Optical generation and transmission of 60GHz signals over 100km of optical fibre using a dual-mode semiconductor laser

An electrically-injected dual-mode DFB semiconductor laser has been used to generate 60GHz signals with relatively high power and extremely high purity (phase noise < ¿73dBc/Hz at 1kHz offset and linewidth < 10Hz). These signals have been transmitted over 100km of standard optical fibre with no observable degradation in purity. A small power penalty has been observed (5dB at 50km), which is attributed to the subharmonic nature of the modulating signal applied to the laser in conjunction with chromatic dispersion in the optical fibre. The dual-mode laser is shown to be a relatively simple and compact optical source of high purity 60GHz signals for long-reach fibre-fed millimetre-wave radio systems.