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Space weather forecasts are of utmost importance in safeguarding navigation, communication, and electric power system operations, satellites from orbital drag, and the astronauts in the International Space Station from hazardous space radiation during extreme space weather conditions. The finest space weather prediction requires a clear understanding of solar wind‐magnetosphere coupling. The in‐situ measurements of the solar wind properties give unique information about the Sun and its activity on smaller to longer timescales. The present work investigates the influence of solar activity on the coupling of solar wind and Earth's magnetosphere during 23–24 solar cycles. The geomagnetic storms with Symmetric H‐component (SYMH) ≤ −85 nT during the 23–24 solar cycles are considered. We present the results of statistical analysis and relationships between the various solar wind parameters such as the total strength of interplanetary magnetic field (B) and its three‐axis components (Bx, By, and Bz), solar wind proton density (Nsw), solar wind speed (Vsw), SYMH indices, the amplitude, duration, and profile of the geomagnetic storms. The integrated electric field and integrated SYMH index during storms show the highest correlation of 0.92, implying that integrated SYMH is a better proxy of the injected solar wind energy in the magnetosphere in the form of the ring current. Moreover, we do see the difference in the solar wind‐magnetosphere coupling efficiency during the phases of 23–24 solar cycles which is intriguing. Key Points: First observation: The Integrated Ey of solar wind and Integrated Symmetric H‐component show a strikingly high correlationSolar Wind (SW)‐Magnetosphere (M) coupling shows higher average efficiency during the 24th solar cycle compared to the 23rdLow solar activity (or solar minimum) shows elevated efficiency of SW‐M coupling [ABSTRACT FROM AUTHOR]

AbstractThe chemical synthesis of guanosine nucleosides generates both the N9 and N7 regioisomers, which require careful separation to obtain the desired N9 isomer. To preferentially obtain the N9 isomer, a bulky diphenylcarbamoyl (DPC) group can be installed at the O6 position of guanine. However, installation of the DPC group presents a challenging task due to low solubility of the N-acetyl protected guanine. Here we report the usage of commercially available 2-amino-6-chloro purine as a new strategy that offers a more efficient route to the synthesis of the guanine phosphoramidite of threose nucleic acid (TNA). [ABSTRACT FROM AUTHOR]

With the continuous development of Internet technology, all areas of social economy have undergone profound changes. The circulation and application of data elements can significantly promote the construction of infrastructure such as big data centers and mobile base stations, and stimulate the market demand for digital consumption such as digital production, e-commerce and digital trade. Data mining technology will provide sustainable impetus for economic development. There is a clearer analysis of the role of data elements in the platform economy, but there is a lack of research in macroeconomics, especially in the coupling of finance and technology. This paper developed a coupling coordination and a coupling efficiency index system, using different methods to measure outcomes and outline the path to achieving high "quantity" and "quality" of finance-technology coupling development. Based on the data mining technology in e-commerce, the fuzzy set qualitative comparative analysis method is used to analyze the complex mechanisms and driving paths of data elements affecting the coordination degree and coupling efficiency of finance-technology coupling performance of China. We empirically document that data mining and data management are necessary to improve coupling coordination; in the absence of other conditions, data mining or data management can produce high coupling coordination, but not sufficient to improve coupling efficiency. [ABSTRACT FROM AUTHOR]

To fully utilize the advantages of Si3N4 and Silicon-On-Insulator to achieve a high-efficiency wideband grating coupler, we propose and numerically demonstrate a grating coupler based on Si3N4 and a Silicon-On-Insulator heterogeneous integration platform. A two-dimensional model of the coupler was established and a comprehensive finite difference time domain analysis was conducted. Focusing on coupling efficiency as a primary metric, we examined the impact of factors such as grating period, filling factor, etching depth, and the thicknesses of the SiO2 upper cladding, Si3N4, silicon waveguide, and SiO2 buried oxide layers. The calculations yielded an optimized grating coupler with a coupling efficiency of 81.8% (−0.87 dB) at 1550 nm and a 1-dB bandwidth of 540 nm. The grating can be obtained through a single etching step with a low fabrication complexity. Furthermore, the fabrication tolerances of the grating period and etching depth were studied systematically, and the results indicated a high fabrication tolerance. These findings can offer theoretical and parameter guidance for the design and optimization of high-efficiency and broad-bandwidth grating couplers. [ABSTRACT FROM AUTHOR]

Quantifying and interpreting the water–energy–food (WEF) nexus is critical to achieve the sustainable development of urban resources. The mismatch between urban water, energy and food allocations is a prominent problem that is particularly acute in the Yellow River Basin (YRB) of China. In this study, models for the WEF coupling degree and coupling efficiency were constructed. The WEF coupling efficiencies of the 94 cities in the YRB from 2011 to 2020 were quantified using a data envelopment analysis (DEA) model. On this basis, the spatial distribution characteristics and evolutionary trends of different urban WEF coupling efficiencies were analysed and explored using an exploratory spatial data analysis (ESDA) model and a parametric kernel density estimation model. The results show that the energy subsystem constrain the development of the WEF nexus, and the food subsystem, in turn, regulates the development of the WEF nexus. In some years, the phenomenon of ‘resource curse’ occurred, in which the WEF coupling degree increased while the coupling efficiency decreased. Overall, the values of the urban WEF coupling efficiency were low, ranging from 0.5300 to 0.6300, which is not effective. Spatial clustering was detected in the urban WEF coupling efficiency. The clustering types were ‘high–high’ clustering areas in less developed regions and ‘low–low’ clustering areas in developed regions. The two clusters and the median contiguous group had different evolutionary trends. Both efficiency and polarisation increased in the high-clustering group, efficiency improved in the low-clustering group, and a new efficiency pole was formed in the median contiguous group. Among the three grouped cities, we discuss the potential of policies such as cross-city cooperation, intra-city multi-sectoral cooperation and cultivating new central growth cities to improve the WEF coupling efficiency in the YRB.

Implementing a compact optical integrated circuit by utilizing subwavelength plasmonic devices requires the design of compact and efficient photonic to plasmonic mode converters. Especially for plasmonic multiple-input devices such as logic gates that require multiple converters, the footprint can be largely penalized by the photonic waveguides, which should be considered in the design. In this work, we simulate and benchmark five photonic to plasmonic mode converter topologies for the application of multiple-input plasmonic devices. Our design includes both directional and end coupling schemes of plasmonic waveguide and Si photonic waveguides of wire and slot configurations. We optimize the performance of the converters considering the pitch mismatch between the photonic and plasmonic waveguides, the total footprint, and mode conversion efficiency.

A theoretical investigation of coupling optics is presented in this paper based on ABCD matrix formulation in order to predict the coupling efficiency involving a laser diode (LD) and some identical single-mode circular core dispersion-shifted fiber (DSF) and dispersion-flattened fiber (DFF) with a cylindrical microlens (CML) in its tip. The authors derive analytical equations for the relevant coupling efficiency by assuming Gaussian distributions of the fields for both the source and the fiber under paraxial approximation. Further, in order to consider the non-Gaussian nature of the field of dispersion managed fibers, we employ spot size of Petermann II in our investigation. The investigations are made for two commonly used wavelengths, namely 1.3 and 1.5 μm. Our suggested technique demands extremely little computing for execution. For stimulation by a LD generating light of wavelength 1.3 μm, the maximum coupling efficiency (η) goes up to 94.41 percent. The proposed formulation also accounts for the limited aperture permitted by the CML. Thus, the analysis should find wide use in the design of CML on the single-mode circular core dispersion-controlled fibers tip to achieve large propagation distance. [ABSTRACT FROM AUTHOR]

The coupling efficiency of the fiber ring resonator has an important influence on the scale factor of the resonant fiber gyroscope. In order to improve the scale factor of the gyroscope, the coupling efficiency of the fiber ring resonator and its influential factors on the scale factor of the gyroscope are analyzed and tested. The results show that the coupling efficiency is affected by both the splitting ratio of the coupler and the loss in the cavity. When the coupling efficiency approaches 0.75 at the under-coupling state, the scaling factor of the gyroscope is the highest. This provides a theoretical reference and an experimental basis for the enhancement of the scaling factor of the resonant fiber gyroscope with the fiber ring resonator as the sensitive unit, providing options for multiple applications such as sea, land, sky and space. [ABSTRACT FROM AUTHOR]

This work reports the efficient excitation of surface plasmons polaritons (SPPs) by optimizing the geometrical parameters of M o S 2 -Au to increase the efficiency of plasmonic-based photovoltaic cells. This technique is quite useful for near-field and far-field analysis which is direly needed to understand the associate phenomenon. The impact of Au nano-grating on light absorption by using the plasmonic effect of noble metals has been investigated. We proposed a simple geometry for enhancing the coupling efficiency between the multilayering of M o S 2 and Au noble metal thin film by varying the slit widths (270–480) nm and material thickness (40–50) nm, while the periodicity was kept constant (720 nm) for unit cell. The efficient SPP excitation occurs at slit widths, near half, and few more than half of periodicity (360–420) nm. Resonance wavelength at different slit widths has also been observed. Efficient SPP excitation tends to increase the electric field around the slit, hence increasing the substrate ability to absorb light. For material thickness 40 nm and 50 nm, it has been observed that changing y-component of electric field (E y) in solar cell is effective in achieving greater absorption. The geometry has been simulated by using COMSOL Multiphysics RF module. This study will have significant impact for enhancing the coupling efficiency of the incident light into SPPs which have potential application to enhance the efficiency of the plasmonic-based solar cell. [ABSTRACT FROM AUTHOR]

One of the most important problems in the plasmonics of the terahertz (THz) range, which is actively developing now, is the efficient generation of surface plasmon polaritons (SPPs). The simplest and most promising technological technique of photon excitation of THz SPPs is through diffraction of radiation on the edge of the conducting surface of the sample (the end-fire coupling technique). In this paper, we experimentally evaluated the efficiency of the generation of monochromatic THz SPPs (λ0 = 141 μm) by this method with a sample in the form of a cylindrical segment, the convex surface of which has a gold layer coated by zinc sulfide (ZnS) with thickness d = 0–2 µm. Such configuration of the surface supporting the SPPs not only shields the detector from parasitic bulk waves arising during diffraction but also enables one to change the distribution of the SPP field in the air by varying the coating layer thickness d. On an uncoated gold surface, the SPP generation efficiency was η ≈ 20%. In the presence of a ZnS layer on the gold, the SPP generation efficiency gradually increased with d, reached the maximum (ηmax ≈ 60%) at d ≈ 1 μm, and then gradually decreased. Theoretical analysis showed that the efficiency of the SPP generation can be raised up to 80% due to the selection of an optimal SPP field profile via variation of the thickness of the dielectric layer on the metal surface, as well as with optimal incidence of the focused radiation on the edge of the sample. [ABSTRACT FROM AUTHOR]

To fully utilize the advantages of Si3N4 and Silicon-On-Insulator to achieve a high-efficiency wideband grating coupler, we propose and numerically demonstrate a grating coupler based on Si3N4 and a Silicon-On-Insulator heterogeneous integration platform. A two-dimensional model of the coupler was established and a comprehensive finite difference time domain analysis was conducted. Focusing on coupling efficiency as a primary metric, we examined the impact of factors such as grating period, filling factor, etching depth, and the thicknesses of the SiO2 upper cladding, Si3N4, silicon waveguide, and SiO2 buried oxide layers. The calculations yielded an optimized grating coupler with a coupling efficiency of 81.8% (−0.87 dB) at 1550 nm and a 1-dB bandwidth of 540 nm. The grating can be obtained through a single etching step with a low fabrication complexity. Furthermore, the fabrication tolerances of the grating period and etching depth were studied systematically, and the results indicated a high fabrication tolerance. These findings can offer theoretical and parameter guidance for the design and optimization of high-efficiency and broad-bandwidth grating couplers.

AimThis study aimed to compare the effectiveness of auditory brainstem response (ABR) and extracochlear electrocochleography (ECochG) in objectively evaluating the coupling efficiency of floating mass transducer (FMT) placement during active middle ear implant (AMEI) surgery.MethodsWe enrolled 15 patients (mean age 58.5 ± 19.4 years) with mixed hearing loss who underwent AMEI implantation (seven ossicular chain and eight round window couplings). Before the surgical procedure, an audiogram was performed. We utilized a clinical measurement system to stimulate and record intraoperative ABR and ECochG recordings. The coupling efficiency of the VSB was evaluated through ECochG and ABR threshold measurements. Postoperatively, we conducted an audiogram and a vibrogram.ResultsIn all 15 patients, ABR threshold testing successfully determined intraoperative coupling efficiency, while ECochG was successful in only eight patients. In our cohort, ABR measurements were more practical, consistent, and robust than ECochG measurements. Coupling efficiency, calculated as the difference between vibrogram thresholds and postoperative bone conduction thresholds, was found to be more accurately predicted by ABR measurements (p = 0.016, R2 = 0.37) than ECochG measurements (p = 0.761, R2 = 0.02). We also found a non-significant trend toward better results with ossicular chain coupling compared to round window coupling.ConclusionOur findings suggest that ABR measurements are more practical, robust, and consistent than ECochG measurements for determining coupling efficiency during FMT placement surgery. The use of ABR measurements can help to identify the optimal FMT placement, especially with round window coupling. Finally, we offer normative data for both techniques, which can aid other clinical centers in using intraoperative monitoring for AMEI placement.

In this paper, the theoretical model of the coupling efficiency of BG beams to few-mode fibers (FMFs) in the case of perfect alignment, lateral or vertical offsets, and random angular jitter is investigated and compared with that of sew-mode fibers (SMFs). Under the same conditions, FMF obtains a higher coupling efficiency with the BG beam and flatter response characteristics to deviations from ideal conditions compared with SMF. At the same time, the effects of the half-cone angle and topological charge of the BG beam on the coupling efficiency and response characteristics during nonideal conditions are studied. According to the precision of the coupling system, a higher coupling efficiency can be obtained by adjusting the half-cone angle, topological charge, and focal length. That makes them a more practical choice for information transmissions, such as mobile platform communication and the transmission of pedestrian data collected during transportation. The research results could help apply the BG beam and other orbital angular momentum (OAM) beams coupled with FMF. [ABSTRACT FROM AUTHOR]

A chaotic adaptive seeker optimization algorithm (CASOA) is proposed in this study to improve the coupling efficiency and accuracy of a butterfly optical communication laser. It primarily relies on chaotic disturbance to improve seeker search performance. The chaotic disturbance enables the algorithm to jump out from local extremes. Furthermore, chaos is associated with a novel strategy for optimizing search paths with a small population. A simulation and experiment are conducted to demonstrate that the CASOA with a few seekers has an excellent search success rate with few iterations in the coupling alignment. These results indicate that the proposed CASOA can reliably improve the coupling accuracy and efficiency of laser diodes and single-mode fibers. [ABSTRACT FROM AUTHOR]

In fiber-based optical receivers such as coherent receiver, the optical signal reaching the receiver's aperture is coupled to the optical fiber through a set of lenses. Due to atmospheric turbulence, however, the coupling efficiency, which is defined by the ratio of the fiber-coupled optical power to the optical power reaching the aperture, fluctuates over time, and thus should be treated as a random variable. Previous theoretical works predict the average coupling efficiency accurately, but fail to estimate the standard deviation, especially when the turbulence is strong. In this study, we propose new theoretical formulas for the standard deviation of coupling efficiency applicable to a wide range of turbulence conditions. For this purpose, we derive a new approximated formula for the second moment of coupling efficiency using the second-order Taylor expansion. Next, a new formula for the second moment of coupled optical power is developed by introducing the spatial filter to the fourth-order coherence function. The computer simulation is carried out to evaluate the accuracy of the formulas. The results show that our formulas agree with the simulation results over a wide range of turbulence strength. Also, the new formulas provide better accuracy than the previously reported ones.

Dip coating technique has the potential to provide a simpler and more cost-effective means of forming an optical fiber microcollimator composed of parabolic Polymethyl methacrylate microlenses for various applications. The effects of dip-coating operating parameters such as withdrawal speed on the thickness of a microlens were investigated in this work. Zemax® software was used to validate the analytical results and to assess the efficiency of the optical coupling. The obtained waist and working distance values, make possible the optimization of the optical coupling between a microcollimator and a laser beam, as well as between a microcollimator and an optical fiber. The simulation results of the coupling between the microcollimator and the laser beam show that the optical coupling efficiency η is about 99% with an optimal microlens radius R = 19.14 μm, a waist size W1 = 2.49 μm and a working distance Zw = 41.78 μm. However, the optimal microlens for the coupling between the microcollimator and the optical fiber has a minimum curvature radius about 28.78 μm. We believe that these results are of a big interest in many applications in optical experiments and laser-optical fibers applications. [ABSTRACT FROM AUTHOR]

Experimental campaigns were undertaken to understand and improve the coupling efficiency of Radio frequency (RF) power into the plasma in three accelerator-based ion sources. Different matching circuit and mechanical engineering setups were used and the network resistance calculated. The efficiency was then measured for a range of RF frequencies and input gas flows. Coupling efficiencies of around 60% were measured in setups using RF-coils mounted external to the plasma chamber. The efficiency is improved to 80% when the coil is immersed in the plasma, allowing closer coupling. As well as the coil geometry, the isolation transformer required for beam production contributes to the overall losses. [ABSTRACT FROM AUTHOR]

An analytical theoretical model for the waveguide grating coupler is developed and applicable to practical deep gratings. The grating-assisted input coupling efficiency is calculated by considering the reciprocal out-coupling problem. The deep grating structure is modelled as an optical layer filled with polarization dipole sources, and the scattered fields are then calculated using the associated Green’s functions and taking into account the multiple reflections and interference from the adjacent layers. The joint loss between the grating region and the waveguide is also considered. Comparison with numerical simulations shows very good agreement and validates the accuracy of the analytical model. The model explicitly describes the importance of multilayer interference of the scattered fields and guided-mode joint loss on the total grating-assisted coupling efficiency and can be used for practical waveguide grating coupler design with negligible computation workload.

Lateral displacement has a great influence on optical communication. We proposed the directional tapered fiber connector to improve the coupling efficiency. To verify its performance, we produce the sample with the flame-brush technique. In the next step, two experiments in the vibration environment are done. The first experiment shows the tapered structure could improve the optical power coupling efficiency. In addition, in this experiment, we discover only the amplitude has an obvious impact on the power coupling efficiency. The second experiment shows the bit error rate of the common receiver is higher than that of the new receiver. It indicates the new receiver performs better also. At the same time, the second experiment shows both the amplitude and frequency have obvious influence on the bit error rate result. This is different from the first experiment. The reason is owing to that the vibration frequency will change the mode of laser transmission. However, the transmission mode has an obvious impact on the bit error rate, but has little influence on the optical power coupling efficiency. [ABSTRACT FROM AUTHOR]

Lateral displacement has a great influence on optical communication. We proposed the directional tapered fiber connector to improve the coupling efficiency. To verify its performance, we produce the sample with the flame-brush technique. In the next step, two experiments in the vibration environment are done. The first experiment shows the tapered structure could improve the optical power coupling efficiency. In addition, in this experiment, we discover only the amplitude has an obvious impact on the power coupling efficiency. The second experiment shows the bit error rate of the common receiver is higher than that of the new receiver. It indicates the new receiver performs better also. At the same time, the second experiment shows both the amplitude and frequency have obvious influence on the bit error rate result. This is different from the first experiment. The reason is owing to that the vibration frequency will change the mode of laser transmission. However, the transmission mode has an obvious impact on the bit error rate, but has little influence on the optical power coupling efficiency. [ABSTRACT FROM AUTHOR]

• Designed a new 6-hole micro-structure silicon dioxide anti-resonant hollow-core fiber (AR-HCF) with a larger core diameter of 78 μm. • The numerical simulation of anti-resonant hollow-core fiber is carried out. • For the first time, the ability to transmit high-energy pulses at 2.79 μm wavelength through a full-silica microstructure hollow-core fiber. • Achieved the transmission efficiency is the best value of 3 μm band erbium laser transmission by silica hollow microstructure fibers. Using anti-resonant hollow-core fibers instead of light guide arms for laser energy transmission can greatly improve the flexibility of medical laser devices, reduce system complexity, and increase laser transmission efficiency. In this paper, a 6-hole anti-resonant air-core fiber (AR-HCF) with a length of 1.5 m and a core diameter of 78 μm is designed to transmit the radiation at 2.79 μm waveband. Utilizing our homemade medical solid-state Cr,Er:YSGG laser and coupling systems, we demonstrate, for the first time, the ability to transmit high-energy pulses at 2.79 μm wavelength through a full-silica microstructure hollow-core fiber. We analyze the characteristics of infrared laser transmission using this fiber. The results show that the average coupling transmission efficiency of this system reached 77.3 %, with a maximum coupling efficiency of 85 %. To our best knowledge, this transmission efficiency is the best value of 3 μm band erbium laser transmission by silica hollow microstructure fibers. The maximum output energy of the fiber is 11.78 mJ, corresponding to an energy density of 350 mJ/cm2, which far exceeds the energy density threshold required for tissue ablation. The uncooled fiber shows no damage during one hour of continuous operation in the experiment. This study's theoretical and experimental research also confirms that the bend radius meets the requirements for clinical medical instrument use. This 6-hole structure AR-HCF opens up a new pathway for medical devices requiring efficient transmission of 2.79 μm Cr,Er:YSGG medical solid-state laser. [ABSTRACT FROM AUTHOR]

The coupling efficiency of the fiber ring resonator has an important influence on the scale factor of the resonant fiber gyroscope. In order to improve the scale factor of the gyroscope, the coupling efficiency of the fiber ring resonator and its influential factors on the scale factor of the gyroscope are analyzed and tested. The results show that the coupling efficiency is affected by both the splitting ratio of the coupler and the loss in the cavity. When the coupling efficiency approaches 0.75 at the under-coupling state, the scaling factor of the gyroscope is the highest. This provides a theoretical reference and an experimental basis for the enhancement of the scaling factor of the resonant fiber gyroscope with the fiber ring resonator as the sensitive unit, providing options for multiple applications such as sea, land, sky and space.

One of the most important problems in the plasmonics of the terahertz (THz) range, which is actively developing now, is the efficient generation of surface plasmon polaritons (SPPs). The simplest and most promising technological technique of photon excitation of THz SPPs is through diffraction of radiation on the edge of the conducting surface of the sample (the end-fire coupling technique). In this paper, we experimentally evaluated the efficiency of the generation of monochromatic THz SPPs (λ0 = 141 μm) by this method with a sample in the form of a cylindrical segment, the convex surface of which has a gold layer coated by zinc sulfide (ZnS) with thickness d = 0–2 µm. Such configuration of the surface supporting the SPPs not only shields the detector from parasitic bulk waves arising during diffraction but also enables one to change the distribution of the SPP field in the air by varying the coating layer thickness d. On an uncoated gold surface, the SPP generation efficiency was η ≈ 20%. In the presence of a ZnS layer on the gold, the SPP generation efficiency gradually increased with d, reached the maximum (ηmax ≈ 60%) at d ≈ 1 μm, and then gradually decreased. Theoretical analysis showed that the efficiency of the SPP generation can be raised up to 80% due to the selection of an optimal SPP field profile via variation of the thickness of the dielectric layer on the metal surface, as well as with optimal incidence of the focused radiation on the edge of the sample.

The population aggregation and economic development caused by urbanization significantly influence the efficiency of urban resource consumption. However, the coupling interactions between crucial resource consumptions such as food, energy and water (FEW) and urbanization processes within highly urbanized areas has not been well-studied. In this study, we constructed an assessment framework for the coupling efficiency measurement of FEW resource consumptions in 10 administrative districts across Shenzhen megacity during 2012–2020, based on the data envelopment analysis (DEA). This study demonstrated that, from the perspective of the FEW nexus, increasing efficiencies in the energy consumption of most districts improved the municipal FEW efficiency, while more than half of the districts did not achieve water resource efficiencies throughout the period. Concerning regional economic development, 80% of the districts improved coupling FEW efficiencies by 2020, the average values of which were higher for Yantian, Nanshan, Luohu and Dapeng, and lower for Baoan, Longgang and Guangming, with a downtrend only being observed in Guangming. Overall, the value of the coupling FEW efficiency of Shenzhen megacity rose by 35% from 2012 to 2020. Correlation analysis showed that synergistic effects of efficient resource consumption occurred in most districts, and economic urbanization was the main driving factor of regional FEW efficiencies within Shenzhen megacity. This study provides instructive insights into the status of urban resource consumption and suggests that the coordination of FEW management should be further improved by fiscal intervention to maintain economic development with the limited resources available, which would have valuable implications for synergistic FEW governance in megacities in China and elsewhere. [ABSTRACT FROM AUTHOR]

Continuous-wave cavity ring-down spectroscopy (CW-CRDS) is an important technical means to monitor greenhouse gases in atmospheric environment. In this paper, a CW-CRDS system is built to meet the needs of atmospheric methane monitoring. The problem of mode matching is explained from the perspective of transverse mode and longitudinal mode, and the influence of laser injection efficiency on measurement precision is further analyzed. The results of cavity ring-down time measurement show that the measurement precision is higher when the laser is coupled with the fundamental mode. In the experiment, DFB laser is used to calibrate the system with standard methane concentration, and the measurement residual is less than ±4 Ă— 10âˆ'4 ÎĽsâˆ'1. The methane concentration in the air is monitored in real time for two days. The results show the consistency of the concentration changes over the two days, which further demonstrates the reliability of the system for the measurement of trace methane. By analyzing the influence of mode matching, it not only assists the adjustment of the optical path, but also further improves the sensitivity of the system measurement. [ABSTRACT FROM AUTHOR]

The efficient lens-to-waveguide light coupling has been an important issue in integrated photonic crystal circuits during the last years. In the present work, we theoretically study a hybrid structure consisting of photonic crystal lenses and waveguides. The lenses are made of circular Zirconia rods with the triangular structure in the air host in which the radii of the rods decrease from the center toward the edges along the transverse direction. We assumed that the rods are hollow and are infiltrated with nematic liquid crystals. The designed lenses are considered alongside square and triangular lattice waveguides made of Zirconia rods, for creating the coupled lens-waveguide structures. Then, the coupling efficiency of all mentioned structures is investigated, using finite-difference time-domain and plane-wave expansion methods. Finally, we study the variation of the coupling efficiency by changing the optical axis orientation of liquid crystals. Our numerical results show that through an appropriate set of optimum geometrical parameters, the coupling efficiency of 8.55 dB was obtained in our simulations, which can be tuned and controlled easily by an applied external static electric field. [ABSTRACT FROM AUTHOR]

We proposed a design scheme to enable the monolithic integration between a silicon waveguide and a 1.3 ÎĽ m wavelength band IIIâ€"V quantum dot laser, which is epitaxially grown on silicon with an asymmetric structure. The IIIâ€"V laser is grown in a deep trench of a silicon-on-insulator wafer by the selective area epitaxy technique, and a GaAs coupling layer is inserted into the lower cladding layer of the laser, which can make the optical field distribution of the laser shift down. Besides, a mode-size converter with a three-segment tapered structure is designed to couple the output laser into the standard single-mode silicon waveguide. For the laser, the composition and the thickness of AlGaAs cladding layers and AlGaAs transition layer are optimized based on the optical waveguide theory. When the upper cladding layer is 0.6 ÎĽ m Al0.7Ga0.3As, the lower cladding layer is 1.2 ÎĽ m Al0.25Ga0.75As, and the transition layer is 20 nm Al0.45Ga0.55As, the optical confinement factors of the active region and the coupling layer are 45.34% and 40.69%, respectively. Then the length of the mode-size converter with a three-segment tapered structure is further optimized by the mode-matching method. When the lengths of the three tapered structures of the mode-size converter are 50 ÎĽ m, 53 ÎĽ m and 10 ÎĽ m respectively, a coupling efficiency of 65% can be obtained between the laser and the Si waveguide. This scheme is expected to realize the efficient optical coupling between the silicon integrated light source and the silicon waveguide, which will promote the development of silicon monolithic photonic integration. [ABSTRACT FROM AUTHOR]

Silicon photonics technology has attracted considerable attention these days. However, the low coupling efficiency due to the difference in spot size between silicon photonic (SiPh) chips and single-mode fibers (SMFs) remains a challenging issue. We have already proposed a unique combination of a microlens and a pillar on the facet of SMF. However, the pillar may have difficulty in keeping a single mode for a signal beam of 1. 55 μ m wavelength due to air cladding. In this study, we clarified the length of the pillar that can support the single mode through simulations and experiments. By the optimum designing, the spot size as the same level as the SiPh chip was obtained. We could show that our coupling device provides high coupling efficiency with a test sample of SiPh chip, and this device also can be applied to multi-core fibers. [ABSTRACT FROM AUTHOR]

An investigation of angled flip-chip integration of a singlemode 850 nm vertical-cavity surface-emitting laser (VCSEL) on a silicon nitride photonic integrated circuit (PIC) is presented. Using numerical FDTD simulations, we consider the conditions under which the VCSEL can be integrated at an angle over a grating coupler with high coupling efficiency and low optical feedback. With both coupling efficiency and feedback decreasing with increasing angle, there is a trade-off. With co-directional coupling, first-order diffraction loss sets in at a critical angle, which further reduces the coupling efficiency. No such critical angle exists for contra-directional coupling. We also experimentally demonstrate angled flip-chip integration of GaAs-based 850 nm single transverse and polarization mode VCSELs over grating couplers on a silicon-nitride PIC. At the output grating coupler, light is either collected by an optical fiber or converted to a photocurrent using a flip-chip integrated GaAs-based photodetector. The latter forms an on-PIC optical link. We measured an insertion loss of 21.9, 17.6 and 20.1 dB with a singlemode fiber, multimode fiber and photodetector over the output grating coupler, respectively. [ABSTRACT FROM AUTHOR]

Lithium niobate (LiNbO 3 ) is emerging as an appealing candidate for integrated optical applications with enhanced complexity, owing to its inherent abundant optoelectronic properties. To compensate for the inability of LiNbO 3 to generate indistinguishable single photons, the evanescent coupling heterointerface constructed between III-V compound semiconductors (e.g., InP) and LiNbO 3 through plasma activation provides a feasible solution for balancing the integration efficiency and interfacial stability while achieving sub-50 nm alignment accuracy between devices, thus offering ultracompact on-chip light sources for classical optoelectronics and quantum optics. However, a challenge remains in the formation of the InP/LiNbO 3 platform due to the huge mismatch in the coefficient of thermal expansion. Here, we demonstrate the InP/LiNbO 3 covalent heterointerface using an asymmetric plasma activation strategy. Different plasmas are used for the activation of InP and LiNbO 3 specifically, balancing the enhancement of surface functional group density with the avoidance of defect generation effectively. More importantly, combined with surface comprehensive characterizations and interface performance, we determine that the introduction of ammonia solution enables the surface hydroxyl groups to be "effective" as LiNbO 3 surface relaxation increases the chance of -OH groups' contact. Therefore, a robust covalent bond network is established across the InP/LiNbO 3 interface at 80 °C with an enhanced bonding strength of 9.7 MPa. Moreover, a hybrid quantum photonic chip based on the InP/LiNbO 3 platform is designed to compute the coupling efficiency and the impact of misalignment on it, demonstrating the potential of extending the platform to hybrid integrated quantum systems.

When two parallel waveguides are close to each other, the power of the two adjacent waveguides will be periodically converted to form a directional coupled waveguide system (). The transverse coupling between two parallel waveguides can be described by mode coupling theory. However, in practical application, due to the limitation of equipment or manual computing capacity, it is impossible to quickly calculate the coupling efficiency of two optical fibers through the current specific formula. Through the form of MATLAB programming, it can determine whether the fiber is a single-mode fiber, solve the characteristic equation to obtain the propagation constant, integrate the coupling coefficients K12 and K21, solve the coupling efficiency in the fiber, and finally output in the form of graphics. The results show that for the directional coupler composed of two fibers, if the core radius and core refractive index change, the mismatching phase constant and coupling efficiency will change correspondingly, and the calculated results are in good agreement with the predicted results. On this background, this paper proposes the form of MATLAB programming to calculate coupling efficiency. The coupling efficiency of fiber directional couplers is analyzed. The theory gives accurate results within the actual parameters.

A chaotic adaptive seeker optimization algorithm (CASOA) is proposed in this study to improve the coupling efficiency and accuracy of a butterfly optical communication laser. It primarily relies on chaotic disturbance to improve seeker search performance. The chaotic disturbance enables the algorithm to jump out from local extremes. Furthermore, chaos is associated with a novel strategy for optimizing search paths with a small population. A simulation and experiment are conducted to demonstrate that the CASOA with a few seekers has an excellent search success rate with few iterations in the coupling alignment. These results indicate that the proposed CASOA can reliably improve the coupling accuracy and efficiency of laser diodes and single-mode fibers.

Non-Kolmogorov turbulence has been widely observed in free-space optical communication links and should be used to evaluate the system performance. We calculated the wavefront residual variance in the condition of the non-Kolmogorov turbulence model and deduced the mathematical expression of the probability density function (PDF) for the coupling efficiency (CE) of a single-mode fiber (SMF). The PDF was simulated, and the results showed its robustness and rationality. Moreover, an experiment was set up to verify the PDF with experimental distribution. The correlation coefficients are above 0.95 in all cases, which means the statistical model of the CE fitted the experimental distribution well. [ABSTRACT FROM AUTHOR]

Strain‐promoted alkyne‐azide cycloaddition (SPAAC) has become an indispensable tool in bioorthogonal conjugation and surface immobilization. While numerous studies have focused on enhancing the reactivity of cyclooctynes, a facile method to evaluate the binding efficiency for cyclooctyne‐azide‐based immobilization without any sophisticated facilities is still missing. In the present work, different derivatives of dibenzocyclooctyne/bicyclononyne (DBCO/BCN) linked to either a fluorophore or a biotin‐moiety are patterned on ultra‐low fouling polymer brushes, which can avoid unspecific protein contamination without any prior blocking steps. The polymer brushes are composed of an antifouling bottom block and azide‐terminated top block. The assessment of binding efficiency is conducted on ordered arrays spotted by microchannel cantilever spotting (μCS) with a normal fluorescent microscope. Both cyclooctynes demonstrate reliable binding performance with azide‐bearing diblock polymer brushes via μCS, but DBCO shows a higher surface density of molecular immobilization according to the protein binding assays. This work provides a reference for choosing appropriate cyclooctyne to couple with azides and can be useful for the design of biosensors or bio‐platforms for analyte detection, cell capture, and other biological applications. [ABSTRACT FROM AUTHOR]

An integrated opto‐mechanical cantilever sensor with a rib waveguide is reported in this paper. The device consists of a rib waveguide cantilever with buried waveguides on silicon. The rib cantilever is introduced to match better with the buried waveguide, further for increasing the interface coupling efficiency. With this configuration, single‐mode operating can be achieved in transverse direction without decreasing the width of optical waveguide cantilever. The system sensitivity is 1.1 μm–1 which is increased by about 21%, compared with the conventional structure. [ABSTRACT FROM AUTHOR]

• The study proposes a measuring methodology. This method offers practical applicability for verifying the engineering integrity of optical fibers already integrated into the system and for real-time monitoring of system status. • The measurement method combines the telescope pointing technique and a superconducting nanowire single photon detector. Analyzing the changes in photon numbers to obtain the actual coupling efficiency of multimode fiber. • Theoretical calculation of the coupling efficiency of multimode fibers in the laser ranging system. The measurement result is in agreement with the theoretical calculation. The receiving system adopts the coupling manner of space beam and the multimode fiber among some space target laser ranging system. The fiber coupling efficiency can affect the number of echo photons and ranging accuracy, especially in lunar laser ranging, high orbit satellite laser ranging and space debris tracking. This article proposes a method utilizing the telescope pointing technique and a four-pixel superconducting nanowire single photon detector (SNSPDs) to measure coupling efficiency of multimode fiber. SNSPDs has the excellent performance with high detection efficiency, low dark count rate, and low recovery time. In the experiment, SNSPDs receives the changing signals caused by adjusting the offset angle of the telescope. The root mean square of deviation between measured results and theoretical calculations is 4.48%. The method is based on existing laser ranging systems and is suitable for scientific engineering verification of optical fibers already installed in the system and monitoring of system status. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of interface angles on the coupling efficiency of a fiber Fabry-Perot interferometer (FFPI) sensor using both simulation and experimental methods. The FFPI sensor, which consists of a single-mode fiber (SMF), hollow-core fiber (HCF), and diaphragm, has its coupling efficiency determined by the generalized scattering matrix of the cascaded fiber system. To obtain the interface angles of the FFPI sensor, a new on-line monitoring system is developed based on microscopic images of the FFPI cavity and an image processing algorithm using OpenCV. By combining the eigenmode expansion method (EME) model and the online interface angle measurement technique, the coupling efficiency and spectral contrast of the FFPI cavity are evaluated and improved. Additionally, the corresponding working point in the intensity demodulation based FFPI sensor can be quickly identified. Using this method, an FFPI sensor with a spectral contrast of over 35 dB is achieved, which is significantly higher than existing similar sensors, and its sensitivity also reaches 50.80 mV/MPa. This work also holds significance for controlling and enhancing the spectral characteristics of other cascaded fiber optic sensors. • Advances FFPI fiber optic sensing to >35 dB spectral contrast & 50.80 mV/MPa pressure sensitivity. [ABSTRACT FROM AUTHOR]

• The Influences of coupling errors on laser transmission were explored with the established geometric and simulation model. • The thresholds of the laser-induced breakdown were measured. The laser transmission efficiency could be larger than 81.2 %. • A Gaussian shape distribution of laser in electrode exit, and the laser processing capability in large depth were verified. Laser and electrochemical machining (LECM) has been increasingly adopted to improve the efficiency and surface quality of micromachining. The coupling and high-efficiency transmission of laser in electrolyte are critical to the implementation of LECM, which were rarely studied in previous research. In this study, the geometric and simulation model of laser coupling and transmission within the electrolyte jet has been established for laser and shaped tube electrochemical machining (Laser-STEM). The critical coupling condition and transmission efficiency of laser beam was investigated theoretically. Influences of laser coupling errors on the laser transmission efficiency and laser power intensity distribution at the exit of hybrid tool electrode were explored. Results indicated that the angular offset had the greatest impact on laser transmission efficiency, while the longitudinal offset impact the least, which were accordance with the experimental results. The thresholds of laser power intensity and the frequency of the laser-induced electrolyte breakdown were measured. The thresholds for laser-induced breakdown in NaNO 3 solution were higher than that in NaCl solution. The laser power intensity threshold of laser-induced electrolyte breakdown increased with the increase of focal length, and the frequency of smaller than 4.5 could be obtained with the laser power density ranging from 2.35e9 to 1.06e10 W/cm2 at the focal spot. The distribution trended to more uniform at the exit with the increase of hybrid tool electrode length. A laser coupling efficiency of larger than 81.2 % has been achieved by utilizing the hybrid tool electrode with NA of 0.534 and acceptance angle of 32.3°. Finally, experiments with a designed raster-shaped workpiece were conducted to verify the feasibility of laser transmission in large depth in the Laser-STEM process. The high aspect-ratio small holes with a depth of 50 mm, and a diameter of 1.3 mm have been processed by using Laser-STEM. [ABSTRACT FROM AUTHOR]

A Large-tolerance Fiber Collimator (LTFC) consisting of a Thermally Expanded Core Fiber (TECF) and an aspherical lens is designed to solve the problems of low beam coupling efficiency and small coupling tolerance of conventional collimators. According to the Gaussian beam coupling theory, the beam deviation coupling model of the LTFC is established to analyze the effects of coupling deviation and fiber Mode Field Diameter (MFD) on the collimator coupling efficiency. Beam coupling simulations are carried out by ZEMAX, which analyzes the influence of the interaction of the three coupling deviations on the beam coupling efficiency. And the final experimental platform is built to test the performance of the designed LTFC in combination with simulation. The results show that the LTFC can achieve a beam coupling efficiency more than 80% with an angular deviation less than 0.06°, a radial deviation less than 0.06 mm, and an axial deviation less than 2 mm. The coupling efficiency can reach 97.24% when the collimator fiber MFD is 28 μ m and all the deviations are extremely small(close to 0). The LTFC has a large coupling tolerance while obtaining a high coupling efficiency, which reduces the difficulty of beam coupling. • We designed the Large-tolerance Fiber Collimator (LTFC) to solve the difficulties of beam collimation coupling and low coupling efficiency. • The coupling efficiency of the collimator at an MFD of 28 μ m increases to 97.24% compared to 52.27% when an SMF is used. • With angular, radial and axial deviation less than 0.06°, 0.06mm and 2mm, respectively, the LTFC can obtain more than 80% beam coupling efficiency. • The research provides a technical reference for the beam coupling and transmission in the rotating state. [ABSTRACT FROM AUTHOR]

A distinctive configuration of rectangular waveguide-fed hemispherical dielectric resonator antenna (HDRA) for high-gain dual-band operation is described in this letter. A cylindrical-shaped hard rubber with a circular slot and $\epsilon_r = 3$ is inserted between HDRA and ground plane to achieve dual-band, excellent coupling, enhanced bandwidth, and high gain. The structure of the antenna is very simple to fabricate. Measured results show that the proposed antenna radiates in two bands with resonant frequencies 7.65 and 10.04 GHz. The first band provides a bandwidth of 4.98% and a high gain of 11.72 dBi with a broadside radiation pattern. The second band enables wideband operation with an impedance bandwidth of 12.68% and a gain of 11.5 dBi. The structure attains high coupling efficiency in both bands. [ABSTRACT FROM AUTHOR]

Objective: To analyze intensity-latency functions of intraoperative auditory evoked brainstem responses (ABRs) to stimulation by the Vibrant Soundbridge (VSB) active middle ear implant with respect to coupling efficiency, VSB evoked ABR thresholds, and coupling modality [oval window (OW) placement vs. Incus placement and vs. round window (RW) placement]. Study Design: Exploratory study. Setting: Bi-centric study at tertiary referral centers. Patients: Twenty-four patients (10 female, 14 male, mean age: 58 years) who received a VSB. Outcome Measures: Wave-V intensity-latency functions of intraoperative VSB evoked ABRs using a modified audio processor programmed to preoperative bone conduction thresholds for stimulation. Threshold level correction to coupling efficiency and ABR thresholds. Individual plots and exponential function fits. Results: After ABR threshold level correction, the latency functions could be aligned. A large variance of latencies was observed at individual threshold level. Wave-V latency was longest in the Incus placement subgroup (9.73 ms, SD: 1.04) as compared to OW placement subgroup (9.47 ms, SD: 1.05), with the shortest latency in the RW placement subgroup (8.99 ms, SD: 0.68). For increasing stimulation levels, the variance decreased with intensity-latency function slopes converging toward a steady-state (saturation) latency caused by saturation of audio processor (stimulation) gain. Latency saturation was reached at a stimulation level of 50 dB nHL for the OW placement subgroup, 35 dB nHL for the Incus placement subgroup, and 30 dB nHL for the RW placement subgroup. The latency and saturation results indicated decreased dynamic range for RW placement, i.e., reverse stimulation. Conclusions: VSB evoked ABR wave-V intensity-latency function slopes were similar to acoustic stimulation at high stimulation levels with a shift toward longer latencies caused by audio processor signal delay. Saturation of latencies occurred for higher stimulation levels due to saturation of audio processor gain. Thus, the analysis of VSB evoked intensity-latency functions appears to allow for the objective assessment of a patient's individual dynamic range. This can further improve diagnostics as well as intraoperative and postoperative quality control. [ABSTRACT FROM AUTHOR]

ObjectiveTo analyze intensity-latency functions of intraoperative auditory evoked brainstem responses (ABRs) to stimulation by the Vibrant Soundbridge (VSB) active middle ear implant with respect to coupling efficiency, VSB evoked ABR thresholds, and coupling modality [oval window (OW) placement vs. Incus placement and vs. round window (RW) placement].Study DesignExploratory study.SettingBi-centric study at tertiary referral centers.PatientsTwenty-four patients (10 female, 14 male, mean age: 58 years) who received a VSB.Outcome MeasuresWave-V intensity-latency functions of intraoperative VSB evoked ABRs using a modified audio processor programmed to preoperative bone conduction thresholds for stimulation. Threshold level correction to coupling efficiency and ABR thresholds. Individual plots and exponential function fits.ResultsAfter ABR threshold level correction, the latency functions could be aligned. A large variance of latencies was observed at individual threshold level. Wave-V latency was longest in the Incus placement subgroup (9.73 ms, SD: 1.04) as compared to OW placement subgroup (9.47 ms, SD: 1.05), with the shortest latency in the RW placement subgroup (8.99 ms, SD: 0.68). For increasing stimulation levels, the variance decreased with intensity-latency function slopes converging toward a steady-state (saturation) latency caused by saturation of audio processor (stimulation) gain. Latency saturation was reached at a stimulation level of 50 dB nHL for the OW placement subgroup, 35 dB nHL for the Incus placement subgroup, and 30 dB nHL for the RW placement subgroup. The latency and saturation results indicated decreased dynamic range for RW placement, i.e., reverse stimulation.ConclusionsVSB evoked ABR wave-V intensity-latency function slopes were similar to acoustic stimulation at high stimulation levels with a shift toward longer latencies caused by audio processor signal delay. Saturation of latencies occurred for higher stimulation levels due to saturation of audio processor gain. Thus, the analysis of VSB evoked intensity-latency functions appears to allow for the objective assessment of a patient's individual dynamic range. This can further improve diagnostics as well as intraoperative and postoperative quality control.

Quantifying and interpreting the water-energy-food (WEF) nexus is critical to achieve the sustainable development of urban resources. The mismatch between urban water, energy and food allocations is a prominent problem that is particularly acute in the Yellow River Basin (YRB) of China. In this study, models for the WEF coupling degree and coupling efficiency were constructed. The WEF coupling efficiencies of the 94 cities in the YRB from 2011 to 2020 were quantified using a data envelopment analysis (DEA) model. On this basis, the spatial distribution characteristics and evolutionary trends of different urban WEF coupling efficiencies were analysed and explored using an exploratory spatial data analysis (ESDA) model and a parametric kernel density estimation model. The results show that the energy subsystem constrain the development of the WEF nexus, and the food subsystem, in turn, regulates the development of the WEF nexus. In some years, the phenomenon of 'resource curse' occurred, in which the WEF coupling degree increased while the coupling efficiency decreased. Overall, the values of the urban WEF coupling efficiency were low, ranging from 0.5300 to 0.6300, which is not effective. Spatial clustering was detected in the urban WEF coupling efficiency. The clustering types were 'high-high' clustering areas in less developed regions and 'low-low' clustering areas in developed regions. The two clusters and the median contiguous group had different evolutionary trends. Both efficiency and polarisation increased in the high-clustering group, efficiency improved in the low-clustering group, and a new efficiency pole was formed in the median contiguous group. Among the three grouped cities, we discuss the potential of policies such as cross-city cooperation, intra-city multi-sectoral cooperation and cultivating new central growth cities to improve the WEF coupling efficiency in the YRB., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Author(s).)

Efficient coupling of micro/nano-optical waveguides with single-mode fibers is the premise for the efficient operation of the integrated photonic chip, which directly determines its optical performance. In this paper, the design principles of periodically segmented waveguide (PSW) structure used for high-efficiency fiber-chip coupling are proposed, and the effects of refractive index difference Δ on coupling efficiency and structural parameters are studied by simulation. It is found that as the Δ of the PSW increases, the period of the PSW tends to be smaller, and the coupling efficiency decreases continuously, reduced by around 0.673 dB in the range of Δ = 3% to Δ = 7%. Through the analysis of PSW optical mechanisms, it demonstrates that the main reason for the decrease of coupling efficiency is that the transmission loss of the tapered section increases sharply with the increase of Δ. High-Δ PSW is difficult to apply to highly integrated silica optical chips due to the unignorably insertion loss. [ABSTRACT FROM AUTHOR]

We report the first experimental characterizations of the coupling efficiencies of a series of e-beam fabricated focusing non-uniform grating couplers interfaced with a horizontal fiber coupling-scheme and designed for multiple Silicon-On-Insulator thicknesses, spanning between the 220 and 340 nm standard platforms. The design of nonuniform grating couplers is tackled either from an engineering perspective focused on to the optimization of the structures for this particular coupling-scheme; and a physics perspective related to the investigation of the scattering process of each structure for a complete comprehension of its performance in support to the experimental findings. Measured coupling efficiencies, up to 83% for the 340 nm platform at 1550 nm, are reported showing to be in excellent agreement with the theoretical findings. The physics behind the scattering process of each structure is investigated taking advantage of the Finite Difference Time Domain method to obtain a deeper understating of the coupling efficiencies. Consequently, a new parameter, the integrated leakage factor, together with the variation of the effective refractive index, across the local pitches, are calculated. Our belief is that any coupling structure for grating coupling can benefit from the proposed designed approach, as a widely applicable technique. [ABSTRACT FROM AUTHOR]

The population aggregation and economic development caused by urbanization significantly influence the efficiency of urban resource consumption. However, the coupling interactions between crucial resource consumptions such as food, energy and water (FEW) and urbanization processes within highly urbanized areas has not been well-studied. In this study, we constructed an assessment framework for the coupling efficiency measurement of FEW resource consumptions in 10 administrative districts across Shenzhen megacity during 2012–2020, based on the data envelopment analysis (DEA). This study demonstrated that, from the perspective of the FEW nexus, increasing efficiencies in the energy consumption of most districts improved the municipal FEW efficiency, while more than half of the districts did not achieve water resource efficiencies throughout the period. Concerning regional economic development, 80% of the districts improved coupling FEW efficiencies by 2020, the average values of which were higher for Yantian, Nanshan, Luohu and Dapeng, and lower for Baoan, Longgang and Guangming, with a downtrend only being observed in Guangming. Overall, the value of the coupling FEW efficiency of Shenzhen megacity rose by 35% from 2012 to 2020. Correlation analysis showed that synergistic effects of efficient resource consumption occurred in most districts, and economic urbanization was the main driving factor of regional FEW efficiencies within Shenzhen megacity. This study provides instructive insights into the status of urban resource consumption and suggests that the coordination of FEW management should be further improved by fiscal intervention to maintain economic development with the limited resources available, which would have valuable implications for synergistic FEW governance in megacities in China and elsewhere.

Bit-error rate (BER) performance of free-space optical communication (FSO) systems is compromised by pointing errors. Few-mode fiber (FMF) based receiver emerges as a promising solution for FSO, because FMF can obtain high coupling efficiency in the presence of pointing errors. The high coupling efficiency allows FMF based system to achieve improved BER performance. In this letter, based on a simplified mode demultiplexer model, we propose a method to use the coupling efficiencies of each mode of FMF to characterize the BER of the FMF based FSO system having nonzero boresight pointing errors. We find that the boresight displacement can significantly deteriorate the BER performance, and the jitter variance can reduce the impact of boresight within a suitable range. [ABSTRACT FROM AUTHOR]

Increased water, energy, and food demand lead to resource risks and environmental threats. There is a complex nexus between the three. Evaluating WEF coupling efficiency based on WEF Nexus helps suggest sustainable resource utilization by analyzing the current resource coupling utilization situation. However, neglecting the influence of the external environment and lacking a clear understanding of the interactions within the WEF system can lead to biased assessments. Therefore, this study considers negative environmental impacts and clarifies interactions within the WEF system based on resource conversion relationships to develop a new framework for evaluating the WEF coupling efficiency. The framework is applied to the Yellow River Basin to provide relevant suggestions for promoting the healthy development of resources and the environment. The results indicate that WEF coupling efficiency in the Yellow River Basin during 2000–2020 was maintained at a medium level with an overall increasing trend. The middle and lower regions are medium to high efficiency, and 65% are on an upward trend. However, the low-efficiency areas are all located upstream, and 80% of them are decreasing. There is a growing gap in WEF coupling efficiency between regions. The increase in efficiency was mainly attributed to improvements in energy and food systems. The water system was the key reason for the lower efficiency. Evaluating environmental impacts based on sensitivity analysis, the energy system's negative environmental factors (NEFs) led to the most significant decrease in WEF coupling efficiency, with an average reduction of up to 8%. Based on the Tobit model to analyze the external drivers of WEF coupling efficiency, WEF coupling efficiency is higher in the case of richer cultivated land resources, more intensive labor force, and less precipitation. In conclusion, promoting technological innovation of the water system, optimizing resource allocation, and controlling pollutant emissions are effective measures to optimize the efficiency of WEF coupling for the high-quality development of the Yellow River Basin. [Display omitted] • A coupling assessment framework was developed based on the water-energy-food nexus. • The framework describes conversion relationships containing environmental impacts. • Emissions from the energy system constrained the increasing WEF coupling efficiency. • Precipitation, labor, and cultivated land significantly affected coupling efficiency. • Recommendations for achieving sustainable resource utilization were proposed. [ABSTRACT FROM AUTHOR]

• Laser diode, graded-index lens, and fiber constitute coupling system. • Component misalignment with various parameters for calculating coupling efficiency. • The results can guide manufacture of fiber-coupled diode lasers. For single emitter fiber coupling module, miniaturization and high stability have always been the goal in the field of industry and medical. Based on the beam propagation principle, a compact, flexible, and simple coupling optical system between laser diode (LD) and multimode fiber (MMF) by graded refractive index (GRIN) lens is proposed, which shows a coupling structure with relatively loose optical tolerance. The coupling efficiency is explored under all kinds of optical coupling system parameters, such as the working distance between the GRIN lens and MMF, incident wavelength, slow axis divergence angle of the LD, fiber diameter, and GRIN lens length. The results show that the maximum coupling efficiency reaches 97.55% in the simulation when not considering the lens refraction loss and fiber end face loss, and the maximum coupling efficiency reaches 90.8% in the experiment, which indicating the rationality and applicability of the designed model. The optimized model allows the fiber and GRIN lens to coaxially assemble, and the axial deviations and transverse displacements for influencing coupling efficiency are also discussed in detail. These results provide an important reference point for the design and manufacture of fiber-coupled diode lasers. [ABSTRACT FROM AUTHOR]