Constant envelope modulation formats for optical communications

SummaryNowadays every tele ommuni ation network ba kbone and all metropolitan (MAN)and lo al (LAN) area networks exploit opti al ommuni ation te hniques. Trans-mission implements usually dire t dete ted intensity modulation (IMDD).One of the advantages of opti al bers is their low attenuation value: howeversignals need regeneration every 80  100 km. As far as ampliers are on erned,EDFA (Erbium Doped Fiber Amplier) te hnology is the most widely used. Anotheroption are SOAs (Semi ondu tor Opti al Amplier): these have a smaller size, lowpower onsumption and ompetitive ost. Anyway, EDFAs are preferred be auseSOAs are not ompatible with intensity modulations, sin e their gain is not linear.TOSCA (Transmission of Opti al Signals exploiting Competitive Ampli ationte hniques) is the proje t on whi h Polite ni o di Torino, S uola Superiore Sant'An-na di Pisa and Università Tor Vergata di Roma have worked two years long: theaim of this proje t is to study and to experiment new WDM (Wavelength DivisionMultiplexing) transmission systems based on SOA te hnology.In order to redu e unwanted ee ts due to SOA nonlinearities, the suggestedsolution is to employ CE (Constant Envelope) modulation formats. In parti u-lar, transmission experiments have been realized using three dierent CE formats:CPFSK (Continuous Phase Frequen y Shift Keying), POLSK (Polarization ShiftKeying) and DPSK (Dierential Phase Shift Keying).This thesis is about the analysis of TX and RX prototypes built in the PhotonLablaboratory for these formats and the evaluation of their performan e.To evaluate the performan e for dierent OSNR (Opti al SignaltoNoise Ra-tio) values we need to generate variable amounts of ASE (Amplied SpontaneousEmission) noise. To do this the noise loading te hnique has been implemented: itrequires an EDFA hain with no input signal. In order to hange the signal andnoise levels, a pair of variable opti al attenuators has been employed.Field trial measurements have been arried on both in ba ktoba k and withpropagation to evaluate dispersion ee ts. It means that TX and RX have been onne ted with some ber meters (in the rst ase) or with tens of kilometers (inthe se ond one). The employed opti al ber is SMF (Single Mode Fiber) grantedby FastWeb operator in Turin. XVII