Reseach Of Optical Orthogonal Frequency Division Multiplexing System Using Polyphase Filter Bank

Coherent optical OFDM(CO-OFDM) provides a viable solution to high-capacity and long-haul transmissions. However CO-OFDM tends to have a large overhead leading to a lower spectral efficiency, mainly caused by the cyclic prefix to tolerate the inter-symbol interference(ISI). Therefore, reduced guard-band interval OFDM(RGI-OFDM) has been proposed. The conventional approach is to lower the excessive overhead of CP by inserting an overlap-save frequency domain equalizer(OFDE) in the receiver. However, the complexity of the OFDE algorithm is too large to implement in reality.We present a novelty SBD-OFDM approach using polyphase filter-bank, which can effectively balance spectral efficiency and system complexity. Since the CP overhead is proportional to the signal bandwidth, by splitting the spectrum into M sub-bands, we can reduce the CP overhead by a factor of M. On the other hand, if the whole band is demultiplexed to M sub-bands, each one occupies only B/M and its corresponding CD delay spread is reduced by a factor of M. Thus, we always can find a value of M large enough to realize demodulation without CD compensation. Therefore, SBD-OFDM is an efficient transmission scheme. The research results are the following two aspects:The first one is the design of digital sub-band-demultiplexing scheme. It consists of three key steps, including analysis filter bank, sub-band processing and subsequent procesing. Using the so-called analyzer filter bank, received signal is splited an into M sub-band signals, which is fed by several brief sub-band processing. Then the last step simply stitches M spectra together to accomplish the conventional CO-OFDM receiver processing. The design of whole scheme includes the selection of filter bank, the judgment of subband number M, subband signal FFT window synchronization method and so on.The second one is the experimental demonstration of the SBD-OFDM approach. We conduct several experimental demonstrations including CO-OFDM, RGI-OFDM and SBD-OFDM systerms. By comparison, we have experimentally demonstrated an efficient RGI-OFDM transmission scheme using digital sub-band demultiplexing, which achieves the same performance but with a much lower overhead.