Single-mode Research Articles

Ptychographic imaging with a fiber endoscope via wavelength scanning

Ptychography has become a popular computational imaging method for microscopy in recent years. In the present work we employ a wavelength scanning ptychography technique enhanced by neural networks for imaging with a fiber endoscope. Illumination of the object at various wavelengths is achieved using a single mode fiber, while a multicore fiber collects diffracted light from a distance. Using a U-Net multilayer convolutional neural network, the diffraction pattern is recovered at the far end of the multicore fiber from the recorded intensity pattern at the proximal end. With the recovered diffraction pattern in place, the phase object can be reconstructed using the ptychography algorithm. The quality of the object reconstruction improves with the number of wavelengths used. Comparison with an end-to-end neural network highlights the effectiveness and practicality of this two-step hybrid system. This alternative and simplified ptychographic endoscopy setup delivers noticeable improvements through neural networks and wavelength scanning.

Torsion and bending sensing based on the specklegrams from a coupled few-mode multi-core fiber

A novel optical torsion and bending dual-parameter sensor based on the detection of a coupled few-mode multi-core fiber (FM-MCF) specklegrams is proposed and experimentally demonstrated. A 3-mm-long multimode fiber (MMF) is used to couple the light from the injection single mode fiber into all cores of the FM-MCF, and thus the fiber structure is formed by the ultra-short MMF and FM-MCF. The specklegrams of the FM-MCF can be detected and segmented to infer the change of the FM-MCF. The torsion angle of 0-360° of the FM-MCF can be determined accurately by detecting the overall rotation angles of the specklegrams. And since the modes in each core of the FM-MCF are strongly coupled and the mode interference is highly sensitive to external disturbance, bending sensing based on the analysis of sub-specklegrams from each outer core is verified within the curvature range of 2.57–12.83 m−1 with the help of deep learning. Furthermore, based on a dual-output layer classification network, the capability of the sensor for torsion and bending sensing simultaneously is tested. The recognition accuracy for 36 combinations of 4 torsion angles and 9 bending states are 100% and 97.12%, respectively. The sensor here proposed has the advantages of low cost, simple structure, ease of interrogation and good accuracy.

A robust and accurate feature matching method for multi-modal geographic images spatial registration

ABSTRACT While the current research has achieved satisfactory results for the registration of single mode data, there has always been a significant challenge in the registration of multi-modal images due to the obvious nonlinear radiation differences caused by different imaging mechanisms and imaging time. For example, multi-temporal visible, visible-synthetic aperture radar, visible-near infrared, near infrared-short wave infrared, visible-MAP, etc. To address this problem, we propose a Robust and Accurate Feature Matching Method for Multi-modal Geographic Images Spatial Registration (RAMMR) to fully extract common key points between images, weaken the radiation difference between data, and finally accurately match more inliers to realize multi-modal image registration. Considering the influence of noise and edge information on key point extraction, RAMMR first constructs a new scale space by introducing the Side Window Filter (SWF); Then, we improve Harris algorithm to extract key points based on the SWF scale space; After that, we propose an enhanced log-polar descriptor based on the gradient angles and gradient amplitudes of the scale space, which effectively improves the quality of the descriptor and avoids the mismatch of key points; Based on the standard Euclidean distance, we design a re-match strategy to obtain the initial matching results, and Random Sample Consensus (RANSAC) is used to eliminate outliers. Finally, the affine transformation parameters are calculated based on inliers, and multi-modal image registration is realized. RAMMR is evaluated on different multi-modal datasets and compared with some state-of-art methods. The experimental results show that RAMMR accurately registers multi-modal geographic images and obtains comparative results compared with benchmark methods. Our source datasets are publicly available at https://github.com/RSmfmr/multimodal-dataset.

“Intelligent tutoring effects on induced emotions and cognitive load of learning-disabled learners”

Purpose This study addresses the learning requirements of learners with learning difficulties by monitoring their learning experience in an Intelligent Tutoring System. Intelligent Tutoring Systems were developed to enrich the teaching-learning process. Materials and Methods In the present work, the interface is designed and developed utilizing the potential of Artificial Intelligence to meet their individual needs. Designing an online learning platform for a learners with learning difficulties requires consideration of their learning problems and preferences. The interface was developed focusing on all the requirements of the LD learners. The objective of the present study is to monitor the learning experience in the form of induced emotions and cognitive load of the learners to determine the impact of learning. Results 83 learners were observed during various stage of learning. The results obtained through the Support Vector machine (SVM) classification technique showed the positive attitude towards intelligent tutoring. The analysis revealed that a total of 0.23% of learners were positively induced. Their learning experience was positive and effective. The cognition load on learners was minimum with single-mode instruction and least disturbed. Conclusions The system was improved based on preference feedback on design features. This helps in improving content design and creating device independent and responsive visual design. The fatigue effect analysis on cognitive load implied that multiple modes of instruction increased drowsiness. Single mode of instruction have a positive impact on the learning process and it reduces the cognitive load of the learners. Implications for Rehabilitation The user interface designed and developed for learners with Dyslexia, Dysgraphia and Dyscalculia has learning disabled-friendly features. These can be used to create a device-independent and responsive design. Learning experience is monitored along with the impact on cognitive load of the learners. The research helps in understanding the stimulation and response of learners with learning disability for different learning conditions. Most existing learning systems are limited to non-learning-disabled learners. The ITS developed during research presents a Universal learning design helpful for all learners with and without learning disability.

Stabilization and correction of aberrated laser beams via plasma channelling.

High-power laser applications, and especially laser wakefield acceleration, continue to draw attention through various research topics, and may bring many industrial applications based on compact accelerators, from ultrafast imaging to cancer therapy. However, one main step towards this is the arch issue of stability. Indeed, the interaction of a complex, aberrated laser beam with plasma involves a lot of physical phenomena and non-linear effects, such as self-focusing and filamentation. Different outcomes can be induced by small laser instabilities (i.e. laser wavefront), therefore harming any practical solution. One promising path to be explored is the use of a plasma channel to possibly guide and correct aberrated beams. Complex and costly experimental facilities are required to investigate such topics. However, one way to quickly and efficiently explore new solutions is numerical simulations, especially Particle-In-Cell (PIC) simulations if, and only if, one is confidently implementing such aberrated beams which, contrary to a Gaussian beam, do not have analytical solutions. In this research, we propose two new advancements: the correct implementation of aberrated laser beams inside a 3D PIC code, showing a great consistency, under vacuum, compared to the calculations with Fresnel theory); and the correction of their quality via the propagation inside a plasma channel. We demonstrate improvements in the beam pattern, becoming closer to a single plasma mode with less distortions, and thus suggesting a better stability for the targeted application. Through this confident calculation technique for distorted laser beams, we are now expecting to proceed with more accurate PIC simulations, closer to experimental conditions, and obtained results with plasma channels indicate promising future research.

High-speed GaN-based laser diode with modulation bandwidth exceeding 5 GHz for 20 Gbps visible light communication

Visible light communication (VLC) based on laser diodes demonstrates great potential for high data rate maritime, terrestrial, and aerial wireless data links. Here, we design and fabricate high-speed blue laser diodes (LDs) grown on c-plane gallium nitride (GaN) substrate. This was achieved through active region design and miniaturization toward a narrow ridge waveguide, short cavity length, and single longitudinal mode Fabry–Perot laser diode. The fabricated mini-LD has a low threshold current of 31 mA and slope efficiency of 1.02 W/A. A record modulation bandwidth of 5.9 GHz (−3 dB) was measured from the mini-LD. Using the developed mini-LD as a transmitter, the VLC link exhibits a high data transmission rate of 20.06 Gbps adopting the bit and power loading discrete multitone (DMT) modulation technique. The corresponding bit error rate is 0.003, satisfying the forward error correction standard. The demonstrated GaN-based mini-LD has significantly enhanced data transmission rates, paving the path for energy-efficient VLC systems and integrated photonics in the visible regime.

Highly-Sensitive Polymer Optical Fiber SPR Sensor for Fast Immunoassay

A new type of human immunoglobulin G (IgG) sensors based on the surface plasmon resonance (SPR) in the low refractive index (RI) plastic optical fiber (POF) and an antibody immobilization method is presented. A 50-nm-thick gold film was formed on the polished D-shaped fiber surface by magnetron sputtering. The RI response of the POF sensor is 30 049.61 nm/RIU, which is 26.5 times higher than that of single mode fiber (SMF) SPR sensors. The proposed SPR biosensor can be developed by simple and rapid modification of the gold film with 11-mercapto undecanoic acid (MUA). Upon immobilization of the goat anti-human IgG antibody, the resonance wavelength shifts by 11.2 nm. The sensor can be used to specifically detect and quantify the human IgG at concentrations down to 245.4 ng/mL with the sensitivity of 1.327 7 nm per µg/mL, which offers an enhancement of 12.5-fold compared to that of the conventional SMF based SPR sensors. The proposed device may find the potential applications in the case of use at the point of care.

Performance investigation of coupling modes for hydrogen circulation in high-power proton exchange membrane fuel cell systems

The economy and stability of the hydrogen recirculation system in high-power fuel cells significantly impact the performance of the stack system. However, there is no consensus on the optimal hydrogen recirculation mode to be employed. To determine the most effective solution across the entire power range of the stack, this study compares the performance of various coupling modes. The dynamic performance variations of the system were investigated under different modes by the Computational Fluid Dynamics (CFD) method. The simulation results demonstrated that within the low and medium power range of the stack, the PUE (Pump Upstream of Ejector) mode had the lowest power consumption of all modes, at 112 W. The power of the PUE mode had a reduction of 56.3% compared to the full-power single hydrogen pump mode, and a reduction of 22.8% compared to the PDE (Pump Downstream of Ejector) mode.

Classification and properties of Bambusa blumeana fiber

This study extracted Bambusa blumeana fiber using alkaline boiling and then applied double-roll pressing in order to develop it, explore the applications of its various parts, and improve its utilization potential. The results showed that the outer bamboo fibers are finer and straighter than the inner and middle fibers, and the fracture mode of the bamboo fibers is brittle. From the inside to the outside, the tensile strength of the fiber bundle gradually increases from the top to the bottom. Moreover, the tensile strength of the outside bamboo fiber is twice that of the inside, reaching a maximum of 982 MPa. The surface of the interior bamboo fiber is relatively smooth and can be used in textile and decorative fields. Compared with internal and central bamboo fiber, the outer fiber has higher thermal stability and higher crystallinity, which makes it more advantageous in the process of strengthening composite materials. Studying the structures of fibers from different parts of Bambusa blumeana can provide substantial scientific support for the differential applications of bamboo fibers.

Spatial and mode selective switch for orbital angular momentum mode division multiplexing.

In analogy to a wavelength selective switch in wavelength-division multiplexing (WDM) optical fiber communication systems, a spatial and optical mode selective switch (SMSS) would be an important component in future ultrahigh capacity optical fiber communication systems based on space and mode division multiplexing. In this work, a free-space SMSS for orbital angular momentum (OAM) mode-division multiplexing (MDM) is proposed and experimentally demonstrated. The SMSS consists of a separating part for transforming OAM modes to spatial modes and a recombining part for selecting and recombining the modes to any spatial channel. The SMSS is able to implement strictly non-blocking switching between a total of 36 SDM/MDM channels configured as four spatial channels each supporting nine OAM mode channels.

Effect of grain size on ductility and failure mechanism of fiber-reinforced coral sand cement-based composites

Fiber offers the potential for enhancing the resistance to deformation in engineering cement-based composites (ECC). However, replacing quartz sand in ECC with coral sand containing a large number of internal pores will make the interaction between aggregate, interface transition zone, and cementitious materials more complex. To investigate the influence of coral sand particle size and Polyvinyl alcohol (PVA) fiber content on the compression behaviour and internal microstructure of fiber-reinforced coral sand cement-based composites (FRCSCC), we conducted uniaxial compressive strength tests and real-time measurements of P-wave and S-wave velocities. We tested various mechanical parameters, such as density, elastic modulus, compressive strength, wave velocities, and toughness index. The findings revealed a notable trend in relation to the coral sand particle size. Specifically, as the particle size increased, the compressive strength of FRCSCC decreased by 26 % and the elastic modulus reduced by 11 %. During uniaxial compression, the calculated cumulative voltage energy (CVE) from P-wave and S-wave can be divided into three stages: elastic deformation, microcrack and macrocrack propagation, and main crack formation. Moreover, the increase of coral sand particle size from 0.075 mm to 1.00 mm resulted in the rise of residual stress from 8.7 % to 18.2 %, followed by the increase of toughness index from 2.5 to 3.2. Scanning electron microscope (SEM) images reveal that the main failure modes of PVA fiber in FRCSCC specimens during uniaxial compression are debonding pull-out and tearing. Larger particle sizes of coral sand are associated with uneven fiber dispersion, increased fiber fractures, and diminished ductility of the specimens. The results establish a theoretical foundation for offshore engineering construction.

Effects of inner cone length on continuous rotating detonation in a variable cross-section combustor

A variable cross-section combustion chamber with different inner cone length L is designed, composing of an annular part with divergent width and a cylinder part without inner cone. Ethylene-air and hydrogen-air continuous rotating detonation (CRD) experimental tests are conducted. The results show that the ethylene-air CRD wave can be achieved in the variable cross-section combustor with the short inner cone. The propagation velocity of ethylene-air CRD wave can be 1661.37 m/s with the equivalence ratio of 0.91 and L of 10 mm. With L increasing from 0 mm to 30 mm, the combustion mode varies in the single wave mode, the sawtooth wave mode, and the hybrid mode. The combustor width is not the main factor leading to the failure of detonation in this study. The acceleration of propellent mixture caused by the expansion of the annulus channel, and the downstream movement and reduction of recirculation zone around the inner cone both increase the difficulty in CRD realization. While the hydrogen-air CRD can self-sustain with the intensive reaction zone in the annular part in the critical configuration of ethylene-air CRD. This study will contribute to the understandings of self-sustaining mechanism of CRD in the divergent combustor and the combustor design of the hollow chamber.

Improved performance of a fiber-optic hydrogen sensor based on a controllable optical heating technology.

A novel, to the best of our knowledge, and compact fiber-optic hydrogen sensor based on light intensity demodulation and controllable optical heating technology is proposed and experimentally investigated. This system employs three photodetectors for optic signal transformation. The first PD is used to receive a little fraction of the amplified spontaneous emission (ASE) for calibration, and the second PD is utilized to detect optic signal reflected by a single mode fiber deposited with WO3-Pd2Pt-Pt composite film. The last PD is utilized to receive the optical power reflected by the short fiber Bragg grating (SFBG) with a central wavelength located in a steep wavelength range (the intensity decreases approximately linearly with the increase of the wavelength) of the ASE light source. A 980 nm laser and proportion integration differentiation (PID) controller were employed to ensure the hydrogen sensitive film working at an operating temperature of 60°C. This sensing system can display a quick response time of 0.4 s toward 10,000 ppm hydrogen in air. In addition, the detection limit of 5 ppm in air can be achieved with this sensing system. The stability of this sensor can be greatly enhanced with a controllable optical heating system, which can greatly promote its potential application in various fields.

High-efficiency self-focusing metamaterial grating coupler in silicon nitride with amorphous silicon overlay

Efficient fiber-chip coupling interfaces are critically important for integrated photonics. Since surface gratings diffract optical signals vertically out of the chip, these couplers can be placed anywhere in the circuit allowing for wafer-scale testing. While state-of-the-art grating couplers have been developed for silicon-on-insulator (SOI) waveguides, the moderate index contrast of silicon nitride (SiN) presents an outstanding challenge for implementing efficient surface grating couplers on this platform. Due to the reduced grating strength, a longer structure is required to radiate the light from the chip which produces a diffracted field that is too wide to couple into the fiber. In this work, we present a novel grating coupler architecture for silicon nitride photonic integrated circuits that utilizes an amorphous silicon (α-Si) overlay. The high refractive index of the α-Si overlay breaks the coupler’s vertical symmetry which increases the directionality. We implement subwavelength metamaterial apodization to optimize the overlap of the diffracted field with the optical fiber Gaussian mode profile. Furthermore, the phase of the diffracted beam is engineered to focalize the field into an SMF-28 optical fiber placed 55 µm above the surface of the chip. The coupler was designed using rigorous three-dimensional (3D) finite-difference time-domain (FDTD) simulations supported by genetic algorithm optimization. Our grating coupler has a footprint of 26.8 × 32.7 µm2 and operates in the O-band centered at 1.31 μm. It achieves a high directionality of 85% and a field overlap of 90% with a target fiber mode size of 9.2 µm at the focal plane. Our simulations predict a peak coupling efficiency of − 1.3 dB with a 1-dB bandwidth of 31 nm. The α-Si/SiN grating architecture presented in this work enables the development of compact and efficient optical interfaces for SiN integrated photonics circuits with applications including optical communications, sensing, and quantum photonics.

High-power and narrow-linewidth nanosecond pulsed intracavity crystalline Raman laser operating at 1.7 µm

We report on a high-power and narrow-linewidth nanosecond pulsed intracavity crystalline Raman laser at 1.7 µm. Driven by an acousto-optically Q-switched 1314 nm two-crystal Nd:YLF laser, the highly efficient cascaded YVO4 Raman laser at 1715nm was obtained within the well-designed L-shaped resonator. Thanks to the absence of spatial hole burning in the stimulated Raman scattering process, significant spectral purification of second-Stokes radiation was observed by incorporating a fused silica etalon in the high-Q fundamental cavity. Under the repetition rate of 4 kHz, the highest average output power for single longitudinal mode operation was up to 2.2 W with the aid of precision vibration isolation and precision temperature controlling, corresponding to the pulse duration of ∼2.8 ns and the spectral linewidth of ∼330 MHz. Further increasing the launched pump power, the second-Stokes laser tended toward be always multimode, and the maximum average output power amounted to 4.8 W with the peak power of ∼0.8 MW and the spectral linewidth of ∼0.08 nm. The second-Stokes emission was near diffraction limited with M2 < 1.4 across the whole pump power range.

Humidity Sensing Using a Multimode Fiber Ring Laser with Thermal Compensation

We propose a multimode fiber laser sensor utilizing PI-SMF (polyimide-coated single mode fiber) for low-error relative humidity (RH) measurement, which is temperature compensated based on FBG. The PI-SMF in the laser cavity is used as a sensing element, and its length varies with humidity and temperature by volume-variation induced strain, which leads to frequency shift of the longitudinal mode beat frequency signal (BFS). When the 2000 MHz BFS is selected as the sensing signal, a RH sensitivity of −2.68 kHz/%RH and a temperature sensitivity of −14.05 kHz/°C are achieved. The peak shift of the FBG-based laser emission spectrum is only sensitive to temperature rather than RH with a temperature sensitivity of 9.95 pm/°C, which is used as the temperature compensation for RH measurements. By monitoring the response of the BFS and the laser wavelength, the cross-sensitivity effect of RH and temperature is overcome, and low-error RH measurement in the temperature range of 20 to 65 °C is realized with errors within ±0.67 %RH (25 to 85 %RH). The scheme does not require the design and production of complex structures and hygroscopic material coating processes, owning the advantages of simple structure, easy operation and high accuracy, and is expected to be practically applied in food safety and environmental monitoring.

Mining Multimodal Travel Mobilities with Big Ridership Data: Comparative Analysis of Subways and Taxis

Understanding traveler mobility in cities is significant for urban planning and traffic management. However, most traditional studies have focused on travel mobility in a single traffic mode. Only limited studies have focused on the travel mobility associated with multimodal transportation. Subways are considered a green travel mode with large capacity, while taxis are an energy-consuming travel mode that provides a personalized service. Exploring the relationship between subway mobility and taxi mobility is conducive to building a sustainable multimodal transportation system, such as one with mobility as a service (MaaS). In this study, we propose a framework for comparatively analyzing the travel mobilities associated with subways and taxis. Firstly, we divided taxi trips into three groups: competitive, cooperative, and complementary. Voronoi diagrams based on subway stations were introduced to divide regions. An entropy index was adopted to measure the mix of taxi trips. Secondly, subway and taxi trip networks were constructed based on the divided regions. The framework was tested based on the automatic fare collection (AFC) data and global positioning system (GPS) data of a subway in Beijing, China. The results showed that the proportions of taxi competition, taxi cooperation, and taxi complements were 9.1%, 35.6%, and 55.3%, respectively. The entropy was large in the central city and small in the suburbs. Moreover, it was found that the subway trip network was connected more closely than the taxi network. However, the unbalanced condition of taxis is more serious than that of the subway.

Conductive dual-network hydrogel-based multifunctional triboelectric nanogenerator for temperature and pressure distribution sensing

Conductive hydrogels are gaining attention in flexible electronics due to their high electrical conductivity and stretchable mechanical properties. Utilizing conductive hydrogels as electrodes in triboelectric nanogenerators (TENG) offers a promising avenue for developing versatile, flexible devices. However, the preparation of a multifunctional hydrogel-based TENG remains a challenging task. Here, a dual-network hydrogel TENG is denoted as DNH-TENG. It comprises poly(3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS)/poly (vinyl alcohol) (PVA)/carboxylated multi-walled carbon nanotube (MWCNT-COOH) and offers the advantages of straightforward fabrication, versatile applications, and efficient output performance. Preparing a double network by combining a conductive network with a soft network improves the tensile properties but reduces its conductivity significantly. Further doping MWCNT-COOH with the dual-network leads to a conjugation effect and hydrogen bonding. This enhancement fortifies the hydrogel structure and augments the electrode's conductivity and mechanical properties. In single electrode mode, the DNH-TENG exhibits a short-circuit current of 16.2 μA, a transfer charge of 97.3 nC, and an open-circuit voltage of 270.5 V. Furthermore, DNH-TENG exhibits an impressive stretchability, allowing it to be extended to 566%. Using DNH-TENG's exceptional stretchability and ultrahigh sensitivity to mechanical and temperature stimuli, we designed DNH-TENG-based sensor arrays to showcase temperature and pressure distribution monitoring applications.

A multiparameter sensing spectroscopic system for remote plastic sorting with a single laser shot: a first information report

The spectroscopic methods have been widely applied for plastic characterization and sorting to assist the recycling process. However, most of the reported works have been carried out in conventional laboratory conditions. In this study, we discuss development and application of a single-shot standoff multimodal LIBS-Raman spectroscopy system for plastic identification by modifying existing optical models for such analyses. By utilizing a unique co-axial back-collection optical geometry in standoff signal collection and a direct signal coupling scheme, the system was able to sense LIBS-Raman signals from plastics in single laser shot mode within 20 ms, with a non-gated CCD detector remotely. We examine the application of the system in characterizing four commodity plastic types of polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and polystyrene (PS)) based on atomic emissions (LIBS) and molecular structure (Raman Spectroscopy) by analyzing the respective standoff spectral data recorded from a distance of 4 m. The capability of the system to classify plastics based on standoff data is evaluated by using principal component analysis (PCA), which shows good segregation of the plastic classes depending on the intrinsic spectral features.

Personalized driving behavior oriented autonomous vehicle control for typical traffic situations

autonomous driving systems not only provide services for human drivers, but also need to consider the personalized driving requirements of human beings. In current road traffic environments, the driving behaviors of drivers differ significantly. This suggests that the various needs of different drivers cannot be met by a single behavior mode in an autonomous driving decision-making system. This paper looks at the personalized characteristics of various drivers and considers the implications of their differences. First, a Proportional Integral Differential (PID) feedback channel is introduced in a traditional Model Predictive Control (MPC) to improve the performance of the controller, and comprehensively considering the collision risk, motion hysteresis and rule constraints, referring to the MPC idea, a collision avoidance method based on Q-ABSAS optimization is proposed. Then based on the Chance Constrained Programming, the control constraint is combined with driver personalization to reflect a variety of driving personality characteristics. Finally, the proposed method is tested using Hardware-in-the-loop (HIL) experiments. The experiment results demonstrate that the proposed method can successfully implement vehicle tracking control and make the vehicle's state of movement match the driver's expectations, which can increase driver comfort and driving safety.