This chapter provides an overview of considerations for the development of semiconductor optical amplifiers SO" for the next generations of packet-switched optical networks. SO" devices are suitable candidates in order to realize highperformance optical gates due to their high extinction ratio and fast switching time. However such devices also introduce linear and nonlinear noise. The impact of SO" devices on several modulation formats via theoretical model, numerical simulation, and experimental validation is studied. Impairments introduced by SO"s are considered in order to derive some general network design rules.Keywords: Semiconductor optical amplifier, optical packet-switched network, coherent communications, network design rules
. IntroductionSince , coherent technology has paved the way toward high-capacity optical communications [ ]. Coherent systems allow transmitting information with multi-level modulation formats over both polarizations [polarization division multiplexing PΓM ] of light, which increases the spectral efficiency [bit/s/Hz b/s/Hz ] while relaxing the need for ultrahigh symbol rates to achieve data rates beyond Gb/s. Such technology is enabled by fast analogto-digital and digital-to-analog converters "ΓC and Γ"C , which, together with coherent receivers and robust digital signal processing ΓSP , allow for the generation and recovery of advanced modulation formats. PΓM-quadrature phase-shift keying QPSK and PΓM--quadrature amplitude modulation Q"M signaling at or Gbaud are currently used to develop and Gb/s transponders used in today's core networks. However, experimental In addition, data centers' global traffic presents a relentless growth, with % of such traffic flowing within data centers. The overall need of capacity together with the drop expected in coherent transponders' cost makes evident the expansion of coherent systems toward other network segments.Furthermore, the ever-emerging bandwidth-on-demand services in optical fiber networks induce distributed and bursty traffic profiles. Network flexibility and high efficiency are then required to handle these new traffic characteristics. Hybrid time/wavelength division multiplexing TΓM /WΓM systems could be the right trade-off between the high capacity provided by the WΓM virtual point-to-point links and the TΓM sub-wavelength switching granularity, allowing very efficient systems. Therefore, the WΓM optical packet-switched network was proposed to unite these benefits and reduce the power consumption compared to circuit-based networks [ ]. Ring nodes collect and aggregate the traffic from the access segment, into fixedduration optical packets and relay them to a WΓM synchronous optical packet-ring network.