The Theoretical Research And Experimental Implementation Of All-optical OFDM System Based On Time Lenses

Orthogonal frequency division multiplexing (OFDM) has drawn significant research interesting owing to its large tolerance of chromatic dispersion, polarization mode dispersion (PMD) and high spectrum efficiency. Until now, there are two methods to implement optical OFDM system. One is coherent optical OFDM (CO-OFDM) system, and the other is all-optical OFDM (OOFDM) system. CO-OFDM depends on electronic processing circuits and is mainly constrained in processing speed of electronic chip. Then people introduce all-optical OFDM system. Time lens based all-optical OFDM system is detailedly discussed in this thesis considering feasibility at technologies and costs.The thesis starts from the space time dualities, replaces the diffraction by dispersion and spatial chirp of a conventional lens by a temporal chirp introduced by a phase modulator, which is called time lens. Based on these, the principle of imaging of a temporal signal is obtained, namely time domain continuous Fourier transform/Inverse Fourier transform (FT/IFT). Then the concrete devices are found to realize the functions of time lens and dispersive medium. The temporal imaging device is made up of a dispersion element, phase modulator and another dispersion element, which is called all-optical time domain continuous FT/IFT device. Then FT/IFT devices are introduced into OOFDM system: at the transmitter, groups of initial optical pulses are transformed into OOFDM symbols by a IFT device; after transmission, a FT device rebuilds the optical pulses.At last, time lens-based OOFDM system is experimentally demonstrated. Experiment results show that 20 Gbit/s signals successfully transmit through 200-km G.655 fibers without any dispersion compensation. Properly dealing with the relationships among different parameters, such as the time width of initial optical pulses, the time window of FT/IFT device, and the dispersion coefficient, this OOFDM system could transmit at higher bit rate over longer distance. And it could overcome chromatic dispersion, PMD, time jitter and higher order dispersion in high speed transmission system.