Study On A Receiver-ended Optical Signal Pre-processing Technique Based On Fractional Fourier Transform In Optical Communications

Fourier transform (FT) plays an indispensible role in signal processing and spectralanalysis owing to its practical utility. Nevertheless, it is widely recognized that the scope ofsignal analyzing has enlarged its extent from stationary signals to non-stationary signals asscientific research keeps proceeding. Acting as a global transform, what FT can yield is onlythe whole spectrum. In contrast, FT fails to describe part time-frequency information, posinga major limit on FT when applied to the field of non-stationary signal analyzing. FractionalFourier Transform (FRFT), normally interpreted as a generalization of FT, facilitates theanalyzing of non-stationary signals and thus has drawn significant research interests since itsemergence. The last decades witnessed a variety of encouraging developments in the field ofFRFT. So far, FRFT has been widely applied to radar communication, image encryption aswell as noise suppression, diffraction theory and chirped signal processing.In the first part of this thesis, a brief introduction to the definition and various propertiesof FRFT is given, followed by its application in different areas. During the next chapters, theoptical implementations of FRFT in the spatial and time domain are derived respectivelybased upon rewriting the definition equation of FRFT and time-space duality. Additionally, anovel receiving end optical signal processing scheme is proposed based on the optical timedomain FRFT module. Simulations are conducted by the commonly used software VPI(VPItransmissionMaker), mainly focusing on the different influences of FRFT onconvergence of signal. In the detailed simulation, the received signals are pre-chirped,followed by the proposed optical time domain FRFT, finally an optimal filtering is extertedto the signal to minimize the in-band white noise.Results show that IM-DD (Intensity Modulation Direct Detection) systems operating at40Gbit/s and100Gbit/s benefit from the proposed FRFT module with the corresponding biterror rate (BER) being reduced by several orders of magnitude.