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- Gustavsson, Johan, 1974, et al.
(author)
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High-speed 850-nm VCSELs for 40 Gb/s transmission
- 2010
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Conference paper (other academic/artistic)abstract
- We have explored the possibility to extend the data transmission rate for standard 850-nm GaAs-based VCSELs beyond the 10 Gbit/s limit of today's commercially available directly-modulated devices. By sophisticated tailoring of the design for high-speed performance we demonstrate that 10 Gb/s is far from the upper limit. For example, the thermal conductivity of the bottom mirror is improved by the use of binary compounds, and the electrical parasitics are kept at a minimum by incorporating a large diameter double layered oxide aperture in the design. We also show that the intrinsic high speed performance is significantly improved by replacing the traditional GaAs QWs with strained InGaAs QWs in the active region. The best overall performance is achieved for a device with a 9 μm diameter oxide aperture, having in a threshold current of 0.6 mA, a maximum output power of 9 mW, a thermal resistance of 1.9 °C/mW, and a differential resistance of 80 Ω. The measured 3dB bandwidth exceeds 20 GHz, and we experimentally demonstrate that the device is capable of error-free transmission (BER
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- Olsson, Petter, 1981-
(author)
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Essentially Lipids : Analytical methods for the characterization of lipid materials
- 2015
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Doctoral thesis (other academic/artistic)abstract
- This thesis describes analytical methods for chromatographic characterizations of lipids in biological and technical systems.Lipids are a group of compounds with a central role in all known forms of life. In addition to the biological roles, lipids are also components in many products of our daily usage. The application areas include food, pharma, cosmetics, biofuels, etc.Analytical characterization of lipids is challenging since a typical lipid extract often contains several hundred unique compounds which also could vary significantly in chemical properties. Separation is in many cases crucial for identification and quantification of individual lipids and here high performance liquid chromatography (HPLC) is regarded as the technique of first choice today.In the present work, methodologies for both normal phase (NP) and reversed phase (RP) HPLC are presented. The focus has been to develop methods that are fast, have low analytical complexity and are compatible with several detection systems. Cyanopropyl coated silica was evaluated as stationary phase for NP-HPLC with the aim to separate all the lipid classes in common lipid extracts. The analytes were eluted with a binary mobile phase system based on hexane, toluene and methanol which yielded in a total runtime of 30 minutes. In a subsequent study, additional stationary phases for NP-HPLC were evaluated for online sample cleanup of polycyclic aromatic hydrocarbons (PAHs) in lipid matrixes. In the demonstrated methodology for RP-HPLC, a binary system consisting of methanol/water was utilized with phenylpropyl coated silica to elute all tested lipid classes in 30 minutes.The methodologies were compatible with various detection techniques including evaporative light scattering detection (ELSD), charged aerosol detection (CAD) as well as electrospray mass spectrometry (ESI-MS) and were applied to characterize lipid materials of both biological and technical nature.
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- Tao, Qiang, 1987, et al.
(author)
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D-A(1)-D-A(2) Copolymers with Extended Donor Segments for Efficient Polymer Solar Cells
- 2015
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In: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 48:4, s. 1009-1016
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Journal article (peer-reviewed)abstract
- Typically a donor-acceptor (D-A) design strategy is used for engineering the bandgap of polymers for solar cells. However, in this work, a series of alternating D-A(1-)D-A(2) copolymers PnTQTI(F) were synthesized and characterized with oligothiophenes (nT, n = 1, 2, 3) as the donor and two electron-deficient moieties, quinoxaline and isoindigo, as the acceptors in the repeating unit. We have studied the influence of the donor segments with different numbers of thiophene units and the effect of the addition of fluorine to the quinoxaline unit of the D-A(1)-D-A(2) polymers. The photophysical, electrochemical, and photovoltaic properties of the polymers were examined via a range of techniques and related to theoretical simulations. On increasing the length of the donor thiophene units, broader absorption spectra were observed in addition to a sequential increase in HOMO levels, while the LUMO levels displayed very small variations. The addition of fluorine to the quinoxaline unit not only decreased the HOMO levels of the resulting polymers but also enhanced the absorption coefficients. A superior photovoltaic performance was observed for the P3TQTI-F-based device with a power conversion efficiency (PCE) of 7.0%, which is the highest efficiency for alternating D-A(1)-D-A(2) polymers reported to date. The structureproperty correlations of the PnTQTI(F) polymers demonstrate that varying of the length of the donor segments is a valuable method for designing high-performance D-A(1)-D-A(2) copolymers and highlight the promising nature of D-A(1)-D-A(2) copolymers for efficient bulk-heterojunction solar cells.
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