Fig. 1: Concept of hybrid Kerr-electro-optic frequency comb.

a 3-D illustration of the hybrid Kerr-EO frequency comb, consisting of a DKS microresonator chip and an EO phase modulator chip. A continuous-wave (CW) optical frequency initiates a near THz-rate DKS frequency comb, which then undergoes EO phase modulation to form a microwave-rate hybrid comb after passing through the modulator. b Photograph showing TFLN photonic chips with EO phase modulator array (left) and Kerr resonators (right). c Scanning electron microscope image of the Kerr resonator. d Optical microscope image of two parallel EO phase modulators. In this work, we use only one phase modulator, where one optical waveguide passes through the ground-signal gap of the coplanar line. e Cross-sectional schematic of the Kerr resonator (top) and the EO phase modulator (bottom), with crystal axes labeled to indicate Z- and X-cut, respectively. f Schematic of the hybrid Kerr-EO frequency comb generation process. A DKS frequency comb (blue) is used as a source, where each comb line generates EO sidebands (red) around it at multiples of the modulation frequency. The final output of the hybrid comb generator consists of both blue and red lines. g Schematic of the variables defined in our work. \({f}_{{DKS}}\): DKS spacing, \({f}_{{RF}}\): hybrid Kerr-EO comb spacing and EO modulation frequency, \(\Delta f\): difference frequency defined by \({f}_{{DKS}}=N\cdot {f}_{{RF}}+\Delta f\)