21 research outputs found
An analysis of 1.55 mu m InAs/InP quantum dash lasers
Calculations show that electron states are not confined in the dashes in 1.55 mu m InAs/InP quantum dash-in-a-well laser structures. The combination of strain and three-dimensional confinement reduces the calculated density of states (DOS) near the valence band maximum, with the conduction and valence DOS then almost equal close to the band edges. Calculations and photoabsorption measurements show strongly polarized spontaneous emission and gain spectra. Experimental analysis shows the room temperature threshold current is dominated by nonradiative current paths. (C) 2008 American Institute of Physics. (DOI: 10.1063/1.2952194
146-GHz millimeter-wave radio-over-fiber photonic wireless transmission system.
We report the experimental implementation of a wireless transmission system with a 146-GHz carrier frequency which is generated by optical heterodyning the two modes from a monolithically integrated quantum dash dual-DFB source. The monolithic structure of the device and the inherent low noise characteristics of quantum dash gain material allow us to demonstrate the transmission of a 1 Gbps ON-OFF keyed data signal with the two wavelengths in a free-running state at 146-GHz carrier wave frequency. The tuning range of the device fully covers the W-band (75 - 110 GHz) and the F-band (90 - 140 GHz)
Integration of high performance silicon optical modulators
We present our recent work on high speed silicon optical modulators developed within the UK silicon photonics and HELIOS projects. Examples of their integration with other photonic and electronic elements are also presented
The ALMA-ALPINE [CII] survey: sub-kpc morphology of 3 main-sequence galaxy systems at z~4.5 revealed by ALMA
Context: From redshift 6 to redshift 4 galaxies grow rapidly from
low mass galaxies towards the more mature massive galaxies we see at the cosmic
noon. Growth via gas accretion and mergers undoubtedly shape this evolution -
however, there currently exists much uncertainty over the contribution of each
of these processes to the overall evolution of galaxies. Furthermore, previous
characterisations of the morphology of galaxies in the molecular gas phase has
been limited by the coarse resolution of previous observations. Aims: The goal
of this paper is to derive the morpho-kinematic properties of 3 main-sequence
systems at , drawn from the ALPINE survey, using brand new
high-resolution ALMA data in band 7. The objects were previously characterised
as one merger with three components, and and two dispersion-dominated galaxies.
Methods: We use intensity and velocity maps, position-velocity diagrams and
radial profiles of [CII], in combination with dust continuum maps, to analyse
the morphology and kinematics of the 3 systems.} Results: In general, we find
that the high-resolution ALMA data reveal more complex morpho-kinematic
properties. We identify in one galaxy interaction-induced clumps, showing the
profound effect that mergers have on the molecular gas in galaxies, consistent
with what is suggested in recent simulations. A galaxy that was previously
classified as dispersion dominated turned out to show two bright [CII] emission
regions, that could either be merging galaxies or massive star-forming regions
within the galaxy itself. The high resolution data for the other dispersion
dominated object also revealed clumps of [CII] that were not previously
identified. Within the sample, we might also detect star-formation powered
outflows (or outflows from Active Galactic Nuclei) which appear to be fuelling
diffuse gas regions and enriching the circumgalactic medium.Comment: Submitted to A&A, 13 page
The ALMA-ALPINE [CII] survey: Kennicutt-Schmidt relation in four massive main-sequence galaxies at <i>z</i> ∼ 4.5
Aims. The Kennicutt-Schmidt (KS) relation between the gas and the star formation rate (SFR) surface density (Σ − Σ) is essential to understand star formation processes in galaxies. To date, it has been measured up to z ∼ 2.5 in main-sequence galaxies. In this Letter our aim is to put constraints at z ∼ 4.5 using a sample of four massive main-sequence galaxies observed by ALMA at high resolution.
Methods. We obtained ∼0.3″-resolution [CII] and continuum maps of our objects, which we then converted into gas and obscured SFR surface density maps. In addition, we produced unobscured SFR surface density maps by convolving Hubble ancillary data in the rest-frame UV. We then derived the average Σ in various Σ bins, and estimated the uncertainties using a Monte Carlo sampling.
Results. Our galaxy sample follows the KS relation measured in main-sequence galaxies at lower redshift, and is slightly lower than the predictions from simulations. Our data points probe the high end both in terms of Σ and Σ, and gas depletion timescales (285–843 Myr) remain similar to z ∼ 2 objects. However, three of our objects are clearly morphologically disturbed, and we could have expected shorter gas depletion timescales (≲100 Myr) similar to merger-driven starbursts at lower redshifts. This suggests that the mechanisms triggering starbursts at high redshift may be different than in the low- and intermediate-z Universe
The ALMA-ALPINE [CII] survey: Kennicutt-Schmidt relation in four massive main-sequence galaxies at z~4.5
The Kennicutt-Schmidt (KS) relation between the gas and the star formation
rate (SFR) surface density (-) is essential
to understand star formation processes in galaxies. So far, it has been
measured up to z~2.5 in main-sequence galaxies. In this letter, we aim to put
constraints at z~4.5 using a sample of four massive main-sequence galaxies
observed by ALMA at high resolution. We obtained ~0.3"-resolution [CII] and
continuum maps of our objects, which we then converted into gas and obscured
SFR surface density maps. In addition, we produced unobscured SFR surface
density maps by convolving Hubble ancillary data in the rest-frame UV. We then
derived the average in various bins, and
estimated the uncertainties using a Monte Carlo sampling. Our galaxy sample
follows the KS relation measured in main-sequence galaxies at lower redshift
and is slightly lower than predictions from simulations. Our data points probe
the high end both in terms of and , and
gas depletion timescales (285-843 Myr) remain similar to z~2 objects. However,
three of our objects are clearly morphologically disturbed, and we could have
expected shorter gas depletion timescales (~100 Myr) similar to merger-driven
starbursts at lower redshifts. This suggests that the mechanisms triggering
starbursts at high redshift may be different than in the low- and
intermediate-z Universe.Comment: 9 pages, 7 figures, 2 tables, accepted by A&A (letter
Bandwidth-limited 0.3~W picosecond pulses (4~ps) from a 1.53~μm microwave modulated DFB laser with fibre compression
International audienc
High performance InGaAsP/InP semiconductor quantum well lasers realized by gas source molecular beam epitaxy
A wide variety of lasers with multiquantum well structures have been sucessfully realized: 1.55 m single longitudinal mode DFB laser (50 mW output power) : 1.48 m Fabry-Perot pump source (190 mW output power) ; multiphase shift DFB laser with narrow linewidth ( kHz) ; multielectrode laser usuable as FM transmitter (tunability 100 GHz with linewidth  MHz) ; multisection distributed Bragg reflector laser (tunability 375 GHz with 10 MHz linewidth). All these devices have been fabricated using Gas Source Molecular Beam Epitaxy (GSMBE) for the double heterostructure growth and Liquid Phase Epitaxy (LPE) for blocking layer regrowth. This process of fabrication leads to a good reproducibility and reliability