Mode Competition Research Articles

Two-sided vertical competition considering product quality in a manufacturing-remanufacturing system

<p style='text-indent:20px;'>We study two-sided vertical competition between a manufacturer and a supplier. The problem is formulated as a dynamic game where the supplier has more pricing power than the manufacturer. Based on the one-sided vertical competition modes with different recyclers as benchmarks, we derive optimal pricing and production decisions of manufacturer and supplier and further study the impacts of product quality on those decisions under the two-sided vertical competition mode. A key finding is that manufacturer/supplier prefers to be a follower rather than the first one to engage in recycling activities. Specifically, when the manufacturer/supplier has engaged in recycling activities, the supplier/manufacturer has an incentive to participate in recycling activities as well. We also find that high-quality remanufactured components/products can benefit manufacturer, supplier and consumers at the same time.</p>

An SCM-G2SFCA Model for Studying Spatial Accessibility of Urban Parks.

The urban park is the main leisure and entertainment place in residents' daily lives. The accessibility of parks is closely related to the physical and mental health of the residents. Although many scholars have conducted a great deal of research on the spatial accessibility of urban parks, they have rarely considered the supply competition among different parks and the impact of multiple travel modes on the spatial accessibility of parks. Therefore, based on Baidu map navigation data, in this paper, the park Baidu score is used to represent the competitive relationship among different parks, and the impact of multiple travel modes on the spatial accessibility of parks is considered. A supply competition and multiple travel modes Gaussian two-step floating catchment area (SCM-G2SFCA) model is established to evaluate the spatial accessibility of the parks in the Wuhou District, Chengdu, China. The results show that (1) compared with traditional methods, the SCM-G2SFCA model can obtain more accurate results using Baidu map navigation data. (2) There are obvious spatial differences in the accessibility distribution of the parks in the Wuhou District, Chengdu, with high accessibility in the south and low accessibility in the north. The Jinyang and Huaxing sub-districts in the southern suburbs have the highest park accessibility and can obtain more adequate park services. The Fangcaojie and Cujin sub-districts in the northern urban areas have the lowest park accessibility and are relatively lacking in park services. The research results of this study have important reference value for the rational planning of urban parks and the improvement of the spatial accessibility of urban parks in the Wuhou District of Chengdu and similar urban areas.

Switchable and stable erbium-doped fiber laser using the reconfigurable Lyot ring filter with WS2 film

A novel switchable and stable erbium-doped fiber laser (EDFL) using the reconfigurable Lyot ring filter (RLRF) with tungsten disulfide (WS2) film is proposed and experimentally demonstrated. The principle of RLRF is that the interference of the polarized lights with phase differences produces a comb spectrum with obvious envelope and uniform fluctuation. The transmission spectrum of RLRF can be changed by adjusting the polarization controllers (PCs) in RLRF. In the experiment, the actual length of the polarization-maintaining fiber (PMF) is 4 m. By adjusting PC1 adjacent to PMF, 2 to 5 wavelengths can be switched. Adjusting PC2 in the ring can change the equivalent length of the PMF in RLRF. When the equivalent length is 8 m, 5 to 8 wavelengths can be switched with a wavelength interval of 0.68 nm. The nonlinear material WS2 film is used as a means to suppress mode competition in the laser cavity, and the fiber laser has a stable output. The switching of the proposed EDFL is simple and flexible, and can be used in wavelength division multiplexing (WDM) systems.

On unstable modes in graph-type circuits

The aim of this communication is to discuss the dynamics of a couple of graphtype circuits that exhibit one or more unstable modes. Examples of finding the sign of un unstable mode as well as mode competition are presented.

Controlling chaotic itinerancy in laser dynamics for reinforcement learning.

Photonic artificial intelligence has attracted considerable interest in accelerating machine learning; however, the unique optical properties have not been fully used for achieving higher-order functionalities. Chaotic itinerancy, with its spontaneous transient dynamics among multiple quasi-attractors, can be used to realize brain-like functionalities. In this study, we numerically and experimentally investigate a method for controlling the chaotic itinerancy in a multimode semiconductor laser to solve a machine learning task, namely, the multiarmed bandit problem, which is fundamental to reinforcement learning. The proposed method uses chaotic itinerant motion in mode competition dynamics controlled via optical injection. We found that the exploration mechanism is completely different from a conventional searching algorithm and is highly scalable, outperforming the conventional approaches for large-scale bandit problems. This study paves the way to use chaotic itinerancy for effectively solving complex machine learning tasks as photonic hardware accelerators.

Complex nonlinear dynamics of polarization and transverse modes in a broad-area VCSEL

Lasers can exhibit nonlinear and chaotic dynamics driven by the interaction of multiple lasing modes, and investigating the different scenarios of mode competition and bifurcations of their dynamics is of great interest on a fundamental level as well as in view of applications. We study the dynamics of a broad-area vertical-cavity surface-emitting laser (VCSEL) in solitary continuous-wave operation with a comprehensive investigation of its polarization state, lasing spectra, near-field distributions, and temporal dynamics. Fluctuations at the frequency of birefringence splitting and other frequency components develop in a series of bifurcations. The bifurcations coincide with changes of the transverse lasing modes and/or the polarization state, demonstrating the importance of both the spatial and polarization degrees of freedom for mode competition. As a consequence, the inherent nonlinear dynamics of broad-area VCSELs is significantly more complex than the dynamics of VCSELs with a single spatial mode.

On the competition of transverse and longitudinal modes of Marangoni convection in a three-dimensional layer of viscoelastic fluid

Within the vast array of applications encompassed by viscoelastic fluids, some lack of knowledge seems to affect the non-linear behavior of Marangoni convection when its typical initial unicellular and steady states are taken over by more complex flow configurations. These still hide a not-fully understood competition of complex and diverse physical mechanisms that determine the prevailing macroscopic behavior. In the present study, relevant insights are sought from consideration of the classical differentially heated rectangular layer of liquid with adiabatic bottom and top free surface. It is shown that, for increasing values of the Marangoni number and/or the elasticity parameter, this problem offers a multifaceted spectrum of different outcomes depending on the non-trivial interplay established between two distinct categories of disturbances (transverse and longitudinal). These are studied using a diversity of model types in which some processes are on or off to discern selectively their effect in the laminar state and their contribution to the evolution of the system toward chaos. The characteristic marks by which the ensuing elastic turbulence can be distinguished from the companion Kolmogorov counterpart are highlighted through analysis of the emerging scaling laws in the velocity spectrum and the sensitivity of these to the intensity of the driving force and the considered elasticity level. It is shown that these two forms of turbulence can coexist in the considered problem.

Design and Experimental Research of a Compact Ku-Band Triaxial Klystron Amplifier With Low Seed Injection Power

A compact Ku-band triaxial klystron amplifier (TKA) with three cascaded single-gap bunching cavities is proposed for the sake of high output efficiency at low seed injection power. The three bunching cavities are specially designed with optimal external quality factors and specific drift tube length to suppress the self-oscillation of these cavities. By decreasing the coupling coefficients and increasing the frequency interval of the three cavities, the asymmetric mode competition can be successfully eliminated in 3D particle-in-cell simulation. The compact TKA is demonstrated to be capable of producing the Ku-band high power radiation with a peak power of 580 MW corresponding to an efficiency of 31 % and a pulse duration of nearly 100 ns in typical experiments. Furthermore, the seed injection power and axial length of the proposed device are reduced to 9 kW and 10 wavelengths, respectively.

Efficient chip-based optical parametric oscillators from 590 nm to 1150 nm.

Optical parametric oscillators are widely used to generate coherent light at frequencies not accessible by conventional laser gain. However, chip-based parametric oscillators operating in the visible spectrum have suffered from pump-to-signal conversion efficiencies typically less than 0.1 %. Here, we demonstrate efficient optical parametric oscillators based on silicon nitride photonics that address frequencies between 260 THz (1150 nm) and 510 THz (590 nm). Pumping silicon nitride microrings near 385 THz (780 nm) yields monochromatic signal and idler waves with unprecedented output powers in this wavelength range. We estimate on-chip output powers (separately for the signal and idler) between 1 mW and 5 mW and conversion efficiencies reaching ≈15 %. Underlying this improved performance is our development of pulley waveguides for broadband near-critical coupling, which exploits a fundamental connection between the waveguide-resonator coupling rate and conversion efficiency. Finally, we find that mode competition reduces conversion efficiency at high pump powers, thereby constraining the maximum realizable output power. Our work proves that optical parametric oscillators built with integrated photonics can produce useful amounts of visible laser light with high efficiency.

Biased managers with network externalities

AbstractIn network industry under Cournot and Bertrand competition, we examine a model when owners of firms hire biased managers who have incorrect market demand. Contrast to previous studies, we show that (i) regardless of the strength of network externalities when consumers form the responsive and passive expectations, owners realize strategic advantage by hiring biased managers to be more aggressive under Cournot and Bertrand competition, (ii) firms prefer facing passive expectations for the weak network externalities and vice versa for the strong network exteranlities under Bertrand and Cournot competition, (iii) if the network size is sufficiently large, then the prisoner's dilemma that firms hire aggressive managers no longer exists under both competition modes. As with no delegation case, we obtain the different rankings of firms' profit depending on both network externalities and forming of expectations under Cournot and Bertrand competition.

Towards Watt-Level THz Sources for High-Resolution Spectroscopy Based on 5th-Harmonic Multiplication in Gyrotrons

We propose the concept of high-power THz radiation sources based on five-fold frequency multiplication in gyrotrons intended for plasma applications. The efficient excitation at the 5th cyclotron harmonic is due to the specific property of the eigenmodes of cylindrical waveguides, as a result of which, the conditions of simultaneous electrodynamic resonance at two selected TE modes are satisfied asymptotically with very high accuracy. Previously, we have verified this principle in experiments with a low-frequency kilowatt-level gyrotron in which, due to the low-density spectrum, the operating mode is excited with no competition from parasitic oscillations. The novel concept is a development of this idea applied to the systems with a denser spectrum, which is inevitable in higher frequency and power devices. Simulations within the averaged time-domain model demonstrate that, despite the mode competition, it is possible to excite Watt-level 1.25 THz 5th cyclotron harmonic in a recently developed sub-MW 0.25 THz gyrotron with TE19,8 operating mode. The obtained results open a possibility for implementation of radiation sources with output power/frequency combination, practically inaccessible using other THz generation methods and highly sought for a number of applications, including high-resolution molecular spectroscopy.

Nd-doped single-mode all-fiber mode-locked cascaded Raman laser operating at 0.94 and 0.98 µm

Based on the Nd-doped single-mode fiber (SMF) as the gain medium and SMF as the Raman medium, an all-fiber mode-locked cascaded Raman laser simultaneously operating at the 0.94 µm and 0.98 µm waveband was demonstrated for the first time. To suppress the mode competition at 1.06 µm, the bending loss of the SMF was introduced by winding the SMF onto a mandrel with a diameter of 10 mm. At the highest pump power of 391 mW, 1st-order and 2nd-order Stokes waves with almost the same intensities were achieved, and the corresponding central wavelengths were 942.37 nm and 983.03 nm, respectively. The cascaded Raman laser simultaneously operating in the 0.94 µm and 0.98 µm obtained in our experiments has the advantages of simple structure and low cost, which can be used as an ideal light source for two-photon microscopy and as a pump source for Er or Yb-doped lasers.

High-order mode interaction structure for a W-band CW sheet beam extended interaction klystron

To solve the problem of mode competition in high-order working modes, this paper presents a fast design method based on the TM31-2π mode for the dumbbell shaped extended interaction cavity. Based on the equivalent circuit theory, the high-frequency characteristics of the structure are studied. In addition, we propose a W-band continuous wave sheet beam extended interaction klystron high-frequency circuit. The circuit was driven by a 20 kV and 0.85 A sheet electron beam, with a 3.2 × 0.3 mm2 section. The beam was focused by a 0.8 T permanent magnet system. The high-frequency system adopts five dumbbell shaped five-gap cavities, and the output system adopts a symmetrical output waveguide. The 3D particle-in-cell simulation shows that more than 1.5 kW power can be obtained at an input power of 0.12 W, and the electron efficiency and gain are 9.2% and 41.2 dB, respectively.

Excitation and suppression of asymmetric modes in a coaxial relativistic klystron amplifier with cascaded single-gap bunching cavities

The excitation and suppression of asymmetric modes in a coaxial relativistic klystron amplifier (RKA) with cascaded single-gap bunching cavities are analyzed in this paper. Through theoretical analysis and simulated verification, we find that the asymmetric modes of cascaded single-gap bunching cavities have low external quality factors, the same resonant frequencies, and negative beam-loading conductance ratios so that they are easily excited by the electron beam. To solve this issue, a feasible method is proposed in this paper to suppress the asymmetric modes of cascaded single-gap bunching cavities, under the conditions of decreasing their coupling coefficients and increasing the frequency separation, choosing an appropriate drift tube length between them. These improved bunching cavities are further examined in an X-band coaxial RKA by 3D particle-in-cell simulation, which shows that high power microwaves with a power of 0.8 GW are generated corresponding to an efficiency of 40%. Furthermore, there is no asymmetric mode competition during 150 ns of simulation time.

Promote the international development of Energy Internet technology standards based on key competition mode

• Propose a promotion strategy for internationalization of Energy Internet standards. • Adopt "key competition mode" to improve internationalization efficiency. • Establish an evaluation model of standard internationalization effect. • The strategy would enhance the international competitiveness of Chinese standards. The construction of the Energy Internet will significantly promote the construction of smart cities. Under the combined conditions of global economic integration and regional economic cooperation, standard and standards-related activities, as the "universal language" of world exchange and the "pass" of international trade, play an essential role in developing and constructing Energy Internet. This paper first analyzes the development of various technical fields and proposes a strategy for promoting the international development of Energy Internet technology standards based on the "key competition mode." Then an evaluation index system for the international development effect of Energy Internet standards is constructed. The internationalization implementation effect of technical standards is analyzed by the fuzzy analytic hierarchy method. The internationalization promotion work is guided according to the quantitative evaluation results. Finally, an example analysis of a standard proposal is carried out, and the results show that the evaluation method of the internationalization effect proposed in this paper has good applicability.

Glassy behavior of modes in lasing systems with varying openness: random and whispering gallery mode lasers

We elucidate lasing characteristics, intensity statistics, and glassy behavior of lasing systems with varying degrees of openness and intrinsic disorder. In this pursuit, we consider three distinct dye-doped polymer based lasing systems, i.e., a planar waveguide random laser (PWRL) and two different geometries of whispering gallery mode resonators (WGMRs), viz., spherical and bottle microresonators. In WGMRs, improved optical confinement enhances the quality factor of resonances and provides a low threshold and fast saturation of the number of lasing modes with pump strength. Additionally, covariance across the lasing mode intensities reveals the presence of strong mode competition. In PWRL, the statistical study reveals bimodal probability distribution (PD) of modal intensity fluctuations near-above threshold with their gradual transition to heavy tail PD far above the threshold, while the PDs for WGMRs were found to remain unimodal throughout the pumped regimes with transition to positively skewed unimodal distribution above the threshold. We also report correspondence between the onset of bimodal PD and the spin glass phase near-above threshold in PWRL. Such observations are absent for WGMRs, wherein the spin glass behavior at and above the threshold are relatively suppressed. The non-zero value of the spectral intensity fluctuation overlap parameter in WGMRs manifests the inherent disorder held by the system. We also discuss the requirement of strong mode coupling achieved by virtue of openness for the realization of glassy behavior in lasing systems.

The study on the gain of signal pulse in gain fibers and its application in simulation of mode-locked fiber lasers

The effect of the signal pulse on the population densities of upper-level particles of doped ions in gain fibers is studied. The population densities of upper-level particles decrease gradually after encountering the signal pulse in both the two-level system and the three-level system, and the decreasing degree is related to the power of the pulse. Since the power of the signal will change greatly in a short time in a pulsed laser, the time dependent rate equations are more suitable for describing the interaction between the pulse signal and doped particles than the steady state rate equations. Based on this, a simulation method of passively mode-locked fiber lasers, in which the gain of the signal is calculated by time dependent rate equations, is proposed. An erbium doped mode-locked fiber laser at 1564nm is simulated as an example, and the pulse width and spectral width in the simulation results are close to the experimental results. By adding noise to the initial pulse, the stability of the model is verified, and the mode competition between different modes in the process of mode locking can be studied. This method can not only provide a reference for building mode-locked fiber lasers, but also provide a method for studying the mechanism of mode locking.

Effect of gain saturation on mode capacity of EDFA

Gain saturation in a mode-division-multiplexed erbium-doped fiber amplifier (MDM-EDFA) has a significant impact on system capacity due to complex mode competition. In this paper, the gain saturation of MDM-EDFA at single and multiple wavelengths is investigated. The gain saturation occurs as a certain negative linear correlation between EDF length and pump power. The saturation performance tends to be flat beyond 49 mode groups transmission. In a “WDM + MDM” system with 36 × 36 channels, the normalized root mean square value of the saturation gain is lower than 3. The results provide a theoretical basis for the application of the upcoming “WDM + MDM” system.

Kerr-Lens Mode-Locking: Numerical Simulation of the Spatio-Temporal Dynamics on All Time Scales

We present a complete numerical analysis and simulation of the full spatio-temporal dynamics of Kerr-lens mode-locking in a laser. This dynamic, which is the workhorse mechanism for generating ultrashort pulses, relies on the intricate coupling between the spatial nonlinear propagation and the temporal nonlinear compression. Our numerical tool emulates the dynamical evolution of the optical field in the cavity on all time-scales: the fast time scale of the pulse envelope within a single round trip, and the slow time-scale between round-trips. We employ a nonlinear ABCD formalism that fully handles all relevant effects in the laser, namely—self focusing and diffraction, dispersion and self-phase modulation, and space-dependent loss and gain saturation. We confirm the validity of our model by reproducing the pulse-formation in all aspects: The evolution of the pulse energy, duration, and gain during the entire cavity buildup, demonstrating the nonlinear mode competition in full, as well as the dependence of the final pulse in steady state on the interplay between gain bandwidth, dispersion, and self-phase modulation. The direct observation of the nonlinear evolution of the pulse in space-time is a key enabler to analyze and optimize the Kerr-lens mode-locking operation, as well as to explore new nonlinear phenomena.

A Simple Method to Build High Power PCSEL Array with Isolation Pattern Design

Photonic crystal surface-emitting lasers (PCSELs) hold promising properties of both edge emitting lasers (EELs) and vertical-cavity surface-emitting lasers (VCSELs). They possess high output power while radiating light vertically, being thought of as the next generation laser source. One of the main advantages of PCSELs is their scalability of size and power, which makes them applicable to high power applications or long-distance detection. However, due to problems such as current injection and mode competition, there are limits on their dimensions. To further increase the power, the capability of two-dimensional array integration paves the way. In this work, we demonstrate a new method to fabricate PCSEL arrays by defining an isolation pattern. We also investigate the influence of aperture size and array arrangement on lasing performance.