Nakaoka Toshihiro

We observed excitonic and biexcitonic Rabi oscillation by using single photoexcited telecommunication-band quantum dot via photocurrent measurements. The biexcitonic population oscillates sinusoidally with the square of the pulse area while the excitonic population oscillates with the pulse area. The pulse area dependence clearly shows that the biexcitonic Rabi oscillation is caused by two-photon absorption. These results demonstrate that the telecom-band excitonic and biexcitonic system is promising for exciton based-quantum information devices compatible with optical fiber networks.

We fabricated InAs quantum-dot (QD) microdisk lasers (MDLs) with air-claddings. The room temperature (RT) lasing by femtosecond pulsed photopumping was achieved due to the sufficient gain in QD layers. The temperature dependence from 3 K to RT showed the degradation of the lasing characteristics, which was caused by the nonradiative recombination and internal absorption. By making the disk sidewall to be vertical, the cavity Q factor was increased, and the RT cw lasing was first achieved in the QD MDL with air claddings. The lasing wavelength was 1.28 μm, the irradiated threshold pump power was 410 μW, and the effective threshold power considering the absorption efficiency was estimated to be 81μW.