The Research On Ultra-large Capacity Fiber-optic Transmission Experiments And Key Technologies For OFDM

The fiber-optic transmissions have increased in capacity by more than one thousand times per ten years sice the past forty years. However, it can not meet the demand on the explosive growth of internet and broadband wireless mobile communication. In order to conquer the scientific issues of low spectral efficiency, serious fiber nonliearity and dispersion in the last generation fiber-optic communication, in this dissertation ultra-large capacity fiber-optic transmission system with orthogonal frequency division multiplexing (OFDM) as the basic method of innovation is proposed. OFDM is a technology that converts higher rate serial data stream into multiple orthogonal data streams with lower rate relatively. Due to its intrinsic advantanges such as high spectral efficiency, robust tolerance against fiber dispersion, robust anti-jamming, low computation complexity and so on, OFDM has been widely researched and used in ultra-large capacity fiber-optic transmission system as a novel and hot technology.To address the above scientific issues, this dissertation carries out systematic and in-depth study. It researches on the application of optical OFDM technology for the related fields in fiber-optic communications, e.g.100-Gb/s low cost direct detection scheme, experiment of1-Tb/s coherent optical signal transmitted over more than10,000km, experiment of wavelength conversion of high order modulation formats using silicon waveguide wavelength converter, experiment of joint compensation of transmitter IQ imbalance and laser phase noise using intensity pilots in CO-OFDM system, experiment of polarization insensitivity pump phase noise cancelled ultra-large capacity wavelength conversion and experiment of C/L-band ultra-large capacity coherent optical signal transmission. The main works and research achievements of this dissertation are summarized as follows:Firstly, to address the hot issue that using current100G coherent detection system in metropolitan area networks leads to high cost and single electrical device with40GHz bandwidth at the receiver could not detect the100-Gb/s optical signal simultaneously, a novel guard-band-shared single-PD direct detection optical OFDM (GBS-DDO-OFDM) scheme is proposed in this dissertation to receive100-Gb/s signal simultaneously. The issue of receiving100-Gb/s signal by one40GHz PD at the same time in non-coherent system is sloved through experiment. The experimental results indicate that the transmission distance over880km SSMF is achieved, the numbers of PDs is decreased from8in current commercial coherent system to1in this scheme, and the numbers of analog-to-digital converter (ADC) is reduced from4to1.Secondly, to address the issue that Kerr nonlinear effect limits the ultra-long-haul fiber transmission reach and the present situation that the reported longest1Tb/s-class transmission is1.15-Tb/s signal over10,000km SSMF in2011accomplished by American NEC lab. A CO-OFDM scheme combined with a kind of characteristic LDPC code and DFT-S technology is proposed in this dissertation. The experimental results show that this scheme can effectively reduce the Kerr nonlinear effect influence in LDPC coded1.031-Tb/s DFT-S OFDM8-PSK signal transmission system. Compared with NEC lab’ work, the transmission distance over SSMF is enhanced from10,000km to12,160km in this scheme. Also, the receiver sensitivity is improved from BER level of0.02(20%FEC limit) to0.07.Thirdly, currently silicon device is becoming a hot research direction in international due to low cost low power consumption, high nonlinear effects and easy to be integrated. To address the present situation that the spectral efficiency of ultra-large capacity transmission is hard to further improve and the highest modulation format used in silicon-based wavelength conversion is16-QAM, a novel wavelength conversion scheme based on silicon waveguide is proposed to slove the issue of OFDM128-QAM signal conversion. The observed constellations in the experiment reveal the impressive on-chip OFDM128-QAM wavelength conversion performance with low OSNR penalty.Fourthly, to address the ubiquitous issue of IQ imbalance in ultra-large capacity CO-OFDM tramsmission system, a frequency domain second moment estimation algorithm (F-SOME) is proposed for the first time in this dissertation. The designed intensity polits can jointly compensate the transmitter IQ imbalance and laser phase noise. The experimental results of17-Gb/s DSB OFDM4-QAM signal indicate that1.2dB receiver sensitivity is improved after F-SOME algorithm compensation.Fifthly, to address the issue that phase noise of input signal and pumps transfers to converted ilders and severely affects the system performance, a polarization insensitivity pump phase noise callanced coherent dual-pump scheme is proposed in this dissertation. The experimental results of92.9-Gb/s PDM-OFDM32-QAM and557-Gb/s PDM-OFDM8-QAM signal reveal that the OSNR penalties of the converted idlers are all below1dB, among which the557-Gb/s is the highest data rate in this kind of scheme.Sixthly, to address the issues of inter symbol interference (ISI), inter carrier interference (ICI) and degradation of signal electrical signal-to-noise ratio (ESNR), which is caused by low sibe lobe suppression ratio (SLSR) of conventional OFDM at transmitter in multi-band ultra-large capacity fiber-optic transmsisson systems. A novel digital pulse shaping technology called offset QAM OFDM (OFDM/OQAM) is proposed in this dissertation, which can basically slove the issue of large ISI and ICI. The experimental results indicate that compared with conventional OFDM, the power spectrum density (PSD) of OFDM/OQAM is improved from15dB to35dB and the SNR is also enhanced from17.37dB to18.56dB in multi-band DDO-OFDM system.Moreover, the author of this dissertation together with other team colleagues designed and performed the experiment of C-and L-band DFT-S PDM-OFDM128-QAM modulated100.3-Tb/s (375×267.27-Gb/s) signal transmission over80-km SSMF. This achievement was picked up by academicians of the Chinese Academy of Sciences and Chinese Academy of Engineering as top10China’s news about progress in science and technology in2014(in the8th palce).