Olga Lozhkina, Ruth Pinheiro Muniz, Shivam Singh
et al.
The growing demand for advanced data storage and signal processing technologies has intensified the search for novel materials with tunable optical and electronic properties. Chiral 2D perovskites have emerged as promising candidates due to their unique ability to selectively absorb and emit circularly polarized light, as well as to interact with polarizable currents. To exploit these properties in applications, chiral 2D perovskites should be integrated as thin films in various device architectures, yet the means to control their crystallization and film formation processes remain underdeveloped. This study demonstrates that additive engineering can be applied to control the microstructure and strain in chiral 2D perovskite thin films. It is shown that the addition of small amounts of hypophosphorous acid to the precursor solution of (R‐3BrPEA)2PbI4 chiral perovskites results in the dissolution of colloids, leading to a significant increase in the grain size and a release of lattice strain. Consequently, the intensity of their photoluminescence is significantly enhanced, demonstrating that grain boundaries and strain lead to nonradiative recombination losses in chiral 2D perovskites. The findings motivate the exploration of novel additive engineering approaches to improve the optoelectronic quality of chiral 2D perovskite thin films.
Photoacoustic microscopy (PAM) enables label-free, quantitative imaging of blood flow and oxygenation in vivo, offering critical insights into microvascular function and tissue metabolism. However, current flow quantification methods suffer from poor accuracy at extreme flow speeds and high computational costs. We present Hybrid Fourier-Derivative Analysis (HFDA), a new method based on frequency analysis of flow-induced modulations in photoacoustic amplitude. Compatible with standard raster scanning, HFDA adaptively integrates Fourier analysis for high-speed flow and derivative analysis for low-speed flow, achieving high accuracy and computational efficiency. Phantom studies validate the accuracy of HFDA across 0.2–20 mm/s, with errors typically less than 7 %. Compared to correlation-based methods, HFDA reduces computational time by 35-fold. In vivo demonstrations in mouse models of hypoxia and hypercapnia further underscore the potential of HFDA as a rapid and precise tool for blood flow quantification in functional and metabolic PAM studies.
Photoacoustic spectroscopy is a powerful tool for investigating semiconductors and determining some of their basic properties. However, generating a signal that is large enough for the investigated samples is still challenging. To address this, the focus is on enhancing photoacoustic (PA) signal intensity in a non-complex way, which does not require changing any part of an experimental setup. The PA signal intensity enhancement is mainly achieved by manipulating the sample volume and its surroundings. MoS2, a layered material that belongs to the van der Waals crystals was selected due to ease of exfoliation to the proper thickness. A reduction in MoS2 thickness from 112 to 7 µm, resulted in enhancement of the PA signal by a factor of ∼50. A simple model has been proposed to describe the results based on thermal processes. Additionally, a method to determine the energy gap in transition metal dichalcogenides from PA measurements is presented.
Gediminas Juska, Simone Varo, Nicola Maraviglia
et al.
This work presents a practical realization of a foundational approach for fabricating arrays of self‐aligned micro‐ and nanopillar structures incorporating individual site‐controlled quantum dots (QDs) for bright nonclassical light extraction. This method leverages the nonplanar surface morphology of pyramidal QD samples to define dielectric masks self‐aligned to the QD positions. The mask size and consequently the lateral dimensions of the pillars, are precisely controlled through a chemical mechanical polishing (CMP) step, obviating the need for any additional lithography step for creating the pillar. This fabrication technique offers several key advantages, including precise control over the pillar sites, and fully deterministic embedding of QD structures. The functionality of the structures is validated by integrating single In0.25Ga0.75 As QDs—upon two‐photon excitation (TPE) of the biexciton state, the emission of single and polarization‐entangled photon pairs is observed. Additionally, an extra fabrication step to deposit dome‐like structures atop the pillars was demonstrated, resulting in a total light extraction efficiency of 9.5% at the first lens—a record within the pyramidal QD family.
Camila Aparecida Zimmermann, Koffi Novignon Amouzou, Dipankar Sengupta
et al.
Abstract Novel poly(dimethylsiloxane) (PDMS) doped with two different spiropyran derivatives (SP) were investigated as potential candidates for the preparation of elastomeric waveguides with UV-dependent optical properties. First, free-standing films were prepared and evaluated with respect to their photochromic response to UV irradiation. Kinetics, reversibility as well as photofatigue and refractive index of the SP-doped PDMS samples were assessed. Second, SP-doped PDMS waveguides were fabricated and tested as UV sensors by monitoring changes in the transmitted optical power of a visible laser (633 nm). UV sensing was successfully demonstrated by doping PDMS using one spiropyran derivative whose propagation loss was measured as 1.04 dB/cm at 633 nm, and sensitivity estimated at 115% change in transmitted optical power per unit change in UV dose. The decay and recovery time constants were measured at 42 and 107 s, respectively, with an average UV saturation dose of 0.4 J/cm2. The prepared waveguides exhibited a reversible and consistent response even under bending. The sensor parameters can be tailored by varying the waveguide length up to 21 cm, and are affected by white light and temperatures up to 70 ℃. This work is relevant to elastomeric optics, smart optical materials, and polymer optical waveguide sensors. Graphical Abstract
This article demonstrates with simulations two polarization independent wavelength division multiplexing receiver platforms based on thin silicon nitride waveguides for optical interconnects at 1 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m. The chosen waveguide base geometry (width = 900 nm × height = 160 nm) is a good tradeoff between mode confinement and propagation loss. We first propose a design using a polarization splitter with an 1×4 demultiplexer based on an arrayed waveguide grating (AWG). This receiver has a reduced size and requires only one etching step. We later propose another simplified receiver design using a polarization splitter-rotator with two identical 1×4 demultiplexers based on cascaded Mach-Zehnder interferometers. The rotator is based on a thicker waveguide (width = 500 nm × height = 400 nm) and is partially etched to rotate the electric field by 90<inline-formula><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula>. Thus, it requires the use of mode size converters at the in/output ports. To keep the fabrication complexity as low as possible for the second design, we limited ourselves to only two etching steps. Therefore, the thickness of the slab of the mode converters and of the rotator is the same as for the main 900 nm (wide) × 160 nm (thick) waveguide. The simulated extinction ratio of the polarization splitter at 1035 nm is 18 dB and the calculated TM-TE and TE-TM polarization conversion efficiency of the polarization rotator at 1035 nm is 99.9<inline-formula><tex-math notation="LaTeX">$\%$</tex-math></inline-formula>.
Fourier ptychography (FP) is a computational imaging technique with the advantage that it can obtain large field-of-view (FOV) and high-resolution (HR) imaging. We propose an algorithm for Fourier ptychography based on reweighted amplitude flow (RAF) with regularization by denoising (RED) and deep decoder (DD), which is an untrained deep generative model. The proposed method includes two loops, using reweighted amplitude flow with regularization by denoising as an inner loop for phase retrieval and deep decoder for further denoising as an outer loop in the Fourier ptychography recovery system. The proposed method does not need any training dataset, just adds a little computer time during the image recovery process. The proposed method has no bias due to training images, which is different from other deep learning methods. The experimental results show that the proposed method can improve the reconstruction quality in both PSNR and SSIM.
The forward-reverse framework based on machine learning for MASnxPb1-xI3 perovskite solar cells is reported. The practicability of bandgap model revealing asymmetrically-bowing shape and optimized Sn:Pb ratio are verified by experiments.
Near-infrared (NIR) light has been shown to produce a range of physiological effects in humans, however, there is still no agreement on whether and how a single parameter, like the flicker frequency of NIR light, affects the brain. An 810nm NIR LED was used as the stimulator. Fifty subjects participated in this experiment. Forty subjects were randomly divided into four groups. Each group underwent a 30-minute NIR LED radiation with four different frequencies (i.e., 0Hz, 5Hz, 10Hz and 20Hz, respectively) on the forehead. The remaining 10 subjects formed the control group, in which they underwent a 30-minute rest period without light radiation. EEG signals of all subjects during each test were recorded. Gravity frequency (GF), relative energy change, and sample entropy were analyzed. The experimental groups had larger GF values compared to the control group. Higher stimulation frequency would cause larger growth of GF (F=14.75, P<0.001). The amplitude of alpha waves relative energy increased, while theta waves decreased remarkably in the experimental groups (p<0.02), and the extent of increase/decrease was larger at higher stimulation frequency, compared to that of the control. Sample entropy of electrodes in the frontal areas were much larger than those in other brain areas in the experimental groups (p<0.001). Larger frequency of the NIR LED light would cause more distinct brain activities in the stimulated areas. It indicates that NIR LED light may have a positive effect on modulating brain activity. These results may help improve the design of photobiomodulation treatments in the future.
Perovskite solar cells (PSCs) have shown remarkable photovoltaics progress with a record‐eminent power conversion efficiency (PCE) of 25.2%. Therefore, the PSCs are potential candidates to replace traditional crystalline silicon‐based solar cells. However, the PCE and stability of PSCs need to be improved for successful commercialization. Recently, the atomic layer deposition (ALD) technology is successfully applied to fabricate the encapsulation layer, which overcomes the long‐standing issues of perovskite‐based solar cells based on others’ pioneering work on ALD in PSCs several years ago. The organic–inorganic alternating encapsulation structure that the team researched has exhibited a water vapor transmittance rate of 1.3 × 10−5 g m−2 day−1, which is the lowest value among the reported thin‐film encapsulation layers of PSCs. Herein, the properties of ALD and how it is used in PSCs, such as device architecture, surface modification, passivation, and encapsulation, which result in higher PCEs and excellent stability, are discussed. In addition, the potential significance of applying ALD in the manufacture of tandem and flexible PSCs and the synthesis of high‐quality perovskite materials is also analyzed.
We propose and demonstrate a rectangular optical lattice filter with reconfigurable bandwidth and wavelength. The proposed reconfigurable rectangular lattice filter consists of three-stage cascaded ring-assisted Mach-Zehnder interferometers (RAMZIs), and each RAMZI unit serves as an approximate optical elliptical filter with optimized shape factor. The scheme and design principle are presented with the method of zero-pole theory. As a proof of concept, the proposed structure is fabricated on the Si<inline-formula><tex-math notation="LaTeX">$_3$</tex-math></inline-formula> N<inline-formula><tex-math notation="LaTeX">$_4$</tex-math></inline-formula> waveguide platform. In the experiment, the 3-dB bandwidth of the proposed filter can be continuously tuned from 14.1 GHz to 4.1 GHz, maintaining a rectangular transmission response, and the wavelength can also be continuously tuned. This reconfigurable rectangular optical lattice filter shows the potential in many practical applications for reconfigurable optical signal processing due to flexibility and reconfigurability.
Assuming weakly guiding approximation, we examine orbital angular momentum (OAM) mode mixing on account of ellipticity in a fiber and derive a complete set of analytic expressions for spatial crosstalk, using scalar perturbation theory that incorporates fully the existing degeneracy between a spatial OAM mode and its degenerate partner characterized by a topological charge of opposite sign. These expressions, consequently, include an explicit formula for calculating the <inline-formula><tex-math notation="LaTeX">$2\pi$</tex-math></inline-formula> walk-off length over which an input OAM mode converts into its degenerate partner, and back into itself. We further explore the applicability of the derived expressions in the presence of spin-orbit interaction. The expressions constitute a useful mathematical tool in the analysis and design of fibers for spatially-multiplexed mode transmissions. Their utility is demonstrated with application to a few mode and a multimode step-index fiber.
Cinnamaldehyde- (CMA-) modified coal tar pitches (CTPs) are prepared in the presence of acids. In this paper, the effect of boric acid and p-toluene sulfonic acid on the pyrolysis and graphitization process of CMA-modified CTP was studied. The pyrolysis process was studied by Fourier transform infrared spectroscopy, thermogravimetric analysis and derivative thermogravimetry, and polarized-light microscopy. In addition, the graphitization process was studied by X-ray diffraction and Raman spectroscopy. The results indicate the carbon yield of CMA-modified CTP with boric acid as catalyst (B7C10) is higher than that of CMA-modified CTP with p-toluene sulfonic acid as a catalyst (P7C10). In addition, under the same experimental condition (heated at 400°C and held for 1 h), the mesophase spheres of B7C10 are more regular than those of P7C10 and the largest diameter of the mesophase spheres can reach to 40 um. Further, after the graphitization process, the graphitization degree of B7C10 is higher than that of P7C10. So, it is more effective to modify CTP with boric acid as a catalyst.
Abstract Background Integral imaging is considered one of the most promising three-dimensional display technologies, while the limited viewing angle is regarded as a primary disadvantage of integral imaging display to reach a commercial level. This paper proposes a viewing angle enhancement method for both liquid crystal display (LCD) and the projection-type three-dimensional integral imaging system. Methods The proposed wide-viewing integral imaging system is established by using the lenslet array coupling with the polarizers, light barriers, and enlarged elemental images array. The size of light barrier and polarizer is equal to the pitch of each lenslet, the light barrier prevents light rays from passing through, and the polarizer controls the passage of light ray in the specific polarization direction. In the projection-type integral imaging system, two orthogonal elemental images arrays (EIA) are projected onto the projection screen simultaneously by the corresponding projectors. In LCD integral imaging system, two orthogonal EIAs are displayed by use of an LCD screen which can switch the polarization direction of the EIA by time-multiplexed technology within the time constant of the eyes’ response time. Results The viewing angle can be enlarged dramatically by the improvement of the size of each elemental image according to the integral imaging principles. The experimental result shows that the proposed method exhibits approximately four times the viewing angle of conventional integral imaging with the same lens array. Conclusions The increment of viewing angle can be determined by the number of light barriers between two adjacently orthogonal polarizers, the more the light barrier, the larger the viewing angle.
In this study we present a new method useful in collecting upwelling radiance (Lu) from a platform submerged in a hydrographic sub-hull or moon pool of a research vessel. The information analyzed here was obtained during a field campaign in the Northwestern European shelf seas aboard the new research vessel SONNE. As the platform was located at the center of the ship, there is minimal effect from pitch and roll which is known to influence upwelling radiance observations. A comparison of the measurements from this platform with a free falling hyperspectral profiler was performed to determine the degree of uncertainty that results from ship shadow. For given Lu(λ) in situ data we observed ±33% intensity deviations compared to profiling measurements that can be attributed to instrument shading during moon pool installation and environmental perturbations. Furthermore Lu(l) in situ spectra variations were observed at lower wavelengths, therefore a form fitting algorithm was adapted to receive corresponding depths with identical spectral form from Lu(z, λ) profiler casts. During an east to west transect in North Sea with a schedule speed up to 12 knots in situ radiance reflectance rrs(7, λ) measurements at 7 meter depth were performed with this novel radiometer setup. In spite of any restrictions originating from the sub-hull installation, water masses mixing zone from CDOM dominated coastal waters in the Skagerrak Strait towards the open North Sea were successfully derived thus offering an underway applicable upwelling radiance sensing not suffering from sun glint or other typical restrictions of above water radiometer installations.
A novel analog photonic link with enhanced spurious-free dynamic range (SFDR) based on an integrated electro-optic dual-polarization modulator is presented and demonstrated. The dual-polarization modulator, which consists of a polarization beam splitter, a polarization beam combiner, and two <inline-formula> <tex-math notation="LaTeX">$z$</tex-math></inline-formula>-cut LiNbO<sub>3</sub> MZMs, can achieve complementary intensity modulation along the orthogonal polarization directions with different modulation indexes. By properly adjusting the power relationship of the orthogonal polarization directions, two third-order intermodulation distortions (IMD3) have equal intensity and opposite phase and cancel each other out. Combined with a low-biasing technique to reduce the noise power, the SFDR of the link can be further improved. A theoretical analysis is presented and validated by a simulation. The IMD3 can be suppressed by 30.6 dB, giving an improvement in SFDR of about 22 dB compared with a conventional optical double-sideband modulation link.
Vandna Nishal, Devender Singh, Raman Kumar Saini
et al.
Synthesis and photoluminescent behaviour of mixed ligand based beryllium complexes with 2-(2-hydroxyphenyl)benzoxazole (HPB) and 5-chloro-8-hydroxyquinoline (Clq) or 5,7-dichloro-8-hydroxyquinoline (Cl2q) or 2-methyl-8-hydroxyquinoline (Meq) or 8-hydroxyquinoline (q) are reported in this work. These complexes, that is, [BeHPB(Clq)], [BeHPB(Cl2q)], [BeHPB(Meq)], and [BeHPB(q)], were prepared and their structures were confirmed by elemental analysis, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and thermal analysis. The beryllium complexes exhibited good thermal stability up to ~300°C temperature. The photophysical properties of beryllium complexes were studied using ultraviolet-visible absorption and photoluminescence emission spectroscopy. The complexes showed absorption peaks due to π-π∗ and n-π∗ electronic transitions. The complexes emitted greenish blue light with peak wavelength at 496 nm, 510 nm, 490 nm, and 505 nm, respectively, consisting of high intensity. Color tuning was observed with changing the substituents in quinoline ring ligand in metal complexes. The emitted light had Commission Internationale d’Eclairage color coordinates values at x=0.15 and y=0.43 for [BeHPB(Clq)], x=0.21 and y=0.56 for [BeHPB(Cl2q)], x=0.14 and y=0.38 for [BeHPB(Meq)], x=0.17 and y=0.41 for [BeHPB(q)]. Theoretical calculations using DFT/B3LYP/6-31G(d,p) method were performed to reveal the three-dimensional geometries and the frontier molecular orbital energy levels of these synthesized metal complexes.