研究目的
To design a mode order converter photonic crystal structure for achieving transformation of the propagating fundamental mode to the higher order mode using an evolutionary algorithm.
研究成果
The study successfully demonstrates the design of a mode order converter photonic crystal structure using a differential evolution algorithm. The optimized structure effectively transforms the fundamental mode to a higher order mode, as confirmed by both numerical simulations and experimental measurements. The mechanism of mode conversion is attributed to the anti-symmetric effective refractive index distribution created by the optimized arrangement of dielectric rods. The all-dielectric nature of the structure minimizes absorption losses, making it suitable for applications in optical mode conversion and communications.
研究不足
The study is limited to the design and verification of a mode order converter for specific modes (TM0 to TM1) at a fixed design frequency. The experimental verification is conducted at microwave frequencies, which may not directly translate to optical frequencies without scaling considerations.
1：Experimental Design and Method Selection:
The study employs a differential evolution (DE) algorithm to design a photonic crystal (PC) structure for mode order conversion. The DE algorithm determines the positions of dielectric alumina rods to achieve the transformation of the fundamental mode to a higher order mode.
2：Sample Selection and Data Sources:
The PC structure consists of dielectric alumina rods distributed in an air medium. The alumina rods have a refractive index of n =
3：13 and a radius of R = 20a, where 'a' is the lattice constant. List of Experimental Equipment and Materials:
Alumina rods with purity of
4：8% and a diameter of 1 mm are used for experimental verification. Microwave signals are generated via an Agilent E5071C ENA vector network analyser, with horn and monopole antennas for excitation and field measurement. Experimental Procedures and Operational Workflow:
The DE algorithm iteratively optimizes the positions of alumina rods to minimize a cost function based on field distribution profiles. Numerical calculations are performed using the finite-difference time-domain (FDTD) method. Experimental verification is conducted at microwave frequencies.
5：Data Analysis Methods:
The electric field and phase distributions are analyzed to evaluate the mode conversion efficiency. Cross-sectional field profiles are compared with predefined mask functions to assess the performance of the designed structure.
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