Kerr Frequency Comb Generation in Microsphere Resonators With Normal Dispersion

In this work, we carry out theoretical investigation of the dispersion relationship both with the radius of the microsphere cavity and wavelength for the first two radial-order mode based on the theory of microcavity dispersion. The results show that the size of the microcavity corresponding to the zero dispersion point of the higher order mode is larger than that of lower order mode at the certain wavelength. The microsphere cavities with slight deformations, which have rich modes and high Q values, have been fabricated and optical frequency comb (OFC) in them with small size is realized by means of mode coupling. We have achieved OFC in cavities as small as 105 μm in diameter by assistance of the theoretical study. The total dispersions are −7.1 MHz in 1550 nm and −14.2 MHz in 1310 nm, which are both in the normal dispersion region.