In-Kag Hwang - Academia.edu (original) (raw)
Papers by In-Kag Hwang
Journal of the Korean Physical Society, 2014
ABSTRACT Vertical-cavity surface-emitting lasers (VCSELs) with oxide layers introduced for modal ... more ABSTRACT Vertical-cavity surface-emitting lasers (VCSELs) with oxide layers introduced for modal property control are relatively weak against reliability-related damage. We propose and demonstrate a method of detecting potential damage without running a long-term burn-in test. For two damage mechanisms, chemical etching and electrostatic discharge, we found that an exceptional increase in the ideality factor (IdV/dI) is closely related to potential damage of the device that will eventually lead to failure in the following burn-in test. The extent and the origin of the damage could also be identified by using the heights and locations of the bumps in the ideality factor curves.
2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006
ABSTRACT All-optical switching is demonstrated in a photonic crystal resonator evanescently coupl... more ABSTRACT All-optical switching is demonstrated in a photonic crystal resonator evanescently coupled with a micro-fiber. Carrier-induced fast blueshift of resonant wavelength by 1.5 nm is observed at 980 nm pump energy of ~300 fJ.
OFC/IOOC . Technical Digest. Optical Fiber Communication Conference, 1999, and the International Conference on Integrated Optics and Optical Fiber Communication, 1999
ABSTRACT We describe an all-fiber add-drop multiplexer constructed with readily available compone... more ABSTRACT We describe an all-fiber add-drop multiplexer constructed with readily available components: a tilted fiber Bragg grating in a two-mode fiber and mode-selective directional couplers. The simple configuration allows the implementation of standard fiber Bragg grating technologies for improved performance
Proceedings of SPIE - The International Society for Optical Engineering
The efficiency of light emitting diode (LED) is limited because large amount of generated light i... more The efficiency of light emitting diode (LED) is limited because large amount of generated light is confined inside of it by total internal reflection. A photonic crystal (PC) layer embedded in LED structure substantially modifies the guiding properties inside the chip and prevents the lateral propagation of light, so that it largely increases the output power of an LED. In this paper, we present both numerical and experiment studies on the enhancement of light extraction of GaN-based light-emitting diodes (LEDs) with hexagonal PC layer. By finite difference time domain (FDTD) simulation, the PC parameters were varied in order to evaluate the enhancement. Best extraction efficiency was obtained with the lattice constant of 400 - 600 nm, the PC thickness of 150 - 200 nm and the ratio of hole radius to lattice constant of 0.3 - 0.4 for the 465 nm LED based on GaN. Furthermore, hexagonal PC GaN-based LED was fabricated using anodic aluminum oxide (AAO) method. The PC layer is located be...
A waveguide grating, by which ultrafast optical amplitude modulation can be realized, is designed... more A waveguide grating, by which ultrafast optical amplitude modulation can be realized, is designed based on periodically poled lithium niobate (PPLN). Structural parameters of the grating that enable the fast operation are also calculated.
OFC/NFOEC 2008 - 2008 Conference on Optical Fiber Communication/National Fiber Optic Engineers Conference, 2008
Recent progresses on wavelength-scale photonic crystal lasers are reported. Electrically-driven n... more Recent progresses on wavelength-scale photonic crystal lasers are reported. Electrically-driven nondegenerate photonic crystal lasers and reconfigurable microfiber-coupled photonic crystal waveguide lasers are discussed in detail. Schemes enabling optical coupling in excess of 80% are also proposed.
2011 International Quantum Electronics Conference (IQEC) and Conference on Lasers and Electro-Optics (CLEO) Pacific Rim incorporating the Australasian Conference on Optics, Lasers and Spectroscopy and the Australian Conference on Optical Fibre Technology, 2011
We report the full-3D FDTD simulation and experimental implementation of 780 nm VCSELs with six a... more We report the full-3D FDTD simulation and experimental implementation of 780 nm VCSELs with six air holes on top surfaces. The optical power and side mode suppression ratio depending on the oxide aperture size in experimental data could be successfully explained by modal loss and field dynamics of simulation data. High-power single-mode operation of 1.7 mW with side mode suppression
CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference, 2009
Manipulation of bio-cells and molecules is an important technique in various medical, biochemical... more Manipulation of bio-cells and molecules is an important technique in various medical, biochemical analysis systems. Here we demonstrate the manipulation of blood cells in micro-capillary tube using flexural acoustic wave propagating along the tube. The capillary tube is used as a mechanical guide for both the blood and the acoustic wave, where the acoustic interaction occurs very efficiently over a
2007 9th International Conference on Transparent Optical Networks, 2007
ABSTRACT Two possible structures that enable highly-efficient photon out-coupling from wavelength... more ABSTRACT Two possible structures that enable highly-efficient photon out-coupling from wavelength-scale resonators are to be discussed. Specifically the vertical beaming scheme and the all-fiber coupling scheme are discussed in detail, showing the possibility of high optical coupling efficiency in excess of 80%.
Optics Express, 2004
We propose a novel design of highly birefringent optical fiber composed of a central elliptical a... more We propose a novel design of highly birefringent optical fiber composed of a central elliptical air hole, a circumferential elliptical ring core, and a circular cladding. The proposed waveguide structure is predicted to produce a linear birefringence higher by an order of magnitude than the solid elliptical core fiber. The large index contrast between the central air and germanosilica elliptical ring core is mainly attributed to the high birefringence and its characteristics are theoretically analyzed in terms of its waveguide parameters.
2007 International Nano-Optoelectronics Workshop, 2007
We report the low-power optical bistability under the continuous wave pumping conditions in photo... more We report the low-power optical bistability under the continuous wave pumping conditions in photonic crystal linear resonators containing the InGaAsP quantum well active medium. The threshold bistable power is measured to be 35 muW at the normalized detuning of -1.724, by employing fiber coupling techniques.
2007 Conference on Lasers and Electro-Optics - Pacific Rim, 2007
We propose and demonstrate reconfigurable microfiber-coupled photonic crystal (PhC) lasers. In th... more We propose and demonstrate reconfigurable microfiber-coupled photonic crystal (PhC) lasers. In this generic configuration, the position of a PhC resonator can be defined (and redefined) repeatedly by simply relocating a curved microfiber along the linear PhC waveguide. In the proximity of the PhC waveguide in contact with the microfiber, the cutoff frequency (effective index) of the PhC waveguide becomes smaller (larger) than that of a bare PhC waveguide. Accordingly, when a curved microfiber is in contact with the PhC waveguide, a linear PhC resonator having Gaussianshaped potential well is formed. Experimentally we confirm the formation of the reconfigurable resonator by observing laser operation slightly below three available band edges.
Optics Letters, 2008
This is a report on an effective simulation method for the bending loss analyses of photonic crys... more This is a report on an effective simulation method for the bending loss analyses of photonic crystal fibers. This method is based on the two-dimensional finite-difference time-domain algorithm and a conformal transformation of the refractive index profile. We observed the temporal dynamics of light waves in a bent fiber in a simulation and obtained the bending loss as a function of bend radius and optical wavelength for the commercial photonic crystal fibers. The accuracy of this method was verified by good agreement between the simulation and experimental data.
2007 Conference on Lasers and Electro-Optics - Pacific Rim, 2007
An efficient three-dimensional finite-difference time domain (3D-FDTD) algorithm with anisotropic... more An efficient three-dimensional finite-difference time domain (3D-FDTD) algorithm with anisotropic resolutions and periodic conditions is developed and optimized for analyses of photonic crystal fibers. The simulation program also allows the calculation based on SEM image of PCF to evaluate the effect of imperfection of the fiber structure.
Optics Express, 2011
Modal properties of vertical cavity surface-emitting lasers (VCSELs) with holey structures are st... more Modal properties of vertical cavity surface-emitting lasers (VCSELs) with holey structures are studied using a finite difference time domain (FDTD) method. We investigate loss behavior with respect to the variation of structural parameters, and explain the loss mechanism of VCSELs. We also propose an effective method to estimate the modal loss based on mode profiles obtained using FDTD simulation. Our results could provide an important guideline for optimization of the microstructures of high-power single-mode VCSELs.
Optics Letters, 1996
We demonstrate an all-f iber acousto-optic tunable f ilter based on two-spatial-mode coupling, wi... more We demonstrate an all-f iber acousto-optic tunable f ilter based on two-spatial-mode coupling, with improved ruggedness and eff iciency, by using a new acoustic-transducer design. We use a rigorous modeling of the f lexural acoustic wave to analyze the mode coupling with better accuracy. Using the acousto-optic tunable f ilter, we demonstrate a novel all-f iber tunable laser with a tuning range of more than 20 nm and a linewidth of 0.2 nm.
Optics Letters, 1996
Experimental and theoretical investigation of a nonlinear response of a two-mode fiber interferom... more Experimental and theoretical investigation of a nonlinear response of a two-mode fiber interferometer to axial strain is described. It is discovered that the nonlinearity dramatically increases as the wavelength approaches the cutoff wavelength of the second-order mode (LP 11 ).
Optics Letters, 1999
We demonstrate a new type of high-performance long-period f iber grating based on arc-induced per... more We demonstrate a new type of high-performance long-period f iber grating based on arc-induced periodic microbends. The fabrication method is simple and does not require special f ibers. Flexibility in controlling the f ilter parameters makes it possible to produce arbitrary f ilter prof iles by use of a simple apodization technique, which is diff icult to do with conventional long-period gratings.
Journal of the Korean Physical Society, 2014
ABSTRACT Vertical-cavity surface-emitting lasers (VCSELs) with oxide layers introduced for modal ... more ABSTRACT Vertical-cavity surface-emitting lasers (VCSELs) with oxide layers introduced for modal property control are relatively weak against reliability-related damage. We propose and demonstrate a method of detecting potential damage without running a long-term burn-in test. For two damage mechanisms, chemical etching and electrostatic discharge, we found that an exceptional increase in the ideality factor (IdV/dI) is closely related to potential damage of the device that will eventually lead to failure in the following burn-in test. The extent and the origin of the damage could also be identified by using the heights and locations of the bumps in the ideality factor curves.
2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006
ABSTRACT All-optical switching is demonstrated in a photonic crystal resonator evanescently coupl... more ABSTRACT All-optical switching is demonstrated in a photonic crystal resonator evanescently coupled with a micro-fiber. Carrier-induced fast blueshift of resonant wavelength by 1.5 nm is observed at 980 nm pump energy of ~300 fJ.
OFC/IOOC . Technical Digest. Optical Fiber Communication Conference, 1999, and the International Conference on Integrated Optics and Optical Fiber Communication, 1999
ABSTRACT We describe an all-fiber add-drop multiplexer constructed with readily available compone... more ABSTRACT We describe an all-fiber add-drop multiplexer constructed with readily available components: a tilted fiber Bragg grating in a two-mode fiber and mode-selective directional couplers. The simple configuration allows the implementation of standard fiber Bragg grating technologies for improved performance
Proceedings of SPIE - The International Society for Optical Engineering
The efficiency of light emitting diode (LED) is limited because large amount of generated light i... more The efficiency of light emitting diode (LED) is limited because large amount of generated light is confined inside of it by total internal reflection. A photonic crystal (PC) layer embedded in LED structure substantially modifies the guiding properties inside the chip and prevents the lateral propagation of light, so that it largely increases the output power of an LED. In this paper, we present both numerical and experiment studies on the enhancement of light extraction of GaN-based light-emitting diodes (LEDs) with hexagonal PC layer. By finite difference time domain (FDTD) simulation, the PC parameters were varied in order to evaluate the enhancement. Best extraction efficiency was obtained with the lattice constant of 400 - 600 nm, the PC thickness of 150 - 200 nm and the ratio of hole radius to lattice constant of 0.3 - 0.4 for the 465 nm LED based on GaN. Furthermore, hexagonal PC GaN-based LED was fabricated using anodic aluminum oxide (AAO) method. The PC layer is located be...
A waveguide grating, by which ultrafast optical amplitude modulation can be realized, is designed... more A waveguide grating, by which ultrafast optical amplitude modulation can be realized, is designed based on periodically poled lithium niobate (PPLN). Structural parameters of the grating that enable the fast operation are also calculated.
OFC/NFOEC 2008 - 2008 Conference on Optical Fiber Communication/National Fiber Optic Engineers Conference, 2008
Recent progresses on wavelength-scale photonic crystal lasers are reported. Electrically-driven n... more Recent progresses on wavelength-scale photonic crystal lasers are reported. Electrically-driven nondegenerate photonic crystal lasers and reconfigurable microfiber-coupled photonic crystal waveguide lasers are discussed in detail. Schemes enabling optical coupling in excess of 80% are also proposed.
2011 International Quantum Electronics Conference (IQEC) and Conference on Lasers and Electro-Optics (CLEO) Pacific Rim incorporating the Australasian Conference on Optics, Lasers and Spectroscopy and the Australian Conference on Optical Fibre Technology, 2011
We report the full-3D FDTD simulation and experimental implementation of 780 nm VCSELs with six a... more We report the full-3D FDTD simulation and experimental implementation of 780 nm VCSELs with six air holes on top surfaces. The optical power and side mode suppression ratio depending on the oxide aperture size in experimental data could be successfully explained by modal loss and field dynamics of simulation data. High-power single-mode operation of 1.7 mW with side mode suppression
CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference, 2009
Manipulation of bio-cells and molecules is an important technique in various medical, biochemical... more Manipulation of bio-cells and molecules is an important technique in various medical, biochemical analysis systems. Here we demonstrate the manipulation of blood cells in micro-capillary tube using flexural acoustic wave propagating along the tube. The capillary tube is used as a mechanical guide for both the blood and the acoustic wave, where the acoustic interaction occurs very efficiently over a
2007 9th International Conference on Transparent Optical Networks, 2007
ABSTRACT Two possible structures that enable highly-efficient photon out-coupling from wavelength... more ABSTRACT Two possible structures that enable highly-efficient photon out-coupling from wavelength-scale resonators are to be discussed. Specifically the vertical beaming scheme and the all-fiber coupling scheme are discussed in detail, showing the possibility of high optical coupling efficiency in excess of 80%.
Optics Express, 2004
We propose a novel design of highly birefringent optical fiber composed of a central elliptical a... more We propose a novel design of highly birefringent optical fiber composed of a central elliptical air hole, a circumferential elliptical ring core, and a circular cladding. The proposed waveguide structure is predicted to produce a linear birefringence higher by an order of magnitude than the solid elliptical core fiber. The large index contrast between the central air and germanosilica elliptical ring core is mainly attributed to the high birefringence and its characteristics are theoretically analyzed in terms of its waveguide parameters.
2007 International Nano-Optoelectronics Workshop, 2007
We report the low-power optical bistability under the continuous wave pumping conditions in photo... more We report the low-power optical bistability under the continuous wave pumping conditions in photonic crystal linear resonators containing the InGaAsP quantum well active medium. The threshold bistable power is measured to be 35 muW at the normalized detuning of -1.724, by employing fiber coupling techniques.
2007 Conference on Lasers and Electro-Optics - Pacific Rim, 2007
We propose and demonstrate reconfigurable microfiber-coupled photonic crystal (PhC) lasers. In th... more We propose and demonstrate reconfigurable microfiber-coupled photonic crystal (PhC) lasers. In this generic configuration, the position of a PhC resonator can be defined (and redefined) repeatedly by simply relocating a curved microfiber along the linear PhC waveguide. In the proximity of the PhC waveguide in contact with the microfiber, the cutoff frequency (effective index) of the PhC waveguide becomes smaller (larger) than that of a bare PhC waveguide. Accordingly, when a curved microfiber is in contact with the PhC waveguide, a linear PhC resonator having Gaussianshaped potential well is formed. Experimentally we confirm the formation of the reconfigurable resonator by observing laser operation slightly below three available band edges.
Optics Letters, 2008
This is a report on an effective simulation method for the bending loss analyses of photonic crys... more This is a report on an effective simulation method for the bending loss analyses of photonic crystal fibers. This method is based on the two-dimensional finite-difference time-domain algorithm and a conformal transformation of the refractive index profile. We observed the temporal dynamics of light waves in a bent fiber in a simulation and obtained the bending loss as a function of bend radius and optical wavelength for the commercial photonic crystal fibers. The accuracy of this method was verified by good agreement between the simulation and experimental data.
2007 Conference on Lasers and Electro-Optics - Pacific Rim, 2007
An efficient three-dimensional finite-difference time domain (3D-FDTD) algorithm with anisotropic... more An efficient three-dimensional finite-difference time domain (3D-FDTD) algorithm with anisotropic resolutions and periodic conditions is developed and optimized for analyses of photonic crystal fibers. The simulation program also allows the calculation based on SEM image of PCF to evaluate the effect of imperfection of the fiber structure.
Optics Express, 2011
Modal properties of vertical cavity surface-emitting lasers (VCSELs) with holey structures are st... more Modal properties of vertical cavity surface-emitting lasers (VCSELs) with holey structures are studied using a finite difference time domain (FDTD) method. We investigate loss behavior with respect to the variation of structural parameters, and explain the loss mechanism of VCSELs. We also propose an effective method to estimate the modal loss based on mode profiles obtained using FDTD simulation. Our results could provide an important guideline for optimization of the microstructures of high-power single-mode VCSELs.
Optics Letters, 1996
We demonstrate an all-f iber acousto-optic tunable f ilter based on two-spatial-mode coupling, wi... more We demonstrate an all-f iber acousto-optic tunable f ilter based on two-spatial-mode coupling, with improved ruggedness and eff iciency, by using a new acoustic-transducer design. We use a rigorous modeling of the f lexural acoustic wave to analyze the mode coupling with better accuracy. Using the acousto-optic tunable f ilter, we demonstrate a novel all-f iber tunable laser with a tuning range of more than 20 nm and a linewidth of 0.2 nm.
Optics Letters, 1996
Experimental and theoretical investigation of a nonlinear response of a two-mode fiber interferom... more Experimental and theoretical investigation of a nonlinear response of a two-mode fiber interferometer to axial strain is described. It is discovered that the nonlinearity dramatically increases as the wavelength approaches the cutoff wavelength of the second-order mode (LP 11 ).
Optics Letters, 1999
We demonstrate a new type of high-performance long-period f iber grating based on arc-induced per... more We demonstrate a new type of high-performance long-period f iber grating based on arc-induced periodic microbends. The fabrication method is simple and does not require special f ibers. Flexibility in controlling the f ilter parameters makes it possible to produce arbitrary f ilter prof iles by use of a simple apodization technique, which is diff icult to do with conventional long-period gratings.