“Measure what is measurable, and make measurable what is not so” (Galileo). Optical frequency comb sources are devices capable to emit light with a comb spectrum composed by narrow lines (i.e. colours) with a fixed frequency spacing. Their introduction gave to Science powerful clockworks capable to measure the frequency of the light and create ultrafast clocks with unprecedented accuracy, unveiling new science in astronomy, geology, biology and many other fields. Their importance in optical metrology has been recognized in the 2005 Nobel Award to T. W. Hänsch. The possibility to miniaturize these sources with strategies meeting the requirements of current electronic platforms would not only produce cheap and low consumption optical sources for ultrafast optical communication and metrological applications, but could bring a greater revolution in the current microchip technology, promoting a “photonic transition” of microelectronics. The recent realization of optical frequency comb sources by exploiting miniaturized resonators represents a fundamental advance towards this direction. However, the impact of these optical sources depends on the full understanding and control of their spectral phase: only when this control is achieved, these devices can be effectively exploited as ultrafast optical clocks. A mode-locking mechanism shaping the phase toward pulse generation was only recently tackled by the applicant and appears a viable solution: this scheme consists in embedding a nonlinear micro-resonator in a fibre laser cavity. It can be considered the precursor of a family of devices implementing phase control by exploiting nested cavities with different nonlinear roles. This project addresses in details this new class of designs, starting from the underlying physics, targeting in perspective the realization of on-chip precision optical clocks with ultra-high repetition rates.