RF spectrum measurement of the versatile microcavity soliton combs

Dissipative Kerr solitons generated in microresonators driven by a continuous wave pump laser have promise for widespread applications in spectroscopy and telecommunications. From the perspective of basic physics research, DKSs exhibit rich nonlinear phenomena and serve as a unique platform to study nonlinear physics. In this paper, an optimized all-optical radio frequency (RF) spectrum analyzer, also named frequency domain light intensity spectrum analyzer (f-LISA), is used to characterize the various stable soliton states. Results show that the optimized f-LISA achieves a measurement bandwidth of 2.2 THz and a frame rate of 20.62 MHz. Therefore, the versatile RF spectral patterns of stable two-soliton states have successfully recorded by f-LISA. More importantly, the relative azimuthal angles between two solitons within the round-trip can be extracted by applying an inverse Fourier transform to the RF spectra, indicating that the ultra-fast and broadband RF spectral measurement enable the visualization of soliton motion. It is believed that the f-LISA can function as a powerful and useful tool to monitor the rich nonlinear dynamical phenomena such as soliton number switching in the microresonators