Contents 1. INTRODUCTION
Continues increase of data traffic due to emerging new and advanced multi-media services - like video streaming, HD TV, 3-dim TV, cloud computing, real time gaming - calls for ongoing improvement and update of optical communication networks. Thus WDM technologies utilizing advanced and spectrally efficient multilevel modulation formats (e.g. Pol-D(Q)PSK, QAM, OFDM) in combination with coherent detection schemes currently attract much attention regarding the development of flexible and economic high capacity optical transmission systems. These techniques offer more bits/symbol to be transmitted, i.e. higher overall bitrates become achievable without a commensurate increase in signal bandwidth of each single active sub-element. As a consequence, increasing component complexity - and thus overall footprint - has to be considered. Obviously, the fabrication of compact transmitter, receiver and transceiver devices intended for volume deployment is a challenging task for device manufacturers. In particular, to provide high performance components while simultaneously enabling economic device fabrication across all given specifications is a big challenge. Different specifications have to be met independently, e.g. on e/o bandwidth, driving voltage, optical insertion loss, power consumption, reproducibility, reliability, device yield, and integration.
