmonic nanostructures offer an unparalleled opportunity for the study of light–matter interactions at the nanoscale and realization of compact nanophotonic devices. In this study, we introduce an ultrathin gold nanoribbon array and demonstrate an electric approach to actively tuning its plasmonic resonance, which leveraging the extreme light confinement capability in the ultrathin plasmonic nanostructure and a robust nanoscale electro-optical effect in indium tin oxide. Optimizing the design (to a total thickness as small as 12 nm for a 2-nm-thick gold nanoribbon array), we numerically demonstrate a spectral shift in the plasmonic resonance up to 36 nm along with an approximately 16% change in the transmission at a gate voltage below 1.7 V at the wavelength of 1.47 μm. This work presents progress towards electric tuning of plasmonic resonances in ultrathin metallic nanostructures for various applications including surface-enhanced spectroscopy, spontaneous emission enhancement, and optical modulation.

Advancing large-scale thin-film PPLN nonlinear photonics with segmented tunable micro-heaters

Thin-film periodically poled lithium niobate (TF-PPLN) devices have recently gained prominence for efficient wavelength conversion processes in both classical and quantum applications. However, the patterning and poling of TF-PPLN devices today are mostly performed at chip scales, presenting a significant bottleneck for future large-scale nonlinear photonic systems that require the integration of multiple nonlinear components with consistent performance and low cost. Here, we take a pivotal step towards this goal by developing a wafer-scale TF-PPLN nonlinear photonic platform, leveraging ultraviolet stepper lithography and an automated poling process. To address the inhomogeneous broadening of the quasi-phase matching (QPM) spectrum induced by film thickness variations across the wafer, we propose and demonstrate segmented thermal optic tuning modules that can precisely adjust and align the QPM peak wavelengths in each section. Using the segmented micro-heaters, we show the successful realignment of inhomogeneously broadened multi-peak QPM spectra with up to 57% enhancement of conversion efficiency. We achieve a high normalized conversion efficiency of 3802% W−1 cm−2 in a 6 mm long PPLN waveguide, recovering 84% of the theoretically predicted efficiency in this device. The advanced fabrication techniques and segmented tuning architectures presented herein pave the way for wafer-scale integration of complex functional nonlinear photonic circuits with applications in quantum information processing, precision sensing and metrology, and low-noise-figure optical signal amplification.

Dynamic multicolor electrochromic skin in high-brightness flexible WO3/Au asymmetric Fabry–Perot nanocavity fabricated on Nylon 66 porous substrate

Recently, the Fabry–Perot (F–P) cavity electrochromic devices, which are constructed by combining nano-size inorganic electrochromic material WO3 and reflective metal layers, have attracted considerable attention due to their potentials in the fields of dynamic multicolor displays and active camouflage. However, in the few studies that have been reported, the peak reflectance of flexible F–P cavity multicolor electrochromic devices in the visible wavelength band is generally lower than 30 %, which limits their reflective display and camouflage effects in high-brightness environments. Thus, we have combined multicolor reflective electrochromic electrodes in WO3/Au asymmetric F–P nanocavity constructed by magnetron sputtering on a Nylon 66 porous substrate with a highly transparent UV-cured gel electrolyte and a PET plastic sealing procedure. As a result, a flexible and dynamic multicolor electrochromic skin with high reflectance (Rmax＞50 %) and excellent flexibility (bending radius of 4 mm) has been fabricated. The WO3 electrochromic layer at the top works as the dynamic dielectric layer in the broadband absorption Fabry–Perot cavity, and the inert metal Au layer at the bottom works as the reflective layer. The WO3/Au asymmetric F–P cavity can acutely capture the variation in optical constants of WO3 due to the thickness change and electric-driven effects. This cavity facilitates the selective reflection and absorption of the energy distribution of the spectrum after the induced interferometric resonance. As a result, the cavity exhibits a rich array of structural colors, including ocher, taupe, yellow, orange, green, and violet. The electrochromic skin exhibits a fast switching time and maintains 99.43 % of the optical modulation amplitude (ΔR) after 110 coloring/bleaching cycles. It provides a potential option in the field of flexible high-brightness reflective displays and dynamic camouflage in the future.

Conceptional Pure-Tungsten Metasurfaces Based on Femtosecond Laser Nanomanufacturing

A laser-induced periodic surface structure (LIPSS), which can be easily produced by femtosecond laser ablation, is a unique nanostructure with a visible refractive color that can be controlled by altering its orientation and uniformity, making it suitable for use in colorful marking, camouflage, and anti-counterfeiting measures. However, single-mode information camouflage can no longer meet increasingly higher-level security requirements. Therefore, metasurfaces offer revolutionary solutions. In this study, conceptual metasurfaces of pure tungsten are theoretically proposed and verified using hierarchical LIPSS/nanoparticle (NP) nanostructures as meta-atoms. The anisotropy of the LIPSS nanostructure enables polarization-sensitive optical modulation, whereas the spatial configuration, particle size, and period of LIPSS in the LIPSS/NP meta-atoms provide flexibility for tailoring broadband optical responses. In x-polarization, the LIPSS/NP meta-atom system provides more visible colors and divergent infrared absorbance (emission) than in y-polarized and unpolarized modes, paving the way for vividly colorful polarization-sensitive displays and information camouflage in infrared bands. A simplified rendition of the world-famous painting “The Starry Night” by Van Gogh is used as a proof-of-concept. Preliminary experimental results are presented, based on which the feasibility and challenges for laser nanomanufacturing of the proposed conceptual metasurfaces are discussed, aiming to provide inspiration for the development of novel metasurfaces through interdisciplinary studies.