Whispering Gallery Mode Electro-Optic Dual Frequency Comb

Whispering gallery mode resonators made from non-linear electro-optic materials are excellent platforms for frequency manipulation of electromagnetic radiation, allowing microwave up-conversion and the generation of frequency combs. By using an x-cut lithium niobate crystal to fabricate our WGM resonator, the resulting electro-optic coefficient varies around the circumference of the resonator, allowing for a simpler microwave geometry. We demonstrate a frequency comb with excellent repetition rate stability, and show results from dual combs with orthogonal polarisations. We measure the relative frequency stability of the dual combs, and find it to be 4 mHz, without any need for stabilisation or post processing.