A novel 40-Gb/s constant envelope optical frequency shift keying （FSK） transmitter and the transmission characteristics are investigated both by simulation and experiment. Meanwhile, to increase the spectrum efficiency of FSK, we propose a novel optical minimum-shift keying （MSK） scheme and analyze its per-formance compared with other MSK schemes and other traditional modulation formats. Simulation and experimental results show that the novel FSK scheme could be a potential candidate for the future high speed transmission and label switching systems. And the novel MSK scheme deserves future deep research for its potential excellent performance.
We propose a novel advanced orthogonal modulation format dark return-to-zero frequency shift keying/differential phase shift keying （DRZ-FSK/DPSK） and its realization scheme. The DRZ-FSK/DPSK is generated by the combination of a 40-Gb/s return-to-zero （RZ） signal and a DRZ signal which is converted from the RZ using a semiconductor optical amplifier （SOA） based on nonlinear cross polarization rotation （XPR） and then re-modulated by high-bit-rate DPSK at 40 Gb/s. The feasibility of the scheme is exper-imentally demonstrated. Bit error rate （BER） results of the total 80-Gb/s DRZ-FSK/DPSK orthogonal modulation signal with a subsequent 100-km single-mode fiber （SMF） transmission link show its potential for future high-speed long-haul optical communication.
