Research On Some Key Technologies Of Optical Orthogonal Frequency Division Multiplexing

Orthogonal frequency division multiplexing (OFDM) is a multi-carrier modulation technology. It converts high speed data into parallel low speed data streams, which are then modulated onto a series of orthogonal subcarriers. Optical OFDM(OOFDM) is a hot research topic in optical communication field with the introduction of OFDM. OOFDM benefits from the advantages of both RF OFDM and optical communication, and optical transmission network with high spectral efficiency and high capacity can be built using it. OOFDM also has strong channel capacity expansibility and transition to higher speed systems can be realized smoothly to make full use of the spectrum resources of fiber link. At present, OOFDM signals can be generated through electrical-optical modulation or all-optical modulation. In this paper, we made research on discrete Hartley Transform(DHT) based constant envelop electrical-optical modulation OOFDM and fiber delay interference based all-optical OFDM.In the DHT-CE-OOFDM design, we use DHT to generate real value baseband OFDM signal and CE modulation to reduce its high PAPR. It shows better performance than traditional OOFDM when transmitted in fiber. The CE method can provide more than7dB PAPR improvement and the PAPR of constant envelop signals is independent of DHT point, data format and PMI. It should be pointed out that PMI needs optimization since OSNR would be reduced with small PMI while the approximation condition would not be satisfied with large PMI in the demodulation. All-optical OFDM attracts attention because it can avoid electrical bottleneck of semiconductor devices in high speed communication systems. We studied the theory of optical FFT(OFFT) by using DI and built a8optical subcarrier OFDM simulation system to verify its performance. The results show that after0-60km fiber transmission, the subcarriers can be separated using OFFT and demodulated well.