Nonlinear dynamics of optical frequency combs (NEMO) (2017-2019)
Optical frequency combs (OFCs) are light sources with a spectrum containing thousands of equally spaced laser lines. OFCs have revolutionized precise optical frequency measurements by making it possible to directly link any optical frequency to a microwave clock. Nowadays they are the indispensable equipment for many other applications, ranging from synchronization of telecommunication systems to astronomical spectral calibration and biomedical or environmental spectrometry. To date, most of the comb spectroscopies rely on table-top mode-locked femtosecond laser systems. As an alternative, passive comb sources based on Kerr microresonators have shown the technological possibility to reduce the size of a comb source to that of a sensing device. The tight confinement of light within the resonator enhances the intensity-dependent nonlinear interaction, thus enabling efficient frequency conversion of pump photons to signal and idler sidebands. However, the threshold power of Kerr combs remains too high for permitting a chip-scale comb source with an integrated pump laser. In the NEMO project we develop novel breakthrough technologies that will enable chip-based OFC sources. The first technology is that of OFCs based on quadratic nonlinear materials, which permits to reduce the pump power threshold down to the microwatt level, and the simultaneous generation of combs in different spectral regions. The second technology is that of frequency combs directly generated from a quantum cascade semiconductor laser. A key requirement for all applications is that the comb should be stable and exhibit low-phase noise operation. This is challenging because both passive and active OFC sources are nonlinear devices that exhibit a highly complex, and essentially chaotic dynamics. To be able to practically utilize OFCs based on quadratic and Kerr nonlinearities, it is crucial to develop a comprehensive theoretical understanding of the nonlinear dynamics for comb generation processes, and study the existence, behavior and stability of these devices. In this project we seek to alleviate this need by developing a novel theoretical framework able to predict the behavior and stability of both passive and active OFC sources.