The Application Research Of Optical OFDM Technology In Short-reach And Long-haul Optical Fiber Communication Systems

Due to its many established merits such as high spectral efficiency(SE), strong tolerance to chromatic dispersion(CD) and polarization mode dispersion(PMD), and excellent scalability to higher level modulation formats, optical orthogonal frequency division multiplexing(OOFDM) has attracted considerable attentions in optical fiber communication domain. Furthermore, OOFDM is prone to be combined with the current optical fiber communication technologies such as polarization division multiplexing(PDM) and wavelength division multiplexing(WDM). Therefore, in pace with the rapid advances in digital signal processing(DSP) technology, OOFDM has the great appllication potentials in short-reach and long-haul fiber communication systems.This dissertation focuses on the analyses and investigations of OOFDM applications in low-cost mutil-mode fiber(MMF) transmission systems in data centers, self-seeded reflective semiconductor optical amplifier(RSOA)-based passive optical network(PON) systems, and high-speed long-haul single mode fiber(SMF) communication systems in backbone optical transmissions. The corresponding designs and solutions for several key issues encountered by OOFDM when it is applied in the above-mentioned optical communication systems are proposed, experimentally demonstrated, and analyzed by using computer simulations in this dissertation. The mainly innovative work contents are summarized as follows:1. Dual-band intensity modulation and direct detection OOFDM(IMDD-OOFDM) technology is proposed to upgrade the transmission capacities of directly modulated vertical cavity surface emitting laser(DM-VCSEL)-based MMF systems for optical interconnects in data centers. By making use of uncooled and free-running VCSELs with 3dB modulation bandwidths as low as 2.2GHz,the aggregated 16.375Gb/s transmissions of real-time dual-band OOFDM signals are experimentally achieved over 200 m OM2 MMFs. Furthermore, the transmission capacity robustness of DM-VCSEL-based dual-band IMDD-OOFDM systems is also experimentally investigated in detail.2. A novel dual-RSOA-based self-seeding architecture is proposed to reduce the optical signals’ relative intensity noises(RINs) and residual intensity modulation crosstalks in conventional self-seed RSOA-based PON systems. On this basis, by making use of two low-cost RSOAs with 3dB modulation bandwidths as low as 1GHz and the developed real-time OFDM transmitter, the first self-seeded RSOA-based real-time OOFDM transmitter is designed, and the experimental investigations are also undertaken of its various dynamic performance characteristics. Then, 10Gb/s over 25 km IMDD-OOFDM systems are experimentally demonstrated by using self-seeded RSOAs. The system optical power penalty is as low as 0.6dB.3. By making use of the 10Gb/s@25km IMDD-OOFDM system based on dual-RSOA-based self-seeding, the detailed experimental explorations are conducted of the accumulated intra-cavity dispersion impacts on the performances of self-seeded RSOA-based PON systems. The experimental results have shown that the intra-cavity dispersion within the fiber cavity can give rise to the following influences: 1) considerably broadening the output optical spectra; 2) increasing the RINs of output optical signals from self-seeding fiber cavities; 3) causing the increases of system optical power penalties. Therefore, the intra-cavity dispersion is identified to be the important physical mechanism limiting the system performances of IMDD-OOFDM PONs based on self-seeded RSOAs.4. A novel constant envelope coherent OOFDM(CE-CO-OFDM) system is proposed to significantly decrease the peak-to-average power ratios(PAPRs) of the launch optical signals. Thus, it can effectively improve the fiber nonlinear tolerance for CO-OFDM when it is applied in long-haul optical fiber communication systems. The simulation results have illustrated that, in comparison with the conventional CO-OFDM system, the maximum lauch powers of the CE-CO-OFDM system can be considerably improved in the standard SMF(SSMF) links with various dispersion managements.5. A joint method based on DSP and RF pilot-tone is proposed to compensate for the fiber nonlinear phase noises when CO-OFDM is utilized to upgrade the current WDM systems employing the none-return-to-zero on-off key(NRZ-OOK) modulation technology. Simulation results have shown that the proposed method can effectively compensate for the nonlinear impairments caused by the intra-channel self-phase modulation(SPM) effect and the cross-phase modulation(XPM) effect originating from neighboring NRZ-OOK channels. Moreover, the impacts of fiber nonlinear effects on in-band crosstalk-induced OSNR penalties are investigated in 112Gb/s PDM-CO-OFDM systems. This study provides a valuable reference for the system OSNR budgets when CO-OFDM systems operating at the nonlinear transmission regimes are utilized in 100 G all optical networks.6. A conventional dual-arm Mach-Zehnder modulator(MZM)-based optical comb generator is proposed to realize the high-speed mutil-band CO-OFDM transmissions. By using of this kind of optical comb generator, 1Tb/s CO-OFDM systems with 16 PDM OFDM bands are verified in computer simulations and the corresponding transmission performances are analyzed. Then, the feasibility of using dual-arm MZM-based optical comb generator is validated to realize the high-speed broadband CO-OFDM transmission. Moreover, the requirements on the overlap size in OFDM receivers incorporating overlap frequency domain equalization(OFDE) for reduced cyclic prefix(CP) CO-OFDM systems are analyzed. The impacts of overlap size on system transmission performances are experimentally investigated. Then, By making use of the reasonable designs of overlap size, 80.4Gb/s CO-OFDM transmissions with reduced CP overheads are experimentally achieved over 5440 km SSMF links without online dispersion compensations.