Bok Hyeon Kim

Residual stress relaxation in the core of optical fiber by CO 2 laser irradiation

We observed residual stress relaxation by CO(2) laser irradiation in the cores of optical fibers by direct stress measurement. It was demonstrated that the mechanical stress was fully relaxed by CO(2) laser irradiation and that the remaining stress in the core was thermal stress that was due to a mismatch of the thermal expansion coefficients of the fiber core and cladding. The net core stresses after relaxation were 17, 68, and 203 MPa in Ge-B-codoped fibers drawn at 0.53, 1.38, and 3.48 N, respectively. Changes in the refractive indices of the cores as a result of residual stress relaxation were also estimated.

Elliptical defected core photonic crystal fiber with high birefringence and negative flattened dispersion

We propose a novel design of photonic crystal fiber (PCF) using an elliptical air hole in the core as a defected core in order to enhance the performance of modal birefringence and to control the properties of chromatic dispersion at the same time. From the simulation results, it is shown that the proposed fiber has high birefringence up to the order of 10(-2), negative flattened chromatic dispersion in a broad range of wavelengths, and low confinement loss less than that of the single mode fiber. The outstanding advantage of the proposed PCF is that high birefringence, negative flattened dispersion, and low confinement loss can be achieved just by adding a small sized elliptical air hole in the core to the elliptical air hole PCF, especially at the same time.

Effect of CO2 laser irradiation on the refractive-index change in optical fibers.

The effect of CO2 laser irradiation on the refractive-index change in optical fibers is investigated by measuring the interference fringe shift formed by a long-period fiber grating pair. The refractive-index decrease on CO2 laser irradiation was due to relaxation of the residual stress, which was formed in optical fibers during the drawing process, and the refractive-index decrease was found to increase linearly with the drawing force. The effect of the CO2 laser output power on residual-stress relaxation, and fiber elongation was also studied.

Large temperature sensitivity of Sagnac loop interferometer based on the birefringent holey fiber filled with metal indium

The large temperature sensitivity of the Sagnac loop interferometer based on the birefringent holey fiber filled with metal indium was experimentally demonstrated. The temperature sensitivities of the wavelength shift of the interferometer and the birefringence the fiber with indium were measured to be -6.3 nm/K and -3.3x10(-6) /K, respectively. The large temperature sensitivity of the fiber was explained by introduction of the fiber birefringence change originated from the large thermal expansion property of the metal indium at the elevated temperature.

Cu 2+ -doped germano-silicate glass fiber with high resonant nonlinearity

We firstly report on the fabrication of Cu(2+)-doped germano-silicate glass fiber for nonlinear optical devices application by using modified chemical vapor deposition and solution doping processes. Broadband absorption near 700nm due to the 3d-shell electron transitions of Cu(2+) ions from the ground state to the excited states was observed. The resonant nonlinearity of the Cu(2+)-doped fiber was estimated to be 5.5x10(-17)m(2)/W by measuring the phase shift of the fringes obtained from the long-period fiber grating pair upon pumping with a laser diode at 980nm and non-resonant nonlinearities were also measured to be 4.114x10(-21)m(2)/W by the continuous wave self-phase modulation method.

Effect of filler metals on the temperature sensitivity of side-hole fiber

Effect of filler metals (Bi, 80Au-20Sn alloy, Sn, and In) on the temperature sensitivity of a birefringent side-hole fiber was investigated. The temperature sensitivity of the fiber was found to increase by introduction of the filler metals and the sensitivity gradually increased with the increase of the thermal expansion coefficient of metals. The sensitivity was larger for the filler metals with the larger thermal expansion coefficient.

Ultra-wide bandpass filter based on long-period fiber gratings and the evanescent field coupling between two fibers

We demonstrate a fiber-based bandpass filter with an ultra-wide spectral bandwidth. The ultra-wide band feature is achieved by inscribing a long-period fiber grating (LPG) in a specially-designed low index core single mode fiber. To get the bandpass function, the evanescent field coupling between two attached fibers is utilized. By applying strain, the spectral shape of the pass-band is adjusted to flat-top and Gaussian shapes. For the flat-top case, the bandwidth is obtained ~ 160 nm with an insertion loss of ~ 2 dB. With strain, the spectral shape is switched into a Gaussian one, which has ~ 120 nm FWHM and ~ 4.18 dB insertion loss at the peak.

Fabrication and optical characteristics of a novel optical fiber doped with the Au nanoparticles.

Optical fibers containing gold metal nanoparticles were developed by modified chemical vapor deposition, in which Au(OH)3 and tetraethyl-orthosilicate (TEOS) was used via sol-gel process to incorporate gold metals by providing the reduction atmosphere. The absorption peak appeared near 490 nm was found to be due to the surface plasmon resonance of the gold nanoparticles incorporated in the fiber core.

High-Sensitivity Temperature Sensor Based on a Selectively-Polymer-Filled Two-Core Photonic Crystal Fiber In-Line Interferometer

A highly sensitive temperature sensor based on an all-fiber Mach-Zehnder interferometer using a selectively polymer-filled two-core photonic crystal fiber is experimentally demonstrated. The sensor fiber was made by the manual gluing and subsequent infiltration of polymer; the cladding air holes surrounding one core were selectively filled with a polymer material with a high thermo-optic (TO) coefficient while leaving those of the other core unfilled, and this led to the large TO mismatch between two cores. It was found from measurements that a very high temperature sensitivity of 1.595 nm/°C could be achieved, which was more than two orders of magnitude higher than that of the sensor fiber before the selective filling process.

All fiber polarimetric modulation using an electro-optic fiber with internal Pb-Sn electrodes

All fiber electro-optic modulation using a polarimetric cell based on an electro-optic fiber with internal Pb-Sn electrodes was demonstrated. For the polarimetric cell, the electro-optic fiber with two 149 cm long internal electrodes was fabricated by injection of a molten Pb-Sn alloy into the holes of the fiber. The characteristics of the modulation were explained by the electric field induced phase retardation due to the polarization dependent electro-optic Kerr effect. The difference in the effective second order nonlinearity between TM and TE polarization directions was obtained to be 0.0035 pm/V at the applied DC voltage of 6.5 kV.