  We propose a method for soliton formation in whispering-gallery-mode (WGM)
resonators through input phase modulation. Our numerical simulations of a
variant of the Lugiato-Lefever equation suggest that modulating the input phase
at a frequency equal to the resonator free-spectral-range and at modest
modulation depths provides a deterministic route towards soliton formation in
WGM resonators without undergoing a chaotic phase. We show that the generated
solitonic state is sustained when the modulation is turned off adiabatically.
Our results support parametric seeding as a powerful means of control, besides
input pump power and pump-resonance detuning, over frequency comb generation in
WGM resonators. Our findings also help pave the path towards ultra-short pulse
formation on a chip.
