Three-Dimensional Resolvable Plasmonic Concentric Compound Lens: Approaching the Axial Resolution from Microscale to Nanoscale

Abstract

We propose the design and working principle of a plasmonic concentric compound lens (CCL) comprising inner circular nanoslits and outer circular nanogrooves. Dualwavelength operations have been achieved for 650 and 750 nm at nanoscale and microscale focal lengths along with their depth of focus (DOF). By tuning the arrangement of nanogrooves, the axial resolution can be modulated and the narrowest DOF is achieved by a design of gradually decreasing groove width. For the ultrahigh tunability of axial resolution, DOF over 400 nm for both working wavelengths is also achieved. We not only developed an approximate-perturbed-focus model for explaining the performance of DOF but also found an extraordinary way to improve the resolution. The enhanced resonance of central disk as nannoantenna in CCL also has great influence on nanofocusing with different deigns of outer nanogrooves. This work provides new sight of focusing ability governed by the general optical nanogrooves. The optimized CCL shows excellent focusing performance with a lateral resolution down to 0.32λ (λ = 650 nm), which is the best resolving ability achieved thus far in the near field region with a long focal length up to 500 nm.

Microscale Diffractive Lenses Integrated into Microfluidic Devices for Size-Selective Optical Trapping of Particles

“…The exact radii are designed and spaced aperiodically to promote constructive interference for the incident wavelength of light (λ) at 10λ from the surface with the following geometric relationship: r i = false( n s + i λ false) 2 − h 2 where r i is the radius of the i-th ring, h is the designed focal distance from the surface, and n s+i is the i-th integer after the minimum integer, s , such that n s λ ≥ h . This geometric relationship is mathematically equivalent to previous reports; , however, the aperture widths presented here are held constant, and ray distances are restricted to integer values of λ, which eliminate the need to account for phase shifts incurred by interactions with surface plasmons. Microlenses designed with concentric rings have been used to tightly focus light. − …”

Efficient modulation of subwavelength focusing via meta-aperture-based plasmonic lens for multifunction applications

“…The phase delays caused by different slit widths are calculated, and they could be extracted from the wavevectors of the metal-insulator-metal configuration. The analytical formula for the propagating wavevector β , which is crucial for the phase delay βd , can be written as 16 – 18 Here, k o represents the wavevector in free space, w is the slit width, and ε air and ε m are the permittivities in air and metal. Slit with specific width can be chosen at specific position by matching the phase delay condition as indicated in Fig.…”