Extending usability of old terrestrial fibre optic cables in Third-World Economic Zones

Communication Fibre Optic Cables (FOC) experience mechanical perturbations while in service thereby deforming their cylindrical shape and increasing birefringence. This leads to Polarization Mode Dispersion (PMD). This work investigated PMD fluctuations in cables that have been buried underground for more than 10 years in a semi-arid climatic region in Kenya. PMD was measured using EXFO-FTB5700 analyzer at hourly intervals in the target cables for 2,480 hours. PMD coefficient of 0.215 √⁄ was recorded. Outage margin () of 2.13 for the 10 Gbps system running an On-Off Keying Non-Return-to-Zero (OOK-NRZ) scheme (with 10ps receiver tolerance) was obtained. Similar analysis for the 100 Gbps system running a Dual Polarization Quadrature Phase-Shift Keying (DPQPSK) scheme (with 30 ps receiver tolerance), revealed an outage margin of 6.38. The availability of 99.29 % (corresponding to a downtime of 53.44 hours per year) revealed that, the cable under test could not sustain PMD limitations in a Dense Wavelength Division Multiplexing (DWDM) system that is deployed with a 10 Gbps transponder in a non-regenerated fibre span exceeding 450 km. 100 Gbps DWDM systems proved more resilient when using DP-QPSK than 10Gbps when using OOK-NRZ. The outage of 53.44 hours per year in a high capacity traffic system can translate to a substantial amount of losses in terms of credit notes to customers for not meeting the standard service level agreement of 99.999 % service availability. To overcome this limitation, it is recommended that 10 Gbps transponders that use OOK-NRZ channel modulation technique be replaced with 100 Gbps that uses DP QPSK technique to mitigate dispersion related outages in the links. This would also effectively provide a lot of idle capacity that can accelerate digitization of institutions and villages

Upper limits for undetected trace species in the stratosphere of Titan

In this paper we describe a first quantitative search for several molecules in Titan's stratosphere in Cassini CIRS infrared spectra. These are: ammonia (NH3), methanol (CH3OH), formaldehyde (H2CO), and acetonitrile (CH3CN), all of which are predicted by photochemical models but only the last of which observed, and not in the infrared. We find non-detections in all cases, but derive upper limits on the abundances from low-noise observations at 25{\deg}S and 75{\deg}N. Comparing these constraints to model predictions, we conclude that CIRS is highly unlikely to see NH3 or CH3OH emissions. However, CH3CN and H2CO are closer to CIRS detectability, and we suggest ways in which the sensitivity threshold may be lowered towards this goal.Comment: 11 pages plus 6 figure file

Impact of Temperature and Relative Humidity on PMD in Directly Buried Optical Fibre Cables in Semi-Arid and Tropical Highlands in Kenya

The telecommunication industry has implemented fibre deployment guidelines that reliably safeguard cable health during installation in the field. While installed fibre cables remain buried in the field, temperature and moisture in the locality subject them to mechanical expansions and corrosion. Directly buried fibre cables experience accelerated degradation that results from exposure to harsh environments. This increases pulse spreading and overlaps, with a mean time duration, known as Differential Group Delay (DGD), on the signal, as it propagates along the cable. DGD is stochastic; thus, Mean DGD is determined and presented as Polarization Mode Dispersion (PMD). This work undertook a real life assessment of how fluctuations in temperature and relative humidity influence PMD in directly buried fibre optical links, in a case study that focused on the fibre cable network owned by Liquid Telecom Kenya. The network spans across two key climatic ecosystems, namely, rift valley highlands and northern lowlands. The analysis revealed that fibre cables experience higher PMD in semi-arid areas by a factor of 2.6, compared to highland areas

HIGH-RESOLUTION SPECTROSCOPY OF NITROUS ACID (HONO) AND ITS DEUTERATED SPECIES (DONO) IN THE FAR- AND MID-INFRARED REGIONS

Author Institution: Laboratoire Interuniversitaire des Systemes Atmospheriques (LISA), CNRS and Universites Paris-7 et -12, Creteil, FranceNitrous acid (HONO) is an important source for OH radicals in tropospheric photochemistry.} Currently it is measured in the atmosphere using its ultraviolet absorption bands} but it has also been detected in the mid-infrared spectral region using a tuneable diode-laser.} In order to complete and extend previous laboratory work on the infrared fundamental bands of {\it trans}-HONO} and {\it cis}-HONO} and also of its deuterated species (DONO)} we have carried out a number of new spectroscopic studies, focusing on \begin{itemize} \item{the first high-resolution spectra of {\it trans-} and {\it cis-}HONO and -DONO in the far-infrared region (30--120 cm$^{-1}$),} \item{the first high-resolution spectra and analysis of the $\nu_1$ bands of {\it trans-} and {\it cis-}DONO around 2600 cm$^{-1}$,} \item{new high-resolution spectra and analysis of the Coriolis-interacting $\nu_5$ and $\nu_6$ bands of HONO around 600 cm$^{-1}$.}} \end{itemize} In this talk we will present the main results and some comparisons with previous studies

The ALMA-PILS survey: First detection of nitrous acid (HONO) in the interstellar medium

Nitrogen oxides are thought to play a significant role as a nitrogen reservoir and to potentially participate in the formation of more complex species. Until now, only NO, N2O, and HNO have been detected in the interstellar medium. We report the first interstellar detection of nitrous acid (HONO). Twelve lines were identified towards component B of the low-mass protostellar binary IRAS 16293–2422 with the Atacama Large Millimeter/submillimeter Array, at the position where NO and N2O have previously been seen. A local thermodynamic equilibrium model was used to derive the column density (∼9 × 1014 cm−2 in a 0 .″5 beam) and excitation temperature (∼100 K) of this molecule. HNO, NO2, NO+, and HNO3 were also searched for in the data, but not detected. We simulated the HONO formation using an updated version of the chemical code Nautilus and compared the results with the observations. The chemical model is able to reproduce satisfactorily the HONO, N2O, and NO2 abundances, but not the NO, HNO, and NH2OH abundances. This could be due to some thermal desorption mechanisms being destructive and therefore limiting the amount of HNO and NH2OH present in the gas phase. Other options are UV photodestruction of these species in ices or missing reactions potentially relevant at protostellar temperatures