Enhanced optical transmission through a nano-slit based on a dipole source and an annular nano-cavity

• We achieve enhancing transmission by using a dipole source and an annular cavity.
• The annular cavity can effectively couple more energy from a dipole source.
• This device utilizes the feature on non-uniform electric field of a dipole source.
• We can improve the transmission by optimizing structure parameters of the device.
• This design holds promise for its application in EOT-based optoelectronic devices.

A novel plasmonic structure, composed of a dipole source and an annular nano-cavity over a nano-slit, is proposed as a surface plasmon polaritons source to enhance the extraordinary optical transmission (EOT) simulated using a finite-difference time-domain (FDTD) method. We find that the annular nano-cavity has an obvious advantage to couple more energy from a dipole source compared with previous EOT configuration. Based on the fact of non-uniform electric field distribution of a dipole source, the transmission through nano-slit is effectively improved by selecting optimized structure parameters. In addition, the transmission spectrum can be well-tuned by adjusting the central angle of the annular nano-cavity, as such, the design holds great promise for its application in EOT-based optoelectronic devices.