Research progress of optical frequency comb in visible light band based on whispering gallery microcavities (Invited)

Optical frequency combs (OFCs) based on optical microcavities have the characteristics of low threshold, wide spectrum, and compact structure, and have important application prospect in the fields of precision measurement, sensing and et al. Therefore, microcavity based OFC has become an international research hotspot in recent years. At present, relevant researches focus on the generation principle and application of mode-locked OFCs in the infrared band. Although the OFCs in the visible light band have special applications in the fields of precision spectroscopy, atomic clocks and biomedicine, the realization of visible light OFCs is extremely challenging. Based on a brief description of the generation principle of OFCs, this paper introduces the main challenges of realizing OFCs in the visible light band, and the current research progress of three implementation schemes, including the use of the second-order and third-order nonlinear effects of materials, the regulation of the geometric dispersion of the microcavity, and the regulation of the dispersion via modal strong coupling effect to generate visible light frequency combs.