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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.
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, Yudeuk,Kim, Dong Wook,Lee, Moon-Hyeok,Lee, Min Hee,Yoo, Dong Eun,Kim, Ki Nam,Jeon, Sang Chul,Kim, Kyong Hon IOP 2016 Journal of optics Vol.18 No.9
<P>An integrated polarization rotator is demonstrated experimentally by forming a strip waveguide with an asymmetric trench on a silicon-on-insulator wafer. The trench is located asymmetrically in the strip waveguide. It induces the evolution of an orthogonal polarization mode upon a linearly polarized beam input, and thus causes polarization rotation. The device is fabricated using a conventional complementary metal oxide semiconductor process with a single dry etching step. The fabricated device shows a maximum transverse electric (TE)-to-transverse magnetic (TM) polarization conversion efficiency of 21.3 dB and an insertion loss of −0.95 dB at a 1550 nm wavelength with a device length of 67 <I>μ</I>m. The device exhibits a polarization conversion efficiency and insertion loss of 21.1 dB and −2.12 dB, respectively, for the TM-to-TE polarization conversion. The optimum parameters for the waveguide size and trench size are investigated by performing numerical simulations, and by demonstrating experimental fabrication and measurement.</P>
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.
Kim, Yoohan,Lee, Moon Hyeok,Kim, Yudeuk,Kim, Kyong Hon The Optical Society 2018 Optics letters Vol.43 No.14
<P>We demonstrate an integrated polarization beam splitter (PBS) of a simple and compact device geometry with high polarization extinction ratios (PERs). A silicon PBS based on a three-waveguide directional coupler is numerically simulated for optimum device parameters, and fabricated experimentally. The measured PER values of the fabricated PBSs are 40.74 dB and 39.01 dB for transverse electric and transverse magnetic modes, respectively, and their corresponding insertion losses are 0.35 dB on average for a coupler length of about 29.4 mu m. (c) 2018 Optical Society of America</P>
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>
Dong Wook Kim,Seung Hwan Kim,Seoung Hun Lee,Kyong Hon Kim,Jong-Moo Lee,El-Hang Lee IEEE 2012 Journal of lightwave technology Vol.30 No.1
<P>We report on a simple and direct method of measuring localized chromatic dispersion (CD) profiles of structured nanowaveguide devices using white-light interferometry. Phase change in the interference fringe of a white-light interferometer (WLI) caused by introducing a sample-under-test into one of the interferometer arms was used to determine a spectral profile of its accurate CD coefficients. This method was tested by measuring the spectral CD profiles of a localized silicon nanowaveguide and of a nonmembrane-type photonic crystal waveguide (PhCW) excluding their optical coupling sections. The measured local CD values of a 500-nm-wide single-line-defect (W1) PhCW with a lattice period of 460 nm and the hole radius of 165 nm formed on 220-nm-thick silicon layer of a silicon-on-insulator (SOI) wafer varied from 0.38 to 0.22 ps/(nm ·cm) for a wavelength range from 1530 to 1570 nm. This method will be very useful in determining the accurate CD profiles of nanophotonic waveguide devices.</P>
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.