| 1. |
- Pougeoise, E., et al.
(författare)
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Experimental study of the lasing modes of 1.3-ÎŒm highly strained InGaAs-GaAs quantum-well oxide-confined VCSELs
- 2009
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Ingår i: IEEE Photonics Technology Letters. - 1041-1135 .- 1941-0174. ; 21:6, s. 377-379
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Tidskriftsartikel (refereegranskat)abstract
- We present an experimental study of the main modes involved in the emission properties of InGaAs-GaAs quantum-well oxide-confined long wavelength vertical-cavity surface-emitting lasers. Lasing properties are dominated by the so-called "oxide modes" and by aperture modes, respectively, for small and large driving currents. We present complementary investigations of the laser emission including far-field angular distribution and spectroscopic near-field optical microscopy to a better understanding of the nature of the "oxide modes."
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| 2. |
- Pougeoise, E., et al.
(författare)
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Strained InGaAs quantum well vertical cavity surface emitting lasers emitting at 1.3 mu m
- 2006
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Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 0013-5194 .- 1350-911X. ; 42:10, s. 584-586
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Tidskriftsartikel (refereegranskat)abstract
- Results on strained InGaAs quantum well vertical cavity surface emitting lasers for optical interconnection applications are reported. Fundamental mode continuous-wave lasing at wavelengths beyond 1300 nm is demonstrated at room temperature. The metal-organic vapour-phase epitaxy grown structure was processed as top p-type distribute Bragg reflector oxide-confined devices.
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| 3. |
- Kopp, C., et al.
(författare)
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Very compact FTTH Diplexer design using advanced wafer level fabrication methods
- 2008
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Ingår i: MICRO-OPTICS 2008. - Strasbourg : SPIE.
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Konferensbidrag (refereegranskat)abstract
- FTTH networks require implementing a diplexer at each user termination. According to most of the standards, this diplexer detects a download signal beam at 1.49ÎŒm and emits an upload signal beam at 1.31ÎŒm on the same single mode fibre. Both signals exhibit datarate speed below 2.5Gbps. Today, most of the diplexers are obtained by actively aligning a set of individual optoelectronic components and micro-optics. However, new manufacturing solutions satisfying very low cost and mass production capability requirements of this market would help to speed the massive spreading of this technology. In this paper, we present an original packaging design to manufacture Diplexer Optical Sub-Assembly for FTTH application. A dual photodiode is stacked over a VCSEL and detects both the download signal beam at 1.49ÎŒm passing through the laser and one part of the upload signal beam at 1.31ÎŒm for monitoring. To satisfy this approach, an innovative VCSEL has been designed to have a very high transmission at 1.49ÎŒm. All these components are mounted on a very small circuit board on glass including also integrated circuits such as transimpedance amplifier. So, the device combines advanced optoelectronic components and highly integrated Multi-Chip-Module on glass approach using collective wafer-level assembling technologies. For the single mode fibre optical coupling, active and passive alignment solutions are considered.
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| 4. |
- Stevens, R., et al.
(författare)
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Microstructured photonic crystal for single-mode long wavelength VCSELs
- 2008
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Ingår i: Semiconductor Lasers and Laser Dynamics III. - : SPIE.
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Konferensbidrag (refereegranskat)abstract
- In this article, we report on long wavelength (1.27 ÎŒm) single-mode micro-structured photonic crystal strained InGaAs quantum wells VCSELs for optical interconnection applications. Single fundamental mode room-temperature continuous-wave lasing operation was demonstrated for devices designed and processed with different two-dimensional etched patterns. The conventional epitaxial structure was grown by Metal-Organic Vapor Phase Epitaxy (MOVPE) and contains fully doped GaAs/AlGaAs DBRs, one oxidation layer and three strained InGaAs quantum wells. The holes were etched half-way through the top-mirror following various designs (triangular and square lattices) and with varying hole's diameters and pitches. We obtained up to 1.7 mW optical output power and more than 30 dB Side-Mode Suppression Ratio (SMSR) at room temperature and in continuous wave operation. Systematic static electrical, optical and spectral characterization was performed on wafer using an automated probe station. Numerical modeling using the MIT Photonic-Bands (MPB [1]) package of the transverse modal behaviors in the photonic crystal was performed using the plane wave method in order to understand the index-guiding effects of the chosen patterns, and to further optimize the design structures for mode selection at the given wavelength.
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| 5. |
- Engelhardt, Ilka. A. D., et al.
(författare)
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Cold electrons at comet 67P/Churyumov-Gerasimenko
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 616
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Tidskriftsartikel (refereegranskat)abstract
- Context. The electron temperature of the plasma is one important aspect of the environment. Electrons created by photoionization or impact ionization of atmospheric gas have energies ∼10 eV. In an active comet coma the gas density is high enough for rapid cooling of the electron gas to the neutral gas temperature (few hundred kelvin). How cooling evolves in less active comets has not been studied before.Aims. To investigate how electron cooling varied as comet 67P/Churyumov-Gerasimenko changed its activity by three orders of magnitude during the Rosetta mission.Methods. We use in-situ data from Rosetta plasma and neutral gas sensors. By combining Langmuir probe bias voltage sweeps and Mutual Impedance Probe measurements we determine when cold electrons form at least 25% of the total electron density. We compare the results to what is expected from simple models of electron cooling, using the observed neutral gas density as input.Results. We demonstrate that the slope of the Langmuir probe sweep can be used as a proxy for cold electron presence. We show statistics of cold electron observations over the 2 year mission period. We find cold electrons at lower activity than expected by a simple model based on free radial expansion and continuous loss of electron energy. Cold electrons are seen mainly when the gas density indicates an exobase may have formed.Conclusions. Collisional cooling of electrons following a radial outward path is not sufficient for explaining the observations. We suggest the ambipolar electric field is important for the observed cooling. This field keeps electrons in the inner coma for much longer time, giving them time to dissipate energy by collisions with the neutrals. We conclude there is need of better models to describe the plasma environment of comets, including at least two populations of electrons and the ambipolar field.
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| 6. |
- Gilet, N., et al.
(författare)
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Observations of a mix of cold and warm electrons by RPC-MIP at 67P/Churyumov-Gerasimenko
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 640
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Tidskriftsartikel (refereegranskat)abstract
- Context. The Mutual Impedance Probe (MIP) of the Rosetta Plasma Consortium (RPC) onboard the Rosetta orbiter which was in operation for more than two years, between August 2014 and September 2016 to monitor the electron density in the cometary ionosphere of 67P/Churyumov-Gerasimenko. Based on the resonance principle of the plasma eigenmodes, recent models of the mutual impedance experiment have shown that in a two-electron temperature plasma, such an instrument is able to separate the two isotropic electron populations and retrieve their properties.Aims. The goal of this paper is to identify and characterize regions of the cometary ionized environment filled with a mix of cold and warm electron populations, which was observed by Rosetta during the cometary operation phase.Methods. To reach this goal, this study identifies and investigates the in situ mutual impedance spectra dataset of the RPC-MIP instrument that contains the characteristics of a mix of cold and warm electrons, with a special focus on instrumental signatures typical of large cold-to-total electron density ratio (from 60 to 90%), that is, regions strongly dominated by the cold electron component.Results. We show from the observational signatures that the mix of cold and warm cometary electrons strongly depends on the cometary latitude. Indeed, in the southern hemisphere of 67P, where the neutral outgassing activity was higher than in northern hemisphere during post-perihelion, the cold electrons were more abundant, confirming the role of electron-neutral collisions in the cooling of cometary electrons. We also show that the cold electrons are mainly observed outside the nominal electron-neutral collision-dominated region (exobase), where electrons are expected to have cooled down. This which indicates that the cold electrons have been transported outward. Finally, RPC-MIP detected cold electrons far from the perihelion, where the neutral outgassing activity is lower, in regions where no electron exobase was expected to have formed. This suggests that the cometary neutrals provide a more frequent or efficient cooling of the electrons than expected for a radially expanding ionosphere.
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| 7. |
- Johansson, Fredrik, et al.
(författare)
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A charging model for the Rosetta spacecraft
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 642
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Tidskriftsartikel (refereegranskat)abstract
- Context. The electrostatic potential of a spacecraft, V-S, is important for the capabilities of in situ plasma measurements. Rosetta has been found to be negatively charged during most of the comet mission and even more so in denser plasmas.Aims. Our goal is to investigate how the negative V-S correlates with electron density and temperature and to understand the physics of the observed correlation.Methods. We applied full mission comparative statistics of V-S, electron temperature, and electron density to establish V-S dependence on cold and warm plasma density and electron temperature. We also used Spacecraft-Plasma Interaction System (SPIS) simulations and an analytical vacuum model to investigate if positively biased elements covering a fraction of the solar array surface can explain the observed correlations.Results. Here, the V-S was found to depend more on electron density, particularly with regard to the cold part of the electrons, and less on electron temperature than was expected for the high flux of thermal (cometary) ionospheric electrons. This behaviour was reproduced by an analytical model which is consistent with numerical simulations.Conclusions. Rosetta is negatively driven mainly by positively biased elements on the borders of the front side of the solar panels as these can efficiently collect cold plasma electrons. Biased elements distributed elsewhere on the front side of the panels are less efficient at collecting electrons apart from locally produced electrons (photoelectrons). To avoid significant charging, future spacecraft may minimise the area of exposed bias conductors or use a positive ground power system.
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| 8. |
- Myllys, M., et al.
(författare)
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Plasma properties of suprathermal electrons near comet 67P/Churyumov-Gerasimenko with Rosetta
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 630
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Tidskriftsartikel (refereegranskat)abstract
- Context: The Rosetta spacecraft escorted comet 67P/Churyumov-Gerasimenko from 2014 to September 2016. The mission provided in situ observations of the cometary plasma during different phases of the cometary activity, which enabled us to better understand its evolution as a function of heliocentric distance.Aims: In this study, different electron populations, called warm and hot, observed by the Ion and Electron Sensor (IES) of the Rosetta Plasma Consortium (RPC) are investigated near the comet during the escorting phase of the Rosetta mission.Methods: The estimates for the suprathermal electron densities and temperatures were extracted using IES electron data by fitting a double-kappa function to the measured velocity distributions. The fitting results were validated using observations from other RPC instruments. We give upgraded estimates for the warm and hot population densities compared to values previously shown in literature.Results: The fitted density and temperature estimates for both electron populations seen by IES are expressed as a function of heliocentric distance to study their evolution with the cometary activity. In addition, we studied the dependence between the electron properties and cometocentric distance.Conclusions: We observed that when the neutral outgassing rate of the nucleus is high (i.e., near perihelion) the suprathermal electrons are well characterized by a double-kappa distribution. In addition, warm and hot populations show a significant dependence with the heliocentric distance. The populations become clearly denser near perihelion while their temperatures are observed to remain almost constant. Moreover, the warm electron population density is shown to be strongly dependent on the radial distance from the comet. Finally, based on our results we reject the hypothesis that hot electron population seen by IES consists of solely suprathermal (halo) solar wind electrons, while we suggest that the hot electron population mainly consists of solar wind thermal electrons that have undergone acceleration near the comet.
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| 9. |
- Pougeoise, E., et al.
(författare)
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Experimental characteristics and analysis of transverse modes in 1.3 μm strained InGaAs quantum well VCSELs
- 2006
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Ingår i: Proc SPIE Int Soc Opt Eng. - : SPIE. - 0819462411 - 9780819462411
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Konferensbidrag (refereegranskat)abstract
- In the context of optical interconnection applications, we report on results obtained on strained InGaAs quantum well Vertical Cavity Surface Emitting Lasers (VCSELs). Our devices are top p-type DBR oxide-confined VCSEL, grown by metalorganic vapour-phase epitaxy (MOVPE). These lasers exhibit low threshold currents and deliver up to 1.77 mW in continuous wave operation at room temperature. Fundamental mode continuous-wave lasing at wavelengths beyond 1300 nm at room temperature is reached for a 4 μm oxide diameter VCSEL. The particular design of the active layer based on a large detuning between the gain maximum and the cavity resonance gives our devices a very specific thermal and modal behaviour. Therefore, we study the spectral and spatial distributions of the transverse modes by near field scanning optical microscopy using a micropolymer tip at the end of an optical fibre.
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