Kyunghwan Oh | Yonsei University (original) (raw)

Papers by Kyunghwan Oh

Optics and Lasers in Engineering

Conference on Lasers and Electro-Optics, 2017

Optics Express, 2021

We proposed and experimentally demonstrated combining a nonlinear optic saturable absorber and a ... more We proposed and experimentally demonstrated combining a nonlinear optic saturable absorber and a wideband-tunable spectral filter in a single graphene oxide (GO) film deposited fiber optic device. The GO film was prepared on the cleaved facet of an optical fiber applying two sequential processes: the electrical deposition to make a thick GO film using an arc fusion splicer, followed by the laser pulse drilling to form a multi-layered GO film. The GO deposited fiber facet and a pristine fiber facet formed an asymmetric Fabry-Perot interferometer (FPI), whose spectral response was flexibly controlled by adjusting the air gap between them. An all-fiber ring laser cavity was built using the proposed device as a tunable saturable absorber along with erbium-doped fiber as a gain medium in the L-band. Stable Q-switching laser pulse trains were successfully generated, whose pulse duration was in the order of a few microseconds and its peak wavelength was tunable over 40nm from 1564 to 1604n...

$Research paper thumbnail of Nanoliter liquid refractive index sensing using a silica V-groove fiber interferometer$

Photonics Research, 2019

A unique all-fiber interferometric sensor was proposed and successfully demonstrated efficient lo... more A unique all-fiber interferometric sensor was proposed and successfully demonstrated efficient low-refractive-index liquid sensing in the range from 1.33 to 1.37, which is compatible with those of bio-liquids. A special silica coreless optical fiber with an open V-groove was used as an optical sensing medium, which provided a high sensitivity for a minute liquid volume in the nanoliter scale. The V-groove fiber (VGF) was serially concatenated between two single-mode fibers (SMFs). The LP01 mode guided along the input SMF excited the higher-order modes in the VGF to generate multimode interference, whose spectrum was transmitted through the output SMF. A single liquid droplet with volume of ∼80 nanoliters wet the entire hydrophilic surface of the VGF, and the transmission spectra shifted corresponding to its refractive index in a very linear manner. The sensor also showed a negligible temperature cross-sensitivity in the range 25°C–75°C, which overlaps with the biological temperature window such that the sensitivity of 159.696 nm per refractive index unit (nm/RIU) remained independent of the temperature variation. Modal properties of VGF were thoroughly analyzed numerically, and detailed processes for the sensor fabrication and sensing experiments were reported.

Journal of Lightwave Technology, 2019

Laser & Photonics Reviews, 2018

Frontiers in Optics 2010/Laser Science XXVI, 2010

Transmission of light through arrays of sub-wavelength holes in the thin silver film was numerica... more Transmission of light through arrays of sub-wavelength holes in the thin silver film was numerically investigated for various arrangements. We also experimentally investigated metalized nano-structured photonic crystal fiber taper to observe an enhanced transmission .

Optical Engineering, 2008

arXiv (Cornell University), Dec 4, 2019

Biosensors

We present a fiber-optic sensor based on the principles of a Fabry–Perot interferometer (FPI), wh... more We present a fiber-optic sensor based on the principles of a Fabry–Perot interferometer (FPI), which promptly, sensitively, and precisely detects blood clot formation. This sensor has two types of sensor tips; the first was crafted by splicing a tapered fiber into a single-mode fiber (SMF), where fine-tuning was achieved by adjusting the tapered diameter and length. The second type is an ultra-compact blood FPI situated on the core of a single-mode fiber. The sensor performance was evaluated via clot-formation-indicating spectrum shifts induced by the varied quantities of a thrombin reagent introduced into the blood. The most remarkable spectral sensitivity of the micro-tip fiber type was approximately 7 nm/μL, with a power sensitivity of 4.1 dB/μL, obtained with a taper fiber diameter and length of 55 and 300 μm, respectively. For the SMF type, spectral sensitivity was observed to be 8.7 nm/μL, with an optical power sensitivity of 0.4 dB/μL. This pioneering fiber-optic thrombosis s...

Scientific Reports, 2021

We report a new method to optically manipulate a single dielectric particle along closed-loop pol... more We report a new method to optically manipulate a single dielectric particle along closed-loop polygonal trajectories by crossing a suite of all-fiber Bessel-like beams within a single water droplet. Exploiting optical radiation pressure, this method demonstrates the circulation of a single polystyrene bead in both a triangular and a rectangle geometry enabling the trapped particle to undergo multiple circulations successfully. The crossing of the Bessel-like beams creates polygonal corners where the trapped particles successfully make abrupt turns with acute angles, which is a novel capability in microfluidics. This offers an optofluidic paradigm for particle transport overcoming turbulences in conventional microfluidic chips.

Fifth Asia-Pacific Optical Sensors Conference, 2015

We investigated various types of optical fiber sensor based on novel structure of photonic crysta... more We investigated various types of optical fiber sensor based on novel structure of photonic crystal fibers (PCFs) including Ge-doped ring defect PCF and Suspended ring core PCF. Furthermore, a new type of fiber named C-type fiber is utilized as a fiberized sensor unit in/outlet. This configuration enabled to package the entire sensor unit in fiber form as well as could overcome prior limitations in PCF-based optical sensors such as too small holes for efficient measurand entry and sophisticated fabrication processes. The experiment and simulation results proved that the designed sensor can improve both sensitivity and response time compare to conventional PCF based sensors.

Optomechatronic Sensors, Actuators, and Control, 2004

We present a novel micro optical waveguide (MOW) on micro actuating platform (MAP) structure that... more We present a novel micro optical waveguide (MOW) on micro actuating platform (MAP) structure that is used for a variable optical attenuator. The device is consists of a fused biconical taper (FBT) coupler mounted on an electromechanical system where an axial stress over the waist of FBT coupler is precisely controlled. Its operation is based on change of coupling constant

Frontiers in Optics 2010/Laser Science XXVI, 2010

We report unique quasi-1-D Bessel-like beam formation from a sub-wavelength slit embedded in 1-D ... more We report unique quasi-1-D Bessel-like beam formation from a sub-wavelength slit embedded in 1-D periodic metallic grooves. Finite-difference time-domain analyses and composite diffractive evanescent wave model provided a good explanation of the unique beam-shaping phenomena.

2010 23rd Annual Meeting of the IEEE Photonics Society, PHOTINICS 2010, 2010

A bend-insensitive C-band erbium-doped fiber is proposed with strong confinement of the LP01 mode... more A bend-insensitive C-band erbium-doped fiber is proposed with strong confinement of the LP01 mode by six air holes around the core. Bending performances for both pump and signal photons were optimized by parametric analysis.

Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, 2009

Abstract We propose and demonstrate a hollow triangular-core fiber (HTCF) having low-fold symmetr... more Abstract We propose and demonstrate a hollow triangular-core fiber (HTCF) having low-fold symmetry in contrast to conventional cylindrical optical fibers. Near-field intensity variations, Fresnel diffraction patterns, and polarization modes of the HTCF were investigated.