Search results for: P.M. Smowton
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The potential of the device is demonstrated through the results of a micro-bead counting experiment. A 0.5 µl sample volume containing 10 µm polystyrene micro-beads in Dl water is deposited into an on-chip inlet reservoir from where it flows, under capillary action, through a buried flow cell. A laser on one side of the cell is forward biased and the opposing laser is operated as a photodiode (Fig...
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InAsP quantum dot (QD) lasers emitting between 660–775nm with 300K threshold current density of 260 Acm−2 for 2mm long uncoated facet devices and operation up to 380K are compared to InP QD lasers emitting at shorter wavelength.
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An order of magnitude improvement in the precision of measurements of internal optical mode losses to better than 0.1cm−1 is demonstrated using a modulated segmented contact method.
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Reductions in non-radiative recombination and αi with increasing Ga composition of the upper-confining-layer in InP self-assembled quantum-dot lasers reduce threshold-current-density and temperature dependence. Carrier population of 2-D layers limits further improvement at higher Ga compositions.
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We demonstrate the p-doping effect on lasing output and threshold current density. The lasing wavelength peak became narrower as the doping concentration increases and has a red shift which consistent with optical absorption ground state.
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Lowering the threshold gain condition in InAs dots, significantly broadens the optical bandwidth for ultra short pulse generation in the non-thermal regime compared to the thermal regime. Rate equations highlight key parameters which influence this.
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We demonstrate dual-wavelength lasers operating with simultaneous emission for a range of difference-wavelengths by accessing the various in homogeneously broadened dot states. We investigate temperature tuning and quantify factors affecting mode stability, including temperature and difference-wavelength.
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Intensity stability with respect to pumping level and temperature is examined in electrically injected dual-λ lasers with separations between 8 and 63 nm that utilise different quantum dot states or quantum dot and quantum well states.
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IEEE Photonics Technology Letters > 2010 > 22 > 2 > 88 - 90
We describe the effect of growth temperature on the optical absorption, gain, and threshold current density of 730-nm emitting, metal-organic vapor phase epitaxy (MOVPE) grown, InP-AlGaInP quantum-dot lasers. Decreasing the growth temperature from 750??C to 690??C leads to an increase in ground state absorption, while sufficient optical gain and low 300 K threshold current density is obtained in the...
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IEEE Journal of Quantum Electronics > 2010 > 46 > 4 > 525 - 532
We have measured the spontaneous emission rates, absorption, and gain spectra of quantum dots between 20 K and 350 K using the segmented contact method, exploiting self assembled dots with a bimodal size distribution. At 20 K, we find a linear relationship between the radiative rates of the ground states of small and large sets of dots, and using absorption data we show the slope corresponds to random...
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IEEE Journal of Quantum Electronics > 2010 > 46 > 2 > 197 - 204
We report a systematic theoretical and experimental investigation of the polarization properties of columnar quantum dots (CQDs) with extremely large aspect ratio and high compositional contrast. A strong variation of the polarization of the dominant interband transitions as a function of the CQD composition and aspect ratio is predicted by the theory and observed experimentally. In optimized InAs...
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We investigate growth and wafer design improvements with two barrier widths each grown at different temperatures to optimise room temperature threshold current density for 2 mm long lasers with uncoated facets. We explain this using sophisticated optical and electrical characterisation.
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We describe the optimization of InP quantum dot material for laser applications, demonstrate some of the interesting physics that results from the nature of this material and describe initial results in promising application areas.
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We experimentally observe truly random to non-thermal to thermal distribution of population of InAs quantum dots with temperature using unamplified spontaneous emission and measure the impact on laser operation.
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We demonstrate the origin of, and quantify the contributions to, the poor external differential efficiency we observe in InP quantum dot lasers. Injection efficiency limits the internal differential quantum efficiency to 50%.
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We quantify contributions to threshold-current in state-of-the-art 1.55 mum GaInNAsSb lasers and the affect of layer design and nitrogen level. Non-radiative current is independent of nitrogen content (3.0-3.3%) but linked to the GaNAs barriers.
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We describe growth and wafer design improvements to reduce 300 K threshold current density to 165 Acm-2 for 2 mm long laser with uncoated facets and, using sophisticated optical and electrical characterisation, we demonstrate how this is achieved.
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IEEE Journal of Quantum Electronics > 2009 > 45 > 4 > 380 - 387
Measurements of the unamplified spontaneous emission spectra from 80 K to 350 K of a dot ensemble show clear evidence for increased population of higher lying states in the inhomogeneous distribution as the temperature is reduced from 200 K to 80 K, indicating a nonthermal population at low temperature and confirming that the recombination processes are localized in individual dots. These conclusions...
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Field-dependent photo-current measurements in Quantum Rod systems show that the orientation of the permanent dipole moment of a standard GaAs/InAs quantum dot can be reversed by fabricating high-aspect ratio Quantum Rod systems.
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We measured different types of damage and 24 (plusmn4) MW/cm2 optical-power-density (pulsed) thresholds for catastrophic optical mirror damage in quantum dot lasers compared with 12 (plusmn2) MW/cm2 for quantum wells, in a comparable structure.
