Antichiral edge states extend the conventional bulk-edge correspondence by allowing edge modes on two parallel boundaries to propagate in the same direction, compensated by counterpropagating bulk states. However, their strong localization at physical boundaries leads to a severe dependence on boundary conditions and a lack of effective radiation suppression, hindering their practical application in optical communications. Here we propose a control mechanism based on local symmetry breaking in a modified Haldane photonic crystal. By tuning the geometric parameters of boundary rods, antichiral edge states can be merged into and hybridized with the projected bulk continuum. By reversing this mechanism, we create internal line defects that induce coupled interface modes inside the crystal. These modes form topological defect states that retain the unidirectional transport and topological origin of the antichiral system, while exhibiting quality factors several orders of magnitude higher than those of edge states. We experimentally demonstrate a defect waveguide and defect cavity and observe selective coupling from traveling waves to discrete circulating resonant modes. The resonant frequency can be tuned by geometric modulation. This work provides a low-loss and internally integrated route for constructing nonreciprocal topological photonic devices.

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• Topological effects in photonic systems