Recently, highly-integrated optical phase-locked loops (OPLLs) have been demonstrated for a number of potential applications including coherent optical communications, light detection and ranging (LiDAR) and frequency metrology. Another particularly interesting application is an optical frequency synthesis (OFS) for which OPLL-based offset locking is recently considered to be one of the most attractive techniques. There have been extensive ongoing research efforts to develop low-cost, compact, robust and power-efficient OFS systems using this OPLL-based technology. In this talk, I will discuss about a power-efficient and highly-integrated photonic system, producing low phase-noise coherent optical signal with a wavelength range of 23 nm in the C-band. In fact, the experimental results on the recently-developed highlyintegrated OFS based on OPLL technology will be presented. The system includes novel InP-photonic integrated coherent receiver circuits that consume record-low (approximately 184 mW) electrical power. By employing a combination of photonic and electronic integration, this low-cost highly-integrated InP-based OFS with low-energy consumption exhibits both compact size and exceptional stability. This work is a major step towards demonstration of the true chip-scale optical frequency synthesizer with programmable <1 Hz frequency resolution, <1 cm3 volume, and <1 W electrical power consumption.