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Träfflista för sökning "WFRF:(Larsson Anders 1957 ) "

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  • Baveja, P. P., et al. (författare)
  • Assessment of VCSEL thermal rollover mechanisms from measurements and empirical modeling
  • 2011
  • Ingår i: Optics Express. - 1094-4087. ; 19:16, s. 15490-15505
  • Tidskriftsartikel (refereegranskat)abstract
    • We use an empirical model together with experimental measurements for studying mechanisms contributing to thermal rollover in vertical-cavity surface-emitting lasers (VCSELs). The model is based on extraction of the temperature dependence of threshold current, internal quantum efficiency, internal optical loss, series resistance and thermal impedance from measurements of output power, voltage and lasing wavelength as a function of bias current over an ambient temperature range of 15-100 degrees C. We apply the model to an oxide-confined, 850-nm VCSEL, fabricated with a 9-mu m inner-aperture diameter and optimized for highspeed operation, and show for this specific device that power dissipation due to linear power dissipation (sum total of optical absorption, carrier thermalization, carrier leakage and spontaneous carrier recombination) exceeds power dissipation across the series resistance (quadratic power dissipation) at any ambient temperature and bias current. We further show that the dominant contributors to self-heating for this particular VCSEL are quadratic power dissipation, internal optical loss, and carrier leakage. A rapid reduction of the internal quantum efficiency at high bias currents (resulting in high temperatures) is identified as being the major cause of thermal rollover. Our method is applicable to any VCSEL and is useful for identifying the mechanisms limiting the thermal performance of the device and to formulate design strategies to ameliorate them.
  • Gustavsson, Johan S., 1974-, et al. (författare)
  • Mode and polarization control in VCSELs using shallow surface structures
  • 2007
  • Ingår i: IET Optoelectronics. ; 1:5, s. 197-205
  • Tidskriftsartikel (refereegranskat)abstract
    • Monolithic techniques for mode and polarisation control in vertical-cavity surface emitting lasers (VCSELs) using shallow surface structures are summarized and put in the context with other techniques in terms of performance and manufacturability. The method of using circular-symmetric surface structures for mode control and their combination with a sub-wavelength surface grating for simultaneous mode and polarisation control is described in detail, and adherent experimental results for both 850-nm and 1.3-µm oxide-confined VCSELs are presented.
  • Hoog, Anders, et al. (författare)
  • Acquired hypermethylation of the P16INK4A promoter in abdominal paraganglioma: relation to adverse tumor phenotype and predisposing mutation.
  • 2012
  • Ingår i: Endocrine-related cancer. - 1479-6821. ; Epub ahead of print
  • Tidskriftsartikel (refereegranskat)abstract
    • Recurrent alterations in promoter methylation of tumor suppressor genes (TSG) and LINE-1 repeat elements were previously reported in pheochromocytoma and abdominal paraganglioma. The present study was undertaken to explore CpG methylation abnormalities in an extended tumor panel, and assess possible relationships to metastatic disease and mutation status. CpG methylation was quantified by bisulphite Pyrosequencing for selected TSG promoters and LINE-1 repeats. Methylation indices (MetI) above normal reference were observed for DCR2, CDH1, P16, RARB, and RASSF1A. Z-scores for overall TSG, and individual TSG methylation levels, but not LINE-1, were significantly correlated with metastatic disease, paraganglioma, disease predisposition or outcome. Most strikingly P16 hypermethylation was strongly associated with SDHB mutation as opposed to RET/MEN2, VHL/VHL or NF1 related disease. Parallel analyses of constitutional, tumor and metastasis DNA implicate an order of events where constitutional SDHB mutations are followed by TSG hypermethylation and 1p loss in primary tumors, later transferred to metastatic tissue. In the combined material P16 hypermethylation was prevalent in SDHB mutated samples, and was associated with short disease-related survival. The findings verify the previously reported importance of P16 and other TSG hypermethylation in an independent tumor series. Furthermore, a constitutional SDHB mutation is proposed to predispose for an epigenetic tumor phenotype occurring before the emanation of clinically recognized malignancy.
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