Coherent Dual Soliton Combs with Mechanically Actuated Kerr Microcombs

Dissipative Kerr soliton (DKS) microcombs have various intriguing applications thanks to their features including compactness, high-repetition rate, low-power operation, and a broadband spectrum covering up to one-octave. Such unique features of DKSs have been utilized in dual-comb technologies to achieve accuracy, a high acquisition rate, and a small footprint simultaneously. However, conventional dual-comb systems using microcombs face challenges in controlling the difference in repetition rates <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\Delta f_{\mathrm{r}\mathrm{e}\mathrm{p}})$</tex> between two soliton combs while maintaining mutual coherence. When independent excitation sources and distinct microresonators are used for dual comb generation [1], it is usually difficult to maintain mutual coherence. On the other hand, the dual-combs with a single excitation source in a counter-propagating method [2] can achieve mutual coherence, but the controllability of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\Delta f_{\mathrm{r}\mathrm{e}\mathrm{p}}$</tex> is limited. In this presentation, we report on a coherent dual-comb system with a shared excitation source using mechanically actuated soliton microcombs [3]. Soliton generation enabled by rapid resonance control allows us to obtain mutually coherent dual-combs with a fixed-frequency excitation source in two individual microresonators, balancing the flexibility of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\Delta f_{\mathrm{r}\mathrm{e}\mathrm{p}}$</tex> and mutual coherence [4]. Figure 1 shows the experimental setup. Magnesium fluoride microresonators with FSRs of ~9.4 GHz are used as platforms. Figure 2(a) shows the combined optical spectrum of the dual soliton combs. The electrical spectrum of the dual-comb is shown in Figs. 2(b, c), where peaks are observed at intervals of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\Delta f_{\mathrm{r}\mathrm{e}\mathrm{p}}$</tex>. Furthermore, we confirmed that the RF comb lines have very narrow linewidth compared to the linewidth when distinct pump lasers and resonators are used to generate dual soliton combs [Fig. 2(d,e)]. This study envisions practical dual comb applications and deployment that fully exploit the features of Kerr microcombs.