Time-domain adjoint optimization for metalens design toward enhanced broadband efficiency and uniformity

Area of Science:

• Nanophotonics
• Computational electromagnetics
• Optical engineering

Background:

• Achromatic metalenses are crucial for advanced optical systems.
• Existing frequency-domain methods face computational limitations for broadband simulations.
• Achieving high efficiency and uniform spectral response simultaneously remains a challenge.

Purpose of the Study:

• To develop an efficient time-domain adjoint optimization method for achromatic metalens design.
• To improve focusing efficiency and spectral uniformity compared to existing methods.
• To demonstrate the computational speed and scalability of the proposed method.

Main Methods:

• Implementation of a time-domain adjoint optimization framework.
• Dynamic adjustment of design variables and incident pulses during optimization.
• Continuous evaluation of the entire frequency band, avoiding discrete frequency sampling.

Main Results:

• Achieved 20%-30% improvement in absolute focusing efficiency for NA 0.99 metalenses.
• Increased average focusing efficiency from 27% to 45%.
• Reduced simulation time per iteration to 4.98 s from 61.8 s (frequency-domain).
• Demonstrated consistent 70%-80% focusing efficiency across various NAs and lens sizes.

Conclusions:

• The time-domain adjoint method provides a computationally efficient and versatile framework for achromatic metalens design.
• This advancement enables high-performance optical devices for applications in imaging, communications, and metrology.
• The method overcomes limitations of frequency-domain approaches, offering superior performance and speed.