  Octave-wide frequency combs in microresonators are essential for
self-referencing. However, it is difficult for the small-size and
high-repetition-rate microresonators to achieve perfect soliton modelocking
over the broad frequency range due to the detrimental impact of dispersion.
Here we examine the stability of the soliton states consisting of one hundred
modes in silicon-nitride microresonators with the one-THz free spectral range.
We report the coexistence of fast and slow solitons in a narrow detuning range,
which is surrounded on either side by the breather states. We decompose the
breather combs into a sequence of subcombs with different carrier envelope
offset frequencies. The large detuning breathers have a high frequency of
oscillations associated with the perturbation extending across the whole
microresonator. The small detuning breathers create oscillations localised on
the soliton core and can undergo the period-doubling bifurcation, which
triggers a sequence of intense sub-combs.
