Most of the existing carbon dot (CD)-based afterglow materials are limited to a single emission mode of either room-temperature phosphorescence (RTP) or delayed fluorescence (DF), which makes it difficult to meet the application requirements of advanced anti-counterfeiting and multi-level information encryption. Therefore, the development of CD-based composite materials with multi-mode afterglow emission, long lifetime and high stability holds significant research significance and application value. In this study, long-afterglow manganese/nitrogen co-doped CDs@boric acid (BA) composites (Mn, N-CDs @BA) are successfully prepared, and their optical properties and emission mechanism are clarified. The results demonstrate that the Mn, N-CDs @BA composites exhibit wavelength-dependent dual-afterglow emission characteristics of RTP and DF. Under 254 nm ultraviolet (UV) light excitation, they exhibit DF emission with an average lifetime of 903.36 ms. Under 365 nm UV light excitation, RTP emission with an average lifetime of 354.43 ms is observed. Moreover, the afterglow color exhibits time dependence. Based on the triple emission modes (fluorescence, RTP and DF) of the Mn, N-CDs @BA composites, optical patterns were designed and fabricated, and counterfeit-resistant and unclonable anti-counterfeiting and high concealment information encryption were successfully achieved. This work develops a potentially feasible approach for next-generation advanced optical anti-counterfeiting and information encryption systems.
Noor Abdulqader Hamdullah, Mesut Çevik, Hameed Mutlag Farhan
et al.
Due to increasing human activities underwater, there is a growing demand for high-speed underwater optical communication (UOWC) data links for security surveillance, environmental monitoring, pipeline inspection, and other applications. Line-of-sight communication is impossible under certain conditions due to misalignment, physical obstructions, irregular usage, and difficulty adjusting the receiver orientation, especially when used in environments with mobile users or submerged sensor networks. Therefore, non-line-of-sight (NLOS) optical communication is used in this study. Advanced modulation schemes—quadrature amplitude modulation and orthogonal frequency-division multiplexing (QAM-OFDM)—were used to transmit the signal underwater between two network nodes. QAM increases the data transfer rate, while OFDM reduces dispersion and inter-symbol interference (ISI). The proposed UOWC system is investigated using a 532 nm green laser diode (LD). Reliable high-speed data transmission of up to 15 Gbps is achieved over horizontal distances of 134 m, 43 m, 21 m, and 5 m in four different aquatic environments—pure water (PW), clear ocean (CLO), coastal ocean (COO), and harbor II (HarII), respectively. The system achieves effectively error-free performance within the simulation duration (BER < 10<sup>−9</sup>), with a received optical signal power of approximately −41.5 dBm. Clear constellation patterns and low BER values are observed, confirming the robustness of the proposed architecture. Despite the limitations imposed by non-line-of-sight (NLOS) communication and the diversity aquatic environments, our proposed architecture excels at underwater long-distance data transmission at high speeds.
The elliptical cylindrical mirror has been utilized in neutron small-angle scattering and reflectometry to enhance the neutron intensity at the sample position. However, the performance of the elliptical cylindrical mirror can be impacted by surface slope errors, reflectivity, and misalignments. In this work, the performance of the elliptical cylindrical mirror under different error conditions has been analyzed comprehensively, and a 250-mm-long elliptical cylindrical mirror was designed and developed. The simulations show that a source size below 1 mm is required to achieve a peak gain above 6, with a theoretical peak gain of 16× with a 0.1 mm source. The rotational misalignment of 0.03° around the <i>Y</i>-axis can decrease gain from 16× to 6×. The designed mirror was fabricated with a surface figure error of 110 nm (RMS), and a roughness below 0.5 nm (RMS), and was coated with an <i>m</i> = 4 supermirror. The mirror was aligned and tested in the dedicated neutron beamline of the Chinese mianyang research reactor, and the results show a peak gain of 12.77 with a 0.1 mm slit source.
Abstract In this paper, we report a coherent beam combining (CBC) system that involves two thulium-doped all-polarization maintaining (PM) fiber chirped pulse amplifiers. Through phase-locking the two channels via a fiber stretcher by using the stochastic parallel gradient descent (SPGD) algorithm, a maximum average power of 265 W is obtained, with a CBC efficiency of 81% and a residual phase error of λ/17. After de-chirping by a pair of diffraction gratings, the duration of the combined laser pulse is compressed to 690 fs. Taking into account the compression efficiency of 90% and the main peak energy proportion of 91%, the corresponding peak power is calculated to be 4 MW. The laser noise characteristics before and after CBC are examined, and the results indicate that the CBC would degrade the low frequency relative intensity noise (RIN), of which the integration is 1.74% in [100 Hz, 2 MHz] at the maximum combined output power. In addition, the effects of the nonlinear spectrum broadening during chirped pulse amplification on the CBC efficiency are also investigated, showing that a higher extent of pulse stretching is effective in alleviating the spectrum broadening and realizing a higher output power with decent combining efficiency. Graphical Abstract
Industrial-grade optical semiconductor films have attracted considerable research interest because of their potential for wafer-scale mass deposition and direct integration with other optoelectronic wafers. The development of optical thin-film processes that are compatible with complementary metal-oxide-semiconductor (CMOS) processes will be beneficial for the improvement of chip integration. In this study, a multilayer periodically structured optical film containing Fabry–Perot cavity was designed, utilizing nine pairs of SiN/SiO<sub>2</sub> dielectrics. Subsequently, the multilayer films were deposited on Si substrates through the inductively coupled plasma chemical vapor deposition (ICPCVD) technique, maintaining a low temperature of 80 °C. The prepared films exhibit narrow bandpass characteristics with a maximum peak transmittance of 76% at 690 nm. Scanning electron microscopy (SEM) shows that the film structure has good periodicity. In addition, when the optical films are exposed to p/s polarized light at different angles of incidence, the cavity mode of the film undergoes a blueshift, which greatly affects the color appearance of the film. As the temperature rises, the cavity mode undergoes a gradual redshift, while the full width at half maximum (FWHM) and quality factor remain relatively constant.
We demonstrate that by using a cascaded configuration of five solid-core photonic crystal fiber (PCF) samples with progressively decreasing core diameters, ultraviolet light with wavelengths as short as ∼300 nm can be generated in a supercontinuum (SC) set-up. With a nanosecond laser as the pump light, the modulation instability effect leads to the generation of multiple optical solitons in the first PCF sample which has a close-to-zero dispersion value at the pump wavelength (∼1064 nm). The following PCF samples with decreasing core diameters enhance the waveguide nonlinearity, and at the same time provide continuously-shorter phase-matching wavelengths for dispersive-wave emission, thereby pushing the short-wavelength edge of the SC spectrum into the deep ultraviolet spectral region. While the PCF splicing technique ensures the compactness of this SC set-up, the generated SC spectrum, spanning ∼350 nm to ∼2000 nm with a flat spectral profile, may be applied in fluorescence microscopy and biochemical imaging.
While most single‐nanocrystal spectroscopy experiments rely on fluorescent emission, recent years have seen an increasing number of experiments based on absorption and scattering, enabling to correlate those with fluorescence intermittency. Herein, it is shown that nonlinear scattering by second‐harmonic generation can also be measured from single CdSe/CdS core/shell nanoplatelets (NPLs) alongside fluorescence despite the weak scattering signal. It is shown that even under resonant two‐photon conditions the second‐harmonic scattering signal is uncorrelated with fluorescence intermittency and follows Poisson statistics.
This research is intended to provide an initial solution to the problem of finding images for processing by photogrammetry in special cases where these do not exist. An overview of existing artificial intelligence-based algorithms that enable the extension of source image dataset is reported. In particular, this research focused on the use of prompt-to-image systems for obtaining images to be used in reconstruction and then in the next step of 3D modelling. Thus, the combined use of these three techniques, AI, photogrammetry, and modelling allowed the creation of a model of a building that never existed except in the collective imagination, which is the tower of Babel. In particular, the case study chosen is the illustration in Kircher book present in the library of the Brixen seminary that is closed to the public and for which it was necessary to create a tool to enhance the value and knowledge of this heritage for external users. Therefore, the creation of an augmented reality app enabled the visualization of the model created by offering possibilities for immersive experiences and dissemination of the research to a wide audience.
Visible-wavelength very large-scale integration photonic circuits have a potential to play important roles in quantum information and sensing technologies. The realization of scalable, high-speed, and low-loss photonic mesh circuits depends on reliable and well-engineered visible photonic components. Here, we report a low-voltage optical phase shifter based on piezo-actuated mechanical cantilevers, fabricated on a CMOS compatible, 200 mm wafer-based visible photonics platform. We show linear phase and amplitude modulation with 6 Vπ cm in differential operation, −1.5 to −2 dB insertion loss, and up to 40 dB contrast in the 700–780 nm range. By adjusting selected cantilever parameters, we demonstrate a low-displacement and a high-displacement device, both exhibiting a nearly flat frequency response from DC to a peak mechanical resonance at 23 and 6.8 MHz respectively, which, through resonant enhancement of Q ∼ 40, further decreases the operating voltage down to 0.15 Vπ cm.
We propose a pipeline for the detection as well as modeling of individual buildings based on multi-source images. It allows to consistently reconstruct whole buildings at Level of Detail 3 (LoD3): the roof from airborne images and the facades including elements such as windows and doors mainly from terrestrial images. We employ a parametrized top-down model – the “shell model” – with the roof as well as the facades semantically and geometrically integrated. This generative model fosters stability for building detection by enabling the use of multi-source data and offers flexibility in modeling by means of a fully CAD-compatible integration of building components. Experiments performed on imagery from different terrestrial and airborne (Unmanned Aerial Vehicle – UAV) cameras demonstrate the potential of the approach.
Fabio Pavanello, Anton Vasiliev, Muhammad Muneeb
et al.
We demonstrate a broadband digital Fourier Transform (dFT) spectrometer addressing wavelength monitoring applications in the 2.3-<inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m wavelength range. The spectrometer is built in a silicon-on-insulator platform and the design allows its fabrication with CMOS-compatible tools. We report an operating bandwidth of 130 nm around 2.3-<inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m wavelength using an efficient algorithm for sparse spectra to retrieve the wavelength with an accuracy of 100 pm. The spectrometer can also resolve two laser lines up for dFT spectrometers, which takes advantage of the sparse nature of the spectrum.
We propose and experimentally demonstrate a photonic millimeter-wave frequency divider based on a super-harmonic injection-locked optoelectronic oscillator (OEO) and an optical frequency comb. The optical frequency comb generator is incorporated into an OEO loop to create broadband comb lines with low noise. By injecting a millimeter-wave with frequency around <italic>N</italic> times of the fundamental oscillating frequency <italic>f<sub>0</sub></italic> of the OEO, the injection signal can be down-converted to an intermediate frequency (IF) signal close to the oscillating frequency of the OEO. The free running OEO is synchronized with the IF signal via an injection locking mechanism. Consequently, it forms an injection-locked frequency divider as the frequency ratio between the injection signal and OEO's output signal is precisely equal to <italic>N</italic>. We carry out an experiment to divide the 45 GHz signal into 7.5 GHz and the experimental results agree well with the theoretical analysis. By changing the frequency of the injection signal, division ratio from 2 to 5 is also demonstrated on one setup. Due to the broadband spectra of the optical comb and low phase noise characteristics of the OEO, it is potential to realize very large division ratio and low phase noise for multiple input frequencies <italic>mf<sub>0</sub></italic>.
Indoor 3D mapping provides a useful three-dimensional structure via an indoor map for many applications. To acquire highly efficient and relatively accurate mapping for large-scale GPS/GNSS-denied scene, we present an upgraded backpacked laser scanning system and a car-mounted indoor mobile laser scanning system. The systems provide both 3D laser scanning point cloud and camera images. In this paper, a simultaneous extrinsic calibration approach for multiple multi-beam LIDAR and multiple cameras is also proposed using the Simultaneous Localization and Mapping (SLAM)-based algorithm. The proposed approach uses the SLAM-based algorithm to achieve a large calibration scene using mobile platforms, registers an acquired multi-beam LIDAR point cloud to the terrestrial LIDAR point cloud to acquire denser points for corner feature extraction, and finally achieves simultaneous calibration. With the proposed mapping and calibration algorithms, we can provide centimetre-lever coloured point cloud with relatively high efficiency and accuracy.
A ZBLAN photonic crystal fiber (PCF) with normal dispersion is theoretically designed and investigated. The designed PCF can provide a large normal dispersion coefficient and a low confinement loss in a broad wavelength range of 1.8–3.6 μm. Especially, the PCF exhibits an ultra large normal dispersion value of −351.3 ps/km/nm and a small confinement loss of 0.05 dB/m at 2.9 <italic>μ</italic> m. By using the designed PCF as a dispersion compensator in a mode-locked ZBLAN fiber laser, stretched pulse with compressed pulse duration of 1.56 ps is numerically achieved.
Air temperature is an essential component of the factors used in landscape planning. At similar topographic conditions, vegetation may show considerable differences depending on air temperature and precipitation. In large areas, measuring temperature is a cost and time-consuming work. Therefore, prediction of climate variables at unmeasured sites at an acceptable accuracy is very important in regional resource planning. In addition, use a more proper prediction method is crucial since many different prediction techniques yield different performance in different landscape and geographical conditions. We compared inverse distance weighted (IDW), ordinary kriging (OK), and ordinary cokriging (OCK) to predict air temperature at unmeasured sites in Malatya region (East Central Anatolia) of Turkey. Malatya region is the most important apricot production area of Turkey and air temperature is the most important factor determining the apricot growing zones in this region. We used mean monthly temperatures from 1975 to 2010 measured at 28 sites in the study area and predicted temperature with IDW, OC, and OCK techniques, mapped temperature in the region, and tested the reliability of these maps. The OCK with elevation as an auxiliary variable occurred the best procedure to predict temperature against the criteria of model efficiency and relative root mean squared error.
Space Technology provides a resourceful-cost effective means to assess soil nutrients essential for soil management plan. Soil
organic matter (SOM) is one of valuable controlling productivity of crops by providing nutrient in farming systems. Geospatial
modeling of soil organic matter is essential if there is unavailability of soil test laboratories and its strong spatial correlation. In the
present analysis, soil organic matter is modeled from satellite image derived spectral color indices. Brightness Index (BI), Coloration
Index (CI), Hue Index (HI), Redness Index (RI) and Saturation Index (SI) were calculated by converting DN value to radiance and
radiance to reflectance from Thematic Mapper image. Geospatial model was developed by regressing SOM with color indices and
producing multiple regression model using stepwise regression technique. The multiple regression equation between SOM and
spectral indices was significant with R = 0. 56 at 95% confidence level. The resulting MLR equation was then used for the spatial
prediction for the entire study area. Redness Index was found higher significance in estimating the SOM. It was used to predict
SOM as auxiliary variables using cokringing spatial interpolation technique. It was tested in seven VDCs of Chitwan district of
Nepal using Thematic Mapper remotely sensed data. SOM was found to be measured ranging from 0.15% to 4.75 %, with a mean
of 2.24 %. Remotely sensed data derived spectral color indices have the potential as useful auxiliary variables for estimating SOM
content to generate soil fertility management plans.