| 摘要 |
An 90 degree AP on-off keying (OOK) transmission format is used to suppress intra-channel FWM and significantly extend reach in high bit rate, long-haul fiber optic transmission systems. The pulse stream with the aforementioned format can be either chirped or chirp-free, and can for example, be generated with a pulse generator (e.g., a Mach-Zehnder (MZ) modulator) by mixing two electrical signals, one used to create an intensity modulation and the other a phase modulation in the pulse generator. The electrical signals can be two properly skewed sinusoidal electrical signals at half of the desired data rate, and can thereby create a pulse stream in which the maximum optical phase modulation occurs at the intensity peak of each pulse and is 90 degrees out of phase with its nearest neighbors. Alternatively, a 90 degree AP pulse train can be generated by a single phase modulator followed by a delay interferometer with a time delay of approximately 2/3 of the bit period of the data in the data stream. If desired, an appropriate optical filter can create a 'phase flattened', or nearly chirp free 90 degree AP pulse stream that is particularly well suited for use in realizing certain phase coding transmission schemes, for example, minimum shift keying.
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