Study On Novel Optical Modulation And Multiplexing Techniques

40Gb/s and even 100Gb/s high-speed digital optical transmission systems are the ideal choices to satisfy the requirement of increasing information transmission quantity. However, with the increase of transmission rate in a single channel, the quality of the signal would be more affected by dispersion, non-linear and so on. Novel modulation and multiplexing techniques are key technologies which could mitigate the transmission impairments in optical transmission system. As the gain bandwidth of commercial optical amplifiers is primarily in C-band, the requirement of high spectrum efficiency is increasing in the limited transmission channel. As a result, multilevel modulation and all-optical OFDM techniques are coming into view. This paper studies on two novel modulation formats named as IRZ, IRZ-DQPSK and the principle of all-optical OFDM transmission technique. Firstly, four kinds of schemes to modulate IRZ signal are studied and a novel way to generate IRZ modulation format is introduced. The dispersion and non-linear tolerance of them are compared. Secondly, with the IRZ scheme we proposed, the modulation and demodulation principles of IRZ-DQPSK are presented. The performance of 40Gb/s IRZ–DQPSK transmission against fiber nonlinearities and residual dispersion are simulated. Results indicate that to balance the performance of amplitude tributary and phase tributary, the duty cycle of IRZ-DQPSK must be adjusted properly. Furthermore, IRZ-DQPSK and ASK-DQPSK in a 40Gb/s single channel long distance (over 1000km LEAF) transmission link is compared by simulation. Results show that IRZ-DQPSK offers much better performance against SPM. Finally, the principle of multiplexing/demultiplexing in all-optical OFDM technique is studied and a 20Gb/s all-optical OFDM back to back system using NRZ modulation and a 100Gb/s all-optical OFDM transmission system using DQPSK modulation are demonstrated successfully.