Mosaic-based waveguide lenses designed by the adjoint method based on the finite-element scheme.

Area of Science:

• Integrated photonics
• Waveguide optics
• Metamaterial applications

Background:

• Waveguide lenses are crucial for manipulating light in integrated photonic circuits.
• Designing complex waveguide structures, especially for multi-port and multi-mode scenarios, presents significant challenges.
• Existing methods may struggle with optimizing refractive index distributions for efficient light control.

Purpose of the Study:

• To propose and experimentally demonstrate novel waveguide lenses utilizing a mosaic structure.
• To showcase the effectiveness of the adjoint method based on the finite-element method (AM-FEM) for designing these complex optical devices.
• To present the first demonstration of multimode waveguide lenses with specific performance characteristics.

Main Methods:

• Design of waveguide lenses using an adjoint method based on the finite-element method (AM-FEM).
• Fabrication and experimental validation of designed 1x2 power splitters and single-mode waveguide lenses.
• Characterization of multimode waveguide lenses for loss and wavelength dependency.

Main Results:

• Successful design and experimental demonstration of mosaic waveguide lenses.
• AM-FEM proved effective for gradient calculation in refractive index distribution, particularly for multi-port/multi-mode problems.
• Single-mode lenses aligned light wavefronts for propagation in unconfined slab regions.
• Novel multimode waveguide lenses exhibited low loss and near wavelength independence.
• Experimental results closely matched theoretical predictions.

Conclusions:

• Mosaic waveguide lenses designed with AM-FEM offer a viable solution for advanced wavefront control.
• The demonstrated AM-FEM approach is highly suitable for complex photonic device design.
• These waveguide lenses hold potential for diverse applications requiring precise light manipulation in integrated systems.