an apparatus for optically generating signals comprises a mode - locked optical radiation source that generates mode - locked optical radiation with emitted modes separated by approximately 10 to approximately 300 ghz . coupled to the optical radiation source is an optical demultiplexer with a demultiplexer input , a first demultiplexer output , and a second demultiplexer output , the demultiplexer input being coupled to said mode - locked radiation source . additionally , the apparatus comprises an optical modulator having a modulator input and a modulator output , the modulator input being coupled to the first demultiplexer output , and an optical multiplexer having a first multiplexer input , a second multiplexer input , and a multiplexer output , the first multiplexer - input being coupled to the modulator output , the second multiplexer input being coupled to said second demultiplexer output .