**6. Conclusions**

Mainly based on the recent work in our group, we have briefly reviewed the aperiodic-order-induced multimode effects in photonic and plasmonic micro/nanostructures and their applications in optoelectronic devices. We present the multimode effects in a series of 1D/2D photonic or plasmonic aperiodic structures. These multimode effects have been employed to achieve optical filters for the WDM systems, open cavities for light–matter strong coupling, multiband waveguides for trapping "rainbow", high-efficiency plasmonic solar cells, transmission-enhanced plasmonic arrays, and other devices. The investigations can be applied to the design of integrated photonic and plasmonic devices, which achieve potential applications in areas of optical communication, optical data storage, energy harvesting, nanoantennas, photonic chips, and so on.

**Author Contributions:** R.W.P., M.W., and H.J. conceived the idea. H.J., J.H., and R.W.P. wrote the paper. R.W.P. and M.W. supervised the research.

**Funding:** This research was funded by the National Key R&D Program of China (2017YFA0303702) and the National Natural Science Foundation of China (Grants No. 11634005 and No. 11674155).

**Conflicts of Interest:** The authors declare no conflict of interest.
