Fig. 1: Schematic diagram of reconfigurable soliton-based radiofrequency photonic filters and their underlying microcomb generation.

a The conceptual setup consists of four parts: microcomb generation, radiofrequency (RF) signal upconversion, dispersive propagation, and photodetection. ECDL external cavity diode laser, MZM Mach–Zehnder modulator, SMF single-mode fiber, PD photodiode, VNA vector network analyzer. Various RF filters are synthesized based on versatile soliton microcombs: (1) single-soliton-based RF filter with a passband centered at f_FSR (blue); (2) N − PSC- (perfect soliton crystals of N equally spaced solitons within one round-trip) based RF filters with a passband centered at f_FSR/N (green, N = 4 is shown); (3) two-soliton microcomb (TSM)-based RF filters with a passband centered at f_FSRα/360° (orange), where α is the relative azimuthal angle between two solitons (α = 90° is shown). b Simulated stability diagram of the Lugiato–Lefever equation (LLE) involving the experimental avoided mode crossing (AMX) condition. Four different stability regions are listed: modulation instability (MI, blue), breathers (red), spatio-temporal and transient chaos (chaos, yellow), and stable dissipative Kerr soliton (DKS, green). PSC and TSM/single-soliton spectra are obtained by distinct approaches. PSC states are accessed under the threshold power to avoid the chaos region. Single-soliton or TSM states are accessed above the threshold power, by either directly falling to the states or backward tuning from a higher number of solitons. c Examples of experimentally generated spectra at resonance of 1555.1 nm: (1) single-soliton, (2) PSC (N = 4), and (3) TSM (α = 132.7°) with envelope fitting. The pump power is also shown for each microcomb generation.