Topological photonics aims to replicate fermionic symmetries as feats of precision engineering. Here I show how to enhance these systems via effects such as gain, loss and nonlinearities that do not have a direct electronic counterpart. This leads to a topological mechanism of mode selection [1,2,3], formation of compactons in at band condensates [4], and topological excitations in lasers when linearized around their working point [5]. The resulting effects show a remarkable practical robustness against disorder, which arises from the increased spectral isolation of the manipulated states. Common to them all are structured intensity distributions of the topological modes which correspond to an anomaly.

[1] Topologically protected midgap states in complex photonic lattices, H. Schomerus, Opt. Lett. 38, 1912 (2013).
[2] Selective enhancement of topologically induced interface states in a dielectric resonator chain, C. Poli, M. Bellec, U.Kuhl, F. Mortessagne, H. Schomerus, Nat. Commun. 6, 6710 (2015).
[3] Topological Hybrid Silicon Microlasers, H. Zhao et al., Nat. Commun. 9, 981 (2018)
[4] Exciton-polaritons in a two-dimensional Lieb lattice with spin-orbit coupling, C. E. Whittaker et al., Phys. Rev. Lett. 120, 097401 (2018).
[5] Topological dynamics and excitations in lasers and condensates with saturable gain or loss, S. Malzard, E. Cancellieri, and H. Schomerus, Opt. Express 26, 22506-22518 (2018).