Optical Frequency Comb Generation in Quadratic Resonator with Spectral Filtering

We propose a novel method for optical frequency combs (OFC) generation in normal dispersion quadratic resonators extending the concept of the gain-through-filtering (GTF) process from Kerr cavities [1], [2]. GTF triggers a modulation instability (MI) leading to sidebands generation due to asymmetric spectral filtering applied on one side of the intracavity continuous wave field frequency. The cascading of higher-order sidebands leads to the formation of an OFC, whose line spacing can be controlled by adjusting the detuning between the pump and filter frequencies. The setup is illustrated in Fig. 1(a), featuring a ring resonator driven by a periodically poled lithium niobate (PPLN) crystal with quadratic nonlinearity, followed by a single mode fiber (SMF) and a spectral filter.