arXiv subjects

Wen-Hsuan Kuan

Publications and source records attributed to Wen-Hsuan Kuan.

12 recordsLinked to original sources

arXiv2026

NIR and visible structured beam generation with a dual-force mechanical long-period fiber grating

This work presents tunable generation of vortex, vector, and flat-top 1060-nm NIR beams in a few-mode fiber with a dual-force mechanical long-period fiber grating. By varying the applied forces on the fiber grating, the core mode to higher-order mode excitation can be adjusted. Manipulating the beam transformation is achieved by controlling the polarization of the fiber eigenmodes and the mode-coupling efficiency. In addition, our dual-force scheme enables greater flexibility in the mode selection by introducing the force gradient as an additional degree of freedom. By precisely tuning the intensity ratio between fundamental and doughnut modes, we arrive at the generation of propagation-invariant flat-top beams, for which the transverse intensity distribution exhibits a near-uniform profile over a propagation distance of 5 m in free space. The transverse optical field of 532-nm green light from a frequency-doubled Nd-doped yttrium vanadate laser can also be manipulated and coupled into various intensity distributions in a few-mode fiber by using a mechanically induced long-period fiber grating. We show that a doughnut beam, Mexican-hat beam, and crater-lake beam can be generated from the input Gaussian beam via the coupling of the fundamental core mode to a series of co-propagating higher-order modes with properly applied forces and polarizations. Our experimental results establish dual-force mechanically induced LPGs as a flexible and reconfigurable fiber-based tool for structured beam engineering, offering a unified platform for in-situ and robust control of phase, polarization, and amplitude of optical fields across different spectral bands.

physics.optics↗

arXiv2026

Driven square lattice of quantum dots in a magnetic field coupled to a cylindrical FIR-photon cavity

We present a comprehensive computational study of driven quantum dot arrays in a square lattice configuration, subject to an external magnetic field and coupled to a cylindrical far-infrared photon cavity. The driving is introduced through a harmonic modulation of the full electron-photon interaction, therefore including both paramagnetic and diamagnetic contributions. The electron-electron Coulomb interactions are treated within density functional theory, while the electron-photon coupling is modeled using a many-body configuration interaction approach at each iteration of the density functional. By exploiting the unique properties of the cylindrical TE$_{011}$ cavity mode, we demonstrate selective enhancement of diamagnetic two-photon transitions. Our results reveal that the effectiveness of harmonic modulation of the electron-photon interaction is strongly dependent on both the driving frequency and the electron occupation number per dot. When the driving frequency approaches twice the cavity photon frequency, the system exhibits resonant behavior characterized by efficient photon pumping, occupation of higher-order photon replicas, and activation of collective radial Coulomb breathing modes. These findings establish a controllable mechanism for manipulating photon states in coupled quantum dot-cavity systems and provide insights into the interplay among harmonic modulation, photonic excitations, magnetic confinement, and many-body electron correlations in dimensionally reduced nanostructures.

cond-mat.mes-hall↗

arXiv2026

Suppression of Bloch Oscillations and Nonreciprocal Landau-Zener Tunneling in Bose-Einstein Quantum Droplets

We investigate the nonlinear Bloch dynamics and Landau-Zener (LZ) tunneling of quantum droplets in optical lattices. We show that the Lee-Huang-Yang (LHY) correction not only stabilizes the self-bound droplet, but also introduces nonlinear phase feedback that competes with the lattice-induced coherent motion. In the deep-lattice regime, applying a generalized super-Gaussian ansatz within the tight-binding model demonstrates that chirp accumulation modifies the internal phase profile and renormalizes mobility. The coherent Bloch oscillations (BO) are progressively arrested in the presence of the LHY interaction without dissipative damping. In the shallow-lattice regime, the system is mapped onto a nonlinear two-level Josephson-analog model in which the mean-field and LHY contributions enter through an effective nonlinear detuning, deforming the adiabatic spectrum and generating looped bands. Using the classical action-angle formulation, we demonstrate that the nonlinear LZ tunneling is governed by the underlying phase-space structure. In particular, the LHY correction suppresses the tunneling probability by modifying the separatrix action and renormalizing the exponential sweep-rate scaling through a nonlinear weighting factor. We further identify pronounced nonreciprocal LZ tunneling arising from branch-dependent population imbalance and the nonlinearly induced inertia. These results establish a unified mechanism in which the LHY interaction suppresses both coherent Bloch dynamics and interband tunneling by reorganizing the dynamical exchange among lattice motion, population imbalance, and internal phase modulation.

cond-mat.quant-gas↗

arXiv2025

Optical bistability of continuous-wave and multi-pulse phase transition within EDFL via low threshold saturable absorber

We demonstrate optical bistability in an erbium-doped fiber laser (EDFL) using a low saturation intensity covalent organic framework (COF) saturable absorber (SA). The COF-SA satisfies the free-energy criterion for bistability, enabling switching among non-lasing, continuous-wave, and mode-locking states. Two optical bistability regions are observed, including a distinctive direct mode-locking to non-lasing transition during pump down-sweep, absent in previous EDFL studies. Stable soliton-like pulses and stepwise pulse-number hysteresis further indicate first-order phase-transition-like dynamics. These results show that low-saturation intensity SAs offer a compact route to bistability-assisted pulse formation in fiber lasers.

physics.optics↗

arXiv2025

Signatures of broken symmetries in the excitations of a periodic 2DEG coupled to a cylindrical photon cavity

In a two-dimensional electron gas (2DEG) in a periodic lateral superlattice subjected to an external homogeneous magnetic field and in a cylindrical far-infrared photon cavity we search for effects of broken symmetries: Static ones, stemming from the unit cell of the system, and the external magnetic field together with the dynamic ones caused by the vector potential of the cavity promoting magnetic types of transitions, and the chirality of the excitation pulse. The Coulomb interaction of the electrons is described within density functional theory, but the electron-photon interactions are handled by a configuration interaction formalism within each step of the density functional approach, both for the static and the dynamic system. In the dynamical calculations we observe weak chiral effects that change character as the strength of the electron-photon interaction and the external magnetic field are increased. From the analysis of the chiral effects we identify an important connection of the para- and diamagnetic electron-photon interactions that promotes the diamagnetic interaction in the present system when the interaction strength is increased. Furthermore, the asymmetric potential in the unit cell of the square array activates collective oscillation modes that are not present in the system when the unit cell has a higher symmetry.

cond-mat.mes-hall↗

arXiv2024

Dynamics of Rapidly Rotating Bose-Einstein Quantum Droplets

This work theoretically investigates \textcolor{black}{the stationary properties} and the dynamics of the rotating quantum liquid droplets confined in a two-dimensional symmetric anharmonic trap. Mimicking the quantum Hall systems, the modified Gross-Pitaevskii equation with the inclusion of the Lee-Huang-Yang nonlinear interaction is analytically solved, and the role of the Landau-level mixing effect is addressed. \textcolor{black}{Via controlling the nonlinear interaction and the rotation speed, the rotating quantum droplet with multiply quantized vortex can be created, and the preference of the energetically favored quantum states can be distinguished in the phase diagram. To better interpret the underlying physics of the phase singularities, a brief comparison of the rotating quantum droplet and the optical vortex is made. The investigation of the long-term evolution of the rotating quantum droplets confirms the stability of the quantum states. At certain rotation speeds, the multi-periodic trajectories and breathings provide evidence of the emergence of the collective excitation of the surface mode in the vortex state. For quantum droplets carrying multiply quantized vortex, the microscopic snapshots of the rotation field adjusted current density distribution show that the combined nonlinear interaction and the anharmonic trapping potential can provide the restoring force to lead the quantum droplet to a regular and stable revolution and reach the dynamic equilibrium, revealing the signature of the generation of superfluids in the new kind of low-dimensional quantum liquids.

cond-mat.quant-gas↗

arXiv2021

Wavelength-tunable doughnut beam generation using few-mode long-period fiber grating

Ultra-broadband long-period fiber grating with 10-dB bandwidth of 155 nm and 3-dB bandwidth of 415 nm is demonstrated around 1060 nm, which has been combined with a tunable ytterbium-doped fiber laser to generate optical doughnut beams in the spectral range from 1030 nm to 1099 nm, and the vector nature of generated optical fields are observed. The long-period fiber grating has also been used to transform the amplified spontaneous emission of an ytterbium-doped fiber amplifier into a broadband optical doughnut beam.

physics.optics↗

arXiv2021

Generalized Jones Calculus for Vortex, Vector, and Vortex-Vector Beam Transformations

The work defines the general form of the Jones vector and establishes the Jones matrix for polarizers, wave plates, Faraday rotators, Q-plates, and spiral phase plates. We establish the generalized Jones calculus for vortex, vector, and vortex-vector beam transformations. Systematic formalism presents the theoretical arrangements in the manipulation of the phase and polarization of the structured lights. The eigenstates and the time-reversal behaviors of optical components and systems are discussed through matrix algebra. The generalized Jones calculus is then used in the characterization of Sagnac interferometers, and the potential applications are proposed.

physics.optics↗

arXiv2018

Manipulation of Gaussian Derivative Pulses and Vector Solitons in an Anomalous-Dispersion Fiber Laser

Both positive- and negative-polarity Gaussian monocycle and doublet pulses, for which the pulse shapes are the first and second derivatives of Gaussian functions respectively, are generated in a ring-cavity erbium-doped fiber laser from polarization-locked vector solitons by using passive optical technology. The pulse states are switchable and are found to be the superposition of bright and dark solitons with different widths, amplitudes, time delays, polarizations, and wavelengths. Qualitative analysis of the properties of vector solitons are performed by solving coupled complex Ginzburg-Landau equations. By theoretical representing the envelopes of bright soliton by sech and dark soliton by tanh functions, the incoherent superposition of these two soliton components have simulated the experimental observations, and the underlying mechanisms on the formation for monocycle and doublet pulses are attributed to the polarization locking of bright and dark solitons. The results of tunable optical vectos solitons are compared with atomic solitons in the system of Bose-Einstein condensation. Since governing equations for soliton generation in fiber lasers and Bose-Einstein condensation have many properties in common and thus the simulation and propagation of pulsating waves may open a new route to explore the classical solitary dynamics in nonlinear optics and its quantum analogy in ultralcold fields.

physics.optics↗

arXiv2017

Femto/nano-second switchable passively mode-locked fiber laser with analytic modeling by cubic-quintic Ginzburg-Landau equation

We report a passively mode-locked erbium-doped fiber laser with pulsewidths switchable from 473 fs to 76.8 ns, where the fundamental mode-locking, noise-like pulse, nanosecond mode-locking, and dual-width mode-locking are obtained by adjusting a polarization controller. Co-existence of femto- and nano-second pulses in dual-width mode-locking is attributed to the gain balancing. Analytic modeling of the fiber laser with cubic-quintic Ginzburg-Landau equation is presented, in which the pulsewidths are calculated as functions of dispersion, saturable absorption, and self-phase modulation. The generation of nanosecond pulses is attributed to weakened intracavity pulse-shortening strength and reduced effective self-phase modulation in the laser cavity.

physics.optics↗

arXiv2017

Magneto-Optical Quantum Switching in a System of Spinor Excitons

In this work we investigate magneto-optical properties of two-dimensional semiconductor quantum-ring excitons with Rashba and Dresselhaus spin-orbit interactions threaded by a magnetic flux perpendicular to the plane of the ring. By calculating the excitonic Aharonov-Bohm spectrum, we study the Coulomb and spin-orbit effects on the Aharonov-Bohm features. From the light-matter interactions of the excitons, we find that for scalar excitons, there are open channels for spontaneous recombination resulting in a bright photoluminescence spectrum, whereas the forbidden recombination of dipolar excitons results in a dark photoluminescence spectrum. We investigate the generation of persistent charge and spin currents. The exploration of spin orientations manifests that by adjusting the strength of the spin-orbit interactions, the exciton can be constructed as a squeezed complex with specific spin polarization. Moreover, a coherently moving dipolar exciton acquires a nontrivial dual Aharonov-Casher phase, creating the possibility to generate persistent dipole currents and spin dipole currents. Our study reveals that a manipulation of the spin-orbit interactions provides a potential application for quantum-ring spinor excitons to be utilized in nano-scaled magneto-optical switches.

cond-mat.mes-hall↗

arXiv2007

Spectral properties and magneto-optical excitations in semiconductor double-rings under Rashba spin-orbit interaction

We have numerically solved the Hamiltonian of an electron in a semiconductor double ring subjected to the magnetic flux and Rashba spin-orbit interaction. It is found that the Aharonov-Bohm energy spectrum reveals multi-zigzag periodic structures. The investigations of spin-dependent electron dynamics via Rabi oscillations in two-level and three-level systems demonstrate the possibility of manipulating quantum states. Our results show that the optimal control of photon-assisted inter-ring transitions can be achieved by employing cascade-type and $Λ$-type transition mechanisms. Under chirped pulse impulsions, a robust and complete transfer of an electron to the final state is shown to coincide with the estimation of the Landau-Zener formula.

cond-mat.mes-hall↗