Submonolayer Quantum Dots for High Speed Surface Emitting Lasers

We report on progress in growth and applications of submonolayer (SML) quantum dots (QDs) in high-speed vertical-cavity surface-emitting lasers (VCSELs). SML deposition enables controlled formation of high density QD arrays with good size and shape uniformity. Further increase in excitonic absorption and gain is possible with vertical stacking of SML QDs using ultrathin spacer layers. Vertically correlated, tilted or anticorrelated arrangements of the SML islands are realized and allow QD strain and wavefunction engineering. Respectively, both TE and TM polarizations of the luminescence can be achieved in the edge-emission using the same constituting materials. SML QDs provide ultrahigh modal gain, reduced temperature depletion and gain saturation effects when used in active media in laser diodes. Temperature robustness up to 100 °C for 0.98 μm range vertical-cavity surface-emitting lasers (VCSELs) is realized in the continuous wave regime. An open eye 20 Gb/s operation with bit error rates better than 10−12has been achieved in a temperature range 25–85 °Cwithout current adjustment. Relaxation oscillations up to ∼30 GHz have been realized indicating feasibility of 40 Gb/s signal transmission

Superlattice Growth via MBE and Green’s Function Techniques

A model has been developed to simulate the growth of arrays consisting of a substrate on which alternating layers of quantum dots (QDs) and spacer layers are epitaxially grown. The substrate and spacer layers are modeled as an anisotropic elastic half-space, and the QDs are modeled as point inclusions buried within the half-space. In this model, the strain at the free surface of this half-space due to the buried point QDs is calculated, and a scalar measure of the strain at the surface is subsequently determined. New point QDs are placed on the surface where the previously calculated scalar strain measure is a minimum. Following available DFT results, this scalar strain measure is a weighted average of the in-plane strains. This model is constructed under the assumption that diffusional anisotropy can be neglected, and thus, the results are more in agreement with results from experiments of growth of SiGe QDs than experiments involving QDs of (In,Ga)As

Nanoscale waveguiding methods

While 32 nm lithography technology is on the horizon for integrated circuit (IC) fabrication, matching the pace for miniaturization with optics has been hampered by the diffraction limit. However, development of nanoscale components and guiding methods is burgeoning through advances in fabrication techniques and materials processing. As waveguiding presents the fundamental issue and cornerstone for ultra-high density photonic ICs, we examine the current state of methods in the field. Namely, plasmonic, metal slot and negative dielectric based waveguides as well as a few sub-micrometer techniques such as nanoribbons, high-index contrast and photonic crystals waveguides are investigated in terms of construction, transmission, and limitations. Furthermore, we discuss in detail quantum dot (QD) arrays as a gain-enabled and flexible means to transmit energy through straight paths and sharp bends. Modeling, fabrication and test results are provided and show that the QD waveguide may be effective as an alternate means to transfer light on sub-diffraction dimensions

Exciton resonance reflectivity study of quantum well wires

We report on the first observation of the exciton resonant reflection from a directly grown array of isolated quantum-well-wires. Structures contaned 30 GaAs/AlAs double layers were grown on (311) GaAs substrate by conventional elemental source MBE. GaAs wire-like clasters with an orientation along [233] and size of 32/10.2 Å were introduced inside one of the central AlAs layers. The expected distance between nearest clusters is about 160 Å. In spite of much smaller effective volume occupied by excitons in these clusters, as compared to that in a single quantum well, the quantum-well-wire structures demonstrate much lager resonance amplitude of the reflection spectra. We extracted excitonic parameters from these spectra and found that the exciton oscillator strength in the quantum-well-wires is more than 10 time higer than that in the enviroment superlattice. A 30% anisotropy of the exciton oscillator strength in the quantum-well-wire have been observed. The theory of non-local dielectric responce is extended to calculate reflection spectra from the structures with a grating of quantum-well-wires. A functional relationship between the reflection coefficient and the envelope wave function of an exciton in the structure has been established

High speed 160 Gb/s DMT VCSEL transmission using pre-equalization

High speed single channel DMT operation of a directly modulated 850 nm VCSEL with 26 GHz bandwidth is presented. Successful transmission of 161, 152, 135 Gb/s over 10, 300, 550 m of OM4 MMF is demonstrated at the SD-FEC BER limit

Influence of annealing on the formation of inGaAs quantum dots in GaAs matrix during metal organic chemical vapor deposition

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InGaAs nanodomains formed in situ on the surface of (Al,Ga)As

International audienceA new method for obtaining InGaAs nanodomains on the surface of GaAs or (Al,Ga)As is suggested. At the first stage, an InGaAs layer with a thickness above the critical value for dislocation formation is deposited onto the substrate surface by metalorganic CVD. Then the InGaAs film is coated with a thin AlAs layer and annealed at an elevated temperature. The “repulsion” of AlAs from plastically relaxed regions near dislocations and the high temperature stability of AlAs result in that evaporation is restricted to the regions containing defects. The self-organization effects favor the formation of an ordered array of coherent nanodomains that can be used for obtaining buried low-dimensional nanostructures and/or nanoheteroepitaxial inclusions