Abstract
Using epsilon-near-zero (ENZ) subwavelength optical multilayer materials with simple structure and thin total thickness to achieve target characteristics is extremely important and beneficial for the realization of on-chip integration and large-scale application of optical devices. Combining with the enhanced genetic algorithm (EGA), this work breaks the limitation of the periodicity of traditional ENZ multilayer structures, and investigates the aperiodic ENZ transparent conducting oxide (TCO)-dielectric multilayer structures. It is realized that under the given conditions, an optimal structure can possess a maximum peak absorption and the broadest absorption bandwidth near the communication wavelength. In the 6-layer structure with a total thickness of 600 nm studied in this work, EGA can optimize the peak absorption from 0.91 to 0.95. Additionally, the absorption bandwidth is optimized from 120 nm to 227 nm, which is enhanced more than 180%. The absorption performance of this optimized structure is comparable to that of a more complex structure with the same total thickness but more layers, or a structure with the same number of layers but a larger total thickness. Conclusively, the proposed EGA optimization method can simplify the structure of the multilayer system, reduce the total thickness of the required ENZ material, and thus greatly simplify the production process and reduce the production cost.
Highlights
EPSILON-NEAR-ZERO (ENZ) materials are a kind of nearzero-index materials [1]
We propose an enhanced genetic algorithm (EGA) method to greatly improve the absorption characteristics of ENZ multilayers
The calculation process of EGA is mainly divided into three stages, which will be described in detail as we introduce the fitness function and the transfer matrix method (TMM), which are all essential concepts in our proposed EGA
Summary
EPSILON-NEAR-ZERO (ENZ) materials are a kind of nearzero-index materials [1]. These ENZ materials possess many unique characteristics, such as strong field enhancement [2]-[4], constant phase transmission [5], [6], tunneling through distorted channels [7], [8] and etc. Multilayer structure is one of the most common methods to realize an effective ENZ point [17]. The optimal absorption effect of fixed numbers of layers with different total thicknesses is studied. The findings of these two aspects are beneficial to give full play to the absorption performance of the limited material and simplify the process of design and fabrication.
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