  We show a new class of bound soliton molecule that exists in a parametrically
driven nonlinear optical cavity with appropriate dispersion characteristics.
The composed solitons exhibit distinctive colors but coincide in time and share
a common phase, bound together via strong inter-soliton four-wave mixing and
Cherenkov radiation. The multicolor bound soliton molecule shows intriguing
spectral locking characteristics and remarkable capability of spectrum
management to tailor soliton frequencies, which may open up a great avenue
towards versatile generation and manipulation of multi-octave spanning
phase-locked Kerr frequency combs, with great potential for applications in
frequency metrology, optical frequency synthesis, and spectroscopy.
