  The investigation of topological state transition in carefully designed
photonic lattices is of high interest for fundamental research, as well as for
applied studies such as manipulating light flow in on-chip photonic systems.
Here, we report on topological phase transition between symmetric topological
zero modes (TZM) and antisymmetric TZMs in Su-Schrieffer-Heeger (SSH) mirror
symmetric waveguides. The transition of TZMs is realized by adjusting the
coupling ratio between neighboring waveguide pairs, which is enabled by
selective modulation of the refractive index in the waveguide gaps.
Bi-directional topological transitions between symmetric and antisymmetric TZMs
can be achieved with our proposed switching strategy. Selective excitation of
topological edge mode is demonstrated owing to the symmetry characteristics of
the TZMs. The flexible manipulation of topological states is promising for
on-chip light flow control and may spark further investigations on
symmetric/antisymmetric TZM transitions in other photonic topological
frameworks.
