| 1. |
- Davani, Hooman A., et al.
(författare)
-
Polarization investigation of a tunable high-speed short-wavelength bulk-micromachined MEMS-VCSEL
- 2012
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276, s. Art. no. 82760T-
-
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.
|
|
| 2. |
- Davani, Hooman A., et al.
(författare)
-
Widely Electro Thermal Tunable Bulk-Micromachined MEMS-VCSEL Operating Around 850nm
- 2011
-
Ingår i: Conference on Lasers and Electro-Optics/Pacific Rim, CLEOPR 2011; Sydney; Australia; 28 August 2011 through 1 September 2011. - 2162-2701. - 9780977565771 ; , s. 32-34
-
Konferensbidrag (refereegranskat)abstract
- We present the highest reported continues tuning range of 37 nm and fastest electro thermal tuning speed of 700 Hz achieved with tunable vertical-cavity surface-emitting lasers (VCSEL) and semiconductor DBRs at 850 nm wavelength range.
|
|
| 3. |
- Davani, Hooman A., et al.
(författare)
-
Widely tunable high-speed bulk-micromachined short-wavelength MEMS-VCSEL
- 2010
-
Ingår i: Semiconductor Laser Conference (ISLC), 2010 22nd IEEE International. - 0899-9406. - 9781424456833 ; , s. 9-10
-
Konferensbidrag (refereegranskat)abstract
- We present the first results of a high-speed bulk-micromachined tunable vertical-cavity surface-emitting laser (VCSEL) operating near 850nm using a half-symmetric resonator with a movable curved microelectromechanical system (MEMS) membrane.
|
|
| 4. |
- Gierl, Christian, et al.
(författare)
-
Tuneable VCSEL aiming for the application in interconnects and short haul systems
- 2011
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819484963 ; 7959
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Widely tunable vertical cavity surface emitting lasers (VCSEL) are of high interest for optical communications, gas spectroscopy and fiber-Bragg-grating measurements. In this paper we present tunable VCSEL operating at wavelength around 850 nm and 1550 nm with tuning ranges up to 20 nm and 76 nm respectively. The first versions of VCSEL operating at 1550 nm with 76 nm tuning range and an output power of 1.3mW were not designed for high speed modulation, but for applications where only stable continious tuning is essential (e.g. gas sensing). The next step was the design of non tunable VCSEL showing high speed modulation frequencies of 10 GHz with side mode supression ratios beyond 50 dB. The latest version of these devices show record output powers of 6.7mW at 20 °C and 3mW at 80 °C. The emphasis of our present and future work lies on the combination of both technologies. The tunable VCSEL operating in the 850 nm-region reaches a modulation bandwidth of 5.5GHz with an output power of 0.8mW.
|
|
| 5. |
- Danninger, Herbert, et al.
(författare)
-
Sintered Steels Prealloyed with Manganese – Chances and Risks
- 2010
-
Ingår i: World Powder Metallurgy Congress and Exhibition, World PM 2010; Florence; Italy; 10 October 2010 through 14 October 2010. - 9781899072125 ; 3, s. 3-10
-
Konferensbidrag (refereegranskat)abstract
- Manganese as an alloying element in sintered steels offers technical and commercial advantages; so far it has been used however only tentatively and added mainly through admixing. Here it is shown that also prealloying can be a viable route since the adverse effect of Mn on the compressibility is markedly less than commonly assumed, and the compacts shrink during sintering, in contrast to expansion with the mixed variants. Sintering of Mn prealloyed steel compacts is similar to the route used for Cr-Mo prealloyed grades, the main reduction stage being carbothermic reduction at T>1000°C, although in reducing atmospheres part of the surface oxides can be removed at T 1200°C is recommended to ensure sufficient oxygen removal. The main problem with Mn, the tendency to Mn loss at the surfaces by evaporation during sintering must be considered also here, but it is alleviated by prealloying compared to admixing, due to the lower initial activity of Mn in prealloyed materials.
|
|
| 6. |
- De Oro Calderón, Raquel, 1982, et al.
(författare)
-
Introduction of Oxidation-Sensitive Elements in Low Alloyed Steels using the Master Alloy Route: Key Aspects for Success
- 2013
-
Ingår i: International Powder Metallurgy Congress and Exhibition, Euro PM 2013; Gothenburg; Sweden; 15 September 2013 through 18 September 2013. - 9781899072408 ; 3, s. 337-342
-
Konferensbidrag (refereegranskat)abstract
- Defining the proper conditions for sintering of steels containing oxidation-sensitive elements requires a deep understanding of the overall gas-gas and solid-gas reactions taking place especially during the heating stage of the sintering process. In this work, Mn and Si have been introduced in sintered steels in the form of a master alloy powder specifically designed to form a liquid phase. The effect of sintering atmosphere (Ar, H2 or N2-10H2) and carbon content on both reduction/oxidation reactions and dimensional stability were studied by advanced thermal techniques. Two different types of base powders (plain iron and Cr-prealloyed steel) were considered with the aim of understanding the effect of chemical interaction between base powder and master alloy. The results show how heterogeneity in chemical activity between the components of the mix modifies the overall reduction reactions, and how dimensional changes are importantly affected by the presence of reducing agents: either H2 from the atmosphere or carbon introduced as graphite.
|
|
| 7. |
- De Oro Calderón, Raquel, 1982, et al.
(författare)
-
New Alloying Systems for Sintered Steels: Critical Aspects of Sintering Behavior
- 2015
-
Ingår i: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623. ; 46:3, s. 1349-1359
-
Tidskriftsartikel (refereegranskat)abstract
- Oxygen-sensitive alloying elements such as Mn, Si, and Cr have a high potential for improving the properties of low alloyed sintered steels while reducing the alloying cost. However, it is necessary to find a way for avoiding, or at least minimizing, the oxidation of these elements especially during the early stages of the sintering cycle. In this study Mn, Si, and Cr were introduced in the form of a master alloy powder designed to be mixed with the iron base powder and provide the final composition of the steel during the sintering process. The reduction/oxidation phenomena taking place during the heating stage were studied by thermogravimetry, dilatometry, and mass spectroscopy, using either reducing (H2) or inert (Ar) atmospheres. The results show how the difference in chemical activity between base iron powder and master alloy causes the so called “internal-getter” effect, by which the reduction of less stable iron oxides leads to oxidation of the elements with higher affinity for oxygen. This effect can be somehow minimized when sintering in H2, since the iron oxides are reduced at lower temperatures at which the reactivity of the elements in the master alloy is lower. However, H2 concentration in the processing atmosphere needs to be carefully adapted to the specific composition of the materials being processed in order to minimize decarburization by methane formation during sintering.
|
|
| 8. |
- Gierl-Mayer, Christian, et al.
(författare)
-
"Internal Gettering” – Metallothermic Reduction Processes In The Early Stage Of Sintering
- 2015
-
Ingår i: International Journal of Powder Metallurgy (Princeton, New Jersey). - 0888-7462. ; 51:3, s. 47-53
-
Tidskriftsartikel (refereegranskat)abstract
- One of the aspects of modern material systems for high strength sintered steel parts is the presence of alloy elements with widely different oxygen affinity. Compared to the base iron, the “new” alloy elements Cr, Mn and Si form oxides with much higher stability. It is shown here that in case of powder mixes this leads to oxygen transfer from the base iron particles to the alloy elements during heating up to sintering temperature, i.e. metallothermic reduction of the iron surfaces. With prealloyed powders, the surface oxides, which are originally mostly iron oxide, are transformed into alloy element oxides during heating unless the iron oxides can be reduced at low temperature with H2. In any case, the heterogeneity of the oxygen affinity is a parameter that has to be considered when defining alloy systems for sintered steels.
|
|
| 9. |
- Gierl-Mayer, Christian, et al.
(författare)
-
“INTERNAL GETTERING” – METALLOTHERMIC REDUCTION PROCESSES IN THE EARLY STAGE OF SINTERING
- 2014
-
Ingår i: Advances in Powder Metallurgy & Particulate Materials-2014. - 9780985339760 ; 5, s. 74-85
-
Konferensbidrag (refereegranskat)abstract
- One of the aspects of modern material systems for high strength sintered steel parts is the presence of alloy elements with widely different oxygen affinity. Compared to the base iron, the “new” alloy elements Cr, Mn and Si form oxides with much higher stability. It is shown here that in case of powder mixes this leads to oxygen transfer from the base iron particles to the alloy elements during heating up to sintering temperature, i.e. metallothermic reduction of the iron surfaces. With prealloyed powders, the surface oxides, which are originally mostly iron oxide, are transformed into alloy element oxides during heating unless the iron oxides can be reduced at low temperature with H2. In any case, the heterogeneity of the oxygen affinity is a parameter that has to be considered when defining alloy systems for sintered steels.
|
|
| 10. |
- Hryha, Eduard, 1980, et al.
(författare)
-
Surface Analysis of Prealloyed Steel Powders: Qualitative and Quantitative Aspects
- 2010
-
Ingår i: World Powder Metallurgy Congress and Exhibition, World PM 2010; Florence; Italy; 10 October 2010 through 14 October 2010. - 9781899072194 ; 1, s. 25-32
-
Konferensbidrag (refereegranskat)abstract
- The amount of oxides, and their composition and spatial distribution within a particle, determine the usefulness and subsequent processing requirements of a powder. The present work summarizes possibilities of qualitative and quantitative analysis of powder surface chemistry and its changes during sintering by a variety of methods, starting from surface-sensitive chemical analyses by XPS, Auger spectroscopy, HR SEM+EDX analysis etc. Utilizing modern thermoanalytical techniques such as DTA, DSC and TG combined with continuous chemical analysis through mass-spectroscopy allows identification of temperature ranges within which degassing and deoxidation of powder occur. The aim of this study was to establish a relationship between the surface composition of the powder and the type and extent of surface chemical reactions during degassing and deoxidation studied by thermoanalytical techniques performed on the same material. A number of water-atomized powders prealloyed with manganese (0.3-1.8%) were chosen as model materials for which qualitative and quantitative analysis of oxides is presented.
|
|
