This paper will report on continuous (sub-)millimetre-wave (cw) generation by photomixing two laser signals at around 1.55μm in ultrafast InAlAs/InGaAs(P) travelling-wave photodetectors (TW-PD). At first TW-PD's are characterised up to 160GHz mm-wave frequency using conventional MMW equipment. Further, photonic THz transmitters with integrated planar slot and bow-tie antenna structures for quasi optical free space coupling will be presented. Resonant slot antenna coupled TW-PD exhibit sufficient power for replacing the 460GHz solid-state-LO of an SIS-based heterodyne receiver while the equivalent device with integrated bow-tie antenna operates in a very broadband frequency range between 20 and 620GHz. Next we report on waveguide coupled TW-PD's and show experimental results in a wide frequency range, up to 1THz. Finally, several low-cost strategies for enhancing the available power as well as the efficiency will be presented.