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A high-bit-rate optic fiber system may be established by multiplexing several low-bit-rate sub-channel signals into a high-bit-rate single channel depend on optical time division multiplexing (OTDM) technique. Because the influence of the third order dispersion (TOD) can not be neglected anymore inside such a high-bit-rate single channel, therefore the intrachannel nonlinear effects, such as self phase modulation (SPM), inter-pulse cross phase modulation (IXPM) and inter-bit four wave mixing (IFWM) must be considered. SPM may be suppressed sufficiently when pre-broadening technique is adopted, and in this case, the IXPM as well as IFWM become the main factors altering the system performance. Pulse position modulation (PPM) is potentially capable of suppressing IXPM and IFWM because of its ability of breaking the resonant of consecutive adjacent pulses and adding guard interval to transmitted pulse sequence. Meanwhile, if we bring the PPM essential capability of increasing transmission capacity into play, then a PPM-OTDM mechanism may be built up, where PPM may act a double role for both suppressing the intra-channel nonlinearities as well as increase the transmission capacity on general OTDM system.

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