中文摘要：

采用单个激光源，通过差分马赫-曾德尔（M—Z）外调制器产生8根等频率间隔为28GHz的光频梳，每根光频梳彼此相干并作为光子载波，经112Gb／s偏分复用（PDM）一正交相移键控（QPSK）信号调制后，波分复用后形成8路宽带的全光正交频分复用（OFDM）信号。接收端通过基于级联M—Z延时干涉仪（MZDI）的光学快速傅里叶变换（OFFT）实现全光OFDM信号的解复用。解复用后的每路信号经光采样后，采用与单载波PDM—QPSK系统中相同的数字相干解调进行数据恢复。提出的8×112Gb／s全光OFDM系统在背靠背情况下，误码率（BER）为10—3时，光信噪比（0sNR）较单载波112Gb／sPDM—QPSK系统多约9dB。8×112Gb／s全光OFDM信号经480km光纤传输后，OSNR损伤约1．6dB。仿真结果表明，全光OFDM系统的数字相干接收机可以较容易地实现对现有单载波系统扩容，并且不影响系统的传输性能。

英文摘要：

As the 100 Ghit/s Ethernet （100 GbE） has gradually become a commerdal reality,the next step of migration is toward 1 Tbit/s Ethernet transport. Coherent optical orthogonal frequency division multiplexing （CO-OFDM） has recently drawon much attention to improve system capacity and transmission distance over fiber for its superior performance in spectrum efficiency, robust chromatic dispersion （CD） tolerance, receiver sensitivity, and polarization mode diversity （PMD） resilience, which has also been considered as a promising candidate for long-haul transmissions. In conventional optical OFDM systems, analog-to-digital converter （AI）C） and digital-to-analog converter （DAC） are needed at transmitter and receiver, respectively. However, the radio frequency （RF） bandwidths and sampling rates of ADC and DAC are limited by current manufacturing. To overcome this problem,an 8 × 112 Gbit/s all-optical OFDM transmission system is proposed in this paper. A single laser source is utilized to generate fre-quency comb source as the sub-carriers of the proposed all-optical OFDM system with frequency spacing of 28 GHz by differential Mach-Zehnder external modulator. Each of 8 carriers of the comb source is encoded with 112 Gbit/s polarization division multiplexing quadrature phase shift keying （PDM-QPSK）. At the receiver,optical fast Fourier transform （FFT） is performed by cascaded Mach-Zehnder delay inter- ferometers （MZDIs） to de-multiplex the all-optical OFDM signal into 8 lower bit rate sub-carrier tributaries which can then be individually processed electronically. The back-to-back simulation results show that the optical signal-to-noise ratio （OSNR） penalty of 8 × 12 Gbit/s all-optical OFDM is about 9 dB compared with 112 Gbit/s single carrier system at bit error rate （BER） of 10-3 ,and its is available to update the current single carrier system using all-optical OFDM and common coherent optical receiver while without introducing signal impairment.