| 摘要 |
In an optical fiber FDM system, the carriers are derived from the output of a high quality Master Oscillator, which output at frequency f0 is applied to a Raman Nath modulator (RNM1) whose other input is a frequency f0 this gives as its outputs (assuming a five channel system) f0-2f, f0-f, f0, f0+f and f0+2f. These are modulated by modulators (CM1, to CM5) with the signals to be sent, and the modulation results combined in a combiner CB for transmission to a remote station. The oscillator output is also sent to the remote stations where it is frequency-shifted by a Bragg modulator (BM) and the resultant similarly dealt with by a Raman Nath device (RNM2) to give five frequencies which are used to demodulate the channels. In an alternative the channel frequencies are switchable.
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