Coexistence of multiple microcombs in monochromatically pumped Si₃N₄ microresonators

Abstract

We experimentally demonstrate that multiple microcombs can coexist in monochromatically pumped Si3N4 microresonators. By pumping around the mode crossing using a CW laser with mixed polarization, three types of coherent microcombs are generated simultaneously: (i) TE-polarized soliton microcomb; (ii) TM-polarized Turing rolls microcomb; and (iii) cross-phase-modulation-induced TM-polarized microcomb. It is proved that the type-(iii) microcomb shares the same comb line spacing with the type-(i) microcomb although the free spectral ranges of TE and TM modes are different. In addition, a 22.95-GHz signal is extracted from a ∼100-GHz microresonator by heterodyning the TE and TM comb lines, and phase noise analysis reveals their coherence characteristics.

Compact microring resonator based on ultralow-loss multimode silicon nitride waveguide

“…The main reason is the two-photon absorption of the telecommunication wavelengths has drastically restricted its applications to occasions requiring low propagation loss at high power, such as tunable lasers 4 and optical frequency combs. 5 To address this challenge, silicon nitride (Si 3 N 4 ) has emerged as an attractive CMOS-compatible alternative to integrated photonics. [6][7][8][9] The 5 eV bandgap of Si 3 N 4 makes it transparent from ultraviolet to mid-infrared, and immune to two-photon absorption in the telecommunication band, which means it has very low propagation loss.…”

“…However, the propagation loss still cannot be reduced sufficiently low. The main reason is the two-photon absorption of the telecommunication wavelengths has drastically restricted its applications to occasions requiring low propagation loss at high power, such as tunable lasers 4 and optical frequency combs 5 . To address this challenge, silicon nitride (Si3normalN4) has emerged as an attractive CMOS-compatible alternative to integrated photonics 6 …”