SeungHun Lee

Large-Signal Analysis of a Transistor Laser

Small- and large-signal analyses of transistor lasers (TLs) are demonstrated for 0.98-μm wavelength GaInAs/GaAs and 1.3-μm AlGaInAs/InP systems. The modulation bandwidth of the TL was larger than that of a laser diode due to the lower damping effect in the former. Comparisons between TLs with different numbers of quantum wells indicated that a large signal response and high modulation bandwidth could be realized simultaneously. However, in the case of large-signal analysis, the calculated eye diagrams were degraded by a resonance oscillation peak. By changing structural parameters such as the facet reflectivity and by controlling the damping effect, the resonance frequency peak was suppressed and clear eye diagrams of >;40 Gb/s were obtained.

Low-Threshold and High-Efficiency Operation of Distributed Reflector Laser With Wirelike Active Regions

A high differential quantum efficiency of about 50% from the front facet and low threshold current operation have been achieved. By modifying the doping profile in 1.55-mum distributed reflector lasers, waveguide loss was reduced from 6-7 to 4 cm-1 . Injection currents of 4.2 and 3.6 mA were obtained to achieve a 1-mW output power for lasers with uniform and phase-shifted grating structures, respectively.

Lateral Junction Waveguide-Type Photodiode Grown on Semi-Insulating InP Substrate

A lateral junction waveguide-type GaInAsP/InP photodetector was fabricated on a semi-insulating InP substrate by two-step organometallic vapor-phase epitaxy (OMVPE) regrowth. Responsivities of 0.9 A/W at 1500 nm and 0.27 A/W at 1550 nm were obtained. A 3-dB bandwidth of 6 GHz and 6-Gbps error-free operation under non-bias conditions were achieved with a stripe width of 1.4 µm and a device length of 220 µm.

Bandwidth enhancement of injection-locked distributed reflector lasers with wirelike active regions

The modulation bandwidth enhancement of distributed reflector (DR) lasers with wirelike active regions utilizing optical injection locking is demonstrated both theoretically and experimentally. By the rate equation analysis, it is shown that DR lasers with wirelike active regions realize a low optical injection power and a large bandwidth enhancement under small operation currents. Experimentally, the small-signal bandwidth is increased to >15 GHz at a bias current of 5 mA, which is 4 times smaller than that for conventional edge-emitting lasers. A large signal modulation at 10 Gbps is also performed at the same bias current of 5 mA and voltage swing of 0.4 V(pp), and error-free detection was confirmed under the low-power conditions.

Low-Threshold-Current Operation of High-Mesa Stripe Distributed Reflector Laser Emitting at 1540 nm

A sub-mA-threshold-current operation (as low as 0.8 mA) of a high-mesa stripe geometry distributed reflector (DR) laser with a wirelike active distributed feedback (DFB) section and passive distributed Bragg reflector (DBR) section was realized under room-temperature continuous-wave conditions utilizing a narrow laser stripe (2.1 µm) and a large index coupling coefficient of 570 cm-1.

GaInAsP/InP Distributed Reflector Lasers and Integration of Front Power Monitor by Using Lateral Quantum Confinement Effect

By using lateral quantum confinement effect, a sub mA threshold current operation of a long wavelength GaInAsP/InP distributed-reflector (DR) laser, consisting of wide and narrow wirelike active regions, was demonstrated for the first time under room-temperature continuous-wave (RT-CW) condition. Eye-patterns have been studied for back-to-back as well as 10-km optical fiber transmission line. Even though devices had broad contact electrodes, clear eye opening was observed up to 2 Gbps pseudo random bit sequence (PRBS; 231 - 1) data. A monolithic integration of a power monitor (PM) at the front side of the DR laser was also demonstrated for the first time. Almost linear photocurrent characteristic with very high isolation resistance of 60 MΩ was obtained by separating the PM section by a narrow (500 nm) and deep groove filled with benzocyclobutene (BCB).

Bit-error-rate measurement of GaInAsP/InP distributed reflector laser with wirelike active regions

Dynamic characteristics of 1.55 mum wavelength distributed reflector (DR) lasers with wirelike active regions were examined for the first time. BER measurements over a wide temperature range were performed. 10 km error-free transmission at 10 Gbit/s was confirmed by using a dispersion-shifted fiber.

Carrier-Transport-Limited Modulation Bandwidth in Distributed Reflector Lasers With Wirelike Active Regions

High-speed direct modulation capability was investigated in 1.55-μm GaInAsP/InP distributed reflector (DR) lasers with wirelike active regions in terms of carrier transport from GaInAsP optical confinement layers (OCLs) to the active regions. Theoretical analysis revealed strong dependence of the modulation bandwidth on the thickness of the OCLs and width of the wirelike active regions. To confirm this prediction, two DR lasers with OCLs of different thicknesses (120 and 40 nm) were fabricated and their 3-dB bandwidths (f3 dB) under small-signal modulation were compared. The device with the narrower OCL exhibited f3 dB exceeding 15 GHz and clear eye opening under 25 Gb/s modulation, whereas that with the thicker OCL had f3 dB of only 2 GHz. These results were in good agreement with the theoretical predictions.

Low-Power-Consumption High-Eye-Margin 10-Gb/s Operation by GaInAsP/InP Distributed Reflector Lasers With Wirelike Active Regions

Low-driving-current and high-eye-margin 10-Gb/s operation was demonstrated by a GaInAsP/InP distributed reflector (DR) laser with wirelike active regions. The reduction of modulation bias currents was realized by the high modulation efficiency of five-stack quantum wirelike active regions as well as thin optical confinement layers for a shorter carrier transit time. A mask test of 10 GbE with 20% margin was passed with a low bias current of 10 mA, and the maximum 3-dB bandwidth was over 15 GHz.

Very High Electric Isolation Resistance between Distributed Reflector Laser and Front Power Monitor through Deeply Etched Narrow Groove

The monolithic integration of a distributed reflector (DR) laser with a front power monitor was realized for the first time, where quantum wirelike active regions were used to obtain the partial absorption necessary for monitoring the photodetector. The electrical isolation between the laser and power monitor sections was realized by deep (3.8 µm) and narrow (500 nm) groove etching, and a moderately high optical transmittivity of about 95% and a very high isolation resistance of 60 MΩ were achieved.