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

The phase-shifted DFB laser is fabricated by the electron-beam lithography and mass-transport technique. The reduction of threshold current and facet reflectivity was achieved by a one-step mass-transport process. Low threshold and stable single-mode operation was obtained. The effect of the phase shift was confirmed from the symmetrical subthreshold spectra.

1.5 μm phase-shifted DFB laser by EBX and mass-transport technique

A new fabrication method for high-density and small-size quantum-wire and quantum-box structures is proposed and demonstrated. Using this method, we realized GaInAs/InP quantum wires with very small size (6 nm×16 nm) and high density and observed room temperature photoluminescence.

https://iopscience.iop.org/article/10.1143/JJAP.31.L535/pdf

Fabrication of GaInAs/InP Quantum Wires by Organometallic-Vapor-Phase-Epitaxial (OMVPE) Selective Growth on Grooved Side Walls of Ultrafine Multilayers

A vector wave analysis is presented of a multimode optical fiber with an α-power law index profile that includes an additional fourth-order term. By optimizing a and the coefficient of the fourth-order term, the ultimate limit of the width of the impulse response is derived. The effect of the second-order material dispersion of the refractive index is completely compensated by the fourth-order term in the index distribution. As a result, the rms width of the impulse response is reduced to 20 ps/km, one-fifth of the value achievable with the ordinary a-power distribution, even if all modes carry equal power and there is no mode coupling. For a fiber whose normalized frequency is less than 40, the ultimate width of the impulse response is determined by the term with the gradient of the square of the index or ∇n2 in the wave equation.

Vector wave analysis of broadband multimode optical fibers with optimum refractive index distribution

Disclosed are a distributed Bragg reflector type semiconductor laser and a method of manufacturing such a laser a high yields, in which the upper surface of an active waveguide is covered by an external waveguide, the external waveguide is disposed on the same surface as the active waveguide at side portions thereof, the external waveguide is coupled with the edge surfaces of the active waveguide without any gap remaining, and the coupling ratio of the active waveguide and external waveguide is high.

Yasuharu Suematsu

Papers

1.5 μm phase-shifted DFB laser by EBX and mass-transport technique

Fabrication of GaInAs/InP Quantum Wires by Organometallic-Vapor-Phase-Epitaxial (OMVPE) Selective Growth on Grooved Side Walls of Ultrafine Multilayers

Vector wave analysis of broadband multimode optical fibers with optimum refractive index distribution

Distributed bragg reflector type semiconductor laser

Reflection noise measurement of dynamic single mode lasers