Focusing of light beyond the diffraction limit by randomly distributed graded index photonic medium

Abstract

Sub-wavelength focusing of light holds great potential in various applications of science and engineering, including nanolithography, optical microscopy, optical measurements, and data storage. In the present paper, we propose a new concept to obtain sub-wavelength focusing of light by using structures composed of all-dielectric materials. The approach utilizes the design of an inhomogeneous refractive index profile with random distributions of individual elements occupying the unit cells of two-dimensional photonic crystals (PCs). Light focusing phenomenon is both systematically and quantitatively analyzed at different selected frequencies and we show that the randomly generated graded index (GRIN)-like photonic medium provides light focusing in air with a spot size below k/3, where k is the wavelength of light. The numerically obtained minimum spot size is equal to 0.260k. Gaussian probability function is used to implement numerous random designs to investigate the optical characteristics of the photonic medium. Specific attention is paid to the sub-wavelength focusing properties of the designed random PC structures. The random ingredient of GRIN PC provides not only narrow focusing of light but also off-centered or asymmetric light focusing at the back side of the structure. Experimental verification conducted at the microwave region shows good agreement with the numerical results. Published by AIP Publishing.

Manipulation of the electromagnetic near‐fields by 3D printed coils: from design to fabrication

“…6 and 7 show the electric and magnetic fields generated by E-field 3D coil and H-field 3D coil along the target path, respectively. In these figures, the results of the designed coil refer to final results that are shown in Table 1, and have been calculated by (1) and (2). Simulation results using CST software show the accuracy and precision of the design procedure.…”

“…The near-field manipulation is of great importance in a wide range of electromagnetic applications from optical [1][2][3] and terahertz [4,5] range to microwave frequencies [6][7][8]. Also, the manipulation of near-fields is widely used at low frequencies in drug delivery [9,10], wireless power transfer [11], magnetic induction tomography [12], and treatment methods based on magnetic pulses [13].…”

Machine learning based compact photonic structure design for strong light confinement

“…Such strong subwavelength focusing property as well as small footprint size imply that the optimized photonic lens can also be considered as an alternative and promising solution for freespace-to-waveguide optical coupling applications. In addition, the optimized structure is all-dielectric so that such a photonic device is free of absorption losses and it may operate in a broadband regime comparing to its metamaterial and plasmonic counterparts [28,29]. The coupling effect is also investigated in detail in the study using proposed machine learning based photonic lens.…”