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| 3. |
- Baveja, P. P., et al.
(författare)
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Assessment of VCSEL thermal rollover mechanisms from measurements and empirical modeling
- 2011
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 19:16, s. 15490-15505
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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.
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| 4. |
- Baveja, P. P., et al.
(författare)
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Impact of photon lifetime on thermal rollover in 850-nm high-speed VCSELs
- 2012
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276
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Konferensbidrag (refereegranskat)abstract
- We present an empirical thermal model for VCSELs based on extraction of temperature dependence of macroscopic VCSEL parameters from CW measurements. We apply our model to two, oxide-confined, 850-nm VCSELs, fabricated with a 9-mu m inner-aperture diameter and optimized for high-speed operation. We demonstrate that for both these devices, the power dissipation due to linear heat sources dominates the total self-heating. We further show that reducing photon lifetime down to 2 ps drastically reduces absorption heating and improves device static performance by delaying the onset of thermal rollover. The new thermal model can identify the mechanisms limiting the thermal performance and help in formulating the design strategies to ameliorate them.
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- Glimelius, B, et al.
(författare)
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The Swedish Council on Technology Assessment in Health Care (SBU) systematic overview of chemotherapy effects in some major tumour types--summary and conclusions
- 2001
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Ingår i: Acta oncologica (Stockholm, Sweden). - : Informa UK Limited. - 0284-186X. ; 40, s. 135-
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Forskningsöversikt (refereegranskat)abstract
- This report by The Swedish Council on Technology Assessment in Health Care (SBU) reviews, classifies, and grades the scientific literature on cancer chemotherapy in some major tumour types, describes the practice of chemotherapy in Sweden, compares practice with scientific knowledge, and analyses the costs and cost-effectiveness of chemotherapy. The report is intended primarily for decision-makers at various levels, both practitioners and administrators. It is also of interest for the medical profession. The extensive body of scientific literature was reviewed according to strict criteria that reflected the scientific weight of the literature. Sixteen experts representing different disciplines (oncology, surgery, internal medicine, health economy and quality of life research) participated in the literature review. Each section was discussed within the project group and was reviewed by at least one, but usually two international researchers. Additional input was provided by national experts representing different scientific disciplines. For the final evaluation to be as close to the objective truth as possible, a concerted effort was made to guarantee objectivity and thorough assessment of current knowledge about the effects of chemotherapy on the selected cancers. The tumour types selected for this assessment include firstly those types where three investigations had shown an increased use of chemotherapy in Sweden during the latest decade. These were non-small cell lung cancer (NSCLC), gastric cancer, pancreatic cancer, colorectal cancer and urinary bladder cancer. Secondly, the two tumour types comprising the greatest number of patients treated with chemotherapy in Sweden, breast cancer and haematological malignancies, were included. Among the haematological malignancies, the most prevalent ones, acute myeloid leukaemia (AML), chronic lymphocytic leukaemia (CLL), Hodgkin's disease (HD), aggressive non-Hodgkin's lymphoma (NHL) of the large B-cell type and indolent NHL of follicular type were evaluated. These constitute about 75%, of all haematological malignancies. Thirdly, ovarian cancer was included since chemotherapy has been extensively used and since, at the time of the planning of this overview, a group of very expensive drugs, the taxanes, had preliminarily shown promising results. A wealth of scientific literature has been published on cancer therapy. The review presented in this report is limited to scientific studies judged to be important for evaluating chemotherapy efficacy. Assessments of the content and quality of these studies, and a critical summary of the results in all stages of the selected tumours, have never before been attempted in this way. However, similar comprehensive overviews of certain stages of the tumours have previously been made. These overviews were also critically evaluated. Totally 1,496 studies involving 558,743 patients were reviewed. The survey of practice of chemotherapy use involved all departments of surgery, urology, gynaecology, internal medicine including haematologic units, pulmonary medicine and general and gynaecologic oncology at 16 hospitals in two health care regions in Sweden, covering 39% of the Swedish population. During the 4 weeks of the survey, all patients with the diagnoses concerned who received chemotherapy were registered. The study included 1,590 patients. The working group's general conclusions are summarised in the following points: The literature on the effects of chemotherapy is extensive. Chemotherapy has a well-documented role in the curative and palliative treatment of patients with several types of cancer. The use of chemotherapy is of utmost importance for the possibility of cure in certain tumour types. In other tumours, chemotherapy increases the possibility of cure when added to local and regional treatments, particularly surgery. In the instances of no possibility of cure, chemotherapy may to a variable extent improve both patient survival and well-being. In Sweden chemotherapy is largely used in accordance with that documented in the scientific literature. The extent of both over- and under-treatment seems to be limited but cannot be excluded at the individual patient level. The literature-based knowledge is scientifically of lower quality in the most chemotherapy sensitive tumours than in tumours showing more limited sensitivity. In the more sensitive tumours, positive effects on a symptomatic stage and survival were seen several decades ago. In those days, clinical treatment studies did not fulfil the current high quality requirements. Small life-prolonging effects of chemotherapy are sometimes very well documented in large, high quality scientific studies. Some of these s
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- Larsson, Anders, 1957, et al.
(författare)
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High-speed tunable and fixed-wavelength VCSELs for short-reach optical links and interconnects
- 2012
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276, s. Article Number: 82760H-
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Konferensbidrag (refereegranskat)abstract
- This paper presents a review of recent work on high speed tunable and fixed wavelength vertical cavity surface emitting lasers (VCSELs) at Chalmers University of Technology. All VCSELs are GaAs-based, employ an oxide aperture for current and/or optical confinement, and emit around 850 nm. With proper active region and cavity designs, and techniques for reducing capacitance and thermal impedance, our fixed wavelength VCSELs have reached a modulation bandwidth of 23 GHz, which has enabled error-free 40 Gbps back-to-back transmission and 35 Gbps transmission over 100 m of multimode fiber. A MEMS-technology for wafer scale integration of tunable high speed VCSELs has also been developed. A tuning range of 24 nm and a modulation bandwidth of 6 GHz have been achieved, enabling error-free back-to-back transmission at 5 Gbps.
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| 9. |
- Davani, Hooman A., et al.
(författare)
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Polarization investigation of a tunable high-speed short-wavelength bulk-micromachined MEMS-VCSEL
- 2012
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276, s. Art. no. 82760T-
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Konferensbidrag (refereegranskat)abstract
- We report the investigation of the state of polarization (SOP) of a tunable vertical-cavity surface-emitting laser (VCSEL) operating near 850 nm with a mode-hop free single-mode tuning range of about 12 nm and an amplitude modulation bandwidth of about 5 GHz. In addition, the effect of a sub-wavelength grating on the device and its influence on the polarization stability and polarization switching has been investigated. The VCSEL with an integrated sub-wavelength grating shows a stable SOP with a polarization mode suppression ratio (PMSR) more than 35 dB during the tuning.
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