Realization of enhanced light directional beaming via a Bull's eye structure composited with circular disk and conical tip

One new plasmonic light beaming structure aiming to improve beaming property, based on the basic Bull's eye pattern but with the central hole blocked by a metal circular disk at the input side and a conical tip added at the output side, is proposed. The FDTD simulation confirms that this composite structure provides an enhanced beaming efficiency of light not only in the signal intensity but also the angular distribution. Compared to that for Bull’s eye structure, the far-field intensity can be enhanced by several times, due to the strong coupling between the circular disk and metal film forming a cavity-like antenna; simultaneously the far-field angular distribution is narrowed obviously, as a result of the focusing effect from the conical tip which significantly localizing the surface plasmon waves excited by the periodic ring grooves. Moreover, the near-field light transmission shows an oscillatory pattern versus circular disk's diameter, however as a whole, the competitive contributions from the collecting area and the metal loss of the circular disk, results in the existence of the optimal transmission.