Abstract: An optical transmission system for an optical communications system that has an optical source, an optical modulator for modulating an optical output of the optical source, and an optical filter arranged to substantially remove one of the upper and lower sidebands of the modulated optical output of the optical source. The optical transmission system further includes a control means to control at least one of the optical source and the optical filter to ensure that substantially only half of the power of the modulated optical output of the optical source is transmitted by the filter, thereby reducing the bandwidth of the optical signals transmitted by the system.

Abstract: An optical transmission system for an optical communications system is disclosed. The optical transmission system includes an optical source 6, an optical modulator 10 for modulating an optical output of the optical source, and an optical filter 12 arranged to substantially remove one of the upper and lower sidebands of the modulated optical output of the optical source 6. The optical transmission system further includes control means 14 to control at least one of the optical source and the optical filter to ensure that substantially only half of the power of the modulated optical output of the optical source 6 is transmitted by the filter, thereby reducing the bandwidth of the optical signals transmitted by the system.

Abstract: An optical device is disclosed for the external modulation of the output 4 of an optical radiation source. The device includes a first optical modulator 2 driven by an NRZ coded electrical data signal 3 so as to modulate the output 4 of an optical radiation source. The device also includes a second optical modulator 6 coupled to the first optical modulator 1 and driven by one or more drive signal sources 7, 8 from electrical circuit 9. The circuit 9 drives modulator 6 so as to provide an optical AND function to convert the NRZ coded optical signal output the first optical modulator 1 into an RZ coded optical signal and to simultaneously introduce a degree of phase modulation (e.g. pre-chirp) in the RZ signals modulated thereby.