The bypass queue in fast packet switching

The telecommunications networks of the future are likely to be packet switched networks consisting of wide bandwidth optical fiber transmission media, and large, highly parallel, self-routing switches. Recent considerations of switch architectures have focused on internally nonblocking networks with packet buffering at the switch outputs. These have optimal throughput and delay performance. The author considers a switch architecture consisting of parallel plans of low-speed internally blocking switch networks, in conjunction with input and output buffering. This architecture is desirable from the viewpoint of modularity and hardware cost, especially for large switches. Although this architecture is suboptimal, the throughput shortfall may be overcome by adding extra switch planes. A form of input queuing called bypass queuing can improve the throughput of the switch and thereby reduce the number of switch planes required. An input port controller is described which distributes packets to all switch planes according to the bypass policy, while preserving packet order for virtual circuits. Some simulation results for switch throughput are presented     

Crystal growth of high doped Nd:YAG

For years, neodymium-doped yttrium aluminum Garnet (Nd:YAG) crystals of dopant levels of up to 1.1% concentration have been produced for military, industrial, medical, and scientific applications. More and more however, a need exists for crystals doped with higher neodymium concentrations. Nd:YAG crystals with dopant levels of 1.3% and 1.4% can produce greater efficiency in Q-switch operations, thus smaller crystals can be used to achieve the desired output power. Additionally, smaller crystals are easier to cool and therefore deleterious thermal effects can be minimized. It is difficult to incorporate the large diameter Nd³⁺ ion into the relatively small Y³⁺ sites of the YAG crystal lattice, which limits the achievable dopant concentration. In this paper, we will present the growth of highly doped Nd:YAG crystals with excellent optical quality achieved by modifying the growth parameters. Spectroscopy results and laser results obtained from our 1.3% and 1.4% Nd:YAG crystals will also be presented.