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.

/pdf/slow-light-in-photonic-crystals-59fjoaj79v.pdf

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 polarisation of the output light of a single-mode optical fibre was controlled and stabilised by an electro-optical feedback system consisting of two LiNbO3 crystals and voltage controllers. Using this system, polarisation mismatching loss was reduced to 0.2 dB.

Electro-optical polarisation control on single-mode optical fibres

A carrier lifetime measurement under lasing conditions using microwave techniques is reported. The direct modulation characteristic of a junction laser is analyzed, based on the rate equations, and a resonance-like phenomenon of the modulated output is calculated at a fixed frequency determined by the parameters of the junction diode. This frequency occurs just before the modulation cutoff frequency of the diode. The minority carrier lifetime in the active region of the junction laser is expressed in terms of this frequency and other parameters. A modulation experiment was performed using a microwave frequency modulated bias pulse current. The resonance-like phenomenon was confirmed experimentally and the carrier lifetime was determined from the analysis presented here.

Carrier lifetime measurement of a junction laser using direct modulation

Low threshold current density (100) GaInAsP/InP DH lasers emitting at 1.3 µm with thin active layer were studied experimentally and theoretically. The two phase solution growth technique was applied with low cooling rate of 0.08°C/min, which gave 0.05 µm thick uniform active layer. The threshold current density was minimized down to 770 A/cm2 with 0.13 µm thick active layer by reducing the concentration of Zn dopant, whereas the normal V–I characteristic was kept. The residual internal and the external absorption losses of the active layer were estimated to be about 70 cm-1 and 30 cm-1, respectively, in order to know the theoretical threshold limit. The narrowest beam divergence obtained was 23° for the active layer 0.05 µm thick. Both the threshold current density dependence on the thickness of the active layer and the beam divergence were in good agreement with the theory which was calculated by using the relative refractive index difference of 8.7%. A narrow stripe laser with undoped thin active layer had a tendency to emit in a single longitudinal mode.

Low Threshold Current Density (100) GaInAsP/InP Double-Heterostructure Lasers for Wavelength 1.3 µm

Theoretical Spontaneous Emission Factor of Injection Lasers

A structure utilizing an exponential tapered active layer to improve the saturation output power and quantum efficiency of a traveling-wave semiconductor laser amplifier is discussed. Both the spatial distributions of the carrier density and the optical field are considered in the analysis. It is shown that an optimum taper geometry for maximizing the efficiency exists and that this structure provides simultaneous improvement in the saturation output power (7 dB) and the quantum efficiency (1.5 times) compared to a conventional device. >

Yasuharu Suematsu

Papers

Electro-optical polarisation control on single-mode optical fibres

Carrier lifetime measurement of a junction laser using direct modulation

Low Threshold Current Density (100) GaInAsP/InP Double-Heterostructure Lasers for Wavelength 1.3 µm

Theoretical Spontaneous Emission Factor of Injection Lasers

A new structure for high-power TW-SLA (Travelling wave semiconductor laser amplifier)