Single-mode Research Articles

Experimental and numerical investigations of the energy performance of a solar seasonal thermal storage heating system under different operation modes in cold-region tunnels

Solar seasonal thermal storage heating (SSTSH) system is a new type of energy-efficient and environment-friendly anti-freezing technology in cold-region tunnels. The purpose of this study is to investigate the energy performance of an SSTSH system operated in different modes by using field experimental tests and numerical simulation. The experimental system is installed in Tianshan Shengli Tunnel of Xinjiang, China. Three operation modes including single heat storage, single heat extraction, and combined operation mode are investigated under different flow rates and inlet temperatures. The thermal performance, system operational efficiency and borehole wall temperature are analyzed and compared under various modes. The experimental results indicate that for the single heat storage operation mode, the thermal storage performance can be improved by enhancing the flow rate and inlet temperature. However, when ensuring the thermal storage amounts, a lower flow rate or inlet temperature should be employed to improve system efficiency. For single heat extraction operation mode, the heat extraction performance is effectively improved by lowering the inlet temperature, while the coefficient of performance (COP) is decreased. It is advisable to maintain a higher inlet temperature to improve operational efficiency of heat extraction. For the combined operation mode, the simulation shows the heat extraction performance of the SSTSH system can be greatly improved by the increasing the heat storage inlet temperature. When the heat storage inlet temperature increases by 5 °C, the growth rate of the average heat extraction amount is 2.45 W/m during the combined operation mode. The seasonal heat stored raises the surrounding rock temperature to a higher level, which is beneficial for increasing the COP of the heat pump, and effectively addresses the thermal imbalance in cold regions. The combined operation mode of the SSTSH system is recommended for the tunnel heating in cold regions.

A comprehensive assessment of gap spacing in tandem cylinders: Lattice Boltzmann technique based simulations

The current study uses the Lattice Boltzmann method (LBM) to analyze flow phenomena around the five square cylinders in a tandem setup. It examines flow characteristics for different gap spacing (g*), ranging from 0.5 to 8 at a Reynolds number Re = 100, and identifies three distinct flow modes: steady flow mode, partially unsteady flow mode, and partially packed vortex street in a single row. It is found that the flow modes reported in literature for the case of inline bodies exist for the present case as well but with a different range of gap ratios. The strength of vorticity in the wakes of the first three upstream cylinders is found to be increasing thus enhancing the Strouhal number as the gap ratio between cylinders increased. The drag mean coefficient (Cdmean) is found to increase with an increase in gap spacing values, while negative Cdmean values are observed for cylinders C2 and C3 in the steady flow mode, due to the emergence of thrust force. The average drag coefficient is found to be minimal for C2 until g* = 6 compared to other cylinders, while for C1 it is found to be higher across all gap spacings. The local minimum average drag coefficient value of 0.1824 is observed for C2 at g* = 1.5 while the local maximum Cdmean value of 1.2849 is observed for C1 at g* = 8 in this study. A similar shedding frequency emerges for the first three cylinders which mostly spanned over the partially packed single row vortex street flow mode. The research also reveals that g* = 4 is the critical spacing value for abrupt fluid flow changes.

Dual-channel SPR sensor based on an MMF-DHSMF-NCF reflective structure

This manuscript introduces a novel dual-channel surface plasmon resonance (SPR) sensor, employing a reflective configuration comprising fused multimode fiber (MMF), dual-hole single mode fiber (DHSMF), and no-core fiber (NCF) for refractive index (RI) and temperature detection simultaneously. By exploiting distinct refractive indices outside the fibers, the sensor enables dual-channel SPR functionality: one channel is activated by a gold-covered DHSMF for RI sensing, while the other utilizes a gold and polydimethylsiloxane (PDMS)-coated NCF for temperature monitoring. Experimental results illustrates sensitivities to refractive index and temperature are 4341 nm/RIU and −2.63 nm/℃, respectively. With its compact design, ease of installation, and robust stability, the sensor is well-suited for concurrent RI and temperature detection.

Hydrogen-induced O–H peak growth in Ge-doped optical fibers: Verification of empirical and theoretical models

Migration of hydrogen in optical fibers and its chemical reactions with the glass fiber core create added optical loss, that may deteriorate the light transmission through the fiber. Although this subject has been extensively studied and a few theoretical and empirical models linking the attenuation to hydrogen pressure, temperature and time were proposed, none of the models was verified in a broad range of experimental conditions. In this work we investigate a single mode germanium doped fiber that was exposed to 25–––100 psi H2 pressures at temperatures in the range 150 – 250 °C and the exposure times up to 28 days. Different aging protocols were applied to the fiber, and the focus was given to O–H peak development. An empirical approach and a theoretical model, that assumes Gaussian distribution of the activation energies were applied to fit the experimental results. From the theoretical model, it was found that the concentration of precursor available for reaction with hydrogen is orders of magnitude higher than that of non-bridging oxygen hole centers, and that at the applied temperatures the reacted sites belong to the lower-energy wing of the Gaussian distribution. It was also found that parameters of the theoretical model cannot be accurately determined via fitting even a large array of experimental data. In contrast, parameters of the empirical model are easily obtainable from the experiment which makes this approach more practical in hydrogen-related lifetime predictions.

Security enhancement for NOMA-PON with 2D cellular automata and Turing pattern cascading scramble aided fixed-point extended logistic chaotic encryption

The non-orthogonal multiple access-passive optical network (NOMA-PON) is facing the dual security threats of primary user interference and unauthorized third-party user eavesdropping, so efficient data security enhancement techniques are crucial. To solve these problems, we propose a fixed-point extended (FE)-logistic chaotic mapping to reduce the computational complexity while employing a two-dimensional (2D) cellular automata (CA) and Turing pattern (TP) cascading scramble (CA-TPCS) encryption algorithm to further improve the sensitivity of the NOMA-PON system. The CA-TPCS consists of 2D-CA dynamic bit encryption and Turing symbol substitution (TSS). By using FE chaos to construct 2D-CA and adopting index sort to extract the TSS matrix, dynamic diffusion of bits and scrambling of a 2D symbol matrix are achieved. To ensure the key privacy, we employ a dual key mechanism, and uplink data is introduced as the private key. To verify the feasibility of the proposed method, a simulation validation is built on a 17.6 Gb/s power division multiplexing-orthogonal frequency division multiplexing (PDM-OFDM) NOMA-PON system transmitted over 25 km standard single mode fiber (SSMF). The results show that the proposed scheme has no effect on the optimal power allocation rate (PAR) values and the values are all 3. Meanwhile, the receiver sensitivity gains of 0.2 and 0.3 dB are obtained for high-power and low-power users after encryption. The ciphertext has good diffusion and statistical properties, and the key space is flexibly controlled by the FE precision f, the length l of the transmitted bit, and the size T of the TP, with the value of 22f+l+T×T. The results show that the proposed scheme is not only very compatible with PDM technology but also can realize the dual defense of internal aggression and external aggression. It has a good application prospect in the future NOMA-PON.

Analysis of the Current Situation of Industry-University-Research Resource Co-construction and Sharing and Suggestions for Countermeasures

This research takes Huizhou City in Guangdong Province as an example to deeply analyze the current situation of industry-university-research resources jointly built and shared, and puts forward corresponding countermeasures and suggestions. The background of the study is based on the location advantage and industrial foundation of Huizhou City as an important node city in the Guangdong-Hong Kong-Macao Greater Bay Area, and explores the important role of IUR cooperation in promoting regional economic development and scientific and technological innovation. The significance of the study is reflected in the fact that through IUR cooperation, Huizhou City is able to accelerate the transformation and industrialization of scientific and technological achievements and enhance the regional innovation capacity. The research aims to solve the problem of how to strengthen the industrial technology innovation capacity of Huizhou City, enhance regional competitiveness, and realize the effective way of transformation of scientific and technological achievements. The research methods adopt literature review, comparative analysis and field research to comprehensively sort out the current situation, internal motivation and external conditions of IUR cooperation in Huizhou City. The result shows that although Huizhou has made some progress in jointly building and sharing resources for IUR cooperation, it still faces the problems of insufficient capital investment, single mode of cooperation, poor flow of talents and unreasonable allocation of resources. The conclusion suggests that Huizhou city needs to increase capital investment, innovate the mode of cooperation, strengthen the cultivation and introduction of talents, and optimize the allocation of resources, in order to promote the efficient joint build and sharing of IUR resources, and to promote the high-quality development of the economy.

Influence of polymer solution parameters on optical fiber Fabry-Perot polymer cavities

Abstract Optical fiber polymer-based Fabry-Perot sensors are commonly utilized to detect and measure a wide range of physical and chemical properties. By dipping the cleaved end of a single mode fiber into the polymer solution, a cavity is formed at the end facet of the fiber, as the solution effectively bonds to the fiber surface. The cavity serves as a sensing structure for the interaction with the analyte, ultimately determining the sensor’s sensitivity. Maintaining consistent thickness of the FP cavities is of utmost importance for the coating mechanism, as it directly impacts the sensitivity of the FP sensor. The main aim of this study is to assess and establish a technique that can effectively generate a cavity at the end facet of a fiber. A simulation study is conducted to examine the influence of variations in polymer solution characteristics on the cavity fabrication. Our experimental work involved creating polymer cavities on varying the polymer viscosity on the end facet of optical fibers. Furthermore, the suitability of this proposed approach has been assessed on a range of polymers, examining the fluctuations in the free spectral range of the fabricated FP cavities. The findings of this research highlight the possibility of achieving a repeatable coating on the end facet of fiber, irrespective of the polymer used.

Uncertainty-Aware Prediction of Remaining Useful Life in Complex Systems

Accurate prediction of the remaining useful life (RUL) of industrial systems is critical to ensuring smooth operation and safety. Various prognostic methods have been developed, but significant challenges remain for field applications. While many methods may achieve high accuracy, they often fall short in quantifying the uncertainty of their predictions. Without uncertainty quantification, it is difficult to assess the confidence level of the prognostic results. Therefore, it is essential to transparently present the uncertainty levels in the predicted results. This Ph.D. project aims to develop novel uncertainty-aware methods for RUL prediction of complex systems. The project will address the following situations where it is more and more uncertain: (a) propose a general framework for data-driven RUL methods to quantify uncertainty and generate adaptive confidence intervals under a single fault mode and a single operating condition; (b) consider both epistemic and aleatoric uncertainties in scenarios with multiple fault modes and multiple operating conditions and then calibrate uncertainty to enhance their accuracy; (c) explore how to predict RUL and quantify uncertainty when there are no run-to-failure data and RUL labels in practice; (d) handle uncertainty propagation from the component level to the system level. Through this research, the project will provide more reliable and comprehensive solutions for RUL prediction in complex systems.

Self-focusing and stimulated Brillouin scattering effect of low-temporal coherence light and corresponding damage characteristics in fused silica

Laser-induced damage thresholds (LIDTs) of input/exit surfaces and filamentation of fused silica under low-temporal coherence light (LTCL) and a corresponding damage mechanism are investigated. By comparing self-focusing effects of fused silica for each incident laser, the lower LIDT of filamentation damage under LTCL irradiation is mainly attributed to stronger self-focusing than traditional single longitudinal mode (SLM) pulse lasers. Meanwhile, differences in LIDTs for input/exit surfaces by LTCL and SLM pulse laser irradiation are attributed to self-focusing effects and backward stimulated Brillouin scattering. Finally, influences of fused silica thickness and incident laser polarization on LIDT are demonstrated. The research contributes to exploring safe boundaries for fused silica application in high-power LTCL devices.

Subradiance and superradiant long-range excitation transport among quantum emitter ensembles in a waveguide

In contrast to free space, in waveguides the dispersive and dissipative dipole–dipole interactions among quantum emitters exhibit a periodic behavior over remarkably long distances. We propose a novel setup, to our knowledge, exploiting this long-range periodicity in order to create highly excited subradiant states and facilitate fast controlled collective energy transport among far-apart ensembles coupled to a waveguide. For sufficiently large ensembles, collective superradiant emission into the fiber modes dominates over its free space counterpart. We show that, for a large number of emitters, a fast transverse coherent pulse can create almost perfect subradiant states with up to 50% excitation. On the other hand, for a coherent excitation of one sub-ensemble above an overall excitation fraction of 50% we find a nearly lossless and fast energy transfer to the ground state sub-ensemble. This transport can be enhanced or suppressed by controlling the positions of the ensembles relative to each other, while it can also be realized with a random position distribution. In the optimally enhanced case this fast transfer appears as superradiant emission with subsequent superabsorption, yet, without a superradiant decay after the absorption. The highly excited subradiant states, as well as the superradiant excitation transfer, appear as suitable building blocks in applications such as active atomic clocks, quantum batteries, quantum information protocols, and quantum metrology procedures such as fiber-based Ramsey schemes.

Spontaneous photon emission by shaped quantum electron wavepackets and the QED origin of bunched electron beam superradiance.

It has been shown that the spontaneous emission rate of photons by free electrons, unlike stimulated emission, is independent of the shape or modulation of the quantum electron wavefunction (QEW). Nevertheless, here we show that the quantum state of the emitted photons is non-classical and does depend on the QEW shape. This non-classicality originates from the shape dependent off-diagonal terms of the photon density matrix. This is manifested in the Wigner distribution function and would be observable experimentally through homodyne detection techniques as a squeezing effect. Considering a scheme of electrons interaction with a single microcavity mode, we present a QED formulation of spontaneous emission by multiple modulated QEWs through a build-up process. Our findings indicate that in the case of a density modulated QEWs beam, the phase of the off-diagonal terms of the photon state emitted by the modulated QEWs is the harbinger of bunched beam superradiance, where the spontaneous emission is proportional to N_e^2 . This observation offers a potential for enhancement of other quantum electron interactions with quantum systems by a modulated QEWs beam carrying coherence and quantum properties of the modulation.

Exploration and Reflection on Promoting Graduate Enrollment under the New Situation

Graduate enrollment is crucial for improving the quality of graduate education and building a high-quality education system. The current enrollment situation in some universities is severe, with problems such as insufficient attention to enrollment promotion and a single mode. To solve these problems, this article proposes measures such as leveraging the joint efforts of schools, formulating enrollment promotion plans at different levels, strengthening the construction of enrollment teams at both the school and college levels, enriching enrollment promotion forms, strengthening the construction of high-quality student sources, and building a quality evaluation system for student sources to attract more students to apply and continuously improve the quality of student sources.

Introduction to the JOCN Special Issue on Spatial Parallelism for Next-Generation High-Capacity Transport Networks

This special issue on Spatial Parallelism for Next-Generation High-Capacity Transport Networks tackles challenging questions of how optical networks will continue to scale in capacity now that the Shannon limit has been reached for single mode fiber systems using the C and L amplifier bands.

Single-longitudinal-mode self-seeded Brillouin fiber laser with an ultra-narrow linewidth achieved utilizing a triple-ring resonator

What we believe to be a novel single longitudinal mode (SLM) triple-ring (T-R) self-seeded Brillouin fiber laser (BFL) featuring outstanding stability, an ultra-narrow linewidth, and a high optical signal-to-noise ratio (OSNR) is proposed and experimentally investigated in this study. The key innovation in this design is eliminating the need for an additional costly ultra-narrow linewidth pump source typically required in conventional BFL. Instead, the laser preferentially excites stimulated Brillouin scattering (SBS) in the fiber through the self-seeded cavity mode dominant in the cavity. This approach generates Brillouin stokes and leverages the Vernier effect of the T-R resonator structure to suppress multimode oscillations, ensuring the generation of a Brillouin laser with an ultra-narrow linewidth and enabling SLM operation. The experimental results show that with the output power of 980-nm LD fixed at 400 mw, the OSNR of the self-seeded BFL spectrum reaches 54 dB, and the side mode suppression ratio (SMSR) is 22 dB. The -3 dB linewidth of the self-seeded BFL can be measured by the heterodyne beat frequency method at 30 Hz, and the output power and wavelength fluctuations are lower than 1.318 dB and ±0.007 nm, respectively, during the sixty minutes observation period. Additionally, the wavelength of the self-seeded BFL can be flexibly tuned within the range of 1560 – 1575 nm. This innovative approach demonstrates significant theoretical and practical implications for the development of low-cost, high-performance BFL systems compared to traditional BFL methods.

Unsupervised Decision Trees for Axis Unimodal Clustering

The use of decision trees for obtaining and representing clustering solutions is advantageous, due to their interpretability property. We propose a method called Decision Trees for Axis Unimodal Clustering (DTAUC), which constructs unsupervised binary decision trees for clustering by exploiting the concept of unimodality. Unimodality is a key property indicating the grouping behavior of data around a single density mode. Our approach is based on the notion of an axis unimodal cluster: a cluster where all features are unimodal, i.e., the set of values of each feature is unimodal as decided by a unimodality test. The proposed method follows the typical top-down splitting paradigm for building axis-aligned decision trees and aims to partition the initial dataset into axis unimodal clusters by applying thresholding on multimodal features. To determine the decision rule at each node, we propose a criterion that combines unimodality and separation. The method automatically terminates when all clusters are axis unimodal. Unlike typical decision tree methods, DTAUC does not require user-defined hyperparameters, such as maximum tree depth or the minimum number of points per leaf, except for the significance level of the unimodality test. Comparative experimental results on various synthetic and real datasets indicate the effectiveness of our method.

Measurement of dynamic deformation during shock loading using a fiber-optic loop-sensor

Abstract Characterizing materials under shock loading has been of interest in fields such as protective material development, biomechanics to study the injury mechanics and high-speed aerodynamic structures. However, shock loading of material is a very short duration phenomenon and it is extremely challenging to develop sensors for dynamic measurements under such loading conditions. Optical fiber sensors that present the possibilities to allow high resolution measurement of force or displacement in such high strain rate loading conditions. This work studies the possibility of developing a single mode optical fiber sensor based on the principle of power losses from the curved section for dynamic measurements under shock loading conditions. The strain measurement results obtained from the optical sensors are validated with the controlled digital image correlation measurements are found to be in close correlation. The sensor was able to provide time sensitivity of better than 1 ms. The results show that the fiber sensor has the characteristics of high sensitivity and high precision, which can be used to measure fine vibration in real-time.

Current-vortex-sheet model of the magnetic Rayleigh-Taylor instability

This study investigates the Rayleigh-Taylor instability in the magnetic field applied parallel to the interface. The motion of the interface is described using a current-vortex-sheet model. The growth rate of the interface is obtained from a linear stability analysis of the model. The interface of a single mode k=1 is linearly stable for RA≤1, where RA denotes the Alfvén number. Further, we conduct numerical computations for the evolution of the interface from the model for both regimes of RA≤1 and RA>1. For RA≤1, the interface oscillates vertically but does not intrude into the opposite phase. The amplitude of the interface and the oscillation period decrease with decrease in RA. For 1<RA≲1.5, the interface undergoes some growth at early times and then decreases. This oscillation is repeated, and no roll-ups are observed at the interface. Therefore, the nonlinear growth of the Rayleigh-Taylor instability is stabilized by a sufficiently strong magnetic field. For RA≳3 the interface is unstable and the pattern of the interface evolution differs from the density ratio. In addition, the magnetic field is greatly amplified as RA increases. Published by the American Physical Society 2024

Highly sensitive liquid level and temperature sensors based on all-fiber intermodal interferometers

Abstract Fiber optic-based precise measurements of liquid level and temperature are crucial for remote controlling in pharmaceutics, chemistry, and bromatology. Thus, it is essential to monitor liquid level and temperature simultaneously. In this paper, we propose all-fiber intermodal interferometers for highly sensitive liquid level and temperature measurements. We fabricated two different structures of single mode fiber-no core fiber-single mode fiber (SMF-NCF-SMF). One of them was used to measure the liquid level when the liquid soaked the NCF, and the other one was further coated with PDMS thermal-optic material and utilized to detect temperature. The measurement sensitivity of liquid level was 580 pm/mm within the range of 0-20 mm, while that of temperature was 1 nm/°C within the range of 28-51°C. A matrix was finally obtained by demodulating the measurements of liquid level and temperature. The proposed liquid level and temperature sensors, exhibiting the merits of high sensitivity, easy fabrication, and low cost, could be a candidate for precise and remote monitoring of liquid levels.

Cooperative game robust optimization control for wind-solar-shared energy storage integrated system based on dual-settlement mode and multiple uncertainties

Aiming at the problems of renewable energy output uncertainties and single scenario operation mode of energy storage systems, a cooperative game robust optimization control method for wind-solar-shared energy storage system based on dual-settlement mode of power market is proposed in this paper. A cooperative game-based energy management framework under dual settlement mode of electricity market is constructed, the profit relationship between shared energy storage under multiple application scenarios and renewable energy are extracted and the corresponding profit models are established. Considering the multiple uncertainties of renewable energy and electricity prices, combined with robust optimization theory, a multi-level two-stage robust optimization model is established to make optimal electricity trading decisions for renewable energy and shared energy storage. Additionally, the cooperative game robust optimization model is solved by i-C&CG algorithm. The effectiveness of proposed control method is verified through actual operating data of a certain power grid in China. The simulation results show that the cooperative game robust optimization model achieves the optimal operation of the wind-solar-shared energy storage system considering multiple uncertainties, which can improve the ability of the system to cope with the uncertainty risk and the reliability of the system.

Dynamic splitting tensile properties of high-strength ultrahigh-toughness cementitious composites (HS-UHTCCs)

In this study, the splitting tests were conducted to examine the effect of strain rate on the splitting tensile performance of high-strength ultrahigh-toughness cementitious composites (HS-UHTCCs). Hydraulic machine and split Hopkinson pressure bar (SHPB) were used to investigate the tensile properties of HS-UHTCCs. The strain rates ranged from 10-6 to 10-3 s−1 for hydraulic machine experiments and from 5 to 15 s−1 for SHPB tests, respectively. The splitting tensile strength, tensile stress-strain curves, dynamic increase factor (DIF) and energy absorption ability of HS-UHTCCs were analyzed. The new DIF models proposed for HS-UHTCCs fit well with the experimental data. In addition, the failure modes of specimens and fibers were investigated. The splitting tensile strain was obtained from digital image correlation (DIC) tests. The results indicate that the strain rate has a significant effect on the splitting tensile strength and energy absorption ability of HS-UHTCCs. On the contrary, the average splitting tensile strain showed a decreasing trend with the increase of strain rate. Besides, the DIF model of HS-UHTCCs was proposed with experimental data. The failure modes of specimens changed at high strain rates, transitioning from remaining intact to completely splitting into half. Two failure patterns of polyethylene (PE) fibers included pull-out failure and rupture were observed, while steel fibers experienced pull-out failure.