Ant colony optimisation-based algorithms for optical burst switching networks

This research developed two novel distributed algorithms inspired by Ant Colony Optimisation (ACO) for a solution to the problem of dynamic Routing and Wavelength Assignment (RWA) with wavelength continuity constraint in Optical Burst Switching (OBS) networks utilising both the traditional International Telecommunication Union (ITU) Fixed Grid Wavelength Division Multiplexing (WDM) and Flexible Spectrum scenarios. The growing demand for more bandwidth in optical networks require more efficient utilisation of available optical resources. OBS is a promising optical switching technique for the improved utilisation of optical network resources over the current optical circuit switching technique. The development of newer technologies has introduced higher rate transmissions and various modulation formats, however, introducing these technologies into the traditional ITU Fixed Grid does not efficiently utilise the available bandwidth. Flexible Spectrum is a promising approach offering a solution to the problem of improving bandwidth utilisation, which comes with a potential cost. Transmissions have the potential for impairment with respect to the increased traffic and lack of large channel spacing. Proposed routing algorithms should be aware of the linear and non-linear Physical Layer Impairments (PLIs) in order to operate closer to optimum performance. The OBS resource reservation protocol does not cater for the loss of transmissions, Burst Control Packets (BCPs) included, due to physical layer impairments. The protocol was adapted for use in Flexible Spectrum. Investigation of the use of a route and wavelength combination, from source to destination node pair, for the RWA process was proposed for ACO-based approaches to enforce the establishment and use of complete paths for greedy exploitation in Flexible Spectrum was conducted. The routing tuple for the RWA process is the tight coupling of a route and wavelength in combination intended to promote the greedy exploitation of successful paths for transmission requests. The application of the routing tuples differs from traditional ACO-based approaches and prompted the investigation of new pheromone calculation equations. The two novel proposed approaches were tested and experiments conducted comparing with and against existing algorithms (a simple greedy and an ACO-based algorithm) in a traditional ITU Fixed Grid and Flexible Spectrum scenario on three different network topologies. The proposed Flexible Spectrum Ant Colony (FSAC) approach had a markably improved performance over the existing algorithms in the ITU Fixed Grid WDM and Flexible Spectrum scenarios, while Upper Confidence Bound Routing and Wavelength Assignment (UCBRWA) algorithm was able to perform well in the traditional ITU Fixed Grid WDM scenario, but underperformed in the Flexible Spectrum scenario. The results show that the distributed ACO-based FSAC algorithm significantly improved the burst transmission success probability, providing a good solution in the Flexible Spectrum network environment undergoing transmission impairments

Laser photofragment spectroscopy of diatomic molecular ions

High resolution (< 0.005 cm−1) electronic spectra of the diatomic molecular ions 70GeH+ and 74GeH+ have been recorded using a fast ion beam irradiated by a cw tunable dye laser. Over 150 transitions between the ground X1∑ + state and near-threshold levels of electronic states correlating to the lowest dissociation asymptotes Ge+(2P3/2) + H(2S) and Ge+(2P1/2) + H(2S) were observed in the range 16500 cm−1 to 18500 cm−1. The majority of the lines arise from a 1π-1∑ transition, where the predissociated excited state levels lie between the fine structure dissociation limits (Feshbach Resonances). The lifetimes of the rovibrational levels are found to increase, then decrease, with increasing rotational quantum number. Evidence for triplet (multichannel) mixing is revealed through the observation of additional lines and proton nuclear hyperfine splittings. Experimental results are compared with predictions of the vibrational and rotational energy levels obtained from a numerical solution of the Schrodinger equation. Least squares fitting yields molecular constants for the 1∑and the 1π states. A new apparatus used to create jet-cold molecular ions in a fast ion beam is detailed. Preliminary results have been obtained for the b4∑− g ← a4πu transition of O+ 2 which allow a rotational temperature for the source to be calculated

Demonstration of 10.7-Gb/s transmission in 50-km PON with uncooled free-running 1550-nm VCSEL

First-known demonstration of an uncooled, free-running 1550 nm VCSEL at 10.7 Gb/s over 50 km PON uplink with 35 km SMF and 15 km inverse dispersion fiber, achieving 24 dB margin for 10−9 BER