Kyunghwan Oh
Yonsei University, Department of physics and applied physics, Department Member
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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... 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...
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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... 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.
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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... 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 .
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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... 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...
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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,... 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.
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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... 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.
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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... 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
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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... 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.
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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.
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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... 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.
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We report a self-assembled water-vacuum microfluidic periodic structures in a hollow optical fiber by one-way flame brushing technology. With this structure, we saw the detailed fabrication process and optical properties characteristics... more
We report a self-assembled water-vacuum microfluidic periodic structures in a hollow optical fiber by one-way flame brushing technology. With this structure, we saw the detailed fabrication process and optical properties characteristics were discussed successfully.
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A new method to evaluate the image quality of the fiber bundle using digital micro-mirror device (DMD) along with accessory light modulator package (ALP) is proposed. We have demonstrated that some characteristics of fiber bundle, such as... more
A new method to evaluate the image quality of the fiber bundle using digital micro-mirror device (DMD) along with accessory light modulator package (ALP) is proposed. We have demonstrated that some characteristics of fiber bundle, such as an extent of blurring, gray-level degradation and color aberration can be evaluated by using a single device DMD-ALP, and we have also proved capability of micron-order analysis. Moreover we measured the transmitted image contrast of the fiber bundle using some line pairs made by DMD-ALP, which can be more convenient than previous methods.
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We have proposed a novel higher-order-mode dispersion compensating technique based on a hollow optical fiber mode converter. The mode converter shows the efficiency of more than 87% in conversion of the LP01 mode of single mode fibre... more
We have proposed a novel higher-order-mode dispersion compensating technique based on a hollow optical fiber mode converter. The mode converter shows the efficiency of more than 87% in conversion of the LP01 mode of single mode fibre (SMF) to the LP02 mode in a ring-core dispersion compensated fibre (DCF). Design parameters for the HOF and the mating ring-core DCF have
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A new type of erbium doped fiber for optical amplifier was reported where erbium was doped in the center of the core and samarium doped in a ring in the cladding. By utilizing the spectral overlap of the absorption cross section of... more
A new type of erbium doped fiber for optical amplifier was reported where erbium was doped in the center of the core and samarium doped in a ring in the cladding. By utilizing the spectral overlap of the absorption cross section of samarium in the inner-cladding and the emission cross section of erbium ion in the core, we demonstrated a
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We presented a novel 2/spl times/2 cross connect switch using monotonic change of coupling constant by torsional stress over the coupling region of a 1310/1550 nm WDM coupler. Within the rotation angle range less than 650/spl deg/,... more
We presented a novel 2/spl times/2 cross connect switch using monotonic change of coupling constant by torsional stress over the coupling region of a 1310/1550 nm WDM coupler. Within the rotation angle range less than 650/spl deg/, continuous control of power splitting ratio from 0 to 100% could be achieved. The switch showed the insertion loss less than 0.15 dB channel isolation over 22 dB and switching time less than 1 sec. The proposed device could be used in a cross connect switching system that routes 1.3 /spl mu/m signal in Giga bit Ethernet system and 1.5 /spl mu/m in DWDM or CWDM systems.
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We report a new type of long period grating fabrication method by curing polymer filled in a hollow optical fiber. In the curing process, a self-assembled polymer-air periodic structure was achieved.
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A new type of novel all-fiber power splitter has been designed and experimentally demonstrated, which could be directly applied to very short reach (VSR) passive optical networks (PON) based on hard polymer clad fibers (HPCF). Overcoming... more
A new type of novel all-fiber power splitter has been designed and experimentally demonstrated, which could be directly applied to very short reach (VSR) passive optical networks (PON) based on hard polymer clad fibers (HPCF). Overcoming silica glass manufacturing difficulties, we successfully developed a 4x4 HPCF star coupler using a micro hydrogen-burner flame brushing. The device showed an excellent uniformity
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ABSTRACT Molybdenum disulfide nano-sheets were all-optically deposited on a single mode fiber facet, and its process was monitored by a reflectometry method. Nonlinear response and power dependent transmission of prepared sample was... more
ABSTRACT Molybdenum disulfide nano-sheets were all-optically deposited on a single mode fiber facet, and its process was monitored by a reflectometry method. Nonlinear response and power dependent transmission of prepared sample was observed by a 1552nm fiber laser.
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Abstract We demonstrated the new bessel beam generator which consisted of polymer lens and hybrid optical fiber under various fabriacting structures. The device was maesured the properties of the spot size and the intensity as propagation... more
Abstract We demonstrated the new bessel beam generator which consisted of polymer lens and hybrid optical fiber under various fabriacting structures. The device was maesured the properties of the spot size and the intensity as propagation distance.
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Research Interests: Food Science and Calcium
Although early treatment of Crohn's disease (CD) patients with anti-tumor necrosis factor (TNF) agents or immunomodulators (IMs) may improve long-term outcomes, especially those with poor prognostic factors, their effectiveness in... more
Although early treatment of Crohn's disease (CD) patients with anti-tumor necrosis factor (TNF) agents or immunomodulators (IMs) may improve long-term outcomes, especially those with poor prognostic factors, their effectiveness in Asians remains unclear. In this study, Korean patients with CD naïve to both intestinal surgery and intestinal complications, and with at least two risk factors for progression (diagnosis at age <40 years, systemic corticosteroid treatment <3 months after diagnosis, and perianal fistula at diagnosis) were retrospectively analyzed. Patients were classified into those who started anti-TNFs, or IMs but not anti-TNFs, within 2 years of diagnosis, and those who started anti-TNFs and/or IMs later. Their probabilities of intestinal surgery and intestinal complications were compared. A total of 670 patients were enrolled, 79 in the early anti-TNF, 286 in the early IM, and 305 in the late treatment group. Kaplan-Meier analysis with the log-rank test showe...
Research Interests: Gastroenterology, Adolescent, Multidisciplinary, Humans, Female, and 15 moreMale, Immunomodulation, Risk factors, PLoS one, Clinical Sciences, Adult, Retrospective Studies, Prognosis, Disease Progression, Risk Factors, Elsevier, Neurosciences, Proportional Hazards Models, Crohn Disease, and Paediatrics and reproductive medicine
Intestinal inflammation and mucosal damage in Crohn's disease (CD) are believed to progress even during clinical remission. We investigated the long-term prognosis of CD patients in clinical remission according to serum C-reactive... more
Intestinal inflammation and mucosal damage in Crohn's disease (CD) are believed to progress even during clinical remission. We investigated the long-term prognosis of CD patients in clinical remission according to serum C-reactive protein (CRP) levels. This study included 339 CD patients in clinical remission (Crohn's disease activity index < 150) for more than 6 months between January 2008 and December 2010. Clinical outcomes were compared between patients with normal and elevated CRP levels during clinical remission. During clinical remission, 150 patients had normal CRP consistently and 189 had elevated CRP at least once. During follow-up (median, 7.9 years [interquartile range, 6.8-8.0]), the Kaplan-Meier analysis with the log-rank test showed that normal CRP group had a longer CD-related hospitalization-free survival (P = 0.007) and a longer CD-related intestinal resection-free survival (P = 0.046) than elevated CRP group. In multivariate analysis, elevated CRP was s...
Research Interests: Gastroenterology, Medicine, Multidisciplinary, Humans, Female, and 14 moreMale, Follow-up studies, Risk factors, PLoS one, Clinical Sciences, C reactive protein, Adult, Survival Rate, Risk Factors, Elsevier, Neurosciences, Crohn Disease, Disease Free Survival, and Paediatrics and reproductive medicine
Jejunal variceal bleeding is less common compared with esophagogastric varices in patients with portal hypertension. However, jejunal variceal bleeding can be fatal without treatment. Treatments include surgery, transjugular intrahepatic... more
Jejunal variceal bleeding is less common compared with esophagogastric varices in patients with portal hypertension. However, jejunal variceal bleeding can be fatal without treatment. Treatments include surgery, transjugular intrahepatic porto-systemic shunt (TIPS), endoscopic sclerotherapy, percutaneous coil embolization, and balloon-occluded retrograde transvenous obliteration (BRTO). Percutaneous coil embolization can be considered as an alternative treatment option for those where endoscopic sclerotherapy, surgery, TIPS or BRTO are not possible. Complications of percutaneous coil embolization have been reported, including coil migration. Herein, we report a case of migration of the coil into the jejunal lumen after percutaneous coil embolization for jejunal variceal bleeding. The migrated coil was successfully removed using surgery.