Soliton mode locking and femtosecond pulse generation
have recently been demonstrated in high-Q optical microcavities
and provide a new way to miniaturize frequency comb
systems, as well as create integrated comb systems on a chip.
However, triggering the mode-locking process is complicated
by a well-known thermal hysteresis that can destabilize the
solitons. Moreover, on a longer time scale, thermal drifting of
the cavity resonant frequency relative to the pumping frequency
causes loss of mode locking. In this Letter, an active
feedback method is used both to capture specific soliton
states and to stabilize the states indefinitely. The capture
and stabilization method provides a reliable way to overcome
thermal effects during soliton formation and to excite a desired
number of circulating cavity solitons. It is also used to
demonstrate a low pumping power of 22 mW for generation
of microwave-repetition-rate solitons on a chip