Kyung-hwan Oh

Novel photonic devices based on a new type of waveguide, hollow optical fibers (HOF), are described. Utilizing unique three layered structure of HOF, the central air hole, germanosilicate ring core, and silica cladding along with its adiabatic mode transformation capability we demonstrated versatile applications in short-haul, long-haul optical communications, and tunable wavelength selective devices. Detailed design parameters, fabrication arts of the fibers, and operation principles of the dev

We have observed oscillation in a Tm(3+) and Ho(3+) codoped silica fiber from the (5)I(7) ? (5)I(8) transition of Ho(3+) in the 2-microm region, by pumping the fiber laser into a Tm(3+) absorption between 800 and 830 nm. By a change in the cavity length, the laser was tunable between 2.037 and 2.096 microm. When the laser was pumped with a Ti:sapphire laser at 820 nm, an absorbed threshold power extracted power of 214mW, a slope efficiency of 4.2%,and maximum extracted power of 12.5 mW were meas

Abstract Two‐dimensional hybrid organic–inorganic perovskites have recently attracted attention in various optoelectronic applications. A novel thin film of 2D perovskite (C 6 H 5 C 2 H 4 NH 3 ) 2 PbI 4 crystallites is synthesized and its nonlinear optical properties are experimentally investigated within the optical gain of an Erbium‐doped fiber. Utilizing its unique nonlinear optical response, efficient mode‐locking of an all‐fiber Erbium laser is demonstrated at the anomalous dispersion regim

We proposed and experimentally demonstrated 3-dimensional dark traps for low refractive index bio-cells using a single optical fiber Bessel beam. The Bessel beam was produced by concatenating single-mode fiber and a step index multimode fiber, which was then focused by a high refractive index glass microsphere integrated on the fiber end facet. The focused Bessel beam provided two dark fields along the axial direction, where stable trapping of low refractive index bio-cells was realized in a hig

We report unique thermo-optical characteristics of DNA-Cetyl tri-methyl ammonium (DNA-CTMA) thin solid film with a large negative thermo-optical coefficient of -3.4×10^-4/°C in the temperature range from 20°C to 70°C without any observable thermal hysteresis. By combining this thermo-optic DNA film and fiber optic multimode interference (MMI) device, we experimentally demonstrated a highly sensitive compact temperature sensor with a large spectral shift of 0.15 nm/°C. The fiber optic M

We report the observation of amplified spontaneous emission in the (3)H(4) ? (3)H(6) transition of Tm(+3) in a Ta(2)O(5)-doped multicomponent silicate fiber. The evolutions of the spectral shape, output power, and center wavelength were measured as a function of fiber length and pump power in the previously unstudied high-power range, where saturation effects dominate. An output power of 1 mW has been achieved at 1.91 microm with a bandwidth of 77 nm.

Synthesis of ε-caprolactam in a twin screw extruder by anionic ring-opening polymerization was successfully carried out to prepare a novel nylon 6 (polyamide 6 (PA6)) containing a small amount of diamine moiety. The produced PA6 shows a remarkable improvement of the physical properties (mechanical properties as well as rheological properties). Added diamine molecules led to some structural changes in the synthesized PA6. The molar ratio of the additive (diamine) to the initiator appeared to be o

, also known as riboflavin. Surfactant-free DNA solid films of high optical quality were successfully deposited on various types of substrates by spin coating of aqueous solutions without additional chemical processes, with thicknesses ranging from 18 to 100 nm. Optical properties of the DNA films were investigated by measuring UV-visible-NIR transmission, and their refractive indices were measured using variable-angle spectroscopic ellipsometry. By doping DNA solid films with riboflavin, the re

In recent years, development of advanced electronic devices and communication instruments has led to increased demand for electromagnetic interference (EMI) shielding because high‐frequency microwave generates undesired noise which can affect the proper operation of commercial, military and scientific electronic devices as well as the health of our human body. In this study, we investigated the effect of crosslinking reaction of polymer matrix on the EMI shielding performance of a Fe–Si–Al alloy