An efficient sharply bent waveguide with a microcavity constructed by an air-bridge type two-dimensional photonic crystal slab is analyzed. The method of solution is the three-dimensional finite difference time domain (FD-TD) method. The bent waveguide has a microcavity structure that connects to an input and an output waveguide ports. The radius and position of air-holes surrounding the microcavity are modified to adjust the resonant frequency to the single-mode regime of the waveguides. It is confirmed that input optical power is transmitted efficiently to the output waveguide due to resonant tunneling caused by the microcavity.

An efficient 12 optical power splitter constructed by a two-dimensional photonic crystal has been analyzed using the finite difference time domain (FD-TD) method. The power splitter has a microcavity which is coupled to an input and two output waveguides. We have confirmed that all optical power is transmitted into output waveguides due to resonant tunneling caused by the microcavity.

We present the theory and experiment of metal-cavity nanolasers and nanoLEDs flip-chip bonded to silicon under electrical injection at room temperature. We first review the recent progress on micro- and nanolasers. We then present the design rule and our theoretical model. We show the experimental results of our metal-cavity surface-emitting microlasers and compare with our theoretical results showing an excellent agreement. We found the important contributions of the nonradiative recombination currents including Auger recombination, surface recombination, and leakage currents. Finally, experimental demonstration of electrical injection nanoLEDs toward subwavelength nanoscale lasers is reported.

We discuss fabrication of InGaAs quantum dot structures using the self-assembling growth technique with the Stranski-Krastanow growth mode in MOCVD, including optical ploperties of the nano-structures. The formation process of the quantum dot islands was clarified by observing the samples grown under various conditions with an atomic force microscope. A trial for self-alignment of the quantum dots was also investigated. On the basis of these results, as the first step toward the ultimate semiconductor lasers in which both electrons and photons are fully quantized, a vertical microcavity InGaAs/GaAs quantum dot laser was demonstrated. Finally a perspective of the quantum dot lasers is discussed, including the bottleneck issues and the impact of the quantum dot structures for reducing threshold current in wide bandgap lasers such as GaN lasers.

A self-induced-transparent (SIT) system that takes advantage of morphology dependent resonances (MDR's) in a Mie-sized microsphere doped with a resonant material is proposed. The present system is doubly resonant: one has microscopic origin (the two-level system), while the other has macroscopic origin (the MDR). In this geometry, owing to the feedback action of MDR's, the pulse area can be much expanded, and thus the electric-field amplitude of the incident pulse can be reduced substantially compared with the conventional one-way SIT propagation. Theoretical results that incorporate dephasing due to structural imperfections are shown.

Several issues on semiconductor lasers with low dimensional quantum systems are discussed. First, described are fabrication techniques for quantum wire and box structures, particularly a selective growth MOCVD growth technique which have been recently developed. Using this technique, we obtained 20 nm15 nm triangular-shaped quantum wire structures. Next, we investigate band structures of the quantum wires having strain effects, including lasing characteristics of quantum wire lasers with the strain effects. Finally we discuss importance to control both the electron wave mode and the optical wave mode for future high performance lasers, which leads to the concept of quantum micro-lasers. In order to demonstrate possibility to control the spontaneous mode in the laser cavity, an experimental result is shown on enhancement and inhibition effects of the spontaneous emission mode in a vertical cavity laser having two kinds of the quantum well.

Several issues on semiconductor lasers with low dimensional quantum systems are discussed. First, described are fabrication techniques for quantum wire and box structures, particularly a selective growth MOCVD growth technique which have been recently developed. Using this technique, we obtained 20 nm 15 nm triangular-shaped quantum wire structures. Next, we investigate band structures of the quantum wires having strain effects, including lasing characteristics of quantum wire lasers with the strain effects. Finally we discuss importance to control both the electron wave mode and the optical wave mode for future high performance lasers, which leads to the concept of quantum micro-lasers. In order to demonstrate possibility to control the spontaneous mode in the laser cavity, an experimental result is shown on enhancement and inhibition effects of the spontaneous emission mode in a vertical cavity laser having two kinds of the quantum well.