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- Streubel, K., et al.
(författare)
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Long wavelength vertical cavity lasers
- 1999
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - San Jose, CA, USA. ; 3625:Bellingham, WA, United States, s. 304-314
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Tidskriftsartikel (refereegranskat)abstract
- We report on three novel vertical cavity laser (VCL) structures for 1.55 Όm operation. Two of the VCL structures utilize an n-type GaInAsP/InP Bragg mirror combined with an Al(Ga)As/GaAs mirror using either wafer-fusion or metamorphic epitaxial growth. The third VCL employs two wafer fused AlGaAs/GaAs mirrors, in which lateral current confinement is obtained by localized fusion of the p-mirror. All three VCLs use strained GaInAsP quantum wells as active material and achieve continuous-wave (CW) operation at room-temperature or above. The single fused VCL operates up to 17 °C and 101 °C in continuous-wave and pulsed mode, respectively. The monolithic VCL-structure with a metamorphic GaAs/AlAs n-type mirror uses a reversed biased tunnel junction for current injection. This laser achieves record high output power (1mW) at room temperature and operates CW up to 45 °C. The double fused VCLs with a 10×10 Όm2 active area operate CW up to 30 °C with threshold current as low as 2.5 mA and series resistance of 30 Ohms. The emission spectra exhibit a single lasing mode polarized with 30 dB extinction ratio and a spectral linewidth of 150 MHz.
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| 6. |
- Hammar, M, et al.
(författare)
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Expression of two csg operons is required for production of fibronectin- and congo red-binding curli polymers in Escherichia coli K-12.
- 1995
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Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 18:4, s. 661-70
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Tidskriftsartikel (refereegranskat)abstract
- Two divergently transcribed operons in Escherichia coli required for the expression of fibronectin- and Congo red-binding curli polymers were identified and characterized by transposon mutagenesis, sequencing and transcriptional analyses, as well as for their ability to produce the curli subunit protein. The csgBA operon encodes CsgA, the major subunit protein of the fibre, and CsgB, a protein with sequence homology to CsgA. A non-polar csgB mutant is unaffected in its production of CsgA, but the subunit protein is not assembled into insoluble fibre polymers. A third open reading frame, orfC, positioned downstream of csgA may affect some functional property of curli since an insertion in this putative gene abolishes the autoagglutinating ability typical of curliated cells without affecting the production of the fibre. The promoter for the oppositely transcribed csgDEFG operon was identified by primer extension and shown, like the csgBA promoter, to be dependent upon the alternate stationary phase-specific sigma factor sigma s in wild-type cells, but not in mutants lacking the nucleoid associated protein H-NS. Insertions in csgD abolish completely trancription from the csgBA promoter. Therefore, any regulatory effect on the csgBA promoter might be secondary to events controlling the csgDEFG promoter and/or activation of CsgD. Insertions in csgE, csgF and csgG abolish curli formation but allow CsgA expression suggesting that one or more of these gene products are involved in secretion/assembly of the CsgA subunit protein. No amino acid sequence homologies were found between the CsgE, CsgF and CsgG proteins and secretion/assembly proteins for other known bacterial fibres, suggesting that the formation of curli follows a novel pathway.
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