We analyze theoretically the oscillator strength and the third-order optical polarizability X 13, due to excitons in semiconductor microcrystallites. The nonlinear optical polarizability is shown to be greatly enhanced for an assembly of such microcrystallites as the exciton is quantized due to the confinement effect and the excitons in a single microcrystallite interact strongly enough to make the excitons deviate from ideal harmonic oscillators.

Very large optical nonlinearity of semiconductor microcrystallites

We review the present status of the rapidly developing field of semiconductor laser diodes based on self-organized quantum dots (QDs). Several milestones have been achieved since the first realization of such a device in 1994: above room-temperature cw operation, the lowest threshold current density of any semiconductor laser diode, high temperature stability, an extended wavelength range on GaAs substrate and high power operation. After a brief introduction we discuss the tremendous advances in epitaxial growth, device performance, and theoretical understanding of QD lasers. Three applications of large commercial interest are discussed in detail: 1300 nm QD lasers on GaAs substrate, QD surface emitting lasers, and high power QD lasers. Finally, we give an outlook on future developments.

The present status of quantum dot lasers

A quantum field-effect directional coupler is described comprised of two quantum waveguides closely spaced apart with an adjacent gate electrode over the space between waveguides. The coupling of electron probability density between waveguides is controlled by the voltage applied to the gate electrode. The coupler implements a voltage-controlled current switch. Several couplers can be connected to perform multiplex/demultiplexing functions.

Quantum field-effect directional coupler

Single quantum wire GaAs/AlGaAs injection lasers were fabricated using organometallic chemical vapor deposition on V‐grooved GaAs substrates. The quantum wire active region has a crescent‐shaped cross section ∼100 A thick and less than 1000 A wide. Amplified spontaneous emission and lasing spectra of the quantum wire lasers exhibit effects due to transitions between quasi‐one‐dimensional subbands separated by ∼10 meV. Single quantum wire laser structures with tight optical confinement exhibited threshold currents as low as 3.5 mA for uncoated devices at room temperature.

Single quantum wire semiconductor lasers

The laser threshold of three-dimensional GaInAsP/InP quantum-box lasers is analyzed. The optimized quantum-box array laser structure for the lowest threshold current density at room temperature is obtained theoretically, taking into account the effect of carrier leakage. The lowest threshold current densities are 14, 27, and 61 A/cm/sup 2/ for 10, 20, and 40 cm/sup -1/ of cavity loss, respectively. The threshold current density is calculated, taking into account fluctuation in quantum-box size. The ideal structure of the quantum-box laser is discussed. It is pointed out that the modulation-doped structure looks promising for the suppression of carrier leakage. >

Threshold current density of GaInAsP/InP quantum-box lasers

Light emitting from quantum-box structure by current injection was observed for the first time. GaInAsP/InP quantum-box structures were fabricated from one-dimensional quantum-well (quantum-film) structures grown by OMVPE. Holographic lithography, wet etching, and LPE regrowth techniques were employed. Three-dimensional quantum size effect was suggested by the wavelength shift of the light emission.

https://iopscience.iop.org/article/10.1143/JJAP.26.L225/pdf

Light Emission from Quantum-Box Structure by Current Injection

Fabrication technique for GaInAsP/InP quantum wire structure by LP-MOVPE

The quantum router is an elementary building block in quantum information processing and quantum communication. This work constitutes a step forward in this direction, i.e., an efficient scheme is proposed for the implementation of a nonreciprocal single-photon quantum router, allowing the routing of a single photon from one side but blocking it from the other side. Our model consists of two directly coupled coplanar-waveguide resonators and a superconducting ring resonator, which are connected together through a transmission line. The nonreciprocity is realized by unidirectionally interacting the rotating microwave modes of the ring resonator with a dissipative magnon mode in an yttrium iron garnet disk. We find that a single-photon signal can be delivered from a given input port to either of the two output ports, but is fully absorbed from the opposite one. The proposed scheme not only enriches the family of nonreciprocal quantum devices, but also finds useful applications in chiral quantum technologies. 

Nonreciprocal single-photon quantum router

Lasing operation of a GaInAsP/InP single-quantum-well laser with very narrow (0.12 μm) wire-likeactive region was obtained for the first time under CW condition at 77 K. It was fabricated by a two-step organometallic vapour phase epitaxy (OMVPE) and wet chemical etching process. The threshold current density of the laser was 810 A/cm2. This lasing operation with such a narrow active region indicates that the technique employed here would be suitable for realising a higher-dimensional quantum-well laser, such as quantum wire and box lasers.

Ming Cao

Papers

Light Emission from Quantum-Box Structure by Current Injection

Fabrication technique for GaInAsP/InP quantum wire structure by LP-MOVPE

Nonreciprocal single-photon quantum router

GaInAsP/InP single-quantum-well (SQW) laser with wire-like active region towards quantum wire laser

Lasing action in GaInAs/GaInAsP quantum-wire structure