| Orthogonal Frequency Division Multiplexing (OFDM) as an advanced multi-carriermodulation technique, with advantages of high spectral efficiency and large dispersiontolerance, has generated lots of interest in the field of optical communications most recently.In not-all-optical OFDM system, the transmission rate is limited by electronic bottleneck.With all-optical OFDM technology, the signal processing operations are achieved in opticaldomain, which can effectively alleviate the dependence of digital signal processing rate intransmitter and receiver with a good prospect.This thesis takes an investigation on the all-optical signal processing device accordingto the basic theory of Optical Inverse Discrete Fourier Transform/Optical Discrete FourierTransform (OIDFT/ODFT). Several results have been carried out as follows:(1) The structure of OIDFT/ODFT device and corresponding functions of eachcomponent are analyzed. The nature of optical orthogonal principle is firstly revealedcombined with the signal feature in time domain and frequency domain.(2) A novel OIDFT/ODFT device based on cascaded polarization interference isproposed by derivation to the transfer function of ODFT device. The detailed designationand functional verification are also described. The frequency response characteristic of thisdevice is studied and specific analysis to the simulation results is introduced.(3) All-optical OFDM systems based on the proposed OIDFT/ODFT device areconducted. In4×25Gbit/s transmission using Non-return-zero (NRZ) format, the receiversensitivity achieves about-21.3dBm and-19.2dBm for back-to-back and after300km opticalfiber link respectively at a bit error rate (BER) of10-9. The main reasons for the performanceat different transmission conditions are discussed. Simulation results show that optimizingthe transmission characteristics of ODFT device and optical sampling gates, as well as usingthe appropriate signal formats of each subchannel will improve the system demultiplexingperformance. |
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