Unidirectional Ring Research Articles

Optical Energy Increasing in a Synchronized Motif-Ring Array of Autonomous Erbium-Doped Fiber Lasers

This work investigates the enhancement of optical energy in the synchronized dynamics of three erbium-doped fiber lasers (EDFLs) that are diffusively coupled in a unidirectional ring configuration without the need for external pump modulation. Before the system shows stable high-energy pulses, different dynamic behaviors can be observed in the dynamics of the coupled lasers. The evolution of the studied system was analyzed using different techniques for different values of coupling strength. The system shows the well-known dynamic behavior towards chaos at weak coupling, starting with a fixed point at low coupling and passing through Hopf and torus bifurcations as the coupling strength increases. An interesting finding emerged at high coupling strengths, where phase locking occurs between the frequencies of the three lasers of the system. This phase-locking leads to a significant increase in the peak energy of the EDFL pulses, effectively converting the emission into short, high amplitude pulses. With this method, it is possible to significantly increase the peak energy of the laser compared to a continuous EDFL single pulse.

An improved multi-operator differential evolution with two-phase migration strategy for numerical optimization

Over the last decade, the multi-operator differential evolution (MODE) has become one of the most popular research areas in the differential evolution (DE) family. Among these MODEs, an improved multi-operator differential evolution (IMODE) has achieved success as the winner in CEC2020. Despite its good performance, the random information sharing strategy may not efficiently handle the balance between exploration and exploitation for the complex numerical optimization. To address this limitation, we propose a two-phase migration strategy (TMS) to improve the performance of IMODE, called IMODE-TMS. In the first phase, the top-ranked individuals in each sub-population are retained for exploitation, and all the bottom-ranked individuals are assigned to three sub-populations to maintain diversity. Furthermore, the second phase plays a crucial role in eliminating stagnation. When a sub-population is identified as stagnant by the stagnation indicator, the optimal individual will migrate to that sub-population following the uni-directional ring structure. This process is mainly used to increase the off-trap capability on some problems with complex fitness landscapes. IMODE-TMS is tested on the CEC2020, CEC2021 and CEC2022 benchmark functions, and seven well-known complex global trajectory optimization problems (GTOP). The experimental results show that IMODE-TMS significantly outperforms not only IMODE but also other state-of-the-art comparison algorithms.

Highly accurate time-frequency synchronized self-reconfiguration network based on a two-fiber unidirectional path ring

Highly accurate time-frequency synchronized self-reconfiguration network based on a two-fiber unidirectional path ring

Dynamic all-optical memory switching based on atomic optical bistable behavior in a three level Λ-type atomic system

We theoretically investigate the atomic optical bistability (AOB) in a three-level Λ-type atomic system confined in a unidirectional optical ring cavity. The role of the intensity or detuning of the control field on AOB is explored, and results show that absorption, dispersion, and nonlinearity can be modified significantly by the control field due to quantum coherence and interference in multilevel atomic systems. Thus, tuning the intensity or detuning of the control field can manipulate the switch-up and switch-down thresholds, as well as the area of the bistable hysteresis loop. According to the controllability of AOB, we design various schemes to realize dynamical all-optical switching between the high and low outputs of two bistable curves for a fixed cavity input. In addition, dynamical all-optical memory switching can be implemented by adding a pulse sequence for the intensity or detuning of the control field. For appropriate parameters, such as the cooperative coefficient, the extinction ratio of the switching can be improved dramatically.

Rate equation analysis for deterministic and unidirectional lasing in ring resonators with an S-shaped coupler

Ring resonators are traditionally popular optical devices that apply to various components in photonic ICs. They also play an important role in the on-chip generation of many novel optical states in topological systems and non-Hermitian systems. Unidirectional lasing of ring resonators is used in many such systems to create exotic states of light including optical vortexes and optical skyrmions, but the unidirectional behavior has not been fully understood. Previous research has constructed a simplified model to explain the steady state behaviors of unidirectional ring resonators, but the carrier dynamics and spontaneous emission were omitted. In this work, we give a numerical analysis of unidirectional ring resonators with an S-shaped coupler. We identified the importance of the gain saturation to robustness against backscattering and high unidirectionality by comparing to the model without saturation. We also discuss the effect of asymmetrical coupling on the deterministic realization of unidirectionality.

Unidirectional ring laser operation and tunable single-frequency emission using differential parametric gain.

In this Letter, a novel approach for unidirectional operation of a 1064 nm solid-state ring laser is demonstrated based on difference frequency mixing. Unidirectional operation is achieved exploiting the directional parametric gain from a single-pass diode laser, facilitated through a periodically poled LiNbO3 crystal. In addition to achieving unidirectional operation, the nonlinear process further enables the generation of single-frequency mid-infrared light. Using a single-pass tapered diode laser, tunable in the range from 780 to 815 nm, the generated mid-infrared signal covers the 2.9 to 3.5 µm range while optimizing the phase-match condition of the difference frequency generation process.

Coupled nano-squares with optical response in nonlinear modes; Suitable substrate to control light by light for quantum applications

Nonlinear response of a nano-structure including two square quantum dots (QDs) of identical material but dissimilar sizes is discussed by considering possible quantum interferences. Density matrix approach is developed to extract physical characteristics of the system by considering Hamiltonians including couplings of the excitons to thermal bath and the possible intra-dot relaxations as well as the near field optical energy transfers (of Yukawa-type potentials) between the probable eight quantum states in subwavelength range. Realization of nonlinear behavior is studied systematically by putting the structure inside a unidirectional ring cavity and driving it by pair of dichromatic fields, that one provides a weak probe, while the other offers a strong driving component. It is shown that the absorption/dispersion properties of the probe field might be controlled by tuning the quantum interference via changing the structural features as well as the externally controlled parameters. Thus adjusting the optical bistability (OB) threshold, hysteresis cycle size or even transition from OB to multi-stability might be possible easily. Moreover, machine learning approach is proposed to evaluate how predictable are the responses of the suggested structure in various preliminary circumstances. Results clearly reflect high potential of the suggested structure for applications such as all-optical switches or memories.

Controlling optical bistability, multistability and all-optical switching through multi-photon excitation process

We present a theoretical study on optical bistability (OB), optical multistability (OM) and tunable all-optical switching in a four-level cascade type atomic system. The density matrix formalism is used to find out the response of the probe laser field. We explore OB and OM under unidirectional optical ring cavity configuration. A comparison between the effects of electromagnetically induced transparency and electromagnetically induced absorption windows on OB is presented. The threshold of OB and the hysteresis width can be tuned effectively by adjusting the applied coherent fields. A transition from OB to OM and vice-versa can be easily achieved by tuning the field parameters and the atomic cooperation parameter. Dynamic control of the probe laser propagating through the medium has been investigated. We also demonstrate conversion of a continuous wave input probe field into output switched pulse. The ON/OFF time of the switched probe pulse can also be controlled by tuning the field parameters.

Observation of Optical Spectrum Dynamics and Longitudinal-Mode Feature in a Single- Frequency Self-Sweeping Fiber Laser

In this study, we constructed and realized a single-frequency self-sweeping fiber laser that can perform both reverse and normal sweeping. The laser can convert sweeping directions using different lengths of fiber saturable absorber (FSA). The maximum sweeping ranges for normal and reverse sweeping are 5.072 and 3.457 nm, respectively, and are optimized results based on a unidirectional ring cavity. We summarized the optical spectra and pulse dynamics of both normal and reverse sweeping, and we also observed the longitudinal-mode feature of the fiber laser, revealing a phenomenon in which the interval of frequency change is twice the spacing of longitudinal-mode. Furthermore, the reflected spectra of FSA at different lengths and wavelengths were calculated to explain the sweeping direction and longitudinal mode features.

Route to Chaos in a Unidirectional Ring of Three Diffusively Coupled Erbium-Doped Fiber Lasers

We numerically investigate the dynamics of a ring consisting of three unidirectionally coupled Erbium-Doped Fiber Lasers (EDLFs) without external pump modulation. The study focuses on the system behavior as the coupling strength is varied, employing a six-dimensional mathematical model that includes three variables for laser intensities and three variables for population inversions of all lasers. Our primary objective is to understand the system evolution towards chaos from a stable equilibrium in the ring, considering the impact of increasing coupling strength. To analyze the system’s behavior, we employ various techniques such as time series analysis, power spectra, Poincaré sections, bifurcation diagrams, and Lyapunov exponents. During the transition to chaos, the system undergoes a Hopf bifurcation and a series of torus bifurcations. An essential aspect of this study is the exploration of a rotating wave propagating along the ring, where the wave nature (periodic, quasiperiodic, or chaotic) depends on the coupling strength. Additionally, we observe the coexistence of periodic and chaotic orbits within a specific range of the coupling strength. However, for very strong coupling, this bistability disappears, resulting in a monostable system with a single limit cycle. This regime exhibits potential for applications that demand short laser pulses with a substantial increase in peak power, reaching nearly 20 times higher levels compared to the continuous mode when the lasers are uncoupled. This discovery holds particular importance for optical communication systems, especially considering the attenuation optical signals experience when transmitted over long distances.

Dynamics of coexisting rotating waves in unidirectional rings of bistable Duffing oscillators

We study the dynamics of multistable coexisting rotating waves that propagate along a unidirectional ring consisting of coupled double-well Duffing oscillators with different numbers of oscillators. By employing time series analysis, phase portraits, bifurcation diagrams, and basins of attraction, we provide evidence of multistability on the route from coexisting stable equilibria to hyperchaos via a sequence of bifurcations, including the Hopf bifurcation, torus bifurcations, and crisis bifurcations, as the coupling strength is increased. The specific bifurcation route depends on whether the ring comprises an even or odd number of oscillators. In the case of an even number of oscillators, we observe the existence of up to 32 coexisting stable fixed points at relatively weak coupling strengths, while a ring with an odd number of oscillators exhibits 20 coexisting stable equilibria. As the coupling strength increases, a hidden amplitude death attractor is born in an inverse supercritical pitchfork bifurcation in the ring with an even number of oscillators, coexisting with various homoclinic and heteroclinic orbits. Additionally, for stronger coupling, amplitude death coexists with chaos. Notably, the rotating wave speed of all coexisting limit cycles remains approximately constant and undergoes an exponential decrease as the coupling strength is increased. At the same time, the wave frequency varies among different coexisting orbits, exhibiting an almost linear growth with the coupling strength. It is worth mentioning that orbits originating from stronger coupling strengths possess higher frequencies.

A single-longitudinal-mode Er:YAG laser and MOPA system based on the Faraday effect

We demonstrate a continuously operating Er:YAG single-longitudinal-mode laser and its amplifier with a corner cube retroreflector based on the Faraday effect. A maximum power of 1.02 W, the central wavelength of 1645.46 nm, Er:YAG single-longitudinal-mode laser with a line-width of 204 kHz has been realized. The slope efficiency is 9.38% and the beam quality factors M2 are 1.16, 1.05 in the × and y directions. Additionally, the single-longitudinal-mode laser is amplified to 1.86 W by the double-pass amplifier. The results indicate that the unidirectional operation ring laser in combination with the corner cube prism provides a 1.6 μm continuous-wave single-longitudinal-mode laser with high-power and stability.

Phase-synchronized oscillations in a unidirectional ring of pump-coupled lasers

The dynamics of a closed chain of lasers with optoelectronic unidirectional delayed coupling is analyzed. Assuming that the number of lasers is sufficiently large, we propose the integro-differential spatially distributed model with periodic boundary conditions. The critical value of the coupling coefficient is determined, at which the stationary state of laser generation becomes unstable. A two-dimensional complex partial differential equation of the Ginzburg–Landau type is derived as a quasi-normal form. Its simplest homogeneous periodic solutions correspond to traveling wave solutions of the distributed model and, in turn, describe phase synchronized oscillations in the ring of coupled lasers. The frequencies and amplitudes of oscillations of the radiation intensity of each laser and the phase difference for adjacent oscillators are determined.

Transitional cluster dynamics in a model for delay-coupled chemical oscillators.

Cluster synchronization is a fundamental phenomenon in systems of coupled oscillators. Here, we investigate clustering patterns that emerge in a unidirectional ring of four delay-coupled electrochemical oscillators. A voltage parameter in the experimental setup controls the onset of oscillations via a Hopf bifurcation. For a smaller voltage, the oscillators exhibit simple, so-called primary, clustering patterns, where all phase differences between each set of coupled oscillators are identical. However, upon increasing the voltage, secondary states, where phase differences differ, are detected, in addition to the primary states. Previous work on this system saw the development of a mathematical model that explained how the existence, stability, and common frequency of the experimentally observed cluster states could be accurately controlled by the delay time of the coupling. In this study, we revisit the mathematical model of the electrochemical oscillators in order to address open questions by means of bifurcation analysis. Our analysis reveals how the stable cluster states, corresponding to experimental observations, lose their stability via an assortment of bifurcation types. The analysis further reveals complex interconnectedness between branches of different cluster types. We find that each secondary state provides a continuous transition between certain primary states. These connections are explained by studying the phase space and parameter symmetries of the respective states. Furthermore, we show that it is only for a larger value of the voltage parameter that the branches of secondary states develop intervals of stability. For a smaller voltage, all the branches of secondary states are completely unstable and are, therefore, hidden to experimentalists.

Single-longitudinal-mode Ho:YLF unidirectional ring laser with single anti-misalignment corner cube retroflector

A single-longitudinal-mode Ho:YLF unidirectional ring laser with single anti-misalignment corner cube retroflector (CCR) for providing the stable local oscillator to 2.05 μm laser lidar was demonstrated in this paper. The single-longitudinal-mode output power of 569 mW at 2051.76 nm was obtained by inserting a half-wave plate and a Faraday rotator to the ring oscillator. The output wavelength was tuned from 2050.94 nm to 2054.18 nm through a 0.3-mm-thick F-P etalon, which close to the free spectrum range of the etalon. In addition, the anti-misalignment characteristic of the unidirectional ring laser was investigated when the single CCR moved along the optical axis and perpendicular to the optical axis. The beam quality factors M2 of the Ho:YLF single-longitudinal-mode laser were 1.05 in the x direction and 1.02 in the y direction, respectively.

Tunable 60 GHz Multiwavelength Brillouin Erbium Fiber Laser

An experimental study of a tunable 60 GHz multiwavelength Brillouin erbium fiber laser is presented in this paper. Two unidirectional ring laser cavities and two pre-amplification laser cavities are used. In the first three cavities, a Brillouin gain medium is presented with a dispersion compensation fiber (DCF) spool, and a single-mode fiber (SMF) spool is used as a Brillouin gain medium in the fourth cavity. Three erbium amplifiers are utilized to supply enough gain to the generated Brillouin Stokes signal and to suppress cavity losses. For these three amplifiers, up to 450 mW (150 mW for each) of a 1480 nm pump power is used. In our proposed configuration, four sextuple Brillouin Stokes signals with a high power of 10 dBm and more than 55 dB as an optical signal-to-noise ratio are achieved. The obtained Brillouin Stokes signals can be tuned over 30 nm (1560–1590 nm) and can be easily used in dense wavelength division multiplexing in optics communication systems.

Unidirectional hybrid diode laser through the integration of a hook-shaped traveling-wave semiconductor optical amplifier and Taiji ring resonator.

We demonstrate a unidirectional ring diode laser based on hybrid integration of a hook-shaped traveling-wave semiconductor optical amplifier (SOA) and a Taiji ring resonator. The additional crossover bending waveguide inside the silicon nitride Taiji ring introduces a non-reciprocal loss in the laser cavity while the gain is provided by a multiple depth etched hook-shaped SOA. We present the detailed design flow for both active and passive components of the unidirectional hybrid diode laser. This work paves the way to use a hook-shaped SOA-based hybrid platform for various applications including optical sensing, all-optical switching, photonic memories, and topological optics.

Coexisting Attractors and Multistate Noise-Induced Intermittency in a Cycle Ring of Rulkov Neurons

We study dynamics of a unidirectional ring of three Rulkov neurons coupled by chemical synapses. We consider both deterministic and stochastic models. In the deterministic case, the neural dynamics transforms from a stable equilibrium into complex oscillatory regimes (periodic or chaotic) when the coupling strength is increased. The coexistence of complete synchronization, phase synchronization, and partial synchronization is observed. In the partial synchronization state either two neurons are synchronized and the third is in antiphase, or more complex combinations of synchronous and asynchronous interaction occur. In the stochastic model, we observe noise-induced destruction of complete synchronization leading to multistate intermittency between synchronous and asynchronous modes. We show that even small noise can transform the system from the regime of regular complete synchronization into the regime of asynchronous chaotic oscillations.

A 1060 nm stretched-pulse mode-locked wavelength-swept laser source providing an A-scan rate of 20 MHz

The laser source is the deciding factor in improving the rapid imaging of swept-source optical coherence tomography (OCT) systems. We introduce an intrinsically stable stretched-pulse mode-locking (SPML) laser operating a tuning range of over 92 nm at a center wavelength of 1060 nm. The laser provides variable A-line rates up to ~20 MHz as a function of the duty cycle. The cavity comprises a unidirectional ring cavity with matched positive and negative continuously chirped fiber Bragg gratings generating ± 556 ps/nm dispersion. We demonstrate the ability of the stretched-pulse mode-locking laser to provide rapid optical signals for optical coherence tomography. Finally, we highlight performance by displaying the 3D datasets acquired at > 19,487 × 103 A-lines/s as cross-sectional images, averaging the complex A-scan signals of the voxel, and examining the inter-frame phase variance without the need for trigger signals and a phase calibration method. By integrating three-dimensional coherence-based optical imaging into a video-rate, camera-like deployment using a high-speed digitizer, this laser may potentially leverage the use of optical coherence tomography of complex tissue dynamics in pre-clinical studies

Wide-Sense Nonblocking Multicast in WDM Optical Linear Array and Ring Networks with 3-Length Extension Under Longest Link First Routing

The modern scientific growths in optical networks based on wavelength division multiplexing (WDM) are more attractive to satisfy the high bandwidth requirements of the modern internet infrastructure. Moreover, they potential to satisfy the future bandwidth requirements.WDM optical networks act as the backbone for telecommunication and high-performance communication networks. Multicast communication is the simultaneous transmission of data from one source node to many destination nodes available in the network over wavelength division multiplexing. It is extensively deployed in high performance computing and communication networks. In this article, a linear array and ring networks are extended by directly linking all nodes which are separated by two intermediate nodes with additional fibers which is referred as linear array and ring network with 3-length extension. The wavelength allotment methods are proposed to realize one-to-many communication over wavelength division multiplexing optical linear array and ring with 2-length extension under longest link first routing and the minimum wavelength number needed is determined. The minimum wavelength number needed to support for the extended linear array is reduced approximately by 20% when compared with that of a linear array network and for the extended unidirectional ring is reduced approximately by 25% when compared with that of a unidirectional ring network. And also, for the extended bidirectional ring the minimum wavelength number is reduced approximately by 33% when compared with that of bidirectional ring network.