Muhan Choi

Control of directional emission in quasistadium microcavity laser diodes with two electrodes

We fabricated the AlGaAs∕GaAs three quantum well quasistadium laser diodes with two electrodes and succeeded in controlling directional laser emission by applying different currents to each electrode. We showed the ratio of laser emission with two different directions is proportional to the ratio of currents injected into two electrodes. These devices are applicable for beam switching and splitting.

Dependence of far-field characteristics on the number of lasing modes in stadium-shaped InGaAsP microlasers

We study spectral and far-field characteristics of lasing emission from stadium-shaped semiconductor (InGaAsP) microlasers. We demonstrate that the correspondence between a lasing far-field emission pattern and the result of a ray simulation becomes better as the number of lasing modes increases. This phenomenon is reproduced in the wave calculation of the cavity modes.

Linewidth properties of active-passive coupled monolithic InGaAs semiconductor ring lasers

We report linewidth properties of active-passive coupled monolithic InGaAs semiconductor ring lasers with various length of passive waveguide. It is experimentally confirmed that the linewidth of the lasers is proportional to the square of the ratio of the length of active part of the cavity over the total length of the cavity. The lasers are applicable for communication and sensing devices, which need the narrow linewidth.

Two Mode Interactions in Quasi-Stadium Laser Diodes

We found alternate oscillations in AlGaAs/GaAs single-quantum-well (SQW) quasi-stadium laser diodes (QSLD). The alternate oscillations in QSLD can be well explained by the interactions of two different cavity modes due to the geometrical symmetry of QSLD. Unlike the alternate oscillations in semiconductor ring lasers that need the waveguides to extract the light signals, the alternate oscillation signals in QSLD are obtained from the emitting lights spreading over the space. We also showed the alternate oscillation frequencies are inversely proportional to the amplitudes of two different cavity modes. This result is consistent with the theory of locking of two modes explaining the locking phenomenon between two nearly degenerated modes due to the nonlinear interactions in an active medium.

Optical Control of Ring Modes Using Tandem Quasi-Stadium Laser Diodes

In order to demonstrate controlling directional emissions corresponding to the ring trajectory modes by using external optical injection, we fabricate the AlGaAs/GaAs single-quantum-well tandem quasi-stadium laser diodes consist of the front slave and the rear master laser diodes. The geometry of the laser cavities have been defined by using a lithography system and a reactive-ion-etching technique. The optical injection is performed from the master laser to the slave laser. The ring mode control with the optical injection is evaluated by far-field patterns for the output from the curved end mirror.

Alternate oscillations with π phase difference in quasi-stadium laser diodes

We found alternate oscillations in AlGaAs/GaAs single-quantum-well (SQW) quasi-stadium laser diodes (QSLD). The alternate oscillations in QSLD can be well explained by the interactions of two different cavity modes due to the geometrical symmetry of QSLD. We also showed the alternate oscillation frequencies are inversely proportional to the amplitudes of two different cavity modes.

Control of Directional Emission in Two-dimensional Quasi-Stadium Micro-Cavity Laser Diodes with Two-Electrodes

We fabricated the AlGaAs/GaAs 3QW quasi-stadium laser diodes with two-electrodes and succeeded in controlling directional laser emission by applying different currents to each electrode. We showed the ratio of laser emission with two different directions is proportional to the ratio of currents injected into two electrodes. These devices are applicable for beam switching and splitting