Publications
http://41.89.164.27:8080/xmlui/handle/123456789/263
2024-03-28T08:45:13ZPerformance of 1550 nm VCSEL at 10 Gb/s in G.655 and G.652 SSMF
http://41.89.164.27:8080/xmlui/handle/123456789/996
Performance of 1550 nm VCSEL at 10 Gb/s in G.655 and G.652 SSMF
Cherutoi, Henry Chepkoiwo
Vertical cavity surface emitting lasers (VCSELs) are now major optical sources in optical communication and
technology. The VCSEL-based transmission systems satisfy the next generation optical fibre access networks requirements such as
low output power, low threshold currents, no optical amplification and use of single fibre for signal transmission. High speed and
long wavelength 1550 nm VCSEL are attractive candidates for use in short distance transmission system due to its cost effectiveness
and low drive currents. The performance of VCSEL, especially with respect to the low output power characteristics, has made
significant progress. However, dispersion and attenuation is a major hurdle to VCSELs transmission at bit rate of 10 Gb/s and above.
In this study, we experimentally and theoretically evaluate the capability of 1550 nm VCSEL to operate upto 10 Gb/s on G.655 and
G.652 fibres. We present VCSEL characterization and BER performance as a function of received power. A 1550 nm VCSEL was
directly modulated with 10 Gb/s NRZ PRBS 27
-1 and transmitted over 25 km ITU. T G.652 and ITU. T G.655 fibres. Error free
transmission (with bit error rate, BER, of 10-9) over 25 km G.655 single mode fibre (SMF) has been demonstrated. The Q factor was
used theoretically to quantify the performance of the VCSEL. The Q factor increased with the increase in the output power at the
receiver. High Q factor values of 6 and above were achieved when 1550 nm VCSEL was transmitted over G.655 fibre. These results
show the feasibility of long-wavelength VCSELs in the deployment of enhanced optical access networks.
2020-01-01T00:00:00ZThe Role of Shell Model in Determining Pairing Interaction in Nuclei
http://41.89.164.27:8080/xmlui/handle/123456789/995
The Role of Shell Model in Determining Pairing Interaction in Nuclei
Cherop, Hezekiah; Muguro, Kennedy; Kapil, Khanna
The role of the shell model in pairing interaction in nuclei is investigated by calculating the pairing energies
of O–O (odd–odd), O–E (odd–even), E–E (even–even) and E–O (even–odd) isotopes of four elements namely; 15P, 25Mn,
40Zr and 60Nd. The pairing energies were computed using the values of binding energy (B) obtained from AME2016
atomic mass evaluation. The graphs of the pairing energies against the mass numbers revealed an increase of the pairing
energies with the occurrence of periodic humps adjacent to the neutron magic numbers. The rise in the pairing energies
is attributed to the bound states of heavy nuclei arising from the neutron-neutron pairs in the shell structures beyond
the Fermi-surface, while in the light and intermediate nuclei, the rise in the pairing energies is due to the increase in the
number of nucleons occupying the surface region. These neutron-neutron pairs formed beyond the Fermi-surface of
nuclei of heavy elements have greater pairing energies, which contribute to greater binding energies associated with the
heavy elements found in the neutron stars. It is concluded that the shell model can predict the existence of isotopes of
heavy elements in the neutron stars and the criterion to ascertain their existence lies on the pairing energies. Calculations
show that the isotopes with highest peaks among the heavy elements can predict the most abundant isotopes of the heavy
elements in the neutron stars, for instance, 90Zr, 91Zr, 142Nd, 145Nd, 146Nd, 148Nd and 150Nd nuclei.
2019-01-01T00:00:00ZAb-initio Simulations ofCopper Oxide Nanowires and Clusters on TiO2(101)Anatase Surface
http://41.89.164.27:8080/xmlui/handle/123456789/686
Ab-initio Simulations ofCopper Oxide Nanowires and Clusters on TiO2(101)Anatase Surface
Meng'wa, Victor
Copper oxides deposited at titania surfaces have a beneficial effect on the photocatalytic activity of TiO2, but their role is not fully understood. In this work, possible nanostructures of copper oxide on TiO2 (101) have been investigated by simulations based on density functional theory. Various stoichiometries, from Cu2O to CuO, and morphologies, from clusters to nanowires, have been considered. Nanowire structures were consistently more stable than isolated clusters. In these structures, a Cu2O stoichiometry was found to be thermodynamically more stable than CuO at room conditions, in contrast to what happens in bulk copper. Occupied Cu 3d and O 2p states extend well into the band gap of titania, whereas the nature of the lowest-lying empty states depend on the stoichiometry: for Cu2O they consist mostly of Ti 3d orbitals, while in CuO unoccupied Cu 3d orbital ∼0.8 eV above the Fermi level are present. Thus, both oxides reduce the band gap of the system with respect to pure titania, but only Cu2O should be effective in separating photogenerated electrons and holes. These results provide insight into the role of copper oxides in the photocatalytic process.
2017-01-01T00:00:00Z