With the rapid developments of ultrafast lasers toward even shorter pulse, it will suffer great technological and experimental challenges for further generation of optical waveforms with single-cycle or sub-cycle in optical wavelength range. The multi-channel coherent synthesis with precise carrier envelope phase (CEP)-controlled waveforms opens the frontier of ultrafast optics for sub-cycle waveforms generation. In this paper, we review the recent progresses on coherent waveform synthesis based on our research works, the mechanics and key technological approaches are analyzed and discussed, which include ultrabroadband supercontinuum generation, dispersion management and CEP-control.