arXiv subjects

Kuei-Huei Lin

Publications and source records attributed to Kuei-Huei Lin.

6 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↗

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↗

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↗