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Kyong Hon Kim,Hak Kyu Lee,Min-Yong Jeon,El-Hang Lee,Cheol Soon Song,Ki Un Namkong 한국광학회 1996 한국광학회지 Vol.7 No.4
We report on comparative results obtained from harmonically mode-locked laser operations of ring-type and figure-of-eight(F8) type erbium-doped fiber lasers by using a directional-coupler type electro-optic modulator as an active mode-locker. The mode-locked and transform-limited pulses of 10.6 ㎰ width were obtained at harmonics of the fundamental cavity frequency with the F8 type laser while mode-locked laser pulses greater than 15 ㎰ were achieved with the ring type laser.
White-Light Interferometer Based on a High-Precision Chromatic Dispersion Measurement Method
Kyong Hon Kim,김승환,이성훈,이석목,이민희,이일항 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.6
We report a high-precision chromatic dispersion measurement method for very short optical fibers by using interference spectra of a Mach-Zehnder interferometer with a white-light source or a broad-band light source. This method is a modified version of the spectral white-light interferometry reported by J.Y.Lee and D.Y.Kim and is very effective for measuring the dispersion of short single- mode fibers (SMFs) whose lengths are les than a few tens centimeters. Our new method utilizes phase changes of the interference spectrum of the interferometer with a ber-under-test (FUT) compared to that with no FUT to eliminate the background effect caused by the optical path itself of the interferometer. Our measured results show that the background effect becomes significantas the length of the FUT is shortened close to10 cm for both standard SMFs and dispersion-shifted fibers (DSFs). This measurement method can be used to investigate the dispersion parameters of very smal-sized waveguides or optical samples, such as nanophotonic devices and of any other optical materials of short lengths.
Kim, Kyong-Hon,Jeon, Min-Yong,Park, Seo-Yeon,Lee, Hak-Kyu,Lee, El-Hang Electronics and Telecommunications Research Instit 1996 ETRI Journal Vol.18 No.1
We have experimentally observed and theoretically analyzed the gain dependent optimum repetition rates of a hybrid-type active and passive mode locked laser pulses in an erbium-doped fiber laser of the figure-of-eight geometry by utilizing a nonlinear amplifier loop mirror (NALM) as a saturable absorber and a directional-coupler type electro-optic modulator as an active mode locker. Transform-limited mode-locked pulses of about 10 ps width were obtained at repetition rates which correspond to harmonics of the cavity fundamental frequency and depend on the optical amplifier gain in the NALM.
Kim, Kyong Hon,Lee, Seoung Hun,Deshmukh, Vijay Manohar Hindawi Limited 2012 Advances in Optical Technologies Vol.2012 No.-
<P>We review the temporal dynamics of the laser output spectrum and polarization state of 1.55 <I>μ</I>m wavelength single-mode (SM) vertical-cavity surface-emitting lasers (VCSELs) induced by external optical beam injection. Injection of an external continuous-wave laser beam to a gain-switched SM VCSEL near the resonance wavelength corresponding to its main polarization-mode output was critical for improvement of its laser pulse generation characteristics, such as pulse timing-jitter reduction, linewidth narrowing, pulse amplitude enhancement, and pulse width shortening. Pulse injection of pulse width shorter than the cavity photon lifetime into the SM VCSEL in the orthogonal polarization direction with respect to its main polarization mode caused temporal delay of the polarization recovery after polarization switching (PS), and its delay was found to be the minimum at an optimized bias current. Polarization-mode bistability was observed even in the laser output of an SM VCSEL of a standard circularly cylindrical shape and used for all-optical flip-flop operations with set and reset injection pulses of very low pulse energy of order of the 3.5<I>~</I>4.5 fJ.</P>
Analytical Determination of Multilayer Waveguide Modes
Sukmock Lee,Kyong Hon Kim 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.I
We present a new analytical method for determining guiding modes in multilayer planar waveguides based on a few simple equations. Compared to the existing numerical approaches, this method enables us to perform easy and accurate numerical calculations of the effective indices, the field distributions, and the mode numbers of the guiding mode for a general N-layer waveguide.
Kim, Ho-Young,Kim, Kyong-Hon,Lee, El-Hang Optical Society of Korea 1998 Current Optics and Photonics Vol.2 No.2
We have theoretically analyzed and experimentally observed the effects of wavelength dependent birefringence inside a laser cavity on the output characteristics of fiber lasers with a figure eight geometry. The spectral and polarization characteristics of fiber lasers are found to be very susceptible to the resultant birefringence composed of the intrinsically existing wavelength dependent birefringence and the externally induced birefringences inside the fiber. For the variation of twist-induced birefringence inside the nonlinear amplifying loop mirror, the laser output power and center wave-length of continuous wave lasers change periodically, but the polarization characteristics remains nearly unchanged. The changes of the birefringence inside the linear loop has little effect on the spectral characteristics but changes the polarization properties such as the polarization direction.
Injection Laser Wavelength-Dependent Timing Jitter Reduction of Gain-Switched Single-Mode VCSELs
Seoung Hun Lee,Kyong Hon Kim,Deshmukh, V M,Dong Wook Kim,Min-Hee Lee IEEE 2010 IEEE journal of quantum electronics Vol.46 No.9
<P>We report the effect of an external injection laser wavelength on reducing the timing jitter of optical pulses generated from gain-switched single-mode 1.5-μm vertical cavity surface emitting lasers (VCSELs). Simultaneous timing jitter reduction, pulse width shortening, and spectral linewidth narrowing without any peak power penalty were observed when the injection laser wavelength was tuned near the spectral peak of the free-running VCSELs spectrum operating in a continuous wave mode. The timing jitter was reduced up to 40% of that without any injection.</P>
Low-Noise Single-Photon Detector for the 1.5-μm Wavelength Region
Seoung Hun LEE,Kyong Hon KIM,Chul-Woo PARK,Joon Tae AHN,Jun-Bum PARK,Kyu Hyun JEONG,Min Hee LEE,Sang Hyun CHOI,Sung MOON 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.1I
This paper describes an experimental demonstration and characterization of a InGaAs avalanchephotodiode (APD)-based low-noise single-photon detector developed for quantum cryptography at a wavelength of 1.5 μm. At the operation temperature of .50 C with a gated Geiger mode, we obtained a quantum efficiency of 21 % with a dark count probability per gate of 2.6 × 10.5 for a gate frequency of 10 kHz. The measured noise equivalent power (NEP) was 8.6 × 10.17 W/Hz1/2, which was the lowest value achieved so far at a thermoelectrically cooled temperature, which is an important factor for low quantum-bit error rates (QBER) in a quantum key distribution (QKD). The afterpulsing probability measured by varying the gate duration and separation indicated that the gate separation should be greater than 40 μs for 2.4-ns gate pulses to avoid the afterpulse effect. The developed single-photon detector turns out to be suitable for a 73-km fiber-optic quantum-key distribution in realistic conditions.덴f