Kyoungyeon Choi

Bio: Kyoungyeon Choi is an academic researcher from Seoul National University. The author has contributed to research in topics: Coupled mode theory & Cladding (fiber optics). The author has an hindex of 1, co-authored 1 publications receiving 4 citations.

Two-mode Fiber with a Reduced Mode Overlap for Uncoupled Mode-division Multiplexing in C+L Band

Abstract: We proposed a two-mode fiber (TMF) design that can effectively reduce the mode overlap between LP01 and LP11 modes by using a W-shaped index profile core structure, which is a primary concern in uncoupled mode division multiplexing (MDM). TMF has a three-layered core structure; central circular core, inner cladding, and outer ring core. We confirmed that in an optimal structure the LP01 mode was highly confined to the central core while the LP11 mode was guided along the outer ring core to result in a minimum overlap integral. We used a full-vectorial finite element method to estimate effective index, differential group delay (DGD), confinement loss, chromatic dispersion, and mode overlap controlling the parameters of the W-shaped structure. The optimized W-profile fiber provided optical characteristics within the ITU-T recommended standards over the entire C+L band.

Hollow Silica Photonic Crystal Fiber Guiding 101 Orbital Angular Momentum Modes Without Phase Distortion in C+L Band

Abstract: We propose a new hollow ring core silica photonic crystal fiber that can support 101 orbital angular momentum (OAM) modes, maintaining a high mode quality without phase distortion, a low confinement loss, and a large effective index difference between the adjacent modes, which could open a new avenue of OAM mode multiplexing applications. The fiber consists of three layers: the circular central air hole, silica ring core, and circumferencing silica-air hole porous inner cladding. Using the full-vectorial finite element method (FEM), the modal characteristics of individual OAM modes in the proposed fiber were thoroughly analyzed by varying the number of air-holes in the circularly symmetric cladding. We found a general selection rule for the number of air-holes in the first layer and the topological charge to cause the phase distortion of OAM modes, for the first time. The phase distribution of the guided OAM modes was thoroughly investigated to select usable modes for mode division multiplexing. Parametric analyses of the proposed PCF are reported to optimize optical properties of the OAM modes.

Simultaneously achieving a large negative dispersion and a high birefringence over Er and Tm dual gain bands in a square lattice photonic crystal fiber

Abstract: We proposed a novel photonic crystal fiber composed of a double-cladding square lattice that could be used in dual-band, Er and Tm optical gain bands, simultaneously supporting a large negative dispersion and a high birefringence. We theoretically investigated the light guiding property through the proposed photonic crystal fiber by using a vectorial finite-element method with a perfectly matched layer. By optimizing the structural parameters, we obtained an ultra-large negative dispersion of −20,186 ps/(nm·km) and a very high birefringence of 9.27 × 10⁻³ at the wavelength of 1.55 μm in the Er gain band and a very large negative dispersion of −8,067 ps/(nm·km) and a high birefringence of 1.0 × 10⁻³ at the wavelength of 1.87 μm in the Tm band. We further discussed the roles of waveguide parameters on the chromatic dispersion, its slope, and the birefringence of the fiber as well as the mode field diameter. The proposed fiber could be directly applied for dual-band dispersion and polarization control in fiber laser cavities as well as optical communications and sensors in the dual bands.

Corrections to “Simultaneously Achieving a Large Negative Dispersion and a High Birefringence Over Er and Tm Dual Gain Bands in a Square Lattice Photonic Crystal Fiber”

Abstract: We proposed a novel photonic crystal fiber composed of a double-cladding square lattice that could be used in dual-band, Er and Tm optical gain bands, simultaneously supporting a large negative dispersion and a high birefringence. We theoretically investigated the light guiding property through the proposed photonic crystal fiber by using a vectorial finite-element method with a perfectly matched layer. By optimizing the structural parameters, we obtained an ultra-large negative dispersion of −20,186 ps/(nm·km) and a very high birefringence of 9.27 × 10−3 at the wavelength of 1.55 μ m in the Er gain band and a very large negative dispersion of −8,067 ps/(nm·km) and a high birefringence of 1.0 × 10−3 at the wavelength of 1.87 μ m in the Tm band. We further discussed the roles of waveguide parameters on the chromatic dispersion, its slope, and the birefringence of the fiber as well as the mode field diameter. The proposed fiber could be directly applied for dual-band dispersion and polarization control in fiber laser cavities as well as optical communications and sensors in the dual bands.

Forward-stimulated Brillouin scattering in silicon-core fibers

Abstract: As a new type of semiconductor fiber, silicon-core fibers have a higher non-linear effect compared with silica fibers. Forward-stimulated Brillouin scattering as a typical optical non-linear effect holds strong promise for applications in, for example, fiber-optic sensing. The study of the FSBS effect in silicon-core fibers facilitates further theoretical exploitation of the potential of FSBS in fiber-optic sensing. In this paper, the FSBS in the silicon-core fiber is studied using the finite element method. The model is based on a silicon-core fiber, whose silicon-core diameter is 4 μ m and silica cladding diameter is 33.4 μ m , and the optical field modes are classified by the vector method to obtain the acoustic field modes excited by FSBS—radial mode (R0m) and torsional radial mode (TR2m). The FSBS gain of the fiber shows that R0m has the best coupling with TM and TE optical modes, and TR2m has the best coupling with HE optical modes. It is concluded that the sound field frequency shift of R0m is more sensitive to the change in the effective refractive index of the optical field than that of TR2m. The factors affecting the gain are refined into photoelastic effects and moving boundary perturbations, and their contributions to the total gain are summarized. Finally, it was confirmed that a strong FSBS gain similar to 365.57 (1/mw) can be obtained with silicon-core fibers without the need to reduce the size to the usual dimensions of silicon waveguides, paving the way for further research studies in areas such as frequency-tunable laser emission, mode-locked pulsed lasers, low-noise oscillators, and optical gyroscopes.