Differential evolution algorithm based photonic structure design: numerical and experimental verification of subwavelength λ/5 focusing of light

Super-oscillatory spots with different inhomogeneous linear polarized states

We present the formation of super-oscillatory (SO) spots by tightly focusing the inhomogeneous linear polarized beam of different polarization states. At the entrance pupil of the focusing lens, a suitable phase manipulation in the incident beam results in a small super-oscillatory spot. Our numerical study based on the vectorial diffraction theory shows that SO spots of controllable size and various polarization combinations are possible. We also discuss the effect of the different polarization patterns of the incident beam on the size and energy distribution of the generated SO spots, which are potentially valuable for the orientation determination of single molecules and polarization-resolved imaging. This study reveals more influence of polarization states on the different components of the focused beam under the utilization of the proposed method rather than the usual tight focusing conditions.

Inverse design of photonic structures using an artificial bee colony algorithm

We adapted the standard artificial bee colony algorithm for a binary search space in order to optimize photonic structures. The artificial bee colony algorithm in conjunction with the finite element method is applied for maximizing photonic bandgaps of photonic crystals. The proposed approach is assessed by two case studies assuming 2D photonic crystals comprised of silicon and air in a triangular lattice. The crystals were optimized to present large photonic bandgaps. The artificial bee colony algorithm presented superior performance when compared with that of a standard genetic algorithm, demonstrating an interesting approach to be used on the inverse design or optimization of photonic structures.

Design of an arbitrary ratio optical power splitter based on a discrete differential multiobjective evolutionary algorithm

Traditional photonic integrated devices are designed to predict their optical response by transforming the structure and parameters, and it is often difficult to obtain devices with excellent performance in all aspects. The nanophotonic computing design method based on the optimization algorithm has revolutionized the traditional photonic integrated device design technology. Here, we report a discrete differential evolution algorithm that simulates a natural selection process to achieve an ultracompact arbitrary power ratio splitter. The footprint of the designed splitter is only ${2.5}\;\unicode{x00B5} {\rm m} \times {2}.{5}\;\unicode{x00B5} {\rm m}$2.5µm×2.5µm, the simulated total transmission efficiency is above 90%, the power ratio error is less than 3%, and it can work normally over the C-band. Our algorithm can provide new ideas for the application of genetic algorithms to the automatic optimization of photonic integrated devices.

Laser-induced subwavelength structures by microdroplet superlens

Nanoscale patterns on rigid or flexible substrates are of considerable interest in modern nanophotonics and optoelectronics devices. Subwavelength structures are produced in this study by using a laser beam and microdroplets that carry nanoparticles to the deposition substrate. These droplets are generated from an aqueous suspension of nanoparticles by electrospray and dispensed through a conical hollow laser beam so that laser-droplet interactions occur immediately above the substrate surface. Each microdroplet serves the dual role as a nanoparticle carrier to the substrate and as a superlens for focusing the laser beam to a subwavelength diameter. This focused beam vaporizes the droplet and sinters the nanoparticles on the substrate. The deposition of subwavelength nanostructures and thin films on a silicon wafer are demonstrated in this paper. This process may be applied to produce novel nanophotonics and electronics devices involving a variety of subwavelength patterns including an ordered array of semiconductor nanoparticles.

Full-wave optimization of three-dimensional photonic-crystal structures involving dielectric rods

We present rigorous optimization and design of three-dimensional photonic-crystal (PhC) structures involving finite dielectric rods. These types of PhCs are known to be useful in diverse applications, such as imaging, power focusing, filtering, and pattern shaping at optical frequencies. Without resorting to their two-dimensional models, which are commonly used in the literature, we consider PhCs as three-dimensional structures, whose electromagnetic characteristics are optimized via genetic algorithms integrated with an efficient and accurate solver based on the multilevel fast multipole algorithm. In addition to the designs of PhCs that can provide desired output patterns, we present sensitivity tests to understand the critical geometric parameters, as well as to test and evaluate the tolerance of the proposed designs to possible fabrication errors.

Optimization-based design of a heat flux concentrator

To gain control over the diffusive heat flux in a given domain, one needs to engineer a thermal metamaterial with a specific distribution of the generally anisotropic thermal conductivity throughout the domain. Until now, the appropriate conductivity distribution was usually determined using transformation thermodynamics. By this way, only a few particular cases of heat flux control in simple domains having simple boundary conditions were studied. Thermal metamaterials based on optimization algorithm provides superior properties compared to those using the previous methods. As a more general approach, we propose to define the heat control problem as an optimization problem where we minimize the error in guiding the heat flux in a given way, taking as design variables the parameters that define the variable microstructure of the metamaterial. In the present study we numerically demonstrate the ability to manipulate heat flux by designing a device to concentrate the thermal energy to its center without disturbing the temperature profile outside it.