  Dissipative solitons can emerge in a wide variety of dissipative nonlinear
systems throughout the fields of optics, medicine or biology. Dissipative
solitons can also exist in Kerr-nonlinear optical resonators and rely on the
double balance between parametric gain and resonator loss on the one hand and
nonlinearity and diffraction or dispersion on the other hand. Mathematically
these solitons are solution to the Lugiato-Lefever equation and exist on top of
a continuous wave (cw) background. Here we report the observation of temporal
dissipative solitons in a high-Q optical microresonator. The solitons are
spontaneously generated when the pump laser is tuned through the effective zero
detuning point of a high-Q resonance, leading to an effective red-detuned
pumping. Red-detuned pumping marks a fundamentally new operating regime in
nonlinear microresonators. While usually unstablethis regime acquires unique
stability in the presence of solitons without any active feedback on the
system. The number of solitons in the resonator can be controlled via the pump
laser detuning and transitions to and between soliton states are associated
with discontinuous steps in the resonator transmission. Beyond enabling to
study soliton physics such as soliton crystals our observations open the route
towards compact, high repetition-rate femto-second sources, where the operating
wavelength is not bound to the availability of broadband laser gain media. The
single soliton states correspond in the frequency domain to low-noise optical
frequency combs with smooth spectral envelopes, critical to applications in
broadband spectroscopy, telecommunications, astronomy and low phase-noise
microwave generation.
