75 research outputs found
Low albedos of hot to ultra-hot Jupiters in the optical to near-infrared transition regime
The depth of a secondary eclipse contains information of both the thermally
emitted light component of a hot Jupiter and the reflected light component. If
the dayside atmosphere of the planet is assumed to be isothermal, it is
possible to disentangle both. In this work, we analyze 11 eclipse light curves
of the hot Jupiter HAT-P-32b obtained at 0.89 m in the z' band. We obtain
a null detection for the eclipse depth with state-of-the-art precision, -0.01
+- 0.10 ppt. We confirm previous studies showing that a non-inverted atmosphere
model is in disagreement to the measured emission spectrum of HAT-P-32b. We
derive an upper limit on the reflected light component, and thus, on the
planetary geometric albedo . The 97.5%-confidence upper limit is <
0.2. This is the first albedo constraint for HAT-P-32b, and the first z' band
albedo value for any exoplanet. It disfavors the influence of large-sized
silicate condensates on the planetary day side. We inferred z' band geometric
albedo limits from published eclipse measurements also for the ultra-hot
Jupiters WASP-12b, WASP-19b, WASP-103b, and WASP-121b, applying the same
method. These values consistently point to a low reflectivity in the optical to
near-infrared transition regime for hot to ultra-hot Jupiters.Comment: accepted for publication in A&
Semiconductor Optical Amplifier (SOA)–Based Amplification of Intensity-Modulated Optical Pulses — Deterministic Timing Jitter and Pulse Peak Power Equalization Analysis
During the last few years, large-scale efforts towards realizing high-photonic integration densities have put SOAs in the spotlight once again. Hence, the need to develop a complete framework for SOA-induced signal distortion to accurately evaluate a system’s performance has now become evident. To cope with this demand, we present a detailed theoretical and experimental investigation of the deterministic timing jitter and the pulse peak power equalization of SOA-amplified intensity-modulated optical pulses. The deterministic timing jitter model relies on the pulse mean arrival time estimation and its analytic formula reveals an approximate linear relationship between the deterministic timing jitter and the logarithmic values of intensity modulation when the SOA gain recovery time is faster than the pulse period. The theoretical analysis also arrives at an analytic expression for the intensity modulation reduction (IMR), which clearly elucidates the pulse peak power equalization mechanism of SOA. The IMR analysis shows that the output intensity modulation depth is linearly related to the respective input modulation depth of the optical pulses when the gain recovery time is faster than the pulse period. This novel theoretical platform provides a qualitative and quantitative insight into the SOA performance in case of intensity-modulated optical pulses
A 160Gb/s (4x40) WDM O-band Tx subassembly using a 4-ch array of silicon rings co-packaged with a SiGe BiCMOS IC driver
We present a 400 (8×50) Gb/s-capable RM-based Si-photonic WDM O-band TxRx with 1.17nm channel spacing for high-speed optical interconnects and demonstrate successful 50Gb/s-NRZ TxRx operation achieving a ~4.5dB Tx extinction ratio under 2.15Vpp drive
GJ1214: Rotation period, starspots, and uncertainty on the optical slope of the transmission spectrum
Brightness inhomogeneities in the stellar photosphere (dark spots or bright
regions) affect the measurements of the planetary transmission spectrum. To
investigate the star spots of the M dwarf GJ 1214, we conducted a multicolor
photometric monitoring from 2012 to 2016. The measured variability shows a
periodicity of 125 +- 5 days, which we interpret as the signature of the
stellar rotation period. This value overrules previous suggestions of a
significantly shorter stellar rotation period. A light curve inversion of the
monitoring data yields an estimation of the flux dimming of a permanent spot
filling factor not contributing to the photometric variability, a temperature
contrast of the spots of about 370 K and persistent active longitudes. The
derived surface maps over all five seasons were used to estimate the influence
of the star spots on the transmission spectrum of the planet from 400 nm to
2000 nm. The monitoring data presented here do not support a recent
interpretation of a measured transmission spectrum of GJ 1214b as to be caused
by bright regions in the stellar photosphere. Instead, we list arguments as to
why the effect of dark spots likely dominated over bright regions in the period
of our monitoring. Furthermore, our photometry proves an increase in
variability over at least four years, indicative for a cyclic activity
behavior. The age of GJ 1214 is likely between 6 and 10 Gyr. The long-term
photometry allows for a correction of unocculted spots. For an active star such
as GJ 1214, there remains a degeneracy between occulted spots and the transit
parameters used to build the transmission spectrum. This degeneracy can only be
broken by high-precision transit photometry resolving the spot crossing
signature in the transit light curve.Comment: 11 pages, 8 figures, accepted for publication in Astronomy &
Astrophysic
On interconnecting and orchestrating components in disaggregated data centers:The dReDBox project vision
Computing systems servers-low-or high-end ones have been traditionally designed and built using a main-board and its hardware components as a 'hard' monolithic building block; this formed the base unit on which the system hardware and software stack design build upon. This hard deployment and management border on compute, memory, network and storage resources is either fixed or quite limited in expandability during design time and in practice remains so throughout machine lifetime as subsystem upgrades are seldomely employed. The impact of this rigidity has well known ramifications in terms of lower system resource utilization, costly upgrade cycles and degraded energy proportionality. In the dReDBox project we take on the challenge of breaking the server boundaries through materialization of the concept of disaggregation. The basic idea of the dReDBox architecture is to use a core of high-speed, low-latency opto-electronic fabric that will bring physically distant components more closely in terms of latency and bandwidth. We envision a powerful software-defined control plane that will match the flexibility of the system to the resource needs of the applications (or VMs) running in the system. Together the hardware, interconnect, and software architectures will enable the creation of a modular, vertically-integrated system that will form a datacenter-in-a-box
Temperature and wavelength drift tolerant WDM transmission and routing in on-chip silicon photonic interconnects
We demonstrate a temperature and wavelength shift resilient silicon transmission and routing interconnect system suitable for multi-socket interconnects, utilizing a dual-strategy CLIPP feedback circuitry that safeguards the operating point of the constituent photonic building blocks along the entire on-chip transmission-multiplexing-routing chain. The control circuit leverages a novel control power-independent and calibration-free locking strategy that exploits the 2nd derivative of ring resonator modulators (RMs) transfer function to lock them close to the point of minimum transmission penalty. The system performance was evaluated on an integrated Silicon Photonics 2-socket demonstrator, enforcing control over a chain of RM-MUX-AWGR resonant structures and stressed against thermal and wavelength shift perturbations. The thermal and wavelength stress tests ranged from 27 degrees C to 36 degrees C and 1309.90 nm to 1310.85 nm and revealed average eye diagrams Q-factor values of 5.8 and 5.9 respectively, validating the system robustness to unstable environments and fabrication variations. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreemen
Probing the atmosphere of HD189733b with the Na I and K I lines
High spectral resolution transmission spectroscopy is a powerful tool to
characterize exoplanet atmospheres. Especially for hot Jupiters, this technique
is highly relevant, due to their high altitude absorption e.g. from resonant
sodium (Na I) and potassium (K I) lines. We resolve the atmospheric K
I-absorption on HD189733b with the aim to compare the resolved K I -line and
previously obtained high resolution Na I-D-line observations with synthetic
transmission spectra. The line profiles suggest atmospheric processes leading
to a line broadening of the order of 10 km/s for the Na I-D-lines, and only a
few km/s for the K I-line. The investigation hints that either the atmosphere
of HD189733b lacks a significant amount of K I or the alkali lines probe
different atmospheric regions with different temperature, which could explain
the differences we see in the resolved absorption lines
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