**4. Conclusions**

In summary, a type of coupled hetero-cavity structure is proposed to produce tunable Fano resonances in a plasmonic MIM system. It consists of a rectangular cavity, a side-coupled waveguide, and an upper-coupled circular cavity with a metal-strip core used to modulate Fano resonances. Three Fano resonances can be realized, which originate from the interference of the modes of the rectangular cavity and the metal-strip-core circular cavity. Due to the different cavity-cavity coupling mechanisms, the three Fano resonances can be divided into two groups, and each group of Fano resonances can be well independently tuned by changing the different cavity parameters, which has the advantage of flexibly modulating Fano resonances. Furthermore, through carefully adjusting the direction angle of the metal-strip core in the circular cavity, the position and lineshape of the Fano resonances can be easily tuned. Notably, reversal asymmetry takes place for one of the Fano resonances when the direction angle of the metal strip is changed to be *ϕ* = 90◦. The results show that a maximum FOM value of 3436 is obtained. This research provides effective guidance to produce and tune multiple Fano resonances, which has important applications in nanosensors, filters, slow-light devices, modulators, and other related plasmonic devices.

**Author Contributions:** Q.W. designed the structure and wrote the paper; M.L. analyzed the theory; Q.L. performed the simulations; Z.O. analyzed the data and revised the whole paper.

**Funding:** This work was financially supported by the National Natural Science Foundation of China (NSFC) (No. 61605128, 61275043, 61307048, 11404220), the Natural Science Foundation of Guangdong Province (No. 2017A030310455), and Start-up Funds for New Teachers of Shenzhen University (No. 2016024).

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