Embodiments of the invention provides methods and systems for synthesizing optical signals with high frequency stability. Using a set of external optical signal manipulators and control systems, embodiments of the invention enhance the resolution of any frequency reference and thereby alleviates the needs for ultra-high-Q cavities in frequency-stable optical signal synthesis. The invention consequently improves the performance of any optical signal generator by a substantial margin, while maintaining the system complexity and power dissipation at levels comparable to the original systems.