Thermal-Controlled Scanning of a Bright Soliton in a Photonic Molecule

Over the last few years, dissipative Kerr solitons (DKS) in microresonators have boosted the development of chip-scale frequency comb sources (microcombs) in a variety of applications, from coherent communications to ultrafast distance ranging [1]. However, the intrinsic large free spectral range (FSR) of microcombs (within the gigahertz regime) is still a drawback for applications such as molecular spectroscopy, in which the comb line spacing dictates the spectral sampling resolution. Overcoming spectral sparsity by scanning the comb modes across a full FSR is challenging for a DKS microcomb, since the soliton operation must be kept while the pump laser is continuously swept. So far, it has been accomplished for a single microresonator by combining a feedback control loop with the thermal tuning of the cavity resonances by means of a microheater [2]. Recently, the use of two linearly coupled cavities (a photonic molecule) has shown to be a promising alternative to generate soliton microcombs with high conversion efficiency and uniform power distribution [3]. In this contribution, we address the challenge of scanning the soliton comb modes of a photonic molecule by thermal tuning. Specifically, we implement a scheme to scan a bright soliton over 60 GHz by tuning simultaneously the pump laser and the resonances of two coupled cavities.