Seongmook Jeong

Development of a highly sensitive compact sized optical fiber current sensor

We have experimentally developed a highly sensitive and a compact size current sensor by using the CdSe quantum dots-doped bend insensitive optical fiber, operating in the visible band of wavelength. The modified sensitivity of this sensor was about 675 microrad/(Turn.A.m) for the loop radius of just 10 mm, which is more than 16 times larger than that of the single mode optical fiber current sensor.

Radial-firing optical fiber tip containing conical-shaped air-pocket for biomedical applications

We report a novel radial-firing optical fiber tip containing a conical-shaped air-pocket fabricated by deforming a hollow optical fiber using electric arc-discharge process. The hollow optical fiber was fusion spliced with a conventional optical fiber, simultaneously deforming into the intagliated conical-shaped region along the longitudinal fiber-axis of the fiber due to the gradual collapse of the cavity of the hollow optical fiber. Then the distal-end of the hollow optical fiber was sealed by the additional arc-discharge in order to obstruct the inflow of an external bio-substance or liquid to the inner air surface during the surgical operations, resulting in the formation of encased air-pocket in the silica glass fiber. Due to the total internal reflection of the laser beam at the conical-shaped air surface, the laser beam (λ = 632.8 nm) was deflected to the circumferential direction up to 87 degree with respect to the fiber-axis.

Effect of heat treatment of optical fiber incorporated with Au nano-particles on surface plasmon resonance

To improve the sensitivity of the surface plasmon resonance (SPR) sensor based on the specialty optical fiber incorporated with Au nano-particles (NPs) in the cladding region, the effect of heat treatment (800 °C - 1000 °C) of the fiber on sensing capability of refractive index (n = 1.418 - 1.448) was investigated. The SPR appeared at a particular wavelength around 390 nm for the corresponding refractive indices regardless of the heat treatment temperature and the SPR wavelength increased with the increase of the index. The SPR sensitivity was found to increase with the increase of heat treatment temperature, 178 nm/RIU, 299 nm/RIU, and 945 nm/RIU at 800 °C, 900 °C, and 1000 °C for an hour, respectively. On the other hand, the SPR absorption intensity decreased with the increase of heat treatment temperature due to the increase of the propagation loss of the incident light and the SPR band became spread due to the increase of the size distribution of the Au NPs at the various refractive indices.

Optical fiber bend sensor based on fiber Bragg grating in germano-silicate glass optical fiber with depressed-index structure

An optical fiber bend sensor based on a fiber Bragg grating by using a germano-silicate glass optical fiber with depressed-index structure has been developed and its novel bend sensing characteristics was demonstrated. With the increase of bending, the transmission spectrum was linearly blue-shifted without change of optical transmission loss. Total blue-shift of the Bragg reflection wavelength upon bending in the radius of curvature from 20 m-1 to 133 m-1 was − 0.13 nm.

NONLINEAR OPTICAL PROPERTIES OF ZINC DOPED GERMANO-SILICATE GLASS OPTICAL FIBER

Zinc doped germano-silicate glass optical fiber was developed by using the modified chemical vapor deposition and the drawing tower process. Absorption peaks of the germano-silicate glass optical fiber preform appeared at 240 nm and 330 nm were due to the incorporated Zn metal nano-particles (MNPs) and ZnO semiconductor nano-particles (SNPs), respectively and the average diameter of nano-particles (NPs) was estimated to be about 2 nm by transmission electron microscopy. However, the absorption peak of the zinc doped optical fiber due to ZnO SNPs was found to appear at 490 nm red-shifted from 330 nm can be explained by the increase in average size of ZnO SNPs in the fiber core due to growth or recrystallization of ZnO SNPs during the fiber drawing process about 2150°C. The nonlinear refractive index coefficient, n2, of the fiber was estimated to be 5.62 × 10-20 m2/W due to the stable dispersion of ZnO SNPs using the continuous-wave self-phase modulation method.

Gamma-Ray Radiation Effect on Non-Resonant Third-Order Optical Nonlinearity of Germano-Silicate Optical Fiber

Gamma-ray radiation effect on the non-resonant third-order optical nonlinearity of the germano-silicate optical fiber has been investigated by the continuous-wave self-phase modulation method. The nonlinear refractive index, n2, of the gamma-ray irradiated optical fiber was found to increase linearly with the increase of the gamma-ray induced absorption. The increased n2 has been mainly ascribed to the NBOs and Ge-realted radiation-induced defects having hyperpolarizabilities.

Demonstration of All-Optical Fiber Isolator Based on a CdSe Quantum Dots Doped Optical Fiber Operating at 660 nm

A novel all-optical fiber isolator with 14 dB isolation at 660 nm was demonstrated using the CdSe quantum dots doped optical fiber, which was fabricated by using the modified chemical vapor deposition and high temperature drawing processes. The Faraday rotation angle of 45 degrees was obtained at the fiber length of 183 cm under the magnetic field of 0.119 T.

PHOTONIC PROPERTIES OF Ti DOPED OPTICAL FIBER

The photonic properties of Ti doped optical fiber were investigated for application of optical nonlinear devices and a fiber-type UV sensor based on its high third order optical nonlinearity and photoluminescence characteristics. The structure and defect states of Ti incorporated in silica glass network of the fiber core were examined by measurement of optical properties such as optical absorption, photoluminescence, Raman shift, and by transmission electron microscopy. The nonlinear refractive index, n2, of the fiber was measured to be 5.73 × 10-20 m2/W by continuous-wave self-phase modulation method, which was 2.5 times larger than that of the same optical fiber without Ti incorporation. The photoluminescence of the Ti doped optical fiber was found to appear over the range from 360 nm to 480 nm upon the Xenon-lamp illumination, and it was found to increase linearly with the increase of the lamp power.

Effect of Cross-Sectional Structure on Optical Properties of Metal-Filled Side-Hole Fiber

The effect of the cross-sectional structure of metal-filled side-hole fiber on the birefringence and thermooptic properties was investigated by the fiber-optic Sagnac loop interferometry. The optical fibers having different cross-sectional structures filled with indium metal were fabricated by drawing a fiber preform with two side holes at different temperatures followed by metal infiltration. The original circular core and two identical holes in the fiber preform were deformed into the fiber core with various core ellipticities and different hole diameters after the drawing. It was found that the fiber birefringence (B} and the temperature dependence were strongly influenced by the deformation of the fiber cross section, the birefringence increased from 5.68 × 10-5 to 1.16 × 10-4 with the increase of the core ellipticity from 0.273 to 0.412. Additional birefringence was found to be induced after the infiltration of indium into holes due to the large thermal expansion mismatch between indium and silica glass of the fiber. The temperature sensitivities of the unfilled side-hole fibers (d(δλn)/dT) were almost the same and found to be constant of ~-0.60 nm/K regardless of the fiber cross sections. On the other hand, the sensitivities of the indium-filled side-hole fibers (d( δλm)/dT) were enhanced 10-15 times larger than those of the unfilled side-hole fibers, increased from -5.98 to -11.03 nm/K with the increase of the filler indium diameter from ~18.5 to 24.1 μm, respectively.

Gamma-Ray Irradiation-Induced Optical Attenuation in Co/Fe Co-Doped Alumino-Silicate Optical Fiber for Dosimeter Application

Dose dependence of radiation-induced optical attenuation (RIA) at 1310 nm of the Co/Fe co-doped alumino-silicate optical fiber was investigated under gamma-ray irradiation at dose rates from 6.7 to 78.3 Gy/min. From the measured RIA, radiation dose sensitivity (ΔRIA/ΔDose) and rate of RIA change with irradiation time (ΔRIA/ΔTime) at the different dose rates were estimated. RIAs at various wavelengths (800 to 1600 nm) of the optical fiber were also measured and the RIA characteristics at 800 and 1310 nm under discrete gamma-ray irradiation were investigated. The measured RIA of the Co/Fe co-doped fiber showed very high dose sensitivity regardless of the dose rates and the ΔRIA/ΔTime was found to show linear response with respect to the dose rate. The significantly large RIA was attributed to Co, Fe, and Al-related defects in the fiber core which were formed by the irradiation, and it became larger at shorter wavelength. The high radiation dose sensitivity, linear response of the ΔRIA/ΔTime with respect to dose rate, and the high reproducibility of the dose dependence of RIA under the discrete irradiation clearly indicate that the Co/Fe co-doped fiber is able to provide highly accurate information of not only total accumulated dose but also dose rate of the radiation with irradiation time.