  Dissipative Kerr soliton (DKS) offers a compact solution of coherent comb
sources and holds huge potential for applications, but has long been suffering
from poor power conversion efficiency when driving by a continuous-wave laser.
Here, a general approach to resolving this challenge is provided. By deriving
the critical coupling condition of a multimode nonlinear optics system in a
generalized theoretical framework, two efficiency limitations of the
conventional pump method of DKS are revealed: the effective coupling rate is
too small and is also power-dependent. Nonlinear couplers are proposed to
sustain the DKS indirectly through nonlinear energy conversion processes,
realizing a power-adaptive effective coupling rate to the DKS and matching the
total dissipation rate of the system, which promises near-unity power
conversion efficiencies. For instance, a conversion efficiency exceeding
$90\:\%$ is predicted for aluminum nitride microrings with a nonlinear coupler
utilizing second-harmonic generation. The nonlinear coupler approach for
high-efficiency generation of DKS is experimentally feasible as its mechanism
applies to various nonlinear processes, including Raman and Brillouin
scattering, and thus paves the way of micro-solitons towards practical
applications.
