1550-nm Band Soliton Microcombs in Ytterbium-Doped Lithium-Niobate Microrings

Micro-optical frequency combs are miniaturized coherent light sources exhibiting a tremendous influence on precision spectroscopy, optical clocks, and high-speed optical communications. The rare-earth-doped lithium niobate (LN) is a promising platform to integrate the lasers and comb sources on the same chip of single material. However, microcombs generated in rare-earth-doped LN thin film (LNTF) have not yet been fully explored. To explore the protocols of generating optical combs in ytterbium-doped LNTF, the comb-like laser is studied in the 1060 nm band, and the dissipative Kerr soliton is experimentally demonstrated in the telecom band in a Z-cut wafer. The over-coupled fundamental transverse electric mode with anomalous dispersion is excited at an on-chip pump power of 75.7 mW to generate the robust bright soliton. The broadband spectrum of the Kerr soliton ranges from 1480 to 1660 nm with 110 comb lines, whose repetition rate is 197.8 GHz. The mode-locking of the soliton can be achieved as a result of the photorefractive effect of ytterbium-doped LNTF instead of complex feedback schemes. Numerical simulations are highly accordant with the experimental results. This work expands the microcomb-generating platform and increases the potential for integrated on-chip applications including precision ranging and frequency division.