Semiconductor Optical Amplifiers (SOAs) are vital elements in future optical networks whether as amplifying elements to boost the optical signal. In addition to be used as amplifiers, SOAs can also be used as switching elements operating either as ON-OFF switches or as wavelength converters for wavelength routing switching. Additionally, their performance is compatible with nowadays and future transmission rates of 10, 40 and 80Gb/s and beyond. Hence, the impact they will have in all future optical networks is paramount and it is unimaginable that there will be any future optical network without them. With this knowledge a look into future optical networks reviles that the modulation format will be influenced by this development due to the physical impacts of the SOAs on the signal transmission. Hence the modulation format needs to be investigated. Here we pursue the investigation of different optical formats by means of optical simulation and do a comparison of the modulation formats with respect to the performance selected for this paper.
By eliminating optical synchronizers in optical IP routers, more complex scheduling algorithms are needed to schedule asynchronous packets. This will result in voids at the switch output thus reducing switch throughput. A novel scheduling algorithm had previously been proposed to reduce these excess losses by filling voids caused by asynchronous and variable length operation. Non-degenerate (i.e. non-uniform) buffer depth has previously been shown to improve the packet loss performance especially under bursty traffic. We investigated the performance of the void filling algorithm by combining non-degenerate and degenerate (uniform) fiber delay lines. Performance is studied for different threshold levels, i.e. the number of uniform delay lines in the feedback delay line before introducing the non-degenerate delay lines. The packet loss performance for combined non-degenerate and degenerate delay lines with void filling algorithm is presented for an optical router with a feedback delay lines buffer under self similar traffic. The recirculating delay lines buffer emulates a two-stage buffer where first stage buffers smaller packets whilst the second stage stores larger packets. This buffering mechanism is similar to SLOB (i.e. Switch With Large Optical Buffer).
A novel architecture is proposed for future multi-terabit IP (internet protocol) routers, employing multiple cascaded stages of optical switching and buffering. WDM is used within the node to facilitate its operation. External synchronization is not required, and a void-filling algorithm is used to simplify hardware requirements. Packet priorities are not implemented in the current version of the switch, and the issue of header table lookup is not considered. Performance with respect to packet loss is studied by simulation, demonstrating that this multi-stage concept results in substantial hardware reduction.
Optical packet switches offer high speed, fine granularity, flexibility and transparency to data rate and format. There has been much work on the design of optical packet switches each having distinct advantages and disadvantages. Nevertheless, their common limitation is optical splitting loss, which is compensated by optical amplifiers, further degrading performance because of the induced amplifier noise. Hence, it is desirable to design an optical packet switch with a low optical splitting loss. This study has focused on the ALCATEL broadcast-and-select switch, which has significant optical splitting and combining losses for large switches. Arrayed-waveguide gratings (AWG) have been chosen to reduce the switch splitting loss replacing the demultiplexers and Semiconductor Optical Amplifier gates (SOA gates) in the ALCATEL switch. The switch still has the same functionality with an AWG which can be used as an interconnect, and has been demonstrated with insignificant crosstalk of approximately 30 dB. In this paper, three optical packet switches using AWGs are studied; the broadcast-and-select switch, the feed-forward delay switch and the feed-back delay switch. An additional novel feature is their use of wavelength division multiplexed inputs and outputs. Here, their optical performance is investigated with respect to bit error rate and power penalty, and compared with the ALCATEL broadcast-and-select switch using SOA gates.