Planar Photonic Crystal Nanocavities with Active Quantum Nanostructures

Extreme photon localization is applicable to constructing building blocks in photonic systems and quantum information systems. A finding fact that photon localization in small space modifies the radiation process was reported in 1944 by Purcell, and advances in fabrication technology enable such structures to be constructed at optical frequencies. Many demands of building compact photonic systems and quantum information systems have enhanced activities in this field. The photonic crystal cavity has potential in providing a cavity that supports only the fundamental mode ∼ (λ/2n)3 together with good confinement of light within a resonator. This thesis addresses experimental and theoretical aspects of building such photon localization blocks embedding active quantum nanostructures in a planar photonic crystal platform. Examples given in this thesis are (1) quantum dot photonic crystal nanolasers, (2) high-speed photonic crystal nanolasers, and (3) light-matter coupling in a single quantum dot photonic crystal cavity system. (1) A combination of quantum dots and photonic crystal nanocavities provides chirpless high-speed nanolasers. Room temperature low-threshold lasing action was demonstrated from a coupled cavity design (0.7 ∼ 1.2(λ/n)3) embedding InAs/GaAs self-assembled quantum dots. The nanolasers showed small (absorbed) pumping power threshold as sub-20 μW and high spontaneous coupling factors∼0.1. Single quantum dot lasing is likely to occur both by proper alignment of the single quantum dot relative to geometries of photonic crystals and by a narrow QD emission line in the high-Q localized mode. (2) Enhancement of radiation process in a small cavity was used to demonstrate high frequency relaxation oscillation up to 130 GHz. Built-in quantum well saturable absorbers enable us to probe the relaxation oscillation of such small lasers. (3) Onset of intermediate light-matter coupling was demonstrated in a single quantum dot photonic crystal cavity system. A tripling in Q/V (quality factor divided by mode volume) is found to enable photons to start a strong interaction with a single quantum dot.