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