  We build on a previously reported frequency comb of mode spacing 0.136 nm in
a fiber ring cavity of varying normal dispersion [1], to generate, for the
first time, a frequency comb of mode spacing 0.144 nm centered at 978.544 nm to
demonstrate the symmetry-breaking. By controlling the birefringence of the
optical cavity through fiber stretching and polarization control, the spacing
of the comb lines increases from 0.136 nm to 0.144 nm, and this small change in
mode spacing generates very different spectral symmetry-breaking in the
frequency comb relative to the frequency comb of mode spacing 0.136 nm.
Interestingly, non-uniform depletion of primary modes is also observed. The
experimental results are an important contribution in the continuing effort of
understanding the dynamics of frequency combs involving large number of modes,
nontrivial nonlinear waves and deterministic chaos.
