The development of optical gain in chemically synthesized semiconductor nanoparticles (nanocrystal quantum dots) has been intensely studied as the first step toward nanocrystal quantum dot lasers. We examined the competing dynamical processes involved in optical amplification and lasing in nanocrystal quantum dots and found that, despite a highly efficient intrinsic nonradiative Auger recombination, large optical gain can be developed at the wavelength of the emitting transition for close-packed solids of these dots. Narrowband stimulated emission with a pronounced gain threshold at wavelengths tunable with the size of the nanocrystal was observed, as expected from quantum confinement effects. These results unambiguously demonstrate the feasibility of nanocrystal quantum dot lasers.

http://science.sciencemag.org/content/sci/290/5490/314.full.pdf

Optical gain and stimulated emission in nanocrystal quantum dots.

Influences on the semiconductor laser properties of external optical feedback, i.e., return of a portion of the laser output from a reflector external to the laser cavity, have been examined. Experimental observations with a single mode laser is presented with analysis based on a compound cavity laser model, which has been found to explain essential features of the experimental results. In particular, it has been demonstrated that a laser with external feedback can be multistable and show hysteresis phenomena, analogous to those of non-linear Fabry-Perot resonator. It has also been shown that the dynamic properties of injection lasers are significantly affected by external feedback, depending on interference conditions between returned light and the field inside the laser diode.

External optical feedback effects on semiconductor injection laser properties

Slow light with a remarkably low group velocity is a promising solution for buffering and time-domain processing of optical signals. It also offers the possibility for spatial compression of optical energy and the enhancement of linear and nonlinear optical effects. Photonic-crystal devices are especially attractive for generating slow light, as they are compatible with on-chip integration and room-temperature operation, and can offer wide-bandwidth and dispersion-free propagation. Here the background theory, recent experimental demonstrations and progress towards tunable slow-light structures based on photonic-band engineering are reviewed. Practical issues related to real devices and their applications are also discussed. The unique properties of wide-bandwidth and dispersion-free propagation in photonic-crystal devices have made them a good candidate for slow-light generation. This article gives the background theory of slow light, as well as an overview of recent experimental demonstrations based on photonic-band engineering.

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Slow light in photonic crystals

1. Introduction and overview 2. Film stress and substrate curvature 3. Stress in anisotropic and patterned films 4. Delamination and fracture 5. Film buckling, bulging and peeling 6. Dislocation formation in epitaxial systems 7. Dislocation interactions and strain relaxation 8. Equilibrium and stability of surfaces 9. The role of stress in mass transport.

Thin Film Materials: Stress, Defect Formation and Surface Evolution

An overview of analog microwave photonics will be presented. The performance requirements for externally-modulated analog microwave photonic links will be reviewed with specific emphasis placed on modulator efficiency, laser noise, detected photocurrent, and link linearity.

http://ieeexplore.ieee.org/iel5/6387506/6403300/06403360.pdf

Microwave photonics

Corrugations of 70 nm pitch and 100nm depth were formed on InP using electron beam lithography and wet chemical etching having the material selective and anisotropic qualities. For this purpose, a thin GaInAs layer grown by MOVPE was used as an etching mask to suppress the undercut etching so as to form very fine structures.

Very fine corrugations formed on InP by wet chemical etching and electron beam lithography

The angles of beam divergence perpendicular to the junction plane have been studied for low-threshold GaInAsP/InP double-heterostructure lasers with a thin active layer emitting at 1.31 μm. The narrowest beam divergence obtained was 23° for a laser diode with an active-layer thickness of 0.05 μm. At an active-layer thickness of 0.13 μm, the beam divergence was 40° with a threshold current density of 770 A/cm2.

Narrow-beam divergence of the emission from low-threshold GaInAsP/InP double-heterostructure lasers

For single-mode optical-fibre cables, power spectra of random bends were estimated to be Gaussian with correlation lengths of around 1 mm. The method was to fit measured curves of loss against wavelength to theoretical ones.

Random bend losses in single-mode optical-fibre cables: power-spectrum estimation from spectral losses

OMVPE conditions for GaInAs/InP heterointerfaces and superlattices

An index-guiding structure capable of providing well-controlled single-mode operation has been realized for Ga x In 1-x AS y P 1-y /InP lasers ( x = 0.28, y = 0.62 , and \lambda = 1.3 \mu m) using a terraced substrate (TS) configuration prepared by single-step LPE growth. The threshold current was reduced to as low as 44 mA and single-transverse and longitudinal mode operation was stably achieved up to 2.8 times the threshold. Continuous operation at room temperature was also demonstrated.

Yasuharu Suematsu

Papers

Very fine corrugations formed on InP by wet chemical etching and electron beam lithography

Narrow-beam divergence of the emission from low-threshold GaInAsP/InP double-heterostructure lasers

Random bend losses in single-mode optical-fibre cables: power-spectrum estimation from spectral losses

OMVPE conditions for GaInAs/InP heterointerfaces and superlattices

Ga x In 1-x As y P 1-y /InP terraced substrate single-mode laser