Propagation Length Research Articles

Enhanced detection accuracy and signal-to-noise ratio of surface plasmon resonance based refractive index sensor with the addition of thicker layer of Silicon

The improvement in the sensitivity performance of conventional surface plasmon resonance (SPR) based sensors with the addition of thin layers of various high index dielectrics (e.g. 5 nm–10 nm of Silicon) is well established. This improvement in sensitivity comes at a price of reduced detection accuracy, deteriorated signal-to-noise ratio (SNR) and small value of Figure of Merit (FOM). Sensors with high detection accuracy and SNR find applications in the direct detection of small molecular (few hundreds of Daltons) interactions or low molecular concentrations (physiological concentration) on the surface of the sensor. The current paper presents design methodology and theoretical analysis of the performance of SPR based refractive index sensor with enhanced SNR, detection accuracy, and FOM attained when a thicker layer of Silicon (60 nm–400 nm thickness) is introduced in the conventional Kretschmann configuration employing angular interrogation technique. The analysis is valid for any high index dielectric layer that is used to enhance the electromagnetic field associated with the surface plasmon (SP) mode excited at the metal-dielectric interface. In the present paper, we show that the SP mode which participates in the sensing applications can be excited at the metal-dielectric interface for multiple thicknesses of Silicon. Analytical expressions are derived to compute the multiple thicknesses of Silicon using a modal analysis as well as the transfer matrix method (TMM) by considering the SPR sensor as a multi-layered optical waveguide structure. The refractive index SPR sensor with thicker silicon layer is shown to exhibit a long propagation length and large penetration depth in the analyte region, resulting in a higher depth-to-width ratio (defined as the SNR) and detection accuracy in its SPR reflectivity spectrum, hence enhancing the measurement precision of the sensor.

Determination of propagation constant and impedance of non-reciprocal networks/lines using a generalized line-line method

A novel “line-line” (LL) method is generalized to determine forward and backward propagation constants (γ+ and γ−) and wave impedances (Z+ and Z−) of non-reciprocal networks/lines. It considers a reference network/line with any propagation constant, impedance, and length for this goal. A theoretical analysis is carried out to examine under which circumstance wave impedance together with propagation constant can be determined by the new general LL method. Measurements of γ+, γ−, Z+, and Z− of a microwave phase shifter (a nonreciprocal network) are conducted to validate our proposed method and examine its accuracy, through normalized root-mean-square and goodness of fit values, using uncalibrated scattering parameter measurements.

Theoretical and experimental research on a spatially modulated femtosecond bessel-like laser for microdrilling in silica glass

Beam shaping has been widely used in laser processing. Compared with Bessel beam, Bessel-like beam has unique advantages of fabricating high-aspect-ratio holes due to its tunable and longer non-diffraction length. However, the theoretical and experimental optimization of Bessel-like beams for laser manufacture has remained to be investigated. In this paper, we established a theoretical model of the intensity distribution and peak energy density of the Bessel-like beams based on a simplified phase of arc axicon. It was found that the longer propagation length and the lower peak energy density of the Bessel-like beams, contributed to the longer ablation length and higher ablation precision in the silica glass. The ablation length of the optimized Bessel-like beams was at least 1.6 times longer than that of the Bessel beam, which furtherly improved the fabrication efficiency of microdrilling.

Custom Nonlinearity Profile for Integrated Quantum Light Sources

Heralded single-photon sources are a fundamental building block for optical quantum technologies. These sources need to be unfiltered and integrated to have good scalability and avoid unnecessary losses. To attain this goal, it is necessary to control the effective nonlinearity seen by the fields as they mix and propagate in a waveguide source. In this paper, we introduce a method to design nonlinear waveguides with arbitrarily shaped effective nonlinearity profiles. The method takes advantage of the fact that the second-order nonlinear response is a tensor quantity and thus the local effective nonlinearity of a material depends on the propagation direction of the fields participating in the interaction. Thus, by locally changing the propagation direction of the fields we can modulate the wave-mixing process. Our method allows for the waveguide fabrication process to be significantly simplified. The material structure of the waveguide is made by a single crystal, no longer needing oriented patterning or periodic poling. We use our method to design waveguides with a nonlinearity profile that is Gaussian in the propagation length, allowing the generation of perfectly pure heralded single photons.

Epsilon‐Near‐Zero Enhancement of Nonlinear Responses from Intersubband Transitions in the Mid‐Infrared

AbstractMany applications of photonics require efficient nonlinear optical interactions with low power and small footprints. However, the current needs for long interaction lengths and strong laser sources of nonlinear optical devices make them unsuitable for nanophotonic integrated optics. New materials and devices with stronger nonlinear properties have been developed using various approaches in the past few years. One of the largest nonlinear optical responses reported to date has been realized with engineered intersubband transitions in n‐doped multiple quantum wells (MQWs) semiconductors. Here, this work proposes to improve further the nonlinear properties of a MQW heterostructure by tailoring its permittivity to reach near‐zero values. Materials with vanishing permittivity, called epsilon‐near‐zero (ENZ) materials, have exotic nonlinear features which can be explored to achieve this goal. To prove this point, this work makes use of In0.53Ga0.47As/Al0.48In0.52As, designs an ultrathin multilayer structure, and couples the designed structure with metasurfaces. Unprecedented nonlinear efficiency within subwavelength propagation lengths is obtained. Such structure with strong second harmonic generation (SHG) enables efficient frequency conversion, while the tunability offered by the metasurface provides new degrees of freedom to control the amplitude, phase, and polarization of the nonlinear light.

Role of SSW on thermal-gradient induced domain-wall dynamics

We study the thermal gradient (TG) induced domain wall (DW) dynamics in a uniaxial nanowire in the framework of the Stochastic-Landau–Lifshitz–Gilbert equation. TG drives the DW in a certain direction, and DW (linear and rotational) velocities increase with TG linearly, which can be explained by the magnonic angular momentum transfer to the DW. Interestingly, from Gilbert damping dependence of DW dynamics for fixed TG, we find that the DW velocity is significantly smaller even for lower damping, and DW velocity increases with damping (for a certain range of damping) and reaches a maximal value for critical damping which is contrary to our usual desire. This can be attributed to the formation of standing spin wave (SSW) modes (from the superposition of the spin waves and their reflection) together with travelling spin wave (TSW) modes. SSW does not carry any net energy/momentum to the DW, while TSW does. Damping α compels the spin current polarization to align with the local spin, which reduces the magnon propagation length and thus α hinders to generate SSWs, and contrarily the number of TSWs increases, which leads to the increment of DW speed with damping. For a similar reason, we observe that DW velocity increases with nanowire length and becomes saturated to maximal value for a certain length. Therefore, these findings may enhance the fundamental understanding as well as provide a way of utilizing the Joule heat in the spintronics (e.g. racetrack memory) devices.

3D Dirac semimetal supported thermal tunable terahertz hybrid plasmonic waveguides.

By depositing the trapezoidal dielectric stripe on top of the 3D Dirac semimetal (DSM) hybrid plasmonic waveguide, the thermal tunable propagation properties have been systematically investigated in the terahertz regime, taking into account the influences of the structure of the dielectric stripe, temperature and frequency. The results manifest that as the upper side width of the trapezoidal stripe increases, the propagation length and figure of merit (FOM) both decrease. The propagation properties of hybrid modes are closely associated with temperature, in that when the temperature changes in the scope of 3-600 K, the modulation depth of propagation length is more than 96%. Additionally, at the balance point of plasmonic and dielectric modes, the propagation length and FOM manifest strong peaks and indicate an obvious blue shift with the increase of temperature. Furthermore, the propagation properties can be improved significantly with a Si-SiO2 hybrid dielectric stripe structure, e.g., on the condition that the Si layer width is 5 µm, the maximum value of the propagation length reaches more than 6.46 × 105 µm, which is tens of times larger than those pure SiO2 (4.67 × 104 µm) and Si (1.15 × 104 µm) stripe. The results are very helpful for the design of novel plasmonic devices, such as cutting-edge modulator, lasers and filters.

Simplified design of a hybrid plasmonic waveguide to maximize propagation length

We design a waveguide for maximizing propagation length using the COMSOL environment based on the finite element method. The proposed design aims to achieve a high propagation distance and a constrained normalized TM mode. The range of propagation length (5−12)mm and the normalized TM mode area range can be achieved in the range of gap thickness (2−17)nm, silver thickness (1−6)nm, and arc radius 50nm. A trade-off will be between having a small mode area and a long propagation length in a successful hybrid plasmonic waveguide (HPW) design. The findings show that, with such a small mode area and long propagation length of SPPs at the wavelength 1.55μm, the suggested waveguide may avoid the unavoidable loss-confinement trade-off, which is desirable for integrated circuits. Balancing the arc radius and gap thickness at the widely used wavelength of 1.55 µm typically yields the required results. A substantial confinement coefficient has been achieved, essential in the HPW field.

Real-space observation of ultraconfined in-plane anisotropic acoustic terahertz plasmon polaritons.

Thin layers of in-plane anisotropic materials can support ultraconfined polaritons, whose wavelengths depend on the propagation direction. Such polaritons hold potential for the exploration of fundamental material properties and the development of novel nanophotonic devices. However, the real-space observation of ultraconfined in-plane anisotropic plasmon polaritons (PPs)-which exist in much broader spectral ranges than phonon polaritons-has been elusive. Here we apply terahertz nanoscopy to image in-plane anisotropic low-energy PPs in monoclinic Ag2Te platelets. The hybridization of the PPs with their mirror image-by placing the platelets above a Au layer-increases the direction-dependent relative polariton propagation length and the directional polariton confinement. This allows for verifying a linear dispersion and elliptical isofrequency contour in momentum space, revealing in-plane anisotropic acoustic terahertz PPs. Our work shows high-symmetry (elliptical) polaritons on low-symmetry (monoclinic) crystals and demonstrates the use of terahertz PPs for local measurements of anisotropic charge carrier masses and damping.

Numerical evaluation of an external environment effectiveness to the surface plasmon mode in Au slot waveguide for design the sensor simulation

The effective permittivity of gold thin films with an external thin dielectric layer on the top and core of the slot waveguide was evaluated as an effective compound semi-metal layer of the surface plasmonic polariton slot waveguide that will vary due to some environmental factors. By uses simple parallel and series permittivity of compound material, this value need for the computation of the effective propagating vector βsp. This takes for a sensor model designing which the external environment effectiveness was changed by the surface plasmonic mode in its slot waveguide. So the resonance length and grating period are evaluated for the sensor model in the first. Further, the propagation of the SPP surface wave mode along the interface between the compound cladding and Si dielectric waveguide is computed, while the effective refractive index of the compound cladding of the slot waveguide is increased from 1 − 1.50. The computation results showed that the TM0 mode power transfer and propagation length seem to vary with this effective refractive index of the compound cladding on the surface plasmonic polariton waveguide. The 140 nm gap width and 3.70 mm long waveguide is also simulated by the finite different time domain method in the optiwave program, where the TM0 mode transition output is corrected, while the refractive index of the environment layer is changed. The results of the simulation showed good agreement with the computation in that the TM0 mode depends on the external refractive of index and input wavelength. This result shows that loss peak ships vary with the external refractive index thin film layer and input wavelength. Thus, they seem to be useful for sensor applications such as the solution concentration analytic.

Atmospheric effects on the laser-driven avalanche-based remote detection of radiation

The effect of realistic atmospheric conditions on mid-IR (λ = 3.9 µm) and long-wave-IR (λ = 10 µm) laser-induced avalanche breakdown for the remote detection of radioactive material is examined experimentally and with propagation simulations. Our short-range in-lab mid-IR laser experiments show a correlation between increasing turbulence level and a reduced number of breakdown sites associated with a reduction in the portion of the focal volume above the breakdown threshold. Simulations of propagation through turbulence are in excellent agreement with these measurements and provide code validation. We then simulate propagation through realistic atmospheric turbulence over a long range (0.1-1 km) in the long-wave-IR regime (λ = 10 µm). The avalanche threshold focal volume is found to be robust even in the presence of strong turbulence, only dropping by ∼50% over a propagation length of ∼0.6 km. We also experimentally assess the impact of aerosols on avalanche-based detection, finding that, while background counts increase, a useful signal is extractable even at aerosol concentrations 105 times greater than what is typically observed in atmospheric conditions. Our results show promise for the long-range detection of radioactive sources under realistic atmospheric conditions.

Waveguide-Integrated Light-Emitting Metal–Insulator–Graphene Tunnel Junctions

Ultrafast interfacing of electrical and optical signals at the nanoscale is highly desired for on-chip applications including optical interconnects and data processing devices. Here, we report electrically driven nanoscale optical sources based on metal-insulator-graphene tunnel junctions (MIG-TJs), featuring waveguided output with broadband spectral characteristics. Electrically driven inelastic tunneling in a MIG-TJ, realized by integrating a silver nanowire with graphene, provides broadband excitation of plasmonic modes in the junction with propagation lengths of several micrometers (∼10 times larger than that for metal-insulator-metal junctions), which therefore propagate toward the junction edge with low loss and couple to the nanowire waveguide with an efficiency of ∼70% (∼1000 times higher than that for metal-insulator-metal junctions). Alternatively, lateral coupling of the MIG-TJ to a semiconductor nanowire provides a platform for efficient outcoupling of electrically driven plasmonic signals to low-loss photonic waveguides, showing potential for applications at various integration levels.

Nonlinearity in surface plasmon polaritons at interface between triple quantum dot and nanocomposite medium

This paper focuses on investigating the generation and manipulation of surface plasmon polaritons (SPPs) at the interfaces between quantum dot (QD) molecules and nanocomposite media. We utilize three different gate voltage values and incident laser field strengths to control the propagation of SPPs. We find a significant improvement in the SPPs' propagation length at the interfaces between the QD molecules and nanocomposite media. Additionally, under the Kerr effect, the gate voltage variation provides opportunities to control the SPPs' propagation. Through modifying the intensity and frequency of the incident probe field, we can manipulate various properties of SPPs at the suggested model's interfaces. Our results indicate a large enhancement in the SPPs' propagation length at the interfaces. Notably, we estimate the skin depth and wavelength of SPPs for three distinct values of the incident probe field and gate voltage applied in the QD molecules.

Plasmon Thermal Conductance and Thermal Conductivity of Metallic Nanofilms

The thermal conductance and thermal conductivity of surface plasmon polaritons propagating along a metallic nanofilm deposited on a substrate are quantified and analyzed, as functions of the film thickness, length, and temperature. This is done by analytically solving the dispersion relation of plasmons for their wave vectors and propagation length. It is shown that the plasmon energy transport along the film interfaces is driven by two modes characterized by symmetric and antisymmetric spatial distributions of the magnetic field. For a gold nanofilm deposited on a silicon substrate, both modes have comparable contributions of the plasmon thermal conductance, which takes higher values for hotter and/or longer nanofilms and saturates for films thicker than 50 nm. This saturation arises from the decoupling of the plasmon modes, the transition of which to a coupled state for thinner films maximizes the plasmon thermal conductivity. For a 1-cm-long gold nanofilm at 300 K, the maximum thermal conductivity appears for a thickness of 10 nm and takes the value of $15\phantom{\rule{0.2em}{0ex}}\mathrm{W}\phantom{\rule{0.1em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.1em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$, which is about 25% of its electron counterpart. As a result of the huge propagation distance ($>1\phantom{\rule{0.2em}{0ex}}\mathrm{cm}$) of plasmons, this plasmon thermal conductivity increases significantly with the film length and temperature and it could therefore be useful to improve the heat dissipation along metallic nanofilms.

Effect of N2 and CO2 on explosion behavior of hydrogen-air mixtures in non-premixed state

In this paper, the suppression effects of non-premixed inert gas (N2, CO2) on hydrogen-air explosion behaviors are experimentally studied. The effects of N2 and CO2 addition on flame propagation, explosion pressure and flame length are analyzed. The results show that N2 and CO2 can effectively reduce the explosion hazard in non-premixed state. The mixing process of non-premixed gases leads to the development of turbulent flame, but the suppression of inert gas on explosion exceeds the promotion of turbulent flame. Under the action of N2 and CO2, the energy of the flame decreases, and the front contour becomes blurred. When the fuel zone is only set at the ignition end, with the suppression of N2 and CO2, the maximum explosion pressure is reduced by 35.1% and 50.6%, respectively. It is worth noting that the high-frequency periodic oscillation and pressure soaring appear in the pressure histories, which are attributed to the rapid phase transition of water. Furthermore, the two inert gases can significantly reduce the chemical reaction rate and heat release rate during the explosion, which is reflected in the decrease of the maximum flame length. It is found that N2 and CO2 have different explosion suppression effects and mechanisms, but CO2 has better suppression performance on hydrogen-air explosion.

Study of workshop network stability based on pinning control in disturbance environment

In the production process, the manufacturing behavior and all the essential factors are affected by several disturbance factors, showing a complex dynamic fluctuation law. It makes the stability control process a difficult problem in environmental constraints. In this paper, the workshop production process is considered, and an improved coupled map lattice workshop production network state model is proposed. On this basis, the controller with the function of resource load protection is designed, and the network state model of the workshop based on the pinning control is developed. Three kinds of stability control strategies, SAC (Self-adaption Control) , SC (Self-acting Control) and PC (Pinning Control) , are designed based on disturbance triggering behavior and node state transition rules. In addition, two control effect evaluation indexes, RTS (Recovery Time Steps) and NFT (Node Failure Times) are designed. Considering the actual production data of diesel fuel injection system parts production workshop as example, the model is simulated and verified. The results show that under different disturbance intensities, compared with the SAC strategy, the RTS-Average value of the PC strategy is reduced by 29.83% on average, and the NFT-Average values are reduced by 46.9% on average. This proves that the pinning control strategy has certain advantages in controlling time length and propagation scale of disturbance propagation.

Characterization of fracture development in geometrical similar ultra-high-performance concrete (UHPC) beams using acoustic emission (AE) technique

The acoustic emission (AE) technique is a common method for evaluating the fracture and damage properties of materials. This study utilized the AE technique to analyze the fracture behavior of ultra-high-performance concrete (UHPC) beams. Experiments were conducted on three differently sized beam specimens that were geometrically similar. The center point bending tests were carried out under crack mouth opening displacement (CMOD) control to study the fracture properties of the UHPC beams. Based on the experimental study, the fracture properties such as crack propagation, parametric-based properties, and fracture process zone (FPZ) length and width were predicted in the present work. The AE waves generated during the cracking can readily differentiate between the concrete matrix failure and fiber bridging following the post-peak response in the UHPC beam. In this work, the AE parameters were used to detect the source location, fracture mode, the position of the crack, and strain localization near the crack tip. The presence of steel fibers in concrete provides complexity in identifying the source localization, and wave dispersion results in attenuation and distortion of the AEs. The occurrence of AE events was observed to increase in the post-peak part compared to pre-peak possibly due to fiber bridging, demonstrating the energy absorption capacity. Based on AE results, the length and width of the fracture process zone were found to increase with the specimen size.

Role of natural fractures with topology structure for hydraulic fracture propagation in continental shale reservoir

Natural fractures tend to further promote fracture network which is initiated by hydraulic fracturing. However, how natural fractures with various topology structures impact hydraulic fracture propagation in continental shale reservoir is still unclear. With Fullbore Microscan Imager (FMI) and geo-statistics of Chang 7 reservoir in Yanchang Formation, typical natural fractures are classified into three topology structures, which are natural fractures with type I, type II and type III nodes respectively, and the average occurrence strikes of natural fractures with type I, type II and type III nodes are SW260°, SW255° and SW255°. Coupling with seepage field and stress field, a model simulating fracture initiation and propagation is established considering the transversely isotropic property of continental shale reservoir. On this basis, the role of typical natural fractures with topology structure for hydraulic fracture propagation is studied qualitatively and quantitatively by Finite Element Method (FEM) with globally embedded cohesive element. Natural fractures with type II nodes have largest effect on inducing hydraulic fracture propagation, hydraulic fractures can communicate most easily with them, and also the length and velocity of hydraulic fracture propagation are the longest and fastest, so fracture network is the most complex after fracturing in naturally fractured continental shale reservoir with type II nodes, which follows by the effect of hydraulic fracture propagation in naturally fractured continental shale reservoir with type III nodes. In comparison, natural fractures with type I nodes have insignificant impacts on hydraulic fracture propagation. The research results are conductive to fracturing design in continental shale reservoir.

All‐Dielectric Huygens’ Meta‐Waveguides for Resonant Integrated Photonics

AbstractThe growing maturity of nanofabrication technology has recently enabled the deployment of high‐quality subwavelength nanostructures on photonic chips. Combining existing photonic waveguide technology with the paradigms adapted from metamaterials opens new avenues towards unprecedented control of guided light waves. However, developing new functionalities while preserving efficiencies and offering compatibility with current technology remains a major challenge in on‐chip nanophotonics. Here, a novel silicon nanophotonic waveguide comprising a chain of resonantly forward scattering nanoparticles empowered by spectrally overlapping electric and magnetic dipolar Mie‐type resonances is proposed and demonstrated. The propagation loss of the meta‐waveguides in the telecom spectral range is as low as 0.4 dB mm−1, exceeding the current record for Mie‐resonant waveguides by more than an order of magnitude. Furthermore, the meta‐waveguides support a negative group index over a broad spectral range of 60 nm and regions of vanishing and anomalous dispersion within the transmission band. Finally, it is shown that meta‐waveguide topologies can implement compact resonance‐protected waveguide bends and efficient splitters within just 320 nm propagation length. This work addresses the fundamental challenges of miniaturization, dispersion, and scattering control in integrated photonics and opens new opportunities for enhancing light–matter interactions, interfacing nanophotonic components, and developing nonlinear, ultrafast, and quantum optics resonant on‐chip devices.

Ab initio Boltzmann approach to coupled magnon-phonon thermal transport in ferromagnetic crystals

We propose an ab initio Boltzmann transport approach taking into account magnon-phonon scattering (MPS) and three-phonon scattering simultaneously to accurately evaluate the thermal transport properties of ferromagnetic crystals. Using this approach, we studied the nonelectronic thermal transport properties of the body-centered cubic iron as a case. The reasonable agreement between our calculation results and the available experimental data suggests that phonons dominate the nonelectronic thermal conduction at high temperatures, and magnons may contribute to the thermal conductivity only at low temperatures. Remarkably, the abnormal increase in the magnon thermal conductivity at high temperatures implies that other magnon-involved scattering events instead of MPS should dominate the magnon thermal conductivity. Moreover, analyses of average scattering rates and heat propagation lengths suggest that hydrodynamic heat transport may occur at low temperatures. This new approach fills the gap in the first-principles evaluation of the coupled magnon-phonon thermal transport properties in magnetic crystals. Our results will provide valuable references for further investigations of the interplay between magnons and phonons and broaden relevant research prospects about heat management and energy manipulation.