Kyung-Hyun Park

Reliability considerations of laser diodes for optical communication system application

The purpose of this paper is to propose a reliability parameter of laser diodes for optical communication system applications. Based on the alarm function in optical communication systems, we have developed a reliability parameter; /spl rho//sub a/(=/spl eta//sub a///spl eta//sub 0/.Ith/sub a//Ith/sub 0/)/spl ges/1.5, which is more applicable to estimate reliability projections and to design LD modules for optical communication systems.

Nonlinear susceptibility of a polycrystalline YBa2Cu3O7−y superconductor near Tc

Abstract We have investigated nonlinear response to applied magnetic field in a YBa2Cu3O7−y polycrystalline superconductor near Tc, by using an a.c. mutual inductance bridge method. The third nonlinear susceptibility χ2 shows a sharp peak with a negative sign and increases logarithmically near the peak temperature Tg. And the weak magnetic field dependence of Tg is found to fit the curve of the quasi-de Almeida-Thouless line. These experimental results are discussed in connection with the superconductive glass state in the high Tc superconducting ceramics.

Phase-coherent conduction in mesoscopic normal-metal/superconductor hybrid junctions

In this paper we report about the transport properties of mesoscopic normal-metal/superconductor (NS) hybrid systems with two different junction layouts. One is a junction fabricated by overlaying S on N wire and the other with S sandwiched between two N wires, forming an NSN structure. At zero bias all the junctions exhibited a sharp decrease of dV=dI; which is believed to arise from the interference between the disorder-scattered and the Andreev-reflected quasiparticles. A small magnetic field corresponding to one flux quantum through the normal metal region, applied in parallel with the NS junction, easily suppressed the anomalous zero-bias conductance enhancement for the sandwich-junction sample. This high sensitivity to a small magnetic field observed in our systems of mesoscopic NS junctions in a diffusive-transport regime directly confirms the electron‐holeinterference origin of the zero-bias anomaly. q 2000 Published by Elsevier Science Ltd. All rights reserved.

Electronic transport properties of coupled single-electron transistors

The electronic transport properties of parallel coupled single-electron transistors (SETs) at strong coupling under asymmetrical voltage bias are investigated theoretically. The binding of electrons and holes on the two islands of the coupled SETs is found to be the key element that governs the transport characteristics. The discrete nature of bound electrons and holes leads to the satellite Coulomb blockade oscillations, the current jumps, and the Coulomb staircases, all of which are distinct transport features of the coupled SETs.

Optical Clock Recovery from RZ and NRZ data using a Multi-Section Laser Diode with a DFB Reflector

We have extracted an optical clock signal from a return-to-zero(RZ) pseudorandom bit sequence(PRBS) and non-return-to-zero(NRZ) PRBS data in a pulsation multi-section laser diode with DFB reflector. The ms timing jitter achieved less than 1 ps for the input 11.727 Gbit/s RZ PRBS and NRZ PRBS data. The PRE data wasconverted from the NRZ data using an NRZ to pseudo-return to zero(PRZ) converter module. The optical clock was extracted from the PRZ data which contains the clock components. Although the input PRZ data gives a timing jitter of 2 ps, the extracted clock has timing jitter of 1 ps.

A Multi-Section Complex-Coupled DFB Laser with a Very Wide Range of Self-Pulsation Frequency and High Modulation Index

We analyze the self-pulsation(SP) characteristics due to mode beating of two modes emitted in a multi-section complex-coupled (CC) DFB laser composed of two DFB sections and a phase control section between them. SP frequency due to mode beating of the two modes is determined by the difference of grating periods in the two CC DFB regions. As the difference of grating periods in the two CC DFB regions increases, the SP frequency increases from very low frequency to the THz region. In the case of a mode which is not located in the stop band of the other DFB region, the mode propagates into the other DFB region without a high reflection, so that output powers emitted in a multi-section CC DFB laser have high modulation indexes due to the large interaction between the two modes.

Analysis of Self-Pulsation Characteristics in Multi-Section Complex-Coupled DFB Lasers With Amplifying Optical Feedback

We investigate the pulsation characteristics in a multi-section DFB laser which is composed of one DFB section, phase tuning section, and gain section. Multi-section DFB lasers with anti-phase (AP) complex-coupled (CC) DFB structure show wide current ranges of gain and phase tuning sections fer stable pulsations compared to those with in-phase CC DFB structure or index-coupled DFB structure. For multi-section DFB lasers with AP CC DFB structure, the current range of a gain section for stable pulsations increases and the tuning range of the pulsation frequency increases as a coupling strength or a gain coupling coefficient increases Also, the tuning range using the phase variation in a phase tuning section increases. For a fixed coupling strength, the current ranges of gain and phase tuning sections for stable pulsations increase and the tuning range of the pulsation frequency increases as the length of a DFB section increases.