On the transmission of sub-wavelength annular apertures based on periodic structure

Abstract

Extraordinary light transmission effect on a metal surface, also known as surface plasmon resonance, has been widely discussed in recent years. Extending from this line of research, surface plasmons generated by subwavelength annular apertures (SAA) on metallic film has been identified to have the ability to create sub-wavelength Bessel-like beams. It has also been found that this type of Bessel beam can be used to produce high-aspect ratio microstructures when adopted in laser micromachining. However, the drawback is that the Bessel beams produced by the SAA structure is often characterized as having a low transmission efficiency and high side lobes. In order to improve these shortcomings, an improved SAA-like structure is proposed in this paper. A new photon-sieve replaces the annular aperture by an array of holes which can lower the side lobes of the emitted Bessel beams. More specifically, the original ring-shaped holes are now replaced by a series of smaller holes arranged in a circular shape to mimic a ring. We show by FDTD (Finite-Difference Time-Domain) simulation that a glass substrate removed from this newly created SAA-like structure can increase transmission efficiency by 27.5%. Considering the absorption of the glass substrate is only in the range of 4%-5%, the additional efficiency can actually be attributed to the surface plasmon effect involved in the symmetric nano-structures. Our simulation results were verified by experimental results. The high-aspect ratio microstructures fabricated are also be detailed.