Hyung B. Kim

Enhanced wavelength tuning range in two-section complex-coupled DFB lasers by alternating gain and loss coupling

A novel tunable two-section complex-coupled distributed feedback (DFB) lasers were demonstrated which exhibited an enhanced wavelength tuning range beyond 7 nm by current injection only. By a simple master-and-slave type of injection current control, either in-phase gain-coupling or antiphase loss-coupling mechanism can be activated, in such a way that one of the two Bragg modes around DFB stopband will become the lasing mode, and its wavelength can be simply and independently tuned by corresponding injection current. More then 45 dB side-mode suppression ratio (SMSR) over entire tuning range were obtained. Good system performance for 375 km transmission with butt-coupled III-V Mach-Zehnder (MZ) modulator at 2.5 Gb/s over nondispersion-shifted fiber was also demonstrated.

Longitudinal carrier density profiling in semiconductor lasers via spectral analysis of side spontaneous emission

A combined experimental and theoretical approach to measuring the variation in carrier density along the length of a semiconductor laser is developed. It is shown that by following the rate of increase of the principal spectral peak, rather than monitoring the optical power at a fixed energy, measurements can be made less susceptible to the effects of heating in the sample. Experimental results showing the development of the longitudinal carrier density profile with injected current are presented and, when compared with the results of self‐consistent modeling, provide insights into the internal operating mechanisms of the laser.

20 Gbit/s directly modulated 1310 nm ridge laser

A 20 Gbit/s directly modulated laser is demonstrated at 1310 nm. MOCVD growth combined with a ridge waveguide design have the potential for a low cost short reach solution at bit rates greater than 10 Gbit/s.

10-Gbit/s 80-km fiber transmission using 1.3-/spl mu/m partly gain-coupled DFB lasers

Summary form only given. We have demonstrated l0-Gbit/s 80-km transmission with a receiver sensitivity better than -24.5 dBm at BER of 10/sup -9/ for the long PRBS 2/sup 23/-1 pattern by using our gain coupled (GC) DFB QW lasers, which have been shown to exhibit a high dynamic single-mode yield, large intrinsic modulation bandwidth, and excellent long term reliability.

Longitudinally resolved measurements of carrier concentration and gain in 980-nm InGaAs/GaAs high-power quantum well lasers

Measurements of longitudinal variation in critical laser parameters such as gain and carrier concentration are invaluable in understanding and diagnosing device performance and failure mechanisms. However, traditional front-facet measurements cannot reveal the variation of these parameters along the length of the laser. Other methods require physical modifications to the laser itself, such as the fabrication of a top window, and are thus invasive. We describe a new experimental technique based on analysis of side spontaneous emission. A tapered optical fiber translated along the side of the laser using a micropositioner collects spontaneous emission from the active region, allowing spatially-resolved gain and carrier concentration measurements to be made. Such measurements can be used to track the evolution of dark lines caused by defects where non-radiative recombination is dominant. We applied this method to a 980 nm high power laser with an In0.2Ga0.8As, 80 angstroms SQW and facets of 90%/10% reflectivity. It was predicted through a 1D rate equation model that the carrier concentration would increase near the high-reflectivity mirror, due to lower optical field intensities. Using the bimolecular recombination equation to determine the carrier density, this expectation was confirmed. The peak modal gain also increased with proximity to the high-reflectivity mirror, and modulations in the gain peak profile attributed to spatial hole burning were observed.